Chapter Twelve – Electrostatic and RF-Properties of MEMS Structures

Publisher Summary This chapter discusses the electrostatic and RF-properties of MEMS structures in detail. Well known examples of micromechanical sensors are accelerometers, pressure sensors and cantilevers that are used as fluid sensors and in various microscopes. In designing and modeling of nano and micromechanical systems the various aspects should be taken into account. A most simplified way of modeling a micromechanical moving system is to form a lumped element model that contains a minimum number of physical parameters. Often in practice an electrical circuit simulator is used to obtain detailed information of the behavior of the mechanical model as a part of an electronic circuit. If the biasing voltage used is a DC voltage UDC, the electrostatic force can be calculated as a negative gradient of energy. Narrow gaps between the electrodes can be used to increase the electromechanical coupling. The oscillating MEMS resonator can be sensed using a DC-biased electrode. The pull-in behavior is observed when the mechanical and electrical forces (and simultaneously also their derivatives) cancel each other. The capacitive coupling has a significant drawback. The parasitic current is often much stronger than the induced motional current. Electrostatic nonlinearities discussed can generate harmful side-effects in capacitively coupled devices. RF-properties are studied from switching point of view. Some aspects related to the RF-properties are discussed here. The RF-properties are usually characterized by concepts as isolation (ISOL), insertion loss, (IL) and reflection. Both the isolation and insertion loss describe the forward power transmission, S21, of the switch.