Model-based high-precision tuning of NOR flash memory cells for analog computing applications

Abstract

High-precision individual cell tuning was experimentally demonstrated, for the first time, in analog integrated circuits redesigned from a commercial NOR flash memory. The tuning is fully automatic, and relies on a write-verify algorithm, with the optimal amplitude of each write pulse determined from runtime measurements, using a compact model of cell's dynamics, fitted to experimental results. The algorithm has allowed tuning of each cell of a 100-cell array to any desired state within a 4-orders-of-magnitude dynamic range. With 10 write pulses, the average tuning accuracy is about 3%, while with 35 pulses the precision reaches ~0.3%. Taking into account the dynamic range, the last number is equivalent to ~1,500 levels, i.e. 10+ bits.