Compute in memory three-dimensional non-volatile nor memory for neural networks

Abstract

A non-volatile memory device for performing compute in memory operations for a neural network uses a three dimensional NOR architecture in which vertical NOR strings are formed of multiple memory cells connected in parallel between a source line and a bit line. Weights of the neural network are encoded as threshold voltages of the memory cells and activations are encoded as word line voltages applied to the memory cells of the NOR strings. The memory cells are operated in the subthreshold region, where the word line voltages are below the threshold voltages. The NOR structure naturally sums the resultant subthreshold currents of the individual memory cells to generate the product of the activations and the weights of the neural network by concurrently applying input voltages to multiple memory cells of a NOR string.