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Superconducting "Weak Link" with Bistable Memory Properties

IP.com Disclosure Number: IPCOM000082064D
Original Publication Date: 1974-Sep-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 34K

Publishing Venue

IBM

Related People

Cuomo, JJ: AUTHOR [+3]

Abstract

"Weak links" in superconductors have been made in a variety of ways, such as a sandwich arrangement with a 10-30 angstroms oxide as a barrier between two superconductors, a sharpened point contact of one superconductor against another, a constricted region of a superconducting wire, etc.

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Superconducting "Weak Link" with Bistable Memory Properties

"Weak links" in superconductors have been made in a variety of ways, such as a sandwich arrangement with a 10-30 angstroms oxide as a barrier between two superconductors, a sharpened point contact of one superconductor against another, a constricted region of a superconducting wire, etc.

It has been found that bistable switches with memory properties such as that made of Si-AlN-W when switched to an "on" or low-resistance state less than approx. 1000 ohms, become superconductors below a certain critical temperature T(c). A preferred structure is shown in Fig. 1 where the contacts are Al and Nb to an AlN film approx. 1 mu thick.

The I-V characteristics are shown in Fig. 2. Above T(c) (curve 1) the low- resistance state is that of a normal resistor. Below T(c) (curve 2), it is that of a superconducting weak link in series with a small contact resistance. The effect of I(c) as the device is switched by application of voltage pulses greater than the switching voltage V(s) is shown in Fig. 3.

At temperatures well below T(c), I(c) follows the rough formula I(c) approx. Vchar over Ron where Vchar. is a voltage in the range of 1-10 mv depending on contacting materials, A1N composition and dimensions, etc., and Ron is the "on" state resistance.

The effect of the magnetic field is shown in Fig. 4 where a field H = H(1) > 0 increases the differential resistance at low bias.

At a sufficiently great H (approx. 50,000 gauss) the superconductivity disappears. The critical temperature T(c) has been as high as 6 degrees K in some devices fabricated and may be much higher.

Substrate materials Nb and W have been used in devices with top contacts of Si, Al, SiC and various alloys of Si and Al and Si and Ge. Devices of this type have...