In Situ Observation of Metal Properties in a Piezoresistive Pressure Sensor

Relaxation phenomena in metal interconnects are a potential source of drift in piezoresistive pressure sensors. Since the properties of a metal film are influenced by its fabrication process, it is of interest to study such phenomena in an environment that resembles a production device. For this purpose, a piezoresistive pressure sensor has been modified for characterization of thin film metallization. Extra metal has been placed on the passivation layer over the piezoresistors such that the strain in the metal can be controlled isothermally by applying a test pressure as well as by temperature. We show that the sensor output signal contains information on the stress development in the metal film. By limiting the design modification to one metal mask only, we have achieved a cost effective approach for characterization of metal properties with test structures that can be processed together with functional devices.