Optimization of Diaphragm Characteristics of an Absolute MEMS Capacitive Polysilicon Pressure Sensor

Abstract:
This paper examines the characteristics of capacitive circular shaped absolute polysilicon pressure sensor diaphragms operating in the non-tactile mode. Using a phase shifting interferometer the main characteristics of diaphragms were investigated under applied pressure with respect to sensitivity, initial deflection and cavity height. Diaphragms with a thickness of 1 µm and an exemplary diameter of 96 µm were investigated in an intended pressure range of applied pressure of about 700 – 2000 hPa. Process parameters with major impact on performance and yield limitations were identified. These include the variance in diaphragm sensitivity and the impact of the variance of the sacrificial oxide layer defining the diaphragm cavity height on the contact pressure point. Summarizing both impacts a maximum variation of the contact pressure point of more than 450 hPa is possible to occur considering a nominal deflection of 300 nm. By optimizing the process of diaphragm deposition the variance in the sensitivity of the diaphragm was decreased by a factor of 2.