Wafer-Scale Low-Temperature Measurements of Transition-Edge Sensors during Fabrication

Authors:
Publisher website
Google Scholar
Abstract
The development of large-scale, high-resolution transition-edge sensor (TES) arrays requires precise, wafer-scale control of the superconducting critical temperature (Tc). For microcalorimeters, this is often achieved with a superconductor-normal metal bilayer where the thickness ratio between the two materials determines Tc through the proximity effect. Reliably achieving a specific Tc across multiple wafers with good uniformity remains challenging as the fabrication process is highly sensitive to substrate quality, deposition parameters, and deposited thin-film thickness. Missing a Tc target results in an array with degraded or unusable performance and wastes fabrication/measurement resources. To help solve these limitations with TES microcalorimeter fabrication, we have developed a method of measuring 76.2 mm wafers after bilayer deposition to screen for Tc accuracy and uniformity. Four-wire resistance measurements of test structures across the wafer provide rapid feedback early in the fabrication process at temperatures down to 20 mK. We leverage the hybrid additive-subtractive TES process to screen TES arrays with multiple Tc values on a single wafer comprised of a single bilayer. After measurement, the bilayer normal metal thickness can be increased with an additional evaporation step to lower Tc or decreased with an ion mill step to raise Tc as needed. We also present a design to expand measurement capability to 150 mm wafers to screen both larger microcalorimeter arrays as well as NIST cosmic microwave background TES bolometer arrays.
Funding Information
  • Advanced Research Projects Agency - Energy
  • U.S. Department of Energy (DE-AR0001693)

This publication has 14 references indexed in Scilit: