AN LTCC-BASED CAPACITIVE PRESSURE SENSOR WITH A DIGITAL OUTPUT

A capacitive pressure sensor, fabricated using low-temperature cofired ceramic (LTCC) materials and technology was considered for an appli- cation in a wireless sensor system. LTCC technology is inherently efficient for 3D structuring and exhibits good dimensional definition and stability, appropriate material flexibility (higher than the commonly used alumina), good chemical resistance, and low moisture absorption, which makes it appropri- ate for a wide range of sensor applications, even in some extreme conditions and harsh environments. However, very often in such applications, remote control and operation in a low power-consumption mode are required. In order to meet such demands, electronics for signal processing and power managing, based on a capacitance-to-digital conversion, were realised by using an Analog Devices AD7746. A sensor characterization system with the corresponding software for an evaluation of the sensor's nonlinearity and temperature sensitivity is presented. The typical characteristics of the capacitive sensing elements were as follows: a sensitivity of 1.7 fF/mbar, a temperature dependence of 9 fF/°C and a temperature dependence of the sensitivity of less than 2 aF/mbar/°C. The digital temperature compensation was performed with a two-dimensional rational polynomial approximation, resulting in a less than 0.4% FS temperature error in the compensation range 10 °C to 75 °C.