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," says Mark Jaffe, IBM's manager of RF front-end development.
7SW is a 130/180 nm hybrid tuned to deliver about 30% more performance and 30% 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."
IBM also improved the linearity of the transistors, achieving about an 8 dB 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.
In the past, companies such as Skyworks dominated the market for making RF front-end chips using gallium arsenide (GaAs). But today "the industry is going through a big shift," to SiGe and SOI processes, says Sara Mellinger, a 14-year IBM vet who markets the foundry service to wireless customers.
Tower Jazz is one of IBM's biggest competitors here, using SOI for RF chips. CMOS giants such as GlobalFoundries and TSMC are said to be getting into SOI to capture some of the business as well.
7SW is still in qualification, with sample parts shipping to key customers. Volume production is expected next year.
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