Investigation of BTI Reliability for Monolithic 3D 6T SRAM with Ultra-thin-body GeOI MOSFETs

Abstract

This paper investigates the impacts of negative and positive bias temperature instabilities (NBTI and PBTI) on the stability and performance of ultra-thin-body (UTB) GeOI 6T SRAM cells integrated in monolithic 3D scheme with interlayer coupling. Various bitcell layouts with different gate alignments of transistors from distinct layers are investigated. The worst case stress scenarios for read and write operations are analyzed. The optimized monolithic 3D UTB GeOI SRAM with the pull-down NFET tier stacked over the pull-up PFET tier and under forward PFET back-gate bias shows improvements in read stability and cell read-access time compared with the 2D UTB GeOI SRAM. Monolithic 3D UTB GeOI SRAM with high threshold voltage (Vth) design can enhance the improvements in stability and performance over 2D SRAM. Moreover, the optimized monolithic 3D UTB GeOI SRAM can mitigate the temporal degradations in stability and performance due to BTI stress because the BTI induced Vth degradations can be suppressed by interlayer coupling in monolithic 3D scheme.