Sequential deselection of word lines for suppressing first read issue

Patent metadata

Field	Value
Publication number	US-9830994-B1
Application number	US-201715422803-A
Country	US
Kind code	B1
Filing date	Feb 2, 2017
Priority date	Feb 2, 2017
Publication date	Nov 28, 2017
Grant date	Nov 28, 2017

Abstract

Systems and methods for reducing trapped electrons within a NAND string are described. During a sensing operation, one or more control circuits may discharge or initiate discharge of control gates corresponding with contiguous memory cell transistors of a NAND string from a read pass voltage (e.g., 10V) to a second voltage less than the pass voltage (e.g., 2V) in an order starting from a first set of the contiguous memory cell transistors closest to the first end of the NAND string and ending with a second set of the contiguous memory cell transistors closest to the second end of the NAND string. Subsequently, the one or more control circuits may either concurrently or simultaneously discharge the control gates corresponding with the contiguous memory cell transistors from the second voltage to a third voltage less than the intermediate voltage (e.g., from 2V to 0V).

First claim

What is claimed is:

1. An apparatus, comprising:
a NAND string including a selected memory cell transistor and sets of contiguous memory cell transistors arranged between a first end of the NAND string and a second end of the NAND string, the selected memory cell transistor and the sets of contiguous memory cell transistors comprise user accessible memory cell transistors within the NAND string; and
a control circuit configured to initiate discharge of control gates corresponding with each set of the sets of contiguous memory cell transistors from a pass voltage to a second voltage less than the pass voltage in an order starting from a first set of the sets of contiguous memory cell transistors closest to the first end of the NAND string and ending with a second set of the sets of contiguous memory cell transistors closest to the second end of the NAND string.

2. The apparatus of claim 1 , wherein:
the first end of the NAND string comprises a drain-side end of the NAND string and the second end of the NAND string comprises a source-side end of the NAND string; and
the sets of contiguous memory cell transistors comprise all user accessible memory cell transistors within the NAND string.

3. The apparatus of claim 1 , wherein:
the control circuit configured to apply a read voltage less than the pass voltage to a control gate of the selected memory cell transistor arranged between the first set of contiguous memory cell transistors and the second set of contiguous memory cell transistors while the pass voltage is applied to the first set of contiguous memory cell transistors and the second set of contiguous memory cell transistors.

4. The apparatus of claim 1 , wherein:
the pass voltage applied to the first set of contiguous memory cell transistors sets each memory cell transistor of the first set of contiguous memory cell transistors into a conducting state.

5. The apparatus of claim 1 , wherein:
the control circuit configured to apply a sensing voltage to a control gate of the selected memory cell transistor while the pass voltage is applied to the first set of contiguous memory cell transistors and the second set of contiguous memory cell transistors.

6. The apparatus of claim 1 , wherein:
the control circuit configured to discharge control gates corresponding with the first set of contiguous memory cell transistors from the pass voltage to the second voltage during a first time period and discharge control gates corresponding with the second set of contiguous memory cell transistors from the pass voltage to the second voltage during a second time period subsequent to the first time period.

7. The apparatus of claim 1 , wherein:
the second voltage comprises one of 0V or 2V.

8. The apparatus of claim 1 , wherein:
the NAND string includes a drain-side select gate and the first set of contiguous memory cell transistors is positioned adjacent to the drain-side select gate.

9. The apparatus of claim 1 , wherein:
the NAND string comprises a vertical NAND string.

10. The apparatus of claim 1 , wherein:
the NAND string is part of a non-volatile memory that is monolithically formed in one or more physical levels of memory cells having active areas disposed above a silicon substrate.

11. An apparatus, comprising:
a NAND string including a selected memory cell transistor and a first set of unselected memory cell transistors arranged between a first end of the NAND string and a second end of the NAND string; and
a control circuit configured to set a control gate of the selected memory cell transistor to a sensing voltage while control gates corresponding with the first set of unselected memory cell transistors are set to a pass voltage greater than the sensing voltage, the control circuit configured to discharge the control gates corresponding with the first set of unselected memory cell transistors from the pass voltage to an intermediate voltage less than the pass voltage, the control circuit configured to initiate discharge of the control gates corresponding with the first set of unselected memory cell transistors from the intermediate voltage to a second voltage less than the intermediate voltage in an order starting from a first memory cell transistor of the first set of unselected memory cell transistors closest to the first end of the NAND string and ending with a second memory cell transistor of the first set of unselected memory cell transistors closest to the second end of the NAND string.

12. The apparatus of claim 11 , wherein:
the first end of the NAND string comprises a drain-side end of the NAND string and the second end of the NAND string comprises a source-side end of the NAND string; and
the intermediate voltage comprises a voltage greater than a threshold voltage corresponding with a highest programmed data state.

13. The apparatus of claim 11 , wherein:
the NAND string includes a second set of unselected memory cell transistors arranged between the first end of the NAND string and the second end of the NAND string; and
the control circuit configured to discharge control gates corresponding with the second set of unselected memory cell transistors from the pass voltage to the intermediate voltage and initiate discharge of the control gates corresponding with the second set of unselected memory cell transistors from the intermediate voltage to the second voltage in an order starting from a third memory cell transistor of the second set of unselected memory cell transistors closest to the second end of the NAND string and ending with a fourth memory cell transistor of the second set of unselected memory cell transistors closest to the first end of the NAND string.

14. The apparatus of claim 11 , wherein:
the pass voltage applied to the control gates corresponding with the first set of unselected memory cell transistors sets each memory cell transistor of the first set of unselected memory cell transistors into a conducting state.

15. The apparatus of claim 11 , wherein:
the control circuit configured to discharge the control gate corresponding with the first memory cell transistor of the first set of unselected memory cell transistors from the intermediate voltage to the second voltage during a first time period and discharge the control gate corresponding with the second memory cell transistor of the first set of unselected memory cell transistors from the intermediate voltage to the second voltage during a second time period subsequent to the first time period.

16. The apparatus of claim 11 , wherein:
the second voltage comprises 0V;
the pass voltage comprises 8V; and
the intermediate voltage comprises 6V.

17. The apparatus of claim 11 , wherein:
the NAND string includes a drain-side select gate and the first set of unselected memory cell transistors is positioned adjacent to the drain-side select gate.

18. A system, comprising:
a NAND string including sets of memory cell transistors arranged between a first end of the NAND string and a second end of the NAND string; and
a control circuit configured to discharge control gates corresponding with each set of the sets of memory cell transistors from a pass voltage to an intermediate voltage less than the pass voltage in an order starting from a first set of the sets of memory cell transistors closest to the first end of the NAND string and ending with a second set of the sets of memory cell transistors closest to the second end of the NAND string, the control circuit configured to concurrently discharge the control gates corresponding with the sets of memory cell tra

Assignees

• Sandisk Technologies Llc

Inventors

• Mitsuhira Noriyuki
• Lai Chun-Hung

Classifications

• G11C16/3459

  Circuits or methods to verify correct programming of nonvolatile memory cells · CPC title

• G11C16/16 Primary

  for erasing blocks, e.g. arrays, words, groups · CPC title

• G11C16/10

  Programming or data input circuits · CPC title

• G11C16/26 Primary

  Sensing or reading circuits; Data output circuits · CPC title

• G11C16/0483

  comprising cells having several storage transistors connected in series · CPC title