The authors review the current status of silicon microprocessors and memories, and briefly contrast this with the current status of superconducting processors and memories. Possible applications for conventional Josephson computers are mentioned, and the difficulties in supplanting silicon technology by any new technology are discussed. An alternate strategy of hybridizing superconductor and semiconductor circuits is proposed. These hybrid circuits will be able to outperform either technology separately. The hybrid circuits combine the virtues of semiconductor circuits which have high density and excellent manufacturability with the virtues of superconductor circuits which are extremely sensitive in detecting currents and have the capability to drive currents in low impedance lines. The authors examine how hybrid circuits can improve two deficiencies of conventional silicon technology, high power dissipation in interconnection circuits and long memory access times, without requiring the use of many superconductive devices.>
The authors review the current status of silicon microprocessors and memories, and briefly contrast this with the current status of superconducting processors and memories. Possible applications for conventional Josephson computers are mentioned, and the difficulties in supplanting silicon technology by any new technology are discussed. An alternate strategy of hybridizing superconductor and semiconductor circuits is proposed. These hybrid circuits will be able to outperform either technology separately. The hybrid circuits combine the virtues of semiconductor circuits which have high density and excellent manufacturability with the virtues of superconductor circuits which are extremely sensitive in detecting currents and have the capability to drive currents in low impedance lines. The authors examine how hybrid circuits can improve two deficiencies of conventional silicon technology, high power dissipation in interconnection circuits and long memory access times, without requiring the use of many superconductive devices.>
Superconducting logic circuits based on Josephson junctions (JJ) are the fastest, lowest power solid state digital circuit technology known. Large scale integration of such circuits has also been demonstrated. By contrast, current superconducting memory circuits based on flux quantization are not equivalently advanced. Very dense memory chips have not been possible to date and seem unlikely to come without new invention. The goal of this project was to explore alternative approaches to memory that would be compatible with Josephson junction logic circuits and capable of much denser memory arrays. Five new approaches were investigated ranging from modification to the current approach, use of semiconductor CMOS and wholly new concepts based on new physical principles. Three of these were identified as worth pursuing. They are use of cooled CMOS, use of cryogenic hybrid JJ/CMOS memory concepts and a totally new magnetoresistive approach to memory based on the superconductor/ferromagnet proximity effect.
In this paper, the author describes studies on electronic devices and circuits utilizing both of superconductors and semniconductors. First, a design of an interface circuit composed of Josephson junctions and MOSFETs is described. The Josephson-MOS interface circuit will be used for realizing high-speed data communication between a Josephson digital circuit and a semiconductor one. Second, fabrication and characterization of MOSFETs with superconductive NbN gate electrodes are described. The use of superconductive gates makes it easy to hybridize MOSFETs with Josephson junctions. Finally, studies of Josephson-CMOS hybrid memory circuits are introduced.
An overview of semiconductor-based and superconductor-based low-temperature electronics is presented. The general issues of reliability and thermal expansion mismatch are discussed. The discussion of semiconductor electronics starts with a description of a cryogenic supercomputer, the ETA, and then covers devices and materials, noise and applications to signal processing for sensors. Superconductor electronics is then discussed, including signal processing, digital systems, and oscillating junctions. The success of electronics with small numbers of Josephson junctions and the outlook for higher-temperature operation are addressed. Hybrid applications, combining semiconductor and superconductor technologies at the device, circuit, or system level, are examined, highlighting the problems of electrical interfacing and interconnections. >
An overview of semiconductor-based and superconductor-based low-temperature electronics is presented. The general issues of reliability and thermal expansion mismatch are discussed. The discussion of semiconductor electronics starts with a description of a cryogenic supercomputer, the ETA, and then covers devices and materials, noise and applications to signal processing for sensors. Superconductor electronics is then discussed, including signal processing, digital systems, and oscillating junctions. The success of electronics with small numbers of Josephson junctions and the outlook for higher-temperature operation are addressed. Hybrid applications, combining semiconductor and superconductor technologies at the device, circuit, or system level, are examined, highlighting the problems of electrical interfacing and interconnections.>
The goal of this program is to explore advanced alternatives to the standard approaches to memory in Josephson junction digital electronics. The work includes the physics, circuits and systems aspects of the problem. It is widely recognized that memory is the weak suit of digital superconductive electronics. There are several problems. They are hard to build, particularly at high densities. Their speed is being challenged by leading edge semiconductor memories, albeit at the expense of high power dissipation. They are susceptible to trapped flux, which is both random in space and likely varying in time. All the current approaches to memory are based on the concept of storage of magnetic flux in a superconducting ring first proposed over 25 years ago by Anacker. Basically, there have been no new ideas in superconductive memory since that time.
The potential of a new technology, based on the superconducting Josephson tunneling effect, has been assessed for use in high-speed computer systems. Josephson tunneling circuits for memory and logic functions can be switched at sub-nanosecond delay, do not require standby power, and dissipate extremely low energy, typically less than 10-13joule during fast switching operation. High-speed circuits with high packing densities, not limited by power dissipation problems, can therefore be expected. Low thermal noise at cryogenic temperatures ensures reliable operation despite the low energy switching signal. Practically lossless signal transmission via superconducting lines can be exploited for high-speed operation even when sizeable memory and logic modules are assembled. Two random access memory modules have been designed on the basis of single device experiments. Operational characteristics leading to the conclusion that 30 Mbit capacity, less than 1 watt refrigeration requirement (at 3.6° K) and cycle times of 40 ns (in one case) and 15 ns (in the second case), can be achieved are presented.