JPH0621521A - Current modulating device - Google Patents

Abstract

PURPOSE:To provide a current modulating device, which can be manufactured according to a micron-order pattern rule, is good in controllability and has sufficient switching characteristics. CONSTITUTION:In a current modulating device, which is provided with a first electrode 1, a channel joint 5, a second electrode 2 and a control electrode 7 and wherein a current, which is made to flow between the electrodes 1 and 2 via the joint 5, is controlled based on a control electrode signal, the channel joint 5 is formed by forming alternately a plurality of layers of superconductor layers 3 and non-superconductor layers 4 in parallel to the direction of flow of the current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current modulator suitable for the field of microelectronics and power electronics (electric power) and capable of high speed and large current capacity.

[0002]

2. Description of the Related Art A typical example of a current modulator intended for high speed and large current capacity is an element using a superconductor.

Current modulators using this superconductor can be generally classified into two terminals, a three-terminal element and a three-terminal element which can be easily highly integrated.

The three-terminal element basically has a structure in which a channel junction is provided between two electrodes (generally a superconductor or metal) and a control electrode is attached to the channel junction. An insulator, a semiconductor, a normal conductor, or a superconductor is used as the channel junction body. Now, a current modulator using a superconductor as a channel junction, in other words, a current modulator having an electrode / channel superconductor / electrode structure is compared with a superconducting current modulator using another channel junction. In addition, there is almost no size limitation of the channel assembly, the control electrode can be easily attached, and a large current capacity can be achieved. This is because, when other channel junctions are used, the tunnel effect and the proximity effect, which are effective only at a size of several Å to several hundred Å or less, dominate the device characteristics, whereas the channel junction has a superconducting effect. This is because when the body is used, the effect that the superconducting carrier of the channel superconductor is modulated by the control electrode signal dominates the device characteristics. Therefore, the only three-terminal element that can be manufactured by the pattern rule of the micron order or more, which can be used in the ordinary photolithography technique, is the current modulator including the structure of the electrode, the channel superconductor, and the electrode.

[0005]

However, the conventional electrode
The current modulator having the structure of the channel superconductor / electrode has the advantage that it is easy to manufacture as described above, but on the other hand, the controllability by the control electrode signal is low and the switching characteristics of other channel junctions are used. There is a drawback that it is inferior to current modulators, especially current modulators that use a semiconductor for the channel junction. Poor switching characteristics impose great restrictions on the application of the current modulator, and limit the fields of application that can take advantage of the ease of manufacturing. Therefore this is a big problem.

The present invention solves the above-mentioned problems, and provides a current modulator which can be manufactured with a pattern rule of the order of microns, has good controllability by control electrode signals, and has sufficient switching characteristics. Especially.

[0007]

A current modulator according to the present invention comprises a first electrode, a channel assembly, a second electrode, and a control electrode, and the first electrode and the first electrode are connected via the channel assembly. Forming a channel junction by alternately forming a plurality of layers of superconductors and non-superconductors in parallel in a current flowing direction in a current modulator for controlling a current flowing between two electrodes by a control electrode signal, The superconductor has two or more layers, the thickness of the non-superconductor is not more than twice the coherent length of the superconductor, and the thickness of the superconductor is not less than 1 unit lattice and not more than 30Å. That the superconductor and the non-superconductor are oxides, and after the intermediate layer having the same composition as the substrate is formed on the substrate, the first electrode, the channel assembly, and the second
And the control electrode and the like are formed.

It is more preferable that the first electrode and the second electrode are superconductors.

[0009]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 1 is a diagram showing a sectional structure of a current modulator according to an embodiment of the present invention. The current modulator includes a first electrode 1, a second electrode 2, a channel junction body 5 in which a superconductor layer 3 and a non-superconductor layer 4 are alternately laminated, a dielectric 6, a control electrode 7, a substrate 8 and an intermediate layer. Composed of layer 9.

The manufacturing process of the current modulator of this embodiment and
The points of the material are as follows. First, SrTiO
₃SrTiO 3 is formed on the substrate 8 made of single crystal.₃Membrane 100 Å ~
Form 300 Å homoepitaxial growth to form the intermediate layer 9
It Next, about 10Å to 30Å HoBa is deposited on the intermediate layer 9.
₂Cu₃O_7-XSuperconductor layer 3 made of a system oxide and La_1.5B
a_1.5Cu₃O_xAlternating non-superconductor layers 4 made of oxide
Stack. La_1.5Ba _1.5Cu₃O_xOxide is a semiconductor property
And a material having a good lattice constant matching with the superconductor layer 3
is there. Since oxide superconductors have anisotropy, epitaxy
Growth is essential and improves lattice parameter matching
That is an important point. ECR active oxygen
Using the MBE device equipped with a mhgun,
The conductor layers 4 are laminated in the same chamber. Film thickness control
Monitors the vibration intensity of RHEED, and based on that information,
This is done by controlling the shutter of the source. In addition, film thickness measurement
In addition to RHEED, X-ray diffraction Laue function analysis (unit case
Number of children) and STM (scanning tunneling microscope)
Value to be determined. Next, a plurality of superconducting layers 3 and non-super
Patterning the conductive layer 4 using photolithography
Then, the channel bonded body 5 is formed. Next, the film thickness
HoBa from 700Å to 2000Å₂Cu₃O_7-XOxides
A first electrode 1 and a second electrode 2 made of a system superconductor
-Pattern. Between this first electrode and second electrode 2
The distance of can be freely set as described in the prior art.
Next, SrTiO₃Formed dielectric 6 and control electrode 7
-Pattern. Here, SrTiO is used as the dielectric.₃For
The reason is that it has a crystal structure close to that of an oxide superconductor and
Easy to grow in the axial direction and little anisotropy in dielectric constant
And 3 points that the film thickness dependence of the dielectric constant is small are raised.
It The current modulator is obtained by the above process.

The features of the current modulator thus obtained will be described below.

This embodiment is a so-called field effect type in which an electric field is applied to the dielectric 6 to modulate and control the carrier density in the channel superconductor layer 3 (for example, forming a depletion layer). The field effect control voltage Vg (gate voltage) and the depth d of the depletion layer
As is well known, the relationship with s is expressed by the following equation (Equation 1).

[0014]

[Equation 1]

Here, n = carrier density (oxide superconductor is 10 ²¹
/ Cm ³ ) di = thickness of dielectric e = charge ε _i = dielectric constant of dielectric ε _s = dielectric constant of superconductor

As can be seen from the equation, when the gate voltage is a voltage (several volts) generally used in semiconductor devices, the depth ds of the depletion layer becomes extremely shallow, 10 to 30 Å. Therefore, in order to obtain the required switching ratio, it is necessary to make the film thickness of the superconductor layer 3 similarly extremely thin. However, as can be seen from FIG. 2, which shows the relationship between the film thickness of the superconductor layer 3 and the critical temperature, as the film thickness of the superconductor layer 3 becomes thinner, the fluctuation increases and the critical temperature sharply drops. (Measurement of the critical temperature is performed on the sample of the structure excluding the non-superconductor layer 4 in FIG. 1) In actual use as a current modulator, superconductivity cannot be used in an unstable state. Therefore, the switching ratio must be reduced.

The present invention suppresses fluctuations by connecting a plurality of thin superconducting layers 3 having fluctuations with a non-superconducting layer 4 having a thickness at which the pair potentials of superconductors can influence each other, thereby suppressing fluctuations in the critical temperature. The decrease is reduced. 3 and 4 show the characteristics. First, FIG. 3 shows the film thickness of the non-superconductor layer 4 in which the superconductor layers 3 can suppress fluctuations by being coupled to each other. The superconductor layer 3 is a-axis oriented in the connecting direction. As can be seen from the figure, the thickness of the non-superconductor layer 4 needs to be 40 Å or less in order to suppress the lowering of the critical temperature. The coherent length ξ _{0 in the} a-axis direction is about 2
Since it is 0Å, it is twice the coherent length ξ ₀ .
The thickness of coherence length similarly to Example where (coherence length xi] ₀ differs by the alignment direction) was investigated changing the kind of and the superconductor crystal orientation direction of the upper limit superconductor xi] ₀
It was about twice as much as The coherent length ξ varies depending on the operating temperature as expressed by the following equation (Equation 2) and increases as the operating temperature rises. In the present invention, the coherent length generally used in the sense of the coherent length. It was almost the same as the value of ξ ₀ .

[0018]

[Equation 2]

Where Tc = critical temperature, T = use temperature,
ξ ₀ = coherent length at absolute zero. The film thickness of the non-superconductor layer 4 differs depending on the carrier density of the non-superconductor layer 4, and when an insulator is used for the non-superconductor layer 4, it must be thinner than the coherent length ξ ₀ × 2.

FIG. 4 shows film thicknesses of 23Å (C) and 12Å (D).
FIG. 6 is a diagram showing the relationship between the number of superconductor layers 3 and the critical temperature when the superconductor layer 3 of 3 and the non-superconductor layer 4 of 23Å are laminated. It can be seen that when the number of superconductor layers 3 is two or more, the decrease in the critical temperature is suppressed rapidly. The thickness of the superconductor layer 3 needs to be 1 unit lattice (superconductivity is expressed in the oxide superconductor by 1 unit lattice) or more, and 30 Å or less where a depletion layer is easily formed. However, a power device having a high gate voltage Vg or a combined effect device such as an electric field effect and a quasi-particle injection effect can make the superconductor layer 3 thicker, which is not the case.

In FIG. 2A, a superconductor is used as the material of the electrode,
B is a sample using Ag, but the superconductor electrode shows a higher critical temperature than the Ag electrode, although the superconductor layer 3 has the same thickness. This is because the pair potential of the superconductor layer 3 is lowered in the junction with the Ag electrode, but the pair potential of the superconductor layer 3 is lowered in the junction with the superconducting electrode due to fluctuations and exudation of the pair. It is considered that a superconducting electrode having a pair potential (here, a superconductor electrode having a small decrease in the pair potential) is pulled up. Therefore, it can be said that the first electrode 1 and the second electrode 2 are preferably made of a superconductor rather than a metal, and are more preferable as the pair potential is higher.

The switching ratio of the obtained current modulator was examined. The measurement temperature was 65 K, and the switching ratio was the ratio of the current flowing between the first electrode 1 and the second electrode 2 when the signal was applied to the control electrode 7 (Jc off /
Jcon).

The results are shown in Tables 1 and 2 together with the comparative examples.

[0024]

[Table 1]

[0025]

[Table 2]

In the comparative example of Table 1, the channel junction body 5 has only the superconductor layer 3, and the film thickness is the total thickness of the superconductor layer 3 of the embodiment (the non-superconductor layer 4 is It is a value close to (excluding thickness). The comparative example in Table 2 is SrTiO 3.
_{3 This} is a sample in which the intermediate layer 9 of the homoepitaxial growth film is not formed on the substrate.

From Table 1, superconductor layer 3 and non-superconductor layer 4 are shown.
It can be seen that the current modulator having the channel junction body 5 in which is laminated with a predetermined film thickness can operate at a high operating temperature and the switching ratio is remarkably improved.

[0028] From Table 2, the switching ratio than the current modulation device without forming an intermediate layer 9 in SrTiO ₃ current modulation device to form an intermediate layer 9 a SrTiO ₃ film made of the same material on a substrate by epitaxial growth SrTiO ₃ substrate It turns out that it is remarkably high. We believe this is due to the following reasons. Generally, the surface of the substrate after polishing is 30
Has irregularities of Å ~ 60Å. Since the film thicknesses of the superconductor layer 3 and the non-superconductor layer 4 of the channel junction body 5 are thinner than the surface value, the surface roughness has crystallinity and crystal orientation of the superconductor layer 3 and the non-superconductor layer 4. , And adversely affects the bondability of the interface, internal stress, strain, mutual diffusion and the like. Therefore, the characteristics of the original material cannot be derived, and the device characteristics fluctuate and the characteristics deteriorate. On the other hand, the surface of the intermediate layer 9 homoepitaxially grown on the surface of the substrate is 15 Å or less, and the surface roughness is improved, so that the influence on the superconductor layer 3 and the non-superconductor layer can be reduced. Therefore, the characteristics possessed by the original material can be derived, and fluctuations in device characteristics can be suppressed, resulting in less deterioration in characteristics. That is, when forming an extremely thin film not only in the embodiment but also in a superconducting device, it is necessary to suppress the roughness of the substrate surface as much as possible, and the method of forming the intermediate layer 9 homoepitaxially grown on the substrate is easy and remarkable. It can be said that it is an effective means to bring about the effect of.

In the embodiment, Ln (trivalent rare earth) Ba ₂ Cu ₃ O _7-x type superconductor is used as the superconductor, but Bi ₂ S is used.
Bi system represented by r ₂ Ca ₂ Cu ₃ O _x , Tl ₂ Ba ₂ Ca
₂ Cu ₃ O _x representative Tl system, Pb ₂ Sr ₂ Y _0.5 Ca
Other superconductors such as Pb-based typified by _0.2 Cu ₃ O _x may be used, and La _1.5 Ba _1.5 Cu ₃ O _x is used as the non-superconductor 4, but PrBa ₂ Cu ₃ O _{7-x is used.} , TbBa ₂ Cu ₃ O
_7-x etc. Ln-based superconductor in which Ln part is substituted with tetravalent element, oxide superconductor having critical temperature lower than operating temperature, SrTiO ₃ , SrVO ₃ , SrTiFeO ₃ , La
AlO ₃ , LaCoO ₃ , LaTiO ₃ , LaVO ₃ , Nd
MnO ₃ , PrAlO ₃ , PrCoO ₃ , PrMnO ₃ , S
mCoO ₃ , SmVO ₃ , La _0.33 NbO ₃ , La _0.33 T
aO ₃ , Sm _0.33 TaO ₃ , GdMnO ₃ , PrMnO ₃ ,
Perovskite structure oxides such as BaFeO ₃ , BaTiO ₃ , EuTiO ₃ , Ti ₃ Zn, Pt ₃ Zn, Pt ₃ Ti,
It may be Pd ₃ Sn, PtMn ₃ , IrMn ₃ or the like.
However, it is necessary that the superconductor and the non-superconductor have the same crystal structure as much as possible and that the lattice constants be well matched.

Further, in addition to the electric field effect, the control can be of a hot electron injection type, a quasi-particle injection type, a composite type (for example, a field effect + quasi-particle injection type), or the like, which has a switching ratio improving effect.

[0031]

As described above, according to the present invention, it is possible to construct a device having only a size on the order of microns or more at a high operating temperature (the decrease in the critical temperature of the channel junction body) and the controllability by the control electrode signal. It is possible to provide a current modulator having good and sufficient switching characteristics.

Since the superconducting current modulator according to the present invention can be easily manufactured by using the usual photolithography technique, its effect is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a current modulator according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the film thickness dependence of the critical temperature.

FIG. 3 is a diagram showing the film thickness dependence of a non-superconductor layer formed between superconductor layers at a critical temperature.

FIG. 4 is a diagram showing the dependency of the critical temperature on the number of superconductor layer stacks.

[Explanation of symbols]

 1 ... 1st electrode 2 ... 2nd electrode 3 ... Superconducting layer 4 ... Non-superconducting layer 5 ... Channel junction body 6 ... Dielectric 7 ... Control electrode 8 ... Substrate 9 ... Intermediate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuya Shimoda 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (6)

[Claims] 1. A control electrode signal comprising a first electrode, a channel assembly, a second electrode, and a control electrode, wherein a current flowing between the first electrode and the second electrode through the channel assembly is a control electrode signal. 1. A current modulator characterized in that a plurality of superconductor layers and non-superconductor layers are alternately formed in parallel with each other in a current flowing direction in a current modulator controlled by the above to form a channel junction. 2. The current modulator according to claim 1, wherein the superconductor layer is two or more layers. 3. The thickness of the non-superconductor is not more than twice the coherent length of the superconductor.
The described current modulator. 4. The superconductor has a thickness of 1 unit cell or more and 3 or more.
The current modulator according to claim 1, wherein the current modulator is 0 Å or less. 5. The current modulator according to claim 1, wherein the superconductor and the non-superconductor are oxides. 6. A current modulation device, comprising: forming an intermediate layer having the same composition as that of a substrate on a substrate and then forming a first electrode, a channel assembly, a second electrode, a control electrode, and the like.