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IBM bolsters RF foundry with SOI, SiGe

Posted: 12 Jun 2014 ?? ?Print Version ?Bookmark and Share

Keywords:SOI? SiGe? RF? GaAs?

IBM is shoring up its foundry business with additional techniques for its silicon-on-insulator and silicon germanium processes for making RF chips. These chips include components customarily fabricated in gallium arsenide processes.

The efforts underscore IBM's deep expertise in process technology. But they come at a time when the unit is operating under the cloud of reports saying the corporation is considering a sale of its chip division.

Both the new processes run in IBM's Burlington fab that solely does foundry work. The 200mm wafer fab once made processors and related chips for IBM's high-end servers, but that work has moved on to IBM's 300mm facility in East Fishkill.

The Burlington fab supports many flavours of CMOS, silicon-on-insulator (SOI), and silicon germanium (SiGe) processes for a wide variety of customers. It is trying to focus on fewer recipes, like its SOI process for making RF chips, a process that now represents the majority and fastest-growing part of its business.

IBM provides no details of the size of the fab or its revenues. However it does say it has sold a total of nearly 7 billion SOI RF chips for handsets and base stations since it started making the parts about four years ago3 billion of them in the last year.

In interviews with four technical and marketing experts from Burlington, none would comment on the impact of the rumoured sale of the division. All are veterans of IBM, parts of small, elite teams doing deep technical work in the area of analogue components for the rapidly growing mobile sector.

Inside IBM's new SOI recipe

IBM's so-called 7SW is its latest SOI recipe for making RF chips, mainly RF switches and some power amplifiers. Cellular and Wi-Fi systems need a growing number of the components to handle the increasing number of frequency bands the standards support.

"Newer smartphones have eight to 12 RF switches per phone. The architecture of the RF front end is getting very complicated because, as we get to things like Advanced LTE with carrier aggregation, there are a lot of carrier paths and frequencies," says Mark Jaffe, IBM's manager of RF front-end development.

7SW is a 130nm/180nm hybrid tuned to deliver about 30 per cent more performance and 30 per cent smaller die area for RF switches.

"We re-engineered the switch transistor completely, focusing on metrics such as resistance-on and capacitance-off, which determine leakage," says Jaffe, a 25-year IBM semiconductor veteran who has managed the RF SOI program for five years.

"Secondly, we increased the breakdown voltage for the switch transistor. Typically you need to stack transistors to withstand high voltage requirements, but now you can build a shorter stack, and that provides a reduction in chip area."

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