A p-channel MOS synapse transistor with self-convergent memory writes

We have developed a p-channel floating-gate-MOS synapse transistor for silicon-learning applications. The synapse stores a nonvolatile analog weight by means of charge on its floating gate, modifies this weight bidirectionally using electron tunneling and hot-electron injection, and allows simultaneous memory reading and writing. The synapse also learns locally-its weight updates depend only on the applied terminal voltages and on the stored weight. We fabricated an array of synapses that computed both the array output, and the weight updates, in parallel. We also demonstrated a self-convergent write procedure that permitted accurate initialization of the synapse weights. Our pFET synapse is small, and is operated at subthreshold current levels; it will permit the development of dense, low-power, silicon learning systems.