Recessed channel with separated ONO memory device
View Patent ↗Systems and methods of fabricating a U-shaped memory device with a recessed channel and a segmented/separated ONO layer are provided. Multibit operation is facilitated by a separated ONO layer, which includes a charge trapping region on sidewalls of polysilicon gate structures adjacent to source/drain regions. Programming and erasing of the memory cells is facilitated by the relatively short distance between acting source regions and the gate. Additionally, short channel effects are mitigated by a relatively long U-shaped channel region that travels around the recessed polysilicon gate thereby adding a depth dimension to the channel length.
1. A U-shaped memory device comprising:
first and second bitline regions formed within a semiconductor substrate;
a partially recessed gate formed within the semiconductor substrate in between the first and second bitline regions;
a U-shaped channel region that extends below the gate between the first and second bitline regions; and
a first and second charge trapping region located adjacent to sidewalls of the polysilicon gate and the first and second bitline regions wherein the first and second charge trapping regions are electrically insulative and configured to trap a first trapped charge and a separate second trapped charge, respectively, to form a multibit cell, wherein the first and second trapped charge corresponds respectively to a first bit and a second bit locally on opposing sides of the polysilicon gate.
2. The device of claim 1 , wherein the first and second charge trapping regions are comprised of a lower oxide, nitride, and an upper oxide.
3. The device of claim 1 , wherein an oxide-nitride-oxide layer is formed over the first and second bitline regions.
4. The device of claim 1 , further comprising a wordline formed over the first and second bitlines and on the gate.
5. The device of claim 1 , wherein the first and second charge trapping regions include a vertical segment of nitride.
6. The device of claim 5 , wherein the vertical segment of nitride includes a gap comprised of oxide.