Nonvolatile semiconductor memory device, and programming method and erasing method thereof

• US 20040257864A1
• Filed: 06/17/2004
• Published: 12/23/2004
• Est. Priority Date: 06/17/2003
• Status: Active Grant

• Current Assignee: Xenogenic Development Limited Liability Company (Intellectual Ventures LLC)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Tamai, Yukio, Inoue, Kohji, Morita, Teruaki
• Granted Patent: US 6,992,920 B2
• Time in Patent Office: Days
• US Class Current: 365/158
• CPC Class Codes: G11C 13/0007 comprising metal oxide memory material, e.g. perovskites
• CPC Class Codes: G11C 13/0069 Writing or programming circuits or methods
• CPC Class Codes: G11C 16/3427 Circuits or methods to prevent or reduce disturbance of the state of a memory cell when neighbouring cells are read or written
• CPC Class Codes: G11C 2013/009 Write using potential difference applied between cell electrodes
• CPC Class Codes: G11C 2213/31 Material having complex metal oxide, e.g. perovskite structure
• CPC Class Codes: G11C 2213/77 Array wherein the memory element being directly connected to the bit lines and word lines without any access device being used

Abstract

One end of each variable resistive element, which forms a memory array, in the same row is connected to the same word line and the other end of each variable resistive element in the same column is connected to the same bit line. A first word line voltage is selected and applied to the selected word line, a second word line voltage is selected and applied to the unselected word lines, a first bit line voltage is selected and applied to the selected bit line, and a second bit line voltage is selected and applied to the unselected bit lines. The voltage difference between the first word line voltage and the first bit line voltage is set at a value that is no less than the first voltage difference that changes the resistance value of a variable resistive element, and the voltage difference between the first word line voltage and the second bit line voltage, the voltage difference between the second word line voltage and the first bit line voltage and the voltage difference between the second word line voltage and the second bit line voltage are respectively set at a value that is no greater than the second voltage difference that does not change the resistance value of a variable resistive element.

Claims

1. A nonvolatile semiconductor memory device comprising:

a memory array formed of a plurality of memory cells, each having a variable resistive element of which the resistance value is changed in a reversible manner by applying a voltage, aligned in the directions of rows and columns, respectively, in a manner where one end of each memory cell in the same row is connected to the same word line while the other end of each memory cell in the same column is connected to the same bit line;

a word line voltage application circuit formed so that one type of word line voltage can be selected from among a plurality of types to be applied to each of said word lines; and

a bit line voltage application circuit formed so that one type of bit line voltage can be selected from among a plurality of types to be applied to each of said bit lines, wherein

said word line voltage application circuit selects a first word line voltage at the time of programming or erasing operation so that the first word line voltage is applied to the selected word line that is connected to a selected memory cell to be programmed or erased, and selects a second word line voltage so that the second word line voltage is applied to the unselected word lines other than said selected word line,

said bit line voltage application circuit selects a first bit line voltage at the time of programming or erasing operation so that the first bit line voltage is applied to the selected bit line that is connected to a selected memory cell to be programmed or erased, and selects a second bit line voltage so that the second bit line voltage is applied to the unselected bit lines other than said selected bit line, and

said first word line voltage, said second word line voltage, said first bit line voltage and said second bit line voltage have particular voltage values in accordance with the programming or erasing operation so that the voltage difference between said first word line voltage and said first bit line voltage is set at a value equal to or more than a first voltage difference which allows the resistance value of said variable resistive element to exceed a predetermined value as a result of a change in the case where the first voltage difference is applied across both ends of said variable resistive element and so that the voltage difference between said first word line voltage and said second bit line voltage, the voltage difference between said second word line voltage and said first bit line voltage and the voltage difference between said second word line voltage and said second bit line voltage are respectively set at values equal to or less than a second voltage difference which does not allow the resistance value of said variable resistive element to exceed a predetermined value as a result of a change in the case where the second voltage difference is applied across the both ends of said variable resistive element.

2. The nonvolatile semiconductor memory device according to claim 1, wherein

said word line voltage application circuit selects said second word line voltage before the start of the programming or erasing operation of said memory array so that the second word line voltage is applied to all of said word lines of said memory array, and

said bit line voltage application circuit selects said second bit line voltage before the start of the programming or erasing operation of said memory array so that the second bit line voltage is applied to all of said bit lines of said memory array.

3. The nonvolatile semiconductor memory device according to claim 1, wherein

said variable resistive element has resistance varying characteristics where the resistance value increases so as to exceed a predetermined value when a voltage which is equal to or more than a first threshold voltage is applied across both ends of the variable resistive element and the resistance value decreases so as to exceed a predetermined value when a voltage which is equal to or more than a second threshold voltage of which the polarities are reversed from those of said first threshold voltage is applied across both ends of the variable resistive element, and

said second voltage difference is set at a value lower than the threshold voltage which is the lower of either said first threshold voltage or said second threshold voltage.

4. The nonvolatile semiconductor memory device according to claim 3, wherein

said second threshold voltage is lower than said first threshold voltage.

5. The nonvolatile semiconductor memory device according to claim 1, wherein

said first word line voltage, said second word line voltage, said first bit line voltage and said second bit line voltage at the time of programming operation are set as follows:

said first word line voltage is higher than said second bit line voltage;

said second bit line voltage is no less than said second word line voltage; and

said second word line voltage is higher than said first bit line voltage.

6. The nonvolatile semiconductor memory device according to claim 5, wherein

the voltage difference between said first word line voltage and said second bit line voltage, the voltage difference between said second word line voltage and said first bit line voltage and the voltage difference between said second word line voltage and said second bit line voltage are equal to one another.

7. The nonvolatile semiconductor memory device according to claim 5, wherein

the voltage difference between said first word line voltage and said second bit line voltage and the voltage difference between said second word line voltage and said first bit line voltage are greater than the voltage difference between said second word line voltage and said second bit line voltage.

8. The nonvolatile semiconductor memory device according to claim 1, wherein

said first word line voltage, said second word line voltage, said first bit line voltage and said second bit line voltage at the time of erasing operation are as follows:

said first word line voltage is lower than said second bit line voltage;

said second bit line voltage is no more than said second word line voltage; and

said second word line voltage is lower than said first bit line voltage.

9. The nonvolatile semiconductor memory device according to claim 8, wherein

the voltage difference between said first word line voltage and said second bit line voltage, the voltage difference between said second word line voltage and said first bit line voltage and the voltage difference between said second word line voltage and said second bit line voltage are equal to one another.

10. The nonvolatile semiconductor memory device according to claim 8, wherein

the voltage difference between said first word line voltage and said second bit line voltage and the voltage difference between said second word line voltage and said first bit line voltage is greater than the voltage difference between said second word line voltage and said second bit line voltage.

11. The nonvolatile semiconductor memory device according to claim 1, wherein

said variable resistive element is made of an oxide having a perovskite structure that contains manganese.

12. The nonvolatile semiconductor memory device according to claim 1, comprising:

a bit line selector circuit for selecting a bit line connected to a selected memory cell to be read and for connecting the selected bit line to a read data line;

a comparator circuit for comparing the potential of said read data line with a reference potential; and

a read circuit that includes a fixed resistor where one end of the fixed resistor is connected to said read data line and a predetermined fixed voltage is applied to the other end of the fixed resistor.

13. The nonvolatile semiconductor memory device according to claim 12, wherein

the resistance value of said fixed resistor is set at a resistance value in a low resistance condition of said variable resistive element, said word line voltage application circuit applies the selected first word line voltage to the selected word line connected to the selected memory cell to be read and applies the selected second word line voltage to the unselected word lines other than said selected word line at the time of the reading operation,

said bit line voltage application circuit is in a high impedance condition where no voltage is applied to any of said bit lines in said memory array at the time of the reading operation, and

said first word line voltage is set so that the voltage difference between said first word line voltage and said second word line voltage is no more than said second voltage difference, and said second word line voltage is set at the value of said predetermined fixed voltage.

14. The nonvolatile semiconductor memory device according to claim 1, wherein

said memory array is formed of a plurality of sub-arrays from which one sub-array can arbitrarily be selected, and

said word line voltage application circuit is formed so as to selectively apply said word line voltage to a word line of the selected sub-array and said bit line voltage application circuit is formed so as to selectively apply said bit line voltage to a bit line of the selected sub-array, respectively.

15. The nonvolatile semiconductor memory device according to claim 14, wherein

a signal for selecting a sub-array from among said plurality of sub-arrays is generated from an address signal.

16. A programming method of a nonvolatile semiconductor memory device, wherein

said nonvolatile semiconductor memory device comprises a memory array formed of a plurality of memory cells, each having a variable resistive element of which the resistance value is changed in a reversible manner by applying a voltage, aligned in the directions of rows and columns, respectively, in a manner where one end of each memory cell in the same row is connected to the same word line and the other end of each memory cell in the same column is connected to the same bit line,

a first word line voltage, a second word line voltage, a first bit line voltage and a second bit line voltage are set at particular voltage values in accordance with programming operation so that the voltage difference between said first word line voltage and said first bit line voltage is no less than a first voltage difference that allows the resistance value of said variable resistive element to exceed a predetermined value as a result of a change in the case where the first voltage difference is applied across both ends of said variable resistive element and so that the voltage difference between said first word line voltage and said second bit line voltage, the voltage difference between said second word line voltage and said first bit line voltage and the voltage difference between said second word line voltage and said second bit line voltage are no more than a second voltage difference that does not allows the resistance value of said variable resistive element to exceed a predetermined value as a result of a change in the case where the second voltage difference is applied across the both ends of said variable resistive element, and

at the time of programming operation, said first word line voltage is selected and applied to the selected word line connected to a selected memory cell to be programmed;

said second word line voltage is selected and applied to the unselected word lines other than said selected word line;

said first bit line voltage is selected and applied to the selected bit line connected to said selected memory cell; and

said second bit line voltage is selected and applied to the unselected bit lines other than said selected bit line.

17. The programming method according to claim 16, wherein

said second word line voltage is selected and applied to all of said word lines in said memory array before the start of the programming operation of said memory array, and said second bit line voltage is selected and applied to all of said bit lines in said memory array.

18. The programming method according to claim 16, wherein

said variable resistive element has resistance varying characteristics where the resistance value of said variable resistive element increases to exceed a predetermined value when a voltage which is equal to or more than a first threshold voltage is applied across both ends of said variable resistive element and the resistance value of said variable resistive element decreases to exceed a predetermined value when a voltage which is equal to or more than a second threshold voltage which has the polarities opposite to those of said first threshold voltage is applied across both ends of said variable resistive element, and

said second voltage difference is set at a value lower than the threshold voltage which is the lower of either said first threshold voltage or said second threshold voltage.

19. The programming method according to claim 18, wherein said second threshold voltage is lower than said first threshold voltage.

20. The programming method according to claim 16, wherein

said first word line voltage, said second word line voltage, said first bit line voltage and said second bit line voltage are set as follows:

said first word line voltage is higher than said second bit line voltage;

said second bit line voltage is no less than said second word line voltage; and

said second word line voltage is higher than said first bit line voltage.

21. The programming method according to claim 20, wherein

the voltage difference between said first word line voltage and said second bit line voltage, the voltage difference between said second word line voltage and said first bit line voltage and the voltage difference between said second word line voltage and said second bit line voltage are equal to one another.

22. The programming method according to claim 20, wherein

the voltage difference between said first word line voltage and said second bit line voltage and the voltage difference between said second word line voltage and said first bit line voltage are greater than the voltage difference between said second word line voltage and said second bit line voltage.

23. The programming method according to claim 16, wherein

said variable resistive element is made of an oxide having a perovskite structure that contains manganese.

24. The programming method according to claim 16, wherein

said memory array is formed of a plurality of sub-arrays from which one sub-array can arbitrarily be selected, and

said first word line voltage is selectively applied to the selected word line of the selected sub-array and said first bit line voltage is selectively applied to the selected bit line of said selected sub-array, respectively.

25. The programming method according to claim 24, wherein

said second word line voltage is selectively applied to said unselected word lines of said selected sub-array in the case where said unselected word lines are included in said selected sub-array, and

said second bit line voltage is selectively applied to said unselected bit lines of said selected sub-array in the case where said unselected bit lines are included in said selected sub-array.

26. The programming method according to claim 24, wherein

a signal for selecting a sub-array from among said plurality of sub-arrays is generated from an address signal.

27. An erasing method of a nonvolatile semiconductor memory device, wherein

said nonvolatile semiconductor memory device comprises a memory array formed of a plurality of memory cells, each having a variable resistive element of which the resistance value is changed in a reversible manner by applying a voltage, aligned in the directions of rows and columns, respectively, in a manner where one end of each memory cell in the same row is connected to the same word line and the other end of each memory cell in the same column is connected to the same bit line,

a first word line voltage, a second word line voltage, a first bit line voltage and a second bit line voltage are set at particular voltage values in accordance with erasing operation so that the voltage difference between said first word line voltage and said first bit line voltage is no less than a first voltage difference that allows the resistance value of said variable resistive element to exceed a predetermined value as a result of a change in the case where the first voltage difference is applied across both ends of said variable resistive element and so that the voltage difference between said first word line voltage and said second bit line voltage, the voltage difference between said second word line voltage and said first bit line voltage and the voltage difference between said second word line voltage and said second bit line voltage are no more than a second voltage difference that does not allows the resistance value of said variable resistive element to exceed a predetermined value as a result of a change in the case where the second voltage difference is applied across the both ends of said variable resistive element, and

at the time of erasing operation, said first word line voltage is selected and applied to the selected word line connected to a selected memory cell to be erased;

said second word line voltage is selected and applied to the unselected word lines other than said selected word line;

said first bit line voltage is selected and applied to the selected bit line connected to said selected memory cell; and

said second bit line voltage is selected and applied to the unselected bit lines other than said selected bit line.

28. The erasing method according to claim 27, wherein

said second word line voltage is selected and applied to all of said word lines in said memory array before the start of the erasing operation of said memory array, and said second bit line voltage is selected and applied to all of said bit lines in said memory array.

29. The erasing method according to claim 27, wherein

said variable resistive element has resistance varying characteristics where the resistance value of said variable resistive element increases to exceed a predetermined value when a voltage which is equal to or more than a first threshold voltage is applied across both ends of said variable resistive element and the resistance value of said variable resistive element decreases to exceed a predetermined value when a voltage which is equal to or more than a second threshold voltage which has the polarities opposite to those of said first threshold voltage is applied across both ends of said variable resistive element, and

said second voltage difference is set at a value lower than the threshold voltage which is the lower of either said first threshold voltage or said second threshold voltage.

30. The erasing method according to claim 29, wherein

said second threshold voltage is lower than said first threshold voltage.

31. The erasing method according to claim 27, wherein

said first word line voltage, said second word line voltage, said first bit line voltage and said second bit line voltage are set as follows:

said first word line voltage is lower than said second bit line voltage;

said second bit line voltage is no more than said second word line voltage; and

said second word line voltage is lower than said first bit line voltage.

32. The erasing method according to claim 31, wherein

the voltage difference between said first word line voltage and said second bit line voltage, the voltage difference between said second word line voltage and said first bit line voltage and the voltage difference between said second word line voltage and said second bit line voltage are equal to one another.

33. The erasing method according to claim 31, wherein

the voltage difference between said first word line voltage and said second bit line voltage and the voltage difference between said second word line voltage and said first bit line voltage are greater than the voltage difference between said second word line voltage and said second bit line voltage.

34. The erasing method according to claim 27, wherein

said variable resistive element is made of an oxide having a perovskite structure that contains manganese.

35. The erasing method according to claim 27, wherein

said memory array is formed of a plurality of sub-arrays from which one sub-array can arbitrarily be selected, and

said first word line voltage is selectively applied to the selected word line of the selected sub-array and said first bit line voltage is selectively applied to the selected bit line of said selected sub-array, respectively.

36. The erasing method according to claim 35, wherein

said second word line voltage is selectively applied to said unselected word lines of said selected sub-array in the case where said unselected word lines are included in said selected sub-array, and

said second bit line voltage is selectively applied to said unselected bit lines of said selected sub-array in the case where said unselected bit lines are included in said selected sub-array.

37. The erasing method according to claim 35, wherein

a signal for selecting a sub-array from among said plurality of sub-arrays is generated from an address signal.