A SiOx resistor load SRAM process for ASIC applications

A silicon oxide film that has been heavily doped with phosphorus and silicon by ion implantation through a capping polysilicon layer has been studied for use as a high-resistance load device in a static random-access memory (SRAM). The fabrication process needs the addition of only one extra mask, for the ion implantation, in the standard CMOS process. The resistance per square micrometer is more than 1 TΩ under 5-V bias. The temperature dependence of this resistor is significantly improved in comparison with the lightly-doped polysilicon resistor which is widely used in SRAMs. An estimated breakdown lifetime in the actual working current density range is more than 100 years at temperatures up to 140°C