Memory device with reduced sense time readout

• US 8,400,858 B2
• Filed: 08/22/2011
• Issued: 03/19/2013
• Est. Priority Date: 03/18/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Meir, Avraham, Sommer, Naftali, Gurgi, Eyal
• Primary Examiner(s): Nguyen, Viet Q
• Application Number:
  US13/214,257
• Publication Number:
  US 20120320671A1
• Time in Patent Office: 575 Days
• Field of Search: 365/207, 365/205, 365/206, 365/204, 365/189.07, 365/189.15, 365/185.03
• US Class Current: 365/207
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 13/0035 Evaluating degradation, retention or wearout, e.g. by counting writing cycles
• CPC Class Codes: G11C 13/004 Reading or sensing circuits or methods
• CPC Class Codes: G11C 13/0061 Timing circuits or methods
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles
• CPC Class Codes: G11C 2211/5641 Multilevel memory having cells with different number of storage levels
• CPC Class Codes: G11C 27/005 with non-volatile charge storage, e.g. on floating gate or MNOS
• CPC Class Codes: G11C 29/00 Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
• CPC Class Codes: G11C 8/12 Group selection circuits, e.g. for memory block selection, chip selection, array selection

Abstract

A method for data storage includes providing at least first and second readout configurations for reading storage values from analog memory cells, such that the first readout configuration reads the storage values with a first sense time and the second readout configuration reads the storage values with a second sense time, shorter than the first sense time. A condition is evaluated with respect to a read operation that is to be performed over a group of the memory cells. One of the first and second readout configurations is selected responsively to the evaluated condition. The storage values are read from the group of the memory cells using the selected readout configuration.

Claims

1. A method for data storage, comprising:

providing at least first and second readout configurations for reading storage values from analog memory cells, such that the first readout configuration reads the storage values with a first sense time and the second readout configuration reads the storage values with a second sense time, shorter than the first sense time;

evaluating a condition with respect to a read operation that is to be performed over a group of the memory cells;

selecting one of the first and second readout configurations responsively to the evaluated condition; and

reading the storage values from the group of the memory cells using the selected readout configuration.

2. The method according to claim 1, wherein the memory cells in the group belong to respective bit lines, wherein the first readout configuration sets at least one of the bit lines to have a first conductivity, and wherein the second readout configuration sets the at least one of the bit lines to have a second conductivity, greater than the first conductivity.

3. The method according to claim 1, wherein the memory cells in the group belong to a word line selected from among multiple word lines, wherein the first readout configuration applies first pass voltages to the word lines other than the selected word lines while reading the group of memory cells, and wherein the second readout configuration applies second pass voltages to the word lines other than the selected word lines, such that at least one of the second pass voltages is higher than a corresponding one of the first pass voltages.

4. The method according to claim 1, wherein the first readout configuration reads the storage values using a first set of read thresholds, and wherein the second readout configuration reads the storage values using a second set of read thresholds, such that at least one of the second read thresholds is higher than a corresponding one of the first read thresholds.

5. The method according to claim 1, wherein the memory cells in the group belong to a word line in a memory block that comprises multiple word lines, and wherein evaluating the condition comprises assessing a number of the word lines in the memory block that are programmed with data.

6. The method according to claim 1, wherein the first readout configuration reads the storage values with a first accuracy, and wherein the second readout configuration reads the storage values with a second accuracy that is coarser than the first accuracy.

7. The method according to claim 1, wherein evaluating the condition comprises assessing a wear level of the group of the memory cells.

8. The method according to claim 1, wherein evaluating the condition and selecting the one of the readout configurations comprise selecting the second readout configuration responsively to determining that the read operation reads the storage values from potentially-interfering memory cells in an interference cancellation process.

9. The method according to claim 1, wherein evaluating the condition and selecting the one of the readout configurations comprise selecting the second readout configuration responsively to determining that the read operation verifies the storage values that were written into the given group of the memory cells.

10. The method according to claim 1, wherein each of the memory cells in the group stores at least first and second bits, and wherein evaluating the condition and selecting the one of the readout configurations comprise selecting the second readout configuration responsively to determining that the read operation reads the first bits from the memory cells, and selecting the first readout configuration responsively to determining that the read operation reads the second bits from the memory cells.

11. The method according to claim 1, wherein evaluating the condition and selecting the one of the readout configurations comprise selecting the second readout configuration responsively to determining that the read operation is used for estimating a statistical distribution of the storage values that were written into the given group of the memory cells.

12. The method according to claim 1, wherein the storage values represent stored data, and wherein evaluating the condition and selecting the one of the readout configurations comprise making an attempt to read the storage values from the memory cells in the group using the second readout configuration and to reconstruct the stored data from the read storage values, and selecting the first readout configuration upon a failure of the attempt.

13. The method according to claim 12, wherein the stored data is encoded with an Error Correction Code (ECC), and wherein making the attempt comprises decoding the ECC.

14. The method according to claim 12, and comprising re-attempting to reconstruct the stored data using both the storage values read by the first readout configuration and the storage values read using the second readout configuration.

15. Apparatus for data storage, comprising:

a plurality of analog memory cells; and

circuitry, which is configured to evaluate a condition with respect to a read operation that is to be performed over a group of the memory cells, to select, responsively to the evaluated condition, between at least first and second readout configurations for reading storage values from the analog memory cells, such that the first readout configuration reads the storage values with a first sense time and the second readout configuration reads the storage values at a second sense time that is shorter than the first sense time, and to read the storage values from the group of the memory cells using the selected readout configuration.

16. The apparatus according to claim 15, wherein the memory cells in the group belong to respective bit lines, wherein the first readout configuration sets at least one of the bit lines to have a first conductivity, and wherein the second readout configuration sets the at least one of the bit lines to have a second conductivity, greater than the first conductivity.

17. The apparatus according to claim 15, wherein the memory cells in the group belong to a word line selected from among multiple word lines, wherein the first readout configuration applies first pass voltages to the word lines other than the selected word lines while reading the group of memory cells, and wherein the second readout configuration applies second pass voltages to the word lines other than the selected word lines, such that at least one of the second pass voltages is higher than a corresponding one of the first pass voltages.

18. The apparatus according to claim 15, wherein the first readout configuration reads the storage values using a first set of read thresholds, and wherein the second readout configuration reads the storage values using a second set of read thresholds, such that at least one of the second read thresholds is higher than a corresponding one of the first read thresholds.

19. The apparatus according to claim 15, wherein the memory cells in the group belong to a word line in a memory block that comprises multiple word lines, and wherein the circuitry is configured to evaluate the condition by assessing a number of the word lines in the memory block that are programmed with data.

20. The apparatus according to claim 15, wherein the first readout configuration reads the storage values with a first accuracy, and wherein the second readout configuration reads the storage values with a second accuracy that is coarser than the first accuracy.

21. The apparatus according to claim 15, wherein the circuitry is configured to evaluate the condition by assessing a wear level of the group of the memory cells.

22. The apparatus according to claim 15, wherein the circuitry is configured to select the second readout configuration responsively to determining that the read operation reads the storage values from potentially-interfering memory cells in an interference cancellation process.

23. The apparatus according to claim 15, wherein the circuitry is configured to select the second readout configuration responsively to determining that the read operation verifies the storage values that were written into the given group of the memory cells.

24. The apparatus according to claim 15, wherein each of the memory cells in the group stores at least first and second bits, and wherein the circuitry is configured to select the second readout configuration responsively to determining that the read operation reads the first bits from the memory cells, and to select the first readout configuration responsively to determining that the read operation reads the second bits from the memory cells.

25. The apparatus according to claim 15, wherein the circuitry is configured to select the second readout configuration responsively to determining that the read operation is used for estimating a statistical distribution of the storage values that were written into the given group of the memory cells.

26. The apparatus according to claim 15, wherein the storage values represent stored data, and wherein the circuitry is configured to make an attempt to read the storage values from the memory cells in the group using the second readout configuration and to reconstruct the stored data from the read storage values, and to select the first readout configuration upon a failure of the attempt.

27. The apparatus according to claim 26, wherein the stored data is encoded with an Error Correction Code (ECC), and wherein the circuitry is configured to make the attempt by decoding the ECC.

28. The apparatus according to claim 26, wherein the circuitry is configured to re-attempt to reconstruct the stored data using both the storage values read by the first readout configuration and the storage values read using the second readout configuration.

29. Apparatus for data storage, comprising:

an interface for communicating with a memory that includes a plurality of analog memory cells; and

circuitry, which is configured to evaluate a condition with respect to a read operation that is to be performed over a group of the memory cells, to select, responsively to the evaluated condition, between at least first and second readout configurations for reading storage values from the analog memory cells, such that the first readout configuration reads the storage values with a first sense time and the second readout configuration reads the storage values at a second sense time that is shorter than the first sense time, and to read the storage values from the group of the memory cells using the selected readout configuration.