DEVELOPMENT OF TI BASED TRANSITION EDGE SENSORS FOR CRYOGENIC DETECTORS G.VENTURA, M.BARUCCI, E.PASCA Department of Physics, University of Florence, Italy E. MONTICONE, M. RAJTERI IEN, Turin Italy Ti based TES (Transition Edge Sensor) both of the single layer type and bilayers have been produced with critical temperatures ranging between 140 and 390 mK. Gain α = T R · dR dT up to 400 have been obtained. A possible application of TES as temperature reference point is examined. 1 Transition Edge Sensors In the last decade transition Edge Sensors (TES) have found application both in calorimeters for particle detection and for high-resolution light detectors from X rays to the infrared waves. TES consists of a superconducting phase transition thermometer evaporated onto a substrate. The detector works within the superconducting-to-normal transition , where the strong temper- ature dependence of the electrical resistance makes the film a very sensitive thermometer. Among the superconducting materials,Ti films 1 and Ti based bilayers 2,3,4 have been investigated by several authors. Ti based TES oper- ating around 300 mK have been used for X-ray detectors and for millimeter waves, both with a single layer 5,6,7 and with bilayers 8,9,10,11 . At lower tem- peratures, TES have applications as sensors to detect dark matter in calori- metric experiments 12,13,14,15,16,17 and as photon counters in the UV-NIR region 5 . In the case of a single layer, T c depends mainly on the residual resistivity 18 . In the case of bilayers, because of the proximity effect, it is possible to tune the transition temperature T c according to the experimental requirements, by varying the relative thicknesses. 2 A brief history of Ti superconducting transition Several authors have investigated the superconducting transition of titanium and the influence of various factors on it since the first observations done by Meissner 19 , who assigned its temperature the value 1.13 K for a single crystal of a claimed purity of 0.9975. Temperature values greater than 1 K were assigned to this transition 20 until 1940, when Shoenberg 21 , using an art-TES: submitted to World Scientific on January 7, 2002 1