High Gauge Factor Piezoresistors Using Aluminium Induced Crystallisation of Silicon at Low Thermal Budget

Ian Chuang,Chee Yee Kwok,Aron Michael

doi:10.3390/proceedings1040354

Abstract

This paper reports on polysilicon piezo-resistors that are fabricated at a low thermal budget using aluminium-induced-crystallization (AIC) of ultra-high-vacuum e-beam evaporated silicon films. By in-situ phosphorus doping of precursor amorphous silicon films e-beam evaporated at room temperature on aluminium layer, we are able to increase and control the gauge factor of the polysilicon films formed by AIC at 450 °C. Piezo-resistors made from the polysilicon films are integrated on microcantilever beams to measure their gauge factors. Gauge factors as high as 62 is obtained for 2 × 1018/cm3 phosphorus doping level in the precursor amorphous silicon film. The measured gauge factors are significantly higher than previously reported values for polysilicon films.

Highlights

Fabricating sensors and actuators at low thermal budget is necessary for post CMOS-MEMS integration
Their use for piezo-resistive applications has been limited due to the formation of polysilicon films with small gauge factor of less than 20 [2,3]. This may be attributed to the formation of small grain size and fixed Al doping of 2.8 × 1018/cm3 in the AIC polysilicon films
We report the enhancement of the gauge factor of AIC polysilicon film by in-situ phosphorus doping of the precursor amorphous silicon that is e-beam evaporated at ultra-high vacuum

Summary

Introduction

Fabricating sensors and actuators at low thermal budget is necessary for post CMOS-MEMS integration. In-situ doping of epitaxially grown c-silicon and LPCVD polysilicon are demonstrated for fabricating silicon piezo-resistors. These processes require high temperature making them incompatible with post CMOS-MEMS integration. AIC polysilicon films formed at temperatures less than 550 °C is commonly used for solar cell applications [1] Their use for piezo-resistive applications has been limited due to the formation of polysilicon films with small gauge factor of less than 20 [2,3]. This may be attributed to the formation of small grain size and fixed Al doping of 2.8 × 1018/cm in the AIC polysilicon films. We report the enhancement of the gauge factor of AIC polysilicon film (formed at 450 °C) by in-situ phosphorus doping of the precursor amorphous silicon that is e-beam evaporated at ultra-high vacuum

Experiment

Results and Discussion

Conclusions