Piezoresistivity of polycrystalline silicon applying the AIC process-route

Piezoresistors of polycrystalline silicon were obtained by the aluminum induced crystallization (AIC) process-route. Tri-layer samples with the layer sequence Si/Al/Si were deposited by means of e-beam evaporation. The Si layer thickness was held constant at 300 nm, whereas the Al thickness was varied between 25 and 125 nm. The annealing was performed in vacuum at temperatures between 330 and 660 °C for up to 6 h. The piezoresistors exhibit gauge factors (GFs) of 4.5 up to 17, with temperature coefficients of resistance (TCR) between −0.4 and −0.1%/K and temperature coefficients of GF (TCGF) between −0.1 and 0.4%/K. These values depend on the annealing conditions applied and the Al layer thickness of the sample. Complementary measurements on a bi-layer system of Al/Si = 300 nm/300 nm were performed after annealing under vacuum conditions and a subsequent wet-etch removal of the Al top-layer. GFs up to 24, TCRs of −0.4 to −0.2%/K, and TCGFs of −0.2 to 0.2%/K were determined for these samples. As piezoresistive AIC-silicon is obtained using much lower process temperatures, compared to common high temperature processes, the process route presented becomes interesting for sensor applications on temperature sensitive substrates.