Strings of memory cells having string select gates, memory devices incorporating such strings, and methods of accessing and forming the same
Strings of memory cells having a string select gate configured to selectively couple ends of a string to a data line and a source line concurrently, memory devices incorporating such strings and methods for accessing and forming such strings are provided. For example, non-volatile memory devices are disclosed that utilize vertical structure NAND strings of serially-connected non-volatile memory cells. One such string including two or more serially-connected non-volatile memory cells where each end of the string shares a string select gate with the other end of the string is disclosed.
1. A string of memory cells, comprising:
a first memory cell formed along a first vertical column;
a second memory cell formed along a second vertical column; and
a single string select gate;
wherein the single string select gate is configured to concurrently selectively couple a first end of the string of memory cells to a data line and a second end of the string of memory cells to a source line.
2. The string of memory cells of claim 1 , further comprising a plane gate configured to selectively couple the first and second memory cells.
3. The string of memory cells of claim 1 , wherein the string of memory cells comprises a NAND configured string of floating gate memory cells.
4. The string of memory cells of claim 1 , wherein the string select gate is formed between the first end of the string of memory cells and the second end of the string of memory cells.
5. The string of memory cells of claim 1 , further comprising a channel wherein the first and second memory cells share the channel.
6. The string of memory cells of claim 1 , wherein the first and second memory cells comprise floating gate memory cells.
7. The string of memory cells of claim 1 , further comprising a first select gate coupled at the first end of the string and a second select gate coupled at the second end of the string.
8. The string of memory cells of claim 7 , wherein the string select gate is configured to selectively couple the first select gate to the data line and the second select gate to the source line.
9. The string of memory cells of claim 7 , wherein the first select gate and the second select gates comprise one of pFET transistors or nFET transistors.
10. The string of memory cells of claim 7 , wherein the first select gate and the second select gates comprise floating gate transistors.
11. A method of forming a string of memory cells, the method comprising:
forming a first column and a second column over a substrate, wherein the first and the second column each comprise alternating structures of dielectric and conductive material;
forming a respective separate, isolated charge storage structure between each of at least a plurality of the dielectric material structures of the first and the second columns so that each separate, isolated charge storage structure is separated and isolated from each other separate, isolated charge storage structure;
forming a continuous channel structure over the separate, isolated charge storage structures and a region of the substrate between the first and the second columns; and
forming a string select gate structure between the first column and the second column.
12. The method of claim 11 , wherein forming the first and the second columns over a substrate comprises forming the first and the second columns over a plane gate structure formed over a semiconductor.
13. The method of claim 11 , further comprising forming a plane gate structure over the substrate and between the first and the second columns.
14. The method of claim 11 , further comprising forming a respective void in each of at least a plurality of the conductive material structures, forming a dielectric to cover walls of each void, forming a respective floating gate structure in each void following forming the dielectric, forming a respective tunnel structure coupled to each floating gate structure following forming each floating gate structure, and forming the continuous channel structure over the tunnel structures.
15. The method of claim 11 , wherein forming a respective separate, isolated charge storage structure further comprises forming a respective separate, isolated floating gate structure.
16. The method of claim 11 , further comprising forming a data line structure and a source line structure above the first and the second columns.
17. The method of claim 16 , further comprising forming a first select gate structure coupled to a first end of the string and forming a second select gate structure coupled to a second end of the string, wherein the string select gate is configured to concurrently selectively couple the first select gate to the data line and the second select gate to the source line.
18. The method of claim 17 , wherein forming a first and second select gate further comprises forming the first and second select gates by forming an oxidized structure between the continuous channel structure and an uppermost conductive structure of the first column and the second column.
19. The method of claim 18 , wherein forming the oxidized structure further comprises forming the oxidized structure by performing a passivation operation on a side wall of the uppermost conductive structure of the first and the second column.
20. The method of claim 18 , further comprising, prior to forming the continuous channel structure, forming a hard mask structure over the uppermost conductive structure of the first and second columns, forming a continuous dielectric structure over the hard mask structure and the first and second columns, performing a partial etch operation to remove the hard mask structure and a portion of the continuous dielectric structure, and performing an oxidizing operation on the uppermost conductive structures of the first and second columns to form the oxidized structures.
21. The method of claim 11 , further comprising forming a respective control gate structure from each of at least a plurality of the conductive material structures.
22. The method of claim 21 , further comprising forming at least a portion of each control gate structure to at least partially cover a respective one of the charge storage structures.
23. The method of claim 21 , further comprising forming a respective dielectric structure between each charge storage structure and a respective one of the control gate structures.
24. The method of claim 23 , wherein each dielectric structure covers a larger portion of the respective charge storage structure than the respective control gate structure covers the respective charge storage structure.
25. A memory device, comprising:
a first column of floating gate memory cells formed vertically over a semiconductor;
a second column of floating gate memory cells formed vertically over the semiconductor and adjacent to the first column of floating gate memory cells; and
a string select gate;
wherein the string select gate comprises a single string select gate that is configured to selectively couple a memory cell of the first column formed furthest from the semiconductor to a data line and to concurrently selectively couple a memory cell of the second column formed furthest from the semiconductor to a source line.
26. The memory device of claim 25 , wherein a memory cell of the first column and a memory cell of the second column each formed nearest the semiconductor are coupled together.
27. The memory device of claim 25 , further comprising a plane gate formed on the semiconductor, wherein a memory cell of the first column and a memory cell of the second column each formed nearest the semiconductor are selectively coupled together by the plane gate.
28. The memory device of claim 25 , wherein the first column of floating gate memory cells and the second column of floating gate memory cells each comprise an equal number of floating gate memory cells.
29. The memory device of claim 25 , wherein each memory cell comprises a respective control gate and a respective floating gate where the respective control gate at least partially covers the respective floating gate of each memory cell.
30. The memory device of claim 29 , wherein each memory cell further comprises a dielectric configured to separate the control gate and the floating gate of each memory cell.
31. The memory device of claim 30 , wherein the dielectric of each memory cell covers a larger portion of the respective floating gate than the respective control gate.
32. The memory device of claim 30 , wherein the dielectric comprises one of an oxide-nitride-oxide (ONO) deposited layer, an nitride-oxide-nitride deposited layer, an oxide-aluminum oxide-oxide layer, or an oxide-hafnium oxide-oxide layer.
33. The memory device of claim 29 , further comprising a continuous channel wherein each memory cell of the first and the second columns of memory cells share the continuous channel.
34. The memory device of claim 33 , further comprising a respective gate dielectric formed between each floating gate and the continuous channel.
35. The memory device of claim 25 , further comprising a first select gate coupled between the data line and an uppermost memory cell of the first column and a second select gate coupled between the source line and an uppermost memory cell of the second column.
36. The memory device of claim 35 , wherein the first and the second select gates comprise floating gate transistors.
37. The memory device of claim 35 , wherein the first and the second select gates comprise one of pFET transistors or nFET transistors.