Voltage regulator for non-volatile semiconductor memory devices

• US 5,576,990 A
• Filed: 01/03/1995
• Issued: 11/19/1996
• Est. Priority Date: 12/31/1993
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: SGS-Thomson Microelectronics, S.R.L. (STMicroelectronics NV)
• Inventors: Casagrande, Giulio, Camerlenghi, Emilio
• Primary Examiner(s): Popek, Joseph A.
• Application Number:
  US08/367,538
• Time in Patent Office: 686 Days
• Field of Search: 365/185.20, 365/185.21, 365/185.23, 365/185.18, 257/314, 257/315, 257/316, 257/318
• US Class Current: 365/185.23
• CPC Class Codes: G11C 16/30 Power supply circuits
• CPC Class Codes: G11C 5/147 Voltage reference generators, voltage or current regulators; Internally lowered supply levels; Compensation for voltage drops G11C5/141 takes precedence

Abstract

A voltage regulator for electrically programmable non-volatile semiconductor memory devices of the type comprising a gain stage (3), supplied by a programming voltage (V_PP) and having an input terminal connected to a divider (6) of said programming voltage (V_PP) and an output terminal (U) connected to a programming line (5) of at least one memory cell (2) comprises at least one circuit element (4) capable of adapting the line programming voltage (5) to the length (L) of the memory cell (2). This solution makes it possible to have on the bit line of the memory device a drain voltage varying according to the actual length of the memory cell.

Claims

1. A circuit for regulating the voltage applied to a bit line of a floating-gate memory, comprising:

a voltage divider network connected between a programming voltage connection and chip ground;

an array of floating-gate field effect transistor memory cells organized in bit lines;

said voltage divider network comprising gate elements of said transistors of said array interconnected as resistive voltage divider elements; and

a voltage regulator circuit, connected to drive at least a selected one of said bit lines of said array with a voltage which is determined by that of an intermediate point in said voltage divider.

2. The integrated circuit of claim 1, further comprising a plurality of bit line selection transistors, interconnected with logic elements so that said voltage regulator circuit is only connected to one of said bit lines at a time, and only during a write mode operation.

3. The integrated circuit of claim 1, wherein said floating-gate memory cells are EEPROM cells.

4. A circuit for regulating the voltage applied to a bit line of a floating-gate memory, comprising:

an array of floating-gate field effect transistor memory cells organized in bit lines;

a voltage divider network, connected between a programming voltage connection and chip ground, comprising gate elements of said transistors of said array interconnected as resistive voltage divider elements; and

a voltage regulator circuit, connected to drive at least a selected one of said bit lines of said array with a voltage which is equal to that of an intermediate point in said voltage divider.

5. The integrated circuit of claim 4, further comprising a plurality of bit line selection transistors, interconnected with logic so that said voltage regulator is only connected to one of said bit lines at a time, and only during a write mode operation.

6. The integrated circuit of claim 4, wherein said floating-gate memory cells are EEPROM cells.

7. A nonvolatile memory integrated circuit, comprising:

an array of floating-gate field effect transistor memory cells, each including a control gate overlying a floating gate which is capacitively coupled to a respective transistor channel, wherein said array is organized in bit lines;

a voltage divider comprising elements in the same thin film layer as said control gate, and configured to provide a dividing ratio which is affected by process variations in said thin film layer; and

a voltage regulator circuit, connected to drive at least a selected one of the bit lines of said array with a voltage which is equal to that of an intermediate point in said voltage divider;

wherein variations in the effective channel length of said memory cells produce corresponding variations in said regulated drain voltage, to provide an optimal regulated drain voltage.

8. The integrated circuit of claim 7, wherein said control gate and said floating gate are both polycrystalline and predominately comprise silicon.

9. The integrated circuit of claim 7, wherein said voltage divider consists of control gate elements of said transistors of said array interconnected as resistive voltage divider elements.

10. The integrated circuit of claim 7, wherein said voltage divider consists of control gate elements and floating gate elements of said transistors of said array interconnected as resistive voltage divider elements.

11. The integrated circuit of claim 7, further comprising a plurality of bit line selection transistors, interconnected with logic elements so that said voltage regulator circuit is only connected to one of said bit lines at a time, and only during a write mode operation.

12. The integrated circuit of claim 7, wherein said floating-gate memory cells are EEPROM cells.

35. The nonvolatile memory integrated circuit of claim 7, wherein said voltage divider is a resistive voltage divider.

13. A nonvolatile memory integrated circuit, comprising:

an array of floating-gate field effect transistor memory cells, each including a control gate overlying a floating gate which is capacitively coupled to a respective transistor channel, wherein said array is organized in bit lines;

a voltage divider comprising elements in the same thin film layer as said control gate, and also comprising elements in the same thin film layer as said floating gate, and configured to provide a dividing ratio which is affected by process variations in said thin film layer; and

a voltage regulator circuit, connected to drive at least a selected one of the bit lines of said array with a voltage which is equal to that of an intermediate point in said voltage divider;

wherein variations in the effective channel length of said memory cells produce corresponding variations in said regulated drain voltage, to provide an optimal regulated drain voltage.

14. The integrated circuit of claim 13, wherein said control gate and said floating gate are both polycrystalline and predominately comprise silicon.

15. The integrated circuit of claim 13, wherein said voltage divider network consists of control gate elements of said transistors of said array interconnected as resistive voltage divider elements.

16. The integrated circuit of claim 13, wherein said voltage divider network consists of control gate elements and floating gate elements of said transistors of said array interconnected as resistive voltage divider elements.

17. The integrated circuit of claim 13, further comprising a plurality of bit line selection transistors, interconnected with logic elements so that said voltage regulator circuit is only connected to one of said bit lines at a time, and only during a write mode operation.

18. The integrated circuit of claim 13, wherein said floating-gate memory cells are EEPROM cells.

36. The nonvolatile memory integrated circuit of claim 13, wherein said voltage divider is a resistive voltage divider.

19. A nonvolatile memory integrated circuit, comprising:

an array of floating-gate field effect transistor memory cells, each including a control gate overlying a floating gate which is capacitively coupled to a respective transistor channel, wherein said array is organized in bit lines;

a voltage divider comprising elements in the same thin film layer as said floating gate, and configured to provide a dividing ratio which is affected by process variations in said thin film layer; and

a voltage regulator circuit, connected to drive at least a selected one of the bit lines of said array with a voltage which is equal to that of an intermediate point in said voltage divider;

wherein variations in the effective channel length of said memory cells produce corresponding variations in said regulated drain voltage, to provide an optimal regulated drain voltage.

20. The integrated circuit of claim 19, wherein said control gate and said floating gate are both polycrystalline and predominately comprise silicon.

21. The integrated circuit of claim 19, wherein said voltage divider network consists of control gate elements of said transistors of said array interconnected as resistive voltage divider elements.

22. The integrated circuit of claim 19, wherein said voltage divider network consists of control gate elements and floating gate elements of said transistors of said array interconnected as resistive voltage divider elements.

23. The integrated circuit of claim 19, further comprising a plurality of bit line selection transistors, interconnected with logic so that said voltage regulator is only connected to one of said bit lines at a time, and only during a write mode operation.

24. The integrated circuit of claim 19, wherein said floating-gate memory cells are EEPROM cells.

37. The nonvolatile memory integrated circuit of claim 19, wherein said voltage divider is a resistive voltage divider.

25. A method for regulating the write voltage applied to bit lines in a memory chip including nonvolatile field-effect transistors, comprising the steps of:

(a.) generating a voltage at an intermediate node of a voltage divider, which includes at least one resistive element in the same thin film layer as at least one gate element of said nonvolatile field-effect transistors, said voltage divider being connected between a programming voltage connection and chip ground; and

(b.) when a bit line is selected for a write operation, using a voltage regulator which references said intermediate node of said voltage divider to apply a constant regulated voltage to said selected bit line;

wherein said regulated voltage has little or no dependence on said programming voltage, and is optimized for the variations in the device characteristics of memory cells of the array.

26. The method of claim 25, wherein said voltage regulator comprises an operational amplifier.

38. The nonvolatile memory integrated circuit of claim 25, wherein said voltage divider is a resistive voltage divider.

27. A voltage regulator for electrically programmable non-volatile semiconductor memory devices of the type comprising a gain stage supplied by a programming voltage and having an input terminal connected to a divider of said programming voltage and an output terminal connected to a programming line of at least one memory cell, comprising at least one circuit element capable of adapting the programming line voltage on the basis of the length of the memory cell.

28. The voltage regulator of claim 27, wherein said element is the divider of the programming voltage and comprises resistances having variable resistance.

29. The voltage regulator of claim 28, wherein said resistances have a resistivity value correlated with the length of the memory cell.

30. The voltage regulator of claim 28, wherein said resistances are provided in a second layer of polysilicon and silicide forming the command gates of the cells of a word line incorporated in the memory device.

31. The voltage regulator of claim 28, wherein said resistances are provided in a first layer of polycrystalline forming the floating gate of the cells of a word line incorporated in the memory device.

32. The voltage regulator of claim 30, wherein said first polysilicon layer and second polysilicon layer are mutually short-circuited.

33. The voltage regulator of claim 30, wherein said memory device comprises a cell matrix wherein said resistances are provided in dummy word lines incorporated in the memory device inside the cell matrix.

34. The voltage regulator of claim 30, wherein said memory device comprises a cell matrix wherein said resistances are provided in dummy word lines incorporated in the memory device outside the cell matrix.

39. The nonvolatile memory integrated circuit of claim 27, wherein said voltage divider is a resistive voltage divider.