Everything about Silicon-germanium totally explained
SiGe (ˈsɪɡɪː), or
silicon-germanium, is a general term for the
alloy Si
1-xGe
x which consists of any molar ratio of
silicon and
germanium. 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. This relatively new technology offers opportunities in
mixed-signal circuit and
analog circuit IC design and manufacture.
Production
SiGe is manufactured on silicon wafers using conventional silicon
processing toolsets. 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 (for example
isobutylgermane, alkylgermanium trichlorides, and dimethylaminogermanium trichloride) have been examined as less hazardous liquid alternatives to germane for
MOVPE deposition of Ge-containing films such as high purity Ge, SiGe, and
strained silicon.
SiGe
foundry services are run by companies including
IBM,
STMicroelectronics,
TSMC,
Freescale (originally
Motorola Semiconductor),
Sony,
Atmel,
Chartered Semiconductor,
Micrel,
Infineon,
TI, IHP, and Jazz Semiconductor (originally
Conexant). AMD disclosed a joint development with IBM for a SiGe stressed-silicon technology, targeting the 65-nm process.
SiGe Transistors
SiGe allows CMOS logic to be integrated with heterojunction bipolar transistors, making it suitable for mixed-signal circuits. Heterojunction bipolar transistors have higher forward gain and lower reverse gain than homojunction bipolar transistors. This translates into better low current and high frequency performance. Being a heterojunction technology, the opportunity for
band gap tuning exists which has normally been available only to
compound semiconductors. Silicon Germanium-on-insulator (SGOI) is a technology similar to the
Silicon-On-Insulator (SOI) technology currently employed in computer chips. SGOI increases the speed of the
transistors inside microchips by stretching the space between the atoms, which forces the electricity to travel faster.
SiGe also is used in
MOSFETs where it's found to increase carrier mobilities and to reduce junction leakage.
Further Information
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