US Patent 7402874 One time programmable EPROM fabrication in STI CMOS technology

The formation of a one time programmable (OTP) transistor based electrically programmable read only memory (EPROM) cell (100) is disclosed. The cell (100) includes multiple concentric rings (108, 110) out of which gate structures are formed. An inner transistor based cell (130) formed from the inner ring (108) is shielded from isolation material (106) by one or more outer rings (110). The lack of overlap between the inner transistor and any isolation material promotes enhanced charge/data retention by mitigating high electric fields that may develop at such overlap regions (30, 32).