Word line dependent programming in a memory device

Patent metadata

Field	Value
Publication number	US-9548124-B1
Application number	US-201514882858-A
Country	US
Kind code	B1
Filing date	Oct 14, 2015
Priority date	Oct 14, 2015
Publication date	Jan 17, 2017
Grant date	Jan 17, 2017

Abstract

A memory device includes memory cells arranged in word lines. Due to variations in the fabrication process, with width and spacing between word lines can vary, resulting in widened threshold voltage distributions. In one approach, a programming parameter is optimized for each word line based on a measurement of the threshold voltage distributions in an initial programming operation. An adjustment to the programming parameter of a word line can be based, e.g., on measurements from adjacent word lines, and a position of the word line in a set of word lines. The programming parameter can include a programming mode such as a number of programming passes. Moreover, the programming parameters from one set of word lines can be used for another set of word lines having a similar physical layout due to the variations in the fabrication process.

First claim

We claim:

1. A method for operating a memory device, comprising:
performing initial programming of memory cells connected to a set of word lines, the initial programming comprising programming of memory cells of each word line of the set of word lines, one word line at a time, wherein the initial programming is performed using a programming parameter set to an initial value, and the programming parameter controls a width of a threshold voltage distribution of the memory cells resulting from the initial programming of the memory cells of the word line;
for each word line of the set of word lines, after the initial programming of the memory cells of the word line, determining a count of the memory cells for which a threshold voltage exceeds a read voltage;
identifying one or more high-count word lines of the set of word lines for which the count exceeds an upper limit;
for each word line of the one or more high-count word lines, determining a respective adjusted value of the programming parameter for use in performing subsequent programming of the memory cells of the word line;
identifying one or more low-count word lines of the set of word lines for which the count is less than a lower limit, lower than the upper limit; and
for each word line of the one or more low-count word lines, determining a respective adjusted value of the programming parameter for use in performing subsequent programming of the memory cells of the word line.

2. The method of claim 1 , further comprising:
identifying one or more medium-count word lines for which the count is between the lower limit and the upper limit; and
for each word line of the one or more medium-count word lines, performing the subsequent programming of memory cells of the word line without adjusting the programming parameter.

3. The method of claim 1 , wherein:
the read voltage distinguishes between memory cells in a particular state and memory cells in a next higher state.

4. The method of claim 1 , wherein:
the read voltage is below a read voltage which distinguishes between memory cells in a particular state and memory cells in a next higher state.

5. The method of claim 1 , further comprising:
for each word line of the one or more high-count word lines, performing the subsequent programming using the respective adjusted value of the programming parameter, wherein the initial programming is one-pass of a multi-pass programming operation, and the subsequent programming is a subsequent pass in the multi-pass programming operation.

6. The method of claim 1 , further comprising:
for each word line of the one or more high-count word lines, setting the respective adjusted value of the programming parameter in proportion to an amount by which the count exceeds the upper limit.

7. The method of claim 1 , wherein:
the initial value of the programming parameter is greater than the respective adjusted value of the programming parameter for the one or more low-count word lines and is less than the respective adjusted value of the programming parameter for the one or more high-count word lines.

8. The method of claim 1 , wherein:
the programming parameter comprises a program voltage step size;
the initial value of the program voltage step size for one word line of the set of word lines is greater than the initial value of the program voltage step size for another word line of the set of word lines when a distance between the one word line and a later-programmed adjacent word line of the one word line is greater than a distance between the another word line and a later-programmed adjacent word line of the another word line;
memory cells of the later-programmed adjacent word line of the one word line are programmed after memory cells of the one word line in a word line programming order of the set of word lines; and
memory cells of the later-programmed adjacent word line of the another word line are programmed after memory cells of the another word line in the word line programming order of the set of word lines.

9. The method of claim 1 , wherein:
the programming parameter comprises a program voltage step size;
the initial value of the program voltage step size for one word line of the set of word lines is greater than the initial value of the program voltage step size for another word line of the set of word lines when a width of a later-programmed adjacent word line of the one word line is less than a width of a later-programmed adjacent word line of the another word line;
memory cells of the later-programmed adjacent word line of the one word line are programmed after memory cells of the one word line in a word line programming order of the set of word lines; and
memory cells of the later-programmed adjacent word line of the another word line are programmed after memory cells of the another word line in the word line programming order of the set of word lines.

10. The method of claim 1 , further comprising:
for at least one word line of the set of word lines, determining a count of program-erase cycles to perform before re-determining a new respective adjusted value of the programming parameter, wherein the count of program-erase cycles is relatively smaller when the count of the memory cells for which the threshold voltage exceeds the read voltage is relatively higher.

11. The method of claim 1 , further comprising:
for the set of word lines, determining a count of program-erase cycles to perform before re-determining a new respective adjusted value of the programming parameter for at least one word line of the set of word line, wherein the count of program-erase cycles is relatively smaller when a count of the one or more high-count word lines is relatively higher.

12. The method of claim 1 , wherein for each word line of the one or more high-count word lines:
the performing the subsequent programming uses the respective adjusted value of the programming parameter;
after the subsequent programming of the memory cells of the word line, a count is determined of memory cells of the word line for which the threshold voltage exceeds the read voltage; and
if the count exceeds the upper limit, an adjustment to the respective adjusted value of the programming parameter is determined for use in further programming of the memory cells of the word line, wherein the adjustment is a function of the count of the memory cells for which the threshold voltage exceeds the read voltage in the subsequent programming and the respective adjusted value of the programming parameter.

13. The method of claim 1 , wherein:
the initial value of the programming parameter is greater than the respective adjusted value of the programming parameter for the one or more high-count word lines and is less than the respective adjusted value of the programming parameter for the one or more low-count word lines.

14. A memory device, comprising:
a set of word lines, each word line connected to memory cells;
a storage location; and
means for performing initial programming of the memory cells of the set of word lines, the means for performing initial programming comprising:
means for applying to each word line of the set of word lines, one word line at a time, an initial set of program voltages which increase by a respective step size to program memory cells of the word line to a state;
means for determining, for each word line of the set of word lines, a respective initial error count, for the memory cells which were programmed to the state, read the memory cells to determine a respective count of the memory cells which have a threshold voltage which does not correspond to a threshold voltage range

Assignees

• Sandisk Technologies Inc
• Sandisk Technologies Llc

Inventors

• Hazeghi Arash
• Hemink Gerrit Jan
• Lee Dana
• Chin Henry
• Lei Bo
• Zhou Zhenming

Classifications

• G11C16/20 Primary

  Initialising; Data preset; Chip identification · CPC title

• G11C16/34

  Determination of programming status, e.g. threshold voltage, overprogramming or underprogramming, retention · CPC title

• G11C16/3495

  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 · CPC title

• G11C16/0483

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

• G11C16/26

  Sensing or reading circuits; Data output circuits · CPC title