Method for controlling threshold value in nonvolatile semiconductor memory device

• US 8,565,019 B2
• Filed: 11/19/2008
• Issued: 10/22/2013
• Est. Priority Date: 11/20/2007
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Honda, Yasuhiko, Hondai, Ryu, Satoh, Manabu
• Primary Examiner(s): Byrne, Harry W
• Assistant Examiner(s): REIDLINGER, RONALD LANCE
• Application Number:
  US12/273,845
• Publication Number:
  US 20090129157A1
• Time in Patent Office: 1,798 Days
• Field of Search: 365/185.03, 365/185.24, 365/185.22
• US Class Current: 365/185.03
• CPC Class Codes: G11C 11/5628 Programming or writing circuits; Data input circuits
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data
• CPC Class Codes: G11C 2211/5621 Multilevel programming verification

Abstract

A method for controlling a threshold value in a nonvolatile semiconductor memory device, includes: performing writing at least once on at least one of the memory cells to be adjusted to a state other than an erased state with an applied voltage that does not cause excess writing, with verify reading being not performed; and performing verify reading by applying a verify voltage corresponding to a target threshold value of the memory cell after the writing is performed on the at least one of the memory cells to be adjusted to the state other than the erased state, and, when the threshold value of the memory cell is determined to be lower than the target threshold value, repeating the writing with the applied voltage that does not cause excess writing and the verify reading until the threshold value of the memory cell becomes equal to or higher than the target threshold value.

Claims

1. A method for controlling threshold values in a nonvolatile semiconductor memory device that includes a plurality of memory cells comprising a first memory cell and a second memory cell, each of the plurality of memory cells being capable of having a multi-value state by adjusting threshold voltages, and a word line connected to the memory cells, writing being performed by applying a write voltage to the word line,

the method comprising:

performing a first operation so that the threshold value of the first memory cell is adjusted to a neighborhood of a first target threshold value, the first operation including a first writing on the first memory cell without verify reading being performed, the first target threshold value being different from the threshold value of an erased state;

performing a second operation after performing the first operation so that the threshold value of the second memory cell is adjusted to a neighborhood of a second target threshold value, the second operation including a second writing on the second memory cell without verify reading being performed, the second target threshold value being different from both the first target threshold value and the threshold value of an erased state;

performing a third operation until a threshold value on the first memory cell becomes equal to or higher than the first target threshold value after performing the second operation, the third operation including a third writing and a first verify reading on the first memory cell; and

performing a fourth operation until a threshold value on the second memory cell becomes equal to or higher than the second target threshold value after performing the third operation, the fourth operation including a fourth writing and a second verify reading on the first memory cell.

2. The method according to claim 1, wherein the first target threshold value is a highest target threshold value, and the second target threshold value is between the threshold value of the erased state and the highest target threshold value.

3. The method according to claim 1, wherein, when a suspend operation is caused during the first to fourth operations, the writing is suspended, when the suspend operation is caused during the third operation, the first verify reading is performed prior to the third writing after the suspend operation is resumed, and when the suspend operation is caused during the fourth operation, the second verify reading is performed prior to the fourth writing after the operation is resumed.

4. A method for controlling threshold values in a nonvolatile semiconductor memory device that includes a plurality of memory cells comprising a first memory cell and a second memory cell, each of the plurality of memory cells being capable of having a multi-value state by adjusting threshold voltages, and a word line connected to the memory cells, writing being performed by applying a write voltage to the word line,

the method comprising:

performing a first operation so that the threshold value of the first memory cell is adjusted to a neighborhood of a first target threshold value, the first operation including a first writing on the first memory cell without verify reading being performed, the first target threshold value being different from the threshold value of an erased state;

performing a second operation after performing the first operation so that the threshold value of the second memory cell is adjusted to a neighborhood of a second target threshold value, the second operation including a second writing on the second memory cell without verify reading being performed, the second target threshold value being different from both the first target threshold value and the threshold value of an erased state;

performing a third operation until a threshold value on the first memory cell becomes equal to or higher than the first target threshold value after performing the second operation, the third operation including a third writing and a first verify reading on the first memory cell;

performing a fourth operation until a threshold value on the second memory cell becomes equal to or higher than the second target threshold value after performing the third operation, the fourth operation including a fourth writing and a second verify reading on the first memory cell;

performing a fifth operation until a threshold value on the first memory cell becomes equal to or higher than a third target threshold value after performing the fourth operation, the fifth operation including a fifth writing and a third verify reading on the first memory cell, the third target threshold value being higher than the first target threshold value; and

performing a sixth operation until a threshold value on the second memory cell becomes equal to or higher than the fourth target threshold value after performing the fifth operation, the sixth operation including a sixth writing and a fourth verify reading on the first memory cell.

5. The method according to claim 4, wherein the first target threshold value is a highest target threshold value, and the second target threshold value is between the threshold value of the erased state and the highest target threshold value.

6. The method according to claim 4, wherein, when a suspend operation is caused during the first to fourth operations, the writing is suspended, when the suspend operation is caused during the third operation, the first verify reading is performed prior to the third writing after the suspend operation is resumed, and when the suspend operation is caused during the fourth operation, the second verify reading is performed prior to the fourth writing after the operation is resumed.

7. A method for controlling a threshold value in a nonvolatile semiconductor memory device that includes a plurality of memory cells each capable of having a multi-value state by adjusting a threshold voltage, and a word line connected to the memory cells, verify reading being performed on the memory cells to be adjusted to a state other than an erased state, writing being performed on the memory cells having not reached a target threshold value by increasing a write voltage to be applied to the word line,

the method comprising:

performing writing simultaneously on a first memory cell to be adjusted to a first target threshold value and a second memory cell connected to the same word line as the first memory cell, when the write voltage to be applied to the word line at the time of writing on the first memory cell becomes equal to or higher than a write start voltage of the second memory cell to be adjusted to a second target threshold value next higher than the first target threshold value;

performing writing collectively on a first predetermined number of the memory cells, with a first negative voltage being applied to unselected ones of the word lines, when the write voltage is lower than a predetermined value; and

performing writing collectively on a second predetermined number of the memory cells, with a second negative voltage higher than the first negative voltage being applied to the unselect word lines, when the write voltage is equal to or higher than the predetermined value, the second predetermined number of the memory cells being smaller than the first predetermined number of the memory cells.

8. A method for controlling a threshold value in a nonvolatile semiconductor memory device that includes a plurality of memory cells each capable of having a multi-value state by adjusting a threshold voltage, and a word line connected to the memory cells, verify reading being performed on the memory cells to be adjusted to a state other than an erased state, writing being performed on the memory cells having not reached a target threshold value by increasing a write voltage to be applied to the word line,

the method comprising:

performing writing simultaneously on a first memory cell to be adjusted to a first target threshold value and a second memory cell connected to the same word line as the first memory cell, when the write voltage to be applied to the word line at the time of writing on the first memory cell becomes equal to or higher than a write start voltage of the second memory cell to be adjusted to a second target threshold value next higher than the first target threshold value;

performing verify reading sequentially on a first memory cell and a second memory cell when the write voltage to be applied to the word line at the time of writing on the first memory cell becomes equal to or higher than a write start voltage of the second memory cell, and performing writing on the first memory cell determined not to have reached a first target threshold value and the second memory cell determined not to have reached a second target threshold value, while the write voltage to be applied to the word line is increased;

performing writing collectively on a first predetermined number of the memory cells, with a first negative voltage being applied to unselected ones of the word lines, when the threshold value distributions of the first memory cell and the second memory cells are adjusted; and

performing writing collectively on a second predetermined number of the memory cells, with a second negative voltage higher than the first negative voltage being applied to the unselect word lines, when the threshold value distribution of the third memory cell is adjusted, the second predetermined number of the memory cells being smaller than the first predetermined number of the memory cells.

9. A method for controlling a threshold value in a nonvolatile semiconductor memory device that includes a plurality of memory cells each capable of having a multi-value state by adjusting a threshold voltage, and performs writing on each of the memory cells by applying one of write voltages suitable for the multi-value state to each of the memory cells,

the method comprising:

performing first writing by applying a first voltage corresponding to a first target threshold value, only a required minimum number of times, to the memory cells to be adjusted to a first state different from an erased state of the multi-value state;

performing second writing with a first initial voltage lower than a voltage corresponding to a second target threshold value on the memory cells to be adjusted to a second state having the second target threshold value lower than the first target threshold value, the second state being different from the erased state and the first state, and, when a threshold value after the second writing on the memory cells to be adjusted to the second state has not reached a intermediate level lower than the second target threshold value performing re-writing with a second voltage increased from the first initial voltage to avoid excess writing; and

performing third writing on first and second memory cells with a second initial voltage lower than a voltage corresponding to a third target threshold value, the first memory cells being to be adjusted to a third state having the third target threshold value lower than the first and second target threshold values, and the second memory cells being to be adjusted to the second state and having the writing performed up to the intermediate level, the third state being different from the erased state, the first state, and the second state, and, when a threshold value after the third writing on the first memory cells to be adjusted to the third state and the second memory cells to be adjusted to the second state and having the writing performed up to the intermediate level has not reached to the third target value and the second target value are not reached, performing re-writing with a third voltage increased from the second initial voltage to avoid excess writing.

10. The method according to claim 9, further comprising fixing a gate voltage of a non-selected one of the memory cells in which writing is not to be performed to a predetermined negative voltage, while the writing and verify reading are performed on the memory cells.