Static information storage and retrieval – Floating gate – Particular connection
Reexamination Certificate
2002-02-26
2003-06-24
Phan, Trong (Department: 2818)
Static information storage and retrieval
Floating gate
Particular connection
C365S185110, C365S185290
Reexamination Certificate
active
06584014
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a technology for rescuing such a storage region in any one of a plurality of nonvolatile memories that encounters a fault occurring time-wise in a nonvolatile storage system that has these memories, for example, to such a technology that is effectively applicable to such a memory card as an Advanced Technology attachment (ATA) memory card mounted with a flash memory.
An electrically rewritable nonvolatile memory such as a flash memory stores information based on a threshold voltage, which varies with an amount of electrons or positive holes injected into the floating gate of the memory cells. The properties of such a threshold voltage of the memory cells will deteriorate time-wise as the number of times of rewriting the memory contents increases. Such a deterioration in the properties results in a write-in error being detected in verification. To solve this problem, there has conventionally been provided a rescue technology for replacing a storage region in which a write-in error occurred with another storage region.
For example, in an ATA memory card used as a file memory, the storage regions of each of nonvolatile memories are divided into such functional sections as a data block regions section, a data-block alternate regions section for rescue, etc. so that each of these functional sections is defined as an aggregate of data blocks given in units of one sector and a corresponding management region. Each of the data blocks is assigned an inherent physical address in each of the memories. If a write-in error occurs in any of these data block regions, a flag indicating the error is set to this region, to set the physical address of such a data block region in said data block alternate regions section that is to substitute for said faulty data block region. Write-in data related to the write-in error is written into a data block of that alternate address. Then, if access is made to the address of said faulty data block, this data block is recognized to be faulty based on the error flag set in its corresponding management region so that access may be made instead to such a data block in the data block alternate regions section that is specified by the alternate address.
SUMMARY OF THE INVENTION
The Inventor, however, recognized a problem that in a case where a faulty data block is to be replaced with another only within the corresponding one of a plurality of nonvolatile memories and there is a deviation in fault occurrence ratio among them, if so many write-in errors occur in any one of these memories that cannot be accommodated by the rescue capacity of the data block alternate data block regions section in this memory, the entire relevant memory card must be treated as being faulty.
Concerning this, there have been disclosed such a conventional technology of having a preliminary nonvolatile memory for a backup purpose that is disclosed in JP-A-3-25798 and such a method for processing data necessary to replace a faulty nonvolatile memory that is disclosed in JP-A-9-200636.
The conventional technologies, however, are based on a premise that a faulty nonvolatile memory is to be replaced or a redundant (spare) nonvolatile memory and so are yet to fully utilize the storage regions of each of nonvolatile memories without replacing a faulty one of them.
In view of the above, it is an object of the present invention to provide a nonvolatile storage system that can improve redressing efficiency for a write-in error occurring as time passes by without replacing a faulty one of nonvolatile memories or using a spare nonvolatile memory in the system.
It is another object of the present invention to provide a nonvolatile storage system that can avoid an overall failure thereof without replacing a faulty one of nonvolatile memories or using a spare nonvolatile memory in the system even if a faulty data block cannot be replaced within any one of these memories.
It is a further object of the present invention to provide a nonvolatile storage system that can utilize the storage regions of each nonvolatile memory without waste when replacing a faulty data block.
The typical contents of the present invention in this application are outlined as follows.
(1) Inter-chip alternate: A nonvolatile storage system according to the present invention comprises a plurality of nonvolatile memories capable of read-out, erasure, and write-in operations and a control unit for controlling the operations of these nonvolatile memories in response to an external request. When having detected a write-in error on an operation-subject one of said plurality of nonvolatile memories, said control unit can set inter-chip alternate information about a fact that a storage region related to the write-in error has been replaced by a storage region in another one of said plurality of nonvolatile memories to the nonvolatile memory related to this error and also, when having received inter-chip alternate information from the current operation-subject nonvolatile memory, can switch the operation-subject memory from it to such another nonvolatile memory that is indicated by the chip alternate information. In the present specification, a write-in error refers to a state where when a write-in voltage is applied to a nonvolatile memory (programming) to then verify it, a predetermined threshold voltage cannot be obtained or a state where when the write-in subject is replaced already, confirmation of whether a alternate destination address can be obtained before start of said programming and programming verification finds that it is impossible.
It is thus possible, in inter-chip alternate, to redress a write-in error which occurred at one nonvolatile memory by using a storage region of another nonvolatile memory. This makes it possible, if a faulty data block cannot be replaced with another within one of a plurality of nonvolatile memories, to avoid an overall system error without replacing the faulty nonvolatile memory or using a preliminary nonvolatile memory.
If a write-in error occurred in a nonvolatile memory in which the number of the remaining storage regions capable of new placement has decreased to a predetermined number or less, preferably inter-chip alternate is allowed to that memory. It is thus possible to enable inter-chip alternate so as to eliminate waste of the data blocks as much as possible. That is, by starting inter-chip alternate before such a nonvolatile memory appears that is exhausted to such an extent that intra-chip alternate is no longer possible, the remaining regions capable of new alternate hardly have a large deviation among themselves, thus making it possible to minimize the number of processing cycles required for inter-chip alternate and intra-chip alternate. This is because, if there is a large deviation in the number of the regions capable of new alternate among nonvolatile memories, the number of such nonvolatile memories of these that can be adopted as a alternate destination is decreased, to increase the number of times of making retrieval retrials for looking for such a nonvolatile memory that can be adopted as an inter-chip alternate destination.
To enable inter-chip alternate so as to eliminate waste in the data blocks, inter-chip alternate can be allowed for a write-in error which occurred in a nonvolatile memory in which the number of the storage regions that can be adopted as a alternate destination has been decreased to a predetermined number of less.
A write-in error that occurred in such a nonvolatile memory that is capable of alternate can be accommodated by intra-chip alternate. For example, if a write-in error occurred in a nonvolatile memory which has the storage regions capable of alternate as many as a predetermined number or more, said control unit sets intra-chip alternate information indicating that a storage region related to the write-in error has been replaced with another storage region to such a nonvolatile memory that has the storage region related to this error and also makes it possible to obtain the intra-c
Hirosawa Seisuke
Ouchi Katsumi
Shirai Masaki
Suzuki Takeshi
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