Method and apparatus for generating temperature-compensated read and verify operations in flash memories

• US 7,277,355 B2
• Filed: 08/29/2005
• Issued: 10/02/2007
• Est. Priority Date: 08/26/2005
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Tanzawa, Toru
• Primary Examiner(s): PHAN, TRONG Q
• Application Number:
  US11/215,836
• Publication Number:
  US 20070047335A1
• Time in Patent Office: 764 Days
• Field of Search: 365/230.06, 365/211, 365/185.22, 365/185.23, 365/185.03
• US Class Current: 365/230.06
• CPC Class Codes: G11C 16/08 Address circuits; Decoders; Word-line control circuits
• CPC Class Codes: G11C 16/30 Power supply circuits
• CPC Class Codes: G11C 5/14 Power supply arrangements , e.g. power down, chip selection or deselection, layout of wirings or power grids, or multiple supply levels
• CPC Class Codes: G11C 7/04 with means for avoiding disturbances due to temperature effects
• CPC Class Codes: G11C 8/08 Word line control circuits, e.g. drivers, boosters, pull-up circuits, pull-down circuits, precharging circuits, for word lines

Abstract

Methods and an apparatuses for generating a word-line voltage are disclosed. A word-line voltage generator includes a first current source, an adjustable current source, adjustable current sink, and a voltage converter, all operably coupled to a current sum node. The first current source generates a first current having a temperature coefficient substantially equal to a temperature coefficient of at least one bit cell. The adjustable current source generates a second current that is substantially independent of a temperature change. The adjustable current sink sinks a third current that is substantially independent of a temperature change. The voltage converter is configured for generating a word-line signal having a word-line voltage proportional to a reference current, wherein the reference current comprises the first current, plus the second current, and minus the third current.

Claims

1. A word-line voltage generator, comprising:

a first current source operably coupled to a current sum node and configured for generating a first current wherein a voltage derived from the first current comprises a temperature coefficient substantially equal to a temperature coefficient of a threshold voltage of at least one bit cell;

an adjustable current source operably coupled to the current sum node and configured for generating a second current that is substantially independent of a temperature change; and

a voltage converter operably coupled to the current sum node and configured for generating a word-line signal having a word-line voltage proportional to a reference current, wherein the reference current comprises a sum of the first current and the second current.

2. The word-line voltage generator of claim 1, wherein the first current source comprises a p-channel transistor, comprising:

a source operably coupled to a voltage source;

a drain operably coupled to the current sum node; and

a gate operably coupled to a temperature-compensated bias signal from a matching current controller.

3. The word-line voltage generator of claim 2, wherein the matching current controller comprises:

a matched current source for generating a first current signal and a substantially equal second current signal, wherein the temperature-compensated bias signal is related to the second current signal;

a first P-N junction element operably coupled between the first current signal and a ground; and

a first resistance element operably coupled between the second current signal and the ground.

4. The word-line voltage generator of claim 2, wherein the matching current controller comprises:

a matched current source for generating a first current signal and a substantially equal second current signal, wherein the temperature-compensated bias signal is related to the second current signal;

a first P-N junction element operably coupled between the first current signal and a ground; and

a first resistance element and a second P-N junction element operably coupled in series between the second current signal and the ground.

5. The word-line voltage generator of claim 2, wherein the matching current controller comprises:

a matched current source for generating a first current signal and a substantially equal second current signal, wherein the temperature-compensated bias signal is related to the second current signal;

a first P-N junction element operably coupled between the first current signal and a ground;

a first resistance element and a second P-N junction element operably coupled in series between the second current signal and the ground; and

a second resistance element operably coupled between the second current signal and the ground.

6. The word-line voltage generator of claim 5, wherein the first resistance element is configured to be selectably variable and the second resistance element is configured to be selectably variable.

7. The word-line voltage generator of claim 2, wherein the matching current controller generates the temperature-compensated bias signal from a biased current flowing through a flash cell substantially similar to the at least one bit cell.

8. The word-line voltage generator of claim 1, wherein the adjustable current source is configured to generate a first source current during a verify process and a second source current during a read process.

9. The word-line voltage generator of claim 1, wherein the adjustable current source further comprises a plurality of current source generators configured for generating the second current at a plurality of different current source levels.

10. The word-line voltage generator of claim 9, wherein one of the plurality of different current source levels is generated during a verify process and another of the plurality of different current source levels is generated during a read process.

11. The word-line voltage generator of claim 9, wherein the at least one bit cell is at least one multi-level bit cell, and wherein at least one of the plurality of different current source levels is generated for a first voltage level of the at least one multi-level bit cell, and wherein at least one additional of the plurality of different current source levels is generated for an additional voltage level of the at least one multi-level bit cell.

12. A word-line voltage generator, comprising:

a first current source operably coupled to a current sum node and configured for generating a first current wherein a voltage derived from the first current comprises a temperature coefficient substantially equal to a temperature coefficient of a threshold voltage of at least one bit cell;

an adjustable current source operably coupled to the current sum node and configured for generating a second current that is substantially independent of a temperature change;

an adjustable current sink operably coupled to the current sum node and configured for sinking a third current that is substantially independent of the temperature change; and

a voltage converter operably coupled to the current sum node and configured for generating a word-line signal having a word-line voltage proportional to a reference current, wherein the reference current comprises the first current, plus the second current, and minus the third current.

13. The word-line voltage generator of claim 12, wherein the first current source comprises a p-channel transistor, comprising:

a source operably coupled to a voltage source;

a drain operably coupled to the current sum node; and

a gate operably coupled to a temperature-compensated bias signal from a matching current controller.

14. The word-line voltage generator of claim 13, wherein the matching current controller comprises:

a matched current source for generating a first current signal and a substantially equal second current signal, wherein the temperature-compensated bias signal is related to the second current signal;

a first P-N junction element operably coupled between the first current signal and a ground; and

a first resistance element operably coupled between the second current signal and the ground.

15. The word-line voltage generator of claim 13, wherein the matching current controller comprises:

a matched current source for generating a first current signal and a substantially equal second current signal, wherein the temperature-compensated bias signal is related to the second current signal;

a first P-N junction element operably coupled between the first current signal and a ground; and

a first resistance element and a second P-N junction element operably coupled in series between the second current signal and the ground.

16. The word-line voltage generator of claim 13, wherein the matching current controller comprises:

a matched current source for generating a first current signal and a substantially equal second current signal, wherein the temperature-compensated bias signal is related to the second current signal;

a first P-N junction element operably coupled between the first current signal and a ground;

a first resistance element and a second P-N junction element operably coupled in series between the second current signal and the ground; and

a second resistance element operably coupled between the second current signal and the ground.

17. The word-line voltage generator of claim 16, wherein the first resistance element is configured to be selectably variable and the second resistance element is configured to be selectably variable.

18. The word-line voltage generator of claim 13, wherein the matching current controller generates the temperature-compensated bias signal from a biased current flowing through a flash cell substantially similar to the at least one bit cell.

19. The word-line voltage generator of claim 12, wherein the adjustable current source is configured to generate a first source current during a verify process and a second source current during a read process.

20. The word-line voltage generator of claim 19, wherein the adjustable current sink is configured to generate a first sink current during the verify process and a second sink current during the read process.

21. The word-line voltage generator of claim 20, wherein the first sink current is substantially zero during the verify process and the first source current is substantially zero during the read process.

22. The word-line voltage generator of claim 12, wherein the adjustable current source further comprises a plurality of current source generators configured for generating the second current at a plurality of different current source levels.

23. The word-line voltage generator of claim 22, wherein one of the plurality of different current source levels is generated during a verify process and another of the plurality of different current source levels is generated during a read process.

24. The word-line voltage generator of claim 12, wherein the adjustable current sink further comprises a plurality of current sink generators configured for generating the third current at a plurality of different current sink levels.

25. The word-line voltage generator of claim 24, wherein one of the plurality of different current sink levels is generated during a verify process and another of the plurality of different current sink levels is generated during a read process.

26. The word-line voltage generator of claim 24, wherein the at least one bit cell is at least one multi-level bit cell, and wherein at least one of the plurality of different current source levels is generated for a first voltage level of the at least one multi-level bit cell, and wherein at least one additional of the plurality of different current source levels is generated for an additional voltage level of the at least one multi-level bit cell.

27. A method, comprising:

generating a first current wherein a voltage derived from the first current comprises a temperature coefficient substantially equal to a temperature coefficient of a threshold voltage of at least one bit cell;

generating a second current from an adjustable current source, wherein the second current is substantially independent of a temperature change;

combining the first current and the second current to generate a reference current; and

converting the reference current to a word-line voltage by directing the reference current through a voltage converter.

28. The method of claim 27, wherein generating the second current further comprises:

generating a first source current during a verify process; and

generating a second source current during a read process.

29. The method of claim 27, wherein generating the second current further comprises:

generating a first source current during a verify process; and

generating a second source current during a read process.

30. The method of claim 27, wherein generating the second current further comprises generating the second current from a plurality of different current source levels.

31. The method of claim 30, wherein generating the second current from a plurality of different current source levels further comprises:

generating one of the plurality of different current source levels during a verify process; and

generating another of the plurality of different current source levels during a read process.

32. The method of claim 27, wherein generating the second current further comprises:

generating one of a plurality of different current source levels for a first voltage level of at least one multi-level bit cell; and

generating another of the plurality of different current source levels for an additional voltage level of the at least one multi-level bit cell.

33. The method of claim 27, further comprising:

generating a third current from an adjustable current sink, wherein the third current is substantially independent of the temperature change; and

combining the third current with the first current and the second current to generate the reference current.

34. The method of claim 33, wherein generating the third current further comprises:

generating a first sink current during a verify process; and

generating a second sink current during a read process.

35. The method of claim 33, wherein generating the third current further comprises generating the third current from a plurality of different current sink levels.

36. The method of claim 35, wherein selecting the third current further comprises:

generating one of the plurality of different current sink levels during a verify process; and

generating another of the plurality of different current sink levels during a read process.

37. The method of claim 35, wherein generating the second current further comprises generating the second current from a plurality of different current source levels.

38. The method of claim 37, wherein generating the second current further comprises:

generating one of the plurality of different current source levels during a verify process; and

generating another of the plurality of different current source levels during a read process.

39. A semiconductor memory including at least one word-line voltage generator, comprising:

a first current source operably coupled to a current sum node and configured for generating a first current wherein a voltage derived from the first current comprises a temperature coefficient substantially equal to a temperature coefficient of a threshold voltage of at least one bit cell;

an adjustable current source operably coupled to the current sum node and configured for generating a second current that is substantially independent of a temperature change; and

a voltage converter operably coupled to the current sum node and configured for generating a word-line signal having a word-line voltage proportional to a reference current, wherein the reference current comprises a sum of the first current and the second current.

40. A semiconductor memory including at least one word-line voltage generator, comprising:

a first current source operably coupled to a current sum node and configured for generating a first current wherein a voltage derived from the first current comprises a temperature coefficient substantially equal to a temperature coefficient of a threshold voltage of at least one bit cell;

an adjustable current source operably coupled to the current sum node and configured for generating a second current that is substantially independent of a temperature change;

an adjustable current sink operably coupled to the current sum node and configured for sinking a third current that is substantially independent of the temperature change; and

a voltage converter operably coupled to the current sum node and configured for generating a word-line signal having a word-line voltage proportional to a reference current, wherein the reference current comprises the first current, plus the second current, and minus the third current.

41. A semiconductor wafer, comprising:

at least one semiconductor device including at least one word-line voltage generator, comprising;

a first current source operably coupled to a current sum node and configured for generating a first current wherein a voltage derived from the first current comprises a temperature coefficient substantially equal to a temperature coefficient of a threshold voltage of at least one bit cell;

an adjustable current source operably coupled to the current sum node and configured for generating a second current that is substantially independent of a temperature change; and

a voltage converter operably coupled to the current sum node and configured for generating a word-line signal having a word-line voltage proportional to a reference current, wherein the reference current comprises a sum of the first current and the second current.

42. A semiconductor wafer, comprising:

at least one semiconductor device including at least one word-line voltage generator, comprising;

a first current source operably coupled to a current sum node and configured for generating a first current wherein a voltage derived from the first current comprises a temperature coefficient substantially equal to a temperature coefficient of a threshold voltage of at least one bit cell;

an adjustable current source operably coupled to the current sum node and configured for generating a second current that is substantially independent of a temperature change;

an adjustable current sink operably coupled to the current sum node and configured for sinking a third current that is substantially independent of the temperature change; and

a voltage converter operably coupled to the current sum node and configured for generating a word-line signal having a word-line voltage proportional to a reference current, wherein the reference current comprises the first current, plus the second current, and minus the third current.

43. An electronic system, comprising:

at least one input device;

at least one output device;

a processor; and

a memory device comprising at least one semiconductor memory including at least one word-line voltage generator, comprising;

a first current source operably coupled to a current sum node and configured for generating a first current wherein a voltage derived from the first current comprises a temperature coefficient substantially equal to a temperature coefficient of a threshold voltage of at least one bit cell;

an adjustable current source operably coupled to the current sum node and configured for generating a second current that is substantially independent of a temperature change; and

a voltage converter operably coupled to the current sum node and configured for generating a word-line signal having a word-line voltage proportional to a reference current, wherein the reference current comprises a sum of the first current and the second current.

44. An electronic system, comprising:

at least one input device;

at least one output device;

a processor; and

a memory device comprising at least one semiconductor memory including at least one word-line voltage generator, comprising;

a first current source operably coupled to a current sum node and configured for generating a first current wherein a voltage derived from the first current comprises a temperature coefficient substantially equal to a temperature coefficient of a threshold voltage of at least one bit cell;

an adjustable current source operably coupled to the current sum node and configured for generating a second current that is substantially independent of a temperature change;

an adjustable current sink operably coupled to the current sum node and configured for sinking a third current that is substantially independent of the temperature change; and

a voltage converter operably coupled to the current sum node and configured for generating a word-line signal having a word-line voltage proportional to a reference current, wherein the reference current comprises the first current, plus the second current, and minus the third current.