JP2009105285A - Spin filter effect element, and spin transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spin filter effect element having a sufficiently high spin filter effect to a semiconductor layer; and a spin transistor having sufficiently high magnetic resistivity between source and drain electrodes. <P>SOLUTION: This spin transistor 10 includes: a source electrode layer 3; a drain electrode layer 7; a semiconductor layer 9 having the source electrode layer 3 and the drain electrode layer 7 formed thereon; and a gate electrode layer GE formed on the semiconductor layer 8 directly or through an insulation layer GI. At least one of the source electrode layer 3 and the drain electrode layer 7 includes ferromagnetic layers SI and DI contacting the semiconductor layer 9, and metal layers SE and DE contacting sides of the ferromagnetic insulation layers SI and DI opposite to the semiconductor 9 sides. The ferromagnetic layers SI and DI form tunnel barriers between the semiconductor layer 9 and the metal layers SE and DE. The semiconductor layer 9 and the metal layers SE and DE are formed of materials coming into Schottky contact when brought into contact with each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spin filter effect element and a spin transistor.

  In recent years, research on spin electronics has attracted attention. Spin transistors are transistors that use electron spin, and are expected to cause innovations in new technologies. The spin transistor can be used as a memory element having a new structure or a multi-function logic circuit. Since the spin transistor is manufactured using a magnetic process, it can be used as a control element of the magnetic element.

  For example, in FIG. 11 of Patent Document 1 below, a nonmagnetic semiconductor layer is provided between a source electrode and a drain electrode made of a ferromagnetic material, and a gate electrode layer is provided on the semiconductor layer via a gate insulating layer. A spin transistor is disclosed.

  In this conventional spin transistor, electrons spin-polarized by the source electrode are injected into the semiconductor layer. That is, the source electrode has a function as a normal electrode and a function as a spin filter effect film, and constitutes a spin filter effect element together with the semiconductor layer. The direction of spin polarization of electrons injected into the semiconductor layer depends on the magnetization direction of the source electrode, and the rate of spin polarization of electrons injected into the semiconductor layer depends on the spin polarization of the source electrode that is a spin filter effect film. Depends on rate.

  Electrons injected into the drain electrode through the channel of the semiconductor layer are scattered depending on the direction of polarization. In other words, electrons injected from the source electrode into the channel in the semiconductor layer are spin-dependently scattered at the interface between the semiconductor layer and the drain electrode. In other words, the drain electrode has both a function as a normal electrode and a function as a spin filter effect film that preferentially accepts electrons polarized in a specific direction, and constitutes a spin filter effect element together with the semiconductor layer. Yes. Therefore, when the magnetization directions of the source electrode and the drain electrode are parallel, the resistance between the source and drain electrodes is small, and when the magnetization direction is antiparallel, the resistance is large.

  When considering application to a storage element of a spin transistor, the rate of change in resistance between the source and drain electrodes (hereinafter referred to as “source / drain” when the magnetization directions of the source electrode and the drain electrode are parallel and antiparallel) The greater the "magnetic resistivity between the electrodes"), the better. The magnetic resistivity between the source and drain electrodes depends on the strength of the spin filter effect of the spin filter effect element composed of the source and drain electrodes and the semiconductor layer, and the strength of the spin filter effect is It depends mainly on the spin polarizability of the ferromagnetic material constituting the source electrode and the drain electrode.

  Examples of the spin filter effect element using a ferromagnetic material having a high spin polarizability include those disclosed in Patent Document 2 below. This spin filter effect element has a structure in which a thin ferromagnetic insulating layer is sandwiched between a ferromagnetic electrode and a non-magnetic electrode, and a spinel ferrite having a high spin polarizability as a thin ferromagnetic insulating layer. Is used. This spin filter effect element has a spin filter effect film composed of a ferromagnetic insulating layer and an electrode made of a ferromagnetic material, and injects spin-polarized electrons from the spin filter effect film into an electrode made of a nonmagnetic material Can be seen. With such a structure, a spin filter effect element capable of injecting electrons having a high spin polarization rate into an electrode made of a nonmagnetic material is realized. However, when considering application to a spin transistor, since it is necessary to inject spin-polarized electrons into the semiconductor layer, such a spin filter effect element cannot be used as it is in a spin transistor.

In addition, in order to realize a spin transistor having a high magnetic resistivity between the source and drain electrodes, in addition to using a ferromagnetic material having a high spin polarizability as the spin filter effect film, an appropriate combination of the spin filter effect film and the semiconductor layer is used. It is known that Schottky contact is required so that a large Schottky barrier is formed. That is, when the spin filter effect film and the semiconductor layer are brought into contact with each other in this manner, spin-polarized electrons in the spin filter effect film ferromagnetic material are spin scattered when passing through the interface between the spin filter effect film and the semiconductor layer. Can reduce the probability. As a result, electrons having a high spin polarizability are injected from the spin filter effect film into the semiconductor layer. For this reason, in the spin transistor disclosed in FIG. 11 of Patent Document 1 below, the material constituting the source electrode and the drain electrode serving as the spin filter effect film is a ferromagnetic material and is appropriately Schottky with the semiconductor layer. What is to be joined is used.
JP 2004-111904 A JP 2004-39672 A

  However, in order to increase the magnetoresistance between the source and drain electrodes in a conventional spin transistor, the spin filter effect film used for it is a ferromagnetic material having a high polarizability and is appropriately shot with a semiconductor layer. The material must satisfy the two conditions of key joining at the same time. For this reason, for example, if a ferromagnetic material having a high polarizability is selected as the material constituting the spin filter effect film, the condition for proper Schottky junction with the semiconductor layer may not be sufficiently satisfied. When a material that appropriately schottky-joins with a semiconductor layer is selected as the material that constitutes the material, the condition of a ferromagnetic material having a high polarizability may not be sufficiently satisfied.

  As a result, the effect of injecting spin-polarized electrons into the semiconductor layer and the effect of causing spin-dependent scattering when spin-polarized electrons are injected from the semiconductor layer (hereinafter referred to as “spin filter effect on the semiconductor layer”) There is a problem that it is difficult to obtain a spin filter effect element that sufficiently exhibits. Furthermore, since it is difficult to obtain a spin filter effect element that sufficiently exhibits the spin filter effect on the semiconductor layer, it is difficult to realize a spin transistor having a sufficiently high magnetoresistance between the source and drain electrodes. There was a problem.

  The present invention has been made in view of such problems, and provides a spin filter effect element having a sufficiently high spin filter effect on a semiconductor layer, and a spin transistor having a sufficiently high magnetic resistivity between source and drain electrodes. The purpose is to do.

  In order to solve the above-described problems, a spin filter effect element according to the present invention is formed by stacking a semiconductor layer, a ferromagnetic insulating layer stacked on the semiconductor layer, and a side opposite to the semiconductor layer side of the ferromagnetic insulating layer. A spin filter effect film having a metal layer, the ferromagnetic insulating layer forms a tunnel barrier between the semiconductor layer and the gold layer, and the semiconductor layer and the metal layer are made of a material that makes a Schottky contact when in direct contact with each other. It is characterized by becoming.

  According to the spin filter effect element of the present invention, the spin filter effect film having the ferromagnetic insulating layer is laminated on the semiconductor layer, and this ferromagnetic insulating layer bears the spin filter effect. Since the ferromagnetic insulating layer forms a tunnel barrier between the semiconductor layer and the gold layer, when a voltage is applied between the metal layer and the semiconductor layer, a tunnel current flows between them. In addition, when the semiconductor layer and the metal layer are in direct contact with each other, a Schottky contact is selected, and since a tunnel current flows through the ferromagnetic insulating layer between them, the semiconductor layer and the metal layer are The same behavior as when Schottky contact is made. As a result, the ferromagnetic insulating layer satisfies the former condition for the condition of using a ferromagnetic material having a high polarizability required for the spin filter effect film used in the semiconductor layer and the condition of making a Schottky contact with the semiconductor layer. The latter condition can be satisfied by the metal layer. That is, in the conventional spin filter effect film, these two conditions must be satisfied by one layer in contact with the semiconductor layer, whereas in the spin filter effect element of the present invention, these two conditions are satisfied. Can be satisfied by separate layers. As a result, the spin filter effect film can be configured so as to more ideally satisfy these two conditions, so that a spin filter effect element having a sufficiently high spin filter effect on the semiconductor layer can be obtained.

  The spin transistor according to the present invention includes a source electrode layer having a ferromagnetic layer, a drain electrode layer having a ferromagnetic layer, a semiconductor layer provided with the source electrode layer and the drain electrode layer, and A gate electrode layer provided via a gate insulating layer, at least one of the source electrode layer and the drain electrode layer being a ferromagnetic insulating layer as a ferromagnetic layer in contact with the semiconductor layer, and a semiconductor of the ferromagnetic insulating layer A material that has a metal layer in contact with the opposite side of the layer side, the ferromagnetic insulating layer forms a tunnel barrier between the semiconductor layer and the metal layer, and the material that makes a Schottky contact when the semiconductor layer and the metal layer are in direct contact with each other It is characterized by comprising.

  According to the spin transistor of the present invention, when a voltage is applied to the gate electrode layer, a channel is formed in the semiconductor layer corresponding to the voltage, so that carriers flowing from the source electrode layer into the channel of the semiconductor layer are generated. To increase. Therefore, the same function as a normal field effect transistor is exhibited. At this time, since the source electrode layer having the ferromagnetic layer functions as a spin filter effect film, carriers spin-polarized in the same direction as the magnetization direction of the source electrode layer are injected into the semiconductor layer.

  Then, spin-polarized carriers injected into the semiconductor layer flow into the drain electrode layer. At this time, since the drain electrode layer having a ferromagnetic layer functions as a spin filter effect film, spin-polarized carriers injected into the semiconductor layer are spin-dependently scattered at the interface between the semiconductor layer and the drain electrode layer. It becomes.

  That is, when the magnetization direction of the source electrode layer is opposite to the magnetization direction of the drain electrode layer, most of the spin-polarized carriers injected into the semiconductor layer are reflected at the interface between the semiconductor layer and the drain electrode layer, It is difficult to flow into the drain electrode layer. On the other hand, when the magnetization direction of the source electrode layer is the same as the magnetization direction of the spin filter layer, most of the spin-polarized carriers injected into the semiconductor layer pass through the interface between the semiconductor layer and the drain electrode layer, and the drain electrode Flows into the layer. For this reason, the resistance value between the source and drain electrode layers differs depending on whether the magnetization directions of the source electrode layer and the drain electrode layer are parallel or antiparallel.

  In the spin transistor of the present invention, at least one of the source electrode layer and the drain electrode layer has a ferromagnetic insulating layer as a ferromagnetic layer. Since the ferromagnetic insulating layer forms a tunnel barrier between the semiconductor layer and the gold layer, when a voltage is applied between the metal layer and the semiconductor layer, a tunnel current flows between them. In addition, when the semiconductor layer and the metal layer are in direct contact with each other, a Schottky contact is selected, and since a tunnel current flows through the ferromagnetic insulating layer between them, the semiconductor layer and the metal layer are The same behavior as when Schottky contact is made.

  As a result, the ferromagnetic insulating layer satisfies the former condition for the condition of using a ferromagnetic material having a high polarizability required for the spin filter effect film used in the semiconductor layer and the condition of making a Schottky contact with the semiconductor layer. The latter condition can be satisfied by the metal layer. That is, in the conventional spin filter effect film, these two conditions must be satisfied by one layer in contact with the semiconductor layer, whereas in the spin filter effect element of the present invention, these two conditions are satisfied. Can be satisfied by separate layers. Therefore, since the spin filter effect film can be configured to more ideally satisfy these two conditions, a spin transistor including a spin filter effect element having a sufficiently high spin filter effect on the semiconductor layer can be obtained. it can. As a result, a spin transistor having a sufficiently high magnetoresistance between the source and drain electrodes can be obtained.

  Furthermore, each of the source electrode layer and the drain electrode layer has a ferromagnetic insulating layer as a ferromagnetic layer in contact with the semiconductor layer, and a metal layer in contact with the opposite side of the ferromagnetic insulating layer to the semiconductor layer side. The magnetic insulating layer forms a tunnel barrier between the semiconductor layer and the metal layer, and the semiconductor layer and the metal layer are preferably made of a material that makes a Schottky contact when brought into direct contact with each other.

  As a result, the source electrode layer and the drain electrode layer become spin filter effect films that more ideally satisfy the above two conditions for the semiconductor layer. As a result, a spin transistor having a higher magnetic resistivity between the source and drain electrodes can be obtained.

  Furthermore, the resistivity of the ferromagnetic insulating layer is preferably 1 Ω · cm or more. As a result, the ferromagnetic insulating layer can reliably form a tunnel barrier between the semiconductor layer and the gold layer. As a result, at least one of the source electrode layer and the drain electrode layer becomes a spin filter effect film that more reliably satisfies the above-described two conditions with respect to the semiconductor layer, so that a highly reliable spin transistor can be obtained.

  Further, the metal film is selected from the group consisting of Be, B, Mg, Al, Ti, Cu, Zn, Zr, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Pt, and Au. It is preferable to contain at least one selected from the above.

  Furthermore, it is preferable that the magnetization direction of the ferromagnetic layer included in at least one of the source electrode layer and the drain electrode layer is fixed. Thereby, it becomes easy to change the relative angles of the magnetization directions of the source electrode layer and the drain electrode layer. As a result, a spin transistor capable of easily changing the resistance value between the source and drain electrodes can be obtained.

  Furthermore, it is preferable that the magnetization direction of the ferromagnetic layer included in at least one of the source electrode layer and the drain electrode layer is fixed by shape anisotropy. Thereby, the magnetization direction can be fixed only by forming at least one of the source electrode layer and the drain electrode layer so as to have an appropriate shape.

  Furthermore, it is preferable that the magnetization directions of the ferromagnetic layers of both the source electrode layer and the drain electrode layer are fixed by shape anisotropy. This makes it easier to change the relative angles of the respective magnetization directions of the source electrode layer and the drain electrode layer. As a result, a spin transistor capable of changing the resistance value between the source and drain electrodes more easily can be obtained.

  Furthermore, the coercive forces of the ferromagnetic layers of the source electrode layer and the drain electrode layer are preferably different from each other. Thereby, it becomes even easier to change the relative angles of the magnetization directions of the source electrode layer and the drain electrode layer. As a result, a spin transistor capable of changing the resistance value between the source and drain electrodes more easily can be obtained.

  Further, the metal layer of at least one of the source electrode layer and the drain electrode layer is an antiferromagnetic layer, and the magnetization direction of the ferromagnetic layer in contact with the antiferromagnetic layer is fixed by an exchange coupling magnetic field from the antiferromagnetic layer. It is preferable. Thereby, the magnetization direction can be reliably fixed regardless of the shape of the source electrode layer and the drain electrode layer.

  Furthermore, it is preferable that the semiconductor layer further includes a magnetization reversal electrode layer for reversing the magnetization direction of the ferromagnetic layer included in either the source electrode layer or the drain electrode layer by spin injection magnetization reversal. As a result, the magnetization direction of the ferromagnetic layer included in either the source electrode layer or the drain electrode layer can be easily changed. In addition, a mechanism for applying an external magnetic field is unnecessary compared to the case of reversing the magnetization direction of the ferromagnetic layer of either the source electrode layer or the drain electrode layer by applying an external magnetic field. The spin transistor can be miniaturized. In addition, when a large number of spin transistors are integrated, it is easy to change only the magnetization direction of the ferromagnetic layer of a specific element. Furthermore, since the transistor functions and the information storage function are combined, if the two states of the source electrode layer and the drain electrode layer in which the magnetization directions are parallel and anti-parallel are associated with one bit, the nonvolatile state is obtained. A spin transistor that can be used as a conductive semiconductor memory can be obtained.

  According to the present invention, a spin filter effect element having a sufficiently high spin filter effect on a semiconductor layer and a spin transistor having a sufficiently high magnetoresistance between source and drain electrodes are provided.

  Hereinafter, a spin filter effect element and a spin transistor according to embodiments will be described in detail with reference to the accompanying drawings. In addition, in each drawing, the same code | symbol is used for the same element and the overlapping description is abbreviate | omitted. In addition, the dimensional ratios in the components in the drawings and between the components are arbitrary for easy viewing of the drawings.

  FIG. 1 is a diagram showing a vertical cross-sectional configuration of a spin transistor 10 including spin filter effect elements 11 and 13 according to the present embodiment.

  The spin transistor 10 includes a semiconductor layer 9, a source electrode layer 3 having a ferromagnetic insulating layer SI and a metal layer SE, and a semiconductor layer having a ferromagnetic insulating layer DI and a metal layer DE. 9 includes a drain electrode layer 7 provided on the gate electrode 9 and a gate electrode layer GE.

  The ferromagnetic insulating layer SI included in the source electrode layer 3 is in contact with the semiconductor layer 9, and the metal layer SE included in the source electrode layer 3 is in contact with the opposite side of the ferromagnetic insulating layer SI from the semiconductor layer 9 side. The ferromagnetic insulating layer SI is thinly formed so as to form a tunnel barrier between the semiconductor layer 9 and the metal layer SE. Therefore, when a voltage is applied between the semiconductor layer 9 and the metal layer SE, a tunnel current can flow between them. Further, the semiconductor layer 9 and the metal layer SE are selected to be in Schottky contact when brought into direct contact with each other.

  The drain electrode layer 7 is provided on the semiconductor layer 9 so as to be separated from the source electrode layer 3, and has the same configuration as the source electrode layer 3. That is, the ferromagnetic insulating layer DI included in the drain electrode layer 7 is in contact with the semiconductor layer 9, and the metal layer DE included in the drain electrode layer 7 is in contact with the opposite side of the ferromagnetic insulating layer DI from the semiconductor layer 9 side. Yes. The ferromagnetic insulating layer DI is thinly formed so as to form a tunnel barrier between the semiconductor layer 9 and the metal layer DE. Therefore, when a voltage is applied between the semiconductor layer 9 and the metal layer DE, a tunnel current can flow between them. Further, the semiconductor layer 9 and the metal layer DE are selected to be in Schottky contact when brought into direct contact with each other.

  The gate electrode layer GE is provided on the opposite side of the semiconductor layer 9 from the side where the source electrode layer 3 and the drain electrode layer 7 are provided via a gate insulating layer GI. The gate electrode layer GE may be provided on the side of the semiconductor layer 9 where the source electrode layer 3 and the drain electrode layer 7 are provided, and is in Schottky contact with the semiconductor layer 9 without passing through the gate insulating layer GI. As described above, the semiconductor layer 9 may be provided.

A gate voltage V _GS can be applied between the source electrode layer 3 and the gate electrode layer GE, and a drain voltage V _DS can be applied between the source electrode layer 3 and the drain electrode layer 7. ing. The presence / absence of application of the gate voltage V _GS and the drain voltage V _DS is interposed between the switch SW1 interposed between the source electrode layer 3 and the gate electrode layer GE and between the source electrode layer 3 and the drain electrode layer 7, respectively. Determined by the switch SW2.

  The magnetization direction SIM of the ferromagnetic insulating layer SI included in the source electrode layer 3 (the magnetization direction SIM of the source electrode layer 3) is directed in the direction along the positive direction of the Y-axis in FIG. It is fixed in that direction. Further, the magnetization direction DIM of the ferromagnetic insulating layer DI included in the drain electrode layer 7 (the magnetization direction DIM of the drain electrode layer 7) is in the direction along the negative direction of the Y axis in FIG. Thus, the direction can be reversed 180 degrees by applying an external magnetic field. The thickness direction of the semiconductor layer 9 is a direction along the Z axis.

As a material constituting the ferromagnetic insulating layers SI and DI, for example, a spinel ferrite material exhibiting ferromagnetic and insulating properties can be used. Specifically as an indication of ferromagnetic and insulating of spinel _{ferrite, A (Fe 1-X Mn} X) 2 O 4 (A is selected from the group consisting of Mn, Co, Ni, Cu, Fe and Mg And any metal and 0 ≦ X ≦ 0.4). Further, the material constituting the ferromagnetic insulating layers SI and DI preferably has a resistivity of 1 Ω · cm or more.

  The materials constituting the metal layers SE and DE include Be, B, Mg, Al, Ti, Cu, Zn, Zr, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Pt, and the like. A metal selected from the group consisting of Au, or an alloy containing at least one selected from these groups is preferable.

As the material constituting the gate electrode layer GE, the same metal or alloy as that of the metal layers SE and DE can be used, and the same metal or alloy as that of the metal layers SE and DE, silicide, polysilicon, or the like is used. You can also. As the nonmagnetic insulating material constituting the gate insulating layer GI, oxides such as SiO ₂ , AlO ₂ , NiO, CoFeO, MnO, and ZnO can be used. In addition, as a material constituting the semiconductor layer 9, a compound semiconductor such as Si or GaAs can be used. The conductivity type of the semiconductor layer 9 may be either n-type or p-type.

  FIG. 2 is a diagram showing a planar configuration of the spin transistor 10 as viewed from the Z-axis direction of FIG.

  As shown in FIG. 2, the source electrode layer 3 has a planar shape extending in the direction along the Y axis. Specifically, the source electrode layer 3 has a source electrode layer intermediate portion 3a having a constant width and two source electrode layer tip portions 3b in contact with both ends in the longitudinal direction of the source electrode layer intermediate portion 3a. Since the source electrode layer 3 has such a shape, the magnetization direction SIM of the source electrode layer 3 is oriented in the longitudinal direction of the source electrode layer 3. Furthermore, since the source electrode layer tip 3b having a sharp shape is formed at both ends in the longitudinal direction of the source electrode layer 3, the source electrode layer 3 has a ferromagnetic insulating layer SI (see FIG. 1). Magnetic domains are difficult to form. Therefore, the magnetization direction SIM of the source electrode layer 3 is very difficult to change even when an external magnetic field is applied, and the magnetization direction SIM of the source electrode layer 3 is fixed.

  That is, the magnetization direction SIM of the source electrode layer 3 is fixed by the shape anisotropy of the source electrode layer 3. Note that the shape anisotropy energy is the same when the magnetization direction SIM of the source electrode layer 3 faces the positive direction of the Y axis in FIG. 2 and the negative direction of the Y axis. As shown in FIG. 2, in order to direct the magnetization direction SIM of the source electrode layer 3 in the positive direction of the Y axis, for example, a very strong external magnetic field may be applied in the positive direction of the Y axis.

  In this specification, “the magnetization direction of the magnetic layer is fixed” means a state in which the magnetization direction is not changed by a noise magnetic field or the like. That is, it means that the direction of magnetization of the magnetic layer is in a certain direction when no external magnetic field is applied. Therefore, if an external magnetic field larger than the coercive force of the magnetic layer is applied, the magnetization direction of the magnetic layer can be changed. The magnitude of the coercive force of the source electrode layer 3 can be set to, for example, 50 to 500 Oe.

  Further, the drain electrode layer 7 has a planar shape extending in the direction along the Y-axis, like the source electrode layer 3. However, the drain electrode layer 7 has the drain electrode layer tip 7b in contact with only one end in the longitudinal direction of the drain electrode layer intermediate portion 7a having a constant width, and the drain electrode layer 7 having a rectangular shape at the other end. It differs from the shape of the source electrode layer 3 in that the rectangular portion 7c is in contact. Since the drain electrode layer 7 has such a shape, the magnetization direction DIM of the drain electrode layer 7 is fixed in the longitudinal direction of the drain electrode layer 7. However, magnetic domains are likely to be formed in the region of the drain electrode layer rectangular portion 7c of the ferromagnetic insulating layer DI (see FIG. 1) of the drain electrode layer 7. Therefore, when an external magnetic field is applied to the drain electrode layer 7, the magnetization direction DIM of the drain electrode layer 7 is easily reversed. That is, the coercive forces of the source electrode layer 3 and the drain electrode layer 7 are different from each other, and the coercive force of the source electrode layer 3 is larger than the coercive force of the drain electrode layer 7. The magnitude of the coercive force of the drain electrode layer 7 can be set to 10 to 100 Oe, for example.

  The width w3a of the source electrode layer intermediate part 3a of the source electrode layer 3 can be set to 0.05 to 2 μm, for example, and the length h3b of the source electrode layer tip part 3b can be set to 0.4 to 5 μm, for example. it can. The length h3 of the source electrode layer 3 can be set to 1 to 100 μm, for example. That is, the ratio of the width w3a to the length h7 is 20 to 1000. In this case, the width w3a has sufficient shape anisotropy, and the magnetization direction SIM can be fixed.

  The width w7a of the drain electrode layer intermediate portion 7a of the drain electrode layer 7 can be set to 0.05 to 2 μm, for example, and the length h7b of the drain electrode layer tip portion 7b can be set to 0.4 to 5 μm, for example. it can. Further, the width w7c of the drain electrode layer rectangular portion 7c can be set to 1 to 10 μm, for example, and the length h7c of the drain electrode layer rectangular portion 7c can be set to 1 to 20 μm, for example. The length h7 of the drain electrode layer 7 can be set to 1 to 100 μm, for example. That is, the ratio between the width w7a and the length h7 is 20 to 1000, and in this case, sufficient shape anisotropy can be imparted.

  Next, the operation of the spin transistor 10 of this embodiment shown in FIG. 1 will be described.

  FIG. 3 is an energy band diagram of the semiconductor layer 9, the metal layer SE of the source electrode layer 3, and the metal layer DE of the drain electrode layer 7 shown in FIG. In this figure, the conductivity type of the semiconductor layer 9 is n-type, and the switch SW1 in FIG. 1 is disconnected and no voltage is applied to the gate electrode layer GE, and the switch SW2 is connected and the voltage is applied to the drain electrode layer 7. The case where it applies is shown. In the energy band diagram, the energy increases as it increases in the vertical positive direction, and the potential increases as it increases in the vertical negative direction.

  The electrons em injected into the ferromagnetic insulating layer SI included in the source electrode layer 3 have a polarized spin in the same direction as the magnetization direction SIM of the source electrode layer 3 (where the sign of the electrons is negative). Since the metal layer SE and the semiconductor layer 9 of the source electrode layer 3 are made of a material that makes a Schottky contact when they are in direct contact with each other, and the ferromagnetic insulating layer SI of the source electrode layer 3 is very thin, the semiconductor layer 9 And the interface SJ of the ferromagnetic insulating layer SI are very close to the interface of the metal layer SE and the ferromagnetic insulating layer SI. For this reason, the metal layer SE and the semiconductor layer 9 exhibit the same behavior as when Schottky contact is made. As a result, a potential barrier (depletion layer) PB is formed in the semiconductor layer 9, and the thickness t of the potential barrier PB is larger than the thickness at which the tunnel effect occurs, so that the electrons em in the source electrode layer 3 are the semiconductor. It is not implanted into layer 9. In the figure, Ec represents the energy level at the lower end of the conduction band of the semiconductor layer 9, and Ev represents the energy level at the upper end of the valence band.

  4 is an energy band diagram of the same portion of the spin transistor 10 as in FIG. This figure shows a case where the switches SW1 and SW2 of FIG. 1 are connected and a voltage is applied to the gate electrode layer GE and the drain electrode layer 7.

  By applying a positive potential to the gate electrode layer GE of FIG. 1, an n-type channel is formed immediately below the gate electrode layer GE in the semiconductor layer 9 corresponding to the positive potential, and at the same time, in the semiconductor layer 9 The thickness t of the potential barrier PB formed in (1) decreases. As a result, the spin-polarized electrons em injected into the ferromagnetic insulating layer SI can tunnel through the potential barrier formed by the ferromagnetic insulating layer SI and the potential barrier PB formed in the semiconductor layer 9. The electrons es flowing into the channel of the layer 9 increase. The electrons es injected from the source electrode layer 3 into the semiconductor layer 9 are spin-polarized in the same direction as the magnetization direction SIM of the source electrode layer 3. That is, the source electrode layer 3 functions as a spin filter effect film that injects spin-polarized electrons em into the semiconductor layer 9, and the source electrode layer 3 and the semiconductor layer 9 constitute a spin filter effect element 11. (See FIG. 1). Note that the ratio of the density of states of the spin electrons parallel to the magnetization direction SIM in the ferromagnetic insulating layer SI and the density of the antiparallel spins is determined by the ratio of the electrons parallel to the magnetization direction SIM in the ferromagnetic insulating layer SI. And the number of antiparallel electrons. Therefore, as described above, the source electrode layer 3 exhibits a spin filter effect.

  When the magnetization direction DIM of the drain electrode layer 7 is opposite to the magnetization direction SIM of the source electrode layer 3, most of the electrons es are between the semiconductor layer 9 and the drain electrode layer 7 due to the spin-dependent scattering effect. It is reflected and hardly flows into the drain electrode layer 7.

  FIG. 5 is an energy band diagram of the same portion of the spin transistor 10 as in FIG. This figure shows a state in which the switches SW1 and SW2 in FIG. 1 are connected to apply a voltage to the gate electrode layer GE and the drain electrode layer 7 and the magnetization direction DIM of the drain electrode layer 7 is reversed. .

  The metal layer DE of the drain electrode layer 7 and the semiconductor layer 9 are made of a material that makes a Schottky contact when they are in direct contact with each other. Since the ferromagnetic insulating layer DI of the drain electrode layer 7 is very thin, the semiconductor layer 9 And the interface SJ of the ferromagnetic insulating layer DI are very close to the interface of the metal layer DE and the ferromagnetic insulating layer DI. Therefore, the metal layer DE and the semiconductor layer 9 exhibit the same behavior as when Schottky contact is made.

  Therefore, in the state shown in FIG. 5, since the magnetization direction DIM of the drain electrode layer 7 is the same as the magnetization direction SIM of the source electrode layer 3, the electrons es injected into the semiconductor layer 9 are spin-dependent scattering. There is no reflection between the semiconductor layer 9 and the drain electrode layer 7 due to the effect, and the majority flows into the drain electrode layer 7. That is, the drain electrode layer 7 functions as a spin filter effect film that preferentially receives electrons that are spin-polarized in a specific direction among the electrons in the semiconductor layer 9, and the drain electrode layer 7 and the semiconductor layer 9 The filter effect element 13 is configured (see FIG. 1). In the ferromagnetic insulating layer DI, the energy differs between an electron state having a spin parallel to the magnetization direction DIM and an electron state having an antiparallel spin. Therefore, as described above, the drain electrode layer 7 exhibits a spin filter effect.

  Further, as described above, the spin transistor 10 generates a magnetoresistive effect between the source electrode layer 3 and the drain electrode layer 7. That is, when the gate voltage applied to the gate electrode layer GE is constant, when the magnetization direction SIM of the source electrode layer 3 and the magnetization direction DIM of the drain electrode layer 7 are parallel, the source electrode layer 3 and the drain electrode layer The resistance value between the source electrode layer 3 and the drain electrode layer 7 is reduced when the magnetization direction SIM of the source electrode layer 3 and the magnetization direction DIM of the drain electrode layer 7 are antiparallel. growing.

Referring also to FIGS. 3 to 5, between the Fermi level E _F of the metal layer DE having a drain electrode layer 7, the lower end of the conduction band E _C of the semiconductor layer 9 for ferromagnetic insulating layer DI adjacent The potential difference φD exists. By applying the gate voltage, the energy band of the semiconductor layer 9 is bent. As a result, the potential barrier PB is thinned, so that the electron em tunnels from the source electrode layer 3 to the conduction band of the semiconductor layer 9, and the current flows to the spin transistor 10. Flows. In the drain electrode layer 7, electrons es move from the semiconductor layer 9 to the drain electrode layer 7 by tunnel conduction, and as a result, a potential difference φD at the interface between the drain electrode layer 7 and the semiconductor layer 9 is determined.

  Next, the case where the conductivity type of the semiconductor layer 9 is p-type will be described. The structure of the spin transistor 10 in this case is the same as that shown in FIG.

  FIG. 6 is an energy band diagram of the semiconductor layer 9 immediately below the gate electrode layer GE of the spin transistor 10 shown in FIG. 1 and the source electrode layer 3 and the drain electrode layer 7 adjacent thereto. In the figure, the conductivity type of the semiconductor layer 9 is p-type, and the switch SW1 in FIG. 1 is disconnected and no voltage is applied to the gate electrode layer GE, and the switch SW2 is connected and the voltage is applied to the drain electrode layer 7. The case where it applies is shown.

  Since the metal layer SE and the semiconductor layer 9 of the source electrode layer 3 are made of a material that makes a Schottky contact when they are in direct contact with each other, and the ferromagnetic insulating layer SI of the source electrode layer 3 is very thin, the semiconductor layer 9 And the interface SJ of the ferromagnetic insulating layer SI are very close to the interface of the metal layer SE and the ferromagnetic insulating layer SI. For this reason, the metal layer SE and the semiconductor layer 9 exhibit the same behavior as when Schottky contact is made.

  Therefore, when no gate voltage is applied, holes in the semiconductor layer 9 are not injected into either the source electrode layer 3 or the drain electrode layer 7, and electrons em in the ferromagnetic insulating layer SI are energy of the semiconductor layer 9. Since the band cannot be crossed, it is not implanted into the semiconductor layer.

  FIG. 7 is an energy band diagram of the same portion of the spin transistor 10 as in FIG. This figure shows a case where the switches SW1 and SW2 of FIG. 1 are connected and a voltage is applied to the gate electrode layer GE and the drain electrode layer 7.

  By applying a positive potential to the gate electrode layer GE in FIG. 1, an n-type channel is formed immediately below the gate electrode layer GE in the semiconductor layer 9 corresponding to the positive potential, and at the same time, The height (energy) of the peak of the energy band decreases, and the electrons em in the ferromagnetic insulating layer SI are injected into the semiconductor layer 9. The electrons es injected from the source electrode layer 3 into the semiconductor layer 9 are spin-polarized in the same direction as the magnetization direction SIM of the source electrode layer 3.

  When the magnetization direction DIM of the drain electrode layer 7 is opposite to the magnetization direction SIM of the source electrode layer 3, most of the electrons es are between the semiconductor layer 9 and the drain electrode layer 7 due to the spin-dependent scattering effect. Is reflected and does not flow into the drain electrode layer 7.

  FIG. 8 is an energy band diagram of the same portion of the spin transistor 10 as in FIG. This figure shows a state in which the switches SW1 and SW2 in FIG. 1 are connected to apply a voltage to the gate electrode layer GE and the drain electrode layer 7 and the magnetization direction DIM of the drain electrode layer 7 is reversed. .

  The metal layer DE of the drain electrode layer 7 and the semiconductor layer 9 are made of a material that makes a Schottky contact when they are in direct contact with each other. Since the ferromagnetic insulating layer DI of the drain electrode layer 7 is very thin, the semiconductor layer 9 And the interface SJ of the ferromagnetic insulating layer DI are very close to the interface of the metal layer DE and the ferromagnetic insulating layer DI. Therefore, the metal layer DE and the semiconductor layer 9 exhibit the same behavior as when Schottky contact is made.

  Therefore, in the state shown in FIG. 8, since the magnetization direction DIM of the drain electrode layer 7 is the same as the magnetization direction SIM of the source electrode layer 3, the electrons es injected into the inversion channel of the semiconductor layer 9 are The semiconductor layer 9 flows into the drain electrode layer 7. The potential difference φD generated at the drain interface is smaller when the magnetization direction DIM of the drain electrode layer 7 is parallel to the magnetization direction SIM of the source electrode layer 3 than when anti-parallel.

  According to the spin filter effect elements 11 and 13 of the present embodiment, the semiconductor layer 9 is laminated with the spin filter effect films 3 and 7 having the ferromagnetic insulating layers SI and DI, and the ferromagnetic insulating layers SI and DI. Bears the spin filter effect (see FIG. 1). As described above, since the ferromagnetic insulating layers SI and DI form a tunnel barrier between the semiconductor layer 9 and the gold layer layers SE and DE, when a voltage is applied between the metal layers SE and DE and the semiconductor layer 9. A tunnel current flows between them. The semiconductor layer 9 and the metal layers SE and DE are selected to be in Schottky contact when brought into direct contact with each other, and a tunnel current flows through the ferromagnetic insulating layers SI and DI between them. The semiconductor layer and the metal layer exhibit the same behavior as when Schottky contact is made.

  Therefore, with respect to the condition that a ferromagnetic material having a high polarizability required for the spin filter effect films 3 and 7 provided in the semiconductor layer 9 and the condition that the semiconductor layer 9 is in Schottky contact, the former condition is changed to ferromagnetic. The insulating layers SI and DI are satisfied, and the latter condition can be satisfied with the metal layers SE and DE. That is, in the conventional spin filter effect film, these two conditions had to be satisfied by one layer in contact with the semiconductor layer, whereas in the spin filter effect elements 11 and 13 according to the present embodiment, These two conditions can each be satisfied by separate layers. As a result, since the spin filter effect films 3 and 7 can be configured to more ideally satisfy these two conditions, the spin filter effect elements 11 and 13 having a sufficiently high spin filter effect on the semiconductor layer 9 are provided. It has become.

  Further, the spin transistor 10 of the present embodiment includes the spin filter effect elements 11 and 13 that have a sufficiently high spin filter effect on the semiconductor layer 9 as described above. As a result, the spin transistor 10 having a sufficiently high magnetic resistivity between the source electrode layer 3 and the drain electrode layer 7 can be obtained.

  Furthermore, in the spin transistor 10 of this embodiment, a material having a resistivity of 1 Ω · cm or more is preferably used as the ferromagnetic insulating layers SI and DI. Therefore, the ferromagnetic insulating layers SI and DI can reliably form a tunnel barrier between the semiconductor layer 9 and the gold layer layers SE and DE. As a result, the source electrode layer 3 and the drain electrode layer 7 become the spin filter effect films 3 and 7 that more reliably satisfy the above two conditions with respect to the semiconductor layer 9, so that the spin transistor 10 has high reliability. It has become.

  Furthermore, in the spin transistor 10 of the present embodiment, the magnetization direction SIM of the ferromagnetic insulating layer SI included in the source electrode layer 3 and the magnetization direction DIM of the ferromagnetic insulating layer DI included in the drain electrode layer 7 are fixed. . Further, the coercivity of the source electrode layer 3 is larger than the coercivity of the drain electrode layer 7. Therefore, it is easy to change the relative angles of the magnetization directions SIM and DIM of the source electrode layer 3 and the drain electrode layer 7. As a result, the spin transistor 10 can easily change the resistance value between the source electrode layer 3 and the drain electrode 7.

  Furthermore, in the spin transistor 10 of the present embodiment, the magnetization direction SIM of the ferromagnetic insulating layer SI included in the source electrode layer 3 and the magnetization direction DIM of the ferromagnetic insulating layer DI included in the drain electrode layer 7 are determined by the source electrode layer 3 and the drain electrode layer 7 are fixed by the shape anisotropy (see FIG. 2). Therefore, the magnetization directions SIM and DIM can be fixed only by forming the source electrode layer 3 and the drain electrode layer 7 so as to have appropriate shapes.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, in the spin transistor 10 in the above embodiment, the coercivity of the source electrode layer 3 is larger than the coercivity of the drain electrode layer 7 (see FIG. 2). The coercive force of the source electrode layer 3 may be larger.

  In the spin transistor 10 in the above-described embodiment, the magnetization direction SIM of the source electrode layer 3 is fixed by the shape anisotropy of the source electrode layer 3 (see FIG. 2). I can't. For example, there is a method using an antiferromagnetic material as the metal layer SE included in the source electrode layer 3. Specifically, as shown in FIG. 9, the magnetization direction SIM of the source electrode layer 3 may be fixed by an exchange coupling magnetic field SEM from a metal layer SE made of an antiferromagnetic material. Further, in this case, the planar shape of the source electrode layer 3 does not have to be a shape as shown in FIG. 2, and may be a rectangle or a circle in addition to a square as shown in FIG. Further, the magnetization direction SIM of the source electrode layer 3 may be fixed by forming the ferromagnetic insulating layer SI of the source electrode layer 3 as a hard magnetic layer. Similarly, for the drain electrode layer 7, the magnetization direction DIM of the drain electrode layer 7 may be fixed by an exchange coupling magnetic field from the metal layer DE made of an antiferromagnetic material. Even in this case, the coercive forces of the ferromagnetic layers SI and DI of the source electrode layer 3 and the drain electrode layer 7 are preferably set to be different from each other.

  The planar shape of the drain electrode layer 7 is not limited to the shape as shown in FIG. 2, and may be a rectangle or a circle in addition to the square as shown in FIG. In that case, induced magnetic anisotropy may be imparted in the direction along the Y axis in FIG. 9 to the ferromagnetic insulating layer DI of the drain electrode layer 7 by thermal annealing in a magnetic field or the like.

  Further, a protective layer made of a metal material or the like for protecting these electrodes may be further provided on the source electrode layer 3 and the drain electrode layer 7.

  Further, as shown in FIG. 10, a spin transistor in which a magnetization reversal electrode layer 15 is further provided in the semiconductor layer 9 for reversing the magnetization direction DIM of the ferromagnetic insulating layer DI of the drain electrode layer 7 by spin injection magnetization reversal. 10a is also possible.

The magnetization switching electrode layer 15 has a ferromagnetic insulating layer RI in contact with the semiconductor layer 9 and a metal layer RE in contact with the opposite side of the ferromagnetic insulating layer RI to the semiconductor layer 9 side. The ferromagnetic insulating layer RI is thinly formed so as to form a tunnel barrier between the semiconductor layer 9 and the metal layer RE, and the semiconductor layer 9 and the metal layer RE are in Schottky contact when brought into direct contact with each other. Is selected. A magnetization reversal voltage V _RD1 or V _RD2 can be applied between the magnetization reversal electrode layer 15 and the drain electrode layer 7 depending on the connection destination of the switch SW3.

As shown in FIG. 10, when the magnetization direction DIM of the drain electrode layer 7 and the magnetization direction RIM of the magnetization switching electrode layer 15 are antiparallel, in order to reverse the magnetization direction DIM of the drain electrode layer 7, the switch SW1 SW2 is disconnected and the switch SW3 is connected to the _VRD1 side. Then, electrons spin-polarized in the direction of the magnetization direction RIM of the magnetization switching electrode layer 15 are injected from the magnetization switching electrode layer 15 into the drain electrode layer 7. As a result, the magnetization direction DIM of the drain electrode layer 7 receives torque that rotates so as to be parallel to the magnetization direction RIM, the magnetization direction DIM is reversed, and the magnetization direction DIM of the drain electrode layer 7 is reversed. It becomes parallel to the magnetization direction RIM of the electrode layer 15. On the other hand, when the magnetization direction DIM of the drain electrode layer 7 and the magnetization direction RIM of the magnetization switching electrode layer 15 are parallel, the switches SW1 and SW2 are disconnected and the switch SW3 is connected to the _VRD2 side. As a result, the magnetization direction DIM of the drain electrode layer 7 receives torque that rotates so as to be anti-parallel to the magnetization direction RIM of the magnetization switching electrode layer 15. The magnetization direction DIM is antiparallel to the magnetization direction RIM of the magnetization switching electrode layer 15. Note that the magnetization switching electrode layer 15 may include a metal ferromagnetic layer in contact with the semiconductor layer 9.

  As described above, by further providing the magnetization switching electrode layer 15, the magnetization direction DIM of the ferromagnetic insulating layer DI included in the drain electrode layer 7 can be easily changed. In addition, a mechanism for applying an external magnetic field is not required as compared with the case where the magnetization direction DIM of the ferromagnetic insulating layer DI of the drain electrode layer 7 is reversed by applying an external magnetic field. 10 downsizing is possible. Further, when a large number of spin transistors 10 are integrated, it is easy to change only the magnetization direction DIM of the ferromagnetic insulating layer DI included in the specific element. Furthermore, as described above, the amount of electrons flowing into the drain electrode layer 7 changes according to the direction of magnetization of the drain electrode layer 7. For this reason, if the two states of the parallel and antiparallel states of the magnetization direction SIM of the source electrode layer 3 and the magnetization direction DIM of the drain electrode layer 7 are made to correspond to one bit, a one-bit semiconductor memory It becomes. Further, N such semiconductor memories can be integrated to form an N-bit memory. The magnetization reversal electrode layer 15 is disposed closer to the source electrode layer 3 than the drain electrode layer 7, and the magnetization reversal electrode layer 15 can change the magnetization direction SIM of the ferromagnetic layer SI of the source electrode layer 3. It is good.

  In a conventional semiconductor MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), the direction of generation of carriers is usually defined as “source”, and the conductivity type of the semiconductor directly under the gate is the source conductivity type. Is different. On the other hand, in the spin transistor 10 of the present embodiment, the carriers are spin-polarized electrons or holes, and the carrier electrode flows into the semiconductor layer 4 regardless of the conductivity type of the semiconductor layer 4 as the source electrode layer. Note that in the case where holes are injected from the source electrode layer, the spins held by the holes are assumed to hold spins opposite to the spins in the electronic state of the missing electrons.

  Hereinafter, in order to further clarify the effects of the present invention, description will be made using examples.

First, an SOI substrate was prepared, and the natural oxide film layer on the surface was removed by ion milling. Thereafter, after forming 3 nm of CoFe ₂ O ₄ to be the ferromagnetic insulating layers SI and DI in FIG. 1 on the SOI substrate later, 10 nm of Al to be the metal layers SE and DE is formed thereon, and further thereon. A laminated film having 2 nm of Ta was formed as a protective layer. Thereafter, patterning was performed to form a source electrode layer 3 and a drain electrode layer 7 having a shape as shown in FIG. The shape of the source electrode layer 3 was h3 = 20 μm, h3b = 2 μm, and w3a = 0.5 μm. Further, the shape of the drain electrode layer 7 was set to h7 = 20 μm, w7c = h7c = 5 μm, and h7b = 2 μm.

  For such an element, the resistance value between the source electrode layer 3 and the drain electrode layer 7 was measured by a four-terminal method, and the magnetic resistivity at room temperature between the source electrode layer 3 and the drain electrode layer 7 was determined. Was about 20%.

It is a figure which shows the longitudinal cross-sectional structure of the spin transistor which concerns on embodiment. It is a figure which shows the planar structure of a spin transistor. It is an energy band figure of a spin transistor. It is an energy band figure of a spin transistor. It is an energy band figure of a spin transistor. It is an energy band figure of a spin transistor. It is an energy band figure of a spin transistor. It is an energy band figure of a spin transistor. It is a figure which shows the plane structure of the modification of a spin transistor. It is a figure which shows the longitudinal cross-section structure of the modification of a spin transistor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Source electrode layer, 4 ... Semiconductor layer, 7 ... Drain electrode layer, 9 ... Semiconductor layer, 10 ... Spin transistor, SE, DE ... Metal layer, SI, DI ... Ferromagnetic insulating layer, GE ... Gate electrode layer, GI ... gate insulation layer.

Claims (11)

A semiconductor layer;
A spin filter effect film having a ferromagnetic insulating layer laminated on the semiconductor layer and a metal layer laminated on the opposite side of the ferromagnetic insulating layer to the semiconductor layer side,
The spin filter, wherein the ferromagnetic insulating layer forms a tunnel barrier between the semiconductor layer and the gold layer, and the semiconductor layer and the metal layer are made of a material that makes a Schottky contact when in direct contact with each other. Effect element. A source electrode layer having a ferromagnetic layer;
A drain electrode layer having a ferromagnetic layer;
A semiconductor layer provided with the source electrode layer and the drain electrode layer;
A gate electrode layer provided directly or via a gate insulating layer on the semiconductor layer;
With
At least one of the source electrode layer and the drain electrode layer has a ferromagnetic insulating layer as the ferromagnetic layer in contact with the semiconductor layer, and a metal layer in contact with the opposite side of the ferromagnetic insulating layer to the semiconductor layer side And having
The spin transistor, wherein the ferromagnetic insulating layer forms a tunnel barrier between the semiconductor layer and the metal layer, and the semiconductor layer and the metal layer are made of a material that makes a Schottky contact when they are in direct contact with each other. Each of the source electrode layer and the drain electrode layer includes a ferromagnetic insulating layer as the ferromagnetic layer in contact with the semiconductor layer, a metal layer in contact with a side opposite to the semiconductor layer side of the ferromagnetic insulating layer, Have
3. The ferromagnetic insulating layer forms a tunnel barrier between the semiconductor layer and the metal layer, and the semiconductor layer and the metal layer are made of a material that makes a Schottky contact when brought into direct contact with each other. The spin transistor according to 1.   The spin transistor according to claim 2 or 3, wherein the ferromagnetic insulating layer has a resistivity of 1 Ω · cm or more.   The metal film is selected from the group consisting of Be, B, Mg, Al, Ti, Cu, Zn, Zr, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Pt, and Au. The spin transistor according to claim 2, further comprising at least one kind.   The spin transistor according to any one of claims 2 to 5, wherein the magnetization direction of the ferromagnetic layer included in at least one of the source electrode layer and the drain electrode layer is fixed.   The spin transistor according to claim 6, wherein the magnetization direction of the ferromagnetic layer included in at least one of the source electrode layer and the drain electrode layer is fixed by shape anisotropy.   8. The spin transistor according to claim 7, wherein the magnetization directions of the ferromagnetic layers of both the source electrode layer and the drain electrode layer are fixed by shape anisotropy. The spin transistor according to claim 8, wherein coercive forces of the ferromagnetic layers of the source electrode layer and the drain electrode layer are different from each other.
  The metal layer of at least one of the source electrode layer and the drain electrode layer is an antiferromagnetic layer, and the magnetization direction of the ferromagnetic layer in contact with the antiferromagnetic layer is exchange coupled from the antiferromagnetic layer. The spin transistor according to claim 6, wherein the spin transistor is fixed by a magnetic field.   11. The magnetization reversal electrode layer for reversing the magnetization direction of the ferromagnetic layer of either the source electrode layer or the drain electrode layer by spin injection magnetization reversal is further provided in the semiconductor layer. The spin transistor according to any one of the above.

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