Block Read Count Voltage Adjustment

• US 20190130980A1
• Filed: 10/31/2017
• Published: 05/02/2019
• Est. Priority Date: 10/31/2017
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Singidi, Harish, Muchherla, Kishore Kumar, Alsasua, Gianni Stephen, Malshe, Ashutosh, Ratnam, Sampath, Besinga, Gary F., Miler, Michael G.
• Granted Patent: US 10,366,763 B2
• Time in Patent Office: Days
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 11/5671 using charge trapping in an insulator
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/08 Address circuits; Decoders; Word-line control circuits
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/3495 Circuits or methods to detect or delay wearout of nonvolatile EPROM or EEPROM memory devices, e.g. by counting numbers of erase or reprogram cycles, by using multiple memory areas serially or cyclically

Abstract

Disclosed in some examples, are methods, systems, and machine readable mediums which compensate for read-disturb effects by shifting the read voltages used to read the value in a NAND cell based upon a read counter. For example, the NAND memory device may have a read counter that corresponds to a group of NAND cells (e.g., a page, a block, a superblock). Anytime a NAND cell in the group is read, the read counter may be incremented. The read voltage, Vread, may be adjusted based on the read counter to account for the read disturb voltage.

Claims

1. A NAND memory device comprising:

a NAND memory array including a first pool of memory;

a controller executing instructions and performing operations comprising;

receiving a command from a host to read a value of at least one cell from the first pool of memory;

determining a read voltage to apply to the at least one cell based upon a count of a number of previous reads during a period of time to a group of cells, the group of cells including the at least one cell; and

applying the read voltage to the at least one cell.

2. The NAND memory device of claim 1, wherein the operations of determining the read voltage to apply to the at least one cell comprises determining a first read voltage for a first page of the NAND memory device, the first page including the at least one cell, and wherein the operations of applying the read voltage to the at least one cell includes applying the first read voltage to the at least one cell to read a first value of the at least one cell.

3. The NAND memory device of claim 2, wherein the operations further comprise:

determining second and third read voltages to apply to the at least one cell based upon the count; and

applying the second and third read voltages to the at least one cell to read second and third values of the at least one cell.

4. The NAND memory device of claim 3 wherein the operations of determining the read voltage comprises adding a first offset value to a base read voltage, wherein determining the second read voltage comprises adding a second offset to a second base read voltage, and wherein determining the third read voltage comprises adding a third offset to a third base read voltage, wherein at least two of the first offset value, the second offset value, and the third offset value are different values.

5. The NAND memory device of claim 1, wherein the operations of determining the read voltage comprises adding a first offset value to a base read voltage, wherein the first offset value is calculated as a linear function of the count.

6. The NAND memory device of claim 1, wherein the operations of determining the read voltage comprises adding a first offset value to a base read voltage, wherein the first offset value is calculated as a stepwise function of the count.

7. The NAND memory device of claim 1, wherein the operations of determining the read voltage to apply to the at least one cell based upon the count comprises determining the read voltage based upon the count and based upon a wear indicator.

8. The NAND memory device of claim 1, wherein the operations further comprise reading the value of the at least one cell and sending the value to the host.

9. The NAND memory device of claim 1, wherein the NAND memory device is a three-dimensional NAND device.

10. A method performed by a NAND memory device, the method comprising:

receiving a command from a host to read a value of at least one cell from a first pool of memory of the NAND memory device;

determining a read voltage to apply to the at least one cell based upon a count of a number of previous reads during a period of time to a group of cells, the group of cells including the at least one cell; and

applying the read voltage to the at least one cell.

11. The method of claim 10, wherein determining the read voltage to apply to the at least one cell comprises determining a first read voltage for a first page of the NAND memory device, the first page including the at least one cell, and wherein applying the read voltage to the at least one cell includes applying the first read voltage to the at least one cell to read a first value of the at least one cell.

12. The method of claim 11, wherein the method further comprises:

determining second and third read voltages to apply to the at least one cell based upon the count; and

applying the second and third read voltages to the at least one cell to read second and third values of the at least one cell.

13. The method of claim 12, wherein determining the read voltage comprises adding a first offset value to a base read voltage, wherein determining the second read voltage comprises adding a second offset to a second base read voltage, and wherein determining the third read voltage comprises adding a third offset to a third base read voltage, wherein at least two of the first offset value, the second offset value, and the third offset value are different values.

14. The method of claim 10, wherein determining the read voltage comprises adding a first offset value to a base read voltage, wherein the first offset value is calculated as a linear function of the count.

15. The method of claim 10, wherein determining the read voltage comprises adding a first offset value to a base read voltage, wherein the first offset value is calculated as a stepwise function of the count.

16. A machine-readable medium comprising instructions, which when performed by a machine, causes the machine to perform operations comprising:

receiving a command from a host to read a value of at least one cell from a first pool of memory cells in a NAND memory device;

determining a read voltage to apply to the at least one cell based upon a count of a number of previous reads during a period of time to a group of cells, the group of cells including the at least one cell; and

applying the read voltage to the at least one cell.

17. The machine-readable medium of claim 16, wherein the operations of determining the read voltage to apply to the at least one cell comprises determining a first read voltage for a first page of the NAND memory device, the first page including the at least one cell, and wherein applying the read voltage to the at least one cell includes applying the first read voltage to the at least one cell to read a first value of the at least one cell.

18. The machine-readable medium of claim 17, wherein the operations further comprise:

determining second and third read voltages to apply to the at least one cell based upon the count; and

applying the second and third read voltages to the at least one cell to read second and third values of the at least one cell.

19. The machine-readable medium of claim 18, wherein the operations of determining the read voltage comprises adding a first offset value to a base read voltage, wherein determining the second read voltage comprises adding a second offset to a second base read voltage, wherein determining the third read voltage comprises adding a third offset to a third base read voltage, wherein at least two of the first offset value, the second offset value, and the third offset value are different values.

20. The machine-readable medium of claim 16, wherein the operations of determining the read voltage comprises adding a first offset value to a base read voltage, wherein the first offset value is calculated as a linear function of the count.

21. The machine-readable medium of claim 16, wherein the operations of determining the read voltage comprises adding a first offset value to a base read voltage, wherein the first offset value is calculated as a stepwise function of the count.

22. The machine-readable medium of claim 16, wherein the operations of determining the read voltage to apply to the at least one cell based upon the count comprises determining the read voltage based upon the count and based upon a wear indicator.

23. The machine-readable medium of claim 16, wherein the operations further comprise reading the value of the at least one cell and sending the value to the host.