Use of Data Latches in Multi-Phase Programming of Non-Volatile Memories

• US 20070097744A1
• Filed: 12/04/2006
• Published: 05/03/2007
• Est. Priority Date: 04/01/2005
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Raul-Adrian Cernea, Yan Li
• Inventors: Cernea, Raul-Adrian, Li, Yan
• Granted Patent: US 7,508,721 B2
• Time in Patent Office: Days
• US Class Current: 365/185.05
• 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 non-volatile memory device, comprising:

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, comprising;

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

bias circuitry to set bias conditions in the memory cells concurrently with the programming waveform being applied to the memory cells, 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

one or more sets of latches each associated with a corresponding one of the memory cells to which the read/write circuitry is connected, wherein a first latch of each of said sets of latches governs which of the programming phases is active.

2. The non-volatile memory device of claim 1, wherein during the first programming phase the channel of selected memory cells is set to ground and during the second programming phase the channel of the selected memory cells is allowed to be at a higher voltage than during the first phase.

3. The non-volatile memory device of claim 1, wherein the number of latches in each of said sets of latches is N+1.

4. The non-volatile memory device 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 non-volatile memory device of claim 4, wherein the first memory latches are initialized based on the data to be programmed into the corresponding memory cell.

6. The non-volatile memory device of claim 1, wherein the read/write circuitry further comprises:

sense circuitry to perform a verify operation for one or more of said N bits of data for selected ones of the memory cells during the course of a program operation, wherein the verify for at least one of said bits of data includes a verify at a first level and a second, higher level, the result of the verify at the first level being stored in the first latch for the governing of the programming phase.

7. The non-volatile memory device of claim 6, wherein the number of latches in each of said sets of latches is N+1.

8. The non-volatile memory device of claim 7, 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.

9. The non-volatile memory device of claim 8, 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 non-volatile memory device 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 non-volatile memory device 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, wherein during a write operation a plurality of selected memory cells are programmed concurrently by said waveform being applied to a selected word line.

12. The non-volatile memory device 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 a first latches governs which of the programming phases is active.

13. The non-volatile memory device of claim 12, where the memory device changes from the first programming phase to the second programming phase by changing the bias level on the bit lines.

14. The non-volatile memory device of claim 13, where the memory cells is 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 non-volatile memory device of claim 11, where the memory device has a NAND-type architecture.

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

17. The non-volatile memory device of claim 15, wherein N equals two and data is stored according to a lower page/upper page format.