Submicron niobium junctions for submillimeter-wave mixers using optical lithography

Abstract

High-current density, submicron-sized superconductor-insulator-superconductor niobium junctions are made with optical lithography. With a novel process junctions as small as 0.8 μm2 are routinely made using a controlled under-etch with the quality parameter Vm up to 67 mV. The junction quality is found to be independent of the amount of under-etch. Used in a 345 and 490 GHz waveguide mixer, noise temperatures have been obtained as low as 131 K double-side band (DSB) and 120 K (DSB), respectively.

Shot noise beyond the Tucker theory in niobium tunnel junction mixers

“…Fabrication details are described in Ref. 11. The junction has an area of 0.8 m 2 and a resistance of 20.5 ⍀, corresponding to a criti-cal current density of 13 kA/cm 2 .…”

Submillimeter superconducting integrated receivers: Fabrication and yield

“…3. The monitor layer is very helpful for the traditional single step definition process; it is used to Nb visually estimate the end of the RIE [13]. This information is used for monitoring of the second RIE of the cross-bar junction.…”

Direct current heating in superconductor–insulator–superconductor tunnel devices for THz mixing applications

“…Fabrication details are described elsewhere. 5 The junctions are sandwiched between leads consisting of either 200-nmthick Nb ͑lower layer͒ and 600 nm Nb ͑upper layer͒ or of 85 nm Al with 20 nm Nb ͑lower layers͒ and 85 nm Al with 400 nm Nb in parallel ͑upper layers͒. 1 In this letter we will first analyze theoretically the heat flow and compare it with experimental results.…”