Precision programming of nonvolatile memory cells

• US 6,038,174 A
• Filed: 11/20/1998
• Issued: 03/14/2000
• Est. Priority Date: 03/06/1997
• Status: Expired due to Term

• Current Assignee: Silicon Storage Technology Incorporated (Microchip Technology Incorporated)
• Original Assignee: Agate Semiconductor, Inc. (Microchip Technology Incorporated)
• Inventors: Korsh, George J., Khan, Sakhawat M.
• Primary Examiner(s): Nelms, David
• Assistant Examiner(s): Ho, Hoai V.
• Application Number:
  US09/197,479
• Time in Patent Office: 480 Days
• Field of Search: 365/185.28, 365/185.18, 365/185.03, 365/185.22, 365/185.29
• US Class Current: 365/185.28
• CPC Class Codes: G11C 11/5621 using charge storage in a floating gate
• CPC Class Codes: G11C 11/5628 Programming or writing circuits; Data input circuits
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/10 Programming or data input circuits
• CPC Class Codes: G11C 16/3454 Arrangements for verifying correct programming or for detecting overprogrammed cells
• CPC Class Codes: G11C 16/3459 Circuits or methods to verify correct programming of nonvolatile memory cells
• CPC Class Codes: G11C 16/3468 Prevention of overerasure or overprogramming, e.g. by verifying whilst erasing or writing
• CPC Class Codes: G11C 2211/5621 Multilevel programming verification
• CPC Class Codes: G11C 2211/5622 Concurrent multilevel programming of more than one cell
• CPC Class Codes: G11C 2211/5645 Multilevel memory with current-mirror arrangements
• CPC Class Codes: G11C 27/005 with non-volatile charge storage, e.g. on floating gate or MNOS
• CPC Class Codes: G11C 7/1048 Data bus control circuits, e.g. precharging, presetting, equalising

Abstract

An integrated circuit memory system and method for precision hot carrier injection programming of single or plurality of nonvolatile memory cells is described. Each program cycle is followed by a verify cycle. Precision programming is achieved by incrementally changing a programming current pulse flowing between the source and drain in the memory cell during successive program cycles and a constant current during successive verify cycles. Current control and voltage mode sensing circuitry reduces circuit complexity, reduces programming cell current, lowers power dissipation, and enables page mode operation. Precision programming is useful for multilevel digital and analog information storage.

Claims

1. An integrated circuit memory system comprising:

control means for controlling operations of said integrated circuit memory system;

a plurality of memory cells, each memory cell comprising a source, drain, control gate and floating gate, said floating gate capable of storing electric charge, said memory cells programmable by hot carrier injection of electric charge to said floating gate corresponding to input signals to said integrated memory system; and

circuit means, responsive to said control means, for iteratively applying incrementally varying voltages to a source, drain, or control gate of a selected memory cell and for controlling a current independently of said input signals, said current flowing between said source and drain during programming of said selected memory cell so that an amount of electric charge stored on said floating gate of said selected memory cell is precisely controlled.

3. The system of claim 1 wherein said circuit means applies incrementally increasing voltages to said control gate of said selected memory cell during iterative programming of said selected memory cell.

4. The system of claim 1 wherein said circuit means applies incrementally decreasing voltages to said control gate of said selected memory cell during iterative programming of said selected memory cell.

5. The system of claim 1 wherein said circuit means applies incrementally increasing voltages to said drain of said selected memory cell during iterative programming of said selected memory cell.

6. The system of claim 1 wherein said circuit means applies incrementally increasing voltages to said source of said selected memory cell during iterative programming of said selected memory cell.

7. The system of claim 1 wherein said circuit means increases current magnitude incrementally during iterative programming of said selected memory cell.

8. The system of claim 1 wherein said circuit means increases current duration incrementally during iterative programming of said selected memory cell.

9. The system of claim 1 wherein said circuit means operates on a selected plurality of memory cells so that said selected plurality of memory cells are programmed as a group.

10. The system of claim 9 wherein said plurality of memory cells are arranged in an array of rows and columns and wherein said circuit means operates on said selected plurality of memory cells in a selected row as a group.

11. The system of claim 10 wherein said circuit means comprises a plurality of control blocks, one of said plurality of control blocks connected to one of said selected plurality of memory cells during programming.

12. The system of claim 10 wherein each memory cell in a row has a source and control gate respectively connected in common to said circuit means, and each memory cell in a column has a drain connected in common to said circuit means.

13. The system of claim 10 wherein each memory cell in a row has a control gate connected in common to said circuit means, and each memory cell in a column has a source and a drain respectively connected in common to said circuit means.

14. The system of claim 1 wherein said circuit means controls said current between said source and drain of said selected memory cell independently of any electrical characteristics of said selected memory cell.

15. The system of claim 1 wherein said circuit means controls said current between said source and drain of said selected memory cell independently of any charge stored in said selected memory cell.

2. In an integrated memory system having a plurality of memory cells, each memory cell comprising a source, drain, control gate and floating gate, said floating gate capable of storing electric charge, said memory cells programmable by hot carrier injection corresponding to input signals to said integrated memory system, a method for programming said memory cells comprising:

iteratively applying incrementally varying voltages to a source, drain, or control gate of a selected memory cell and controlling a current independently of said input signals, said current flowing between said source and drain of said selected memory cell so that an amount of electric charge stored on said floating gate of said selected memory cell is precisely controlled.

42. The method of claim 2 wherein said iterative applying and controlling step comprises applying incrementally increasing voltages to said control gate of said selected memory cell.

43. The method of claim 2 wherein said iterative applying and controlling step comprises applying incrementally increasing voltages to said drain of said selected memory cell.

44. The method of claim 2 wherein said iterative applying and controlling step comprises applying incrementally increasing voltages to said source of said selected memory cell.

45. The method of claim 2 wherein said iterative applying and controlling step comprises incrementally increasing current magnitude.

46. The method of claim 2 wherein said iterative applying and controlling step comprises incrementally increasing current duration.

47. The method of claim 2 further comprising:

selecting a plurality of said memory cells; and

applying incrementally varying voltages to a source, drain, or control gate and controlling the current flowing between said source and drain of each of said selected plurality of memory cells as a group independently of said input signals so that an amount of electric charge stored on said floating gate of each of said selected plurality of memory cells is precisely controlled to program said selected plurality of memory cells as a group.

48. The method of claim 47 further comprising:

arranging said plurality of memory cells in an array of rows and columns; and

wherein said selecting step comprises;

selecting one of said rows and selecting a plurality of memory cells within said selected row.

49. The method of claim 2 wherein said applying voltage and current controlling step comprises controlling said current between said source and drain of said selected memory cell independently of any electrical characteristics of said selected memory cell.

50. The method of claim 2 wherein said applying voltage and current controlling step comprises controlling said current between said source and drain of said selected memory cell independently of any charge stored in said selected memory cell.

16. An integrated circuit memory system comprising:

control means for controlling operations of said integrated circuit memory system;

a plurality of memory cells, each memory cell comprising a source, drain, control gate and floating gate, said floating gate capable of storing electric charge, said memory cells programmable by hot carrier injection of electric charge to said floating gate corresponding to input signals to said integrated circuit memory system; and

circuit means, responsive to said control means, for iteratively applying preselected voltages to a source, drain, and control gate of a selected memory cell and for controlling a current independently of said input signals, said current flowing between said source and drain during programming of said selected memory cell, said current varying incrementally during said iterative programming so that an amount of electric charge stored on a floating gate of said selected memory cell is precisely controlled.

17. The system of claim 16 wherein said circuit means increases current magnitude incrementally during iterative programming of said selected memory cell.

18. The system of claim 16 wherein said circuit means increases current duration incrementally during iterative programming of said selected memory cell.

19. The system of claim 16 wherein said circuit means operates on a selected plurality of memory cells so that said selected plurality of memory cells are programmed as a group.

20. The system of claim 19 wherein said plurality of memory cells are arranged in an array of rows and columns and wherein said circuit means operates on said selected plurality of memory cells in a selected row as a group.

21. The system of claim 20 wherein said circuit means comprises a plurality of control blocks, one of said plurality of control blocks connected to one of said selected plurality of memory cells during programming.

22. The system of claim 20 wherein each memory cell in a row has a source and control gate respectively connected in common to said circuit means, and each memory cell in a column has a drain connected in common to said circuit means.

23. The system of claim 20 wherein each memory cell in a row has a control gate connected in common to said circuit means, and each memory cell in a column has a source and a drain respectively connected in common to said circuit means.

24. The system of claim 16 wherein said circuit means controls said current between said source and drain of said selected memory cell independently of any electrical characteristics of said selected memory cell.

25. The system of claim 16 wherein said circuit means controls said current between said source and drain of said selected memory cell independently of any charge stored in said selected memory cell.

26. An integrated circuit memory system comprising:

a system control block;

an array of memory cells, each memory cell having a first terminal, a second terminal, a control gate and a floating gate, said floating gate capable of storing electric charge, said memory cells programmable by hot carrier injection of electric charge to said floating gate corresponding to input signals to said integrated circuit memory system;

a first control block connected to a first terminal of a memory cell selected for programming, said first control block generating preselected programming voltages independently of said input signals;

a second control block connected to a second terminal of said selected memory cell, said second control block generating preselected controlled currents independently of said input signals; and

a third control block connected to a control gate of said selected memory cell, said third control block generating incrementally varying programming voltages independently of said input signals;

whereby said first, second and third control blocks, responsive to said system control block, cooperatively control currents flowing between said first terminal and said second terminal during iterative programming of said selected memory cell so that an amount of electric charge stored on a floating gate of said selected memory cell is precisely controlled.

27. The system of claim 26 wherein said third control block generates incrementally increasing programming voltages independently of said input signals.

28. The system of claim 26 wherein said third control block generates incrementally decreasing programming voltages independently of said input signals.

29. The system of claim 26 wherein said first, second and third control blocks operate on a selected plurality of memory cells so that said selected plurality of memory cells is programmed as a group.

30. The system of claim 26 wherein said second control block comprises:

a current control circuit connected to said second terminal of said selected memory cell and driving said controlled currents through said selected memory cell during programming.

31. The system of claim 30 wherein said current control circuit iteratively drives said controlled currents through said selected memory cell during programming of said selected memory cell, said controlled currents increasing in magnitude in subsequent iterations.

32. The system of claim 31 wherein said controlled currents have a magnitude range of 0.5 μ

A to 50 μ

A.

33. The system of claim 30 wherein said current control circuit iteratively drives said controlled currents through said selected memory cell during programming of said selected memory cell, said controlled currents increasing in duration in subsequent iterations.

34. The system of claim 33 wherein said controlled currents have a duration of 1 μ

s to 10 μ

s.

35. An integrated circuit memory system comprising:

a system control block;

an array of memory cells, each memory cell having a first terminal, a second terminal, a control gate and a floating gate, said floating gate capable of storing electric charge, said memory cells programmable by hot carrier injection of electric charge to said floating gate corresponding to input signals to said integrated circuit memory system;

a first control block connected to a first terminal of a memory cell selected for programming, said first control block generating incrementally increasing programming voltages independently of said input signals;

a second control block connected to a second terminal of said selected memory cell, said second control block generating preselected controlled currents independently of said input signals; and

a third control block connected to a control gate of said selected memory cell, said third control block generating preselected programming voltages independently of said input signals;

whereby said first, second and third control blocks, responsive to said system control block, cooperatively control currents flowing between said first terminal and said second terminal during iterative programming of said selected memory cell so that an amount of electric charge stored on a floating gate of said selected memory cell is precisely controlled.

36. The system of claim 35 wherein said first, second and third control blocks operate on a selected plurality of memory cells so that said selected plurality of memory cells is programmed as a group.

37. The system of claim 35 wherein said second control block comprises:

a current control circuit connected to said second terminal of said selected memory cell and driving said controlled currents through said selected memory cell during programming.

38. The system of claim 37 wherein said current control circuit iteratively drives said controlled currents through said selected memory cell during programming of said selected memory cell, said controlled currents increasing in magnitude in subsequent iterations.

39. The system of claim 38 wherein said controlled currents have a magnitude range of 0.5 μ

A to 50 μ

A.

40. The system of claim 37 wherein said current control circuit iteratively drives said controlled currents through said selected memory cell during programming of said selected memory cell, said controlled currents increasing in duration in subsequent iterations.

41. The system of claim 40 wherein said controlled currents have a duration of 1 μ

s to 10 μ

s.

51. In an integrated memory system having a plurality of memory cells, each memory cell comprising a source, drain, control gate and floating gate, said floating gate capable of storing electric charge, said memory cells programmable by hot carrier injection corresponding to input signals to said integrated memory system, a method for programming said memory comprising:

iteratively applying preselected voltages to a source, drain, and control gate of a selected memory cell and controlling a current independently of said input signals, said current flowing between a source and drain of said selected memory cell, said current varying incrementally so that an amount of electric charge stored on a floating gate of said selected memory cell is precisely controlled.

52. The method of claim 51 wherein said iterative applying and controlling step comprises increasing current magnitude incrementally.

53. The method of claim 51 wherein said iterative applying and controlling step comprises increasing current duration incrementally.

54. The method of claim 51 further comprising:

selecting a plurality of said memory cells; and

iteratively applying preselected voltages to a source, drain, and control gate and controlling the current flowing between said source and drain, said current varying incrementally, of each of said selected plurality of memory cells as a group independently of said input signals so that an amount of electric charge stored on said floating gate of each of said selected plurality of memory cells is precisely controlled to program said selected plurality of memory cells as a group.

55. The method of claim 54 further comprising:

arranging said plurality of memory cells in an array of rows and columns; and

wherein said selecting step comprises;

selecting one of said rows and selecting a plurality of memory cells within said selected row.

56. The method of claim 51 wherein said applying voltage and current controlling step comprises controlling said current between said source and drain of said selected memory cell independently of any electrical characteristics of said selected memory cell.

57. The method of claim 51 wherein said applying voltage and current controlling step comprises controlling said current between said source and drain of said selected memory cell independently of any charge stored in said selected memory cell.

58. In an integrated circuit memory system having an array of memory cells, each memory cell comprising a first terminal, a second terminal, a control gate and a floating gate, said floating gate capable of storing electric charge, said memory cells programmable by hot carrier injection corresponding to input signals to said integrated circuit memory system, a method for programming a selected memory cell comprising:

applying erase voltages to said first terminal, said second terminal, and said control gate of said selected memory cell so that said electric charge corresponding to input signals is removed from said floating gate to erase said selected memory cell;

applying preselected programming voltages to said first terminal, said second terminal, and control gate and controlling the current flowing between said first terminal and said second terminal of said selected memory cell independently of said input signals so that an amount of electric charge stored on said floating gate is precisely controlled to program said selected memory cell; and

applying programming verify voltages to said first terminal and said control gate, comparing said voltage at said second terminal of said selected memory cell with respect to a program reference voltage to verify that said selected memory cell is programmed; and

repeating said programming voltages and programming verify voltages applying steps until a programming verify voltages applying step verifies that said selected memory cell is programmed, said preselected programming voltages incrementally increasing on said first terminal, said second terminal, or said control gate of said selected memory cell at each repetition.

59. The method of claim 58 wherein said programming voltage applying and current controlling step comprises incrementally increasing said programming voltages applied to said control gate of said selected memory cell in subsequent repetitions.

60. The method of claim 59 further comprising applying said erase voltages, said programming voltages and said programming verify voltages to a selected plurality of memory cells as a group to program said selected plurality of memory cells.

61. The method of claim 59 wherein said programming voltage applying and current controlling step comprises incrementally increasing magnitude of said current flowing between said first terminal and said second terminal in subsequent repetitions.

62. The method of claim 61 wherein said magnitude of said current is in a range of 0.5 μ

A to 50 μ

A.

63. The method of claim 59 wherein said programming voltage applying and current controlling step comprises incrementally increasing duration of said current flowing between said first terminal and said second terminal in subsequent repetitions.

64. The method of claim 63 wherein said duration of said current is in a range of 1 μ

s to 10 μ

s.

65. The method of claim 58 wherein said programming voltage applying and current controlling step comprises incrementally increasing said programming voltages applied to said first terminal of said selected memory cell in subsequent repetitions.

66. The method of claim 58 further comprising applying said erase voltages, said programming voltages and said programming verify voltages to a selected plurality of memory cells as a group to program said selected plurality of memory cells.

67. The method of claim 65 wherein said programming voltage applying and current controlling step comprises incrementally increasing magnitude of said current flowing between said first terminal and said second terminal in subsequent repetitions.

68. The method of claim 67 wherein said magnitude of said current is in a range of 0.5 μ

A to 50 μ

A.

69. The method of claim 65 wherein said programming voltages applying and current controlling step comprises incrementally increasing duration of said current flowing between said first terminal and said second terminal in subsequent repetitions.

70. The method of claim 69 wherein said duration of said current is in a range of 1 μ

s to 10 μ

s.