Download this article in .PDF format
This file type includes high resolution graphics and schematics.

Cold temperatures can mean minimal signal losses with superconducting circuits. With digital superconductor specialist HYPRES, Inc., those circuits are now available from a new six-layer planarized process that offers a higher integration level of Josephson junction superconducting integrated circuits (ICs). The new fabrication process supports higher current densities on superconducting ICs for energy-efficient solutions in a wide range of applications, including for high-speed computers, advanced wireless communications systems, medical imaging systems, and test and measurement systems. HYPRES is extending the new process in support of its many high-performance standard solutions as well as for the most demanding custom requirements.

Oleg Mukhanov, Ph.D. is Chief Technology Officer at HYPRES. He is also the co-inventor of Rapid Single Flux Quantum (RSFQ) logic, in which binary bits are encoded in the form of individual magnetic flux quanta. “This is an exciting milestone for HYPRES, its customers, and the superconductor electronics community,” says Mukhanov. “Next-generation superconductor circuit development requires commercially available fabrication processes well beyond today’s four metal layers and critical current densities. We have made six planarized layers—and soon, more—and various increased critical current densities available as part of our commercial foundry services. We made our first customer delivery earlier this year and have new orders in process.”

Of course, HYPRES has already accomplished a great deal using as many as four layers of its existing niobium-based superconducting process—including the high-speed digital circuits that make the company attractive for so many different commercial, medical, and military applications. The firm has fabricated high-resolution analog-to-digital converters (ADCs) capable of 100-dB spurious-free dynamic range (SFDR) while operating at clock rates over 30 GHz, as well as a 20 GHz 8-b Arithmetic Logic Unit (ALU) and multichip modules communicating at speeds past 50 Gb/s (Fig. 1).

1. HYPRES has already demonstrated a host of high-speed ADCs capable of 100-dB SFDR performance at clock rates over 30 GHz.

The additional layers, using the company’s proven niobium on silicon 150-mm wafers and sub-1-μm minimum feature size, enable higher circuit density and increased functionality on a chip. Essentially, this makes possible greater circuit complexity in a vertical direction on the superconducting ICs.

These niobium-based superconducting circuits employ Josephson junctions rather than transistors as active devices. A Josephson junction consists of two superconducting metal layers separated by a weak link—usually some form of an insulator tunnel barrier. It was named after British physicist Brian Josephson (1973 Nobel Prize laureate), who predicted the mathematical relationships for the current and voltage across the weak link.

The junction enables direct conduction of electron pairs between the two superconducting layers. Among its other capabilities, a Josephson junction can act as a perfect voltage-to-frequency converter. It can support the flow of current through the junction without an applied voltage.

Already recognized for the design and fabrication of high-speed ICs—such as ADCs and digital signal processing (DSP) circuits for a variety of systems-level and instrumentation applications—HYPRES has used its existing four-niobium-layer fabrication capabilities to produce high-volume circuits, typically with six weeks’ turnaround time. Circuit layouts are generally received at HYPRES in GDS II format for mask preparation, and digital and mixed-signal circuits with as many as 12,000 Josephson junctions have been fabricated with the four-layer process.

HYPRES analog ICs, such as commercial voltage standard circuits, are being produced with 23,000 Josephson junctions. The high-quality circuit fabrication is supported by Class-100 clean rooms and proprietary software simulation tools, in addition to the use of industry-standard software simulation tools.

Download this article in .PDF format
This file type includes high resolution graphics and schematics.