More companies are utilizing RF silicon-on-insulator chip technology (SOI) amid the boom for smartphones and tablets. The RF applications include power amplifiers (PAs), switches, tunable capacitors and filters. For many generations, the PA and switch have been based on gallium arsenide (GaAs) chip technology, while tunable capacitors and filters have utilized a broader range of materials. Tunable capacitor growth is partially driven by the wider frequency range of bands necessary and the need to reduce antenna size- without a performance trade-off in mobile devices. Thus, companies are exploring alternatives to GaAs.
RF SOI is one of those alternatives to GaAs, with essentially equivalent insertion loss and noise isolation characteristics. RF SOI also enables OEMs to integrate various chips on the same die. The RF version of SOI combines CMOS with a highly-resistive, thick-film SOI substrate. RF SOI and its sister technology, silicon-on-sapphire (SOS), recently have made headway in RF switches versus GaAs. Most PAs are still based on GaAs, but SOS and SOI modules are on the rise.
RF content continues to increase in the latest mobile devices, as smartphones and tablets continue to transform the semiconductor industry. The PA market is expected to grow from $1.7 billion in 2008 to $3.8 billion by 2015, according to RBC Capital Markets. This firm also estimates the multi-throw RF switch market is projected to grow from $262 million in 2008 to $1.2 billion by 2015. Furthermore, the tunable capacitor market is expected to reach $500 million by 2016, opening the door even more for alternative technologies like SOI. One major contributing factor for the growth in RF front-end design in smartphone chips is the more intensive performance specs required for the overhaul of wireless networks from 3G to 4G/LTE.
The fact that Apple and other OEMs have adopted SOS and RF SOI for the RF switch, has offered the technology additional exposure and momentum. As a result, more top-tier chip companies like Qualcomm as well as foundries have added these technologies to their core roadmaps. Interestingly enough, Peregrine Semiconductor is developing an SOS-based PA for a future smartphone at Apple, according to RBC. Generally, RF chipmakers such as RF Microdevices develop GaAs-based devices in their own fabs. Chips based on RF CMOS, RF SOI and SOS are typically outsourced to foundries, since most of these companies are capital-constrained and the future RF roadmap is still emerging. However, RF SOI is not a difficult technology to develop, which makes for a highly competitive foundry market. In one effort to ensure additional capacity, IBM recently signed a second-source foundry deal for its 0.18-micron, RF SOI process with Altis.
IBM is a clear leader in SOI technology right now, but TSMC in Taiwan is quickly emerging on this front, both of which can capitalize on economies of scale as opposed to smaller foundries like TowerJazz in the early phase. However, as more mobile devices incorporate SOI over GaAs, there will be opportunities for lower volume foundries due to supply chain expansion and increased competition.
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