JPS6334984A - Superconducting circuit device and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable the adjustment of superconducting critical current of loose coupling parts to be performed at the room temperature and atmospheric pressure or with a technically easy process by a method wherein a substrate is provided with a pair of isolated superconducting electrodes and multiple electrodes to be loose coupling parts between the superconducting electrodes. CONSTITUTION:After forming a pair of superconducting electrodes at high superconducting critical temperature and melting point, splitted microbridge type loose coupling parts 2 are formed of multiple patterns in parallel using a material in high superconducting coherence length. At this time, the superconducting critical current as a microbridge is equivalent to the multiple of splitted numbers of superconducting critical current per piece of splitted loose coupling parts 2. Therefore, the superconducting critical current value can be easily adjusted to a designed value by dividing a part of splitted loose coupling parts 2 by a trimming device. Furthermore, if the superconducting critical current per piece of splitted loose coupling parts 2 is measured before trimming process to count the numbers of loose coupling parts 2 to be removed by trimming process, the trimming process can be performed at the room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a superconducting circuit device and a method for manufacturing the same, and particularly to a superconducting circuit device and a method for manufacturing the same suitable for application to a quantum flux parametron circuit.

[Prior Art] Conventionally, when forming a weak coupling part of a superconducting circuit device, it is difficult to adjust the superconducting critical current Im.
As described in Japanese Patent No. 189275, the weak coupling portion 10 is formed by exposing a substrate cooled to liquid helium temperature to a reactive gas and applying an electron beam 5 to form a conductive pattern on the substrate. (See Figure 2) [Problems to be Solved by the Invention] The above-mentioned conventional technology does not take into account technical difficulties such as cooling the substrate to a cryogenic temperature in an electron beam exposure machine and introducing a reactive gas. First, there were problems with feasibility. SUMMARY OF THE INVENTION An object of the present invention is to provide a superconducting circuit device and a method for manufacturing the same, in which the superconducting critical current of a weak coupling portion can be adjusted at room temperature and atmospheric pressure, or by a technically easy method.

[Means for solving the problem] The above purpose is to create a parallel connection structure of a plurality of weak coupling parts of weak / J%, and when adjusting the superconducting critical current, the weak coupling parts are connected in parallel. This is achieved by removing part of the parallel connection of the parts with a trimming device.

[Action] The superconducting critical current at the weak coupling part of a superconducting circuit in which multiple minute parallel connections are used as weak coupling parts is
It is normalized to an integral multiple of the critical current per individual. Therefore, if the critical current per minute parallel connection is known,
The number of minute parallel connections that achieve the required critical current can be determined and trimmed to the required number using a trimming device at room temperature and atmospheric pressure. Therefore, technical problems such as cryogenic cooling in the electron beam exposure machine and the need for four people to handle the reactant gas can be eliminated.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram illustrating a first embodiment. After forming the superconducting electrode 1 such as Nb, which has a high superconducting critical temperature and a high melting point, a material having a large superconducting coherence length, for example,
A microbridge-shaped divided weak coupling portion 2 is formed by forming a plurality of patterns in parallel, each having a length of 1 to 3 μm and a width of approximately 1 μm, using a button and a button-indium alloy. At this time, the superconducting critical current as a microbridge is multiplied by the number of divided superconducting critical currents per one divided weak coupling part 2. Until now, no effective method has been found to control the superconducting critical current value of microbridges, and it has been extremely difficult to adjust it to the designed value.

According to this embodiment, the superconducting critical current value can be easily adjusted to the design value by removing a portion of the divided weak coupling portion 2 using a trimming device. Furthermore, if you measure the superconducting critical current for each of the weak coupling parts 2 divided into 5 parts before trimming, you can know the number of weak coupling parts to be removed by trimming, which has the advantage that trimming can be performed at room temperature. There is. In addition, since there is a specific relationship between the resistance value of the weak coupling part and the superconducting critical current value at room temperature, there is an effect that trimming can be performed at the same time as the resistance value measurement, similar to the trimming of a normal resistance pattern. This has the advantage that a conventionally used trimming device can be used as is.

In this case, by providing the weak coupling part protection electrode 3 in parallel with the weak coupling part as in the second embodiment shown in FIG. It has the effect of being able to be trimmed. After the trimming is completed, the weak coupling portion protection electrode 3 is also removed.

Figure 4 shows that during trimming, a small search coil 6 formed on a separate chip is brought close to the weak coupling part, and the resonant frequency is measured when the divided weak coupling part 2 is regarded as a minute inductance loop. It is a figure explaining the 3rd example which performs trimming.

The divided weak coupling portion 2 has a plurality of overlapping inductance loops. When the number of divided weak connections 2 is 2 and 3
Comparing the case of 2 inductances, there is one inductance loop and one resonance point, but in the case of 3 inductances, there is a small loop made by 2 and 2 loops. One large loop corresponding to the outside is created. There are two resonance points, one corresponding to a small loop and one corresponding to a large loop (where the frequency is halved). Similarly, there are the number of resonance points equal to the number of divided weak connections minus one. Due to the number of resonance points, trimming can be performed while checking the minute weak coupling portion to be trimmed. This embodiment has the advantage that trimming can be performed without electrical connection to the chip to be trimmed. In addition, if the chip can be cooled to an extremely low temperature in the trimming device, the divided weak coupling parts 2 can constitute a quantum flux parametron circuit (a circuit using magnetic flux quanta as a signal medium), and the search coil 6 and the same substrate as the search coil 6 can be connected. The above quantum flux parametron circuit detects a portion of the magnetic flux generated by the output current of the quantum flux parametron to be trimmed, and can perform trimming so that the detected magnetic flux is maximized. In this example,
There is no restriction on the atmosphere of the sample installation part of the trimming device, and there is an effect that an atmosphere suitable for cooling can be selected. Further, the search coil 6 only needs to be close enough to detect the magnetic flux of the sample to be trimmed, and does not need to be on the same substrate as the sample or extremely close to the sample.

Even if the quantum flux parametron circuits are cascaded, it is sufficient to simply move the search coil 6 close to the quantum flux parametron circuit to be adjusted. In particular, when the search coil 6 is formed on a transparent substrate, trimming using a laser beam becomes possible, and there is an advantage that there is no need to remove the search coil 6 during trimming.

FIG. 5 is a diagram illustrating a fourth embodiment in which a tunnel junction is divided into minute junction portions 8 as divided weak coupling portions, which has the advantage that it can also be applied to the production of conventional Josephson circuits.

FIG. 6 is a diagram illustrating a fifth embodiment in which a trimming electrode 9 is installed in advance in the lower layer of each weak coupling part of the divided weak coupling parts 2, and when trimming, mechanical means, ion beam, particle beam means such as electron beam,
A desired weak weak coupling portion can be removed by applying current, without using optical means such as a laser. This embodiment has the advantage that trimming can be performed without using a special device such as a trimming device.

In the above embodiments, a method of removing unnecessary portions during trimming is adopted. In addition, if a specific weak coupling part is irradiated with an ion beam or an electron beam to change the superconducting characteristics of the weak coupling part, a value other than an integer multiple of the superconducting critical current of one divided weak coupling part 2 can be obtained. It can be trimmed to.

This embodiment has the advantage that the superconducting critical current can be trimmed accurately.

Furthermore, when adjusting the superconducting critical current of a proximity effect bridge formed by placing superconducting electrodes close to each other on a semiconductor substrate, it is possible to adjust the superconducting critical current by irradiating the weak coupling part with an ion beam, electron beam, or light beam. In this case, as in the embodiment shown in FIG. 4, there is an effect that the superconducting critical current can be adjusted while observing the output of the electron flux parametron circuit using the search coil 6.

[Effects of the Invention] According to the present invention, the superconducting critical current of the weak coupling portion of the Josephson junction can be accurately corrected, so that the Josephson circuit can operate at higher speeds and with higher margins. In particular, the use of microbridge-type weak coupling sections with precisely controlled superconducting critical currents in quantum flux parametron circuits has the effect of realizing circuits that are faster and consume less power than conventional Josephson circuits.

[Brief explanation of the drawing]

1 and 3 to 6 are perspective views showing different embodiments of the present invention, and FIG. 2 is a perspective view of the prior art. 1...Superconducting electrode, 2...Divided weak coupling part, 3...
・Weak coupling part protection electrode, 4... Insulating film, 5... Electron beam, 6... Search coil, 7... Divided upper electrode,
8... Divided tunnel junction, 9... Trimming electrode, 10... Weak coupling part.

Claims (1)

[Claims] 1. A substrate, and at least one substrate separately provided on the substrate.
A superconducting circuit device comprising a pair of superconducting electrodes and a plurality of electrodes serving as weak coupling portions between the pair of superconducting electrodes. 2. A superconducting circuit device according to claim 1, wherein a material having a large superconducting coherence length is used for the plurality of electrodes. 3. The method includes the steps of forming at least one pair of superconducting electrodes, forming a plurality of electrodes that serve as weak coupling portions between the pair of superconducting electrodes, and trimming a portion of the plurality of electrodes. A method for manufacturing a superconducting circuit device characterized by: