Depletion-mode charge-trapping flash device
A memory device includes a plurality of semiconductor lines, such as body-tied fins, on a substrate. The lines including buried-channel regions doped for depletion mode operation. A storage structure lies on the plurality of lines, including tunnel insulating layer on the channel regions of the fins, a charge storage layer on the tunnel insulating layer, and a blocking insulating layer on the charge storage layer. A plurality of word lines overlie the storage structure and cross over the channel regions of the semiconductor lines, whereby memory cells lie at cross-points of the word lines and the semiconductor lines.
1. A nonvolatile memory device comprising:
a semiconductor substrate having a particular conductivity type;
a plurality of semiconductor fins integral with the semiconductor substrate, the semiconductor fins including buried-channel regions doped for depletion mode operation having a first conductivity type opposite said particular conductivity type;
a doped isolation region in the semiconductor fins having said particular conductivity type to separate the buried-channel regions from the semiconductor substrate, and wherein a first region of the semiconductor fin between the semiconductor substrate and the doped isolation region is more lightly doped than the doped isolation region;
a storage structure on the plurality of semiconductor fins, including a tunnel insulating layer on the buried-channel regions of the semiconductor fins, a charge storage layer on the tunnel insulating layer, and a blocking insulating layer on the charge storage layer;
a plurality of word lines on the storage structure and crossing over the buried-channel regions of the semiconductor fins, whereby memory cells lie at cross-points of the word lines and the semiconductor fins; and
a controller and biasing voltage supply circuits, adapted to execute an erase operation including applying voltage across the word line and the buried-channel regions.
2. The device of claim 1 , wherein the buried-channel regions are doped with a n-type dopant.
3. The device of claim 1 , wherein the buried-channel regions are doped with the first conductivity type, and including doped source/drain regions on the semiconductor fins on opposite sides of said word lines, the doped source/drain regions having dopants of said first conductivity type in higher concentration than the buried-channel regions.
4. The device of claim 1 , wherein said tunnel insulating layer of a particular memory cell contacts a surface of the buried-channel region of the particular memory cell, and comprises a combination of materials arranged to establish a relatively low valence band energy level near the surface of the buried-channel region, and an increase in valence band energy level at a first distance of less than 2 nm from the surface of the buried-channel region and a decrease in valence band energy at a second distance more than said first distance from the surface of the buried-channel region.
5. The device of claim 1 , including an insulator between the word lines in the plurality of word lines.
6. The device of claim 1 , including a particular fin in the plurality of fins includes an access transistor having a channel in said particular fin doped for enhancement mode operation.
7. The device of claim 1 , wherein said memory cells are arranged in a NAND-array.
8. The device of claim 1 , wherein said buried-channel regions of the memory cells have n-type dopant with a concentration less than 1×10 18 /cm 3 .
9. The device of claim 8 , wherein the doped isolation regions in said plurality the semiconductor fins having p-type dopant with a concentration between 1×10 17 /cm 3 and 1×10 18 /cm 3 , and said semiconductor substrate has p-type dopant.
10. The device of claim 1 including a controller and biasing voltage supply circuits, adapted to execute a program operation, an erase operation and a read operation, said erase operation including applying a negative voltage between the word line and the buried-channel regions to induce hole tunneling.
11. An integrated circuit memory device, comprising:
a semiconductor fin, which is integral with and extends away from a p-type semiconductor substrate and having a distal ridge, the semiconductor fin including a buried-channel region along the distal ridge doped with n-type dopant for depletion mode operation;
a doped p-type isolation region in the semiconductor fin to separate the buried-channel region from the semiconductor substrate, and wherein a first p-type region of the semiconductor fin between the semiconductor substrate and the doped p-type isolation region is more lightly doped than the doped p-type isolation region;
a plurality of memory cell gates arranged over the buried-channel region along the distal ridge of the semiconductor fin, the plurality of memory cell gates including a first memory cell gate and a last memory cell gate, with insulating members isolating memory cell gates in series from adjacent memory cell gates in the series;
a charge storage structure including dielectric charge trapping locations beneath more than one of the plurality of memory cell gates in the series, the charge storage structure including a multilayer tunnel insulating structure, a charge storage layer disposed above the tunnel insulating structure, and a blocking insulating layer disposed above the charge storage layer; and
a string select gate over the distal ridge of the semiconductor fin, spaced away from the first memory cell gate, and having a p-type channel region on the distal ridge of the semiconductor fin.
12. The device of claim 11 , including doped source/drain regions on the semiconductor fin on opposite sides of memory cell gates in the plurality of memory cell gates, the doped source/drain regions having n-type dopants.
13. The device of claim 11 , wherein said multilayer tunnel insulating layer contacts a surface of the buried-channel region, and comprises a combination of materials arranged to establish a relatively low valence band energy level near the surface of the buried-channel region, and an increase in valence band energy level at a first distance of less than 2 nm from the surface of the buried-channel region and a decrease in valence band energy at a second distance more than said first distance from the surface of the buried-channel region.
14. The device of claim 11 , wherein the n-type dopant in said buried-channel region has a concentration less than 1×10 18 /cm 3 .
15. The device of claim 14 , wherein the doped p-type isolation region in said semiconductor fin includes p-type dopant with a concentration between 1×10 17 /cm 3 and 1×10 18 /cm 3 .
16. The device of claim 11 , including a controller and biasing voltage supply circuits, adapted to execute a program operation, an erase operation and a read operation, said erase operation comprising including applying a negative voltage between a gate of a selected cell and the buried-channel region to induce hole tunneling.