Word line-dependent and temperature-dependent pass voltage during programming
Techniques are provided for avoiding over-programming which can occur on memory cells connected to a data word line at a source-side of a block of word lines. A gradient in the channel potential is created during a program voltage between the data word line and an adjacent dummy word line. This gradient generates electron-hole pairs which can contribute to over programming, where the over programming is worse at higher temperatures. In one aspect, pass voltages of unselected word lines are set to be relatively lower when the temperature is relatively higher, and when the selected word line is among a set of one or more source-side word lines. On the other hand, the pass voltages are set to be relatively higher when the temperature is relatively higher, and when the selected word line is not among the one or more source-side word lines.
1. An apparatus, comprising:
a set of word lines;
a string comprising a set of data memory cells extending from a group of one or more source-side data memory cells at a source-side of the string to a drain-side data memory cell at a drain-side of the string, wherein the string is among a plurality of strings of memory cells;
a temperature-sensing circuit configured to provide data indicative of a temperature; and
a control circuit, the control circuit, to program a selected data memory cell in the set of data memory cells in the string, where the selected data memory cell is connected to a selected word line in the set of word lines, is configured to concurrently apply a program voltage to the selected word line and apply a pass voltage to unselected word lines in the set of word lines, and to set a magnitude of the pass voltage inversely proportional to the temperature when the selected data memory cell is among the group of one or more source-side data memory cells in the string and proportional to the temperature when the selected data memory cell is not among the group of one or more source-side data memory cells in the string; wherein:
the group of one or more source-side data memory cells in the string comprises a first data memory cell which is at a source-side of the string and a second data memory cell which is adjacent to the first data memory cell; and
the control circuit is configured to set the magnitude of the pass voltage to a first value when the selected data memory cell is the first data memory cell and a second value, higher than the first value, when the selected data memory cell is the second data memory cell.
2. The apparatus of claim 1 , wherein:
a magnitude of the pass voltage increases with a distance from the source-side of the string when the selected data memory cell is among the group of one or more source-side data memory cells in the string.
3. The apparatus of claim 1 , wherein:
the control circuit is configured to set the magnitude of the pass voltage inversely proportional to a magnitude of the program voltage when the selected data memory cell is among the group of one or more source-side data memory cells.
4. The apparatus of claim 1 , wherein:
the group of one or more source-side data memory cells in the string is adjacent to a dummy memory cell at the source-side of the string; and
the control circuit is configured to set a control gate voltage of the dummy memory cell proportional to the temperature when the selected data memory cell is among the group of one or more source-side data memory cells in the string.
5. The apparatus of claim 1 , wherein:
the group of one or more source-side data memory cells in the string comprises no more than 10% of the set of data memory cells in the string.
6. The apparatus of claim 1 , wherein:
the string extends vertically in a three-dimensional memory device.
7. The apparatus of claim 1 , wherein:
the magnitude of the pass voltage is sufficiently high to provide data memory cells connected to the unselected word lines in a conductive state.
8. The apparatus of claim 1 , wherein:
the set of word lines extend in sub-blocks of memory cells;
the control circuit is configured to program the sub-blocks in a sub-block programming order; and
the magnitude of the pass voltage is adjusted based on when a sub-block of the selected string is programmed in the sub-block programming order.
9. A method, comprising:
obtaining data indicative of a temperature; and
concurrently applying a program voltage to a selected word line and a pass voltage to unselected word lines, wherein a selected data memory cell is connected to the selected word line and, when the temperature is above a specified level, a magnitude of the pass voltage is lower when the selected data memory cell is among a group of one or more source-side data memory cells in a string than when the selected data memory cell is not among the group of one or more source-side data memory cells in the string.
10. The method of claim 9 , wherein:
when the temperature is below the specified level, the magnitude of the pass voltage is independent of whether the selected data memory cell is among the group of one or more source-side data memory cells.
11. The method of claim 9 , wherein:
when the temperature is above the specified level, the magnitude of the pass voltage is inversely proportional to the temperature when the selected data memory cell is among the group of one or more source-side data memory cells in the string.
12. The method of claim 9 , wherein:
when the temperature is above the specified level, the magnitude of the pass voltage is proportional to the temperature when the selected data memory cell is not among the group of one or more source-side data memory cells in the string.
13. The method of claim 9 , wherein the group of one or more source-side data memory cells in the string is adjacent to a dummy memory cell at the source-side of the string, the method further comprising, when the temperature is above the specified level:
setting a magnitude of a control gate voltage of the dummy memory cell higher when the selected data memory cell is among the group of one or more source-side data memory cells in the string than when the selected data memory cell is not among the group of one or more source-side data memory cells in the string.
14. The method of claim 9 , wherein the group of one or more source-side data memory cells in the string comprises a first data memory cell which is at a source-side of the string and a second data memory cell which is adjacent to the first data memory cell, the method further comprising, when the temperature is above the specified level:
setting the magnitude of the pass voltage to a first value when the selected data memory cell is the first data memory cell and a second value, higher than the first value, when the selected data memory cell is the second data memory cell.
15. The method of claim 9 , further comprising:
setting the magnitude of the pass voltage inversely proportional to a magnitude of the program voltage when the selected data memory cell is among the group of one or more source-side data memory cells.
16. An apparatus, comprising:
means for concurrently applying a program voltage to a selected word line of a block; and
means for applying, during the program voltage, a pass voltage to unselected word lines of the block, wherein when a temperature is above a specified level, a magnitude of the pass voltage is lower when the selected word line is among a group of one or more source-side data word lines than when the selected word line is not among the group of one or more source-side data word lines.
17. The apparatus of claim 16 , wherein:
when the temperature is above the specified level, the magnitude of the pass voltage decreases with an increase in the temperature when the selected word line is among the group of one or more source-side data word lines.
18. The apparatus of claim 16 , wherein:
when the temperature is above the specified level, the magnitude of the pass voltage increases with an increase in the temperature when the selected word line is not among the group of one or more source-side data word lines.
19. The apparatus of claim 16 , wherein:
the magnitude of the pass voltage is inversely proportional to a magnitude of the program voltage when the selected word line is among the group of one or more source-side data word lines.