U-shaped common-body type cell string
View Patent ↗A flash device comprising a well and a U-shaped flash cell string, the U-shaped flash cell string built directly on a substrate adjacent the well. The U-shaped flash cell string comprises one portion parallel to a surface of the substrate, comprising a junctionless bottom pass transistor, and two portions perpendicular to the surface of the substrate that comprise a string select transistor at a first top of the cell string, a ground select transistor at a second top of the cell string, a string select transistor drain, and a ground select transistor source.
1. A flash device comprising:
a semiconductor substrate;
a well impurity region within the semiconductor substrate; and
a U-shape flash cell string including a first vertical portion, a second vertical portion and a horizontal portion connecting the first vertical portion and the second vertical portion, wherein
the first vertical portion includes a first channel portion, the second vertical portion includes a second channel portion and the horizontal portion includes a third channel portion,
the first channel portion and the second channel portion include a semiconductor material,
the first channel portion and the second channel portion are in contact with a top surface of the semiconductor substrate and extend vertically to the surface of the semiconductor substrate, and
the third channel portion is located within the semiconductor substrate and forms an integral part of the semiconductor substrate and the well impurity region.
2. The flash device of claim 1 , wherein the flash cell string includes a plurality of NAND (Not AND) string cells.
3. The flash device of claim 1 , wherein the conductivity type of a body of the flash cell string and the conductivity type of the semiconductor substrate are the same during an erase operation.
4. The flash device of claim 3 , wherein the body of the flash cell string and the semiconductor substrate are electrically directly connected without being separated by a region of a different conductivity type.
5. The flash device of claim 1 , wherein a body of the flash cell string and the semiconductor substrate are both of p-type conductivity and the well impurity region is a p-type impurity region.
6. The flash device of claim 1 , wherein a non-conductive trench is located between two adjacent flash cell strings to electrically isolate channels of a turned-on adjacent flash cell string.
7. The flash device of claim 1 , wherein
the horizontal portion is formed by a bottom pass transistor located directly on the substrate, and
the body and channel of the bottom pass transistor are formed by the semiconductor substrate.
8. The flash device of claim 7 , wherein the bottom pass transistor does not include any n+ implemented source or drain and the conductivity of the bottom pass transistor is entirely based on a conductive channel that is formed when the bottom pass transistor is in a turned-on state.
9. A flash memory device comprising:
a semiconductor substrate;
a well impurity region within the semiconductor substrate; and
a cell string including a vertical portion and a horizontal portion, wherein the first vertical portion includes a vertical channel portion and the horizontal portion includes a horizontal channel portion,
the vertical channel portion includes a semiconductor material,
the vertical channel portion is in contact with a top surface of the semiconductor substrate and extends vertically to the surface of the semiconductor substrate, and
the horizontal channel portion is located within the semiconductor substrate and forms an integral part of the semiconductor substrate and the well impurity region.
10. The flash memory device of claim 9 , wherein
the horizontal portion is formed by a bottom pass transistor,
a portion of the bottom pass transistor and a portion of the cell string are in direct contact with the semiconductor substrate, and
during an erase operation when the semiconductor substrate is biased with an erase voltage, the portion of the cell string and the semiconductor substrate form a single common electrical node.
11. The flash memory device of claim 9 , wherein the cell string includes a plurality of NAND string cells.
12. The flash memory device of claim 9 , wherein the conductivity type of a body of the cell string and the semiconductor substrate are the same during an erase operation.
13. The flash memory device of claim 12 , wherein the semiconductor substrate is biased to a high positive erase voltage during the erase operation.
14. The flash memory device of claim 13 , wherein the body of the cell string is charged with the same erase voltage when the semiconductor substrate is biased to the erase voltage.
15. The flash memory device of claim 9 , wherein a body of the cell string may surround a non-conductive dielectric core and may form a silicon on insulator (SOI) structure.
16. The flash memory device of claim 9 , wherein a charge trap layer formed with a non-conductive material is utilized to store data bit in a string cell.
17. A device comprising:
a flash memory including a semiconductor substrate, a well impurity region, and a cell string including a first vertical portion, a second vertical portion and a horizontal portion connecting the first vertical portion and the second vertical portion, wherein
the first vertical portion includes a first channel portion, the second vertical portion includes a second channel portion and the horizontal portion includes a third channel portion,
the first channel portion and the second channel portion include a semiconductor material,
the first channel portion and the second channel portion are in contact with a top surface of the semiconductor substrate and extend vertically to the surface of the semiconductor substrate, and
the third channel portion is located within the semiconductor substrate and forms an integral part of the semiconductor substrate and the well impurity region.
18. The device of claim 17 , wherein
a body of the horizontal portion is formed by a bottom pass transistor, and
the semiconductor substrate is of p-type conductivity.
19. The device of claim 17 , wherein during an erase operation the semiconductor substrate is biased with a positive erase voltage and is of the same conductivity type as a body of the cell string.
20. The device of claim 17 , wherein a body of the cell string and the semiconductor substrate form a single common electrical node during an erase operation.
21. The device of claim 18 , wherein
the bottom pass transistor has a conductive channel when the bottom pass transistor is in a turned-on state, and
the conductive channel connects to the first channel portion and the second channel portion.