A CMOS UV-programmable non-volatile synaptic array

A CMOS floating-gate-based nonvolatile analog circuit that implements an array of simple processing synaptic elements is described. In this implementation, unfocussed ultraviolet (UV) radiation is utilised to photo-activate electrons in the silicon conduction band across an oxide barrier onto another slab of silicon that forms an isolated gate of a transistor. It is based on a four-quadrant analog multiplier circuit requiring both X and Y differential inputs, where one such Y-input node is UV programmable. This method relies on exposing the synaptic array with UV light and serially writing the connection weights. These non volatile multiplier cells have been implemented as a fully connected 32×32 cross-bar synaptic matrix using standard p-well CMOS VLSI fabrication process with a 2-μm feature size