Memory device having a negatively ramping dynamic pass voltage for reducing read-disturb effect
View Patent ↗The present disclosure includes methods, devices, modules, and systems for operating memory cells. One method embodiment includes applying sensing voltages to selected access lines for sensing selected memory cells. The method also includes applying a dynamic pass voltage to unselected access lines while the sensing voltages are applied.
1. A method for operating a memory device, comprising:
applying one or more sensing voltages to one or more selected access lines for sensing one or more selected memory cells; and
applying a negatively ramping dynamic pass voltage to one or more unselected access lines while the one or more sensing voltages are applied.
2. The method of claim 1 , wherein applying the negatively ramping dynamic pass voltage includes applying a pass voltage that is not constant.
3. The method of claim 1 , wherein applying the negatively ramping dynamic pass voltage includes decreasing the pass voltage while the one or more sensing voltages are applied.
4. The method of claim 3 , wherein decreasing the pass voltage includes applying the negatively ramping pass voltage to the one or more unselected access lines.
5. The method of claim 1 , further including:
precharging one or more data lines associated with the one or more selected memory cells; and
decreasing the negatively ramping dynamic pass voltage while the one or more sensing voltages are applied after the one or more data lines begin to discharge.
6. The method of claim 5 , wherein decreasing the negatively ramping dynamic pass voltage includes decreasing the negatively ramping dynamic pass voltage by an amount approximately equal to an amount by which the one or more data lines discharge.
7. The method of claim 1 , wherein applying the one or more sensing voltages includes performing at least part of an operation selected from the group including a read operation and a program verify operation.
8. A method for operating a memory device, comprising:
applying a sensing voltage to a selected access line for a particular time to sense a selected memory cell; and
applying a negatively ramping dynamic pass voltage to a number of unselected access lines during at least a portion of the particular time to put a number of unselected memory cells in a conductive state.
9. The method of claim 8 , further including starting the negatively ramping dynamic pass voltage at an initial pass voltage compensated for changes in threshold voltage due to temperature.
10. The method of claim 9 , further including compensating the initial pass voltage for changes in threshold voltage due to body effect.
11. The method of claim 9 , including applying the negatively ramping dynamic pass voltage to the number of unselected access lines without reducing an overdrive voltage on unselected memory cells.
12. The method of claim 8 , wherein:
applying the sensing voltage includes applying a positively ramping sensing voltage that increases linearly; and
applying the negatively ramping dynamic pass voltage includes decreasing the dynamic pass voltage linearly.
13. The method of claim 8 , further including applying an approximately constant voltage to a source select gate coupled in series with the selected and the unselected memory cells.
14. The method of claim 8 , wherein applying a negatively ramping dynamic pass voltage includes decreasing the pass voltage by at least 200 millivolts.
15. A method for sensing memory cells, comprising:
applying one or more sensing voltages to an access gate of a selected memory cell;
applying a dynamic pass voltage to access gates of one or more unselected memory cells coupled in series to the selected memory cell;
wherein applying the dynamic pass voltage includes decreasing the dynamic pass voltage while applying the one or more sensing voltages; and
wherein applying the dynamic pass voltage includes starting the dynamic pass voltage at an initial temperature compensated voltage.
16. A memory device, comprising:
one or more arrays of memory cells, each array including one or more strings of memory cells, each of the one or more strings coupled to a data line, and each memory cell coupled to an access line;
control circuitry coupled to the one or more arrays and configured to:
apply one or more sensing voltages to a selected access line to sense a selected memory cell; and
apply a negatively ramping dynamic pass voltage to one or more unselected access lines while the one or more sensing voltages are applied.
17. The memory device of claim 16 , wherein the negatively ramping dynamic pass voltage is a decreasing pass voltage.
18. The memory device of claim 17 , wherein the control circuitry is configured to decrease the negatively ramping dynamic pass voltage in proportion to an increase in operating temperature.
19. The memory device of claim 17 , wherein:
each of the one or more strings is coupled to at least one data line; and
the control circuitry is configured to decrease the negatively ramping dynamic pass voltage in proportion to a decrease in voltage on the at least one data line while the one or more sensing voltages are applied to the selected access line.
20. The memory device of claim 16 , wherein the selected access line and the one or more unselected access lines are coupled to control gates of memory cells in at least one of the one or more strings of memory cells.
21. The memory device of claim 16 , wherein the control circuitry is configured to decrease the negatively ramping dynamic pass voltage by at least 200 millivolts while the one or more sensing voltages are applied to the selected access line.
22. A memory device comprising:
one or more NAND arrays of memory cells including one or more strings of memory cells;
a data line coupled to each of the one or more strings of memory cells;
control circuitry coupled to the one or more NAND arrays and configured to:
precharge the data line with a first voltage;
apply one or more sensing voltages to an access line coupled to a selected memory cell until the data line discharges to a second voltage;
apply a dynamic pass voltage to one or more access lines coupled to one or more unselected memory cells while the one or more sensing voltages are applied; and
decrease the dynamic pass voltage from a first pass voltage to a second pass voltage while the data line discharges.
23. The memory device of claim 22 , wherein the control circuitry is configured to decrease the dynamic pass voltage in proportion to discharge of the data line from the first voltage to the second voltage.
24. The memory device of claim 22 , wherein the control circuitry is configured to apply the first pass voltage at a value approximately equal to:
PV max +Vt width +γ*(√(1+V BL )−1)+V s +Vt max
wherein:
PV max =a verify voltage for a maximum threshold voltage that corresponds to a data state;
Vt max =the maximum threshold voltage that corresponds to the data state;
Vt width =a voltage range of a threshold voltage distribution;
γ=a body effect parameter;
V BL =a voltage on the data line; and
V s =a source voltage.
25. The memory device of claim 24 , wherein the control circuitry is further configured to compensate the first pass voltage for operating temperature.
26. The memory device of claim 22 , wherein the control circuitry is further configured to decrease the first and the second pass voltages in proportion to an increase in operating temperature.
27. A memory system, comprising:
a processor;
a memory device coupled to the processor, the memory device comprising:
one or more strings of memory cells coupled to one or more data lines;
an access line coupled to each memory cell; and
control circuitry coupled to the one or more strings of memory cells and configured to:
apply one or more sensing voltages to one or more access lines corresponding to one or more selected memory cells; and
apply a negatively ramping dynamic pass voltage to one or more access lines corresponding to one or more unselected memory cells.
28. The memory system of claim 27 , wherein the control circuitry is configured to apply the negatively ramping dynamic pass voltage at substantially the same time as the one or more sensing voltages.
29. The memory system of claim 27 , wherein:
the control circuitry is configured to linearly decrease the negatively ramping dynamic pass voltage from a first voltage to a second voltage; and
the first and the second voltages are dynamically compensated for an operating temperature.
30. The memory system of claim 29 , wherein the operating temperature is selected from the group including:
an operating temperature of a particular memory cell;
an average operating temperature of a number of memory cells;
an operating temperature of the memory device; and
an operating temperature of the memory system.
31. The memory system of claim 29 , wherein the first and the second voltages are decreased in proportion to an increase in the operating temperature.
32. The memory system of claim 31 , wherein the first and the second voltages are decreased by a same amount.
33. The memory system of claim 27 , wherein:
the one or more strings of memory cells include one or more memory cells coupled in series source to drain, and coupled to a data line; and
the control circuitry is configured to linearly decrease the negatively ramping dynamic pass voltage in proportion to a decrease in a voltage on the data line while the one or more sensing voltages are applied to the one or more access lines corresponding to one or more selected memory cells.