ONE TIME PROGRAMMABLE MEMORY AND METHOD OF OPERATION

摘要

A one time programmable (OTP) memory (10) has two-bit cells (14) for increasing density. Each cell (14) has two select transistors (20, 24) and a programmable transistor (22) in series between the two select transistors. The programmable transistor (22) has two independent storage locations (22). One is between the gate (48) and a first source/drain region (66) and the second is between the gate (48) and a second source/drain region (68). The storage locations (72) are portions of the gate dielectric (60) where the sources or drains (66, 68) overlap the gate (48) and are independently programmed by selectively passing a programming current (44) through them. The programming current (44) is of sufficient magnitude and duration to permanently reduce the impedance by more than three orders of magnitude of the storage locations (72) to be programmed. The programming current (44) is limited in magnitude to avoid damage to other circuit elements and is preferably induced at least in part by applying a negative voltage to the gate (48) of the programming transistor (22).