Bilayer thin films have been utilized in superconducting transition-edge sensors (TES) for photodetector development. A TES is formed with a normal metal conductor film and a superconductor film, so called bilayer, deposited on a subtract. In its,transition temperature region, the resistance of the superconductor film is extremely sensitive to the temperature. When an incident radiation ray arrives, the temperature of the bilayer increases, leading the resistance increases tremendously. A superconducting quantum interference device measures the current variation for read-out. By varying the relative thickness of the normal metal conductor layer and the superconductor layer, one can adjust the transition temperature of the bilayer to a desired range according to the proximity effect. TES bilayers are fabricated on Si-based substrates for the development of infrared, ultra-violet, and x-ray detectors.
Various normal and superconducting metal combinations are considered as bilayer candidates. When two metals are brought together, the concerns usually rise to those materials issues that may affect TES performance.