Method for non-volatile memory with background data latch caching during read operations

• US 7,447,078 B2
• Filed: 05/05/2006
• Issued: 11/04/2008
• 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: Li, Yan
• Primary Examiner(s): Hoang; Huan
• Assistant Examiner(s): Weinberg; Michael J
• Application Number:
  US11/381,994
• Publication Number:
  US 20060221696A1
• Time in Patent Office: 914 Days
• Field of Search: 365/185
• US Class Current: 365/185.21
• CPC Class Codes: G06F 12/0893 Caches characterised by their organisation or structure
• CPC Class Codes: G06F 2212/2022 Flash memory
• CPC Class Codes: G06F 2212/3042 being part of a memory device, e.g. cache DRAM
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 2207/2245 Memory devices with an internal cache buffer
• CPC Class Codes: G11C 7/22 Read-write [R-W] timing or clocking circuits; Read-write [R-W] control signal generators or management

Abstract

Part of the latency from memory read or write operations is for data to be input to or output from the data latches of the memory via an I/O bus. Methods and circuitry are present for improving performance in non-volatile memory devices by allowing the memory to perform some of these data caching and transfer operations in the background while the memory core is busy with a read operation. A scheme for caching read data is implemented so that even when the read for a current page on a current wordline must be preceded by a prerequisite read of data on an adjacent wordline, the prerequisite read along with any I/O access is preemptively done in the cycle for reading a previous page so that the current read can be performed while the previously read page is busy with the I/O access.

Claims

1. A method of reading a non-volatile memory having addressable pages of memory cells on associated wordlines, comprising:

sensing and latching a page of data in each of a series of reading cycles, wherein said sensing and latching in a current reading cycle are directed to a current page of data on a current wordline and are performed responsive to prerequisite data from an adjacent wordline so as to correct for any perturbation effects therefrom;

preemptively sensing and latching the prerequisite data for the current page prior to the current reading cycle; and

performing in the current reading cycle, other than the first reading cycle, said sensing and latching of the current page while outputting a previous page sensed and latched in the just passed reading cycle.

2. The method of claim 1, wherein the memory cells each stores one bit of data.

3. The method of claim 1, wherein the memory cells each stores more than one bit of data and each page of memory cells on a wordline is associated with more than one page of binary data corresponding to the individual bits of each memory cell.

4. The method of claim 3, wherein said sensing and latching of the prerequisite data for the current page further comprises:

outputting a first flag obtained as part of the prerequisite data from said prerequisite sensing;

adjusting the prerequisite data responsive to the first flag; and

latching the adjusted prerequisite data to indicate whether corrections need to be made for the current page.

5. The method of claim 4, wherein the first flag indicates whether the prerequisite page of memory cells on the adjacent wordline has been programmed with all the bits.

6. The method of claim 5, further comprising:

when the first flag indicates that the adjacent wordline has not been programmed with all the bits, adjusting the prerequisite data to indicate no correction is needed.

7. The method of claim 5, further comprising:

when the first flag indicates that the adjacent wordline has been programmed with all the bits, adjusting the prerequisite data to indicate that correction is needed.

8. The method of claim 4, wherein said sensing and latching of a current page further comprises:

performing said sensing of the current page with corrections from the adjusted prerequisite data;

outputting a second flag obtained as part of the current page;

responsive to the second flag, refreshing the current page by one of the group steps consisting of;

(1) leaving the page unchanged;

(2) adjusting the page to a predetermined value; and

(3) replacing with a new pabe obtained by repeating said sensing of the current page under another set of sensing conditions; and

latching the refreshed current page for outputting in the next reading cycle.

9. The method of claim 8, wherein said sensing of the current page for those memory cells that needs correction as indicated by the adjusted prerequisite data is performed at a wordline voltage with a predetermined boost.

10. The method of claim 8, wherein the second flag indicates whether the current page of memory cells on the current wordline has been programmed with all the bits.

11. The method of claim 10, wherein:

when the second flag indicates that the adjacent wordline has been programmed with all the bits, said refreshing the current page is a null operation which leaves the current page unchanged.

12. The method of claim 10, wherein:

the memory cells each stores two bits of data;

the page of memory cells is constituted from a lower-bit page and an upper-bit page; and

when the second flag indicates that the adjacent wordline has not been programmed with all the bits, and the current page being sensed is an upper-bit page, said refreshing the current page is by resetting the current page data all to a predetermined bit value indicating the upper-bit page has not been programmed.

13. The method of claim 10, wherein:

the memory cells each stores two bits of data;

the page of memory cells is constituted from a lower-bit page and an upper-bit page; and

when the second flag indicates that the adjacent wordline has not been programmed with all the bits, and the current page being sensed is a lower-bit page, said refreshing the current page is by sensing the current page relative to another predetermined reference.