PIEZORESISTANCE OF BORON-DOPED PECVD AND LPCVD POLYCRYSTALLINE SILICON FILMS

An investigation into the structural, electrical and piezoresistive properties of SOI (silicon-on-insulator) type structures is reported. The aim of our work is to evaluate how deposition and annealing conditions may change these properties. Various characterization experiments have been undertaken in order to investigate LPCVD and PECVD thin films. A theoretical model for the piezoresistivity is developed that requires experimentally determined parameters (active dopant concentration, grain size, texture, resistivity, barrier height). Moreover, the hypothesis of constant strain or stress has been considered for the spatial average. The measured gauge factors, in the range 25-45 for LPCVD films and 20-30 for PECVD films, fall in the tight interval defined by the theoretical estimates.