Non-volatile semiconductor memory device and semiconductor...

Details Non-volatile semiconductor memory device and semiconductor... Non-volatile semiconductor memory device and semiconductor...

2002-07-26

2004-03-30

Hoang, Huan (Department: 2818)

Static information storage and retrieval

Floating gate

Particular connection

C365S052000, C365S063000, C365S189050

Reexamination Certificate

active

06714452

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a non-volatile semiconductor memory device and a semiconductor disk device. Specifically, the invention relates to the technique useful for non-volatile memory devices that are capable of having blocks of stored information erased electrically at once (hereinafter referred to as “flash memory”) and for semiconductor disk devices which use such flash memory.
BACKGROUND OF THE INVENTION
FIG. 1
shows an example of the conventional semiconductor disk device. This semiconductor disk device
99
is made up of a disk controller
1
and one or more chips of flash memory
3
. The controller
1
includes a host interface logic circuit
14
a flash control interface logic circuit
17
, I/o buffers
15
and
16
, an MPU
12
, an MPU interface logic circuit
13
, and a data transfer logic circuit
11
. It implements data writing to the flash memory
3
in response to a write request and for data
25
transferred from the host
2
, which is a workstation, personal computer, or the like.
FIG. 2
shows an example of the arrangement of the flash memory
3
. This example shows the arrangement including eight flash memory chips indicated by
31
through
38
. The flash memory chips have individual lines
521
through
528
of chip select signals wired from the controller
1
(the chip select signal lines
521
-
528
are shown generically as a wiring
52
at the controller
1
and the interconnection is not shown). Another wiring
51
represents a data bus, address bus and various control signal lines, and it is a common wiring to all flash memory chips. In other words, the data-pin, the address pin, and the control signal lines other than the wiring
52
have in common the eight flash memory chips, and for example, a signal line A
0
in the address bus is connected with each terminal A
0
of the eight flash memory chips.
In this arrangement, the controller
1
controls each flash memory chip by selecting a chip in accordance with the chip select signal end issuing a command and address for data to be written.
FIG. 3
shows the write operation of the conventional semiconductor disk device which is arranged as shown in FIG.
2
. The case of sequential and cyclic data writing to the flash memory chips
31
-
38
is shown by the flow chart.
Each block STSn (n=31,32, . . . ,38) is the operation of the controller
1
to check the operational state of a flash memory chip n, and it branches in the direction of “Ready” if the chip is in a Ready status or in the direction of “Busy” if the chip is in a Busy status. Each block DTn (n=31,32, . . . ,38) is the operation of the host
2
to issue a write command to a flash memory chip n and to issue a command of initiating the automatic write operation within the chip for data to be written which is held by the data buffer. Following the operation of DTn, the flash memory chip n writes the data to memory cells based on the in-chip automatic write operation, and it stays in Busy status until the end of the writing.
The foregoing arrangement and operation enable the transfer of data and the issuance of a write command to the next flash memory chip during the automatic write operation within the former chip, and accomplishes the speed-up of data writing based on the parallel writing to multiple flash memory chips.
Recently, an efficient flash memory
15
access method has been devised based on the early execution of a write operation for a flash memory chip which is detected early to be Ready, as illustrated by
FIG. 10
of Japanese Patent Unexamined Publication No. H10-63442.
This patent publication No. H10-63442, shown by
FIG. 10
,
20
is a semiconductor disk having
16
flash memory chips, and for one pattern of the write operation, it can proceed to the write operation for any flash memory chip which becomes Ready among three flash memory chips having high, medium and low write-in priority levels.
However, a description is given of the problem which occur when the write operation is performed with the aforementioned configuration
The case is considered in which, as shown in
FIG. 4
, a flash memory chip indicated by chip No.
1
(hereinafter, called chip
1
) is a high write-in priority chip, chip
2
is a medium write-in priority chip and chip
3
is a low write-in priority chip. When chips No.
8
and No.
13
are in Ready status and other chips than the chips No.
8
and No.
13
are in Busy status, the write operation is performed according to the flow chart in
FIG. 10
of the patent publication No. H10-63442. Although the chip in which the write operation is performed has its execution ability at the steps S
19
, S
21
and S
23
as in the
FIG. 10
, the decision of the execution ability is performed only for a high priority chip (chip
1
) in the step S
19
, for a medium priority chip (chip
2
) in the step S
21
, and for a low priority chip (chip
3
) in the step S
23
. Despite the existence of chips (chips No.
8
and No.
13
) being in the Ready status where the write operation is available, the decision that the write operation is unavailable is made and while the write operation is not performed, the next step S
25
is carried out.
In other words, in the conventional configuration, even if one or more flash memory chips exist in a Ready status after the write operation is completed, the problem is raised in which the next write operation can not be performed immediately.
Recently, in Symp. on VLSI Circuits Tech. Digest, 1996, pp. 174-175, a flash memory having multiple banks (hereinafter called “multi-bank flash memory”) as a scheme of increasing the number of bits of simultaneous writing on a flash memory chip has been introduced. However, the multi-bank flash memory chip has Busy status during the writing of data to memory cells of one bank, while other banks are left inaccessible. Therefore, this flash memory is problematic in that individual banks cannot be controlled separately from the outside.
SUMMARY OF THE INVENTION
The present invention is intended to deal with the foregoing situation, and its prime object is to provide a semiconductor disk device which has a plurality of flash memory chips or one or more multi-bank flash memory chips, and which is capable of writing immediately to a bank of flash memory chips or multi-bank flash memory chips which have reached Ready status, and to provide a non-volatile semiconductor memory device having a multi-bank flash memory capable of having its banks controlled separately from the outside.
These and other objects and novel features of the present invention will become apparent from the following description of the specification, taken in conjunction with the accompanying drawings.
In the present invention disclosed in this specification, other objects and novel features are summarized as follows The inventive device has a plurality of banks, allows each bank to operate independently to write data from its data register to memory cells, and is capable of transferring write data from the outside to the data register of each bank, even during the write operation of other banks from the data register to memory cells.
The inventive device has a bank selection register which releases a signal for designating one of the banks in accordance with the bank status, which is established by an external input signal.
The device has a plurality of input terminals of bank enable signals and produces an internal control signal which designates one of the banks based on the combination of the bank enable signals. Data to be written from the outside is transferred to the data register of the designated bank. The device can indicate the status of the designated bank in response to the external status check command. The external read command, erase command, write command and status polling command act on a designated bank.
The inventive device incorporates one or more non-volatile semiconductor memory devices and provides access to said non-volatile semiconductor memory devices in response to disk access requests from a host, wherein the non-volat

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