Design study of a capacitive pressure sensor in non-silicon materials

Abstract

This article reports on the design of a capacitive pressure sensor fabricated in non-silicon materials. The sensor consists of a thin membrane placed parallel to a rigid reference plane. The membrane and the reference plane act as two electrodes of a capacitor. Deflection of the membrane due to pressure differences results in changes in capacity. These capacity changes are processed to calculate the pressure on the membrane. Several thermo-mechanical performance aspects of the sensor were addressed during the design stage. Promising variants of the sensor were built and subjected to mechanical tests. In addition, numerical techniques were utilized to assess the performance of certain variants before building and testing physical prototypes. The application of this combination of physical experiments and numerical simulations is demonstrated for the selection of a suitable membrane material and membrane dimensions (diameter and thickness), the specification of the substrate thickness in case the sensor is mounted on the backside of an electronics housing, and the selection of a suitable solder interconnect material and interconnect dimensions. A critical aspect in the latter case was the creep behaviour of the solder material, which had to be minimized in order to obtain an acceptable long-term accuracy of the sensor. A sensor membrane and an interconnect design were finally specified on the basis of the outcome of the design studies. It proved to meet the functional demands imposed by the targeted application on a laboratory scale. It will be subjected to reliability and lifetime assessment tests in a next phase.

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