Analysis of Temperature Variation Influence on Capacitance Inertial Sensors Parameters

Inertial MEMS sensors such as accelerometers and gyroscopes, whose principle of operation is based on the displacement of inertial mass under change in motion speed or the appearance of non-zero rotational speed, measure these quantities using micro capacitances. Changes in these capacitances come from the movement of the capacitor plates attached to the inertial mass. Unfortunately, these capacitances are 10
^-14
F order and their changes are difficult to measure and moreover - very sensitive to external factors. Due to the fact that such sensors are solid objects, temperature becomes the one of the most important factor that can degrade the performance parameters of these devices and at the same time - affect their usability. For both accelerometers and gyroscopes, change in temperature affects the change of coefficients such as the spring constant (affected also by the spring softening effect) and the damping coefficient, which consequently affect significantly changes in individual modes of vibration, i.e. natural frequencies, and before all - mismatching. The authors present the results of simulations performed in Matlab / SIMULINK and COMSOL environments for various geometries of inertial sensors and also present comparative analysis of the effect of temperature on capacitance fluctuation what consequently change performance parameters. For a given rotational speed, a variation in temperature significantly changes the output capacitances. As already mentioned, the output capacitances are very small, so each unwanted change disrupts the correct measurement of physical quantities such as linear acceleration or rotational speed. In the case of electrostatic actuators, temperature changes distort the amplitude of vibrations due to the thermal expansion of comb structures as well as springs, which in turn distorts the characteristics of electrostatic force in the time domain, and consequently - the amplitude of vibrations. Thermal expansion of solids causing stress and deformation of comb structures causes that particular electrodes of one structure stop being parallel to others, what introduces changes to capacitances. The multidimensional problem of the influence of temperature on the operation of inertial sensors with electrostatic excitation and electrostatic measurement is presented by the authors based on FEM simulations. Because the topic is very extensive authors limits themselves to analysis of capacitance variation in dependency of temperature changes.