Read operation for non-volatile storage with compensation for coupling
View Patent ↗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 account for this coupling, the read process for a particular memory cell will provide compensation to an adjacent memory cell in order to reduce the coupling effect that the adjacent memory cell has on the particular memory cell.
1. A method for reading data from non-volatile storage, comprising:
reading from a neighboring word line of a selected word line, said selected word line is connected to a set of selected non-volatile storage elements, said reading from a neighboring word line includes determining conditions of non-volatile storage elements that are neighbors to said set of selected non-volatile storage elements;
performing at least two read processes for said selected word line including applying a different voltage to said neighboring word line for each of said at least two read process; and
individually choosing data from one of said read processes for each of said set of selected non-volatile storage elements based on conditions of said non-volatile storage elements that are neighbors to said set of selected non-volatile storage elements.
2. A method according to claim 1 , wherein:
said performing at least two read processes includes performing one read process for each potential state of said non-volatile storage elements that are neighbors to said set of selected non-volatile storage elements.
3. A method according to claim 1 , wherein:
said performing at least two read processes includes applying a pass voltage to non-selected word lines for said at least two read processes, said pass voltage is different than at least one voltage concurrently applied to said neighboring word line during said read processes.
4. A method according to claim 1 , wherein:
said non-volatile storage element being read is a multi-state NAND flash memory device.
5. A method for reading data from a set of selected non-volatile storage elements, each non-volatile storage element of said set has a respective neighboring non-volatile storage element, said method comprising:
sensing condition information for said respective neighboring non-volatile storage elements;
performing a first read process for said selected non-volatile storage elements, said first read process includes applying a read voltage to said selected non-volatile storage elements and a first pass voltage to said respective neighboring non-volatile storage elements;
performing a one or more additional read processes for said selected non-volatile storage elements, said one or more additional read processes includes applying said read voltage to said selected non-volatile storage elements and additional pass voltages to said respective neighboring non-volatile storage elements; and
individually for each of said selected non-volatile storage elements, choosing data from said first read process or said additional processes based on said condition information for said respective neighboring non-volatile storage elements.
6. A method according to claim 5 , wherein:
said set of selected non-volatile storage elements and said respective neighboring non-volatile storage elements are part of NAND strings;
said NAND strings also include other unselected non-volatile storage elements; and
said first read process and said one or more additional read processes include applying a particular pass voltage to other unselected non-volatile storage elements, said particular pass voltage is different than at least one of said additional pass voltages.
7. A method according to claim 5 , wherein said one or more additional read processes comprise:
performing a second read process for said selected non-volatile storage elements, said second read process includes applying said read voltage to said selected non-volatile storage elements and a second pass voltage to said respective neighboring non-volatile storage elements, said step of choosing data includes choosing data from said first read process or said second read process based on said condition information for said respective neighboring non-volatile storage elements.
8. A method according to claim 5 , wherein said one or more additional read processes comprise:
performing a second read process for said selected non-volatile storage elements, said second read process includes applying said read voltage to said selected non-volatile storage elements and a second pass voltage to said respective neighboring non-volatile storage elements;
performing a third read process for said selected non-volatile storage elements, said third read process includes applying said read voltage to said selected non-volatile storage elements and a third pass voltage to said respective neighboring non-volatile storage elements; and
performing a fourth read process for said selected non-volatile storage elements, said fourth read process includes applying said read voltage to said selected non-volatile storage elements and a fourth pass voltage to said respective neighboring non-volatile storage elements;
said step of choosing data includes choosing data from said first read process, said second read process, said third read process or said fourth read process based on said condition information for said respective neighboring non-volatile storage elements.
9. A method for reading data non-volatile storage, comprising:
providing a compare voltage to a selected non-volatile storage element;
sensing a condition of a non-volatile storage element neighboring said selected non-volatile storage element;
providing compensation to said non-volatile storage element neighboring said selected non-volatile storage element based on said condition; and
sensing data for said a selected non-volatile storage element in response to said compare voltage and said compensation.