FinFETs-on-SOI able to double battery life

July 30, 2012 // By Peter Clarke
Fully depleted FinFET style transistors made on SOI wafers are likely to allow between half and one-third the leakage current of FinFETs made on bulk silicon according to TCAD simulations performed by Gold Standard Simulations Ltd. (Glasgow, Scotland).

Professor Asen Asenov, CEO of GSS, has written a series of blogs on the company's website discussing simulations of FinFETs that use the company's simulation tools. A starting point was shape of Intel's FinFETs in a 22-nm bulk silicon process. The simulations are performed using the company's Garand statistical 3-D TCAD simulator. He came to the conclusion that Intel may find it necessary to move to FinFET-on-SOI to shrink its process below 22-nm and that foundries yet to introduce FinFET processes would be advised to pay attention.

In May GSS performed simulation making use of newly acquired information that what Intel calls tri-gate transistors, are in fact trapezoidal, almost triangular, rather than rectangular in cross-section. In June GSS pointed out that rectangular FinFET structures have superior performance and that by opting for slope-sided fins Intel is missing out on some performance. Professor Asenov suggested that adopting FinFET on SOI wafers might make for the easier production of rectangular fins of a pre-determined and non-varying height.

In his latest blog Professor Asenov has conducted a series of simulations that compare rectangular FinFETs of different gate lengths and widths on bulk and SOI. The FinFETs are all roughly compatible with a 20-nm channel length process node. The consclusion is that FinFET-on-SOI is marginally better than FinFET-on-bulk in terms of drive current but a lot better in terms of leakage current.

Figure 1 shows that the SOI FinFETs deliver on average 5 percent higher drive current than bulk FinFETs. The SOI advantage tends to diminish with fin width and gate length.

Click on image to enlarge.

Figure 1: Comparison of overdrive current boost for SOI compared to bulk. Overdrive voltage is the difference between threshold voltage and the supply voltage. Source: GSS.

Figure 2 shows that SOI FinFETs deliver between half and 30 percent of the leakage current of the same dimensioned FinFETs on bulk silicon. This could more than double battery life