JPH01265576A - Ceramic superconductive transistor - Google Patents

Abstract

PURPOSE:To obtain an excellent superconductive transistor by a method wherein a semiconductor layer, which is formed at the grain boundary of a ceramic superconductor through a heat treatment, is interposed between the superconductors at an extremely small space, and the transistor is controlled in characteristics through the kind and the amount of additive elements. CONSTITUTION:A semiconductor channel extremely short in length consists of the thickness of a semiconductor ceramic particle interface separated at a grain boundary 3 of a ceramic superconductor particle 4, where the semiconductor channel denotes the channel of a field effect ceramic superconductive transistor. The grain boundary 3 is separated off when a crystal grain between the interfaces 3 is made to grow, and the interface 3 is made not to be superconductive but semiconductive in a compositional ratio and controlled in a semiconductivity by mixing 1% or so of an additive such as SiO2 or Bi2O3 other the composition of a superconductor and making it separate off at the particle interface. The property is controlled through the kind and the amount of an additive element. By these processes, an excellent superconductive transistor can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a ceramic superconducting transistor in which the conductivity of grain boundaries is controlled by intervening grain boundaries.

<Prior Art> Superconducting transistors are being developed to provide amplification characteristics to superconducting elements that are characterized by ultra-high-speed operation. The developed superconducting transistors are field-effect transistors, or superconducting base transistors, in which a junction is created between a superconductor and a semiconductor such as Si or InAs, and the spread of superconducting electrons due to the proximity effect is increased by increasing the carrier concentration in the semiconductor. As a result, there were bipolar transistors that achieved higher speed by reducing base resistance.

<Problems to be solved by the invention> In conventional transistors, Nb or a compound thereof is used as a superconductor to form a junction with a semiconductor such as Si or InAs, and its critical temperature Tc is below 20°C. It was cooled with liquid helium. Furthermore, when manufacturing a field effect transistor, the channel length of Si or the like must be less than .mu.m even at liquid helium temperatures, which requires advanced manufacturing technology.

Furthermore, if we avoid the cryogenic liquid helium cooling described above and create a superconductor transistor using a ceramic superconductor, its coherence length is less than nm, and the channel length is extremely short, about 10 nm, which is an extremely difficult technology. will be required. Furthermore, there remains the problem that a technique for forming a bond between a ceramic superconductor and conventional Si or InAs has not been established.

The present invention solves the problems of the above-mentioned superconducting transistors, and provides a ceramic superconducting transistor that does not require extensive precision processing and is relatively easy to handle.

<Means for Solving the Problems> In order to achieve the object of the present invention, a ceramic superconductor with a high Tc is used as the superconductor, and the grain boundaries formed between the superconducting particles are given semiconductor characteristics. In addition, the thickness of the semiconductor grain boundary is set to a length that allows superconducting electrons leaking from the superconducting particles due to the proximity effect to be spread by the voltage of the control gate electrode to form a channel for the superconducting electrons at the grain boundary. I'm looking at it. ``Even if a ceramic superconductor is manufactured to be a uniform superconductor, grain boundaries are formed around superconducting crystal grains after steps such as firing. When forming semiconductor grain boundaries instead of superconducting particles, the semiconductor properties of the grain boundaries and their thickness can be controlled by adjusting the elements added to the superconductor raw material, their amounts, and the firing conditions. By adjusting the superconductor, a superconductor having semiconductor grain boundaries having the above-mentioned characteristics can be obtained.

A field effect superconducting transistor can be formed by providing the above superconductor with a saw 7 and a drain electrode at appropriate intervals, and providing a game electrode for controlling the gap therebetween.

<Function> The extremely short semiconductor channel length of the field-effect ceramic superconducting transistor is made up of the thickness of the semiconductor ceramic grain boundaries that are precipitated at the grain boundaries of the heptalamic superconductor particles, and it is added to the raw material of the ceramic superconductor. The thickness and characteristics of the semiconductor grain boundaries can be controlled by the type and amount of elements and firing conditions.

Therefore, a ceramic superconducting transistor with an extremely short semiconductor channel length can be obtained without using any special precision technology.

Example Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of the structure when the present invention is applied to a field-effect superconducting transistor 9, and FIG. 2 is a front view of this transistor 9.

Transistor 9 has an area of 10XIO and a thickness of 0.
Stabilized zirconia (YSZ) of approximately 100^ is deposited on the surface of an n-type silicon (Si) single crystal substrate 1 of
) Membrane 2 was produced.

On the other hand, a fine powder of YB a 2 Cu30y-a synthesized by a coprecipitation method that reduces the constituent elements such as nitrates is made into a paste with a solvent etc., and it is placed in the center of the substrate 1 to a thickness of about 1 mm.
The film was coated with a width of 0.5 ff and a length of about 10 ff.

After coating, the solvent was evaporated at a low temperature of about 200°C, and then baked in air at 930°C for 7 hours. After baking, slow cooling was performed, including temperature control at 380°C for 4 hours.

When a ceramic high-temperature superconductor is produced by a firing method, superconducting particles and grain boundaries surrounding the particles are formed.

These grain boundaries are precipitated when the grains grow, and either the composition ratio is changed to semiconducting rather than superconducting, or an additional element other than the superconducting composition, such as 5i02 or cloud 1203, is mixed into the grain. It is possible to control semiconductor properties by precipitating in a field. A trace amount of Mn may be added to the additive element 5i02.

As described above, it is possible to control the thickness of grain boundaries or their characteristics by changing the manufacturing conditions of ceramic superconductors, the type and amount of added elements, or the composition ratio of elements constituting the superconductor. can.

YBa2Cu307-δ produced by the method of this example
FIG. 5 shows an example of measurement using a scanning tunneling electron microscope (STM).

This figure shows tunnel/I from the surface of a mirror-polished sample.
This is a map scanned under control using a feedback voltage to maintain a current of 100 pA.

The height of the curve in FIG. 5 corresponds to the local resistance value of the sample. In the figure, A is a region that exhibits superconductivity, and region B is a region with semiconductor characteristics whose resistance value at room temperature is about three orders of magnitude higher than that of region A, and the grain boundary region of C is a semiconductor that is almost the same as region B. It turned out to be.

The fabricated superconducting film has a thickness of approximately 1μ as shown in Figure 1.
It is composed of one crystal grain in the thickness direction, and
The grain size in the lateral direction of the crystal grains is also the same as the film thickness,
And the adjacent particles are approximately 10nm, which allows current to flow due to superconducting electrons by applying a control voltage from the outside.
They were connected through grain boundaries with a semiconducting layer having a thickness of m.

The fabricated superconducting film has a source electrode 5 formed by vapor deposition of gold (Au) in the center except for the approximately 50 μm area that will become the channel 8.
- and a train electrode 5' were formed. A silicon oxide film is formed by CVD or the like on the electrode formed as above, or
It is covered with an insulating film 6 of silicon nitride film and further covered with aluminum (A
A transistor 9 was fabricated by depositing the shield electrode 7 of Ij).

The manufactured superconducting transistor 9 was measured using a measuring circuit having the configuration shown in FIG. In the figure, in order to keep the superconducting transistor 9 below the critical temperature Tc, it was placed in a dual bottle 10 containing liquid nitrogen LN and maintained at 77K. A variable voltage source VG up to 2V is connected to the silicon substrate that will become the gate electrode, and -2V and +2V are applied to the source electrode 5 and drain voltage [5', respectively.
V power supply was connected.

The characteristics obtained with the above measurement circuit are as shown in FIG. As is clear from the figure, the superconducting transistor 9 exhibited transistor operation in which the current flowing through its channel was controlled by the gate voltage.

In Figure 4, when the gate voltage is not applied and the drain current is 0, the drain current is approximately 200 μA, which is different from the resistance value tolerance at room temperature. This is thought to be due to the thin thickness and the energy gap between the semiconducting grain boundary and the superconducting crystal.

It is believed that the characteristics, antibacterial properties, etc. of the above embodiments can be improved by improving the elemental composition of the superconducting film of the present superconducting transistor and its manufacturing method. In addition, by establishing microfabrication technology for superconducting films, it is possible to create practical superconducting transistors that can be integrated at high density.

<Effects of the Invention> The superconducting transistor of the present invention uses a semiconductor layer that is formed by depositing a semiconductor layer, which should be interposed between superconductors at extremely small intervals, at the grain boundaries of a ceramic superconductor by heat treatment or the like. It is. The density, thickness, and semiconductor properties of the semiconductor layer formed by precipitation can be controlled by the manufacturing conditions or the number and amount of different elements added to the superconductor.

Therefore, it is possible to construct a superconducting transistor that operates at ultra high speed and has amplification characteristics without using extreme precision processing techniques.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view of a ceramic superconducting transistor of the present invention, Fig. 2 is a front view of an embodiment of the present invention, Fig. 3 is a measurement circuit diagram thereof, Fig. 4 is a characteristic diagram of the superconducting transistor, and Fig. 5 The figure is a diagram showing resistance value distribution measured by STM on the surface of a superconducting ceramic. 1 is silicon substrate, 2 is ysz, @edge film, 3 is grain boundary, 4 is superconducting crystal grain, 5 and 5' are source and drain electrodes, 6 is insulation, edge film, 7 is shield electrode, 8 is channel, 9 is a superconducting transistor. Agent: Patent attorney Takeshi Sugiyama (and 1 other person), number 2
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Voice actor 93 car transistor 3g measurement circuit n

Claims (1)

[Scope of Claims] 1. A ceramic superconducting transistor characterized in that the grain boundaries of superconducting ceramic particles are made of semiconductor ceramic, and the spread of superconducting electrons to the semiconductor ceramic grain boundaries is controlled. 2. The semiconductor ceramic grain boundary layer between the ceramic superconducting particles has a thickness that is at least twice the coherent length of superconducting electrons at the ceramic superconducting grain boundaries. Ceramic superconducting transistor. 3. The ceramic superconducting transistor according to claim 1 or 2, wherein the thickness of the superconducting layer having grain boundaries constituting the superconducting transistor is approximately equal to the grain size of the ceramic superconducting particles.