STUDYING THE EFFECT OF N-TYPE STRAINED SILICON ON THE TEMPERATURE COEFFICIENT OF RESISTANCE

As a step in employing the strained silicon in enhancing a MEMS piezoresistive based 3D stress sensor performance, this paper studies the influence of pre-stretching silicon atoms on the temperature coefficient of resistance (TCR). Extracting accurately the TCR is very influential for the piezoresistive based stress sensor. For this purpose, a piezoresistive sensing rosette was fabricated on strained and unstrained silicon substrates. The pre-strained state was integrated during microfabrication using an intrinsic stress produced by highly compressive plasma enhanced chemical vapor deposition (PECVD) silicon nitride layer, which induces global biaxial tensile pre-strain onto the substrate. Under a stress free thermal loading, the TCR for both strained and unstrained chips were calibrated using an environmental chamber. Comparing the calibration results in both strained and unstrained silicon, the tensile pre-strained silicon has larger TCR than that in unstrained silicon. Moreover, over the surface concentration range used in this work, the strained silicon shows the same unstrained silicon trend, which is, the TCR is increased proportionally with the surface concentration.