JP3463027B2 - Non-volatile semiconductor memory - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-volatile semiconductor memory.

[0002]

2. Description of the Related Art As is well known, a memory cell MC having a floating gate used in a NAND type EEPROM is constructed as shown in FIG. That is, the floating gate F. G. The gate insulating film GO between the channel region CA and the channel region CA is formed so thin that a tunnel effect occurs. Then, the control gate CG is set to 0V, and the substrate S
By applying a high voltage to b, the floating gate FG is transferred to the substrate Sb.
Electrons are emitted to write one of binary data. On the contrary, by setting the substrate Sb, the source S and the drain D to 0V and setting the control gate CG to a high voltage, electrons are injected from the substrate Sb to the floating gate FG to write the other binary data. FIG. 29 shows a part of an integrated circuit in which a plurality of such memory cells MC are connected in a matrix.
It shows in (a). FIG. 29B is a voltage waveform of each node in FIG. When programming data in the memory cells MC, first, all the row lines WL1 to WLn connected to the control gates CG are set to 0V and the substrate is set to a high voltage so that the floating gates FG of all the memory cells MC are transferred to the substrate. Emits electrons. Next, the gate S of the select transistor ST of the memory cell MC in which data is to be written is set to a high potential. At the same time, the signal φ is set to 0 V to turn off the transistor 10 and disconnect the memory cell MC from the reference potential V _SS . When injecting electrons into the floating gate FG of the memory cell MC, the corresponding row line WL is set to the high potential V1 and the corresponding column line D is set to 0V. At this time the floating gate FG
The potential difference between the substrate and the substrate Sb (channel) becomes a value sufficient to cause a tunnel, and the floating gate FG is removed from the substrate Sb.
Electrons are injected into. On the other hand, the non-selected row line WL is set to a potential V2 lower than the previous high potential V1. At this time, even if the potential of the column lines D (D1, D2, ...) Is 0 V, the potential V2 is low, so that the potential difference between the floating gate FG and the substrate Sb (channel) is a sufficient value to cause a tunnel. Therefore, no electrons are injected into the floating gate FG. Line W
Even if L is set to the high potential V1, if the column line D is set to the potential V3, the floating gate FG is also set at this time.
The potential difference between the substrate and the substrate Sb (channel) is not a sufficient value to cause a tunnel, and no electrons are injected into the floating gate FG. That is, as can be seen from FIG. 29B, at time T1, electrons are injected into the floating gate of the memory cell 2n, and no electrons are injected into the floating gate FG of the memory cell 1n. Similarly, at time T2, electrons are injected into the floating gate FG of the memory cell 11, and no electrons are injected into the floating gate FG of the memory cell 21.

In such a memory cell MC, if electrons are injected into the floating gate FG, the threshold voltage becomes a positive value, and if electrons are emitted from the floating gate FG, the threshold voltage is increased. The voltage has a negative value. Memory cell M
When C is selected, its gate is a logical "0", eg 0.
Set to V. Floating gate FG with a negative threshold voltage
The memory cells MC from which electrons have been emitted remain on, but the memory cells MC from which electrons have been injected into the floating gate FG having a positive threshold voltage are turned off. In this way, the selected memory cell MC having a gate of 0 V stores data depending on whether it is on or off. On the other hand, the gate of the non-selected memory cell MC is set to logic "1", for example, 5V, and the memory cell MC in which electrons are injected into the floating gate FG is also turned on.

Next, reading of data will be described with reference to FIG.

For example, a depletion type MOS transistor L1 acting as a load element, a selection MOS transistor (enhancement type) ST, and memory cell MOS transistors M1 to M8 are connected in series to the power source V _DD and the ground point (V _SS ). Connected. The gate of the MOS transistor L1 is connected to the connection point (node N1) between the MOS transistor L1 and the selection MOS transistor ST. The gates of the selection MOS transistors ST have memory cell MOS transistors M1 to M8.
Signal X for selecting the memory block 11 consisting of Signals W1 to W8 for selecting one memory cell MOS transistor in the memory block 11 are supplied to the gates of the memory cell MOS transistors M1 to M8, respectively. And
The stored data is read from the selected memory cell MOS transistor by supplying the potential of the node N1 to the sense amplifier 12 and amplifying it.

In the circuit of FIG. 30, for example, electrons are emitted from the floating gates of the memory cell MOS transistors M2 and M4, the threshold voltage is negative, and the memory cell MOS transistor M4 is selected. And
At this time, as shown in the timing chart of FIG. 31, the signal X is set to the “1” level and the signals W1 to W3 and W5 to W are set.
8 is set to "1" level and the signal W4 is set to "0" level. As a result, the selection MOS transistor ST
And memory cell MOS transistors M1 to M3 and M
5 to M8 are turned on. In addition, MOS for memory cells
Since the threshold voltage of the transistor M4 is negative, this transistor M4 is also turned on. Therefore, the node N1
Is discharged, and the stored data is read by detecting and amplifying this by the sense amplifier 12. Next, it is assumed that the memory cell MOS transistor M3 is selected. In this case, the signal W3 is set to "0" level, and all other signals are "1".
Set to level. At this time, since the memory cell MOS transistor M3 has electrons injected into the floating gate and the threshold voltage is positive, the transistor M3 is turned off. As a result, the discharge path of the node N1 is cut off, and the node N1 is charged by the load MOS transistor L1. By detecting and amplifying this by the sense amplifier 12, data is read from the memory cell MOS transistor M3.

However, if data "1" and "0" are stored depending on whether the threshold voltage of the memory cell MOS transistor is negative or positive, the threshold value in the memory cell block 11 is stored. When the ratio of the number of MOS transistors having a positive voltage to the number of MOS transistors having a negative threshold voltage is different, the magnitude of the current flowing through the memory cell block 11 is different. That is, the discharge speed of the node N1 and the potential of the “0” level at the time of discharge are the ratio of the positive threshold voltage of the memory cell MOS transistors connected in series to the number of MOS transistors having the negative threshold voltage. Will be different.

For example, as shown in FIG. 32 (a), the memory cell MOS transistors M1 to M7 in the memory cell block 11 have a positive threshold voltage due to the injection of electrons into their floating gates, and only the transistor M8. Is a negative threshold voltage, all other transistors M are selected when the memory cell MOS transistor M8 is selected.
Since 1 to M7 are positive threshold voltages, the current flowing through the memory cell block 11 is the smallest. On the other hand, as shown in FIG.
MOS transistors M1 to M8 for memory cells
If all have negative threshold voltages, the memory cell current is the largest. This is because the threshold voltage is negative
This is because if the potentials of the signals W1 to W8 are the same as those in FIG. 32A, a MOS transistor having a negative threshold voltage flows more current than a MOS transistor having a positive threshold voltage. Therefore, in the circuit shown in FIG. 30, the memory cell block 11 shown in FIG.
There is a disadvantage that the discharge speed becomes the slowest when the data is read from, and the data read speed is determined in such a memory cell block. In addition, since the current flowing through the memory cell block at this time is the smallest, it is necessary to determine the current driving capability of the load transistor L1 accordingly, and the current driving capability of the load transistor L1 cannot be increased and the node N1 is charged. It also has the drawback of being slow.

Further, in the conventional memory, one memory cell block corresponds to one column line. Therefore, the area occupied by the memory cell array has come to be determined by the connection between the memory cell block and the column line between adjacent memory cell blocks. Also, the large number of column wirings has affected the yield.

Further, in the memory cells and devices of FIGS. 28 and 29, as described above, electrons are emitted from the floating gates of all the memory cells at a time, and the threshold voltage of the memory cells is set to a negative value. Then, one of the binary data is written, and then the other of the binary data is written by selectively injecting electrons into the floating gate.

In reading the data from the memory cell, the selected row line is set to logic "0", for example, 0V,
Non-selected row lines are set to logic "1", eg 5V. A memory cell connected to a non-selected row line has a row line which is its gate having a logic "1". Therefore, even if electrons are injected into the floating gate of a non-selected memory cell and the threshold voltage is positive, even if electrons are emitted from the floating gate of the memory cell and the threshold voltage of the memory cell is negative, Turn on. However, the selected row line is 0V. Therefore, the selected memory cell is turned off when the threshold voltage is positive, and turned on when the threshold voltage is negative. Whether the memory cell selected in this way turns on or off,
Detecting whether the data stored in the memory cell is a logical "1" or a logical "0" is as described above. The threshold voltage of the memory cell in which electrons are injected into the floating gate must be set to be on when it is not selected and off when it is selected. Therefore, attention must be paid to the amount of injected electrons. Therefore, the injection of electrons into the memory cell and the reading for checking the injection amount are repeated, and the injection of electrons is stopped when the injection amount becomes appropriate. However, since the electrons are injected through the extremely thin gate insulating film,
Due to variations in the manufacturing process, the amount of electrons injected into the floating gate may vary among memory cells due to variations in the thickness of the gate insulating film and defects. That is, the threshold voltage of the memory cell into which electrons are injected varies with a certain width. Therefore, the difference in threshold voltage between the memory cell with the lowest threshold voltage and the memory cell with the highest threshold voltage becomes the difference in the current flowing through the memory cell, and the data read speed from the selected memory cell is It depends on the cell. That is, since the data is detected by the current flowing through the non-selected memory cells connected in series, the variation of the threshold voltage of the non-selected memory cells becomes the variation of the current flowing through the memory cells as it is, and the data reading speed There will be variations. In order to increase the data reading speed, the larger the current flowing in the memory cell, the better. However, since the threshold voltage of the memory cell into which electrons are injected must be a positive value, even if the threshold voltage of the memory cell with the lowest threshold voltage is set to a value slightly higher than 0V, the memory cell It is inevitable that the threshold voltage value of the memory cell having the highest threshold voltage becomes much higher than 0V due to the variation of the threshold voltage distribution.

Further, a conventional NOR type flash EEP is also used.
In the ROM, when data is rewritten, electrons are temporarily injected into the floating gates of all the memory cells, the amount of electrons stored in the floating gates is made uniform for all the memory cells, and then the floating gates of all the memory cells are changed. Electrons are emitted from the gate and one of binary data is stored. After that, a high voltage is applied to the control gate and drain of the memory cell to flow a channel current, and electrons are selectively injected from the channel region to the floating gate of the memory cell to write the other binary data. Such a conventional NOR flash EEP
In the ROM, if electrons are emitted from the floating gate too much, the threshold voltage of the memory cell becomes a negative value, and the selection operation cannot be performed. Therefore, the electrons are emitted and then read out to check whether or not the threshold voltage has become appropriate. In order to prevent excessive emission of electrons, the emission period of electrons is set to be short, and emission and readout are repeated many times to obtain an appropriate threshold voltage. However, in this emission, electrons are emitted from the floating gate to the source or drain by tunnel effect by setting the control gate to 0V and applying a high voltage to the source or drain. Alternatively, set the control gate to 0V,
High voltage is applied to the semiconductor substrate on which the memory cells are made,
Electrons are emitted from the floating gate to the channel region by utilizing the tunnel effect. Therefore, the gate insulating film between the floating gate and the channel is made extremely thin, for example, about 100 Å so that the tunnel effect occurs. Therefore, due to variations in the manufacturing process, the threshold voltage of the memory cells after the emission of electrons does not have a uniform value in all memory cells but varies with a certain width. The larger the current flowing through the memory cell, the faster the data read speed and the larger the margin.
Therefore, it is preferable that the threshold voltage of the memory cell is low. However, if electrons are emitted from the memory cell having the highest threshold voltage among the variations until the optimum threshold voltage is reached, the lowest threshold voltage of the variation is low. The threshold voltage of the memory cell becomes a negative value, which is not preferable. For this reason, in such a semiconductor memory, the threshold voltage of the memory cell having the lowest threshold voltage among the variations is prevented from becoming a negative value, so that the read speed is increased in the memory cell having the highest threshold voltage. Once decided, it was difficult to increase the data reading speed.

FIG. 33 shows an example of such a conventional NOR type flash EEPROM memory cell array.
33A is a plan view, FIG. 33B is a sectional view taken along the line AA ′,
34C is a sectional view taken along the line BB ′, FIG. 34D is a sectional view taken along the line CC ′, and FIG. 34 is a symbol diagram thereof. In FIG. 33,
A row line 1 forms a control gate of the memory cell. 2 is a floating gate, 3 is a channel region, and 4 is a gate insulating film. Reference numeral 5 denotes a column line made of aluminum, for example, and a drain 6 shared by adjacent memory cells is connected to the column line 5. Reference numeral 8 is a wire made of aluminum, for example, which supplies a reference potential (for example, ground potential) at the time of reading data and a high voltage at the time of emitting electrons from the floating gate. To be shared by the memory cells, it is connected to the source 7 of the memory cell at connection location 9.

The conventional flash E having the above structure
In an EPROM, even when a row line, that is, a non-selected memory cell whose control gate is 0V, is turned on when the threshold voltage of the memory cell becomes a negative value by emitting too many electrons from the floating gate. Therefore, the column line 5 and the wiring 8 are connected to each other, and a current flows from the column line 5 to the wiring 8 even through a non-selected memory cell. As a result, even if a voltage is applied to the column line 5 at the time of reading data or writing data, a current flows through the non-selected memory cells and the voltage drops. Therefore, even if the selected memory cell is turned off when reading data, current will flow through the non-selected memory cells, and incorrect data will be read. We cannot supply. Therefore, as described above, it is necessary to set the threshold voltage of the memory cell having the lowest threshold voltage to a positive value among the variations in the threshold voltage of all the memory cells after the electrons are emitted from the floating gate. However, there is a drawback that the data reading speed cannot be increased because the data reading speed is determined by the memory cell having the highest threshold voltage.

As described above, so-called EEPRO
In the memory cell of M, through the oxide film of about 100 angstroms, which is much thinner than the gate oxide film,
Data is rewritten by injecting or emitting electrons into the floating gate. FIG. 35 shows a conventional EEPR that rewrites data by a different method.
OM is a symbol diagram of the cell transistors that make up such a memory cell, where the control gate voltage is V _CG , the drain voltage is V _D , the source voltage is V _S , and the drain current is I.
_{Assuming D} , the drain current I _{D with} respect to the control gate voltage V _CG exhibits the characteristics shown in FIG. In FIG. 36, a curve A is the characteristic in the initial state, and a curve B is the characteristic when electrons are injected into the floating gate, and the threshold voltage rises due to the injection of electrons. Curve C is the characteristic of the state where electrons are emitted from the floating gate, and the threshold voltage decreases due to the emission of electrons and becomes negative. In a memory cell using such a cell transistor, data "0" and "1" are stored by utilizing the characteristics of the curves B and C.

FIG. 37 shows an example of the circuit configuration of such an EEPROM in which the cell transistors shown in FIG. 35 are arranged in a matrix, and the currently commercially available EEPROM has such a circuit configuration. Many. As shown, each cell transistor CT has a selection MOS.
One memory cell 1 in which transistors ST are connected in series
4 is composed of two transistors CT and ST.

In the above structure, when electrons are injected into the floating gate of the cell transistor CT, the gate of the selection transistor ST and the cell transistor C are selected.
The high voltage V _G , V _CG is applied to the control gate of T, and the column line 15 is set to 0V. On the other hand, when electrons are emitted, the gate of the selection transistor ST and the column line 15 are set to a high voltage, and the control gate of the cell transistor CT is set to 0V. As a result, a high voltage is applied to the drain of the cell transistor CT, and electrons are emitted from the floating gate to the drain.

FIG. 38A is a pattern plan view of the region 16 surrounded by the alternate long and short dash line in the circuit shown in FIG. 37, and shows the sectional structure taken along the line AA ′ of FIG. 38A. 38 (b). 38 (a) and (b),
The same reference numerals are given to the portions corresponding to FIG. 37,
Reference numeral 17 denotes a source region of the cell transistor CT, 18 denotes a drain of the cell transistor CT and a selection transistor S.
The source region of T, 19 is the drain region of the selection transistor ST, 20 is the floating gate of the cell transistor CT,
Reference numeral 21 is a control gate of the cell transistor CT, 22 is a gate of the selection transistor ST, 23 is a thin oxide film portion, 2
Reference numeral 4 denotes a contact portion between the column line 15 and the drain of the selection transistor ST.

In such an EEPROM, a latch circuit L is provided for each column line 15 as shown in FIG. 39 in order to shorten the time for programming data in the memory cell. Then, the data to be programmed in the memory cells 14 connected to the corresponding column lines 15 is latched in the latch circuit L, and the memory cells 14 for one row are simultaneously programmed based on the latched data. ing. In the EEPROM configured as described above, the time for programming data is shortened, but since the latch circuit L is provided for each column line, the chip size is increased by the amount of the latch circuit and the chip cost is increased. It had the drawback of being expensive.

[0020]

[Problems to be Solved by the Invention]

In the conventional nonvolatile semiconductor memory described with reference to FIGS. 28 and 29, as described above, it is caused by variations in the thickness of the gate insulating film of the memory cell due to variations in the manufacturing process, crystal defects, and the like. As a result, the amount of electrons injected into the floating gate of the memory cell varies.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a non-volatile semiconductor memory in which variations in the distribution of the threshold voltage of a memory cell in which electrons are injected into a floating gate are reduced. It is in.

[0023]

According to a first aspect of the present invention, a floating gate and a control gate are provided, and data is stored according to the charge accumulation state of the floating gate, and the data is stored according to the charge amount of the floating gate. A memory cell array in which memory cells having transistors whose threshold voltages change are arranged in a matrix; a row line to which the transistors in the same row are connected; and a column line to which the memory cells in the same column are connected,
Corresponding to programming data in the memory cell by simultaneously injecting electrons into the floating gate of the one of the plurality of transistors connected to one of the row lines that requires electron injection. A program means for supplying a program voltage to the row line, the threshold voltage of the transistor after supplying the program voltage having a first voltage value to inject electrons into the floating gate of the transistor. When the voltage is lower than a predetermined value, the program voltage having a second voltage value higher than the first voltage value is supplied to the floating gate of the transistor having a threshold voltage lower than the predetermined value. The electrons are injected again, the program voltage having the second voltage value is supplied, and the transistor having the threshold voltage lower than the predetermined value is supplied. The threshold voltage after the electrons are injected into the floating gate of the transistor by supplying the program voltage having the first voltage value while the electrons are injected into the floating gate of the transistor again. Higher than the value of the transistor to prevent electrons from being injected into the floating gate of the transistor, after supplying the program voltage having the first voltage value to inject electrons into the floating gate of the transistor. The column line to which the transistor having a threshold voltage higher than the predetermined value is connected is set to a predetermined voltage.

A second aspect of the present invention is a transistor which has a floating gate and a control gate, stores data in accordance with a charge accumulation state of the floating gate, and has a threshold voltage which changes according to the amount of the charge in the floating gate. Injecting electrons into a memory cell array having memory cells arranged in a matrix, a row line to which the transistors in the same row are connected, a column line to which the memory cells in the same column are connected, and the floating gate. In order to do so, by supplying a program voltage to the row line, a programming means for programming desired data in the transistor forming the memory cell, and a plurality of voltage values connected to the programming means Program voltage generating means for generating the program voltage, and the transistor constituting the memory cell In order to prevent electrons from being injected into the floating gate, a program preventing unit for setting a voltage of the column line to a predetermined value is provided, and a plurality of program lines connected to one of the row lines are provided. By injecting electrons into the floating gate of one of the transistors that requires electron injection at the same time, data is programmed in the memory cell, and when the memory cell is injecting electrons, the memory In order to prevent electrons from being injected into the memory cells connected to the same row line as the cells that do not need to be injected with electrons, the corresponding column line is set to the predetermined value by the program prevention means. The plurality of voltage values of the program voltage generated by the program voltage generating means is at least two voltage values, and the plurality of voltage values before the first voltage value are set. After the program voltage is generated and electrons are injected into the transistor, when the threshold voltage of the transistor into which the electrons are injected is lower than a predetermined value, it is higher than the program voltage of the first voltage value. The program voltage having the second voltage value is generated to inject electrons into the transistor having the threshold voltage lower than a predetermined value, and the same transistor as the transistor having the threshold voltage lower than the predetermined value. In order to prevent electrons from being injected into the transistor, which is connected to a row line and has a threshold voltage higher than the predetermined value, the electrons are injected into the corresponding column line by the program prevention means. The voltage is set to the predetermined value.

A third aspect of the present invention is a transistor which has a floating gate and a control gate, stores data in accordance with a charge accumulation state of the floating gate, and has a threshold voltage which changes according to the amount of the charge in the floating gate. A memory cell array having memory cells arranged in a matrix, a row line to which the transistors in the same row are connected, a column line to which the memory cells in the same column are connected, and one of the row lines. A program voltage is applied to the corresponding row line to program data into the memory cell by simultaneously injecting electrons into the floating gate of the transistor that requires electron injection among the plurality of connected transistors. And a programming means for supplying the programming voltage, and supplying the programming voltage to the transistor of the first memory cell. When electrons are injected into the Yu gate,
The second memory cell is connected in order to prevent electrons from being injected into the second memory cell which does not need to be injected with electrons connected to the same row line as the first memory cell. When the column line is set to a predetermined voltage and the threshold voltage of the transistor of the first memory cell after injecting the electrons is lower than a predetermined value, the column line has a voltage higher than the program voltage. The program voltage is supplied to re-inject electrons into the floating gate of the transistor forming the first memory cell, and the program voltage having a voltage higher than the program voltage is supplied to supply the program voltage to the first gate. When reinjecting electrons into the floating gate of the transistor forming the memory cell, the previous program voltage connected to the same row line as the first memory cell is supplied. In order to prevent electrons from being injected into the transistor forming the third memory cell, the threshold voltage after the injection of electrons is higher than the predetermined value. The column line to which the cells are connected is configured to be set to a predetermined voltage.

A fourth aspect of the present invention is a transistor which has a floating gate and a control gate, stores data according to a charge accumulation state of the floating gate, and whose threshold voltage changes according to the amount of the charge of the floating gate. A plurality of cells are connected in series, and a memory cell array in which memory cells, each of which is composed of a selection transistor whose one end is connected to one end of a transistor connected in series, are arranged in a matrix, and the transistors in the same row are connected. A first row line connected to the first row line and a second row line connected to the selection transistors in the same row.
Row line, a column line to which the other end of the selection transistor in the same column is connected, and the transistor requiring electron injection among the plurality of transistors connected to one of the first row lines To inject electrons into the floating gate of
Programming means for programming desired data in the transistors forming the memory cell by supplying a programming voltage to the first row line;
Program voltage generating means connected to the program means for generating the program voltage having a plurality of voltage values, and for preventing electrons from being injected into the floating gate of the transistor forming the memory cell. And a program preventing means for setting the column line to a voltage of a predetermined value, and simultaneously injecting electrons into the floating gate of the transistor which is required to inject electrons connected to the first row line. By injecting, data is programmed into the memory cell, and when electrons are injected into the transistor, electrons are injected into the transistor connected to the same row line as this transistor and need not be injected into the transistor. The corresponding column line is set to the predetermined value by the program prevention means in order to prevent The plurality of voltage values of the program voltage generated from the program voltage generating means are at least two voltage values, the program voltage having a first voltage value is generated, and electrons are injected into the transistor, When the threshold voltage of the electron-injected transistor is lower than a predetermined value, the program voltage having a second voltage value higher than the program voltage having the first voltage value is generated, and the threshold voltage is increased. Electrons are injected into the transistor lower than a predetermined value, and the threshold voltage connected to the same first row line as the transistor whose threshold voltage is lower than the predetermined value is the predetermined threshold voltage. Corresponding to the column line in order to prevent electrons from being injected into the transistor that has been injected with electrons higher than the value of What configured as those to set the voltage of the predetermined value.

[0027]

According to the present invention, when programming a memory cell, a program voltage is applied to the row line. In this program, injection of electrons into the floating gate and checking of the injection amount are sequentially repeated. Then, as the program voltage, one higher than the previous one is sequentially added. As a result, electrons are optimally injected into each memory cell regardless of variations in the manufacturing process, and variations in the threshold voltage of each memory cell are reduced.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first example relating to the present invention will be described below with reference to the drawings. In FIG. 1, a bit check MOS transistor CT whose conduction is controlled by a signal C is provided between the selection MOS transistor ST and the memory cell MOS transistor M1 shown in FIG. The function of the bit-check MOS transistor CT is different from the memory cell block 111 including the bit-check MOS transistor CT, and it is stored in one memory cell block 111 of "1" or "0" of stored data. One of the two, MO, which has a negative threshold voltage at which electrons are emitted from the floating gate
It is to remember whether or not it is assigned to the S transistor.
That is, “1” is set for each memory cell block 111.
It is changed whether the data of is stored at the negative threshold voltage or at the positive threshold voltage. That is, if the number of “1” s stored in one memory cell block 111 is large, the data of “1” is assigned to a negative threshold voltage, and if the number of “0s” is large, “0” is assigned. Is assigned to the negative threshold voltage. By doing this, the memory cell MO in the memory cell block 111 is
More than half of the S transistors M1 to M8 have a negative threshold voltage.

Hereinafter, this will be described in detail with reference to FIG. In the example shown in FIG. 2, the memory cell block 1
When 8 memory cell MOS transistors exist in 11, the number of "1", "0" and "1",
The threshold voltage of the transistor corresponding to “0” and the threshold voltage of the transistor for bit check are shown. For example, no. 3 has two "1" data,
This is a case where there are 6 pieces of "0" data. In this case,
"0" data is a MOS transistor having a negative threshold voltage, and "1" data is a MOS transistor having a positive threshold voltage.
Assign to each transistor. Then, this allocation is stored by setting the bit-check MOS transistor CT to a positive threshold voltage. In addition, no. 6
Is the case where there are 5 pieces of "1" data and 3 pieces of "0" data. In this case, "1" data is assigned to a MOS transistor having a negative threshold voltage, and "0" data is assigned to a MOS transistor having a positive threshold voltage. Then, this allocation is stored by setting the bit check MOS transistor CT to a negative threshold voltage. In addition, no. As shown in FIG. 5, when the number of “1” data and the number of “0” data are the same, the data of “1” is positively applied to the MOS transistor having the negative threshold voltage. The bit check MOS transistor CT is set to a negative threshold voltage by assigning it to each MOS transistor having a threshold voltage.

According to such a structure, the number of MOS transistors having a negative threshold voltage, in which electrons are emitted from the floating gate in the memory cell block 111, can be always more than half. Therefore, the current flowing through the memory cell block 111 can be increased, and the load transistor L1 having a large current driving capability can be used, so that the reading speed can be significantly improved.

In FIG. 2, the memory cell block 111
Has been described by taking as an example the case in which the memory cell has eight MOS transistors for memory cells. However, it is needless to say that the number of transistors is not limited to this and may be another number such as 16 or 32.

FIG. 3 shows the memory cell block shown in FIG.
Formed by arranging the racks 111 in a matrix
A storage device is shown. In FIG. 3, 113 and 114 are memos.
It is a re-cell array. These memory cell arrays 11
3, 114 are a plurality of arrays 113, respectively₁, 113₂
And 114₁, 114₂Is divided into And
Selection in these memory cell arrays 113 and 114
Transistors S1R, S2R, ... And S1L, S2
L, ... Are output signals X1 of the row decoder 115, respectively.
Selected by R, X2R, ... and X1L, X2L ,.
Is continually controlled. Also, bit check MOS transistor
Transistors CT1R, CT2R, ... and CT1L, C
T2L, ... Are output signals of the row decoder 115, respectively.
By C1R, C2R, ... And C1L, C2L, ...
The conduction is selectively controlled. Similarly, MOS for memory cells
Transistors M1R, M2R, ..., M8R and M1
L, M2L, ..., M8L are also the row decoders, respectively.
115 output signals W11R, W12R, ..., W18R
And W11L, W12L, ..., W18L selectively
Continuity is controlled. Reference numeral 116 is a column decoder. This column
Output signals Y1R, Y2R, ..., YnR of the decoder 116
And Y1L, Y2L, ..., YnL
, CG1R, CG2R, ..., CGnR and CG1
L, CG2L, ..., CGnL are selectively controlled to conduct.
It The select gates CG1R, CG2R, ..., CG
nR and one end of CG1L, CG2L, ..., CGnL
Respectively for each array 113₁, 113₂, 114₁
And 114₂Each node is commonly connected to the node N1.
These common connection point (node Ni) and power supply V_DDBetween
Are load MOS transistors L1, L1, ...
Are connected. Each load MOS transistor L
The node N1 as one end of 1, L1, ...
Are connected to the sense amplifiers 112, 112, ...
It Sense amplifier 112 connected to node N1 (3)
Connected to output D1R of (3) and node N1 (2)
The output D1L of the sense amplifier 112 (2)
Data determination circuit 117₁Is supplied to. This data judgment
Circuit 117₁Is the inverter 118, 119, P channel
Type MOS transistors Q1 to Q4 and N channel
Type MOS transistors Q5 to Q8. This judgment
Circuit 117₁Is one array 113₁For memory cells
Stored data read from the MOS transistor M
Array 114₁Bit check MOS transistor
Depending on whether the star CT is a positive threshold voltage or a negative threshold voltage.
Then flip it or leave it as it is
MOS transistor for output or selected memory cell
Data stored in the
The data that is not transferred is output to an output buffer (not shown).
Similarly, the determination circuit 117₁Is one array 114₁No
Memory data read from the MOS transistor M for memory cell
The other array 113₁Bit check MO
S-transistor CT has positive or negative threshold voltage
Depending on whether it is inverted or not
Output as it is or select the MOS transistor for the selected memory cell.
Determine the data stored in the transistor and check if it is the inverted data.
Or output the data that is not inverted to an output buffer not shown.
Force Sense amplifier 1 connected to node N1 (4)
Connect to output D2R of 12 (4) and node N1 (1)
The continued output D2L of the sense amplifier 112 (1) is
The data determination circuit 117, respectively₂Is supplied to. This device
Data determination circuit 117₂Is the data determination circuit 117₁
It has the same structure as. This determination circuit 117₂Is one
Array 113₂MOS transistor for memory cell
The storage data read from M is used for the other array 114. ₂of
Bit check MOS transistor CT has a negative threshold
Inverted or not depending on voltage or positive threshold voltage
Is output as it is without being inverted,
Memory data of the selected memory cell MOS transistor M
Data and determine whether the data is inverted or not.
Data to an output buffer (not shown). Similarly judgment times
Road 117₂Is one array 114₂MO for memory cells
The memory data read from the S transistor M is stored in the other memory.
Ray 113₂Bit check MOS transistor C
Invert depending on whether T is negative or positive threshold voltage
Output or output as it is without inversion
MOS Transistor for selected memory cell
Data stored in M
Output the data that is not inverted to the output buffer (not shown).
It

As shown in the figure, in the circuit of FIG. 3, two memory cell arrays 113 and 114 are arranged on the right side and the left side of the row decoder 115, respectively. Bit check M for checking the data in the memory cell array 113 on the right side
The OS transistor CT is incorporated in the corresponding left memory cell array 114. On the contrary, the bit check transistor for checking the data in the memory cell array 114 on the left side corresponds to the memory cell array 11 on the right side.
It is built into 3. For example, bit check MO
The S transistor CT1R has memory cells M1L to M8L.
It is for checking. Transistor CT1L
Are for checking the memory cells M1R to M8R. Thus, in the configuration example of FIG. 3, the row decoder 1
One side of the pair of memory cell blocks existing symmetrically on the left side and the right side has a bit check MOS transistor CT for the other side. However, this is a symbolic circuit, and it is not necessary to take an actual pattern and make it symmetrical.

Next, the circuit operation of the above configuration will be described with reference to the truth table shown in FIG. D1L and D1R are data read by the sense amplifiers 112 and 112, as shown in FIG. This sense amplifier 11
When a memory cell composed of a MOS transistor having a negative threshold voltage is selected, reference numerals 2 and 112 output "0" data, and a memory cell composed of a transistor having a positive threshold voltage is selected. If it does, the data of "1" is output. Now, when the address signal A0 is "0", it is assumed that the data from the memory cell in the left cell array 114 is read and the bit check data in the right cell array 113 is read. in this case,
The data D1L is data read from the left cell array, and the data D1R is data read from the right cell array. Z1 is the data output from the data determination circuit 117 ₁ to the output buffer based on these data D1L and D1R. The data determination circuit 117 ₁ shown in FIG. 3 is configured to satisfy this truth table. When the data D1L read by the sense amplifier 112 is "0" and D1R is also "0", the storage data of the memory cell and the bit check data D1.
Since R is "0", the memory cell MOS transistor and the bit check MOS transistor have a negative threshold voltage. Therefore, as shown in FIG. 2, the memory cell stores "1" data. Therefore, the output Z1 is set to "1". On the other hand, the output D1L of the sense amplifier 112
Is "1" and D1R is "0", M for memory cell
The OS transistor has a positive threshold voltage. Since the bit check MOS transistor has a negative threshold voltage, the memory cell MOS transistor stores "0" and the output Z1 is "0". Further, the output D1L of the sense amplifier 112 is "0" and D1R is "1".
Since the memory cell MOS transistor has a negative threshold voltage and the bit check MOS transistor has a positive threshold voltage, the memory cell MOS transistor stores "0" and the output Z1 Is "0". Further, the outputs D1L and D1R of the sense amplifier 112
When both are "1", the memory cell MOS transistor and the bit check MOS transistor have a positive threshold voltage, so that the memory cell MOS transistor stores "1". Therefore, the output Z1 is set to "1".

The same applies when the address signal A0 is "1", where D1R is memory cell data and D1L is check data. Thus, whether "1" or "0" is stored in each memory cell block is a MOS transistor having a positive threshold voltage in which electrons are injected into the floating gate, or electrons are emitted from the floating gate. Is it a MOS transistor with a negative threshold voltage?
Selected by bit check data.

In the above description, the address signal A
When 0 is "0", data is read from the memory cell in the left memory cell array 114, and when the address signal A0 is "1", data is read from the memory cell in the right memory cell array 113. However, the present invention is not limited to such an aspect, and the point is that when data is read from a certain memory cell block, the bit check data may be simultaneously read from the transistors having the bit check data corresponding to the memory cell block. Good.

Next, a case where data is read from the memory cell M1R will be described as an example with reference to FIG. At this time, the output signals Y2R, Y2L of the column decoder 116 are "1" and the other output signals Y1R, Y1L, YnR, YnL.
Are all "0". Therefore, the select gate CG2
R and CG2L are turned on. Also, the row decoder 11
5 output signals X1R and X1L are set to "1" level and X2
.., X2L, .. are set to the "0" level. As a result, the MOS transistors S2R, ..., S2L, ... To which the signals X2R ,. On the other hand, the MOS transistors S1R and S1L supplied with the signals X1R and X1L are turned on.
Bit check MOS transistor CT1R connected to selected memory cell MOS transistor M1R
The signal C1R for controlling the signal is at "1" level. A signal C1L for controlling the bit check MOS transistor CT1L corresponding to the memory cell MOS transistor M1R
Is a "0" level. Of the signals W11R to W18R,
Signal W11 for selecting MOS transistor M1R
Only R is "0" level, and other signals W12R to W18R
Are all "1" level. On the other hand, signals W11L to W18L that oppose these memory cell MOS transistors W11R to W11R with row decoder 115 interposed therebetween are all at "1" level. Therefore, in the memory cell array 113 on the right side, the storage data of the memory cell M1R whose gate is at “0” level is read out, and the sense amplifier 112 is read.
(3) detects this and outputs a "1" level. On the other hand, in the memory cell array 114 on the left side, data is read from the bit-check MOS transistor CT1L whose gate is at "0" level. At this time, since the bit-check MOS transistor has a positive threshold voltage, the sense amplifier 112 (2) detects this and outputs a "1" level. Therefore, the sense amplifier 112
Since the outputs of (2) and 112 (3) are both at "1" level, the output signal Z1 of the data determination circuit 117 ₁ is "1".
And the memory cell MOS transistor M1R
It can be seen that the stored data of "1" is "1".

FIG. 6 shows the signals X1R and C as described above.
1R, W11R to W18R, X1L, C1L, W11L
In the truth table of W18L to W18L, the above signals are generated from the address signals A0, A1, A2 and A3 in this example. That is, the circuit may be assembled so as to satisfy the truth table. Further, although a truth table for outputting the signals X1R, X2R, ... Is not shown, this is the same as the conventional one, and addresses such as address signals A4 and A5 are further added, and one of them is selected according to the memory cell capacity. One should be selected. Further, in FIG. 6 described above, one memory cell block is 8
In the case of being composed of memory cell MOS transistors, for example, in the case of being composed of 16 or 32 transistors, an address signal is added corresponding to this.
It should have the same function.

According to the first example described above, more than half of the memory cell MOS transistors forming one memory cell block can have a negative threshold voltage, so that a larger amount of current flows through the memory cell block than in the conventional case. Since the load MOS transistor L1 that can be set and has a large current driving capability can be used, the read can be performed at a higher speed.

Next, a second example similarly related to the present invention will be described with reference to FIG. In this example, one column line is commonly connected to two memory cell blocks. That is, the column line D1 is connected to the selection transistor T at the node N1.
1 (1), T2 (1); T1 (2), T2 (2) are connected to the memory cell blocks MB (1), MB (2). Further, the column line D2 is connected to the node N2 at the selection transistors T1 (3), T2 (3); T1 (4), T2.
Memory cell blocks MB (3), MB via (4)
It is connected to (4). Further, the other end of each memory cell block MB is connected to the reference potential via the transistor 10. When the signal S1 becomes logic "1", for example, the transistor T1 (1) is newly turned on, and the left memory cell bundles MB (1) and MB (2) are selected. The transistors T2 (1), T1 (2), T2 (3) and T1 (4) are
It is a depletion type and remains on even if the signal S1 or the signal S2 is a logic "0". Instead of these depletion type transistors, wiring such as a diffusion layer may simply be used.

Also in the second example, as in the conventional case, when data is programmed in the memory cell, as shown in FIG.
As can be seen from the above, first, all the row lines WL1 to WLn connected to the control gates of the memory cells are set to 0V, and the substrate is set to a high voltage to emit electrons from the floating gates of all the memory cells to the substrate. At the time of programming data to the memory cells, the signal φ is set to 0V to turn off the transistor 10 to disconnect the memory cell bundle from the reference potential, as in the conventional case. After that, the signals S1 and S2 supplied to the selection transistors T1 and T2 are both set to the high potential V1 (t1).
Further, all the row lines WL1 to WLn corresponding to the selected memory cell block are set to the potential V2. Then, the potential V3 is supplied to the column lines D1 and D2 to charge the memory cell block from the potential V3. After that, the signal S2 is set to 0V, and the selection transistor T2 which is not written is turned off (t2). That is, in FIG. 7A, when the memory cell blocks MB (2) and MB (4) on the right side are not programmed, the signal S2 is set to 0 V and the selection transistors T2 (2) and T2 (4) on the right side are set. Turn off.
Since the transistor 10 is also off, the potential V3 is applied to the memory cell blocks MB (2) and MB (4) on the right side.
The electric potential charged from is kept as it is. After that, the potentials of the column lines D1 and D2 are set to 0 V or the potential V3
Depending on the setting, programming is performed in the left memory cell blocks MB (1) and MB (3) as in the conventional case. Right memory cell block MB (2), MB (4)
Is charged from the potential V3, the potential difference between the floating gate and the substrate (channel) is not sufficient to cause a tunnel even if the row line WL is set to the high potential V1. , No electrons are injected into the floating gate. At time t2, the row line WLn becomes the high potential V1,
The unselected row line WL is set to a potential V2 lower than V1, the column line D1 is set to 0V, and the column line D2 is set to a potential V3. Therefore, the potential difference between the floating gate of only the memory cell Mn (1) and the substrate (channel) becomes a value sufficient to cause a tunnel, and electrons are injected from the substrate to the floating gate. Similarly, at time t3, the memory cell M2
At (1), at time t4, electrons are injected into the floating gate of the memory cell M1 (1).

As described above, according to the second example, the programming procedure peculiar to the second example is added, that is, two adjacent memory cell blocks are set to one.
Connected in common to two column lines, the non-selected memory cell block is charged from the potential V3 so that an electron tunnel does not occur between the floating gate and the substrate, and then the selection transistor of the non-selected memory cell block is Since a programming procedure has been added to turn off the memory cell block and keep the charge potential in the non-selected memory cell block, one column line can be shared by adjacent memory cell blocks. For this reason, the number of column lines can be halved as compared with the conventional case, and the area occupied by the memory cell array between the memory cell blocks adjacent to each other and the column line cannot be determined.

The potential of the column line does not have to be 0V as described above. In order to prevent the potential charged from the potential V3 from being discharged to the adjacent 0V column line through the parasitic field transistor, it is desirable to keep the potential at about 1V and 2V.

Next, examples of the present invention will be described.
In this embodiment, variations in the amount of electrons injected into the floating gate are suppressed.

Prior to the description of this embodiment, an outline of the present invention will be described.

The present invention achieves the above object by making the high voltage supplied to the control gate of the memory cell higher than the previous voltage value each time data is read for checking the threshold voltage of the memory cell. It was done. That is, as described above, due to variations in the manufacturing process,
The film pressure of the gate insulating film is not uniform and varies from memory cell to memory cell. Due to this variation, the amount of electrons injected into the floating gate varies. In order to make the threshold voltage of each memory cell equal, the voltage value applied to the row line (that is, the control gate of the memory cell) must be changed according to the variation of the gate insulating film. Conventionally, the same voltage is applied to the control gate and electrons are injected into all the memory cells, so that the threshold voltage of the memory cells varies. On the other hand, in the present invention, when injecting electrons into the floating gate of the memory cell, the row line is set to a high voltage and the column line connected to the memory cell to which the electron is to be injected is set to 0V. On the other hand, the column line to which the memory cell that does not inject electrons is connected to reduce the electric field between the floating gate and the channel to the extent that tunneling does not occur.
It is set to a predetermined voltage V3. In this way, the row line is set to a high voltage and each column line is set to 0 V or V3, and electrons are selectively injected into the floating gate of the memory cell for a predetermined period. After that, reading for checking is performed. When the threshold voltage of a memory cell reaches a predetermined value, the column line to which this memory cell is connected is set to another memory cell so that no more electrons are injected into this memory cell. The voltage is set to V3 when electrons are injected into the floating gate. In the reading for checking, similarly to the normal reading, it is sufficient to set the selected row line to 0 V and see whether the memory cell is turned off. After the reading for checking is completed, a high voltage of a voltage higher than that of the previous time is applied to the row line. This high voltage is, for example, 0.
A value as high as 5V or 1V is sufficient. Then, the column line to which the memory cell with insufficient electron injection is connected is set to 0 V to cause electron injection. Further, the column line to which the memory cells to which electrons are not desired to be injected are connected and the column line to which the memory cells to which electrons have been sufficiently injected are connected are set to the potential of V3, respectively, and electrons to the floating gate are set. Prevent injection. After the subsequent check reading, the row line is set to a higher voltage. After this, as above,
The column lines to which the memory cells with insufficient electron injection are connected are set to 0 V to inject electrons, and the column lines to which the memory cells to which electrons are not desired to be injected are connected and the electrons are sufficiently injected. The column line to which the memory cell being connected is connected is set to the potential of V3 to prevent injection of electrons into the floating gate. Such an operation is sequentially repeated, and the potential of the row line is increased each time. That is, in the case where the electron injection is completed by the check reading, the potential of the column line is raised so that the electron injection is not performed any more, and the electron injection is insufficient (such a gate insulating film is used). , Which may be made thicker), further raises the potential of the row line to inject electrons. In this way, the potential of the row line is sequentially increased to inject the electrons into the floating gate, so that the electrons can be injected into each memory cell at an almost optimal potential.

A circuit for generating the potential of the row line according to the present invention will be described with reference to FIG. FIG. 8A shows a potential generation circuit PG for generating the potential of the row line, and FIG. 8B shows a row decoder RD as an example. The row decoder RD receives the output VP 'of the potential generating circuit PG and outputs this VP' to the selected row line. Figure 8
The circuit PG in (a) has a predetermined potential due to resistance division.
Signals 1 to 1 are created step by step from low potential to high potential.
By sequentially setting 5 to logic "1", the potential VP 'is sequentially increased and output for each program. When the signals 1 to 5 are logic "1", the potential thereof is VP, and when the logic "0" is ground potential, that is, 0V.

That is, the potential generation circuit PG of FIG.
A resistor R, which is connected in series between the high-voltage side reference potential VP and the ground potential,
, And the transistor T10 are connected. Gates of the transistors T1 to T5 are connected to nodes N1 to N5, which are connection points of the two resistors R and R. One ends of these transistors T1 to T5 are connected to the high-voltage side reference potential V _p , and the other ends thereof are respectively transistors T11 to T55.
Via the output terminal OUT1 for outputting the potential VP '. Further, the power supply potential VC is connected to the output end OUT1 via the depletion type transistor T6.

Further, the row decoder RD in FIG.
Is a transistor T between the ground potential and the power supply potential VC.
21 to T24 are connected in series. Transistor T
Address A is added to the gates of 21 to T23. The gate of the transistor T24 is grounded. The gate of the node N10 between the transistors T24 and T23 is VC.
Via the transistor T25 connected to the node N1
1, that is, connected to the gates of the transistors T27 and T28. These transistors T27 and T28 are shown in FIG.
It is connected in series between the potential VP 'output from the circuit PG in (a) and the ground potential. The connection point (node N12) of these transistors T27 and T28 is the output terminal OU.
It is T2 and is connected to the row line. Further, the transistor T26 is connected between the potential VP 'and the node N11. The node N12 is connected to the gate of the transistor T26. Here, the transistors T24, T26, T27 are P-channel type.

When injecting electrons into the floating gate, the signal P
To logic "1" and the signal / P to logic "0". After that, the signals 1 to 5 sequentially become logic "1" and the potential VP 'is sequentially output for each program.

At the time of reading data for checking and at the time of normal reading, the signal P becomes a logic "0", the signal / P becomes a logic "1", and VC is output to VP '. 9 and 10 show a circuit for producing these signals 1 to 5, and FIG.
Is the signal waveform of each node in FIGS. 9 and 10. The circuit of FIG. 9 has a block B1 having three NOR circuits.
B2, ... Are connected in multiple stages in series. That is, in the block B1, the pair of NOR circuits NOR11 and N
The OR 12 has a flip-flop circuit in which the output terminals of one NOR circuit are connected to each other and one input terminal of the other NOR circuit. The signal P is applied to the other input end of the NOR circuit NOR11. The signal CL is applied to the other input end of the NOR circuit NOR12. NOR circuit N
The output of OR11 is applied to one input end of NOR circuit NOR1 and signal S2 is applied to the other input end of NOR circuit NOR1.
Is added. The block B1 is thus configured. The other blocks B2, B3, ... Have almost the same configuration. However, of the NOR circuits NOR1, NOR2, ...
The signal S2 is input to the odd-numbered ones, and the signal S1 is input to the even-numbered ones. Then, in connecting these blocks B1, B2, ... In series, in FIG.
Upper NOR circuits NOR1 and NOR in each block
The outputs of 2, ... Are added to the input ends of the NOR circuits NOR21, NOR31 ,. Then, the odd-numbered blocks B1,
Lower and middle NOR circuits NOR12, B3, ...
Are obtained from the NOR 32, ...; NOR 11, NOR 31 ,.

The circuit of FIG. 10 shows a circuit for producing the signal n from the signal n '. In this circuit, the input terminal (node N0) is connected to the gates of the P-channel type transistors T1 and T2. A series circuit of these transistors T1 and T2 and an N-channel type transistor T8 are connected between the power supply potential VC and the ground potential. The signal P is supplied to the gate of the transistor T8. A node N1 between the two transistors T1 and T2 is connected via an N-channel type transistor T4,
The node N2 is connected to the gates of the P-channel type transistor T6 and the N-channel type transistor T7.
The power supply potential VC is supplied to the gate of the transistor T4. The transistors T6 and T7 have a high-voltage power supply potential VP.
Is connected in series between the ground potential and the ground potential. The intermediate node N3 of the transistors T6 and T7 serves as an output terminal, and the signal n is output. A P-channel transistor T3 is connected between the power supply potential VC and the node N1, and a signal P is applied to its gate. Further, a P-channel type transistor T5 is connected between the high voltage side power source VP and the node N2, and its gate is connected to the node N3.

As can be seen from FIG. 11, when the injection of electrons into the floating gate is started, the signal CL becomes logic "1" (t1) and the flip-flop in the circuit of FIG. 9 is initialized. After that, the signal P becomes logic "1" (t2), and in response thereto, the signal S1 becomes logic "0" (t2). The signal 1'is made into a logic "1" by the signal P, and VP is outputted as the signal 1 having a logic "1" by the circuit shown in FIG. As described above, the circuit for outputting the signals 2 to 5 has the same configuration, and the input signals 2 ', 3', 4 ', 5'are set to 2,
Output as 3, 4, and 5. When the predetermined time has passed, the signal P becomes logic "0" (t3) and the injection of electrons into the floating gate is stopped. In response to the signal P becoming logic "0", the signal S2 becomes logic "0". Signal P is logic "0"
During the period (t3), the reading for checking the injection state of electrons into the floating gate is performed (t3).
3). As described above, the column line connected to the memory cell in which electrons are sufficiently injected is set to the potential of V3,
Prevent injection of electrons into the floating gate. In this example, the electrons are injected only once when the signals 1 to 4 become logic "1", but this may be repeated twice or three times. Is also good.

When the reading is completed and the column line connected to the memory cell in which electrons are sufficiently injected into the floating gate is set to the potential of V3, the signal P becomes logic "1" again (t4). . In response to this, the signal S1 becomes logic "0" and the signal 2'is made logic "1". With this,
Signal 2 is also set to logic "1", and VP 'is set to a value higher than the last time. After the lapse of the predetermined time, the signal P is set to the logic "0" (t5), and in response thereto, the signal S2 becomes the logic "0". After that, the column line connected to the memory cell in which the electrons have been sufficiently injected is set to the potential V3 again so that the electrons are not injected into the floating gate. This electron injection and the electron injection state check are repeated. Then, the signal 5 becomes a logic "1" V
When the potential of P'becomes the highest (t6), the signal 5'has the logic "1" until electrons are sufficiently injected into the floating gates of all the memory cells and the threshold voltage of the memory cells becomes a predetermined value. In this state, the electron injection and the electron injection state check are repeated. In the example of FIG. 11, the signal 5
Shows a logic "1" twice and electron injection is performed twice when VP 'has the highest potential.

When the threshold voltage of all the memory cells to be injected with electrons reaches a predetermined value, the electron injection and the reading for checking the electron injection amount are stopped, and the signal CL becomes logic "1" ( At t7), the flip-flop of the circuit of FIG. 9 is returned to the initial state.

As described above, according to the present embodiment, the value of the voltage for injecting electrons is gradually increased, and the injection amount of electrons is checked each time, and the voltage becomes the predetermined threshold voltage. Since we try to stop the injection of electrons in order,
It is possible to absorb variations in the gate insulating film thickness due to variations in the manufacturing process. As a result, each memory cell can be set to the optimum threshold voltage. Therefore, the variation in the threshold voltage of the memory cell after the injection of electrons is completed can be made smaller than before. Therefore, it is possible to provide a non-volatile semiconductor memory in which the reading speed is faster than in the past.

FIG. 12 shows another embodiment for generating the voltage VP 'according to the present invention. In this embodiment, signals 1 to
5 is input to the gate by N-channel type transistors T1 to T5 and the current ratio between the leak circuit LC, V
It determines the potential of P '. In this circuit, the transistor T1 is provided between the high voltage power supply potential VP and the common node N.
To T5, and an N-channel depletion type transistor T0 is connected between the power supply potential VC and the common node N. Signals 1 to 5 and / P are supplied to the gates of the transistors T1 to T5 and T0, respectively. A leak circuit LC is connected between the common node N and the ground potential. Then, the potential VP 'is taken out from this common node N.

In this circuit, the signals 1 to 5 sequentially become the logic "1". Therefore, the potential VP 'is lowest when the signal 1 is logic "1", and highest when all the signals 1 to 5 are logic "1". These signals 1-5 are
It is supplied from the circuits shown in FIGS. 9 and 10 described above.

In the above embodiments, five kinds of voltages for injecting electrons into the floating gate of the memory cell are set, and the voltages are sequentially increased. However, the number of types is not limited to five, and may be set to an optimum number according to the manufacturing process. The essence of the present invention is to sequentially increase the voltage at the time of injecting electrons, thereby injecting electrons at an optimum voltage for each memory cell, and the present invention is not limited to the circuit of the above embodiment. Not something.

Next, examples related to the present invention will be described.

This example relates to a flash EEPROM having a high read speed.

This example will be schematically described with reference to the drawings.

In this example, a high voltage is applied to the control gate and drain of the memory cell to cause a channel current to flow, thereby generating hot electrons and writing one of binary data. As compared with the conventional one in which electrons are extracted from the floating gate by the tunnel effect and one of binary data is written, the width of the variation in the threshold voltage of the memory cell is reduced and the read speed is faster. This is a flash EEPROM implementation.

In this example, the layout and circuit configuration of the memory cell array are such that data can be written in the memory cell even when the threshold voltage of the memory cell is negative.

That is, in this example, first, the control gate of the memory cell is set to 0 V, and a high voltage is applied to the drain of the memory cell or the semiconductor substrate on which the memory cell is formed. In this way, electrons are emitted from the floating gate to the drain or channel region by utilizing the tunnel effect. At this time, since the threshold voltage of the memory cells may be negative, electrons are emitted so that the threshold voltages of all the memory cells are negative. After that, a high voltage is applied to the row lines of the memory cells and the drains of a predetermined number of memory cells, a channel current is passed through the memory cells, electrons are injected from the channels to the floating gate, and one of binary data is Write in a cell. After that, the row line of the memory cell in which the data is written is set to a predetermined voltage value, and at the same time, the data is simultaneously read from the plurality of written memory cells. Repeat this data write and data read,
Writing is stopped when the memory cell reaches a predetermined threshold voltage. Generally, when a high voltage is applied to the drain and control gate to flow a channel current and electrons are injected from the channel to the floating gate, the threshold voltage of the memory cell after injection is the value of the voltage applied to the control gate. Proportional to.
That is, if the value of the voltage applied to the control gate is high, many electrons will be injected into the floating gate, and the threshold voltage after injection will be high. On the other hand, if the voltage applied to the control gate is lower than this value, the amount of electrons injected into the floating gate is small and the threshold voltage after injection is also low. In this example, the voltage applied to the control gate of the memory cell is set to a somewhat low value to inject electrons into the floating gate of the memory cell. Therefore, variations in the threshold voltage of the memory cell can be reduced, and the threshold voltage of the memory cell can be controlled to a small positive value. In addition, since the reading after the implantation is also performed for a small number of memory cells and the writing and reading are repeated in these memory cells, the variation in the threshold voltage between the memory cells can be further reduced. When the injection of electrons into the floating gates of all the memory cells is completed and the writing of one of the binary data described above is completed in all the memory cells, this time, a higher voltage is applied to the control gates to selectively perform the selective operation. A high voltage is applied to the drain to inject electrons into the floating gate to selectively write the other binary data. In this way, data is written corresponding to the binary data to be written in all the memory cells. The value of the threshold voltage of the memory cell after the first injection of electrons into the floating gate is such that the memory cell is turned off when the control gate is unselected at 0V and is in the selected state where about 5V is applied to the control gate. Is set to a value that will turn it on. The potential of the control gate at the time of the second electron injection is made higher than that at the first time, and the threshold voltage of the memory cell after the electron injection is raised to such an extent that it does not turn on when selected. In this way, one or the other of the binary data is stored depending on whether the memory cell is turned on when the memory cell is selected.

The above example will be described with reference to FIG. Figure 1
3 is an example of a memory cell array of the flash EEPROM of this example. 13A is a plan view and FIG. 13B is A-.
A'line sectional view, (c) is a BB 'line sectional view, (d) is C
A cross-sectional view taken along the line -C ', and (e) is a symbol view thereof. Figure 3
The same parts as those in No. 3 will be described with the same numbers. Reference numeral 1 forms a row line and a control gate of the memory cell. Reference numeral 2 is a floating gate, 3 is a channel region, and 4 is a gate insulating film.
5 is a column line made of aluminum, for example. A drain 6 shared by adjacent memory cells is connected to the column line 5. Reference numeral 8 is a wiring for supplying a reference potential (for example, ground potential) made of, for example, aluminum, which is connected to a source 7 of a memory cell shared by adjacent memory cells via a transistor 10 and a connection position 9. Connected by. Sb is a P-type semiconductor substrate.

In the example of such a configuration, since the source of the memory cell is connected to the reference potential via the transistor 10, even if the threshold voltage of the memory cell becomes negative, the column line The potential of does not decrease. When the electrons are injected into the memory cell in which the threshold voltage is negative due to the emission of electrons, the electrons are simultaneously injected into two adjacent memory cells with the source 7 of the memory cell interposed therebetween. Then, the wiring 8 is provided for each block of the memory cells into which electrons are simultaneously injected.
Is provided, and the block including the wiring 8 and the memory cell connected to the wiring 8 into which electrons are simultaneously injected is
The source region 7 is separated from the other blocks. Since the transistor 10 is off in the unselected block in which the row line is 0 V, even if the memory cell has a negative threshold voltage and is turned on, the unselected block set to the column line and the reference potential is unselected. No current path is created between the block and the wiring 8. Therefore, a current flows through the selected memory cell whose row line is set to a high voltage through the transistor 10 which is also turned on, and electrons are injected into the floating gate of the memory cell. That is, in the present invention,
Since electrons are simultaneously injected into the memory cells arranged adjacent to each other with the plurality of sources 7 sandwiched between them, only the transistors 10 corresponding to those which simultaneously inject electrons can be turned on. Only can be connected to the reference potential. As described above, the electrons can be simultaneously injected into the memory cells sandwiching the source, but the electrons can also be injected into the block of the memory cells connected to the same row corresponding to the transistor 10.

This example will be described in more detail with reference to FIG. FIG. 14 shows a memory device configured by using the memory block MB equivalent to that shown in FIG. This memory block MB has P surrounded by a chain line.
It is constructed on the well. A voltage is supplied to the P well from the terminal VE. This memory block MB
, WLn are connected to the row decoder RD. The memory cells in this memory block MB are divided into a plurality of blocks B1, B2, .... Each block B1, B2, ... Has a transistor array 100A, 100A ,. These transistor rows 100A, 100A, ... Are commonly connected to the reference potential VS. Each transistor row 100A has a plurality of transistors 100, 100, .... Column line 5 in each block B1, B2, ...
5, ... through the transistors 200, 201 ,.
Commonly connected to the node N1. These transistors 2
The output of the column decoder CD1 is connected to the gates of 00, 201, .... Further, the nodes N1, N1, ...
Through the transistors 300, 301, ...
Commonly connected to. The node N2 is connected to the load circuit / sense amplifier LCSA and the data input circuit DIN. Data D _in is added to the data input circuit DIN from the input terminal IN.

In the device of FIG. 14, when removing electrons from the floating gate of the memory cell, the row lines WL1 to WLn are set to 0.
The voltage is set to V, a high voltage is applied to VE, and the P well is set to a high voltage.
Along with this, the electrons stored in the floating gate of the memory cell are emitted from the floating gate toward the well. As a result, the threshold voltage of all memory cells becomes a negative value. Next, electrons are injected into the floating gates of the memory cells having these negative threshold voltages. This electron injection adjusts the value of the voltage supplied to the control gate to inject electrons into the floating gate so that the memory cells are turned off when the memory cell is not selected and turned on when the memory cell is selected. The reference potential VS is supplied to the memory cell via the transistor 100, and the reference potential supplied via the transistor 100 is shared. For example, the operations are simultaneously performed on the memory cells connected to the row lines WL1 and WL2. At this time, the transistors 200, 201, ..., 200m controlled by the column decoder CD1 are simultaneously turned on. The transistors 300, 301, 302, ... Controlled by the output of the column decoder CD2 are
Only one selected transistor of them is turned on and the remaining unselected transistors are turned off. In this way, in order to inject electrons into the floating gate of the memory cell, the drain of the target memory cell is
The high voltage from the data input circuit DIN is applied to the transistor 1
Is supplied to the selected one of the blocks B1, B2, ... Now, it is assumed that the block B1 is selected and the row lines WL1 and WL2 are selected and set to a high voltage. At this time, the transistors 100 (1) and 100 (2) connected to the row lines WL1 and WL2 are turned on, and the reference potential VS is applied to the row lines WL1 and WL1 via the turned-on transistors 100 (1) and 100 (2). It is supplied to the source of the memory cell connected to WL2. The high voltage output from the data input circuit DIN causes a current to flow from the data input circuit DIN to the transistor 300, the transistors 200, 201, ...
200m, memory cell, transistor 100 turned on
(1) and 100 (2) flow to the reference potential VS, and electrons are injected into the floating gate. The row lines WL1 and WL2 are
Since it is set to an appropriate high voltage, too many electrons are not injected into the floating gate, and the floating gate and the control gate are capacitively coupled, the floating gate and the drain are capacitively coupled,
Electrons are injected into the floating gate only up to a value determined by the capacitive coupling between the floating gate and the channel, the capacitive coupling between the floating gate and the source, and the potentials of the control gate and the drain. Therefore, this state may be continued for a long time until the electron injection is saturated, but in order to shorten the electron injection time at this time, the electron injection time is set short, and the electron injection amount is changed each time. If the check is performed and the injection of electrons is stopped when the injection amount becomes appropriate, there is an advantage that injection can be completed in a short time. In this check, the potentials of the two row lines into which electrons have been injected are set to a predetermined value lower than the potential to perform normal reading, and data is read from the memory cell and electrons are injected into the memory. It should be stopped when the cell turns off. This check is for multiple memory cells that have been injected with electrons.
The steps may be performed simultaneously, or may be performed for each memory cell.

Non-selected row lines such as WLn, WLn-1
Is set to 0V. Therefore, the transistors 100 (n) and 100 (n connected to the two row lines are connected.
-1) is off, and the sources of the memory cells connected to the row lines WLn and WLn-1 are separated from the reference potential VS. Therefore, there is no current outflow through the memory cells connected to the non-selected row line, and the drain potential of the selected memory cell does not drop. Therefore, electrons can be efficiently injected into the floating gate.

Further, in the example of FIG. 14, in each memory block B1, B2, ... Only one transistor 100 is provided for one row line. It is desirable to set the optimum number in consideration of the resistance on the source side of the cell. Similarly, in each memory block, the number of memory cells connected to one row line should be set to the number that allows the most efficient injection of electrons. However, in this case, in each memory block, if the number of memory cells connected to one row line is reduced, the efficiency of electron injection is improved, but on the other hand, the chip size is increased and the cost is increased. In consideration of cost, the number should be optimal.

As described above, it is not necessary to inject electrons into the memory cells related to two row lines at the same time, and only one row line is set to a high voltage to inject electrons into the memory cells related to one row line. You can go. For example, the row line WL1
Are selected and set to a high voltage, and the other unselected row lines WL
Assuming that 2, ..., WLn are 0V, no current flows out through the non-selected row lines other than the row line WL2 as described above. However, since the row line WL1 is set to the high voltage, the transistor 100 connected to the row line WL1 is on. Therefore, the reference potential VS is supplied to the sources of the memory cells connected to the row line WL1, and thus the reference potential VS is also supplied to the sources of the memory cells on the row line WL2. High voltage VE in P well
The threshold voltage of the memory cell has become negative after the electrons have been supplied and electrons have been emitted from the floating gate. From this,
A current flows to the reference potential VS through the memory cells connected to the row line WL2. However, when the row line WL2 is set to a high voltage and the two row lines are set to a high voltage at the same time to inject electrons, in this case, the row line WL2 is larger than the current flowing in the memory cell connected to the row line WL2. Is 0V, the current flowing through the memory cell connected to the row line WL2 to the reference potential VS is much smaller. Therefore, even if only one row line is set to a high voltage to inject electrons into the floating gate of the memory cell, there is no concern that the drain voltage of the memory cell will drop.

In this way, the threshold voltage of all memory cells is set to a value that turns off when not selected and turns on when selected, and after writing one of binary data, Selectively writes the other of the binary data to each of the memory cells to store the corresponding binary data in all the memory cells. At this time, the data is written in the same manner as in a well-known conventional NOR type EEPROM or ultraviolet erasing type ordinary EPROM. That is, one selected row line is set to a higher voltage, and the column decoder CD1 causes the transistor 20
One of 0, 201, ..., 200 m is turned on, and the column decoder CD2 causes the transistors 300, 301, 30 to be turned on.
One of 2, 2, ... Is turned on to select one column line. Then, a high voltage is applied to the control gate and drain of the memory cell arranged at the intersection of the selected row line and the selected column line, and electrons are further injected into the floating gate of the memory cell to select the selected gate line. The threshold voltage is increased until it turns off. In this way, the other of the binary data is selectively written in each memory cell. In this embodiment, the memory cell is formed on the P well, and the P well is set to a high voltage to emit electrons from the floating gate so that the threshold voltage of the memory cell becomes a negative value. Without using
Control gates of memory cells (ie row lines) as before
May be set to OV and a high voltage may be supplied to the drain (that is, the column line) of the memory cell so that electrons are emitted from the floating gate to the drain. Alternatively, the drain and source of the memory cell and the semiconductor substrate on which the memory cell is formed are set to OV, and a negative voltage is supplied from the row decoder to the row line which is the control gate of the memory cell, and the floating gate causes the memory cell to operate. Electrons may be emitted to the drain, the source, and the substrate, and various applications are possible.

FIGS. 15A and 15B are used when electrons are emitted from the floating gate of the memory cell described above.
Different circuit examples suitable for generating the voltage VE are shown. For example, by utilizing the tunnel effect through an extremely thin gate insulating film of about 100 Å,
When injecting or releasing electrons into the floating gate, it is necessary to apply an electric field that causes a tunnel effect to the gate insulating film. However, when a strong electric field is suddenly applied to the gate insulating film, It is known to accelerate deterioration. Therefore, when injecting electrons into the floating gate, it is necessary to gradually increase the voltage applied to the control gate. Further, even when electrons are emitted from the floating gate, it is necessary to gradually increase the voltage VE applied to the well. FIGS. 15A and 15B are examples of circuits that are optimal for use in generating the voltage VE as described above.

First, in FIG. 15A, a level shift circuit 500 having transistors T1 to T6 is connected to an input terminal IN to which a signal E is applied. This circuit 500 is based on the circuit diagram shown in FIG.
The circuit 500 having the same circuit configuration as that of the circuit in which T8 and T8 are removed is a circuit for level-shifting a signal of the power supply VC (for example, 5V) level to a signal of the high voltage VP level. The node N1 on the output side of the circuit 500 has an N-channel type transistor 402, a P-channel type transistor 403, and a P-channel type transistor 410,
The gate of the N-channel type transistor 411 is connected. The transistors 403 and 402 are connected in series between the high voltage VP and the ground potential. Transistor 4
The N-channel tepletion type transistor 40 is connected between the node N2 at the connection point of 03 and 402 and the high voltage VP.
1, P-channel type transistor 400 is connected in series. The gate of the transistor 401 is connected to the node N2. The gate of the transistor 400 is connected to the node N3 at the connection point of the transistors 401 and 400. This node N3 is a P-channel type transistor 4
It is connected to the gate of 05. This transistor 40
5 and the N-channel type transistor 406 are connected to the high voltage VP.
And ground potential are connected in series. On the other hand, the transistors 410 and 411 are connected in series between the high voltage VP and the ground potential. Transistors 410 and 41
Between the node N5, which is the connection point with 1, and the ground potential,
N-channel depression type transistor 407, N-channel transistor 408, N-channel transistor 40
9 are connected in series. Transistors 407 and 40
The gate of 8 is connected to a node N6 which is a connection point of those transistors. The node N6 is connected to the gate of the transistor 406. Further, the output terminal of the inverter I2 connected between the power supply VC and the ground potential is connected to the gate of the transistor 409. The output terminal of the inverter I1 connected between the power supply VC and the ground potential is connected to the input terminal of the inverter I2, and the input terminal of the inverter I1 is connected to the node N4.
The node N4 is a connection point between the transistors 405 and 406, and the voltage VE is output. When emitting electrons from the floating gate, the signal E supplied to the input terminal IN is set to logic "1". The signal E is level-shifted to a high voltage VP level signal by the circuit 500. That is, when the signal E becomes the logic "1", the node N1 becomes the level-shifted logic "1" and is output as the voltage VP. Therefore, the transistor 402 is turned on and the transistor 40
3 turns off. That is, the transistors 400 and 40
A current flows from the voltage VP to the ground potential through 1,402. This current value is determined by the depletion-type N-channel transistor 401, and the current flowing through the transistor 405 having the gate connected to the drain of the P-channel transistor 400 having the gate and drain connected is determined by the current flowing through the transistor 400. Be done. The transistor 400 and the transistor 405 form a current mirror circuit, and the current flowing through the transistor 405 is the same as the transistor 405 and the transistor 40.
It is determined according to the ratio of 0 transistor sizes. That is, the rate of increase in the potential of VE charged by the transistor 405 is adjusted by adjusting the current flowing through the transistor 401. Similarly, when discharging VE, the current flowing in the transistor 406 can be changed by adjusting the current flowing in the transistor 407, and thus the discharge speed of VE can be arbitrarily adjusted depending on the transistor size of the transistor 407. it can.

When the signal E becomes logic "0" and VE is discharged, the node N1 becomes logic "0", the transistor 411 is turned off, and the transistor 410 is turned on. V
When E is charged, this VE is the inverter I1.
Also, the signal is transmitted to the gate of the transistor 409 through the inverter I2 and the transistor 409 is turned on. As a result, a current path from the high voltage VP to the ground potential is formed through the transistors 410, 407, 408, 409. When VE is discharged below a predetermined potential, inverter I1 detects this and sets its output to logic "1".
Along with this, the inverter I2 outputs its output to logic "0".
Then, the transistor 409 is turned off. Therefore, VE
Is below a predetermined potential, the transistors 410, 40
There is no current path through 7, 408 and 409, the gate of transistor 406 is charged to VP and VE is discharged to ground potential through transistors 410 and 407.

When VP is a power supply supplied from the outside, the current supply capability is considered to be large. Therefore, even if a current flows through the transistors 410, 407, 408, 409, VP does not drop in potential. However, in the case of the type in which the high voltage VP is generated inside the chip by utilizing VC, the current supply capacity is small. Therefore, the current flowing through the current path causes a potential drop in VP, and there is a possibility that a sufficiently high voltage cannot be obtained.

Next, FIG. 15B shows an optimum VE for a type in which a high voltage is generated inside the chip and electrons are injected into and discharged from the floating gate by utilizing this high voltage. It is an example of a circuit for generating. The circuit of FIG. 15B is different from that of FIG.
0,401 is omitted, and the node N2 is directly connected to the transistor 40.
5 and the source of the transistor 410 is connected to VC instead of the power supply VP. The other configurations are the same. In this circuit, VP generated internally does not require adjustment of the potential rising speed by the transistors 400 and 401 shown in FIG. 15A because the voltage boosting speed by the internal boosted potential generating circuit is slow. Therefore, these transistors 400 and 401 could be omitted. Therefore, there is no current flow through these transistors. Further, in FIG. 15A, the source of the transistor 410 is connected to VP,
In (b), since this is changed to VC, the transistor 41
The current paths of 0, 407, 408, and 409 were between VC and the ground potential, and the current outflow path from VP disappeared. Therefore, it is possible to sufficiently use the internal high voltage generated by the voltage boosting circuit inside the chip.

FIG. 16 shows an example of the row decoder circuit. Transistors T0 to T4 are connected in series between the power supply SW and the ground potential. P-channel type transistor T0
The gate of is grounded. The address A is input to the gates of the N-channel type transistors T1 to T3. The signal / E is input to the gate of the N-channel type transistor T4. Node N1 at the connection point of transistors T0 and T1
Are connected to the respective gates of the P-channel type transistor T5 and the N-channel type transistor T6. These transistors T5 and T6 are connected between the power supply SW and the ground potential. A decode signal is output from the node N2 at the connection point of the transistors T5 and T6. signal/
E becomes logic "0" when electrons are emitted from the floating gate, and sets all the row lines WL to logic "0", that is, 0V.

FIG. 17 shows an example of a circuit for generating power SW of the row decoder circuit shown in FIG. FIG. 18 shows the signal waveform of each of these nodes.

As can be seen from FIG. 17, this circuit has resistors R1, R2 and N between the power supply potential VC and the ground potential.
The channel type transistor 707 is connected in series. The signal CE is applied to the gate of the transistor 707. Further, between the power supply potential VC and the ground potential, a P-channel type transistor 708, a P-channel type transistor 704, and an N-channel type transistor 705 are provided.
The N-channel depletion type transistor 703 is connected in series. The signal V is applied to the gate of the transistor 708. The gate of the transistor 704 is connected to the node N1 which is a connection point of the resistors R1 and R2. There is a signal at the gate of transistor 705
R is added. The gate of transistor 703 is connected to its source. Further, the power supply potential VC,
A P-channel type transistor 710 and N are provided between a node N2 which is a connection point of the transistors 704 and 705.
The channel depletion type transistor 711 is connected in series. These transistors 710,711
Signals / R and R are respectively supplied to the gate of. Further, between the high voltage power supply potential VP and the node N2,
N-channel type transistors 700 to 702 are connected. The signal W1 is supplied to the gate of the transistor 700. The gates of the transistors 701 and 702 are
Each is connected to its drain. Further, an N-channel type transistor 712 is connected between the high voltage power supply potential VP and the node N2, and a signal W2 is supplied to the gate thereof. Then, the power supply SW is obtained from the node N2.

As can be seen from FIG. 18, during the period T1 in which electrons are emitted from the floating gate of the memory cell, the signal / E is set to logic "0", the signal R is set to logic "1", and the signal / R is set.
Are respectively set to logic "0". At this time, power SW
The potential of VC appears at, and the row decoder circuit operates by this VC.

One of binary data is stored in all memory cells by injecting electrons into the floating gate to make a threshold voltage that turns off when the memory cell is not selected and turns on when the memory cell is selected. Signal / E to logic "1"
Signal W1 to logic "1", signal R to logic "0",
Signal / R is set to logic "1" respectively. This signal W
The potential corresponding to the logic "1" of 1 is VP or this V
It is higher than P by the threshold voltage of the N-channel enhancement type transistor. When the signal W1 is the potential of VP, the potential of the power supply SW is lower than VP by the sum of the threshold voltages of the N-channel enhancement type transistors 700, 701 and 702. This SW
Is set so as to satisfy the threshold voltage condition of the memory cell as described above. As described above, when the period is set to be short and the threshold voltage of the memory cell is checked and electrons are sequentially injected, the signal V is set to logic "1" (periods T3 and T5) and the signal W1 is set to logic "1". Return to 0 "and perform. The signal CE has a logic "1" when the chip is in the selected state, the gate potential of the transistor 704 is determined by the ratio of the resistors R1 and R2, and the potential of SW is the potential of the connection node N1 of the resistors R1 and R2. Is set to a potential lower than that by the threshold voltage of the N-channel enhancement type transistor. The potential SW is supplied to the control gate of the selected memory cell, and the memory cell turns off when the memory cell is turned off.

Further, the period T6 is a period in which electrons are injected into the floating gate of the memory cell and the voltage is raised to a threshold voltage that is turned off when selected. At this time, the signal W2
Is set to logic "1", that is, a value higher than VP by the threshold voltage of the N-channel enhancement type transistor. At this time, the potential of VP is output to SW as it is, and sufficient electrons are injected into the floating gate to be turned off when selected.

A period T7 indicates a normal read mode, the signal R is set to logic "1", the signal / R is set to logic "0", and VC is output to SW. In the periods T2 to T6, the signal / R becomes logic “1”, the transistor 705 in FIG. 17 is turned on, and SW is discharged through the transistor 703. These transistors 705, 70
3 is provided to prevent the SW from being in an electrically floating state, and can be omitted.

FIG. 19 shows a data input circuit D according to the present invention.
An example of IN is shown.

The input terminal IN to which the data D _in is input is connected to the gates of the P-channel type transistor 811 and the N-channel type 812. These transistors 81
1, 812 are connected in series between the power supply potential VC and the ground potential. These transistors 811 and 812
A node N1 which is a connection point of is connected to the gates of the P-channel type transistor 813 and the N-channel type transistor 814. These transistors 813, 81
4 and the N-channel type transistor 815 are connected to the power supply potential V
It is connected in series between C and the ground potential. The signal W1 is supplied to the gate of the transistor 815. A node N2 which is a connection point of the transistors 813 and 814
Is connected to the node N3 via the N-channel transistor 818. The gate of the transistor 818 is connected to the power supply potential VC. Power supply potential VC and node N2
, And a P-channel transistor 817 is connected between them and the signal W1 is supplied to the gate thereof. A P-channel transistor 819 is connected between the power supply potential VC and the node N3, and its gate is connected to the node N4. The node N3 is connected to the gates of the P-channel type transistor 821 and the N-channel type transistor 822, and these transistors 821 and 822 are connected in series between the power supply potential VP (or VC) and the ground potential. The connection point with these transistors 821 and 822 is connected to the node N4.

The node N1 has a P-channel type transistor 823 and an N-channel type transistor 824.
Is connected to the gate. These transistors 82
3, 824 and the N-channel type transistor 825 are connected in series between the power supply potential VC and the ground potential.
The signal W2 is supplied to the gate of the transistor 825. A node N7, which is a connection point of the transistors 823 and 824, is connected via an N-channel transistor 828.
It is connected to the node N8. The gate of the transistor 828 is connected to the power supply potential VC. Between the power supply potential VC and the node N7, P whose signal W2 is supplied to the gate
A channel type transistor 827 is connected. A P-channel transistor 829 is connected between the power supply potential VP (or VC) and the node N8. The node N9 is connected to the gate of the transistor 829. The node N8 is a P-channel transistor 831 and N
It is connected to the gate of the channel transistor 832. These transistors 831 and 832 are connected in series between the power supply potential VP (or VC) and the ground potential. The connection point of these transistors 831 and 832 is connected to the node N9. This node N9
It is connected to the gate of the N-channel type transistor 800. The transistor 800 is connected between the power supply potential VP (or VC) and the node N10. Further, an N-channel transistor 801 is connected between the power supply potential VP (or VC) and the node N10. The node N4 is connected to the gate of the transistor 801. The node N10 is the node N2 of FIG.
The data is transmitted from this node N10 to the memory cell.

In the above circuit, when electrons are injected into the floating gate, the potential of the floating gate may be lower than the potential of the control gate. Therefore, the voltage applied to the drain of the memory cell may be VC instead of VP. good. When injecting electrons into the floating gate and storing one of the binary data,
Since electrons are simultaneously injected into a plurality of memory cells, more current flows. Therefore, in this embodiment, when writing one of binary data and writing the other,
The transistor for applying a voltage to the drain of the memory cell is changed. That is, the current supply capacity of the transistor used when writing one of the binary data is made larger than the current supply capacity of the transistor used when writing the other of the binary data. More specifically, when a plurality of memory cells are selected and one of binary data is written, the input D _{in is set} to the logic “0” and the signal W is set to the signal W.
Set 1 to logical "1". At this time, the transistor 801
Is turned on, and a voltage is applied to the drain of the memory cell. Then, when writing the other binary data, the input D _{in is set} to logic “0” and the signal W2 is set to logic “1” to turn on the transistor 800 and apply a voltage to the drain of the memory cell. As described above, the current supply capacity of the transistor 801 is set larger than that of the transistor 800 so that the voltage of the drain of the memory cell can be kept sufficiently high when electrons are injected into the floating gates of the plurality of memory cells. I have to.

As described above, according to this example, electrons are emitted from the floating gate of the memory cell to make the threshold voltage of the memory cell negative, and then electrons are injected into the floating gate of the memory cell. Since the electrons are injected into the floating gates of all the memory cells to store one of the binary data, the width of the variation of the threshold voltage of the memory cells can be suppressed to a small level, and thus the read speed of the memory cells can be reduced. It has become possible to speed up.

Next, another example related to the present invention will be described. This example is configured to prevent an increase in chip size due to the provision of the latch circuit.

This example will be schematically described with reference to the drawings.

In this example, the data writing to the memory cell of the EEPROM as described above is carried out by utilizing the tunnel current, and when electrons are injected into the floating gate,
Alternatively, it is based on the fact that almost no current is consumed when electrons are emitted from the floating gate.

In the conventional EEPROM, as described above, the above-mentioned latch circuit is provided adjacent to the memory cell array. Therefore, each latch circuit has to be arranged at the pitch of the memory cells.
As a result, on the contrary, the pattern layout is restricted and the pattern area is increased. According to the fifth aspect of the present invention, the latch circuit is placed at a position apart from the memory cell array, so that the layout of the latch circuit can be freely set and the vacant place of the chip can be effectively used. This has made it possible to make the chip size smaller than before.

This example will be described with reference to FIG.

As can be seen from FIG. 20, a row decoder RD for selecting the row is connected to the memory cell array MCA. Each column line 15 of the memory cell array MCA
Are connected to the node N1 via the column gate transistors C1, C2, .... Each transistor C1, C
2, ... Decode signal h from the first column decoder CD1
ON / OFF control is selectively performed by 1, h2, .... The node N1 is connected to the load circuit LC via a transistor Q2 whose gate is supplied with the signal (R) / (/ P). The load circuit LC is connected to the sense amplifier SA. Further, the node N1 is connected to the node N2 via a transistor Q1 whose gate is supplied with a signal (/ R) / (P). At node N2,
Input data D _in is supplied via the latch circuits L, L, .... Decode signals h1 ', h2', ... And a signal P from the second column decoder CD2 are supplied to these latch circuits L, L ,. In this embodiment, the data to be written in the memory cell is latched by the latch circuits L, L, ... These latch circuits L, L are arranged in a place different from the memory cell array MCA.
The data to be written to the memory cells in the same row is latched at each address in the latch circuits L, L, ... Corresponding to the outputs h1 ', h2', ... Of the second column decoder. After this, the signal (/ R) / (P) is set to a high potential, and the transistor Q1
Turns on. The column gate transistors C1, C2, ... Are sequentially turned on by the output of the first column decoder CD1.
Then, the second column decoder CD2 causes the latch circuits L,
Control L, ... In this way, the data is transmitted from the latch circuits L, L, ... To the columns of each memory cell array. Each column line 15 has the data from the latch circuit L
It can be charged to a high voltage or discharged. Due to this charged potential, electrons are emitted from the floating gate of the memory cell. The charged potential is gradually discharged due to the leakage current of the P-N junction and the like, and the potential drops. Therefore, the first column decoder CD1
And the second column decoder CD2 causes the latch circuits L,
The data from L, ...
2, ... are sequentially turned on and transmitted to the corresponding column lines. With this configuration, it is not necessary to provide the latch circuit for each column adjacent to the memory cell array MCA, and the latch circuits L, L, ... Can be provided at arbitrary positions, and the latch circuit occupies the chip. The area can be reduced. The transistors Q1, Q2, C1 shown in FIG.
~ Cm is an N-channel type.

FIG. 23 shows the waveform of each signal. signal(/
R) / (P) is set to a high voltage (logic "1") when writing data (t1). Output h1 of the second column decoder CD2 ', h2', ......, when hm 'is logic "1", the input data D _in, latch circuits L, L, latch ... to (t2, t3, t4, ...). At this time, the gates of all memory cells (that is, V _CG ) are set to a high voltage, and electrons are injected into the floating gates of all memory cells (t1). After this injection, V _CG becomes 0
It is set to V to prepare for the next electron emission (t5). next,
The signals h1 ′, h2 ′, ..., hm, and the signals h1, h
2, ..., hm are sequentially set to high voltage (logic “1”),
When the signal P is logic "1", the latched data is transmitted to the corresponding column line (t2 ', t3', t4 '). The column line 15 is either set to a high voltage or remains at 0V depending on the latched data.
Electrons are emitted from the floating gate of the selected memory cell connected to the column line 15 set to a high voltage,
The selected memory cell connected to the 0V column line still has electrons injected into the floating gate. The data is written in this way.

FIG. 21 shows another embodiment of the fifth invention. This embodiment is different from that of FIG. 20 in that a capacitor C is connected to each column line 15 via an N-channel type transistor Q3, and is the same as FIG. 20 except for this point. . Signal / R / P is applied to the gate of transistor Q3.
Has been added.

When writing data, after the data from the latch circuit L is transmitted, the column gate transistors C1,
C2, ... turn off. As a result, each column line 15 is electrically floated. Therefore, the latch circuit L should be as long as possible.
A capacitor C is provided to hold the data transmitted from the. When reading data, use transistor Q3
Is trying to turn off. Therefore, the capacity C does not hinder the data reading speed.

FIG. 22 shows a modification of this example. FIG. 22
In the above example, the latch circuit is omitted from that of FIG.
In FIG. 20 and FIG. 21, the write data is once latched in the latch circuit L and then written. On the other hand, in the example of FIG. 22, the latch circuit L is not provided and the input data D _in is directly transmitted to each column line 15. That is, in order to write the data to the memory cells corresponding to each column, the input data is sequentially given to the column gate transistors C1, C2,
Are sequentially turned on to transmit data to the column line 15.

FIG. 24 shows the waveform of each signal of the nonvolatile semiconductor memory shown in FIG.

As can be seen from FIG. 24, the signal (/
R) / (P) is set to a high voltage (logic "1") when writing data, and the signal (R) / (/ P) is set to logic "0" (t1). Next, the gates of all the memory cells (that is, V _CG ) are set to a high voltage to inject electrons into the floating gates of all the memory cells. When this injection is completed, V _CG is set to 0 V to prepare for the next electron emission (t2). The signals h1, h2, ... The column line 15 is either set to a high voltage or remains at 0V depending on the input data. Electrons are emitted from the floating gate of the selected memory cell connected to the column line 15 set to a high voltage, and electrons are discharged to the floating gate of the selected memory cell connected to the 0V column line 15. Remains infused. The data is written in this way.

FIG. 25 shows still another modification of this example, in which the circuit CIR is added to the example of FIG. 22 without using the latch circuit L as in the example of FIG. .

That is, in FIG. 25, the circuit CIR includes a P-channel transistor 901 having a gate supplied with the signal / φ1 between the high-voltage power supply potential VP and the node N300.
Are connected. A series circuit of P-channel type transistor 902 and N-channel type transistor 903 and a series circuit of P-channel type transistor 904 and N-channel type transistor 905 are connected in parallel between node N300 and node N400. A transistor 907 whose signal φ1 is supplied to the gate is connected between the node N400 and the ground potential. Node N200
It is connected to the connection point of the transistors 902 and 903 and the gates of the transistors 904 and 905, respectively. The node N100 is connected to the connection point of the transistors 904 and 905 and the gates of the transistors 902 and 903, respectively. A P-channel type transistor 911 and an N-channel type transistor 912 are connected in parallel with each other between the nodes N100 and N200.
A signal / φ2 is applied to the gates of the transistors 911 and 912.
And the signal φ2 are respectively supplied. Node N10
0 is a connection point of the resistors R1 and R2 connected in series between the high-voltage power supply potential VP and the ground potential. Node N200
Is the output end of the data input circuit DIC.

In the example of FIG. 22, data must be input many times in order to prevent the potential drop due to the leak current of the column line 15 and the like, whereas in the example of FIG. 25, the circuit CIR is used. Is provided, the potential of the column line 15 is detected and amplified again. Therefore, you only have to enter the data once.

26 and 27 show the waveform of each signal. As in the case of FIG. 22, the signal (/ R) / (P) is set to a high voltage (logic “1”) when writing data, and the signal (R) / (/ P) is set to logic “0”. It is set (t1).
Next, the gates of all the memory cells, that is, V _CG are set to a high voltage to inject electrons into the floating gates of all the memory cells (t1). When this injection is completed, V _CG is set to 0 V to prepare for the next electron emission (t2). Column decoder C
The signals h1, h2, ..., hm from D1 are sequentially set to a high voltage (logic "1"), and the input data is transmitted to the corresponding column line (t3 to tm). The column line 15 is either set to a high voltage or remains at 0V depending on the input data. Electrons are emitted from the floating gate of the selected memory cell connected to the column line 15 set to a high voltage, and electrons are emitted from the floating gate of the selected memory cell connected to the 0V column line. It remains infused.

The circuit CIR includes nodes N100 and N100.
The potentials of 200 are compared, and the node N
It amplifies the potential of 200. The potential of the node N100 is obtained from the connection point between the resistors R1 and R2 and takes a value between the high potential level and the low potential level of the node N200. A kind of flip-flop FF composed of transistors 902 to 905 is connected between the node N100 and the node N200.
F amplifies the potential of the node N200. 27 is the same as FIG.
The signals φ1 and φ2 shown in FIG. 3 and the output h of the column decoder CD1
The relationship between 1 and h2 is enlarged for easier understanding and is shown together with the potential states of the nodes N100 and N200 and the column line 15. As shown in FIG. 27, when the signal φ2 becomes logic "1", the node N100 and the node N200 are connected.
Are connected, and the potentials of N100 and N200 become substantially equal (t11). After this, the column line CD 1
5 is selected and the potential of the selected column line 15 is the node N2.
Appears at 00. If the selected column line 15 is charged to a high potential, the potential of the node N200 rises (t1
2). After that, the signal φ1 is set to logic “1” to activate the flip-flop FF (t13). In the flip-flop FF, the potential of the node N200 is the node N100.
Since it is higher than the potential of the
And raises the voltage of the node N100 to almost 0V. on the other hand,
If the selected column line is 0V, the potential of the node N200 drops and becomes lower than the potential of the node N100 (t
14). Therefore, when the signal φ1 becomes the logic "1",
The flip-flop FF discharges the potential of the node N200 to 0V (t15). As described above, in the embodiment of FIG. 25, the column line 15 is selected, the potential of the selected column line 15 is monitored, and the potential is again amplified to the original potential. Therefore, the latch circuit L is not necessary. If there is a margin in chip size and if such a circuit CIR can be provided for each column line, all column lines can be amplified at the same time, and the column decoder does not need to control each column line.

As described above, according to the above example,
Paying attention to the fact that electrons are ejected and injected from the floating gate by the tunnel effect, and the fact that the memory cell portion consumes almost no current when programming data was used. The nonvolatile semiconductor memory can be provided at an arbitrary location, and thus a nonvolatile semiconductor memory with a reduced chip size can be provided.

Further, according to this example, the potential of the column line 15 is monitored, and this potential is amplified so that the potential of the column line 15 does not drop. Therefore, the latch circuit is not particularly required, and the chip size is further reduced. A small non-volatile semiconductor memory can be realized.

The present invention is not limited to the non-volatile semiconductor memory having the memory cells as described above, but may be any one as long as electrons are injected and emitted from the floating gate by utilizing the tunnel effect. But it can be applied. Since the present invention relates to control of a potential of a column line when writing data to a memory cell, regardless of a data writing method, the potential of the column line is used to emit electrons from a floating gate of the memory cell. Alternatively, as long as electrons are injected into the floating gate of the memory cell, any type can be applied. For example, if the memory cell is NAN
It goes without saying that it can also be applied to a D-type EEPROM. In this case, first, electrons are emitted from the floating gates of all the memory cells to set the threshold value of the memory cells to a negative value.
In addition, an appropriate voltage V3 that does not cause a tunnel effect is supplied to the column line for those that do not inject electrons. At this time, it is desirable that the power supplied to the flip-flop FF is also V3. If the method of applying the voltage to the column lines is variously changed in this way, it can be applied to any type.

[0111]

As described above, according to the present invention, the threshold voltage of each memory cell after the injection of electrons into the floating gate can be reduced in data programming, and the read speed can be increased. is there.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a main part of an example related to the present invention.

FIG. 2 is a chart showing various aspects in FIG.

FIG. 3 is a semiconductor memory device configured by using the circuit of FIG.

FIG. 4 is a truth table of the circuit shown in FIG.

5 is an explanatory diagram illustrating a read operation in FIG.

FIG. 6 is a truth table of various signals.

FIG. 7 is a circuit diagram and timing chart of a main part of an example related to the present invention.

FIG. 8 is a circuit and column decoder for generating a potential of a row line according to the embodiment of the present invention.

FIG. 9 is a circuit for producing signals n'and / n '.

FIG. 10 is a circuit for producing n from signals / n ′.

FIG. 11 is a signal waveform diagram of each node in FIGS. 9 and 10.

FIG. 12 is another circuit for generating the voltage VP ′.

FIG. 13 is a plan view of a main part of an example related to the present invention, A-
A'line sectional view, BB 'line sectional view, CC' line sectional view,
And symbol diagram.

FIG. 14 is a more detailed example using FIG.

FIG. 15 shows different examples of circuits that generate a voltage VE.

FIG. 16 shows an example of a circuit of a row decoder.

FIG. 17 is an example of a circuit that generates a power supply SW.

FIG. 18 is a signal waveform diagram in each node of FIGS.

FIG. 19 shows an example of a data input circuit.

FIG. 20 is an example related to the present invention.

FIG. 21 is another example related to the present invention.

FIG. 22 is yet another example relevant to the present invention.

FIG. 23 is a waveform diagram of each signal in FIG. 20.

FIG. 24 is a waveform chart of each signal in FIG. 22.

FIG. 25 is an example related to the present invention.

FIG. 26 is a waveform diagram of each signal in FIG. 25.

FIG. 27 is a waveform diagram of each signal in FIG. 25.

FIG. 28 is a cross-sectional view of a memory cell of a conventional NAND type EEPROM.

FIG. 29 is a circuit diagram of a main part of a NAND type EEPROM and a voltage waveform diagram of each node thereof.

FIG. 30 is an explanatory diagram for explaining reading of data from the NAND type EEPROM.

FIG. 31 is a timing chart thereof.

FIG. 32 is an explanatory diagram showing different threshold states of the memory cells of the NAND type EEPROM.

FIG. 33 is a plan view of a main part of a conventional EEPROM, A-
The sectional view along the line A ′, the sectional view along the line BB ′, and the sectional view along the line CC ′.

FIG. 34 is a symbol diagram of FIG. 33.

FIG. 35 is a memory cell of an EEPROM.

FIG. 36 is a characteristic diagram thereof.

37 is a circuit diagram of an essential part of an EEPROM using the memory cell of FIG. 35.

38 is a plan view and a cross-sectional view taken along the line AA ′ of FIG. 37.

FIG. 39 is a circuit diagram showing a portion of an EEPROM latch circuit.

[Explanation of symbols]

1 line 2 floating gate 3 channel area 4 Gate insulation film 5 column lines 6 drain 7 sources 8 wiring 9 Connection position 10 transistors 11 memory blocks 12 sense amplifier 14 memory cells 15 column lines 16 areas 17 Source Area 18 Drain / source region 19 drain region 20 floating gate 21 control gate 22 gates 23 Oxide film part 24 Contact part

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H01L 27/115 H01L 27/10 434 29/788 29/78 371 29/792 (56) Reference JP-A-5-182474 (JP , A) JP 5-144277 (JP, A) JP 5-28780 (JP, A) JP 62-24499 (JP, A) JP 1-159895 (JP, A) JP 63-153799 (JP, A) JP-A-2-23595 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11C 16/00-16/34

Claims (6)

(57) [Claims] 1. A memory cell having a floating gate and a control gate, and having a transistor for storing data according to a charge accumulation state of the floating gate, and having a threshold voltage which changes according to the amount of charge of the floating gate. Memory cells arranged in a matrix, row lines to which the transistors in the same row are connected, column lines to which the memory cells in the same column are connected, and a plurality of row lines connected to one of the row lines . Of the transistor
Program means for supplying a program voltage to the corresponding row line in order to program data into the memory cell by simultaneously injecting electrons into the floating gate of the transistor requiring injection of electrons. If the threshold voltage of the transistor after supplying the program voltage having a first voltage value to inject electrons into the floating gate of the transistor is lower than a predetermined value, the first voltage value is Supplying the program voltage having a second higher voltage value to inject electrons again into the floating gate of the transistor having a threshold voltage lower than the predetermined value, and having the second voltage value. When a program voltage is supplied to re-inject electrons into the floating gate of the transistor having a threshold voltage lower than the predetermined value, Electrons are injected into the floating gate of the transistor whose threshold voltage is higher than the predetermined value after the program voltage having the first voltage value is supplied to inject electrons into the floating gate of the transistor. And a transistor having a threshold voltage higher than the predetermined value after supplying the program voltage having the first voltage value and injecting electrons to the floating gate of the transistor, The non-volatile semiconductor memory is characterized in that the column line is set to a predetermined voltage. 2. A memory cell having a floating gate and a control gate, and having a transistor for storing data in accordance with a charge accumulation state of the floating gate and having a threshold voltage changing according to the amount of the charge of the floating gate. Memory cells arranged in a matrix, row lines to which the transistors in the same row are connected, column lines to which the memory cells in the same column are connected, and to inject electrons into the floating gate, By supplying a program voltage to a row line, a programming unit for programming desired data in the transistor forming the memory cell, and a programming voltage having a plurality of voltage values, the programming voltage being connected to the programming unit. Generating program voltage generating means, and the floating gate of the transistor forming the memory cell. In order to prevent the electrons are injected into the preparative, comprising a program inhibition means for setting said column lines to a voltage of a predetermined value, a plurality of said transistors connected to one of said row lines of
By injecting electrons into the floating gate of the transistor that needs electron injection at the same time, data is programmed in the memory cell, and when electrons are injected into the memory cell, the same as the memory cell. The corresponding column line is set to the voltage of the predetermined value by the program preventing means in order to prevent electrons from being injected into the memory cells connected to the row lines, which do not require the injection of electrons. And a program generated from the program voltage generating means
The plurality of voltage values of voltage are at least two voltage values.
The program voltage of the first voltage value is generated,
After the electron is injected into the transistor, the electron is injected
The threshold voltage of the transistor is lower than a predetermined value.
When it is lower than the program voltage of the first voltage value,
Before the program voltage of the second voltage value which is also higher
The threshold voltage is lower than the specified value.
When the electrons are injected, the threshold voltage becomes a predetermined value.
Connected to the same row line as the transistor whose value is lower than
In addition, the electrons with a threshold voltage higher than the predetermined value are injected.
Prevents injection of electrons into the inserted transistor
The corresponding column line to prevent the program
A non- volatile semiconductor memory in which the voltage is set to the predetermined value depending on the stage . 3. A memory cell which has a floating gate and a control gate, and which has a transistor for storing data according to a charge accumulation state of the floating gate and having a threshold voltage changing according to the amount of the charge of the floating gate. Memory cells arranged in a matrix, a row line to which the transistors in the same row are connected, a column line to which the memory cells in the same column are connected, and a plurality of row lines connected to one of the row lines . Of the transistor
Program means for supplying a program voltage to the corresponding row line in order to program data into the memory cell by simultaneously injecting electrons into the floating gate of the transistor requiring injection of electrons. , When injecting electrons into the floating gate of the transistor forming the first memory cell by supplying the program voltage, injecting electrons connected to the same row line as the first memory cell In order to prevent electrons from being injected into the unnecessary second memory cells, a column line to which the second memory cells are connected is set to a predetermined voltage,
When the threshold voltage of the transistor of the first memory cell after injecting the electrons is lower than a predetermined value,
Supplying the program voltage having a voltage higher than the program voltage to inject electrons again into the floating gate of the transistor forming the first memory cell;
When the program voltage having a voltage higher than the program voltage is supplied to inject electrons again into the floating gate of the transistor forming the first memory cell, the same voltage as that of the first memory cell is used. An electron is injected into the transistor forming the third memory cell, which has a threshold voltage higher than a predetermined value after the electrons are injected by supplying the program voltage to the row line. In order to prevent this, a non-volatile semiconductor memory is characterized in that a column line connected to the third memory cell is set to a predetermined voltage. Wherein said memory cell comprises a plurality of said transistor and the selection transistor, to claims 1 to 3 one end of the selection transistor is characterized in that it is adapted to be connected to the column line The nonvolatile semiconductor memory described. 5. A plurality of transistors, each of which has a floating gate and a control gate, stores data in accordance with a charge accumulation state of the floating gate, and whose threshold voltage changes according to the amount of the charge of the floating gate. A memory cell array in which memory cells, each of which is connected to and connected to one end of a transistor connected in series, and a selection transistor whose one end is connected, are arranged in a matrix; and a first row to which the transistors in the same row are connected. Line, a second row line connected to the selection transistor in the same row, a column line connected to the other end of the selection transistor in the same column, and connected to one of the first row lines A plurality of said transitions
In order to inject electrons into the floating gate of the transistor that needs to be injected with electrons, a program voltage is supplied to the first row line, so that the transistors forming the memory cell can be provided with a desired voltage. Program means for programming data, program voltage generating means connected to the program means for generating the program voltage having a plurality of voltage values, and the floating gate of the transistor forming the memory cell. In order to prevent electrons from being injected, a program preventing means for setting the column line to a voltage of a predetermined value is provided, and the injection of electrons connected to the first row line is required. Program data in the memory cell by simultaneously injecting electrons into the floating gate of the transistor and In order to prevent electrons from being injected into the transistor which is not required to be injected into the same row line as the transistor when electrons are injected into the transistor, the corresponding column A program generated by the program voltage generating means by setting a line to the predetermined value by the program preventing means.
The plurality of voltage values of voltage are at least two voltage values.
The program voltage of the first voltage value is generated,
After the electron is injected into the transistor, the electron is injected
The threshold voltage of the transistor is lower than a predetermined value.
When it is lower than the program voltage of the first voltage value,
Before the program voltage of the second voltage value which is also higher
The threshold voltage is lower than the specified value.
When the electrons are injected, the threshold voltage becomes a predetermined value.
Said first row line identical to said transistor lower than the value
Connected to, before the threshold voltage is higher than the specified value
Electrons are injected into the transistor that has been injected with electrons.
The corresponding column line to prevent the
The voltage of the predetermined value is set by the ram prevention means.
A non- volatile semiconductor memory characterized in that 6. The nonvolatile semiconductor memory according to claim 5 , wherein the injection of electrons into the floating gate is performed by utilizing a tunnel effect.