JP2001160298A - Semiconductor memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor memory in which rewriting with a block unit can be performed and the number of times of substantial rewriting can be increased. SOLUTION: Non-volatile storage elements in which accumulated electric charges of a floating gate are erased by a tunnel current through a tunnel insulation film are arranged in a matrix state, the above erasing can be performed for each block to which plural non-volatile storage elements of which control gates are coupled to the same word line are divided, a ground potential of a circuit is given to a block selected at the time of write-in for a source line of non-volatile storage elements being common to each block, potential difference between a floating gate and a source/drain is made less for a non- selection block. Or in one memory block, occurrence of a tunnel current is prevented or reduced by making such constitution of word lines and source lines that high voltage is not supplied to word lines in a memory block being non-selection at the time of write-in.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor memory device, and more particularly, to a semiconductor memory device which is effective when used in a batch erase type EEPROM (electrically erasable & programmable read only memory) in which erasing can be performed for each block. It is about technology.

[0002]

2. Description of the Related Art As nonvolatile storage devices, there are an EPROM (erasable & programmable read only memory) in which stored information can be erased by ultraviolet rays and the above-mentioned electrically erasable EEPROM. EPROM
Is suitable for large storage capacity due to the small memory cell area, but requires a windowed package to erase stored information by irradiating ultraviolet rays, and removes from the system at the time of rewriting for writing by a programmer There is a problem such as necessity.

An EEPROM can be electrically rewritten in a system.
Therefore, it is not suitable for increasing the storage capacity because it is about 2.5 to 5 times as large as. Therefore, recently, an electrically erasable EEPROM has been used as a nonvolatile storage device intermediate between the two.
What is called is being developed. Electrical batch erase type E
The EPROM is a nonvolatile storage device having a function of collectively electrically erasing a chip or a group of memory cells at a time. The size of the memory cell can be made as small as an EPROM. Such a batch erase EEPROM is described in the page of the 1980 International Solid State Conference (ISSCC).
Page 7 of 152 and 1987 International Solid State Conference (ISSCC)
6, and IEE Journal of Solid-State Circuits, Vol. 23, No. 5, 1988, pp. 1157--1163 (IEEE, J. Solid-S
tate Cicuits, vol.23 (1988) pp.1157-1163).

FIG. 14 shows a memory cell of an electrically erasable EEPROM which was announced at the International Electron Device Meeting in 1987. The memory cell shown in FIG.
It has a two-layer gate structure very similar to a PROM. The write operation is performed by injecting hot carriers generated near the junction of the drain 3 into the floating gate 4 as in the memory cell of the EPROM. The threshold voltage as viewed from the control gate 6 of the memory cell is increased by the write operation. On the other hand, in the erasing operation, the control gate 6 is grounded, and a high voltage is applied to the source 5 to generate a high electric field between the floating gate 4 and the source 5 and utilize the tunnel phenomenon through the thin oxide film 7. This is performed by extracting electrons accumulated in the floating gate 4 to the source 5. Due to the erasing operation, the threshold voltage viewed from the control gate 6 becomes lower. In reading, a low voltage of about 1 V is applied to the drain 3 so that weak writing is unlikely to occur, and about 5 V is applied to the control gate 6 so that the magnitude of the flowing channel current corresponds to "0" and "1" of information. In the figure, 8 is a P-type silicon substrate, 9 is an N-type diffusion layer, 10 is a low-concentration N-type diffusion layer, and 11 is a P-type diffusion layer.

[0005]

Prior to the present invention, the present inventors can divide one memory array (or memory mat) into a plurality of blocks and erase each block as shown in FIG. A non-volatile memory device was considered. In the same drawing, the memory cell exemplarily shown is constituted by a nonvolatile memory element as shown in FIG.

In FIG. 1, when writing (1 → 0) to the memory cell M1 of the memory block MB0, the word line W0 is set to a high level such as 12V and the data line D
0 is set to 6V by the activated write amplifier WA.
Is supplied. An erase circuit ERS provided corresponding to each of the memory blocks MB0 to MBn is provided at the source of the memory cell at times other than the erase operation.
A circuit ground potential of 0 V is applied through 0 to ERSn. As a result, the above-mentioned hot electrons are generated in the memory cells of the memory block MB0,
It is injected into the floating gate to change the threshold voltage high as described above.

At this time, in the memory cell M5 in the erased state (1 state) of the memory block MBn in which the writing is not performed as exemplified, the word line W0 is set.
Is raised to a high voltage such as 12V, the floating gate is raised to about 7V.
As a result, a relatively high electric field acts between the floating gate and the source, a weak tunnel current is generated through the thin tunnel oxide film, and electrons are injected into the floating gate. In the erasing operation for each memory block as described above, in the worst case, other memory blocks MB0 except the memory block MBn are used.
When the erase and the write are repeatedly performed in the above-described steps, the weak write operation by the tunnel current is repeatedly performed on the erased memory cells in the memory block MBn each time. As shown, it has been found that there arises a problem that the erasing level of the memory cell to be maintained at around 1 V is greatly changed. For this reason, when one memory array is divided into a plurality of memory blocks and a selective erase operation (rewrite) is performed for each memory block, the number of rewritable times is greatly reduced,
The usability becomes extremely bad. Note that the characteristic diagram of FIG. 15 is obtained by the present inventors and the like using simulation by a computer.

An object of the present invention is to provide a semiconductor memory device capable of performing rewriting in block units and substantially increasing the number of times of rewriting. The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0009]

The following is a brief description of an outline of a typical invention among the inventions disclosed in the present application. That is, nonvolatile memory elements for erasing stored charges in a floating gate by a tunnel current through a tunnel insulating film are arranged in a matrix, and a plurality of nonvolatile memory elements each including a plurality of nonvolatile memory elements each having a control gate coupled to the same word line. In a nonvolatile memory device having a memory array in which the above-mentioned erasing is enabled for each block, the source line of the nonvolatile memory element shared for each block is selected at the time of writing. A source which applies a predetermined bias voltage for reducing the potential difference between the floating gate and the source and drain to unselected blocks and a predetermined high voltage at the time of erasing is applied to unselected blocks. A switch circuit is provided. Or,
In one memory block, a word line and a source line are configured so that a high voltage is not supplied to a word line in a non-selected memory block at the time of writing.

According to the above-described means, a predetermined bias voltage for reducing the potential difference between the floating gate and the source and drain is applied to the unselected block at the time of writing, or the word line is provided for each block. And the source line are divided, it is possible to prevent or reduce the occurrence of an undesired tunnel current due to the write operation in the unselected memory block.

[0011]

FIG. 1 is a block diagram showing an embodiment of an electrically erasable EEPROM (hereinafter also referred to as a flash memory) to which the present invention is applied.
Each circuit block shown in the figure is not particularly limited, but is formed on one semiconductor substrate by a well-known semiconductor integrated circuit technology. Further, in the same figure, “○” marks indicate external terminals provided in the flash memory.

In FIG. 1, a plurality of word lines, a plurality of data lines arranged so as to intersect these word lines, and a non-volatile memory element provided at each intersection of the word lines and the data lines ( A memory array (or memory mat) in which memory cells are arranged in a matrix.
Are divided into memory blocks MB0 to MBn. In a memory array, a word line is arranged to extend in a horizontal direction, and a control gate of a memory cell is coupled to the word line. In addition, a data line (or a bit line or a digit line) and a source line are arranged to extend in a vertical direction, and the drain and the source of the memory cell correspond to the data line and the source line, respectively. Connected in common.

ADB is an address buffer which receives external address signals A0 to Ai supplied through external terminals and receives an internal address signal ax corresponding to an X-system address signal and an Y-system address signal. Internal address signal a
Form y. XDC is an X-system decoder that receives the internal address signal ax formed by the address buffer ADB and decodes the internal address signal ax. Although not particularly limited, in this embodiment, the address buffer ADB and the X-system decoder XDC are common to each of the memory blocks MB0 to MBn of the memory array. That is, the X-system decoder XDC
Decodes the internal address signal ax to obtain the memory array (memory blocks MB0 to MB
A word line selection signal for selecting one word line specified by the internal address signal ax is formed from the plurality of word lines in each of n). Thereby, one word line common to each of the memory blocks MB0 to MBn is selected.

In FIG. 1, YDC is a Y-system decoder, which decodes an internal address signal ay formed by the address buffer ADB, and outputs an internal address signal a.
A data line selection signal according to y is formed. One data line designated by the internal address signal ay among a plurality of data lines provided in each of the memory blocks MB0 to MBn of the memory array is replaced with a common data line (not shown) commonly provided in each memory block. Y to be combined with
A gate YG is provided. The Y gate YG receives the data line selection signal formed by the Y-system decoder, and connects the one data line to a corresponding common data line.

Thus, the memory blocks MB0 to MB0
In the memory array composed of MBn, one word line and one data line according to the X-system internal address signal ax and the Y-system internal address signal ay corresponding to the address signals A0 to Ai supplied from the outside. Is selected, and the memory cell provided at the intersection of the selected word line and data line is selected. That is, a memory cell coupled to the selected word line and data line is selected from a plurality of memory cells in the memory array.

When a plurality of memory cells are selected by one memory access, in other words,
When writing / reading data of a plurality of bits, a plurality of memory arrays as described above are provided. Although not particularly limited, in this embodiment, data writing / reading is performed in units of 8 bits. At this time, the memory array as described above has 8
Are provided.

In this embodiment, a write operation or a read operation is performed almost simultaneously on the memory cells selected from each of the eight memory arrays as described above. That is, the information writing or reading operation is performed in units of 8 bits. For this purpose, the flash memory of the present embodiment is provided with eight external input / output terminals D0 to D7, and is provided between the eight memory arrays and the corresponding external input / output terminals D0 to D7. An input / output circuit IOB including a data input buffer and a data output buffer, a sense amplifier SA as a read circuit, and a write amplifier WA as a write circuit are provided. Eight of these sense amplifiers SA and write amplifiers are prepared in accordance with the eight memory arrays as described above, and each of them is provided with an external input / output terminal D.
0 to D7.

In FIG. 1, CLG is a control circuit having a control function of automatic erasure. The control circuit CLG controls the external terminals CEB, OEB, and WEB, the external signal or voltage supplied to the high voltage VPP, and the signal from the internal circuit. In response, a timing signal necessary for a series of erase operations is formed. Terminal CEB
Is a control input terminal to which a chip enable signal is input, OEB is a control input terminal to which an output enable signal is input, and WEB is a control input terminal to which a write enable signal is input. Also, VCC
Is an external terminal for supplying a power supply voltage VCC such as about 5 V to each circuit, and GND is an external terminal for supplying a circuit ground potential of 0 V to each circuit block. VP
P is a high voltage terminal to which a high voltage such as 12 V is input during writing and erasing.

In this embodiment, in order to enable erasing for each block, the source switch circuits SS0 to SSn are connected to a common source line in which the sources of the memory cells provided in the memory blocks MB0 to MBn are shared. Provided. The source switch circuits SS0 to SSn have a ternary output function, and generate a bias voltage according to an operation mode according to a write control signal PROG, an erase control signal ERASE, and a block selection signal S0 to Sn formed by a control circuit CLG. One voltage is selectively output from the bias voltage VS, the high voltage VPP, and the ground potential 0 V of the circuit formed by the circuit BVG.

The control circuit CLG generates a Y-system address signal ay from among the Y-system address signals ay in order to generate the selection signals S0 to Sn for a plurality of memory blocks as described above. A signal is input. The control circuit CLG sends a control signal to the input / output circuit IOB through the signal line IOC for controlling the write and read operations, and is not particularly limited.
It receives commands input from terminals D0 to D7 in a specific input mode and forms mode signals for various internal sequence operations. Further, the control signal CLG supplies a control signal PROG to the write amplifier WA.

When the terminal CEB is at a high level and a high voltage is not supplied to the terminal VPP, the EEPROM is not selected. If the terminal CEB is at a low level, the terminal OEB is at a low level, and the terminal WEB is at a high level, the read mode is set. When the terminal CEB is at a low level and the terminal WEB is at a low level in a state where the high voltage is supplied to the terminal VPP, a command input mode is set, and various program modes are executed according to input bit patterns input from the terminals D0 to D7. . The program mode includes, for example, a write mode, a batch erase for all blocks, a selective erase mode for each block, and the like. The number of control terminals may be increased so that the internal operation mode is instructed only by a combination of the control terminals without using the above-mentioned command.

FIG. 2 shows an EEPR to which the present invention is applied.
A circuit diagram of a memory array unit and main peripheral circuits as one embodiment of the OM is shown. Although not particularly limited, each circuit element in the figure is formed on a semiconductor substrate such as a single crystal silicon by a known CMOS (complementary MOS) integrated circuit manufacturing technique. In the figure, a P-channel MOSFET has an N-channel MOSFET by adding an arrow to its channel (back gate) portion.
It is distinguished from OSFET. This is the same in other drawings.

Although not particularly limited, the integrated circuit is formed on a semiconductor substrate made of single-crystal P-type silicon. The N-channel MOSFET is formed of polysilicon formed on the surface of the semiconductor substrate between the source region and the drain region, and between the source region and the drain region, with a thin gate insulating film interposed therebetween. Composed of simple gate electrodes. P-channel MOSFET
It is formed in an N-type well region formed on the surface of the semiconductor substrate. Thereby, the semiconductor substrate forms a common substrate gate of the plurality of N-channel MOSFETs formed thereon, and the ground potential of the circuit is supplied. The N-type well region has a P-channel MOSFET formed thereon.
Of the substrate gate. The substrate gate of the P-channel MOSFET, ie, the N-type well region, is coupled to power supply voltage Vcc. However, in the case of a high-voltage circuit, the N-type well region in which the corresponding P-channel MOSFET is formed is connected to an externally applied high voltage VPP, an internally generated high voltage, or the like. Alternatively, the integrated circuit is a single crystal N
It may be formed on a semiconductor substrate made of mold silicon. In this case, the N-channel MOSFET and the nonvolatile memory element are formed in the P-type well region, and the P-channel MOSFET is formed.
T is formed on an N-type substrate. In the present invention, MOSFET is used in the meaning of an insulated gate field effect transistor (IGFET).

As the above-mentioned memory array, two memory blocks MB0 and MBn are exemplarily shown as representatives. This memory array has a memory cell (nonvolatile memory element... MOSFETM1 to M8) having a stacked gate structure having a control gate and a floating gate shown as an example, and word lines W0 to Wm.
And data lines D0, D1 to Dj, Dj + 1. Although not particularly limited, the memory cells M1 to M8 have the same structure as that of FIG. That is, as described above, these memory cells M1 to M8
It has a structure similar to that of a memory cell of a ROM, but the point that the erasing operation is electrically performed by using a tunnel phenomenon between a floating gate and a source coupled to a source line as described later is different from a conventional ultraviolet light. This is different from the EPROM erasing method used.

The memory cells MB1 and MBn shown in the above-mentioned example are arranged in the same row as the memory cells M1.
And the control gates of M2 and M5 and M6 (M3 and M4 and M7 and M8)
(Wm). Word lines W0 and Wm are connected to level conversion circuits LVC0 and LVC constituting a word driver.
driven by m. When the output of the decoder circuit DEC is set to the low level, the low level is transmitted through the cutting MOSFET Q10 and the N-channel type MOSF
ETQ8 is turned off and P-channel MOSFET Q
7 is turned on. Thereby, high voltage VPP is transmitted to word line W0. When the output signal of the decoder circuit DEC is at a high level, the cutting MOSFET Q
The N-channel MOSFET Q8 is turned on through 10 to lower the word line W0 to a low level such as the ground potential of the circuit. This low level turns on the feedback P-channel MOSFET Q9, raising the input signal to the high voltage VPP. Thus, the P-channel MOSFET Q7 can be turned off. With the rise of such an input signal, the cutting MOSF
Since the ETQ 10 is turned off, a direct current is prevented from flowing from the high voltage VPP to the decoder circuit DEC operating at the power supply voltage VCC and forming a high-level output signal. In the case of a read operation, VPP
Is switched to VCC.

Memory cells M1, M3 arranged in the same column
, M2 and M4 drains are connected to corresponding data lines D
0 and D1, and the memory cells M5, M7, M6 and M
8 drains respectively correspond to data lines Dj and Dj +
1 connected. The sources of the memory cells M1 to M4 of the memory block MB0 are connected to the corresponding common source line CS0, and the sources of the memory cells M5 to M8 of the memory block MBn are connected to the corresponding common source line C0.
Connected to Sn.

Although there is no particular limitation, since writing / reading is performed in units of a plurality of bits such as 8 bits (or 16 bits), the memory array has a total of 8 bits.
A plurality of sets such as a set (or 16 sets) are provided. FIG. 1 shows a circuit corresponding to one bit.

The data lines D0 to Dj + 1 constituting the one memory array are connected to column (column) selection switch MOSFETs Q20 and Qj which receive selection signals Y0, Y1 to Yj and Yj + 1 formed by the Y-system decoder YDC.
It is connected to the common data line CD via 21 to Q24 and Q25. The common data line CD is connected to the write amplifier WA0.
Output terminal. This write amplifier WA0
Of the external terminals D0 to D7, the MOSFET Q15 receiving the output signal Di of the write data input buffer receiving the write signal input from the corresponding D0 terminal, the MOSFET Q16 receiving the bias voltage VP, and the MOSFET Q17 receiving the control signal PROG. And transmits the voltage of the high voltage terminal VPP to the common data line CD. MOSFET Q16 is MOSFET
This is to prevent a high voltage such as the high voltage VPP from being directly applied between the drain and the gate of the Q17 or Q15, and to supply an intermediate high voltage VP to the gate.
By inserting the ETQ16, these voltages are divided to reduce the voltages applied to the individual MOSFETs Q17 and Q15.

On the other hand, the sense amplifier SA is connected to the common data line CD via the switch MOSFET Q11.
0 is coupled to the input terminal of the input stage circuit. MOSFETs Q12 to Q14 for performing an amplification operation of the input stage, inverter circuits N2 and N3 for controlling the MOSFETs, and a CMOS inverter circuit N
4 is called a sense amplifier SA0. The operating voltage VCC 'of the sense amplifier SA0 is not particularly limited, but is supplied with a power supply voltage VCC such as 5 V at the time of normal reading, and is switched to a predetermined voltage lower than 5 V at the time of erase verify as described later. The MOSFET Q11 has a control signal PRO.
It is controlled by the output signal of the inverter circuit N1 receiving G, and is turned off during a write operation. As a result, a relatively high potential of the common data line CD during writing is not supplied to the input of the sense amplifier SA0.

The memory level of the memory cell read to the common data line CD is set to the MO level which is turned on at the time of reading.
Through the SFET Q11, the source is connected to the source of the connected N-channel type amplifying MOSFET Q12. Between the drain of the amplification MOSFET Q12 and the power supply voltage terminal VCC ', there is provided a P-channel type load MOSFET Q13 whose gate and source are connected. The load MOSFET Q13 performs an operation of flowing a precharge current to the common data line CD for a read operation.

In order to increase the sensitivity of the amplification MOSFET Q12, the voltage of the common data line CD via the switch MOSFET Q11 is supplied to the inputs of the inverter circuits N2 and N3 acting as inverting amplification circuits. An output signal of the inverter circuit N3 as an inverting amplifier circuit is supplied to the gate of the amplifier MOSFET Q12. In addition, a MOSFET acting as a limiter is connected to the source input.
Charge-up is performed from the power supply terminal VCC 'via Q14. The output signal of the inverter circuit N2 as an inverting amplifier is supplied to the gate of the MOSFET Q14.

At the time of reading from a memory cell, the memory cell has a higher or lower threshold voltage with respect to a selected level of a word line according to information charges stored in a floating gate. If the memory cell selected by the X-system and Y-system decoders XDC and YDC is turned off despite the word line being set to the selected level, the common data line CD
Is set to a relatively high level by current supply from MOSFETs Q12 and Q14. On the other hand, when the selected memory cell is turned on by the word line selection level, the common data line CD is set relatively low.

In this case, the high level of the common data line CD is such that the output voltage of a relatively low level formed by the inverting amplifier circuit receiving this high level potential is a MOSFET.
The potential is limited to a relatively low potential by being supplied to the gate of Q14. On the other hand, as for the low level of the common data line CD, a relatively high level voltage formed by an inverting amplifier circuit receiving this low level potential is the MOSFET Q1.
4 to a relatively high potential. By such a level limiting action of the common data line CD, the signal change speed when the storage information continuously read from the memory cell changes from the 1 level to the 0 level or when the storage information changes from the 0 level to the 1 level. Can be substantially faster.

The amplifying MOSFET Q12 performs an amplifying operation on a gate-grounded source input, and transmits an output signal to an input of the CMOS inverter circuit N4. CMOS
The inverter circuit N4 shapes the waveform of the drain output signal of the amplifying MOSFET Q12 and transmits it to the input of the corresponding data output buffer DOB. Data output buffer DOB
Amplifies the signal from the sense amplifier SA0 and sends it out from the corresponding external terminal D0. Although not shown in the figure, the write signal supplied from the external terminal D0 is input to the data input buffer, and the output signal Di is supplied to the gate of the MOSFET Q15 of the write amplifier WA0.

In this embodiment, each memory block MB0
To the common source lines CS0 to Cn of the memory blocks MB0 to MBn in order to enable the selective erasing operation for each of the memory blocks MB0 to MBn.
Source switch circuits SS0 to SSn as erase control circuits are provided corresponding to Sn, respectively. In the figure, a specific circuit of the source switch circuit SS0 is illustratively shown as a representative.

The source switch circuit SS0 includes a P-channel MOSFET Q6 for supplying a high voltage VPP to the source line CS0 during erasing, and a common source line CS0 during writing.
N-channel MOSFET that supplies 0 V to the ground potential
There is provided a P-channel MOSFET Q4 for supplying an intermediate bias voltage VS formed by a bias voltage generation circuit BVG described later. This MOSF
ETQ4 and Q5 are switch-controlled complementarily during writing.

The gate of the P-channel MOSFET Q6 has a block selection signal S0 and an erase control signal ERASE.
Receiving the output signal of the NAND gate circuit G1. The gate of the P-channel MOSFET Q4 is supplied with the output signal of the inverter circuit N receiving the block selection signal S0 and the output signal of the NAND gate circuit G2 receiving the write control signal PROG. The output signal of the OR gate circuit G5 is supplied to the gate of the N-channel MOSFET Q5. This OR gate circuit G
5 is supplied with an output signal of a NOR gate circuit G3 receiving an erase control signal ERASE and a write control signal PROG, and an output signal of an AND gate circuit G4 receiving a write control signal PROG and a block selection signal S0.

In a read operation other than write / erase, the control signals ERASE and PROG are both set to low level "0". Therefore, the output signal of the NOR gate circuit G3 becomes high level "1", and the output signal of the OR gate circuit G5 becomes high level.
OSFET Q5 is turned on. At this time, the output signals of the NAND gate circuits G1 and G2 are equal to the signal ERAS.
The level is set to a high level in response to the low level "0" of E and PROG, and both the P-channel MOSFETs Q4 and Q6 are turned off. As a result, the ground potential of the circuit is supplied to the common source line CS0 by the MOSFET Q5 turned on.

In the write operation, when the erase control signal ERASE is at a low level and the write control signal PRO is
G is set to high level. In the memory block MB0 where writing is performed, the output signal of the AND gate circuit G4 becomes high level by the high level of the write control signal PROG and the high level of the block selection signal S0, and the output signal of the OR gate circuit G5 becomes high as described above. To level. As a result, the MOSFET Q5 is turned on, and the ground potential of the circuit is supplied to the common source line CS0. At this time, the output signal of the NAND gate circuit G1 is set to a high level by the low level of the erase control signal ERASE, and the MOSFET Q6 is turned off. In addition, since the output signal of the inverter circuit N is set to low level by the high level of the block selection signal S0, the output signal of the NAND gate circuit G2 is set to high level. As a result,
MOSFET Q4 is also turned off.

In a write operation in which the erase control signal ERASE is at a low level and the write control signal PROG is at a high level, when data is not written in the memory block MB0 due to data being written in another memory block. The output signal of the NAND gate circuit G2 becomes low level according to the high level of the output signal of the inverter circuit N receiving the low level of the block selection signal S0 and the high level of the write control signal PROG. As a result, the P-channel MOSFET Q4 is turned on, and the bias voltage VS generated by the bias voltage generation circuit BVG is applied to the common source line CS0. At this time, the output signal of the NAND gate circuit G1 is set to a high level by the low level of the erase control signal ERASE, and the MOSFET Q6 is turned off. Further, the output signal of the AND gate circuit G4 is at the low level due to the low level of the block selection signal S0, and the output signal of the NOR gate circuit G3 is at the low level according to the high level of the write control signal PROG.
5 is also at the low level, and the MOSFET Q5 is turned off.

In the erase operation, the erase control signal E
RASE is at high level, and write control signal PROG is at low level. Memory block M to be erased
In B0, the output signal of the NAND gate circuit G1 becomes low level due to the high level of the erase control signal ERASE and the high level of the block selection signal S0, and the P-channel MOSFET Q6 is turned on. As a result, the high voltage VPP is supplied to the common source line CS0. At this time, due to the low level of the write control signal PROG, the output signal of the NAND gate circuit G2 goes high, turning off the MOSFET Q4. Further, since the output signals of the NOR gate circuit G3 and the AND gate circuit G4 are both set to the low level by the low level of the write control signal PROG, the output signal of the OR gate circuit G5 is also set to the low level, and the MOSFET Q5 is also turned off.

In the erase operation, the erase control signal E
RASE is at high level, and write control signal PROG is at low level. When erasure of memory block MB0 is not performed in response to erasure of another memory block, common source line CS0 is placed in a high impedance state. That is, since the output signal of the NAND gate circuit G2 becomes high level due to the low level of the write control signal PROG, the MOSFET Q4 is in the off state, and the output signal of the NOR gate circuit G3 is low level according to the high level of the erase control signal ERASE. Since the output signal of AND gate circuit G4 is at a low level in accordance with the low level of control signal PROG, MOS
The FET Q5 is off and the output signal of the NAND gate circuit G1 is at high level in response to the low level of the block selection signal S0, so that the MOSFET Q6 is off. Instead of this configuration, in the erase operation, the common source line CS0 of the memory block that is not erased may be set to the circuit ground potential. That is, the erase control signal ERASE and the block selection signal inverted by the inverter circuit may be supplied to the AND gate circuit, and the output signal may be supplied to the input of the OR gate circuit G5. Other source switch circuits SS1 to SS1 (not shown)
The configuration and operation of SSn are the same as those of the above-described circuit, and thus description thereof is omitted.

The bias voltage generation circuit BVG is composed of the following circuits. Zener diode ZD and current limiting MOSFET Q2 are connected in series. This series circuit is supplied with a high voltage VPP via a P-channel MOSFET Q1 which is switch-controlled by an output signal of an inverter circuit receiving a write control signal PROG. Although not particularly limited, the MOSFET is connected to the Zener voltage.
The voltage is added to the threshold voltage between the gate and the source of Q2 and divided by the series resistors R1 and R2. This divided voltage is transmitted to the gate of the source follower output MOSFET Q3. The drain of the MOSFET Q3 is connected to the power supply voltage VCC, and the bias voltage VS is output from the source.

In this embodiment, the MOSFETs Q2 and Q3
Is approximately equal, the Zener constant voltage by the Zener diode ZD is divided by the resistors R1 and R2, so that a constant voltage independent of the power supply voltage VCC or the high voltage VPP can be formed. it can. By supplying such a constant voltage VS to a common source line of a memory block in which writing is not performed in a writing operation, a voltage difference between a floating gate and a source of a memory cell in an erased state in a memory block in which writing is not selected. Is reduced so that the tunnel injection current flowing therethrough is substantially prevented.

FIG. 3 is a circuit diagram of one embodiment of the block selection signal generating circuit. FIG. 3 shows select signals S0 and S0 corresponding to one memory block MB0 and MBn.
The circuit forming n is illustratively shown as a representative.
Although this circuit is not particularly limited, the control circuit CL shown in FIG.
G. Y-system address signals ay corresponding to a plurality of blocks into which the memory array is divided are supplied to NAND gate circuits NAND1 and NAND2 as decode circuits.

For example, when the memory array is divided into eight memory blocks, the upper three bits of the Y-system address signal composed of a plurality of bits are used, and eight combinations of the decode signals are used depending on the combination. Is formed. The write control signal PROG and the erase control signal ERASE are input to the NOR gate circuit NOR3.
The output signal of the NOR gate circuit NOR3 is used as a gate control signal of the NOR gate circuits NOR1 and NOR2 that output the output signals of the NAND gate circuits NAND1 and NAND2. That is, the above decoded signal is
Write control signal PROG or erase control signal ERASE
Only when a writing operation or an erasing operation is instructed by, any one selection signal corresponding to the Y-system address signal ay is output. When the batch erase function is added, a logic gate may be added so that the decode output is invalidated by the batch erase control signal and all the signals S0 to Sn are set to the high selection level.

FIG. 4 is a circuit diagram showing another embodiment of the bias voltage generating circuit. In the figure, for the sake of simplicity of the drawing, circuit symbols given to circuit elements are partially overlapped with others, but it should be understood that each has a separate circuit function. This is the same in other drawings described below. In this embodiment, FIG.
Resistors R1 and R2 of the bias voltage generation circuit BVG shown in FIG.
, MOSFETs Q4 and Q5 are used. That is, the gates and drains of the N-channel MOSFETs Q4 and Q5 are commonly connected and used as a resistance element. In this embodiment, the voltage division ratio is set by the conductance ratio corresponding to the ratio between the channel widths of the MOSFETs Q4 and Q5.

FIG. 5 is a circuit diagram showing another embodiment of the bias voltage generating circuit. In this embodiment, FIG.
Instead of forming a constant voltage once by the Zener diode ZD shown in (1) and dividing the constant voltage to obtain a bias voltage, the high voltage VPP is divided by the conductance ratio of the P-channel MOSFET Q4 and the N-channel MOSFET Q5. Is obtained. MOSFETs Q4 and Q5
Are formed in a relatively large size. Therefore, the current limiting MOSFET Q1 is inserted in series to
This limits the DC current flowing through Q4 and Q5. The N-channel MOSFET Q5 is controlled by the write control signal PROG so that the bias voltage is output only during the write operation, and the P-channel MOSFET is inverted by the signal inverted by the inverter circuit N1.
Q4 is controlled. With this configuration, a special manufacturing process for forming a Zener diode on a semiconductor substrate can be omitted.

FIG. 6 is a circuit diagram showing still another embodiment of the bias voltage generating circuit. In this example,
N-channel MOSFE of FIG. 5 as a current limiting element
A depletion type MOSFET Q6 is used instead of TQ1. Thus, depletion type MOS
When the FET Q6 is used, a current limiting operation is performed by a constant current by connecting the gate and the source thereof, and the high voltage VPP is divided by the MOSFETs Q4 and Q5. It is possible to eliminate the influence of voltage variations.

FIG. 9 is a characteristic diagram showing the relationship between the number of times of rewriting of the flash memory according to the present invention and the threshold voltage in the erased state. In the flash memory shown in FIG. 2, for example, the memory cell M1 of the memory block MB0 is similarly provided.
Write (1 → 0) to the word line W0
A high level such as 2V is applied, and a high level such as 6V is supplied to the data line D0 by the activated write amplifier WA. The above-mentioned hot electrons are generated in the memory cells of the memory block MB0 and injected into the floating gate to change the threshold voltage to a high level as described above. At this time, in the other memory blocks MB1 to MBn where writing is not performed, a predetermined bias voltage VS is applied through the source switch circuits SS1 to SSn. As a result, the potential difference between the floating gate and the source is reduced in the memory cells M5, M6, etc. by being coupled to the word line W0 of the memory blocks MB1 to MBn where no writing is performed and being set to "1" in the erased state. Tunnel current through the tunnel oxide film can be prevented or greatly restricted.

In the figure, the bias voltage VS is set to 0 V, 1
V, 2 V, and 3 V show the results of the computer simulation. That is, when the bias voltage VS is set to 0 V as in the related art, the threshold voltage increases after about 1000 rewrites, resulting in a substantially erroneous write state. On the other hand, when the bias voltage VS is increased to 1 V, 2 V, and 3 V, the increase in the threshold voltage decreases with the increase in the voltage, and no change in the threshold voltage is observed at 3 V.

FIG. 10 is a characteristic diagram showing the relationship between the number of rewrites of the flash memory according to the present invention and the threshold voltage in the written state. In the figure, the characteristics of the write level on the non-selected word lines of the memory blocks to which no write is performed are obtained. That is, the effect of increasing the bias voltage VS to 3V, 4V, 5V and 6V was examined. When the potential of the common source line in a non-selected memory block in which writing is not performed as described above is increased, an electric field in the opposite direction acts on a memory cell coupled to the non-selected word line. That is, the potential of the unselected word line is 0 V, and when the potential of the source is raised to 3 V or more as described above, an electric field acts between the floating gate and the source in the opposite direction, and the write operation causes the write state “0”. , The threshold voltage of the memory cell placed at "" decreases. In other words, the erase operation is substantially performed.

From the above, it can be seen that there is an upper limit on the bias voltage applied to the common source line of the non-selected memory block during the write operation in the flash memory performing the block erase operation. Accordingly, the bias voltage VS is kept constant in consideration of the thickness and quality of the tunnel insulating film of the memory cell, the capacitance ratio between the parasitic capacitance of the control gate and the floating gate, and the parasitic capacitance of the floating gate and the source. The voltage is set to the upper limit.

When the bias voltage VS is a constant voltage using a Zener diode or the like, the power supply voltage V
A constant voltage that is not affected by CC. When the source potential is too high as described above, it adversely affects the memory cell in the written state, and when the source potential is low, the improvement in the retention characteristics of the memory cell in the erased state is weakened. Therefore, it is desirable to use a constant voltage in order to guarantee the number of times of rewriting.

FIG. 7 is a main part circuit diagram of another embodiment of the flash memory according to the present invention. In this embodiment, the memory array is divided into two, that is, two memory blocks MB0 and MB1. The word line is divided at the center and separated to the left and right, and level conversion circuits LVC0L and LVC0R as word drivers are provided for each. The source switch circuits SS0 and S0 according to the memory blocks MB0 and MB1 divided into two as described above.
S1 is provided.

In this configuration, for example, the memory block MB
When writing to 0, all the word lines of the memory block MB1 to be deselected can be set to the unselected low level. Therefore, in the unselected memory block MB1, no tunnel current flows in the memory cells in the erased state. Thus, in the unselected memory block MB1, the potential of the source line may be set to the ground potential of the circuit in the write operation as in the read operation without applying the intermediate bias voltage VS as described above. . From this, the source switch circuit SS
0 can be greatly simplified. That is, since the potential of the source line may be the ground potential of the circuit except for the erasing operation, a P-channel MOSFET transmitting the high voltage VPP
The gate of Q6 is supplied with an output signal of a NAND gate circuit G1 receiving a block selection signal S0 and an erase control signal ERASE, and a P-channel type M transmitting the ground potential of the circuit.
The gate of the OSFET Q5 has an erase control signal ERASE
Receiving the output signal of the inverter circuit N0.

FIG. 8 is a circuit diagram of a main part of still another embodiment of the flash memory according to the present invention. In this embodiment, the memory array is divided into a plurality of blocks for each word line. That is, one memory block is configured using a plurality of word lines as a unit. The sources of the memory cells in this memory block are shared and connected to a source line. Therefore, although not particularly limited, it is convenient from the viewpoint of layout that the source line does not extend in parallel with the data line as in the above embodiment, but extends in parallel with the word line. In this configuration, the block selection signal uses an X-system address signal instead of the Y-system address signal corresponding to the data line as described above. Although not shown,
When a word line of a memory array is divided into eight to form eight memory blocks, eight block selection signals are used as block selection signals by using upper three bits of the X-system address signal. It is formed.

In this configuration, since one word line is always selected in the memory array, for example, when writing to memory block MB0, the word line of another memory block MBn or the like which is not selected is selected. Are all set to the unselected low level. Therefore, in another unselected memory block Bn or the like, a tunnel current does not flow in a memory cell in an erased state. As a result, in the unselected memory block MBn or the like, the potential of the source line is set to the ground potential of the circuit in the same manner as the read operation during the write operation without applying the intermediate bias voltage VS as shown in FIG. Is also good. From this, the source switch circuit SS0 can be greatly simplified as in the embodiment of FIG. That is, the potential of the source line may be the ground potential of the circuit during the operation other than the erasing operation.
The output signal of the NAND gate circuit G1 receiving the block select signal S0 and the erase control signal ERASE is supplied to the gate of the P-channel MOSFET Q6 which transmits the ground potential of the circuit.
Is supplied with an output signal of the inverter circuit N0 receiving the erase control signal ERASE.

In the above configuration, the source line is set to the high impedance state for the memory block which is not erased at the time of the erase operation as described above. If the potential of the source line of the memory block which is not erased in the erase operation is to be set to the ground potential of the circuit, for example, the erase control signal ERASE
And an AND gate circuit for receiving an inverted signal of block selection, and an output thereof and an output signal of the inverter circuit N0 may be supplied to the gate of the MOSFET Q5 through an OR gate circuit.

FIG. 11 is a flowchart showing an example of an algorithm of the erase mode in the flash memory of this embodiment. In the figure, a series of pre-write operations as shown by the dotted lines in the figure are executed prior to the actual erase operation. That is, the storage information of the memory cell in the memory block before erasing, in other words, the threshold voltage of the storage element varies in accordance with the presence or absence of writing as described above. The above-described pre-write operation is performed by performing writing to all the memory elements prior to the electrical erasing operation, so that the unwritten memory cells, that is, the memory cells in the erased state, that is, the internal automatic erasing according to this embodiment are performed. This is to prevent the occurrence of a memory cell having a negative threshold voltage due to the operation.

In general, in electrical erasing, the threshold voltage when erasing is continued for a long time can be a negative value, unlike the threshold voltage in a thermal equilibrium state. When erasing is performed by ultraviolet rays as in the EPROM, the storage device is settled at the threshold value at the time of manufacture, which is in contrast to the fact that the storage device can be controlled by a manufacturing method. In the above-mentioned memory cell, when the threshold value becomes negative, reading is adversely affected. In this prewrite operation, in step (1), address setting is performed such that an address signal for selecting an individual memory cell is generated by an address counter circuit.

In step (2), writing (pre-writing) is performed by generating a writing pulse. After this writing, in step (3), the address counter circuit is operated to increment (+1).
Performs address increment. Then, in step (4), it is determined whether or not the current address is the last address, and the pre-write is not performed until the last address (N
In the case of O), the flow returns to the writing step (2) to perform writing. This is repeated until the last address of one memory block. As described above, whether or not the final address is determined is performed after the address increment (3), so that the actually determined address is the final address + 1.

When the above pre-write is completed, the following erasing operation is executed. In step (5), an address for the erase operation is initialized.
In this embodiment, since erasure is performed in units of blocks, it is absolutely necessary to initialize this address. This address setting is also required for the erase verify performed thereafter.

In step (6), an erase pulse for batch erase of blocks is generated. Thereafter, a verify operation is performed in step (7) according to the address setting. In this verify operation, the operation voltage is switched to a lower voltage, for example, 3.5 V, which is lower than the low voltage VCC, and the above-described read operation is performed. In this read operation, the read signal is “0”
Then, since it is recognized that the threshold voltage has been set to the erased state of 3.5 V or less, the address increment is performed in step (8).

It is determined whether or not the address is the last address in the same manner as in the prewrite operation described above.
In O), the flow returns to step (7), and the same verify operation as described above is performed. This operation is repeated until the last address, thereby completing the erasing operation. In this erasing operation, since the memory block is erased at once as described above, the number of erasures is determined by the memory cell having the highest threshold voltage by the writing operation among the memory cells in the block. That is, the memory cell having the highest threshold voltage can be read at the above-mentioned 3.5 V,
That is, the erase pulse in step (6) is performed based on the result of the verification in step (7) until it has a low threshold voltage. By such a controlled erase operation, the threshold voltage of the memory cell can be accurately set to a predetermined voltage without making the threshold voltage negative.

FIG. 12 is a block diagram showing one embodiment of a microcomputer system using the flash memory according to the present invention. The microcomputer system according to the present embodiment mainly includes a microprocessor (CPU) and a ROM (read / read) storing programs and the like.
Only memory), R used as main memory device
AM (random access memory), input / output port I
/ OPORT, the batch erase type EEPROM according to the present invention
OM, liquid crystal display device or CRT (cathode ray tube) as a monitor connected via control circuit CONTROLLER
Are address bus ADDRESS and data bus DATA
And a control bus exemplarily shown and transmitting a control signal CONTROL.

In this embodiment, the display device LCD or C
The 12V power supply RGU required for RT operation is
Also used as high voltage VPP of ROM. Therefore, in this embodiment, the power supply RGU is a microprocessor CPU
Control signal from the terminal V during the read operation.
A function of switching PP to 5V such as VCC is added. FIG. 13 also shows the microprocessor CPU and E
The connection relation of each signal focusing on the EPROM is shown.

An address signal indicating the address space allocated to the EEPROM among the system addresses is supplied to the terminal CEB of the flash memory to the decoder circuit DEC to generate the chip enable signal CEB. Further, the timing control circuit TC includes a microprocessor C
It receives an R / W (read / write) signal, DSB (data strobe) signal and WAIT (wait) signal from the PU, and generates an output enable signal OEB and a write enable signal WEB.

In the microcomputer system of this embodiment, since the flash memory has the above-mentioned automatic erasing function, the microprocessor CPU
The flash memory is addressed to generate a signal CEB, and at the same time, to generate a command through the data bus DATA and the signals OEB, WEB, and the signal CEB specifying the mode in combination with the signals R / W, DSB, and WAIT. Thereafter, the flash memory enters an automatic erase mode internally as described above. When the flash memory enters the erasing mode, the address terminal, data terminal and all control terminals become free as described above, and are separated from the microprocessor CPU.

Therefore, the microprocessor CPU
Means that the flash memory is only instructed to be in the erase mode, and thereafter, data processing involving the exchange of information with another memory device ROM or RAM or an input / output port is performed using the system bus. Can be. This allows you to sacrifice system throughput,
The flash memory can be erased while placed in the system in the same manner as a full-function (rewritable by byte) EEPROM. Microprocessor C
After instructing the erase mode as described above, the PU designates the data polling mode for the EEPROM at appropriate time intervals, for example, when the level of the terminal D7 of the data bus is low / high. A determination is made to determine whether or not the erasing operation has been completed. If the erasing is completed and there is data to be written in the flash memory, a write instruction is issued.

The operation and effect obtained from the above embodiment are as follows. That is, (1) a nonvolatile memory element for erasing stored charges in a floating gate by a tunnel current through a tunnel insulating film is arranged in a matrix, and a plurality of nonvolatile memory elements in which a control gate is coupled to the same word line. In a nonvolatile storage device having a memory array in which a storage element is divided into a plurality of blocks and the above-described erasing is enabled for each block, writing is performed to a source line of the nonvolatile storage element shared for each block. The ground potential of the circuit is applied to the block which is occasionally selected, and the floating gate and the source are supplied to the unselected block.
A source switch circuit is provided which applies a predetermined bias voltage to reduce the potential difference between the drains and applies a predetermined high voltage at the time of erasing. In this configuration, a predetermined bias voltage that reduces the potential difference between the floating gate and the source and drain is applied to a non-selected block at the time of writing, or a word line and a source line are divided for each block. Therefore, an effect is obtained that the occurrence of an undesired tunnel current due to the write operation can be prevented or reduced in the unselected memory blocks.

(2) In one divided memory block, a non-selected memory block is configured such that a high voltage is not supplied to a word line in a non-selected memory block at the time of writing. An effect is obtained that the generation of an undesired tunnel current due to the write operation in the block can be prevented. (3) The upper limit of the bias voltage is a potential at which substantially no tunnel emission current is generated in the non-volatile memory element of the non-selected memory block at the time of writing.
The effect is obtained that the information retention characteristics of the erased state and the written state in the EPROM can be improved.

(4) The generation of an undesired tunnel current with high precision can be prevented by setting the bias voltage to be a constant voltage substantially independent of the power supply voltage and the write voltage. The effect is obtained. (5) The memory block to be erased performs a write operation on all the non-volatile storage elements in the memory block prior to the erase, so that an unwritten memory cell becomes negative by executing the erase operation. Is obtained.

(6) A nonvolatile memory element for erasing stored charges in a floating gate by a tunnel current through a tunnel insulating film is arranged in a matrix,
A plurality of nonvolatile memory elements each having a control gate coupled to the same word line are divided into a plurality of blocks, and the nonvolatile memory of the one memory block is provided for the memory array in which the erasing is enabled for each block. In the write operation of the element, the write operation is performed by applying a constant bias voltage to the source or the drain to which the nonvolatile memory element in the unselected memory block is coupled so as to reduce the potential difference between the floating gate and the source and the drain. By adopting this method, a predetermined bias voltage for reducing the potential difference between the floating gate and the source and drain is applied to the unselected blocks at the time of writing, or the word line and the source line are provided for each block. Is divided into unselected memory blocks. There effect that the occurrence of undesired tunneling current due to the write operation can be prevented or reduced.

Although the invention made by the inventor has been specifically described based on the embodiment, the invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the invention. Needless to say. For example,
As the storage element, in addition to a MOS transistor having a stacked gate structure used for an EPROM, a FLOTOX type nonvolatile storage element using a tunnel phenomenon for a write operation may be used. The high voltage VPP for writing / erasing is not limited to the one using a high voltage supplied from the outside. That is, if the current flowing at the time of writing / erasing is small, the low voltage VC
It is also possible to use a voltage boosted from C by a known charge pump circuit or the like. Further, the internal boosted power supply and the external high voltage VPP may be used in combination.

The configuration of the circuit part for controlling normal writing / reading and the like and the circuit part for controlling the erasing algorithm in the flash memory are any circuits as long as they perform the above-described operation sequence. It doesn't matter. The above-described erasing algorithm may be performed by an instruction from an external microprocessor or the like.
The circuit for controlling the erasing algorithm is not only a random logic circuit, but also a programmable logic array (PLA), a microcomputer and software incorporated, or an asynchronous circuit as in the above embodiment, but a synchronous circuit. No problem. in this way,
A circuit for realizing the above operation sequence can adopt various embodiments. Flash EEPR
The specific circuit configuration of the memory array and its peripheral circuits constituting the OM can adopt various embodiments. Further, the EEPROM or the like may be built in a digital semiconductor integrated circuit device such as a microcomputer.

The present invention can be widely applied to a nonvolatile memory device and a writing method in which a selective erase operation is performed for each block by a tunnel current.

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, nonvolatile memory elements for erasing stored charges in a floating gate by a tunnel current through a tunnel insulating film are arranged in a matrix, and a plurality of nonvolatile memory elements each including a plurality of nonvolatile memory elements each having a control gate coupled to the same word line. In a nonvolatile memory device having a memory array in which the above-described erasing is enabled for each block, a source line of a nonvolatile memory element shared for each block is selected during writing. The ground potential of the circuit is applied to the selected block, a predetermined bias voltage for reducing the potential difference between the floating gate and the source and drain is applied to the unselected blocks, and a predetermined high voltage is applied for erasing. Provide a source switch circuit or write data in one memory block. In a non-selected memory block, a word line and a source line are configured so that a high voltage is not supplied to the word line, so that the potential difference between the floating gate and the source / drain is reduced for the non-selected block during writing. To prevent or reduce the occurrence of an undesired tunnel current due to a write operation in a non-selected memory block because a predetermined bias voltage is applied to the memory block or a word line and a source line are divided for each block. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical erasing type EEP to which the present invention is applied;
FIG. 2 is a block diagram illustrating an embodiment of a ROM.

FIG. 2 is a circuit diagram of a memory array section and main peripheral circuits showing an embodiment of a flash memory to which the present invention is applied.

FIG. 3 is a circuit diagram showing one embodiment of a block selection signal generation circuit.

FIG. 4 is a circuit diagram showing another embodiment of the bias voltage generation circuit.

FIG. 5 is a circuit diagram showing another embodiment of the bias voltage generation circuit.

FIG. 6 is a circuit diagram showing still another embodiment of the bias voltage generation circuit.

FIG. 7 is a circuit diagram of a memory array section and main peripheral circuits showing another embodiment of the flash memory to which the present invention is applied.

FIG. 8 is a circuit diagram of a memory array section and main peripheral circuits showing still another embodiment of the flash memory to which the present invention is applied.

FIG. 9 is a characteristic diagram showing a relationship between the number of times of rewriting of the flash memory according to the present invention and a threshold voltage in an erased state.

FIG. 10 is a characteristic diagram showing a relationship between the number of times of rewriting of the flash memory according to the present invention and a threshold voltage in a written state.

FIG. 11 is a flowchart illustrating an example of an algorithm of an erase mode in the flash memory according to the present invention.

FIG. 12 is a block diagram showing an embodiment of a microcomputer system using a flash memory according to the present invention.

FIG. 13 is a block diagram showing a connection relationship between a microprocessor CPU and a flash memory.

FIG. 14 is a structural cross-sectional view for explaining an example of a conventional memory cell.

FIG. 15 is a characteristic diagram showing a relationship between the number of rewrites when erasing is performed in block units and a threshold voltage in an erased state.

FIG. 16 is a main part circuit diagram showing an example of a flash memory designed to perform erasing in block units considered prior to the present invention.

[Explanation of symbols]

ADB: Address buffer, XDC: X-system decoder, Y
DC: Y system decoder, MB0 to MBn: memory block, YG: Y gate, SA: sense amplifier, WA: write amplifier, IOB: input / output circuit, SS0 to SSn: source switch circuit, BVG: bias voltage generation circuit, C
LG: control circuit, LVC0, LVCm: level conversion circuit, CPU: microprocessor, ROM: read only memory, RAM: random access memory, I / OPORT: input / output port, EEPROM (F
LASH) ... Flash nonvolatile storage device, RGU ... 1
2V power supply, LCD: liquid crystal display, CRT: cathode ray tube, ADDRESS: address bus, DATA: data bus, DEC: decoder circuit, TC: timing control circuit, 3: drain, 4: floating gate, 5:
Source: 6: Control gate, 7: Thin oxide film (tunnel oxide film), 8: P-type silicon substrate, 9: N-type diffusion layer, 10: Low-concentration N-type diffusion layer, 11: P-type diffusion layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiaki Nishimoto 5-20-1, Kamizuhoncho, Kodaira-shi, Tokyo Inside Musashi Plant, Hitachi, Ltd. (72) Inventor Kazuhiro Komori 5 Kamimihoncho, Kodaira-shi, Tokyo Hitachi, Ltd. Musashi Plant, No. 20-1 (72) Inventor Hitoshi Kume 1-280, Higashi Koikebo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (12)

[Claims] A plurality of word lines, a plurality of data lines,
A memory array having a plurality of source lines and a plurality of memory cells, wherein the memory cells have their control electrodes coupled to the word lines, their drain electrodes coupled to the data lines, and A semiconductor memory device commonly coupled to a source electrode of a memory cell in the memory block for each block, and electrically erasable and writable by a potential change of the word line and the source line, wherein each of the word lines Is provided so as not to be extended to a plurality of memory blocks, and further includes means for selectively supplying a potential to the source line, wherein the means includes: When the first potential is applied to any one of the memory cells and the memory cell to be erased is to be erased, The second in passing source line 2
A semiconductor memory device for supplying the same potential. 2. The semiconductor memory device according to claim 1, wherein said first potential is a circuit ground potential, and said second potential is about 12 volts. 3. A plurality of word lines, a plurality of data lines,
A memory array having a plurality of source lines and a plurality of memory cells, wherein the memory cells have their control electrodes coupled to the word lines, their drain electrodes coupled to the data lines, and A semiconductor memory device commonly coupled to a source electrode of a memory cell in the memory block for each block, and electrically erasable and writable by a potential change of the word line and the source line, wherein each of the word lines Are not extended to a plurality of memory blocks, the plurality of memory blocks are arranged in a direction in which the word line extends, and a means for selectively supplying a potential to the source line; A word for selecting an arbitrary word line from a plurality of word lines in the memory block by an address signal supplied from outside A semiconductor memory device further comprising: a line selection unit. 4. The apparatus according to claim 3, wherein said means applies a first potential to said source line when writing to any one of said memory cells, and applies a first potential to said memory cell when erasing one of said memory cells. A common source line of a memory block to which the memory cell to be erased belongs.
A semiconductor memory device supplying a potential of 5. The semiconductor memory device according to claim 3, wherein the first potential is a ground potential of a circuit, and the second potential is about 12 volts. 6. The apparatus according to claim 3, further comprising a control unit, wherein the control unit receives an address signal from outside, and generates a block selection signal for selecting an arbitrary memory block from a plurality of memory blocks. Receiving an external control signal and generating an erasure control signal indicating an erasure mode, wherein the means receives the block select signal and the erasure control signal from the control means, and when the erasure control signal indicates the erasure mode, A semiconductor memory device wherein a predetermined high potential is supplied to a source line of a memory block selected by a block selection signal, and a circuit ground potential is supplied to a source line of a memory block not selected. 7. The device according to claim 6, wherein the control unit further receives an external signal, invalidates a block selection signal formed by the address signal,
A semiconductor memory device for generating a block selection signal for selecting all of the plurality of memory blocks. 8. A plurality of word lines, a plurality of data lines,
A memory array having a plurality of source lines and a plurality of memory cells, wherein the memory cells have their control electrodes coupled to the word lines, their drain electrodes coupled to the data lines, and A semiconductor memory device commonly coupled to a source electrode of a memory cell in the memory block for each block, and electrically erasable and writable by a potential change of the word line and the source line, wherein each of the word lines Are not extended to a plurality of memory blocks, the plurality of memory blocks are arranged in a direction in which the word line extends, and a means for selectively supplying a potential to the source line; Word line selecting means for selecting an arbitrary word line from the plurality of memory blocks according to an address signal supplied from the outside; A semiconductor memory device further provided. 9. The method according to claim 8, wherein said means applies a first potential to said source line when writing to any of said memory cells, and erases said data when erasing any of said memory cells. A common source line of a memory block to which the memory cell to be erased belongs.
A semiconductor memory device supplying a potential of 10. The semiconductor memory device according to claim 8, wherein the first potential is a ground potential of a circuit, and the second potential is about 12 volts. 11. The control device according to claim 8, further comprising control means, wherein said control means receives an address signal from outside and generates a block selection signal for selecting an arbitrary memory block from a plurality of memory blocks. Receiving an external control signal and generating an erase control signal indicating an erase mode, wherein the means receives the block selection signal and the erase control signal from the control means, and when the erase mode is indicated by the erase control signal, A semiconductor memory device wherein a predetermined high potential is supplied to a source line of a memory block selected by the block selection signal, and a circuit ground potential is supplied to a source line of a memory block not selected. 12. The control unit according to claim 11, wherein the control unit further receives an external signal, invalidates a block selection signal formed by the address signal,
A semiconductor memory device for generating a block selection signal for selecting all of the plurality of memory blocks.