Effect of voltage induced electrostatic forces on MEMS capacitive accelerometer

In this paper the effect of electrostatic forces due to applied excitation voltage on MEMS capacitive accelerometer has been presented. A set of parallel plates often termed as combs or fingers along with a proof mass and a set of spring constitute the basic structure of a capacitive accelerometer. Some of the fingers are fixed while others are movable. The proof mass moves so that the movable fingers attached with it with applied acceleration. This movement changes the gap between the fixed and movable fingers and capacitance between the fixed and movable fingers changes which is measured through proper electronic circuitry for electrical output. A few numbers of fingers are also included in the structure for self test purpose, called as actuation fingers. This type of structure is often tested electro-statically by applying external voltage signal to the actuation fingers. This external voltage on the actuation fingers generates electrostatic force which causes the proof mass along with the movable fingers attached with it to move. In this paper the effect of applied voltage and the electrostatic force caused by it has been analyzed. The nature of the displacement of the proof mass has also been described. In the electrostatic analysis semi double frequency component is observed when the structure is actuated with an external electrical voltage.