Virtual ground single transistor memory cell, memory array incorporating same, and method of operation thereof

Abstract

An asymmetrical virtual ground single transistor floating gate memory cell has a floating gate that overlies a channel region in a p-well, the channel region lying between a heavily doped n+ drain region and a lightly doped n− source region. A heavily doped p+ region known as a 'halo' is disposed in the channel adjacent the heavily doped n+ drain. The floating gate is spaced away from the channel region by a generally thin tunnel oxide. A lightly doped source with a graded source/channel junction reduces source side CHE generation. In one variation, a thicker oxide between the source and the floating gate reduces CHE injection from the source side. A heavily doped drain with a halo implant in the channel adjacent the drain enhances drain side CHE generation.