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IBM flexes foundry arm for RF chips

Posted: 12 Jun 2014     Print Version  Bookmark and Share

Keywords:IBM  RF chip  foundry  BiCMOS  silicon-on-insulator 

IBM has announced that it is scaling up its silicon-on-insulator and silicon germanium processes with the objective of increasing its share of the foundry business for RF chips. Many of the components are traditionally made in more exotic gallium arsenide processes, the company noted.

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

Both the latest processes run in IBM's Burlington, Vt., 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, N.Y.

The Burlington fab supports many flavours of CMOS, silicon-on-insulator (SOI), and silicon germanium (SiGe) processes for a variety of customers. It is trying to focus on fewer recipes, such as its SOI process for making RF chips, a process that 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 seven billion SOI RF chips for handsets and base stations since it started making the parts about four years ago, three 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 analog components for the rapidly growing mobile sector.

IBM's so-called 7SW is its latest SOI recipe for making RF chips, mainly RF switches and some power amplifiers. Cellular and WiFi 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," said Mark Jaffe, IBM's manager of RF front-end development.

7SW is a 130/180nm 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," noted 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."

IBM also improved the linearity of the transistors, achieving about an 8dB decrease in the third harmonic distortion.

The core team behind 7SW comprised only about 10 people working 18 months. The group has been working on SOI for RF chips since about 2006. For a second source, they use an old IBM fab in France spun off as a separate company called Altis.

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