ERASING METHOD USED IN FLASH MEMORY

Abstract

An erasing method used in a flash memory comprising at least one memory block divided into a plurality of memory sectors is illustrated. Whether the memory block or the memory sector corresponding to an address has at least one under-erased transistor memory cell according to a sector enable signal is verified, wherein the sector enable signal is determined according to whether the memory block has at least one over-erased transistor memory cell. The transistor memory cells of the memory block or the memory sector will be erased according to the sector enable signal if the memory block or the memory sector corresponding to the address has the under-erased transistor memory cell.

Claims

1. An erasing method used in a flash memory comprising at least one memory block divided into a plurality of memory sectors, comprising: verifying whether the memory block or the memory sector corresponding to an address has at least one under-erased transistor memory cell according to a sector enable signal, wherein the sector enable signal is determined according to whether the memory block has at least one over-erased transistor memory cell; and erasing transistor memory cells of the memory block or the memory sector according to the sector enable signal if the memory block or the memory sector corresponding to the address has the under-erased transistor memory cell.

2. The erasing method according to claim 1, wherein if the sector enable signal is asserted, and the memory sector corresponding to the address has the under-erased transistor memory cell, the transistor memory cells of the memory sector will be injected with an erasing shot at least one time until the memory sector does not have the under-erased transistor memory cell.

3. The erasing method according to claim 2, wherein the address will be added with an increment if the memory sector does not have the under-erased transistor memory cell, and then if another one the memory sector corresponding to the address has at least one under-erased transistor memory cell, transistor memory cells of the other one memory sector will be injected with the erasing shot at least one time until the other one memory sector does not have the under-erased transistor memory cell.

4. The erasing method according to claim 3, further comprising: when the address reaches a maximum address, verifying whether the memory block has the over-erased transistor memory cell and performing over-erased correction on the over-erased transistor memory cell if there is the over-erased cell in the memory block.

5. The erasing method according to claim 1, further comprising: verifying and pre-programming the transistor memory cells of the memory block before verifying and erasing the transistor memory cells of the memory block.

6. The erasing method according to claim 1, wherein the sector enable signal is initially de-asserted, if the memory block corresponding to the address has the under-erased transistor memory cell, the transistor memory cells of the memory block will be injected with an erasing shot at least one time until the memory block is verified to have the over-erased transistor memory cell.

7. The erasing method according to claim 6, wherein when the memory block is verified to have the over-erased transistor memory cell, an over-erased correction shot is injected to the over-erased transistor memory cells, and the sector enable signal is set to be asserted.

8. A flash memory, comprising: a memory module, comprising at least one memory block divided into a plurality of memory sectors; a memory management apparatus, electrically connected to the memory module; wherein the memory management apparatus verifies whether the memory block or the memory sector corresponding to an address has at least one under-erased transistor memory cell according to a sector enable signal, wherein the sector enable signal is determined according to whether the memory block has at least one over-erased transistor memory cell; and the memory management apparatus erases transistor memory cells of the memory block or the memory sector according to the sector enable signal if the memory block or the memory sector corresponding to the address has the under-erased transistor memory cell.

9. The flash memory according to claim 8, wherein if the sector enable signal is asserted, and the memory sector corresponding to the address has the under-erased transistor memory cell, the transistor memory cells of the memory sector will be injected with an erasing shot at least one time by the memory management apparatus until the memory sector does not have the under-erased transistor memory cell.

10. The flash memory according to claim 9, wherein the address will be added with an increment if the memory sector does not have the under-erased transistor memory cell, and then if another one the memory sector corresponding to the address has at least one under-erased transistor memory cell, transistor memory cells of the other one memory sector will be injected with the erasing shot at least one time by the memory management apparatus until the other one memory sector does not have the under-erased transistor memory cell.

11. The flash memory according to claim 10, wherein when the address reaches a maximum address, the memory management apparatus verifies whether the memory block has the over-erased transistor memory cell and performs over-erased correction on the over-erased transistor memory cell if there is the over-erased cell in the memory block.

12. The flash memory according to claim 8, wherein the memory management apparatus further verifies and pre-programs the transistor memory cells of the memory block before verifying and erasing the transistor memory cells of the memory block.

13. The flash memory according to claim 8, wherein the sector enable signal is initially de-asserted, if the memory block corresponding to the address has the under-erased transistor memory cell, the transistor memory cells of the memory block will be injected with an erasing shot at least one time by the memory management apparatus until the memory block is verified to have the over-erased transistor memory cell.

14. The flash memory according to claim 13, wherein when the memory block is verified to have the over-erased transistor memory cell, an over-erased correction shot is injected to the over-erased transistor memory cells, and the sector enable signal is set to be asserted.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order that the present disclosure may be better understood and readily carried into effect, certain embodiments of the present disclosure will now be described with reference to the accompanying drawings, wherein:

[0024] FIG. 1 is a flow chart of a conventional erasing method;

[0025] FIG. 2 is a schematic diagram showing another one conventional erasing method performed on a memory block; and

[0026] FIG. 3 is a flow chart of an erasing method used in a flash memory according to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] To make it easier for the examiner to understand the objects, characteristics and effects of this present disclosure, embodiments together with the attached drawings for the detailed description of the present disclosure are provided.

[0028] An embodiment of the present disclosure provides an erasing method used in a flash memory, at the verification and erasing step, the provided erasing method verifies whether the memory block has at least one over-erased transistor memory cell after an erasing shot is injected to all the transistor memory cells of the memory block (i.e. erasing all the transistor memory cells of the memory block). The provided erasing method injects the erasing shot to the transistor memory cells of the memory sector (i.e. erasing all the transistor memory cells of the memory sector) while the memory block has at least one over-erased transistor memory cell, and then the provided erasing method verifies whether all the transistor memory cells of the memory sector are erased. The provided erasing method erases the transistor memory cells of the memory sector at least one time until the transistor memory cells of the memory sector are erased. Next, the provided erasing method erases the memory sector of another one memory sector in the same memory block at least one time until the transistor memory cells of the other one memory sector are erased. When the transistor memory cells all of the memory sectors in the memory block are erased, the similar erasing scheme is performed on another one memory block. Accordingly, the provided erasing method does not need additional flag registers for recording the statuses of the memory sectors, and does not cost much erasing verification time, either.

[0029] Referring to FIG. 3, FIG. 3 is a flow chart of an erasing method used in a flash memory according to one embodiment of the present disclosure. The flash memory (not shown in the drawings) comprises a memory module and a memory management apparatus electrically connected to the memory module, wherein the memory module comprises a plurality of memory banks, each memory bank comprises a plurality of memory blocks, and each memory block is divided into a plurality of memory sectors. For example, the memory block has 64Kbytes (i.e. 64*8 Kbits), and the memory sector has 4Kbytes (i.e. 4*8 Kbits), and the present disclosure is not limited thereto.

[0030] At step S31, the memory management apparatus verifies and pre-programs transistor memory cells of the memory module. Then, at step S32 (i.e. erasing and verification step), the memory management apparatus verifies and erases the transistor memory cells of the memory module. It is noted that, at step S32, the provided erasing method can erase the transistor memory cells of the memory block or the memory sector based upon whether the over-erased correction shot is injected to the transistor memory cell(s) of the memory block (i.e. whether the memory block has at least one over-erased transistor memory cell). Finally, to prevent the leakage current of the over-erased transistor memory cell from rendering the flash memory inoperative, at step S33, the memory management apparatus verifies all transistor memory cells of the memory module and performs over-erased correction on the over-erased transistor memory cell(s) of the memory module.

[0031] Specifically, step S32 comprises steps S321 through S329. At step S321, the memory management apparatus verifies whether the transistor memory cells of the memory block or the memory sector corresponding to an address are erased to generate a verification result. When a sector enable signal SEC_EN corresponding to the memory block is asserted, the transistor memory cells of the memory sector is verified; and when the sector enable signal SEC_EN corresponding to the memory block is de-asserted, the transistor memory cells of the memory block is verified, wherein the sector enable signal SEC_EN corresponding to the memory block is determined according to whether the memory block has at least one over-erased transistor memory cell. If the memory block or sector has at least one under-erased transistor memory cell, the memory management apparatus will determine the verification result is failed; and if the memory block or the memory sector does not have at least one under-erased transistor memory cell, the memory management apparatus will determine the verification result is passed.

[0032] At step S322, the memory management apparatus checks whether the verification result is failed or passed. If the verification result is failed, step S323 will be executed; otherwise, step S328 will be executed. At step S323, the memory management apparatus injects the erasing shot into transistor memory cells of the memory block or the memory sector according to the sector enable signal SEC_EN corresponding to the memory block. If the sector enable signal SEC_EN corresponding to the memory block is asserted, the memory management apparatus will inject the erasing shot into transistor memory cells of the memory block; otherwise, the memory management apparatus will inject the erasing shot into transistor memory cells of the memory sector.

[0033] At step S324, the memory management apparatus checks whether the sector enable signal SEC_EN corresponding to the memory block is asserted. If the sector enable signal SEC_EN corresponding to the memory block is asserted, step S321 will be executed; otherwise, step S325 will be executed. At step S325, the memory management apparatus verifies whether the memory block has at least one over-erased transistor memory cell, and performs over-erased correction on the transistor memory cell(s) of the memory block while the memory block has at least one over-erased transistor memory cell.

[0034] Next, at step S326, the memory management apparatus checks whether the over-erased correction is performed (i.e. whether the memory block has at least one over-erased transistor memory cell, or whether an over-erased correction (OEC) shot is injected to the over-erased transistor memory cell(s) of the memory block). If the over-erased correction is performed, step S327 will be executed; otherwise, step S321 will be executed. At step S327, the memory management apparatus set the sector enable signal SEC_EN corresponding to the memory block to be asserted. At step S328, the memory management apparatus checks whether the address is the maximum address. At step S329, the memory management apparatus adds the address with an increment, wherein the increment corresponding to the size of the memory sector.

[0035] Initially, the sector enable signal SEC_EN corresponding to the memory block is de-asserted when the provided erasing method firstly erases the transistor memory cells of the memory block. For example, the transistor memory cells of the memory block are verified at step S321 firstly, there are under-erased transistor memory cell in the memory block, and thus the erasing shot is injected to the transistor memory cells of the memory block at step S323. Next, since the sector enable signal SEC_EN corresponding to the memory block is de-asserted, whether the memory block has at least one over-erased transistor memory cell is check at step S325. Generally, after the provided erasing method erases the transistor memory cells of the memory block several times or once, there are over-erased transistor memory cell in the memory block, and thus at step S327, the sector enable signal SEC_EN corresponding to the memory block is set to be asserted.

[0036] Next, the transistor memory cells of the memory sector corresponding to the address are verified at step S321 and injected with the erasing shot at S323 until the transistor memory cells of memory sector are erased. If the transistor memory cells of the memory sector corresponding to the address are erased, the address will be added with an increment at S329, and the transistor memory cells of another one memory sector corresponding to the address in the same memory block is verified at step S321 and injected with the erasing shot at step S323 until the transistor memory cells of other one memory sector are erased. Hence, the transistor memory cells of all the memory sectors in the memory block are erased, and the provided erasing method will perform the similar erasing scheme on the next memory block.

[0037] In conclusion, at the verification and erasing step, the provided erasing method used in the flash memory according to one embodiment of the present disclosure erases the transistor memory cells of the memory sector or the memory block according to whether the memory block has at least one over-erased transistor memory cell, such that the erasing method does not need additional flag registers for recording statuses of the memory sectors. Furthermore, the conventional method in FIG. 2 injects an erasing shot to erase and verify the whole memory block (p.s. the unit for verification is 8 bits or more bits), but the erasing method in the present disclosure injects an erasing shot to perform the OEC verification on the bit lines of the whole memory block (p.s. the unit for verification is 8 bits or more bits), such that the erasing method of the present disclosure can save much time. Moreover, the slower and faster erased transistor memory cells in the memory sectors have a little probability to connect to a same bit line, and the erasing method of the present disclosure obtains a small erased threshold voltage distribution as that obtained by the conventional method of FIG. 2, such that the problem which the over-erased transistor memory cells mask the under-erased transistor memory cells can be avoided, and the over-erased transistor memory cells will not suffer long over-erased correction time and post-over-erased correction time.

[0038] While the present disclosure has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the present disclosure set forth in the claims.