Adjacent memory cell interference mitigation
A control circuit on a control die compensates for interference caused by adjacent memory cells on target memory cells on a memory die. The compensation may be based on the data states of the adjacent memory cells. Data latches may be used to store data states of the memory cells. However, reading the target memory cells can over-write the data states of the adjacent memory cells in the data latches. The control die may store data state information for the adjacent memory cells prior to sensing the target memory cells (e.g., prior to a decoding error of a codeword in the target cells). Saving the data state information on the control die reduces storage requirements of the memory die and alleviates the need to sense the adjacent memory cells again if decoding the codeword in the target memory cells fails.
1. An apparatus, comprising:
storage, wherein the storage comprises data latches and data state information storage; and
a control circuit connected to the storage, the control circuit configured to connect to a memory die comprising first non-volatile memory cells connected to a first word line in a block and second non-volatile memory cells connected to a second word line in the block adjacent to the first word line, the control circuit configured to:
sense the first memory cells;
store first sense information from sensing the first memory cells into the data latches;
store, into the data state information storage, data state information for each of the first memory cells based on the first sense information from sensing the first memory cells in the data latches, the storing occurs prior to sensing the second memory cells in a set of reads of word lines in the block;
sense the second memory cells;
store second sense information from sensing the second memory cells into the data latches thereby overwriting the first sense information; and
determine conditions of the second non-volatile memory cells based on the stored data state information, including use the stored data state information for the first memory cells to determine the conditions of the second non-volatile memory cells after overwriting the first sense information.
2. The apparatus of claim 1 , wherein the control circuit is further configured to:
use the stored data state information to determine a hard bit for each of the second memory cells; and
use the stored data state information to determine a soft bit for each of the second memory cells in response to a decoding error with respect to the hard bits for the second memory cells.
3. The apparatus of claim 1 , wherein:
the control circuit and the storage reside on a control die that is bonded to the memory die;
the memory die comprises bit lines associated with the first memory cells and with the second memory cells; and
the control circuit is further configured to sense the first memory cells and the second memory cells by sensing the bit lines.
4. The apparatus of claim 1 , wherein the control circuit is further configured to:
determine the condition of a selected memory cell connected to the second word line based on a reference voltage applied to the selected memory cell, wherein the reference voltage provides compensation for interference on the selected memory cell that corresponds to the stored data state information for an adjacent memory cell to the selected memory cell.
5. The apparatus of claim 1 , wherein the control circuit and the storage reside on a control die that is affixed to the memory die, wherein the control circuit is further configured to:
determine initial state information from the second sense information;
use the stored data state information to perform equalization of the initial state information, wherein the equalization compensates for interference of the first memory cells on the second memory cells; and
determine data states of the second memory cells based on the equalization.
6. The apparatus of claim 1 , wherein the control circuit is further configured to:
determine a hard bit for each of the second memory cells based on the stored data state information;
transfer the hard bit for each second memory cell to a memory controller;
provide soft bits to the memory controller in response to a request from the memory controller for the soft bits, comprising:
apply soft bit read reference voltages to the second word line;
sense each second non-volatile memory cell in response to application of the soft bit read references voltages, wherein soft bit sense data is generated for each second memory cell for each of the soft bit read references voltages;
use the stored data state information for a first memory cell adjacent to a respective second memory cell to select which soft bit sense data to use for each respective second memory cell; and
determine the soft bit for each of the second memory cells based on the selected soft bit sense data for each respective second memory cell.
7. The apparatus of claim 1 , wherein the control circuit is configured to:
store, into the data state information storage, the data state information for each of the first memory cells prior to a failure to decode a codeword stored in the second memory cells; and
determine the conditions of the second non-volatile memory cells based on the stored data state information in response to the failure to decode the codeword stored in the second memory cells.
8. The apparatus of claim 1 , wherein the control circuit is configured to read the first word line immediately prior to reading the second word line in the reads of the word lines in the block.
9. A method comprising:
sensing first non-volatile memory cells connected to a first word line, the first non-volatile memory cells and the first word line reside on a memory die that is affixed to a control die, the sensing controlled by a control circuit on the control die;
storing first sense information for each respective first memory cell into data latches on the control die based on sensing the first memory cells;
storing data state information in data state information storage on the control die for each respective first memory cell based on the first sense information in the data latches prior to sensing second non-volatile memory cells connected to a second word line adjacent to the first word line in a sequential read of the first and second word lines, the data state information for each respective first memory cell specifies a set of one of more data states in which the respective first memory cell resides;
compensating for interference of the first memory cells on the second memory cells based on the stored data state information after over-writing the first sense information in the data latches with second sense information of the second memory cells; and
determining data states of the second memory cells as a result of the compensation.
10. The method of claim 9 , wherein compensating for interference of the first memory cells on the second memory cells based on the stored data state information comprises:
applying different hard bit read reference voltages to the second word line to test for whether respective second memory cells have a threshold voltage above or below a hard bit reference level, wherein each of the different hard bit read reference voltages applies a different amount of compensation; and
sensing each respective second memory cell for one of the different hard bit read reference voltages that is based on the stored data state information;
wherein the second sense information in the data latches corresponds to a hard bit read reference voltage that provides an amount of compensation that corresponds to the interference caused by an adjacent first memory cell to the respective second memory cell.
11. The method of claim 10 , wherein compensating for interference of the first memory cells on the second memory cells based on the stored data state information further comprises:
applying different soft bit read reference voltages to the second word line to test for whether respective second memory cells have a threshold voltage above or below a soft bit reference level, wherein each of the different soft bit read reference voltages applies a different amount of compensation;
sensing each respective second memory cell for a subset of the different soft bit read reference voltages that is based on the stored data state information; and
storing third sense information for each respective second memory cell into the data latches on the control die based on sensing the second memory cells, wherein the third sense information over-writes the second sense information, wherein the stored third sense information corresponds to a subset of the soft bit read reference voltages that provide an amount of compensation that corresponds to the interference caused by the adjacent first memory cell to the respective second memory cell.
12. The method of claim 9 , wherein compensating for interference of the first memory cells on second memory cells based on the stored data state information comprises:
determine initial state information from the second sense information of the second memory cells; and
performing equalization, based on the stored data state information, on the initial state information that provides an amount of compensation for each respective second memory cell that corresponds to the interference caused by an adjacent first memory cell to the respective second memory cell.
13. A non-volatile storage system, comprising:
a memory die comprising non-volatile memory cells, a plurality of word lines connected to the memory cells, and bit lines associated with the memory cells; and
a control die bonded to the memory die by way of bond pads, wherein the control die comprises:
sensing means for sensing bit lines by way of the bond pads, the bit lines associated with first non-volatile memory cells connected to a first word line of the plurality of word lines;
data state storage means for storing data state information for each of the first memory cells prior to a failure to decode a codeword stored in second memory cells connected to a second word line adjacent to the first word line, the data state information based on the sensing and specifying a range of one of more data states in which the respective first memory cell resides; and
compensation means for applying data state dependent compensation to the second memory cells based on the stored data state information.
14. The non-volatile storage system of claim 13 , wherein the compensation means is configured to:
use the stored data state information to determine a hard bit for each of the second memory cells, the hard bits for the second memory cells forming the codeword; and
use the stored data state information to determine a soft bit for each of the second memory cells in response to a failure to successfully decode the codeword.
15. The non-volatile storage system of claim 14 , wherein the data state storage means is configured to:
store first data states of the first memory cells into data latches on the control die; and
over-write the first data states of the first memory cells in the data latches with second data states of the second memory cells when using the stored data state information to determine a hard bit for each of the second memory cells.
16. The non-volatile storage system of claim 14 , wherein:
the compensation means is configured to apply different hard bit read reference voltages to the second memory cells, wherein each of the different hard bit read reference voltages applies a different amount of data state dependent compensation;
the sensing means is configured to provide sense information for each respective second memory cell for at least a hard bit read reference voltage that provides compensation for interference from an adjacent first memory cell to the respective second memory cell; and
the compensation means is configured to use the sense information that provides compensation for interference from the adjacent first memory cell to the respective second memory cell to determine a condition of the respective second memory cell.
17. The non-volatile storage system of claim 13 , wherein:
the compensation means is further configured to apply different soft bit reference voltages to the second memory cells;
the sensing means is configured to generate sense information for each respective second memory cell for at least a set of the soft bit reference voltages that provide compensation for interference from an adjacent first memory cell to the respective second memory cell; and
the compensation means is configured to use the sense information for the set of the soft bit reference voltages that provide compensation for interference from the adjacent first memory cell to the respective second memory cell to determine a condition of the respective second memory cell.
18. The non-volatile storage system of claim 13 , wherein:
the data state storage means is configured to store first data states of the first memory cells into data latches on the control die, and over-write the first data states of the first memory cells in the data latches with second data states of the second memory cells; and
the compensation means for applying state dependent compensation to the first memory cells is configured to perform equalization on the second data states that provides an amount of state dependent compensation for each respective second memory cell that corresponds to data state of an adjacent first memory cell to the respective second memory cell after over-writing the first data states of the first memory cells in the data latches with second data states of the second memory cells.
19. A non-volatile storage system, comprising:
storage, wherein the storage comprises data latches and data state information storage; and
a control circuit connected to the storage, the control circuit configured to connect to a memory die comprising first non-volatile memory cells connected to a first word line in a block and second non-volatile memory cells connected to a second word line in the block adjacent to the first word line, the control circuit configured to:
sense the first memory cells;
store, into the data state information storage, data state information for each of the first memory cells based on sensing the first memory cells, the storing occurs prior to sensing the second memory cells in a set of reads of word lines in the block and prior to a failure to decode a codeword stored in the second memory cells; and
determine conditions of the second non-volatile memory cells based on the stored data state information in response to the failure to decode the codeword stored in the second memory cells.
20. A non-volatile storage system, comprising:
a memory die comprising non-volatile memory cells, a plurality of word lines connected to the memory cells, and bit lines associated with the memory cells; and
a control die bonded to the memory die by way of bond pads, wherein the control die comprises storage and a control circuit in communication with the storage and with the memory die, wherein the storage comprises data latches and data state information storage, wherein the control circuit is configured to:
sense first memory cells connected to a first word line in a block on the memory die;
store, into the data state information storage, data state information for each of the first memory cells based on sensing the first memory cells, the storing occurs prior to sensing second memory cells connected to a second word line in the block in a set of reads of word lines in the block;
sense the second memory cells connected to the second word line;
transfer sense information from sensing the second memory cells from the memory die to the storage;
determine initial state information for the second memory cells from the sense information in the data state information storage; and
use the stored data state information for the first memory cells to perform equalization of the initial state information for the second memory cells, wherein the equalization compensates for interference of the first memory cells on the second memory cells; and
determine data states of the second memory cells based on the equalization.