Thermal Drift and Chip Size in Capacitive Pressure Sensors

Anodic bonding and anisotropic etching have been used to fabricate silicon / Pyrex capacitive pressure sensors. Their thermal behaviour has been evaluated by 3D finite element structural analysis and measured from-30oC to 180oC. Experimental and modelling results have revealed that the thermal coefficient is a strong function of dimensions. In order to minimise the thermal drift due to thermo-mechanical deformations it has been shown that the ratio of the chip and internal cavity widths should be approximately equal to 3/2. Based on this exemplary case, it has been inferred that the best metrological characteristics can be reached by effecting an in-depth structural analysis taking into account not only the active parts of micro devices but also their passive parts.