Polycrystalline silicon-based sensors

Abstract This paper describes the processes now most often used to deposit polycrystalline, microcrystalline or amorphous Si films, and their applications for sensors. The processes are low pressure chemical vapour deposition (LPCVD), plasma enhanced-CVD (PECVD) and a chemical transport reaction. It is shown why the process in the above sequence require decreasing deposition temperatures ranging from 650°C to below 200°C. Lower temperatures allow for a wider selection of sensor substrates and membranes. Amorphous Si has to be laser recrystallized into poly-Si. Qualitative explanations are given for the adjustment of sensor properties such as temperature coefficient (TC) and gauge factor by doping with boron or phosphorus. Gauge factors of up to 27 with temperature coefficient of resistance (TCR) ≈ 0 are feasible. Temperature sensors will be presented as well as pressure sensors, the latter operating in the range of 0 to 1 bar or 2 bar and exhibiting sensitivities up to 10 mV/V bar. Remarks on radiation and magnetic field sensors and future trends conclude the paper.

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