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Planarized process for single-flux-quantum circuits with self-shunted Nb/NbxSi1-x/Nb Josephson junctions



David I. Olaya, Manuel C. Castellanos Beltran, Javier Pulecio, John P. Biesecker, Soroush Khadem, Theodore Lewitt, Peter F. Hopkins, Paul D. Dresselhaus, Samuel P. Benz


We describe the single-flux-quantum (SFQ) circuit fabrication process employed at NIST's Boulder Microfabrication Facility. The process includes four superconducting metal layers, one palladium-gold resistor layer, and a contact pad layer. Chemical-mechanical planarization is done on the two lower insulating layers. This process is based on Josephson junctions with niobium superconducting electrodes and self- shunted amorphous niobium-doped silicon barriers on the insulating side near the metal- insulator transition. The barrier material is deposited by co-sputtering of silicon and niobium and the junction properties are controlled by the relative sputtering powers and the duration of the barrier deposition step. The profiles of the deposition rates across 3-inch wafers give a corresponding critical current density (J_c) radial profile that increases by 46 % from the center to the edge of the wafer. Junction critical current (I_c) uniformity has been measured on test chips across a wafer for 2.7 um diameter junctions. Within a 5 mm x 5 mm area, the standard deviation of I_c is ~ 2 % for chips near the center of the wafer and up to ~ 7 % for chips near the edge. Circuits fabricated and planned will be used to explore metrology and signal control and processing for advanced computing, communications, and quantum information applications. We also describe anticipated process changes and innovations aimed towards increasing circuit density and high-speed performance.
IEEE Transactions on Applied Superconductivity


Josephson junctions, self-shunted junction, RSFQ, superconducting integrated circuit, superconductor electronics


Olaya, D. , Castellanos, M. , Pulecio, J. , Biesecker, J. , Khadem, S. , Lewitt, T. , Hopkins, P. , Dresselhaus, P. and Benz, S. (2019), Planarized process for single-flux-quantum circuits with self-shunted Nb/NbxSi1-x/Nb Josephson junctions, IEEE Transactions on Applied Superconductivity, [online], (Accessed October 26, 2021)
Created February 18, 2019, Updated July 18, 2019