Physical Compact Model for Three-Terminal SONOS Synaptic Circuit Element

A well-posed physics-based compact model for a three-terminal silicon-oxide-nitride-oxide-silicon (SONOS) synaptic circuit element is presented for use by neuromorphic circuit/system engineers. Based on technology computer aided design (TCAD) simulations of a SONOS device, the model contains a nonvolatile memristor with the state variable Q(M) representing the memristor charge under the gate of the three-terminal element. By incorporating the exponential dependence of the memristance on Q(M) and the applied bias V for the gate, the compact model agrees quantitatively with the results from TCAD simulations as well as experimental measurements for the drain current. The compact model is implemented through VerilogA in the circuit simulation package Cadence Spectre and reproduces the experimental training behavior for the source-drain conductance of a SONOS device after applying writing pulses ranging from -12 V to +11 V, with an accuracy higher than 90%.