JP2941811B2 - Superconducting transistor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a superconducting transistor, in particular, to an injection superconducting transistor.

[Summary of the Invention]

According to the present invention, a gate portion provided with a gate electrode in contact with a superconductor constituting an oxide-based superconducting channel is provided via an insulating thin film, and the insulating thin film is separated from the gate electrode by a voltage applied to the gate portion. The carrier concentration of the superconducting channel is modulated by tunnel injection of passing carriers, whereby the transition temperature Tc is changed so that modulation by switching between the superconducting and normal states can be performed.

[Conventional technology]

Originally, electronic active devices using superconducting materials include two-terminal devices using the Josephson effect, various field-effect superconducting transistors using the proximity effect of electron pairs, and bipolar devices based on superconductors. There are proposals such as transistor elements. Among them, a field effect transistor utilizing a proximity effect to a semiconductor has many advantages in circuit configuration and is expected to be large. In this case, the element configuration is such that the superconductor is a source and a drain, a portion corresponding to the gate is a semiconductor, and the leaching rate of electron pairs from the superconductor into the semiconductor is determined by a third electrode (gate electrode). To control. Therefore, in this case, the interval between the source and the drain needs to be about the length of the leaching of the wave function of the electron pair from the superconductor, resulting in an extremely fine structure. One measure is the coherent length. However, there is an inverse correlation between the coherent length and the superconducting transition temperature Tc of the superconductor, and the higher the temperature of the superconductor, the shorter the coherent length.

On the other hand, in recent years, development of high-temperature superconductors and research on characteristics have been rapidly advanced. For example, Japanese Journal of Applied Physics
Applied Physics) vol.27, No.1, 1 January, the 1988, the carrier of the superconductor _{Nd 1 + K Ba 2-K} Cu 3 O 7-δ ( hole) [Cu-
0] ⁺ has been reported on the relationship between the change in the concentration of ^{+ and} the change in the superconducting transition temperature Tc.

[Problems to be solved by the invention]

The present invention provides a superconducting transistor which can be constituted by a high-temperature superconductor to solve the above-mentioned problems.

[Means for solving the problem]

As shown in FIG. 1, the present invention relates to an oxide-based superconducting material having a layered perovskite structure containing CuO, for example.
_{Nd 1 + K Ba 2-K} Cu 3 O 7-δ than consisting superconductor (1), a thin film thickness of the insulating film (2) to a degree that may cause tunnel carrier to the superconductor (1) A gate portion (4) is formed by disposing a gate electrode (3) made of a normal conductor, for example, a metal or a superconductor. Then, first and second electrode portions (5) and (6), that is, source and drain electrodes are provided on both sides of the gate portion (4). Then, carriers are injected through the insulating thin film (2) under the gate portion (4) of the superconductor by the voltage applied to the gate electrode (3), and between the first and second electrode portions (5) and ( 6) The carrier concentration in the channel portion is modulated to change the superconducting transition temperature, thereby switching between the superconducting state and the normal conducting state of the channel portion.

[Action]

In the above configuration, when a required voltage is applied to the gate electrode (3), carriers such as electrons are transferred from the gate electrode (3) to the superconductor (1) below the tunnel gate portion (4) through the insulating thin film (2). Tunnel injection is performed.
This modulates the carrier concentration of the superconductor (1). That is, for example, the superconductor (1) is made of Nd _{1 + K} Ba
When a _{2-K Cu 3 0 7-} δ, [Cu ₃ O _7] ⁺ That will be the concentration of holes decreases, lowering the transition temperature Tc of super conductivity. Therefore, for example, in a superconducting state in which the specific resistance characteristic of the channel portion shows a transition temperature Tco higher than the temperature Ts as shown by a curve (21) in FIG. It is switched to the normal state by a decrease in the Tc ₁ transition temperature Tc as shown in FIG. 2 curve (22), first and second electrode portions between (source and drain) (5) and (6) For example, it can be switched to the off state.

〔Example〕

As shown in FIG. 1, a superconductor (1) having a thickness of 1000 mm or less is sputtered into a thin film on an insulating substrate (7) of, for example, MgO, SrTiO ₃ or the like, or a raw material is mist-formed to form a chemical vapor. It is formed by a so-called MT-CVD method or the like that grows in phase.
This superconductor (1) is, for example, an oxide-based superconductor having a layered perovskite structure containing CuO, for example, Nd _{1 + K} Ba _2-K
Cu ₃ O _7-δ or, for example, one in which Nb is partially substituted with Y, one in which Ba is partially substituted with Sr, one in which O is partially substituted with F or S, or the like can be used. The carrier concentration of this superconductor shows a strong correlation between this concentration and the superconducting transition temperature Tc, for example, 10 ²² cm ^-3 or less.
²¹ cm ^-3 units.

Then, for example, SiO ₂ is deposited on the superconductor (1) by a known technique to a thickness of 500 mm or less, for example, 100 mm, which is thin enough to cause tunnel injection of electric charges, and a gate is formed thereon. The gate (4) is formed by applying the electrode (3). The first and second electrodes serving as a source and a drain are formed by depositing, for example, an Ag electrode on both sides of the channel part (8) under the gate part (4) of the superconductor (1). (5) and (6) are applied.

〔The invention's effect〕

As described above, according to the present invention, the charge is injected into the channel portion by the voltage applied to the gate electrode (3) to modulate the carrier concentration in the channel portion. since so as to shift between the superconducting transition temperature Ts higher temperatures Tco and low temperature Tc _1, and can perform remarkable modulation of conductivity, also, with a simple structure, and the coherence length order fine There is great industrial benefit because no processing is required.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an example of a transistor according to the present invention, and FIG. 2 is a temperature characteristic curve diagram of specific resistance. (1) is a superconductor, (2) is an insulating thin film, (3) is a gate electrode, and (5) and (6) are first and second electrode portions.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takao Miyajima 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-A-62-88381 (JP, A) 1-2202874 (JP, A)

Claims (1)

(57) [Claims] An oxide-based superconductor, a gate portion including a gate electrode provided on the oxide-based superconductor via an insulating thin film, and a gate portion of the oxide-based superconductor. And first and second electrode portions provided on both sides of the oxide superconductor. Carrier is injected under the gate portion of the oxide-based superconductor through the insulating thin film by a voltage applied to a gate electrode. Modulating the carrier concentration of the channel portion between the first and second electrode portions to change the transition temperature of the superconductor to switch between the superconducting and normal conduction states of the channel portion. Superconducting transistor characterized.