A transducer fabricated with IC fabrication technology. The most common and well known example is the accelerometer used in airbags for automobiles. Another common name is MEMS.
A vast array of sensors and actuators can be fabricated on chips. These typically convert magnetic, chemical, mechanical, optical, thermal energy into an electrical signal or vice versa.
Some fabrication processes are compatible with standard CMOS fabrication, and some are not. Typically silicon structures are etched with chemical etchants. Anisotrpic etchants etch one crystal face preferentially. This can be used to free cantilevers, beams and other structures to move.
Many sensing methods can be used. For example, acceleration can be measured by detecting the motion of a proof mass, if it alters a capacitance (i.e. moving plates), or if it strains a piezoelectric or piezoresistive material.
An example of a microactuator is the new TI Digital Light Processing chips, which have a million microscopic mirrors which are actuated to alted the path of light through the chip.