JP2012043530A - Nonvolatile semiconductor memory device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a writing speed while increasing storage capacity by suppressing influence of capacity coupling to reduce interference of an adjacent memory cell in a NAND type flash memory.SOLUTION: A nonvolatile semiconductor memory device comprises a plurality of word lines 130, a plurality of bit lines 140 and a plurality of memory cell arrays 100 having a plurality of memory cell transistors 112 having two or more numbers of storage statuses. The numbers of storage statuses stored in the memory cell transistors 112 differ by memory cell transistors 112 which are adjacent each other in a word line direction and a bit line direction. Writing is performed by each even number bit line 140 and odd number bit line 140 in the page unit. The potential of the bit line 140 to which writing is not performed during writing is controlled at a predetermined potential.

Description

The present invention relates to a nonvolatile semiconductor memory, and more particularly to a NAND flash memory.

In recent years, in order to lower the unit price per bit in a non-volatile memory such as a NAND flash memory and to increase the storage capacity, a so-called binary or more information amount flash memory that stores a plurality of bit data in one memory cell Has been developed. When 2-bit data is stored in one memory cell, there are four threshold distributions of the memory cell corresponding to four-value data.

In general, the threshold distribution shape of the memory cell including such a NAND flash memory is desired to be narrow and sharp in consideration of a decrease in power supply voltage and manufacturing variations. For this reason, the step-up width of the write voltage Vpgm is desired. Narrowing is done. However, in the memory cell, on the other hand, the threshold distribution is widened by adjacent cell interference caused by capacitive coupling of adjacent cells. And this influence has become remarkable with miniaturization.

In addition, by narrowing the step-up width of the write voltage Vpgm and writing, it is possible to suppress the spread of the threshold distribution. Leads to a decrease in writing speed.

JP 2005-267687 A JP 2005-267821 A JP 2004-152405 A JP 2004-327865 A

An object of the present invention is to improve the writing speed while increasing the storage capacity by suppressing the influence of capacitive coupling and reducing the influence of adjacent memory cell interference in a NAND flash memory.

A nonvolatile semiconductor memory device according to an embodiment of the present invention includes a plurality of word lines, a plurality of bit lines, and a plurality of electrically rewritable memory cell transistors having two or more storage state numbers. A non-volatile semiconductor memory device having a memory cell array, wherein the number of storage states stored in the memory cell transistors is different between adjacent memory cell transistors in a word line direction and a bit line direction, and an even bit line and an odd bit It is characterized in that the potential of the bit line which is written in units of pages for each line and not written at the time of writing is controlled to a predetermined potential.

According to the present invention, in the NAND flash memory, it is possible to suppress the influence of capacitive coupling and reduce the influence of adjacent memory cell interference, thereby improving the writing speed while increasing the storage capacity.

1 is a schematic configuration diagram of a nonvolatile semiconductor memory device according to a first embodiment of the present invention. 1 is a schematic configuration diagram of a memory cell array of a nonvolatile semiconductor memory device according to a first embodiment of the present invention. 1 is a schematic configuration diagram in a memory cell block of a nonvolatile semiconductor memory device according to a first embodiment of the present invention. 1 is a schematic diagram of a layout of a NAND cell of a nonvolatile semiconductor memory device according to a first embodiment of the present invention. FIG. 4 is a diagram showing a potential relationship at the time of writing in the memory cell block BLOCKi shown in FIG. 3. It is a figure which shows the relationship between quaternary data and a threshold potential. It is a figure which shows the write-in sequence of the non-volatile semiconductor memory device concerning one Embodiment of this invention. It is a schematic diagram of a threshold distribution showing the influence of capacitive coupling of NAND type cells. It is a schematic diagram showing the influence of capacitive coupling of NAND type cells of the nonvolatile semiconductor memory device according to the first embodiment of the present invention. It is a schematic diagram of the handling assignment of binary data and quaternary data to the memory cell of the nonvolatile semiconductor memory device according to the first embodiment of the present invention. It is a schematic diagram of the handling assignment of binary data and 8-level data to the memory cell of the nonvolatile semiconductor memory device according to the second embodiment of the present invention. It is a schematic diagram of the handling assignment of 4-level data and 8-level data to the memory cell of the nonvolatile semiconductor memory device according to the third embodiment of the present invention. It is a schematic diagram of the handling allocation of binary data, quaternary data, and octet data to the memory cell of the nonvolatile semiconductor memory device according to the fourth embodiment of the present invention. It is a schematic diagram of handling assignment of binary data and quinary data to a memory cell of a nonvolatile semiconductor memory device according to a fifth embodiment of the present invention. It is a schematic diagram of the handling assignment of binary data and 6-value data to the memory cell of the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention. It is a schematic diagram of the handling assignment of binary data and 7-value data to the memory cell of the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention. It is a schematic diagram of handling assignment of ternary data and ternary data to a memory cell of a nonvolatile semiconductor memory device according to a sixth embodiment of the present invention. It is a schematic diagram of handling assignment of quinary data and quinary data to a memory cell of a nonvolatile semiconductor memory device according to a sixth embodiment of the present invention. It is a schematic diagram of the handling assignment of binary data and quinary data to the memory cell of the nonvolatile semiconductor memory device according to the seventh embodiment of the present invention. It is a 2nd schematic diagram of the handling allocation of binary data and quinary data to the memory cell of the non-volatile semiconductor memory device which concerns on the 8th Embodiment of this invention. It is a schematic diagram of handling assignment of ternary data and ternary data to a memory cell of a nonvolatile semiconductor memory device according to an eighth embodiment of the present invention. It is a schematic diagram of the handling assignment of binary data, ternary data, quaternary data, and hex data to the memory cell of the nonvolatile semiconductor memory device according to the ninth embodiment of the present invention. It is a schematic diagram of the handling assignment of binary data, ternary data, 6-value data, and 8-level data to the memory cell of the nonvolatile semiconductor memory device according to the ninth embodiment of the present invention. It is a schematic diagram of the handling assignment of binary data, quaternary data, hex data, and octo data to the memory cell of the nonvolatile semiconductor memory device according to the ninth embodiment of the present invention. It is a schematic block diagram of the flash memory provided with the 2 transistor type cell which concerns on the 10th Embodiment of this invention.

Hereinafter, a nonvolatile semiconductor memory device according to a first embodiment of the present invention will be described in detail with reference to the drawings, taking a NAND flash memory as an example. The embodiments show examples of the nonvolatile semiconductor memory device of the present invention, and the nonvolatile semiconductor memory device of the present invention is not limited to these embodiments.

The flash memory changes the threshold value by changing the amount of electric charge stored in the floating gate electrode of the memory cell, and stores data. For example, when the threshold value of the memory cell is negative, it corresponds to “1” data, and when it is positive, it corresponds to “0” data.

In recent years, so-called multi-level flash memories have been developed in which a plurality of bit data is stored in one memory cell in order to lower the bit unit price or increase the storage capacity. When 2-bit data is stored in one memory cell, there are four threshold distributions of the memory cell corresponding to four-value data.

In such a NAND flash memory, the threshold distribution of memory cells needs to include a threshold distribution according to the amount of information to be written in a predetermined potential range in order to write binary information amount data. That is, a plurality of threshold distributions must be inserted between the read potential Vread (referring to the gate voltage of a non-selected cell in the NAND cell, for example, 5V) and 0V. Therefore, in the NAND flash memory, it is necessary to narrow the step-up width of the write potential Vpgm in order to obtain a threshold distribution having a narrow width and sharpness. Here, the floating gate (FG) of the memory cell is capacitively coupled to the floating gates of adjacent cells in the bit line (BL) direction, the word line (WL) direction, and the diagonal direction. Therefore, even if an attempt is made to make the threshold distribution of the memory cell narrow and sharp in order to store binary amount of information data, the threshold distribution of the memory cell is widened due to the influence of capacitive coupling. It is difficult to realize a narrow and sharp threshold distribution. The effect of such capacitive coupling becomes more conspicuous with miniaturization, and this effect is particularly remarkable because the capacitance in the bit line (BL) direction and the word line (WL) direction is large.

Therefore, in order to realize further miniaturization and larger capacity at the same time in the future, when storing information data of two or more values in a memory cell, the influence of capacitive coupling is suppressed to reduce interference between adjacent memory cells, and integration It is necessary to improve the writing speed while increasing the degree. The nonvolatile semiconductor memory device according to the embodiment of the present invention can suppress the influence of such capacitive coupling, reduce interference between adjacent memory cells, and improve the writing speed while increasing the degree of integration.

FIG. 1 shows a schematic configuration diagram of a NAND flash memory according to the first embodiment of the nonvolatile semiconductor memory device of the present invention. A nonvolatile semiconductor memory device 10 shown in FIG. 1 includes a memory cell array 100 in which a plurality of electrically rewritable memory cells MC111 are arranged in a matrix, a row decoder 20, a column decoder 30, a sense amplifier 40, and an input / output buffer 50. , An address buffer 60, a voltage generation circuit 70, a power-on reset circuit 80, a control circuit 90, and a latch circuit 200. Further, a state machine, a command interface, a selection circuit, and the like are further provided, but are not shown in FIG. The nonvolatile semiconductor memory device 10 according to the present embodiment transmits and receives data and control signals (commands) to and from the external I / O pad 210.

In the nonvolatile semiconductor memory device 10 according to the first embodiment of the present invention, data and control signals are input from the external I / O pad 210 to the command interface and column decoder 30 through the data input / output buffer 50. The state machine controls the column decoder 30 and the row decoder 20 based on the control signal and data. The state machine outputs access information for the memory cell MC111 of the memory cell array 100 to the column decoder 30 and the row decoder 20. The row decoder 20 controls the selection circuit based on the access information and data, and activates the memory cell MC111. The column decoder 30 is provided between the sense amplifier 40 and the data bus, reads 8-bit or 16-bit data from the latch of the sense amplifier 40 of the selected address, transfers the data to the data bus, and externally passes through the data input / output buffer 50. Output to the I / O pad 210. At the time of writing, data is loaded into the latch of the sense amplifier 40. The sense amplifier 40 connected to each bit line 140 of the memory cell array 100 has a latch function for storing read data and write data, and senses and amplifies the potential of the bit line 140 during page reading to latch the read data. At the time of writing, the externally input write data is latched and the write data is loaded onto the bit line 140.

Here, the configuration of the memory cell array is shown in FIG. As shown in FIG. 2, the memory cell array 100 of the nonvolatile semiconductor memory device according to the first embodiment of the present invention includes a total of m blocks (BLOCK0, BLOCK1, BLOCK2,..., BLOCKi,..., BLOCKm. ). Here, the “block” is a minimum unit of data erasure.

In addition, the memory cell array 100 of the nonvolatile semiconductor memory device according to the first embodiment of the present invention includes trimming data for timer adjustment and various voltage adjustments in addition to the normal memory cell area 110 for storing data. It has a ROM area 120 for storing various data (fuse data) that need to be read after power-on and replacement address data for replacing defective cells existing in the memory cell array 110 with other redundant cells.

The fuse data stored in the ROM area 120 is sent to the latch circuit 200 via the sense amplifier 40 and the column decoder 30 and held therein. The operation of reading the fuse data stored in the ROM area 120 and setting it in the latch circuit 200 is called a ROM read operation.

Each of the blocks BLOCK0 to BLOCKm is composed of six NAND strings 0 to 5 like a block BLOCKi typically shown in FIG. FIG. 3 is a configuration diagram of the memory cell block BLOCKi of the nonvolatile semiconductor memory device according to the embodiment of the present invention. Here, the NAND string indicates a configuration in which the memory cells MC are connected in series and both ends are sandwiched between the select gate transistors ST.

In the present embodiment, each NAND string is configured by connecting five memory cells MC0 to MC4 (111) in series, and one end of the NAND string includes a selection gate transistor ST0 (113) connected to the drain side selection gate line SGD150. Through the bit line BL140 (BL0, BL1, BL2, BL3, BL4, BL5), and the other end is connected to the common source line CELSRC160 via the selection gate transistor ST1 (113) connected to the source side selection gate line SGS150. ing. The control gate of each memory cell MC111 is connected to the word line WL130 (WL0 to WL4). FIG. 3 shows a case where there are five word lines as an example, but the present invention is not limited to this.

Here, in the six memory cells MC111 connected to one word line WL130, each memory cell MC111 stores a plurality of bits of data (multi-valued bit data) corresponding to the electron injection amount. These six memory cells MC111 constitute a unit called “page”.

In the present embodiment, the number of blocks constituting the memory cell array is set to m, and one block includes six NAND columns each including five memory cells MC. However, the present invention is not limited to this. However, the number of blocks, the number of memory cells MC, and the number of NAND columns may be changed in accordance with a desired capacity. In this embodiment, an example of a NAND flash memory in which one NAND string is connected to one bit line BL has been described. However, the NAND flash memory according to the present invention includes a plurality of NAND strings. It may be connected to one bit line BL.

FIG. 4 is a diagram schematically showing the layout of the NAND cell of the nonvolatile semiconductor memory device according to the first embodiment of the present invention. Each NAND column is arranged in a line-symmetrical direction around the bit line contact. Since the selection gate lines SGD150b and SGS150a are important wirings related to access at the time of reading, they are shunted by a wiring metal layer (not shown). The reason why the wiring metal layer (not shown) is shunted is that the selection gate line SGD150 has a high resistance, so that the resistance is lowered by being electrically connected to the low resistance wiring layer. The drain-side selection gate line SGD150b is used as a common wiring with the adjacent NAND column unit because there is not enough area because the resistance of the shunt line is made as small as possible. The diffusion layer 114 forming the channel of the memory cell MC is arranged in a straight line in the vertical direction toward FIG. 4, and is a contact between the diffusion layer and M0 (hereinafter referred to as CB contact 115) in a region sandwiched between the selection gate lines SGD150b. Is connected to M0 by a contact between the M1 and M0-M1 (hereinafter referred to as a V1 layer) of a bit line running in a straight line in the same vertical direction as the diffusion layer (not shown). On the other hand, in the region surrounded by the selection gate line SGS150a, it is connected to M0 by the CB contact 115, and is connected to the source line of the cell array region by the cell source line of the M0 layer 116 commonly connected in the horizontal direction toward FIG. .

The row decoder 20 controls the selection circuit based on the decoded address signal and activates the memory cell MC111.

The column decoder 30 is provided between the sense amplifier 40 and the data bus, reads 8-bit or 16-bit data from the latch of the sense amplifier 40 of the selected address, transfers the data to the data bus, and externally passes through the data input / output buffer 50. Output to the I / O pad 210.

The sense amplifier 40 has a latch function for storing read data and write data, senses and amplifies the potential of the bit line 140 during page read, latches read data, latches write data input from the outside, and writes Sometimes write data is loaded into the bit line 140.

The address buffer 60 encodes address information input from the outside, and selects a word line 130 and a bit line 140 to be accessed by being decoded by the row decoder 20 and the column decoder 30.

The voltage generation circuit 70 receives a mode signal, a voltage generation timing control signal, and a voltage level setting signal from the control circuit 90, and uses the power supply voltage VCC supplied from the outside to generate a reference voltage Vref for reference, a program voltage Vpgm, and the like. An internal voltage necessary for various modes is generated and output to a circuit that requires the voltage, such as the row decoder 20 and the sense amplifier 40.

The power-on reset circuit 80 detects that power is turned on, resets the register of the control circuit, and outputs a signal for performing an initialization operation. The power-on reset circuit 80 generates a power-on reset signal that is at a low level until the power supply voltage reaches a predetermined voltage level after the power is turned on, and that attains a high level after reaching the predetermined voltage level. , Output to the control circuit 90.

The control circuit 90 receives a command input from the outside and generates a mode signal for a read operation, a write operation, an erase operation, and the like, and a timing control signal for generating a necessary voltage for each mode, and a voltage setting level A voltage setting signal, an address control signal, and an access control signal to the memory cell are output in accordance with a register storing.

The control circuit 90 initializes the address buffer 60, the column decoder 30, the row decoder 20, the sense amplifier 40, the latch circuit 200, and the voltage generation circuit 70 in FIG. 1 based on the power-on reset signal. The control signal is output.

That is, the control circuit 90 includes an initialization control circuit 91 that outputs a control signal for initialization and a ROM read control circuit 92 that outputs a control signal for controlling a ROM read operation.

The operations of the power-on reset circuit 80 and the control circuit 90 are as follows. That is, when the power supply voltage VCC rises and the value reaches the power-on detection level, a power-on reset signal is output, and a control signal for controlling the ROM read operation is output from the ROM read control circuit 92 to read the ROM. Is activated.

Write and read operations of the nonvolatile semiconductor memory device according to an embodiment of the present invention having such a configuration will be described. In the nonvolatile semiconductor memory device according to one embodiment of the present invention, since information amount data of two or more values is written in the memory cell MC111, there is a difference from the writing / reading operation of a general nonvolatile semiconductor memory device. . Therefore, as a premise, a write / read operation of a general nonvolatile semiconductor memory device will be described.

FIG. 5 is a diagram showing a potential relationship at the time of writing in the memory cell block BLOCKi shown in FIG. In FIG. 5, a case where data is written to the memory cell MC111 connected to the even (Even) bit line of the word line WL2 will be described as an example. In the NAND flash memory, writing is performed with 0 V on the bit line 140 of the memory cell MC111 to be written, that is, the memory cell MC111 of “0” data, and the bit line of the memory cell MC111 that is not to be written, that is, the memory cell MC of “1” data. VDD is applied to the drain side select gate line SGD150, and 0 V is applied to the source side select gate line SGS150. Therefore, in this example, 0 V is applied to the bit lines BL0, BL2, and BL4 (140), and VDD is applied to the bit lines BL1, BL3, and BL5. Further, VDD is applied to the drain side select gate line SGD150b, and 0 V is applied to the source side select gate line SGS150a.

By applying the voltage, the channel in the selected NAND string becomes 0 V for the channel to be written and the potential of the channel not to be written (VDD−Vth_SGD).

Thereafter, the write voltage Vpgm (about 20 V) is applied to the selected word line WL2 (130), and the intermediate voltage Vpass (about 10 V) is applied to the unselected word lines WL0, WL1, WL3 to WL5 (130). At this time, the channel potential in the NAND string is raised by capacitive coupling with the word line 130.

When the channel potential of the bit lines BL1, BL3, and BL5 (140) to which VDD is applied becomes higher than (VDD−Vth), the drain-side selection gate line SGD150b is cut off, so that the capacitance ratio between the word line and the cell channel Boosted to a determined voltage Vbst.

On the other hand, in the NAND string connected to the bit lines BL0, BL2 and BL4 to which 0V is applied from the bit line, the drain side selection gate line SGD150b is not cut off, and therefore 0V is continuously applied to the channel potential. As a result, the memory cell channel of the NAND string to which 0V of the bit lines BL0, BL2 and BL4 is applied becomes 0V, the memory cell channel of the NAND string to which VDD is applied becomes Vbst, and the memory cell MC of 0V is written by the tunnel current. On the other hand, a state is realized in which the Vbst memory cell MC is not written.

Through the above-described operation, page writing to the even-side word line WL2 (130) of the bit lines BL0, BL2, and BL4 (140) can be realized. The bit lines BL1, BL3, and BL5 (140) serve as shield lines for preventing read noise, and the Odd side bit lines BL1, BL3, and BL5 (140) are all VDD when writing on the Even side. It is in a state (ALL1) where writing is not performed. When the even-side write is completed, write data is applied to the odd-side write (specifically, write data is applied to the bit lines BL1, BL3, and BL5 (140), and VDD is applied to the bit lines BL0, BL2, and BL4 (140)). )I do.

Next, a write / read operation in the case where information amount data of two or more values is written to the memory cell MC in one chip will be described. Here, a case where quaternary data (2-bit data) is written in the memory cell MC will be described as an example.

One memory cell stores quaternary data (2-bit data). In one embodiment of the present invention, write data is “0 (write)” and “1 (not write)”, and quaternary data is a combination of the write data “11”, “10”, “01”, “00”. " One bit of the quaternary data (2-bit data) is stored in the same memory cell as Lower Page data, and the other 1 bit is stored as Upper Page data.

The relationship between the quaternary data (“11”, “10”, “01”, “00”) and the threshold voltage of the memory cell is as shown in FIG. In FIG. 6, Lower Page data is indicated by a white square, and Upper Page data is indicated by a white circle.

When controlling writing and reading of quaternary data, one negative threshold voltage for erasing is assigned, and three positive threshold voltages for writing and reading are assigned. The positive threshold voltage is normally assigned between 0V and 5V, and is generally stepped up at a constant rate while taking a margin. As an example, 0V is assigned to the write state “10”, 1V is assigned to “00”, and 2V is assigned to “01”.

In FIG. 6, Vcgv10 is a read potential used for the verify read of data “10”, and is set with a certain margin (for example, 0.4 V). Vcgv01 is a read potential (for example, 1.4 V) used for verify read of data “01”, and Vcgv00 is a read potential (for example, 2.4 V) used for verify read of data “00”. Vread is a transfer potential applied to an unselected word line.

In FIG. 6, the E state “11” is an erased state. In the erased state, the value of Lower Page data and the value of Upper Page data are both “1”. An erased memory cell has a negative threshold voltage Vth.

Similarly, in FIG. 6, the A state “10”, the B state “01”, and the C state “00” are write states. The memory cell in the written state has a positive threshold voltage Vth. Of the write states, the A state “10” has the lowest threshold voltage, the C state “00” has the highest threshold voltage, and the B state “01” state is the A state “10”. It has an intermediate threshold voltage of the C state “00”.

The quaternary data consists of lower page data and upper page data, and is written into the memory cell MC by two write operations. There are various ways of writing, but in order to simplify the explanation, it is assumed that the E state is changed to the E or A state, the E state is changed to the B state, or the A state is changed to the C state in order. In this case, the former writing (E to E or A) is referred to as “Lower Page writing”, and the latter writing (E to B or A to C) is referred to as “Upper Page writing”.

First, lower page data is written. Here, for the sake of explanation, it is assumed that all memory cells are initially in an erased state, that is, in an E state “11”. When writing the lower page data, the distribution of the threshold voltage Vth of the memory cell MC is divided into two according to the value “1” or “0” of the write data (lower page data).

That is, when the lower page data is “1”, the bit line is set to “H” (the word line is the write potential Vpgm) so that a high electric field is not applied to the tunnel oxide film of the memory cell MC. An increase in the MC threshold voltage Vth is prevented. As a result, the memory cell MC maintains the erased state (E state “11”) (writing of the lower page data “1”).

On the other hand, when the lower page data is “0”, a high electric field is applied to the tunnel oxide film of the memory cell MC by setting the bit line to “L” (the word line is the write potential Vpgm), and the floating gate electrode Electrons are injected into the memory cell to increase the threshold voltage Vth of the memory cell by a predetermined amount. As a result, the memory cell changes to a write state (A state “10”) (write of Lower Page data “0”). Thereafter, Upper Page data is written.

When the upper page data is “1”, the bit line is set to “H” (the word line is a write potential) so that a high electric field is not applied to the tunnel oxide film of the memory cell MC, and the threshold value of the memory cell MC is set. The rise of the voltage Vth is prevented. As a result, the memory cell MC in the E state “11” (erased state) in which the Lower Page data is “1” maintains the E state “11” as it is (writing of the Upper Page data “1”). Further, the memory cell MC in the A state “10” in which the Lower Page data is “0” maintains the A state “10” as it is (writing of the Upper Page data “1”).

On the other hand, when the upper page data is “0”, by setting the bit line to “L”, a high electric field is applied to the tunnel oxide film of the memory cell MC, and electrons are injected into the floating gate electrode. The threshold voltage Vth of the cell MC is increased by a predetermined amount. As a result, the memory cell in the E state “11” (erased state) in which the Lower Page data is “1” changes to the B state “01” (writing of the Upper Page data “0”). Further, the memory cell in the A state “10” in which the lower page data is “0” changes to the C state “00” (writing of the upper page data “0”).

As described above, the distribution of the threshold voltage Vth of the memory cell is divided into four (“11”, “10”, “01”, “00”) by two write operations. In this example, when the upper page data is “0”, the memory cell in the E state “11” changes to the B state “01”, and the memory cell in the A state “10” changes to the C state “00”. To do.

When the threshold voltage of the memory cell MC is less than Vcgr10, the data of the memory cell MC is “11” and the threshold voltage of the memory cell MC exceeds Vcgr10 and falls below Vcgr01. The data of the memory cell MC is “10”, and when the threshold voltage of the memory cell MC exceeds Vcgr01 and falls below Vcgr00, the data of the memory cell MC is “01” and the threshold voltage of the memory cell MC When Vcgr00 exceeds Vcgr00, the data in the memory cell MC is “00”.

The normal reading of the lower page data can be realized by, for example, two reading operations (“READ00” and “READ10”). READ00 is a read operation using Vcgr00 (for example, 2V) as a read potential, and READ10 is a read operation using Vcgr10 (for example, 0V) as a read potential. Further, reading of Upper Page data can be realized by, for example, a single read operation (READ “01”). READ01 is a read operation using Vcgr01 (for example, 1V) as a read potential.

Further, the operation of writing, erasing and reading information data having two or more values will be described when the word line WL2 and the even-numbered bit lines BL0, BL2 and BL4 are selected at the time of writing and reading.

Tables 1 and 2 show the potential of each part in the flash memory during erase, write, read, and write verify. In Tables 1 and 2, BLe is the even-numbered bit line, BLo is the odd-numbered bit line, SGD is the select gate line of the drain side (bit line side) select gate transistor, and SGS is the source side (source line side). Select gate lines of the select gate transistor, WL1, WL2, WL3, WL4 are word lines, C-source is a source line, and C-p-well is a well (cell p-well) in which a memory cell is formed.

In the initial state, the memory cell is in the “11” state. In the erase operation, the cell p-well C-p-well is set to 20V, and all the word lines WL0, WL1, WL2, WL3 in the selected block are set to 0V, so that the memory cells in the selected block. Then, electrons are emitted from the floating gate, and the state becomes “11”.

During the erase operation, the word lines, all bit lines, control gate lines, and source lines in the non-selected block are brought into a floating state. For this reason, the potentials of these conductive lines rise to around 20 V due to capacitive coupling with the cell p well Cp-well.

Writing is performed by applying 14V to 20V as the write potential Vpgm to the selected word line WL2. Since the selected bit line BLe is set to 0 V, electrons are injected into the floating gate electrode in the selected memory cell connected to the selected word line WL2 and the selected bit line BLe, The threshold value rises rapidly (first stage writing).

When the threshold value of the selected memory cell rises close to the target value, the selected bit line BLe is set to 0.4 V in order to keep the threshold value of the selected memory cell close to the target value so as to suppress the rising speed of the threshold value. Raise to the extent (second stage writing).

For the non-selected memory cell, the bit line BLe is set to the power supply potential (for example, about 3 V) Vdd (write prohibition) in order to prohibit the increase of the threshold value.

Reading is performed by applying 0V, 1V, or 2V as a read potential to the selected word line WL2.

At this time, if the threshold value of the selected memory cell is lower than the read potential, the bit line BLe and the common source line C-source are short-circuited, and the potential of the bit line BLe becomes low level “L”. On the other hand, if the threshold value of the selected memory cell exceeds the read potential, the bit line BLe and the common source line C-source are non-conductive, so that the potential of the bit line BLe is at the high level “H”. become.

Whether the memory cell is in the “11” state, the “10” state, the “01” state, or the “00” state can be determined by setting the reading potential to 0 V (10 readings). Whether the memory cell is in the “11” state, “10” state, “01” state, or “00” state can be determined by setting the read potential to 1 V (01 read). . Further, whether the memory cell is in the “11” state, the “10” state, the “01” state, or the “00” state can be determined by setting the reading potential to 2 V (00 reading). .

The lower limit of the threshold distribution of the memory cell in the “10” state is, for example, a value of 0.4 V or more, in this example, 0. Set to 4V. Whether or not the threshold value of all the memory cells in the “10” state is 0.4 V or higher is verified by 10-write verification. Then, with respect to the memory cell whose threshold value has reached 0.4V, thereafter, writing is prohibited and the increase of the threshold value is prohibited.

Similarly, the lower limit of the threshold distribution of the memory cell in the “01” state is, for example, a value of 1.4 V or more in this example in order to provide a read margin of 0.4 V or more with respect to the read potential of 01 read of 1 V. , 1.4V. Whether or not the threshold values of all the memory cells in the “01” state are 1.4 V or higher is verified by 01 write verify. Then, for the memory cell whose threshold value has reached 1.4V, after that, writing is prohibited and the increase of the threshold value is prohibited.

In addition, the lower limit of the threshold distribution of the memory cell in the “00” state is, for example, a value of 2.4 V or more in order to have a read margin of 0.4 V or more with respect to the read potential of 2 V of 00 reading. Set to 2.4V. Whether the threshold value of all memory cells in the “00” state is 2.4 V or higher is verified by 00 write verify. Then, for a memory cell whose threshold value has reached 2.4 V, thereafter, writing is prohibited and the increase of the threshold value is prohibited.

Write verification is performed by applying Vcgv10 (= 0.4 V), Vcgv01 (= 1.4 V), and Vcgv00 (= 2.4 V) as verification potentials to the selected word line WL2.

Here, in order to narrow the width of the threshold distribution, it is effective to perform two-step write verification. The two-stage write verification is verification in which two types of verification potentials, a normal value and a value lower than that, are prepared, and write verification is executed using these two types of verification potentials.

For example, in the 10 write verify, first, 0.2 V is applied as the verify potential Vcgv10 to the selected word line WL2, and the 10 first step write verify is performed. Then, for the memory cells for which the 10 first step write verification has been completed, 0.4 V is applied as the verify potential Vcgv10 individually, and the 10 second step write verify is performed.

Similarly, in the 01 write verify, 1.2V (01 first step write verify) and 1.4V (01 second step write verify) are used as the verify potential Vcgv01, and in the 00 write verify, the verify potential Vcgv00 is 2 .2V (00 first step write verify) and 2.4V (00 second step write verify) are used.

When the threshold value of the memory cell does not reach the verify potential, the bit line BLe and the common source line C-source are short-circuited, so that the potential of the bit line BLe becomes low level “L”. When the threshold value of the memory cell exceeds the verify potential, the bit line BLe and the common source line C-source are rendered non-conductive, so that the potential of the bit line BLe becomes high level “H”.

In a multi-level flash memory, n (n is a plurality) bits or 2 ⁿ level data is stored in one memory cell. Therefore, the threshold distribution of the memory cell is desired to be steep and narrow. In order to obtain such a steep and narrow threshold distribution, in the semiconductor memory device according to the first embodiment of the present invention, the following write and threshold control methods are employed.

The write potential Vpgm is stepped up at a constant rate Dvpgm (for example, 0.2 V) from the initial value. The write potential Vpgm is applied to the memory cell as a pulse signal (write pulse), and the height (write potential Vpgm) increases each time the pulse signal is applied to the memory cell.

When 0 V is applied to the bit line connected to the memory cell to be written, after several pulse signals are applied, the threshold of the memory cell has the same rate of increase (0. 2V / pulse).

Write verification is performed after writing is performed using a pulse signal. In the write verify, for the memory cell whose threshold reaches the write verify potential, the potential of the bit line connected to the memory cell is set to Vdd (power supply potential). That is, for each memory cell, it is verified whether or not writing is completed, and the memory cell for which writing has been completed is individually set to a write-inhibited state. According to such a writing and threshold control method, the threshold distribution width can be suppressed to the same level as the threshold increase rate per pulse, that is, 0.2V.

The writing is represented as a series of sequences as shown in FIG. FIG. 7 is a diagram showing a write sequence of the nonvolatile semiconductor memory device according to one embodiment of the present invention. FIG. 8 is a schematic diagram of a threshold distribution showing the influence of capacitive coupling of NAND cells. There are various ways of writing, but in order to simplify the explanation, it is assumed that the E state is changed to the E or A state, the E state is changed to the B state, or the A state is changed to the C state in order. In this case, the former writing (E to E or A) is referred to as “Lower Page writing”, and the latter writing (E to B or A to C) is referred to as “Upper Page writing”.

First, write data (0 data) or not (1 data) is applied to the even-side bit lines BL0, BL2, and BL4. In the case of 2-bit multilevel, there are four Vth distribution states as shown in FIG.

First, the even bit lines BL0, BL2, and BL4 (140) are selected for writing. A write voltage 0V or a non-write voltage VDD is applied to the even bit lines BL0, BL2 and BL4 (140). Then, LowerPage writing is performed, and then UpperPage writing is performed.

Subsequently, the odd bit lines BL1, BL3, and BL5 (140) are selected. A sequence of a sequence in which a write voltage 0V or a non-write voltage VDD is applied to the odd bit lines BL1, BL3, and BL5 (140), followed by lower page write, and then upper page write.

In the case of 2-bit multilevel writing, the above-described writing sequence is used, but the problem here is the influence of capacitive coupling between adjacent cells. FIG. 9 is a schematic diagram showing the influence of capacitive coupling of a NAND cell.

The floating gate (FG) of the memory cell MC111 is capacitively coupled to the floating gate of the adjacent memory cell MC111 in the bit line direction, the word line direction, and the diagonal direction. The floating gates of the memory cells MC2-2 shown in FIG. 9 are connected to the adjacent memory cells MC1-1, MC1-2, MC1-3, MC2-1, MC2-3, MC3-1, MC3-2 and MC3-3. Are connected. However, in particular, capacitive coupling between the adjacent memory cells MC2-1 and MC2-3 in the bit line direction and the adjacent memory cells MC1-2 and MC3-2 in the word line direction causes the adjacent memory cells MC1-1 in the oblique direction. , MC1-3, MC3-1, and MC3-3 are larger than the capacitive coupling, so that the influence becomes large. On the other hand, the memory cells MC1-1, MC1-3, MC3-1 and MC3-3 in the oblique direction are also capacitively coupled, but the influence is small.

Assuming a series of write sequences shown in FIG. 7, the influence of the capacitive coupling appears in a form as shown in FIG. In FIG. 8, a memory cell MC connected to the even bit lines BL0, BL2, and BL4 (hereinafter referred to as “even memory cell MC”) is taken as an example, and the memory cells MC connected to the adjacent odd bit lines BL1, BL3, and BL5. FIG. 5 is a schematic diagram showing distribution of threshold values when data is written (hereinafter referred to as “Odd memory cell MC”) and when data is further written into an adjacent Even memory cell MC. In order to make the description easy to understand, the memory cell MC2-2 in FIG. 9 will be described as an example.

First, the even bit lines BL0, BL2, and BL4 are selected and a write voltage is applied. At this time, the threshold distribution of the memory cell MC2-2 is in the upper state of FIG. Next, when the odd bit lines BL1, BL3, and BL5 are selected and written, the memory cell MC2-2 is capacitively coupled to the adjacent memory cells MC1-2 and MC3-2. The threshold distribution of -2 is in the state shown in the middle part of FIG. The threshold distribution is broadened due to the influence of capacitive coupling with the odd memory cell MC.

Further, when the word line WL3 is selected and the memory cell MC2-3 connected to the same Even bit line BL2 is written, the memory cell MC2-3 is also capacitively coupled. As shown in the lower part of FIG. 8, the threshold distribution further widened by writing to the odd memory cell MC is further widened.

That is, when the adjacent memory cell MC is written, the threshold value of the odd memory cell MC at the time of reading appears to fluctuate due to the influence of the fluctuation of the charge amount of the floating gate FG. Since this influence depends on the threshold value written in the adjacent cell, strictly speaking, the uniform threshold distribution does not spread as shown in the figure. However, when the adjacent memory cell MC is written, the original memory cell The distribution width is always wider than the threshold distribution.

Therefore, in a memory storing multiple values, since a plurality of values are written in one memory cell, the number of times of writing increases synergistically. Therefore, the threshold distribution is made as narrow as possible to make Data Retention (Data Retention Characteristics) and Read Disturb. In spite of taking a margin of memory cell MC fluctuation in reliability such as (stress fluctuation due to read voltage application), the threshold distribution spreads due to capacitive coupling of adjacent memory cells MC, and margin for reliability by miniaturization Is starting to decrease.

The spread of the threshold distribution can be suppressed by reducing the write voltage step width. However, when the step width is simply reduced, the number of times of application of the write voltage is increased and the entire write time is lengthened, leading to a decrease in write speed, which is not realistic. Therefore, suppressing the decrease of the writing speed while suppressing the spread of the threshold distribution is an important technical problem in promoting the multi-value.

In the present invention, at the time of writing to and reading from the memory cell MC, each memory cell MC is stored in a memory cell MC storing data with a small amount of information based on the address of the memory cell MC and a larger amount of information than the data. By allocating to the memory cell MC to be performed, the influence of capacitive coupling from adjacent memory cells in the bit line direction and word line direction with large capacitive coupling is suppressed.

FIG. 10 is a schematic diagram of memory cell MC assignment in the nonvolatile semiconductor memory device according to the first embodiment of the present invention. In the present embodiment, each memory cell MC is assigned to a memory cell MC that stores binary data and a memory cell MC that stores quaternary data. The present embodiment is characterized in that each memory cell MC adjacent in the bit line direction and the word line direction is assigned in a so-called checker flag shape so as to store data of different information amounts.

That is, when a specific memory cell MC is assigned to store binary data, the memory cell MC adjacent to both sides on the same bit line with respect to the memory cell MC and the same word for the memory cell MC Memory cells MC adjacent to both sides on the line are assigned to store quaternary data.

This assignment is determined by the address of the memory cell. In the first embodiment of the present invention, the bit line 140 is divided into an even bit line 140 and an odd bit line, and the word line 130 is also divided. Similarly, an even (Even) word line 130 and an odd (Odd) word line 130 are divided, and a combination of a bit line 140 and a word line 130 is an even-even, odd-odd memory cell MC is a first memory cell group. The other memory cells MC are classified as the second memory cell group. In the nonvolatile semiconductor memory device according to the first embodiment of the present invention, since the write to the memory cell MC is started from the Even bit line 140 in order to suppress the influence of capacitive coupling, the first memory The cell groups are assigned such that each memory cell MC stores binary data, which is data with a small amount of information, and the second memory cell group is such that each memory cell MC stores quaternary data. Assigned to.

Specifically, in FIG. 10, when the memory cell MC2-2 included in the first memory cell group is assigned to use binary data, the adjacent memory cell MC2-2 on the same bit line BL2 (140). 1, MC2-3 and adjacent memory cells MC1-2 and MC3-2 on the same word line WL2 (130) are all assigned to store quaternary data. Similarly, when looking at the memory cell MC 3-2, the memory cell MC is assigned to store quaternary data, but adjacent memory cells MC 3-1, MC 3-3, MC 2-2 and MC 4-2 are stored. Are all assigned to store binary data.

This assignment is determined by the address of the memory cell MC as described above, and is stored as fuse data in the ROM area 120 of the memory cell array 100 shown in FIG. The fuse data stored in the ROM area is called a ROM fuse. The fuse data is read from the ROM area 120 by the ROM read operation and set in the latch circuit 200. Therefore, in the first embodiment of the present invention, all the memory cells MC store the binary data according to the set fuse data (hereinafter, the operation mode to be handled is referred to as a binary cell mode). A memory cell MC to which such handling is assigned is referred to as a binary cell), or a memory cell MC that stores quaternary data (hereinafter, such an operation mode is referred to as a quaternary cell mode. The memory cell MC to which the handling is assigned can also be referred to as a quaternary cell. By switching the operation mode, it can be used in binary cell mode, quaternary cell mode and binary & quaternary checkered flag mixed mode.

In this embodiment, data is allocated to the memory cells MC of the entire memory by the ROM fuse. However, two fuse circuits are provided in the power-on reset circuit 80, and fuse data is assigned according to each address. The fuse data may be read out and supplied to the delay circuit 82 immediately after power-on. Further, it may be controlled by an external input.

The write sequence in the first embodiment of the present invention will be described in detail with reference to FIG. Writing is performed from the even bit lines BL0, BL2, and BL4 (140). First, the word line WL0 (130) is selected. Next, the even bit lines BL0, BL2, and BL4 (140) are selected to perform page writing. In this case, the memory cells MC0-0, MC2-0 and MC4-0 connected to the word line WL0 (130) and connected to the bit line are all set to store binary data. Therefore, binary data is written.

When the writing is completed, the odd bit lines BL1, BL3, and BL5 (140) are selected this time, and page writing is performed. In this case, the memory cells MC1-0, MC3-0, MC5-0 connected to the word line WL0 (130) and connected to the bit line are all memory cells MC for storing quaternary data. Therefore, quaternary data is written. First, lower page writing is performed, and then upper purge writing is performed.

In the writing, the influence of capacitive coupling due to writing to the memory cell MC connected to the odd-side bit line (140) reaches the memory cell MC connected to the adjacent even-side bit line (140). However, since binary data is already written in the adjacent memory cells MC0-0, MC2-0 and MC4-0, a margin for fluctuation can be absorbed.

Subsequently, writing is performed on the memory cell MC connected to the word line WL1. After selecting the word line WL1, the even bit lines BL0, BL2, and BL4 (140) are selected to perform writing. In this case, since the memory cells MC0-1, MC2-1, MC4-1 connected to the word line WL1 and connected to the bit line are memory cells MC for storing quaternary data, 4 Value data is written.

Even in the write operation, the memory cells MC0-0, MC2-0, and MC4-0 that are adjacent along the bit line 140 are affected by capacitive coupling, but the memory cells MC0-0, MC2-0, and MC4-0 Since binary data has already been written, fluctuations can be absorbed.

Further, the odd bit lines BL1, BL3, BL5 (140) are selected and written. At this time, since the memory cells MC1-1, MC3-1 and MC5-1 connected to the word line WL1 (130) and connected to the bit line are memory cells storing binary data, 2 Value data is written.

Also in the writing, the memory cells MC1-0, MC3-0 and MC5-0 connected to the word line WL0 (130) adjacent to the selected odd bit lines BL1, BL3 and BL5 (140) are Although it varies due to the influence of capacitive coupling, the memory cells MC1-0, MC3-0 and MC5-0 have already been written with quaternary data, and the memory cells MC1-1, MC3-1 and MC5 Since writing to -1 is binary data, there is little fluctuation and the influence of capacitive coupling is small.

As described above, with respect to the quaternary cell, the memory cell MC adjacent in the word line direction and the bit line direction with large capacitive coupling is set as a binary cell (that is, binary data is stored in the memory cell MC). By assigning, the influence of fluctuation due to capacitive coupling can be suppressed for the quaternary cell. On the other hand, since the binary cell has a margin with respect to the threshold distribution, the influence from the quaternary cell to the binary cell can be absorbed. Further, when writing to a binary cell, the read voltage of the non-selected word line can be set lower than that for a quaternary cell, so that Read Disturb (stress fluctuation due to read voltage application) can be suppressed. In one embodiment of the present invention, it is possible to suppress the spread of threshold distribution due to capacitive coupling of adjacent memory cells with respect to memory cells storing information data of two or more values, and to reduce the influence of interference of adjacent memory cells. .

In the first embodiment of the present invention, the data stored in the memory cell MC is changed to the checkered flag mixed mode (binary and quaternary mixed mode) of binary data and quaternary data by switching the operation mode. Therefore, since the number of times of writing is small at the time of writing to the binary cell, the stress at the time of writing is reduced for the quaternary cell. Further, since half of the memory cells MC are binary cells, the writing speed of the entire memory can be increased.

Further, when the writing speed is required by the operation mode switching, the entire memory can be used as a high-speed writable memory in the binary cell mode, while a larger capacity is required than the writing speed. In some cases, the entire memory can be used as a quaternary cell mode by switching the operation mode and used as a memory capable of storing a large capacity. Furthermore, when both the writing speed and the large capacity are required, it is possible to meet the request by using the binary & quaternary mixed mode by switching the operation mode. Since the same memory can respond to various user requests, the production line can be made more efficient, so that the production cost can be reduced and the memory chip cost can be reduced.

In the first embodiment of the present invention, as described above, the binary & quaternary mode is an operation mode that reduces the stress of writing and reading while improving the writing performance. Therefore, in the case of a quaternary cell, the reliability is high. On the other hand, when reliability becomes severe, it is very effective in the sense that it can be realized with the same chip for a high-end market where reliability and performance are important.

The nonvolatile semiconductor memory device according to the second embodiment of the present invention is characterized in that data stored in the memory cell MC is allocated in a checkered flag form of binary data and 8-level data.

In order to increase the storage capacity due to the high integration of memory chips, it is necessary to make the memory capacity finer than before, but on the other hand, a large number of data (information data of two or more values) is stored in one memory cell. It is possible to increase the storage capacity by storing. In this case, many different threshold values are required for writing and reading, and the threshold distribution needs to be narrowed and the step-up width also needs to be narrowed. However, if the threshold distribution is narrow, the influence of capacitive coupling with adjacent memory cells becomes even greater, and the number of times that the write voltage is applied increases when storing information data of two or more values. Decreases.

Accordingly, when the data stored in the memory cell MC is the same amount or more information data (for example, 8-level data) for the entire memory chip, the threshold distribution is narrow, so that the word line direction and the bit line direction are the same. The influence of capacitive coupling with adjacent memory cells MC becomes very large. In the nonvolatile semiconductor memory device according to the second embodiment of the present invention, even when 8-level data is stored in the memory cell, capacitive coupling with the memory cell MC adjacent in the word line direction and the bit line direction is performed. Can be suppressed.

FIG. 11 is a schematic diagram of memory cell allocation in the nonvolatile semiconductor memory device according to the second embodiment of the present invention. In FIG. 11, when a specific memory cell MC is assigned so as to store information amount data (eight-value data in this case) having two or more values, it is adjacent to both sides on the same bit line with respect to the memory cell MC. The memory cell MC and the memory cell MC adjacent to both sides of the memory cell MC on the same word line have data (in this case, binary) having a smaller amount of information than the information data (binary data) of binary or higher. Assigned to remember.

Specifically, in FIG. 11, when the memory cell MC2-2 is assigned to use binary data, adjacent memory cells MC2-1 and MC2-3 and the same word line on the same bit line BL2 (140). All the adjacent memory cells MC1-2 and MC3-2 on WL2 (130) are assigned to store 8-level data. Similarly, when looking at the memory cell MC 3-2, the memory cell MC is assigned to store 8-level data, but adjacent memory cells MC 3-1, MC 3-3, MC 2-2 and MC 4-2 are stored. Are all assigned to store binary data.

As in the first embodiment of the present invention, the assignment is assigned in advance based on the address of the memory cell, stored in the ROM fuse as fuse data, read from the ROM area by the ROM read operation, and latched. Set in the circuit. Of course, as in the first embodiment of the present invention, it is possible to use a method in which a fuse circuit is provided in the power-on reset circuit. It is also possible to set the operation mode to be switched by an external input.

When controlling writing and reading of 8-level data, one negative threshold voltage for erasing is assigned, and seven positive threshold voltages for writing and reading are assigned. The positive threshold voltage is set between 0 V and 5 V while stepping up from 0 V with the same width, and the setting of the read potential used for the verify read is the same as in the first embodiment.

In addition, in order to narrow the width of the threshold distribution, two-step write verification is performed as in the first embodiment.

Writing is performed in order from the word line WL0 (130), the even bit line 140 connected to the word line WL0 (130) is selected and written, and then the odd bit line 140 is selected and written. . Such writing is also controlled by fuse data. This is the same as in the first embodiment of the present invention described above.

According to the present invention, the memory cells MC adjacent in the word line direction and the bit line direction are allocated so as to store different data by the allocation of the information amount to be stored in the memory cells MC and the control of the writing procedure. In the nonvolatile semiconductor memory device according to the second embodiment, since the adjacent memory cells MC are set to store different data at the time of writing, the memory cells MC adjacent to each other in the word line direction and the bit line direction are set. The influence of capacitive coupling can be suppressed. This point is the same as in the first embodiment.

That is, with respect to the memory cell MC storing binary or higher information amount data (in this case, 8-level data), the memory cell MC adjacent in the word line direction and the bit line direction is more than the binary or higher information amount data. Is also assigned to store data with a small amount of information. In addition, when data is written to the memory cell MC, after data is written to the memory cell MC storing data with a small amount of information connected to the same word line, the information amount data of two or more values connected to the same word line Is controlled so that data is written into the memory cell MC storing the. This write control is performed by fuse data stored in the ROM fuse. For example, when the Even bit line is written, the Odd bit line is in a write-inhibited state and serves as a shield line. As a result, coupled with the control of the data writing procedure, the influence of capacitive coupling with the memory cells MC adjacent in the word line direction and the bit line direction on the memory cells MC storing binary data amount data is reduced. It can be minimized. On the other hand, since the memory cell MC storing data with a small amount of information is written first, the influence of capacitive coupling can be absorbed. Therefore, the influence of capacitive coupling can be suppressed as a whole memory. In this embodiment, the writing to the memory cell MC is controlled so as to be written from the memory cell MC storing data with a small amount of information, but the present invention is not necessarily limited to this. The same effect can be obtained if the memory cells MC adjacent in the word line direction and the bit line direction are assigned so as to store data of different amounts of information and are written for each bit line.

Also, in the case where information amount data (in this case, 8-level data) of two or more values is stored in the entire memory, the number of times of application of the write voltage is drastically increased by reducing the threshold step-up width, and the write speed is increased. Become slow. In this regard, in the nonvolatile semiconductor memory device according to the third embodiment of the present invention, since about half of the entire memory cells store data having a smaller amount of information than the above-described information data of two or more values, writing is performed. Although the number of times of voltage application can be reduced and the storage capacity is reduced, a decrease in writing speed can be suppressed to a certain limit.

In addition, when writing data with a small amount of information (here, binary data), the read voltage of the unselected word line can be set lower than when writing data with a large amount of information (here, 8-level data). Therefore, Read Disturb can be suppressed. Therefore, it is possible to maintain high reliability as compared with the case where all the memory cells MC store information data having a binary value or more.

Furthermore, in the nonvolatile semiconductor memory device according to the second embodiment of the present invention, an information amount data storage memory having two or more values can be obtained by switching an operation mode according to fuse data for the same memory. A memory for storing data with a smaller amount of information than the amount of information data of a plurality of pieces, and a plurality of pieces of data having different information amounts, that is, information amount data with two or more values and data with a smaller amount of information than the information amount data with two or more values Can be used as a memory that can Therefore, if importance is attached to the storage capacity according to the purpose of use, an information amount data storage memory of two or more values is used. On the other hand, when a constant writing speed is required, a memory for storing data of different information amounts is provided. When emphasizing reliability, it can be used as a memory for storing data having a smaller amount of information than the information amount data of two or more values. Since there is no need to use different types of memory separately, it can be manufactured in large quantities, so that it is possible to reduce manufacturing costs and, in turn, to reduce selling prices, and to enable stable product supply through mass production, thus maintaining high quality. It becomes.

When storing binary data or more information amount data in the memory cell MC, the threshold voltage distribution is narrowed by reducing the step-up width of the write voltage, and a plurality of threshold voltage distributions are set between the non-selected read voltage and VSS. Into. Therefore, the influence of capacitive coupling with the adjacent memory cell MC is increased by increasing the threshold voltage by inserting a plurality of threshold distributions. That is, the greater the amount of information stored in the memory cell MC, the higher the threshold voltage, and the greater the influence of capacitive coupling.

In the nonvolatile semiconductor memory device according to one embodiment of the present invention, the potential stored in the memory cells MC adjacent in the word line direction and the bit line direction is assigned and controlled so as to store data of different amounts of information. With the advancement of control technology, it is possible to provide a highly reliable binary information amount data storage memory.

The nonvolatile semiconductor memory device according to the third embodiment of the present invention is characterized in that the data stored in the memory cell MC is assigned in the form of a checkered flag of 4-level data and 8-level data.

FIG. 12 is a schematic diagram of memory cell allocation in the nonvolatile semiconductor memory device according to the third embodiment of the present invention. In FIG. 12, when a specific memory cell MC is assigned so as to store information amount data (in this case, 8-level data) of two or more values, the memory cell MC is adjacent to both sides on the same bit line. The memory cell MC and the memory cell MC adjacent to both sides on the same word line with respect to the memory cell MC have data (in this case, four values) having a smaller amount of information than the information data (binary data) of binary or higher value. Assigned to remember.

The assignment is assigned in advance based on the address of the memory cell, stored in the ROM fuse as fuse data, read out from the ROM area by the ROM read operation, and set in the latch circuit. Of course, as in the first embodiment of the present invention, it is possible to use a method in which a fuse circuit is provided in the power-on reset circuit. It is also possible to set the operation mode to be switched by an external input. This is the same as in the first to second embodiments of the present invention described above.

Specifically, in FIG. 12, when the memory cell MC2-2 is assigned to use quaternary data, adjacent memory cells MC2-1 and MC2-3 and the same word line on the same bit line BL2 (140). All the adjacent memory cells MC1-2 and MC3-2 on WL2 (130) are assigned to store 8-level data. Similarly, when looking at the memory cell MC 3-2, the memory cell MC is assigned to store 8-level data, but adjacent memory cells MC 3-1, MC 3-3, MC 2-2 and MC 4-2 are stored. Are all assigned to store quaternary data.

Writing is performed in order from the word line WL0 (130), the even bit line 140 connected to the word line WL0 (130) is selected and written, and then the odd bit line 140 is selected and written. . Such writing is also controlled by fuse data. This is the same as in the first embodiment of the present invention described above.

By performing the allocation and writing as described above, the nonvolatile semiconductor memory device according to the third embodiment of the present invention has an effect of suppressing the capacitive coupling with the adjacent memory cell MC. Further, as in the first embodiment, it is possible to suppress a decrease in the writing speed to a certain limit, and to obtain an effect of suppressing Read Disturb and maintaining high reliability. In addition, by switching the operation mode, the amount of data stored in one memory can be switched according to the purpose of use, and the manufacturing cost can be reduced and the selling price can be reduced, enabling stable product supply. Therefore, the effect of maintaining high quality can also be obtained as in the first embodiment.

The nonvolatile semiconductor memory device according to the fourth embodiment of the present invention is characterized in that three types of data, that is, binary data, quaternary data, and 8-level data, are allocated as data stored in the memory cell MC.

When storing information amount data of binary or more in the memory cell MC, the step-up width of the threshold distribution is narrowed by the two-step write verification, and advanced technology is required by controlling the potential in the memory. In particular, the influence of capacitive coupling with adjacent memory cells MC increases as the threshold distribution step-up width becomes narrower.

In the nonvolatile semiconductor memory device according to one embodiment of the present invention, the potential control technique is used to allocate and control the data stored in the memory cells MC adjacent in the word line direction and the bit line direction so as to store different data. As the level of sophistication increases, it is possible to provide a highly reliable binary data storage memory.

When the information technology of two or more values advances and the reliability of the potential control technology increases, the data stored in the memory cell MC is not limited to two types of data. If three types of data can be stored, higher capacity and higher integration can be realized while maintaining a certain level of reliability. The nonvolatile semiconductor memory device according to the fourth embodiment of the present invention can store three types of binary or more information amount data in the memory cell MC while suppressing the influence of capacitive coupling between adjacent memory cells MC. It is possible to do.

FIG. 13 is a schematic diagram of memory cell allocation in the nonvolatile semiconductor memory device according to the fourth embodiment of the present invention. When three types of data having different information amounts are α, β, and γ (α <β <γ), half the memory cells MC of the memory are allocated so as to store the data α having the smallest information amount, and the rest Data β and data γ are assigned to the memory cells MC. The allocation method is based on the address of the memory cell MC determined by the bit line 140 and the word line 130, and the memory cell MC connected to the even bit line 140, the even word line 130, the odd bit line 140, and the odd word line 130. And assigned as a memory cell MC for storing data α. Subsequently, the memory cell MC connected to the even bit line 140 and the odd word line 130 is a memory cell MC for storing data β, and the memory cell MC connected to the odd bit line 140 and the even word line 130 is stored for data γ. Memory cell MC to be used. The allocation of the memory cells storing the data β and the data γ may be the opposite allocation as described above.

Specifically, in FIG. 13, the memory cell MC located on the Even bit line 140 and the Even word line 130 is assigned as a memory cell MC for storing binary data, so that the memory cell MC2-2 uses binary data. Assigned to. Next, adjacent memory cells MC2-1 and MC2-3 on the same Even bit line BL2 (140) are assigned so as to store intermediate data quaternary data. The memory cells MC1-2 and MC3-2 connected to the adjacent odd bit lines BL1 and BL3 (140) on the same Even word line WL2 (130) are all assigned to store 8-level data.

As in the first to third embodiments of the present invention, the assignment is pre-assigned based on the address of the memory cell, stored in the ROM fuse as fuse data, and the ROM area by the ROM read operation. Is read from the signal and set in the latch circuit. Of course, as in the first embodiment of the present invention, it is possible to use a method in which a fuse circuit is provided in the power-on reset circuit. It is also possible to set the operation mode to be switched by an external input.

Adjacent memory cell interference caused by capacitive coupling with adjacent memory cells when writing is performed in the nonvolatile semiconductor memory device to which such allocation is performed will be described. Specifically, description will be made by taking the memory cell MC2-2 of FIG. 13 as an example. Memory cell MC2- is assigned to store binary data. Writing is performed sequentially from the memory cell MC connected to the word line WL0 (130), and Vpp is applied to the word line WL2 (130) in order to write to the memory cell MC2-2. In this state, 0V or VBB is applied to the even bit lines BL0, BL2, and BL4. As a result, in the memory cell MC connected to the word line WL2 and connected to the bit lines BL0, BL2 and BL4 to which VBB is applied, electrons are injected into the floating gate, and also in the memory cell MC2-2. Writing is performed.

At this time, since all the memory cells MC are memory cells MC connected to the even word line (130) and the even bit line (140), binary data is written. In this case, capacitive coupling is caused by the adjacent memory cells MC1-2 and MC3-2 on the same word line WL2 and MC2-1 and MC2-3 adjacent on the same bit line BL2. However, since binary data is written into the memory cell MC2-2, the width of the threshold distribution is wide and the influence of adjacent memory cell interference due to the influence is small. In addition, the memory cell MC2-1 connected to the word line WL1 has already been written with data (in this case, quaternary data writing), so that the influence can be absorbed.

Subsequently, in this state, 0 V or VBB is applied to the odd bit lines BL0, BL2, and BL4 (140). As a result, data is written to the memory cells MC1-2 and MC3-2 adjacent to the memory cell MC2-2 on the same word line WL2. Since the adjacent memory cells MC are memory cells MC for storing 8-level data, a potential is applied while finely stepping up to write 8-level data. Therefore, the memory cell MC2-2 is affected by adjacent memory cell interference. However, since binary data has already been written, the width of the threshold distribution is wide and the influence can be absorbed. In addition, the memory cell MC in which quaternary data has already been written, for example, the memory cell MC2-1, is not on the same word line 130 and on the same bit line 140 as the memory cell MC in which quaternary data has been written. The impact is extremely small.

Thereafter, the word line WL3 is selected and Vpp is applied, and even bit lines BL0, BL2 and BL4 are selected and VBB is applied in the same procedure. Then, quaternary data is written into the memory cell MC2-3 adjacent to the memory cell MC2-2 on the same bit line BL2, and adjacent memory cell interference caused by capacitive coupling also reaches the memory cell MC2-2. However, since the binary data has already been written in the memory cell MC2-2, the width of the threshold distribution can be widely absorbed. In addition, the memory cell MC in which 8-level data has already been written, for example, the memory cell MC1-2, is different from the memory cell MC2-3 in that the bit line 140 and the word line 130 are different from each other. Does not occur.

As described above, the nonvolatile semiconductor memory device according to the fourth embodiment of the present invention is allocated so that adjacent memory cells MC store different data, and stores data with a small amount of information at the time of writing. Since data is written from the memory cell MC, capacitive coupling with the adjacent memory cell MC can be suppressed. In this embodiment, the writing to the memory cell MC is controlled so as to be written from the memory cell MC storing data with a small amount of information, but the present invention is not necessarily limited to this. The same effect can be obtained if the memory cells MC adjacent in the word line direction and the bit line direction are assigned so as to store data of different amounts of information and are written for each bit line.

In addition, since half of the memory cells MC in the entire memory are memory cells that store binary data, the write potential of the memory cell MC in the entire memory is smaller than that in the case where the memory cells MC in the entire memory store binary data or more. As a result of the number of times of application being reduced as a whole memory, it is possible to secure the effect of suppressing a decrease in the writing speed to a certain limit and the effect of suppressing the Read Disturb and maintaining high reliability.

Furthermore, one memory can be used by switching the amount of data stored in accordance with the purpose of use, and as a result, the manufacturing cost can be reduced and the selling price can be lowered, thereby enabling stable product supply. The effect of maintaining high quality is the same as in the first to third embodiments described above.

As described above, in the nonvolatile semiconductor memory device according to one embodiment of the present invention, the data stored in the memory cell MC is changed to a checkered flag-like mixed mode of binary data and information amount data of binary or higher by switching the operation mode ( (Binary and binary information amount data mixed mode).

Here, as the information amount data of two or more values, conventionally, a numerical value of a multiplier of 2 such as binary (1 bit), 4-value (2 bits), and 8-value (3 bits) has been considered. However, in particular, when using a steep and narrow threshold distribution equal to or greater than 8-level (3-bit) data, the influence of adjacent memory cell interference due to capacitive coupling is large, and thus control is not easy. Therefore, by adopting the virtual page cell architecture, two memory cells on the same word line are paired (therefore, the two memory cells are connected to adjacent bit lines on the same word line). ), And by assigning three different page addresses (virtual page addresses) to the memory cells of the pair, the role of the three virtual memory cells is fulfilled, so that the memory of the two pairs It has been proposed to store binary data × binary data × binary data = eight-value data for three binary memory cells.

This proposal is aimed at increasing the capacity of the entire memory. However, even when this method is used to write information data having a binary value or more, there is an influence of adjacent memory cell interference resulting from capacitive coupling with adjacent memory cells MC in the bit line direction and the word line direction.

In the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention, the allocation control is performed so that the data stored in the memory cells MC adjacent in the word line direction and the bit line direction are stored with different amounts of information. Therefore, it is possible to increase the storage capacity of the entire memory while suppressing adjacent memory cell interference caused by capacitive coupling.

This will be specifically described with reference to FIG. FIG. 14 is a schematic diagram of memory cell allocation in the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention. In FIG. 14, when a specific memory cell MC is allocated so as to store information amount data of two or more values (here, quinary data), the memory cell MC is adjacent to both sides on the same bit line. The memory cell MC and the memory cell MC adjacent to both sides of the memory cell MC on the same word line receive data (binary data) having a smaller amount of information than the information data (binary data) of binary or higher. Assigned to remember.

As in the first to fourth embodiments of the present invention, the assignment is pre-assigned based on the address of the memory cell, stored in the ROM fuse as fuse data, and the ROM area by the ROM read operation. Is read from the signal and set in the latch circuit.

Specifically, in FIG. 14, the memory cell MC located on the even word line 130 and the even bit line 140 and the memory cell MC located on the odd word line 130 and the odd bit line 140 store binary data. Assigned as MC. On the other hand, the remaining memory cells MC, that is, the memory cell MC located on the even word line 130 and the odd bit line 140 and the memory cell MC located on the odd word line 130 and the even bit line 140 are memory cells that store quinary data. Assigned as MC.

The assigned memory cell MC is a memory cell MC (hereinafter referred to as a virtual memory cell) that is adjacent on the same word line 130 and stores data of different values as a pair. To be treated. In FIG. 14, memory cells MC2-2 and MC3-2 are handled as a pair.

A virtual page address is assigned to this pair of memory cells MC separately from the actual address. For example, a virtual page address m is assigned to the pair of memory cells MC2-2 and MC3-2. The allocation of the virtual page address is the same as the allocation of data stored in the memory cell MC. Like the first to third embodiments described above, the virtual page address is allocated in the memory cell array 100 shown in FIG. It is stored as fuse data in the ROM area 120.

By assigning the virtual page address, multi-bit data can be stored in the virtual memory cell. That is, the memory cell MC2-2 is assigned to store binary data, and the MC3-2 is assigned to store quinary data. However, by treating the memory cell MC2-2 as a virtual memory cell, the memory cell MC2-2 is assigned. 2 can be handled as the first data page of the virtual memory cell, and MC3-2 can be handled as the second data page of the virtual memory cell. In addition, the first data page stores first data of input data to be processed by a sense amplifier described later, and the second data page stores second data of input data. Therefore, data of 2 values × 5 values = 10 values> 8 values (3 bits) can be stored. As a result, while suppressing the adjacent memory cell interference, it is possible to secure the same capacity as when the entire memory stores the quaternary data.

Virtual memory cells can also be set between memory cells that store different values adjacent in the direction of the bit line 140. However, as described in the first embodiment, in the lower page write and the upper page write, the bit line 140 is, for example, when the even bit lines BL0, BL2, and BL4 are written, the odd bit lines BL1, BL3, BL5 is all set to VDD and not written (ALL1), and can serve as a shield line for preventing read noise. Therefore, a pair is set between memory cells adjacent in the direction of the word line 130.

Writing to the virtual memory cell is performed by controlling the two even and odd bit lines 140 connected to the virtual memory cell. In the virtual memory cells of the memory cells MC2-2 and MC3-2 of FIG. 10, the even bit line BL2 (140) and the odd bit line BL3 (140) are controlled and written to MC2-2 by the first data write. Write to MC3-2 with 2 data write.

Here, in the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention, the memory cell MC is assigned so as to store binary data and quinary data. do not use. This is because the semiconductor memory device stores data by the binary system of “0” and “1”. However, in consideration of threshold distribution control, when writing 8-level data to the memory cell MC, one negative threshold potential and seven positive values generally set with a margin between 0V and 5V are taken. A threshold potential is required. In this case, the threshold value is controlled to be steep and narrow, but for example, due to the influence of adjacent memory cell interference or the like, the width of the threshold distribution increases as shown in FIG. The narrower the width, the more difficult the control. Therefore, it is assumed that the 8-value data cannot be handled stably.

In such a case, the two memory cells MC are handled in pairs, divided into a first data page and a second data page, and written into two adjacent memory cells MC handled as one virtual memory cell, It is possible to handle quinary data. In this case, in order to write and erase quinary data, one negative threshold value and four positive threshold values are required. However, there are four threshold values with a predetermined margin between 0V to 5V. Setting the threshold is easier than setting seven thresholds between the same potentials. On the other hand, there is no problem for one of the pair of memory cells MC because binary data is used for writing and erasing.

As described above, the input / output data is divided into the first data and the second data, and the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention is shown in FIG. The sense amplifier 40 has a function of latching and calculating data.

The sense amplifier 40 determines and amplifies the data “1” and “0” stored in the memory cell MC during the read operation, outputs the amplified data via the input / output buffer 50, and inputs / outputs during the write operation. Write data is input to the sense amplifier 40 through the buffer 50 and stored. Therefore, the sense amplifier 40 has a function of calculating input / output data by associating a regular address with a virtual page cell address.

An example of calculation of input / output data corresponding to an address will be described by taking the memory cells MC2-2 and MC3-2 of FIG. 14 as an example. When storing 3 bits of data in the virtual memory cell, there are 8 types of data to be stored: “000” “001” “010” “011” “100” “101” “110” “111”. The input from the outside is input by specifying the virtual page address m.

In the sense amplifier 40 shown in FIG. 1, for example, the input data is assigned a numerical value of hundreds as the first data of the virtual memory cell, and the remaining two digits are the second data of the virtual memory cell. Assigned as. The allocated data includes binary data corresponding to the address of the normal memory cell MC2-2. For example, “0” in the hundreds is “0” in the binary, “1” in the hundreds. "Is assigned to the binary value" 1 ". On the other hand, the second data is calculated as quinary data for the address of the normal memory cell MC3-2. However, since 8-value data is converted into 2-value × 5-value = 10-value data, 8-value data is not assigned to two of the 10-value data. Thus, for example, the remaining last two digits “00” are assigned to the five values “0”, similarly “01” is assigned “1”, “10” is assigned “2”, and “11” is assigned “3”. It is done. According to this assignment, “010” of the 8-level data becomes “02” of the virtual memory cell.

The data “02” is written by writing “0” to the memory cell MC2-2 by the first data write to the virtual memory cell and “2” to the memory cell 3-2 by the second data write. .

Similarly, in the read operation, “0” is read from the memory cell MC2-2 as the first data of the virtual memory cell, and “2” is read from the memory cell MC3-2 as the second data of the virtual memory cell and latched by the sense amplifier 40. Then, the reverse operation is performed by the sense amplifier 40, and the data is output to the outside as "010" data of the virtual memory cell.

As the writing, the first data writing and the second data writing are sequentially performed. However, since the memory cell MC2-2 to which the first data is written is assigned so as to store the binary data, the second data is written. MC3-2 is affected by adjacent memory cell interference due to capacitive coupling, but because of binary writing, and the bit line BL3 (140) serves as a shield line, the influence is small. . Further, the memory cell MC3-2 to which the second data is written is affected by the adjacent memory cell MC2-2 because the quinary data is written, but the memory cell MC2-2 already has a wide threshold distribution width. Since binary data is written and the bit line BL2 (140) serves as a shield line, the influence can be absorbed.

As described above, in the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention, adjacent memory cells are allocated so as to store different amounts of information, and memory cells MC that store small amounts of information are stored. Therefore, it is possible to suppress the adjacent memory cell interference in combination with the role of the bit line serving as a shield line. Further, by arranging the memory cells MC in such a configuration, it is possible to store multi-bit data by storing data by regarding two adjacent memory cells on the same word line as one virtual memory cell. Thus, the capacity of the entire memory can be increased. In this embodiment, the writing to the memory cell MC is controlled so as to be written from the memory cell MC storing data with a small amount of information, but the present invention is not necessarily limited to this. The same effect can be obtained if the memory cells MC adjacent in the word line direction and the bit line direction are assigned so as to store data of different amounts of information and are written for each bit line.

In addition, since the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention allocates the data to be stored to the memory cells by fuse data, the entire memory has the same amount of data according to the purpose. It can be assigned to store, or it can be assigned to store data of different amounts of information. Therefore, one memory can be used by switching the amount of data to be stored in accordance with the purpose of use, and as a result, the manufacturing cost can be reduced, and the selling price can be lowered, so that stable product supply can be achieved. The effect of maintaining high quality is the same as in the first to fourth embodiments described above.

Note that, according to the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention, it is possible to suppress adjacent memory cell interference due to capacitive coupling. It is also possible to store 7-value data.

In this case, naturally, control of the threshold distribution becomes difficult for quinary data, but the range of 0 V to 5 V, which is generally used as a range for setting a positive threshold potential, should be expanded and dealt with. For example, when handling is performed in the range of 0V to 6V, it is not difficult to increase one or two positive threshold values from 5 values to 6 values to 7 values. FIGS. 15 and 16 show the memory cell of the nonvolatile semiconductor memory device according to the fifth embodiment of the present invention when the data stored in the memory cell is binary, binary, binary, and binary, respectively. It is a schematic diagram of allocation. Corresponding to the improvement of the threshold distribution control technique, according to an embodiment of the present invention, it is possible to assign to such memory cells.

In one embodiment of the present invention, as described in the above fifth embodiment, data of different information amounts are allocated to adjacent memory cells MC to store two different data on the same word line. By storing memory cells MC storing information amount data as a pair as one virtual memory cell, it is possible to suppress adjacent memory cell interference and increase the capacity of the entire memory.

The nonvolatile semiconductor memory device according to the sixth embodiment of the present invention is characterized in that adjacent memory cells MC are assigned to a memory cell MC that stores ternary data and a memory cell MC that stores ternary data. To do.

FIG. 17 is a schematic diagram of memory cell allocation in the nonvolatile semiconductor memory device according to the sixth embodiment of the present invention. In FIG. 17, the memory cell MC located on the even word line 130 and the even bit line 140 and the memory cell MC located on the odd word line 130 and the odd bit line 140 are assigned as memory cells MC storing ternary data. On the other hand, the remaining memory cells MC, that is, the memory cells MC located on the even word line 130 and the odd bit line 140, and the memory cells MC located on the odd word line 130 and the even bit line 140 are memory cells storing six-value data. Assigned as MC. The allocation method is the same as that in the first to fifth embodiments described above in that it is performed by fuse data stored in the ROM fuse. Of course, as in the first embodiment of the present invention, it is possible to use a method in which a fuse circuit is provided in the power-on reset circuit. It is also possible to set the operation mode to be switched by an external input.

The allocated memory cells MC are treated as virtual memory cells as a pair of memory cells MC storing data of different values adjacent on the same word line 130. A virtual page address is assigned to the virtual memory cell. This assignment is the same as in the fifth embodiment of the present invention described above.

Furthermore, the nonvolatile semiconductor memory device according to the sixth embodiment of the present invention has a function of latching and calculating data in the sense amplifier. This is the same as in the fifth embodiment described above.

In the fifth embodiment described above, the first data write and the second data write to the virtual memory cell are performed while the ternary data and the hex data are latched by the sense amplifier and calculated. It is the same.

Characteristically, three-value data and six-value data are used as data to be stored. The control of the threshold distribution is accompanied by a fine technique, and even if the threshold distribution cannot be stably controlled because of 8-level data, the present invention is the same when one negative threshold potential and five positive threshold potentials can be controlled. It is possible to allocate so as to store 6-value data in one of the memory cells storing data of two different information amounts adjacent on the word line. Further, when the threshold distribution of quaternary data can be controlled stably, it is not difficult to control the ternary data, that is, the threshold for writing and erasing with one negative threshold and two positive thresholds.

According to this allocation of data handling, data of 3 values × 6 values = 18 values> 16 values = 2 ⁴ (4 bits) can be stored in a pair of memory cells MC, and binary × 8 values are allocated. Even when the threshold distribution for 8-level data cannot be stably controlled, if the calculation is performed for the entire memory, it is possible to secure a capacity equivalent to that for all memory cells MC storing 8-level data. Therefore, the capacity can be increased more realistically.

In the nonvolatile semiconductor memory device according to the sixth embodiment of the present invention, adjacent memory cells MC are allocated so as to store data of different information amounts, and memory for storing data with a small amount of information By writing from the cell MC, the bit line connected to the memory cell MC not to be written serves as a shield line, so that it is possible to suppress adjacent memory cell interference caused by capacitive coupling. For example, it is possible to store 6-value data or 7-value data. In this embodiment, the writing to the memory cell MC is controlled so as to be written from the memory cell MC storing data with a small amount of information, but the present invention is not necessarily limited to this. The same effect can be obtained if the memory cells MC adjacent in the word line direction and the bit line direction are assigned so as to store data of different amounts of information and are written for each bit line.

Therefore, when the data stored in two adjacent memory cells MC forming the virtual memory cell are quinary data and quinary data, the memory cell MC of the pair has five values × 7 values = 35 values> Data of 32 values = 2 ⁵ (5 bits) can be stored.

FIG. 18 is a schematic diagram of memory cell allocation in the case of storing quinary data and quinary data in the nonvolatile semiconductor memory device according to the sixth embodiment of the present invention. When 4-level data and 8-level data are stored and it is difficult to control the threshold distribution of 8-level data, and the threshold distribution of 8-level data can be controlled, but the spread of the threshold width due to adjacent memory cell interference is suppressed. However, according to the sixth embodiment of the present invention, since adjacent memory cell interference can be suppressed, it is possible to cope with this by arranging the memory cells. According to the sixth embodiment of the present invention, it is possible to allocate such memory cells while suppressing interference between adjacent memory cells due to capacitive coupling, and the entire memory has 5 bits × number of memory cells × 1 / 2 capacities can be stored.

In one embodiment of the present invention, as described above, the memory cells MC adjacent to each other in the bit line direction and the word line direction are allocated so as to store data of different information amounts, but further, a writing speed is required. In some cases, data of a small amount of information among different amounts of data is stored in two consecutive memory cells of three memory cells (trio memory cells) adjacent on the word line. By assigning, the writing speed can be improved.

FIG. 19 is a schematic diagram of memory cell allocation in the nonvolatile semiconductor memory device according to the seventh embodiment of the present invention. FIG. 19 shows the case of binary data and quinary data as data stored in the memory cell MC.

Allocation of data stored in the memory cell MC is performed by allocating one virtual page cell address with the two consecutive memory cells MC as the virtual memory cell A among the three adjacent memory cells MC on the same word line. One virtual page cell address is assigned to the remaining memory cell MC among the memory cells MC as a virtual memory cell B. In FIG. 19, for example, the memory cells MC0-2, MC1-2, and MC2-2 constitute a trio memory cell, and the memory cells MC0-2 and MC1-2 constitute a virtual memory cell A. For example, a virtual page Assign cell address a. On the other hand, the remaining memory cell MC2-2 of the trio memory cells constitutes a virtual memory cell B and is assigned a virtual page address b.

A trio memory cell is configured in a similar manner by three adjacent memory cells located on the same bit line as the trio memory cell and connected to an adjacent word line. At this time, the virtual page cell address b is A memory cell MC adjacent to the allocated memory cell MC on the same bit line is always arranged so that a virtual memory cell A composed of two memory cells MC is located, and a virtual page address a is allocated. To be able to. In FIG. 19, memory cells MC0-1, MC1-1 and MC2-1 and MC0-3, MC1-3 and MC2− located on a word line adjacent to the memory cells MC0-2, MC1-2 and MC2-2. 3, the memory cells MC0-1 and MC0-3 are treated as virtual memory cells B by themselves and assigned a virtual page cell address b. On the other hand, MC1-1 and MC2-1 constitute a virtual memory cell A, MC1-3 and MC2-3 constitute a virtual memory cell A, and a virtual page cell address a is assigned to each. Then, the memory cell MC to which the virtual page cell address a is assigned is assigned so as to store binary data, while the memory cell MC to which the virtual page cell address b is assigned is stored with quinary data. Assign as you want.

As in the first to sixth embodiments of the present invention, the assignment is pre-assigned based on the address of the memory cell, and is stored in the ROM fuse as fuse data. Is read from the signal and set in the latch circuit. Of course, as in the first embodiment of the present invention, it is possible to use a method in which a fuse circuit is provided in the power-on reset circuit. It is also possible to set the operation mode to be switched by an external input.

Writing to the virtual memory cells A and B is controlled by a virtual page cell address. The bit line connected to the virtual memory cell A is controlled as if it were an Even bit line, while the bit line connected to the virtual memory cell B is controlled as if it was an Odd bit line. The writing of the virtual page address a to the virtual memory cell A is set so that the first data writing and the second data writing are performed. The control method of the first data write and the second data write is the same as that of the fifth embodiment and the sixth embodiment of the present invention described above.

In FIG. 19, writing to the memory cells MC0-2 and MC1-2 is performed based on the virtual page cell address a, and after the first data writing to the memory cell MC0-2 is performed, the memory cell MC1-2 is written. Writing is performed by second data writing. In FIG. 19, binary data is written into the two memory cells MC.

On the other hand, writing is performed on the memory cell MC2-2 based on the virtual page cell address, but since the memory cell MC is quinary data writing, a voltage stepped up in increments of 0.2V, for example, is applied. The

Therefore, at the time of writing, adjacent memory cell interference caused by capacitive coupling has already occurred in the memory cells MC1-2 and MC3-2 adjacent to the memory cell MC2-2 on the same word line WL2 (130). Since the value is written, the influence can be absorbed. Further, binary writing has already been performed on the adjacent memory cell MC2-1 on the same bit line BL2 (140), and the influence can be absorbed. On the other hand, on the same bit line BL2 (140), MC2-3 positioned on the opposite side of MC2-1 across the memory cell MC2-2, the next time the word line WL3 (130) is selected and binary data Therefore, there is no effect even if adjacent memory cell interference occurs.

On the other hand, for the memory cell MC2-2 in which the quinary data is written, when the adjacent memory cell MC2-3 is subsequently written on the bit line BL2, adjacent memory cell interference occurs, but the memory cell MC2-2 Since 3 is binary data writing, it has little influence.

Such write control is latched and controlled by a sense amplifier as in the fifth and sixth embodiments of the present invention. Accordingly, the nonvolatile semiconductor memory device according to the seventh embodiment of the present invention is characterized in that the sense amplifier has a function of calculating input / output data by associating a normal address and a virtual page cell address.

As described above, in the nonvolatile semiconductor memory device according to the seventh embodiment of the present invention, binary data is stored in 2/3 of the memory cells MC of the entire memory while suppressing the influence of adjacent memory cell interference. Since the data is stored as a memory cell, a decrease in writing speed can be suppressed.

In addition, since the nonvolatile semiconductor memory device according to the seventh embodiment of the present invention allocates data to be stored to the memory cell by fuse data, the entire memory has data of the same information amount according to the purpose. It can be assigned to store, or it can be assigned to store data of different amounts of information. Therefore, one memory can be used by switching the amount of data to be stored in accordance with the purpose of use, and as a result, the manufacturing cost can be reduced, and the selling price can be lowered, so that stable product supply can be achieved. The effect of maintaining high quality is the same as in the first to sixth embodiments described above.

According to the seventh embodiment of the present invention, although not shown in the figure, the data to be stored is binary data, 6-value data, 2-value data, 8-value data, etc., and the capacity of the entire memory is secured. However, it is also possible to suppress a decrease in writing speed.

If the seventh embodiment of the present invention described above is developed, it is possible to further increase the capacity of the entire memory while suppressing a decrease in write speed. In the nonvolatile semiconductor memory device according to the eighth embodiment of the present invention, the capacity of the entire memory can be significantly increased while suppressing a decrease in writing speed.

FIG. 20 is a schematic diagram of memory cell allocation in the nonvolatile semiconductor memory device according to the eighth embodiment of the present invention when the data stored in the memory cell is binary data and quinary data. In FIG. 20, the arrangement of the memory cells MC is the same as that in FIG.

However, the virtual memory cell setting method is different from the seventh embodiment of the present invention shown in FIG. That is, in the seventh embodiment of the present invention, a trio memory cell is formed by three adjacent memory cells MC on the same word line, and consecutive memory cells MC for storing binary data are made one virtual memory cell. On the other hand, the remaining memory cell MC for storing the five-value data is set as another virtual memory cell. A virtual page cell address is set for each. In the eighth embodiment of the present invention, the trio memory cell is formed in the same manner, but the setting of the virtual memory cell is different.

In the eighth embodiment of the present invention, the memory cell MC that stores continuous binary data is not used as one virtual memory cell, but one memory cell that stores binary data is used as one virtual memory. On the other hand, another virtual memory cell is configured with the memory cell MC that handles the five-value data adjacent on the same word line as the memory cell MC that stores the remaining binary data. The virtual page cell address is assigned to each virtual memory cell as in the seventh embodiment of the present invention. In the eighth embodiment of the present invention, the word line 130 is divided into an even word line 130 and an odd word line 130. The memory cell MC stores binary data and the memory cell MC stores quinary data. It is characterized in that the arrangement of the binary data memory cell and the quinary data memory cell in the configured virtual memory cell is reversed. For example, in the even word line 13, when the memory cell MC that stores the binary data in the virtual memory cell is arranged on the odd bit line 140 side, the binary data in the virtual memory cell is stored in the odd word line. The memory cell MC to be operated is arranged on the even bit line 140 side, and the memory cell MC for storing quinary data is arranged on the odd bit line 140 side.

In FIG. 20, for example, the memory cells MC0-2, MC1-2, and MC2-2 located on the even word line 130 constitute a trio memory cell, and the memory cell MC0-2 constitutes a virtual memory cell A. A virtual page cell address a is assigned. On the other hand, the remaining memory cells MC1-2 and MC2-2 of the trio memory cells constitute a virtual memory cell B and, for example, a virtual page address b is allocated. In the virtual memory cell B, the memory cell MC1-2 connected to the odd bit line BL1 (140) receives binary data, and the memory cell MC2-2 connected to the even bit line BL2 (140) receives quinary data. Assigned to remember. On the other hand, the memory cells MC0-3, MC1-3, MC2-3 located on the adjacent odd word line WL3 constitute a trio memory cell, and the memory cells MC0-3 and MC1-3 constitute a virtual memory cell B. In the virtual memory cell B, MC0-3 located on the Even bit line BL0 (140) is assigned to store quinary data, and MC1-3 located on the Odd bit line BL1 (140) is assigned to store binary data. .

As in the first to sixth embodiments of the present invention, the assignment is pre-assigned based on the address of the memory cell, and is stored in the ROM fuse as fuse data. Is read from the signal and set in the latch circuit. Of course, as in the first embodiment of the present invention, it is possible to use a method in which a fuse circuit is provided in the power-on reset circuit. It is also possible to set the operation mode to be switched by an external input.

The writing to the virtual memory cell is controlled by the virtual page cell address as in the seventh embodiment of the present invention. The bit line connected to the virtual memory cell A is controlled as if it were an Even bit line, while the bit line connected to the virtual memory cell B is controlled as if it was an Odd bit line. The writing of the virtual page address b to the virtual memory cell B is set so that the first data writing and the second data writing are performed. The control method of the first data writing and the second data writing is the same as that of the fifth to seventh embodiments of the present invention described above.

However, in the eighth embodiment of the present invention, the writing to the virtual memory cell B is further controlled by dividing the word line 130 into the even word line 130 and the odd word line 130. That is, when writing to the virtual memory cell B to which the virtual page cell address b connected to the even word lines WL0, WL2, WL4 (130) is assigned, the first data write is performed from the side of the odd bit lines BL1, BL3, BL5, for example. On the other hand, when writing to the virtual memory cell B to which the virtual page cell address b connected to the odd word lines WL1, WL3, WL5 (130) is assigned, for example, the first from the Even bit lines BL0, BL2, BL4 side. Control to write data. This is because in writing to a virtual memory cell composed of two memory cells MC storing binary data and quinary data, writing is always performed from the memory cell side storing binary data.

Such control is possible by latching data in the sense amplifier and providing an arithmetic function. Therefore, in the nonvolatile semiconductor memory device according to the eighth embodiment of the present invention, the sense amplifier has a data latch function and Has an arithmetic function. This is the same as in the fifth to seventh embodiments of the present invention.

With this configuration, in the eighth embodiment of the present invention, one virtual memory cell stores binary data (1 bit), while the other virtual memory cell has binary × 5 values = 10 values> 8 values = 2 ³ (3-bit) data can be stored. Therefore, the capacity can be increased in the entire memory.

In the eighth embodiment of the present invention, as shown in FIG. 21, it is possible to store ternary data and hex date, and in this case, in the virtual memory cell B, Since 3 values × 6 values = 18 values> 16 values = 2 ⁴ (4 bits) data can be stored in the pair of memory cells, the storage capacity of the entire memory can be increased.

In the nonvolatile semiconductor memory device according to the eighth embodiment of the present invention, it is possible to suppress the adjacent memory cell interference and suppress the spread of the threshold distribution. In addition, the storage capacity of the entire memory can be increased while suppressing a decrease in writing speed. Furthermore, one memory can be used by switching the amount of data stored in accordance with the purpose of use, and as a result, the manufacturing cost can be reduced and the selling price can be lowered, thereby enabling stable product supply. High quality can be maintained.

In one embodiment of the present invention, as described above, adjacent memory cells MC are assigned to store data of different information amounts, and writing is performed from the memory cells MC storing data of adjacent information amounts on the same word line. By performing control so as to be performed, it is possible to increase the capacity of the entire memory while suppressing adjacent memory cell interference caused by capacitive coupling. According to an embodiment of the present invention, it is possible to further increase the storage capacity of the entire memory while suppressing adjacent memory cell interference.

FIG. 22 is a schematic diagram showing allocation of memory cells MC in the nonvolatile semiconductor memory device according to the ninth embodiment of the present invention. The ninth embodiment of the present invention is characterized in that four memory cells connected to two adjacent bit lines and two adjacent word lines store data of four different information amounts. . In FIG. 18, the data stored in the memory cell MC is binary, ternary, quaternary, or ternary data.

The allocation of the handling data to the memory cell MC is set based on the address of the memory cell MC, stored in the ROM fuse as fuse data, read out from the ROM area by the ROM read operation, and set in the latch circuit. In the ninth embodiment of the present invention, a pair is formed by two adjacent memory cells on the same word line, and each memory cell MC is assigned to store data of different information amount. Further, a pair is set with two memory cells MC on the same word line adjacent to the pair of memory cells and on the same bit line as the pair of memory cells MC. Each memory cell MC is assigned so as to store data different from the memory cell.

Specifically, in FIG. 22, a pair is formed by two adjacent memory cells MC on the even word lines WL0, WL2, WL4 (130), and on the adjacent odd word lines WL1, WL3, WL5 (130). A pair is formed by two memory cells MC adjacent to each of the pair of memory cells MC on the same bit line. In FIG. 22, the memory cells MC0-0 and MC1-0 adjacent on the even word line WL0 (130) form a pair, and on the odd word line WL1 (130) adjacent to the word line WL0 (130), The memory cells MC0-1 and MC1-1 adjacent to the pair of memory cells MC on the same bit line form a pair. In addition, binary, ternary, quaternary, and hexanary data are allocated to the four memory cells MC.

When allocating data, the smallest amount of data and the second largest amount of data of the four information amounts are used so that the information amount of data stored in adjacent memory cells MC on the same word line is not an approximate value. Combine with numerical data,
Combine the 3rd largest numerical data and the 1st largest numerical data. The memory cells MC that store the data having the largest numerical value and the data having the second largest numerical value are arranged on different bit lines. Specifically, in FIG. 18, the memory cells MC0-0 and MC1-0 that are adjacent to each other on the same word line WL0 (130) form a pair and are positioned on the adjacent word line WL1 (130). A pair is formed by memory cells MC0-1 and MC1-1 adjacent to MC0-0 and MC1-0 on the same bit line. Then, ternary data is assigned to the memory cells MC0-0 and hex value data is assigned to the memory cells MC1-0. The memory cell MC0-1 located on the bit line BL0 is allocated to the memory cell MC located on a bit line different from the bit line BL1 to which the memory cell MC1-0 is connected so as to store the second largest data. Are assigned to store the second largest quaternary data. Therefore, inevitably, the memory cell MC1-1 is assigned to store binary data. Note that this assignment is an example, and is not limited to this assignment.

Writing is performed from the memory cell MC connected to the normal Even bit line, and then written to the memory cell MC connected to the Odd bit line. In the ninth embodiment of the present invention, even bit lines BL0, BL2, and BL4 (130) are written in the even word lines WL0, WL2, and WL4 (130) and odd word lines WL1, WL3, and WL5 (130). 140), and the order of writing to the memory cells MC connected to the odd bit lines BL1, BL3, BL5 (140) is controlled. That is, in FIG. 22, when writing to the even word lines WL0, WL2, and WL4, first, the even bit lines BL0, BL2, and BL4 (140) are written, and then the odd bit lines BL1, BL3, and BL5 (140) are written. . On the other hand, when writing to the odd word lines WL1, WL3, WL5, the writing is first performed from the odd bit lines BL1, BL3, BL5 (140), and then the even bit lines BL0, BL2, BL4 (140) are written.

This write control is to perform writing from memory cells MC storing data with a small amount of information between adjacent memory cells MC in order to suppress adjacent memory cell interference due to capacitive coupling. Therefore, in response to the allocation of the handling data to the memory cell MC, the setting is changed so as to write from the memory cell MC storing the data with a small amount of information. This control is stored in the ROM fuse as fuse data, read from the ROM area by the ROM read operation, and set in the latch circuit. Of course, as in the first embodiment of the present invention, it is possible to use a method in which a fuse circuit is provided in the power-on reset circuit. It is also possible to set the operation mode to be switched by an external input. In this embodiment, the writing to the memory cell MC is controlled so as to be written from the memory cell MC storing data with a small amount of information, but the present invention is not necessarily limited to this.

With this arrangement and write control, in the nonvolatile semiconductor memory device according to the ninth embodiment of the present invention, it is possible to suppress adjacent memory cell interference and to prevent the threshold distribution from widening. In addition, the storage capacity of the entire memory can be increased while suppressing a decrease in writing speed. Furthermore, one memory can be used by switching the amount of data stored in accordance with the purpose of use, and as a result, the manufacturing cost can be reduced and the selling price can be lowered, thereby enabling stable product supply. High quality can be maintained.

Note that the data to be stored is not limited to binary, ternary, quaternary, and hexary data, but combinations of ternary, ternary, hexary, and ternary data as shown in FIGS. 23 and 24, and ternary values. Combinations of 4-value, 6-value, and 8-value data are also possible, and other numerical data can be combined. The effect in that case is the same as that described above.

The tenth embodiment of the present invention is characterized in that binary data and quaternary data are assigned to data stored in a memory cell MC of a flash memory having a two-transistor type cell.

In recent years, a flash memory including a two-transistor cell that combines the advantages of both a NOR flash memory and a NAND flash memory has been proposed. This flash memory includes a memory cell including two MOS transistors, and one MOS transistor functioning as a nonvolatile memory portion has a structure including a control gate and a floating gate, and is connected to a bit line. The other MOS transistor is connected to the source line and is used for selecting a memory cell.

In a flash memory including such a two-transistor type cell, the area of one memory cell is large, so that it is necessary to store information amount data of two or more values in order to secure a storage capacity. However, when storing information data of two or more values, adjacent memory cell interference occurs due to the influence of capacitive coupling between adjacent memory cells, as in the NAND flash memory. In one embodiment of the present invention, the data stored in the memory cell MC is changed to a checkered flag-like mixed mode (binary and binary information amount mixture mode) of binary data and binary information amount data by switching the operation mode. Mode) and the influence of capacitive coupling between adjacent memory cells can be suppressed, which is also effective in a fresh memory having a two-transistor type cell. A nonvolatile semiconductor memory device according to a thirteenth embodiment of the present invention is a flash memory including a two-transistor cell that assigns binary data and quaternary data as data stored in the memory cell MC.

FIG. 25 is a schematic configuration diagram of a flash memory including a two-transistor cell according to the tenth embodiment of the present invention. The memory cell array has a plurality of ((m + 1) × (n + 1), where m and n are natural numbers) memory cells MC0-0 to MCm-n arranged in a matrix. For the sake of explanation, memory cells MC0-0 to MC5-5 are shown. Each of the memory cells MC has a memory cell transistor MT and a select transistor ST whose current paths are connected in series. Memory cell transistor MT has a stacked gate structure having a floating gate formed on a semiconductor substrate with a gate insulating film interposed therebetween, and a control gate formed on the floating gate with an inter-gate insulating film interposed therebetween. Yes. The source region of the memory cell transistor MT is connected to the drain region of the selection transistor ST. Further, the memory cells MC adjacent in the column direction share the source region of the select transistor ST or the drain region of the memory cell transistor MT.

The control gates of the memory cell transistors MT of the memory cells MC in the same row are commonly connected to one of the word lines WL0 to WL5, and the gates of the select transistors ST of the memory cells in the same row are the select gate lines SG0 to SG5. Connected to either. The drains of the memory cell transistors MT of the memory cells MC in the same column are commonly connected to any of the bit lines BL0 to BL5. The sources of the select transistors ST of the memory cells MC are commonly connected to the source line CELSRC160.

Data writing in a flash memory having such a two-transistor type cell is performed collectively for all the memory cells connected to one of the word lines. Then, “0” data and “1” data are written depending on whether electrons are injected into the floating gate of the memory cell transistor MT. The injection of electrons into the floating gate is performed by Fowler-Nordheim (FN) tunneling.

First, in FIG. 25, write data (“1”, “0”) is input from an I / O terminal (not shown). The write data is input to each latch circuit (not shown) provided for each bit line. When “1” data is stored in the latch circuit, 0 V is applied to the bit line. Conversely, when “0” data is stored, VBB (−6 V) is applied to the bit line.

A first row decoder (not shown) selects one of the word lines WL0 to WL5 and applies Vpp (for example, 10 V) to the selected word line. A second row decoder (not shown) applies VBB (−6 V) to select gate lines SG0 to SG5. The substrate of the memory cell is also VBB (-6V). Accordingly, all the select transistors ST are turned off. Therefore, the selection transistor ST and the source line CELSRC 160 are electrically separated.

As a result, a potential corresponding to “1” data or “0” data is applied to the drain region of the memory cell transistor MT via the bit lines BL0 to BL5. Then, Vpp (10 V) is applied to the selected word line WL, 0 V is applied to the drain region of the memory cell transistor MT to which “1” data is to be written, and the drain of the memory cell transistor MT to which “0” data is to be written. VBB (-6V) is applied to the region. Accordingly, in the memory cell transistor MT in which “1” data is to be written, the potential difference (10 V) between the gate and the drain is not sufficient, so that electrons are not injected into the floating gate, and the memory cell transistor MT maintains a negative threshold value. . On the other hand, in the memory cell transistor MT to which “0” data is to be written, since the potential difference (16 V) between the gate and the drain is large, electrons are injected into the floating gate by FN tunneling. As a result, the threshold value of the memory cell transistor MT changes positively.

Data can be read at once from a plurality of memory cells connected to any one of the word lines. In FIG. 25, a second row decoder (not shown) selects any one of the select gate lines SG0 to SG5. An “H” level (for example, Vcc) is applied to the selected select gate line. All unselected select gate lines are at the “L” level (eg, 0 V). Accordingly, the select transistor ST connected to the selected select gate line is turned on, and the select transistor ST connected to the unselected select gate line is turned off. As a result, the select transistor ST in the selected memory cell is electrically connected to the source line CELSRC160. The first row decoder (not shown) sets all the word lines WL0 to WL5 to the “L” level (0 V). A source line driver (not shown) sets the potential of the source line CELSRC 160 to 0V.

Subsequently, a voltage of about 1 V, for example, is applied to each of the bit lines BL0 to BL5. Then, the memory cell transistor MT of the memory cell MC in which “1” data is written is turned on because the threshold voltage is negative. Accordingly, in the memory cell MC connected to the selected select gate line, a current flows from the bit line toward the source line CELSRC 160 through the current path of the memory cell transistor MT and the select transistor ST. On the other hand, the memory cell transistor MT of the memory cell MC in which “0” data is written is in the off state because the threshold voltage is positive. Therefore, no current flows from the bit line toward the source line CELSRC 160. As a result, the potentials of the bit lines BL0 to BL5 change, and the amount of change is amplified by a sense amplifier (not shown), so that a read operation is performed.

Data is erased collectively for all memory cells sharing the well region. In FIG. 25, the first row decoder (not shown) sets the potentials of all the word lines WL0 to WL5 to VBB (−6V). The potential of the semiconductor substrate (well region) is Vpp (10V). As a result, electrons are extracted from the floating gate of the memory cell transistor of the memory cell MC to the semiconductor substrate by FN tunneling. As a result, the threshold voltage of all the memory cells MC becomes negative and data is erased.

Even in a flash memory including a two-transistor cell in which writing, reading, and erasing are performed by the operation as described above, when writing information amount data of two or more values, the writing potential Vpgm is used to narrow the width of the threshold distribution. Are stepped up at a constant rate Dvpgm smaller than the binary write from the initial value. The write potential Vpgm is applied to the memory cell as a pulse signal (write pulse), and the height (write potential Vpgm) increases each time the pulse signal is applied to the memory cell. Therefore, it is affected by the capacitive coupling of adjacent memory cells MC.

The flash memory including the two-transistor type cell according to the tenth embodiment of the present invention is assigned such that adjacent memory cells MC store different data (binary data and quaternary data). In FIG. 25, when a specific memory cell MC is allocated so as to store information amount data (in this case, quaternary data) having a binary value or more, the memory cell MC is adjacent to both sides on the same bit line. The memory cell MC and the memory cell MC adjacent to both sides of the memory cell MC on the same word line have data (in this case, binary) having a smaller amount of information than the information data (binary data) having the binary value or more. Assigned to remember. A method of assigning data to be assigned to the memory cell MC based on the address of the memory cell MC is the same as in the first embodiment.

Specifically, in FIG. 25, when the memory cell MC2-2 is assigned to use binary data, adjacent memory cells MC2-1, MC2-3 and the same word on the same bit line BL2 (140). All the adjacent memory cells MC1-2 and MC3-2 on the line WL2 (130) are assigned to store quaternary data. Similarly, when looking at the memory cell MC3-2, the memory cell MC is assigned to store quaternary data, but adjacent memory cells MC 3-1, MC 3-3, MC 2-2 and MC 4-2 are stored. Are all assigned to store binary data.

Here, for example, capacitive coupling with adjacent memory cells when data is written in the memory cell MC2-2 in FIG. 25 will be described. In FIG. 25, the memory cell MC2-2 is assigned to store binary data.

First, the word line WL2 (130) is selected by a first row decoder (not shown), and Vpp is applied. The other word lines WL0, WL1, WL3 to WL5 are at 0V. All the select gate lines SG0 to SG5 are VBB (-6V). In this state, 0 V or VBB is applied to each of the even bit lines BL0, BL2, and BL4. Then, in the memory cells MC0-2, MC2-2, and MC4-2 connected to the word line WL2 and connected to the bit line to which VBB is applied, electrons are injected into the floating gate.

On the other hand, in the memory cells MC connected to the word lines WL0, WL1, WL3 to WL5, since the potentials of the word lines WL0, WL1, WL3 to WL5 are 0V, they are floating regardless of the potentials of the bit lines BL0 to BL5. Electrons are not injected into the gate. Therefore, writing is not performed in the memory cells MC2-1 and MC2-3 adjacent to the memory cell MC2-2 in the bit line direction. Here, the memory cells MC2-1 and MC2-3 are affected by the fact that the write voltage is applied to the adjacent memory cell MC2-2 to change the threshold value of MC2-2 and capacitive coupling. However, since the memory cell MC2-2 is writing binary data, it is not necessary to increase the threshold value, and the threshold value change of the memory cell MC2-2 is small. Therefore, the influence of adjacent memory cell interference due to capacitive coupling of the memory cells MC2-1 and MC2-3 is small.

Next, the odd bit lines BL1, BL3, BL5 are selected, and 0V or VBB is applied. Then, in the memory cells MC1-2, MC3-2 and MC5-2 connected to the word line WL2 and connected to the bit line to which VBB is applied, electrons are injected into the floating gate and written. Since the memory cells MC1-2, MC3-2, and MC5-2 are assigned to store quaternary data, a voltage stepped up finely is applied to the memory cells MC. Therefore, for example, the influence of adjacent cell interference due to capacitive coupling on the memory cells MC3-1 and MC3-3 adjacent in the bit line direction and the memory cells MC2-2 and MC4-2 adjacent in the word line direction to the memory cell MC3-2. It will reach.

However, since binary data has already been written into the memory cell MC3-1 and the memory cells MC2-2 and MC4-2, the influence of such adjacent cell interference can be absorbed. The memory cell MC3-3 is not yet written with data, and therefore is affected by adjacent cell interference. Thereafter, the word line WL3 (130) is selected, and the binary data for the memory cell is newly generated. There will be no effect because of the writing.

As described above, with respect to the memory cell MC storing binary data or more information amount data, the memory cell MC adjacent to the memory cell MC in the word line direction and the bit line direction stores data with a small amount of information. And writing to the memory cell MC for each word line is written to the memory cell MC connected to the even (even) bit line connected to the word line, and then connected to the odd (odd) bit line. By controlling to write to the memory cell MC, the influence of capacitive coupling with the memory cell MC adjacent in the word line direction and the bit line direction can be minimized. On the other hand, the memory cell MC that stores data with a small amount of information can absorb the influence of capacitive coupling because data is written first. Therefore, the influence of capacitive coupling can be suppressed as a whole memory. In this embodiment, the writing to the memory cell MC is controlled so as to be written from the memory cell MC storing data with a small amount of information, but the present invention is not necessarily limited to this.

In addition, since half of the memory cells MC store binary data having a smaller number of writes than four-value data, there is an effect that a decrease in the write speed of the entire memory can be suppressed to a certain limit. Furthermore, since the read voltage of the non-selected word line can be set lower than in the case of quaternary cells when binary data is handled, there is an effect that Read Disturb can be suppressed and reliability can be maintained high. These effects are the same as those in the NAND flash memory.

Further, in the flash memory including the two-transistor type cell according to the tenth embodiment of the present invention, the data stored in one memory cell is performed by the operation mode switching by the fuse data based on the address of the memory cell MC. This can be easily performed, and there is an effect that the information amount of data to be stored can be switched according to the purpose of use. Such an effect further brings about an effect of maintaining the high quality because the manufacturing cost can be reduced and the selling price can be lowered, and the stable product supply can be achieved. These effects are also the same as those in the NAND flash memory.

In the tenth embodiment of the present invention, the data to be stored is binary data and quaternary data. However, the present invention is not limited to this. For example, ternary data, hex data, quaternary data, Eight-value data or other combinations may be used. Similar effects can be obtained by allocating memory cells MC adjacent to each other on the same bit line and the same word line so as to store data of different amounts of information and controlling writing.

10: nonvolatile semiconductor memory device 100: memory cell array 110: memory cell region 111: memory cell MC
112: Memory cell transistor MT
113: Selection transistor ST
120: ROM area 130: Word line 140: Bit line 150: Selection gate line 150a: Source side selection gate line (SGS)
150b: Drain side select gate line (SGD)
160: Source line (CELSRC)
20: row decoder 30: column decoder 40: sense amplifier 50: input / output buffer 60: address buffer 70: voltage generation circuit 80: power on reset circuit 81: power on level sensing circuit 82: delay circuit 90: control circuit 91: initial Control circuit 92: ROM read control circuit 200: Latch circuit 210: External I / O pad

Claims (2)

Multiple word lines,
Multiple bit lines,
A non-volatile semiconductor memory device having a plurality of memory cell arrays having a plurality of electrically rewritable memory cell transistors having two or more memory states,
The number of storage states stored in the memory cell transistors is different between adjacent memory cell transistors in the word line direction and the bit line direction.
It is written in page units for each even bit line and odd bit line.
A nonvolatile semiconductor memory device, wherein a potential of a bit line to which data is not written at the time of writing is controlled to a predetermined potential. Multiple word lines,
Multiple bit lines,
A plurality of memory cell arrays having a plurality of electrically rewritable memory cell transistors having two or more storage states;
A non-volatile semiconductor memory device having a plurality of sense amplifiers connected to the plurality of bit lines and amplifying and outputting signals read from the plurality of memory cell transistors;
The memory cell transistor has a first address and a second address assigned in common to two memory cell transistors adjacent in the word line direction,
The plurality of sense amplifiers have an arithmetic function of latching input / output data and converting the input / output data into a predetermined signal based on the second address;
The number of storage states stored in the memory cell transistors is different between adjacent memory cell transistors in the word line direction and the bit line direction.
Based on the second address, each even bit line and odd bit line are written in page units,
A nonvolatile semiconductor memory device, wherein a potential of a bit line to which data is not written at the time of writing is controlled to a predetermined potential.