COMPENSATING FOR COUPLING DURING READ OPERATIONS OF NON-VOLATILE MEMORY

• US 20070109849A1
• Filed: 12/27/2006
• Published: 05/17/2007
• Est. Priority Date: 04/05/2005
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Chen, Jian
• Granted Patent: US 7,301,813 B2
• Time in Patent Office: Days
• US Class Current: 365/185.30
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data
• CPC Class Codes: G11C 16/3422 Circuits or methods to evaluate read or write disturbance in nonvolatile memory, without steps to mitigate the problem
• CPC Class Codes: G11C 2211/5634 Reference cells
• CPC Class Codes: G11C 2211/5648 Multilevel memory programming, reading or erasing operations wherein the order or sequence of the operations is relevant

Abstract

Shifts in the apparent charge stored on a floating gate (or other charge storing element) of a non-volatile memory cell can occur because of the coupling of an electric field based on the charge stored in adjacent floating gates (or other adjacent charge storing elements). The problem occurs most pronouncedly between sets of adjacent memory cells that have been programmed at different times. To compensate for this coupling, the read process for a given memory cell will take into account the programmed state of an adjacent memory cell.

Claims

1. A method for reading a set of non-volatile storage elements, comprising:

for each non-volatile storage element of at least a subset of said non-volatile storage elements, determining an offset from a predetermined set of offsets based on a charge level stored in an adjacent storage element; and

performing a set of read processes for said set of non-volatile storage elements, each read process of said set uses a different one of said predetermined set of offsets and is performed on all of said set of non-volatile storage elements, there is at least one read process for each offset, each of at least said subset of said set of non-volatile storage element provides final data from an appropriate one of said read processes associated with said offset determined for the respective non-volatile storage element.

2. A method according to claim 1, wherein:

said set of non-volatile storage elements store a first page of data; and

said set of non-volatile storage elements are connected to a first word line.

3. A method according to claim 1, wherein:

said determining an offset from a predetermined set of offsets includes reading a state of said adjacent storage element and correlating said state with said set of offsets.

4. A method according to claim 1, wherein said set of read processes comprises:

performing a first read process using a first offset and storing results for one or more non-volatile storage elements having an adjacent non-volatile storage element in a first state;

performing a second read process using a second offset and storing results for one or more non-volatile storage elements having an adjacent non-volatile storage element in a second state; and

performing a third read process with using a second offset and storing results for one or more non-volatile storage elements having an adjacent non-volatile storage element in a third state.