JPH01217980A - Bridge type grain boundary josephson element - Google Patents

Abstract

PURPOSE:To obtain a bridge type grain boundary Josephson element exhibiting a clear Chapiro step at a liquid nitrogen temperature (77 deg.K), by specifying the grain boundary number on a current flowing path in a bridge. CONSTITUTION:Oxide superconductor particles constituting a bridge communicate with each other via grain boundary, and connected from one bank to the other bank in a superconducting state. It is important that the number of grain boundary by linking particles in the bridge is 1-5. The dimension of bridge is not limited, but available for 500mum or less in width, 100mum or less in length and 50mum or less in thickness. At the forming method of the bridge having 1-5 grain boundaries is as follows; Factors of manufacturing process, such as the grain diameter of film forming material and annealing treatment conditions are suitably selected, and a prescribed grain number is obtained by growing the layer in a crystal of specified size. In other way, after a film of superconductor particles is formed, the grain diameter in a bridge forming region is measured, the film is worked so as to have a desired number of grain boundaries, and the bank and the bridge are formed.

Description

[Detailed description of the invention] [A. Field of industrial application] The present invention is a Shapiro step (constant voltage step) in which the number of grain boundaries formed by oxide superconductor particles in a bridge is 1 to 6.
Regarding large Josephson elements.

[Background Art] Josephson Juncti
on) is an element made based on the Josephson effect,
Applications in the electronics field are attracting attention as devices for detecting broadband or weak electromagnetic waves.

Several types of such Josephson elements have been developed in the past, and the bridge type of the present application is one of them.

The basic structure of a bridge-type grain boundary Josephson element, as shown in Figure 1, consists of a substrate l made of alumina, zirconia, etc., two banks 2.3 made of superconductor, and a bridge 4 connected to them. Consisting of

In this element using an oxide superconductor, the superconductor particles in the bridge contact each other to form grain boundaries, and the Josephson effect appears at the grain boundaries.

To take an example of a conventional bridge type grain boundary Josephson element, (Y,Er)Ba is deposited on a substrate at a critical temperature (Tc) of 81.
A CuO film was formed by sputtering, and then heated at 890°C for 8
After annealing in an oxygen atmosphere for an hour and then wet etching with 85% phosphoric acid, the bridge has a width of 4 μm, a length of 20 μm, and a thickness of 4 μm. Those with 2 to 4μ chains are known (IEICE technical research report S CE 8
? -38 (, 1987)).

[Problem to be solved by the invention] Since the bridge of the conventional bridge type grain boundary Josephson element is simply formed by densely forming small-diameter superconductor particles, the number of grain boundaries through which current passes is small. There were significantly more.

Therefore, the bridge type grain boundary Josephson element is
When a current is applied while cooling at 77 K) and electromagnetic waves are irradiated, each time the current passes through a grain boundary, it is interfered with and the I-V
Due to the characteristics, the Shapiro step that should appear in a step-like manner at a constant voltage was very small, or in some cases disappeared.

Therefore, the conventional bridge type grain boundary Josephson element was insufficient to be applied to the above-mentioned detector at liquid nitrogen temperature.

[Means for Solving Problem 28] Therefore, in order to create an element with a large Shapiro step, the present inventor conducted research on grain boundaries in the bridge, and determined the number of grain boundaries on the current path in the bridge. As a result, they discovered that a clear Shapiro step phenomenon was exhibited, and completed the invention as described below.

That is, the present invention provides a bridge type grain boundary Josephson element in which oxide superconductor particles in the bridge connect two banks with one to five grain boundaries.

The present invention will be explained in detail below.

In the present invention, oxide superconductor particles constituting the bridge of a bridge type grain boundary Josephson element are connected via grain boundaries, and one bank is connected to the other bank in a superconducting state.

The connected form of oxide superconductor particles includes linear,
Although various shapes such as a zigzag shape, an X-shape, a Y-shape, etc. can be seen, the present invention does not particularly specify these shapes.

It is particularly important in the present invention that the number of grain boundaries due to particles connected within the bridge is 1 to 5.

The number of grain boundaries is counted within the bridge, and includes grain boundaries at the boundary between the bank and the bridge.

A groove in which the number of grain boundaries is less than 1 (that is, zero) means that, for example, within a bridge, oxide superconductor particles are discontinuous between banks, and such a bridge does not exhibit the Shapiro step phenomenon, or vice versa. If the number of grain boundaries is 6 or more, interference by electromagnetic waves will increase and the Shapiro step will become smaller, which is not preferable.

The size of the bridge is not particularly limited in the present invention, but it is approximately 500μ in width or less, 100μ or less in length, and 50μ in thickness.
Applicable to things below μ.

In addition, in the present invention, there are no particular limitations on the size of the conductor particles and the manner in which they are arranged depending on the difference in diameter within the bridge.

Any method may be used to create a bridge having a grain boundary number of 1 to 50. Specifically, if the bridge dimensions are determined, the grain size of the film forming raw material, annealing treatment conditions, etc. A method of growing crystals of the required size and a specified number of grain boundaries by selecting factors appropriately, or if the bridge size is arbitrary, after forming a film of superconductor particles on the substrate surface. , a method of forming a bank and a bridge by measuring the grain size at a location where a bridge is expected and processing the film so as to have a desired number of grain boundaries.

The material of the oxide superconductor particles is B a-L a-Cu-0
system, B a-Y -Cu-0 system, B a-E r-Cu
-0 system, 4-element system such as B i-9r-Cu-0 system, B
a-3r-Y -Cu-0 system, Bi-white r-Ca-Cu
-0 series, five element systems, etc. Specifically, B azY C
u30? -δ, B a2E rCu307-δ, B
iS rCaCu20 x etc. are shown.

Conventional substrate materials are used, and are not particularly limited in this application.

Next, the present invention will be explained based on examples.

[E, Examples] Examples 1 to 2 Comparative Example I Superconductor powder (Ba2YCu
A slip (solid content concentration 20x) in which 307-δ) was dispersed in ethanol was added dropwise and dried at 110'C.

After repeating the dropping and drying process 5 times,
, form a film by annealing in an oxygen atmosphere for 2 hours,
Three laminated boards were made.

As a result of measuring the critical temperature of these films using the four-probe method, it was found that 92
It was in ~93.

Next, while observing the film of the laminated substrate with a magnifying glass, use a cutter to determine whether the number of connected grain boundaries is (A) 2 to 3, (B)
4-5 and (C) 6-8, a bridge type grain boundary Josephson element having a shape as shown in FIG. 1 was fabricated. The length of the bridge is 20μ and 40μ respectively.
column, it was 75μ Akebono. The diameter of the superconductor particles constituting the bridge was 2 to 10 μ-.

Next, current and voltage measurement terminals were attached to the banks of Josephson elements (A), (B), and (C), and electromagnetic waves (8,
The AC Josephson effect at 77K was measured by irradiating with 15G H2) to obtain each Shapiro step.
Regarding the obtained results, (A) is shown in Figure 2, and (B) is shown in Figure 3.
(Example 1.2 above), (C) is shown in Figure 4 (Comparative Example 1).
) are shown respectively.

As a result, the bridge-type grain boundary Josephson device with five or fewer grain boundaries exhibited a clear Shapiro step.

[Effects of the Invention] The present invention has focused on the number of grain boundaries in the bridge, which has not been taken into account in the past, and has researched the Shapiro step of a grain-bounded Josephson element. We have developed a bridge-type grain-boundary Josephson device that exhibits a clear Shapiro step at 77K). As a result, it is possible to detect and measure weak electromagnetic waves at high temperatures, which was previously impossible. Figure 1 shows the overall view of a bridge-type grain boundary Josephson element, and Figures 2 to 4 show Shapiro steps with different numbers of grain boundaries. .

Patent applicant: Nippon Cement Co., Ltd. M1 diagram 2 banks 3 banks 1 board Voltage (μV)

Claims (1)

[Claims] A bridge type grain boundary Josephson device characterized in that oxide superconductor particles in the bridge connect two banks with 1 to 5 grain boundaries.