JP2006155750A - Semiconductor memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor memory device capable of accelerating a reading speed. <P>SOLUTION: A memory unit 110 is configured by including an amplifier circuit 115 in addition to a cel string constituted of stacked type memory cell transistors C10 to C115, and selection transistors 112, 113, and 114, the gate electrode of the amplifier transistor 115 is connected to one end (node ND 11) of the cell string, and the amplifier circuit 115 drives a bit line BL 11 by reflecting the penetrating current of the cell string 111. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor memory device, and more particularly to a semiconductor memory device that stores data with a difference in threshold value of a field effect transistor (FET) constituting a memory cell, such as a flash memory or a mask ROM. Is.

  In recent years, flash memory has attracted attention as a storage medium for digital still cameras and mobile computer devices.

Flash memory is a semiconductor memory that uses tunneling or hot electron acceleration to pass electrons through a gate insulating film, inject them into a floating gate or trap layer, and change the threshold value of the cell transistor to store data. It is.
In such a flash memory, since a memory cell can be configured with only one transistor using a stacked gate structure, an MNOS structure, or the like, an inexpensive and large-capacity memory can be realized.
A typical example is a NAND flash memory.

FIG. 1 is a diagram illustrating an internal configuration example of a NAND flash memory.
In the NAND flash memory of FIG. 1, a plurality (4 in the example of FIG. 1) of memory units 1-1 to 1-4 are arranged in an array (in the example of FIG. 1, a 2 × 2 matrix array). . The memory units 1-1 to 1-4 are connected to the bit lines BL1 and BL2. The bit lines BL1 and BL2 are connected to sense amplifiers (SA) 2-1 and 2-2.

  As shown in FIG. 1, the memory unit 1-1 has a configuration in which a cell string STRG1 in which, for example, 16 memory cell transistors C0 to C15 are connected in series is disposed between selection transistors 11 and 12. . The gate electrodes of the selection transistors 11 and 12 are connected to the selection lines SL1 and SL2, and the gate electrodes of the memory cell transistors C0 to C15 are connected to the word lines WL0 to WL15. The configurations of the other memory units 1-2 to 1-4 are the same.

Each memory cell has a stacked gate structure and stores data according to the amount of charge accumulated in the floating gate. That is, when data is written into the cell and many electrons are injected into the floating gate, the threshold value of the transistor rises.
At this time, for example, the memory cell transistor C0 that is in the ON state when the gate is 0 V changes to the OFF state. Therefore, at the time of reading from the memory cell transistor C0, the gates of the memory cell transistors C1 to C15 are forcibly turned on with the power supply voltage Vcc, and the gate of only the memory cell transistor C0 is set to 0 V, so that the through current of the cell string STRG1 can be seen. It ’s fine.

  Usually, the above determination is performed by, for example, charging the bit line BL1 to Vcc and detecting whether or not the electric charge is discharged through the selected memory unit 1-1. Actually, a plurality of such memory units are arranged vertically and horizontally in the cell array.

As described above, the memory cell is composed of FETs, and the memory unit is configured based on the cell string in which the memory cells are connected in series. It has been adopted.
The mask ROM does not use the stacked gate structure as described above, and programming is performed by changing the threshold value of each transistor by implanting impurities into the channel region during the manufacturing process.

  Since such an array configuration does not require a contact region to the bit line for each cell, it is particularly suitable for a medium of a large capacity and inexpensive storage device.

When the above-described cell string is used, the arrangement efficiency improves as the number of memory cells connected in series increases, and the cell occupation efficiency in the chip increases.
However, the current driving capability of each cell string is reduced accordingly, and therefore it takes time to extract the charge of the charged bit line, and there is a disadvantage that the reading speed becomes slow.

In addition, when cells are to be arranged at a higher density in order to increase the capacity in the future, stacking transistors using TFTs (Thin Film Transistors) can be considered as a promising option.
However, in general, the capability of a transistor laminated with polysilicon or the like without using a silicon substrate is extremely low as compared with a normal transistor. Therefore, further connecting them in series in a string shape has a disadvantage that the reading speed is extremely deteriorated and is not suitable for practical use.

  An object of the present invention is to provide a semiconductor memory device capable of improving the reading speed.

  In order to achieve the above object, a semiconductor memory device according to a first aspect of the present invention includes a bit line and at least one memory unit connected to the bit line, and the memory unit includes a plurality of memory cells. Are connected in series, and an amplification drive circuit that drives the bit line reflecting the through current of the cell string, and each memory cell stores different data according to different threshold values. It is formed by an effect transistor.

  Preferably, the amplification drive circuit includes an amplification field effect transistor having one end of the source and drain connected to the first constant voltage source and the other end connected to the bit line, and one end of the cell string is Connected to the gate electrode of the amplifying field effect transistor, the other end is connected to the second constant voltage source.

  Preferably, when reading data from the memory, the gate of the driving field effect transistor is charged to a constant potential via the bit line, and the gate potential is changed by a through current via the cell string.

  Preferably, the cell string is laminated on an upper layer of the amplification drive circuit formed on a silicon substrate.

  Preferably, the field effect transistor forming the memory cell of the cell string is formed on a side wall of a groove formed in a semiconductor layer deposited on the amplification driving circuit via an insulating film.

  A semiconductor memory device according to a second aspect of the present invention includes a bit line and at least one memory unit connected to the bit line, and the memory unit includes a plurality of memory cells connected in series. A plurality of strings, and an amplification driving circuit for driving the bit line reflecting one through current arbitrarily selected from the cell string, wherein each memory cell stores different data according to a different threshold value. It is formed by a field effect transistor.

  Preferably, the amplification driving circuit is an amplification field effect transistor having one end of the source and drain connected to the first constant voltage source and the other end connected to the bit line, and one end of the plurality of cell strings. Are connected to the second constant voltage source, and the other end is connected to the gate electrode of the field effect transistor via an independent selection transistor.

  Preferably, the gate electrodes of the plurality of memory cells forming each of the plurality of cell strings are short-circuited between the plurality of cell strings, and are connected to independent drive circuits.

  Preferably, the cell string is laminated on at least two layers above the amplification driving circuit formed on the silicon substrate.

According to the present invention, a memory array is configured by combining an amplifier circuit with the cell string as described above, and using a memory unit including the unit as a unit and arranging them in an array.
When reading data from the memory, first, the gate of the driving field effect transistor is charged to a constant potential via the bit line. Next, the gate potential is changed by a through current through the cell string.
Further, for example, by forming a cell string with TFTs and stacking them on the amplifier circuit, the overhead associated with the area occupied by the amplifier circuit is eliminated while ensuring high-speed access.
Alternatively, by sharing a single amplifier circuit among a plurality of cell strings, the overhead is reduced while ensuring high-speed access.
Further, in addition to the circuit configuration, a plurality of cell strings are formed of TFTs, and these are stacked on each other, whereby high-speed access is performed while dramatically improving the degree of integration.

According to the present invention, it is possible to realize a semiconductor memory suitable for high-speed reading while having a highly integrated cell string structure in which memory cell transistors are connected in series.
Further, the degree of integration can be dramatically improved by adopting a laminated structure using TFTs or the like for the cell transistors.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 2 is a circuit diagram showing a first embodiment of the amplification type semiconductor memory device according to the present invention. FIG. 3 is a sectional view of a device structure corresponding to the circuit configuration of FIG.

The amplification type semiconductor memory device 100 according to the first embodiment of the present invention has a NAND flash memory as a basic component, and includes at least one memory unit 110 (only one is shown in the example of FIG. 2). They are arranged in an array (in the example of FIG. 2, a 1 × 1 matrix array). The memory unit 110 is connected to the bit line BL11. The bit L line BL11 is connected to a sense amplifier (SA) 120.
A plurality (N) of memory units similar to the memory unit 110 can be connected to the bit line BL11. Further, the memory units are arranged in a matrix array (N × M) by arranging a plurality of bit lines (M lines) in parallel.

As shown in FIG. 2, the memory unit 110 includes an amplification transistor 115 in addition to a cell string 111 composed of stacked memory cell transistors C <b> 10 to C <b> 115 and selection transistors 112, 113, and 114.
The cell string 114 is configured by, for example, 16 memory cell transistors C10 to C115 connected in series between nodes ND11 and ND12.
One end of the cell string 111 is connected to the node ND11, and the other end is connected to the node ND12.

  As shown in FIG. 3, the memory cell transistors C10 to C115 have floating gates (FG) on a channel formation region between the source / drain regions 201 (S / D) formed on the silicon substrate 200 via a gate insulating film 202. ) 203 and a control gate (CG) 205 connected to the word line via the interlayer insulating film 204 is formed on the floating gate 203.

The source of the selection transistor 112 is connected to the node ND11, and the drain is connected to the node ND13. The drain of the selection transistor 113 is connected to the node ND12, the source is connected to the ground potential GND (second constant voltage source), the drain of the selection transistor 114 is connected to the node ND11, and the source is connected to the node ND14. Yes.
The drain of the amplification transistor 115 is connected to the node ND14, and the source is connected to the ground potential (first constant voltage source).
A node ND13 formed by a connection point between the drain of the selection transistor 112 and the drain of the selection transistor 114 is connected to the bit line BL11.

  As shown in FIG. 3, the selection transistors 112 to 114 and the amplification transistor 115 have a control gate 206 formed on the channel formation region between the source / drain regions 201 formed on the silicon substrate 200 via the gate insulating film 202. Formed by a field effect transistor (FET).

The gate electrodes of the memory cell transistors C10 to C115 of the cell string 111 are connected to the word lines WL10 to WL115 (or the control gate 205 of the memory cell transistor is formed as a word line).
The gate electrodes of the selection transistors 112, 113, and 114 are connected to selection lines SL11, SL12, and SL13, respectively (or the control gate 206 of the selection transistor is formed as a selection line).

The gate of the amplification transistor 115 is connected to one end (node ND11) of the cell string 111.
The source / drain region 201 constituting the node ND11 and the gate electrode 206 of the amplification transistor 115 are connected by a wiring 208 such as aluminum through a contact hole formed in the interlayer insulating film 207.

In the amplification type semiconductor memory device 100 having such a configuration, the presence or absence of current penetration in the cell string 111 at the time of reading is reflected once in the gate potential of the amplification transistor 115, and the bit line BL 11 is driven by the amplification transistor 115.
Since only the gate charge of the amplifying transistor 115 needs to be extracted by the cell string 111, processing can be performed at a very high speed even if the driving capability is small.
On the other hand, the effective gate length of the amplifying transistor 111 can be reduced to 1/10 or less than that of the cell string 111 and can have a much higher driving capability, so that the bit line can be driven easily.
Therefore, even if many cell transistors are connected to the cell string 111, the reading speed does not deteriorate, and random access necessary for direct execution of a program on the memory can be performed at high speed, for example.

4A to 4G are timing charts for explaining an example of a specific access procedure of the amplification type semiconductor memory device according to the first embodiment.
4A shows the potential of the selection line SL2, FIG. 4B shows the potential of the selection line SL1, FIG. 4C shows the potential of the selection line SL3, and FIG. 4D shows the potential of the bit line BL11. 4E shows the potential of the word line WL10, FIG. 4F shows the potential of the word line WL11, and FIG. 4G shows the potential of the node ND11.
Here, an electron-injected and written state (threshold value is high) is defined as “0”, and an erased state (threshold value is low) is defined as “1”.

  For example, when writing is selectively performed from the erased state to the cell of the memory cell transistor C10, the writing procedure is performed as follows.

  1. The selection line SL1 for selecting the selection transistor 112 for writing is raised to Vcc. The bit line BL11 is charged to 0V when writing "0" (selected state), and charged to Vcc when not writing (unselected state).

  2. Next, all control gates including the word lines WL10 and WL11 connected to the memory cell transistors C10 to C115 in the cell string 111 are raised to 7V. At this time, the node ND11 including the gate of the amplification transistor 115 in the memory unit 111 is in a floating state when the bit line BL11 is Vcc (non-selected state), and rises to around 7 V in response to coupling with the control gate. On the other hand, when the bit line BL11 is 0V (selected state), 0V is transmitted as it is.

  3. Further, only the word line WL10 is raised to about 15V. As a result, 15 V is fully applied between the channel of the corresponding cell connected to the bit line BL11 to be written and the control gate (WL10). As a result, electrons are injected from the channel to the floating gate by FN tunneling, and “0” is written.

  4). The word lines WL10 and WL1 are sequentially returned to 0V, the write selection line SL11 is returned to 0V, the selection transistor 112 is turned off (closed), and the writing is completed.

  On the other hand, data reading from the memory cell transistor C10 can be performed smoothly and at high speed by charging the gate (node ND111) of the amplification transistor 115 simultaneously when charging the bit line BL11 as described below.

  1. The selection line SL11 for writing and the control gate (word line WL11 etc.) of the non-selected cells are set to Vcc, and the bit line BL11 is charged to Vcc. As a result, the node BL11 is also charged to Vcc via the bit line BL11.

  2. The selection line SL11 for writing is returned to 0V, the selection transistor 112 is turned off (closed), and the bit line BL11 and the node ND11 are separated.

  3. The selection line 113 for reading on the cell string 111 side is set to Vcc, the selection transistor 113 is turned on (opened), and the other end of the cell string 111 is connected to the ground. Thereby, when the state of the memory cell transistor C10 is “1” (erased state), a through current flows through the cell string 111, and the node ND11 is quickly discharged to 0V. On the other hand, when the memory cell transistor C10 is “0” (write state), the potential of the node ND11 is held at Vcc. Along with this, the amplification transistor 115 is turned off in the former and turned on in the latter.

  4). The selection transistor SL13 for reading is set to Vcc, the selection transistor 114 is turned on (opened), and the bit line BL11bl11 is discharged by the amplification transistor 115. Accordingly, the bit line BL11 is discharged to 0V only when the state of the memory cell transistor C10 is “0”. The potential of the bit line BL11 is received by the sense amplifier 120 or the latch, and data determination is performed.

  In addition, erasing is performed as a unit as usual, for example, by setting the substrate 200 to 10 V, applying -10 V to each control gate, and extracting electrons from the floating gate to the substrate.

By the way, when the transistors are arranged in a planar shape as shown in FIG. 3, the area occupied by the unit is increased by the addition of the transistors in the present invention, and the chip area is increased.
Therefore, it is possible to employ the second device structure as shown in FIG. 5 and form the cell string portion 111a with a polysilicon TFT and stack it on the amplification transistor 115a.

In this structure, the amplification transistor 115a, the write selection transistor 112a, and the read selection transistors 113a and 114a are formed on the silicon substrate 200, and the cell string 111a is formed in the upper layer.
As a result, the area occupied by the memory unit is almost determined only by the cell string 111a, and higher integration than before is possible.

In general, a transistor using a polysilicon TFT has a lower mobility than a transistor formed on normal silicon and has a driving capability of only about 1/3 to 1/10.
However, in this embodiment, the extra charge that is driven by the cell string 111a is only the charge of the amplifying transistor 115a, so that the extraction is performed instantaneously, and a decrease in drive capability is hardly a problem.
On the other hand, the amplifying transistor 115a and the reading selection transistor 114a for driving a large-capacity bit line are formed on the silicon substrate 200 and have sufficient driving capability.
Therefore, the combination of the present invention and the cell transistor by TFT is extremely effective in achieving both high-speed access and integration.

Note that electrical erasure cannot be performed with the device having the structure shown in FIG. Therefore, it is suitable to be used for storing programs as an alternative to OTP and EPROM.
If a path for applying a fixed potential to the TFT substrate is created, electrical erasing can be performed.

  In addition, regarding the cell transistor, since there is only a mechanism for reflecting the difference in stored data in different threshold values, many variations are conceivable. The transistors in FIGS. 6A and 6B are an example.

  1) Grooves are formed by batch processing in the sequentially deposited insulating layer 300, polysilicon layer 301, and insulating layer 302, and the surface thereof is covered with a composite film 303 of a silicon oxide film and a silicon nitride film. Such a composite film 303 has a property of accumulating electric charges at the interface between the silicon nitride film and the silicon oxide film, and by replacing it with a gate insulating film, the threshold value of the transistor can be changed to have a memory effect. Is possible.

  2) A cell transistor is formed on the side wall of the trench of the polysilicon layer 301 by covering the control gate electrodes 304 and 305 thereon.

In such a transistor, it is known that a control layer is sandwiched between two directions of a polysilicon layer, and the controllability of the channel electric field is improved.
This makes it easy to cope with a particularly short gate length, so that the structure is more suitable for miniaturization of a memory unit using the present invention.

  In addition, although an example of a memory that can be electrically programmed has been described so far, as with other normal mask ROMs, the threshold value is changed by selectively implanting impurities into the channel part during the manufacturing process, and programming is performed. You can go. Such a memory does not require a laminated gate structure or the composite film, and a simple MOSFET can be used as a memory cell.

  FIG. 7 is a circuit diagram showing a second embodiment of the amplification type semiconductor memory device according to the present invention.

In the second embodiment, an amplification transistor 115, a read selection transistor 114, and a write selection transistor 112 are provided as in the first embodiment, but they are shared by two cell strings 111a and 111b. Has been.
The cell string 111a is separated from each other by transistors (FETs) 116 and 113a, and the cell string 111b is separated from each other by transistors 117 and 113b. Either one of the cell strings is alternatively selected by the transistor 116 or 117 at the time of reading and writing. Accessed.
The transistors 113 and 113b are transistors corresponding to the transistor 113 of the first embodiment (FIG. 2), and their gates may be controlled simultaneously by one selection line SL13. For isolation, a separate transistor is installed for each string.
The gate of the transistor 116 is connected to the selection line SL14, and the gate of the transistor 117 is connected to the selection line SL15.
A memory unit 110A including the transistor group and the cell strings 111a and 111b is connected to the bit line BL11. Further, a plurality (N) of memory units similar to 110A can be connected to the bit line BL11. Further, the memory units are arranged in a matrix array (N × M) by arranging a plurality of bit lines (M lines) in parallel.

The read and write operations are the same as those in the first embodiment except that one of the string selection transistors 116 and 117 is turned on and the other is turned off (shown in the timing chart of FIG. 4).
Although the cell transistors share the word lines WL10, WL11 and the like between the strings, the transistor 117 (113b) on the non-selected string 111b side is turned off, for example, when the cell string 111a is written.
Therefore, the cell string 111b is in a floating state, and its behavior is the same as that of the cell string on the non-written bit line, so that no erroneous writing occurs. Further, it is possible to connect more cell strings such as four or eight with the same configuration.

In the configuration of the second embodiment, with the addition of one cell string, for example, 111b, it is necessary to add two selection / separation transistors 117, 113b. However, each cell string includes three transistors 112, 114, 115. Since they are shared with each other, the number of transistors per string decreases as strings are added. Therefore, the area efficiency is improved even if all the transistors are arranged in a plane.
However, if TFTs are used for each cell string and they are stacked on each other, the occupied area per cell is further dramatically reduced.

  FIG. 8 is a diagram illustrating an example of a device structure in which a TFT is used as a cell string in the amplification type semiconductor memory device according to the second embodiment.

  The cell strings 111a and 111b are formed of TFTs and stacked on each other. On the other hand, the amplification transistor 115, the reading selection transistor 114, and the writing selection transistor 112 are all formed on the silicon substrate 200a.

Here, since the amplifying transistor 115 and the reading selection transistor 114 drive a large-capacity bit line, high current driving capability is required, and it is desirable to form them on the silicon substrate 200a.
On the other hand, since the other transistors do not drive the bit lines, they may be formed on the silicon substrate 200a or formed as an upper layer as a TFT. Here, in order to omit the extra contact region and simplify the layout to obtain the highest degree of integration, the cell strings are selected and separated 116, 117, 113a, and 113b on the same polysilicon layer as the corresponding cell string. It is formed with.

By the way, when the cell strings are stacked in the structure as shown in FIG. 8, it is necessary to form a gate electrode, a gate insulating film, a source / drain, etc. for each TFT layer, which increases the number of manufacturing steps.
Here, if the above-mentioned sidewall transistor is used, cell transistors over a plurality of layers can be manufactured at once, and the manufacturing process can be greatly reduced.

  9A, 9B, 10A, 10B, and 11 show an example of the manufacturing process.

  1) As shown in FIG. 9A, a first polysilicon layer 401, an insulating layer 402, and a second polysilicon layer are formed on a substrate on which transistors and bit lines similar to those in FIG. A silicon layer 403 is sequentially deposited. Note that an N-type impurity such as phosphorus is introduced into the predetermined regions 404 and 405 in the polysilicon layers 402 and 403.

  2) As shown in FIG. 9B, contact holes are collectively formed in predetermined positions of the substrate circuit so as to penetrate each of the layers 400, 401, 402, 403, and phosphorus-doped polysilicon is embedded to form a contact plug. 406 and 407 are formed. Further, an insulating layer 408 is deposited.

  3) As shown in FIG. 10A, grooves for separating each memory unit are formed in a lump for each of the layers 401, 402, 403, and 408. The groove is also formed in the depth direction of the drawing so as to separate adjacent memory units. Polysilicon layers 401 and 403 are exposed on the side walls of the trench.

  4) As shown in FIG. 10B, a composite film 409 of a silicon oxide film and a silicon nitride film is formed as a charge storage layer, and the entire surface is covered. Further, a gate electrode such as 410 is formed. As a result, sidewall transistors serving as memory cells are formed at the intersections between the surfaces of the polysilicon layers 401 and 403 exposed on the sidewalls of the trenches and the gate electrodes.

  5) As shown in FIG. 11, N-type impurities such as phosphorus are introduced into the polysilicon layers 401 and 402 by oblique ion implantation using the gate electrode as a mask.

  Through these steps, the selection and separation transistors 116 and 113a and the cell string 111a are formed in the lower polysilicon layer 401, and the selection and separation transistors 117 and 113b and the cell string are formed in the upper polysilicon layer 402. 111b is formed all at once.

In this configuration, the separation and selection transistor has the same structure as the cell transistor. In this case, the cell transistor in the erased state is used for separation and selection, but when the threshold value is the same as that of the cell transistor, it may be turned on when the gate is 0V.
In such a case, it is effective to turn off the gates of these transistors with a negative bias.

  FIG. 12 shows a bird's eye view of the sidewall transistor in the device structure of FIG.

The surfaces of the polysilicon layers 401 and 403 exposed on the side walls of the trench are covered with a composite film 409 of a silicon oxide film and a silicon nitride film. Each transistor is formed.
The two-layer TFT is manufactured all at once for film processing, gate insulating film (charge storage film) and gate electrode formation, and introduction of source / drain impurities.
These can be manufactured all at once even if the TFT layer has four or eight layers. The additional steps required to add each TFT layer are only film deposition and one-time partial impurity introduction, and the memory capacity can be increased to 2 times, 4 times, or 8 times by itself. .

It is a figure which shows the example of an internal structure of a NAND type flash memory. 1 is a circuit diagram showing a first embodiment of an amplification type semiconductor memory device according to the present invention. FIG. 3 is a cross-sectional view of a device structure corresponding to the circuit configuration of FIG. 2. 4A to 4G are timing charts for explaining an example of a specific access procedure of the amplification type semiconductor memory device according to the first embodiment. FIG. 3 is a diagram illustrating an example of a device structure using TFTs as cell strings in the amplification type semiconductor memory device according to the first embodiment. It is a figure which shows the other example of the device structure which used TFT for the cell string in the amplification type semiconductor memory device which concerns on 1st Embodiment. FIG. 5 is a circuit diagram showing a second embodiment of an amplification type semiconductor memory device according to the present invention. It is a figure which shows the example of the device structure which used TFT for the cell string in the amplification type semiconductor memory device which concerns on 2nd Embodiment. It is a figure for demonstrating an example of the manufacturing method of the device which used TFT for the cell string in the amplification type semiconductor memory device which concerns on 2nd Embodiment. It is a figure for demonstrating an example of the manufacturing method of the device which used TFT for the cell string in the amplification type semiconductor memory device which concerns on 2nd Embodiment. It is a figure for demonstrating an example of the manufacturing method of the device which used TFT for the cell string in the amplification type semiconductor memory device which concerns on 2nd Embodiment. It is a bird's-eye view of the side wall transistor in the device structure of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100,100A ... Amplification type semiconductor memory device, 110, 100A ... Cell unit, 111, 111a, 111b ... Cell string, 112 ... Selection transistor for writing, 113, 113a, 113b ... Transistor for selection / separation, 114 ... Selection for reading Transistor 115, amplification transistor 116, selection / separation transistor 117, selection / separation transistor BL11, bit line, WL10 to WL115, word line, SL11-SL15, SL13a, selection line.

Claims (11)

Bit lines,
And at least one memory unit connected to the bit line,
The memory unit includes a cell string in which a plurality of memory cells are connected in series, and an amplification drive circuit that drives the bit line reflecting the through current of the cell string,
Each of the memory cells is formed of a field effect transistor that stores different data according to different threshold values. The amplification driving circuit includes an amplifying field effect transistor having one end of a source and a drain connected to a first constant voltage source and the other end connected to the bit line,
The semiconductor memory device according to claim 1, wherein one end of the cell string is connected to a gate electrode of the amplifying field effect transistor, and the other end is connected to a second constant voltage source. 3. When reading data from the memory, the gate of the driving field-effect transistor is charged to a constant potential through the bit line, and the gate potential is changed by a through current through the cell string. Semiconductor memory device. The semiconductor memory device according to claim 1, wherein the cell string is stacked on an upper layer of the amplification drive circuit formed on a silicon substrate. 2. The semiconductor memory device according to claim 1, wherein the field effect transistor forming the memory cell of the cell string is formed on a side wall of a groove formed in a semiconductor layer deposited on the amplification driving circuit via an insulating film. . Bit lines,
And at least one memory unit connected to the bit line,
The memory unit includes a plurality of cell strings in which a plurality of memory cells are connected in series, and further includes an amplification driving circuit that drives the bit line by reflecting one through current arbitrarily selected from the cell strings.
Each of the memory cells is formed of a field effect transistor that stores different data according to different threshold values. The amplification drive circuit is an amplification field effect transistor having one end of a source and a drain connected to a first constant voltage source and the other end connected to a bit line,
The semiconductor memory device according to claim 6, wherein one end of each of the plurality of cell strings is connected to a second constant voltage source, and the other end is connected to a gate electrode of the field effect transistor via an independent selection transistor. 8. The semiconductor memory device according to claim 7, wherein at the time of data reading, the gate of the driving field effect transistor is charged to a constant potential via a bit line, and the gate potential is changed by a through current via the selected cell string. . The semiconductor memory device according to claim 6, wherein gate electrodes of a plurality of memory cells forming each of the plurality of cell strings are short-circuited between the plurality of cell strings, and are connected to independent drive circuits. The semiconductor memory device according to claim 6, wherein the cell string is stacked over at least two layers on an upper layer of the amplification drive circuit formed on a silicon substrate. 7. The semiconductor memory according to claim 6, wherein the field effect transistor forming the memory cell of the cell string is formed on a side wall of a groove formed in a semiconductor layer deposited on the amplification driving circuit via an insulating film. apparatus.

Images