Design of latchup immunity memory cell for Monolithic Active Pixel Sensors

Monolithic Active Pixel Sensors (MAPS) are intended to be used in STAR experiment at relativistic heavy ion collider (RHIC) accelerator for their good performances on particle tracking. Based on commercial CMOS processes, SRAMs built in MAPS are vulnerable to single event latch-up (SEL). Two SEL immunity memory cells are proposed in this paper for construction of radiation tolerant memories. The radiation hard cells have been realized. The tradeoffs among the cell areas and radiation tolerance are significantly considered. The designed cells satisfy the radiation tolerance requirements of STAR experiment. The cell areas are 4.6 × 7.975 μm² and 4.55 × 5.45 μm² for 6T and 2T cells respectively in 0.35 μm standard CMOS process. The area of the 6T cell is about 40 % of the area of a radiation tolerant 6T SRAM cell used in previous contribution and the area of the 2T cell is about 26 % of that.