Roger A. Davidheiser

'Sail' high temperature superconductor digital logic: improvements and analysis

High-temperature superconductor step-edge junctions have been incorporated into a series array interferometer logic (SAIL) design, resulting in improvements in voltage and temperature performance. The junctions provide an I/sub c/R/sub n/ (critical-current normal-resistance) product of 300 mu V at 65 K, which makes it possible to have 100 mu V switching of gates at cryocooler temperatures. With improvements in I/sub c/ uniformity, the architecture should allow use in gate arrays. The present analysis indicates that the current I/sub c/R/sub n/ is sufficient to run up to 10 GHz; while this is slow compared to other superconducting logic families, it is competitive with bipolar semiconductors, with good prospects for improvement. DC design models have been compared to JSIM simulations, and a sketch of the theoretical margins is presented in this context.<<ETX>>

Applications to digital logic of YBCO dc SQUIDs

Abstract The advent of High-Tc materials has generated excitement for developing faster and more reliable superconducting computer systems. The new materials allow for the use of relatively inexpensive cryo-coolers, allowing portability and furthering interest in space-based on-board processing. Presently available YBCO junctions are, however, naturally damped SNS devices which do not have the hysteresis that most traditional superconducting circuits rely upon. A simple alternative to these architecture is the SAIL architecture we have developed at TRW 1). These are composed of a Series Array of dc SQUIDs (Interferometer Logic), and use non-hysteretic devices. It is much like CMOS semiconductor designs, including the voltage bias, in contrast to current bias more typical of superconducting circuits. Further, it relies on only a few SQUIDs to implement all of the binary logic functions, including a very natural invertor, without recourse to dual-rail outputs. Since the logical function of a gate is determined by the final wiring layer, gate array applications are a natural use of this architecture. In 1991 we published a demonstration of low speed operation using then available YBa2Cu3O7 dc SQUIDs 2). These tests showed mat the devices will work using supplied voltage rails and do not latch at intermediate voltages as early models had predicted. Our current efforts are geared toward placing much improved devices 3),4) in this architecture and testing at high (2 GHz and higher) speed at higher temperatures (above 65 K) Our modelling indicates that generally speed will be limited by the inductive input coils, a problem not faced by RSFQ 5) Iogic fcr example. The larger SAIL operating margins, its simplicity of design, and more generous production latitude will allow early use in many important application. SAIL modelling and experimental results will be compared to other designs, and RSFQ in particular, with respect to speed, performance, and margins.

Demonstration of a series array interferometer logic (SAIL) superconductive digital circuit

TRW is developing High Temperature Superconducting (HTS) electronics to dramatically improve the performance of space- based communications systems. These systems demand high speed analog-to-digital converters, high speed digital multiplexers, and quadriphase modulation of rf carrier signals. TRW has demonstrated an HTS high-speed multiplexer and a digital phase modulator that operates at microwave frequencies. The latter is the fundamental building block of a Quadriphase Modulator Exciter (QME). TRW has also developed an HTS cryogenic packaging subsystem which uses a commercially available palm-sized cryocooler. This package represents the first demonstration of an HTS self-supporting system. Package verification tests revealed that the package is capable of supporting high speed I/O and demonstrates reliable connectivity through multiple interfaces. The successful operation of a digital phase modulator has been demonstrated with this package.