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Applied Physics Letters

Transmission of single-flux-quantum pulse between superconductor chips

Yoshihito Hashimoto, Shinichi Yorozu, Toshiyuki Miyazaki

Published Feb 4, 2005• 15 citations
Publisher

Abstract

Single-flux-quantum (SFQ) pulse transmission between superconductor chips mounted on a passive microstrip carrier is reported. In contrast to the earlier work based on a double-flux-quantum (DFQ) driver, we used an SFQ driver; that is, the simplest driver. To deal with transmission loss at solder-bump bonds, we improved the receiver’s sensitivity by reducing its critical current, and optimized the SFQ driver to have as large an output amplitude as possible with a sufficient bias margin. Chip-to-chip transmission on a passive microstrip carrier with 50μm solder-bump bonds up to 60Gbps has been achieved at a junction critical current density of 2.5KA∕cm2.

DOI
10.1063/1.1864239

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IEEE Transactions on Applied Superconductivity•Mar 1, 1993•83 citations
Single-flux-quantum (SFQ) pulse transmission between superconductor chips mounted on a passive microstrip carrier is reported. In contrast to the earlier work based on a double-flux-quantum (DFQ) driver, we used an SFQ driver; that is, the simplest driver. To deal with transmission loss at solder-bump bonds, we improved the receiver’s sensitivity by reducing its critical current, and optimized the SFQ driver to have as large an output amplitude as possible with a sufficient bias margin. Chip-to-chip transmission on a passive microstrip carrier with 50μm solder-bump bonds up to 60Gbps has been achieved at a junction critical current density of 2.5KA∕cm2.
We report a demonstration of single-flux-quantum (SFQ) pulse transmission between superconductor chips at throughputs beyond 100 Gbps. A fabrication process with a high junction critical current density of 10kA∕cm2 was used to increase the operation speed of a pulse driver and receiver. The chips were flip-chip bonded on a passive microstrip carrier using small solder bumps with diameters of 30μm. With experiments based on a ring-shaped circuit, chip-to-chip SFQ pulse transmission has been demonstrated up to 117 Gbps with an error rate of less than 10−15. The power dissipated by the driver and receiver was only 0.24μW at 117 Gbps.
We recently reported communication up to 60 Gb/s between digital superconductor chips mounted on a passive carrier, using a novel driver circuit that produces a double-flux-quantum pulse. Here, we answer various practical questions pertaining to chip-to-chip and on-chip communication in greater detail. On-chip, the traditional single-flux-quantum driver is adequate, although margins and bit error rate degrade significantly at the microstrip resonance frequency. Chip-to-chip, using the double-flux-quantum driver, shows little frequency dependence, in spite of 13% reduction of signal current in the chip-to-chip transitions. Appropriate microstrip impedance is in the range 4-8 /spl Omega/ for a 4 kA/cm/sup 2/ Josephson junction IC process. Data includes bit errors rates for pseudo-random data in the range 3-27 Gb/s.
We have developed an interchip data transmission scheme through passive transmission lines on a multi-chip-module (MCM) carrier and 100-/spl mu/m solder bump bonds. In rapid single flux quantum (RSFQ) logic, digital data are in the form of single flux quantum (SFQ) pulses. A reliable scheme for transmission of SFQ pulses through non-superconducting solder bumps between chips through a passive MCM substrate is yet to be established. Therefore, we have devised a scheme that converts SFQ pulses into toggles in a voltage waveform for interchip transmission. Data in the form of SFQ pulses are reconstructed from this voltage waveform using a sensitive quantizing pulse receiver. Our objective is to eliminate the need for amplification of the transmitted signal. This is achieved by increasing the receiver sensitivity. However, a sensitive receiver, a dc SQUID, may produce more than one SFQ pulse for each rising/falling edge of the voltage waveform. A simple circuit, pulse resurrection logic (PRL), is employed to discard any extra SFQ pulses. Together with the sensitive quantizer, the PRL circuit makes our scheme error tolerant. We have demonstrated the receiver operation using 3-/spl mu/m Nb RSFQ circuits at frequencies up to 20 GHz.
Chip-to-chip propagation of a single flux quantum (SFQ) pulse has been demonstrated using an active multichip module (MCM) technique in which active transmitters and receivers are integrated on an MCM substrate as well as on a chip. A chip-to-chip SFQ transfer circuit has been designed and implemented by a standard Nb-trilayer process and solder-bumped flip-chip technology. The correct operation of the circuit has been confirmed by low-frequency testing. Experimental margins for the global factor for bias currents have been as large as /spl plusmn/33%.
Superconductor digital devices using single-flux-quantum (SFQ) data encoding offer higher speed at lower power than any other integrated circuit technology. For this very reason, interconnect is challenging. We report SFQ data transfer between chips flip chip mounted on a passive microstrip carrier. The flip-chip structure achieves bandwidths greater than 250 GHz. Unlike previous designs, our signal lines are terminated at both ends; this is accomplished using a driver that produces a double-flux-quantum signal. We measured the circuit for pseudorandom data in the range of 10–60 Gb/s. Bit error rates are measured down to 1E−10 and extrapolate to negligible values. The signal power on the microstrip is only 30 nW at 60 Gb ps.
The authors analyzed, designed, and tested drivers and receivers which make it possible to connect distant circuits of the rapid single-flux-quantum (RSFQ) logic/memory family by passive superconducting microstrip lines. Using these circuits implemented with a niobium trilayer fabrication technology, reliable transmission and reception of the SFQ pulses over distances up to 1 cm, with margins of bias currents as wide as +or-30%, have been demonstrated. The pulses can be passed along wide lines (20 mu m for 3.5 mu Nb-Al/sub 2/O/sub 3/-Nb Josephson junction technology) over such distances and can be picked up by the RSFQ receiver.>