Use of data latches in multi-phase programming of non-volatile memories

• US 7,508,721 B2
• Filed: 12/04/2006
• Issued: 03/24/2009
• Est. Priority Date: 04/01/2005
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Cernea, Raul-Adrian, Li, Yan
• Primary Examiner(s): Nguyen; Tuan T
• Assistant Examiner(s): LE, TOAN K
• Application Number:
  US11/566,583
• Publication Number:
  US 20070097744A1
• Time in Patent Office: 841 Days
• Field of Search: 365/189.01, 365/185.01, 365/185.21, 365/189.05, 365/189.08, 365/220, 365/189.011
• US Class Current: 365/189.011
• CPC Class Codes: G11C 16/3468 Prevention of overerasure or overprogramming, e.g. by verifying whilst erasing or writing

Abstract

A non-volatile memory device includes circuitry for governing a multi-phase programming process in a non-volatile memory. The exemplary embodiment uses a quick pass write technique where a single programming pass is used, but the biasing of the selected memory cells is altered to slow programming as the memory cells approach their target values by raising the voltage level of the channels of the selected memory cells. A principle aspect of the present invention introduces a latch associated with the read/write circuitry connectable to each selected memory cell along a corresponding bit line for the storage of the result of the verify at this lower level.

Claims

1. A method of performing a programming operation in a non-volatile memory device having one or more memory cells each capable of storing N bits of data, where N is greater than or equal to one, and read/write circuitry connectable to the memory cells, the read/write circuitry including programming circuitry, bias circuitry to set bias conditions in the memory cells and one or more sets of latches each associated with a corresponding one of the memory cells to which the read/write circuitry is connected, the method comprising:

applying a monotonically non-decreasing programming waveform from the programming circuitry to the memory cells;

concurrently with applying said programming waveform, setting bias conditions in the memory cells by said bias circuitry, wherein a first set of bias conditions is used during a first programming phase and a second set of bias conditions is used during a second programming phase; and

governing which of the programming phases is active by a first latch of each of said sets of latches.

2. The method of claim 1, wherein setting bias conditions during the first programming phase includes setting to ground the channel of selected memory cells and wherein setting bias conditions during the during the second programming phase includes allowing the channel of the selected memory cells to be at a higher voltage than during the first phase.

3. The method of claim 1, wherein the number of latches in each of said sets of latches is N+1.

4. The method of claim 3, wherein the N latches other than the first latch in each of said sets of latches is used to hold data to be programmed into the corresponding memory cell.

5. The method of claim 4, further comprising initializing the first memory latches based on the data to be programmed into the corresponding memory cell.

6. The method of claim 1, wherein the read/write circuitry further includes sense circuitry, the method further comprising:

performing a verify operation by sense circuitry for one or more of said N bits of data for selected ones of the memory cells during the course of the program operation, wherein the verify operation for at least one of said bits of data includes;

verifying at a first level; and

verifying at a second, higher level, the result of the verify at the first level being stored in the first latch for governing of the programming phase.

7. The method of claim 6, wherein the number of latches in each of said sets of latches is N+1.

8. The method of claim 7, further including:

holding in the N latches other than the first latch in each of said sets of latches data to be programmed into the corresponding memory cell.

9. The method of claim 8, wherein the value of the latches used to hold data to be programmed into the corresponding memory cell are updated based on the result of the verify at the second level for the corresponding memory cell.

10. The method of claim 6, wherein N is greater than one and the verify for at least one of said bits of data includes a verify at only a single level.

11. The method of claim 1, wherein said one or more memory cells is a plurality formed into an array along a plurality of bit lines and a plurality of word lines, and wherein during the programming operation a plurality of selected memory cells are programmed concurrently by said waveform being applied to a selected word line.

12. The method of claim 11, where each of said selected memory cells is connectable along one of the bit lines to the corresponding set of latches, each of the sets of latches including the first latch that governs which of the programming phases is active.

13. The method of claim 12, further including:

changing from the first programming phase to the second programming phase by changing the bias level on the bit lines.

14. The method of claim 13, where the memory cells are connectable along one of the bit lines to the corresponding set of latches though a corresponding clamp element, the clamp elements being commonly controlled, and wherein the changing of the bias on the bit lines from the first programming phase to the second programming phase is effected by controlling the clamp elements.

15. The method of claim 11, where the memory device has a NAND-type architecture.

16. The method of claim 15, where the memory device has a NAND-type architecture using an all bit line arrangement.

17. The method of claim 15, wherein N equals two and data is stored according to a lower page/upper page format.