On the Variability in Planar FDSOI Technology: From MOSFETs to SRAM Cells

In this paper, an in-depth variability analysis, i.e., from the threshold voltage VTof metal-oxide-semiconductor field-effect-transistors (MOSFETs) to the static noise margin (SNM) of static random-access memory (SRAM) cells, is presented in fully depleted silicon-on-insulator (FDSOI) technology. The local VTvariability σ(V)Tlower than A(V)T= 1.4 mV · μm is demonstrated. We investigated how this good VTvariability is reported on the SNM fluctuations σSNMat the SRAM circuit level. It is found experimentally that σSNMis correlated directly to the σ(V)Tof SRAM transistors without any impact of the mean SNM value. The contributions of the individual MOSFETs in the SRAM cells have been determined quantitatively by using a homemade Simulation Program with Integrated Circuit Emphasis compact model calibrated on our FDSOI electrical characteristics. The VTvariability in n-channel MOSFETs (nMOSFETs) is more critical than that in p-channel MOSFETs for SNM fluctuations, and σ(V)Tin drive nMOSFETs is the key parameter to control for minimizing σSNM.