High density semiconductor memory cell and memory array using a single transistor having a buried N+ connection
View Patent ↗A programmable memory cell comprised of a transistor located at the crosspoint of a column bitline and a row wordline is disclosed. The transistor has its gate formed from the column bitline and its source connected to the row wordline. The memory cell is programmed by applying a voltage potential between the column bitline and the row wordline to produce a programmed n+ region in the substrate underlying the gate of the transistor. Further, the row wordline is formed from a buried N+ layer allowing for higher density integration.
1. A programmable memory cell useful in a memory array having column bitlines and row wordlines, the memory cell comprising:
a transistor having a gate, a gate dielectric between the gate and over a substrate such that there is a stack comprising said gate, gate dielectric, and substrate, without any intervening conductive material, and first and second doped semiconductor regions formed in said substrate adjacent said gate and in a spaced apart relationship to define a channel region therebetween and under said gate, the gate being formed from one of said column bitlines; and
a programmed doped region formed in said substrate in said channel region when said memory cell has been programmed;
wherein the second doped semiconductor region of the transistor is connected to one of said row wordlines, wherein said row wordlines are formed from a buried N+ layer.
2. The memory cell of claim 1 wherein the gate dielectric of the transistor is thicker proximal to the first and second doped semiconductor regions than at said channel region.
3. The memory cell of claim 1 wherein the gate and said second doped semiconductor region is laterally separated by a distance D.
4. The memory cell of claim 3 wherein said distance D is sufficient to prevent a short circuit with said first or second doped semiconductor regions.
5. A programmable memory array comprising a plurality of row wordlines, a plurality of column bitlines, and a plurality of memory cells at respective crosspoints of the row wordlines and column bitlines, each of the memory cells comprising:
a transistor having a gate, a gate dielectric between the gate and over a substrate such that there is a stack comprising said gate, gate dielectric, and substrate, without any intervening conductive material, and first and second doped semiconductor regions formed in said substrate adjacent said gate and in a spaced apart relationship to define a channel region therebetween and under said gate, the gate being formed from one of said column bitlines; and
a programmed doped region formed in said substrate in said channel region when said memory cell has been programmed;
wherein the second doped semiconductor region of the transistor is connected to one of said row wordlines, wherein said row wordlines are formed from a buried N+ layer.
6. The memory array of claim 5 wherein said column bitlines are connected to said gate by a column bitline segment.
7. The memory array of claim 6 wherein the gate dielectric of the transistors are thicker proximal to the respective first and second doped semiconductor regions than at said channel region.
8. The memory array of claim 6 wherein said transistors have their gate and said second doped semiconductor region is laterally separated by a distance D.
9. The memory array of claim 8 wherein said distance D is sufficient to prevent a short circuit from the gate to said first or second doped semiconductor regions.
10. The memory array of claim 6 wherein said memory cells further including a programmed doped region formed in said substrate in said channel region when said memory cell has been programmed.
11. The memory array of claim 5 wherein the gates of said transistors do not overlap either of said first and second n+ doped semiconductor regions of said respective transistor.
12. A programmable memory cell useful in a memory array having column bitlines and row wordlines, the memory cell comprising:
a transistor having a gate, a gate dielectric between the gate and over a substrate such that there is a stack comprising said gate, gate dielectric, and substrate, without any intervening conductive material, and first and second doped semiconductor regions formed in said substrate adjacent said gate and in a spaced apart relationship to define a channel region therebetween and under said gate, the gate being formed from one of said column bitlines; and
a programmed doped region formed in said substrate in said channel region when said memory cell has been programmed;
wherein the second doped semiconductor region of the transistor is connected to one of said row wordlines, wherein said row wordlines are formed from a buried P+ layer.
13. The memory cell of claim 12 , wherein the gate dielectric of the transistor is thicker proximal to the first and second doped semiconductor regions than at said channel region.
14. The memory cell of claim 12 wherein the gate and said second doped semiconductor region is laterally separated by a distance D.
15. The memory cell of claim 14 wherein said distance D is sufficient to prevent a short circuit with said first or second doped semiconductor regions.