The design and improvement of LTCC-based capacitive pressure sensors employing finite element analysis

In recent years there was a raising interest in capacitive sensors. Their rate on today´s sensor market is steadily rising due to the decreasing of the technology cost, their stability and the employment of simple conditioning circuits interfacing. These sensors can be used to measure a wide variety of physical quantities: flow, pressure, liquid level and others. The capacitive pressure sensors this paper focuses on are constructed on a LTCC base with a circular edge-clamped diaphragm (membrane) overlapped to a ring fixed on the substrate. Assembled this structures form a cylindrical chamber. One of the electrodes is deposited on the bottom side of the membrane; the other is placed opposite - directly on the substrate. Changes of the distance between the electrodes, which appear as a result of an applied pressure, imply a change in capacitance. A few samples of this sensor have been produced and characterized. In the construction of this sensor materials with different characteristics are used (LTCC Du Pont 951, AgPd, brass). A virtual model of the sensor was consequently developed using ANSYS. The results of the performed measurements were compared with the simulated ANSYS model. Changes in design and their influence on the sensitivity and reliability of the sensor have been implemented as well. The aim of this paper is to introduce the finite element model and some of the ways this model can be used to improve the performances of the sensor by optimizing its design.