Sugiyama, Hideyuki (Yokohama-Shi, JP)
Inokuchi, Tomoaki (Kawasaki-Shi, JP)
Plaque It!
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1. A spin MOSFET comprising: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer being a tunnel insulator and provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable and a magnetization direction of the magnetization pinned layer being fixed; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film.
2. The spin MOSFET according to claim 1, wherein the magnetization free layer includes a stacked structure containing a second ferromagnetic layer, a second nonmagnetic layer, and a third ferromagnetic layer, and the second and third ferromagnetic layers are antiferromagnetically coupled to each other.
3. The spin MOSFET according to claim 1, wherein a first antiferromagnetic layer is provided on the first magnetic film, and a second antiferromagnetic layer is provided on the magnetization pinned layer.
4. The spin MOSFET according to claim 3, wherein the first and second antiferromagnetic layers are made of different materials from each other.
5. The spin MOSFET according to claim 1, wherein the first magnetic film includes a stacked structure containing the first ferromagnetic layer, a second nonmagnetic layer, and a second ferromagnetic layer, and the first and second ferromagnetic layers are antiferromagnetically coupled to each other.
6. The spin MOSFET according to claim 1, wherein the magnetization pinned layer includes a stacked structure containing a second ferromagnetic layer, a second nonmagnetic layer, and a third ferromagnetic layer, and the second and third ferromagnetic layers are antiferromagnetically coupled to each other.
7. The spin MOSFET according to claim 1, wherein a tunnel insulating film is provided between the semiconductor substrate and the first and second magnetic films.
8. The spin MOSFET according to claim 1, wherein the magnetization direction of the magnetization free layer is inclined at an angle of more than 0 degree but 45 degree or less with respect to the magnetization direction of the first ferromagnetic layer.
9. The spin MOSFET according to claim 8, wherein the second magnetic film has a shape of a parallelogram in a film plane.
10. The spin MOSFET according to claim 8, wherein the second magnetic film has a shape of a hexagon in a film plane.
11. The spin MOSFET according to claim 1, wherein the semiconductor substrate has a surface formed with a IV group semiconductor, or a III-V or II-VI group compound semiconductor.
12. A spin MOSFET comprising: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable and a magnetization direction of the magnetization pinned layer being pinned and antiparallel to the magnetization direction of the first ferromagnetic layer; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film, a gate voltage that causes a negative magnetoresistance effect being applied when writing is performed, a gate voltage that causes a positive magnetoresistance effect being applied when reading is performed.
13. The spin MOSFET according to claim 12, wherein a first antiferromagnetic layer is provided on the first magnetic film, and a second antiferromagnetic layer is provided on the magnetization pinned layer.
14. The spin MOSFET according to claim 13, wherein the first and second antiferromagnetic layers are made of different materials from each other.
15. The spin MOSFET according to claim 12, wherein the first magnetic film includes a stacked structure containing the first ferromagnetic layer, a second nonmagnetic layer, and a second ferromagnetic layer, and the first and second ferromagnetic layers are antiferromagnetically coupled to each other.
16. The spin MOSFET according to claim 12, wherein the magnetization pinned layer includes a stacked structure containing a second ferromagnetic layer, a second nonmagnetic layer, and a third ferromagnetic layer, and the second and third ferromagnetic layers are antiferromagnetically coupled to each other.
17. The spin MOSFET according to claim 12, wherein a tunnel insulating film is provided between the semiconductor substrate and the first and second magnetic films.
18. The spin MOSFET according to claim 12, wherein the magnetization direction of the magnetization free layer is inclined at an angle of more than 0 degree but 45 degree or less with respect to the magnetization direction of the first ferromagnetic layer.
19. The spin MOSFET according to claim 18, wherein the second magnetic film has a shape of a parallelogram in a film plane.
20. The spin MOSFET according to claim 18, wherein the second magnetic film has a shape of a hexagon in a film plane.
21. The spin MOSFET according to claim 12, wherein the semiconductor substrate has a surface formed with a IV group semiconductor, or a III-V or II-VI group compound semiconductor.
22. A spin MOSFET comprising: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable and a magnetization direction of the magnetization pinned layer being pinned and parallel to the magnetization direction of the first ferromagnetic layer; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film, a gate voltage that causes a positive magnetoresistance effect being applied when writing is performed, a gate voltage that causes a negative magnetoresistance effect being applied when reading is performed.
23. The spin MOSFET according to claim 22, wherein a first antiferromagnetic layer is provided on the first magnetic film, and a second antiferromagnetic layer is provided on the magnetization pinned layer.
24. The spin MOSFET according to claim 23, wherein the first and second antiferromagnetic layers are made of different materials from each other.
25. The spin MOSFET according to claim 22, wherein the first magnetic film includes a stacked structure containing the first ferromagnetic layer, a second nonmagnetic layer, and a second ferromagnetic layer, and the first and second ferromagnetic layers are antiferromagnetically coupled to each other.
26. The spin MOSFET according to claim 22, wherein the magnetization pinned layer includes a stacked structure containing a second ferromagnetic layer, a second nonmagnetic layer, and a third ferromagnetic layer, and the second and third ferromagnetic layers are antiferromagnetically coupled to each other.
27. The spin MOSFET according to claim 22, wherein a tunnel insulating film is provided between the semiconductor substrate and the first and second magnetic films.
28. The spin MOSFET according to claim 22, wherein the magnetization direction of the magnetization free layer is inclined at an angle of more than 0 degree but 45 degree or less with respect to the magnetization direction of the first ferromagnetic layer.
29. The spin MOSFET according to claim 28, wherein the second magnetic film has a shape of a parallelogram in a film plane.
30. The spin MOSFET according to claim 28, wherein the second magnetic film has a shape of a hexagon in a film plane.
31. The spin MOSFET according to claim 22, wherein the semiconductor substrate has a surface formed with a IV group semiconductor, or a III-V or II-VI group compound semiconductor.
32. A spin MOSFET comprising: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable, the magnetization free layer including a stacked structure containing a second ferromagnetic layer, a second nonmagnetic layer, and a third ferromagnetic layer, the second and third ferromagnetic layers being antiferromagnetically coupled to each other, and a magnetization direction of the magnetization pinned layer being pinned and antiparallel to the magnetization direction of the first ferromagnetic layer; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film, a gate voltage that causes a negative magnetoresistance effect being applied when writing is performed, a gate voltage that causes a negative magnetoresistance effect being applied when reading is performed.
33. The spin MOSFET according to claim 32, wherein a first antiferromagnetic layer is provided on the first magnetic film, and a second antiferromagnetic layer is provided on the magnetization pinned layer.
34. The spin MOSFET according to claim 33, wherein the first and second antiferromagnetic layers are made of different materials from each other.
35. The spin MOSFET according to claim 32, wherein the first magnetic film includes a stacked structure containing the first ferromagnetic layer, a third nonmagnetic layer, and a fourth ferromagnetic layer, and the first and fourth ferromagnetic layers are antiferromagnetically coupled to each other.
36. The spin MOSFET according to claim 32, wherein the magnetization pinned layer includes a stacked structure containing a fourth ferromagnetic layer, a third nonmagnetic layer, and a fifth ferromagnetic layer, and the fourth and fifth ferromagnetic layers are antiferromagnetically coupled to each other.
37. The spin MOSFET according to claim 32, wherein a tunnel insulating film is provided between the semiconductor substrate and the first and second magnetic films.
38. The spin MOSFET according to claim 32, wherein the magnetization direction of the magnetization free layer is inclined at an angle of more than 0 degree but 45 degree or less with respect to the magnetization direction of the first ferromagnetic layer.
39. The spin MOSFET according to claim 38, wherein the second magnetic film has a shape of a parallelogram in a film plane.
40. The spin MOSFET according to claim 38, wherein the second magnetic film has a shape of a hexagon in a film plane.
41. The spin MOSFET according to claim 32, wherein the semiconductor substrate has a surface formed with a IV group semiconductor, or a III-V or II-VI group compound semiconductor.
42. A spin MOSFET comprising: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable, the magnetization free layer including a stacked structure containing a second ferromagnetic layer, a second nonmagnetic layer, and a third ferromagnetic layer, the second and third ferromagnetic layers being antiferromagnetically coupled to each other, and a magnetization direction of the magnetization pinned layer being pinned and parallel to the magnetization direction of the first ferromagnetic layer; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film, a gate voltage that causes a positive magnetoresistance effect being applied when writing is performed, a gate voltage that causes a positive magnetoresistance effect being applied when reading is performed.
43. The spin MOSFET according to claim 42, wherein a first antiferromagnetic layer is provided on the first magnetic film, and a second antiferromagnetic layer is provided on the magnetization pinned layer.
44. The spin MOSFET according to claim 43, wherein the first and second antiferromagnetic layers are made of different materials from each other.
45. The spin MOSFET according to claim 42, wherein the first magnetic film includes a stacked structure containing the first ferromagnetic layer, a third nonmagnetic layer, and a fourth ferromagnetic layer, and the first and fourth ferromagnetic layers are antiferromagnetically coupled to each other.
46. The spin MOSFET according to claim 42, wherein the magnetization pinned layer includes a stacked structure containing a fourth ferromagnetic layer, a third nonmagnetic layer, and a fifth ferromagnetic layer, and the fourth and fifth ferromagnetic layers are antiferromagnetically coupled to each other.
47. The spin MOSFET according to claim 42, wherein a tunnel insulating film is provided between the semiconductor substrate and the first and second magnetic films.
48. The spin MOSFET according to claim 42, wherein the magnetization direction of the magnetization free layer is inclined at an angle of more than 0 degree but 45 degree or less with respect to the magnetization direction of the first ferromagnetic layer.
49. The spin MOSFET according to claim 48, wherein the second magnetic film has a shape of a parallelogram in a film plane.
50. The spin MOSFET according to claim 48, wherein the second magnetic film has a shape of a hexagon in a film plane.
51. The spin MOSFET according to claim 42, wherein the semiconductor substrate has a surface formed with a IV group semiconductor, or a III-V or II-VI group compound semiconductor.
52. A spin MOSFET comprising: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer containing a first half-metal ferromagnetic layer, and a second ferromagnetic layer that is provided on the first ferromagnetic layer and contains a CoFe layer, a magnetization direction of the first half-metal ferromagnetic layer being pinned; a first antiferromagnetic layer provided on the second ferromagnetic layer of the first magnetic film; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer containing a second half-metal ferromagnetic layer, a tunnel insulating layer provided on the magnetization free layer, a magnetization pinned layer provided on the tunnel insulating layer, a third ferromagnetic layer provided on the magnetization pinned layer and containing a CoFe layer, and a second antiferromagnetic layer provided on the third ferromagnetic layer, a magnetization direction of the second half-metal ferromagnetic layer being changeable, and a magnetization direction of the magnetization pinned layer being pinned; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film.
53. The spin MOSFET according to claim 52, wherein the second and third ferromagnetic layers each have a three-layer structure containing a CoFe layer, a Ru layer, and a CoFe layer.
54. The spin MOSFET according to claim 52, wherein the first and second half-metal ferromagnetic layers are made of a full Heusler alloy.
55. The spin MOSFET according to claim 54, wherein the full Heusler alloy is Co2FeSi1-xAlx (0.1<x<0.9).
56. The spin MOSFET according to claim 52, wherein a tunnel insulating film is provided between the semiconductor substrate and the first and second magnetic films.
57. The spin MOSFET according to claim 52, wherein the semiconductor substrate has a surface formed with a IV semiconductor, or a III-V or II-VI compound semiconductor.
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-244656 filed on Sep. 8, 2006 in Japan, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to spin MOSFETs.
2. Related Art
In recent years, intensive studies are being made to develop devices such as spin MOSFETs having novel functions. One of those devices is a spin MOSFET that has the source-drain region formed with a magnetic material. Such a spin MOSFET is characterized in that the output characteristics can be controlled simply by reversing the spin moment direction of the magnetic material of the source-drain region. This feature can be utilized to form spin MOSFETs that have amplifying functions as well as reconfigurable functions, and to form a reconfigurable logic circuit with those spin MOSFETs.
To put such spin MOSFETs and a reconfigurable logic circuit having amplifying functions as well as reconfigurable functions into practical use, it is necessary to overcome the following two problems.
One of the two problems is to be eliminated by reducing the current when writing is performed and the spin moment direction of the magnetic material of the source-drain region is reversed, and the other one is to be eliminated by increasing the change in output characteristics observed when the spin moment direction is reversed.
To solve the first one of the problems, a writing method utilizing spin injection has been suggested (see the specification of U.S. Pat. No. 6,256,223, for example). A spin reversal can be performed by spin-injecting a spin-polarized current. However, in a case where this spin injecting technique is applied to a spin tunnel device, a problem of a defective device is caused by breakdown of the tunnel insulating film, for example. This reduces the reliability of the device. Also, to maintain reasonable scalability, which is an ultimate objective, a spin injection reversal should be performed at a low current density in a structure that is not affected by a heat fluctuation when the structure is made smaller.
Therefore, it is necessary to provide a spin memory that maintains a low current density so as not to cause breaking of the device at the time of writing by the spin injecting technique, exhibits high resistance to heat fluctuations, and performs a spin reversal at a low current density.
To solve the second problem, the use of a half-metal material for the magnetic material has been suggested (see APL84 (2004) 2307, for example). Where such a half-metal material is employed, a sufficient output difference is not achieved, and a larger increase in the output difference is expected.
As described above, a spin MOSFET structure that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal has not been produced yet.
SUMMARY OF THE INVENTION
The present invention has been made in view of these circumstances, and an object thereof is to provide a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
A spin MOSFET according to a first aspect of the present invention includes: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer being a tunnel insulator and provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable and a magnetization direction of the magnetization pinned layer being fixed; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film.
A spin MOSFET according to a second aspect of the present invention includes: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable and a magnetization direction of the magnetization pinned layer being pinned and antiparallel to the magnetization direction of the first ferromagnetic layer; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film, a gate voltage that causes a negative magnetoresistance effect being applied when writing is performed, a gate voltage that causes a positive magnetoresistance effect being applied when reading is performed.
A spin MOSFET according to a third aspect of the present invention includes: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable and a magnetization direction of the magnetization pinned layer being pinned and parallel to the magnetization direction of the first ferromagnetic layer; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film, a gate voltage that causes a positive magnetoresistance effect being applied when writing is performed, a gate voltage that causes a negative magnetoresistance effect being applied when reading is performed.
A spin MOSFET according to a fourth aspect of the present invention includes: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable, the magnetization free layer including a stacked structure containing a second ferromagnetic layer, a second nonmagnetic layer, and a third ferromagnetic layer, the second and third ferromagnetic layers being antiferromagnetically coupled to each other, and a magnetization direction of the magnetization pinned layer being pinned and antiparallel to the magnetization direction of the first ferromagnetic layer; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film, a gate voltage that causes a negative magnetoresistance effect being applied when writing is performed, a gate voltage that causes a negative magnetoresistance effect being applied when reading is performed.
A spin MOSFET according to a fifth aspect of the present invention includes: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer, a magnetization direction of the first ferromagnetic layer being pinned; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer, a first nonmagnetic layer provided on the magnetization free layer, and a magnetization pinned layer provided on the first nonmagnetic layer, a magnetization direction of the magnetization free layer being changeable, the magnetization free layer including a stacked structure containing a second ferromagnetic layer, a second nonmagnetic layer, and a third ferromagnetic layer, the second and third ferromagnetic layers being antiferromagnetically coupled to each other, and a magnetization direction of the magnetization pinned layer being pinned and parallel to the magnetization direction of the first ferromagnetic layer; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film, a gate voltage that causes a positive magnetoresistance effect being applied when writing is performed, a gate voltage that causes a positive magnetoresistance effect being applied when reading is performed.
A spin MOSFET according to a sixth aspect of the present invention includes: a semiconductor substrate; a first magnetic film formed on the semiconductor substrate and including a first ferromagnetic layer containing a first half-metal ferromagnetic layer, and a second ferromagnetic layer that is provided on the first ferromagnetic layer and contains a CoFe layer, a magnetization direction of the first half-metal ferromagnetic layer being pinned; a first antiferromagnetic layer provided on the second ferromagnetic layer of the first magnetic film; a second magnetic film formed on the semiconductor substrate to separate from the first magnetic film and including a magnetization free layer containing a second half-metal ferromagnetic layer, a tunnel insulating layer provided on the magnetization free layer, a magnetization pinned layer provided on the tunnel insulating layer, a third ferromagnetic layer provided on the magnetization pinned layer and containing a CoFe layer, and a second antiferromagnetic layer provided on the third ferromagnetic layer, a magnetization direction of the second half-metal ferromagnetic layer being changeable, and a magnetization direction of the magnetization pinned layer being pinned; a gate insulating film provided at least on the semiconductor substrate between the first magnetic film and the second magnetic film; and a gate electrode formed on the gate insulating film.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a spin MOSFET in accordance with an embodiment of the present invention;
FIGS. 2A through 2C show the spin dependence conduction via the channel region when the gate voltage of the spin MOSFET shown in FIG. 1 is varied;
FIG. 3 is a cross-sectional view of a spin MOSFET in accordance with a first embodiment;
FIGS. 4A and 4B are cross-sectional views showing example structures of the second magnetic film of the spin MOSFET in accordance with the first embodiment;
FIG. 5 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the first embodiment;
FIG. 6 is a cross-sectional view of a spin MOSFET in accordance with a second embodiment;
FIGS. 7A through 7D are cross-sectional views showing example structures of the first and second magnetic films of the spin MOSFET in accordance with the second embodiment;
FIG. 8 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the second embodiment;
FIG. 9 is a cross-sectional view of a spin MOSFET in accordance with a third embodiment;
FIG. 10 is a cross-sectional view of a spin MOSFET in accordance with a fourth embodiment;
FIG. 11 is a cross-sectional view of a spin MOSFET in accordance with a fifth embodiment;
FIGS. 12A and 12B are cross-sectional views showing example structures of the second magnetic film of the spin MOSFET in accordance with the fifth embodiment;
FIG. 13 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the fifth embodiment;
FIG. 14 is a cross-sectional view of a spin MOSFET in accordance with a sixth embodiment;
FIGS. 15A through 15D are cross-sectional views showing example structures of the first and second magnetic films of the spin MOSFET in accordance with the sixth embodiment;
FIG. 16 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the sixth embodiment;
FIG. 17 is a cross-sectional view of a spin MOSFET in accordance with a seventh embodiment;
FIG. 18 is a cross-sectional view of a spin MOSFET in accordance with an eighth embodiment;
FIG. 19 is a cross-sectional view of a spin MOSFET in accordance with a ninth embodiment;
FIGS. 20A and 20B are cross-sectional views showing example structures of the second magnetic film of the spin MOSFET in accordance with the ninth embodiment;
FIG. 21 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the ninth embodiment;
FIG. 22 is a cross-sectional view of a spin MOSFET in accordance with a tenth embodiment;
FIGS. 23A through 23D are cross-sectional views showing example structures of the first and second magnetic films of the spin MOSFET in accordance with the tenth embodiment;
FIG. 24 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the tenth embodiment;
FIG. 25 is a cross-sectional view of a spin MOSFET in accordance with an eleventh embodiment;
FIG. 26 is a cross-sectional view of a spin MOSFET in accordance with a twelfth embodiment;
FIG. 27 is a cross-sectional view of a spin MOSFET in accordance with a thirteenth embodiment;
FIGS. 28A and 28B are cross-sectional views showing example structures of the second magnetic film of the spin MOSFET in accordance with the thirteenth embodiment;
FIG. 29 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the thirteenth embodiment;
FIG. 30 is a cross-sectional view of a spin MOSFET in accordance with a fourteenth embodiment;
FIGS. 31A through 31D are cross-sectional views showing example structures of the first and second magnetic films of the spin MOSFET in accordance with the fourteenth embodiment;
FIG. 32 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the fourteenth embodiment;
FIG. 33 is a cross-sectional view of a spin MOSFET in accordance with a fifteenth embodiment;
FIG. 34 is a cross-sectional view of a spin MOSFET in accordance with a sixteenth embodiment;
FIGS. 35( a ) and 35 ( b ) show a spin MOSFET in accordance with a seventeenth embodiment;
FIGS. 36( a ) and 36 ( b ) show a spin MOSFET in accordance with a first modification of the seventeenth embodiment;
FIGS. 37( a ) and 37 ( b ) show a spin MOSFET in accordance with a second modification of the seventeenth embodiment;
FIGS. 38( a ) and 38 ( b ) show a spin MOSFET in accordance with a third modification of the seventeenth embodiment;
FIGS. 39( a ) and 39 ( b ) show a spin MOSFET in accordance with a fourth modification of the seventeenth embodiment;
FIGS. 40( a ) and 40 ( b ) show a spin MOSFET in accordance with a fifth modification of the seventeenth embodiment;
FIG. 41 shows the inclination angle dependence of the spin reversal energy barrier of the magnetization free layer;
FIG. 42 shows the inclination angle dependence of the spin torque;
FIG. 43 is a circuit diagram showing a logic circuit in accordance with an eighteenth embodiment;
FIG. 44 shows the floating gate voltage dependence of the output of the logic circuit of the eighteenth embodiment;
FIG. 45 shows a logical table that is used where the logic circuit of the eighteenth embodiment functions as an AND circuit;
FIG. 46 shows a logical table that is used where the logic circuit of the eighteenth embodiment functions as an OR circuit;
FIG. 47 is a circuit diagram showing a logic circuit in accordance with a first modification of the eighteenth embodiment;
FIG. 48 is a circuit diagram showing a logic circuit in accordance with a second modification of the eighteenth embodiment;
FIGS. 49A and 49B are cross-sectional views showing the procedures for manufacturing the spin MOSFET of each embodiment;
FIG. 50 shows the source-drain voltage dependence of the drain current at the time of reading in the spin MOSFET in a first example;
FIG. 51 shows the source-drain voltage dependence of the drain current at the time of reading in the spin MOSFET in a second example;
FIG. 52 shows the source-drain voltage dependence of the drain current at the time of reading in the spin MOSFET in a third example;
FIG. 53 shows the source-drain voltage dependence of the drain current at the time of reading in the spin MOSFET in a fourth example;
FIG. 54 is a cross-sectional view of a spin MOSFET in accordance with a nineteenth embodiment;
FIG. 55 is a cross-sectional view showing example structure of the second magnetic film of the spin MOSFET in accordance with the nineteenth embodiment;
FIG. 56 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the nineteenth embodiment;
FIG. 57 is a cross-sectional view of a spin MOSFET in accordance with a modification of the nineteenth embodiment;
FIG. 58 is a cross-sectional view of a spin MOSFET in accordance with a twentieth embodiment;
FIG. 59 is a cross-sectional view showing example structure of the second magnetic film of the spin MOSFET in accordance with the twentieth embodiment;
FIG. 60 shows the magnetization directions of the ferromagnetic layers of the first and second magnetic films of the spin MOSFET in accordance with the twentieth embodiment;
FIG. 61 is a cross-sectional view of a spin MOSFET in accordance with a modification of the nineteenth embodiment;
FIG. 62 shows the source-drain voltage dependence of the drain current at the time of reading in the spin MOSFET in fifth through seventh examples;
FIG. 63 is a cross-sectional view of a spin MOSFET in accordance with an embodiment; and
FIG. 64 is a cross-sectional view of a spin MOSFET in accordance with an embodiment.
DETAILED DESCRIPTION OF THE INVENTION
First, before describing the embodiment of the present invention, the course of events for achieving the present invention will be described below.
The inventors produced a spin MOSFET shown in FIG. 1 as a test sample. In this spin MOSFET, a pair of tunnel insulating films 4 is formed on an n-type silicon substrate 2 . The tunnel insulating films 4 are made of MgO and are separated from each other. A first magnetic film 6 including a CoFeB magnetic layer in which a magnetization direction 20 A is pinned is formed on one of the tunnel insulating films 4 . A second magnetic film 8 including a CoFeB magnetic layer (a magnetization free layer) in which a magnetization direction 20 B is changeable is formed on the other one of the tunnel insulating films 4 . A gate insulating film 10 made of MgO is formed on the portion of the silicon substrate 2 located between the pair of the tunnel insulating films 4 , and a gate electrode 12 made of CoFeB is formed on the gate insulating film 10 . In this spin MOSFET, one of the first magnetic film 6 and the second magnetic film 8 serves as the source, and the other one serves as the drain. When a gate voltage is applied to the gate electrode 12 , a spin-polarized current 22 flows from the source to the drain.
FIGS. 2A, 2 B, and 2 C show the results obtained when gate voltages of 0.4 V, 0.8 V, and 1.2 V were applied to the spin MOSFET as a test sample, and the ratio of the magnetoresistance change between the source and drain were measured. This measurement was carried out at room temperature, and the gate length L of the MOSFET was 25 μm. In each of FIGS. 2A, 2 B, and 2 C, the abscissa axis indicates the external magnetic field, and the ordinate axis indicates the resistance observed between the source and drain. When the gate voltage Vg of 0.4 V was applied to the spin MOSFET, a positive magnetoresistance effect was observed (FIG. 2A). When the gate voltage Vg of 0.8 V was applied to the spin MOSFET, a negative magnetoresistance effect was observed (FIG. 2B). When the gate voltage Vg of 1.2 V was applied to the spin MOSFET, a positive magnetoresistance effect was observed (FIG. 2C). Those results imply that the sign of the magnetoresistance change varies with the size of the gate voltage Vg. This phenomenon shows that the electron spins injected into a semiconductor are rotated due to a spin orbit interaction, but the rotation can be controlled by adjusting the gate voltage. Based on this finding, the inventors developed the spin MOSFETs of the following embodiments of the present invention. When a positive magnetoresistance effect is observed, the spin direction of spin-polarized electrons injected to a semiconductor (channel) from one of the source and drain is reversed 180 degrees while the electrons are passing through the semiconductor (channel), and the electrons then reach the other one of the source and drain. When a negative magnetoresistance effect is observed, the spin direction of spin-polarized electrons injected to the channel from one of the source and drain is not reversed, and the electrons reach the other one of the source and drain.
First Embodiment
FIG. 3 is a cross-sectional view of a spin MOSFET in accordance with a first embodiment of the present invention. The spin MOSFET of this embodiment has a semiconductor substrate 2 made of silicon, for example, and a first magnetic film 6 and a second magnetic film 8 arranged at a distance from each other on the semiconductor substrate 2 . The first magnetic film 6 in which a magnetization direction is pinned serves as a source or a drain. The second magnetic film 8 in which a magnetization direction is changeable serves as a source or a drain. A tunnel insulating film 4 is formed in the junction plane between the semiconductor substrate 2 and the first and second magnetic films 6 and 8 . A gate insulating film 10 is formed on a region 3 (a channel region 3 ) of the semiconductor substrate 2 between the first and second magnetic films 6 and 8 . A gate electrode 12 is formed on the gate insulating film 10 . An antiferromagnetic layer 7 that pins the magnetization direction of the first magnetic film 6 is formed on the first magnetic film 6 . In FIG. 3, I indicates the spin injection current.
In this embodiment, the first magnetic film 6 is formed with a single-layer ferromagnetic layer, and the second magnetic film 8 is formed with a stacked structure that has ferromagnetic layers and nonmagnetic layers alternately stacked. FIG. 4A shows the structure of a first specific example of the second magnetic film 8 . The second magnetic film 8 of this first specific example has a ferromagnetic layer (a magnetization free layer) 8 1 in which a magnetization direction is changeable, a nonmagnetic layer 8 2 , a ferromagnetic layer 8 3 in which a magnetization direction is pinned, a nonmagnetic layer 8 4 , a ferromagnetic layer 8 5 in which a magnetization direction is pinned, and an antiferromagnetic layer 9 that are stacked in this order. In this first specific example, the ferromagnetic layer 8 3 , the nonmagnetic layer 8 4 , and the ferromagnetic layer 8 5 form a synthetic magnetization pinned layer. This magnetization pinned layer has the magnetization of which a direction is pinned by virtue of the antiferromagnetic layer 9 . The ferromagnetic layer 8 3 and the nonmagnetic layer 8 5 are antiferromagnetically coupled to each other via the nonmagnetic layer 8 4 . In this case, the synthetic magnetization pinned layer is more firmly pinned, so that excellent device stability can be achieved. In a spin MOSFET having the first specific example structure as the second magnetic film 8 , the antiferromagnetic layer 7 and the antiferromagnetic layer 9 may be made of the same material, and the magnetization directions of the ferromagnetic layer of the first magnetic film 6 and the ferromagnetic layers 8 3 and 8 5 of the second magnetic film 8 can be pinned simply through the annealing performed for pinning magnetization directions.
FIG. 4B shows the structure of a second specific example of the second magnetic film 8 . The second magnetic film 8 of this second specific example has a ferromagnetic layer (a magnetization free layer) 8 1 in which a magnetization direction is changeable, a nonmagnetic layer 8 2 , a ferromagnetic layer 8 3 in which a magnetization direction is pinned, and an antiferromagnetic layer 9 that are stacked in this order. In a spin MOSFET having the second specific example structure as the second magnetic film 8 , the antiferromagnetic layer 7 and the antiferromagnetic layer 9 need to be made of different materials from each other, and the magnetic field needs to be reversed 180 degrees through the annealing performed for pinning magnetization directions.
FIG. 5 shows the magnetization (spin) directions of the ferromagnetic layer of the first magnetic layer 6 and the ferromagnetic layers 8 1 , 8 3 , and 8 5 of the second magnetic film 8 in a case where the first specific example structure shown in FIG. 4A is employed as the second magnetic film 8 . In this example, the magnetization direction of the first magnetic film 6 is opposite (antiparallel) to the magnetization directions of the ferromagnetic layers 8 3 and 8 5 of the magnetization pinned layer. In this specification, the magnetization direction of the magnetization pinned layer is the magnetization direction of the ferromagnetic layer closest to the magnetization free layer (the ferromagnetic layer 8 3 in this example), and the magnetization direction of the first magnetic film 6 is the magnetization direction of the ferromagnetic layer in which electrons flow into the channel 3 . However, in a case where the first magnetic film 6 is formed with two or more staked ferromagnetic layers constituting a multilayer structure, the magnetization direction of the first magnetic film 6 is the magnetization direction of the ferromagnetic layer that is the lowermost layer of the first magnetic film 6 and is closest to the semiconductor substrate 2 (for example, the ferromagnetic layer 6 1 in the later described second embodiment).
In a spin MOSFET of this embodiment, a gate voltage that causes the negative magnetoresistance effect shown in FIG. 2B is used for writing. In other words, a gate voltage that does not cause a change in the spin direction of spin-polarized electrons when the electrons are passing through the channel 3 is used. In this embodiment, the magnetization direction of the ferromagnetic layer 8 3 has the spin arrangement shown in FIG. 5, or the spin arrangement opposite (antiparallel) to the magnetization direction of the ferromagnetic layer serving as the magnetization pinned layer of the first magnetic film 6 . Accordingly, in a case where the spin direction of the ferromagnetic layer 8 1 serving as a magnetization free layer extends antiparallel to the spin direction of the first magnetic film 6 , spin-polarized electrons are injected into the channel 3 from the first magnetic film 6 , so that the spin direction of the spin-polarized electrons is not changed when the spin-polarized electrons are passing through the channel 3 , and the spin-polarized electrons reach the ferromagnetic layer 8 1 . In this manner, the spin torque is applied onto the ferromagnetic layer 8 1 . Further, the electrons having passed through the ferromagnetic layer 8 1 are reflected by the ferromagnetic layer 8 3 and flow back into the ferromagnetic layer 8 1 . Accordingly, the spin torque is doubly applied onto the ferromagnetic layer 8 1 serving as a magnetization free layer, and the inversion current density at the time of a magnetization reversal caused by the spin injection can be reduced. Meanwhile, in a case where the spin direction of the ferromagnetic layer 8 1 serving as a magnetization free layer extends parallel to the spin direction of the first magnetic film 6 , spin-polarized electrons are injected from the ferromagnetic layer 8 3 into the channel 3 via the ferromagnetic layer 8 1 serving as a magnetization free layer, so that the electrons spin-polarized by the ferromagnetic layer 8 3 reach the ferromagnetic layer 8 1 serving as a magnetization free layer, and the spin torque is applied onto the ferromagnetic layer 8 1 . Further, the electrons having passed through the ferromagnetic layer 8 1 reach the ferromagnetic layer 6 , without a change caused in the spin direction when the electrons are passing through the channel 3 . The spin-polarized electrons are then reflected by the ferromagnetic layer 6 . The reflected electrons then reach the ferromagnetic layer 8 1 , without a change caused in the spin direction when the electrons are passing through the channel 3 . Accordingly, the spin torque is doubly applied onto the ferromagnetic layer 8 1 serving as a magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced. Thus, with the use of a gate voltage that causes a negative magnetoresistance effect at the time of writing, the spin torque is doubly applied to the ferromagnetic layer 8 1 serving as a magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced.
When reading is performed, a gate voltage that causes the positive magnetoresistance effect shown in FIG. 2A is used. In other words, a gate voltage that changes the spin direction of the electrons 180 degrees when the electrons are passing through the channel 3 is used. When reading is performed with the use of the gate voltage in the spin arrangement shown in FIG. 5, the spin direction of electrons passing through the channel 3 is rotated 180 degrees. Accordingly, in a case where the spin direction of the ferromagnetic layer 8 1 serving as a magnetization free layer extends parallel to the spin direction of the first magnetic film 6 , the resistance of the channel 3 is higher than in a case where the spin direction of the electrons passing through the channel 3 is not rotated 180 degrees (where a gate voltage that causes a negative magnetoresistance effect is used). Here, the magnetization direction of the ferromagnetic layer 8 1 extends antiparallel to the magnetization direction of the ferromagnetic layer 8 3 . Accordingly, the resistance between the ferromagnetic layers 8 1 and 8 3 is higher than in a case where the magnetization direction of the ferromagnetic layer 8 1 extends parallel to the magnetization direction of the ferromagnetic layer 8 3 .
Meanwhile, in a case where the spin direction of the ferromagnetic layer 8 1 serving as a magnetization free layer extends antiparallel to the spin direction of the first magnetic film 6 , the resistance of the channel 3 is lower than in a case where the spin direction of the electrons passing through the channel 3 is not rotated 180 degrees (where a gate voltage that causes a negative magnetoresistance effect is used). Here, the magnetization direction of the ferromagnetic layer 8 1 extends parallel to the magnetization direction of the ferromagnetic layer 8 3 . Accordingly, the resistance between the ferromagnetic layers 8 1 and 8 3 is lower than in a case where the magnetization direction of the ferromagnetic layer 8 1 extends antiparallel to the magnetization direction of the ferromagnetic layer 8 3 .
As described above, as a gate voltage that causes a positive magnetoresistance effect is used for reading in this embodiment, the difference between the resistance of the channel 3 and the total resistance between the ferromagnetic layers 8 1 and 8 3 in a case where the magnetization direction of the ferromagnetic layer 8 1 serving as a magnetization free layer is changed is larger than in a case where a gate voltage that causes a negative magnetoresistance effect is used. The rate of magnetoresistance change of the multilayer structure is added to the rate of magnetoresistance change through the channel region 3 . Accordingly, the reading output is greatly increased.
Since the gate voltages suitable for writing and reading vary with the kind of the substrate and the dope amount for the substrate, it is necessary to adjust the gate voltages when necessary. However, as long as the same type of substrate is used and the dope amount for the substrate is made constant, the gate voltages also become constant. In this embodiment, the tunnel insulating film 4 is provided between the semiconductor substrate 2 and the first and second magnetic films 6 and 8 . Accordingly, diffusion of the semiconductor and the magnetic materials can be prevented, and a rate of magnetoresistance change through the channel region 3 can be observed at room temperature, as shown in FIGS. 2A, 2 B, and 2 C, even if materials having low resistance are used for the magnetic materials. Thus, better characteristics can be achieved.
As described above, this embodiment provides a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
In this embodiment, the magnetic materials for the ferromagnetic layers of the first and second magnetic films are not particularly limited. It is possible to employ thin films made of at least one material selected from the group consisting of Ni—Fe alloys, Co—Fe alloys, Co—Fe—Ni alloys, amorphous materials such as (Co, Fe)—(B), (Co, Fe, Ni)—(B), (Co, Fe, Ni)—(B)—(P, Al, Mo, Nb, Mn) based or Co—(Zr, Hf, Nb, Ta, Ti) based alloys, Huesler materials such as Co—Cr—Fe—Al based, Co—Cr—Fe—Si based, Co—Mn—Si based, and Co—Mn—Al based alloys, thin films made of half-metal materials such as Fe 3 Si based alloys produced through solid-phase diffusion of Fe and Si, or multilayer films formed with any of those thin films.
In a later described Schottky spin MOSFET not having the tunnel insulating film 4 , the magnetic materials of the ferromagnetic layers should preferably have high resistance. Accordingly, the ferromagnetic layers should preferably be formed with thin films made of at least one material selected from the group consisting of amorphous materials such as (Co, Fe)—(B), (Co, Fe, Ni)—(B), (Co, Fe, Ni)—(B)—(P, Al, Mo, Nb, Mn) based or Co—(Zr, Hf, Nb, Ta, Ti) based alloys, and Heusler materials such as Co—Cr—Fe—Al based, Co—Cr—Fe—Si based, Co—Mn—Si based, and Co—Mn—Al based alloys, or half-metal materials such as Fe 3 Si based alloys produced through solid-phase diffusion of Fe and Si.
The magnetization pinned layer should preferably have unidirectional anisotropy, and the magnetization free layer should preferably have uniaxial anisotropy. The thickness of each of those layers should preferably be in the range of 0.1 nm to 100 nm. Furthermore, the film thickness of each of those ferromagnetic layers needs to be so large as not to have super paramagnetism, and should preferably be 0.4 nm or larger.
The magnetic characteristics of those magnetic materials can be adjusted by adding thereto a nonmagnetic element such as Ag (silver), Cu (copper), Au (gold), Al (aluminum), Mg (magnesium), Si (silicon), Bi (bismuth), Ta (tantalum), B (boron), C (carbon), O (oxygen), N (nitrogen), Pd (palladium), Pt (platinum), Zr (zirconium), Ir (iridium), W (tungsten), Mo (molybdenum), or Nb (niobium). Also, other physical properties such as crystallinity, mechanical properties, and chemical properties can be adjusted. Particularly, the ferromagnetic layer close to the tunnel insulating film should preferably be made of Co—Fe, Co—Fe—Ni, Fe-rich Ni—Fe, or the like, which has high MR (magnetoresistance). The ferromagnetic layers that are not in contact with the tunnel insulating film should preferably be made of Ni-rich Ni—Fe, Ni-rich Ni—Fe—Co, or the like. With this arrangement, the switching magnetic field can be reduced, while the high MR is maintained.
The material for the nonmagnetic layer 8 2 may be made of a metal element such as Cu, Ag, or Au, or an alloy containing those metals, or an oxide such as AlOx or MgO. It is particularly preferable to use an oxide tunnel insulating film made of Al 2 O 3 (aluminum oxide) or MgO (magnesium oxide). With this arrangement, the output at the time of reading becomes larger.
In a case where the nonmagnetic layer 8 2 is formed with a tunnel insulating film, the insulating layer (or a dielectric layer) provided between the magnetization pinned layer 6 and the magnetization free layer 8 1 may be formed with an insulator (a dielectric) such as SiO 2 (silicon oxide), AlN (aluminum nitride), Bi 2 O 3 (bismuth oxide), MgF 2 (magnesium fluoride), CaF 2 (calcium fluoride), SrTiO 2 (strontium titanium oxide), AlLaO 3 (aluminum lanthanum oxide), or Al—N—O (aluminum oxynitride).
Those compounds may not necessarily be precise compositions in terms of stoichiometry, but may be devoid of oxygen, nitrogen, or fluorine, or may have oxygen, nitrogen or fluorine overages or shortages. Also, the thickness of this insulating layer (the dielectric layer) is preferably so small as to allow a tunnel current to flow, but should preferably be 10 nm or less in practice.
The nonmagnetic layer 8 4 is preferably made of Ru, Rh, or Ir, or an alloy of those materials. With the use of those materials, the magnetization of the magnetization pinned layers 8 3 , 8 4 , and 8 5 can be stably fixed.
More specifically, to fix the ferromagnetic layers in one direction, it is preferable to use a stacked film having a three-layer structure consisting of Co(Co—Fe)/Ru (ruthenium)/Co(Co—Fe), a stacked film having a three-layer structure consisting of Co(Co—Fe)/Ir (iridium)/Co(Co—Fe), a stacked film having a three-layer structure consisting of Co(Co—Fe)/Os (osmium)/Co(Co—Fe), a laminated film having a three-layer structure consisting of Co(Co—Fe)/Re (rhenium)/Co(Co—Fe), a stacked film having a three-layer structure consisting of an amorphous material layer such as a Co—Fe—B layer, a Ru (ruthenium) layer, and a Co—Fe layer, a stacked film having a three-layer structure consisting of an amorphous material layer such as a Co—Fe—B layer, an Ir (iridium) layer, and a Co—Fe layer, a stacked film having a three-layer structure consisting of an amorphous material layer such as a Co—Fe—B layer, an Os (osmium) layer, and a Co—Fe layer, or a stacked film having a three-layer structure consisting of an amorphous material layer such as a Co—Fe—B layer, a Re (rhenium) layer, and a Co—Fe layer. In a case where those stacked films are used for the magnetization pinned layer, it is desirable to provide an antiferromagnetic layer in contact with the stacked films. Such an antiferromagnetic layer may be formed with Fe—Mn, Pt—Mn, Pt—Cr—Mn, Ni—Mn, Ir—Mn, NiO, Fe 2 O 3 , or the like, as described above. With this structure, the magnetization of the magnetization pinned layer cannot be easily affected by a magnetic field induced by a current from the bit lines or the word lines, and is firmly secured. Also, the stray field from the magnetization pinned layers can be reduced (or adjusted), and the magnetization shift of the magnetization free layer can be controlled by changing the film thickness of the two ferromagnetic layers constituting the magnetization pinned layer. The film thickness of each of those ferromagnetic layers needs to be so large as not to cause super paramagnetism, and should preferably be 0.4 nm or larger. As for the nonmagnetic material, it is possible to employ Rh (rhodium), Ru (ruthenium), Os (osmium), Re (Rhenium), or Ir (iridium), or an alloy of those materials.
As for the magnetization free layer, the magnetic characteristics of the magnetic material can be adjusted by adding thereto a nonmagnetic element such as Ag (silver), Cu (copper), Au (gold), Al (aluminum), Ru (ruthenium), Os (osmium), Re (rhenium), Mg (magnesium), Si (silicon), Bi (bismuth), Ta (tantalum), B (boron), C (carbon), O (oxygen), N (nitrogen), Pd (palladium), Pt (platinum), Zr (zirconium), Ir (iridium), W (tungsten), Mo (molybdenum), or Nb (niobium).
Also, other physical properties such as crystallinity, mechanical properties, and chemical properties can be adjusted.
Also, the antiferromagnetic film may be formed with PtMn, Ir—Mn, FeMn, Pt—Cr—Mn, or Ni—Mn.
The tunnel insulating film 4 may be formed with an oxide such as Al 2 O 3 (aluminum oxide) or MgO (magnesium oxide). Particularly, in a case where the tunnel insulating film 4 is formed with MgO, the magnetic layers 6 and 8 1 to be formed on the tunnel insulating film 4 can be epitaxially grown, and excellent magnetic characteristics can be achieved.
The semiconductor substrate 2 may be a substrate formed with a semiconductor such as Si or Ge, or a compound semiconductor such as GaAs or ZnSe. It is also possible to employ a substrate that has a surface formed with a IV group semiconductor such as Si or Ge, or a III-V or II-VI group compound semiconductor such as GaAs or ZnSe.
Second Embodiment
FIG. 6 is a cross-sectional view of a spin MOSFET in accordance with a second embodiment of the present invention.
The spin MOSFET of this embodiment is the same as the spin MOSFET of the first embodiment shown in FIG. 3, except that the antiferromagnetic layer 7 is removed, and the first magnetic film 6 as a single-layer ferromagnetic layer is replaced with a first magnetic film 6 A that has a stacked structure formed with a synthetic magnetization pinned layer and an antiferromagnetic layer 6 a . As shown in FIG. 7A, the magnetization pinned layer has a stacked structure formed with a ferromagnetic layer 6 1 , a nonmagnetic layer 6 2 , and a ferromagnetic layer 6 3 , and the antiferromagnetic layer 6 a pins the magnetization direction of the magnetization pinned layer. The ferromagnetic layer 6 1 and the ferromagnetic layer 6 3 are antiferromagnetically coupled to each other via the nonmagnetic layer 6 2 .
FIG. 7B shows a first specific example of the second magnetic film 8 of this embodiment. The second magnetic film 8 includes a ferromagnetic layer (a magnetization free layer) 8 1 in which a magnetization direction is changeable, a nonmagnetic layer 8 2 , a ferromagnetic layer 8 3 in which a magnetization direction is pinned, a nonmagnetic layer 8 4 , a ferromagnetic layer 8 5 in which a magnetization direction is pinned, a nonmagnetic layer 8 6 , a ferromagnetic layer 8 7 in which a magnetization direction is pinned, and an antiferromagnetic layer 9 , which are stacked in this order. In this first specific example structure, the ferromagnetic layer 8 3 , the nonmagnetic layer 8 4 , the ferromagnetic layer 8 5 , the nonmagnetic layer 8 6 , and the ferromagnetic layer 8 7 constitute a synthetic magnetization pinned layer, and the magnetization direction of the magnetization pinned layer is pinned by the antiferromagnetic layer 9 . Also, the ferromagnetic layer 8 3 , the ferromagnetic layer 8 5 , and the ferromagnetic layer 8 7 are antiferromagnetically coupled via the nonmagnetic layer 8 4 and the nonmagnetic layer 8 6 . In this case, the synthetic magnetization pinned layer can be more firmly pinned, and excellent device stability can be achieved. In a spin MOSFET having the first specific example structure as the second magnetic film 8 , the antiferromagnetic layer 6 a and the antiferromagnetic layer 9 may be made of the same material, and the magnetization directions of the ferromagnetic layers 6 1 and 6 3 of the first magnetic film 6 A and the ferromagnetic layers 8 3 , 8 5 , and 8 7 of the second magnetic film 8 can be pinned simply by the annealing performed for pinning magnetization directions.
FIG. 7C shows a second specific example of the second magnetic film 8 . The second magnetic film 8 of the second specific example includes a ferromagnetic layer (a magnetization free layer) 8 1 in which a magnetization direction is changeable, a nonmagnetic layer 8 2 , a ferromagnetic layer 8 3 in which a magnetization direction is pinned, a nonmagnetic layer 8 4 , a ferromagnetic layer 8 5 in which a magnetization direction is pinned, and an antiferromagnetic layer 9 , which are stacked in this order. In this second specific example structure, the ferromagnetic layer 8 3 , the nonmagnetic layer 8 4 , and the ferromagnetic layer 8 5 constitute a synthetic magnetization pinned layer, and the magnetization direction of the magnetization pinned layer is pinned by the antiferromagnetic layer 9 . Also, the ferromagnetic layer 8 3 and the ferromagnetic layer 8 5 are antiferromagnetically coupled via the nonmagnetic layer 8 4 . In this case, the synthetic magnetization pinned layer can be more firmly pinned, and excellent device stability can be achieved. In a spin MOSFET having the second specific example structure as the second magnetic film 8 , the antiferromagnetic layer 6 a and the antiferromagnetic layer 9 need be formed with different materials from each other, and it is necessary to reverse the magnetic field 180 degrees by the annealing performed for fixing magnetization directions.
FIG. 7D shows a third specific example of the second magnetic film 8 . The second magnetic film 8 of the third specific example includes a ferromagnetic layer (a magnetization free layer) 8 1 in which a magnetization direction is changeable, a nonmagnetic layer 8 2 , a ferromagnetic layer 8 3 in which a magnetization direction is pinned, and an antiferromagnetic layer 9 , which are stacked in this order. In a spin MOSFET having the third specific example structure as the second magnetic film 8 , the antiferromagnetic layer 6 a and the antiferromagnetic layer 9 may be made of the same material, and the magnetization directions of the ferromagnetic layers 6 1 and 6 3 of the first magnetic film 6 A and the ferromagnetic layer 8 3 of the second magnetic film 8 can be pinned simply by the annealing performed for pinning magnetization directions.
FIG. 8 shows the magnetization directions of the ferromagnetic layers 6 1 and 6 3 of the first magnetic film 6 A and the ferromagnetic layers 8 1 , 8 3 , 8 5 , and 8 7 of the second magnetic film 8 in a case where the first specific example structure shown in FIG. 7B is employed as the second magnetic film 8 .
In a spin MOSFET of this embodiment, a gate voltage that causes the negative magnetoresistance effect shown in FIG. 2B is used for writing. Here, the magnetization direction of the ferromagnetic layer 8 3 has the spin arrangement shown in FIG. 8, or the spin arrangement opposite (antiparallel) to the magnetization direction of the ferromagnetic layer 6 1 of the first magnetic film 6 A. In this manner, the spin torque is doubly applied onto the ferromagnetic layer 8 1 serving as a magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced.
When reading is performed, a gate voltage that causes the positive magnetoresistance effect shown in FIG. 2A is used. When reading is performed with the use of the gate voltage in the spin arrangement shown in FIG. 8, the rate of magnetoresistance change of the multilayer structure is added to the rate of magnetoresistance change through the channel region 3 . Accordingly, the reading output is greatly increased.
Since the gate voltages suitable for writing and reading vary with the kind of the substrate and the dope amount for the substrate, it is necessary to adjust the gate voltages when necessary. However, as long as the same type of substrate is used and the dope amount for the substrate is made constant, the gate voltages also become constant. In this embodiment, the tunnel insulating film 4 is provided between the semiconductor substrate 2 and the first and second magnetic films 6 A and 8 . Accordingly, diffusion of the semiconductor and the magnetic materials can be prevented, and a rate of magnetoresistance change through the channel region 3 can be observed at room temperature, as shown in FIGS. 2A, 2 B, and 2 C, even if materials having low resistance are used for the magnetic materials. Thus, better characteristics can be achieved.
As described above, this embodiment provides a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
In this embodiment, the nonmagnetic layer 8 2 may be made of the same material as the nonmagnetic layer 8 2 of the first embodiment, which is Cu, Ag, Au, AlOx, MgO, or the like. The nonmagnetic layers 6 2 , 8 4 , and 8 6 may be made of the same material as the nonmagnetic layer 8 4 of the first embodiment, which is Ru, Rh, Ir, or the like.
Also, the ferromagnetic layers of the first and second magnetic films 6 A and 8 may be made of the same materials as the first and second magnetic films 6 and 8 of the first embodiment.
Third Embodiment
FIG. 9 is a cross-sectional view of a spin MOSFET in accordance with a third embodiment of the present invention. The spin MOSFET of this embodiment is a Schottky spin MOSFET, and is the same as the spin MOSFET of the first embodiment shown in FIG. 3, except that the tunnel insulating film 4 is removed from the structure.
Accordingly, a specific example structure of the second magnetic film 8 of this embodiment has the multilayer structure shown in FIG. 4A or 4 B, like the second magnetic film 8 of the first embodiment. In a case where the second magnetic film 8 has the multilayer structure shown in FIG. 4A, the ferromagnetic layer of the first magnetic film 6 and the ferromagnetic layers 8 1 , 8 3 , and 8 5 of the second magnetic film 8 have the magnetic directions shown in FIG. 5, as in the first embodiment.
As in the first embodiment, a gate voltage that causes the negative magnetoresistance effect shown in FIG. 2B is used for writing. In this manner, the inversion current density at the time of the magnetization reversal caused by spin injection can be reduced.
As in the first embodiment, when reading is performed, a gate voltage that causes the positive magnetoresistance effect shown in FIG. 2A is used. The rate of magnetoresistance change of the multilayer structure is added to the rate of magnetoresistance change through the channel region 3 . Accordingly, the reading output is greatly increased.
Like the first embodiment, this embodiment also provides a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
Fourth Embodiment
FIG. 10 is a cross-sectional view of a spin MOSFET in accordance with a fourth embodiment of the present invention. The spin MOSFET of this embodiment is a Schottky spin MOSFET, and is the same as the spin MOSFET of the second embodiment shown in FIG. 6, except that the tunnel insulating film 4 is removed from the structure.
Accordingly, as in the second embodiment, a specific example structure of the first magnetic film 6 A of this embodiment has the multilayer structure shown in FIG. 7A, and a specific example structure of the second magnetic film 8 of this embodiment have the multilayer structure shown in FIG. 7B, 7 C or 7 D. In a case where the first magnetic film 6 A has the multilayer structure shown in FIG. 7A, and the second magnetic film 8 has the multilayer structure shown in FIG. 7B, the ferromagnetic layers 6 1 and 6 3 of the first magnetic film 6 A and the ferromagnetic layers 8 1 , 8 3 , 8 5 , and 8 7 of the second magnetic film 8 have the magnetic directions shown in FIG. 8, as in the second embodiment.
As in the second embodiment, a gate voltage that causes the negative magnetoresistance effect shown in FIG. 2B is used for writing. In this manner, the inversion current density at the time of the magnetization reversal caused by spin injection can be reduced.
As in the second embodiment, when reading is performed, a gate voltage that causes the positive magnetoresistance effect shown in FIG. 2A is used. The rate of magnetoresistance change of the multilayer structure is added to the rate of magnetoresistance change through the channel region 3 . Accordingly, the reading output is greatly increased.
Like the second embodiment, this embodiment also provides a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
Fifth Embodiment
FIG. 11 is a cross-sectional view of a spin MOSFET in accordance with a fifth embodiment of the present invention. The spin MOSFET of this embodiment is the same as the spin MOSFET of the first embodiment shown in FIG. 3, except that the second magnetic film 8 is replaced with a second magnetic film 18 having a stacked structure formed with ferromagnetic layers and nonmagnetic layers alternately stacked. As shown in FIG. 12A, a first specific example of the second magnetic film 18 includes a ferromagnetic layer (a magnetization free layer) 18 1 in which a magnetization direction is changeable, a nonmagnetic layer 18 2 , a ferromagnetic layer 18 3 in which a magnetization direction is pinned, a nonmagnetic layer 18 4 , a ferromagnetic layer 18 5 in which a magnetization direction is pinned, and an antiferromagnetic layer 19 , which are stacked in this order. In this first specific example structure, the ferromagnetic layer 18 3 , the nonmagnetic layer 18 4 , and the ferromagnetic layer 18 5 constitute a synthetic magnetization pinned layer, and the magnetization direction of the magnetization pinned layer is pinned by the antiferromagnetic layer 19 . Also, the ferromagnetic layer 18 3 and the ferromagnetic layer 18 5 are antiferromagnetically coupled via the nonmagnetic layer 18 4 . In this case, the synthetic magnetization pinned layer can be more firmly pinned, and excellent device stability can be achieved. In a spin MOSFET having the first specific example structure as the second magnetic film 18 , the antiferromagnetic layer 7 and the antiferromagnetic layer 19 need be formed with different materials from each other, and it is necessary to reverse the magnetic field 180 degrees by the annealing performed for fixing magnetization directions.
FIG. 12B shows a second specific example of the second magnetic film 18 . The second magnetic film 18 of the second specific example includes a ferromagnetic layer (a magnetization free layer) 18 1 in which a magnetization direction is changeable, a nonmagnetic layer 18 2 , a ferromagnetic layer 18 3 in which a magnetization direction is pinned, and an antiferromagnetic layer 19 , which are stacked in this order. In a spin MOSFET having the second specific example structure as the second magnetic film 18 , the antiferromagnetic layer 7 and the antiferromagnetic layer 19 may be made of the same material, and the magnetization directions of the ferromagnetic layer of the first magnetic film 6 and the ferromagnetic layer 18 3 of the second magnetic film 18 can be pinned simply by the annealing performed for fixing magnetization directions.
FIG. 13 shows the magnetization directions of the ferromagnetic layer of the first magnetic film 6 and the ferromagnetic layers 18 1 , 18 3 , and 18 5 of the second magnetic film 18 in a case where the first specific example structure shown in FIG. 12A is employed as the second magnetic film 18 .
In a spin MOSFET of this embodiment, a gate voltage that causes the positive magnetoresistance effect shown in FIG. 2A is used for writing. In other words, a gate voltage that changes the spin direction of the electrons 180 degrees when the electrons are passing through the channel 3 is used. In this embodiment, the magnetization direction of the ferromagnetic layer 18 3 has the spin arrangement shown in FIG. 13, or the spin arrangement same as (parallel to) the magnetization direction of the ferromagnetic layer serving as the magnetization pinned layer of the first magnetic film 6 . Accordingly, in a case where the spin direction of the ferromagnetic layer 18 1 serving as a magnetization free layer extends parallel to the spin direction of the first magnetic film 6 , spin-polarized electrons are injected into the channel 3 from the first magnetic film 6 , so that the spin direction of the spin-polarized electrons is rotated 180 degrees when the spin-polarized electrons are passing through the channel 3 , and the spin-polarized electrons reach the ferromagnetic layer 18 1 . In this manner, the spin torque is applied onto the ferromagnetic layer 18 1 . Further, the electrons having passed through the ferromagnetic layer 18 1 are reflected by the ferromagnetic layer 18 3 and flow back into the ferromagnetic layer 18 1 . Accordingly, the spin torque is doubly applied onto the ferromagnetic layer 18 1 serving as a magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced. Meanwhile, in a case where the spin direction of the ferromagnetic layer 18 1 serving as a magnetization free layer extends antiparallel to the spin direction of the first magnetic film 6 , spin-polarized electrons are injected from the ferromagnetic layer 18 3 into the channel 3 via the ferromagnetic layer 18 1 serving as a magnetization free layer, so that the electrons spin-polarized by the ferromagnetic layer 18 3 reach the ferromagnetic layer 18 1 serving as a magnetization free layer, and the spin torque is applied onto the ferromagnetic layer 18 1 . Further, the spin direction of the electrons having passed through the ferromagnetic layer 18 1 is rotated 180 degrees when the electrons are passing through the channel 3 . The electrons then reach the ferromagnetic layer 6 , and are reflected by the ferromagnetic layer 6 . The spin direction of the reflected electrons is rotated 180 degrees when the reflected electrons are passing through the channel 3 . The electrons then reach the ferromagnetic layer 18 1 . Accordingly, the spin torque is doubly applied onto the ferromagnetic layer 18 1 serving as a magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced. Thus, with the use of a gate voltage that causes a positive magnetoresistance effect at the time of writing, the spin torque is doubly applied to the ferromagnetic layer 18 1 serving as a magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced.
When reading is performed, a gate voltage that causes the negative magnetoresistance effect shown in FIG. 2B is used. In other words, a gate voltage that does not cause a change in the spin direction of spin-polarized electrons when the electrons are passing through the channel 3 is used. When reading is performed with the use of the gate voltage in the spin arrangement shown in FIG. 13, the spin direction of electrons passing through the channel 3 is not changed. Accordingly, in a case where the spin direction of the ferromagnetic layer 18 1 serving as a magnetization free layer extends parallel to the spin direction of the first magnetic film 6 , the resistance of the channel 3 is lower than in a case where the spin direction of the electrons passing through the channel 3 is rotated 180 degrees (where a gate voltage that causes a positive magnetoresistance effect is used). Here, the magnetization direction of the ferromagnetic layer 18 1 extends parallel to the magnetization direction of the ferromagnetic layer 18 3 . Accordingly, the resistance between the ferromagnetic layers 18 1 and 18 3 is lower than in a case where the magnetization direction of the ferromagnetic layer 18 1 extends antiparallel to the magnetization direction of the ferromagnetic layer 18 3 .
Meanwhile, in a case where the spin direction of the ferromagnetic layer 18 1 serving as a magnetization free layer extends antiparallel to the spin direction of the first magnetic film 6 , the resistance of the channel 3 is higher than in a case where the spin direction of the electrons passing through the channel 3 is rotated 180 degrees (where a gate voltage that causes a positive magnetoresistance effect is used). Here, the magnetization direction of the ferromagnetic layer 18 1 extends antiparallel to the magnetization direction of the ferromagnetic layer 18 3 . Accordingly, the resistance between the ferromagnetic layers 18 1 and 18 3 is higher than in a case where the magnetization direction of the ferromagnetic layer 18 1 extends parallel to the magnetization direction of the ferromagnetic layer 18 3 .
As described above, as a gate voltage that causes a negative magnetoresistance effect is used for reading in this embodiment, the difference between the resistance of the channel 3 and the total resistance between the ferromagnetic layers 18 1 and 18 3 in a case where the magnetization direction of the ferromagnetic layer 18 1 serving as a magnetization free layer is changed is larger than in a case where a gate voltage that causes a positive magnetoresistance effect is used. The rate of magnetoresistance change of the multilayer structure is added to the rate of magnetoresistance change through the channel region 3 . Accordingly, the reading output is greatly increased.
As described above, this embodiment provides a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
In this embodiment, the nonmagnetic layer 18 2 may be made of the same material as the nonmagnetic layer 8 2 of the first embodiment, which is Cu, Ag, Au, AlOx, MgO, or the like. The nonmagnetic layer 18 4 may be made of the same material as the nonmagnetic layer 8 4 of the first embodiment, which is Ru, Rh, Ir, or the like.
Also, the ferromagnetic layers of the first and second magnetic films 6 and 18 may be made of the same materials as the first and second magnetic films 6 and 8 of the first embodiment.
Sixth Embodiment
FIG. 14 is a cross-sectional view of a spin MOSFET in accordance with a sixth embodiment of the present invention. The spin MOSFET of this embodiment is the same as the spin MOSFET of the second embodiment shown in FIG. 6, except that the second magnetic film 8 is replaced with a second magnetic film 18 having a stacked structure formed with ferromagnetic layer and nonmagnetic layers alternately stacked.
The first magnetic film 6 A of this embodiment has a stacked structure of a synthetic magnetization pinned layer and an antiferromagnetic layer 6 a . As shown in FIG. 15A, the magnetization pinned layer has a stacked structure formed with a ferromagnetic layer 6 1 , a nonmagnetic layer 6 2 , and a ferromagnetic layer 6 3 , and the antiferromagnetic layer 6 a pins the magnetization direction of the magnetization pinned layer. The ferromagnetic layer 6 1 and the ferromagnetic layer 6 3 are antiferromagnetically coupled to each other via the nonmagnetic layer 6 2 .
FIG. 15B shows a first specific example of the second magnetic film 18 of this embodiment. The second magnetic film 18 includes a ferromagnetic layer (a magnetization free layer) 18 1 in which a magnetization direction is changeable, a nonmagnetic layer 18 2 , a ferromagnetic layer 18 3 in which a magnetization direction is pinned, a nonmagnetic layer 18 4 , a ferromagnetic layer 18 5 in which a magnetization direction is pinned, a nonmagnetic layer 18 6 , a ferromagnetic layer 18 7 in which a magnetization direction is pinned, and an antiferromagnetic layer 19 , which are stacked in this order. In this first specific example structure, the ferromagnetic layer 18 3 , the nonmagnetic layer 18 4 , the ferromagnetic layer 18 5 , the nonmagnetic layer 18 6 , and the ferromagnetic layer 18 7 constitute a synthetic magnetization pinned layer, and the magnetization direction of the magnetization pinned layer is pinned by the antiferromagnetic layer 19 . Also, the ferromagnetic layer 18 3 , the ferromagnetic layer 18 5 , and the ferromagnetic layer 18 7 are antiferromagnetically coupled via the nonmagnetic layer 18 4 and the nonmagnetic layer 18 6 . In this case, the synthetic magnetization pinned layer can be more firmly pinned, and excellent device stability can be achieved. In a spin MOSFET having the first specific example structure as the second magnetic film 18 , the antiferromagnetic layer 6 a and the antiferromagnetic layer 19 need to be made of different materials from each other, and it is necessary to reverse the magnetic field 180 degrees by the annealing performed for fixing magnetization directions.
FIG. 15C shows a second specific example of the second magnetic film 18 . The second magnetic film 18 of the second specific example includes a ferromagnetic layer (a magnetization free layer) 18 1 in which a magnetization direction is changeable, a nonmagnetic layer 18 2 , a ferromagnetic layer 18 3 in which a magnetization direction is pinned, a nonmagnetic layer 18 4 , a ferromagnetic layer 18 5 in which a magnetization direction is pinned, and an antiferromagnetic layer 19 , which are stacked in this order. In this second specific example structure, the ferromagnetic layer 18 3 , the nonmagnetic layer 18 4 , and the ferromagnetic layer 18 5 constitute a synthetic magnetization pinned layer, and the magnetization direction of the magnetization pinned layer is pinned by the antiferromagnetic layer 19 . Also, the ferromagnetic layer 18 3 and the ferromagnetic layer 18 5 are antiferromagnetically coupled via the nonmagnetic layer 18 4 . In this case, the synthetic magnetization pinned layer can be more firmly pinned, and excellent device stability can be achieved. In a spin MOSFET having the second specific example structure as the second magnetic film 18 , the antiferromagnetic layer 6 a and the antiferromagnetic layer 19 may be made of the same material, and the magnetization directions of the ferromagnetic layers 6 , and 6 3 of the first magnetic film 6 A and the ferromagnetic layers 18 3 and 18 5 of the second magnetic film 18 can be pinned simply by the annealing performed for pinning magnetization directions.
FIG. 15D shows a third specific example of the second magnetic film 18 . The second magnetic film 18 of the third specific example includes a ferromagnetic layer (a magnetization free layer) 18 1 in which a magnetization direction is changeable, a nonmagnetic layer 18 2 , a ferromagnetic layer 18 3 in which a magnetization direction is pinned, and an antiferromagnetic layer 19 , which are stacked in this order. In a spin MOSFET having the third specific example structure as the second magnetic film 18 , the antiferromagnetic layer 6 a and the antiferromagnetic layer 19 need to be made of different materials from each other, and it is necessary to reverse the magnetic field 180 degrees by the annealing performed for fixing magnetization directions.
FIG. 16 shows the magnetization directions of the ferromagnetic layers 6 1 and 6 3 of the first magnetic film 6 A and the ferromagnetic layers 18 1 , 18 3 , 18 5 , and 18 7 of the second magnetic film 18 in a case where the first specific example structure shown in FIG. 15B is employed as the second magnetic film 18 .
In a spin MOSFET of this embodiment, a gate voltage that causes the positive magnetoresistance effect shown in FIG. 2A is used for writing. Here, the magnetization direction of the ferromagnetic layer 18 3 has the spin arrangement shown in FIG. 16, or the spin arrangement same as (parallel to) the magnetization direction of the ferromagnetic layer 6 1 of the first magnetic film 6 A. In this manner, the spin torque is doubly applied onto the ferromagnetic layer 18 1 serving as a magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced.
When reading is performed, a gate voltage that causes the negative magnetoresistance effect shown in FIG. 2B is used. When reading is performed with the use of the gate voltage in the spin arrangement shown in FIG. 16, the rate of magnetoresistance change of the multilayer structure is added to the rate of magnetoresistance change through the channel region 3 . Accordingly, the reading output is greatly increased.
As described above, this embodiment provides a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
In this embodiment, the nonmagnetic layer 18 2 may be made of the same material as the nonmagnetic layer 8 2 of the first embodiment, which is Cu, Ag, Au, AlOx, MgO, or the like. The nonmagnetic layers 6 2 , 18 4 , and 18 6 may be made of the same material as the nonmagnetic layer 8 4 of the first embodiment, which is Ru, Rh, Ir, or the like.
Also, the ferromagnetic layers of the first and second magnetic films 6 A and 18 may be made of the same materials as the first and second magnetic films 6 and 8 of the first embodiment.
Seventh Embodiment
FIG. 17 is a cross-sectional view of a spin MOSFET in accordance with a seventh embodiment of the present invention. The spin MOSFET of this embodiment is a Schottky spin MOSFET, and is the same as the spin MOSFET of the fifth embodiment shown in FIG. 11, except that the tunnel insulating film 4 is removed from the structure.
Accordingly, a specific example structure of the second magnetic film 18 of this embodiment has the multilayer structure shown in FIG. 12A or 12 B, like the second magnetic film 18 of the fifth embodiment. In a case where the second magnetic film 18 has the multilayer structure shown in FIG. 12A, the ferromagnetic layer of the first magnetic film 6 and the ferromagnetic layers 18 1 , 18 3 , and 18 5 of the second magnetic film 18 have the magnetic directions shown in FIG. 13, as in the fifth embodiment.
As in the fifth embodiment, a gate voltage that causes the positive magnetoresistance effect shown in FIG. 2A is used for writing. In this manner, the inversion current density at the time of the magnetization reversal caused by spin injection can be reduced.
As in the fifth embodiment, when reading is performed, a gate voltage that causes the negative magnetoresistance effect shown in FIG. 2B is used. The rate of magnetoresistance change of the multilayer structure is added to the rate of magnetoresistance change through the channel region 3 . Accordingly, the reading output is greatly increased.
Like the fifth embodiment, this embodiment also provides a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
Eighth Embodiment
FIG. 18 is a cross-sectional view of a spin MOSFET in accordance with an eighth embodiment of the present invention. The spin MOSFET of this embodiment is a Schottky spin MOSFET, and is the same as the spin MOSFET of the sixth embodiment shown in FIG. 14, except that the tunnel insulating film 4 is removed from the structure.
Accordingly, as in the sixth embodiment, a specific example structure of the first magnetic film 6 A of this embodiment has the multilayer structure shown in FIG. 15A, and a specific example structure of the second magnetic film 18 of this embodiment have the multilayer structure shown in FIG. 15B, 15 C or 15 D. In a case where the first magnetic film 6 A has the multilayer structure shown in FIG. 15A, and the second magnetic film 18 has the multilayer structure shown in FIG. 15B, the ferromagnetic layers 6 1 and 6 3 of the first magnetic film 6 A and the ferromagnetic layers 18 1 , 18 3 , 18 5 , and 18 7 of the second magnetic film 18 have the magnetic directions shown in FIG. 16, as in the sixth embodiment.
As in the sixth embodiment, a gate voltage that causes the positive magnetoresistance effect shown in FIG. 2A is used for writing. In this manner, the inversion current density at the time of the magnetization reversal caused by spin injection can be reduced.
As in the sixth embodiment, when reading is performed, a gate voltage that causes the negative magnetoresistance effect shown in FIG. 2B is used. The rate of magnetoresistance change of the multilayer structure is added to the rate of magnetoresistance change through the channel region 3 . Accordingly, the reading output is greatly increased.
Like the sixth embodiment, this embodiment also provides a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
Ninth Embodiment
FIG. 19 is a cross-sectional view of a spin MOSFET in accordance with a ninth embodiment of the present invention. The spin MOSFET of this embodiment is the same as the spin MOSFET of the first embodiment shown in FIGS. 3 through 5, except that the second magnetic film 8 is replaced with a second magnetic film 8 A. FIG. 20A shows a first specific example of the second magnetic film 8 A. This first specific example of the second magnetic film 8 A includes a synthetic magnetization pinned layer and an antiferromagnetic layer 9 . The magnetization pinned layer has a stacked structure formed with a magnetization free layer 8 1 consisting of a ferromagnetic layer 8 11 , a nonmagnetic layer 8 12 , and a ferromagnetic layer 8 13 , a nonmagnetic layer 8 2 , a ferromagnetic layer 8 3 , a nonmagnetic layer 8 4 , and a ferromagnetic layer 8 5 . The antiferromagnetic layer 9 pins the magnetization direction of the magnetization pinned layer. In the magnetization pinned layer of the second magnetic film 8 A, the ferromagnetic layer 8 3 and the ferromagnetic layer 8 5 are antiferromagnetically coupled via the nonmagnetic layer 8 4 . In this case, the synthetic magnetization pinned layer can be more firmly fixed, and excellent device stability can be achieved. In a spin MOSFET having the first specific example structure as the second magnetic film 8 A, the antiferromagnetic layer 7 and the antiferromagnetic layer 9 need be formed with different materials from each other, and it is necessary to reverse the magnetic field 180 degrees by the annealing performed for fixing magnetization directions.
FIG. 20B shows a second specific example of the second magnetic film 8 A. The second magnetic film 8 A of the second specific example includes a magnetization free layer 8 1 consisting of a ferromagnetic layer 8 11 , a nonmagnetic layer 8 12 , and a ferromagnetic layer 8 13 , a nonmagnetic layer 8 2 , a ferromagnetic layer 8 3 in which a magnetization direction is pinned, and an antiferromagnetic layer 9 , which are stacked in this order. In a spin MOSFET having the second specific example structure as the second magnetic film 8 A, the antiferromagnetic layer 7 and the antiferromagnetic layer 9 may be made of the same material, and the magnetization directions of the ferromagnetic layer of the first magnetic film 6 and the ferromagnetic layer 18 3 of the second magnetic film 8 A can be pinned simply by the annealing performed for pinning magnetization directions.
FIG. 21 shows the magnetization directions of the ferromagnetic layer of the first magnetic film 6 and the ferromagnetic layers 8 1 , 8 3 , and 8 5 of the second magnetic film 8 A in a case where the first specific example structure shown in FIG. 20B is employed as the second magnetic film 8 A.
In a spin MOSFET of this embodiment, the magnetization direction of the ferromagnetic layer of the first magnetic film 6 extends parallel to the magnetization direction of the ferromagnetic layer 8 3 , and the ferromagnetic layer 8 1 serving as a magnetization free layer has a synthetic structure formed with the ferromagnetic layer 8 11 , the nonmagnetic layer 8 12 , and the ferromagnetic layer 8 13 . Therefore, a gate voltage that causes the positive magnetoresistance effect shown in FIG. 2A is used for writing and reading. In other words, a gate voltage that changes the spin direction of the electrons 180 degrees when the electrons are passing through the channel 3 is used.
In this embodiment, the magnetization direction of the ferromagnetic layer 8 3 has the spin arrangement shown in FIG. 21, or the spin arrangement same as (parallel to) the magnetization direction of the ferromagnetic layer serving as the magnetization pinned layer of the first magnetic film 6 . Accordingly, in a case where the spin direction of the ferromagnetic layer 8 11 serving as a magnetization free layer extends parallel to the spin direction of the first magnetic film 6 , spin-polarized electrons are injected into the channel 3 from the first magnetic film 6 , so that the spin direction of the spin-polarized electrons is rotated 180 degrees when the spin-polarized electrons are passing through the channel 3 , and the spin-polarized electrons reach the ferromagnetic layer 8 11 . In this manner, the spin torque is applied onto the ferromagnetic layer 8 11 . Further, the electrons pass through the ferromagnetic layers 8 11 , and 8 13 , and reach the ferromagnetic layer 8 3 . The electrons are then reflected by the ferromagnetic layer 8 3 , and flow back into the ferromagnetic layer 8 11 , through the ferromagnetic layer 8 13 . In this manner, the spin torque is again applied onto the ferromagnetic layer 8 11 . Accordingly, the spin torque is doubly applied onto the magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced.
Meanwhile, in a case where the spin direction of the ferromagnetic layer 8 11 serving as a magnetization free layer extends antiparallel to the spin direction of the first magnetic film 6 , spin-polarized electrons are injected into the magnetization free layer from the ferromagnetic layer 8 3 , so that the spin-polarized electrons reach the ferromagnetic layer 8 11 through the ferromagnetic layer 8 13 , and the spin torque is applied onto the ferromagnetic layer 8 11 . Further, the spin direction of the electrons having reached the ferromagnetic layer 8 11 , is rotated 180 degrees when the electrons are passing through the channel 3 . The electrons then reach the ferromagnetic layer 6 , and are reflected by the ferromagnetic layer 6 . The spin direction of the reflected electrons is rotated 180 degrees when the reflected electrons are passing through the channel 3 . The electrons then reach the ferromagnetic layer 8 11 . Accordingly, the spin torque is doubly applied onto the magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced. Thus, with the use of a gate voltage that causes a positive magnetoresistance effect at the time of writing, the spin torque is doubly applied to the magnetization free layer, and the inversion current density at the time of the magnetization reversal caused by the spin injection can be reduced.
When reading is performed in the spin arrangement shown in FIG. 21, the spin direction of electrons passing through the channel 3 is changed 180 degrees. Accordingly, in a case where the spin direction of the ferromagnetic layer 8 11 , serving as a magnetization free layer extends parallel to the spin direction of the first magnetic film 6 , the resistance of the channel 3 is higher than in a case where the spin direction of the electrons passing through the channel 3 is not changed (where a gate voltage that causes a negative magnetoresistance effect is used). Here, the magnetization direction of the ferromagnetic layer 8 13 extends antiparallel to the magnetization direction of the ferromagnetic layer 8 3 . Accordingly, the resistance between the ferromagnetic layers 8 13 and 8 3 is higher than in a case where the magnetization direction of the ferromagnetic layer 8 13 extends parallel to the magnetization direction of the ferromagnetic layer 8 3 .
Meanwhile, in a case where the spin direction of the ferromagnetic layer 8 11 serving as a magnetization free layer extends antiparallel to the spin direction of the first magnetic film 6 , the resistance of the channel 3 is lower than in a case where the spin direction of the electrons passing through the channel 3 is not changed (where a gate voltage that causes a negative magnetoresistance effect is used). Here, the magnetization direction of the ferromagnetic layer 8 13 extends parallel to the magnetization direction of the ferromagnetic layer 8 3 . Accordingly, the resistance between the ferromagnetic layers 8 13 and 8 3 is lower than in a case where the magnetization direction of the ferromagnetic layer 8 13 extends antiparallel to the magnetization direction of the ferromagnetic layer 8 3 .
As described above, as a gate voltage that causes a positive magnetoresistance effect is used for reading in this embodiment, the difference between the resistance of the channel 3 and the total resistance between the ferromagnetic layers 8 13 and 8 3 in a case where the magnetization direction of the magnetization free layer is changed is larger than in a case where a gate voltage that causes a negative magnetoresistance effect is used. The rate of magnetoresistance change of the multilayer structure is added to the rate of magnetoresistance change through the channel region 3 . Accordingly, the reading output is greatly increased.
As described above, this embodiment provides a spin MOSFET that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal.
In this embodiment, the nonmagnetic layer 8 2 may be made of the same material as the nonmagnetic layer 8 2 of the first embodiment, which is Cu, Ag, Au, AlOx, MgO, or the like. The nonmagnetic layers 8 12 and 8 4 may be made of the same material as