SOI Sauce

Speed and Power. Published results from IBM show a 20-35% frequency (speed) performance gain, or a two- to three-fold reduction in power at the same frequency. When developing a custom LSI chip for a radio wave solar watch, OKI showed that watch batteries lasted four times longer if the IC was produced on SOI rather than conventional bulk CMOS.

So you're not IBM and your application isn't a James Bond watch. How about this: compare a standard ARM7-based controller operating at 33MHz on SOI and bulk(y) CMOS.

See what I mean? Opinionated - yes; Uninformed - No. The numbers speak for themselves.

So why is it only the leaders that have already made the move away from bulk CMOS to SOI - why hasn't everyone followed? Well, they will but there are two issues - let's deal with the easy one first.

There is a perceived (and maybe actual) lack of support in terms of design tools availability. In reality, my company has developed our SOI-based products using standard EDA tools from the big three vendors, Cadence, Synopsys and Mentor. It is true some Simulations can be slow but this too is being addressed. Following its acquisition of SOISIC, leading IP developer ARM now offers standard cell libraries, embedded SRAM memory compilers and I/Os in SOI technologies, as they say "enabling the benefits of SOI to expand beyond full custom-designed ICs into the mainstream SoC market". And more companies are following.

So to the more fundamental objection: $€£¥. Whilst it is true that SOI wafers cost roughly three times more than bulk CMOS ones, the situation is changing. The number one wafer supplier and SOI pioneer, SOITEC is ramping production with a new fab in Singapore, and other companies are lining up to deliver increased wafer capacity. Huge corporations such as Shin Etsu Handotaï (SEH) have begun industrial production of SOI wafers, and three years ago Siltronic (a division of Wacker-Chemie) also signed a license with SOITEC. As other companies move into SOI wafer production this will surely lead to a price drop.

But there is another dynamic in play (and here's the two second commercial!). At Innovative Silicon Inc we introduced our Z-RAM memory IP a little over two years ago. Z-RAM is five times as dense as embedded SRAM and up to twice as dense as embedded DRAM. With memory now accounting for at least 50% of the die area in most SoCs, simply by switching to a combination of SOI and Z-RAM, chip builders will offset the additional cost of the SOI wafer, and actually start to make cheaper chips.

Back to that IBM data: their startling conclusion was that moving from bulk CMOS to SOI provides the equivalent of about two years' progress in bulk CMOS technology. What's it like to be living in 2005?