Patent ID: 6870233

Claim:
A multi-bit Read Only Memory (ROM) cell comprising: a semiconductor substrate of a first conductivity type, having a first concentration; a first region of a second conductivity type in said substrate; a second region of said second conductivity type in said substrate, spaced apart from said first region; a channel between said first region and said second region; said channel having three portions: a first, a second and a third portion; a gate spaced apart and insulated from at least said second portion of said channel; said ROM having one of a plurality of states characterized by: (a) a first extension region in said first portion of said channel adjacent to said first region, with said first extension region being of a conductivity type or a concentration different from said first conductivity type and said first concentration, and said third portion of said channel adjacent to said second region being said first conductivity type having said first concentration; or (b) a second extension region in said third portion of said channel adjacent to said second region, with said second extension region being of a conductivity type or a concentration different from said first conductivity type and said first concentration, and said first portion of said channel adjacent to said first region being said first conductivity type having said first concentration.