<title>Design and fabrication of novel photodetector arrays</title>

Abstract

Abstract We are developing novel photodetector arrays based on superconducting transition-edge sensor (TES) and pop-up detector(PUD) technologies. The TES has the potential for a new generation of high sensitivity photodetectors from the infrared tothe x-ray. This is directly due to the sharpness of the resistance change with temperature at the superconducting transition.The TESs are deposited on the PUD arrays and serve as the sensing elements. The PUDs are close-packed, folded membranearrays that provide the TES substrate and the thermal isolation required by the bolometers and microcalorimeters. This paperpresents the processing-related characterization results of preliminary TES and PUD designs. The goal of this work is tofabricate a new generation of x-ray calorimeters and infrared bolometers for space flight projects.Al-Ag and Mo-Au TES bilayers were fabricated by electron-beam deposition in an ultra-high vacuum system. To achieve thedesired transition temperatures and stability, materials-related properties such as adhesion, surface morphology, film stress,and electrochemical reaction ofthe bilayers were studied. Mo-Au bilayers showed better chemical and electrical stability thanAl-Ag bilayers. The PUD arrays were fabricated with a 0.2mm pitch on silicon wafers. MEMS techniques were used in thefabrication of PUD arrays. Mechanical folding tests were conducted to inspect the mechanical stress distribution for the arraystructures. The test results showed yields for fourteen designs. Mechanical modeling was conducted using non-linear staticand dynamic simulations. The simulations agreed with the trends of mechanical folding tests. Scanning electron microscopywas utilized to examine the flatness of detectors and the alignment of detectors in arrays.Key Words: Superconducting transition edge sensor, Pop-up detector, Mo-Au bilayer, Al-Ag bilayer, bolometer,microcalorimeter, Anisotropic etching, FEM simulation.