Fabricating bi-directional nonvolatile memory cells

Abstract

A memory transistor having a pair of separate floating gates overlying end regions of a channel and a control gate that overlies the floating gates and a central region of the channel effectively operates as a pair of floating gate transistors with an intervening select transistor. Each floating gate can be charged to store a distinct binary, analog, or multi-bit value. An erase operation can use a negative voltage on the control and a positive voltage on an underlying well or source/drain region to cause tunneling that discharges one or both floating gates. Applying a limited current to a source/drain region during an erase operation can cause the source/drain region and a floating gate to rise together and avoid band-to-band tunneling and resulting hole injection into the floating gate.