MicroElectroMechanical Systems

It consists of mechanical elements and electronic circuits. A microelectromechanical system is an integration of mechanical elements, sensors, actuators and electronics on a common silicon substrate through micro fabrication technology. It is a device made up from extremely small parts, micro parts.

It is a small-integrated device or system, which combines electrical and mechanical components. The MEMS range from sub-micrometer to millimeter level an can be fabricated from few to millions in a particular system.

MEMS Microsensor

Bulk Micromachining This method is commonly used for production of micro sensors and accelerometers. In bulk micromachining the material is removed from the bulk substrates to form the desired three dimensional geometry of microstructures. Etching is the process used to remove the material.

The substrates are silicon, silicon carbide (SiC), Gallium Arsenide (GiAs) and quartz. There are two methods of etching Dry Etching Wet Etching

Dry Etching In dry etching the substrate material is removed by gaseous etchants without using wet chemicals or rinsing. There are three methods of etching-Plasma etching, reactive ion etching(RIE). Deep reactive ion etching (DRIE) is the etching process used for producing thin protective films of a few micrometers. It uses high-density plasma ion etching of the substrate material and deposition of etching protective material.

Wet Etching In wet etching, etchants are used different for different substrate materials. Isotropic etchants is HNA. Anisotropic etchants for silicon are potassium hydroxide(KOH), ethylene-diamine and pyrocateol (EDP), tetramethyl ammonium hydroxide (TMAH) and hydrazine. In bulk micromachining, isotropic and anisotropic etching techniques are used

Isotropic Etching: Substrate is etched uniformly in all directions. Anisotropic Etching: Orientation based etching.Substrate is etched faster in preferred direction, high precision complex three-dimensional shapes like V-grooves, membranes can be manufactured.

Application oF MEMS

You are using KOH etching to define a 200 mm thru-hole in a wafer You are using KOH etching to define a 200 mm thru-hole in a wafer. What should the dimensions on your mask be if you are using a: a) 400 µm thick wafer b) 600 µm wafer.