Capacitive pressure sensors realized with LTCC technology

This work is focused on pressure sensors designed as a ceramic capsule consisting of a circular edge-clamped deformable diaphragm, which is bonded to the rigid ring, and the ring is fixed on the base substrate. These three elements form the cavity of the pressure sensor. The capacitive pressure sensor is based on changes of the capacitance values between two electrodes. One thick-film electrode is deposited on the diaphragm and the other on the rigid substrate. The distance between electrodes and the area of electrodes define the initial capacitance of the capacitive pressure sensor, and together with the geometry and flexibility of the diaphragm define the sensitivity of the sensor. The diaphragm with the diameter of 9 mm made with low-temperature cofired ceramic (LTCC) has a thickness of 200 mum and the distance between electrodes is about 70 mum. The initial capacitance is around 10 pF. The capacitive ceramic pressure sensor is the part of the electronic conditioning circuit with the frequency output. The typical output frequency is about 10 kHz and sensitivities are between 2.5 and 3.5 Hz/kPa.