Switching Activity Factor-Based ECSM Characterization (SAFE): A Novel Technique for Aging-Aware Static Timing Analysis

We propose SAFE (Switching Activity Factor-based Effective Current Source Model) for aging-aware static timing analysis (STA), a new technique for estimating the timing performance of digital circuits. SAFE is based on the development of device-level variation-aware analytical timing models of stacked and multistage logic cells (commonly employed transistor topologies in a synthesized netlist of a random logic path), which drastically reduces the recharacterization efforts of the standard cells. The models developed are derived as a function of input transition time (TR) and load capacitance (CL). The timing performance of a standard cell degrades with threshold voltage (Vth) degradation in a MOS device due to various aging mechanisms. SAFE, makes the entire STA process aging aware by updating its model coefficients with Vth degradation caused by aging. It is achieved by proposing a method for estimating Vth degradation under various stress conditions, including static, dynamic, and asymmetric, that applies to any process design kit (PDK). To consider asymmetric aging, we have developed a method to find effective switching activity factor (αeff) for N-stage stacked and N-stage parallel logic which is used to find the value of switching activity factor (α) at intermediate nodes in pipelined logic circuits. Our simulations are performed in Mentor Graphics Eldo SPICE environment using STMicroelectronics 28 nm and 65 nm CMOS process. The proposed technique provides a high simulation accuracy (2.5% average error) when compared with SPICE simulations. Finally, we achieved a ˜98.14% reduction in the required number of simulations using SAFE when compared with a completely SPICE/Aging simulation-based approach.