In a recent press release, the SOI wafer leader Soitec said that chips built on its SOI wafers were found in over half of the smartphones and tablets in the market worldwide. 50%? That’s a lot! How do they figure that? The answer: RF.
With all the talk right now about FD-SOI for application processors, the importance of the RF chips might seem to get a little lost. Don’t expect that to last. If app chips are the heart of the smartphone, RF is really the soul, the raison d’etre, if you will.
Soitec’s wafer shipments for RF apps have increased by 400 percent in the last two years. In their current fiscal year (which ends this month), the company says it will have shipped over 200,000 engineered wafers to customers making chips for mobile comm. Those wafers translate into about 2.5 billion ICs for RF front-end module apps, which covers half of the 600 million smart phones and 100 million tablets expected to be produced this year.
Soitec, of course, does several flavors of SOI (including bonded silicon-on-sapphire aka BSOS, and high-resistivity (HR) SOI, which Soitec markets as their Wave SOI™ product line) as well as epitaxial GaAs wafers. It all adds up.
In terms of chips and substrates, the RF side of the mobile world is much more complicated than the app side. Different functions have different needs, and those needs have traditionally been best met by disparate starting substrates. Devices can have eight of more chips and modules, and the chips in any given set can have different starting substrates, depending on the critical parameters.
The advent of LTE – “long-term evolution” aka 4G – will have a phenomenal impact on the RF components market, with analysts looking for RF components to almost double in value over the next five years. Look for an alphabet soup of new chip modules designed to handle the enormous complexity of evermore frequency bands.
Front-end modules (FEMs), which handle the back-and-forth of signals between the transceiver and the antenna, already contain multiple parts, including switches, power amplifiers, antenna tuning, power management and filters. With FEM real-estate reduction tracking at 15%/year and market growth continuing to increase at 15%/year for at least another five years, the quest is on for better, cheaper FEM solutions. Some are targeting SoCs, some will be multi-chip modules.
A couple years ago, Soitec put together a really useful white paper on substrate technologies for RF. You can see, for example, that in choosing a substrate for switches, linear resistivity is the key parameter. This is something that can be addressed by several substrates, including GaAs, SoS and HR-SOI: the deciding factors are the trade-offs between performance and cost.
There are huge opportunities in RF for the greater SOI & engineered substrates communities, so in coming issues of ASN, we’ll be covering more about the apps. If you’re working on one yourself and would like us to cover it, or submit an article, let us know.
Next up look for an article by Professor Jean-Pierre Raskin of UCL. His group is did pioneering work on HR-SOI in the late ’90’s. Now, in collaboration with Soitec, he’s been working on a new generation of HR-SOI with enhanced signal integrity (eSI – referred to in the early papers as “trap-rich”), which holds great promise for further FEM integration.