Low energy consumption thick-film pressure sensors

This paper is focused on three different types of ceramic pressure sensors for the use in low-energy-consumption applications. We investigated the design issues for low energy consumption of sensing elements and compared the results and other sensors' characteristics for three different types of thick-film pressure sensors. The first type is the capacitive sensor, which is based on changes to the capacitance values between two electrodes: one electrode is fixed and the other is movable. The displacement of the movable electrode depends on the applied pressure. The energy consumption depends mostly on the values of operating frequency and the capacitance of the capacitor. The second type is the piezoelectric, resonant pressure sensor, which is based on the shifting of the resonant frequency of the diaphragm. The thick-film piezoelectric actuator structure on the diaphragm generates the vibration of the diaphragm in the resonant-frequency mode. This resonant frequency then shifts due to the static deflection of the diaphragm caused by the applied pressure. The energy consumption depends mostly on the values of operating frequency and the capacitance of the actuator. The third type is the piezoresistive pressure sensor, which is made with four thick-film resistors on the diaphragm. Each thick-film resistor acts as a strain gauge, which is capable of translating the strain into an electrical signal. The energy consumption depends mostly on the value of resistance of thick-film resistors and the operating voltage. All three types of pressure sensors were made with low-temperature cofired ceramic (LTCC) and designed as ceramic capsules consisting of a circular edge-clamped deformable diaphragm that is bonded to a rigid ring and the base substrate. This construction forms the cavity of the pressure sensor. The diaphragm has a radius of 4.5 mm and a thickness of 200 mum. The depth of the cavity is from 100 to 250 mum.