SEMICONDUCTOR STORAGE DEVICE HAVING NONVOLATILE SEMICONDUCTOR MEMORY

• US 20130238836A1
• Filed: 03/06/2012
• Published: 09/12/2013
• Est. Priority Date: 03/06/2012
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Suzuki, Akifumi, Tsunehiro, Takashi
• Granted Patent: US 9,299,455 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/0629 Configuration or reconfiguration of storage systems
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G11C 16/00 Erasable programmable read-only memories G11C14/00 takes precedence
• CPC Class Codes: G11C 16/3431 Circuits or methods to detect disturbed nonvolatile memory cells, e.g. which still read as programmed but with threshold less than the program verify threshold or read as erased but with threshold greater than the erase verify threshold, and to reverse the disturbance via a refreshing programming or erasing step
• CPC Class Codes: G11C 16/3495 Circuits or methods to detect or delay wearout of nonvolatile EPROM or EEPROM memory devices, e.g. by counting numbers of erase or reprogram cycles, by using multiple memory areas serially or cyclically
• CPC Class Codes: G11C 29/021 in voltage or current generators
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters

Abstract

A semiconductor storage device has a nonvolatile semiconductor memory comprised from multiple storage areas, and a controller, which is coupled to the nonvolatile semiconductor memory. The controller (A) identifies a storage area state, which is the state of a storage area, (B) decides, based on the storage area state identified in the (A), a read parameter, which is a parameter for use when reading data from a storage area with respect to a storage area of this storage area state, and (C) uses the read parameter decided in the (B) with respect to a read-target storage area and reads data from this read-target storage area.

Claims

1. A semiconductor storage device, comprising:

a nonvolatile semiconductor memory comprised of multiple storage areas; and

a controller, which is coupled to the nonvolatile semiconductor memory,

wherein;

(A) the controller identifies a storage area state, which is the state of a storage area;

(B) the controller, based on the storage area state identified in the (A), decides on a read parameter, which is a parameter for use when reading data from a storage area with respect to a storage area of this storage area state; and

(C) the controller uses the read parameter decided in the (B) with respect to a read-target storage area and reads data from this read-target storage area.

2. A semiconductor storage device according to claim 1, wherein the controller stores storage area management information denoting the number of erases, which is the number of times an erase has been performed, and a post-erase initial programming time for one or more storage areas, and read parameter management information denoting the corresponding relationship among a read parameter, the number of erases, and a programming elapsed time, and updates the storage area management information for each storage area when an erase is executed and when a post-erase initial programming is performed,

in the (A), the controller identifies the number of erases and a programming elapsed time of the read-target storage area as the storage area state based on the storage area management information, and

in the (B), the controller identifies on the basis of the read parameter management information a read parameter corresponding to the number of erases and the programming elapsed time identified in the (A).

3. A semiconductor storage device according to claim 2, wherein the read parameter identified in the (B) is a parameter identified on the basis of the temperature of the read-target storage area.

4. A semiconductor storage device according to claim 3, wherein the read parameter management information comprises a read parameter for a storage area at a prescribed standard temperature,

in the (A), the controller converts to a standard elapsed time, which is a programming elapsed time at the standard temperature, based on a difference between the read-target storage area temperature and the standard temperature, and

the read parameter identified in the (B) is a read parameter identified using the number of erases of the read-target storage area and the standard elapsed time converted in the (A).

5. A semiconductor storage device according to claim 4, wherein each storage area is comprised of multiple cells, and

the read parameter includes at least one of the following (x) through (z):

(x) a voltage value of a read voltage supplied to the cell of the nonvolatile semiconductor memory;

(y) a read time for waiting for a measurement of an output voltage from a cell at the time of a read with respect to the cell; and

(z) a voltage value of a pass voltage and information for identifying a word line, which changes a pass voltage supplied to another word line, which does not include the cell.

6. A semiconductor storage device according to claim 1, wherein:

(D) the controller determines whether or not data read in the (C) is normal;

(E) in a case where the result of the determination in the (D) is negative, the controller searches for a read parameter for acquiring normal data from the read-target storage area; and

(F) the controller registers a read parameter found in the (E) in the read parameter management information with respect to the read-target storage area.

7. A semiconductor storage device according to claim 1, wherein the controller, upon receiving a read request from a higher-level apparatus, reads data by treating a storage area, which conforms to this read request, as a read-target storage area,

the (B) is a process performed at a time that differs from the read process performed after receiving a read request from a higher-level apparatus, and

in the (B), the controller, in accordance with executing a read process with respect to one or more storage areas of the nonvolatile semiconductor memory, searches for a read parameter, which makes it possible for a number of fail bits in data read from the storage area(s) to be equal to or less than a prescribed threshold, and registers the found read parameter in the read parameter management information for the relevant one or more storage areas.

8. A semiconductor storage device according to claim 7, wherein the read parameter search in the (B) is performed on a regular basis.

9. A semiconductor storage device according to claim 7, wherein:

(P) the controller determines, based on the value of the read parameter found in accordance with the search, whether or not it is necessary to execute a refresh for moving the storage area data to another storage area; and

(Q) in a case where the result of the determination in the (P) is affirmative, the controller executes a refresh with respect to the storage area.

10. A semiconductor storage device according to claim 9, wherein the controller stores a threshold related to a read parameter, which constitutes a criteria for determining that a refresh is needed for the storage area,

in the (P), the controller compares the read parameter found in the search to the threshold, and

in a case where the value of the read parameter exhibits a state, which is worse than the threshold-denoted state, the result of the determination in the (P) is affirmative.

11. A semiconductor storage device according to claim 7, wherein the controller correspondingly stores date/time information identifying a date/time of a post-erase initial programming with respect to the storage area,

wherein:

(R) the controller correspondingly stores in the storage area as a degree of deterioration a value obtained by dividing the difference between a prescribed standard value and the value of the read parameter corresponding to the storage area by an elapsed time from the date/time of a post-erase initial programming of the storage area identified in accordance with the date/time information until a prescribed point in time; and

(S) in a case where the controller receives a data write request from a higher-level apparatus and allocates a new storage area for storing the relevant data, the controller preferentially allocates a storage area for which the value of the degree of deterioration is relatively small.

12. A semiconductor storage device according to claim 1, wherein each storage area is comprised of multiple cells,

the nonvolatile semiconductor memory is configured such that data is read from a cell by supplying a read voltage supplied from the controller to the cell, which forms the storage area,

the read parameter includes a voltage value of a read voltage at the time data is read from a cell forming the storage area, and

in the (C), the controller reads data from the storage area by supplying a read voltage corresponding to the voltage value included in the identified read parameter to the nonvolatile semiconductor memory.

13. A storage system, comprising:

a storage controller for sending a read request; and

a nonvolatile semiconductor storage device, which is coupled to the storage controller,

wherein the semiconductor storage device comprises;

a nonvolatile semiconductor memory comprised of multiple storage areas; and

a controller, which is coupled to the nonvolatile semiconductor memory and performs a read process for reading data from a storage area in accordance with the read request,

wherein;

(A) the controller identifies a storage area state, which is the state of a storage area;

(B) the controller, based on the storage area state identified in the (A), decides on a read parameter, which is a parameter for use when reading data from a storage area with respect to a storage area of this storage area state; and

(C) the controller uses the read parameter decided in the (B) with respect to a read-target storage area and reads data from this read-target storage area.

14. A method for reading data from a nonvolatile semiconductor memory comprising multiple storage areas,

the method comprising:

(A) identifying a storage area state, which is the state of a storage area;

(B) deciding, based on the storage area state identified in the (A), a read parameter, which is a parameter for use when reading data from a storage area with respect to a storage area of this storage area state; and

(C) using the read parameter decided in the (B) with respect to a read-target storage area and reading data from this read-target storage area.