JP3621367B2 - Spin transistor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spin transistor. More specifically, the present invention relates to a magnetic sensor such as a magnetic head for high-density magnetic recording / reading, a magnetic random access memory (RAM), a magnetic read only memory (MROM), or the like. The present invention relates to a spin transistor suitable for use as a high-density memory element, a light detection element, or the like.
[0002]
[Prior art]
Along with the improvement of the magnetic recording medium, the increase in the density and the speed of the magnetic recording are mostly due to the progress of the magnetic recording apparatus, particularly the magnetic head used for writing and reading of the magnetic recording. For example, as the magnetic recording medium becomes smaller and larger in capacity, the relative speed between the magnetic recording medium and the read magnetic head decreases, but even in that case, a new type of read magnetic head that can extract a large output is huge. Development of a magnetoresistive head (GMR head) is underway.
[0003]
The GMR head has a large magnetoresistance change rate (MR ratio) and an excellent characteristic as compared with a conventional MR (Magneto Resistance effect) head. Recently, a tunnel junction type GMR head, which is expected to have better characteristics, has rapidly attracted attention.
[0004]
A conventional magnetic recording medium functions as a magnetic disk, that is, a file memory, and the information is once read into a semiconductor memory (DRAM, SRAM) of the computer main body and used. A semiconductor memory has many excellent characteristics, but also has a major drawback of consuming a large amount of power for storing data. In recent years, flash memory, FRAM (Ferroelectric Memory) and the like that do not require power for storing data have been developed, but all have a great disadvantage that the number of rewrites is limited.
[0005]
On the other hand, the development of a magnetic memory (MRAM) that can be repeated indefinitely has been started. In order to realize this, development of a material or device exhibiting a large MR ratio is desired. “Magnetic tunnel junction elements” are attracting attention as elements that exhibit a higher MR ratio than conventional spin valve films, and magnetic heads and magnetic memories can be manufactured using them or by combining them with MOS transistors. Attempts to form are underway.
[0006]
Furthermore, the development of spin transistors and spin valve transistors, which are expected to have better characteristics than magnetic tunnel junction elements, has begun. Such a spin transistor is, for example, S.I. By Datta et al., Appl. Phys. Lett. , 56, (1990) p. 665.
[Problems to be solved by the invention]
FIG. 12 is a schematic diagram showing the configuration of the main part of a conventional spin transistor. FIG. 12 (a) is a schematic diagram showing the cross-sectional configuration, and FIG. 12 (b) is a schematic diagram showing the planar configuration.
[0007]
This transistor includes a ferromagnetic Fe1 that forms part of a source S, a ferromagnetic Fe2 that forms a part of a drain D, and a two-dimensional electron gas channel C formed in a semiconductor layer provided therebetween. And its basic configuration.
[0008]
Spin-polarized electrons are injected into the channel portion C according to the magnetization direction of the source-side ferromagnetic material F1. On the other hand, the magnitude of the drain current varies depending on the magnetization direction of the ferromagnetic material F2 constituting a part of the drain D. When the ferromagnet F2 is magnetized in the same direction as the ferromagnet F1, the channel current easily flows, whereas when it is magnetized in the opposite direction, the channel current hardly flows.
[0009]
That is, the channel current varies depending on the magnetization direction of the ferromagnetic material Fe2 relative to the magnetization direction of the ferromagnetic material Fe1. Therefore, it can be used for applications such as a magnetic sensor.
[0010]
However, the conventional spin transistor as illustrated in FIG. 12 has a large drawback that current change due to the direction of magnetization of the ferromagnetic Fe2 is small, and thus high-speed reading is difficult.
[0011]
The present invention has been made on the basis of recognition of such a problem, and an object of the present invention is to provide a spin transistor that is highly dependent on magnetization of a drain current and excellent in high-speed reading.
[Means for Solving the Problems]
In order to achieve the above object, the first spin transistor of the present invention includes:
A source part having a spin-polarized part for generating spin-polarized electrons, a drain part having a magnetic material,
A channel part for guiding electrons from the source part to the drain part;
With
The channel portion has a shape converging toward the drain portion, and a point contact is provided between the channel portion and the drain portion.
[0012]
Further, the second spin transistor of the present invention has
A source part having a spin-polarized part for generating spin-polarized electrons;
A drain portion having a magnetic material;
A semiconductor layer provided between the source part and the drain part;
A gate electrode that forms a channel part for guiding electrons from the source part to the drain part by applying a voltage to the semiconductor layer;
With
A point contact is formed between the channel portion and the drain portion by providing a constricted portion in the shape of the gate electrode.
[0013]
According to the configuration of the first and second transistors, by providing the point contact, a high MR ratio can be obtained, and the magnetic detection sensitivity and the reading speed can be greatly improved as compared with the conventional case.
[0014]
Here, “point contact” refers to a junction limited to a size that produces a quantum effect on spin-polarized electrons, and the length in the direction perpendicular to the direction in which electrons flow. It is assumed that it is about the wavelength of electrons or less.
[0015]
For example, when the channel portion is formed of a semiconductor and the wavelength of electrons in the semiconductor is 10 nm, the size of the point contact is 10 nm or less.
[0016]
In the case of the second spin transistor, a fine point contact can be reliably and easily formed by processing the gate electrode.
[0017]
Further, if the spin-polarized portion is made of a compound semiconductor that excites spin-polarized electrons by irradiation of circularly polarized light, it can be used as a polarization detecting element.
[0018]
Further, at least one of the spin-polarized portion and the magnetic body is made of iron (Fe), nickel (Ni), cobalt (Co) or an alloy containing these oriented in a certain crystal orientation. Strong spin magnetization can be easily obtained, high MR ratio can be obtained, high sensitivity, and stable operation of a spin transistor can be realized.
[0019]
If the source part has a tunnel junction, the spin polarization rate of electrons supplied to the channel part can be further increased.
[0020]
In addition, if at least one of the spin-polarized part and the magnetic material is made of a compound magnetic semiconductor, the compatibility with the semiconductor layer constituting the channel part and the like is good, and epitaxial growth is facilitated. The injection efficiency of spin-polarized electrons can be increased.
[0021]
If the channel portion is a two-dimensional electron gas region formed in a semiconductor, the probability that electrons lose spin information due to scattering in the channel portion can be reduced.
As a result of the study by the present inventor, it has been found that the following three factors can be cited as causes of a small change in drain current accompanying a change in the direction of magnetization in the conventional spin transistor illustrated in FIG.
[0022]
The first factor is that the interface resistance between the channel portion C and the drain D depending on the magnetization direction is smaller than the resistance of the channel portion C not depending on the magnetization direction. That is, the magnitude of the drain current is determined by the voltage applied between the source and the drain and the resistance value between the source and the drain, but the latter is the sum of the interface resistance between the source / channel and the channel / drain and the resistance of the channel portion. Only the interface resistance between the channel / drain depends on the direction of magnetization of the ferromagnetic material F2.
[0023]
That is, in order to increase the magnetization direction dependence (MR (Magneto-resistance) ratio of the element) of the drain current, it is necessary to increase the channel / drain interface resistance.
[0024]
The second factor with a small MR ratio of the element is that the dependence of the interface resistance on the magnetization direction itself is small. Therefore, it is necessary to increase the magnetization direction dependency by some means.
[0025]
The third factor is that the spin polarization rate of electrons injected from the source into the channel is small. The MR ratio of the element depends on the spin polarization of electrons that flow through the channel and flow to the drain, and the spin polarization of the ferromagnetic material of the drain. Therefore, the MR ratio can be further increased by injecting electrons having a high spin polarization rate from the source into the channel by some method.
[0026]
As a result of the above considerations, the present inventor has adopted a “point contact” made of a semiconductor / metal junction at the channel / drain junction, whereby the conventional spin transistor due to the first and second factors described above is employed. I came up with removing the shortcomings.
[0027]
In order to solve the third factor with a small MR ratio, it is necessary to inject electrons with a high spin polarization rate into the channel. In the spin transistor of the present invention, the source is composed of a compound semiconductor, and electrons having high spin polarization are injected into the channel region by injecting spin-polarized electrons excited in the compound semiconductor by circularly polarized light into the channel region. be able to. Alternatively, electrons having a high spin polarization can be injected into the channel by using a magnetic tunnel junction as a source and applying a voltage between the upper electrode and the lower electrode of the magnetic tunnel junction.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0028]
FIG. 1 is a schematic diagram showing a main configuration of a spin transistor according to an embodiment of the present invention. That is, FIG. 4A shows the cross-sectional configuration, and FIG. 4B shows the planar configuration.
[0029]
The transistor of the present invention includes a spin polarization portion F1 that forms part of a source S, a ferromagnetic material F2 that forms part of a drain D, and a channel portion C formed in a semiconductor layer provided therebetween. Is the basic configuration.
[0030]
The spin-polarized portion F1 provided in the source S has a function of generating spin-polarized electrons. For example, in addition to those made of a ferromagnetic material as shown in FIG. In addition, a compound magnetic semiconductor, a compound semiconductor that generates electrons that are spin-polarized by circularly polarized light, and the like are also included.
[0031]
Injection of spin-polarized electrons from the source S to the channel portion C is the same as that of the conventional transistor illustrated in FIG. That is, spin-polarized electrons are injected into the channel portion C according to the magnetization direction of the source-side spin-polarized portion F1. When the ferromagnet F2 constituting a part of the drain D is magnetized in the same direction as the spin polarization part F1, the channel current is easy to flow, whereas when it is magnetized in the opposite direction, the channel current Is difficult to flow.
[0032]
In the transistor of the present invention, a point contact QP is formed between the channel portion C and the drain D. The point contact QP is provided with a fine contact to the extent that a quantum size effect can be generated with respect to the ferromagnetic material. That is, in the case of the transistor of the present invention, such fine contacts are formed on the ferromagnetic material F2 constituting a part of the drain D so that electrons are supplied from the channel portion C.
[0033]
The concept of “point contact” in the present invention will be described first.
[0034]
FIG. 2 is a conceptual diagram showing a reference example of a point contact element made of a magnetic material.
[0035]
This element is a two-terminal element having a constricted portion N between the upper and lower magnetic electrodes 110 and 120, and the resistance changes depending on the magnetization direction of the upper and lower electrodes. A very large value of several hundred percent has been reported so far as the rate of change in resistance, but the reason for the large rate of change has been explained as a phenomenon associated with ballistic conduction of quantized electrons. A point contact is an excellent element exhibiting a large rate of change in resistance, but in order to fabricate it, it is necessary to fabricate a constricted portion N having an electron wavelength. Although the wavelength of conduction electrons in a metal is about 1 nm, it is difficult to produce a constricted portion having a width of about 1 nm with good reproducibility by current technology, so this element remains at the basic research stage.
[0036]
It is to be noted that such a point contact element is disclosed as a magnetic microcontact in which two acicular nickel (Ni) are attached together or a magnetic microcontact in which two magnetites are in contact with each other. Garcia, M.M. Munoz, and Y.M. -W. Zhao, Physical Review Letters, vol. 82, p2923 (1999) and J. Am. J. et al. Versluijs, M.M. A. Bari and J.M. M.M. D. Coey, Physical Review Letters, vol. 87, p26601-1 (2001).
[0037]
Returning to FIG. 1 again and continuing the description, by providing such a point contact QP in the spin transistor, the current change due to the direction of magnetization of the ferromagnetic material F2 constituting a part of the drain D is greatly increased. High-speed reading is also possible.
[0038]
The point contact QP can be realized, for example, by changing the shape of the gate electrode G to the shape of the channel portion C in FIG. That is, the gate electrode G having a shape that converges toward the drain D corresponding to the channel portion C in FIG.
[0039]
When a gate voltage is applied to such a gate electrode G, depletion or inversion occurs in a region corresponding to the shape of the gate electrode G in the semiconductor layer to be a channel, and a channel portion C is formed. Electrons can be confined in the constricted portion, that is, the point contact QP, by the potential barrier of the channel portion C formed in this way. Since the wavelength of electrons in the semiconductor is 10 nm or more, the width of the constricted portion, that is, the point contact QP may be about several tens of nm. The formation of such a point contact QP is sufficiently possible with the current technology.
[0040]
The point contact QP can also be realized by patterning a semiconductor layer constituting the channel. For example, a semiconductor layer that can become the channel portion C may be etched to form a mesa having the shape of the channel portion C in FIG.
[0041]
Alternatively, only the portion of the channel portion C in FIG. 1B may be left as an active region by selectively injecting an inactivating element into the semiconductor layer. In this case, as an inactivating element, for example, hydrogen, proton, oxygen, iron, and various other elements can be appropriately selected and used according to the semiconductor material.
[0042]
According to the present invention, by providing the point contact QP between the channel portion C and the drain D, the contact resistance between the channel portion C and the drain D is remarkably increased as compared with the channel resistance, and the contact resistance is increased. Since the magnetization dependency of the drain current increases, the magnetization direction dependency (MR ratio) of the drain current can be dramatically increased.
[0043]
If a memory cell as shown in FIG. 3 is formed using such a spin transistor, it can be used in principle as a new type of solid magnetic memory (MRAM).
[0044]
For example, the magnetization direction of the ferromagnetic material used as the spin polarization portion F1 is fixed, and the magnetization of the ferromagnetic material F2 is made parallel to the magnetization of F1 by a magnetic field generated by a write current (omitted in FIG. 3). By making an antiparallel transition, binary code can be written. The code is read by applying a voltage to the word line WL connected to the gate G of the transistor to turn on the transistor and observing the drain current flowing through the bit line BL to thereby change the direction of magnetization of the ferromagnetic material F2. Can be detected.
[0045]
In the conventional MRAM using the magnetic tunnel junction, one tunnel junction and one transistor are required as one-bit components, whereas in the case of the memory cell shown in FIG. One bit can be composed of only transistors.
[0046]
Moreover, according to the present invention, the current change due to the direction of magnetization of the ferromagnetic material F2 of the spin transistor is large, which is further advantageous in that high-speed reading is possible.
[0047]
On the other hand, the magnetization direction dependency (MR ratio) of the drain current also depends on the spin polarization rate of electrons injected from the source S into the channel portion C. Since the spin polarization rate of conduction electrons existing in a ferromagnetic material such as iron (Fe) and cobalt (Co) is at most about 50%, the polarization of electrons injected into the channel portion C from these spin polarization portions F1. The rate is also about 50% at most.
[0048]
In order to inject electrons having a higher spin polarization rate, a compound semiconductor is used for the source S in one embodiment of the present invention. Irradiation with circularly polarized light excites electrons with high spin polarization in the compound semiconductor and injects the electrons into the channel portion C to further increase the MR ratio of the element.
[0049]
Further, by using a magnetic tunnel junction for the source S, electrons with a higher spin polarization can be injected into the channel, and the MR ratio can be increased.
[0050]
In order for electrons to reach the drain D from the source S without losing spin information, it is necessary to suppress scattering in the channel portion C. From this point of view, it is desirable that the channel portion C satisfies a condition for forming a so-called two-dimensional electron gas.
[0051]
The material of the spin polarization parts F1 and F2 may be simple substance such as iron (Fe), cobalt (Co), nickel (Ni), or iron (Fe), cobalt (Co), nickel (Ni), chromium. An alloy containing at least one element of (Cr), a NiFe alloy called “permalloy”, a CoNbZr alloy, a FeTaC alloy, a CoTaZr alloy, a FeAlSi alloy, a FeB alloy, a CoFeB alloy, etc. Soft magnetic materials, Heusler alloys and CrO ₂ , Fe ₃ O ₄ , La _1-X Sr _X MnO ₃ A half metal magnetic material such as can be used. That is, from these materials, a material having characteristics according to the semiconductor material or application of the transistor may be appropriately selected and used.
[0052]
【Example】
Hereinafter, embodiments of the present invention will be described in more detail with reference to examples.
[0053]
(First embodiment)
First, a spin transistor using a Si (silicon) -MOS (Metal-Oxide-Semiconductor) inversion layer as a channel will be described as a first embodiment of the present invention.
[0054]
FIG. 4 is a schematic diagram showing the main configuration of the spin transistor of this example. That is, FIG. 4A shows the cross-sectional configuration, and FIG. 4B shows the planar configuration.
[0055]
In this embodiment, the structure of a MOS transistor in which the gate insulating layer 20 is provided on the p-type silicon substrate 10 and the inversion layer 12 is formed immediately below when a voltage is applied to the gate G is employed.
[0056]
As the source S and the drain D, ferromagnetic layers F1 and F2 made of iron (Fe) having a thickness of 200 nm are used. Further, the magnetization of the F1 film on the source S side is fixed in the direction of arrow M in the figure by an exchange magnetic field from the iridium / manganese layer IrMn, which is an antiferromagnetic material. On the other hand, the magnetization of the ferromagnetic film F2 of the drain D can be rotated in the plane by an external magnetic field.
[0057]
This transistor has a channel length of 1 μm and a channel width of 5 μm, and an aluminum (Al) gate electrode G is formed through a gate insulating film 20.
[0058]
The shape of the gate electrode G is a special shape having a constricted portion QP having a width of 50 nm. When a positive voltage is applied to the gate electrode G, a channel portion (inversion layer) C is formed immediately below the gate electrode G and a drain current flows. The current depends on the magnetization direction of the ferromagnetic layer F2 constituting the drain D. Change.
[0059]
The movement of electrons flowing through the narrow part QP of the electron wavelength is limited to electrons that travel almost parallel to the direction of passing through the constriction part, and the wavelength (and energy) is quantized. Dependency increases.
[0060]
In the transistor of this example, the interface resistance between the channel portion C and the drain D is sufficiently larger than the interface resistance and channel resistance between the source S and the channel portion C.
[0061]
FIG. 5A shows the drain current-gate voltage (I) of the transistor of this embodiment. _D -V _G ) Is a graph showing characteristics. Where drain voltage V _D Was fixed at 0.5V. Further, the solid line in the figure represents the case where the magnetization of the ferromagnetic material F2 of the drain D is parallel to the magnetization of the ferromagnetic material F1 of the source S, and the dotted line represents the case of antiparallel.
[0062]
As can be seen from this graph, the gate voltage is the threshold voltage (V _T Exceeding 0.12 V), drain current began to flow, and the change in current (MR ratio) depending on the direction of magnetization was about 12%.
[0063]
FIG. 5B shows the drain current-drain voltage (I _D -V _D ) Is a graph showing characteristics. Where the gate voltage V _G Was fixed at 1V. Similarly to FIG. 5A, the solid line represents the case where the magnetization of the ferromagnet F2 of the drain D is parallel to the magnetization of the ferromagnet F1 of the source S, and the dotted line represents the antiparallel case.
[0064]
Pinch-off voltage V _P = V _G -V _T In the following, an MR ratio of about 12% is obtained as in FIG. _D Is V _P It has been observed that the MR ratio rapidly decreases beyond this value, and the drain current does not depend on the magnetization direction of F2.
[0065]
V _D Is V _P In the above saturation region, a potential barrier is generated due to depletion between the channel / drain electrodes, and the drain current is determined by the resistance of the barrier, so that it is considered that it hardly depends on the direction of magnetization.
[0066]
Here, as a comparative example with respect to the present embodiment, a spin transistor having a Si-MOS inversion layer having the same configuration except for the point contact QP as a channel was also prototyped. That is, in this comparative example, the shape of the gate electrode G is not converged as shown in FIG. 1B, but is provided over the entire surface of the channel semiconductor layer in the same manner as a normal transistor.
[0067]
The threshold voltage of the transistor of this comparative example was almost the same as that of the transistor of this embodiment, but the drain current at a gate voltage of 0.2 V increased to about 1 μA. The MR ratio of this element was as extremely low as about 0.5%.
[0068]
That is, it was confirmed that the MR ratio can be significantly increased by providing the point contact QP formed by patterning the gate electrode G.
[0069]
(Second embodiment)
Next, as a second embodiment of the present invention, a spin transistor using a two-dimensional electron gas having a selectively doped heterostructure made of n-type InAlAs / InGaAs was prototyped.
[0070]
FIG. 6 is a schematic diagram showing the main configuration of the spin transistor of this example. That is, FIG. 4A shows the cross-sectional configuration, and FIG. 4B shows the planar configuration.
[0071]
In this example, an InAlAs layer 40 was provided on the InGaAs layer 30, and a spin transistor having a two-dimensional electron system 30A formed at the InAlAs / InGaAs heterojunction interface as a channel was manufactured.
[0072]
The size and shape of the gate electrode G were the same as in the first example, but the ferromagnetic material F2 of the drain D was epitaxially grown on the InGaAs layer 30. The surface orientation of the end surface in contact with the film surface and the channel of the ferromagnetic material F2 is a (001) plane.
[0073]
In the spin transistor of this embodiment, the drain current changes depending on the magnetization direction of the ferromagnetic material F2, as in the transistor of the first embodiment, but the rate of change is about three times that of the transistor of the first embodiment. Yes, an MR ratio of about 35% was observed. The reason why a large MR ratio was obtained in this example compared to the first example is considered as follows.
[0074]
That is, the MR ratio of the transistor is generated because the interface resistance at the interface of the semiconductor (channel) / magnetic material (F2) depends on the magnetization direction of the ferromagnetic material F2, but the cause that depends on the magnetization direction is the electron transmitted through the interface. This is due to the band structure of the magnetic material.
[0075]
A band structure is generally expressed in a wave number space called a Brillouin zone. For example, an electron traveling in the [001] direction in a Fe crystal is expressed as a point on the Δ line of the Brillouin zone. They are distinguished by symmetry, and are usually described by symbols such as Δ1 and Δ2 using irreducible expressions in group theory.
[0076]
As shown in FIG. 7, the band structure of iron (Fe) is complicated, but the up spin band has a symmetry of Δ1 in the vicinity of the Fermi level, and the down spin band is Δ2, Δ2 ′, It has a symmetry of Δ5. On the other hand, the electron band traveling in the [001] direction in the InGaAs channel has Δ1 symmetry. Since electrons can travel without reflection between bands having the same symmetry, upspin electrons traveling in the [001] direction can pass through the semiconductor (channel) / magnetic body (F2) interface, but have different symmetry. Since electrons cannot travel between bands, downspin electrons are strongly reflected.
[0077]
In other words, the [001] direction semiconductor (channel) / magnetic body (F2) interface has a strong spin dependence, and it is considered that a high MR ratio was obtained in this element.
[0078]
In the transistor of the first embodiment, since the ferromagnetic material F2 is polycrystalline, the spin dependency of the semiconductor (channel) / magnetic material (F2) interface is relatively small. It is considered that the spin dependency is further increased and the MR ratio is also increased.
[0079]
(Third embodiment)
Next, a spin transistor in which the source S is made of a compound semiconductor will be described as a third embodiment of the present invention.
[0080]
FIG. 8 is a schematic diagram showing the main configuration of the spin transistor of this example. That is, FIG. 4A shows the cross-sectional configuration, and FIG. 4B shows the planar configuration.
[0081]
Also in this example, an InAlAs layer 40 was provided on the InGaAs layer 30, and a spin transistor having a channel formed by the two-dimensional electron system 30A formed at the InAlAs / InGaAs heterojunction interface was produced.
[0082]
However, in this embodiment, gallium arsenide GaAs is provided as the source S. The size and shape of the gate electrode G were the same as in the first and second examples.
[0083]
Also in the case of the transistor of this embodiment, the drain current changes according to the direction of magnetization of the ferromagnetic material F2, as in the first and second embodiments.
[0084]
Here, when GaAs of the source S was irradiated with right-circularly polarized light L, the direction of magnetization of the ferromagnetic material F2 was reversed and the change in the drain current was measured, an MR ratio of 50% was observed. The reason why the MR ratio has increased is considered to be that electrons with a high polarization rate were excited in the GaAs of the source S by circularly polarized light and injected into the channel portion C. As is apparent from this operation principle, the transistor of this embodiment can also be used as a circularly polarized light detecting element.
[0085]
(Fourth embodiment)
Next, a spin transistor in which the source S has a tunnel junction will be described as a fourth embodiment of the present invention.
[0086]
FIG. 9 is a schematic diagram showing a cross-sectional configuration of a main part of the spin transistor of this example.
[0087]
Also in this example, an InAlAs layer 40 was provided on the InGaAs layer 30, and a spin transistor having a channel formed by the two-dimensional electron system 30A formed at the InAlAs / InGaAs heterojunction interface was produced.
[0088]
However, as the source S, a magnetic tunnel junction having a laminated structure of iron cobalt (FeCo) alloy / aluminum (Al) oxide film / iron (Fe) was provided. Electrons are supplied from the magnetic tunnel junction to the channel portion C of the two-dimensional electron gas at the InAlAs / InGaAs junction interface. Similar to the first to third embodiments, the gate electrode G is patterned to form a point contact QP between the channel portion C and the ferromagnetic material F2. The drain D was provided with a FeNi alloy as a ferromagnetic material.
[0089]
In order to efficiently inject electrons into the two-dimensional electron channel portion C, the transistor has a mesa shape as shown in FIG. 9, and a source S and a drain D are provided on the side surfaces thereof. Here, the channel length of the transistor was 1 μm, and the channel width was 5 μm.
[0090]
The upper and lower magnetic bodies Fe and FeCo in the laminated structure provided in the source S were magnetized in the same direction. In this transistor, the drain current changes according to the direction of magnetization of the ferromagnetic material FeNi of the drain D. Gate voltage V _G = 1V, drain voltage V _D When = 0.5 V, the MR ratio was 38%.
[0091]
The reason why the MR ratio is increased in this embodiment is that the spin refraction rate of electrons injected from the source S consisting of the magnetic tunnel junction into the channel portion C is only the magnetic material as in the first embodiment. This is considered to be larger than the comparison.
[0092]
Furthermore, similar improvement in MR ratio was also observed in the spin transistor having the structure shown in FIG. That is, in the case of the transistor shown in the figure, the magnetic tunnel junction provided in the source S is a laminate of iron (Fe) / gold (Au) / iron (Fe) / aluminum (Al) oxide film / aluminum (Al). It has a structure. Iron (Fe) / gold (Au) / iron (Fe), which is a part of this laminated structure, is a so-called “spin valve” structure. However, in this example, the two layers of iron (Fe) in the spin valve film were magnetized in the same direction.
[0093]
In the case of the transistor shown in FIG. 10 as well, the reason why the MR ratio is increased is considered to be that the spin polarization rate of electrons injected into the channel portion C is increased.
[0094]
(Fifth embodiment)
Next, as a fifth embodiment of the present invention, a spin transistor in which the source S and the drain D are made of a magnetic semiconductor will be described.
[0095]
FIG. 11 is a schematic diagram showing a cross-sectional configuration of a main part of the spin transistor of this example.
[0096]
Also in this example, an InAlAs layer 40 was provided on the InGaAs layer 30, and a spin transistor having a channel formed by the two-dimensional electron system 30A formed at the InAlAs / InGaAs heterojunction interface was produced.
[0097]
However, a spin transistor in which the source S and the drain D are each made of gallium, manganese, and arsenic magnetic semiconductor GaMnAs and the point contact QP is formed by patterning the gate electrode G was manufactured.
[0098]
GaMnAs was epitaxially deposited using a molecular beam epitaxy method. The channel length was 1 μm and the channel width was 5 μm.
[0099]
In the transistor of this example, the MR ratio was 50%. The reason why the MR ratio is greatly improved is that there is little disorder of the crystal at the interface between the GaMnAs of the source S and the channel part C. Therefore, when electrons are injected from the GaMnAs into the channel part C, This is probably because loss is unlikely to occur and electrons with a high polarization rate can be injected into the channel portion C.
[0100]
Similarly, in the drain D, since the disorder of the crystal at the interface with the channel portion C is small, the loss of spin information of electrons flowing through the point contact QP hardly occurs, contributing to the improvement of the MR ratio. It is thought that there is.
[0101]
The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. For example, a person skilled in the art appropriately selects a specific dimensional relationship and material of each element constituting the spin transistor, and other shapes and materials such as a substrate, an electrode, a conductivity type, a dopant, and an insulating structure from a well-known range. As long as the present invention can be carried out in the same manner and the same effect can be obtained, it is included in the scope of the present invention.
[0102]
In addition, the constituent elements such as the ferromagnetic material, the channel part, and the spin polarization part in the spin transistor of the present invention may be formed as a single layer, or may have a structure in which two or more layers are stacked.
[0103]
In addition, all spin transistors that can be implemented by those skilled in the art based on the above-described spin transistors as embodiments of the present invention are also within the scope of the present invention.
[0104]
【The invention's effect】
As described above in detail, according to the present invention, spin-polarized electrons are injected from a source into a channel region such as a two-dimensional electron gas system, and the drain current changes depending on the magnetization direction of the magnetic material constituting the drain. In the FET, by forming a point contact between the channel region and the drain, a practical device having a large MR ratio can be provided, and the industrial merit is great.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration of a main part of a spin transistor according to an embodiment of the present invention.
FIG. 2 is a conceptual diagram illustrating a reference example of a point contact element made of a magnetic material.
FIG. 3 is a schematic diagram showing an MRAM memory cell configured using the spin transistor of the present invention.
FIG. 4 is a schematic diagram showing a main configuration of a spin transistor according to an embodiment of the present invention.
FIG. 5A shows the drain current-gate voltage (I) of the transistor of this example. _D -V _G ) Is a graph showing characteristics, and (b) shows drain current-drain voltage (I _D -V _D ) Is a graph showing characteristics.
FIG. 6 is a schematic diagram showing a main configuration of a spin transistor according to an embodiment of the present invention.
FIG. 7 is a schematic diagram showing a band structure of iron (Fe).
FIG. 8 is a schematic diagram showing a main configuration of a spin transistor according to an embodiment of the present invention.
FIG. 9 is a schematic diagram showing a cross-sectional configuration of a main part of a spin transistor according to an embodiment of the present invention.
FIG. 10 is a schematic diagram showing a cross-sectional configuration of a main part of a spin transistor according to an embodiment of the present invention.
FIG. 11 is a schematic diagram showing a cross-sectional configuration of a main part of a spin transistor according to an embodiment of the present invention.
FIGS. 12A and 12B are schematic views showing a main part configuration of a conventional spin transistor, in which FIG. 12A is a cross-sectional configuration and FIG. 12B is a schematic view showing a planar configuration.
[Explanation of symbols]
10 Silicon substrate
12 Inversion layer
20 Gate insulation layer
30 InGaAs
30A 2D electronic system
40 InAlAs
110, 120 Magnetic electrode
BL bit line
WL Word line
C channel part
F1 Spin polarization part
F2 ferromagnet
G Gate electrode
L light
M Magnetization
QP point contact
S source
D drain

Claims (7)

A source part having a spin-polarized part for generating spin-polarized electrons;
A drain portion having a magnetic material;
A channel part for guiding electrons from the source part to the drain part;
With
The spin transistor, wherein the channel portion has a shape converging toward the drain portion, and a point contact is provided between the channel portion and the drain portion. A source part having a spin-polarized part for generating spin-polarized electrons;
A drain portion having a magnetic material;
A semiconductor layer provided between the source part and the drain part;
A gate electrode that forms a channel part for guiding electrons from the source part to the drain part by applying a voltage to the semiconductor layer;
With
A spin transistor, wherein a point contact is formed between the channel portion and the drain portion by providing a constricted portion in the shape of the gate electrode. 3. The spin transistor according to claim 1, wherein the spin-polarized portion is made of a compound semiconductor that excites spin-polarized electrons by irradiation with circularly polarized light. At least one of the spin-polarized portion and the magnetic body is made of iron (Fe), nickel (Ni), cobalt (Co) or an alloy containing these oriented in a certain crystal orientation. Item 3. The spin transistor according to Item 1 or 2. The spin transistor according to claim 1, wherein the source part has a tunnel junction. 3. The spin transistor according to claim 1, wherein at least one of the spin-polarized portion and the magnetic body is made of a compound magnetic semiconductor. The spin transistor according to claim 1, wherein the channel portion is a two-dimensional electron gas region formed in a semiconductor.

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