Diagnostic of silicon piezoresistive pressure sensors by low frequency noise measurements

Low frequency noise measurements can be used as a tool in diagnostics of silicon diaphragm-based piezoresistive pressure sensors after the sensor encapsulation and oil filling process are finished. We measured noise in piezoresistors comprising the Wheatstone bridge of the sensor. Our results show that oil filling process causes a noise decrease, particularly in the low frequency range. This is correlated with the oxide quality and the concentration of surrounding ions above the free oxide surface, as well with the fluctuation of adsorption–desorption (AD) processes of charged particles at the free oxide surface and trapping/detrapping processes at the oxide/silicon interface. A model for the piezoresistor noise due to fluctuations caused by the AD processes and a criterion for screening the sensors based on noise measurements are proposed.