Bulk logic designs can be ported directly to FD-SOI for high-performing, low-power mobile apps.
Fully-depleted (FD)-SOI is a potential alternative to BULK 20nm. But what sort of the impact will that have on the design flow? The short answer is: very little.
Designs for low-power mobile applications in 28nm bulk benefit significantly in terms of increased performance and decreased power when ported to 20/22nm fully-depleted (FD)-SOI. From the designer’s perspective, the port is essentially direct – really no different from any standard port to a smaller geometry.
Interconnects, routing and RC parasitics are identical. Logic, memories, low- and high-voltage I/O and analog parts are handle in the same way as on bulk. Where there are differences, they are more at the device/process level, and do not pose any particular challenges to the designer at this point. This includes SPICE models, antenna effect, ESD protection, I/O and analog, and back-gate bias.
|Synthesis||Design Compiler||RTL Compiler||Talus Design|
|Place & route||IC Compiler||SoCE Nanoroute||Talus|
|Timing analysis||PrimeTime (NLDM, CCS)||ETS (NLDM, ECSM)||Talus (NLDM, CCS)|
|Power analysis||PTPX, PrimeRail (NLDM, CCS)||EPS, VoltageStorm||Talus|
ARM uses standard packages from the leading EDA vendors in SOI ASIC design
To get some clear figures on power and performance, ARM recently ported a Cortex-M0 from 28nm bulk to 20nm FD-SOI. We used the Cortex M0 implementation flow that was proven in 22nm SOI. This included:
In any next-node port, you typically expect to get a 25% improvement in performance, but in porting from 28nm bulk to 20nm FD-SOI, FD-SOI boosted the improvement far beyond the expected 25%. At a Vdd (supply voltage) of 1.0V, we saw a 40% improvement in performance. At 0.9V, we saw 66%. For Vdd of 0.8, we saw an 80% improvement. And for Vdd of 0.7, we saw an improvement of 125%.
Power is consistently reduced by 30%, and leakage holds steady.
Remember, this is a straight port, which gives us a baseline figure. There are several powerful process and design optimization techniques that can boost those numbers even higher without significantly increasing the complication factor.
The conclusions we have drawn are that:
FD-SOI should give tremendous advantages in terms of both power and performance. These low-voltage, high-performance chips are perfect for low-power applications, with the undoped channel in the low voltage SRAM resulting in higher margins. For some applications, RF features will also be improved if designers choose high-resistivity substrates.
FD-SOI is all a designer needs for high-performing, low-power mobile applications. And happily from the designer’s point of view, FD-SOI is as simple as designing in bulk.
This article was adapted from “FDSOI Design Portability from BULK at 20nm Node”, which was presented at the 2011 IEEE SOI Conference.