High Density Fabrication Process for Single Flux Quantum Circuits

Abstract

We implemented, optimized and fully tested over multiple runs a superconducting Josephson junction fabrication process tailored for the integrated digital circuits that are used for control and readout of superconducting qubits operating at millikelvin temperatures. This process was optimized for highly energy efficient single flux quantum (ERSFQ) circuits with the critical currents reduced by factor of ~10 as compared to those operated at 4.2 K. Specifically, it implemented Josephson junctions with 10 uA unit critical current fabricated with a 10 uA/um2 critical current density. In order to circumvent the substantial size increase of the SFQ circuit inductors, we employed a NbN high kinetic inductance layer (HKIL) with a 8.5 pH/sq sheet inductance. Similarly, to maintain the small size of junction resistive shunts, we used a non-superconducting PdAu alloy with a 4.0 ohm/sq sheet resistance. For integration with quantum circuits in a multi-chip module, 5 and 10 um height bump processes were also optimized. To keep the fabrication process in check, we developed and thoroughly tested a comprehensive Process Control Monitor chip set.

10 pages, 5 figures, 1 table

References in corpus (3)

• ERSFQ 8-bit Parallel Arithmetic Logic Unit
• Progress toward superconductor electronics fabrication process with planarized NbN and NbN/Nb layers
• Commercially fabricated antenna-coupled Transition Edge Sensor bolometer detectors for next generation Cosmic Microwave Background polarimetry experiment

Cited by in corpus (4)

• Discriminating the Phase of a Coherent Tone with a Flux-Switchable Superconducting Circuit
• Estimation of the FR4 Microwave Dielectric Properties at Cryogenic Temperature for Quantum-Chip-Interface PCBs Design
• Simulation of a rapid qubit readout dependent on the transmission of a single fluxon
• Detection of low-energy fluxons from engineered long Josephson junctions for efficient computing