Integrated SRAM and FLOTOX EEPROM memory device

• US 8,331,150 B2
• Filed: 01/05/2009
• Issued: 12/11/2012
• Est. Priority Date: 01/03/2008
• Status: Expired due to Fees

• Current Assignee: Aplus Flash Technology, Inc.
• Original Assignee: Aplus Flash Technology, Inc.
• Inventors: Hsu, Fu-Chang, Lee, Peter Wung
• Primary Examiner(s): LE, TOAN K
• Application Number:
  US12/319,241
• Publication Number:
  US 20090190402A1
• Time in Patent Office: 1,436 Days
• Field of Search: 365/185.08, 365/185.18, 365/185.29, 365/154, 365/189.05
• US Class Current: 365/185.08
• CPC Class Codes: G11C 14/00 Digital stores characterised by arrangements of cells having volatile and non-volatile storage properties for back-up when the power is down
• CPC Class Codes: G11C 14/0063 and the nonvolatile element is an EEPROM element, e.g. a floating gate or MNOS transistor
• CPC Class Codes: Y10T 29/49002 Electrical device making

Abstract

A nonvolatile SRAM circuit has an SRAM cell and one or two FLOTOX EEPROM cells connected to the data storage terminals of the SRAM cell. In programming to a first data level, the threshold voltage of a FLOTOX EEPROM transistor is brought to a programmed voltage level greater than a read voltage level and erasing to a second data level, the threshold voltage of the FLOTOX EEPROM transistor is brought to an erased voltage level less than the read voltage level. The nonvolatile SRAM array provides for restoring data to an SRAM cell from a FLOTOX EEPROM memory cell(s) at a power initiation and storing data to the FLOTOX EEPROM memory cell(s) to the SRAM cell at power termination. A power detection circuit for providing signals indicating power initiation and power termination to instigate restoration and storing of data between an SRAM cell and a FLOTOX EEPROM cell(s).

Claims

1. An integrated nonvolatile static random access memory circuit formed on a substrate, the integrated nonvolatile static random access memory circuit comprising:

a static random access memory cell connected to receive and retain a digital signal indicative of a data bit at a first bit line and a complementary digital signal indicative of a complementary data bit a second bit line and in communication with an SRAM word line for controlling access to the first and second bit lines; and

a first EEPROM element in communication with the static random access memory cell to receive and permanently retain the digital signal from the static random access memory cell;

wherein the first EEPROM element comprises;

a first floating gate tunnel oxide transistor comprising an EEPROM control gate connected to an EEPROM word line for controlling activation of the first floating gate tunnel oxide transistor and a floating gate placed over a channel region between a drain and source of the first floating gate tunnel oxide transistor for permanently retaining the digital signal and placed over an insulating layer wherein the insulating layer has a first tunnel window placed in proximity to the source of the first floating gate tunnel oxide transistor for providing a path for transfer of charge between the floating gate and the source during erasing to set an erased threshold voltage level of the first floating gate tunnel oxide transistor and providing a path for transfer of charge between the floating gate and the channel for programming to set a programmed threshold voltage level of the first floating gate tunnel oxide transistor,

a first select gating transistor having a drain connected to the static random access memory cell, a source connected to the drain of the floating gate tunnel oxide transistor, and a gate connected to a first select gating signal for controlling access between the floating gate tunnel oxide transistor and the static random access memory cell, and

a second select gating transistor having a drain connected to the source of the floating gate tunnel oxide transistor, a source connected to a source line, and a control gate connected to a second select gating signal for controlling access between the floating gate tunnel oxide transistor and the source line.

2. The integrated nonvolatile static random access memory circuit of claim 1 further comprising:

a second EEPROM element in communication with the static random access memory cell through the second data terminal to receive and permanently retain a complement of the digital signal from the static random access memory cell, wherein the second EEPROM element comprises;

a second floating gate tunnel oxide transistor comprising a control gate connected to the EEPROM word line for controlling activation of the second floating gate tunnel oxide transistor and a floating gate placed over a channel region between a drain and source of the second floating gate tunnel transistor for permanently retaining the complement of the digital signal and placed over an insulating layer wherein the insulating layer has a second tunnel window placed in proximity to the source of the second floating gate transistor for providing a path for transfer of charge between the floating gate and the source during erasing to set an erased threshold voltage level of the second floating gate transistor and providing a path for transfer of charge between the floating gate and the channel for programming to set a programmed threshold voltage level of the first floating gate tunnel transistor,

a third select gating transistor having a source connected to the drain of the second floating gate tunnel oxide transistor, a drain connected to the static random access memory cell, and a gate connected to a first select gating signal for controlling access to the second floating gate tunnel oxide transistor, and

a fourth select gating transistor having a drain connected to the source of the second floating gate tunnel oxide transistor, a source connected to the source line, and a control gate connected to the second select gating signal for controlling access to the second floating gate tunnel oxide transistor from the source line.

3. The integrated nonvolatile static random access memory circuit of claim 2 wherein programming to a first data level increases the threshold voltage of the second floating gate tunnel oxide transistor to the programmed voltage level greater than a read voltage level by applying a program signal that is from approximately +15V to approximately +20V to the EEPROM word line and thus to the control gate of the first and the second floating gate tunnel oxide transistors to set the threshold voltage to the programmed voltage level that is greater than a read voltage level for programming and erasing to a second data level, the first and second floating gate tunnel oxide transistors decreases the threshold voltage of the second floating gate tunnel oxide transistor to the erased voltage level less than the read voltage level by applying an erase signal from approximately +15V to approximately +20V to the source line has to set the threshold voltage to the erased voltage level that is less than the read voltage level.

4. The integrated nonvolatile static random access memory circuit of claim 2 wherein:

the static random access memory cell comprises

a latched memory element to retain the data bit at the first data terminal and the complementary data bit a second data terminal, and

a first access transistor connected to allow control access of the bit line and a second access transistor connected to allow control access of a complementary bit line to the latched memory element for writing and reading the digital signal to and from the latched memory element, the first and second access transistors having control gates in communication with an SRAM word line for controlling access of the latched memory element to the first and second bit lines; and

wherein the first data terminal is connected to a storage node between the first access transistor and the latched memory element to transfer the digital signal to the first EEPROM element; and

the second data terminal is connected to a complementary storage node between the second access transistor and the latched memory element to transfer the digital signal to the second EEPROM element.

5. The integrated nonvolatile static random access memory circuit of claim 4 wherein:

the drain of the first floating gate tunnel oxide transistor is connected to the source of the first gating transistor of the first floating gate tunnel oxide EEPROM element such that when the first select gating signal is activated the drain of the first floating gate tunnel oxide transistor is connected to first data terminal of the latched memory element; and

the source of the second floating gate tunnel oxide transistor is connected to the drain of the first gating transistor of the second floating gate tunnel oxide EEPROM element such that when the first select gating signal is activated the drain of the second floating gate tunnel oxide transistor is connected to the second data terminal of the latched memory element.

6. The integrated nonvolatile static random access memory circuit of claim 5 wherein the static random access memory cell retains the digital signal as volatile digital data by setting the first select gating signal such that the first select gating transistors of the first and second EEPROM elements are deactivated and the static random access memory cell is isolated from the first and second EEPROM elements.

7. The integrated nonvolatile static random access memory circuit of claim 4 wherein:

a source line signal is applied to the source line for reading, programming, and erasing the first and second floating gate tunnel oxide transistors.

8. The integrated nonvolatile static random access memory circuit of claim 7 wherein at detection of a powering up of the integrated nonvolatile static random access memory circuit the digital signal the complement digital signal retained in the first and second floating gate tunnel oxide transistors are restored to the static random access memory cell by reading the first and second EEPROM elements.

9. The integrated nonvolatile static random access memory circuit of claim 8 wherein the first and second EEPROM elements are read by the steps of:

setting the source line to a voltage level of a power supply voltage source;

setting the first and second select gating signals to a very large positive voltage level to activate the first and second select gating transistors of the first and second EEPROM elements;

setting the EEPROM word line to a read voltage level to activate the first or second floating gate tunnel oxide transistors if the first or second floating gate tunnel oxide transistor is programmed with the data signal at a first data level and to remain inactive if the first or second floating gate tunnel oxide transistor is programmed with the data signal at a second data level such that if the first floating gate tunnel oxide transistor is activated and the second floating gate tunnel oxide transistor is deactivated, the first data level is transferred to the static random access memory cell and if the first floating gate tunnel oxide transistor is not activated and the second floating gate tunnel oxide transistors is activated, the second data level is transferred to the static random access memory cell; and

setting the SRAM word line to a voltage level that will not turn on the first and second access transistors to prevent the static random access memory cell from being connected to the bit line and the complementary bit line.

10. The integrated nonvolatile static random access memory circuit of claim 8 wherein subsequent to restoring the digital signal to the static random access memory cell, the first and second EEPROM elements are erased.

11. The integrated nonvolatile static random access memory circuit of claim 10 wherein first and second EEPROM elements are erased by the steps of:

setting the first select gating signal to a voltage level that will turn off the first select gating transistor of each of the first and second EEPROM elements to isolate the static random access memory cell from the first and second EEPROM elements;

setting the EEPROM word line to a ground reference voltage level; and

setting the second select gating signal and the source line signal to the very large positive voltage level such that charge is extracted from the floating gates of the first and second floating gate tunnel oxide transistors.

12. The integrated nonvolatile static random access memory circuit of claim 10 wherein subsequent to the erasing the first and second EEPROM elements, the first and second EEPROM elements are isolated from the static random access memory cell and the static random access memory cell is operated in a normal mode.

13. The integrated nonvolatile static random access memory circuit of claim 12 wherein at detection of a powering down of the integrated nonvolatile static random access memory circuit, the digital signal and the complementary digital signal retained in the static random access memory cell are programmed to the first and second EEPROM elements.

14. The integrated nonvolatile static random access memory circuit of claim 13 wherein the first and second floating gate tunnel oxide EEPROM transistors are programmed by the steps of:

setting the first select gating signal to the very high positive voltage level to activate the first select gating transistor of each of the first and second EEPROM elements;

setting the second select gating signal to turn off the second select gating transistor of each of the first and second EEPROM elements; and

setting the EEPROM word line to the very high positive voltage level such that if the data signal at the first data terminal is the first data level, charge is placed on the floating gate of the first floating gate tunnel oxide transistor and charge is inhibited from entering the floating gate of the second floating gate tunnel oxide transistor and if the first data terminal is at the second data level, charge is placed on the floating gate of the second floating gate tunnel oxide transistor and charge is inhibited from entering the floating gate of the first floating gate tunnel oxide transistor.

15. The integrated nonvolatile static random access memory circuit of claim 2 wherein:

the control gates of the first and second floating gate tunnel oxide transistors are connected to the EEPROM word line to receive read, program, and erase signals.

16. The integrated nonvolatile static random access memory circuit of claim 1 wherein programming to a first data level increases the threshold voltage of the first floating gate tunnel oxide transistor to the programmed threshold voltage level greater than a read voltage level by applying a program signal that is from approximately +15V to approximately +20V to the EEPROM word line and thus to the control gate of the first floating gate tunnel oxide transistor to set the threshold voltage to the programmed voltage threshold level that is greater than a read voltage level for programming and wherein erasing to a second data level, the first floating gate tunnel oxide EEPROM element decreases the threshold voltage of the first floating gate tunnel oxide transistor to an erased threshold voltage level less than the read voltage level by applying an erase signal of from approximately +15V to approximately +20V to the source line of the first floating gate tunnel oxide transistor to set the threshold voltage to the erased threshold voltage level that is less than the read voltage level for erasing.

17. The integrated nonvolatile static random access memory circuit of claim 1 wherein the static random access memory cell comprises:

a latched memory element to retain the data bit at the first data terminal and the complementary data bit a second data terminal, and

a first access transistor connected to allow control access of the bit line and a second access transistor connected to allow control access of a complementary bit line to the latched memory element for writing and reading the digital signal to and from the latched memory element, the first and second access transistors having control gates in communication with an SRAM word line for controlling access of the latched memory element to the first and second bit lines; and

wherein the first data terminal is connected to a storage node between the first access transistor and the latched memory element to transfer the digital signal to the first EEPROM element.

18. The integrated nonvolatile static random access memory circuit of claim 17 wherein:

the drain of the first floating gate tunnel oxide transistor is connected to the source of the first gating transistor such that when the first select gating signal is activated, the drain of the first floating gate tunnel oxide transistor is connected to the first data terminal of the latched memory element.

19. The integrated nonvolatile static random access memory circuit of claim 18 wherein the static random access memory cell retains the digital signal as volatile digital data by setting the first select gating signal such that the first select gating transistors of the first EEPROM element is deactivated and the static random access memory cell is isolated from the first EEPROM elements.

20. The integrated nonvolatile static random access memory circuit of claim 17 wherein:

a source line signal is applied to the source line for reading, programming, and erasing the first floating gate tunnel oxide transistor.

21. The integrated nonvolatile static random access memory circuit of claim 20 wherein at detection of a powering up of the integrated nonvolatile static random access memory circuit the digital signal retained in the first floating gate tunnel oxide transistor is restored to the static random access memory cell by reading the first EEPROM element.

22. The integrated nonvolatile static random access memory circuit of claim 21 wherein the first EEPROM element is read by the steps of:

setting the source line to a voltage level of a power supply voltage source;

setting the first and second select gating signals to a very large positive voltage level to activate the first and second select gating transistors;

setting the EEPROM word line to a read voltage level to activate the first floating gate tunnel oxide transistor if it is programmed with the data signal at a first data level and to remain inactive if the first floating gate tunnel oxide transistor is programmed with the data signal at a second data level such that if the first floating gate tunnel oxide transistor is activated the first data level is transferred to the static random access memory cell and if the first floating gate tunnel oxide transistor is not activated, the second data level is transferred to the static random access memory cell; and

setting the SRAM word line to a voltage level that will not turn on the first and second access transistors to prevent the static random access memory cell from being connected to the bit line and the complementary bit line.

23. The integrated nonvolatile static random access memory circuit of claim 21 wherein subsequent to restoring the digital signal to the static random access memory cell, the EEPROM element is erased.

24. The integrated nonvolatile static random access memory circuit of claim 23 wherein EEPROM element is erased by the steps of:

setting the first select gating signal to a voltage level that will turn off the first select gating transistor to isolate the static random access memory cell from the first EEPROM element;

setting the EEPROM word line to a ground reference voltage level;

setting the second select gating signal and the source line signal to the very large positive voltage level such that charge is extracted from the floating gate of the first floating gate tunnel oxide transistor.

25. The integrated nonvolatile static random access memory circuit of claim 23 wherein subsequent to the erasing the first EEPROM element, the first EEPROM element is isolated from the static random access memory cell and the static random access memory cell is operated in a normal mode.

26. The integrated nonvolatile static random access memory circuit of claim 25 wherein at detection of a powering down of the integrated nonvolatile static random access memory circuit, the digital signal retained in the static random access memory cell is programmed to the first floating gate tunnel oxide transistor.

27. The integrated nonvolatile static random access memory circuit of claim 26 wherein the first EEPROM element is programmed by the steps of:

setting the first select gating signal to the very high positive voltage level to activate the first select gating transistor;

setting the second select gating signal to turn off the second select gating transistor; and

setting the EEPROM word line to the very high positive voltage level such that if the data signal at the first data terminal is the first data level, charge is placed on the floating gate and if the data signal at the first data terminal is the second data level, charge is inhibited from entering the floating gate and the first floating gate tunnel oxide transistor remains erased.

28. The integrated nonvolatile static random access memory circuit of claim 1 wherein:

the control gate of the first floating gate tunnel oxide transistor is connected to the EEPROM word line to receive read, program, and erase signals.

29. A nonvolatile static random access memory array comprising:

a plurality of integrated nonvolatile static random access memory circuits arranged in an array of rows and columns, each of the integrated nonvolatile static random access memory circuits comprising;

a static random access memory cell connected to receive and retain a digital signal indicative of a data bit at a first bit line of a plurality of bit lines and a complementary digital signal indicative of a complementary data bit a second bit line of the plurality of bit lines and in communication with an SRAM word line for controlling access to the first and second bit lines; and

a first EEPROM element in communication with the static random access memory cell to receive and permanently retain the digital signal from the static random access memory cell;

wherein the first EEPROM element comprises;

a first floating gate tunnel oxide transistor comprising an control gate connected to an EEPROM word line for controlling activation of the first floating gate tunnel oxide transistor and a floating gate placed over a channel region between a drain and source of the first floating gate tunnel oxide transistor for permanently retaining the digital signal and placed over an insulating layer wherein the insulating layer has a first tunneling window placed in proximity to the source of the first floating gate tunnel oxide transistor for providing a path for transfer of charge between the floating gate and the source during erasing to set an erased threshold voltage level of the first floating gate tunnel oxide transistor and providing a path for transfer of charge between the floating gate and the channel for programming to set a programmed threshold voltage level of the first floating gate transistor,

a first select gating transistor having a drain connected to the static random access memory cell, a source connected to the drain of the floating gate tunnel oxide transistor, and a gate connected to a first select gating signal for controlling access to the floating gate tunnel oxide transistor, and

a second select gating transistor having a drain connected to the source of the floating gate tunnel oxide transistor, a source connected to a source line, and a control gate connected to a second select gating signal for controlling access between the floating gate tunnel oxide transistor and the source line.

30. The nonvolatile static random access memory array of claim 29 wherein the each of the integrated nonvolatile static random access memory circuit further comprises:

a second EEPROM element in communication with the static random access memory cell through the second data terminal to receive and permanently retain a complement of the digital signal from the static random access memory cell, wherein the second EEPROM element comprises;

a second floating gate tunnel oxide transistor including a control gate connected to the EEPROM word line for controlling activation of the second floating gate tunnel oxide transistor and a floating gate placed over a channel region between a drain and source of the second floating gate tunnel transistor for permanently retaining the complement of the digital signal and placed over an insulating layer wherein the insulating layer has a second tunneling window placed in proximity to the source of the second floating gate tunnel oxide transistor for providing a path for transfer of charge between the floating gate and the source during erasing to set an erased threshold voltage level of the second floating gate tunnel oxide transistor and providing a path for transfer of charge between the floating gate and the channel for programming to set a programmed threshold voltage level of the second floating gate tunnel transistor,

a third select gating transistor having a drain connected to the drain of the second floating gate tunnel oxide transistor, a drain connected to the static random access memory cell, and a gate connected to a first select gating signal for controlling access to the second floating gate tunnel oxide transistor, and

a fourth select gating transistor having a drain connected to the source of the second floating gate tunnel oxide transistor, a source connected to the source line, and a control gate connected to the second select gating signal for controlling access to the second floating gate tunnel oxide transistor from the source line.

31. The nonvolatile static random access memory array of claim 30 wherein programming to the first data level increases the threshold voltage of the second floating gate tunnel oxide transistor to the programmed voltage level greater than a read voltage level by applying a program signal that is from approximately +15V to approximately +20V to the EEPROM word line to set the threshold voltage of a selected row of the first and second floating gate tunnel oxide transistors to the programmed voltage level that is greater than a read voltage level and erasing to a second data level, the second floating gate tunnel oxide EEPROM element decreases the threshold voltage of the second floating gate tunnel oxide transistor to the erased voltage level less than the read voltage level by applying an erase signal of from approximately +15V to approximately +20V to the source line to set the threshold voltage of a selected row of the first and second floating gate tunnel oxide transistors to the erased voltage level that is less than the read voltage level.

32. The nonvolatile static random access memory array of claim 30 further comprising a power detection circuit in communication with the plurality of integrated nonvolatile static random access memory circuits to detect a power interruption and a power initiation and communicate the detection of the power interruption and detection of the power initiation to the plurality of integrated nonvolatile static random access memory circuits.

33. The nonvolatile static random access memory array of claim 32 wherein:

the drain of the first floating gate tunnel oxide transistor is connected to the source of the first gating transistor of the first EEPROM element such that when the first select gating signal is activated the drain of the first floating gate tunnel oxide transistor is connected to first data terminal of the latched memory element; and

the drain of the second floating gate tunnel oxide transistor is connected to the source of the first gating transistor of the second EEPROM element such that when the first select gating signal is activated the drain of the second floating gate tunnel oxide transistor is connected to the second data terminal of the latched memory element.

34. The nonvolatile static random access memory array of claim 30 wherein the static random access memory cell comprises:

a latched memory element to retain the data bit at the first data terminal and the complementary data bit a second data terminal, and

a first access transistor connected to allow control access of the bit line and a second access transistor connected to allow control access of a complementary bit line to the latched memory element for writing and reading the digital signal to and from the latched memory element, the first and second access transistors having control gates in communication with an SRAM word line for controlling access of the latched memory element to the first and second bit lines; and

the first data terminal is connected to a storage node between the first access transistor and the latched memory element to transfer the digital signal to the first EEPROM element; and

the second data terminal is connected to a complementary storage node between the second access transistor and the latched memory element to transfer the digital signal to the second EEPROM element.

35. The nonvolatile static random access memory array of claim 34 wherein:

a source line signal is applied to the source line for reading, programming, and erasing the first and second floating gate tunnel oxide transistors.

36. The nonvolatile static random access memory array of claim 35 wherein the power detection circuit detects the power initiation of the integrated nonvolatile static random access memory circuit the digital signal the complement digital signal retained in the first and second floating gate tunnel oxide transistors are restored to the static random access memory cell by reading the first and second EEPROM elements.

37. The nonvolatile static random access memory array of claim 36 wherein the first and second EEPROM elements are read by the steps of:

setting the source line to a voltage level of a power supply voltage source;

setting the first and second select gating signals to a very large positive voltage level to activate the first and second select gating transistors of the first and second EEPROM elements;

setting the EEPROM word line to a read voltage level to activate the first or second floating gate tunnel oxide transistors if it one is programmed with the data signal at a first data level and to remain inactive if the first or second floating gate tunnel oxide transistor is programmed with the data signal at a second data level such that if the first floating gate tunnel oxide transistor is activated and the second floating gate tunnel oxide transistor is deactivated, the first data level is transferred to the static random access memory cell and if the first floating gate tunnel oxide transistor is not activated and the second floating gate tunnel oxide transistors is activated, the second data level is transferred to the static random access memory cell; and

setting the SRAM word line to a voltage level that will not turn on the first and second access transistors to prevent the static random access memory cell from being connected to the bit line and the complementary bit line.

38. The nonvolatile static random access memory array of claim 36 wherein subsequent to restoring the digital signal to the static random access memory cell, the first and second EEPROM elements are erased.

39. The nonvolatile static random access memory array of claim 38 wherein first and second EEPROM elements are erased by the steps of:

setting the first select gating signal to a voltage level that will turn off the first select gating transistor to isolate the static random access memory cell from the first and second floating gate tunneling oxide EEPROM elements;

setting the EEPROM word line to a ground reference voltage level; and

setting the second select gating signal and the source line signal to the very large positive voltage level such that charge is extracted from the floating gate of the first and second floating gate tunnel oxide transistors.

40. The nonvolatile static random access memory array of claim 38 wherein subsequent to the erasing the first and second EEPROM elements, the first and second EEPROM elements are isolated from the static random access memory cell and the static random access memory cell is operated in a normal mode.

41. The nonvolatile static random access memory array of claim 40 wherein the power detection circuit detects the power interruption of the integrated nonvolatile static random access memory circuit, the digital signal the complementary digital signal retained in the static random access memory cell are programmed to the first and second floating gate tunnel oxide transistors.

42. The nonvolatile static random access memory array of claim 41 wherein the first and second floating gate tunnel oxide EEPROM transistors are programmed by the steps of:

setting the first select gating signal to the very high positive voltage level to activate the first select gating transistor;

setting the second select gating signal to turn off the first select gating transistor; and

setting the EEPROM word line to the very high positive voltage level such that if the data signal at the first data terminal is the first data level, charge is placed on the floating gate of the first floating gate tunnel oxide transistor and charge is inhibited from entering the floating gate of the second floating gate tunnel oxide transistor and if the first data terminal is at the second data level, charge is placed on the floating gate of the second floating gate tunnel oxide transistor and charge is inhibited from entering the floating gate of the first floating gate tunnel oxide transistor.

43. The nonvolatile static random access memory array of claim 34 wherein the static random access memory cell retains the digital signal as volatile digital data by setting the first select gating signal such that the first select gating transistors of the first and second EEPROM elements are deactivated and the static random access memory cell is isolated from the first and second EEPROM elements.

44. The nonvolatile static random access memory array of claim 30 wherein:

the control gates of the first and second floating gate tunnel oxide transistors is connected to the EEPROM word line receive read, program, and erase signals.

45. The nonvolatile static random access memory array of claim 29 wherein programming to a first data level increases a threshold voltage of the first floating gate tunnel oxide transistor to a programmed voltage level greater than a read voltage level by applying a program signal that is from approximately +15V to approximately +20V to the EEPROM word line to set the threshold voltage of a selected row of the selected floating gate tunnel oxide transistors to the programmed voltage level that is greater than a read voltage level and erasing to a second data level, the first floating gate tunnel oxide EEPROM element decreases the threshold voltage of the first floating gate tunnel oxide transistor to an erased voltage level less than the read voltage level by applying an erase signal of from approximately +15V to approximately +20V to the source line to set the threshold voltage of a selected row of the first floating gate tunnel oxide transistors to the erased voltage level that is less than the read voltage level.

46. The nonvolatile static random access memory array of claim 29 further comprising a power detection circuit in communication with the plurality of integrated nonvolatile static random access memory circuits to detect a power interruption and a power initiation and communicate the detection of the power interruption and detection of the power initiation to the plurality of integrated nonvolatile static random access memory circuits.

47. The nonvolatile static random access memory array of claim 46 wherein the static ransom access memory cell is connected to a storage node between the first access transistor and the latched memory element to transfer the digital signal to the first floating gate tunnel oxide EEPROM element.

48. The nonvolatile static random access memory array of claim 47 wherein the static random access memory cell retains the digital signal as volatile digital data by setting the first select gating signal such that the first select gating transistors of the first EEPROM element is deactivated and the static random access memory cell is isolated from the first EEPROM element.

49. The nonvolatile static random access memory array of claim 47 wherein:

a source line signal is applied to the source line for reading, programming, and erasing the first floating gate tunnel oxide transistor.

50. The nonvolatile static random access memory array of claim 49 wherein when the power detection circuit detects the power initiation of the integrated nonvolatile static random access memory array the digital signal retained in the first floating gate tunnel oxide transistor is restored to the static random access memory cell by reading the first EEPROM element.

51. The nonvolatile static random access memory array of claim 50 wherein the first EEPROM element is read by the steps of:

setting the source line to a voltage level of a power supply voltage source;

setting the first and second select gating signals to a very large positive voltage level to activate the first and second select gating transistors;

setting the EEPROM word line to a read voltage level to activate the first floating gate tunnel oxide transistor if it is programmed with the data signal at a first data level and to remain inactive if the first floating gate tunnel oxide transistor is programmed with the data signal at a second data level such that if the first floating gate tunnel oxide transistor is activated the first data level is transferred to the static random access memory cell and if the first floating gate tunnel oxide transistor is not activated, the second data level is transferred to the static random access memory cell; and

setting the SRAM word line to a voltage level that will not turn on the first and second access transistors to prevent the static random access memory cell from being connected to the bit line and the complementary bit line.

52. The nonvolatile static random access memory array of claim 50 wherein subsequent to restoring the digital signal to the static random access memory cell, the EEPROM element is erased.

53. The nonvolatile static random access memory array of claim 52 wherein first floating gate tunnel oxide EEPROM element is erased the by the steps of:

setting the first select gating signal to a voltage level that will turn off the first select gating transistor to isolate the static random access memory cell from the first EEPROM element;

setting the EEPROM word line to a ground reference voltage level;

setting the second select gating signal and the source line signal to the very large positive voltage level such that charge is extracted from the floating gate of the first floating gate tunnel oxide transistor.

54. The nonvolatile static random access memory array of claim 53 wherein subsequent to the erasing the first EEPROM element, the first EEPROM element is isolated from the static random access memory cell and the static random access memory cell is operated in a normal mode.

55. The nonvolatile static random access memory array of claim 54 wherein when the power detection circuit detects a power interruption of the integrated nonvolatile static random access memory circuit, the digital signal retained in the static random access memory cell is programmed to the first floating gate tunnel oxide transistor.

56. The nonvolatile static random access memory array of claim 55 wherein the first EEPROM element is programmed by the steps of:

setting the first select gating signal to the very high positive voltage level to activate the first select gating transistor;

setting the second select gating signal to turn off the first select gating transistor; and

setting the EEPROM word line to the very high positive voltage level such that if the data signal at the first data terminal is the first data level, charge is placed on the floating gate and if the data signal at the first data terminal is the second data level, charge is inhibited from entering the floating gate and the first floating gate tunnel oxide transistor remains erased.

57. The nonvolatile static random access memory array of claim 29 wherein:

the drain of the first floating gate tunnel oxide transistor is connected to the source of the first gating transistor such that when the first select gating signal is activated the drain of the first floating gate tunnel oxide transistor is connected to the first data terminal of the latched memory element.

58. The nonvolatile static random access memory array of claim 29 wherein:

the control gate of the first floating gate tunnel oxide transistor is connected to the EEPROM word line to receive read, program, and erase signals.

59. A method for forming an integrated nonvolatile static random access memory comprises the steps of:

forming a plurality of integrated nonvolatile static random access memory circuits;

connecting each of the static random access memory cells to one of a plurality first bit lines to receive and retain a digital signal indicative of a data bit;

connecting each of the static random access memory cells to one of a plurality of complementary bit lines to receive and retain a complementary digital signal indicative of a complementary data bit;

connecting each of the static random access memory cells to one of a plurality of SRAM word lines for controlling access to the one of the bit lines and complementary bit lines;

forming a first EEPROM element for each of the integrated nonvolatile static random access memory circuits by the steps of;

forming a first floating gate tunnel oxide transistor including an EEPROM control gate and a floating gate placed over a channel region between a drain and source of the first floating gate tunnel oxide transistor for permanently retaining the digital signal,

connecting the control gate to one of a plurality of EEPROM word lines for controlling activation of the first floating gate tunnel oxide transistor,

placing the floating gate over an insulating layer wherein the insulating layer has a first tunnel window placed in proximity to the source of the first floating gate tunnel oxide transistor for providing a path for transfer of charge between the floating gate and the source during erasing to set an erased threshold voltage level of the first floating gate tunnel oxide transistor and providing a path for transfer of charge between the floating gate and the channel for programming to set a programmed threshold voltage level of the first floating gate tunnel oxide transistor,

forming a first select gating transistor having a drain connected to the static random access memory cell, a source connected to the drain of the first floating gate tunnel oxide transistor, and a gate connected to one of a plurality of first select gating signals for controlling access between the floating gate tunnel oxide transistor and the static random access memory cell, and

forming a second select gating transistor having a drain connected to the source of the first floating gate tunnel oxide transistor, a source connected to one of a plurality of a source lines, and a control gate connected to one of a plurality of second select gating signals for controlling access to the first floating gate tunnel oxide transistor from the source line;

arranging the plurality of integrated nonvolatile static random access memory circuits in an array of rows and columns.

60. The method for forming an integrated nonvolatile static random access memory of claim 59 wherein forming the each of the integrated nonvolatile static random access memory circuit further comprises the steps of:

forming a second EEPROM element for each of the integrated nonvolatile static random access memory circuits by the steps of;

forming a second floating gate tunnel oxide transistor including an EEPROM control gate and a floating gate placed over a channel region between a drain and source of the second floating gate tunnel oxide transistor for permanently retaining the digital signal,

connecting the control gate to the one of EEPROM word lines for controlling activation of the second floating gate tunnel oxide transistor,

placing the floating gate over an insulating layer wherein the insulating layer has a second tunnel window placed in proximity to the source of the second floating gate tunnel oxide transistor for providing a path for transfer of charge between the floating gate and the source during erasing to set an erased threshold voltage level of the second floating gate tunnel oxide transistor and providing a path for transfer of charge between the floating gate and the channel for programming to set a programmed threshold voltage level of the second floating gate tunnel oxide transistor,

forming a third select gating transistor having a drain connected to the static random access memory cell, a source connected to the drain of the floating gate tunnel oxide transistor, and a gate connected to one of a plurality of first select gating signals for controlling access to the second floating gate tunnel oxide transistor, and

forming a fourth select gating transistor having a drain connected to a source of the second floating gate tunnel oxide transistor, a source connected to one of a plurality of source lines, and a control gate connected to one of a plurality of second select gating signals for controlling access to the second floating gate tunnel oxide transistor from the one source line.

61. The method for forming an integrated nonvolatile static random access memory of claim 60 further comprising programming selected first and second EEPROM elements to the first data level by increasing the threshold voltage of the selected second floating gate tunnel oxide transistors to the programmed voltage level greater than a read voltage level by applying a program signal that is from approximately +15V to approximately +20V to the EEPROM word line to set the threshold voltage of a selected row of the first floating gate tunnel oxide transistors to the programmed voltage level that is greater than a read voltage level.

62. The method for forming an integrated nonvolatile static random access memory of claim 60 further comprising erasing the first and second EEPROM element erasing selected second EEPROM elements to a second data level by decreasing the threshold voltage of the second selected floating gate tunnel oxide transistors to the erased voltage level less than the read voltage level by applying an erase signal of from approximately +15V to approximately +20V to the source line to set the threshold voltage of a selected row of the first floating gate tunnel oxide transistors to the erased voltage level that is less than the read voltage level.

63. The method for forming an integrated nonvolatile static random access memory of claim 60 further comprising the steps of;

detecting a power initiation of the plurality of integrated nonvolatile static random access memory circuits;

detecting a power interruption of the plurality of integrated nonvolatile static random access memory circuits; and

communicating the detecting of the power interruption and detecting of the power initiation to the plurality of integrated nonvolatile static random access memory circuits.

64. The method for forming an integrated nonvolatile static random access memory of claim 63 further comprising:

restoring the digital signal retained in the first and second floating gate tunnel oxide transistors to the static random access memory cell by reading the first and second EEPROM elements upon detecting the power initiation of the integrated nonvolatile static random access memory circuit.

65. The method for forming an integrated nonvolatile static random access memory of claim 64 wherein the first and second EEPROM elements are read by the steps of:

setting the source line to a voltage level of a power supply voltage source;

setting the first and second select gating signals to a very large positive voltage level to activate the first and second select gating transistors of the first and second EEPROM elements;

setting the EEPROM word line to a read voltage level to activate the first or second floating gate tunnel oxide transistors if it one is programmed with the data signal at a first data level and to remain inactive if the first or second floating gate tunnel oxide transistor is programmed with the data signal at a second data level such that if the first floating gate tunnel oxide transistor is activated and the second floating gate tunnel oxide transistor is deactivated, the first data level is transferred to the static random access memory cell and if the first floating gate tunnel oxide transistor is not activated and the second floating gate tunnel oxide transistors is activated, the second data level is transferred to the static random access memory cell; and

setting the SRAM word line to a voltage level that will not turn on the first and second access transistors to prevent the static random access memory cell from being connected to the bit line and the complementary bit line.

66. The method for forming an integrated nonvolatile static random access memory of claim 64 wherein erasing the first and second EEPROM elements is subsequent to restoring the digital signal to the static random access memory cell.

67. The method for forming an integrated nonvolatile static random access memory of claim 66 wherein erasing the first and second EEPROM elements comprise the steps of:

setting the first select gating signal to a voltage level that will turn off the first select gating transistor to isolate the static random access memory cell from the first and second EEPROM elements;

setting the EEPROM word line to a ground reference voltage level; and

setting the second select gating signal and the source line signal to the very large positive voltage level such that charge is extracted from the floating gate of the first and second floating gate tunnel oxide transistors.

68. The method for forming an integrated nonvolatile static random access memory of claim 66 further comprises the steps of:

isolating the first and second EEPROM elements from the static random access memory cell; and

operating the static random access memory cell in a normal mode subsequent to the erasing the first and second EEPROM elements.

69. The method for forming an integrated nonvolatile static random access memory of claim 68 wherein programming the digital signal the complementary digital signal retained in the static random access memory cell to the first and second floating gate tunnel oxide transistors occurs upon detecting the power interruption of the integrated nonvolatile static random access memory circuit.

70. The method for forming an integrated nonvolatile static random access memory of claim 69 wherein programming the first and second floating gate tunnel oxide transistors comprises the steps of:

setting the first select gating signal to the very high positive voltage level to activate the first select gating transistor;

setting the second select gating signal to turn off the first select gating transistor; and

setting the EEPROM word line to the very high positive voltage level such that if the data signal at the first data terminal is the first data level, charge is placed on the floating gate of the first floating gate tunnel oxide transistor and charge is inhibited from entering the floating gate of the second floating gate tunnel oxide transistor and if the first data terminal is at the second data level, charge is placed on the floating gate of the second floating gate tunnel oxide transistor and charge is inhibited from entering the floating gate of the first floating gate tunnel oxide transistor.

71. The method for forming an integrated nonvolatile static random access memory of claim 59 further comprises programming the first EEPROM elements to a first data level by increasing a threshold voltage of the selected first floating gate tunnel oxide transistors to a programmed voltage level greater than a read voltage level by applying a program signal that is from approximately +15V to approximately +20V to the one EEPROM word line to set the threshold voltage of a selected row of the first floating gate tunnel oxide transistors to the programmed voltage level that is greater than a read voltage level.

72. The method for forming an integrated nonvolatile static random access memory of claim 60 wherein forming each of the integrated nonvolatile static random access memory circuits comprises steps of:

forming a static random access memory cell for each of the integrated nonvolatile static random access memory circuits by the steps of;

forming a latched memory element to retain a digital signal indicative of a data bit at a first data terminal and a complementary digital signal indicative of a complementary data bit a second data terminal, and

forming a first access transistor connected to allow control access of a bit line and a second access transistor connected to allow control access of a complementary bit line to the latched memory element for writing and reading the digital signal to and from the latched memory element, the first and second access transistors having control gates in communication with an SRAM word line for controlling access of the latched memory element to the first and second bit lines; and

connecting each of the static random access memory cells to one of a plurality first bit lines to receive and retain a digital signal indicative of a data bit;

connecting each of the static random access memory cells to one of a plurality of complementary bit lines to receive and retain a complementary digital signal indicative of a complementary data bit;

connecting each of the static random access memory cells to one of a plurality of SRAM word lines for controlling access to the one of the bit lines and complementary bit lines; and

the method for forming an integrated nonvolatile static random access memory further comprises the step of connecting the first data terminal to a storage node between the first access transistor and the latched memory element to transfer the digital signal to the first EEPROM element; and

connecting the second data terminal to a complementary storage node between the second access transistor and the latched memory element to transfer the digital signal to the second floating gate tunnel oxide EEPROM element.

73. The method for forming an integrated nonvolatile static random access memory of claim 72 wherein:

forming the first floating gate tunnel oxide transistor comprises the step of;

connecting the drain of the first floating gate tunnel oxide transistor to the source of the first gating transistor of the first EEPROM element such that when the first select gating signal is activated the drain of the first floating gate tunnel oxide transistor is connected to the one bit line; and

forming the second floating gate tunnel oxide transistor comprises the step of;

connecting the drain of the second floating gate tunnel oxide transistor to the source of the first gating transistor of the second EEPROM element such that when the first select gating signal is activated the drain of the second floating gate tunnel oxide transistor is connected to the one complementary bit line.

74. The method for forming an integrated nonvolatile static random access memory of claim 72 further comprises the step of setting the first select gating signal such that the first select gating transistors of the first and second EEPROM elements are deactivated and the static random access memory cell is isolated from the first and second EEPROM elements so that the static random access memory cell retains the digital signal as volatile digital data.

75. The method for forming an integrated nonvolatile static random access memory of claim 60 wherein forming the first and second floating gate tunnel oxide transistor comprises the step of connecting the control gate of the first and second floating gate tunnel oxide transistor to receive read, program, and erase signals.

76. The method for forming an integrated nonvolatile static random access memory of claim 60 further comprises the step of applying a source line signal to the source line for reading, programming, and erasing the first floating gate tunnel oxide transistor.

77. The method for forming an integrated nonvolatile static random access memory of claim 59 further comprising erasing the first floating gate tunnel oxide EEPROM elements to a second data level by decreasing the threshold voltage of the selected first floating gate tunnel oxide transistors to an erased voltage level less than the read voltage level by applying an erase signal of from approximately +15V to approximately +20V to the one source line to set the threshold voltage of a selected row of the first floating gate tunnel oxide transistors to the erased voltage level that is less than the read voltage level.

78. The method for forming an integrated nonvolatile static random access memory of claim 59 further comprising the steps of;

detecting a power initiation of the plurality of integrated nonvolatile static random access memory circuits;

detecting a power interruption of the plurality of integrated nonvolatile static random access memory circuits; and

communicating the detecting of the power interruption and detecting of the power initiation to the plurality of integrated nonvolatile static random access memory circuits.

79. The method for forming an integrated nonvolatile static random access memory of claim 78 further comprising restoring the digital signal retained in the first floating gate tunnel oxide transistor to the static random access memory cell by reading the first EEPROM element upon detecting the power initiation of the integrated nonvolatile static random access memory circuit.

80. The method for forming an integrated nonvolatile static random access memory of claim 79 wherein reading the first EEPROM element comprises the steps of:

setting the source line to a voltage level of a power supply voltage source;

setting the first and second select gating signals to a very large positive voltage level to activate the first and second select gating transistors;

setting the EEPROM word line to a read voltage level to activate the first floating gate tunnel oxide transistor if it is programmed with the data signal at a first data level and to remain inactive if the first floating gate tunnel oxide transistor is programmed with the data signal at a second data level such that if the first floating gate tunnel oxide transistor is activated the first data level is transferred to the static random access memory cell and if the first floating gate tunnel oxide transistor is not activated, the second data level is transferred to the static random access memory cell; and

setting the SRAM word line to a voltage level that will not turn on the first and second access transistors to prevent the static random access memory cell from being connected to the bit line and the complementary bit line.

81. The method for forming an integrated nonvolatile static random access memory of claim 79 further comprising the step of erasing the first EEPROM element, subsequent to restoring the digital signal to the static random access memory cell.

82. The method for forming an integrated nonvolatile static random access memory of claim 81 further comprises the steps of:

isolating the first EEPROM element from the static random access memory cell; and

operating the static random access memory cell in a normal mode, subsequent to the erasing the first floating gate tunnel oxide EEPROM element.

83. The method for forming an integrated nonvolatile static random access memory of claim 81 wherein erasing the first EEPROM element comprises the steps of:

setting the first select gating signal to a voltage level that will turn off the first select gating transistor to isolate the static random access memory cell from the first EEPROM element;

setting the EEPROM word line to a ground reference voltage level;

setting the second select gating signal and the source line signal to the very large positive voltage level such that charge is extracted from the floating gate of the first floating gate tunnel oxide transistor.

84. The method for forming an integrated nonvolatile static random access memory of claim 83 further comprising the steps of programming the digital signal retained in the static random access memory cell to the first floating gate tunnel oxide transistor detects the power interruption of the integrated nonvolatile static random access memory circuit.

85. The method for forming an integrated nonvolatile static random access memory of claim 84 wherein programming the first EEPROM element comprises the steps of:

setting the first select gating signal to the very high positive voltage level to activate the first select gating transistor;

setting the second select gating signal to turn off the first select gating transistor; and

setting the EEPROM word line to the very high positive voltage level such that if the data signal at the first data terminal is the first data level, charge is placed on the floating gate and if the data signal at the first data terminal is the second data level, charge is inhibited from entering the floating gate and the first floating gate tunnel oxide transistor remains erased.

86. The method for forming an integrated nonvolatile static random access memory of claim 59 wherein forming each of the integrated nonvolatile static random access memory circuits comprises steps of:

forming a static random access memory cell for each of the integrated nonvolatile static random access memory circuits by the steps of;

forming a latched memory element to retain a digital signal indicative of a data bit at a first data terminal and a complementary digital signal indicative of a complementary data bit a second data terminal, and

forming a first access transistor connected to allow control access of a bit line and a second access transistor connected to allow control access of a complementary bit line to the latched memory element for writing and reading the digital signal to and from the latched memory element, the first and second access transistors having control gates in communication with an SRAM word line for controlling access of the latched memory element to the first and second bit lines; and

connecting each of the static random access memory cells to one of a plurality first bit lines to receive and retain a digital signal indicative of a data bit;

connecting each of the static random access memory cells to one of a plurality of complementary bit lines to receive and retain a complementary digital signal indicative of a complementary data bit;

connecting each of the static random access memory cells to one of a plurality of SRAM word lines for controlling access to the one of the bit lines and complementary bit lines; and

the method for forming an integrated nonvolatile static random access memory further comprises the step of connecting the first data terminal to a storage node between the first access transistor and the latched memory element to transfer the digital signal to the first EEPROM element.

87. The method for forming an integrated nonvolatile static random access memory of claim 86 forming the first floating gate tunnel oxide transistor comprises the step of:

connecting the drain of the first floating gate tunnel oxide transistor to the source of the first gating transistor such that when the first select gating signal is activated the drain of the first floating gate tunnel oxide transistor is connected to the one bit line.

88. The method for forming an integrated nonvolatile static random access memory of claim 86 further comprises the step of setting the first select gating signal such that the first select gating transistors of the first EEPROM element is deactivated and the static random access memory cell is isolated from the first EEPROM elements so that the static random access memory cell retains the digital signal as volatile digital data.

89. The method for forming an integrated nonvolatile static random access memory of claim 59 wherein forming the first floating gate tunnel oxide transistor comprises the step of connecting the control gate of the first floating gate tunnel oxide transistor to receive read, program, and erase signals.

90. The method for forming an integrated nonvolatile static random access memory of claim 59 further comprises the step of applying a source line signal to the source line for reading, programming, and erasing the first floating gate tunnel oxide transistor.