Reliability study of AlTi/TiW, polysilicon and ohmic contacts for piezoresistive pressure sensors applications

This paper presents a study on the thermal drift and long term stability of AlTi (with a TiW diffusion barrier) metal lines, polysilicon gauges and metal on polysilicon contact resistances for piezoresistive pressure sensors operating in harsh environments. Test structures have been exposed at 150°C for a cumulated time of almost six months. All metal lines structures show a relative resistance decrease of around 4×10^-3. On the other hand, polysilicon resistivity variations were not observable except for a few samples that showed a relative increase up to 7×10^-3. Polysilicon contact resistance showed no particular trend with aging time. The impact of these results on the overall sensor reliability has also been discussed.