Long-Term Stability of Metal Lines, Polysilicon Gauges, and Ohmic Contacts for Harsh-Environment Pressure Sensors

This paper presents a study on the long-term stability of AlTi (with a TiW diffusion barrier) metal lines, polysilicon gauges, and metal on polysilicon contacts resistances for piezoresistive pressure sensors operating in harsh environments. Test structures have been exposed at 150 degC for a cumulated time of almost five months. Only the polysilicon resistivity proved to be stable over time, metal lines, and ohmic-contacts resistances showing irreversible drifts. Finally, the influence of such drifts over the long-term offset stability of piezoresistive pressure sensors has been discussed