A RESISTOR COUPLED JOSEPHSON POLARITY-CONVERTIBLE DRIVER

A polarity-convertible driver is necessary as a basic component of sev eral Josephson random access memories. This driver must be able to inj ect a current having positive or negative polarity into a load transmi ssion line such as a word or bit line of the RAM. In this paper, we pr opose a resistor coupled Josephson polarity-convertible driver which i s highly sensitive to input signals and has a wide operating margin. T he driver consists of several Josephson junctions and several resistor s. The input signal is directly injected to the driver through the res istors. The circuit design is discussed on the operating principle of the driver. The driver is fabricated by 1.5 mum Nb technology with Nb/ AlO(x)/Nb Josephson junctions, two layer Nb wirings, an Nb ground plan e, Mo resistors, and SiO2 insulators. The Nb/AlO(x)/Nb Josephson junct ions are fabricated using technology refined for sub-micron size junct ions. The insulators between wirings are formed using bias sputtering technique to obtain good step coverage. The driver circuit size is 53 mum x 34 mum. Measurements are carried out at 10 kHz to quasistaticall y test the polarity-convertible function and the operating margin of t he driver. Proper polarity-convertible operation is confirmed for a la rge operating bias margin of +/- 70% at a fairly small input current o f 0.3 mA.