MST (Micro -Systems Technology) or MEMS (Micro-Electro-Mechanical Systems) is the engineering of small scale sensors or actuators chips with features of the order of micrometers. These are made generally using silicon machining (both depositing materials and etching using lithography) as performed in integrated circuit manufacture although many other techniques have been added, allowing metals, elastomer, optical, piezoelectric and many other materials to be used. The alternative names are a matter of choice, although MEMS appears to be more common, with variants such as MOEMS (adding 'optical' too).
The more standard silicon based machining is becoming standardised and can be offered in multi- wafer runs by some foundries. Many of the other technologies require more specialist know-how and development but are often available as individual services.
Nanotechnology can overlap MEMS in that some devices thought as micrometer sized can have feature sizes of nanometers. So the 'top-down' methods of nanotechnology - the processes to make nanometer sized devices -usually are the same as MEMS. 'Bottom-up' processes build nanotechnology devices from self-assembly or atom-by-atom and are usually quite different.
The market for MEMS products is large and growing - $5.7billion for chips in 2005 and $38billion for products (Yole no.24). For long it was dominated by printing, along with optical telecoms for a period - now RF MEMS and bio MEMS are growing significantly with products such as accelerometers and gyros commercially becoming main-stream.