Simulation of in-circuit operation of OTP memory devices

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One Time Programmable (OTP) memories can be found in a variety of applications, ranging from analog trimming, calibration code, ID tags, and processor configuration, etc. Sidense's OTP memory device is based on anti-fuse programming that involves a permanent structural change to the memory cell. When a bit cell is subjected to a programming voltage, the thin gate oxide over the transistor channel melts locally and recrystallizes into silicon nano-crystal, forming a conductive channel. Due to the irreversible physical changes during programming, the write circuit operation cannot be simulated using traditional approach. Sidense has an urgent need to develop a simulation approach to facilitate the design of reliable, power and area efficient read/write circuits for their OTP devices. It is important to model the effect of in-circuit oxide breakdown and recrystallization to ensure the proper programing of their OTP devices. This project proposes the development of a novel process/device/circuit simulation methodology that takes into account the real-time physical changes to the OTP devices during programming. The research methodology involves the development of an automated self-iterating mixed mode process/device simulation using Crosslight's CSUPREM and APSYS TCAD tools. The simulation under different programming conditions will be compared and calibrated to experimental data provided by Sidense. This work will facilitate the optimization of the bit-cell programming algorithms and the derivation of a compact OTP device model suitable for circuit simulation. Different modeling approaches using simple look up tables (LUTs), empirical piecewise linear equations, or sub-circuits with user controlled current and/or voltage sources will also be examined. The proposed process/device/circuit simulation methodology is a new design technique. This is essential to furthering the commercialization of OTP technology.