US Patent 9391151 Split gate memory device for improved erase speed

Some embodiments relate to a memory device with an asymmetric floating gate geometry. A control gate is arranged over a floating gate. An erase gate is arranged laterally adjacent the floating gate, and is separated from the floating gate by a tunneling dielectric layer. A sidewall spacer is arranged along a vertical sidewall of the control gate, and over an upper surface of the floating gate. A portion of the floating gate upper surface forms a “ledge,” or a sharp corner, which extends horizontally past the sidewall spacer. A sidewall of the floating gate forms a concave surface, which tapers down from the ledge towards a neck region within the floating gate. The ledge provides a faster path for tunneling of the electrons through the tunneling dielectric layer compared to a floating gate with a planar sidewall surface. The ledge consequently improves the erase speed of the memory device.