The polysilicon nanofilms have significant piezoresistive characteristics. In this paper, an analysis of tunneling piezoresistive effect of p-type polysilicon nanofilms is presented based on the experimental data. The analysis results show that the tunneling piezoresistive effect is much remarkable than piezoresistive effect of neutral region, and the former is about 1.3 to 1.5 times of the latter. The higher is doping concentration, the more remarkable tunneling piezoresistive effect is. This advantage can be utilized to improve the temperature characteristics of polysilicon piezoresistive sensor.

The gauge factor and nonlinearity of 80nm polysilicon nanofilms with different doping concentration were tested. The experimental results show that, from 8.1×1018cm-3 to 2.0×1020cm-3, the gauge factors first increase then decrease, which like the common polysilicon films (thickness is larger than 100nm). From 2.0×1020cm-3 to 7.1×1020cm-3, the gauge factors do not change with doping concentration almost, which can be explained by tunneling piezoresistive theory. When doping concentration is low than 4.1×1019cm-3, the nonlinearities are big, and the nonlinearities become small when doping concentration is high than 4.1×1019cm-3. The nonlinearity is related to the occupied condition of trapping states in grain boundary. The longitudinal gauge factor and nonlinearity are smaller than transverse ones. Take the gauge factor and nonlinearity both into consideration, the optimal doping concentration should be 4.1×1019cm-3. The conclusions are very useful for design and fabrication of polysilicon nanofilms piezoresistive sensor.

The polycrystalline silicon films with same doping concentration and different thickness were prepared by low pressure chemical vapor deposition. The gauge factors of the films samples were tested, the results show that the piezoresistive properties of nanopolycrystalline silicon film (NPSF) exceed that of common polycrystalline silicon film (CPSF). To apply the NPSF to MEMS piezoresistive device effectively, the Youngs modulus of the NPSF were tested by in-situ nanomechanical test system, the results show that the Youngs modulus of the NPSF is about between 155GPa and 158GPa. It is very useful to investigate the piezoresistive and mechanics properties of NPSF, the results show that NPSF is a suitable material in MEMS piezoresistive device.

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