The manufacture of MEMS of this type also involves glass components, which are used as stabilizers and insulators. High demands on quality are made regarding the surface finish of these glass substrates. They must be flat, parallel and free from defects according to stringent specifications. These are requirements which can be met by alkali-free AF 45 and low alkali D263 T borosilicate glass from SCHOTT Displayglas.
For acceleration sensors in airbag systems, reliability and efficiency are decisive criteria. In an emergency, they must work reliably in fractions of a second even after years in service. Conversely, of course, there must be no chance of them detonating prematurely. Special glasses such as “BOROFLOAT” with their extreme resistance to chemical, thermal and mechanical influences and their electrical insulation properties are ideal substrate materials for this type of application.
Microtechnology under extreme conditions
Integrated silicon pressure sensors are particularly suitable for use in harsh environments, such as the measurement of suction pressure in combustion engines. In the manufacture of these, a silicon wafer containing a number of sensor elements is located on a glass plate, which provides insulation and stabilization. A process known as anodic bonding is used to firmly bond the two materials to each other by ion exchange. Since they now react as a unit, the material must behave virtually identically when subjected to temperature fluctuations. In such cases “BOROFLOAT” 33 special glass made by SCHOTT Jenaer Glas GmbH is used since its thermal expansion is virtually the same as that of the silica.
The manufacture of cars is just one such application in which microsystems will play an important role in the future. With the ever-increasing requirements for safety, reliability and comfort, there is growing demand for sensor, control and operating elements: airbags, electronic seat adjustment, air-conditioning and digital road maps with satellite positioning all require a wide variety of electronic, mechanical and optical components.
Miniature machines are also gaining ground in biology – for example in biosensorics – and medicine and they will play a crucial role with future developments.