Josephson 4 K-bit cache memory design for a prototype signal processor. II. Cell array and drivers

A detailed optimized design of a 1 K-bit memory cell array with drivers and reset gates has been carried out based upon a set of projections for achievable tolerances in linewidths, resistances, and Josephson critical currents in a 2.5-μm technology employing niobium edge junctions. The cell operating regions were significantly widened relative to a predecessor Pb-alloy design by adjusting gate and cell inductances, adjusting current levels, and by employing a different timing sequence for application of write controls. Much-improved control of array-line current oscillations, without loss of speed, was achieved by employing a distributed filtering scheme using distributed damping. The design employs trimming of currents to accommodate ±8% chip-to-chip differences in the average critical current. The cell size is 63×63 μm. Monte Carlo calculations of threshold curve tolerances and operating current sensitivities and tolerances lead to a design-limited yield of about 95% for 4 K bits.