Silicium-germanium

SiGe (ˈsɪɡiː or ˈsaɪdʒiː), or silicon–germanium, is an alloy with any molar ratio of silicon and germanium, i.e. with a molecular formula of the form Si1−xGex. It is commonly used as a semiconductor material in integrated circuits (ICs) for heterojunction bipolar transistors or as a strain-inducing layer for CMOS transistors. IBM introduced the technology into mainstream manufacturing in 1989. This relatively new technology offers opportunities in mixed-signal circuit and analog circuit IC design and manufacture. SiGe is also used as a thermoelectric material for high-temperature applications (>700 K). The use of silicon–germanium as a semiconductor was championed by Bernie Meyerson. The challenge that had delayed its realization for decades was that Germanium atoms are roughly 4% larger than Silicon atoms. At the usual high temperatures at which silicon transistors were fabricated, the strain induced by adding these larger atoms into crystalline silicon produced vast numbers of defects, precluding the resulting material being of any use. Meyerson and co-workers discovered that the then believed requirement for high temperature processing was flawed, allowing SiGe growth at sufficiently low temperatures such that for all practical purposes no defects were formed. Once having resolved that basic roadblock, it was shown that resultant SiGe materials could be manufactured into high performance electronics using conventional low cost silicon processing toolsets. More relevant, the performance of resulting transistors far exceeded what was then thought to be the limit of traditionally manufactured silicon devices, enabling a new generation of low cost commercial wireless technologies such as WiFi. SiGe processes achieve costs similar to those of silicon CMOS manufacturing and are lower than those of other heterojunction technologies such as gallium arsenide. Recently, organogermanium precursors (e.g.