Error detection/correction and fault detection/recovery – Pulse or data error handling – Memory testing
Reexamination Certificate
1999-11-02
2001-04-24
Chung, Phung M. (Department: 2184)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Memory testing
Reexamination Certificate
active
06223311
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a memory device using an electrically rewritable nonvolatile semiconductor memory as a storage medium.
BACKGROUND ART
A magnetic disk device is the mainstream of a file data storage device in an information processing system such as a personal computer, or the like, at present. The magnetic disk device has a lot of merits such as low price, large capacity, high reliability, high performance, etc. and is most popular. With the gradual increase of demands for reduction in size, improvement in portability, reduction in consumed electric power, etc., a semiconductor memory device using a semiconductor as a recording medium has begun to be highlighted because the semiconductor memory device is more excellent in portability and low consumed electric power than the magnetic disk device.
A file device using a nonvolatile memory as a recording medium is disclosed in JP-A-5-27924. This technique concerns a memory device using a flash memory as a recording medium, and particularly discloses a system in which the life of a flash memory limited in the number of times of erasing required for rewriting is prolonged. Specifically, the number of times by which erasing is allowed is averaged for all regions in a file storage device which is apt to be rewritten locally, so that the apparent life is prolonged.
In the aforementioned invention, the number of times of erasing is used as an indicator for expressing deterioration of each flash memory cell and considered on the basis of the guaranteed value of the erasable number of times specified as characteristic data of the flash memory. The guaranteed value of the erasable number of times specified for each of various flash memories is, however, an average value or a minimum value in terms of characteristic, while the number of times by which erasing is allowed in practice varies according to the individual memory cells. That is, all the cells do not necessarily become unusable even when the number of times by which erasing is allowed reaches the guaranteed value. Accordingly, while the number of times by which erasing is allowed may be counted as an indicator for deterioration of each cell, there is some case where it cannot be said that memory cells are used most efficiently.
Therefore, an object of the present invention is to provide a method or semiconductor memory device in which deterioration of a memory can be grasped without consciousness of the guaranteed number of times and the current number of times by which the aforementioned electrically erasable/rewritable nonvolatile memory is allowed to be erased/rewritten, and, further, to provide a memory management method or semiconductor memory device using the same.
Another object of the present invention is to provide a method or semiconductor memory device in which the aforementioned electrically erasable/rewritable nonvolatile memory can be used up to the detected actual erasable/rewritable limit.
A further object of the present invention is to provide a method or semiconductor memory device for detecting the number of times by which the aforementioned electrically erasable/rewritable nonvolatile memory is allowed to be actually erased/rewritten.
DISCLOSURE OF THE INVENTION
In order to achieve the above objects, according to the present invention, in a semiconductor memory device using an electrically rewritable nonvolatile memory as a storage medium, there are provided: an erasing time measurement means for measuring erasing time required for erasing of the nonvolatile memory; a characteristic detection means for comparing the erasing time measured by the erasing time measurement means with an erasing time reference value to thereby determine environmental characteristic; a writing time measurement means for measuring writing time required for writing of the nonvolatile memory; a correction means for correcting the writing time measured by the writing time measurement means on the basis of the environmental characteristic determined by the characteristic detection means; and a nonvolatile memory deterioration determining means for detecting a degree of deterioration in a rewriting region of the nonvolatile memory on the basis of the corrected writing time.
Further, according to the present invention, in a semiconductor memory device using an electrically rewritable nonvolatile memory as a storage medium, there are provided: an electric source voltage detection means for detecting an electric source voltage value applied to the nonvolatile memory; a temperature detection means for detecting an ambient temperature of the semiconductor memory device; a characteristic detection means for determining environmental characteristic from detection values of the electric source voltage detection means and the temperature detection means; a writing time measurement means for measuring writing time required for writing of the nonvolatile memory; a correction means for correcting the writing time measured by the writing time measurement means on the basis of the environmental characteristic determined by the characteristic detection means; and a nonvolatile memory deterioration determining means for detecting a degree of deterioration in a rewriting region of the nonvolatile memory on the basis of the corrected writing time.
Further, according to the present invention, in a semiconductor memory device using an electrically rewritable nonvolatile memory as a storage medium, there are provided: an erasing time measurement means for measuring erasing time required for erasing of the nonvolatile memory; a writing time measurement means for measuring writing time required for writing of the nonvolatile memory; a characteristic detection means for comparing the writing time measured by the writing time measurement means with a writing time reference value to thereby determine environmental characteristic; a correction means for correcting the erasing time measured by the erasing time measurement means on the basis of the environmental characteristic determined by the characteristic detection means; and a nonvolatile memory deterioration determining means for detecting a degree of deterioration in a rewriting region of the nonvolatile memory on the basis of the corrected erasing time.
Further, according to the present invention, in a semiconductor memory device using an electrically rewritable nonvolatile memory as a storage medium, there are provided: an electric source voltage detection means for detecting an electric source voltage value applied to the nonvolatile memory; a temperature detection means for detecting an ambient temperature of the semiconductor memory device; a characteristic detection means for determining environmental characteristic from detection values of the electric source voltage detection means and the temperature detection means; an erasing time measurement means for measuring erasing time required for erasing of the nonvolatile memory; a correction means for correcting the erasing time measured by the erasing time measurement means on the basis of the environmental characteristic determined by the characteristic detection means; and a nonvolatile memory deterioration determining means for detecting a degree of deterioration in a rewriting region of the nonvolatile memory on the basis of the corrected erasing time.
Further, according to the present invention, in the above-mentioned semiconductor memory device, there are further provided: a deterioration-degree storage means for storing a degree of deterioration in every region detected by the nonvolatile memory deterioration determining means while the degree of deterioration in each of the regions is divided into a plurality of stages; a deterioration degree comparing means for comparing a degree of deterioration determined at the time of rewriting of each region with the degree of deterioration determined at the time of previous rewriting and stored in the deterioration-degree storage means; a low-deterioration-degree-region retrieval means for detecting a region having the lowest
Katayama Kunihiro
Naito Masashi
Shiota Shigemasa
Tamura Takayuki
Antonelli Terry Stout & Kraus LLP
Chung Phung M.
Hitachi , Ltd.
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