JP3737070B2 - Semiconductor memory device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor memory device, and more particularly, to an electrically erasable nonvolatile semiconductor memory device such as a flash memory.
[0002]
Conventionally, EPROM has been used as a nonvolatile semiconductor memory device that can be erased and electrically written by ultraviolet rays, and in recent years, flash memory has attracted attention as an electrically rewritable nonvolatile semiconductor memory device. There is a demand for improvements in redundant circuits and write circuits in these nonvolatile semiconductor memory devices, or measures for over-erasing.
[0003]
[Prior art]
FIG. 11 shows a memory cell (MC) used in the semiconductor memory device to which the first embodiment of the present invention is applied, and a cell transistor (memory cell MC) in the electrical batch erase nonvolatile semiconductor memory device (flash memory). It is a figure for demonstrating operation | movement of. As shown in the figure, the cell transistor includes a floating gate FG that is insulated between the source and drain regions, and a control gate CG formed on the floating gate FG.
[0004]
At the time of writing, the drain voltage Vd applied to the drain region DD is almost the power supply voltage Vcc, the gate voltage Vg applied to the control gate CG is a positive high voltage (about +10 volts), and the source voltage Vs applied to the source region SS. Is zero volts, electrons are injected from the drain terminal (DD) to the floating gate (FG), and data “0” is written. Here, if the power supply voltage Vpp for writing exists, the drain voltage Vd can be used. Further, as the high voltage applied to the gate voltage Vg, the above-mentioned write voltage Vpp may be used, or a voltage generated by boosting from the power supply voltage Vcc may be used.
[0005]
At the time of erasing, the gate voltage Vg is set to a negative high voltage (about −10 volts), the drain voltage Vd is opened (the drain region DD is in a floating state), the source voltage Vs is set to the power supply voltage Vcc, and the floating gate (FG ) To the source terminal (SS) to remove electrons (write data “1”). Further, at the time of reading, the data written in the cell transistor depending on whether or not the drain current flows with the gate voltage Vg as the power supply voltage Vcc, the drain voltage Vd as approximately 1 volt, and the source voltage Vs as 0 volt. Is “1” or “0”.
[0006]
FIG. 2 is a block circuit diagram showing an example of a related-art semiconductor memory device corresponding to the first embodiment of the semiconductor memory device according to the present invention. In the figure, reference numeral 111 is a row address buffer, 112 is a row decoder, 113 is a column address buffer, 114 is a column decoder, 115 is a data I / O buffer, 116 is a write circuit, 117 is a sense amplifier, and 118 is a negative voltage. A generation circuit and 119 indicate a source power supply circuit. Reference symbol BL indicates a bit line, WL indicates a word line, W indicates a write control signal that is at a high level “H” during writing, and E indicates an erase control signal that is at a high level “H” during erasing. Yes.
[0007]
In the semiconductor memory device shown in FIG. 2, at the time of reading, one word line WL and one bit line BL are selected by a row address and a column address, respectively, and a memory cell MC (cell transistor) selected by the sense amplifier 117 is a current. Whether the data written in the selected cell transistor is data “1” or data “0” is determined and output.
[0008]
At the time of data writing, the write control signal W is set to the high level “H”, the write voltage is supplied from the write circuit 116 to the bus line BUS, the bus decoder BUS is connected to the predetermined bit line BL by the column decoder 114, and the row decoder 112 supplies a write voltage to the word line WL. At the time of erasing, the erasing control signal E is set to the high level “H”, the erasing voltage is applied to the source line of the cell transistor MC by the source power supply circuit 119, and the bit line BL is deselected by the column address buffer 113. . Further, a predetermined number of word lines WL are simultaneously selected by the row address buffer 111, a low level “L” is applied to the word lines WL selected by the row decoder 112, and a high level is applied to WL for unselected word lines. A level “H” is applied, and the negative voltage generation circuit 118 sets the low-level “L” level word line WL to a negative voltage.
[0009]
3 is a circuit diagram showing an example of the column address buffer 113 in the semiconductor memory device of FIG. 2, FIG. 4 is a circuit diagram showing an example of the row address buffer 111, FIG. 5 is a circuit diagram showing an example of the row decoder 112, and FIG. 6 is a circuit diagram showing an example of the column decoder 114.
[0010]
First, since the erase control signal E is at a low level “L” at the time of reading, the column address buffer 113 shown in FIG. 3 and the row address buffer 111 shown in FIG. 4 output positive and negative logic with respect to the input address. Will do. In the row decoder 112 shown in FIG. 5, the reference symbol φ is a signal that has an amplitude at a predetermined frequency during erasing and writing, and φ_R Is a signal that is at a high level “H” for a while when an address is input.
[0011]
In the row decoder 112 shown in FIG. 5, since the write control signal W is at the low level “L” at the time of reading, the transistor T₁, T₂ The power supply voltage Vcc is introduced by the above and a predetermined decoder is selected by the address input (output from the row address buffer 111) (for example, the node N in FIG. 5)._Three Becomes high level “H”). In this state, the signal φ_R When a high level “H” pulse signal is applied to the node N,₂, N_Four Is reset to zero volts and the signal φ_R Node N in response to the return to low level "L"₂ Is charged to the power supply voltage Vcc. In addition, transistor T₆, T₇ Node N due to the self-bootstrap effect of_Four Is also charged to the power supply voltage Vcc level. Here, the operation of the column decoder 114 is the same as that of the row decoder 112 described above. As a result, the power supply voltage Vcc is applied to the predetermined word line WL, and the predetermined bit line BL is connected to the sense amplifier 117. It is supposed to be.
[0012]
FIG. 7 is a circuit diagram showing an example of the write circuit 116 in the semiconductor memory device of FIG. 2, and FIG. 8 is a circuit diagram showing an example of the source power supply circuit 119.
[0013]
In the write circuit 116 shown in FIG. 7, when the write control signal W is at the high level “H” and the data is at the low level “L” (the inverted level signal / DATA is at the high level “H”), the bus line BUS A high voltage obtained by boosting the voltage Vcc is supplied, so that a write process can be performed on a predetermined cell transistor. Here, / DATA is a signal transferred from the data I / O buffer 115 to the write circuit 116 as a write signal.
[0014]
At the time of erasing, the erasing control signal E is at the high level “H”, and both the outputs A and / A are at the low level “L” in the column address buffer 113 of FIG. These outputs A and / A are input to the column decoder 114, the column (bit line BL) is deselected, and the bit line BL is electrically disconnected from any node. The row address buffer 111 is configured to apply the erase control signal E to m out of n in total. As a result, 2^m The word lines can be simultaneously selected by the row decoder 112 of FIG. In the row decoder 112, since the erase control signal E is at the high level “H”, the node N₂ Becomes zero volts and node N_Five A high level “H” is applied to. As a result, the low level “L” can be applied to the selected word line WL, and the high level “H” can be applied to the non-selected word line WL.
[0015]
Here, the low-level "L" word line WL is set to the erase voltage by the negative voltage generation circuit 118, and the high-level "H" word line WL is the output N of the NOR gate in FIG.₆ Is always at a low level “L”, and the signal φ becomes the node N₆ Since the signal is not transmitted to the capacitor connected to, the high level “H” is maintained. At this time, the power source voltage Vcc is applied to the source SS of the cell transistor MC by the source power source circuit 119 shown in FIG. As a result, 2^m It becomes possible to simultaneously erase the data of the cell transistors in the word line block in units of one word line.
[0016]
FIG. 9 is a circuit diagram showing an example of the sense amplifier 117 in the semiconductor memory device of FIG.
[0017]
In the sense amplifier 117 shown in FIG. 9, the drain current of the selected cell transistor MC is the transistor T₈ The output of the sense amplifier 117 is set to a high level “H” or a low level “L” depending on whether it is larger or smaller than the current that can flow. Here, the transistor T₉, T_Ten, T₁₁, T₁₂Constitutes a bias circuit for setting the potential of the bus line BUS to about 1 volt.
[0018]
At the time of writing, the write control signal W is set to the high level “H”, and the signal φ is amplified at a predetermined frequency. At this time, the node N₁ The transistor T_Four, T_Five Thus, the write voltage is supplied. And the signal φ_R When a high level “H” pulse is applied in the same manner as in reading by, node N₂ Is charged to the write voltage and the node N_Four Also transistor T₆, T₇ Node N due to self-bootstrap effect by₂ Is charged to the same level. The operation is the same in the column decoder 114. As a result, the write voltage is supplied to the predetermined word line WL and the bit line BL is connected to the write circuit 116.
[0019]
[Problems to be solved by the invention]
As described with reference to FIGS. 2 to 9, in a semiconductor memory device (flash memory) as a related technique, an erase cell block is usually usually in units of a large capacity of about 512 kbit, If there is a defective cell in this block, only a redundancy system can be used in which this large block is replaced with a redundant cell block having a large capacity as it is. Therefore, it is difficult to carry out efficient redundancy (replace many defective cells with few spare cells). Specifically, for example, the memory cell MC in FIG.₁₁If the memory cell MC is overerased,₁₁Via the bit line BL₁ Current always flows, and accurate read processing and write processing cannot be performed.
[0020]
FIG. 10 is a diagram showing an example of a write characteristic curve in a semiconductor memory device (flash memory).
[0021]
In the configuration of the semiconductor memory device according to the related art described above, since the write drain voltage is boosted from the power supply voltage Vcc, a large current is passed through the bit line due to the limit of the driving capability of the write circuit to the bit line. The bit line potential is lowered. Depending on the characteristics of the cell transistor that has been over-erased, as shown by the solid line in FIG. 10, the writing characteristic curve of the cell transistor collides with the load curve of the writing circuit 116 and the area A where writing cannot be performed. It is conceivable that the situation becomes impossible (writing is not possible unless points D to B). The word line voltage for erasure and write verification is generally used by stepping down the external write voltage. However, in this configuration, since the external write voltage is not used, the verify operation can be performed. It is difficult, and even if a cell transistor that has been over-erased in the case of word line redundancy is simply replaced with a spare cell (spare word line), normal operation of the device cannot be expected. In this case, rewriting to the cell that has been over-erased eliminates over-erasing and normal redundancy operation can be realized. However, the over-erased cell has a larger current near the point A in FIG. For this reason, writing can be more difficult for the above reason.
[0022]
  An object of the present invention (fifth embodiment of the present invention) is to accurately read data even if there is a cell transistor that has caused excessive erasure.The
[0023]
[Means for Solving the Problems]
  According to the present invention, a plurality of word lines, a plurality of bit lines, and a threshold value from the outside depending on the presence or absence of charge injection to the floating gate provided at each word line and each bit line intersection. And a memory cell array having a plurality of memory cell transistors composed of MIS transistors capable of controlling the voltage, and a semiconductor that can simultaneously erase charges by simultaneously discharging charges from the floating gates of the plurality of memory cell transistors of the memory cell array It is a storage device, usually for the selected word line when readingA first row decoder that selects a memory cell transistor connected to the selected word line, and a power supply voltage of a predetermined potential to the source of the memory cell transistor connected to the selected word line In addition, a voltage for applying a non-selected state to the sources of all the memory cell transistors connected to the non-selected word line at the time of reading, including the memory cell transistors that have been over-erased by the batch erase, is applied. 2 row decoders, wherein the memory cell transistors are composed of enhancement-type N-channel MIS transistors, and the second row decoder is lower than the source of the memory cell transistors connected to the selected word line. Apply the power supply voltage of the potential to the source of all memory cell transistors connected to the unselected word line. And to apply a level above the voltage of the selected bit line with respect to the scanA semiconductor memory device is provided.
[0025]
FIG. 1 is a circuit diagram showing one embodiment of a first mode of a semiconductor memory device according to the present invention.
[0026]
According to the first aspect of the present invention, a plurality of 2ⁿ A plurality of non-volatile elements each composed of a word line WL, a plurality of bit lines BL, and MIS transistors that are respectively provided at intersections of the word lines and the bit lines and that can electrically control the threshold voltage from the outside. Memory cell MC, a write circuit 106 for writing data to the memory cell located at the intersection of the selected word line and bit line, and a sense amplifier 107 for detecting and outputting the data held in the memory cell. A semiconductor memory device, whereinⁿ 2 of the word lines^m Means 101, 102, 120 for simultaneously selecting word lines in a word line block composed of word lines (n> m);^m 2 in a word line block composed of two word lines^k Means (101), (102), (120) for deselecting a word line block composed of books (m> k),^m 2 in a word line block^k If a word line in a word line block is defective, the 2^m 2 in a word line block^k The word line in the word line block is not selected and the 2ⁿ 2 existing outside the word line block composed of books^k There is provided a semiconductor memory device characterized by selecting 101, 102, 120; 120, 130 for selecting a word line in a word line block constituted by a single word line.
[0027]
According to the first embodiment of the semiconductor memory device of the present invention, 2^m 2 in a word line block^k 2 if the word line in the word line block is defective.^m 2 in a word line block^k The word line in the word line block is not selected and 2ⁿ 2 existing outside the word line block composed of books^k A word line in a word line block composed of word lines is selected. Here, for the writing process, the gate voltage is controlled so that the writing curve of the cell is realized so as not to exceed the current value of the load curve of the writing circuit as shown by the dotted line in FIG. That's fine. As for verification, the word line voltage is generated by raising and lowering Vcc, or the data determination current value of the sense amplifier is controlled. Furthermore, in order to provide redundancy relief for an over-erased cell, redundancy is performed after data is written again to the over-erased cell.
[0028]
As described above, according to the first embodiment of the semiconductor memory device of the present invention, efficient word line redundancy is possible, and even when the external write power supply is eliminated (for example, a single 5 volt power supply). You can write effectively. Furthermore, according to the first embodiment of the semiconductor memory device of the present invention, it is possible to write in the over-erased cell, the redundancy of the over-erased cell is possible, and the verify can be performed well.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a semiconductor memory device according to the present invention will be described below with reference to the drawings.
[0030]
First, a first embodiment of a semiconductor memory device according to the present invention will be described with reference to FIGS. 1 and 11 to 19.
[0031]
FIG. 1 is a block circuit diagram showing an embodiment of a first embodiment of a semiconductor memory device (flash memory) according to the present invention. As is apparent from FIG. 1, the semiconductor memory device of this embodiment is different from the semiconductor memory device of the related art shown in FIG. 2 in that a matching circuit 120 for comparing an input address and a defective address and a redundant row decoder 130 are provided. It has been added. Here, the row address buffer 101, the row decoder 102, the column address buffer 103, the column decoder 104, the data I / O buffer 105, the write circuit 106, the sense amplifier 107, the negative voltage generation circuit 108, in the semiconductor memory device of this embodiment. The source power supply circuit 109 includes a row address buffer 111, a row decoder 112, a column address buffer 113, a column decoder 114, a data I / O buffer 115, a write circuit 116, and a sense amplifier 117 in the related art semiconductor memory device of FIG. , Corresponding to the negative voltage generation circuit 118 and the source power supply circuit 119.
[0032]
The operation in this embodiment will be described. First, at the time of reading and at the time of writing, if the defective address stored in the coincidence circuit 120 matches the input address, the output signal from the coincidence circuit 120 is the row address buffer. 101 and the redundant row decoder 130 are input, the row decoder 102 is set in a non-selected state, and the redundant row decoder 130 is set in a selected state. Thereby, a redundant cell can be accessed instead of accessing a defective cell. At the time of erasing, the erasing control signal E becomes high level “H” and is input to the column address buffer 103, the row address buffer 101, the row decoder 102, the coincidence circuit 120, and the redundant row decoder 130.
[0033]
First, when there is no defective cell transistor (defective cell) in the cell array (when there is no redundancy), the same operation as described above is performed. That is, the redundancy control signal RED from the coincidence circuit 120 has a logic that does not cause any circuit to redundantly operate.
[0034]
Next, consider a case where a defective cell exists on a certain lead wire and the address of the defective cell is stored in the matching circuit 120. In this embodiment, the total number of word lines is 2ⁿ The size of the erase block is 2^m It consists of two word lines and 2^k A configuration having a spare word line is taken as an example. Considering the time of writing and the time of reading, the required number of bits of the memory element for storing defective addresses in the coincidence circuit 120 is nk, and the number of word lines in the erase block is 2.^m Since this is a book, in order to select an erase block, the number of bits of nm addresses is required. At the time of erasure^m In order to select a word line block constituted by books, nm word line block selection addresses are input. This input address is compared with the mn higher-order addresses among the nk address bits stored in the coincidence circuit 120, and if this input address is stored with the nm addresses stored therein. If they match, it contains 2 defects^k Indicates that a word line block is present in the erase block.
[0035]
2 above^m 2 in the word line block composed of books^k The address information indicating the word line block constituted by the book is indicated by the remaining bits indicated by m−k of the address information stored in the matching circuit 120. That is, the semiconductor memory device of this embodiment is designated by m−k addresses 2^m 2 in a word line block^k The word line block constituted by the book is deselected by the row decoder 102, and when the mn addresses coincide with each other, the redundant row decoder 130 is selected at the time of erasure by selecting 2^m 2 of the erase blocks composed of books^k Erase redundancy of the word line block configured in units of this unit can be performed.
[0036]
12 is a circuit diagram showing an example of the row address buffer 101 in the semiconductor memory device of FIG. 1, FIG. 13 is a circuit diagram showing an example of a main part of the row decoder 102, and FIG. 14 is a circuit showing an example of the coincidence circuit 120. FIG.
[0037]
As shown in FIG. 12, the erase control signal E is inputted to the lower m of the n row address buffers 101 as a whole.^m All the word lines are selected at the time of erasing. Here, the redundancy control signal RED is input to any one of the m address buffers, so that when the redundancy control signal RED is at the high level “H” at the time of writing and reading (defects) The word line WL is deselected (when the address matches the input address).
[0038]
Here, the redundancy control signal RED is an output signal of the coincidence circuit 120 shown in FIG.^k 2 word line blocksⁿ An address storage fuse necessary for selecting from the word lines and a fuse (RUSE) for storing a redundant use signal are provided. Since the erase control signal E is at the low level “L” except at the time of erasing, the redundancy control signal RED does not become the high level “H” unless the information of all the fuses matches the input address. , Address A_RBm +1 to A_RBn The redundancy control signal RED is set to the high level “H” only by matching (that is, the upper nm addresses). Address A_{RBk + 1} ~ A_RBm The data of the fuse (m−k addresses) is taken out directly and inputted to the NAND gate shown in FIG. 2^m 2 of the word lines in the book^k A block composed of one word line can be deselected. At the same time, the redundancy control signal RED is input to the redundancy row decoder 2 to select the spare word line.^m 2 in an erase block composed of one word line^k Arbitrary word line blocks composed of books can be made redundant.
[0039]
By the way, in a flash memory, the yield is often lowered due to a defect due to excessive erasure. In the configuration of the semiconductor memory device described above, since the bit line is common to the spare cell and the real cell, redundancy cannot be repaired only by replacing the overerased cell with the spare cell. Specifically, for example, in FIG. 11, a memory cell (cell transistor) MC₁₁Is an overerased cell, the overerased cell MC₁₁Redundant cell MCR₁₁Word line WL₁ Overerased cell MC even if low level is low₁₁Since the current flows, this bit line BL₁ This is because the cell data (data “0”) existing above cannot be read normally. However, this problem can be easily solved by writing data “0” in the cell before redundancy of the overerased cell, that is, injecting electrons into the floating gate and then performing redundancy.
[0040]
In the over-erased cell, since the floating gate is positively charged, the current at point A further increases in the cell writing characteristic curve shown in FIG. 10, and writing cannot be performed. In order to solve this, it is necessary to control the gate level at the time of writing so that the current of the cell transistor near the point A does not exceed the load curve of the writing circuit 106. This can be easily achieved by operating the word line WL in a continuous pulse shape at the time of writing. That is, when the word line WL is operated in a continuous pulse manner, the word line WL is changed from the low level “L” to the high level “H” or from the high level “H” in the write characteristic curve of FIG. During the transition to the level “L”, the curve C (characteristic curve indicated by the broken line in FIG. 10) can always be realized, and writing is possible regardless of the state of the floating gate.
[0041]
FIG. 15 is a circuit diagram showing a main part of an example of the row decoder 102 in the semiconductor memory device of FIG. 1, and corresponds to the input portion B in the row decoder 112 of the related-art semiconductor memory device described with reference to FIG. It is a figure which shows a circuit structure. Here, the signal φW supplied to the input of the NOR gate of FIG. 15 has a pulse-like waveform shown in FIG. As a result, the node N in FIG.₂ Can be continuously amplified between zero volt and the write potential, and a continuous pulse can be applied to the word line WL. Here, the writing process and the erasing process are generally performed while verifying, and these verifying is generally performed by applying a verify voltage to the word line and reading the data. It is. The verify voltage is desirably constant even if the ambient environment of the device changes (power supply voltage etc.) changes. For this purpose, the verify voltage is generated by boosting with reference to the reference potential (Vss) of the device. Is effective. In addition to applying a pulse, a circuit that generates an intermediate voltage for the word line may be used.
[0042]
FIG. 17 is a circuit diagram showing an example of verify voltage generating circuit 150 in the semiconductor memory device of FIG. 1, and a node N in row decoder circuit 112 (102) shown in FIG.₁ This is a circuit for generating a verify voltage to be applied to.
[0043]
As shown in FIG. 17, the verify voltage generation circuit 150 includes a clamp circuit 151, an oscillation circuit 152, and a booster circuit 153. In the clamp circuit 151, the transistor T₁₃, T₁₄Is a circuit for determining a clamp voltage, and P-channel and N-channel MOS transistors are diode-connected in series. Here, in the CMOS process, since each channel region is created in the same process, the threshold shift in each transistor is complementarily canceled, and as a result, a stable clamp voltage can be obtained.
[0044]
Transistor T₁₅Is an N-channel MOS transistor having a threshold value of ~ 0 volts and supplies a clamp voltage to the oscillation circuit 152. Further, the booster circuit 153 operates with reference to the low power supply voltage (ground voltage) Vss, whereby the verify voltage (node N₁ Can be a stable value regardless of the power supply voltage. Further, the erase verify and the write verify have different voltage values. This is because the number of transistors of the clamp circuit 151 (T₁₃, T₁₄;)) Can be changed to easily generate a clamp voltage of a predetermined potential. Here, reference sign V_R Is a signal that is at a high level “H” during verification. Each verify can also be realized by changing the judgment current of the sense amplifier.
[0045]
FIG. 18 is a circuit diagram showing an example of the sense amplifier 107 in the semiconductor memory device of FIG. As shown in the figure, the sense amplifier 107 is a P-channel type transistor T as a load transistor._L1, T_L2It has. Here, the current supply capacity of each transistor is T_L1> T_L2Are in a relationship. There are three read modes for the flash memory: erase verify, normal read, and write verify. The size of the load transistor (total) in these three modes requires a relationship of erase verify> normal read> write verify. Note that the above relationship in the circuit of FIG._R1= V_R2= "L", normal read: V_R1= "L", V_R2= "H", write verify: V_R1= "H", V_R2= “L”.
[0046]
FIG. 19 shows the control signal V supplied to the sense amplifier of FIG._R1, V_R2It is a circuit diagram which shows an example of the logic circuit which produces this. In the figure, reference numeral Wv indicates a write verify signal, and Ev indicates an erase verify signal. When this configuration is adopted, there is an advantage that the power supply circuit of the row decoder necessary for generating the verify voltage can be simplified. As described above, according to this configuration, it is possible to apply to the erase verify in the flash memory by adding the logic circuit for load control.
[0047]
Next, a second embodiment of the semiconductor memory device according to the present invention will be described with reference to FIGS.
[0048]
FIG. 20 is a block circuit diagram showing an example of the redundant circuit 210 in the conventional semiconductor memory device corresponding to the second embodiment of the semiconductor memory device according to the present invention. In the figure, reference numeral 211 denotes a fuse, which is an element for storing a defective address (defective address designating means), and stores a high level “H” or a low level “L” depending on whether or not it is disconnected. It is supposed to let you. Reference numeral 214 indicates an address comparison circuit for comparing and determining whether the information in the fuse 211 matches the external input address. If they match, for example, the address match signal is set to a high level “H”. It is like that.
[0049]
FIG. 21 is a diagram showing a configuration example of the conventional redundant circuit shown in FIG. In the configuration example of the redundant circuit 2100 shown in the figure, a plurality of redundant circuits 210 shown in FIG. 20 are provided, and their outputs are output via a NAND gate and an inverter to generate a redundant signal. Only when each input address matches the information of the fuse (211) in all the redundant circuits 210, the redundant signal is set to the high level “H” and the data of the redundant cell is read out.
[0050]
FIG. 22 is a block diagram showing an example of a semiconductor memory device using the conventional redundant circuit 2100 shown in FIG. In the configuration diagram of the entire semiconductor memory device shown in the figure, when a redundant signal is output from the redundant circuit 2100, the real cell selection circuit 217 prohibits the reading of the real cell 218, and the redundant cell selection circuit 215 reads the redundant cell 216 instead. Done. As a result, the defective real cell portion is replaced with a redundant cell. Here, in FIG. 22, reference numeral 219 indicates a data read circuit for reading data of a selected cell transistor (memory cell) of the redundant cell 216 or the real cell 218.
[0051]
In the conventional method described above, one address comparison circuit is required for each fuse. Therefore, in order to replace a large number of defective portions, as many fuses and address comparison circuits as the number of replacements are required. As a result, the conventional redundant circuit increases the chip area and increases the cost.
[0052]
As described above, in the conventional redundancy system in the semiconductor memory device, there is a problem to be solved that the chip area increases when the number of replacements increases due to an increase in the number of circuits and also leads to an increase in cost.
[0053]
FIG. 23 is a block circuit diagram showing one embodiment of the redundant circuit in the second mode of the semiconductor memory device according to the present invention. As can be seen from the figure, in the redundant circuit 200 of this embodiment, the transistor T2 is used as the fuse 211 in the redundant circuit 210 of FIG._A And fuse 201A and transistor T_B And fuse 201B are provided, and fuses 201A and 201B are selected by the logic of external input address An (/ An: inverted signal of address An). Here, the address An (/ An) indicates an upper address indicating a block selection address for selecting a real cell divided into a plurality of blocks. As described above, according to the redundant circuit 200 of this embodiment, by sharing one address comparison circuit 214 with the two fuses 201A and 201B, the number of the address comparison circuits 214 as a whole can be reduced, and the chip area can be reduced. The increase and cost increase are suppressed.
[0054]
FIG. 24 is a diagram showing the configuration of the real cell 208 and the redundant cell 206 in the semiconductor memory device to which the redundant circuit of the present invention shown in FIG. 23 is applied. As shown in the figure, the real cell 208 includes, for example, a first real cell block 208A in which a block selection address An is selected at a low level “L”, and a block selection address An in a high level “H” (/ An comprises a second real cell block 208B selected at a low level "L"). The redundant cell 206 also includes, for example, a first redundant cell block 206A for making the first real cell block 208A redundant and a second redundant cell block 206B for making the second real cell block 208B redundant. It is comprised by. As a result, an address common to the divided real cell blocks 206A and 206B (for example, A_n-1, A_n-2..) Includes a defective cell, a predetermined range of the real cell including the defect is replaced with a redundant cell in the block designated by the logic of the block address An.
[0055]
FIG. 25 is a block diagram showing an example of a semiconductor memory device using the redundant circuit of the present invention shown in FIG. In the configuration diagram of the entire semiconductor memory device shown in the figure, when a redundant signal is output from the redundant circuit 200, the real cell selection circuit 207 prohibits the reading of the real cell 208, and the redundant cell selection circuit 205 reads the redundant cell 206 instead. Done. Here, as is clear from the comparison of the block diagrams of the semiconductor memory devices of FIGS. 22 and 24, in the semiconductor memory device of this embodiment, the address input (block selection address An) is also supplied to the redundant cell selection circuit 205. The redundant cells 206A and 206B corresponding to the fuses 201A and 201B selected by the logic of the address An in the redundant circuit 200 are selected. That is, the redundant cell selection circuit 205 receives the block address An and selects the redundant cells 206A and 206B corresponding to the real cell blocks 208A and 208B selected by the block address An to perform the redundancy processing. ing. In FIG. 24, reference numeral 209 indicates a data read circuit for reading data of a selected cell (memory cell) of the redundant cell 206 or the real cell 208.
[0056]
As described above, by using the address comparison circuit 204 in common for the plurality of redundant cells 206A and 20B, the defective real cell portion can be replaced with a redundant cell as in the conventional semiconductor memory device shown in FIG. it can. Here, in the above description, the 1-bit block selection address An is configured to select one of the real cells divided into two. For example, the 2-bit block selection address An, A_n-1 In this case, one of the real cells divided into four may be selected and one of the redundant cells divided into four may be selected.
[0057]
FIG. 26 is a block circuit diagram showing another embodiment 200 ′ of the redundant circuit in the second mode of the semiconductor memory device according to the present invention. In the figure, reference numeral 220 is a cell selection circuit, 221 and 223 are redundant information storage cell arrays, and 222 and 224 are readout circuits.
[0058]
As shown in FIG. 26, the redundant circuit 200 ′ of this embodiment includes two sets of redundant information storage cell arrays 221 and 223 and read circuits 222 and 224.
[0059]
The redundant information storage cell arrays 221 and 223 are composed of, for example, a plurality of nonvolatile memory cell transistors such as EPROMs, and are used to write data to defective addresses in external input addresses. The cell selection circuit 220 selects the redundant information storage cell arrays 221 and 223 by address input. The outputs of the readout circuits 222 and 224 are output as four redundant signals via AND gates 225A, 225B, 225C and 225D and inverters 226A and 226B. In this embodiment, data is read in parallel from the two redundant information storage cell arrays 221 and 223 in two bits, so that four defective portions can be replaced with redundant cells. However, it is needless to say that data of 3 bits or more can be read in parallel.
[0060]
27 is a block circuit diagram showing still another embodiment 200 "of the redundant circuit in the second mode of the semiconductor memory device according to the present invention, and FIG. 28 is a semiconductor using the redundant circuit of the present invention shown in FIG. It is a block diagram which shows an example of a memory | storage device.
[0061]
In the redundant circuit 200 ′ shown in FIG. 26, a method of reading a plurality of bits (2 bits) in parallel is shown. However, only a single bit can be read and a plurality of defective portions in the real cell 208 can be replaced with the redundant cell 206.
[0062]
In the redundant circuit 200 "shown in FIG. 27, a single bit is read by an address input and a redundant signal is output by its logic. FIG. 28 uses the redundant circuit 200" shown in FIG. 1 shows a configuration of a semiconductor memory device. Here, the redundant cell selection circuit 205 ′ and the real cell selection circuit 207 ′ are supplied with a redundancy signal from the redundancy circuit 200 ″ and a part of the address input (real cell block selection address An). Thereby, it is determined which redundant cell is used for redundancy of the real cell among the plurality of redundant cells.
[0063]
Next, a third embodiment of the semiconductor memory device according to the present invention will be described with reference to FIGS.
[0064]
By the way, in recent years, there has been proposed a nonvolatile semiconductor memory device capable of electrically writing / erasing information, particularly a so-called flash memory having a mode in which writing or erasing is automatically performed by an internal algorithm. .
[0065]
In such a flash memory, writing (or erasing) is performed by first applying a writing pulse and then performing reading processing (verification). If the reading processing does not reach a sufficient writing depth, writing is performed again. A method of repeatedly applying a pulse is applied. The maximum number of times of application of the write pulse (number of verifications) is defined in the specification, and this control is all controlled from the outside.
[0066]
Also, recent flash memories have been proposed that automatically write or erase data with this algorithm inside. In this automatic writing or erasing method, the maximum writing (erasing) time is presented to the user.
[0067]
However, for example, in a semiconductor memory device (flash memory) shipping test, the maximum time alone cannot guarantee the deterioration of the number of rewrites due to an increase in the number of rewrites, and the semiconductor memory device that has passed the shipping test becomes defective on the user side. There is a possibility that.
[0068]
Therefore, in the third embodiment of the semiconductor memory device according to the present invention, in addition to the maximum number of times on the user side, the maximum number of times expecting an increase in the rewrite time due to deterioration during a test on the manufacturing side (for example, a shipping test). The purpose of this is to guarantee the maximum number of times on the user side.
[0069]
FIG. 29 is a flowchart showing an example of an internal write algorithm as a basis in the third embodiment of the semiconductor memory device according to the present invention.
[0070]
First, when the write process is started, a write pulse is applied in step S301, and the process further proceeds to step S302 to perform verification. That is, in step S302, it is determined whether reading has been performed and a sufficient writing depth has been reached. If it is determined in step S302 that the sufficient writing depth has been reached, the writing process ends. If it is determined that the sufficient writing depth has not been reached, the process proceeds to step S303, where the pulse It is determined whether the number of times has reached N. That is, in step S303, it is determined whether or not the number of verifications has reached a predetermined N. If N has not been reached, the processing in steps 301 and S302 is repeated, and if N has been reached, Writing fails. That is, even if the write pulse is applied N times, sufficient write processing cannot be performed on the cell transistor.
[0071]
In the third embodiment of the present invention, for example, the shipping test is performed with the maximum number of application times of the write pulse being less than the normal N, and the shipping test is performed under conditions stricter than usual. . As described above, according to the third aspect of the present invention, the maximum number N on the user side is guaranteed by performing the shipping test with the maximum number n (n <N) in which the rewriting time is expected to increase due to deterioration. be able to.
[0072]
FIG. 30 is a block diagram showing one embodiment of the third mode of the semiconductor memory device of the present invention. In the figure, reference numeral 311 indicates a write control circuit, 312 indicates a write pulse generation circuit, 313 indicates a cell array, 314 indicates a pulse counter, 315 indicates a switch unit, 316 indicates a stop signal generation circuit, and 317 indicates a high voltage detection circuit. ing.
[0073]
The write control circuit 311 receives an external control signal and a write stop signal, and controls the write pulse generation circuit 312 to perform write processing to each cell transistor of the cell array 313. The output (write pulse) of the write pulse generation circuit 312 is supplied to the cell array 313 and also supplied to the pulse counter 314 to count the number of applied write pulses (the number of verifications). Note that the pulse counter 314 is pre-fabricated in advance with wiring that directly inputs to the input of the NAND circuit and wiring of the output of the inverter so that the count number can be easily added. The wiring may be selectively connected.
[0074]
The switch unit 315 is configured to switch between the normal maximum pulse application number N and, for example, the maximum pulse application number n (n> N) at the time of a shipping test. The write stop signal WS is supplied to the write control circuit 311 in accordance with the maximum number of applied pulses N or n. Here, the switching operation of the switch unit 315 is performed according to a switch control signal SC that is output by detecting whether or not an external high voltage is applied from the high voltage detection circuit 317.
[0075]
FIG. 31 is a diagram showing a circuit example of a main part in the semiconductor memory device of FIG. 30, and FIG. 32 is a timing diagram for explaining the operation of the circuit of FIG. Here, in FIGS. 31 and 32, reference numeral QC0i represents the output of the number of stages of the pulse count.
[0076]
As shown in FIG. 31 and FIG. 32, the stop signal WS (N) corresponding to the normal maximum pulse application number N is generated from the pulse count outputs QCO2, QCO3, QCO4. The stop signal WS (n) corresponding to the number of pulse applications n is generated from the pulse count outputs QCO0, QCO1, QCO2. Here, when the output (switch control signal) SC of the high voltage detection circuit (EWCMGN) 317 is at the low level “L”, that is, when the high voltage is not applied, the stop corresponding to the normal maximum pulse application frequency N The signal WS (N) is output at the 21st timing of the pulse signal QCO0. On the contrary, when the output SC of the high voltage detection circuit 317 is at a high level “H”, that is, when a high voltage is applied to a predetermined terminal, for example, it corresponds to the maximum pulse application number n at the time of a shipping test. The stop signal WS (n) to be output is output at the fourth timing of the pulse signal QCO0.
[0077]
In the above description, for example, the number of application of the write pulse until the stop signal WS is output is configured to be changed between the normal time (when used by the user) and the shipping test. Instead, the pulse width of the write pulse may be changed. That is, for example, at the time of a shipping test, the pulse width of the write pulse may be shortened so as to be stricter than usual. Also in this case, for example, the pulse width of the write pulse during the shipping test may be shortened by detecting application of a high voltage to a predetermined terminal. Further, although the above description has been given of the writing process, the same applies to the erasing process.
[0078]
As described above, according to the third embodiment of the semiconductor memory device of the present invention, for example, a semiconductor memory device that has passed a shipment test can be obtained by varying the allowable value for writing or erasing information with respect to the memory cell in the internal algorithm. Can be prevented from becoming defective on the user side.
[0079]
Next, a fourth embodiment of the semiconductor memory device according to the present invention will be described with reference to FIGS.
[0080]
FIG. 33 shows a memory cell (MC in the fourth embodiment of the semiconductor memory device according to the present invention.₀), And a cell transistor (memory cell MC) in an electrically erasable nonvolatile semiconductor memory device (flash memory)₀It is a figure for demonstrating operation | movement of (). As shown in the figure, the cell transistor includes a floating gate FG that is insulated between the source and drain regions, and a control gate CG formed on the floating gate FG.
[0081]
First, at the time of reading, the gate voltage Vg is set to the power supply voltage Vcc, the drain voltage Vd is set to about 1 volt, and the source voltage Vs is set to the ground level Vss. It is determined whether the data is “1” or “0”.
[0082]
At the time of writing, the drain voltage Vd applied to the drain region DD is set to a high voltage (usually Vcc <high voltage <Vpp), and the gate voltage Vg applied to the control gate CG is set to a writing voltage Vpp (about +10 volts). The source voltage Vs applied to the source region SS is set to the ground level Vss, and electrons are injected from the drain terminal (DD) to the floating gate (FG) to write data “0”. Here, with the recent decrease in the write voltage, the need to efficiently apply the write voltage to the drain terminal is increasing.
[0083]
FIG. 34 is a block circuit diagram showing an example of a semiconductor memory device (flash memory) as a related technique corresponding to the fourth embodiment of the semiconductor memory device of the present invention. In the figure, reference numeral 411 is a row address buffer, 412 is a row decoder, 413 is a column address buffer, 414 is a column decoder, 415 is a buffer circuit, 416 is a write voltage supply transistor, 417 is a sense amplifier, and 418 is A bus line is shown. Reference numeral BL indicates a bit line, WL indicates a word line, / WD indicates write data (inversion level), and W indicates a write control signal.
[0084]
In the semiconductor memory device shown in FIG. 34, at the time of reading, one word line WL and one bit line BL are selected by the row address and the column address, respectively, and the selected memory cell MC is selected by the sense amplifier 417.₀Whether the content written in the selected cell transistor is data “1” or data “0” is determined depending on whether or not (cell transistor) flows current.
[0085]
At the time of data writing, the selection signal for each word line and bit line is set to the write voltage Vpp by the write control signal W. At this time, when write data / WD is input, the transistor 416 is turned on and the bus line 418 (cell transistor MC₀ A write voltage Vpp (a voltage lower by the threshold voltage of the transistor 416) is applied to the drain terminal). Here, in the flash memory (semiconductor memory device) shown in FIG. 34, for example, a sufficiently high voltage can be used as the write voltage Vpp, so that the write voltage supply transistor 416 is an N-channel MOS transistor. It could be composed of transistors. That is, when an N-channel MOS transistor is used as the write voltage supply transistor 416, the write voltage Vpp becomes lower by the threshold voltage of the N-channel MOS transistor and the cell transistor MC₀ To be applied to the drain of each other.
[0086]
By the way, in recent years, even when a flash memory is used, for example, it is necessary to lower the voltage for writing in response to a request for a single power source of 5 volts. Thus, for example, when the flash memory is driven by a single 5 volt power supply, the threshold voltage of the write voltage supply transistor 416 causes the supply voltage to be lower than the write voltage Vpp, resulting in an efficient write voltage. Supply to the drain terminal becomes difficult.
[0087]
According to a fourth embodiment of the semiconductor memory device of the present invention, good data can be written even when the write voltage is lowered by preventing the write drain voltage from being lowered by the threshold voltage in the write voltage supply transistor. It aims to be realized.
[0088]
FIG. 35 is a block circuit diagram showing one embodiment of the fourth mode of the semiconductor memory device of the present invention. As apparent from the comparison with the related-art semiconductor memory device shown in FIG. 34, in the semiconductor memory device of the present embodiment, the write voltage supply transistor is composed of a P-channel MOS transistor 406 and the buffer circuit 405 includes The write data to be supplied is a positive logic signal WD. Here, the row address buffer 401, row decoder 402, column address buffer 403, column decoder 404, and buffer circuit 405 of this embodiment shown in FIG. 35 are the same as the row address buffer 411 and row decoder of the related art shown in FIG. 412, column address buffer 413, column decoder 414, and buffer circuit 415. Reference numeral BL indicates a bit line, WL indicates a word line, and W indicates a write control signal.
[0089]
In the semiconductor memory device shown in FIG. 35, at the time of reading, one word line WL and one bit line BL are selected by the row address and the column address, respectively, and the selected memory cell MC is selected by the sense amplifier 407.₀Whether the content written in the selected cell transistor is data “1” or data “0” is determined depending on whether or not (cell transistor) flows current.
[0090]
At the time of data writing, the selection signal for each word line and bit line is set to the write voltage Vpp by the write control signal W. At this time, the write data WD is converted by the buffer circuit 405 into a signal at the level of the write voltage Vpp. When the gate signal of the write voltage supply transistor 406 becomes low level “L”, the transistor 406 is turned on and the write voltage Vpp is supplied to the bus line 408. Here, in the flash memory (semiconductor memory device) of this embodiment shown in FIG. 35, the write voltage supply transistor 406 is composed of a P-channel MOS transistor, so that the write applied to the source of the transistor 406 The voltage Vpp can be raised to the vicinity of the write voltage Vpp without being dropped by the threshold voltage of the transistor 406, and the cell transistor MC₀ The write voltage Vpp can be efficiently applied to the drain terminal. Therefore, for example, even when the flash memory is used with a single power source of 5 volts, it is possible to effectively perform data write processing using the write voltage Vpp whose voltage has been lowered.
[0091]
FIG. 36 is a circuit diagram showing the main part of another embodiment of the fourth aspect of the semiconductor memory device of the present invention, corresponding to the write voltage supply transistor and buffer circuit in the semiconductor memory device of the related art shown in FIG. It is a circuit diagram which shows the part to perform.
[0092]
As shown in FIG. 36, in this embodiment, the write voltage supply transistor 426 is composed of an N-channel MOS transistor, as in the related-art semiconductor memory device shown in FIG. However, the buffer circuit 417 in the semiconductor memory device of the related art shown in FIG. 34 is configured by a bootstrap circuit including N-channel MOS transistors 4251, 4252, 4253, inverters 4255, 4256, 4257, and a capacitor 4253. ing. Here, in the bootstrap circuit shown in FIG. 36, when the write data WD changes from the high level “H” to the low level “L”, the gate of the transistor 4251 becomes the high level “H”, and then the gate of the transistor 4252 Node N by going to low level “L”₄₀The potential increases. At this time, the gate of the transistor 4251 is further boosted by the capacitor 4253, and finally rises to a level of about Vpp + Vcc. When this potential is applied to the gate of the write voltage supply transistor 426, the potential of the bus line (418) rises to almost the write voltage Vpp.
[0093]
As a result, a data signal boosted to the write voltage Vpp or higher is applied to the gate of the write voltage supply transistor 426 composed of an N-channel MOS transistor, and the same voltage as the write voltage Vpp is applied to the bus line. Data writing processing can be effectively performed using the voltage Vpp for writing that has been lowered by supplying a voltage.
[0094]
As described above, according to the fourth embodiment of the semiconductor memory device of the present invention, it is possible to reduce the write voltage by preventing the write drain voltage from being lowered by the threshold voltage in the write voltage supply transistor. Data writing can be realized.
[0095]
Next, a fifth embodiment of the semiconductor memory device according to the present invention will be described with reference to FIGS.
[0096]
FIG. 37 is a block circuit diagram showing an example of a conventional semiconductor memory device (flash memory) corresponding to the fifth embodiment of the semiconductor memory device according to the present invention. In the figure, reference numeral 512 indicates a row decoder, 514 indicates a column decoder, 517 indicates a sense amplifier, and 519 indicates a source power supply circuit. Reference symbol MC denotes a memory cell transistor (memory cell) formed of an N-channel MIS transistor, WL denotes a word line, BL denotes a bit line, and SL denotes a source line. Here, the source power supply circuit 519 is connected to the source of each memory cell transistor in the memory cell array via the source line SL, and can be electrically erased collectively. The memory cell MC is the same as that shown in FIG.
[0097]
FIG. 38 is a circuit diagram showing the configuration of the row decoder 512 in the semiconductor memory device of FIG. 37, FIG. 39 is a circuit diagram showing the configuration of the column decoder 514, and FIG. 40 shows the configuration of the bit line transfer gate 5145 in the column decoder 514. FIG.
[0098]
As shown in FIG. 38, the row decoder 512 includes a power supply circuit 5121, a gate RG to which a row address is supplied.₁ ~ RGn, the gate RG₁ Transistors 5122, provided between RGn and power supply circuit 5121, and an inverter for controlling the level of word line WL provided between power supply circuit 5121 and low potential power supply Vss (ground level GND: 0 volts) Transistors 5123 and 5124) are provided. As a result, for example, all the input row addresses become high level “H” and the gate RG₁ The output (Vcc) of the power supply circuit 5121 is applied to the word line (selected word line) WL corresponding to the address to which RGn is turned on via the transistor 5123, and the transistor 5124 is applied to the other non-selected word lines WL. A low potential voltage (Vss: 0 volt) is applied.
[0099]
As shown in FIG. 39, the column decoder 514 includes a power supply circuit 5141, a gate CG to which a column address is supplied.₁ ~ CGm, the gate CG₁ ... CGm and a power supply circuit 5141 between a transistor 5142, a bit line transfer gate 5145, and an inverter (transistor 5143) provided between a power supply circuit 5121 and a low potential power supply Vss to control the bit line transfer gate 5145. , 5144). As a result, for example, all input column addresses become high level “H” and the gate CG₁ A bit line (selected bit line) BL corresponding to an address for which .about.CGm is turned on is connected to the sense amplifier 517.
[0100]
Here, as shown in FIG. 40, a plurality of bit line transfer gates 51451 to 5145m are connected to one sense amplifier 517 via a bus line (BUS), and the selected 1 in the bit line transfer gates 51451 to 5145m is selected. Only one bit line (selected bit line) is connected to the sense amplifier 517. Then, the contents of the memory cell MC that coincides with the intersection of the selected word line and the selected bit line are output via the sense amplifier 517.
[0101]
By the way, the flash memory is capable of batch erasing all bits electrically. Generally, when performing batch erasing, it is generally the same for all cell transistors (memory cells MC) at the same time because of the simplicity of circuit technology. Erase operation is performed. This erase operation is repeated until all cell transistors are erased. However, for statistical reasons, there are a mixture of cell transistors that are relatively easy to erase and cell transistors that are relatively difficult to erase. Therefore, when all the bits are erased at once by the above-described method, if the characteristic difference between the cell transistor that is easy to erase and the cell transistor that is difficult to erase is very large, the erase operation for the cell transistor that is easy to erase. Will be made more than necessary. Here, the characteristic difference between the cell transistors can appear relatively easily due to wafer process fluctuations, stress due to repeated writing / erasing over a long period of time, and the like.
[0102]
In addition, writing and erasing operations on the cell transistors of the flash memory are usually performed by injecting and discharging charges to and from the floating gates of the cell transistors. For this reason, in the memory cell MC that has been erased more than necessary as described above, the charge having the opposite polarity to that at the time of writing is injected into the floating gate (the floating gate is positively charged). become. Such a state is called an overerased state.
[0103]
In the case of a nonvolatile semiconductor memory device (flash memory), the cell array generally has a configuration called NOR type. In this NOR type non-volatile semiconductor memory device, the drains of the cell transistors (N-channel type MIS transistors) are commonly connected to each bit line and only biased to the gates of the cell transistors to be selected. A predetermined cell transistor (memory cell) is selected by applying a bias (positive voltage) and not applying a bias (0 volts) to the gate of the non-selected cell transistor. Note that the sources of all the cell transistors are grounded via a source power supply circuit 519. Here, since the enhancement type MIS transistor (N-channel type MIS transistor) is used as the cell transistor, the non-selected cell transistor does not flow current, and only the selected cell transistor depends on the amount of charge in the floating gate. Current may or may not flow. Data “0” and data “1” are assigned according to the current flowing through the selected cell transistor.
[0104]
In a flash memory, when the above-described over-erasure occurs for an enhancement type cell transistor, the cell transistor apparently changes its characteristics to a depletion type. When a NOR type cell array is used, a non-selected cell transistor does not pass a current in a state where a bias is not applied to the gate, but a cell transistor in which excessive erasure occurs apparently has a depletion type characteristic. For the sake of illustration, even a non-selected cell transistor causes a current to flow. For this reason, even if the selected cell transistor does not flow current, since the over-erased non-selected cell transistor flows current, data “0” and data “1” are erroneously determined. There is a problem that occurs.
[0105]
The fifth embodiment of the semiconductor memory device according to the present invention aims to accurately read data even when there is a cell transistor which has caused excessive erasure.
[0106]
FIG. 41 is a block circuit diagram showing one embodiment of the fifth mode of the semiconductor memory device (flash memory) according to the present invention. In the figure, reference numeral 502 denotes a row decoder, 504 denotes a column decoder, 507 denotes a sense amplifier, and 509 denotes a source power supply circuit. Here, the semiconductor memory device of this embodiment is basically the same as the semiconductor memory device described with reference to FIG. 37, and the description thereof is omitted, but the configuration of the row decoder 502 is different.
[0107]
FIG. 42 is a circuit diagram showing a configuration of row decoder 502 in the semiconductor memory device of FIG. As shown in the figure, the row decoder 502 of this embodiment includes a positive power supply circuit 5021 that generates a predetermined positive voltage, a gate RG to which a row address is supplied.₁ ~ RGn, the gate RG₁ ~ RGn and a transistor 5022 provided between the positive power supply circuit 5021, a negative power supply circuit 5025, and an inverter (transistor provided between the positive power supply circuit 5021 and the negative power supply circuit 5025 for controlling the level of the word line WL. 5023, 5024). As a result, for example, all the input row addresses become high level “H” and the gate RG₁ The output (Vcc) of the positive power supply circuit 5021 is applied to the word line (selected word line) WL corresponding to the address to which RGn is turned on via the transistor 5123, and the transistor 5024 is applied to the other unselected word lines WL. The output (negative voltage) of the negative power supply circuit 5025 is applied via the. As a specific circuit of the negative power supply circuit 5025, it is needless to say that the negative voltage generating circuit 118 in the semiconductor memory device shown in FIG. 5 can be applied.
[0108]
Here, when the output of the negative power supply circuit 5025 is applied to the gate of the depletion type cell transistor MC caused by over-erasing, the over-erased cell transistor MC is set in a non-selected state to pass a current. It is a voltage to prevent it. That is, the output of the negative power supply circuit 5025 is a negative voltage such that the gate voltage of the depletion type N-channel MIS transistor (over-erased cell transistor) is equal to or lower than the threshold voltage. As a result, even if there is an overerased cell transistor on the selected bit line, the contents written in the cell transistor selected by the word line are accurately output via the sense amplifier 507. Become.
[0109]
FIG. 43 is a block circuit diagram showing another embodiment of the fifth mode of the semiconductor memory device according to the present invention. In the figure, reference numeral 5221 is a first row decoder corresponding to the row decoder 502 in FIG. 41, and 5222 is a function of the source power supply circuit 509 in FIG. 41 and a source line SL corresponding to an unselected word line WL. A second row decoder for applying a voltage higher than the level of the selected bit line is shown. Here, the configuration of the column decoder 524, the sense amplifier 527, etc. is the same as that shown in FIG.
[0110]
In the semiconductor memory device of this embodiment, the first row decoder 5221 applies a normal voltage Vcc to the selected word line WL at the time of reading, and the memory cell (cell transistor) connected to the selected word line WL. Select MC. The second row decoder 5222 applies a low-potential power supply voltage Vss: 0 volts to the source (SWL) of the cell transistor connected to the selected word line, and applies it to the unselected word line at the time of reading. A voltage higher than the level (drain voltage) of the selected bit line is applied to the sources of all the connected cell transistors. Thus, when the cell is in the non-selected state, the cell voltage that has been over-erased by the batch erasing can be cut off (non-selected) because the gate voltage is lower than the source voltage. Here, the voltage applied to the source of the memory cell connected to the unselected word line at the time of reading may be set to the same voltage as the level of the selected bit line. That is, even if a channel is generated due to over-erasing, current does not flow unless there is a potential difference between the drain and source, so that the non-selected over-erased cell transistor does not affect the read operation. .
[0111]
44 is a circuit diagram showing an example of the first row decoder 5221 and the second row decoder 5222 in the semiconductor memory device of FIG. 43, and FIG. 45 is a circuit diagram showing a part of the second row decoder of FIG. It is.
[0112]
As shown in FIG. 44, the first row decoder 5221 includes a power supply circuit (Vcc) 52221, a NAND gate 52212 to which a row address is supplied, and an inverter 52213, and the second row decoder 5222 includes: A power supply circuit (Vcc) 52221, a NAND gate 52222 to which a row address is supplied, inverters 52223 and 52224, and a power supply circuit 5225 are included. Here, the power supply circuit 52225 is for supplying a voltage higher than the level (drain voltage) of the selected bit line applied to the source of the cell transistor connected to the unselected word line at the time of reading. FIG. 45 shows an example of the circuit.
[0113]
As described above, according to the fifth embodiment of the semiconductor memory device of the present invention, even if, for example, an overerased memory cell is generated by batch erase in the flash memory, the data “0” is normally obtained. Alternatively, the data “1” can be read out accurately, and even if there is excessive erasing due to fluctuations in the wafer process or repeated writing / erasing over a long period of time, the data can be read out accurately to improve the yield and A significant improvement in device reliability can be expected.
[0114]
Next, a sixth embodiment of the semiconductor memory device according to the present invention will be described with reference to FIGS. First, in the sixth embodiment as well, as in the fifth embodiment of the semiconductor memory device of the present invention described above, accurate data is read even when overerased memory cells are generated by batch erase in the flash memory. It is a thing.
[0115]
That is, as described with reference to FIGS. 37 to 40, the flash memory can electrically erase all bits at once, and generally performs circuit erasure from the viewpoint of circuit technology. The same erase operation is simultaneously performed on all the cell transistors (memory cells MC), and this erase operation is repeated until all the cell transistors are erased. However, since cell transistors that are relatively easy to erase and cell transistors that are relatively difficult to erase are mixed in the cell array, if all bits are erased at once, the erase operation for the cell transistors that are easy to erase is performed. It will be over-erased if necessary. The characteristic difference between the cell transistors can appear relatively easily due to wafer process fluctuations, stress due to repeated writing / erasing over a long period of time, and so overerased cells appear relatively frequently. It has become. Here, the writing and erasing operations on the cell transistors of the flash memory are as described with reference to FIGS.
[0116]
In the case of a flash memory, the cell array generally has a configuration called NOR type, and the drains of N-channel MIS transistors (cell transistors) are commonly connected to each bit line and uniformly applied with a bias. In this state, a positive bias voltage is applied only to the gate of the selected cell transistor, and no bias is applied to the gate of the non-selected cell transistor (0 volt), so that a predetermined cell transistor is selected. It has become. Here, since the enhancement type N-channel MIS transistor is used as the cell transistor, the non-selected cell transistor does not flow current, and only the selected cell transistor flows current according to the amount of charge in the floating gate. Or do not flush. Data “0” and data “1” are assigned according to the current flowing through the selected cell transistor.
[0117]
In a flash memory, when the above-described over-erasure occurs for an enhancement type cell transistor, the cell transistor apparently changes its characteristics to a depletion type. When a NOR type cell array is used, a non-selected cell transistor does not pass a current in a state where a bias is not applied to the gate, but a cell transistor in which excessive erasure occurs apparently has a depletion type characteristic. For the sake of illustration, even a non-selected cell transistor causes a current to flow. For this reason, even if the selected cell transistor does not flow current, since the over-erased non-selected cell transistor flows current, data “0” and data “1” are erroneously determined. There is a problem that occurs.
[0118]
A sixth aspect of the semiconductor memory device according to the present invention is to relieve overerased cells and read out accurate data when cell transistors that have undergone overerasure occur.
[0119]
FIG. 46 is a circuit diagram showing the main part of the sixth embodiment of the semiconductor memory device according to the present invention. In the figure, reference numeral 602 indicates a row decoder, 604 indicates a column decoder, and 607 indicates a sense amplifier. Reference symbol MC denotes a memory cell transistor (memory cell) composed of an N-channel MIS transistor, WL.₁, WL₂ Indicates a word line, and BL indicates a bit line. Here, the memory cell MC is the same as that shown in FIG.
[0120]
FIG. 47 is a circuit diagram showing an example of the sense amplifier 607 of the semiconductor memory device in FIG. 46, which is composed of N-channel MOS transistors 6071, 6072, 6073, 6074, 6075, 6077 and P-channel MOS transistors 6076, 6078. ing.
[0121]
In the sixth embodiment, for example, in order to detect cell transistors (over-erased cells) that have undergone over-erasure due to collective erase, the row decoder 602 first applies all to the memory cell array subjected to the collective erase processing. Word line WL₁, WL₂,... Are set to the low level “L”, and the column gates G601, G602,.₁, BL₂,... Are sequentially connected to the sense amplifier 607. At this time, the output of the sense amplifier 607 is at a low level “L” when a bit line to which an overerased cell is connected is selected, so the bit line at which the output of the sense amplifier 607 is at a low level “L”. In this state, the transistor 6077 of the sense amplifier 607 is turned on to increase the drive current of the sense amplifier 607 so that the overerased cell does not flow current. Furthermore, the word line WL is sent by the row decoder 602.₁, WL₂,... Are scanned and a cell transistor in which the output of the sense amplifier 607 is at a high level “H” is detected as an overerased cell.
[0122]
FIG. 48 is a block diagram schematically showing an example of a system to which the sixth embodiment of the semiconductor memory device according to the present invention is applied. In the figure, reference numeral 610 indicates a flash memory, 620 indicates a read only memory (ROM), and 630 indicates a central processing unit (CPU).
[0123]
In the system shown in FIG. 48, an algorithm shown in FIG. 49 to be described later is stored in the ROM 620, and the CPU 630 controls the flash memory 610 according to the algorithm. That is, the CPU 630 relieves overerased cells in the flash memory 610 in accordance with the algorithm stored in the ROM 620.
[0124]
FIG. 49 is a flow chart for explaining an example of processing in the sixth mode of the semiconductor memory device according to the present invention. As shown in the drawing, when the erase process of the flash memory is started, a pre-erase write process is performed in step S611. This pre-erase write process is a process of writing data “0” to all the cell transistors of the memory cell array before erasing the memory cell array of the flash memory at once.
[0125]
Next, batch erase is performed in step S612, and erase verify is performed in step S613. That is, the erase process is performed by causing all the cell transistors of the memory cell array to emit electrons from the floating gate little by little at a time. In step S614, an overerase check is performed to determine whether or not there are overerased cells. Here, if it is determined in step S614 that there are no overerased cells (if the overerased check is passed), the erasing process is terminated, and if it is determined that there are overerased cells (failed by overerased check). ) Go to step S615. Note that the over-erasure check in step S614 detects only one cell transistor that is over-erased, as described with reference to FIGS.
[0126]
In step S615, a write process is performed for one overerased cell (overerased bit) detected in step S614, and the process proceeds to step S616 to perform an overerase check similar to step S614. If it is assumed that the overerased state of one overerased cell detected in step S614 has disappeared due to the writing process in step S615 and a normal erase state has been established, and there is no other overerased cell, the process proceeds to step S617. Thus, erase verify similar to that in step S613 is performed. If the erase verify in step S617 is passed, the erase process is completed. If the file is obtained by the erase verify in step S617, the erase and erase verify are performed in steps S618 and S619.
[0127]
On the other hand, as a result of the writing process in step S615, the overerased state of one overerased cell detected in step S614 has disappeared and the normal erased state has been reached, but if there are other overerased cells, in step S616 Another overerased cell different from the overerased cell detected in step S614 is detected, and the process returns to step S615 to perform the writing process. In this manner, one overwriting process is performed on all the overerased cells in the memory cell array, and all the overerased cells are brought into a normal erase state.
[0128]
The erase process shown in FIG. 49 can be stored in the ROM 620 of the system shown in FIG. 48 and read and processed by the CPU 630 as described above. A logic circuit or the like that implements the erasing process shown in FIG.
[0129]
As described above, according to the sixth embodiment of the semiconductor memory device of the present invention, it is possible to relieve the cell transistor that has caused excessive erasure and to read out accurate data, and to prevent fluctuations in the wafer process. Even if excessive erasure occurs due to repeated writing / erasing over a long period of time, it is possible to expect improvement in yield and significant improvement in device reliability by accurately reading data.
[0130]
Next, a seventh embodiment of the semiconductor memory device according to the present invention will be described with reference to FIGS.
[0131]
FIG. 50 shows a memory cell (MC) used in the seventh embodiment of the semiconductor memory device of the present invention, and shows the operation of the cell transistor (memory cell MC) in the electrical batch erase nonvolatile semiconductor memory device (flash memory). It is a figure for demonstrating. As shown in the figure, the cell transistor includes a floating gate FG that is insulated between the source and drain regions, and a control gate CG formed on the floating gate FG.
[0132]
At the time of writing, the drain voltage Vd applied to the drain region DD is, for example, 6 volts, the gate voltage Vg applied to the control gate CG is the writing voltage (erasing voltage) Vpp, and the source voltage Vs applied to the source region SS. Is zero volts, electrons are injected from the drain terminal (DD) to the floating gate (FG), and data “0” is written.
[0133]
At the time of erasing, the gate voltage Vg and the drain voltage Vd are opened (floating state), the source voltage Vs is set as the erasing voltage Vpp, and electrons are extracted from the floating gate (FG) to the source terminal (SS) (data “1”). Write). At the time of reading, the gate voltage Vg is set to the power supply voltage Vcc, the drain voltage Vd is set to about 1 volt, and the source voltage Vs is set to zero volt. It is determined whether it is “1” or “0”.
[0134]
FIG. 51 is a block circuit diagram showing an example of a related-art semiconductor memory device corresponding to the seventh embodiment of the semiconductor memory device according to the present invention. In the figure, reference numeral 710 is a block address buffer, 7101 and 7102 are block selection gates, 711 is a row address buffer, 712 is a row decoder, 713 is a column address buffer, 714 is a column decoder, 715 is a data I / O buffer, Reference numeral 716 denotes a writing circuit, 717 denotes a sense amplifier, and 7911 and 7192 denote source power supply circuits. Reference numeral BL indicates a bit line, WL indicates a word line, MC indicates a memory cell, W indicates a write control signal that is at a high level “H” during writing, E indicates an erase that is at a high level “H” at the time of erasure A control signal is shown.
[0135]
The operation of the semiconductor memory device shown in FIG. 51 is basically the same as that of the related art semiconductor memory device shown in FIG. 2, for example. However, in the semiconductor memory device shown in FIG. Selection gates 7101 and 7102 are further provided. That is, in the semiconductor memory device shown in FIG. 51, a plurality of blocks B1 and B2 are provided, and the block selection gates 7101 and 7102 are selected by a block selection signal from the block address buffer 710 to write an arbitrary block. 716 or a sense amplifier 717 is connected. Here, the memory cell array is composed of two blocks B1 and B2 having a common source, and the source power supply circuit 7911 and 7192 provided in each block B1 and B2 can perform erasure (block erasure) for each block. It has become.
[0136]
In the semiconductor memory device of FIG. 51, at the time of erasing, an erasing signal E that is at a high level “H” is input to the row address buffer 711 and the column address buffer 713, and the outputs of the row address buffer 711 and the column address buffer 713 are not selected. (For example, both complementary outputs are at a low level “L”), and all the word lines WL and bit lines BL are not selected. Further, the erase signal E is input to the source power supply circuit 7191 and 7192 together with the block selection signal from the block address buffer 710. For example, the erase signal E is used to erase a predetermined one source power supply circuit whose block selection signal is at the high level “H”. A predetermined block is erased as the voltage Vpp.
[0137]
At the time of writing, a write control signal W that is at a high level “H” is input to the row address buffer 711 and the column address buffer 713, and is input to the row decoder 712 and the column decoder 714, whereby the word line WL is set to the write level. The bit line BL is connected to the write circuit 716 via the block selection gates 7101 and 7102 selected by the block selection signal. Here, a write voltage (for example, 6 volts) is supplied to a predetermined bit line BL of the block selected from the write circuit 716, and the write is executed.
[0138]
In the related-art semiconductor memory device shown in FIG. 51 described above, block erasure can be executed, but both blocks (a plurality of blocks) cannot be erased simultaneously. That is, in the semiconductor memory device of FIG. 51, the erasure for each block is performed sequentially to erase a plurality of blocks. Further, with respect to verification after erasure, verification for each erased block is performed sequentially. Therefore, when erasing a plurality of blocks, it takes a long time and the verification process is also complicated.
[0139]
A seventh aspect of the semiconductor memory device according to the present invention is to erase a plurality of blocks at the same time and easily perform verification even when the plurality of blocks are erased at the same time.
[0140]
FIG. 52 is a block circuit diagram showing an embodiment of the seventh mode of the semiconductor memory device according to the present invention. In the figure, reference numeral 701 is a block address buffer, 7021 and 7022 are expected value data storage circuits, 7031 and 7032 are coincidence circuits, 704 is a logic circuit (Nand gate), 721 is a row address buffer, 722 is a row decoder, and 723 is A column address buffer, 724 is a column decoder, 725 is a data I / O buffer, 7271 and 7262 are write circuits, 7271 and 7272 are sense amplifiers, and 7091 and 7092 are source power supply circuits. Reference numeral BL indicates a bit line, WL indicates a word line, MC indicates a memory cell, W indicates a write control signal that is at a high level “H” during writing, E indicates an erase that is at a high level “H” at the time of erasure A control signal is shown. That is, the embodiment shown in FIG. 52 has an expected value data storage circuit 7021, 7022, coincidence circuit 7031, 7032, multiplexer (data I / O buffer) 725, and A NAND gate 704 is added.
[0141]
First, at the time of erasing, the selection signal is latched at one of the source power supply circuits 7091 and 7092 selected by the output signal from the block address buffer 701 with the latch control signal LT as the high level “H”. Thereafter, the erase control signal E is set to the high level “H” to operate all of the source power supply circuits in which the selection signals are latched, thereby simultaneously erasing a plurality of blocks.
[0142]
53 is a circuit diagram showing an example of the source power supply circuit in the semiconductor memory device of FIG. 52, FIG. 54 is a circuit diagram showing an example of the expected value data storage circuit, and FIG. 55 is a circuit diagram showing an example of the coincidence circuit. It is.
[0143]
As shown in FIG. 53, the source power supply circuit 7091 (7092) includes a NAND gate 731 to which a block address signal (block selection signal) and a latch control signal are input, a NAND gate 732 and an inverter 733 constituting the latch circuit, A NAND gate 734 to which the output of the latch circuit and the erase control signal E are inputted, and P-channel MOS transistors 736 and 737 and an N-channel MOS transistor 738 to which an erase power supply (Vpp) is applied are configured. As shown in FIG. 54, the expected value data storage circuit 7021 (7022) includes inverters 741, 744, 745, 746, 750, and NAND gates 742, 743, 747, 748, 749. Here, the NAND gate 743 and the inverter 744 constitute a latch circuit, and the output of the latch circuit is controlled in accordance with the inversion control signal INV. Further, as shown in FIG. 55, the matching circuit 7031 (7032) includes an inverter 753, NAND gates 751, 752, 755, and an exclusive OR gate 754. Here, the NAND gate 752 and the inverter 753 form a latch circuit, and whether the output (sense amplifier data) of the sense amplifier 7271 (7272) matches the output (reference data) of the expected value data storage circuit 7021 (7022) or not. Whether or not is determined.
[0144]
In each of the circuits described above, first, in the erase operation performed by latching the block address signal, only the latched erase circuit is operated with the erase control signal “E”. Similarly, the write data “0” is latched in the expected value data storage circuit 7021 (7022) by setting the latch control signal LT to the high level “H”. In this case, data “0” is transferred from the data I / O buffer 725 to the expected value data storage circuit 7021 (7022) selected by the block address signal, and the latch control signal LT is set to the high level “H”. "To latch. Here, the output of the coincidence circuit 7031 (7032) is forcibly output at a high level “H” except for the selected block. As described above, when the write control signal W is set to the high level “H” to execute the write, the plurality of selected blocks are simultaneously written.
[0145]
Next, at the time of verification, the expected value data stored in the expected value data storage circuit 7021 (7022) and the output of the sense amplifier 7271 (7272) are compared, and the outputs of the match circuits 7031 and 7032 are sent to the NAND gate 704. If the writing is sufficiently performed, the sense amplifier output becomes low level “L”. Therefore, the coincidence signal output becomes high level “H”. When data is written in all the cell blocks, the verify output VER of the NAND gate 704 is output. Becomes low level “L”, and it can be confirmed that the writing is completed at a predetermined address of all blocks. Here, at the time of erase verify, if the expected value data is inverted by the inversion signal INV and verified, if the predetermined address data in all the selected blocks becomes data “1”, the same as in the write It can be detected that the data is erased when the verify output VER is at a low level "L". As described above, according to the semiconductor memory device of this embodiment, only when all the outputs of the coincidence circuit 7031 (7032) are at the high level “H”, the output of the NAND gate 704 is at the low level “L”. If there is a coincidence circuit whose output is low level “L”, it is confirmed that there is a defective bit.
[0146]
FIG. 56 is a block circuit diagram showing another embodiment of the seventh mode of the semiconductor memory device according to the present invention. The semiconductor memory device shown in FIG. 56 is obtained by replacing the expected value data storage circuit 7021 (7022) in the semiconductor memory device of FIG. 52 described above with an expected value data generating circuit 7041 (7042).
[0147]
In the semiconductor memory device shown in FIG. 52, since the reference data necessary for writing and erasing before erasure is data “0” or data “1”, means for storing random data is used. It can be realized without it. However, in the present embodiment shown in FIG. 56, the expected value data generation circuit 7041 (7042) selected by the block address signal is latched by setting the latch control signal LT to the high level “H”. It has become. Then, the latched expected value data generation circuit 7041 (7042) forcibly generates data “0”. Further, at the time of erasing, if the expected value data is inverted by the inversion control signal INV, the erase verify similar to that described above can be performed.
[0148]
FIG. 57 is a circuit diagram showing an example of an expected value data generation circuit in the semiconductor memory device of FIG. As shown in the figure, the expected value data generation circuit 7041 (7042) includes inverters 763, 764, 767, 768, NAND gates 761, 762, 766, 769, 770, and a NOR gate 765. Here, the NAND gate 762 and the inverter 763 constitute a latch circuit. In the expected value data generation circuit 7041 (7042) shown in FIG. 57, when the address data signal (block selection signal) is latched by the latch circuit (762, 763), the reference data is forcibly set to the low level “L” and inverted. When the control signal INV is at a high level “H”, the reference data is at a high level “H”.
[0149]
FIG. 58 is a block circuit diagram showing still another embodiment of the seventh mode of the semiconductor memory device according to the present invention. In the embodiment shown in FIG. 58, the expected value data storage circuit 7021 (7022), the write circuit 7261 (7262) and the match circuit 7031 (7032) of FIG. 52 are replaced with the block selection signal storage circuit 7051 (7052) and the write circuit 7161. (7162) and the data inversion circuit 7061 (7062). That is, in this embodiment, the pre-erase write and its verify and erase verify are controlled by the select signal stored in the block select signal storage circuit 7051 (7052).
[0150]
In the semiconductor memory device shown in FIG. 58, first, at the time of writing before erasing, writing is performed to cells of a predetermined block by a block selection signal (block dress signal). Here, the data inversion circuit 7061 (7062) has a function of inverting the data of the sense amplifier 7271 (7272) at the time of erase verify and at the time of write verify, and when the write and erase are sufficiently performed, the output becomes a high level “ H ”. At this time, the non-selected block is always set to the high level “H” by the output signal of the block selection signal storage circuit 7051 (7052). Thereby, the pre-erase writing and erasure as described above can be realized.
[0151]
59 is a circuit diagram showing an example of a block selection signal storage circuit in the semiconductor memory device of FIG. 58, FIG. 60 is a circuit diagram showing an example of a write circuit, and FIG. 61 is a circuit diagram showing an example of a data inverting circuit. .
[0152]
As shown in FIG. 59, the block selection signal storage circuit 7051 (7052) includes a NAND gate 771 to which a block address signal (block selection signal) and a latch control signal are input, a NAND gate 772 and an inverter 773 that constitute the latch circuit. It is configured. As shown in FIG. 60, the write circuit 7161 (7162) includes an inverter 781, a NOR gate 782, a NAND gate 783, and P-channel MOS transistors 785 and 786 to which a write power supply (Vpp) is applied, and an N-channel MOS transistor. A transistor 787 is provided. Further, as shown in FIG. 61, the data inversion circuit 7061 (7062) includes inverters 792, 793 and NAND gates 791, 794, 795, 796. Then, the output of the sense amplifier 7271 (7272) is inverted according to the inverted signal INV and supplied to the NAND gate 704.
[0153]
In the block selection signal storage circuit 7051 (7052) shown in FIG. 59, the block address signal is latched in the latch circuit (772,773) in accordance with the high level “H” of the latch control signal LT. In the block in which the selection signal is latched, the write voltage Vpp is applied to the bus line by setting the write control signal W to the high level “H” regardless of the level of the input data.
[0154]
In the data inversion circuit 7061 (7062) shown in FIG. 61, when the inversion control signal INV is set to the low level “L” during the write verification, the output of the sense amplifier 7271 (7272) is set to the low level “L” (the state in which the writing has been performed). ) And the output to the NAND gate 704 becomes high level “H”. At the time of erase verify, the inversion control signal INV is set to the high level “H”. Here, in the non-selected block, the block selection signal (block address signal) is at the low level “L”, and the output to the NAND gate 704 is forcibly set at the high level “H”. As a result, it becomes possible to execute erasure of arbitrary blocks simultaneously. The multiplexer 725 controls whether write data and sense amplifier data are supplied to a predetermined block in accordance with a block selection address, and whether data of the predetermined block is output.
[0155]
As described above, according to the seventh embodiment of the semiconductor memory device of the present invention, the source power supply circuit of each cell block includes the block selection signal latch circuit and simultaneously operates each cell source power supply circuit. By providing each cell block with a sense amplifier, an expected value data generation circuit for verification, a circuit for confirming a match between the sense amplifier output and the expected value, and a circuit for calculating the logical product of the outputs of the match circuit, Erase and verify can be performed.
[0156]
【The invention's effect】
  As described above in detail, according to the semiconductor memory device of the present invention (the fifth embodiment of the semiconductor memory device of the present invention), data can be accurately read even if there is a cell transistor that has caused excessive erasure. CanThe
[Brief description of the drawings]
FIG. 1 is a block circuit diagram showing an example of a first mode of a semiconductor memory device according to the present invention;
FIG. 2 is a block circuit diagram showing an example of a related-art semiconductor memory device corresponding to the first embodiment of the semiconductor memory device according to the present invention;
3 is a circuit diagram showing an example of a column address buffer in the semiconductor memory device of FIG. 2;
4 is a circuit diagram showing an example of a row address buffer in the semiconductor memory device of FIG. 2;
5 is a circuit diagram showing an example of a row decoder in the semiconductor memory device of FIG. 2;
6 is a circuit diagram showing an example of a column decoder in the semiconductor memory device of FIG. 2;
7 is a circuit diagram showing an example of a write circuit in the semiconductor memory device of FIG. 2;
8 is a circuit diagram showing an example of a source power supply circuit in the semiconductor memory device of FIG. 2;
9 is a circuit diagram showing an example of a sense amplifier in the semiconductor memory device of FIG. 2;
10 is a diagram showing an example of a write characteristic curve in the semiconductor memory device of FIG. 2;
FIG. 11 is a diagram for explaining the operation of a memory cell used in a semiconductor memory device to which the present invention is applied;
12 is a circuit diagram showing an example of a row address buffer in the semiconductor memory device of FIG. 1. FIG.
13 is a circuit diagram showing a main part of an example of a row decoder in the semiconductor memory device of FIG. 1;
14 is a circuit diagram showing an example of a coincidence circuit in the semiconductor memory device of FIG. 1;
15 is a circuit diagram showing a main part of an example of a row decoder in the semiconductor memory device of FIG. 1;
16 is a diagram showing a waveform of a signal applied to the circuit of FIG.
FIG. 17 is a circuit diagram showing an example of a verify voltage generation circuit in the semiconductor memory device of FIG. 1;
18 is a circuit diagram showing an example of a sense amplifier in the semiconductor memory device of FIG. 1;
19 is a circuit diagram showing an example of a logic circuit that creates a control signal to be supplied to the sense amplifier of FIG. 18;
FIG. 20 is a block circuit diagram showing an example of a redundant circuit in a conventional semiconductor memory device corresponding to the second embodiment of the semiconductor memory device according to the present invention.
FIG. 21 is a diagram showing a configuration example of the conventional redundant circuit shown in FIG. 20;
22 is a block diagram showing an example of a semiconductor memory device using the conventional redundant circuit shown in FIG.
FIG. 23 is a block circuit diagram showing one embodiment of a redundancy circuit in the second mode of the semiconductor memory device according to the present invention;
24 is a block diagram showing the configuration of real cells and redundant cells in a semiconductor memory device to which the redundant circuit of the present invention shown in FIG. 23 is applied.
25 is a block diagram showing an example of a semiconductor memory device using the redundant circuit of the present invention shown in FIG.
FIG. 26 is a block circuit diagram showing another embodiment of the redundant circuit in the second mode of the semiconductor memory device according to the present invention;
FIG. 27 is a block circuit diagram showing still another embodiment of the redundancy circuit in the second mode of the semiconductor memory device according to the present invention;
28 is a block diagram showing an example of a semiconductor memory device using the redundant circuit of the present invention shown in FIG. 27. FIG.
FIG. 29 is a flowchart showing an internal write algorithm in the third embodiment of the semiconductor memory device according to the present invention.
FIG. 30 is a block diagram showing an example of the third mode of the semiconductor memory device of the present invention;
31 is a diagram showing a circuit example of a main part in the semiconductor memory device of FIG. 30;
32 is a timing chart for explaining the operation of the circuit of FIG. 31;
FIG. 33 is a diagram for explaining the operation of the memory cell in the fourth embodiment of the semiconductor memory device according to the invention.
FIG. 34 is a block circuit diagram showing an example of a semiconductor memory device as related technology corresponding to the fourth embodiment of the semiconductor memory device of the present invention;
FIG. 35 is a block circuit diagram showing an example of the fourth mode of the semiconductor memory device of the present invention.
FIG. 36 is a circuit diagram showing the main part of another example of the fourth mode of the semiconductor memory device of the present invention;
FIG. 37 is a block circuit diagram showing an example of a conventional semiconductor memory device corresponding to the fifth mode of the semiconductor memory device according to the present invention.
38 is a circuit diagram showing a configuration of a row decoder in the semiconductor memory device of FIG. 37;
39 is a circuit diagram showing a configuration of a column decoder in the semiconductor memory device of FIG. 37;
40 is a circuit diagram showing a configuration of a bit line transfer gate in the column decoder of FIG. 39. FIG.
FIG. 41 is a block circuit diagram showing an example of the fifth mode of the semiconductor memory device according to the present invention;
42 is a circuit diagram showing a configuration of a row decoder in the semiconductor memory device of FIG. 41;
FIG. 43 is a block circuit diagram showing another example of the fifth mode of the semiconductor memory device according to the present invention;
44 is a circuit diagram showing an example of first and second row decoders in the semiconductor memory device of FIG. 43;
45 is a circuit diagram showing a part of the second row decoder of FIG. 44; FIG.
FIG. 46 is a circuit diagram showing the main part of the sixth mode of the semiconductor memory device according to the present invention;
47 is a circuit diagram showing an example of a sense amplifier of the semiconductor memory device in FIG. 46;
FIG. 48 is a block diagram schematically showing an example of a system to which the sixth embodiment of the semiconductor memory device according to the present invention is applied.
FIG. 49 is a flowchart for explaining an example of processing in the sixth embodiment of the semiconductor memory device according to the present invention;
FIG. 50 is a diagram for explaining the operation of the memory cell used for the seventh embodiment of the semiconductor memory device of the invention.
FIG. 51 is a block circuit diagram showing an example of a related-art semiconductor memory device corresponding to the seventh embodiment of the semiconductor memory device according to the present invention;
FIG. 52 is a block circuit diagram showing an example of the seventh mode of the semiconductor memory device according to the present invention.
53 is a circuit diagram showing an example of a source power supply circuit in the semiconductor memory device of FIG. 52;
54 is a circuit diagram showing an example of an expected value data storage circuit in the semiconductor memory device of FIG. 52;
55 is a circuit diagram showing an example of a coincidence circuit in the semiconductor memory device of FIG. 52;
FIG. 56 is a block circuit diagram showing another example of the seventh mode of the semiconductor memory device according to the present invention.
57 is a circuit diagram showing an example of an expected value data generation circuit in the semiconductor memory device of FIG. 56. FIG.
FIG. 58 is a block circuit diagram showing still another example of the seventh mode of the semiconductor memory device according to the present invention.
59 is a circuit diagram showing an example of a block selection signal storage circuit in the semiconductor memory device of FIG. 58;
60 is a circuit diagram showing an example of a write circuit in the semiconductor memory device of FIG. 58. FIG.
61 is a circuit diagram showing an example of a data inverting circuit in the semiconductor memory device of FIG. 58;
[Explanation of symbols]
101… Row address buffer
102 ... Row decoder
103 ... Column address buffer
104… Column decoder
105… Data I / O buffer
106… Write circuit
107 Sense amplifier
108… Negative voltage generator
109… Source power supply circuit
120 ... Match circuit
130 ... Redundant row decoder
140… Verify voltage generator
200 ... Redundant circuit
201A, 201B… Fuse
202… Resistor
203… Inverter
204… Address comparison circuit
205 ... Redundant cell selection circuit
206… Redundant cells
207 ... Real cell selection circuit
208… Real Cell
209 ... Data reading circuit
311… Write control circuit
312 ... Write pulse generator
313 ... cell array
314 ... Pulse counter
315… Switch part
316 ... Stop signal generation circuit
317… High voltage detection circuit
401 ... Row address buffer
402 ... Row decoder
403 ... column address buffer
404 ... column decoder
405… Buffer circuit
406... Write voltage supply transistor (P-channel MOS transistor)
407… Sense amplifier
408… Bus line
502 ... Row decoder
504 ... Column decoder
507… Sense amplifier
509… Source power supply circuit
5221 ... First row decoder
5222 ... Second row decoder
602 ... row decoder
604 ... column decoder
607… Sense amplifier
610 ... Flash memory
620… ROM
630 ... CPU
704… Logic circuit (Nand gate)
721… Row address buffer
722 ... Row decoder
723 ... column address buffer
724 ... Column decoder
725 ... Data I / O buffer (multiplexer)
7021,7022… Expected value data storage circuit
7031,7032… Match circuit
7041,7042… Expected value data generation circuit
7051,7052… Block selection signal storage circuit
7061,7062 ... Data inversion circuit

Claims (2)

A plurality of word lines, a plurality of bit lines, and MIS transistors that are provided at intersections of the word lines and the bit lines, respectively, and that can electrically control the threshold voltage from the outside depending on whether or not charges are injected into the floating gate. A memory cell array having a plurality of memory cell transistors, and a semiconductor memory device capable of simultaneously erasing by simultaneously discharging charges from the floating gates of the plurality of memory cell transistors of the memory cell array,
A first row decoder that applies a normal voltage to a selected word line at the time of reading and selects a memory cell transistor connected to the selected word line;
A power supply voltage having a predetermined potential is applied to the source of the memory cell transistor connected to the selected word line, and the batch erasure is performed on the sources of all the memory cell transistors connected to the unselected word line at the time of reading. And a second row decoder for applying a voltage for making a non-selected state including a memory cell transistor in an over-erased state by
The memory cell transistor is composed of an enhancement type N-channel MIS transistor,
The second row decoder applies a low power supply voltage to the source of the memory cell transistor connected to the selected word line, and applies to the source of all the memory cell transistors connected to the unselected word line. A semiconductor memory device characterized in that a voltage higher than a level of a selected bit line is applied. Said second row decoder, a semiconductor memory equipment according to claim 1 in which the power from the power supply circuit for generating a level above the voltage of the bit line, characterized in that it is supplied.

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