APPLICATIONS TO DIGITAL LOGIC OF YBCO DC SQUIDS

The advent of High-Tc materials has generated excitement for developin g faster and more reliable superconducting computer systems. The new m aterials allow for the use of relatively inexpensive cryo-coolers, all owing portability and furthering interest in space-based on-board proc essing. Presently-available YBCO junctions are, however, naturally dam ped SNS devices which do not have the hysteresis that most traditional superconducting circuits rely upon. A simple alternative to these arc hitecture is the SAIL architecture we have developed at TRW 1). These are composed of a Series Array of dc SQUIDs (Interferometer Logic), an d use non-hysteretic devices. It is much like CMOS semiconductor desig ns, including the voltage bias, in contrast to current bias more typic al of superconducting circuits. Further, it relies on only a few SQUID s to implement all of the binary logic functions, including a very nat ural invertor, without recourse to dual-rail outputs. Since the logica l function of a gate is determined by the final wiring layer, gate arr ay applications are a natural use of this architecture. In 1991 we pub lished a demonstration of low speed operation using then available YBa 2Cu3O7 dc SQUIDs 2). These tests showed that the devices will work usi ng supplied voltage rails and do not latch at intermediate voltages as early models had predicted. Our current efforts are geared toward pla cing much improved devices 3),4) in this architecture and testing at h igh (2 GHz and higher) speed at higher temperatures (above 65 K). Our modelling indicates that generally speed will be limited by the induct ive input coils, a problem not faced by RSFQ 5) logic for example. The larger SAIL operating margins, it's simplicity of design, and more ge nerous production latitude will allow early use in many important appl ication. SAIL modelling and experimental results will be compared to o ther designs, and RSFQ -in particular, with respect to speed, performa nce, and margins.