Silicon germanium (SiGe) is set to enter the mainstream after decisions by STMicroelectronics (ST) and Taiwan Semiconductor Manufacturing (TSMC) to bring the technology into production.
By bolting SiGe on to existing processes, ST reckons it can build faster, lower-noise RF circuits more cheaply than companies with dedicated SiGe processes.
Jean-Pierre Aubert, ST's RF business development manager, says the company is using non-selective epitaxy to put SiGe on to chips made on its 0.35µm BiCMOS6M process.
ST will move to a selective version, where SiGe is deposited in only parts of the device in future, finer, geometry processes.
Aubert said: "We don't see a performance difference between selective and non-selective, but we are looking at selective for new developments."
A spokesman for TSMC says it plans a similar roadmap, kicking off with a blanket SiGe process and moving to a selective version for 0.18µm.
"When 0.18µm goes online, it will have TSMC's vanilla logic. It is intended for circuits like fast mixers," he said. This process will come on-stream in September 2002.
As it targets analogue and RF IC production, TSMC is lining up a portfolio of design kits and intellectual property (IP) libraries for its SiGe processes. It has signed up IP-generator suppliers such as Antrim Design Systems, Barcelona Design and NeoLinear for its CMOS analogue process.
Nelson Seiden, vice-president of marketing for Antrim, said: "We are developing the models for SiGe. It is the next thing we will move into."
Aubert says ST prefers non-selective epitaxy because "we are focusing on cost and reliability".
"We don't see a specific price increase linked to [the use of] SiGe. For us, the cost is mainly linked to volume," he continued.
He says that the base 0.35µm process on which the SiGe module is being deployed is already running in volume across a number of ST fabs.
"Low-cost SiGe can be used for low-end phones. Its main benefit is in LNA [low-noise amplifier] integration," said Aubert. "At close to 2GHz, it is very challenging to build dual-band LNAs in BiCMOS. SiGe can deliver a two-times improvement in power consumption and improved noise figures."
Aubert adds that ST is looking at more advanced processes such as carbon-based SiGe: "At the moment, it is at the R&D stage." He says the company has been encouraged to look at carbon additions by the research performed by Motorola SPS.
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