A Resistor Coupled Josephson Polarity-Convertible Driver

Shuichi TAHARA
Hideaki NUMATA

IEICE TRANSACTIONS on Electronics   Vol.E77-C    No.8    pp.1176-1180
Publication Date: 1994/08/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Superconducting Devices)
Category: LTS
superconductive electronics,  Josephson device,  driver,  low temperature device,  

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A polarity-convertible driver is necessary as a basic component of several Josephson random access memories. This driver must be able to inject a current having positive or negative polarity into a load transmission line such as a word or bit line of the RAM. In this paper, we propose a resistor coupled Josephson polarity-convertible driver which is highly sensitive to input signals and has a wide operating margin. The driver consists of several Josephson junctions and several resistors. The input signal is directly injected to the driver through the resistors. The circuit design is discussed on the operating principle of the driver. The driver is fabricated by 1.5 µm Nb technology with Nb/AlOx/Nb Josephson junctions, two layer Nb wirings, an Nb ground plane, Mo resistors, and SiO2 insulators. The Nb/AlOx/Nb Josephson junctions are fabricated using technology refined for sub-micron size junctions. The insulators between wirings are formed using bias sputtering technique to obtain good step coverage. The driver circuit size is 53 µm34 µm. Measurements are carried out at 10 kHz to quasistatically test the polarity-convertible function and the operating margin of the driver. Proper polarity-convertible operation is confirmed for a large operating bias margin of 70% at a fairly small input current of 0.3 mA.