Microelectromechanical systems (MEMS) are devices or systems with both electrical and mechanical elements, where the size of the latter is on the order of micrometers or less. They are made using a variety of microfabrication techniques, including photolithography, etching, deposition, and sometimes milling. MEMS devices can be found in a wide range of applications, from automotive sensors to biomedical implants.
One type of MEMS device is known as a microelectronic-mechanical system, or MEMS. This type of device typically consists of two parts: an electronic circuit (the “micro” part) and a mechanical structure (the “mechanical” part). The electronic circuit can be used to control the movement of the mechanical structure, or vice versa. For example, a MEMS accelerometer might have a proof mass that is moved by acceleration forces; this movement can then be detected and converted into an electrical signal by the electronic circuit. Alternatively, an electrostatic actuator might be used to move the proof mass; in this case, applying voltage to the actuator would cause it to attract or repel the proof mass, resulting in movement.
MEMS devices are often fabricated using surface micromachining techniques; that is, they are built up on top of an underlying substrate material such as silicon wafers. In surface micromachining, various thin film materials are deposited onto the substrate to form different layers within the device. These layers may include structural elements such as beams and plates, actuation elements such as electrodes and springs, and sensing elements such as strain gauges and accelerometers. By carefully patterning these different materials using photolithographic techniques, it is possible to create complex three-dimensional structures with very small features (on the order of micrometers).