Impact of CnRx Structure on Soft Error Rates of Flip-Flop Designs at 22-nm FD SOI Node

Embedded Silicon Germanium (eSiGe) is used in the channel region of PFET devices at the 22-nm FD SOI node. The use of eSiGe results in channel regions becoming strained, which results in better hole mobility and increased performance. However, if the active diffusion regions are too short on each side of a PFET gate, then the effect of channel strain is reduced, and performance is reduced. The Continuous Active Diffusion (CnRx) layout construct suggested by the foundry is a way to help keep channel strain present within a single-cell design. In this article, the CnRx construct is implemented in a 22-nm FD SOI test chip and soft error rates (SER) of stacked-transistor flip-flops (FFs) are shown to increase with heavy ion irradiation. The effect of channel strain on PFETs results in higher collected charges from ion strikes, and charges are more easily passed between adjacent transistors through strained channels. However, with careful schematic and layout design, these effects can be mitigated to produce both high-performance and radiation-tolerant cells using the CnRx construct.