The industry research firm Yole Développement says that more than 65 percent of substrates used in fabricating switches for handsets are SOI-based. This is a high-growth part of the market, putting up double-digit increases.
Like a standard SOI wafer, an RF SOI substrate has an active (“top”) layer on which CMOS transistors are built, with an isolating (“BOx”) layer under it. The main difference is that the bottom “base” layer under the layer of isolation is a high-resistivity material. This reduces noise and interference, which helps the finished die reach its target performance in terms of signal integrity, handling RF power and integration density. SOI-based devices can reach a figure of merit for on-series resistance and off-equivalent capacitance (Ron.Coff ) below 200 fs (femtoseconds) with potential for further reduction. This directly relates to improved device performance and smaller die size.
At Semicon West SOI wafer manufacturer Soitec announced that its SOI technologies are now mainstream for manufacturing switches and antenna-tuners, key RF components for cell phones and tablets.
There are also new challenges as the industry moves from from 3G to 4G/LTE and further LTE Advanced using carrier aggregation. With SOI, designers can beat the demanding linearity requirements such as intermodulation distortion (IMD), going far beyond -110 dBm, thereby helping avoid interference between networks, says Soitec.
“RF SOI technologies enable the device integration, cost effectiveness and high performance needed for high-volume 3G and LTE applications,” explains Bernard Aspar, vice president, Communication & Power Business Unit at Soitec. “RF, with over 100 percent revenue growth last year, remains a strategic market in which we have been continuously investing for more than a decade.”
Aspar says that as the leading supplier of engineered wafers, Soitec is looking to catch the next growth wave in the RF market.
Based on recent demonstrations, Soitec sees power amplifiers as likely be the next RF components based on SOI. The technology enables highly tunable amplifiers to address multi-region requirements on a single platform. The RF SOI substrates also offer a path towards further integration, such as more mixed-signal and digital content.
Soitec explains that its approach is to offer a wide choice of engineered substrates, so that RF device manufacturers can choose the solution that aligns best with their market strategies – from low-cost GSM handsets to multi-band, multi-mode LTE smartphones and tablets.
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