Design and testing of high-speed interconnects for superconducting multi-chip modules

Abstract

Abstract. Superconducting single flux quantum (SFQ) circuits can process information at extremely high speeds, in the range of hundreds of GHz. SFQ circuits are based on Josephson junction cells for switching logic and ballistic transmission for transferring SFQ pulses. Multi-chip modules (MCM) are often used to implement larger complex designs, which cannot be fit onto a single chip. We have optimized the design of wideband interconnects for transferring signals and SFQ pulses between chips in flip-chip MCMs and evaluated the importance of several design parameters such as the geometry of bump pads on chips, length of passive micro-strip lines (MSL)s, number of corners in MSLs as well as flux trapping and fabrication effects on the operating margins of the MCMs. Several test circuits have been designed to evaluate the above mentioned features and fabricated in the framework of 4.5-kA/cm 2 HYPRES process. The MCMs bumps for electrical connections have been deposited using the waferlevel electroplating process. We have found that, at the optimized configuration, the maximum operating frequency of the MCM test circuit, a ring oscillator with chip-to-chip connections, approaches 100 GHz and is not noticeably affected by the presence of MCM interconnects, decreasing only about 3% with respect to the same circuit with no inter-chip connections.

Qubit compatible superconducting interconnects

“…Hybrid devices have become ubiquitous in the semiconductor industry, finding applications in everything from cell phones to the Large Hadron Collider [9]. Cryogenic applications are fewer; bolometer arrays for submillimeter astronomy [10,11] and single flux quantum devices [12,13] have utilized this technology. Low resistance cryogenic bump bonds [14,15] and superconducting bump bonds that proximitize normal metals have also been fabricated [16].…”

Fan-out and fan-in properties of superconducting neuromorphic circuits

“…Looking forward, there are many possible advantages to a future superconducting neuromorphic processor: (i) the ability to use superconducting multi-chip modules (MCMs) 24 to connect many chips together with no cost in dissipation; (ii) the availability 25 of low-power superconducting digital electronics to provide interfacing, multiplexing and readout between analog units; (iii) the ability of the JJ neuron to attain biological realism 1 with only two junctions; and (iv) possible optical interface to truly expand to brain-sized networks. In this work, we demonstrate that both a fan-in and fan-out of order 100 are completely reasonable for existing superconducting fabrication.…”

New AC-Powered SFQ Digital Circuits

“…Factor 8x is a good number for hardware saving. For example, transferring data over microstrip lines with around 100 GHz rates is routinely reached with DC-biased drivers and receivers [13]- [15]. Now, the AC/DC conversion technique suggested here can be used to feed the drivers and receivers as well as simple DC-biased multiplexers and demultiplexers.…”