Non-volatile memory erase circuitry

• US 6,934,188 B2
• Filed: 06/18/2004
• Issued: 08/23/2005
• Est. Priority Date: 07/19/2002
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Roohparvar, Frankie Fariborz
• Primary Examiner(s): HO, HOAI V
• Application Number:
  US10/871,919
• Publication Number:
  US 20040228201A1
• Time in Patent Office: 431 Days
• Field of Search: 365/185.18, 365/185.19, 365/185.28, 365/182.29, 365/185.29
• US Class Current: 365/185.18
• CPC Class Codes: G11C 16/30 Power supply circuits

Abstract

A non-volatile memory device includes floating gate memory cells, a pulse counter and voltage pump control circuitry. The control circuitry selectively activates pumps in response to a count output of the counter. In one embodiment, the pump output current is increased as the counter output increases. The memory allows for erase operations that reduce leakage current during initiation of an erase operation.

Claims

1. A non-volatile memory device comprising:

an array of memory cells;

a counter circuit coupled to count voltage pulses applied to the memory cells and generate a count output in response to the counted voltage pulses; and

a voltage pump circuit for generating an elevated output voltage from an input voltage, the voltage pump circuit coupled to the counter circuit such that the elevated output voltage adjusts in response to the count output.

2. The device of claim 1 wherein the voltage pump circuit comprises a plurality of parallel voltage pumps, wherein the input voltage is V_CC and the elevated voltage output is a multiple of V_CC.

3. The device of claim 1 wherein the voltage pulses are erase pulses to erase at least a portion of the array of memory cells.

4. The device of claim 1 wherein the array of memory cells is a flash memory array comprising a plurality of floating gate memory cells.

5. The device of claim 2 wherein each of the plurality of parallel pump stages are selectively activated in response to the count output.

6. The device of claim 5 wherein a number of activated parallel pumps increases in response to a corresponding count increase of the output of the counter circuit.

7. A flash memory device comprising:

an array of memory cells;

a first voltage pump coupled to produce an output voltage from an input voltage, wherein the output voltage is produced by sequentially elevating the input voltage through first series coupled pump stages;

a second voltage pump coupled in parallel to the first voltage pump to produce the output voltage from the input voltage, wherein the output voltage is produced by sequentially elevating the input voltage through second series coupled pump stages;

a counter for generating a count output comprising a quantity of voltage pulses applied to the array during memory operations; and

a control circuit coupled to the first and second voltage pumps and the counter, wherein the control circuit selectively activates, during the memory operations, the first and second voltage pumps in response to the count output.

8. The device of claim 7 wherein the first and second voltage pumps are adapted to be selectively activated to increase a cumulative output current of the first and second voltage pumps in response to an increasing count output.

9. A flash memory device comprising:

an array of memory cells; and

control circuitry for performing an erase operation on the memory cells, the control circuitry controlling a series of voltage pulses applied to the memory cells and adjusting a current limit of the voltage pulses in response to an input voltage pulse count indicative of a quantity of voltage pulses applied to the memory cells during memory operation.

10. The device of claim 9 and further comprising:

a first and second parallel voltage pumps each coupled to produce an output voltage from an input voltage, wherein the output voltage is produced by sequentially elevating the input voltage through series coupled pump stages;

a counter for generating the voltage pulse count wherein the control circuitry is coupled to the first and second parallel voltage pumps and the counter to selectively activate the first and second parallel voltage pumps in response to the voltage pulse count.

11. A method for erasing a flash memory device comprising:

pre-programming a block of memory cells;

generating an erase voltage from a supply voltage using a voltage pump circuit having a plurality of parallel coupled pumps, the erase voltage being a multiple of the supply voltage;

applying a plurality of erase pulses to the block of memory cells, each erase pulse having a voltage level substantially equal to the erase voltage;

counting the erase pulses applied to the block of memory cells; and

adjusting a current limit of the erase voltage by selectively activating the plurality of parallel coupled pumps in response to an increasing count of the erase pulses.

12. The method of claim 11 wherein erase current limit is increased in response to the increasing count.

13. The method of claim 11 wherein adjusting the erase current limit comprises:

activating a first plurality of pumps of the voltage pump circuit while an output count of a counter circuit is equal to or less than X counts, such that the pump circuit provides an output voltage with a first current limit; and

activating the first plurality of pumps and a second plurality of pumps of the voltage pump circuit while an output count of the counter circuit is greater than X counts, such that the pump circuit provides the output voltage with a second current limit that is greater than the first current limit.

14. A non-volatile memory system comprising:

a processor that generates memory signals; and

a non-volatile memory device coupled to the processor, the memory device comprising;

an array of memory cells;

a counter circuit coupled to count voltage pulses applied to the memory cells, the counter circuit generating a count output in response to a quantity of voltage pulses; and

a voltage pump circuit for generating an elevated voltage output from an input voltage; and

control circuitry coupled to the voltage pump circuit for adjusting, during predetermined memory operations, a current sourced by the voltage pump circuit in response to the count output.

15. The device of claim 14 wherein an erase current limit of the voltage pump circuit increases as the count output increase and decreases as the count output decreases.

16. The device of claim 14 wherein the non-volatile memory device is a floating gate flash memory cell.

17. The device of claim 14 wherein the input voltage is V_CC and the elevated voltage output is greater than V_CC.

18. The device of claim 14 wherein the memory signals are address and data signals.