TEMPERATURE CHARACTERISTICS OF MICROCRYSTALLINE AND POLYCRYSTALLINE SILICON PRESSURE SENSORS

Abstract The temperature characteristics of p-type microcrystalline silicon (μc-Si) and polycrystalline silicon (poly-Si) pressure sensors are studied. Based on a comprehensive consideration of the effects of crystalline and boundary behaviour, doping concentration, grain size, as well as trap state density, novel expressions for calculating the temperature coefficient of resistance (TCR) and the longitudinal gauge factor (TCG) in p-type poly-Si are derived theoretically. The samples used to measure the TCR and TCG in the range 20–150°C are SOM pressure sensors which are made up of μc-Si:H and μc-Si:F:H piezoresistive films with average grain size 32–85 nm deposited on SiO 2 -coated covar substrates by PECVD and photo-CVD techniques. Measured TCR values between −4.1 × 10 −3 /°C and +1.2 × 10 −3 /°C with a minimum of 5 × 10 −5 /°C were obtained for the samples with doping concentrations from 1 × 10 18 to 2 × 10 20 /cm 3 ; the measured TCG values are always negative and in the range −4.5 × 10 −4 to −3.5 × 10 −3 /°C. The experimental results are in agreement with the derived theory.