Advanced MOSFET Designs and Implications for SRAM Scaling
- Author(s): Shin, Changhwan
- Advisor(s): King Liu, Tsu-Jae
- et al.
Continued planar bulk MOSFET scaling is becoming increasingly difficult due to increased random variation in transistor performance with decreasing gate length, and thereby scaling of SRAM using minimum-size transistors is further challenging. This dissertation will discuss various advanced MOSFET designs and their benefits for extending density and voltage scaling of static memory (SRAM) arrays. Using threedimensional (3-D) process and design simulations, transistor designs are optimized. Then, using an analytical compact model calibrated to the simulated transistor current-vs.-voltage characteristics, the performance and yield of six-transistor (6-T) SRAM cells are estimated. For a given cell area, fully depleted silicon-on-insulator (FD-SOI) MOSFET technology is projected to provide for significantly improved yield across a wide range of operating voltages, as compared with conventional planar bulk CMOS technology. Quasi-Planar (QP) bulk silicon MOSFETs are a lower-cost alternative and also can provide for improved SRAM yield. A more printable "notchless" QP bulk SRAM cell layout is proposed to reduce lithographic variations, and is projected to achieve six-sigma yield (required for terabit-scale SRAM arrays) with a minimum operating voltage below 1 Volt.