US20070257313A1 - Semiconductor memory device including an SOI substrate - Google Patents

Abstract

A semiconductor memory device includes a plurality of N and P channel MOS transistors. The plurality of MOS transistors are formed on an SOI (Silicon On Insulator) substrate. Each MOS transistor includes a source region, a drain region, and a body region located between the source region and the drain region. The body region of at least one N channel MOS transistor is electrically fixed. The body region of at least one P channel MOS transistor is rendered floating.

Description

RELATED APPLICATIONS
• This application is a divisional of Application Ser. No. 10/893,964 filed Jul. 20, 2004, now U.S. Pat. No. 7,138,684, which is a divisional of application Ser. No. 10/421,928 filed Apr. 24, 2003, now U.S. Pat. No. 6,768,662, which is divisional of application Ser. No. 10/094,918, filed Mar. 12, 2002, now U.S. Pat. No. 6,577,522, which is a divisional of application Ser. No. 09/816,402, filed Mar. 26, 2001, now U.S. Pat. No. 6,385,159, which is a divisional of application Ser. No. 09/499,368, filed Feb. 7, 2000, now U.S. Pat. No. 6,288,949, which is a divisional of application Ser. No. 09/146,031 filed Sep. 2, 1998, now U.S. Pat. No. 6,091,647, which is a divisional of application Ser. No. 08/876,755 filed Jun. 16, 1997, now U.S. Pat. No. 5,825,696, which is a continuation of application Ser. No. 08/353,276 filed Dec. 5, 1994, now abandoned, which in turn claims the benefit of Japanese application no. 6-260355 filed Oct. 25, 1994, Japanese application no. 6-208393 filed Sep. 1, 1004, and Japanese application no. 5-304162 filed Dec. 3, 1993, the disclosures of which applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to semiconductor memory devices, and more particularly to a dynamic random access memory (DRAM) formed on an SOI (Silicon On Insulator) substrate.
• 2. Description of the Background Art
• A semiconductor memory device is typically divided into a volatile memory such as a RAM, and a non-volatile memory such as a ROM. The volatile memory is further divided into a DRAM and a static random access memory (SRAM). The non-volatile memory includes a mask ROM, an EPROM, a flash memory, an EEPROM, a fuse ROM, and the like.
• A DRAM has data stored by accumulating charge in the capacitor of a memory cell. Although such a DRAM requires a refresh operation, a DRAM having a large storage capacity can be manufactured at a low cost due to its simple structure of the memory cell.
• Because data is stored by accumulating charge in a capacitor in a DRAM, the amount of charge stored in a capacitor is altered according to a particles emitted from its package or interconnection material. This change in the amount of charge will result in data inversion, i.e., soft error.
• The demand for DRAMs having a higher integration density is also great. The potential of mass production is appreciable for DRAMs having a large storage capacity such as 256M bits and 1 G bits. Although the gate length is generally reduced to increase the integration density of a DRAM, this reduction in gate length has a limitation due to a significant short channel effect as the channel length is reduced.
• In recent years, large scaled integrated circuits (LSI) are developed having circuit elements such as transistors formed on an SOI substrate with an insulation layer buried in the semiconductor substrate.
• FIG. 92 is a plan view showing a structure of a MOS transistor formed on an SOI substrate.FIGS. 93 and 94 are sectional views of the MOS transistor shown inFIG. 92 taken along lines93-93 and94-94, respectively.
• Referring toFIGS. 92-94, an MOS transistor includes an n⁺type source region1, an n⁺type drain region2, a ptype body region3, and agate electrode4.Body region3 is located betweensource region1 and drainregion2. When a predetermined potential is applied togate electrode4, a channel is formed inbody region3.
• This MOS transistor is completely enclosed by aLOCOS oxide film5 for isolation from an adjacent element. This MOS transistor is formed on anSOI substrate6.SOI substrate6 includes asilicon substrate7, a buriedoxide film8 of SiO₂, and an SOIactive layer9.Source region1,drain region2, andbody region3 are formed in this SOIactive layer9.
• Body region3 attains a floating state electrically since it is enclosed by LOCOSoxide film5 and isolated fromsilicon substrate7 by buriedoxide layer8. Whenbody region3 attains a floating state, the breakdown voltage between the source and drain becomes as low as approximately 3V due to a parasitic bipolar operation. There is also a possibility of a leakage current flow between the source and the drain. Furthermore, abody region3 attaining a floating state induces the generation of a kink to disturb the drain current Id—drain voltage Vd characteristics. Therefore, the transistor cannot operate stably.
SUMMARY OF THE INVENTION
• In view of the foregoing, a main object of the present invention is to provide a semiconductor memory device formed on an SOI substrate.
• Another object of the present invention is to provide a DRAM with almost no generation of a soft error.
• A further object of the present invention is to provide a DRAM having a greater storage capacity.
• Still another object of the present invention is to further increase the data retaining time in a memory cell.
• A still further object of the present invention is to improve the breakdown voltage between the source and drain of a MOS transistor in a semiconductor memory device.
• Yet a further object of the present invention is to reduce leakage current between the source and drain of a MOS transistor in a semiconductor memory device.
• Yet another object of the present invention is to operate a MOS transistor stably in a semiconductor memory device.
• Yet a still further object of the present invention is to minimize increase in the layout area.
• A semiconductor memory device according to an aspect of the present invention includes a plurality of N and P channel MOS semiconductor elements. The plurality of N and P channel MOS semiconductor elements are formed on an SOI substrate. Each MOS semiconductor element includes a source region, a drain region, and a body region located between the source and drain regions. At least one N channel MOS semiconductor element of the plurality of N channel MOS semiconductor elements has its body region electrically fixed. At least one P channel MOS semiconductor element of the plurality of P channel MOS semiconductor elements has its body region rendered floating electrically.
• A semiconductor memory device according to another aspect of the present invention includes a plurality of N and P channel MOS semiconductor elements. The plurality of N and P channel MOS semiconductor elements are formed on an SOI substrate. Each MOS semiconductor element includes a source region, a drain region, and a body region located between the source and drain regions. Any body region of the plurality of N channel MOS semiconductor elements is fixed electrically. All the body regions of the plurality of P channel MOS semiconductor elements are rendered floating electrically.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of N and P channel MOS semiconductor elements. The plurality of N and P channel MOS semiconductor elements are formed on an SOI substrate. Each MOS semiconductor element includes a source region, a drain region and a body region located between the source and drain regions. All the body regions of the plurality of N channel MOS semiconductor devices are fixed electrically. All the body regions of the plurality of P channel MOS semiconductor elements are rendered floating.
• A semiconductor memory device according to still another aspect of the present invention includes a plurality of MOS capacitors. The plurality of MOS capacitors are formed on an SOI substrate. Each MOS capacitor includes a source region, a drain region connected to the source region, and a body region located between the source and drain regions. At least one MOS capacitor of the plurality of MOS capacitors has its body region connected to its own source region.
• A semiconductor memory device according to still a further aspect of the present invention includes a plurality of MOS transistors and a plurality of bit line pairs for storing data. The stored data is read out via a bit line pair. The plurality of MOS transistors and the plurality of bit line pairs are formed on an SOI substrate. Each MOS transistor includes a source region, a drain region, and a body region located therebetween. The body region of a MOS transistor out of the plurality of MOS transistors having a source region or a drain region connected to any of the plurality of bit line pairs is electrically fixed.
• A semiconductor memory device according to yet a further aspect of the present invention includes a plurality of MOS transistors. The plurality of MOS transistors are formed on an SOI substrate. Each MOS transistor includes a source region, a drain region, and a body region located therebetween. A variable potential is supplied to the body region of at least one of the plurality of MOS transistors. This variable potential is the reverse voltage with respect to the PN junction between one of the source and drain regions and the body region. Preferably, the body region of the at least one MOS transistor is connected to its own source region.
• A semiconductor memory device according to yet another aspect of the present invention includes a plurality of bit line pairs, and a plurality of sense amplifiers. The plurality of sense amplifiers are provided corresponding to the plurality of bit line pairs. Each sense amplifier amplifies the potential difference between a corresponding bit line pair. The plurality of bit line pairs and the plurality of sense amplifiers are formed on an SOI substrate. Each sense amplifier includes first and second N channel MOS transistors connected in series between the corresponding bit line pair. The body region of the first N channel MOS transistor located between the source region and the drain region is connected to its own source region. The body region of the second N channel MOS transistor located between the source region and the drain region is connected to its own source region.
• Preferably, each sense amplifier further includes first and second P channel MOS transistors connected in series between a corresponding bit line pair. The body region of the first P channel MOS transistor located between the source region and the drain region is connected to its own source region. The body region of the second P channel MOS transistor located between the source region and the drain region is connected to its own source region.
• A semiconductor memory device according to yet a still further aspect of the present invention includes a plurality of MOS transistors and output terminals for storing data. The stored data is externally output via the output terminal. The plurality of MOS transistors are formed on an SOI substrate. Each MOS transistor includes a source region, a drain region, and a body region located therebetween. Out of the plurality of the MOS transistors, the body region of the MOS transistor having the source region connected to the output terminal is connected to its own source region.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of MOS transistors. A predetermined power supply voltage is supplied to the semiconductor memory device. The plurality of MOS transistors are formed on an S1O substrate. Out of the plurality of the MOS transistors, the body region of the MOS transistor having a voltage higher than the power supply voltage supplied between the source region and the drain region is electrically fixed.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of MOS transistors. The plurality of MOS transistors are formed on an SOI substrate. Out of the plurality of MOS transistors, the body region located between the source region and the drain region of a MOS transistor carrying out an analog operation is electrically fixed. Preferably, the MOS transistor that carries out an analog operation is a MOS transistor in a circuit that processes a signal of an amplitude smaller than that of power supply voltage supplied to the semiconductor memory device.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of MOS transistors and input/output lines for storing data. The stored data is read/written via the input/output line. The plurality of MOS transistors and the input/output lines are formed on an SOI substrate. Each MOS transistor includes a source region, a drain region, and a body region located therebetween. Out of the plurality of MOS transistors, the body region of a MOS transistor having the source region or the drain region connected to the input/output line is electrically fixed.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of MOS transistors. The plurality of MOS transistors are formed on an SOI substrate. Out of the plurality of MOS transistors, the body region located between the source and drain region of the MOS transistor in the input stage receiving an externally applied signal is electrically fixed.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of MOS transistors. The plurality of MOS transistors are formed on an SOI substrate. Out of the plurality of MOS transistors, the body region located between the source and drain regions of the MOS transistor at an output stage for outputting a signal is electrically fixed.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of MOS transistors. Any N channel MOS transistors out of the plurality of MOS transistors are connected in series between an output node for providing a signal and a ground node. The plurality of MOS transistors are formed on an SOI substrate. Out of the any of the N channel MOS transistors, the body region located between the source region and the drain region of at least one N channel MOS transistors that does not have a source region directly connected to the ground node is electrically fixed.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of MOS transistors. The plurality of MOS transistors are formed on an SOI substrate. Out of the plurality of MOS transistors, the body region located between the source region and the drain region of a MOS transistor having a gate length shorter than a predetermined gate length is electrically fixed. Out of the plurality of MOS transistors, the body region located between the source region and the drain region of a MOS transistor having a gate length longer than the predetermined gate length is rendered floating electrically.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of first and second conductive channel type MOS transistors. The plurality of first and second conductive channel type MOS transistors are formed on an SOI substrate. At least one first conductive channel type MOS transistor of the plurality of first conductive channel type MOS transistors has a first threshold voltage. At least one first conductive channel MOS transistor of the plurality of first conductive channel MOS transistors has a second threshold voltage differing from the first threshold voltage.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of first and second conductive channel type MOS transistors. The plurality of first and second conductive channel type MOS transistors are formed on an SOI substrate. A second conductivity type body region located between a first conductivity type source region and a first conductivity type drain region of at least one first conductive channel MOS transistor of the plurality of first conductive channel type MOS transistors includes a conductive layer having a first impurity concentration on the surface thereof. A second conductivity type body region located between the first conductivity type source region and the first conductivity type drain region between at least another first conductive channel type MOS transistor of the plurality of first conductive channel type MOS transistors includes a conductive layer having a second impurity concentration differing from the first impurity concentration at the surface thereof.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of first and second conductive channel type MOS transistors. The plurality of first and second conductive channel type MOS transistors are formed on an SOI substrate. A second conductivity type body region located between a first conductivity type source region and the first conductivity type drain region of at least one first conductive channel type MOS transistor out of the plurality of first conductive channel type MOS transistors receives a first potential. A second conductivity type body region located between the first conductivity type source region and the first conductivity type drain region of at least another first conductive channel type MOS transistor out of the plurality of first conductive channel type MOS transistors receives a second potential differing from the first potential.
• A semiconductor memory device according to a further aspect of the present invention includes a memory cell array of a plurality of first MOS transistors, and a peripheral circuit of a plurality of second MOS transistors. The plurality of first and second MOS transistors are formed on an SOI substrate. The plurality of first MOS transistors have a threshold voltage higher than that of the plurality of second MOS transistors.
• A semiconductor memory device according to a further aspect of the present invention includes a plurality of MOS semiconductor elements. The plurality of MOS semiconductor elements are formed on an SOI substrate. The source and drain regions of any MOS semiconductor elements out of the plurality of MOS semiconductor elements are brought into contact with an insulation layer in the SOI substrate.
• A semiconductor memory device according to a further aspect of the present invention includes a memory cell array of a plurality of first MOS transistors, and a peripheral circuit of a plurality of second MOS transistors. The memory cell array and the peripheral circuit are formed on an SOI substrate. The source and drain regions of the plurality of first MOS transistors are brought into contact with an insulation layer of the SOI substrate.
• A semiconductor memory device according to a further aspect of the present invention includes at least one first semiconductor element and at least one second semiconductor element. An element isolation film for isolating the first and second semiconductor elements are formed on an SOI substrate. The element isolation film is brought into contact with an insulation layer in the SOI substrate.
• A semiconductor memory device according to a further aspect of the present invention is formed on an SOI substrate. The SOI substrate includes a semiconductor substrate, a buried insulation layer formed on the semiconductor substrate, and a semiconductor active layer formed on the buried insulation layer. The semiconductor memory device further includes a supply circuit. The supply circuit supplies a predetermined substrate potential to the semiconductor substrate of the SOI substrate.
• Because the above-described semiconductor memory device in which all semiconductor elements are formed on an SOI substrate has the body region of at least one N channel MOS semiconductor element electrically fixed, leakage current between the source and drain is reduced and the breakdown voltage between the source and drain is increased. Because there is almost no kinks in the fixed body region, a stable Id-Vd characteristic can be obtained. Furthermore, because the body region of at least one P channel MOS semiconductor element is rendered floating electrically, wiring for fixing the body region is not required, and increase of the layout area is minimized. In general, the breakdown voltage between the source and drain in an N channel MOS semiconductor element is smaller than that of the P channel MOS semiconductor element. Here, the body region of an N channel MOS transistor is fixed, so that the breakdown voltage between the source and drain thereof is similar to that of a P channel MOS semiconductor element.
• Because the body region of a MOS capacitor is connected to its own source region, the body region thereof is fixed. Therefore, this MOS capacitor can operate stably. Furthermore, because the body region is connected to the source region, wiring for supplying potential to the body region is not required. Thus, there is almost no increase in the layout area.
• Because the body region of the MOS transistor connected to the bit line pair is fixed, leakage current flowing from the bit line pair via the MOS transistor, or the leakage current flowing to the bit line pair via the MOS transistor is reduced.
• Because a variable potential is applied to the body region of a MOS transistor that becomes a reverse voltage with respect to the PN junction formed of the body region and the source/drain region, the transistor does not carry out bipolar operation, and body effect does not occur. Therefore, this MOS transistor operates stably.
• Because the body region of the MOS transistor to which high voltage is applied between the source and drain is fixed, the breakdown voltage between the source and drain is increased, so that this transistor will operate properly even when high voltage is applied between the source and drain.
• Because the body region of a MOS transistor carrying out an analog operation is fixed, there is almost no kinks in that transistor. Therefore, this transistor always operates stably.
• Because the body region of a MOS transistor having source/drain regions connected to an input/output line is fixed, a great leakage current will not flow between the source and drain, so that accurate data can be input and output.
• Because the body region of a MOS transistor at an input stage is fixed, a great leakage current will not flow between the source and drain, so that a desired input impedance can be obtained.
• Because the body region of a MOS transistor at an output stage is fixed, a great amount of leakage current will not flow between the source and drain, so that a desired output impedance can be obtained.
• Because the body region of an N channel MOS transistor that is not directly connected to a ground node is fixed, the threshold voltage of the transistor including that fixed body region is reduced, whereby the transistor operates more speedily. Therefore, those transistor can operate properly even when the power supply voltage is low.
• Because the body region of a MOS transistor having a short gate length is fixed, the breakdown voltage between the source and drain of that transistor is equal to that of a transistor having a greater gate length. Also, the level of the leakage current flowing between the source and drain of the transistor of the short gate length is similar to that of the transistor of the long gate length. Furthermore, because the body region of the MOS transistor of the long gate length is rendered floating, wiring for providing potential to the body region is not required, so that increase in the layout area can be suppressed to a minimum.
• Because transistors of the same conductivity type have more than one type of threshold voltage, these transistors operate stably.
• The junction capacitance of the source/drain region is reduced since a semiconductor element is formed in the thin SOI active layer.
• Because an element isolation film such as a Locos oxide film is formed in a thin SOI active layer, the element isolation film comes into contact with the insulation layer of the SOI substrate.
• Because a predetermined substrate potential is supplied to the.semiconductor substrate of an SOI substrate, the semiconductor substrate is electrically fixed. Therefore, the potential of the semiconductor substrate will not change, so that change in the potential of the semiconductor active layer will also not occur. As a result, semiconductor elements such as a transistor formed on the semiconductor active layer operates stably.
• The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a circuit diagram showing partially a structure of a memory cell, a sense amplifier, and an input/output circuit in a DRAM according toembodiment 1 of the present invention.
• FIG. 2 is a block diagram showing the entire structure of a DRAM.
• FIG. 3 is a timing chart showing an operation of the DRAM ofFIG. 1.
• FIG. 4 is a timing chart showing another operation of the DRAM ofFIG. 1.
• FIG. 5 is a plan view showing a structure of the sense amplifier and the precharge circuit ofFIG. 1.
• FIG. 6 is a sectional view of the sense amplifier ofFIG. 1 taken along line6-6.
• FIG. 7 is a plan view showing a general structure of a transistor in the bit line select circuit, the column select circuit or the memory cell shown inFIG. 1.
• FIGS. 8 and 9 are plan views showing the structure of a sense amplifier and a precharge circuit of a DRAM according toembodiment 2 andembodiment 3, respectively, of the present invention.
• FIGS. 10-12 are circuit diagrams showing a partial structure of a memory cell, a sense amplifier, and an input/output circuit of a DRAM according toembodiment 4,embodiment 5, andembodiment 6, respectively, of the present invention.
• FIG. 13 is a plan view showing the structure of the sense amplifier and the precharge circuit shown inFIG. 12.
• FIG. 14 is a plan view showing a structure of the sense amplifier and the precharge circuit in a DRAM according toembodiment 7 andembodiment 8, respectively, of the present invention.
• FIG. 15 is a plan view showing the sense amplifier and precharge circuit of a DRAM according toembodiment8.
• FIGS. 16-19 are circuit diagrams showing a partial structure of a memory cell, a sense amplifier, and an input/output circuit of a DRAM according toembodiment 9,embodiment 10,embodiment 11, andembodiment 12, respectively, of the present invention.
• FIGS. 20 and 21 are circuit diagrams showing structure of a word line driving circuit of a DRAM according toembodiment 13 andembodiment 14, respectively, of the present invention.
• FIG. 22 is a plan view showing a structure of an N channel MOS transistor in the word line driving circuit ofFIG. 21.
• FIGS. 23 and 24 are circuit diagrams showing a structure of boost signal predecode circuit of a DRAM according toembodiment 15 andembodiment 16, respectively, of the present invention.
• FIG. 25 is a plan view showing a structure of an N channel MOS capacitor in a DRAM according toembodiment 17 of the present invention.
• FIG. 26 is a plan view showing a structure of a P channel MOS capacitor of a DRAM according toembodiment 18 of the present invention.
• FIG. 27 is a plan view showing a structure of an N channel MOS capacitor of a DRAM according toembodiment 19 of the present invention.
• FIG. 28 is a plan view showing a structure of a P channel MOS capacitor of a DRAM according toembodiment 20 of the present invention.
• FIG. 29 is a circuit diagram showing the entire structure of a boosted power supply generation circuit of a DRAM according to embodiment 21 of the present invention.
• FIG. 30 is a circuit diagram showing a structure of an output preamplifier and a write circuit of a DRAM according toembodiment 22 of the present invention.
• FIG. 31 is a circuit diagram showing a structure of an input/output line precharge circuit and an input/output line equalize circuit of a DRAM according toembodiment 23 of the present invention.
• FIG. 32 is a circuit diagram showing a structure of a row address buffer of a DRAM according toembodiment 24 of the present invention.
• FIGS. 33-36 are circuit diagrams of a structure of a column address buffer of a DRAM according to embodiments 25-28, respectively, of the present invention.
• FIGS. 37-40 are circuit diagrams of a structure of a clock input buffer of a DRAM according to embodiments 29-32, respectively, of the present invention.
• FIG. 41 is a circuit diagram showing a structure of the sense amplifier driving circuit of a DRAM according toembodiment 33 of the present invention.
• FIG. 42 is a timing chart showing an operation of the sense amplifier driving circuit ofFIG. 41.
• FIG. 43 is a circuit diagram showing a structure of a CAT circuit of a DRAM according toembodiment 34 of the present invention.
• FIG. 44 is a timing chart showing an operation of the CAT circuit ofFIG. 43.
• FIGS. 45 and 46 are circuit diagrams showing a structure of an N-N buffer of a DRAM according toembodiment 35 andembodiment 36, respectively, of the present invention.
• FIG. 47 is a circuit diagram showing a structure of a NAND circuit of a DRAM according to embodiment 37 of the present invention.
• FIG. 48 is a plan view showing a partial structure of the NAND circuit ofFIG. 47.
• FIGS. 49-52 are plan views showing a partial structure of the NAND circuit of a DRAM according to embodiments 38-41, respectively, of the present invention.
• FIG. 53 is a plan view showing a partial structure of the NAND circuit ofFIG. 52.
• FIGS. 54-59 are circuit diagrams showing a structure of a NAND circuit of a DRAM according to embodiments 42-47, respectively, of the present invention.
• FIG. 60 is a sectional view of a memory cell in a DRAM according toembodiment 48 of the present invention.
• FIG. 61 is a sectional view of the memory cell ofFIG. 60 taken along the direction of a word line.
• FIG. 62 is a sectional view showing a structure of a memory cell in a DRAM according to embodiment 49 of the present invention.
• FIG. 63 is a sectional view of the memory cell ofFIG. 62 taken along the direction of a word line.
• FIG. 64 is a sectional view of a memory cell of a DRAM according toembodiment 50 andembodiment 51, respectively, of the present invention.
• FIG. 65 is a sectional view of a memory cell unit taken along the bit line direction of a DRAM according toembodiment 51.
• FIGS. 66-69 are layout diagrams showing the entire structure of a DRAM according to embodiments 52-55, respectively, of the present invention.
• FIGS. 70-76 are diagrams showing the concept of a DRAM according to embodiments 56-62, respectively, of the present invention.
• FIG. 77 is a sectional view of two P channel MOS transistors in a DRAM shown inFIG. 76.
• FIG. 78 is a diagram showing the concept of a DRAM according to embodiment 63 of the present invention.
• FIG. 79 is a sectional view of a sense amplifier of a DRAM according to embodiment 64 of the present invention.
• FIG. 80 is a sectional view of a memory cell of a DRAM ofFIG. 79.
• FIG. 81 is a sectional view of a memory cell ofFIG. 80 taken along the direction of a word line.
• FIG. 82 is a sectional view showing a structure of a memory cell of a DRAM according toembodiment 65 of the present invention.
• FIG. 83 is a diagram showing the concept of a partial structure of a DRAM according toembodiment 66 of the present invention.
• FIG. 84 is a sectional view showing a partial structure of a DRAM according toembodiment 67 of the present invention.
• FIG. 85-87 are perspective views showing a structure of a DRAM according to embodiments 68-70, respectively, of the present invention.
• FIGS. 88 and 89 are diagrams of the concept of a partial structure of a DRAM according toembodiments 71 and 72, respectively, of the present invention.
• FIG. 90 is a circuit diagram showing a partial structure of a memory cell, a sense amplifier, and an input/output circuit of a DRAM according toembodiment 73 of the present invention.
• FIG. 91 is a timing chart showing an operation of the DRAM ofFIG. 90.
• FIG. 92 is a plan view showing a structure of a conventional N channel MOS transistor formed on an SOI substrate.
• FIGS. 93 and 94 are sectional views of the transistor ofFIG. 92 taken along lines93-93, and94-94, respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• The embodiments of the present invention will be described hereinafter with reference to the drawings. In the drawings, the same reference characters denote the same or corresponding components.
Embodiment 1
• FIG. 2 is a BL0ck diagram showing an entire structure of a DRAM according toembodiment 1 of the present invention. Referring toFIG. 2, aDRAM10 includes amemory cell array11, arow decoder12, acolumn decoder13, asense amplifier group14, an input/output circuit15, a row-and-column address buffer16, aninput buffer17, anoutput buffer18, and aclock generation circuit19.
• Inmemory cell array11, a plurality of word lines (not shown) are disposed along the row direction, and a plurality of bit line pairs (not shown) are disposed along the column direction, with a plurality of memory cells (not shown) at the crossings thereof.Row decoder12 responds to a row address signal fromaddress buffer16 to select and drive one of the plurality of word lines.Column decoder13 responds to a column address signal fromaddress buffer16 to select one of the plurality of bit line pairs.Sense amplifier group14 includes a plurality of sense amplifiers. The plurality of sense amplifiers are provided corresponding to the plurality of bit line pairs. Each sense amplifier amplifies the potential difference of a corresponding bit line pair. Input/output circuit15 provides the potential of the bit line pair selected bycolumn decoder13 tooutput buffer18.Output buffer18 amplifies the provided potential to output the same as output data DQ₁-DQ₄.Input buffer17 amplifies externally applied input data DQ₁-DQ₄. Input/output circuit15 provides the input data amplified ininput buffer17 to the bit line pair selected bycolumn decoder13.Address buffer16 selectively provides externally applied address signals A0-A11 to rowdecoder12 andcolumn decoder13.
• FIG. 1 is a circuit diagram showing in detailmemory cell array11,sense amplifier group14 and input/output circuit15 ofFIG. 12 partially. Referring toFIG. 1, word lines WL1, WL2, . . . and bit line pairs BL0, /BL0, BL1, /BL1 crossing these word lines are disposed inmemory cell array11. Amemory cell27 is disposed at the crossing between bit lines BL0, /BL0 and word lines WL1, WL2.
• Onesense amplifier20 is disposed corresponding to two bit line pairs BL0, /BL0 and BL1, /BL1. Bit lines BL0 and /BL0 are connected to senseamplifier20 via a bit lineselect circuit26A. Bit lines BL1 and /BL1 are connected to senseamplifier20 via a bit lineselect circuit26B. Bit lineselect circuit26A responds to a bit line select signal BLI0 to connect bit line pair BL0, /BL0 to senseamplifier20, wherebysense amplifier20 amplifies the potential difference between bit lines BL0 and /BL0. Bit lineselect circuit26B responds to a bit line select signal BLI1 to connect bit lines BL1 and /BL1 to senseamplifier20, wherebysense amplifier20 amplifies the potential difference between bit lines BL1 and /BL1. Thus,embodiment 1 employs the so-called shared sense amplifier system.
• One bit lineprecharge circuit23 is provided corresponding to senseamplifier20.Precharge circuit23 corresponds to a bit line equalize signal BLEQ to precharge bit line pairs BL0, /BL0, BL1, /BL1 to a predetermined potential V_BL.
• Also, one columnselect circuit29 is provided corresponding to one or a plurality ofsense amplifiers20. Columnselect circuit29 responds to a column select signal CSL to connect bit line pairs BL0, /BL0, BL1, /BL1 to an input/output line pair10 and /IO.
• A drive lineprecharge circuit22 is provided between senseamplifier drive lines21A and21B to drivesense amplifier20.Precharge circuit22 responds to an equalize signal BLEQ to precharge senseamplifier drive lines21A and21B to a predetermined potential V_BL. Senseamplifier drive line21A is also connected to a ground node via an N channel MOS transistor Qs1 which becomes conductive in response to control signal SQF. Senseamplifier drive line21A is also connected to a ground node via an N channel MOS transistor Qs2 which becomes conductive in response to control signal SON. Senseamplifier drive line21B is connected to a power supply node via a P channel MOS transistor Qs3 which becomes conductive in response to a control signal SOP.
• Dummy word lines DWL1 and DWL2 are disposed parallel to word lines WL1 and WL2. Adummy cell28 is disposed at the respective crossings between dummy word lines DWL1, DWL2 and bit lines BL0, /BL0. When word lines WL1 and WL2 rise,dummy cell28 cancels the noise generated in bit lines BL0 and /BL0.
• Sense amplifier20 includes N channel MOS transistors Qnl and Qn2 connected in series between a bit line pair, and P channel MOS transistors Qp1 and Qp2 connected in series between a bit line pair. Transistors Qn1 and Qp1 have their gate electrodes connected to bit lines /BL0 and /BL1, and transistors Qn2 and Qp2 have their gate electrodes connected to bit lines BL0 and BL1. Transistors Qn1 and Qn2 have their source electrodes connected to sense amplifier driven line21a,and transistors Qp1 and Qp2 have their source electrodes connected to sense amplifier drive line21b.
• Eachmemory cell27 includes an N channel MOS transistor Qm that serves as a transfer gate, and a capacitor Cm for storing data. Transistor Qm has its gate electrode connected to a corresponding word line WL1 or WL2, and one of the source/drain electrodes connected to a corresponding bit line BL0 or /BL0. Capacitor Cm has one electrode connected to the other source/drain electrode of transistor Qm. Cell plate potential Vcp is supplied to the other electrode of capacitor Cm.
• Similar tomemory cell27, eachdummy cell28 includes an N channel MOS transistor Qd and a capacitor Cd. Transistor Qd has its gate electrode connected to a corresponding dummy word line DWL1 or DWL2, and one source/drain electrode connected to a corresponding bit line BL0 or /BL0. Capacitor Cd has one electrode connected to the other source/drain electrode. Cell plate potential Vcp is supplied to the other electrode of capacitor Cd.
• Bit lineselect circuit26A includes two N channel MOS transistors Qb which become conductive in response to bit line select signal BLIO. Bit lineselect circuit26B includes two N channel MOS transistors Qb that become conductive in response to bit line select signal BLI1.
• Bit lineprecharge circuit23 includes an N channel MOS transistor Qe connected between a bit line pair, and two N channel MOS transistors Qpc connected in series between a bit line pair. Transistors Qe and Qpc have their gate electrodes connected to an equalizeline24. Transistors Qpc have their source electrodes connected toprecharge line25.
• Columnselect circuit29 includes an N channel MOS transistor Qio connected between bit lines BL0, BL1 and input/output line I0, and which becomes conductive in response to column select signal CSL, and an N channel MOS transistor Qio connected between bit lines /BL0, /BL1 and input/output line /I0, and which becomes conductive in response to column select signal CSL.
• A drive dedicatedprecharge circuit22 includes an N channel MOS transistor Qse connected betweendrive lines21A and21B, and two N channel MOS transistors Qsp connected in series betweendrive lines21A and21B. Transistors Qse and Qsp have their gate electrodes connected to equalizeline24. Transistors Qsp have their source electrodes connected toprecharge line25.
• The operation of the circuitry shown inFIG. 1 will be described with reference to the timing chart ofFIG. 3.
• Referring toFIG. 3(a), address signals A0-A11 are strobed in response to a fall of external row address strobe signal /RAS. When bit line pair BL0, /BL0 is selected according to that address signal, bit line select signal BLIO rises as shown inFIG. 3(d). Bit line select signal BLT1 is maintained at a L Level (logical low). Therefore, bit line pair BL0, /BL0 is connected to senseamplifier20.
• Since bit line equalize signal BLEQ attains a H level (logical high) as shown inFIG. 3(f), transistors Qpc of bit lineprecharge circuit23 are both conductive. Therefore, precharge potential Vb1 is applied to bit line pair BL0, /BL0. Because transistor Qe of bit lineprecharge circuit23 is also conductive, the potentials of bit lines BL0 and /BL0 are equal to each other. The potential of bit line pair BL0, /BL0 takes an intermediate level between a H level and a L level as shown inFIG. 3(j) because a potential V_CC/2 which is half the power supply potential is supplied as precharge potential Vb1.
• This equalize signal BLEQ of a H level is also applied to the gate electrodes of transistors Qse and Qsp of drive dedicatedprecharge circuit22, so that senseamplifier drive lines21A and21B are precharged to potential V_CC/2 which is half the power supply potential, similar to bit line pair BL0, /BL0.
• Then, when word line WL1 rises as shown inFIG. 3(b), transistor Qd of acorresponding memory cell27 is rendered conductive, whereby the charge in capacitor Cm is read out on bit line BL0. When data of a L level is stored inmemory cell27, the potential of bit line BL0 becomes a slightly lower than precharge potential Vb1 as shown inFIG. 3(j). As a result, a potential difference is generated between bit lines BL0 and /BL0.
• Then, when control signal SOF rises as shown inFIG. 3(g), transistor Qs1 is rendered conductive, whereby the charge of senseamplifier drive line21A flows to the ground node via transistorˆQs1. This causes potential SAN of senseamplifier drive line21A to decrease towards ground potential V_SS.
• Then, when control signal SON rises as shown inFIG. 3(h), transistor Qs2 is rendered conductive, whereby the charge of senseamplifier drive line21A flows to the ground node via transistor Qs2. As a result, potential SAN of senseamplifier drive line21A further decreases towards ground potential V_SS.
• When control signal SOP falls as shown inFIG. 3(i), transistor Qs3 is rendered conductive, whereby charge is supplied from the power supply node to senseamplifier drive line21B via transistor Qs3. As a result, potential SAB of senseamplifier drive line21B gradually increases towards power supply potential V_CC.
• Because sense amplifier drive signal SAN gradually decreases towards ground potential V_SSand sense amplifier drive signal SAP gradually increases towards power supply potential V_CCas described above,sense amplifier20 reduces the potential of bit line BL0 to a L level, and the potential of bit line /BL0 to a H level, as shown inFIG. 3(j). Therefore,sense amplifier20 latches complementary data corresponding to the data ofmemory cell27.
• Then, when column select signal CSL rises, transistors Qio of columnselect circuit29 both attain a conductive state. This causes the potential of bit line BL0 to be provided to input/output line IO via transistor Qio and the potential of bit line /BL0 to input/output line /IO via transistor Qio. The potentials at input/output lines IO and /IO are amplified byoutput buffer18 to be output as output data.
• Although the case where a bit line pair is precharged to V_CC/2 is described here, the bit line pair may be precharged to V_CC. In this case, the capacitance of capacitor Cd indummy cell28 must be different from that of capacitor Cm inmemory cell27. For example, the capacitance of capacitor Cd may be half that of capacitor Cm.
• FIG. 4 is a timing chart of a bit line pair precharged to V_CC. When bit line equalize signal BLEQ attains a H level as shown inFIG. 4(f), the bit line pair. is precharged to a H level, i.e. to power supply potential V_CC, as shown inFIG. 4(j). By pulling up DWL2 simultaneously to the rise of word line WL1, a potential difference is generated between the bit line pair.
• When the power supply level is established in a hierarchical manner, an internal power supply potential is generated by down-converting external power supply potential, and an internal ground potential is generated by boosting the external ground potential. In this case, sense amplifier drive signal SAN gradually decreases from precharge potential towards internal ground potential which is higher than external ground potential, and sense amplifier drive signal SAP gradually increases towards internal power supply potential which is lower than the external power supply potential. Therefore,sense amplifier20 raises the potential of one sense amplifier to the level of internal power supply potential, and the potential of the other bit line to the level of internal power supply potential.
• Insense amplifier20 ofembodiment 1, a constant ground potential Vss is applied to the body regions of N channel MOS transistors Qn1 and Qn2, whereby the body regions are electrically fixed. Also, a constant power supply potential V_CCis applied to the body regions of P channel MOS transistors Qp1 and Qp2, whereby the body regions are electrically fixed.
• Therefore, a kink will not be generated in these transistors Qn1, Qn2, Qp1, and Qp2, so that a stable Id-Vd characteristic is obtained. Thus,sense amplifier20 carries out a stable analog operation.
• Because the body regions of transistors Qn1, Qn2, Qp1 and Qp2 are fixed, the leakage current between the source and drain is reduced. Therefore, the charge of bit lines BL0, /BL0, BL1 and /BL1 will not leak via transistors Qn1, Qn2, Qp1 and Qp2. Thus, the potential difference generated between a bit line pair when data is read out frommemory cell27 can be maintained at a sufficient high level.
• Inmemory cell27 ofembodiment 1, a constant ground potential V_SSis applied to the body region of an N channel MOS transistor, so that the body region is electrically fixed. Therefore, the subthreshold characteristic is improved, and the leakage current approximates the physical limit value. Thus, charge that leaks from capacitor Cm via transistor Qm is determined by the leakage at the PN junction. In a transistor formed on a thin film SOI, there is at least no PN junction plane that is parallel with an SOI substrate. The leakage current at a PN junction is proportional to the surface area of the PN junction, so that data retaining time period is increased. Indummy memory cell28, a constant ground potential V_SSis applied to the body region of N channel MOS transistor Qd, so that the body region is electrically fixed, similar tomemory cell27.
• In bit lineprecharge circuit23 ofembodiment 1, constant ground potential V_SSis applied to the body regions of N channel MOS transistors Qe and Qpc, so that the body regions are electrically fixed. Therefore, the charge in the bit line will not leak via these transistors Qe and Qpc. This prevents the read out potential difference generated between bit lines from being reduced, so that the potential difference is reliably amplified by a sense amplifier.
• In drive dedicatedprecharge circuit22, a constant ground potential V_SSis applied to the body regions of transistors Qse and Qsp, so that the body regions are electrically fixed, similar to bit lineprecharge circuit23. Also, constant ground potential V_SSis applied to the body regions of N channel MOS transistors Qs1 and Qs2, so that the body regions are electrically fixed. Power supply potential V_CCis applied to the body region of P channel MOS transistor Qs3, so that the body region. is electrically fixed.
• In bit lineselect circuits26A and26B inembodiment1, a constant ground potential V_SSis applied to the body region of N channel MOS transistor Qp, so that the body region is electrically fixed. The charge in the bit lines do not leak via transistor Qb, so that the read out potential difference is maintained sufficiently.
• In columnselect circuit29 ofembodiment 1, a constant ground potential V_SSis applied to the body region of N channel MOS transistor Qio, so that the body region is electrically fixed. Therefore, the charge in the bit lines will not leak via transistor Qio, so that the read out potential difference is maintained sufficiently. Thus, correct data is read out to input/output lines IO and /IO via columnselect circuit29.
• FIG. 5 is a plan view ofsense amplifier20 partially andprecharge circuit23 entirely shown inFIG. 1.FIG. 6 is a sectional view ofsense amplifier20 ofFIG. 5 taken along line6-6. InFIG. 5, only an N channel sense amplifier formed of N channel MOS transistors Qn1 and Qn2 is shown.
• Referring toFIGS. 5 and 6, an n⁺type source region1 of transistor Qn1 is common to the source region of transistor Qn2.Source region1 is connected to senseamplifier drive line21A to which a sense amplifier drive signal SAN is provided via contact hole CH.
• An n⁺type drain region2 of transistor Qn1 is connected to bit line BL1 via a contact hole CH. n⁺type drain region2 of transistor Qn2 is connected to bit line /BL1 via contact hole CH. Transistor Qn1 has itsgate electrode4 connected to bit line /BH1 via contact hole CH. Transistor Qn2 hasgate electrode4 connected to bit line BL1 via contact hole CH.
• A p⁺type contact region31 is formed on a ptype body region3 of transistor Qn1. Contactregion31 is connected to abody fix line30C via anintermediate layer32 such as of a polypad. Ground potential V_SSis supplied tobody fix line30C. A constant ground potential V_SSis supplied tobody region3. Contactregion31 is also formed inbody region3 of transistor Qn2.Body region3 of transistor Qn2 is connected tobody fix line30B viacontact region31 andintermediate layer32. Ground potential V_SSis also supplied tobody fix line30B. Therefore, ground potential V_SSis also provided tobody region3 of transistor Qn2.
• Referring toFIG. 6, a firstinterlayer insulation film33 is formed ongate electrode4. Contact hole CH is formed at a predetermined position ininterlayer insulation film33.Intermediate layer32 is formed on contact hole CH. A secondinterlayer insulation film34 is formed on firstinterlayer insulation film33 andintermediate layer32. Contact hole CH is formed at a predetermined position of secondinterlayer insulation film34. Bit lines BL and /BL are formed on secondinterlayer insulation film34.
• A thirdinterlayer insulation film35 is formed on secondinterlayer insulation film34 and bit lines BL and /BL. Contact hole CH is formed at a predetermined position of thirdinterlayer insulation film35. Contact hole CH is provided aboveintermediate layer32.Body fix lines30B and30C are formed on thirdinterlayer insulation film35.Body fix line30C is formed above contact hole CH to form contact withintermediate layer32. A fourthinterlayer insulation film36 is formed on thirdinterlayer insulation film35 and body fix lines30B and30C.
• Transistor Qn1 ofsense amplifier20 is formed on anSOI substrate6. Because a buriedoxide layer8 is provided at a shallow region in this SOI substrate, the thickness of an SOIactive layer9 is small. As a result, the bottom ofL0COS oxide film5 reaches buriedoxide layer8.Source region1 and drainregion2 of transistor Qn1 also reach buriedoxide layer8. As a result,body fix line30C is connected tobody region3 of transistor Qn1 which is completely isolated from its periphery byLOCOS oxide film5 and buriedoxide film8. Therefore ground potential V_SSis provided thereto.
• Inprecharge circuit23, equalizeline24 forms the gate electrodes of all transistor Qe and Qpc. Therefore, ptype body region3 of these transistors Qe and Qpc are common to each other. A p⁺type contact region31 is formed inbody region3. Contactregion31 is connected tobody fix line30A via contact hole CH. Ground potential V_SSis supplied tobody fix line30A. Therefore, ground potential V_SSis applied tobody regions4 of transistors Qe and Qpc.
• Driveprecharge circuit22 has a structure similar to that of bit lineprecharge circuit23.
• FIG. 7 is a plan view showing a general structure of transistors Qm, Qd, Qb and Qio ofmemory cell27,dummy cell28, bit lineselect circuits26A and26B, and columnselect circuit29. Referring toFIG. 7, p⁺type contact region31 is formed in ptype body region3 of these transistors. Ground potential V_SSis supplied to contactregion31. As a result,body region3 is fixed electrically.
• Because a DRAM according toembodiment 1 is formed on an SOI substrate so that asilicon substrate7 is electrically isolated by SOIactive layer9 and buriedoxide layer8, the charge generated insilicon substrate7 due to a particles impinging thereto will not flow intosource region1, drainregion2, andbody region3. Furthermore, there is almost no generation of charges due to a particles insource region1, drainregion2, andbody region3 since theregions1,2 and3 are extremely small. Thus, there is almost no generation of the so-called soft error.
• Because the bottom of the source/drain region of transistor Qm formingmemory cell27 also reaches buriedoxide layer8, there is no PN junction plane parallel toSOI substrate6. Only a PN junction plane perpendicular toSOI substrate6 exists. The leakage current in a PN junction is proportional to the surface area of the PN junction. Therefore, the charge leaking from capacitor Cm via the source/drain regions is reduced according to the surface area, and the retaining time period of data is increased accordingly. Furthermore, because the junction capacitance of the source/drain region is also reduced, the read out potential difference generated between the bit lines is increased, and power consumption becomes lower.
• The charge of the bit line will not leak via a transistor connected to the bit line since its body region is fixed. Therefore, the read out potential difference generated between the bit lines is maintained sufficiently. Furthermore, there are almost no kinks in this transistors since the body region of the transistor ofsense amplifier20 is also fixed. Thus,sense amplifier20 amplifies the read out potential difference stably.
Embodiment 2
• FIG. 8 is a plan view showing a structure ofsense amplifier20 partially andprecharge circuit23 entirely in a DRAM according toembodiment 2 of the present invention.
• Referring toFIG. 8,embodiment 2 has bothbody regions3 protruding in the same direction with acontact region31 formed at that protruding portion. Bothcontact regions31 are connected to onebody fix line30C via respective contact holes CH. Also, bothgate electrodes4 protrude in the same direction. The protruding portions thereof are connected to bit lines BL1 and /BL1 via respective contact holes CH.
• Embodiment 2 has a layout area smaller than that ofembodiment 1 sincebody fix line30C for fixingbody regions3 of transistors Qn1 and Qn2 are common.
Embodiment 3
• FIG. 9 is a plan view showing a structure ofsense amplifier20 partially andprecharge circuit23 entirely of a DRAM according toembodiment 3 of the present invention. Referring toFIG. 9,precharge circuit23 differs from the precharge circuit ofembodiment 1 in that it is disposed in a 180° rotated position.Body regions3 of transistors Qe and Qpc inprecharge circuit23 are connected tobody fix line30B viacontact region31 and contact hole CH.Body region3 of transistor Qn2 ofsense amplifier20 is also connected tobody fix line30B viacontact region31 and contact hole CH.
• Embodiment 3 has a layout area smaller than that ofembodiment 1 sincebody fix line30B for fixingbody region3 of transistor Qn2 ofsense amplifier20 is common to the body fix line for fixingbody region3 of transistors Qe and Qpc inprecharge circuit23.
Embodiment 4
• FIG. 10 is a circuit diagram showing a memory cell array, a sense amplifier, and an input/output circuit partially.of a DRAM according toembodiment4. Referring toFIG. 10,embodiment 4 has a negative potential VBB supplied to the body region of transistor Qm ofmemory cell27, different from the potential ofembodiment 1. Negative potential VBB is also applied to the body region of transistor Qd indummy cell28. Therefore, the N channel MOS transistors inembodiment 4 have two types of threshold voltages.
• Because only the threshold voltages of transistors Qm and Qd inmemory cell27 anddummy cell28 are great, sub threshold current does not easily flow in transistors Qm and Qd inembodiment 4. Therefore, the dynamic data retention of the bit line amplitude according to a sense operation is further improved in a deselect memory cell. Therefore, the data retaining time period of a memory cell is increased.
Embodiment 5
• FIG. 11 is a circuit diagram showing a memory cell array, a sense amplifier, and an input/output circuit partially of a DRAM according toembodiment 5 of the present invention.
• Referring toFIG. 11,embodiment 5 has negative potential V_BBapplied to the body regions of all N channel MOS transistors Qm, Qd, Qb, Qpc, Qe, Qn1, Qn2, and Qio. A negative potential Vbb may be applied to the body region of all N channel MOS transistors as inembodiment 5.
Embodiment 6
• FIG. 12 is a circuit diagram showing a memory cell array, a sense amplifier, and an input/output circuit partially of a DRAM according toembodiment 6 of the present invention. Referring toFIG. 12,embodiment 6 has the body regions of four transistors Qn1, Qn2, Qp1, and Qp2 ofsense amplifier20 connected to its own source electrode. More specifically, the body regions of transistors Qn1 and Qn2 are connected to senseamplifier drive line21A. The body regions of transistors Qp1 and Qp2 are connected to senseamplifier drive line21B. Therefore, a variable potential is applied to the body regions of transistors Qn1 and Qn2 that gradually decreases towards ground potential V_SSfrom precharge potential V_BL. Also, a variable potential is provided to the body regions of transistors Qp1 and Qp2 that increases towards power supply potential V_CCfrom precharge potential V_BL. Therefore, the so-called body effect is not generated in transistors Qn1, Qn2, Qp1 and Qp2 since the same voltage is always applied to the PN junction between the body region and the source region. Therefore, the sensitivity ofsense amplifier20 is improved in comparison with that ofembodiment 1.Sense amplifier20 can operate speedily even in the case where a low power supply voltage is supplied.
• When a DRAM is formed on asilicon substrate1, the sense amplifier must be completely isolated from the substrate and other wells in order to provide synchronization between the substrate potential of the transistor in the sense amplifier and the source potential as shown inFIG. 12. Therefore, a triple well structure is generally employed. Furthermore, in order to reduce leakage current by subthreshold in a writing operation, the well must be fixed at a constant potential. This causes increase in power consumption since the charge in the junction capacitance of that well is charged/discharged. Furthermore, a region for fixing the well potential is required when a triple well structure is employed. This results in increase in the layout area.
• In contrast,embodiment 6 has the bottom of the body region brought into contact with the buried oxide layer, so that the junction capacitance is extremely small. Also, leakage current due to subthreshold will not increase since the body region is fixed. Furthermore, the layout area is small since it is not necessary to form a well or the like.
• FIG. 13 is a plan view showingsense amplifier20 partially andprecharge circuit23 ofFIG. 12. Referring toFIG. 13, a p⁺ typecommon region38 is formed at a portion ofsource region1.Body region3 of transistor Qn1 is connected to sourceregion1 viacommon region38.Body region3 of transistor Qn2 is connected to sourceregion1 viacommon region38. Because sense amplifier drive signal SAN is provided to thissource region1 via contact hole CH, thesebody regions3 are electrically fixed during the application of forward voltage in the PN junction betweencommon region38 andsource region1. More specifically, the potential ofbody region3 is always higher than the potential ofsource region1 by the barrier potential of the PN junction. Because body fix lines30B and30C do not have to be provided in theembodiment 6, the layout area is smaller than that ofembodiment 1.
Embodiment 7
• FIG. 14 is a plan view showing a sense amplifier and a precharge circuit of a DRAM according toembodiment 7 of the present invention. Referring toFIG. 14,embodiment 7 has a p⁺ typecommon region38 of a size substantially equal to that ofsource region1 formed betweenbody regions3.Source region1 is connected to senseamplifier drive line21A via contact hole CH.Common region38 is also connected to senseamplifier drive line21A via contact hole CH.Body region3 of transistor Qn1 is connected to senseamplifier drive line21A viacommon region38 and contact hole CH.Body region3 of transistor Qn2 is connected to senseamplifier drive line21A viacommon region38 and contact hole CH. Therefore,body regions3 are always electrically fixed since the potentials ofcommon region38 andsource region8 are always the same.
Embodiment 8
• FIG. 15 is a plan view showing a sense amplifier and a precharge circuit of a DRAM according toembodiment 8. Referring toFIG. 15, a p⁺ typecommon region38 is connected to either side ofsource region1. Also, two contact hole CH are formed oversource region1 andcommon region38. Therefore,body region3 of transistor Qn1 is connected to senseamplifier drive line21A via twocommon regions38 and two contact holes CH, andbody region3 of transistor Qn2 is connected to senseamplifier drive line21A via twocommon regions38 and two contact holes CH. Inembodiment 8, the effective channel length of transistors Qn1 and Qn2 is increased since a smallcommon region38 is formed at either side ofsource region1.Body regions3 of transistors Qn1 and Qn2 are reliably fixed even when the effective channel length thereof is long by virtue of the provision of twocommon regions38. The potential ofbody region3 promptly follows potential SAN of senseamplifier drive line21A even when located remote fromcommon region38. As a result, this sense amplifier operates more stably than that ofembodiment 7 ofFIG. 14.
Embodiment 9
• FIG. 16 is a circuit diagram showing a memory cell array, a sense amplifier, and an input/output circuit partially of a DRAM according toembodiment 9. Referring toFIG. 16,embodiment 9 the body regions of transistors Qb and Qio in bit lineselect circuits26A and26B and columnselect circuit29 are set to a floating state electrically. A great amount of leakage current will not flow in these transistors Qb and Qio even when rendered to a floating state.
• Embodiment 9 has the number of the body fix lines reduced in comparison with that ofembodiment 6 ofFIG. 12 since the body regions of several N channel MOS transistors are electrically fixed, and the body regions of the remaining n channel MOS transistors are rendered floating. Therefore, the region for a body fix line is reduced, resulting in a smaller layout area.
Embodiment 10
• FIG. 17 is a circuit diagram showing a memory cell array, a sense amplifier, and an input/output circuit of a DRAM according toembodiment 10 of the present invention. Referring toFIG. 17,embodiment 10 has the body regions of all P channel MOS transistors set to a floating state electrically. More specifically, the body regions of transistors Qp1 and Qp2 insense amplifier20 are rendered floating. The body regions of all N channel MOS transistors are fixed electrically.
• Because the breakdown voltage between the source and drain of a P channel MOS transistor is generally higher than that of an N channel MOS transistor, the body region of an N channel MOS transistor should be fixed.Embodiment 10 has a layout area smaller than that ofembodiment 1 since a body fix region and a body fix line for fixing the body region of a P channel MOS transistor are not required.
Embodiment 11
• FIG. 18 is circuit diagram showing a structure of a memory cell array, a sense amplifier, and an input/output circuit of a DRAM according toembodiment11 of the present invention. Referring toFIG. 18,embodiment 11 has bit lines BL0 and /BL0 disposed at either side ofsense amplifier20. In other words, the so-called open bit line structure is employed.
• Similar to the above-describedembodiment 1, inembodiment 11, ground potential V_SSis applied to the body regions of N channel MOS transistors Qn1 and Qn2 insense amplifier20, and power supply potential V_CCis applied to the body regions of P channel MOS transistors Qp1 and Qp2. Ground potential V_SSis applied to the body regions of N channel MOS transistors Qe and Qpc in bit lineprecharge circuit23. Also, ground potential V_SSis applied to the body regions of N channel MOS transistors Qse and Qsp in sense amplifier drive lineprecharge circuit22. Ground potential V_SSis applied to the body region of N channel MOS transistor Qio in column select circuit. Ground potential V_SSis also applied to the body region of N channel MOS transistor Qm ofmemory cell27. Ground potential V_SSis also applied to the body region of N channel MOS transistor Qd indummy cell28.
• In addition to the advantages ofembodiment 1,embodiment11 can have amemory cell27 disposed at all the crossings of a word line and a bit line since the open bit line structure is employed.
Embodiment 12
• FIG. 19 is a circuit diagram showing a structure of a memory cell array, a sense amplifier, and an input/output circuit of a DRAM according toembodiment 12 of the present invention. Referring toFIG. 19, the body regions of four transistors Qn1, Qn2, Qp1, and Qp2 ofsense amplifier20 are connected to its own source electrode. Therefore, sense amplifier drive signal SAN is applied to the body regions of N channel MOS transistors Qn1 and Qn2. Sense amplifier drive signal SAP is applied to the body regions of P channel MOS transistors Qp1 and Qp2.
• In addition to the advantages ofembodiment 6 ofFIG. 12,embodiment 12 can havememory cell27 provided at all the crossings between a word line and a bit line since an open bit line structure is employed.
Embodiment 13
• FIG. 20 is a circuit diagram showing a row decoder partially of a DRAM according toembodiment 13 of the present invention. Referring toFIG. 20, a word line drive circuit in a row decoder includes eight N channel MOS transistors Qr1-Qr8 at the final stage. Transistors Qr1-Qr2 are connected in series, and the source electrode of transistor Qr1 is connected to word line WL0. Transistors Qr3 andQr4 are connected in series, and the source electrode of transistor Qr3 is connected to word line WL1. Transistors Qr5 and Qr6 are connected in series, and the source electrode of transistor Qr5 is connected to word line WL2. Transistors Qr7 and Qr8 are connected in series, and the source electrode of transistor Qr7 is connected to word line WL3.
• This word line drive circuit is activated in response to signals Xj, Xk and Xl which are predecoded row address signals. When the word line drive circuit is activated and one of boost signals RXO-RX3 is applied to the drain electrode of a corresponding transistor, a corresponding one of word lines WL0-WL3 rises. Because boost signals RX0-RX3 are at potentials higher than power supply potential V_CC, word lines WLO-WL3 rise to a potential higher than power supply potential V_CC. Therefore, a voltage greater than the power supply voltage is applied between the source and drain of transistors Qr1-Qr8.
• When boost signals RXO-RX3 are applied when this word line drive circuit is not activated, the potential of the body regions of transistors Qr1, Qr3, Qr5 and Qr7 rise due to coupling of the parasitic capacitance, resulting in reduction of the threshold value. This causes leakage of the boosted potential via transistors Qr1, Qr3, Qr5 and Qr7, so that the boosted potential becomes insufficient. When the leaking boosted potential is applied to a de-select word line, data will leak from the de-select memory cell.
• Inembodiment 13, ground potential V_SSis applied to the body regions of transistors Qr1-Qr12, whereby the body regions thereof are electrically fixed. This causes increase in the breakdown voltage between the source and drain of transistors Qr1-Qr12, so that this word line drive circuit operates properly. This word line drive circuit operates stably since reduction in the threshold value due to coupling of the parasitic capacitance is suppressed.
Embodiment 14
• FIG. 21 is a circuit diagram showing a row decoder partially of a DRAM according toembodiment 14 of the present invention. Referring toFIG. 21,embodiment 14 has the body regions of transistors Qr1-Qr12 connected to its own source region. More specifically, the body regions of transistors Qr1, Qr3, Qr5, and Qr7 are connected to word lines WLO-WL3. The body regions of transistors Qr2, Qr4, Qr6 and Qr8 are connected to the ground node. The body regions of transistors Qr9-Qr12 are connected to the node located at the side where the potential does not rise by self bootstrap.
• FIG. 22 is a plan view showing a general structure of transistors Or1-Or12 of the word line drive circuit shown inFIG. 21. Referring toFIG. 22, transistors Qr1-Qr12 include an n⁺type source region1, an n⁺type drain region2, a p⁺type body region3, agate electrode4, and a p⁺ typecommon region38.Common region38 is formed adjacent to sourceregion1 andbody region3. Therefore,body region3 is connected to sourceregion1 viacommon region38 to be electrically fixed.
• Becauseembodiment 14 has the body regions of transistors Qr1, Qr3, Qr5 and Qr7 connected to word lines WLO-WL3, the potentials of thebody regions3 follow the potentials of word lines WLO-WL3. This suppresses generation of a body effect in transistors Qr1; Qr3, Qr5 and Qr7, so that the potentials of word lines QLO-WL3 promptly rise.
• It is not necessary to provide a body fix line since thebody regions3 of transistors Qr1-Qr12 are connected to its own source region. Accordingly, the layout area ofembodiment 14 is smaller than that ofembodiment 13 ofFIG. 20.
Embodiment 15
• FIG. 23 is a circuit diagram showing a structure of a boost signal predecode circuit according to aembodiment15 of the present invention. This boost signal predecode circuit serves to provide boost signals RX0-RX3 to the word line drive circuit shown inFIGS. 20 and 21.
• Referring toFIG. 23, this boost signal predecode circuit includes transistors Qr13-Qr15, and inverters I1 and I2. Transistors Qr13 and Qr14 are connected in series. Boost signal RX which is an output of the boost voltage generation circuit is provided to the drain electrode of transistor Qr13. Row address signal X is applied to one source/drain electrode of transistor Qr15 via inverters I1 and I2. The output of inverter I1 is provided to the gate electrode of transistor Qr14.
• This boost signal predecode circuit is activated in response to a row address signal X. When a boost signal RX is applied during its activation, the gate potential of transistor Qr13 rises by self bootstrap, so that transistor Qr13 attains a complete conductive state. Therefore, the applied boost signal RX is output as boost signals RX0-RX3 via transistor Qr13.
• As apparent from the above-described operation, a voltage greater than the power supply voltage is applied between the source and drain of transistors Qr13-Qr15. Inembodiment15, ground potential V_SSis applied to the body regions of transistors Qr13-Qr15, so that the body region is electrically fixed. This causes increase in the breakdown voltage between the source and drain of transistors Qr13-Qr15, so that this boost signal predecode circuit operates properly.
Embodiment 16
• FIG. 24 is a circuit diagram showing a structure of a boost signal predecode circuit of a DRAM according toembodiment16 of the present invention. Referring toFIG. 24, the body regions of transistors Qr13-Qr15 are connected to its own source region.
• Inembodiment 16, the body region of transistor Qr13, in particular, is connected to its own source region. Therefore, the potential of the body region of transistor Qr13 rises following the output boost signals RX0-RX3. This suppresses generation of the body effect in transistor Qr13, so that boost signals RX0-RX3 rise promptly. It is not necessary to provide a body fix line since each body region is connected to its own source region. Therefore, the layout area ofembodiment 16 is smaller than that ofembodiment 15 ofFIG. 23.
Embodiment 17
• FIG. 25 is a plan view showing a structure of an N channel MOS capacitor of a DRAM according toembodiment 17 of the present invention. This MOS capacitor is used in a word line drive circuit, a boost signal predecode circuit, a circuit for generating a voltage V_PPwhich is a boosted power supply voltage, and the like.
• Referring toFIG. 25, this MOS capacitor includes an n⁺type source region1, a ptype body region3 enclosed bysource region1, agate electrode4, and a p⁺ typecommon region38.Common region38 is inserted in a part ofsource region1. In other words,common region38 is formed adjacent to sourceregion1 andbody region3. Therefore,body region3 is connected to sourceregion1 viacommon region38. This causesbody region3 to be fixed electrically, so that this MOS capacitor operates stably. Furthermore, it is not necessary to provide a body fix line sincebody region3 is connected to sourceregion1 viacommon region38 which is partially inserted intosource region1. Therefore, the layout area ofembodiment17 is similar to that of the conventional case.
• The present invention is not limited to the above-describedembodiment 17 wherecommon region38 is inserted into a portion ofsource region1.Source region1 andcommon region38 may be connected to the body fix line via a contact hole by forming one contact hole above the joining portion ofsource region1 andcommon region38. This provides the advantage thatbody region3 can be electrically fixed even when the potential ofsource region1 becomes higher than the potential ofcommon region38.
Embodiment 18
• FIG. 26 is a plan view showing a structure of a P channel MOS capacitor in a DRAM according toembodiment 18 of the present invention. Referring toFIG. 26, this P channel MOS capacitor includes a p⁺type source region1, an ntype body region3 enclosed bysource region1, agate electrode4, and an n⁺ typecommon region38.Embodiment 18 has the conductivity type of each region opposite to those inembodiment 17 ofFIG. 25.
Embodiment 19
• FIG. 27 is a plan view showing a structure of an N channel MOS capacitor of a DRAM according toembodiment 19 of the present invention. Referring toFIG. 27, this N channel MOS capacitor includes two n⁺type source region1, a ptype body region3 located between thesesource regions1, agate electrode4, and a p⁺type contact region31. The twosource regions1 are connected to each other. Contactregion31 is inserted into a portion of body regions, and is formed adjacent to only thatbody region3.
• A potential identical to that applied to sourceregion1 is provided to contactregion31, wherebybody region3 is connected to sourceregion1 viacontact region31. Therefore, this N channel MOS capacitor operates stably since thatbody region3 is electrically fixed.
• Because a potential identical to that applied to sourceregion1 is provided to contactregion31 inembodiment19, ground potential V_SSor negative potential V_BBmay be applied to contactregion31.
Embodiment 20
• FIG. 28 is a plan view showing a structure of a P channel MOS capacitor of a DRAM according toembodiment 20 of the present invention. Referring toFIG. 28, this P channel MOS capacitor includes two p⁺type source regions1, an ntype body region3 located therebetween, agate electrode4, and an n⁺type contact region31. A predetermined potential is provided to contactregion31, wherebybody region3 is electrically fixed.Embodiment 20 has the conductivity type of each region opposite to that ofembodiment 19 ofFIG. 27.
Embodiment 21
• FIG. 29 is a circuit diagram showing a structure of a boost power supply generation circuit of a DRAM according toembodiment 20 of the present invention. Referring toFIG. 29, this boost power supply generation circuit includes three MOS capacitors Cbs1-Cbs3, and an N channel MOS transistor Qbs at the final stage. This boost power supply generation circuit generates a boost potential V_PPhigher than power supply potential V_CCin response to a clock signal CK.
• In transistor Qbs of this boost Dower supply generation circuit, the potential of the drain electrode (output node) is always higher than the potential of the source electrode. Therefore, the body region of transistor Qbs is connected to its own source region. As a result, the breakdown voltage between the source and drain of transistor Qbs is increased. There is also the advantage that a body fix line does not have to be provided since the body region is connected to the source region. Therefore, the layout area according to embodiment 21 is substantially equal to that of a conventional one.
Embodiment 22
• FIG. 30 is a circuit diagram showing a structure of an output preamplifier and a write circuit of a DRAM according toembodiment 22 of the present invention. Referring toFIG. 30, a current mirrortype output preamplifier40 includes P channel MOS transistors Qp5-Qp11, and N channel MOS transistors Qn5-Qn12. An output preamplifier is generally susceptible to a kink since the potentials of input/output lines IO and /IO are amplified in an analog manner. Therefore, the body regions of P channel MOS transistors Qp5-Qp11 are connected to its own source region. The body regions of N channel MOS transistor Qn5-Qn12 are connected to its own source region.
• Becauseembodiment 22 has the body regions of transistors Qp5-Qp11 and Qn5-Qn12 electrically fixed, a kink will not be generated in these transistors. Accordingly,output preamplifier40 can amplify stably the potential of input/output lines IO and /IO.
• Writecircuit41 includes four N channel MOS transistors Qn13-Qn16. Ground potential V_SSis applied to the body region of transistors Qn13-Q16, so that these body regions are electrically fixed. Therefore, a great leakage current will not flow between the source and drain of transistors Qn13-Qn16.
Embodiment 23
• FIG. 31 is a circuit diagram showing a structure of an input/output line precharge circuit and an input/output line equalize circuit of a DRAM according toembodiment23. Referring toFIG. 31, an input/output lineprecharge circuit42 includes P channel MOS transistors Qp21 and Qp22, and N channel MOS transistors Qn21 and Qn22. P channel MOS transistor Qp21 and N channel MOS transistor Qn21 form a transfer gate. Also, P channel MOS transistor Qp22 and N channel MOS transistor Qn22 also form a transfer gate. Input/output lineprecharge circuit42 responds to a precharge signal YN to precharge input/output lines IO and /IO to a predetermined potential.
• The input/output line equalize circuit includes a P channel MOS transistor Qp20 and an N channel MOS transistor Qn20. Transistors Qp20 and Qn20 form a transfer gate. This input/output line equalize circuit responds to input/output line equalize signals IOEQ and /IOEQ to equal the potential of input/output lines IO and /IO to each other.
• Inembodiment23, power supply potential V_CCis applied to the body regions of P channel MOS transistors Qp20-Qp22. Ground potential V_SSis applied to the body regions of N channel MOS transistors Qn20-Qp22. As a result, the body regions of transistors Qp20-Qp22 and Qn20-Qn22 are electrically fixed. Therefore, a great amount of leakage current will not flow between the source and drain of these transistors. Thus, correct data is transmitted via input/output lines IO and /IO.
Embodiment 24
• FIG. 32 is a circuit diagram showing a row address buffer in a DRAM according toembodiment 24 of the present invention. Referring toFIG. 32, this dynamic latch type row address buffer includes P channel MOS transistors Qp25-Qp28, and N channel MOS transistors Qn25-Qn30. This address buffer responds to an external address signal ext. An to generate internal row address signals RAn and /RAn. This address buffer compares external address signal ext.An to a reference signal VREF to make determination whether external address signal ext.An attains a H level or a L level.
• Inembodiment 24, the body regions of transistors Qp25-Qp28 are connected to the source electrode. Ground potential V_SSis applied to the body regions of transistors Qn25, Qn26, Qn29 and Qn30. This dynamic latch type row address buffer responds to a fall of control signal /RADBE to latch an address signal. In an active state, a reverse voltage will not be applied to the PN junction between the body region and the source region. Therefore, it is possible to connect the body regions of transistors Qn27 and Qn28 to its own source region.
• Because the body regions of transistors Qp25-Qp28 and Qn25-Qn30 are electrically fixed, this row address buffer carries out an analog operation stably. Because transistors Qp27 and Qp28 are impervious to the body effect, this row address buffer can make determination whether external address signal ext.An attains a H level or a L level stably and speedily.
Embodiment 25
• FIG. 33 is a circuit diagram showing a structure of a column address buffer of a DRAM according toembodiment 25 of the present invention. Referring toFIG. 33, this column address buffer includes P channel MOS transistors Qp31-Qp34, and N channel MOS transistors Qn31-Qn34. Transistors Qp31, Qp32, Qn31 and Qn32 form an NOR circuit. Transistors Qp33, Qp34, Qn33 and Qn34 form a clocked inverter of a subsequent stage. This column address buffer responds to an external address signal ext.An to generate internal column address signals CAn and /CAn.
• The body regions of all transistors Qp31, Qp32, Qn31, Qn32 forming this NOR circuit are connected to its own source region. Therefore, ground potential V_SSis applied to the body region of N channel MOS transistors Qn31 and Qn32. The body regions of all transistors Qp33, Qp34, Qn33 and Qn34 forming the inverter are set to a floating state.
• Inembodiment 25, the body regions of transistors Qp31, Qp32, Qn31, and Qn32 of the input stage are electrically fixed, so that correct determination can be made whether external address signal ext.An attains a H level or a L level. Furthermore, because the body regions of transistors Qp33, Qp34, Qn33 and Qn34 forming the clocked inverter of the subsequent stage, and the body regions of transistors forming other logical gates are set to a floating stage, it is not necessary to provide a body fix line. Therefore, increase in the layout area is suppressed to a minimum.
Embodiment 26
• FIG. 34 is a circuit diagram showing a structure of a column address buffer of a DRAM according to embodiment26 of the present invention. Referring toFIG. 34, embodiment 26 has a negative potential V_BBapplied to the body regions of N channel MOS transistors Qn31 and Qn32 forming an NOR circuit. As described above, a negative potential V_BBinstead of ground potential V_SSmay be applied to the body regions of N channel MOS transistors Qn31 and Qn32.
Embodiment 27
• FIG. 35 is a circuit diagram showing a column address buffer of a DRAM according toembodiment 27 of the present invention.Embodiment 27 has the body regions of transistors Qp33, Qp34, Qn33 and Qn34 forming the inverter connected to its own source region. According toembodiment 27, the body regions of the transistors forming the input stage and the clocked inverter of the subsequent stage are electrically fixed. Therefore, although there is a slight increase in the layout area, this column address buffer operates stably in comparison with the case where the body regions thereof are not fixed.
Embodiment 28
• FIG. 26 is a circuit diagram showing a structure of a column address buffer of a DRAM according toembodiment 28 of the present invention. Differing from the column address buffer shown inFIG. 27,embodiment 28 has negative potential V_BBapplied to the body regions of N channel MOS transistors Qn31 and Qn32. Thus, a negative potential V_BBmay be applied instead of ground potential Vss to the body regions of N channel MOS transistors Qn31 and Qn32.
Embodiment 29
• FIG. 37 is a circuit diagram showing a structure of a clock input buffer of a DRAM according toembodiment 29 of the present invention. Referring toFIG. 37, this clock input buffer includes P channel MOS transistors Qp35-Qp37, an N channel MOS transistor Qn35, and inverters I3-I5. This clock input buffer responds to external row address strobe signal ext./RAS of a MOS level or a TTL level to generate internal row address strobe signals RAS and /RAS.
• Inembodiment 29, the body regions of transistors Qp35-Qp37 of the input stage and transistor Qn35 are connected to its own source region. Therefore, ground potential V_SSis applied to the body region of N channel MOS transistors Qn35.
• Because the body regions of transistors Qp35-Qp37 and Qn35 are electrically fixed, accurate determination can be made whether external row address strobe signal ext./RAS attains a H level or a L level. Furthermore, it is not necessary to provide a body fix line since the body regions of transistors Qp35-Qp37 and Qn35 are connected to its own source region. Accordingly, the layout area of this clock input buffer is similar to that of a conventional case.
Embodiment 30
• FIG. 38 is a circuit diagram showing a structure of a clock input buffer of a DRAM according toembodiment 30 of the present invention. Inembodiment 30, negative potential V_BBis applied to the body region of N channel MOS transistor Qn35 of the first input stage. Therefore, negative potential V_BBmay be applied, instead of ground potential V_SS, to the body region of N channel MOS transistor Qn35.
Embodiment 31
• FIG. 39 is a circuit diagram showing a structure of a clock input buffer of a DRAM according toembodiment 31 of the present invention. Similar toembodiment 29 ofFIG. 37, this clock input buffer ofFIG. 39 includes P channel MOS transistors Qp35-Qp37, an N channel MOS transistor Qn35, and inverters I3-I5. Inverter I4 includes a P channel MOS transistor Qp38, and an N channel MOS transistor Qn38. Inverter I5 includes a P channel MOS transistor Qp39, and an N channel MOS transistor Qn39.
• Inembodiment 31, the body regions of P channel MOS transistors Qp38 and Qp39 forming inverters I4 and15 are connected to its own source region. Also, a negative potential V_BBis applied to the body regions of N channel MOS transistors Qn38 andQn39 forming inverters14 and I5.
• Becauseembodiment 31 has the body regions of transistors Qp38, Qp39, Qn38 and Qn39 of the last stage electrically fixed, the clock skew of internal row address strobe signals RAS and /RAS generated by this clock input buffer is reduced.
Embodiment 39
• FIG. 40 is a circuit diagram showing a structure of a clock input buffer of a DRAM according toembodiment32 of the present invention. Inembodiment 32, the body regions of N channel MOS transistors Qn38 and Qn39 are connected to its own source region.
• Because the body regions of N channel MOS transistors Qn38 and Qn39 are connected to its own source region inembodiment 32, it is not necessary to provide a body fix line. Therefore, increase of the layout area can be suppressed to a minimum. Ground potential V_SSmay be applied, instead of negative potential V_BB, to the body regions of transistors Qn38 and Qn39 of the last stage.
Embodiment 33
• FIG. 41 is a circuit diagram showing a structure of a sense amplifier drive circuit of a DRAM according toembodiment 33 of the present invention. Referring toFIG. 41, this sense amplifier drive circuit includes a plurality of inverters connected in series, and a plurality of MOS capacitors Csp1-Csp3, and Csnl-Csn3. This sense amplifier drive circuit responds to a boost signal RX to generate control signals SOF, SON, and /SOP to drivesense amplifier20.
• FIG. 42 is a timing chart showing the operation of the sense amplifier drive circuit ofFIG. 41. Referring toFIG. 42, control signal SOF rises after a predetermined time period from the rise of boost signal RX. Control signal SON rises after a predetermined time period from the rise of control signal SOF. Then, control signal /SOP falls after a predetermined time period from the rise of control signal SON.
• In the sense amplifier drive circuit ofembodiment 33, the body regions of all MOS capacitors Csp1-Csp3 and Csn1-Csn3 are electrically fixed. Therefore, the threshold values of MOS capacitors Csp1-Csp3 and Csn1-Csn3 do not become unstable, so that the time period from a rise of boost signal RX to a rise of control signal SOF, or the time period from a rise of control signal SOF to a rise of control signal SON will not be reduced. As a result, there is no reduction in the operation margin ofsense amplifier20.
• Inembodiment33, power supply potential V_CCis applied to the body regions of P channel MOS capacitors Csp1-Csp3. Ground potential V_SSis applied to the body regions of N channel MOS capacitors Csn1-Csn3. However, negative potential V_SSmay be applied, instead of ground potential V_SS, to the body regions of N channel MOS capacitors Csn1-Csn3.
Embodiment 34
• FIG. 43 is a circuit diagram showing a structure of a CAT (Column Address Transition) circuit of a DRAM according toembodiment 34 of the present invention. Referring toFIG. 43, this CAT circuit includes three inverters I20-I22, three NOR circuits NR1-NR3, two P channel MOS capacitors Ctp1 and Ctp2, and N channel MOS capacitors Ctn1 and Ctn2. This CAT circuit responds to control signal CAD to generate a control signal CAT. Here, power supply potential Vm is applied to the body regions of P channel MOS capacitors Ctp1 and Ctp2. Ground potential V_SSis applied to the body regions of N channel MOS capacitors Ctn1 and Ctn2.
• FIG. 44 is a timing chart showing an operation of the CAT circuit ofFIG. 43. Referring to the timing chart ofFIG. 43, the potential of an output node A of NOR circuit NR1 falls immediately when control signal CAD rises. The potential of an output node B of NOR circuit NR3 rises after a predetermined time period from the fall of the potential of node A. Then, the potential of node B falls immediately when control signal CAD falls. The potential of node A rises after a predetermined time period from the fall of the potential of node B.
• Control signal CAT rises immediately when the potential of node A falls. Control signal CAT falls immediately when the potential of node B rises. Also, control signal CAT rises immediately when the potential of node B falls. Control signal CAT falls immediately when the potential of node A rises.
• If the body regions of MOS capacitors Ctp1, Ctp2, Ctn1 and Ctn2 attain a floating state here, the threshold values of the capacitors thereof becomes unstable due to change in the potential of the body region. There is a possibility that the capacitance of the capacitors thereof becomes unstable. This causes delay in the fall time of control signal CAT1 or an early fall of control signal CAT2 as shown in the timing chart ofFIG. 44. The operation margin of this CAT circuit is reduced when control signal CAT2 is delayed in its fall.
• Inembodiment 34, the body regions of MOS capacitors Ctp1, Ctp2, Ctn1 and Ctn2 are electrically fixed. Therefore, a control signal CAT that is always stable is generated.
Embodiment 35
• FIG. 45 is a circuit diagram showing a structure of an N-N buffer of a DRAM according toembodiment 35 of the present invention. Such an N-N buffer is used as a data output buffer of a DRAM.
• Referring toFIG. 45, this N-N buffer includes N channel MOS transistors Qnn1 and Qnn2 connected in series. The body regions of N channel MOS transistors Qnn1 and Qnn2 are connected to its own source region. Therefore, the body region of N channel MOS transistor Qnn1 is connected to output node OUT.
• In this N-N buffer, complementary signals Do and /Do are connected to the gate electrodes of transistors Qnn1 and Qnn2, respectively. When signal Do attains a H level and signal /Do attains a L level, transistor Qnn1 attains a conductive state, and transistor Qnn2 attains a non-conductive state. Therefore, a signal of a H level is output.
• In the N-N buffer ofembodiment35, the body regions of N channel MOS transistors Qnn1 and Qnn2 are electrically fixed, so that the threshold value will not become unstable. As a result, a great leakage current will not flow between the source and drain of transistors Qnn1 and Qnn2. Leakage current will not flow outwards via transistor Qnn1, or flow in from an external source via transistor Qnn2.
• Because the body regions of transistors Qnn1 and Qnn2 are connected to its own source region in this N-N buffer, there is no increase in the layout area. Furthermore, because the body region of transistor Qnn1 is connected to the output node, the potential of the body region thereof follows the potential of the output node. Therefore, the threshold value will not rise due to a body effect in transistor Qnn1. The output signal of the present N-N buffer rises promptly to the level of power supply potential V_CC
Embodiment 36
• FIG. 46 is a circuit diagram showing a structure of an N-N buffer of a DRAM according toembodiment 36 of the present invention. Inembodiment 36, ground potential Vss is supplied to the body regions of transistors Qnn1 and Qnn2. Thus, ground potential V_SSmay be applied, instead of the source potential, to the body regions of transistors Qnn1 and Qnn2.
Embodiment 37
• FIG. 47 is a circuit diagram showing a structure of a 2-input NAND circuit of a DRAM according to embodiment 37 of the present invention. Such a NAND circuit is used in various places of a DRAM such as in a clock input buffer that generates an internal row address strobe signal /RAS.
• Referring toFIG. 47, this CMOS type NAND circuit includes two input terminals. This NAND circuit includes P channel MOS transistors Qgp1-Qgp2 connected in parallel between the power supply node andoutput node50, and N channel MOS transistors Qgn1 and Qgn2 connected in series betweenoutput node50 andground node51. An input signal IN1 is applied to the gate electrodes of transistors Qgp1 and Qgn1. An input signal IN2 is applied to the gate electrodes of transistors Qgp2 and Qgn2. Output signal OUT is provided fromoutput node50.
• In the present NAND circuit, the body regions of P channel MOS transistors Qgp1 and Qgp2 are set to a floating state, whereas the body regions of N channel MOS transistors Qgn1 and Qgn2 are connected to its own source region. Therefore, these body regions are electrically fixed. As a result, the threshold value of transistor Qgn1 is stable and reduced, so that this NAND circuit operates at high speed. Thus, this NAND circuit operates properly even when power supply potential V_CCis low.
• FIG. 48 is a plan view showing a structure of N channel MOS transistors Qgn1 and Qgn2 in the NAND circuit ofFIG. 47. Referring toFIG. 48, transistor Qgn1 includes an n⁺type drain region52, an n⁺ type source/drain region53, a ptype body region57, and agate electrode59. Transistor Qgn2 includes an n⁺ type source/drain region53 common to transistor Qgn1, an n⁺ source region54, a ptype body region58, and agate electrode60.Drain region52 of transistor Qgn1 is connected tooutput node50 of aluminum via contact hole CH.Source region54 of transistor Qgn2 is connected to groundnode51 of aluminum via contact hole CH.
• A p⁺ typecommon region55 is formed in a portion of source/drain region53. Contact hole CH is formed above the junction portion of source/drain region53 andcommon region55 with anintermediate layer61 of aluminum therebetween. Therefore,body region57 is connected to source/drain region53 viacommon region55 to be electrically fixed.
• A p⁺ typecommon region56 is formed in a portion ofsource region54. Contact hole CH is formed above the junction portion ofsource region54 andcommon region56. Therefore,body region58 is connected to sourceregion54 viacommon region56 to be electrically fixed.
Embodiment 38
• FIG. 49 is a plan view showing another structure of N channel MOS transistors Qgn1 and Qgn2 in the NAND circuit ofFIG. 47. Referring toFIG. 49, anintermediate layer62 of polysilicon is formed ondrain region52, source/drain region53, andsource region54 inembodiment38.Intermediate layer62 serves as an etching stopper. The SOI substrate is prevented from being etched during the formation of contact hole CH by an etching process.
Embodiment 39
• FIG. 50 is a plan view showing another structure of N channel MOS transistors Qgn1 and Qgn2 of the NAND circuit ofFIG. 47. Referring toFIG. 50, a source/drain region65 partially protrudes betweengate electrodes59 and60. A p⁺ typecommon region66 is formed adjacent to the protruding portion of source/drain region65. Contact hole CH is formed above the junction portion of the protruding portion of source/drain region65 andcommon region66 with anintermediate layer67 of aluminum therebetween.
• In embodiment 39,body region57 is connected to sourceregion65 viacommon region66 to be electrically fixed. Because a contact hole is not formed betweengate electrodes59 and60, the distance betweengate electrodes59 and60 can be reduced.
Embodiment40
• FIG. 51 is a plan view showing another structure of N channel MOS transistors Qgn1 and Qgn2 of the NAND circuit shown inFIG. 47. Referring toFIG. 51, anintermediate layer68 of polysilicon is formed abovedrain region52, source/drain region65, andsource region54 inembodiment 40. Therefore, the SOI substrate will not be etched during the formation of contact hole CH which is carried out by an etching process.
Embodiment 41
• FIG. 52 is a circuit diagram showing a structure of a 3-input NAND circuit of a DRAM according toembodiment41 of the present invention. Referring toFIG. 52, this 3-input NAND circuit includes P channel MOS transistors Qgp5, Qgp4, Qgp3 connected in parallel between the power supply node and anoutput node70, and N channel MOS transistors Qgn3, Qgn4, and Qgn5 connected in series betweenoutput node70 and aground node71. An input signal IN1 is provided to the gate electrodes of transistors Qgp3 and Qgn3. An input signal IN2 is provided to the gate electrodes of transistors Qgp4 and Qgn4. An input signal IN3 is provided to the gate electrodes of transistors Qgp5 and Qgn5. An output signal OUT is provided fromoutput node70.
• In this NAND circuit, the body regions of transistors Qgp3-Qgp5 are set to a floating state, and the body regions of transistors Qgn3-Qgn5 are connected to the source region to be electrically fixed. This causes reduction in the threshold value of transistors Qgn3 and Qgn4. Thus, this 3-input NAND circuit operates at high speed. Furthermore, it is not necessary to provide a body fix line since the body regions of transistors Qgp3-Qgp5 are set to a floating state. Thus, there is almost no increase in the layout area.
• FIG. 53 is a plan view showing a structure N channel MOS transistors Qgn3-Qgn5 in the 3-input NAND circuit shown inFIG. 52. Referring toFIG. 53, transistor Qgn3 includes an n⁺type drain region72, an n⁺ type source/drain region73, a ptype body region79, and agate electrode82. Transistor Qgn4 includes a source/drain region37 common to transistor Qgn3, an N⁺ source/drain region74, and a ptype body region80. Transistor Qgn5 includes a source/drain region74 common to transistor Qgn4, an n⁺type source region75, a ptype body region81, and agate electrode84.
• Drain region72 of transistor.Qgn3 is connected tooutput node70 via two contact holes CH. p⁺ typecommon region76 is formed in a part of source/drain region73. Therefore,body region79 of transistor Qgn3 is connected to source/drain region73 viacommon region76 to be electrically fixed. Contact hole CH is formed on the junction portion of source/drain region73 andcommon region76 with anintermediate layer85 of aluminum therebetween.
• p⁺ typecommon region77 is formed in a portion of source/drain region74. Therefore,body region80 of transistor Qgn4 is connected to sourceregion74 viacommon region77 to be electrically fixed. Contact hole CH is formed on the junction portion of source/drain region74 andcommon region77 with anintermediate layer85 of aluminum therebetween.Source region75 of transistor Qgn5 is connected to groundnode71 via two contact holes CH. p⁺ typecommon region78 is formed at a portion ofsource region75. The body region of transistor Qgn5 is connected to sourceregion75 viacommon region78 to be electrically fixed.
Embodiment 42
• FIG. 54 is a plan view showing another structure of N channel MOS transistors Qgn3—Qgn5 in the 3-input NAND circuit ofFIG. 52. Referring toFIG. 54,embodiment 42 hasintermediate layer86 of polysilicon formed ondrain region72, source/drain regions73,74 andsource region75. Therefore, the SOI substrate will not be etched during the formation of contact hole CH carried out by an etching process.
Embodiment 43
• FIG. 55 is a plan view showing another structure of N channel MOS transistors Qgn3-Qgn5 in the 3-input NAND circuit ofFIG. 52. Referring toFIG. 55, a source/drain region90 protrudes from betweengate electrodes82 and83 in embodiment 43. A source/drain region91 also protrudes from betweengate electrodes83 and84. A p⁺ typecommon region92 is formed adjacent to the protruding portion of source/drain region90. Therefore,body region79 of transistor Qgn3 is connected to source/drain region90 viacommon region92 to be electrically fixed. A p⁺ typecommon region93 is formed adjacent to the protruding portion of source/drain region91. Therefore,body region80 of transistor Qgn4 is connected to source/drain region91 viacommon region93 to be electrically fixed. A p⁺ typecommon region78 is formed at a portion ofsource region75. Therefore,body region81 of transistor Qgn5 is connected to sourceregion75 to be electrically fixed.
• A contact hole CH is formed on the junction portion of source/drain region90 andcommon region92 with anintermediate layer94 of aluminum therebetween. A contact hole CH is formed on the junction portion of source/drain region91 andcommon region93 with anintermediate layer94 of aluminum therebetween.
• Because a contact hole is not formed betweengate electrodes82 and83 in embodiment 43, the distance betweengate electrodes82 and83 can be made shorter. Also, the distance betweengate electrodes83 and84 can be made shorter since a contact hole is not formed therebetween.
Embodiment 44
• FIG. 56 is a plan view showing another structure of N channel MOS transistors Qgn3-Qgn5 in the 3-input NAND circuit ofFIG. 52. Referring toFIG. 56, animmediate layer95 of polysilicon is formed ondrain region72, source/drain regions90,91 andsource region75 inembodiment44. Therefore, the SOI substrate is not etched during the formation of contact hole CH which is carried out by an etching process.
Embodiment 45
• FIG. 57 is a circuit diagram showing a structure of a 3-input NAND circuit of DRAM according toembodiment 45 of the present invention. Referring toFIG. 57, the body region of transistor Qgn3 is connected to the source/drain region common to transistors Qgn4 and Qgn5. Also, the body regions of transistors Qgn4 and Qgn5 are set to a floating state. When the potential ofoutput node70 falls to a L level in such a NAND circuit, the potential of the body region of transistor Qgn3 is always at the level of the ground potential.
• It is appreciated fromembodiment 45 that at least the body region of transistor Qgn3 directly connected tooutput node70 should be electrically fixed. The body region of transistor Qgn3 may be connected, not to its own source region, but to the source/drain region common to transistors Qgn4 and Qgn5.
• Inembodiment 45, the potential applied to the body region of transistor Qgn3 is not constant, and rises according to the rise of the potential ofoutput node70. Therefore, a body effect is not generated in this transistor Qgn3, so that this 3-input NAND circuit operates at high speed.
Embodiment 46
• FIG. 58 is a circuit diagram showing a structure of a 2-input NAND circuit of a negative logic (a 2-input NOR circuit of a positive logic) of a DRAM according toembodiment 46 of the present invention. Referring toFIG. 58, this 2-input NAND circuit includes N channel MOS transistors Qgn6 and Qgn7 connected in parallel betweenground node51 andoutput node50, and P channel MOS transistor Qgp6 and Qgp8 connected in series betweenoutput node50 and the power supply node. An input signal IN1 is applied to the gate electrodes of transistors Qgn7 and Qgp6. An input signal IN2 is applied to the gate electrodes of transistors Qgn6 and Qgp7. An output signal OUT is provided fromoutput node50.
• In this NAND circuit, the body regions of transistors Qgn6 and Qgn7 are set to a floating state. The body regions of transistors Qgp6 and Qgp7 are connected to its own drain region. Therefore, the body region of transistor Qgp6 is supplied with a drain potential that rises in response to the rise of output signal OUT. A constant ground potential V_SSis applied to the drain region of transistor Qgp7. Therefore, this NAND circuit operates at high speed since the threshold value of transistor Qgp6 is reduced. This NAND circuit can operate properly even when the power supply potential V_CCis low.
Embodiment 47
• FIG. 59 is a circuit diagram showing a structure of a 2-input NAND circuit of a DRAM according toembodiment 47 of the present invention. Referring toFIG. 59, power supply potential V_CCis applied to the body region of P channel MOS transistor Qgp6 to be electrically fixed in this NAND circuit. Although a body effect is generated in transistor Qgp6 inembodiment 47, the body region of transistor Qgp6 may be supplied with power supply potential V_CCinstead of its own drain potential.
Embodiment 48
• FIG. 60 is a sectional view of a planar type memory cell portion taken along the bit line direction of a DRAM according toembodiment 48 of the present invention.FIG. 61 is a sectional view of the memory cell portion ofFIG. 60 taken along the word line direction.
• As shown inFIGS. 60 and 61, a source/drain region44, aLOCOS oxide film5, agate electrode4, and acell plate electrode45 are formed on anSOI substrate6.Gate electrode4 andcell plate electrode45 are formed within firstinterlayer insulation film33. Here, two source/drain regions44,body region3 therebetween, andgate electrode4 form one N channel MOS transistor. One source/drain region44,body region3, andcell plate electrode45 form one N channel MOS capacitor.
• Source/drain region44 common to the two transistors is connected to bit line BL via anintermediate layer32 of a polypad. A secondinterlayer insulation film34 is formed on firstinterlayer insulation film33 andintermediate layer32. Bit line BL is formed on secondinterlayer insulation film34. Bit line BL is connected tointermediate layer32 via a contact hole. A thirdinterlayer insulation film35 is formed on bit line BL. On thirdinterlayer insulation film35, apillar word line46 of aluminum is formed.Pillar word line46 is connected to word line WL that formsgate electrode4 via a contact hole at every constant interval. Therefore, when drive voltage is supplied to word line WL, a signal propagation delay generated by word line WL is reduced.
• Referring toFIG. 61,contact region31 is formed in a portion ofbody region3 of the transistor. Therefore,body region3 is connected tobody fix line30 viacontact region31 andintermediate layer32 to be electrically fixed. Becausebody region3 of the transistor forming a memory cell is electrically fixed, the threshold value of that transistor does not become unstable, and a great leakage current will not flow between the source and drain. Therefore, the data retaining time period in this memory cell is increased. Even when charge is generated insilicon substrate7 due to introduction of a particles into thisSOI substrate6, the charge will not enterbody region3 becausebody region3 andsilicon substrate7 are electrically isolated byburied oxide layer8. Because thisbody region3 is extremely thin, there is almost no generation of charge caused by a particles inbody region3. Therefore, there is almost no generation of the so-called soft error.
Embodiment 49
• FIG. 62 is a sectional view of a memory cell portion of a DRAM taken along the bit line direction according to embodiment 49 of the present invention.FIG. 63 is a sectional view of the memory cell portion ofFIG. 62 taken along the word line direction. In embodiment 49 shown inFIGS. 62 and 63, afield shield electrode47 is formed instead of a LOCOS oxide film onSOI substrate6. Thisfield shield electrode47 is formed in firstinterlayer insulation film33.
• Ground potential V_SSor a negative potential is applied tofield shield electrode47, whereby the portion of SOIactive layer9 beneathfield shield electrode47 is rendered non-conductive. Therefore, this transistor and this capacitor are electrically isolated from an adjacent element. It is appreciated from embodiment 49 that elements such as a transistor may be isolated, not by a LOCOS, but by other isolation methods such as a field shield.
Embodiment 50
• FIG. 64 is a sectional view of a memory cell portion of a DRAM taken along the bit line direction according toembodiment 50 of the present invention.FIG. 64 shows a stacked type memory cell isolated byLOCOS oxide film5.
• Referring toFIG. 64, a source/drain region44, aLOCOS oxide film5, and agate electrode4 are formed onSOI substrate6. The two source/drain regions44,body region3 located therebetween, andgate electrode4 form one N channel MOS transistor.
• Source/drain region44 common to the two transistors is connected to bit line BL viaintermediate layer32. Astorage node48 and acell plate electrode45 are formed on the other source/drain region44 of that transistor.Storage node48 andcell plate45 form the electrode of the capacitor. Therefore, the above-referred N channel MOS transistor and capacitor form a memory cell.
• A contact region (not shown) is formed in a portion ofbody region3 of a transistor. Therefore,body region3 is connected to a body fix line (not shown) via that contact region to be electrically fixed.
Embodiment 51
• FIG. 65 is a sectional view of a memory cell unit taken along the bit line direction of a DRAM according toembodiment51 of the present invention.FIG. 65 shows a stacked type memory cell isolated by a field shield.
• Referring toFIG. 65,embodiment51 has afield shield electrode47 formed instead of a LOCOS oxide film onSOI substrate6. Also, a contact region (not shown) is formed at a portion ofbody region3 of this transistor. Therefore,body region3 is connected to a body fix line (not shown) via the contact region. Ground potential Vss or V_BBis applied to the body fix line. Therefore,body region3 of the transistor is electrically fixed.
Embodiment 52
• FIG. 66 is a layout diagram showing an entire structure of a DRAM according toembodiment 52 of the present invention. Referring toFIG. 66, this DRAM includes fourmemory cell arrays11, tworow decoders12, twocolumn decoders13, and aperipheral circuit99. Eachrow decoder12 is disposed between twomemory cell arrays11. Eachcolumn decoder13 is disposed at one side of twomemory cell arrays11.
• Inembodiment 52, the elements inmemory cell array11 are isolated by a LOCOS. A negative potential V_BBis applied to the body region of the N channel MOS transistor forming each memory cell in the memory cell array to be electrically fixed.
• Row decoder12 includes a plurality of P channel MOS transistors and a plurality of N channel MOS transistors. The body region of the P channel MOS transistor inrow decoder12 is supplied with power supply potential V_CC, whereby the body region is electrically fixed. The body region of the N channel MOS transistor inrow decoder12 is supplied with the ground potential V_SS, whereby the body region is electrically fixed.
• Column decoder13 includes a plurality of N channel MOS transistors. The body region of the N channel MOS transistor incolumn decoder13 is supplied with ground potential V_SSto be electrically fixed.
• Peripheral circuit99 located betweencolumn decoders13 includes a plurality of P channel MOS transistors. Power supply potential V_CCis applied to the body region of the P channel MOS transistor inperipheral circuit99, whereby the body region is electrically fixed. The otherperipheral circuit99 includes a plurality of N channel MOS transistors. Ground potential V_SSis applied to the body region of the N channel MOS transistor inperipheral circuit99, whereby the body region is electrically fixed.
• As described above, all the body regions in the MOS transistors in this DRAM are electrically fixed. It is to be noted that the body region of the P channel MOS transistor is supplied with power supply potential V_CC. Furthermore, negative potential V_BBis applied to the body regions of the transistors inmemory cell array11 out of the N channel MOS transistors. Ground potential V_SSis applied to the body regions of the other N channel MOS transistors.
• Therefore, the threshold voltage of the N channel MOS transistor inmemory cell array11 becomes greater than that of other N channel MOS transistors. Therefore, the leakage current flowing in the transistors forming the memory cell is reduced, resulting in a longer data retaining time period of the memory cell.
Embodiment 53
• FIG. 67 is a layout diagram showing an entire structure of a DRAM according toembodiment 53 of the present invention. Referring toFIG. 67, all the body regions in the N channel MOS transistors inmemory cell array11 are set to a floating state.
• In general,memory cell array11 has transistors arranged at a density higher than that ofperipheral circuit99. Therefore, there is almost no increase in the layout area even when a body fix line is disposed inrow decoder12,column decoder13, andperipheral circuit99. Furthermore, because it is not necessary to provide a body fix line inmemory cell array11, the layout area is similar to that of a conventional one.
Embodiment 54
• FIG. 68 is a layout diagram showing an entire structure of a DRAM according toembodiment 54 of the present invention. Referring toFIG. 68, the elements inmemory cell array11 are isolated by a field shield inembodiment 54. The body region in the transistor inmemory cell array11 is supplied with negative potential Vbb, as inFIG. 66.
• By isolating at least the elements inmemory cell array11, the body region of the transistor in thatmemory cell array11 can be electrically fixed without having to provide a body fix line inmemory cell array11. Therefore, the layout area of the DRAM ofembodiment 54 is smaller than that ofembodiment 52. Although the layout area ofembodiment 54 is substantially equal to that ofembodiment 53, there is almost no leakage current in the transistors ofmemory cell array11 since the body region is electrically fixed. Therefore, the data retaining time period according toembodiment 54 is longer than that ofembodiment 53.
Embodiment 55
• FIG. 69 is a layout diagram showing an entire structure of a DRAM according toembodiment 55. Referring toFIG. 69, the body region of the N channel MOS transistor in memory cell array is supplied with ground potential V_SSto be electrically fixed. Therefore, ground potential V_SSis applied to all the body regions of N channel MOS transistors, and power supply potential V_CCis applied to all the body regions of P channel MOS transistors. Thus, ground potential V_SSmay be applied to the body region in the transistor ofmemory cell array11.
Embodiment 56
• FIG. 70 is a diagram showing the concept of a DRAM according toembodiment 56 of the present invention. Referring toFIG. 70, this DRAM includes a plurality of N channel MOS transistors and a plurality of P channel MOS transistors. Ground potential V_SSis applied to the body region of several transistors of the N channel MOS transistors, and negative potential V_BBis applied to the body region of the other N channel MOS transistors. Power supply potential V_CCis applied to all the body regions of all P channel MOS transistors.
• Therefore, inembodiment 56, the body region of all MOS transistors are electrically fixed. Because the threshold voltage of the transistor having a body region to which negative potential V_BBis supplied is greater than the threshold voltage of the transistor having a body region to which ground potential V_SSis supplied, these plurality of N channel MOS transistors have two types of threshold voltages.
Embodiment 57
• FIG. 71 is a diagram showing the concept of a DRAM according toembodiment 57 of the present invention.
• Referring toFIG. 71, the body region of some N channel MOS transistors are set to a floating state. Because it is not necessary to provide a body fix line in the N channel MOS transistor region having a body region of a floating state, the layout area is smaller than that ofembodiment 56.
Embodiment 58
• FIG. 72 is a diagram showing the concept of a DRAM according toembodiment 58 of the present invention. Referring toFIG. 72, the body region of all P channel MOS transistors is set to a floating state inembodiment 58. Therefore, the body regions of all N channel MOS transistors are electrically fixed, and the body regions of all P channel MOS transistors are set to a floating state inembodiment 58. Although the breakdown voltage between the source and drain of an N channel MOS transistor having a body region of a floating state is generally lower than that of a P channel MOS transistor, the breakdown voltage between the source and drain of an n channel MOS transistor is increased substantially to the level of that of a P channel MOS transistor since the body region of N channel MOS transistor is electrically fixed inembodiment 58. It is therefore not necessary to provide a body fix line in the region of the P channel MOS transistor since the breakdown voltage between the source and drain of all transistors is high and the body region of a P channel MOS transistor is not electrically fixed. Thus, the layout area of the DRAM ofFIG. 58 is smaller than that ofembodiment 56.
• Although ground potential V_SSis applied to the body region of some N channel MOS transistors inembodiment 58, a negative potential V_BBmay be applied, instead of potential V_SS.
Embodiment 59
• FIG. 73 is a diagram showing the concept of a DRAM according toembodiment 59 of the present invention. Referring toFIG. 73, the body region of some N channel MOS transistors are set to a floating state. Therefore, the body regions of some N channel MOS transistors are fixed, and the body regions of all P channel MOS transistors are set to a floating state. Because it is not necessary to provide a body fix line in the region of the some N channel MOS transistors, the layout area ofembodiment 59 is smaller than that ofembodiment 58.
Embodiment 60
• FIG. 74 is a diagram showing the concept of DRAM according toembodiment 60 of the present invention. Referring toFIG. 74, all P channel MOS transistors are isolated by a LOCOS. Some N channel MOS transistor are isolated by a LOCOS, and the remaining N channel MOS transistors are isolated by a field shield (FS). Negative potential V_BBis applied to the body region of the N channel MOS transistor isolated by a field shield, and ground potential V_SSis applied to the body region of the N channel MOS transistor isolated by a LOCOS. Power supply potential V_CCis supplied to the body regions of all P channel MOS transistors. It is to be noted that ground potential V_SSmay be applied to the body regions of the N channel MOS transistor isolated by a field shield.
Embodiment 61
• FIG. 75 is a diagram showing the concept of a DRAM according toembodiment 61 of the present invention. Referring toFIG. 75, some P channel MOS transistors are isolated by a field shield, and the remaining P channel MOS transistors are isolated by a LOCOS. All N channel MOS transistors are isolated by a LOCOS. Power supply potential V_CCis applied to the body regions of all P channel MOS transistors. Some N channel MOS transistors have their body regions set to a floating state. The remaining N channel MOS transistors have their body regions supplied with ground potential V_SS. Inembodiment 61, the body regions of some N channel MOS transistors are electrically fixed, and the body regions of all P channel MOS transistors are electrically fixed.
Embodiment 62
• FIG. 76 is a diagram showing a concept of a DRAM according toembodiment 62 of the present invention. Referring toFIG. 76, this DRAM includes a plurality of P channel MOS transistors, and a plurality of N channel MOS transistors. Some P channel MOS transistors have athreshold voltage V_thp1, and the remaining P channel MOS transistors have athreshold voltage V_thp2. All the N channel MOS transistors have a threshold voltage of V_thn. Therefore, these P channel MOS transistors have two types of threshold voltages. The N channel MOS transistors have one type of threshold voltage. Thus, a channel type MOS transistor of the same conductivity type may have two types of threshold voltages.
• In order to provide two types of threshold voltages in a transistor, two types of potentials are applied to the body regions of those transistors. This is because difference in the potential applied to a body region will result in different threshold voltages due to a body effect.
• Alternatively, impurities differing in concentration may be doped into the n type body region of Pchannel MOS transistor3 as shown inFIG. 77. Regions of different impurity concentration will be formed in the proximity of the surface ofbody region3, whereby the two P channel MOS transistors have different threshold voltages.
• Alternatively, agate electrode4 differing in material may be formed of the transistors. In this case, the threshold voltages of these transistors will differ from each other according to the work function specific to these materials.
• Alternatively, SOIactive layer9 may be partially etched to result in a thick portion and a thin portion with transistors formed thereon. The transistor formed on the thin SOIactive layer9 approximates the so-called fully depleted transistor. The threshold voltage of a fully depleted transistor is generally smaller than that of a partially depleted transistor. Therefore, the transistor formed on the thin SOIactive layer9 has a threshold voltage smaller than that of the transistor formed on the thick SOIactive layer9.
• The threshold voltage of a transistor may be changed by varying the film thickness or the material of the gate insulation film.
• Although the P channel MOS transistors have two types of threshold voltages inembodiment 62, the N channel MOS transistors may have two types of threshold voltages. Furthermore, the transistor may have more than two types of threshold voltages.
• As described above, the DRAM may operate more stably if many transistors in the DRAM formed on a SOI substrate have more than one type of threshold voltages.
Embodiment 63
• FIG. 78 is a diagram showing the concept of a DRAM according to embodiment 63 of the present invention. Referring toFIG. 78, the body region of the transistor of a short gate length is electrically fixed, and the body region of the transistor of a long gate length is electrically floating. In general, the breakdown voltage between the source and drain of a transistor of a long gate length is higher than that of a transistor of a short gate length. Therefore, when the body region of the transistor of the short gate length is fixed, the threshold voltage thereof becomes approximately equal to that of a transistor having a body region of a floating state and a long gate length. In this case, there is hardly no increase in the layout area since it is not necessary to arrange a body fix line in the region of the transistor of the long gate length.
Embodiment 64
• FIG. 79 is a sectional view showing a structure of the sense amplifier of a DRAM according to embodiment64 of the present invention. Referring toFIG. 79, SOIactive layer9 is etched in a mesa-manner, and theLOCOS oxide film5 ofFIG. 6 is not formed.
• FIGS. 80 and 81 are sectional views of a memory cell of a DRAM shown inFIG. 79. This memory cell has a planar structure. SOIactive layer9 is etched in a mesa-manner differing from that ofFIGS. 60 and 61.
• Such a structure is manufactured by steps set forth in the following.
• After source/drain region44,contact region31, and the like are formed in SOIactive layer9, SOIactive layer9 is completely etched except for the element active region. As a result, the element active region is formed in a mesa-manner. Then, a gate oxide film is formed so as to cover the mesa element active region. Agate electrode4 is formed on this oxide film.
• In the case of the LOCOS isolation shown inFIG. 6, there is a problem that boron implanted into Ptype body region3 is absorbed intoLOCOS oxide film5 during formation ofLOCOS oxide film5 carried out by thermal oxidation of SOIactive layer9. This absorption of boron frombody region3 intoLOCOS oxide film5 causes reduction in the impurity concentration ofedge portion3aofbody region3. As a result, a parasitic MOS transistor of a low threshold value is formed in thisedge portion3a.Therefore, the so-called hump phenomenon appears in the drain current-gate voltage characteristics of transistor Qn1. This hump phenomenon is considered to be caused also by a bird's beak specific to LOCOS isolation providing stress to the thin SOIactive layer9.
• In contrast, the impurity concentration of the edge portion inbody region3 does not decrease in the case of mesa isolation shown inFIGS. 79-81. This is because SOIactive layer9 is not subjected to thermal oxidation, and becausebody region3 is covered by a gate oxide film andgate electrode4. Furthermore, stress will not be generated in the edge portion ofbody region3 because an oxide film, a nitride film, or the like is deposited asinterlayer insulation film33 by CVD. Thus, a hump phenomenon will not appear in the drain current-gate voltage characteristics of this transistor. This transistor can operate in a further stable manner.
Embodiment 65
• FIG. 82 is a sectional view of a memory cell of a DRAM according toembodiment 65 of the present invention. Referring toFIG. 82, this memory cell has a stack structure. SOIactive layer9 is etched in a mesa-manner. It is appreciated fromembodiments64 and65 that mesa isolation may be employed instead of LOCOS isolation.
Embodiment 66
• FIG. 83 is a diagram showing the concept of a DRAM partially according toembodiment 66 of the present invention. Although the above-described embodiment does not mention the potential ofsilicon substrate7, it is preferable to supply a predetermined substrate potential V_BBtosilicon substrate7 as shown inFIG. 83. This substrate potential V_BBis generated by a substratepotential generator100.
• InSOI substrate6,silicon substrate7 is isolated from SOIactive layer9 by buriedoxide layer8. However SOIactive layer9 is connected tosilicon substrate7 via a parasitic capacitance. Therefore, whensilicon substrate7 is electrically floating, the potential ofbody region3 is apt to become unstable in accordance with the potential variation ofsilicon substrate7. Inembodiment 66, the potential ofsilicon substrate7 does not change since a predetermined substrate potential V_BBis provided tosilicon substrate7 so that it is electrically fixed. Thus, a, semiconductor element such as a transistor formed onSOI substrate6 operates stably.
Embodiment 67
• FIG. 84 is a diagram showing the concept of a DRAM according toembodiment 67 of the present invention. The DRAM ofembodiment 67 differs from that ofFIG. 83 in thatsilicon substrate7 is connected to groundnode51. Because ground potential V_SSis supplied tosilicon substrate7,silicon substrate7 is electrically fixed. Therefore, a semiconductor element such as a transistor formed onSOI substrate6 operates stably. It is appreciated fromembodiment 67 that the potential is not particularly limited in the present invention. Not only substrate potential V_BB, but also ground potential V_SSmay be applied tosilicon substrate7.
Embodiment 68
• FIG. 85 is a perspective view of a structure to supply substrate potential V_BBtosilicon substrate7 as shown inFIG. 83. Referring toFIG. 85, a substratepotential generator100 is formed onSOI substrate6. Abonding pad102 is formed onSOI substrate6. Substrate potential V_BBis provided tobonding pad102 from substratepotential generator100.
• SOI substrate6 is provided on a die pad (conductor plate)106 disposed in the package.Bonding pad102 is connected to diepad106 via awire104. Since the back face ofSOI substrate6 is in contact withdie pad106, substrate potential V_BBgenerated by substratepotential generator100 is provided tosilicon substrate7 viabonding pad102,wire104, and diepad106. Thus,silicon substrate7 is electrically fixed.
Embodiment 69
• FIG. 86 is a perspective view showing a specific structure to provide ground potential V_SStosilicon substrate7 as shown inFIG. 84.Bonding pad102 ofFIG. 86 serves to supply ground potential V_SSto the circuit formed onSOI substrate6.Bonding pad102 is connected to leadframe110 to which ground potential V_SSis supplied viawire104.
• In the present embodiment, diepad106 is connected to leadframe110 viawire104. Therefore, ground potential V_SSis supplied tosilicon substrate7 vialead frame110,wire104 and diepad106. Therefore,silicon substrate7 is electrically fixed.
Embodiment 70
• FIG. 87 is a perspective view showing another example for supplying ground potential V_SStosilicon substrate7. Referring toFIG. 87,SOI substrate6 is provided on adie pad112 of a L shape.Bonding pad102 serves to provide ground potential V_SSto the circuit onSOI substrate6.Bonding pad102 is connected to diepad112 viawire104. Therefore, ground potential V_SSis supplied tobonding pad102 viadie pad112,wire104, and also tosilicon substrate7 viadie pad112. Therefore,silicon substrate7 is electrically fixed.
Embodiment 71
• FIG. 88 is a sectional view showing another example of providing substrate potential V_BBtosilicon substrate7. Referring toFIG. 88, acontact trench118 is formed inSOI substrate6.Trench118 goes through buriedoxide layer8 tosilicon substrate7. A contact hole CH is formed ontrench118. Asubstrate fix line114 is formed on contact hole CH.Substrate fix line114 is connected tosilicon substrate7 via contact hole CH.
• Inembodiment 72, substrate potential V_BBgenerated by substratepotential generator100 is supplied tosubstrate fix line114. Therefore, substrate potential V_BBis supplied tosilicon substrate7 viasubstrate fix line114. Therefore,silicon substrate7 is electrically fixed.
Embodiment 72
• FIG. 89 is a sectional view showing another example of providing substrate potential V_BBor ground potential Vss tosilicon substrate7 of FIGS.83 or84.Substrate fix line114 is connected tobonding pad102.Bonding pad102 is formed onSOI substrate6 as shown inFIG. 86 or87. Ground potential V_SSor substrate potential V_BBis supplied tobonding pad102. Therefore, potential V_SSor V_BBofbonding pad102 is supplied tosilicon substrate7 viasubstrate fix line114. Therefore,silicon substrate7 is electrically fixed.
Embodiment 73
• FIG. 90 is a circuit diagram showing a structure of a memory cell, a sense amplifier, and an input/output circuit of a DRAM according toembodiment 74 of the present invention. Referring toFIG. 90, a boosted sense groundpotential generator120 is provided. Boosted sense ground potential V_BSGgenerated bygenerator120 is applied to the source electrodes of transistors Qs1 and Qs2.
• FIG. 91 is a timing chart showing an operation of this DRAM. As shown inFIG. 91(j), the potential of one bit line only falls to the level of boosted sense ground potential V_BSG. This potential V_BSCis higher than ground potential V_SSby ΔV.
• Although the gate potential of transfer gate Qm in a deselect memory cell is 0V (a L level), the source potential of transfer gate Qm falls only to the level of boosted sense ground potential V_BSG. Therefore, the source potential thereof is higher than the gate potential by ΔV. Therefore, transfer gate Qm attains a more heavy non-conducting state in comparison with those of the above-described embodiment. In other words, the threshold value of this transfer gate Qm is substantially higher. Therefore, in ade-select memory cell27, the disturb type subthreshold leakage current is significantly suppressed.
• According to such a boosted sense ground method, the threshold value of transfer gate Qm can be substantially increased without doping impurities into the body region thereof. Therefore, the carrier mobility will not be reduced by doping. The manufacturing process is simplified since such a doping step is not required.
• The potential is not limited to that described in the above embodiments where a ground potential V_SSor a negative potential V_BBis applied to the body region of a N channel MOS transistor, and any potential lower than a source potential of the N channel MOS transistor may be applied. Furthermore, although the power supply potential V_CCis supplied to the body region of a P channel MOS transistor, any potential higher than a source potential of the P channel MOS transistor may be applied.
• Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims (3)

1-36. (canceled)

37. A semiconductor memory device comprising at least one first semiconductor element and at least one second semiconductor element,

wherein an element isolation film for isolating said first semiconductor element and said second semiconductor element from each other is formed on an SOI substrate,

wherein said element isolation film is in contact with an insulation film in said SOI substrate.

38-43. (canceled)

Images