JP2009059820A - Spin transistor, and semiconductor memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spin transistor with a sufficient magnetoresistance change rate of a source electrode and drain electrode, and provide a semiconductor memory using such the spin transistor. <P>SOLUTION: The spin transistor 1 comprises a source electrode layer S formed of ferromagnetic material, a drain electrode layer D formed of ferromagnetic material, a semiconductor SUB having the source electrode layer S and the drain electrode layer D and schottky-contacting with the source electrode layer S, a gate electrode layer GE provided on the semiconductor SUB directly or through a gate insulating layer GI, and a spin filter layer F provided on the semiconductor SUB through the source electrode layer S for injecting electrons em which is spin-polarized in a same direction as a magnetization direction SM of the ferromagnetic material, which forms the source electrode layer S. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spin transistor and a semiconductor memory.

  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 (see Patent Documents 1 and 2) or a multifunctional logic circuit (see Patent Document 3), and is manufactured using a magnetic process. Therefore, it can be considered to use the magnetic element as a control element.

  In particular, in Patent Document 1, spin transistors having various structures have been proposed. In particular, in FIG. 11 of Patent Document 1, between two ferromagnetic metals (FM) constituting a source electrode and a drain electrode, A spin transistor in which a nonmagnetic semiconductor layer is provided and a gate electrode is provided on the semiconductor layer via a gate insulating layer is disclosed. A Schottky contact is formed at the interface between the source and drain electrodes and the semiconductor layer.

  Spin-polarized electrons are injected from the source electrode through the Schottky barrier into 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 spin polarization rate of carriers injected into the semiconductor layer depends on the spin polarization rate of the source electrode.

Electrons injected into the drain through the channel of the semiconductor layer are scattered depending on the direction of the polarization. In other words, electrons injected from the source electrode through the Schottky barrier and injected into the semiconductor channel are spin-dependently scattered on the drain electrode side. 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.
JP 2004-111904 A International Publication WO2004 / 0779827 Pamphlet International Publication WO2004 / 086625 Pamphlet

  When considering the application of a spin transistor to a storage element, etc., the rate of change in magnetoresistance between the source and drain electrodes when the magnetization directions of the source electrode and the drain electrode are parallel and antiparallel as described above. Is larger the better. The rate of change in magnetoresistance between the source and drain electrodes depends on the spin polarization rate of electrons injected from the source electrode into the semiconductor layer, that is, on the spin polarization rate of the source electrode.

  However, since the spin polarization of a ferromagnetic metal material generally used as a source electrode is about 50%, electrons having a sufficient spin polarization cannot be injected from the source electrode into the semiconductor layer. . Although it is conceivable to use a half metal with a spin polarization of ideally 100% as the source electrode, it is technically difficult to create a half metal in such an ideal state at present. Yes. Therefore, there has been a problem that a spin transistor having a sufficiently large magnetoresistance change rate between the source and drain cannot be obtained.

  The present invention has been made in view of such a problem, and an object thereof is to provide a spin transistor having a sufficiently large magnetoresistance change rate between a source electrode and a drain electrode and a semiconductor memory using such a spin transistor. To do.

  In order to solve the above-described problem, a spin transistor according to the present invention includes a source electrode layer made of a ferromagnetic material, a drain electrode layer made of a ferromagnetic material, and a source electrode layer and a drain electrode layer. A semiconductor in Schottky contact, a gate electrode layer provided directly on the semiconductor or via a gate insulating layer, and a magnetization of a ferromagnetic material provided on the semiconductor via a source electrode layer and constituting the source electrode layer And a spin filter layer that injects spin-polarized electrons in the same direction as the direction.

  According to the spin transistor of the present invention, by applying a positive potential to the gate electrode layer, an n-type channel is formed in the semiconductor corresponding to the positive potential, and at the same time, between the source electrode layer and the semiconductor. The thickness of the potential barrier formed by the Schottky contact decreases, and the number of electrons flowing into the semiconductor channel increases. At this time, spin-polarized electrons are injected into the source electrode layer by the spin filter layer in the same direction as the magnetization direction of the source electrode layer. Then, the spin-polarized electrons injected into the source electrode layer further increase in the spin polarization rate by the action of the source electrode layer magnetized in the same direction as the spin-polarized direction, and are injected into the semiconductor. .

  Therefore, when the magnetization direction of the drain electrode layer is opposite to that of the source electrode layer, most of the spin-polarized electrons injected into the semiconductor are reflected at the interface between the semiconductor and the drain electrode layer. Do not flow. On the other hand, when the magnetization direction of the drain electrode layer is the same as that of the source electrode layer, most of the spin-polarized electrons injected into the semiconductor pass through the interface between the semiconductor and the drain electrode layer and flow into the drain electrode layer. Therefore, a spin transistor can be obtained in which the rate of change of the amount of electrons flowing into the drain electrode layer according to the direction of magnetization of the drain electrode layer, that is, the rate of change in magnetoresistance between the source electrode layer and the drain electrode layer is larger than that of the conventional one.

  Further, the spin filter layer is provided on the opposite side of the first nonmagnetic layer and the source electrode layer of the first nonmagnetic layer so as to be in contact with the first nonmagnetic layer, and the spin filter layer includes It is preferable to have a first ferromagnetic layer magnetized in the same direction as the magnetization direction of the magnetic material. As a result, spin-polarized electrons are generated in the first ferromagnetic layer, and spin-polarized electrons are injected into the source electrode layer.

  Furthermore, the spin filter layer is provided on the source electrode layer side of the first nonmagnetic layer so as to be in contact with the first nonmagnetic layer, and is magnetized in the same direction as the magnetization direction of the ferromagnetic material constituting the source electrode layer. It is preferable to further have a second ferromagnetic layer. As a result, spin-polarized electrons generated in the first ferromagnetic layer further increase in spin-polarization rate in the second ferromagnetic layer and are injected into the source electrode layer.

Furthermore, at least one of the source electrode layer, the first ferromagnetic layer, and the second ferromagnetic layer is made of Co, Fe, Ni, (La _1-X Sr _X ) MnO ₃ (where 0.07 ≦ X ≦ 0.46), preferably including at least one selected from the group consisting of SrFeMoO ₆ , NiMnSb and Co ₂ MnSi. By using such a material for the source electrode layer, the first ferromagnetic layer, and the second ferromagnetic layer, spin-polarized electrons are generated in the spin filter layer and the source electrode layer, and the source electrode layer Injected into.

  Furthermore, the spin filter layer preferably further includes a second nonmagnetic layer provided on the source electrode layer side of the second ferromagnetic layer so as to be in contact with the second ferromagnetic layer. As a result, the spin-polarized current generated in the first ferromagnetic layer and the second ferromagnetic layer can be injected into the source electrode layer through the second nonmagnetic layer.

Furthermore, at least one of the first nonmagnetic layer and the second nonmagnetic layer includes MgO, Al ₂ O ₃ , MgAl ₂ O ₄ , ZnO, Cu / ZnO / Cu, TiO ₂ , HfO ₂ , Cu and It is preferable to include at least one selected from the group consisting of Ru. By using such a material for the first nonmagnetic layer and the second nonmagnetic layer, the spin-polarized electrons generated in the first ferromagnetic layer and the second ferromagnetic layer are tunneled. Or can be injected into the source electrode layer by ohmic conduction.

  Furthermore, it is preferable to further include a spin resistance adjustment layer for adjusting the spin resistance value between the source electrode layer and the semiconductor. Accordingly, a spin transistor having an appropriate spin resistance value and high injection efficiency of spin-polarized electrons can be obtained.

  Further, a pair is provided at a position spaced apart from the source electrode layer in the film surface direction of the source electrode layer, and the static magnetic field generated by the residual magnetization is the same as the direction of the source electrode layer with respect to the source electrode layer and the spin filter layer. It is preferable to further include a bias magnetic field application layer applied in the direction. Accordingly, the magnetization direction of the source electrode layer and the spin filter layer is stabilized by the bias magnetic field applied by the pair of bias magnetic field application layers, and thus the operation of the spin transistor is stabilized. Further, since the residual magnetization of the bias magnetic field application layer is used, no other member is required to generate the bias magnetic field, and the spin transistor can be reduced in size.

  Further, the bias magnetic field application layer preferably contains at least one selected from the group consisting of CoPt, CoPtTa, and CoCrTa. By forming the bias magnetic field application layer with such a hard magnetic material, a static magnetic field is generated by the residual magnetization of the bias magnetic field application layer, and this static magnetic field can be applied as a bias magnetic field to the source electrode layer and the spin filter layer. it can.

  Further, it is preferable that the semiconductor is further provided with a magnetization switching electrode layer for switching the magnetization direction of the drain electrode layer by spin injection magnetization switching. As a result, the magnetization direction of the drain electrode layer can be easily reversed, so that a spin transistor using a change in magnetoresistance between the source electrode layer and the drain electrode layer can be obtained. Further, since a mechanism for reversing the magnetization direction of the drain electrode layer by an external magnetic field is not required, the spin transistor can be reduced in size.

  In addition, a semiconductor memory according to the present invention includes the above-described spin transistor, and associates two states of a state in which the magnetization direction of the source electrode layer and the magnetization direction of the drain electrode layer are parallel and anti-parallel with one bit. It is characterized by that.

  According to the semiconductor memory of the present invention, since the spin transistor has both a switching function and an information storage function necessary for a semiconductor memory, a high-performance semiconductor memory can be realized.

  According to the present invention, a spin transistor having a sufficiently large magnetoresistance change rate between a source electrode and a drain electrode and a semiconductor memory using such a spin transistor are provided.

Hereinafter, the spin transistor according to the embodiment will be described. Note that the same reference numerals are used for the same elements, and redundant description is omitted.
(First embodiment)

FIG. 1 is a diagram showing a longitudinal sectional configuration of a spin transistor 1 according to the first embodiment.
The spin transistor 1 includes a source electrode layer S made of a ferromagnetic material, a drain electrode layer D made of a ferromagnetic material, and a semiconductor SUB provided with the source electrode layer S and the drain electrode layer D and in Schottky contact with the source electrode layer S. A spin filter layer F provided on the semiconductor SUB via the source electrode layer S, and a gate electrode layer GE provided on the semiconductor SUB via the gate insulating layer GI.

On each spin filter layer F, drain electrode layer D, and gate electrode layer GE, contact layers S1, D1, and G1 for applying a bias voltage are provided in electrical contact with each other. A drain voltage _VDS is applied between the source electrode layer S and the drain electrode layer D via the contact layers S1, D1, and between the source electrode layer S and the gate electrode layer GE via the contact layers S1, G1. A gate voltage V _GS is applied to. The presence / absence of application of the drain voltage V _DS and the gate voltage V _GS depends on the switch SW2 interposed between the drain electrode layer D and the source electrode layer S and the switch interposed between the gate electrode layer GE and the source electrode layer S, respectively. Determined by SW1.

  In a conventional semiconductor MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), the direction of carrier generation is usually defined as “source”, and the conductivity type of the semiconductor directly under the gate is different from the conductivity type of the source. Yes.

  In the spin transistor of the embodiment of the present invention, the carrier is a spin-polarized electron or hole, and the carrier flows into the semiconductor SUB regardless of the conductivity type of the semiconductor SUB. Note that in the case where holes are injected from the source, the spins held by the holes are assumed to hold spins opposite to the spins of the electrons that have escaped.

  In the figure, the magnetization direction SM of the source electrode layer S faces the positive direction of the X axis, and the magnetization direction DM of the drain electrode layer D faces the negative direction of the X axis. The thickness direction of the semiconductor SUB is the Z-axis direction.

Examples of the material constituting the source electrode layer S and the drain electrode layer D include, for example, an alloy containing at least one of Co, Fe, and Ni, or an alloy obtained by adding B to such an alloy, half metal, strong An artificial lattice type metal multilayer film in which a large number of magnetic layers and nonmagnetic layers are alternately laminated can be used. Specific examples of the half metal include perovskite type Mn oxidation such as (La _1-X Sr _X ) MnO ₃ (where 0.07 ≦ X ≦ 0.46, preferably 0.18 ≦ X ≦ 0.46). And a double perovskite type Mn oxide such as SrFeMoO ₆ , a half-Heusler alloy such as NiMnSb, a full Heusler alloy such as Co ₂ MnSi, and a garnet-based oxide. Moreover, as an artificial lattice type | mold metal multilayer film, what laminated | stacked many Cr layers and Fe layers alternately is mentioned, for example.

As a material constituting the gate electrode layer GE and the contact layers S1, D1, and G1, metals such as Al, Cu, and W, silicide of these metals, or polysilicon can be used, and a material that constitutes the gate insulating layer GI. For example, oxides such as SiO ₂ , AlO ₂ , NiO, CoFeO, MnO, and ZnO can be used. Further, as a material constituting the semiconductor SUB, a compound semiconductor such as Si or GaAs can be used.

  Next, details of the spin filter layer F will be described with reference to FIG. FIG. 2 is an enlarged view of the vicinity of the spin filter layer F of the spin transistor 1 in FIG.

  As shown in FIG. 2, the spin filter layer F is provided so as to be in contact with the ferromagnetic layer F1 (first ferromagnetic layer) in contact with the contact layer S1 and the source electrode layer S side of the ferromagnetic layer F1. A nonmagnetic layer F2 (first nonmagnetic layer) and a ferromagnetic layer F3 (second ferromagnetic layer) provided between the nonmagnetic layer F2 and the source electrode layer S so as to be in contact with these layers; Consists of. The magnetization direction F1M of the ferromagnetic layer F1 and the magnetization direction F3M of the ferromagnetic layer F3 are the same direction as the magnetization direction SM of the source electrode layer S (the positive direction of the X axis).

  When a drain current flows through the spin transistor 1, electrons are injected from the contact layer S1 into the spin filter layer F. The injected electrons are spin-polarized in the same direction as the magnetization directions F1M and F2M of the ferromagnetic layers F1 and F3 by the action of the ferromagnetic layers F1 and F3 of the spin filter layer F, and then enter the source electrode layer S. Injected. Then, the electrons em injected into the source electrode layer S are further spin-polarized in the same direction as the magnetization direction SM of the source electrode layer S, and then injected into the channel of the semiconductor SUB as described later. Therefore, according to the spin transistor 1 of the present embodiment, the spin polarization rate of the electrons es injected into the channel of the semiconductor SUB is increased as compared with the conventional spin transistor that does not include the spin filter layer F. be able to. In particular, in the present embodiment, the spin filter layer F has two ferromagnetic layers (ferromagnetic layers F1 and F3), and therefore, the spin of electrons em injected from the spin filter layer F into the source electrode layer S. The polarization rate is particularly high. As a result, the spin polarization rate of the electrons es injected from the source electrode layer S into the semiconductor SUB can be particularly increased.

As the material constituting the ferromagnetic layers F1 and F3, the same material as that of the source electrode layer S can be used. Further, as a material constituting the nonmagnetic layer F2, for example, an oxide such as MgO, Al ₂ O ₃ , MgAl ₂ O, Cu / ZnO / Cu, TiO, or HfO ₂ or a metal such as Cu or Ru is used. be able to.

  Therefore, electrons passing through the spin filter layer F are tunnel-conducted or ohmic-conducted in the nonmagnetic layer F2, depending on the material constituting the nonmagnetic layer F2. In an ideal case where the scattering of electrons in the nonmagnetic layer F2 is negligible, electrons passing through the spin filter layer F conduct ballistic conduction in the nonmagnetic layer F2. When the nonmagnetic layer F2 is made of a metal material, the magnetization directions F1M and F3M of the ferromagnetic layers F1 and F3 may be coupled to be parallel to each other by exchange coupling via the nonmagnetic layer F2. .

  Next, the operation of the above-described spin transistor 1 will be described.

  FIG. 3 is an energy band diagram of the semiconductor SUB immediately below the gate electrode layer GE of the spin transistor 1 shown in FIG. 1 and the source electrode layer S and the drain electrode layer D adjacent thereto. In this figure, the conductivity type of the semiconductor SUB 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 a voltage is applied to the drain electrode layer D. Shows the case. 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 metal source electrode layer S have polarized spins in the same direction as the magnetization direction SM of the source electrode layer S (however, the sign of the electrons is negative). The thickness t of the potential barrier (depletion layer) PB formed by the Schottky contact SJ between the source electrode layer S and the semiconductor SUB is larger than the thickness at which the tunnel effect occurs, and the electrons em in the source electrode layer S are the semiconductor. It is not injected into the SUB. In the figure, Ec represents the energy level at the lower end of the conduction band of the semiconductor SUB, and Ev represents the energy level at the upper end of the valence band.

  FIG. 4 is an energy band diagram of the same portion as that of FIG. 2 of the spin transistor 1. 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 D.

  By applying a positive potential to the gate electrode layer GE in FIG. 1, an n-type channel is formed in the semiconductor SUB immediately below the gate electrode layer GE corresponding to the positive potential. The thickness t of the potential barrier PB formed by the Schottky contact SJ with the semiconductor SUB decreases, and the electrons es flowing into the channel of the semiconductor SUB increase.

  As described above, the electrons es injected from the source electrode layer S into the semiconductor SUB are spin-polarized in the same direction as the source electrode layer S. The ratio of the density of states of spin electrons parallel to the magnetization direction SM and the density of states of antiparallel spins is the ratio of the number of electrons parallel to the magnetization direction SM to the number of antiparallel electrons. It becomes.

  When the magnetization direction DM of the drain electrode layer D is opposite to the magnetization direction SM of the source electrode layer S, most of the electrons es are reflected at the interface between the semiconductor SUB and the drain electrode layer D due to the magnetoresistance effect. The drain electrode layer D hardly flows.

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

  In the state shown in FIG. 5, since the magnetization direction DM of the drain electrode layer D is the same as the magnetization direction SM of the source electrode layer S, the electrons es injected into the semiconductor SUB are converted into the semiconductor SUB by the magnetoresistance effect. Is not reflected at the interface between the drain electrode layer D and most of it flows into the drain electrode layer D.

  The ferromagnetic material constituting the drain electrode layer D has spontaneous magnetization, and has a magnetic moment even when no external magnetic field is present. The energy differs between an electron state having a spin parallel to the direction of the magnetic moment and an electron state having an antiparallel spin. Therefore, the number of electrons conducted varies depending on the direction of spin.

  In addition, when electrons flow from the semiconductor SUB to the drain electrode layer D as described above, a magnetoresistive effect is generated. That is, when electrons pass through the interface between the semiconductor SUB and the drain electrode layer D and move to the drain electrode layer D of the ferromagnetic material, the relative direction between the spin direction of the electrons and the magnetization direction DM of the ferromagnetic material. Depending on the direction, the probability that electrons pass through the interface between the semiconductor SUB and the drain electrode layer D changes. That is, since the direction of electron spin is determined by the magnetization direction SM of the source electrode layer S, the resistance value between the source electrode layer S and the drain electrode layer D changes in magnetoresistance. The magnetoresistance change rate at this time depends on the spin polarization rate of electrons es injected from the source electrode layer S into the semiconductor SUB.

  In the spin transistor 1 of the present embodiment, the spin polarization rate of the electrons es injected into the channel of the semiconductor SUB is higher than that in the conventional spin transistor due to the action of the spin filter layer F as described above. It has become. Therefore, the rate of change of the amount of electrons flowing into the drain electrode layer D according to the magnetization direction DM of the drain electrode layer D, that is, the magnetoresistance change rate of the source electrode layer S and the drain electrode layer D of the spin transistor 1 is higher than that of the conventional case. Become bigger.

  As described above, in the above-described spin transistor 1, the source electrode layer S is a ferromagnetic metal, the conductivity type of the semiconductor SUB is n-type, the work function φm of the ferromagnetic metal, and the work of the semiconductor SUB. The function φs satisfies the relationship φm> φs.

  That is, the source electrode layer S and the semiconductor SUB form a Schottky contact SJ, and the thickness t of the potential barrier PB formed by the Schottky contact SJ depends on the potential applied to the gate electrode layer GE. It can be reduced below the thickness where the effect occurs.

  When the work function satisfies the relationship φm> φs, a spike-like potential barrier PB is formed between the source electrode layer S and the semiconductor SUB. Until the positive potential (positive voltage between the source and the gate) is applied to the gate electrode layer GE by this potential barrier PB, in the equilibrium state (FIG. 3), electrons em are transferred from the source electrode layer S to the semiconductor SUB. However, when the gate potential is increased (FIGS. 4 and 5), the energy of the semiconductor SUB decreases according to the applied potential, and the thickness t of the spike-like potential barrier PB decreases. Electrons em can flow from the source electrode layer S into the semiconductor SUB due to the tunnel effect.

  3 to 5, a potential difference φD exists between the Fermi level EF of the metal constituting the drain electrode layer D and the lower end of the conduction band EC of the semiconductor SUB adjacent thereto. Yes. By applying the gate voltage, the energy band of the semiconductor SUB is bent. As a result, the potential barrier PB is thinned, so that the electrons em tunnel from the source electrode layer S to the semiconductor conduction band, and a current flows through the spin transistor 1. In the drain electrode layer D, electrons es move from the semiconductor SUB to the drain electrode layer D by diffusion conduction or, in an ideal case, ballistic conduction in the absence of scattering, and as a result, the drain electrode layer D and the semiconductor SUB The potential difference φD at the interface is determined.

  Next, a case where the conductivity type of the semiconductor SUB is p-type will be described. The structure of the spin transistor 1 in this case is the same as that shown in FIG.

  FIG. 6 is an energy band diagram of the semiconductor SUB immediately below the gate electrode layer GE of the spin transistor 1 shown in FIG. 1 and the source electrode layer S and drain electrode layer D adjacent thereto. In this figure, the conductivity type of the semiconductor SUB 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 a voltage is applied to the drain electrode layer D. Shows the case.

  The interface between the source electrode layer S and the semiconductor SUB forms a Schottky contact SJ. When no gate voltage is applied, holes in the semiconductor SUB are not injected into either the source electrode layer S or the drain electrode layer D. The electrons em in the source electrode layer S cannot be injected into the semiconductor SUB because they cannot cross the peak of the energy band of the semiconductor SUB.

  FIG. 7 is an energy band diagram of the same portion of the spin transistor 1 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 D.

  By applying a positive potential to the gate electrode layer GE of FIG. 1, an n-type channel is formed in the semiconductor SUB immediately below the gate electrode layer GE corresponding to the positive potential, and at the same time, the energy band of the semiconductor SUB. As a result, the height (energy) of the peaks decreases and the electrons em in the source electrode layer S are injected into the semiconductor SUB. Since the source electrode layer S is made of a ferromagnetic material, the electrons es injected from the source electrode layer S into the semiconductor SUB have a unidirectional spin.

  When the magnetization direction DM of the drain electrode layer D is opposite to the magnetization direction SM of the source electrode layer S, most of the electrons es are reflected at the interface between the semiconductor SUB and the drain electrode layer D due to the magnetoresistive effect. However, it does not flow into the drain electrode layer D.

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

  In the state shown in FIG. 8, since the magnetization direction DM of the drain electrode layer D is the same as the magnetization direction SM of the source electrode layer S, the electrons es injected into the inversion channel of the semiconductor SUB are separated from the semiconductor SUB. It passes through the interface of the drain electrode layer D and flows into the drain electrode layer D. The potential difference φD generated at the drain interface is smaller when the magnetization direction DM of the drain electrode layer D is parallel to the magnetization direction SM of the source electrode layer S than when anti-parallel.

  As described above, in the spin transistor 1 having the p-type conductivity type of the semiconductor SUB, the source electrode layer S is a ferromagnetic metal, the work function φm of the ferromagnetic metal constituting the source electrode layer S, and the semiconductor SUB. Work function φs satisfies the relationship of φm <φs, the source electrode layer S and the semiconductor SUB are in Schottky contact, and the potential at the lower end of the conduction band of the semiconductor SUB is applied to the gate electrode layer GE. Depending on the potential, the electrons can rise from the source electrode layer S to the semiconductor SUB.

  When the work function satisfies the relationship of φm <φs, a potential barrier PB against holes is generated between the upper end Ev of the valence band and the metal, while in the vicinity of the interface with the metal of the semiconductor SUB. Since there is a gradual energy barrier EP with respect to the electrons em (see FIG. 6), no carrier movement occurs and no electrons flow from the source electrode layer S into the semiconductor SUB in an equilibrium state. When the gate potential is raised, electrons are gathered immediately below the gate electrode layer GE as the gate potential is raised. At the same time, the gentle energy barrier EP is lowered according to the applied potential. In other words, the potential at the lower end of the conduction band Ec increases, and electrons em can flow from the source electrode layer S into the semiconductor SUB.

  Note that the present embodiment can be modified in various ways other than the above-described configuration.

  For example, as shown in FIG. 9, the spin filter layer F may have one ferromagnetic layer F1. Even in this case, it is possible to make the spin polarization rate of the electrons es injected from the source electrode layer S into the semiconductor SUB higher than that of the conventional spin transistor as compared with the case without the spin filter layer F. is there.

  As shown in FIG. 10, a nonmagnetic layer F4 (second nonmagnetic layer) is further provided between the ferromagnetic layer F3 and the source electrode layer S with respect to the spin filter layer F having the configuration of FIG. A configuration of the spin filter layer F is also possible. Even in this case, the spin polarization rate of the electrons es injected from the source electrode layer S into the semiconductor SUB is higher than that of the conventional spin transistor for the same reason as when the spin filter layer F having the configuration of FIG. 2 is used. Can also be increased.

  As shown in FIG. 11, a spin transistor further including a spin resistance adjustment layer SR for adjusting a spin resistance value between the spin filter layer F and the semiconductor SUB is also possible.

It is known that in order to inject spin-polarized electrons from the source electrode layer S to the semiconductor SUB with high efficiency, it is necessary to appropriately adjust the spin resistance value at the interface between the source electrode layer S and the semiconductor SUB. Therefore, as shown in FIG. 11, by providing the spin resistance adjustment layer SR at the interface between the source electrode layer S and the semiconductor SUB, spin-polarized electrons can be injected into the semiconductor SUB with high efficiency. As a material constituting the spin resistance adjustment layer SR, for example, MgO, ZnO, HfO ₂ , TiO ₂ or the like can be used.

  Further, as shown in FIG. 12, in addition to the above-described configuration of the spin transistor, a mode in which a pair of bias magnetic field application layers H is further provided is possible. The pair of bias magnetic field application layers H are provided at positions separated from the source electrode layer S in the X direction, which is one of the film surface directions (XY plane direction) of the source electrode layer S. That is, the pair of bias magnetic field application layers H are arranged so as to sandwich the source electrode layer S. The pair of bias magnetic field application layers H is composed of a hard magnetic layer, and the residual magnetization HM is parallel to the magnetization direction SM of the source electrode layer S. Therefore, the static magnetic field HMS generated from the residual magnetization HM of the pair of bias magnetic field application layers H is applied to the spin filter layer F and the source electrode layer S in the same direction as the magnetization directions F1M, F3M, and SM. Therefore, since the magnetization directions F1M, F3M, and SM of the spin filter layer F and the source electrode layer S are stabilized, the operation of the spin transistor is stabilized. In addition, since the residual magnetization HM of the bias magnetic field application layer H is used, no other member is required to generate the static magnetic field HMS, and the spin transistor is downsized.

  As a material constituting the bias magnetic field application layer H, for example, CoPt, CoPtTa, CoCrTa, or the like can be used.

In the present embodiment, the gate electrode layer GE is provided on the semiconductor SUB via the gate insulating layer GI (see FIG. 1). However, the gate electrode layer GE, the semiconductor SUB, and the gate insulating layer GI are not provided. May be brought into Schottky contact. For this, each material may be selected so that the work function of the material constituting the gate insulating layer GI is larger than the work function of the material constituting the semiconductor SUB. In this case, the Schottky barrier generated by the Schottky contact between the gate electrode layer GE and the semiconductor SUB serves as the gate insulating layer GI.
(Second embodiment)

  Next, a semiconductor memory according to a second embodiment of the present invention will be described with reference to FIG.

In addition to the configuration of the spin transistor of the first embodiment, the semiconductor memory 10 of the present embodiment includes a magnetization switching electrode layer R for switching the magnetization direction DM of the drain electrode layer D by spin injection magnetization switching, and a magnetization switching. A contact layer R1 for applying a bias voltage to the electrode layer R is provided. The contact layer R1 is in electrical contact with the magnetization switching electrode layer R, and a magnetization switching voltage _VRD1 or _VRD2 selected by the switch SW3 is applied between the magnetization switching electrode layer R and the drain electrode layer D. It is possible.

When the magnetization direction DM of the drain electrode layer D and the magnetization direction RM of the magnetization switching electrode layer R are antiparallel as shown in FIG. 13, in order to reverse the magnetization direction DM of the drain electrode layer D, the switch SW1 and SW2 is disconnected and the switch SW3 is connected to the _VRD1 side. Then, electrons spin-polarized in the direction of magnetization RM of the magnetization switching electrode layer R are injected from the magnetization switching electrode layer R into the drain electrode layer D. As a result, the magnetization direction DM of the drain electrode layer D receives torque that rotates to be parallel to the magnetization direction RM, the magnetization direction DM is reversed, and the magnetization direction DM of the drain electrode layer D is reversed. This is parallel to the magnetization direction RM of the electrode layer R. Conversely, when the magnetization direction DM of the drain electrode layer D and the magnetization direction RM of the magnetization switching electrode layer R 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 DM of the drain electrode layer D receives torque that rotates so as to be anti-parallel to the magnetization direction RM of the magnetization switching electrode layer R, and the magnetization direction DM is reversed. The magnetization direction DM is antiparallel to the magnetization direction RM of the magnetization switching electrode layer R.

  As described above, the amount of electrons flowing into the drain electrode layer D changes according to the direction of magnetization of the drain electrode layer D. For this reason, if the two states of the magnetization direction SM of the source electrode layer S and the magnetization direction DM of the drain electrode layer D are parallel and anti-parallel, one bit corresponds to one bit. It becomes. The semiconductor memory according to the present embodiment uses a spin transistor that has both a switching function and an information storage function necessary as a semiconductor memory, and thus a high-performance semiconductor memory can be realized with a simple configuration. . Further, N such semiconductor memories can be integrated to form an N-bit memory.

  In addition, as a material which comprises the magnetization reversal electrode layer R, it can be set as the material similar to the source electrode layer S and the drain electrode layer D in 1st embodiment. However, the film thickness of the magnetization switching electrode layer R is preferably larger than that of the drain electrode layer D from the viewpoint of effectively causing the magnetization reversal of the magnetization direction DM of the drain electrode layer D described above. Moreover, as a material which comprises contact layer R1, it can be set as the material similar to contact layer S1, D1, G1 in 1st embodiment.

It is a figure which shows the longitudinal cross-sectional structure of the spin transistor 1 which concerns on 1st Embodiment. FIG. 2 is an enlarged view in the vicinity of a spin filter layer F of the spin transistor 1 in FIG. 1. 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 longitudinal cross-section structure of the modification of the spin transistor 1 which concerns on 1st Embodiment. It is a figure which shows the longitudinal cross-section structure of the modification of the spin transistor 1 which concerns on 1st Embodiment. It is a figure which shows the longitudinal cross-section structure of the modification of the spin transistor 1 which concerns on 1st Embodiment. It is a figure which shows the longitudinal cross-section structure of the modification of the spin transistor 1 which concerns on 1st Embodiment. It is a figure which shows the longitudinal cross-sectional structure of the semiconductor memory 10 which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Spin transistor, D ... Drain electrode layer, F ... Spin filter layer, GE ... Gate electrode layer, GI ... Gate insulating layer, S ... Source electrode layer, em, es ... Spin-polarized electrons.

Claims (11)

A source electrode layer made of a ferromagnetic material;
A drain electrode layer made of a ferromagnetic material;
A semiconductor provided with the source electrode layer and the drain electrode layer, and in Schottky contact with the source electrode layer;
A gate electrode layer provided directly or via a gate insulating layer on the semiconductor;
A spin filter layer that is provided on the semiconductor via the source electrode layer and injects spin-polarized electrons in the same direction as the magnetization direction of the ferromagnetic material forming the source electrode layer;
A spin transistor comprising: The spin filter layer is
A first nonmagnetic layer;
Provided on the opposite side of the first nonmagnetic layer from the source electrode layer so as to be in contact with the first nonmagnetic layer, and magnetized in the same direction as the magnetization direction of the ferromagnetic material constituting the source electrode layer A first ferromagnetic layer;
The spin transistor according to claim 1, comprising: The spin filter layer is
The second non-magnetic layer is provided on the source electrode layer side of the first non-magnetic layer so as to be in contact with the first non-magnetic layer, and is magnetized in the same direction as the magnetization direction of the ferromagnetic material constituting the source electrode layer. The spin transistor according to claim 2, further comprising a ferromagnetic layer. At least one of the source electrode layer, the first ferromagnetic layer, and the second ferromagnetic layer is made of Co, Fe, Ni, (La _1-X Sr _X ) MnO ₃ (where 0.07 ≦ 4. The spin transistor according to claim 3, comprising at least one selected from the group consisting of X ≦ 0.46), SrFeMoO ₆ , NiMnSb, and Co ₂ MnSi. The spin filter layer is
5. The method according to claim 3, further comprising a second nonmagnetic layer provided on the source electrode layer side of the second ferromagnetic layer so as to be in contact with the second ferromagnetic layer. Spin transistor. At least one of the first nonmagnetic layer and the second nonmagnetic layer includes MgO, Al ₂ O ₃ , MgAl ₂ O ₄ , ZnO, Cu / ZnO / Cu, TiO ₂ , HfO ₂ , Cu and 6. The spin transistor according to claim 5, comprising at least one selected from the group consisting of Ru.   The spin transistor according to claim 1, further comprising a spin resistance adjustment layer for adjusting a spin resistance value between the source electrode layer and the semiconductor.   A pair is provided at a position spaced apart from the source electrode layer in the film surface direction of the source electrode layer, and a static magnetic field generated by residual magnetization is applied to the source electrode layer and the spin filter layer. The spin transistor according to claim 1, further comprising a bias magnetic field application layer that applies the same direction as the magnetization direction.   9. The spin transistor according to claim 8, wherein the bias magnetic field application layer includes at least one selected from the group consisting of CoPt, CoPtTa, and CoCrTa.   The spin transistor according to any one of claims 1 to 9, further comprising a magnetization reversal electrode layer for reversing the magnetization direction of the drain electrode layer by spin injection magnetization reversal. .   The spin transistor according to claim 10, wherein two states of a state in which the magnetization direction of the source electrode layer and a direction of magnetization of the drain electrode layer are parallel and anti-parallel are associated with one bit. A semiconductor memory.

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