cessing, and data acquisition features." The term MEMS refer to the devices that are on a millimetre scale with micro-resolution. It is the integration of mechanical elements, sensors, actuators and electronics on common silicon substrate through the utilization of microfabrication technology .
There are several broad categories of MEMS fabrication technologies. They are Bulk micromachining, Surface micromachining, LIGA, Deep reactive ion etching and the integrated MEMS technologies. The brief  of each of the technologies is given below
Bulk micromachining is a fabrication technique which builds mechanical elements by starting with a silicon wafer, and then etching away unwanted parts, and being left with useful mechanical devices .'The advantages are less cost high reliability, manufacturability, and good repeatability . Surface Micromachining builds devices up from the wafer layer-by-layer . Surface Micromachining requires more fabrication steps than Bulk Micromachining, and hence is more expensive.' It is able to create much more complicated devices, capable of sophisticated functionality. LIGA is a technology which creates small, but relatively high aspect ratio devices using x-ray lithography . Unlike traditional Bulk Micromachining, which uses a wet chemical etch, Deep Reactive Ion Etching micromachining uses'a plasma etch to create features allowing greater flexibility in the etch profiles, enabling a wider array of mechanical elements . Since MEMS devices are created with the same tools used to create integrated circuits, in some cases it is also possible to fabricate Micro-machines and Microelectronics on the same piece of silicon .'
MEMS has a very wide range of applications, particularly of its sensors which are used many of the automotive, medical and other consumer products. The technology development is immense and there are several in the literature to quote from in evidence of this fact. The MEMS related technology and literature work is very huge and hence effort has been made only to cover the key developments from random authors.
One technique developed in the United States at the University of Wisconsin uses thin film polysilicon for the sensor diaphragm . The polysilicon devices are correspondingly smaller and hence they cost less.
Another technique, result in much smaller sensor dies than standard bulk micromachining techniques NovaSensor in the United States, employs high temperature fusion bonding of silicon wafers to form inward tapering cavities under single crystal silicon diaphragms . These devices are used in medical catheters.
An improvement in low pressure measurement has also been suggested as by using advanced MEMS micromachining