LTCC-based capacitive pressure sensor in a harsh environment

In this paper the initial capacitances of pressure sensors consisting primarily of the capacitance of an air-gap capacitor and the parasitic capacitance of sensors realized with LTCC (low-temperature cofired ceramics) materials are described. The capacitances at different temperatures (from 10°C to 75°C) and different levels of humidity (from 20% to 80% relative humidity) were measured with an LCR meter at two frequencies, i.e., 10 and 100 kHz. At the lower humidity the temperature coefficient of the capacitance was around 200×10^-6/K, while at the higher humidity the temperature dependence of the capacitance was much higher, up to 800×10^-6/K. In all cases the dependences of the capacitance versus temperature were almost linear. The humidity has a significant and nonlinear influence on the capacitance at lower frequencies, while at higher frequencies the influence is smaller.