Memories with cylindrical read/write stacks
View Patent ↗A three-dimensional memory is formed as an array of memory elements across multiple layers positioned at different distances above a semiconductor substrate. Cylindrical stacks of memory elements are formed where a cylindrical opening has read/write material deposited along its wall, and a cylindrical vertical bit line formed along its central axis. Memory elements formed on either side of such a cylinder may include sheet electrodes that extend into the read/write material.
1. A three-dimensional array of read/write elements comprising:
a plurality of horizontal line stacks, each horizontal line stack comprising a plurality of electrically-conductive horizontal lines that extend in a first direction and are vertically separated from each other by insulating material, individual stacks separated from adjacent stacks in a second direction that is perpendicular to the first direction;
a plurality of cylinders of read/write material located between a first horizontal line stack and a second horizontal line stack so that each cylinder of the plurality of cylinders is in electrical contact with horizontal lines of the first and second horizontal line stacks;
a plurality of vertical lines, each vertical line extending through a corresponding cylinder of read/write material to form read/write elements between the vertical line and horizontal lines of the first and second horizontal line stacks;
wherein the electrically-conductive horizontal lines of the first and second horizontal line stacks include sheet electrodes that extend towards the vertical lines, a sheet electrode having a vertical thickness that is less than the total vertical thickness of a horizontal line; and
wherein the sheet electrode extends horizontally into a cylinder of read/write material.
2. The three-dimensional array of claim 1 wherein the sheet electrode is formed of Titanium Nitride (TiN).
3. The three-dimensional array of claim 2 wherein the electrically-conductive horizontal lines further comprise Tungsten (W).
4. The three-dimensional array of claim 3 wherein Tungsten is insulated from direct contact with read/write material by an insulator.
5. The three-dimensional array of claim 4 wherein the sheet electrode extends horizontally under the insulator.
6. The three-dimensional array of claim 1 wherein each of the plurality of vertical lines is cylindrical and extends through a central area of a corresponding cylinder of read/write material.
7. The three-dimensional array of claim 1 wherein a portion of the sheet electrode that extends horizontally into the cylinder of read/write material defines an effective anode width of a read/write element.
8. The three-dimensional array of claim 7 wherein the effective anode width is a function of the radius of the cylinder of read/write material.
9. A three-dimensional nonvolatile memory cell comprising:
a first electrode that is formed by a cylinder of a first electrically-conductive material, the cylinder having an axis that extends in a first direction;
a second electrode that is formed from a sheet of a second electrically-conductive material that extends along a plane that is perpendicular to the first direction;
a read/write material between the first electrode and the second electrode the read/write material formed with a cylindrical outer surface; and
the second electrode extending through the cylindrical outer surface.
10. The three-dimensional nonvolatile memory cell of claim 9 wherein the read/write material is formed in a cylindrical opening that extends to encompass a portion of the sheet of the second electrically-conductive material.
11. The three-dimensional nonvolatile memory cell of claim 9 wherein the second electrode is connected to electrodes of other cells through a word line that is formed from the sheet of the second electrically-conductive material and additional portions of a third electrically-conductive material.
12. The three-dimensional array of claim 9 wherein the second electrode is formed of Titanium Nitride (TiN).
13. The three-dimensional array of claim 12 wherein the second electrode is part of an electrically-conductive horizontal line that further comprises Tungsten (W).
14. The three-dimensional array of claim 13 wherein Tungsten is insulated from direct contact with read/write material by an insulator.