RAPID SINGLE FLUX QUANTUM RANDOM-ACCESS MEMORY

A new design concept for the Josephson-junction random access memory ( RAM) has been developed. In contrast to previous RAMs based on single flux quantization (SFQ), in our system READ and WRITE operations emplo y ballistic transfer of SFQ pulses along bit lines (either Josephson t ransmission lines, or passive superconducting microstrip lines, or the ir combination). The basic memory cells are the single-junction SQUIDs , connected serially by the bit lines and inductively coupled to word lines. READ and WRITE operations are performed by sending SFQ pulses i n appropriate directions along bit lines, and de currents of appropria te polarity into word lines. This approach allows design of very dense memories with n less than or equal to 2 Josephson junctions per bit, memory cell area smaller than 80 lambda(2) where lambda is the minimum feature size), and the critical parameter margin well above +/-20%. I n this paper we present the general structure of the RSFQ RAM, as well as design and results of testing of the basic memory cell and decoder circuitry using Hypres' 3.5-mu m, 1-kA/cm(2) Nb-trilayer technology.