JP2010182419A - Semiconductor memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that when a smaller semiconductor memory device is manufactured, offset of a sense amplifier is increased, a malfunction occurs during reading, and a yield of a chip is deteriorated. <P>SOLUTION: A semiconductor device has a sense amplifier constituted of a plurality of pull-down circuits and one pull-up circuit. In one of the plurality of pull-down circuits, a transistor constituting the pull-down circuit has a constant such as channel length and channel width larger than that of a transistor constituting the other pull-down circuit. Furthermore, out of the plurality of pull-down circuits, the pull-down circuit having the larger constant of the transistor is activated first, then the other pull-down circuit and the pull-up circuit are activated and reading is performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor memory device. In particular, the present invention relates to a low power, high speed, highly integrated semiconductor memory device and a differential amplification operation portion of a semiconductor device in which a logic circuit and a semiconductor memory device are integrated.

Dynamic random access memory (DRAM), one of the semiconductor storage devices, is the main memory of large computers and personal computers, and the work memory of digital home appliances such as mobile phones and digital cameras. Are installed in various electronic devices that are used daily. In addition to this, along with the recent needs for lower power consumption and higher performance of devices, there is a strong demand for higher performance such as lower power, higher speed, and larger capacity for the installed DRAM.
In order to realize a high-performance DRAM, the most effective means is to miniaturize cell transistors and cell capacitors used in DRAM memory cells. The memory cell can be made smaller by miniaturization. As a result, the data line length is shortened and the parasitic capacitance of the data line can be reduced, so that low voltage operation is possible and low power can be realized. Further, since the parasitic capacitance of the data line can be reduced, high-speed sense amplifier operation is possible. Furthermore, the benefits received from miniaturization, such as the high performance of the equipment due to the increased memory capacity, are enormous. Therefore, it is considered that not only current products but also products developed in the future are generally improved in performance by miniaturization.

  However, as with current products, the 0.1mm node or later 0.065mm and 0.045mm nodes have various side effects as the miniaturization progresses, in addition to the effects of higher performance as described above. . The side effect is a malfunction that occurs when a signal of a memory cell is read due to variations in element characteristics that increase due to miniaturization. Here, the variation in element characteristics is, for example, the threshold voltage of the cell transistor and the dispersion value (deviation from the average value) of the magnitude of the leak current flowing from the cell transistor. Thus, when the variation in element characteristics is large, the data retention characteristics of the DRAM are deteriorated, causing a problem that the yield of the chip is lowered. In particular, there is a concern that the variation in the threshold voltage of the sense amplifier circuit will increase significantly in the future. The reason is that in recent DRAMs, the data line pitch of memory cells is very narrow, and therefore it is necessary to arrange the sense amplifier circuits connected to the data lines in a small layout. For this reason, the processing error of the transistors constituting the sense amplifier increases, and the variation of the threshold voltage of the paired transistors increases. This problem is generally referred to as a sense amplifier offset, and is one of the matters that greatly affects the performance of the DRAM. Further, the offset problem of the sense amplifier is described in detail in Non-Patent Document 1, and it is well known that reducing the offset greatly contributes to improving the yield of the DRAM. Therefore, in order to realize high performance by miniaturization, it will become a very important technology in the future to take circuit measures not only to reduce processing errors by process improvement but also to suppress sense amplifier offset.

  As an example of recent attempts to solve such a problem, Non-Patent Document 2 discloses a technique for offsetting the offset of the sense amplifier. This method can substantially reduce the offset of the sense amplifier by using the current mirror operation amplifier and correcting the precharge voltage of the data line. However, this method adds a large number of elements to the sense amplifier, increases the area of the sense amplifier, and increases the chip size. Furthermore, since the number of control signals to be driven increases, the timing margin increases, and there is a concern that the speed may decrease. Non-Patent Document 3 discloses a charge transfer type sense amplifier. This method is a method in which charges accumulated in a peripheral circuit such as a sense amplifier are transferred to a data line on the memory cell side via a switch transistor connected to the data line, and a large potential difference is generated in the sense amplifier. For this reason, even when the offset of the sense amplifier increases, a potential difference equal to or greater than the offset can be applied to the sense amplifier, which is inherently resistant to variations and excellent in low voltage operation. However, this method also has a problem that the number of additional elements such as an additional precharge circuit and a rewrite switch transistor is large, resulting in an increase in chip size.

Japanese Unexamined Patent Publication No. 7-226081 JP-A-2-146177

Kiyoo Itoh, "VLSI Memory Chip Design", pp.195-247, Springer, 2001 Sang Hoon Hong et al., ISSCC2002 Dig. Tech. Papers, pp.154-155 Jae-Yoon Simm et al., 2003 Symposium on VLSI Circuits Dig. Tech. Papers, pp.289-292

Under the circumstances described above, the problem to be solved by the present invention is to realize a sense amplifier circuit that can operate at high speed with a small number of additional elements and that can reduce the offset of the sense amplifier.
In order to solve the above-mentioned problems, the present inventors examined the influence of the offset of the sense amplifier on the read operation and the configuration of the sense amplifier capable of reducing the offset that can be realized by adding a minimum number of transistors.

  FIG. 18 is a diagram showing a circuit configuration of a typical DRAM. In FIG. 18, the memory cell MC includes an access transistor TN0 whose drain is connected to the data line DLB, and a cell capacitor CS0 whose one side is connected to the source of the access transistor TN0. In the following description, it is assumed that the L potential is held in the memory cell MC. The data line pair DLT, DLB to which a plurality of memory cells are connected is connected to the sense amplifier circuit SA0 via the switch transistor SHR. The sense amplifier circuit SA0 includes a column switch YSW, a precharge circuit PCH, a pull-down circuit NDRV, and a pull-up circuit PDRV. FIG. 19 is a timing waveform when the signal of the memory cell MC is read using the conventional sense amplifier circuit SA0 of FIG. 18, and shows that a malfunction has occurred. First, the precharge circuit PCH is driven to precharge the data line. Thereafter, the precharge circuit PCH is negated, the switch transistor SHRL on the selected subarray SARY side is kept driven high, and the other switch transistor SHRR is negated low. When the sub word line WL0 is asserted, a minute signal corresponding to L is output from the memory cell MC to the data line DLB, and a signal difference dVsig appears on the data line pair.

  After that, by driving the common source line CSN of the pull-down circuit NDRV and the common source line CSP of the pull-up circuit PDRV to the ground voltage VSS and the data line voltage VDL, respectively, a small potential difference dVsig is normally obtained as shown by the broken line. Are amplified to the high level VDL and the low level VSS, and transferred to the subsequent circuit via the column switch YSW and the local data lines LIOT and LIOB. However, as described above, as the miniaturization progresses, the offset of the sense amplifier increases. For example, in FIG. 18, the difference between the threshold voltage VTN1 of the NMOS transistor TN1 of the pull-down circuit NDRV and the threshold voltage VTN2 of the NMOS transistor TN2, VTN1-VTN2 becomes larger than the minute signal difference dVsig, and at the same time, the pull-up circuit PDRV The difference between the threshold voltage VTP1 of the PMOS transistor TP1 and the threshold voltage VTP2 of the PMOS transistor TP2 and VTP1−VTP2 may be larger than the minute signal difference dVsig. In this case, since the data line DLT is driven to the L side more strongly than the data line DLB, a read malfunction occurs as shown by the solid line in FIG.

  In order to prevent such a malfunction, the offset of the transistor constituting the pull-down circuit NDRV or the pull-up circuit PDRV is increased to reduce the offset, or the minute signal difference dVsig is amplified to at least a voltage difference greater than the offset. Add a preamplifier function. As the concrete means of the former, there is a method of simply reducing the offset by increasing the channel length and channel width of the transistors constituting the pull-down circuit NDRV and the pull-up circuit PDRV, TN1, TN2, TP1, and TP2. . However, with this method, the channel length increases, the drive current of the sense amplifier circuit SA0 may decrease, and the memory access speed may increase. On the other hand, as a method of adding the preamplifier function, for example, another pull-down circuit NDRV may be added. If the added pull-down circuit is driven first and the data line is preamplified to a voltage difference equal to or greater than the offset of the pull-down circuit and the pull-up circuit from the beginning, there is a possibility that a read malfunction can be prevented.

Also, there are only two additional transistors, and the area increase can be minimized. As known examples of such a circuit configuration, Patent Documents 1 and 2 disclose sense amplifier circuits using a plurality of pull-down circuits. The disclosed technique has few additional circuits and a small area overhead. However, although these methods have been studied for increasing the speed of the sense amplifier circuit, a means for reducing the offset and preventing the read malfunction is not considered. In other words, the disclosed method does not have a preamplifier function, and thus the problem of offset cannot be solved in principle.
Under the circumstances as described above, one of the objects of the present invention is to reduce a sense amplifier offset that will become remarkable in the future, and to prevent a read malfunction. Another object of the present invention is to increase the layout area of the sense amplifier circuit SA0 while reducing the offset.

The following is a brief description of an outline of typical inventions disclosed in the present application.
In a semiconductor memory device including a plurality of memory cells and a plurality of sense amplifier circuits, the sense amplifier circuit has at least two pull-down circuits. In addition, after driving one of the pull-down circuits first to amplify the data line more than the offset of the subsequent pull-down circuit and the pull-up circuit, the subsequent pull-down circuit and the subsequent pull-up circuit are driven. . At this time, in the pull-down circuit that is driven first, the channel length and the channel width of the transistor are preferably increased in advance so that the offset of the transistor is reduced. Further, the sense amplifier may be composed of a plurality of pull-up circuits.

  According to the present invention, the offset of the sense amplifier can be reduced in a semiconductor integrated circuit including a plurality of memory cells and a plurality of sense amplifier circuits. As a result, low voltage operation and high speed read operation are possible. Further, since the offset can be reduced, the data line length can be increased and the memory cell occupation ratio can be increased. That is, a highly integrated semiconductor memory device can be realized.

1 is a first embodiment showing a basic configuration of a sense amplifier circuit portion of a semiconductor memory device of the present invention. It is an example of the bank comprised using the sense amplifier circuit of the Example of FIG. FIG. 2 is a diagram showing an example of operation waveforms of the sense amplifier of FIG. FIG. 3 is a diagram showing a part of a planar layout of the sense amplifier array of FIG. FIG. 3 is a diagram showing a part of a planar layout of the sense amplifier array of FIG. FIG. 2 is a diagram showing an example of a planar layout of memory cells in FIG. 3 is an example of a cross-sectional structure of a part of the bank in FIG. FIG. 2 is an example of a block diagram of a semiconductor memory device configured using the sense amplifier of FIG. FIG. 3 is a diagram showing an example of a modification of the planar layout of the sense amplifier array of FIG. 10 is an example of operation waveforms of the sense amplifier when the layout of the sense amplifier of FIG. 9 is implemented. It is a figure which shows the circuit structure of a negative subword driver. FIG. 12 is a second example showing an example of operation waveforms when the negative subword driver of FIG. 11 is implemented in the sense amplifier of the present invention. 4 is a third embodiment showing a basic configuration of a sense amplifier circuit portion of a semiconductor memory device of the present invention. FIG. 14 is a diagram illustrating an example of operation waveforms of the sense amplifier of FIG. FIG. 14 is a diagram showing an example of a planar layout of a sense amplifier array configured by using a plurality of sense amplifiers of FIG. 4 is a fourth embodiment showing a basic configuration of a sense amplifier circuit portion of a semiconductor memory device of the present invention. FIG. 17 is a diagram illustrating an example of operation waveforms of the sense amplifier of FIG. It is a figure which shows an example of the conventional sense amplifier circuit. It is a figure which shows an example of the operation waveform of the conventional sense amplifier circuit.

  Embodiments of the present invention will be described below with reference to the drawings. The transistors constituting each block of the embodiment are not particularly limited, but are formed on a single semiconductor substrate such as single crystal silicon by a known integrated circuit technology such as a CMOS (complementary MOS transistor). That is, after the step of forming the well, the element isolation region, and the oxide film, the step includes forming the gate electrode and the first and second semiconductor regions for forming the source / drain regions. Circuit symbols of MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) that do not have a circle on the gate represent an N-type MOSFET (NMOS), and are distinguished from a P-type MOSFET (PMOS) that has a circle on the gate. Hereinafter, the MOSFET is simply referred to as a MOS or a MOS transistor. However, the present invention is not limited to a field effect transistor including an oxide film provided between a metal gate and a semiconductor layer, and is not limited to a general MISFET (Metal Insulator Semiconductor Field Effect Transistor) including an insulating film. Applies to circuits using FETs.

  FIG. 1 is a diagram showing a sense amplifier circuit SA0 according to the first embodiment of the present invention and a plurality of memory cells MC connected thereto. FIG. 2 shows a sense amplifier circuit array SAA-R, SAA-L composed of the sense amplifier circuit SA0 according to the first embodiment of the present application, a subarray SARY0 composed of a plurality of memory cells MC, and a plurality of subword drivers SWD. FIG. 2 is a diagram showing a bank BANK composed of subword arrays SWDA-U and SWDA-D composed of FIG. 3 is a diagram showing timing waveforms of the sense amplifier circuit SA0 shown in FIG. 4 and 5 are layout diagrams of the sense amplifier circuit SA0 shown in FIG. FIG. 6 is a planar layout of the plurality of memory cells MC shown in FIG. FIG. 7 is a diagram illustrating a part of a cross-sectional view of the plurality of memory cells MC and the sense amplifier circuit SA0 illustrated in FIG. FIG. 8 shows a block diagram of a DRAM configured using a plurality of banks BANK shown in FIG.

  FIG. 9 shows a variation of the layout of sense amplifier circuit SA0 shown in FIG. FIG. 10 is a diagram showing timing waveforms of the sense amplifier circuit SA0 shown in FIG. FIG. 11 is a specific example of a sub word driver circuit for applying a negative voltage to a word line. FIG. 12 shows operation waveforms of the second embodiment in which a negative subword driver is applied to the sense amplifier circuit of the present embodiment. FIG. 13 shows a third embodiment of the present invention, which is an example of a sense amplifier circuit configured using a plurality of pull-up circuits. FIG. 14 is a diagram showing operation waveforms of the sense amplifier circuit of FIG. FIG. 15 is a plan layout of a sense amplifier array configured by using a plurality of sense amplifier circuits of FIG. FIG. 16 shows a fourth embodiment of the present invention, which is an example of a sense amplifier circuit configured by using one pull-down circuit and one pull-up circuit. FIG. 17 is a diagram showing operation waveforms of the sense amplifier circuit of FIG. FIG. 18 shows a conventional sense amplifier circuit. FIG. 19 is a diagram for explaining the operation waveform of the conventional sense amplifier circuit of FIG. 18 and its malfunction.

Hereinafter, FIGS. 1 to 10 will be described first. In the embodiment of FIG. 1, a plurality of pull-down circuits NDRV0, NDRV1, a single pull-up circuit PDRV, a switch transistor SHR, a column switch YSW, a precharge circuit PCH, and a plurality of memory cells MC A configured subarray SARY0 is described. Also, the respective symbols are common source lines CSN0 and CSN1 for driving the pull-down circuits NDRV0 and NDRV1, common source lines CSP for driving the pull-up circuit PDRV, switch transistor drive lines SHRR and SHRL, column switch drive lines YS, and local data lines LIOT, LIOB, precharge drive line DLEQ, precharge voltage VDLR, sub word lines WL0-WL3, data lines DLT, DLB, access transistor TN0, cell capacitor CS0, and plate electrode PLT are shown.
The plurality of memory cells MC are DRAM memory cells each including an N-type channel MOS transistor TN0 and a capacitor CS0. The pull-up circuit PDRV is composed of a P-channel MOS transistor pair in which one gate and the other drain are connected to each other, and each of the pull-down circuits NDRV0 and NDRV1 is an N in which one gate and the other drain are connected to each other. It consists of a pair of type MOS transistors.

  As shown in FIG. 1, among the plurality of pull-down circuits in the present embodiment, the transistors constituting the pull-down circuit NDRV0 are, for example, longer in channel length and wider in channel width than the transistors constituting the pull-down circuit NDRV1. Thus, the driving force (constant) of the transistor is large. The reason why the transistor constant is increased is that the drive current of the pull-down circuit NDRV0 can be increased and the offset can also be reduced. At this time, it is desirable that the NMOS transistor constituting the other pull-down circuit NDRV1 has a short channel length or a wide channel width. This is because the drive current of the pull-down circuit NDRV0 may decrease because the channel length of the transistors constituting the pull-down circuit NDRV0 is long. Therefore, if the channel length of the transistors constituting the pull-down circuit NDRV1 is shortened or the channel width is widened to increase the drive current, the data line can be amplified at a higher speed. In this way, only the pull-down circuit NDRV0 with sufficiently reduced offset is added, the common source line CSN0 is driven, and the data line pair is preamplified to a voltage difference larger than the offset of the pull-down circuit NDRV1 and the pull-up circuit PDRV in the subsequent stage. As long as this is done, it is possible to prevent malfunction of reading. Details of the operation will be described later.

  FIG. 2 shows a bank BANK configured using sense amplifier arrays SAA-R, SAA-L and a subarray SARY0, subword drivers SWDA-U, SWDA-D using a plurality of sense amplifier circuits SA0 according to an embodiment of the present invention. It is a specific example. In the example of FIG. 2, the common source control lines ΦCSN0, ΦCSN1, and ΦCSP are arranged one by one for the plurality of sense amplifier circuits SA0 to SA5. The circuits VSS_DRV0, VSS_DRV1, and VDL_DRV that drive the common source lines controlled by the common source control lines ΦCSN0, ΦCSN1, and ΦCSP are provided for each subarray SARY0, and the sense amplifier arrays SAA-R and SAA-L are so-called A distributed drive system is used. Subword drivers SWDA-U and SWDA-D are provided for each subarray SARY0, and drive the subword lines WL0, WL1, WL2, WL3, WL4, and WL5 in the subarray SARY0 by selecting addresses. VSS-U and VSS-D are ground voltages.

  The sense amplifier circuit SA0 of FIG. 1 has a very small area increase compared to the configuration of FIG. 18 because the additional transistor is only a pair of NMOS transistors. Therefore, a layout with a narrow data line pitch as shown in FIG. 2 can be performed, and an increase in chip size can be suppressed. The sense amplifier circuit SA0 has the same configuration as that of the conventional sense amplifier circuit except for the addition of the pull-down circuit NDRV0. Therefore, if the sense amplifier circuit SA0 of the present embodiment is used, the layout and wiring configuration can be suppressed with a minimum change. Further, although FIG. 2 shows a folded data line type array configuration in which a data line pair intersects a sub word line, of course, the present invention is not limited to this. For example, it is needless to say that various modifications are possible without departing from the spirit of the present invention, not to mention the so-called open data linear array configuration.

  FIG. 3 is an operation waveform for explaining the operation of the sense amplifier circuit SA0 implemented in FIG. First, the precharge drive line DLEQ is asserted to precharge the data line pair to the precharge potential VDLR. There are various methods for driving the precharge drive line DLEQ. For example, a row address signal or a subarray selection signal may be used. Similarly, the switch transistor SHRR is negated using a row address or the like. By doing so, the data line pair of the selected sub-array SARY0 and the sense amplifier array SAA-R are electrically connected. Next, when the sub word line WL1 is asserted, signals held from the plurality of selected memory cells are output to the data lines. For example, a minute signal corresponding to L of the memory cell MC in FIG. 2 is output to the data line DLT0. Thereafter, when the common source line CSN0 is driven to the ground voltage VSS, the data line DLT0 is driven to the VSS side more strongly than the data line DLB0.

  Since the channel length and channel width of the transistor of the pull-down circuit NDRV0 are increased and the offset is sufficiently reduced, the data line DLT0 can be more selectively driven to the L level VSS. Using the pull-down circuit NDRV0, the data line DLT0 is amplified to a voltage difference greater than the offset of the pull-down circuit NDRV1 and the pull-up circuit PDRV, and then the common source lines CSN1 and CSP are driven to drive the data line pair DLT0 and DLB0 to low level. Amplifies up to VSS and high level VDL respectively. The paired common source lines CSN1 and CSP are driven based on the same control signal, and as a result, are changed from VDLR to VSS and VDL potentials at substantially the same timing. After rewriting the memory cell MC, the sub-word line WL0 is negated. Thereafter, the common source lines CSN0, CSN1, and CSP are precharged to the precharge voltage VDLR, the precharge drive line DLEQ is asserted, and the data line pair is precharged to a desired precharge potential VDLR. The above is the operation of the sense amplifier circuit SA0 according to the embodiment of the present invention.

  As described above, by adding the pull-down circuit NDRV0 in which the offset is sufficiently reduced, a read malfunction can be prevented. In addition, the so-called sense amplifier offset margin in the DRAM signal amount design can be suppressed. Therefore, even when the data line voltage VDL is lowered to reduce the signal amount, the above-described sense amplifier offset margin is almost unnecessary, so that a stable read operation is possible. That is, low voltage operation is possible, and low power consumption can be realized. Further, a stable read operation can be performed even if the data line length is increased. The reason for this will be briefly described below. In general, when the data line length is increased, the data line parasitic capacitance increases, so that the amount of signal output to the data line decreases. As a result, the voltage difference applied to the sense amplifier circuit becomes small and the sense amplifier operation becomes unstable. However, if the sense amplifier circuit SA0 of the present embodiment is used, even if the voltage difference applied to the sense amplifier circuit SA0 is small, the offset of the pull-down circuit NDRV0 is sufficiently small, so that the data line can be preamplified. That is, since the data line can be preamplified using the pull-down circuit NDRV0 beyond the offset of the pull-down circuit NDRV1 and the pull-up circuit PDRV, a stable read operation can be performed even if the data line length is increased. In other words, a highly integrated semiconductor memory device with a high memory occupancy rate can be realized.

  4 and 5 are plan layouts of a sense amplifier array SAA-R configured by using a plurality of sense amplifier circuits SA0 according to the embodiment of FIG. A part of a symbol indicating a part surrounded by a broken line part corresponds to each circuit constituting the sense amplifier circuit SA0 of FIG. Other than that, YS0-YS2 indicate column switch drive lines, and LIO0T, LIO0B, LIO1T, and LIO1B indicate local data lines. FIG. 5 shows an example of the wiring layout of the contact V2 and the second wiring layer M2. The meanings of the symbols in FIGS. 4 and 5 are the gate contact FGCNT, diffusion layer LN, LP, gate electrode FG, diffusion layer LN, LP that connect the gate electrode and the first wiring layer M1 (data line). A diffusion layer contact LCNT connecting the wiring layer M1, and a contact V2 connecting the second wiring layer M2 and the third wiring layer M3. Note that the contact V1 connecting the first wiring layer M1 and the second wiring layer M2 is not shown. In FIG. 4, common source drivers VSS_DRV0, VSS_DRV1, and VDL_DRV are used to drive the common source lines CSN0, CSN1, and CSP, for example, so-called one each arranged in a plurality of sense amplifier circuits SA0 to SA5. An example of a distributed drive layout is shown.

  That is, for one subarray SARY0, a plurality of pull-down circuits NDRV0 and circuits VDL_DRV, VSS_DRV0, driving a plurality of common source lines between a plurality of pull-down circuits NDRV1 and a plurality of pull-up circuits PDRV operating as a pair. VSS_DRV1 is distributed. The control lines ΦCSN0, ΦCSN1, and ΦCSP that control these drive circuits for VDL_DRV, VSS_DRV0, and VSS_DRV1 are common to the power supply line that supplies the precharge voltage VDLR and the local data lines LIOT, LIO0T, LIO1T, LIOB, LIO0B, and LIO1B The source lines CSN0, CSN1, CSP, and CSP and the power supply line that supplies the data line voltage VDL and the ground voltage VSS extend in the same direction and are formed of the same wiring layer. These wirings are formed in the same direction as the word lines. The column switch drive lines YS0 to YS2 are connected to the column switch YSW via the contact V2, are formed in the third wiring layer M3 above the second wiring layer M2, and extend in the same direction as the data lines. To do.

As described above, the common source line can be driven at high speed by distributing the drive circuit for each sense amplifier array SAA-R corresponding to the subarray SARY0, and the pull-down circuit NDRV1 and the pull-up circuit PDRV can be driven. By arranging them in between, it becomes possible to perform layout efficiently. Note that a part of the wiring layer is omitted because the drawing becomes complicated.
As shown in FIGS. 4 and 5, the pull-down circuit NDRV0 is the only additional circuit of the sense amplifier circuit SA0 implemented in FIG. Therefore, as can be seen from FIG. 4, the area increase of the sense amplifier circuit SA0 is also small. In addition, since the layout has excellent symmetry, there is also an advantage that the data line noise is small. Furthermore, a layout similar to that of the conventional pull-down circuit NDRV1 is possible, and the additional wiring accompanying the additional circuit is only the common source line CSN0, which is easy to realize. The gates of the transistors in the pull-down circuits NDRV0 and NDRV1 and the pull-up circuit PDRV are formed by ring-shaped transistors. Thus, by making the gate electrode into a ring shape, the offset of the sense amplifier circuit can be further reduced.

  In FIG. 4, the shape of the gate electrode FG such as the pull-down circuit NDRV0 is shown in a ring shape, but the present invention is of course not limited to this. Various modifications such as a U-shaped or rectangular gate electrode FG are possible. Further, the common source driver VSS_DRV0 has a channel width narrower than the channel width shown in FIG. 4, or the common source control line ΦCSN0 is slowly driven to apply the common source line CSN0 shown in FIG. The sense amplifier circuit SA0 may be operated at a lower drive speed. By doing so, there is an advantage that the data line DLT0 can be accurately preamplified even when the offset of the pull-down circuit NDRV0 becomes large. Although not shown in the figure, the common source line CSP may be used in combination with a so-called overdrive system that boosts the data line to a high level VDL or higher. Even in such a case, effects such as low voltage operation and high speed operation can be obtained. As described above, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

  FIG. 6 is a diagram showing a planar layout of the memory cell MC shown in FIG. 1 and sense amplifier arrays SAA-L and SAA-R connected thereto. Access transistor TN0 includes sub word line WL and diffusion layer ACT, and cell capacitor CS0 includes storage node SN and plate electrode PLT. For other symbols, cell contact CCNT for connecting diffusion layer ACT to the wiring or contact above it, data line DLT, data line contact DLCNT for connecting DLB and cell contact CCNT, landing pad LPAD and cell contact CCNT are connected The storage node contact SNCNT. Here, the landing pad LPAD is a contact connecting the storage node SN and the storage node contact SNCNT, and the position of the cell capacitor CS0 can be optimized, so that the surface area of the cell capacitor CS0 can be increased. Of course, if the capacity of the cell capacitor CS0 can be sufficiently secured, the landing pad LPAD may not be used. In that case, since process steps can be reduced, costs can be reduced.

  Further, as shown in FIG. 6, the layout of the memory cell MC can be variously modified. FIG. 6 (a) shows a so-called folded data line structure, and since the diffusion layer ACT is a simple rectangle, there is an advantage that miniaturization is easy. FIG. 6B shows a pseudo folded data line structure. The difference from (a) is that the diffusion layer ACT is laid out obliquely with respect to the sub-word line WL. For this reason, since the channel width can be effectively increased, there is an advantage that the on-current of the access transistor TN0 can be increased. Therefore, when combined with the sense amplifier circuit SA0 of the present embodiment, a semiconductor memory device capable of higher speed operation can be realized. FIGS. 6C and 6D show an open data line structure. Compared to the folded data line structure, there is an advantage that the cell area can be reduced. In FIG. 6C, since the data line pitch is wide, the data line parasitic capacitance can be reduced. Therefore, by combining with the sense amplifier circuit SA0 of the present embodiment, a semiconductor memory device capable of higher integration and low voltage operation can be realized. In FIG. 6D, the cell area can be further reduced as compared with FIG. 6C, and a highly integrated semiconductor memory device can be realized by combining with the sense amplifier circuit SA0 of this embodiment.

  Of course, the layout applicable to the sense amplifier of the present invention is not limited to this. For example, in the open data line structure of (d), the diffusion layer ACT laid out obliquely with respect to the sub-word line WL may be laid out so as to be orthogonal as shown in (a). In that case, since the shape is rectangular, there is an advantage that miniaturization is easy. Furthermore, the sub-word line SWLA can share the diffusion layer ACT of the adjacent cells on the left and right sides, and can always be applied to the sub-word line WLA by applying a low level VSS to the element isolation. In this case, since it is not necessary to form an element isolation region made of an insulator in a direction parallel to the data line, process steps can be reduced and costs can be reduced.

FIG. 7 is a diagram illustrating a part of a cross-sectional view of the plurality of memory cells MC and the sense amplifier circuit SA0 illustrated in FIG. Symbols in the figure are the second wiring layer M2, the third wiring layer M3, the P well substrate PW, the N well substrate NW, the deep N well substrate DNWELL, and the P type substrate PSUB. Since these forming methods are the same as those of a general semiconductor memory device, particularly a so-called general-purpose DRAM, the detailed description thereof is omitted here. Further, the structure of the cell capacitor CS0 is not limited to this. Needless to say, various modifications are possible including, for example, a crown type capacitor.
As described above, the sense amplifier circuit SA0 according to the present embodiment is easy to implement because only two NMOS transistors and a common source line CSN0 need to be added. The diffusion layer of the NMOS transistor of the pull-down circuit NDRV0 can be configured in the same P-type well PW as the diffusion layer of the NMOS transistor of the pull-down circuit NDRV1. Further, since there is no need to arrange additional wiring above the subarray SARY0, no wiring noise is generated. Therefore, the memory operation is not adversely affected.

  FIG. 8 shows an example of a block diagram of a DRAM configured using a plurality of banks BANK shown in FIG. Symbols shown in the figure are address buffer ADDRESS BUFFER, column address buffer COLUMN ADDRESS BUFFER, column address counter COLUMN ADDRESS COUNTER, row address buffer ROW ADDRESS BUFFER, refresh counter REFRESH COUNTER, bank select BANK SELECT, mode register MODE RESISTER, row decoder ROW DEC, column decoder COLUMN DEC, main sense amplifier SENSE AMP, memory cell array MEMORY CELL ARRAY, data input buffer Din BUFFER, data output buffer Dout BUFFER, data buffer DQS BUFFER, delay locked loop DLL, control logic CONTROL LOGIC, clock CLK, / CLK, clock enable signal CKE, chip select signal / CS, row address strobe signal / RAS, column address strobe signal / CAS, write enable signal / WE, data write signal DW, data strobe signal DQS, data It is a DQ. Note that the control method of these circuits and signals is the same as that of a known SDRAM or the like, and the description thereof is omitted here. By configuring the bank BANK as shown in FIG. 8 using the sense amplifier circuit SA0 of this embodiment, a semiconductor memory device such as a synchronous dynamic memory SDRAM can be realized. Needless to say, it is needless to say that the use of the sense amplifier circuit SA0 of this embodiment has the effect of enabling a low voltage operation as described above. Further, the configuration of the block is not particularly limited to FIG. The number of memory cell arrays MEMORY CELL ARRAY may be increased, and various changes can be made without departing from the gist of the present idea.

  FIG. 9 is a modification of the planar layout of the sense amplifier array SAA-R configured using a plurality of sense amplifier circuits SA0 shown in FIG. The difference from FIG. 4 is that the gate electrode shape of the pull-down circuit NDRV2 is not a ring type but a rectangle. As shown in FIGS. 4 and 5, when a ring-type gate electrode is used, the drive current of the pull-down circuit NDRV1 may be small. In that case, the drive current can be increased by making the gate electrode rectangular as shown in FIG. 9, and a more stable read operation is possible. The layout of the contact V1, the second wiring layer M2, and the contact V2 is substantially the same as that in FIG.

  FIG. 10 shows operation waveforms when the layout of the sense amplifier shown in FIG. 9 is applied. The basic operation is the same as in FIG. The difference from FIG. 3 is that when the pull-down circuit NDRV2 and the pull-up circuit PDRV are driven, the drive current of the pull-down circuit NDRV2 is larger than that of the ring-type pull-down circuit NDRV1 in FIG. It can be amplified at higher speed. Therefore, a semiconductor memory device capable of high speed operation can be realized. Further, FIG. 9 shows the case where the pull-down circuit NDRV2 is configured using the rectangular gate electrode FG, but it may be applied to the pull-up circuit PDRV. Also in this case, since a large drive current can be obtained for the pull-up circuit PDRV, a high-speed operation is possible as described above. The above is the description of the first embodiment.

  In the first embodiment, the case where the ground voltage VSS is applied to the sub-word line WL of the memory cell MC when not selected has been described, but a negative voltage may be applied. 11 and 12 show the case where the negative word driver NSWD is applied to the sense amplifier circuit SA0 of the present embodiment. FIG. 11 shows a modification of the sub word driver SWD constituting the sub word arrays SWDA-U and SWDA-D in FIG. Symbols in the figure are a word line voltage VPP, a negative word line voltage VKK, a main word line MWL, sub word line control signals FX and FXB, and inverters INV0 and INV1. Since the control method of each signal is the same as that of a general sub-word driver, description thereof is omitted here.

  FIG. 12 shows operation waveforms when the negative sub-word driver NSWD of FIG. 11 is applied to the sense amplifier circuit SA0 of the present embodiment. The difference from the operation waveform of FIG. 3 is that the word line voltage when not selected is a negative voltage lower than the potential when the pull-down circuit is driven. Thus, the threshold voltage of the access transistor can be effectively increased by applying a negative voltage when the word line is not selected. In other words, even if the threshold voltage of the access transistor TN0 is set low, there is no possibility that the so-called retention characteristic of the DRAM is deteriorated. That is, since the impurity concentration in the channel region can be reduced, the junction electric field between the diffusion layer ACT and the P well substrate PW can be reduced. As a result, the leakage current flowing through the diffusion layer ACT can be reduced, so that a semiconductor memory device with less power consumption can be realized. Further, since the impurity concentration can be reduced, the variation in threshold voltage of the access transistor TN0 can also be reduced. As a result, the word line voltage VPP need not be set higher than necessary in the write operation. That is, since the gate insulating film thickness of the access transistor TN0 can be reduced, miniaturization is facilitated and a highly integrated semiconductor memory device can be realized.

  In addition, it goes without saying that a further effect can be obtained by combining the sense amplifier circuit SA0 of the present embodiment. That is, as described above, the sense amplifier circuit SA0 of this embodiment can realize a sufficiently stable read operation even when the read signal amount is reduced when the voltage is lowered. Furthermore, it goes without saying that high-speed operation is possible when used in combination with a layout to which a rectangular gate electrode shape as shown in FIG. 9 is applied. Further, if the negative sub word driver NSWD is used, the access transistor TN0 can be miniaturized, that is, the memory cell MC can be further miniaturized, so that the data line parasitic capacitance can be reduced. As a result, it goes without saying that a low-voltage operation and a highly integrated semiconductor memory device can be realized.

  In the first and second embodiments, the case where a plurality of pull-down circuits are applied is shown. In this case, the magnitude of the offset of the pull-down circuit determines whether stable read operation is possible or malfunction occurs. Therefore, since it is not necessary to reduce the offset of the pull-up circuit more than necessary, a so-called buried channel type PMOS transistor can be used to reduce the number of masks necessary for forming the PMOS transistor. The present invention is not limited to the above-described embodiment, and the sense amplifier circuit SA0 may be configured using a plurality of pull-up circuits. In this case, the PMOS transistor constituting the pull-up circuit may be formed of a so-called dual gate transistor rather than a so-called buried channel transistor. In this way, the number of masks necessary for forming the PMOS transistor increases, but the transistor structure is simplified, so that variations in the threshold voltage of the PMOS transistor can be suppressed.

13 to 15 show circuit diagrams, operation waveforms, and a planar layout of the sense amplifier circuit SA0 using a plurality of pull-up circuits.
As shown in FIG. 13, the sense amplifier circuit SA0 of this embodiment is composed of a plurality of pull-up circuits PDRV0 and PDRV1. Other symbols are the same as those in the above-described embodiment, and a description thereof will be omitted. Similarly to the above-described embodiment, the PMOS transistor that constitutes the pull-up circuit PDRV0 shown in FIG. ) Is big. This is because the offset of the pull-up circuit PDRV0 is sufficiently reduced and the data line pair is sufficiently preamplified to a voltage difference larger than the offset of the pull-up circuit PDRV1 and the pull-down circuit NDRV that are driven in the subsequent stage. By doing so, a read malfunction can be prevented.

  FIG. 14 is an operation waveform for explaining the operation of the sense amplifier circuit SA0 implemented in FIG. Since the basic operation is the same as that in FIG. 3, detailed description thereof is omitted. The difference from Fig. 3 is that after a minute signal difference dVsig is output to the data line pair, the common source driver VDL_DRV is asserted to drive the common source line CSP0 to the data line voltage VDL and activate the pull-up circuit PDRV0 In other words, the data line pair is preamplified. By doing so, the data line DLB0 is driven to the VDL side more strongly than the data line DLT0. Next, the pull-up circuit PDRV1 and the pull-down circuit NDRV are driven to amplify the data line pair to the high level VDL and the low level VSS. The above is the operation of the sense amplifier circuit SA0 of the third embodiment.

  FIG. 15 is an example of a planar layout of a sense amplifier array SAA-R configured using a plurality of sense amplifier circuits SA0 of the third embodiment. The difference from FIG. 4 is that a plurality of pull-up circuits PDRV0 and PDRV1 and common source drivers VDL_DRV0 and VDL_DRV1 for driving them are provided. In addition, since symbols in the drawings other than these are the same as those in the above-described embodiment, description thereof will be omitted. The layout of the contact V1, the second wiring layer M2, and the contact V2 is the same as that in FIG. As shown in FIG. 15, even when a plurality of pull-up circuits are used, the symmetry of the layout is excellent and the data line noise is small. It can be seen that the number of additional transistors is two, the number of additional wirings is small, and implementation is easy.

  Although the third embodiment has been described with reference to FIGS. 13 to 15, the present invention is of course not limited thereto. For example, a pull-up circuit having a rectangular gate electrode shape as shown in FIG. 9 may be applied, or a negative subword driver NSWD may be used as in the second embodiment. Further, in the example of FIG. 15, as in FIG. 4, an example of a so-called distributed drive system layout is shown, but of course the present invention is not limited to this. The common source line CSP0 may be used in combination with a so-called overdrive system that boosts the data line to a high level VDL or higher. In this case, it goes without saying that the effects as described above can be obtained. As described above, various modifications can be made without departing from the gist of the present idea.

  In the first to third embodiments, the sense amplifier circuit is configured using a plurality of pull-down circuits or a plurality of pull-up circuits. However, when high speed operation is not required, one pull-down circuit and one pull-down circuit are used. In some cases, a sense amplifier circuit may be configured using an up circuit. In that case, for example, the channel length of the pull-down circuit and the transistors constituting the pull-up circuit is increased or the channel width is increased to reduce the offset. Furthermore, for example, by driving the pull-down circuit prior to the pull-up circuit, the data line pair may be preamplified beyond the offset of the pull-up circuit.

  FIG. 16 is a diagram illustrating the sense amplifier circuit SA0 of the present embodiment. The difference from the previous embodiment is that there is only one pull-down circuit and one pull-up circuit. Further, the symbols in the figure are the same as those in the above-described embodiment, and thus the description thereof is omitted here. Thus, in this embodiment, since there is no additional circuit compared to the conventional sense amplifier circuit, the area of the sense amplifier circuit SA0 can be reduced as compared with the above-described embodiment. Further, since there is no additional drive signal, no additional wiring for the control signal is required, and the process cost can be reduced. That is, it is possible to realize a semiconductor memory device that achieves both a stable read operation and a reduced area of the sense amplifier.

  FIG. 17 is a diagram showing operation waveforms of the embodiment shown in FIG. Since the basic operation is the same as that in FIG. 3, detailed description thereof is omitted. The difference from FIG. 3 is that after a minute signal difference dVsig is output to the data line pair, the common source driver VSS_DRV is asserted to drive the common source line CSN to VSS, and the pull-down circuit NDRV is first activated. After the data line DLT0 is sufficiently amplified up to the offset of the pull-up circuit PDRV, the common source driver VDL_DRV is asserted, the common source line CSP is driven to the high level VDL, and the pull-up circuit PDRV is activated. Since the data line DLT0 is sufficiently amplified by the pull-down circuit NDRV activated in advance, the pull-up circuit PDRV can amplify the data line DLB0 to the high level VDL without malfunction. The above is the operation of the sense amplifier circuit SA0 of the fourth embodiment.

  In this embodiment, the pull-down circuit NDRV is activated in advance, but it goes without saying that the same effect can be obtained even if the pull-up circuit PDRV is driven in advance. In addition, it goes without saying that, in combination with the above-described embodiments, effects such as low voltage operation and high integration can be obtained. Thus, it goes without saying that various modifications can be made in the present embodiment without departing from the gist of the present invention. The memory cell MC described in the first to fourth embodiments has been described as a one-transistor type DRAM cell, but may be a two-transistor type so-called twin cell. Also, a so-called OR cell that takes the logical sum of two memory cells may be used. Of course, instead of a DRAM cell, a 6-transistor type static random access memory may be used, and various memory cells and the sense amplifier circuit of the present invention can be used in combination.

  In addition, specific examples of increasing the channel length of the transistor and increasing the channel width have been described as means for reducing the offset, but the present invention is of course not limited thereto. Means may be used in which the impurity concentration of the transistor substrate constituting the sense amplifier is lowered to suppress variation in threshold voltage due to impurity fluctuation. Further, the sense amplifier may be configured by lowering the threshold voltage of the NMOS transistor or the PMOS transistor constituting the sense amplifier circuit. In this case, since the voltage applied to the sense amplifier circuit is effectively increased, higher speed operation is possible. Further, when the threshold voltage is lowered, the impurity concentration is lowered, so that variations in the threshold voltage can be suppressed. Therefore, since the offset can be reduced, the driving force (constant) of the transistor such as the channel length and channel width of the transistor of the pull-down circuit or pull-up circuit does not need to be increased more than necessary. That is, the area of the sense amplifier circuit can be reduced. Alternatively, the substrate voltage of the transistors constituting the above-described sense amplifier circuit may be dynamically changed during the read operation. Also in this case, since the voltage difference applied to the sense amplifier circuit is effectively increased, higher speed operation is possible.

  In order to dynamically change the substrate voltage of the transistor, an additional circuit is required, but since it can be easily realized by a general circuit change, the drawing is omitted here. In this case, it is necessary to apply different substrate voltages to the memory cell portion and the sense amplifier portion, but since this can be realized by a simple circuit change, the description is omitted here. As described above, the sense amplifier circuit according to the present invention can be variously modified in accordance with purposes such as low voltage operation, high speed operation, and high integration.

SA0-SA2 Sense amplifier circuit, SHR-Switch transistor, SHRL, SHRR-Switch transistor drive line, YSW-Column switch, YS, YS0, YS1, YS2 Column switch drive line, LIOT, LIO0T, LIO1T, LIOB, LIO0B, LIO1B Local Data line, PCH precharge circuit, DLEQ precharge circuit drive line, VDLR precharge voltage, NDRV, NDRV0, NDRV1, NDRV2 pull-down circuit, PDRV, PDRV0, PDRV1 pull-up circuit, CSN, CSN0, CSN1, CSP, CSP0, CSP1 -Common source line, ΦCSN0, ΦCSN1, ΦCSP Common source control line, WL, WL0-WL5 sub word line, DLT, DLT0-DLT2, DLB, DLB0-DLB1, data line, MC memory cell, CS0 cell capacitor, PLT plate electrode, TN0-Access transistor, SAA-R, SAA-L-Sense amplifier array, SARY, SARY0-Subarray, VSS-U, VSS-D-Ground voltage, SWD-Subword driver, SWDA-U, SWDA-D Subword driver Eva array, BANK, BANK0-BANK3-Bank, VDL_DRV, VDL_DRV0, VDL_DRV1, VSS_DRV, VSS_DRV0, VSS_DRV1 Common source driver, CCNT cell contact, FGCNT gate contact, LCNT-Diffusion layer contact, DLCNT-Data line contact, SN-Storage node, SNCNT- Storage node contact, LPAD-Landing pad, LN, LP, ACT Diffusion layer and diffusion layer wiring layer, FG-Gate electrode and gate wiring layer, M1 First layer metal wiring layer, M2 Second layer metal wiring layer , M3 3rd layer metal wiring layer, V1, V2 contact, PW P well substrate, NW N well substrate, DNWELL deep N well substrate, PSUB P type substrate, VBB-substrate potential, SDRAM synchronous dynamic memory, ADDRESS BUFFER- Address buffer, COLUMN ADDRESS BUFFER-Column address buffer, COLUMN ADDRESS COUNTER-Column address counter, ROW ADDRESS BUFFER-Row address Buffer, REFRESH COUNTER-Refresh counter, BANK SELECT-Bank select, MODE RESISTER-Mode register, ROW DEC-Row decoder, COLUMN DEC-Column decoder, SENSE AMP-Main sense amplifier, MEMORY CELL ARRAY-Memory cell array, Din BUFFER-Data Input buffer, Dout BUFFER-Data output buffer, DQS BUFFER-Data buffer, DLL delay locked loop, CONTROL LOGIC-Control logic, CLK, / CLK-Clock, CKE-Clock enable signal, / CS-Chip select signal, / RAS- Row address strobe signal, / CAS-column address strobe signal, / WE-write enable signal, DW-data write signal, DQS-data strobe signal, DQ data, INV0, INV1 inverter, TN1-TN4-NMOS transistor, TP1-TP3 -PMOS transistor, VPP word line voltage, VKK negative word Line voltage, VDL data line voltage, VSS ground voltage, MWL main word line, FX, FXB sub word line control signal, NSWD-Negative sub word driver.

Claims (9)

Multiple word lines,
Multiple data lines,
A memory array comprising a plurality of memory cells disposed at the intersection;
A first source line;
A second source line;
A third source line;
A plurality of sense amplifier circuits connected to the plurality of data lines;
The plurality of sense amplifier circuits include a first conductivity type first MISFET pair in which one gate and the other drain are connected to each other and a source is connected to the first source line, and one gate and the other drain are connected to each other. The second conductivity type second MISFET pair whose source is connected to the second source line, one gate and the other drain are connected to each other, and the source is connected to the third source line. A third MISFET pair,
The threshold voltage of the transistors constituting the first MISFET pair is lower than the threshold voltage of the transistors constituting the second MISFET pair,
The first source line and the second source line change from a first voltage to a second voltage,
The semiconductor device in which the third source line changes from the first voltage to a third voltage different from the second voltage. In claim 1,
The first conductivity type is N-type;
The second voltage is lower than the first voltage;
The semiconductor device in which the third voltage is higher than the first voltage. In claim 1,
The semiconductor device in which the first source line is driven before the second source line. In claim 3,
The semiconductor device in which the second source line and the third source line change from the first voltage to the second voltage and from the first voltage to the third voltage, respectively, according to the same signal. In claim 1,
A first drive circuit for changing the first source line from the first voltage to the second voltage;
A second drive circuit that changes the second source line from the first voltage to the second voltage;
The semiconductor device in which the offset of the MISFET in the second drive circuit is smaller than the offset of the MISFET in the first drive circuit. In claim 3,
The first MISFET pair is composed of a ring-shaped transistor with a gate shape,
The second MISFET pair is a semiconductor device configured with a transistor having a rectangular gate shape. In claim 3,
The plurality of sense amplifier circuits are arranged along two opposing sides of the memory array, and the sources of the plurality of first MISFET pairs arranged on one side thereof are commonly connected to the first source line . In claim 2,
A semiconductor device in which a voltage lower than the second voltage is supplied to an unselected word line among the plurality of word lines. In claim 1,
The plurality of memory cells each include a MISFET and a capacitor,
The semiconductor device in which the diffusion layer of the MISFET in the plurality of memory cells is formed in the same well as the diffusion layer of the first MISFET pair and the second MISFET pair.

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