These systems have both electrical and mechanical components. Today there are many more fabrication techniques and materials available. Sensors and actuators are the two main categories of MEMS . Sensors are used to measure parameters of the environment while actuators modify this environment. Micro sensors are interesting because their small physical size allows them to be less intrusive.
Micro actuators are useful when small and very precise displacement is needed.
Polysilicon Resonator Transducers are an example of a MEMS sensor using a stress controlled thin film polysilicon process, which is a modification of integrated circuit fabrication techniques. The sensor uses a mechanically free beam of polysilicon whose resonant frequency can be measured electronically. Environmental changes can be converted to a change in resonant frequency of the micro beam and can be sensed. It is interesting to note that the first MEMS device was a gold resonating MOS gate structure. MEMS can be used to create parts of systems where high tolerances are necessary.