Ta-based Josephson junctions using insulating ALD TaN tunnel barriers*

Josephson junctions (JJs) are critical for superconducting quantum computing and sensing. The conventionally used Al/Al oxide JJs are susceptible to degradation at elevated temperatures. We introduce junctions employing superconducting α-phase tantalum (Ta) electrodes and insulating TaN tunnel barriers, fabricated on 300 mm diameter, high-resistivity silicon wafers using advanced processes including 193 nm optical lithography, atomic layer deposition (ALD) of TaN, and chemical mechanical planarization of Ta. We assessed critical current density, sub-gap resistance, and gap voltage for JJs sized 100 nm to 3 μm. We detail the temperature dependence of junctions from 50 mK to 3.8 K, demonstrate area scaling, as well as the scaling of critical current with ALD TaN thickness. We also report the across-wafer uniformity of junction resistance, measured at 300 K. Remarkable stability of JJ characteristics over three months of room temperature storage, and the behavior of JJ arrays and 2-junction SQUIDs are described. Our approach holds promise for thermally stable junctions on 300 mm wafers with consistent performance, marking an important step towards offering advanced qubit fabrication at 300 mm scale, in the near future, in a Quantum Foundry operated by a non-profit entity.