Studying the Influence of n-Type Strained (111) Silicon on the Piezoresistive Coefficients

This paper investigates the effect of inducing a pre-strain state into the (111) silicon substrate on the piezoresistive coefficients. For this purpose, a ten-element sensing rosette has been fabricated on strained and unstrained silicon substrates and fully calibrated using uniaxial, thermal, and hydrostatic loading. The strained silicon technique was integrated during the microfabrication process using a highly compressive film produced by plasma enhanced chemical vapor deposition silicon nitride. This layer induces a tensile strain at the front side of the substrate where the sensing elements were fabricated. The calibration results show that the tensile strained silicon has smaller longitudinal and transverse piezoresistive coefficients than those on unstrained silicon. On the other hand, the shear piezoresistive and the pressure coefficients were increased by 23% and 30%, respectively.