JPH07281842A - Semiconductor memory device - Google Patents

Abstract

PURPOSE:To prevent a semiconductor memory device from deteriorating and becoming short in life owing to the frequent rewriting of a flash memory by using a ferroelectric memory which is high in rewritable frequency as the substitute memory. CONSTITUTION:This device consists of the flash memory 1 as the main memory for data storage, the ferroelectric memory 2 as the substitute memory, a controller 3 which performs access control over files, memory control, and substitution control, a management table 4 wherein data for file management and the deterioration management of the flash memory are recorded, and an external bus 5 for a host information equipment. Consequently, in a FAT(file allocation table) which is rewritten frequently, the ferroelectric memory 2 is substituted for the storage area. When the substituted memory has, at least, the capacity of the FAT, the deterioration of the flash memory 1 due to the rewriting of the FAT is eliminated to prolong the service life of the device, and increases in price and mount area at this time can be suppressed to be small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage device using a semiconductor as a storage medium, and more particularly to a method for extending the life of a small and inexpensive data file storage device using a flash memory as a main storage medium.

[0002]

2. Description of the Related Art A flash memory is one of the cheapest electrically rewritable memories, and has a feature of nonvolatility, and is attracting attention as a storage medium for a large-capacity external storage device. Conventionally, a magnetic disk storage device was most commonly used as an external storage device. However, in portable information equipment, due to problems such as impact resistance performance and power consumption,
A storage device using a flash memory as a storage medium is in the limelight. However, the number of rewritable times of the flash memory is about 10 to the power of 5, which is far inferior to that of the magnetic disk device, and it is a general view that the flash memory cannot be directly replaced as a storage medium instead of the magnetic disk. Therefore, it is necessary to incorporate a method for protecting the flash memory. Japanese Patent Application No. 4-99891 discloses the method, and by this method, an external storage device compatible with a magnetic disk device using a flash memory as a storage medium can be realized. The feature of this conventional example is that, in addition to a flash memory array having the same storage capacity as an external storage device, a flash memory is provided to replace a memory that has become unusable after the number of rewritable times has exceeded. In other words, it is a method in which a flash memory that has become unusable is not used, and instead its storage area is moved to a previously prepared alternative memory. As a result, even if a certain storage area is frequently rewritten and becomes unusable, the entire device can continue to operate without problems.

[0003]

When the flash memory is used by replacing it with a magnetic disk, the life of the flash memory becomes a problem because file management is performed by FAT (file allocation table). FAT is a table showing the physical storage location of files, and management information for all stored files is collected. Although the FAT is also stored as one file on the disc, it becomes a file that is always rewritten when the stored file is written or rewritten. Therefore, the total number of rewrites of all files is FAT.
Is the number of rewrites. If file rewriting occurs once per minute, 500,000 or more FAT rewritings will occur in one year. If this is done on the flash memory, for example, if the guaranteed number of times of rewriting of the flash memory is 100,000, it is necessary to perform the replacement process 5 times in one year. FA of file device with 100MB capacity
If the capacity of T is about 200 KB, 1 MB of alternative memory is required. If this storage device is used for 5 years, it will be an alternative memory of 5MB. That is, under the above conditions, an alternative memory having a storage capacity of 5% is required. It can be said that this is wasteful both in terms of price and mounting area. Further, in a usage environment under more severe conditions, a larger alternative memory capacity is required. The above points are not considered in the conventional technology.

[0004]

The above problem is solved by using a ferroelectric memory instead of a flash memory as an alternative memory. The ferroelectric memory has a cell structure similar to that of a DRAM and uses a ferroelectric for a stack capacitor. In a normal DRAM, since the dielectric constant of the capacitor is low, data cannot be stored unless refreshed, and the data is naturally lost if the power supply is stopped. However, in the ferroelectric memory, even if the power supply is stopped, the data can be stored at the level of many years. The life of this memory is regulated by the number of times of data inversion, but some guarantee 100 million times or more at present. This is a value that guarantees 200 years even if rewriting occurs every minute. Therefore, if a ferroelectric memory is used as the alternative memory, the above problem can be solved.

[0005]

According to the above means, rewriting frequently occurs in the FA.
The storage area of T will be replaced with a ferroelectric memory. Even if the FAT stored in the ferroelectric memory is frequently rewritten thereafter, it is practically impossible to make the ferroelectric memory unusable in practical use. That is, if the alternative memory has at least the capacity of FAT, the deterioration of the flash memory due to the rewriting of FAT is eliminated and the life of the device can be extended. In addition, the increase in price and mounting area at that time can be reduced.

[0006]

Embodiments of the present invention will be described with reference to the drawings. Figure 1
1 is a block diagram of an embodiment of the present invention, in which 1 is a flash memory which is a main memory for storing data, 2 is a ferroelectric memory as a substitute memory, 3 is file access control and memory control. , Controller for alternative control, 4
Is a management table for recording data for file management and flash memory deterioration management, and 5 is an external bus of the host information device. FIG. 2 is a diagram showing an internal configuration of the controller 3, 11 is an interface control circuit which includes a register for receiving an access request and access contents from the host bus, and which controls input / output of data,
Reference numeral 12 is a CPU that performs all control such as processing settings of other control circuits, management of stored file data, and determination of rewriting frequency according to a program, 13 is a ROM that stores programs and data for the CPU 12 to perform various controls, and 14 is CP
U12 is a RAM used as a work area when executing a program, 15 is a memory control circuit for accessing the flash memory 1 or the ferroelectric memory 2, and 16 is a check of a writing or erasing time limit of the flash memory 1. This is the timer used. FIG. 3 is a flow chart showing the operation of the program executed by the CPU 12 stored in the ROM 13 to implement the present invention. Next, the operation of the present invention will be described with reference to the flow chart of FIG. 3 using the configuration diagrams of FIGS. First, after completing the initialization process (a) such as self-diagnosis and initial setting of internal registers, the process waits for an access request from the host via the external bus 5 (b). The access request from the host and the access content are the interface control circuit 11 of the controller 3.
CPU 12 determines the access contents and calculates the storage location (address) of the data to be accessed from the data received from the host (c). Then, the data of the management table 4 corresponding to the calculated storage location is read, and it is determined whether the access target is on the flash memory 1 or the ferroelectric memory 2 (d). If it is on the flash memory 1, it is distinguished whether the requested access is read or write (e). If it is a read access, the flash memory 1 is read (f), and if it is completed, the process returns to waiting for an access request from the host. In the case of write access, the area to which data is to be written is first erased (g). Then, the deterioration information is recorded in the management table 4 (h), and the frequency of rewriting is determined (i). If it is determined from the deterioration information that the area is frequently written, the area is not written to the flash memory 1 but is written to the ferroelectric memory 2 (j) and the stored information is managed. Write to table 4 (k). If the frequency of writing is not so high, or if it is still at a stage where it cannot be determined, writing is performed to the erased area of the flash memory (l). Then, the process returns to waiting for an access request from the host. On the other hand, if the access is to the ferroelectric memory 2 in (d), the management table is read to confirm the address to be accessed (m), and the ferroelectric memory 2 is accessed according to the access request (n). When this is finished, the process waits for an access request. Further, FIG. 6 (l) shows a flowchart of the operation when performing a write access to the flash memory. The steps (g) to (l) in the flowchart of FIG. 3 are embodied according to a method of diagnosing the frequency based on the number of times of erasing the flash memory. A program for executing the above operation is stored in the ROM 13, and the CPU 12 reads and executes the program to access a memory outside the controller 3, such as the flash memory 1, the ferroelectric memory 2, or the management table 4. In doing so, the memory control circuit 15 is instructed to operate. Further, the RAM 14 is appropriately used when temporarily storing data. Next, management table 4
The detailed description of FIG. 4 shows an example of the management table 4, in which 31 is a 16-bit (2-byte) storage area in the table, which is the minimum unit of table data. Each table data is stored in a logical data storage address specified by the host information device.
It corresponds to one-to-one. 32 is this unit table data 3
A bit indicating whether the memory storing the data of the logical address corresponding to 1 is the flash memory 1 or the ferroelectric memory 2. 33 is a storage memory bit 32
Indicates a flash memory 1 and a bit group indicating the number of erases, and indicates a ferroelectric memory 2 a bit group indicating a storage address on the ferroelectric memory 2. Two usage examples are also shown in the lower part of the figure. Next, a method of using the table of this embodiment will be described. First, at the initial stage of operation of the memory device, it is assumed that no erase block has deteriorated in the flash memory 1, and the storage memory bit 32 of any unit table data 31 indicates the flash memory 1 (“0” in the figure). And)). In this state, in the case of an access request from the host, it suffices to simply find the physically relevant area on the flash memory 1 from the given logical address and access. When the file data is rewritten and an erase block in the flash memory is erased, the bit group 33 counts up from 0 to record the erase count. Then, when the record of the number of times of erasure reaches a prescribed value, it is determined that the area in which rewriting to the flash memory frequently occurs. That is, in this embodiment, (i) in the flowchart of FIG.
The deterioration management information of will be represented by the number of deletions, and
It corresponds to the operation of (l). When the replacement of the flash memory 1 with the ferroelectric memory 2 occurs, the storage memory bit 32 needs to be rewritten so as to indicate the ferroelectric memory 2 (indicated as "1" in the figure), and the bit group 33 needs to record the erase count. Therefore, the content of this bit group is changed so as to record the storage address in the ferroelectric memory 2. Then, in the subsequent access to the area corresponding to the unit data table 31, the address of the ferroelectric memory 2 shown in the bit group 33 is accessed.

Since the storage capacity of the ferroelectric memory 2 is limited, the capacity that can be transferred from the flash memory 1 to the ferroelectric memory 2 is also limited. The capacity of the ferroelectric memory 2 must be determined from the expected value of the device life and the rewriting frequency. If the ferroelectric memory 2 is used up by substitution, the rewriting frequency management and substitution processing are no longer necessary, so the operation of the flowchart of FIG. 3 should be changed to the flowchart of FIG.

Some ferroelectric memories have a structure that requires an operation called polarization. Ferroelectric memory, as the name implies, stores data by storing charges in the ferroelectric. This ferroelectric substance deteriorates by inverting data, that is, by storing and releasing electric charges (polarization). This occurs because the charge of the ferroelectric substance is discharged not only when writing data but also when reading data. Therefore, a ferroelectric memory having a mode in which data can be read and written without changing the charge of the ferroelectric has been put into practical use so that the polarization of the ferroelectric does not always occur. Of course, in this mode, the data is in a volatile storage state, and if the power supply is stopped, the data will be lost. In other words, when it is necessary to back up data, it is only necessary to transfer charges to and from the ferroelectric substance. As the timing of this polarization, time is calculated from the life of the number of polarization times of the ferroelectric memory and the target life of the device. The calculation formula is shown as (Formula 1).

(Apparatus life years) × 365 × 24 × 60 × 60 / (guaranteed number of polarizations) (Equation 1) By performing polarization every time (unit: second) equal to or more than the value calculated by this equation, The ferroelectric memory will not deteriorate and become unusable within the life of the device. For example, assuming that the target device life is 10 years and the guaranteed number of polarizations of the ferroelectric memory to be used is 100 million times, the target can be achieved by polarization every approximately 3.2 seconds. If the calculated value is about several seconds as in this example, it can be said that the polarization interval is an appropriate time.
The user of the storage device can turn off the power after several seconds or more have passed since the storage device was used. Alternatively, if an auxiliary power supply that allows operation for a few seconds after the main power is shut off is provided, it will be possible to cope with sudden power failures.

By sharing the ferroelectric memory 2 in the management table of FIG. 4, the number of parts can be reduced. It is optimal to use the ferroelectric memory 2 for the management table because it is possible to rewrite in small units and is non-volatile. Therefore, by providing the management table area in the same ferroelectric memory 2 separately from the alternative memory area, the alternative memory area is reduced, but it is possible to realize a small and inexpensive storage device, for example, a card type storage device. Is effective.

According to this embodiment, the RO in the controller is
By appropriately changing the program on M, it is relatively easy to select and apply the various methods described so far. Further, since the capacity of each memory can be easily changed, there is flexibility in setting the storage capacity and the device life even after the system is constructed. Further, since the unit of the management table is 16 bits, it is easy to handle in units of 2 bytes, and the number of erasures can be recorded up to 30,000 times or more. The storage address for substitution is also 30,000 or more areas, and if one area is 512 bytes, it is possible to have an alternative area of 16 Mbytes. The size of the management table may need to be adjusted to 8 bits, 24 bits, or another number of bits depending on the storage capacity, the frequency management method, the capacity of the alternative area, and the like. As another effect, when the replacement of all areas of the ferroelectric memory is completed, the frequency management is stopped, and the processing speed can be improved.

In the next embodiment, the size of the rewriting frequency is judged from the actual deterioration of the flash memory. Figure 6
(2) is a flow chart for realizing the present embodiment, and shows the write access execution part of the flow chart of FIG. 3 (FIG. 3: g to l). When erasing, the timer 16 is started to measure the time required for erasing, and the deterioration degree is determined based on its length. This utilizes the property that the erase time is delayed as a symptom of deterioration due to an increase in the number of rewrites of the flash memory. It is possible to detect that the deterioration progresses by dividing the length of the erasing time into two or more stages from the length at the start of use to the guaranteed maximum length. A method of measuring the writing time to grasp the progress of the deterioration degree is also possible. Depending on the flash memory, the degree of deterioration can be grasped more accurately depending on the size of the writing time than on the size of the erasing time. From the structure of the flash memory and the characteristics of the device, it is necessary to select and apply a method that enables more accurate understanding of deterioration. In any case, in the present embodiment, since it is not necessary to record the number of times of erasing, it is not necessary to record the bit group 33 in FIG. 4 until the replacement occurs. If it is necessary to know the degree of deterioration of each area, the deterioration level obtained from the time required for erasing or writing may be described. According to the present embodiment, since there is no recorded data for frequency management, the management table can be simplified. Further, since the actual degree of deterioration can be used as frequency management data, it is the most effective method in terms of extending the life.

In the above embodiment, when the flash memory is deteriorated and reaches a certain stage, the area is replaced with the ferroelectric memory to maintain the reliability. , Erase, write time measurement,
The purpose is not to monitor the progress of deterioration of the flash memory, but to grasp the size of the rewriting frequency of the area. Therefore, if it is possible to identify the one with a relatively high rewriting frequency, it is not necessary to monitor the deterioration of the flash memory any more. As one way of thinking, it is possible to make the specified number of times equal to the guaranteed number of times of erasure, and to perform substitution after erasing the guaranteed limit. Alternatively, if the number of times of erasing is not recorded and the erasing or writing becomes impossible, the substitution is performed to simplify the process.
According to this, using the flash memory to the limit,
This is very useful in terms of reliability, because alternatives will be made when reliability is lost. However, continuing to use the flash memory until it becomes unusable is a waste of the flash memory. If it can be judged that the frequency of rewriting is high, immediately replace it with a ferroelectric memory,
Flash memory should be used effectively. For example, in the determination of deterioration due to the number of times of erasing, if replacement is performed at 10% of the limit of the number of times of rewriting the flash memory, the remaining
0% erase count is available. In the measurement of the erasing / writing time, if the estimated time required in a usage state of about 10% of the life is set as an alternative prescribed time, the remaining about 90% of the rewriting use can be similarly used elsewhere. If it is insufficient to judge the rewriting frequency at the time of 10% use, it may be necessary to use 20% or more. On the contrary, if it is considered that the frequency can be determined without using up to 10%, the substitution may be performed at a usage time of 5% or less. Then, an embodiment in which the flash memory, which has been replaced and can be applied to other applications, is actually used is shown in FIG.
It was shown to. FIG. 7 (1) shows an embodiment which is used as a substitute for a flash memory which has become unusable after all the substitute memories by the ferroelectric memory have been used and are no longer ready for substitution. is there. Figure 7 (2)
Is an embodiment in which the replaced flash memory is added as a new storage area to increase the storage capacity. In the figure, 1 and 2 are a flash memory and a ferroelectric memory, respectively, as described above. Reference numeral 51 is a unit storage area of the flash memory 1 which is a main storage memory, and is also a unit of data managed by the host. Usually, the size is equal to the erase block unit of the flash memory or is a size of an integral fraction thereof. 52 is a logical storage address of the file data stored in that area. In other words, it is a logical address value that the host side specifies at the time of access. Reference numeral 53 is a unit storage area of the ferroelectric memory 2, which is an alternative memory, and has the same capacity as that of the flash memory 1. The area marked with a circle like 54 is an area of the flash memory which is placed in a usable state by replacing a certain area of the ferroelectric memory 2. Like 55
The area marked with indicates that the area cannot be used. In the embodiment of FIG. 7A, the area A-3 of the flash memory 1 has the logical address number {3}.
However, it is determined that the rewriting frequency is high, and the substitution is performed in the area α-1 of the ferroelectric memory 2. Similarly, the areas A-4 and B-2 of the flash memory 1 are also replaced with α-2 and α-3. Then, all the regions of the ferroelectric memory 2 are in a state of being used up for substitution. In this state, it is assumed that rewriting frequency management has already stopped. Then, since F-5 of the flash memory 1 could not substitute for the ferroelectric memory 2, the number of times of erasing exceeded the limit, and the flash memory 1 became unusable. At this time, A-3 of the flash memory 1 is used as an alternative area of F-5 of the flash memory 1. Logical address number {45} originally stored in F-5 in A-3
Is stored. A-3 should be used without any problems because it has been replaced by the one with a low degree of deterioration. In FIG. 7 (2), the substitution with the ferroelectric memory 2 is performed to some extent, but the area A-3 of the flash memory 1 in which the substitution has already been performed can be stored in the entire flash memory 1. The data of logical address number {65}, which exceeds the data of 64 areas, is stored. After this is replaced, by using it as a new storage area,
The storage capacity is increasing. That is, the ferroelectric memory 2 is also used as a storage area in addition to the total capacity. A further application of this is shown in FIG. Although the same symbols as in FIG. 7 are used, the difference from FIG. 7 (2) is that the ferroelectric memory 2 is used as a storage area from the beginning, and is used as an exchange area instead of a replacement area. That is, the area of the flash memory 1 that is determined to have a high rewrite frequency is replaced with the area of the ferroelectric memory 2, and the data having a low rewrite frequency is replaced, and the data having a high rewrite frequency is collected in the ferroelectric memory 2. The idea is to end up. At this time, FAT used in DOS (disk operating system)
Since the (file allocation table) is often stored in the relatively first logical address in all files, it is better to allocate a region with a smaller logical address in the ferroelectric memory 2 than in the area exchange. There is a high possibility that the trouble of will be saved. This is practiced in Figure 7. Note that the management table 4 stores the information for judging the replacement or replacement of the area performed in FIGS. 7 and 8 and the information indicating the result.
Need to record. For example, in the embodiment of FIG. 7A, the information of the management table corresponding to the area A-3 indicates that the data of the logical address number {3} is stored in the area α-1 of the ferroelectric memory 2. Since the data is recorded, the data indicating that the area A-3 stores the data of the logical address number {45} should be stored in the management table corresponding to the area F-5. At this time, bit 32 of the management table 31 in FIG. 4 indicates that the bit is stored in the flash memory, and the bit group 33 stores the storage address (A-3).
To record. In the original operation of the erase count management system, when the bit 32 indicates a flash memory, the erase count is recorded in the bit group 33, but the ferroelectric memory 2 is used as an alternative area. After the rewriting frequency is no longer managed, the control may be switched so that the bit group 33 always records the storage address. On the other hand, in the embodiment of FIG. 7B, it is necessary to prepare in advance a management table corresponding to a logical address which is a new storage area. That is, using FIG. 7, it is sufficient to virtualize areas I-1 and I-2 that do not actually exist and to provide a management table corresponding thereto. In this case, since the frequency management of the virtual area is also required, it is necessary to record both the erase count and the storage address in the erase count management method. Therefore, it is necessary to increase the number of bits in the management table. Must be recognized and controlled. In FIG.
Not only the area of the flash memory 1 but also the ferroelectric memory 2
It is necessary to provide a management table for the area. Moreover, in the erase count management method, it is also necessary to record the erase count of the area of the ferroelectric memory 2. This is because, if a frequently-used one can be identified in the flash memory area, a less frequently-used one should be searched and replaced in the ferroelectric memory 2. If it is replaced with a frequently used one in the ferroelectric memory 2, the meaning of the replacement becomes meaningless, and it may worsen in some cases.

According to this embodiment, both the flash memory and the ferroelectric memory can be efficiently used, and it is effective in reducing the reliability or the number of parts.

[0015]

As an effect of the present invention, the life of the alternative memory is greatly extended by using the ferroelectric memory as the alternative memory which can be rewritten many times. That is, by storing the data that is frequently rewritten, the alternative memory does not become unusable one after another. On the contrary, if all the data storage memories are ferroelectric memories, the high integration of the ferroelectric memory has not progressed, so that the price becomes high and the mounting area becomes large, which is not practical. Generally, when a general user uses a storage device of an information device, not much data is rewritten so frequently as to destroy the flash memory. Sufficient data is stored in a flash memory that is inexpensive and highly integrated, and data that is insufficient in rewriting resistance of the flash memory is stored in a ferroelectric memory, so that the system is optimized in terms of price, area, and performance.

To estimate the rewriting frequency, it is possible to accurately predict the frequency by recording the number of times of rewriting. Moreover, since the data recording only increments the previous data, the processing is simple. Further, since the setting of the alternative specified value is the number of times of erasing and is easy to understand and change, the optimum setting can be easily made from the system environment, the performance of the memory used, the device performance, and the like. On the other hand, in the method of using the measured value of the erase or write time in the estimation of the rewriting frequency, rather than the estimation of the rewriting frequency, the judgment is based on the concept of the usage rate with respect to the life of the memory. The error of can be reduced. Further, since the judgment is made based on the value measured at the time of rewriting, it is possible to eliminate the need for data for recording.

Ferroelectric memories are all used as alternatives,
It can be expected that the processing performance thereafter will be improved by stopping the frequency management when the free space is exhausted.

By storing the management table in the ferroelectric memory which is an alternative memory, the number of parts can be reduced, which contributes to the reduction in size and weight of the device. Moreover, since the management table is frequently rewritten in small units and is required to be non-volatile, use of a ferroelectric memory that can be accessed at high speed and has high reliability can also improve device performance. Contribute.

By the rewriting frequency management, the data is rewritten at a frequency at which it can be expected that the flash memory will be significantly deteriorated. Since the stored data is moved, this area can be reused for another purpose. As one of them, after replacing with the ferroelectric memory, the device life can be further extended by using the area as a replacement for the area of the flash memory which has become unusable. . This also leads to saving of an alternative memory, a ferroelectric memory. Alternatively, the storage capacity can be increased by allocating the area as a new data storage area after the replacement with the ferroelectric memory.
That is, the capacity of the alternative memory can also be regarded as the storage capacity. Further, if the ferroelectric memory is treated as a storage area from the beginning, it is possible to eliminate the waste that the ferroelectric memory is not used at all until the replacement is performed. By configuring the ferroelectric memory on the smaller side as the address of the storage memory, the FAT is normally placed in a place having a smaller file address, so that the FAT is stored in the ferroelectric memory from the beginning and waste of replacement can be eliminated.

By transferring data having a high rewriting frequency to the ferroelectric memory, rewriting is performed on the ferroelectric memory having a higher rewriting speed than that of the flash memory, so that the access performance is improved. Can be expected.

[Brief description of drawings]

FIG. 1 is a configuration diagram of the present invention.

FIG. 2 is an internal configuration diagram of a controller in the configuration of the present invention.

FIG. 3 is a flowchart of a basic operation program.

FIG. 4 is a diagram showing a usage example of a management table.

FIG. 5 is a flowchart of an operation program after all the ferroelectric memories are assigned to the basic operation program as alternatives.

FIG. 6 is a flowchart of an operation in write access to a flash memory.

FIG. 7 is a diagram showing a usage example of a region of a flash memory in which a ferroelectric memory is replaced.

FIG. 8 is a diagram showing an example in which a ferroelectric memory is used as each Umemori from the initial stage of use of the device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Flash memory, 2 ... Ferroelectric memory, 3 ... Controller, 4 ... Management table, 5 ... External bus, 11 ... Interface control circuit, 12 ... CPU, 13 ... ROM, 31 ... One example of management table, 32 ... Storage Memory bits, 33 ... Bit group.

Claims (15)

[Claims] 1. In a storage device using a flash memory as a storage medium, bus connection means for inputting / outputting storage data, bus control means for controlling connection with the bus, and rewriting frequency of the flash memory are managed. Memory management means, alternative storage means for replacing the flash memory with a ferroelectric memory as a storage medium, and memory control means for controlling the memories of the flash memory and the alternative storage means,
When the memory management unit determines that the data is not the data to be stored in the flash memory, the transfer unit that transfers to the alternative storage unit, the storage management unit that stores the storage location of the stored data, and the respective units are integrated. A semiconductor memory device comprising central processing means for controlling processing. 2. The semiconductor memory device according to claim 1, further comprising, as the memory management means, a rewrite frequency recording means for recording the rewrite frequency for each storage block of the flash memory, and when the rewrite frequency reaches a specific frequency. In addition, the semiconductor memory device is characterized in that it judges that the data of the block should not be stored in the flash memory. 3. The semiconductor memory device according to claim 2, wherein a specific number of times of rewriting for judging that a certain block of data should not be stored in the flash memory is regarded as an upper limit of the number of times of rewriting of the flash memory. A semiconductor memory device characterized by a smaller number. 4. The semiconductor memory device according to claim 1, wherein said memory management means includes processing confirmation means for erasing or writing data, and when the processing confirmation means confirms that processing is impossible, the data of the block is stored. A semiconductor memory device characterized by determining that it should not be stored in a flash memory. 5. The semiconductor memory device according to claim 1, wherein the memory management means includes a processing time monitoring means for monitoring a time required for erasing or writing data, and the processing time monitoring means increases the processing time. A semiconductor memory device, characterized in that, when it is confirmed that the flash memory has deteriorated, the data of the block should not be stored in the flash memory. 6. The semiconductor memory device according to claim 1, wherein the ferroelectric memory is polarized every time derived from the following equation (1) or every longer time, and data is made non-volatile. A semiconductor memory device characterized by the above. [Equation 1] 7. The semiconductor memory device according to claim 2, wherein a ferroelectric memory is used as the rewrite frequency storage means. 8. The semiconductor memory device according to claim 2, wherein a ferroelectric memory is used as the storage management means. 9. The semiconductor memory device according to claim 1, wherein when all of the alternative memories are assigned to alternatives and cannot be replaced, the memory management means stops the function and does not judge the rewriting frequency, and the flash memory is used. A semiconductor memory device characterized in that it continues to be used until the memory falls into an unusable state. 10. The semiconductor memory device according to claim 9, wherein when an area of the flash memory which is in an unusable state occurs after all the alternative memories are assigned to the alternative and cannot be replaced, A semiconductor memory device, wherein an area of a flash memory replaced by an alternative memory is used as an area for replacement. 11. The semiconductor memory device according to claim 10, wherein information indicating a substitution relationship between an unusable area of the flash memory and an area of the flash memory that replaces the area is recorded in a storage location of the stored data. A semiconductor memory device characterized by being stored in a storage management means. 12. The semiconductor memory device according to claim 1, wherein after a certain area of said flash memory is replaced by said alternative memory, it becomes a new memory area to increase the entire memory capacity. Semiconductor memory device. 13. The semiconductor memory device according to claim 1, wherein the ferroelectric memory functions as a normal data storage area and is replaced by the flash memory until an area to be replaced by the flash memory is generated. A semiconductor memory device characterized in that, when a region to be generated is generated, the memory regions are exchanged with each other so that region data having a high rewriting frequency is gradually collected in a ferroelectric memory. 14. The semiconductor memory device according to claim 2, wherein said rewriting frequency recording means is replaced when a certain area on said flash memory stores data having a high rewriting frequency. It is characterized in that the record of the number of rewrites corresponding to the area is erased, instead the storage location in the alternative memory is recorded, and the rewrite count recording means and the storage management means are shared by one recording means. Semiconductor memory device. 15. The semiconductor memory device according to claim 13, wherein the data stored in the ferroelectric memory and the flash memory are stored in order of decreasing logical address until the memory areas thereof are exchanged. A semiconductor memory device characterized in that it is assigned to the ferroelectric memory, and the flash memory is assigned an address larger than a logical address assigned to the ferroelectric memory.