A Thin Film Amorphous Semiconductor Temperature Sensor

Thin film temperature sensors for use in the liquid helium temperature range have been fabricated from an amorphous semiconductor-metal alloy of germanium and copper. The amorphous material (0.5 – 1.0 µm thick) is sandwiched between two thin film metal electrodes. The active area of the sensor is between 0.1 – 1.0 mm square. The resistive amorphous material is protected from exposure to light and the atmosphere because it is sandwiched between the electrodes. The sensors can be fabricated on any smooth, non-conducting surface which can be placed in the vacuum chamber of an evaporation system and heated to about 80°C. Thin films of silicon oxide insulation have been used to allow fabrication of sensors on a sheet of stainless steel foil. Non-ohmic conduction begins for electric fields exceeding about 10,000 V/m. A transition between conduction mechanisms at low temperatures or high electric fields produces a region in which the resistance is almost inversely proportional to temperature when measured with a constant excitation current. The magnetoresistance, measured from 0–0.6 tesla at 4.36 K, is negative and obeys a power law of the form △R/R = a Bn where exponent n is 0.72. At 0.6 tesla, △R/R is −1.3%.