CAM NAND with OR function and full chip search capability

• US 8,780,634 B2
• Filed: 08/01/2013
• Issued: 07/15/2014
• Est. Priority Date: 11/09/2012
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Li, Yan, Sprouse, Steven T.
• Primary Examiner(s): Byrne, Harry W
• Application Number:
  US13/957,198
• Publication Number:
  US 20140133233A1
• Time in Patent Office: 348 Days
• Field of Search: 36518501-18533
• US Class Current: 365/185.17
• CPC Class Codes: G11C 15/046 using non-volatile storage elements
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series

Abstract

Various techniques for extending the capabilities of CAM NAND type memories are discussed. Multi-block or even full chip search operations can be performed. In addition to the inherent AND property of NAND strings, the memory array has an inherent OR property between NAND string from different blocks along the same bit line that can be exploited through multi-block CAM-type operations. To reduce data-dependent word line to word line effects, in multiple data dependent sensing operations, the sensing can be broken up into sub-operations that avoid data dependent values on adjacent word lines. To improve data protection, subsequent to writing a memory block with indices, the word lines are read back and compared bit-by-bit with their intended values and the results are accumulated to determine whether any of indices include error. A bloom filter can also be used as an initial check during data search operations in order to provide increased data protection.

Claims

1. A memory circuit comprising:

an array of non-volatile memory cells arranged along a plurality of word lines and a plurality of M bit lines into a NAND type of architecture, the array formed of multiple blocks, each of the blocks including a plurality of M NAND strings connected along a corresponding one of the M bit lines and each having a plurality of N memory cells connected in series with a plurality of N word lines spanning the M NAND strings, each of the N word lines connected to a corresponding one of the N memory cells thereof;

word line driving circuitry connectable to the word lines, whereby one or more word lines in a plurality of blocks can be concurrently and individually be set to one of a plurality of data dependent read values corresponding to a respective data pattern for each of the plurality of blocks; and

sensing circuitry connectable to the M bit lines individually determine those of the M bit lines where at least one of the NAND strings connected therealong are conducting in response the word line driving circuitry applying said respective data patterns to the corresponding plurality of blocks.

2. The memory circuit of claim 1, where the memory array is of a flash type memory where the block is the unit of erase.

3. The memory circuit of claim 1, wherein the plurality of blocks is all of the block of the array.

4. The memory circuit of claim 1, wherein the sensing circuitry includes a plurality of latches associated with each of the bit lines to independently store the results of a plurality of multi-block sensing operations.

5. The memory circuit of claim 4, wherein the sensing circuitry can perform logical/arithmetical operation on the results from the multi-block sensing operations stored in the latches.

6. The memory circuit of claim 5, wherein the logical/arithmetical operation is part of a join operation.

7. The memory circuit of claim 1, further comprising control circuitry wherein the memory circuit performs a sequence of two or more multi-block sensing operations, where the control circuitry determines one or more of the operations of the sequence based upon the result of a preceding operation of the sequence.

8. The memory circuit of claim 7, wherein the sequence of multi-block sensing operations is binary search type of operation determine to which block a NAND string conductive in response to a data pattern being applied thereto belongs.

9. The memory circuit of claim 1, wherein the memory array stores a first data set in a first of the blocks and a copy of the first data set in a second of the blocks.

10. The memory circuit of claim 1, wherein the memory array stores a first data set in a first of the blocks and a copy of the first data set in inverted form in a second of the blocks.

11. The memory circuit of claim 1, further comprising:

programming circuitry connectable to the memory array to write in pages of data received from a host into the memory array.

12. The memory circuit of claim 11, wherein the programming circuit includes logic circuitry whereby a page of data corresponding to the inverted form of a received page of data can be generated.

13. A method of operating a memory system, the memory system including a memory circuit having an array of non-volatile memory cells arranged into a plurality of blocks, each of the blocks including a first plurality NAND strings and a plurality word lines spanning the NAND strings, each of the word lines connected to a corresponding one of the memory cells thereof, where a first plurality of bit lines span the blocks with each of the blocks having one of the NAND strings thereof connected along a corresponding one of the bit lines, the method comprising:

receiving for each of a first plurality of the blocks a corresponding first search data pattern from a host device to which the memory system is connected;

concurrently biasing one or more word lines of the first plurality of blocks according to the corresponding first search data patterns; and

concurrently determining those of the bit lines that conduct in response to the one or more word lines of the first plurality of blocks being concurrently biased according to the first corresponding first data search patterns.

14. The method of claim 13, further comprising:

storing in a first latch associated with each of the bit lines the result of said determining those of the bit lines that conduct in response to the one or more word lines of the first plurality of blocks being concurrently biased according to the corresponding first data search patterns.

15. The method of claim 14, further comprising

receiving for each of a second plurality of the blocks a corresponding second search data pattern from a host device to which the memory system is connected;

concurrently biasing one or more word lines of the second plurality of blocks according to the corresponding second search data patterns;

concurrently determining those of the bit lines that conduct in response to the one or more word lines of the second plurality of blocks being concurrently biased according to the corresponding second data search patterns;

storing in a second latch associated with each of the bit lines the result of said determining those of the bit lines that conduct in response to the one or more word lines of the second plurality of blocks being concurrently biased according to the corresponding second data search patterns; and

subsequently performing on the memory circuit a logical/arithmetical operation on the contents of the first and second latches.

16. The method of claim 15, wherein the logical/arithmetical operation is part of a join operation.

17. The method of claim 13, wherein the first plurality of the blocks is all of the blocks of the array.

18. The method of claim 13, further comprising:

based on the result of said determining those of the bit lines that conduct in response to the one or more word lines of the first plurality of blocks being concurrently biased according to the first corresponding first data search patterns, determining one or more second blocks;

concurrently biasing one or more word lines of the one or more second blocks according to one or more corresponding second search data patterns; and

concurrently determining those of the bit lines that conduct in response to the one or more word lines of the second blocks being concurrently biased according to the one or more second corresponding first data search patterns.

19. The method of claim 18, wherein in the second blocks are determined as part of performing a binary search type of operation determine to which block a NAND string conductive in response to a data pattern being applied thereto belongs.

20. The method of claim 13, wherein the first plurality of blocks includes a first block storing a data pattern on each of the NAND strings thereof and a second block storing the same data pattern in inverted form on each of the bit lines, and wherein concurrently biasing one or more word lines of the first plurality of blocks according to the corresponding first search data patterns includes biasing the word lines of the second block with search data pattern applied to the first block in inverted form.

21. The method of claim 20, further comprising prior to said receiving for each of the first plurality of the blocks the corresponding first search data pattern:

receiving on the memory circuit data pages corresponding to the data of the first block;

generating on the memory circuit data pages corresponding to the data of the second block; and

writing the data pages corresponding to the first and second data blocks into the first and second data blocks.

22. The method of claim 13, wherein the first plurality of blocks includes a first block storing a data pattern on each of the NAND strings thereof and a second block storing the same data pattern on each of the bit lines, and wherein concurrently biasing one or more word lines of the first plurality of blocks according to the corresponding first search data patterns includes biasing the word lines of the second block with search data pattern applied to the first block.

23. The method of claim 22, wherein said concurrently biasing one or more word lines of the first plurality of blocks according to the corresponding first search data patterns includes biasing a corresponding first word line on both the first and second blocks according to the same search data pattern as part of a range search operation.