Piezoresistive properties of polycrystalline silicon

The piezoresistive gage factor of boron-doped CVD polysilicon films deposited with a boron-to-silicon ratio of 2×10−4–1.2 ×10−2 on an aluminum-oxide-insulated molybdenum substrate is found to be between 15 and 27. Annealing increases the gage factor. The higher the doping, the lower is the gage factor. Over the range 20–140 °C, the gage factor is not temperature sensitive if the boron-to-silicon ratio is higher than 2×10−3 during deposition. The temperature dependence increases as the doping concentration is decreased. Our analysis shows that the piezoresistive properties in polysilicon is mainly due to the bulk crystallites.