JP2000077648A - Functional element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a very small function element with a very high on/on ratio, by allowing an active region to transit from a first condition, in terms of electron spin's order state, to a second state under application of a magnetic field. SOLUTION: An element comprises a source region S, a drain region D, and an active region C sandwiched between them. A and B are conductive lines extending vertically to the paper surface, and the active region C is applied with a magnetic field when a current is applied in opposite directions each other. When a current flows in the same direction through the conductive lines A and B, or no current flows, no magnetic field is applied to the active region C. When the conductive lines A and B are supplied with a current to apply the active region C with a magnetic field, quantum transition occurs for switching operation. Here, two conductive lines are provided to enhance the magnetic field applied to the active region C. However, only A or B may be provided so long as a sufficient magnetic field is provided with a single conductive line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a functional element. More specifically, the present invention relates to a functional element to which spin electronics is applied and which has a high resistance ratio, low power consumption, and a small switching function of the element size.

[0002]

2. Description of the Related Art In semiconductor devices that have supported the electronics industry since the invention of transistors, only the electron charge transport phenomenon is used, and another important property of electrons called "spin" is applied. There was no. This is because the electron spin relaxes as the transport distance increases. However, with the advance of microfabrication technology, when this transport distance becomes about the same as the relaxation distance of electron spin, we will create new electrochronics that uses both quantum phenomena due to electron spin and conventional charge transport phenomena. The tide of trying, or "spin electronics," has emerged.

[0003]

However, all of the functional elements (for example, spin transistors) which have been proposed as the basis of spin electronics have a smaller ON / OFF resistance ratio than conventional semiconductor devices. There was a problem. For this reason, its application range has been limited to the storage unit and the like of the semiconductor storage device. That is, the main part such as the control circuit part had to rely on the conventional semiconductor element.

The present invention has been made based on the recognition of such a problem. That is, the purpose is ON /
By proposing a functional element having a switching function whose resistance ratio at OFF is as high as a conventional semiconductor element,
It is to realize the dramatic development of spin electronics.

[0005]

In order to achieve the above object, a functional device of the present invention comprises an active region, and a magnetic field generating means for applying a magnetic field to the active region. A functional element that changes an electric resistance value of the active region by a magnetic field to be applied, wherein the active region is
By applying a magnetic field, the order state of electron spins becomes first
From the first state to a second state different from the first state.

Alternatively, a functional device according to the present invention includes an active region, and a magnetic field generating means for applying a magnetic field to the active region, wherein the electric resistance of the active region is changed by a magnetic field generated by the magnetic field generating means. Functional element, wherein the active region is in a state where no magnetic field is applied,
Is open is large energy gap E _G than the thermal energy of the ambient temperature between the energy state of the energy state and spin number S ₂ spin number S _1, and the magnetic field generating means capable of generating magnetic field maximum value H _{Using the maximum} [O _e ], the effective g-factor g, and the temperature T [k], the relative magnetic permeability is

[0007]

(Equation 2) It is characterized by being composed of a larger substance.

As a preferred embodiment of the present invention, the critical magnetic flux density is calculated by using the Bohr magneton β and the Boltzmann constant k.
_G / gβ (S ₁ + S ₂ ), the ambient temperature T
The temperature E _G / where [k] is expressed using the Boltzmann constant k
k, when the magnetic flux density of the magnetic field applied to the active region by the magnetic field generating means is larger than the critical magnetic flux density, the active region has conductivity, and the magnetic flux density is equal to the critical magnetic flux density. When smaller than the active region is electrically insulating, or conversely, when the magnetic flux density is greater than the critical magnetic flux density, the active region is electrically insulating. When the magnetic flux density is smaller than the critical magnetic flux density, the active region has conductivity.

In a preferred embodiment of the present invention, the active region is formed of a single crystal of a substance having a ladder-like portion in a crystal lattice structure, and the conductivity appears in a longitudinal direction of the ladder. The material having the ladder-like portion is a V (vanadium) -based oxide, M
n (manganese) -based oxide, Ca (calcium) -based oxide, Sr (strontium) -based Cu (copper) -O (oxygen)
And a compound selected from the group consisting of a compound and a La (lanthanum) -based Cu (copper) -O (oxygen) compound.

In a preferred embodiment of the present invention, the magnetic field generating means includes a conductive region that conducts a current, a distance between a center line of the conductive region and the active region is a, and a cutoff of the conductive region. the area lambda, the permeability of the material constituting the active region mu, Bohr magneton can flow more current than the critical current density _{aE G / λgμβ (S 1 +} S 2) , expressed as a β There is a feature.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The devices using spin electronics proposed so far have the following two fatal problems when constructing an integrated circuit even if cost is ignored. Was. (1) The resistance ratio between ON and OFF is too small. (2) It has no clear threshold.

The most widely used MOSFET (Metal Oxide Semiconductor Field Ef) in the current semiconductor industry
In fect Transistor), the gate voltage exceeds the threshold (V _t), the concentrations of electrons and holes reversed in the vicinity of the surface of the semiconductor substrate, road transport (channel) opens the charge. Then, the current can easily flow by the drain voltage. On the other hand, a state where the gate voltage is closed if smaller channels than V _t, can not be made to flow currents no matter how high the drain voltage. The switchgrass bridging functions, the resistance value of the substrate surface by the V _t as a boundary is achieved by also varying 9 orders of magnitude. Is regarded herein as instead the view order of the concentration ratio of electrons and holes the parameters, it can be said that the MOSFET is a device utilizing a phase transition in which the V _t to the critical point.

On the other hand, none of the spin transistors proposed so far utilizes such a phase transition phenomenon. Therefore, the ON / OFF resistance ratio changes only by about 20% at most. Was.

On the other hand, in the present invention, the order state created by the quantum interaction between the electron spins is broken by applying a magnetic field having a magnetic flux density larger than the critical magnetic flux density (B _c ), and the phase transition is broken. Take advantage of what causes.

FIG. 1 is a conceptual diagram illustrating a functional device according to an embodiment of the present invention. That is, the device shown in FIG. 1 is a schematic sectional view of a spin transistor according to the present invention. The device shown in the figure has a source region S and a drain region D.
And an active region C interposed therebetween. A and B in the figure are conductors extending in a direction perpendicular to the plane of the drawing. When a current flows in opposite directions, a magnetic field is applied to the active region C. When currents of the same direction flow through the conductors A and B or when no current flows, no magnetic field is applied to the active region C.

Hereinafter, the operation of the spin transistor of the present invention will be described.

First, the concept of the quantum phase transition used in the spin transistor of the present invention will be described with reference to an energy band diagram.

FIG. 2 is a conceptual diagram of an energy band for explaining a quantum transition used in the functional device of the present invention. That is, the spin number S ₁ having a certain quantum order
On top of the energy band composed of a quantum state of a finite energy gap (E _G) is open. Above the energy gap, another energy band exists. This energy band is composed of quantum states having a different quantum order or having no spin order and having a spin number of S ₂ . Note that the following discussion is the same even when considering the case where the state of the spin number S ₁ has no order and only the state of the spin number S ₂ has order.

Here, the state of the spin number S ₁ and the spin number S
_In the state ( ₂ ), the quantum order is different, so that the electric resistance when carriers are injected can be significantly different. That is, if the resistance value in the state of the spin number S ₁ is R ₁ and the resistance value in the state of the spin number S ₂ is R ₂ , R ₁ >> R
₂ or R ₁ << R ₂ .

When a magnetic field → B (vector B) is applied to a substance having such an energy band structure, energy is shifted by the magnetic field. According to the equation of quantum mechanics, the amount of energy shift is

[0021]

(Equation 3) Becomes Here, g is an effective g-factor, and is 2 if the quenching of the orbital angular momentum is perfect. Β is a Bohr magneton, → S (vector S) is a spin operator, and (→ B · → S) is an inner product of the operator → B and the operator → S. Thus, the energy gap E _G due to application of a magnetic _{field, ΔE G = -gβB (S 1} + S 2) (2) it can be seen that the only change. Here, B is the magnetic flux density of the applied magnetic field. From this equation, it can be seen that the energy gap is closed by the application of the magnetic field. When the energy gap is completely closed, the energy state of the number of spins S _{1 and} the energy state of the number of spins S ₂ are switched, so that the quantum order is also switched and a quantum phase transition occurs.

FIG. 3 is a conceptual diagram illustrating a quantum phase transition caused by applying a magnetic field. That is, in the example shown in the figure, when no magnetic field is applied as shown at the left end, the energy band corresponding to the ordered state (Ordered) S ₁ and the disordered state (Disordered state)
d) the energy gap of the E _G between the energy bands corresponding to the S ₂ are open.

When a magnetic field is applied to this system with S ₁ = O, the energy level in the disordered state (Disordered) decreases as the magnetic flux density increases, and the energy gap between the disordered state and the ordered state closes. Then, the energy gap in the critical magnetic flux density B _c is zero.
At this time, the critical magnetic flux density B _c is given by B _c = E _G / gβ (S ₁ + S ₂ ) (3) That is, the magnetic flux density B <
For Bc, the system resistance R = R ₁ (ordered resistance), and conversely, for magnetic flux density B> B _C , the system resistance R = R ₂
(Disordered resistance). That is, when the applied magnetic flux density is low, the resistance value of the system is determined by the state of the spin number S ₁ , and the applied magnetic flux density becomes the critical magnetic flux density B _c
Becomes higher than the resistance value of the system will be determined by the state of the spin number S _2.

The resistance value in the state of the number of spins S _{1 and} the state of the number of spins S ₂ can be variously controlled. For example, as shown in the lower part of FIG. 3, holes (ho
le), the ordering (Ordered)
) Achieves high conductivity and is disordered (Disor
dered), an extremely high resistance value can be obtained. This specific example will be described later in detail.

On the other hand, in order to cause such a phase transition, the band gap E _G (Δ) must be higher than the temperature energy due to the ambient temperature of the system. That is,
The following equation must be satisfied. E _G > kT (4) where k is Boltzmann's constant and T is temperature. Since it is necessary to apply a B _c greater than the magnetic field as a condition of the device operation, the maximum magnetic flux density of the applied magnetic field (B _{max) is, B max> kT / gβ (} S 1 + S 2) (5) must satisfy . LSI (Large Scale Inte
maximum value of the magnetic field (H
_max , where H _max = B _max / μ) is converted into a magnetic flux density and substituted into the above equation, as an equation to be satisfied by the relative magnetic permeability (γ):

[0026]

(Equation 4) Is obtained. Here, A = k / βμ _o １1.49 × 10
⁴ [Oe / K], the μ _o vacuum magnetic permeability, μ is the magnetic permeability. As an example, _Hmax = 100 [Oe], g = 2, S
_{When 1} = 2, S ₂ = 3, and T = 300 [K], γ> 4
Get 500.

The active region C of the spin transistor illustrated in FIG. 1 is formed using such a material. And
By supplying a current to the conductors A and B and applying a magnetic field to the active region C, a quantum transition can be generated and a switching operation can be performed. Here, two conductors are provided in order to increase the magnetic field applied to the active region C. Therefore, if a magnetic field strong enough to satisfy the equation (5) can be obtained even with one conductor, the conductor is only A or
B alone may be used. Further, the magnetic field generating means for applying a magnetic field to the active region C is not limited to the conductor as illustrated. Similar effects can be obtained by using other means that can be appropriately selected by those skilled in the art.

FIG. 4 is a graph illustrating the relationship between the drain current density and the magnetic field of the spin transistor according to the present embodiment. That is, the figure illustrates the relationship between the magnetic field (B) applied to the spin transistor and the drain current density (J _sd ) in the case of R ₂ << R ₁ . According to the present invention, switching characteristics having such a clear threshold value and a high resistance ratio can be realized.

FIG. 5 shows the drain current density (J _sd ) and the drain voltage (V) of the spin transistor of this embodiment.
It is a graph which shows the relationship with _d ). That is, when the magnetic flux density B <Bc, the drain current hardly flows. On the contrary, when the magnetic flux density B> Bc, the conductivity of the active region increases and the drain current flows. As will be described later in detail, according to the present invention, the drain voltage during operation can be extremely reduced. As a result, a spin transistor with extremely low power consumption can be realized.

On the other hand, although not shown, in the case of R2 >> R1, the characteristics of the spin transistor can be represented by a graph in which the horizontal axis is 1 / B in FIG.

As a specific material constituting the active region C of the spin transistor illustrated in FIG. 1, for example, a spin ladder including a ladder-like lattice in a crystal lattice structure is used.
r) series substances. FIG. 6 is a conceptual view illustrating a part of a crystal lattice structure of a spin ladder system.
That is, in the spin ladder system, spin 1/2,
Electrons having a charge -e (e is an elementary charge) are localized in monovalent cations at lattice points of the ladder lattice. Further, electron spins between chains form a singlet pair having a spin number of 0 due to the spin-exchange interaction. Spin ladder system illustrated in the figure, under B _c smaller field, because it has an ordered such singlet pair is infinitely longitudinally aligned, the total number of spins this ordered state is 0 is there. Another feature of the spin ladder system is that an energy gap is opened above the quantum ground state having a spin number of 0, and the above-described disordered state having a spin number of 1 exists thereon. That is, S ₁ = 0,
S ₂ = 1.

In the ordered state (S ₁ ) having a spin number of 0, the electrons are localized in the cations at the ladder-like lattice points, so that electric conduction does not occur. However, when holes are doped under this order, the singlet pair Are replaced by holes and become carriers called hole singlets (spin 0, charge 2e). This carrier can be transported only in the longitudinal direction of the ladder (left-right direction in FIG. 6), and therefore has electrical conductivity in only one axial direction.

On the other hand, in the state of spin number 1 (S ₂ ), since there is no such order, even if the holes are doped, the above-mentioned carriers are not generated, and the electric resistance remains high.

In such a spin ladder system, as shown in FIG. 3, by applying a magnetic field larger than the critical magnetic flux density B _c , the state of the spin number 0 (S ₁ ) to the state of the spin number 1 (S ₁ ) Transfer to S ₂ ).

As described above, in the spin ladder material illustrated in FIG. 6, by doping holes, a low-resistance ordered state (S ₁ ) and a high-resistance disordered state (S ₂ ) are obtained. Is obtained, and by applying a magnetic field, a transition can be made from the ordered state (S ₁ ) to the disordered state (S ₂ ).

Therefore, the active region C is aligned with the source region S and the drain region D in FIG.
If a single crystal of this spin ladder material is provided in
A spin transistor having a high OFF resistance ratio can be realized.

As an example of the spin ladder system, an Sr (strontium) -based Cu (copper) -O (oxygen) compound or a La (lanthanum) -based Cu (copper)-O (oxygen) compound can be given. In the case of Sr ₂ Cu ₄ O ₆ , the lattice constant in the longitudinal direction of the ladder is less than 4 Å, and the influence of crystal disorder on the surface of the crystal reaches only about 5 times the lattice constant (less than 20 Å). It is sufficient to adopt a structure in which about 100 pairs are connected in series. That is, a spin transistor having a gate length of 40 nm can be realized.

On the other hand, another spin ladder system, La ₂ C
In u ₂ O ₅ , the lattice constant in the longitudinal direction of the ladder is slightly less than 2 Å, so that the gate length can be reduced to about 20 nm, and a fine and ultra-high-speed functional element can be realized.

The doping of holes (holes) into these spin ladder materials can be performed, for example, as follows. That is, when a substrate in the course of manufacturing an integrated circuit in a state where the single crystal thin film portion of the spin ladder is exposed is subjected to high-temperature and high-pressure treatment in a mixed gas of SrCO ₃ , La ₂ O ₃ , and CuO, a portion of La (lanthanum) is obtained. Is S
It is replaced by r (strontium), and is converted into a La _1-x Sr _x CuO _2.5 crystal in which a single crystal thin film of a spin ladder is doped with holes. Here, x is the hole concentration, which can be adjusted by the ratio of the mixed gas. X = 0
When the resistance is changed from x to 0.20, the resistance becomes 10 ⁶
[Ωcm] to 10 ⁻⁴ [Ωcm]. That is, the resistance can be reduced by about 10 digits due to the generation of carriers (hole singlets). That is, this embodiment corresponds to the case of R1 << R2 described above.
Therefore, when B < _Bc, the resistance is low, and when B> _Bc , the resistance is high.

The material of this spin ladder system is ON
When the resistance is normal silicon substrate (impurity concentration 10 ¹⁷ [c
m.sup.- ³ ], which is about three orders of magnitude lower than ^{10.sup.- 1} [.OMEGA.cm], and the driving voltage for obtaining the same driving current as that of the silicon device is as extremely low as about 3.3 [mV]. If the voltage is lowered by this amount, the effect of the bias becomes smaller than the thermal energy at room temperature. Therefore, it is actually desirable to operate at a voltage of about 0.03 [V] or more. That is,
According to the present invention, the drive voltage can be reduced to the thermal statistical lower limit at room temperature operation, and a functional element with reduced power consumption to the minimum can be realized.

Next, the relationship between the currents ( _Ia , _Ib ) flowing through the conductors A and B shown in FIG. 1 and the density ( _Jsd ) of the current flowing between the source and drain will be described. Here, R
It cited the case of ₁ >> R ₂ as an example. Also, for simplicity,
The sectional shapes of the conductors A and B shown in FIG. 1 are circular, and the distance from the center of the circle to the active region C is set to a.

FIG. 7 is a sectional view taken along line PQ of FIG. First, when I _a = I _b in FIG. 7, no magnetic field is applied to the active region C, so that R = R ₁ . Also, I _a =
When −I _b ≠ 0, the applied magnetic field is the same as the magnetic field applied by the DC current 2I _a ,

[0043]

(Equation 5) It is. Here, using equation (3), the critical current I _c2 :

[0044]

(Equation 6) Get. Assuming that the cross-sectional area of the conductor is 4F ² , the critical current density J _c2 is

[0045]

(Equation 7) It is. Here, F is the minimum processing dimension length. I _a > I
Since B> B _c is achieved when _c2, the R = R _2.

[0046] Figure 8 is a graph showing the relationship between J _sd and J _a. Here, J _a is the current density of the current flowing through the conductor A. Critical current density J _c3 when I _a > 0 and I _b = 0
Is

[0047]

(Equation 8) _Which is twice as large as J _c2 . The same applies to the case where I _a = 0 and I _b ≠ 0. J _sd -J _a characteristic of this case is as shown in FIG.

Next, a case using a circular current will be described. FIG. 9 is a sectional view taken along line PQ of FIG. That is,
In this example, the conductor is provided in an annular shape around the active region C. The magnetic field caused by the circular current (I _a ) flowing through such an annular conductor is

[0049]

(Equation 9) Therefore, the critical current density J _c1 is

[0050]

(Equation 10) Becomes In this case, also shown in J _sd -J _a characteristic FIG.

[0051] Further, FIG. 10 is a graph showing the relationship between the resistance between the source and the drain with (R _sd) and J _a corresponding to these specific examples.

As can be seen from the above-mentioned relational expression, in order to reduce the critical current density, it is desirable that the structure in which the length of the conducting wire whose distance from the active region C is the shortest is as long as possible. As an example, g = 2, γ = 5000, S ₁ =
2, S ₂ = 3, E _G = 0.05 [eV], a = 100
[Nm] and F = 0.25 [μm], the critical current density J _c1 can be simply estimated as J _c1 １．１1.1 × 10 ⁶ [A /
cm ² ]. Therefore, in this embodiment, in order to actually cause a quantum phase transition in the active region, 1 × 10
A conductive wire that does not cause electromigration even when a current of about ⁴ [A / cm ² ] flows is sufficient.

The energy gap of the spin ladder system is an energy value of the order of the spin-exchange interaction, and the spin-exchange interaction is the same as that of the constituent elements, composition, lattice constant, type and concentration of the impurities even in the same spin ladder system. because differs depending on, it appears dependent materials and impurities in the critical magnetic flux density B _c. Furthermore, the effective g-factor and S ₁ , S ₂
Also, material and impurity dependencies appear. Therefore, a high-performance functional element can be realized by appropriately selecting various spin ladder materials. Examples of such a spin ladder-based material include various materials such as a vanadium (V) -based material and a calcium (Ca) -based material, in addition to those described above.

Specifically, (VO) ₂ P ₂ O ₇ , NaV
₂ O ₅ , (La, Sr, Ca) ₁₄ Cu ₂₄ O _{41 and the} like.

Further, besides the spin ladder type material,
If a combination of a material and an impurity satisfying the above-described formulas (4) and (6) is used for the active region in FIG. 1, a functional element having a high on / off ratio can be realized similarly to the above. .

[0056]

According to the present invention, a very small functional element having an extremely high on / off ratio and an extremely large size can be realized by utilizing a quantum critical phenomenon peculiar to electron spin. it can. Specifically, by applying a magnetic field, the on / off resistance can be changed by about 10 digits, and a new spin transistor having a gate length of about 20 nm can be realized.

Further, according to the present invention, the operating voltage in the ON state can be extremely reduced. As a result,
It is possible to reduce power consumption at room temperature operation to the lower limit of thermal statistics.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a functional element according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram of an energy band for explaining a quantum transition used in the functional element of the present invention.

FIG. 3 is a conceptual diagram illustrating a quantum phase transition caused by applying a magnetic field.

FIG. 4 is a graph illustrating the relationship between the source / drain current density and the magnetic field of the spin transistor according to the embodiment of the present invention.

FIG. 5 shows the source / drain current density (J _sd ) and drain voltage (V _d ) of the spin transistor according to the embodiment of the present invention.
FIG. 6 is a graph showing the relationship between

FIG. 6 is a conceptual diagram illustrating a part of a crystal lattice structure of a spin ladder system.

FIG. 7 is a sectional view taken along line PQ of FIG. 1;

8 is a graph showing the relationship between J _sd and J _a.

FIG. 9 is a sectional view taken along line PQ of FIG. 1;

10 is a graph showing the relationship between the resistance between the source and the drain with (R _sd) and J _a corresponding to embodiments of the present invention.

[Explanation of symbols]

 S Source region C Active region D Drain region A, B Conductor

Claims (5)

[Claims] 1. A functional element comprising: an active region; and a magnetic field generating means for applying a magnetic field to the active region, wherein the functional element changes an electric resistance value of the active region by a magnetic field generated by the magnetic field generating means. The function that the active region is configured to change the order state of electron spins from a first state to a second state different from the first state by applying a magnetic field. element. 2. A functional element comprising: an active region; and a magnetic field generating means for applying a magnetic field to the active region, wherein the functional element changes an electric resistance value of the active region by a magnetic field generated by the magnetic field generating means, the active region, in a state where no magnetic field was applied, and open a large energy gap E _G than the thermal energy of the ambient temperature between the energy state of the energy state and spin number S ₂ spin number S _1, and the Using the maximum value H _max [O _e ] of the magnetic field that can be generated by the magnetic field generating means, the effective g-factor g, and the ambient temperature T [k], the relative magnetic permeability is given by: A functional element comprising a larger substance. 3. The critical magnetic flux density is set to E _G using a Bohr magneton β.
/ Gβ (S ₁ + S ₂ ), the ambient temperature T
The temperature E _G / where [k] is expressed using the Boltzmann constant k
k, when the magnetic flux density of the magnetic field applied to the active region by the magnetic field generating means is larger than the critical magnetic flux density,
The active region is conductive, and when the magnetic flux density is smaller than the critical magnetic flux density, the active region is electrically insulating; or, conversely, the magnetic flux density is equal to the critical magnetic flux density. The active region has an electrically insulating property when the magnetic flux density is larger than the threshold value, and has an electrical conductivity when the magnetic flux density is smaller than the critical magnetic flux density. Functional element. 4. The active region is made of a single crystal of a substance having a ladder-like portion in a crystal lattice structure, and is configured so that the conductivity appears in a longitudinal direction of the ladder. The above-mentioned substances include V (vanadium) -based oxide, Ca (calcium) -based oxide, Sr (strontium) -based Cu (copper) -O (oxygen) compound, and La (lanthanum) -based Cu (copper)-O ( The functional element according to claim 2, wherein the functional element is made of any one selected from the group consisting of (oxygen) compounds. 5. The magnetic field generating means comprises a conductive region through which a current flows, wherein the distance between the center line of the conductive region and the active region is a, the sectional area of the conductive region is λ, and the active region is formed. Critical current density 2aE _G / λgμβ (S ₁ + S ₂ ) expressed by μ as the magnetic permeability of the material to be changed and β as the Bohr magneton
The functional element according to claim 2, wherein a larger amount of current can flow.