Post-Breakdown IV Characteristics and Instabilities in Dense OTP Anti-Fuse Memories

Instability phenomena in dense one-time-programmable memories based on the breakdown of ultra-thin silicon dioxide layers are discussed. During stress at programming condition, cell IV characteristics are found to evolve between quasi-linear and highly non-linear characteristics. Extensive characterization of this instability is carried on as a function of stress duration and programming conditions to maximize post-breakdown current and guarantee values above the program-verify threshold. Read current instability is also observed during reading cycles and associated to a switching behavior between two or more states of the breakdown path that has been minimized by a proper cell design. Post-breakdown IV characteristics of the OTP cell are modeled based on the quantum-point contact model. Peculiar temperature dependence of the IV characteristics of programmed cells is nicely described by the proposed model.