Abstract: A standard cell for a plurality of power supplies comprises a first power line and a second power line electrically isolated from the first power line. An N well is arranged in spaced relation with the whole peripheral boundaries of the standard cell. In the case where the standard cells are arranged adjacently to each other in the direction along the power lines or in the direction orthogonal thereto, the N well in the standard cell for a plurality of power supplies is isolated from the N wells of the adjacent standard cells in the direction along the power lines or in the direction orthogonal thereto, as the case may be.

Abstract: A wire width and a wiring space of each of signal wires 1 and ground/power wires 2 are determined to be a wire width W1 (the minimum wire width) and a wiring space S1, respectively. A wire width and a wiring space of the via-hole neighboring region 1a or 2a are determined to be a wire width W2 (>W1) and a wiring space S2 (<S1), respectively. The wire widths W1 and W2 and the wiring spaces S1 and S2 are respectively determined so as to maintain the minimum wiring pitch P. The wiring space S1 is determined also so as to satisfy {S1/P≧0.6}. Further, the signal wires 1 and the ground/power wires 2 have the same wire thickness of a wire thickness T1 which allows an aspect ratio (T1/W1) to be equal to, or higher than, 2.

Abstract: A semiconductor memory device includes a plurality of bit line structures arranged in parallel on a semiconductor substrate and having a plurality of bit lines and an insulating material surrounding the bit lines, an isolation layer formed in a portion in spaces between the bit line structures to define a predetermined active region and having substantially the same height as the bit line structures, a semiconductor layer formed in the predetermined active region surrounded by the bit line structures and the isolation layer and having substantially the same height as the bit line structures and the isolation layer, a plurality of word line structures arranged in parallel on the bit line structures, the isolation layer, and the semiconductor layer, and comprising a plurality of word lines and an insulating material surrounding the word lines, and source and drain regions formed in the semiconductor layer on either side of the word line structures.

Abstract: In the manufacture of a semiconductor device, there are provided a method that enables reduction in the number of manufacturing steps thereof and a structure for realizing the method, to thereby realize improvement in yield and reduction in manufacturing cost. Wirings (source wiring, drain wiring, and the like), which are respectively formed in a row direction and a column direction on an element substrate, are formed of the same conductive film. In this case, one of the respective wirings in the row direction and the column direction is discontinuously formed at a portion where the wirings intersect with each other, and an insulating film is formed on the wirings. Thereafter, a connection wiring for connecting discontinuous wirings is formed of the same film as that for forming an electrode provided on the insulating film. As a result, a continuous wiring is formed.

Abstract: Bit lines are arranged with minimum width and minimum space in a chip, and each bit line is given a maximum of first potential difference. The minimum space is the value which will not make a line short-circuit in a line due to dielectric strength, when the first potential difference is applied across the bit lines. This value may be the design rule or the minimum dimensions capable of being processed by lithography. A second potential difference lager than the first potential difference is applied across a shielded power line and the bit lines. The shielded power line is not adjacent to the bit lines in the wiring width direction in the area where the bit lines are arranged with the minimum space.

Abstract: A semiconductor memory device provided with a plurality of memory cells each including first transistors having first conductivity type and second transistors having a second conductivity type, each memory cell comprising a first active region where channels of the first transistors are formed and a second active region where channels of the second transistors are formed, the first and second active regions being arranged so that the directions of channel currents of the transistors become parallel to each other in each cell and being separated between adjoining memory cells in a direction perpendicular to the directions of channel current.

Abstract: A power and ground shield mesh to remove both capacitive and inductive signal coupling effects of routing in integrated circuit device. An embodiment describes the routing of a shield mesh of both power and ground lines to remove noise created by capacitive and inductive coupling. Relatively long signal lines are routed in between fully connected power and ground shield mesh which may be generated by a router during the signal routing phase or during power mesh routing phase. Leaving only the odd tracks or the even tracks for signal routing, power mesh (VDD) and ground mesh (VSS) are routed and fully interconnected leaving shorter segments and thereby reducing the RC effect of the circuit device. Another embodiment presents a technique where the signals are shielded using the power and ground mesh for a gridless routing. Another embodiment presents a multi-layer grid routing technique where signals are routed on even grid and the power and ground lines are routed on odd grid.

Abstract: A wire width and a wiring space of each of signal wires 1 and ground/power wires 2 are determined to be a wire width W1 (the minimum wire width) and a wiring space S1, respectively. A wire width and a wiring space of the via-hole neighboring region 1a or 2a are determined to be a wire width W2 (>W1) and a wiring space S2 (<S1), respectively. The wire widths W1 and W2 and the wiring spaces S1 and S2 are respectively determined so as to maintain the minimum wiring pitch P. The wiring space S1 is determined also so as to satisfy {S1/P≧0.6}. Further, the signal wires 1 and the ground/power wires 2 have the same wire thickness of a wire thickness T1 which allows an aspect ratio (T1/W1) to be equal to, or higher than, 2.

Abstract: A modularly expandable semiconductor component includes at least one carrier layer, at least one intermediate layer, at least one coverlayer, at least one semiconductor chip, external contacts and a conductor configuration. The intermediate layer is provided with at least one opening, into which the at least one semiconductor chip is inserted. The carrier layer, the intermediate layer and the coverlayer are connected one above another and form a submodule. If a plurality of submodules are installed above one another, a semiconductor component is provided in which the semiconductor chips are located in several mutually overlying planes. The semiconductor chips can be interconnected. A method for producing a semiconductor component is also provided.

Abstract: An interconnect bus for a microelectromechanical system is disclosed. Various attributes for an electrical trace bus that facilitate the routing of signals throughout at least a portion of the system and/or the layout of the microelectromechanical system on a wafer are disclosed.

Abstract: A unit cell is disclosed that facilitates the creation of a layout of at least a portion of a microelectromechanical system. The unit cell includes a plurality of electrical traces. Some of these electrical traces pass through the unit cell. Other electrical traces extend only part way through the unit cell. At least certain boundary conditions exist for the unit cell that allow the same to be tiled in a row and in a manner that results in adjacently disposed unit cells in the row being electrically interconnected in the desired manner.

Abstract: A semiconductor memory device includes a memory cell which has a transistor and a ferroelectric capacitor, the transistor having a source-drain path and a gate connected to a word line, the capacitor being connected at a first end to a plate line and connected at a second end to a bit line through the source-drain path. A control circuit controls, during a test-mode operation, the memory cell so that a plate-line signal sent through the plate line to the memory cell and a bit-line signal sent through the bit line to the memory cell are set at a same potential.

Abstract: A multi-chip device which includes a plurality of integrated circuit die disposed one over another. Each integrated circuit die includes one or a plurality of bond pads. One or a plurality of conductors are disposed to electrically couple the bond pads of vertically adjacent integrated circuit die. Each conductor is designed, calculated, specified and/or predetermined to have a length so as to behave as a segment in a multi-drop transmission line. The multi-drop transmission line may be terminated at one end or utilized in a flow-through approach. In one embodiment, an integrated circuit die may be horizontally offset with respect to a vertically adjacent integrated circuit die to expose the periphery region. In another embodiment, each integrated circuit die may be stacked and aligned in a vertical column. In this embodiment, a spacer such as a thermally conductive spacer is disposed between each integrated circuit die in the stack.

Abstract: In a semiconductor device having a dual isolation structure, and a method of fabricating the same, an epitaxial layer is formed on the entire surface of the semiconductor device. A device region including the semiconductor device and the epitaxial layer is defined by a device isolation layer. The device isolation layer has a dual structure that includes a diffused isolation layer and a trench isolation layer. The diffused isolation layer is formed in the semiconductor substrate, and surrounds the base and the bottom sidewall of the device region, and the trench isolation layer surrounds the upper sidewall of the device region by vertically penetrating the epitaxial layer.

Abstract: An metal programmable integrated circuit apparatus and method of manufacture and design using elevated metal layers for design-specific customization. The lower metal layer are used to form core cells and to provide power and clocking signals to the core cells. These core cell are customizable by the designer using only the upper metal layers. This new architecture allows faster turn-around time and fewer masks while keeping the time-to-market advantages of gate array structures.

Abstract: A gate array comprises a core cell having a plurality of logic gates, a power supply pattern provided beside the core cell for providing electrical power to the core cell, and a border element provided beside the power supply pattern for providing capacitance or resistance to the core cell. The border element has a capacity cell including a transistor that provides the capacitance to the core cell, a resistor cell including a transistor that provides resistance to the core cell, and a material having resistance to be provided to the core cell.

Abstract: A semiconductor device includes a semiconductor chip and a circuit formed in the semiconductor chip. Pads are arranged in a plurality of rows on the semiconductor chip and electrically connected to the circuit. The pads on adjacent rows are offset from each other. Leads are provided on the semiconductor chip and bonding wires selectively connect the leads to the pads.

Abstract: A semiconductor device includes a real pattern and dummy patterns in respective different coordinate systems. Using a dummy pattern in a single coordinate system does not allow an effective dummy pattern arrangement. To the contrary, if the dummy patterns in different coordinate systems are used, minimum interval requirements may be satisfied in one coordinate system while such requirements are not met in another coordinate system.

Abstract: A semiconductor chip has standard cells which are disposed in a plurality of mutually adjacent rows, wiring channels are disposed between the rows and at at least one location along at least one wiring channel, the width of the wiring channel determined by a prescribed unambiguous and variable assignment specification. The width of the wiring channels can thus be varied in a flexible manner, so that a circuit can be fabricated in a space-saving manner.

Abstract: An integrated circuit has a plurality of metal layers separated by a plurality of insulating layers. The integrated circuit comprises a pair of conductors on a first metal layer; at least one conductive fill element disposed between the conductors; and a via connecting the fill element to a ground contact on a metal layer adjacent to said first metal layer, where the via is formed of a conductive material.

Abstract: An integrated circuit includes first circuit elements with a supply voltage which is equal to the external supply voltage of the IC, and second circuit elements with a supply voltage which is smaller than the external supply voltage and is derived as an internal supply voltage from the first supply voltage. An active voltage divider supplies the internal supply voltage and includes a first resistance voltage divider connected between the supply voltage terminal and the reference potential, an impedance transformer connected after the first resistance voltage divider, and a circuit for controlling the scaled voltage at the tap of the first resistance voltage divider as a function of the load of the second circuit elements.

Abstract: A base cell is configured such that P-type regions 11 to 13 are arrayed in a column direction in an N-type well 10, N-type regions 21 to 23 are arrayed in a column direction in a P-type well 20 next to the N-type well, gate lines 34A and 35B passing above a channel between the P-type regions and further between the N-type regions are formed in a row direction, and well contact regions 16C and 26C are formed in the wells 10 and 20 at outer ends thereof, respectively, while no gate contacts are formed at the outer ends. Power supply lines VDD and VSS connected to the well contact regions are formed in the column direction in a second wiring layer above a first wiring layer.

Abstract: A field effect transistor (30) has an array of transistors (31) made up of bonding pads (45-47) and sub-arrays of transistors (41-43). The bonding pads (45-47) are distributed between the sub-arrays of transistors (41-43) to reduce the maximum temperature that any portion of the FET (30) is exposed to while the FET (30) is in a conducting state. A similar effect can be appreciated by adjusting the threshold voltage or pinch-off resistance of the transistors in a portion (101) of an array of transistors (95).

Abstract: A semiconductor integrated circuit includes cells, cell rows and potential feeders. Each cell includes a partial trunk that is used to constitute a power supply trunk and/or a ground trunk, and that is electrically isolated from the remaining components within the cell. Each cell row includes a plurality of cells placed adjacently, and the power supply trunk and/or ground trunk composed of the partial trunks. The potential feeders selectively connect one of the power supply trunk and ground trunk of any one of the plurality of cell rows to the components within the cells to supply them with the potential of the power supply trunk and/or ground trunk. This enables the components in the adjacent cells to be supplied with different potentials.

Abstract: A field effect transistor (30) has an array of transistors (31) made up of bonding pads (45-47) and sub-arrays of transistors (41-43). The bonding pads (45-47) are distributed between the sub-arrays of transistors (41-43) to reduce the maximum temperature that any portion of the FET (30) is exposed to while the FET (30) is in a conducting state. A similar effect can be appreciated by adjusting the threshold voltage or pinch-off resistance of the transistors in a portion (101) of an array of transistors (95) or by providing transistors with a higher thermal breakdown in the center of the field effect transistor (30).

Abstract: Development efficiency and mass production efficiency of a semiconductor chip (LSI) is improved, whereby the LSI on which an integrated circuit is formed has plural pad parts connecting the integrated circuit with an external circuit. The pad part is provided with a first junction consisting of a window formed in the protective film and the pad exposed from the window, and a second junction consisting of a window formed in the protective film and a bump deposited on the pad exposed from the window. When it is required that the LSI is to be connected with an external circuit by wire bonding, the first junction is connected with the external circuit using a wire. When it is required to connect the LSI with an external circuit by the TAB method or the COG method, the second junction is directly connected to the external circuit.

Abstract: A technique is disclosed which facilitates the layout of op amp cells, for example, two-stage op amp cells or three-stage op amp cells, to provide larger operational amplifiers. In accordance with one aspect, the op amp cells can be suitably coupled in parallel to provide a larger operational amplifier. This paralleling aspect can be facilitated by connecting the respective negative and positive inputs of a predetermined number of input gm stages together, connecting the outputs of a predetermined number of output gm stages together, and connecting a predetermined number of intermediate internal nodes between the input gm stages and the output gm stages together, without the occurrence of saturation of the internal nodes. In addition, the input and output characteristics of operational amplifier can be suitably improved.

Abstract: A memory array including a bit cell row, a strap cell row, a first power supply line, and a first offset supply line is provided. The bit cell row may include a bit cell that includes a first transistor disposed in a first bit cell body region. The first transistor may include a first active region. The strap cell row may include a strap cell that includes a first strap cell body region. The first strap cell body region may be conductively coupled to the first bit cell body region. The first power supply line may be electrically coupled to the first active region and may provide a first supply voltage potential to the first active region. The first offset supply line may be electrically coupled to the first strap cell body region and may provide a first offset voltage potential to the first bit cell body region via the first strap cell body region. The first supply voltage potential is operable to be different from the first offset voltage potential.

Abstract: An electronic power circuit substrate including a wafer of electrically insulating material, wherein said wafer presents a face supporting one or more conductive tracks directly connected to one or more electronic power components, said conductive tracks being obtained by fine metallization of said face to a thickness that is less than 150 &mgr;m.

Abstract: An electrical bus grid (108) for an application specific integrated circuit (ASIC) chip (102). The bus grid is generally formed by mutually orthogonal wires (28′, 30′) contained within two metal layer (M6′, M7′). The bus grid is located within each of a plurality of contiguous rectangular regions (32′), which are defined by electrical contacts (12′). Due to the regular pattern of the electrical contacts, the bus grids within the contiguous rectangular regions are identical to one another, such that the bus grid forms a repeatable pattern. The widths of the wires in each of the two metal layers vary depending upon the magnitude of the current carried by the corresponding wire. The magnitude of the current in the power bus may be determined by simulation and modeling performed prior to placement of cells (e.g., 18, 20, 22) within the ASIC chip.

Abstract: A method and apparatus for improving the laminate performance of the solder balls in a BGA package. Specifically, the ball pads on the substrate are configured to increase the shear force necessary to cause delamination of the solder balls. Conductive traces extending planarly from the pads and arranged in specified configurations will increase the shear strength of the pad.

Abstract: A first signal path of a circuit 300 of the present invention is formed by connecting a restricted area 331 in the electrically disconnected state, restricted areas 321 and 311 in the electrically connected state in series, using conductors 330, 320, and 310, and contacts 351 and 352. The circuit 300 is constructed by connecting in parallel six signal paths each being divided by a combination of one or two restricted areas provided thereon. Every time the circuit state is switched, a signal path disconnected by one restricted area is changed suitably to a signal path disconnected by two restricted areas, and vice versa, so as to maintain a signal path disconnected by a combination of restricted areas. By doing so, the switch of the circuit between the disconnected state and the connected state can be repeated an unlimited number of times by a change in one freely-chosen layer.

Abstract: A program-controlled unit includes a plurality of semiconductor chips distributed between a plurality of chip carriers that are disposed one above the other and are connected to one another through a bus. Such program-controlled units can be developed, produced, and tested simply, rapidly, and cost-effectively even when they have to be adapted to special requirements.

Abstract: A semiconductor device and a method of laying out the same includes routing primary power and ground distributions in the second metallization layer, rather than the first metallization as is conventionally done. This improves routability in the first metallization layer while providing sufficient current handling ability in the power and ground distributions.

Abstract: In one embodiment of the invention, an embedded enclosure includes a power plane and first and second ground planes. The power plane has a power surface and a power periphery, and couples power to signals of an integrated circuit operating at a fundamental frequency. The first and second ground planes have first and second ground surfaces and first and second ground peripheries, respectively. The first and second ground planes couple ground to the signals. The first and second ground planes are separated from the power plane by first and second distances, respectively. The first and second ground surfaces are larger than the power surface. The first and second ground peripheries extend at least third and fourth distances from the power periphery, respectively. The third and fourth distances are N and M times larger than the first and second distances, respectively.

Abstract: A semiconductor device includes a bonding pad formed on a substrate and a mark region formed on the substrate right underneath the bonding pad, such that the mark region is covered by the bonding pad.

Abstract: Development efficiency and mass production efficiency of a semiconductor chip (LSI) is improved, whereby the LSI on which an integrated circuit is formed has plural pad parts connecting the integrated circuit with an external circuit. The pad part is provided with a first junction consisting of a window formed in the protective film and the pad exposed from the window, and a second junction consisting of a window formed in the protective film and a bump deposited on the pad exposed from the window. When it is required that the LSI is to be connected with an external circuit by wire bonding, the first junction is connected with the external circuit using a wire. When it is required to connect the LSI with an external circuit by the TAB method or the COG method, the second junction is directly connected to the external circuit.

Abstract: An integrated circuit chip includes a substrate having edges defining an inner area; circuit modules located on the substrate; and input/output terminals for inputting and outputting one or more signals to and from the circuit modules. The input/output terminals include (i) input/output terminals used for operation, which input/output one or more operation signals during operation of the circuit modules, and (ii) input/output terminals used for inspection of the circuit modules. The input/output terminals used for operation are arranged along the edges of the substrate, and the circuit modules and the input/output terminals used for inspection are arranged on the inner area of the substrate.

Abstract: Integrated circuits are tested on the wafer level through an additional circuit part that is electrically connected via at least one connecting line with the associated integrated circuit. The additional circuit part is integrated into an interspace between the integrated circuits of the wafer. Functions of the integrated circuit can be controlled via the connecting line. For example, in the case of a memory module such as a DRAM, internal voltages and/or currents of the integrated circuit can advantageously be measured even on internal lines which are otherwise only accessible with difficulty. Following the wafer-level testing and dicing of the integrated circuits into individual chips, the additional circuit part becomes unusable.

Abstract: A method and apparatus for providing a meshed power and signal bus system on an array type integrated circuit that minimizes the size of the circuit. In a departure from the art, through-holes for the mesh system are placed in the cell array, as well as the peripheral circuits. The power and signal buses of the mesh system run in both vertical and horizontal directions across the array such that all the vertical buses lie in one metal layer, and all the horizontal buses lie in another metal layer. The buses of one layer are connected to the appropriate bus(es) of the other layer using through-holes located in the array. Once connected, the buses extend to the appropriate sense amplifier drivers. The method and apparatus are facilitated by an improved subdecoder circuit implementing a hierarchical word line structure.

Abstract: Memory chips containing memory devices are arranged to be mounted in a memory package with the major axis of the memory chip aligned substantially parallel with the major axis of its memory package. Memory chips include a first power input chip bond pad in each of at least three quadrants of the memory chip. Memory chips include a second power input chip bond pad in each of at least three quadrants of the memory chip. The chip bond pads are interposed between memory banks of the memory device and the sides of the memory chip containing the memory device. Lead-over-chip leadframes for coupling the chip bond pads to the interconnect pins of a memory package contain at least one composite lead for coupling an interconnect pin to chip bond pads in multiple quadrants or on opposite sides of the memory chip. Memory assemblies include memory chips having chip bond pads on both sides of the memory chip shorted to each other by a single lead of the lead-over-chip leadframe.

Abstract: A lead frame for an integrated circuit includes a ground for the integrated circuit to ground the integrated circuit, the lead frame having at least one corner connected to the ground; and a connector between the corner of the lead frame and the ground located on the integrated circuit.

Abstract: A semiconductor integrated circuit device comprises vertical power supply wiring 12 divided into first and second narrow-width vertical power supply wirings 12a and 12b, vertical ground wiring 14 disposed in parallel with vertical power supply wiring 12 and divided into first and second narrow-width vertical ground wirings 14a and 14b, auxiliary vertical power supply wiring 22 connecting first narrow-width vertical power supply wiring 12a and second narrow-width vertical power supply wiring 12b, and auxiliary vertical ground wiring 24 connecting first narrow-width vertical ground wiring 14a and second narrow-width vertical ground wiring 14b.

Abstract: A semiconductor wafer having dice that include circuitry that is placed into a mode when the circuitry receives an alternating signal having certain characteristics. The alternating signal may be supplied from a system controller through a probe, probe pad, and conductive path on the wafer. In a preferred embodiment, the conductive path simultaneously carries a VCC power signal and the alternating signal to the circuitry. However, the alternating signal may be carried on a conductive path different from the one carrying the VCC signal. A great deal of information may be conveyed through the alternating signal, making other signals unnecessary in controlling, testing, stressing, and repairing dice on the wafer. For example, clocking information may be conveyed through the alternating signal. The circuitry may be placed in different modes in response to different characteristics of the alternating signal. The alternating signal and a VCC power signal are received through a single contact on each die.

Abstract: A pin grid array package comprises a number of signal pins and ground pins. At least one of the signal pins is a controlled impedance signal pin, i.e. a signal pin whose impedance is adjusted and/or reduced according to the present invention. The pin grid array package also includes a number of ground planes and signal planes. A controlled impedance signal pin is coupled to one of the signal planes by means of a signal via. A number of ground pins surround the controlled impedance signal pin. By varying the arrangement, number, and separation distance between the ground pins and the controlled impedance signal pin, the impedance of the signal pin is adjusted and/or reduced. Depending on the particular circuit or logic function assigned to a signal pin and its adjacent signal pin, a different degree of impedance control and/or reduction can be achieved by the present invention.

Abstract: A basic cell is disclosed, which is small in area and has sufficient connection flexibility. for achieving a semiconductor integrated circuit with a higher density and a reduced manufacturing cost. In a basic cell, a terminal wire, which is connected to a transistor terminal with a contact, is placed in a first metal wiring layer, and a plurality of terminal wire connection points, which can be connected to a second metal wire through a first via, are provided on the terminal wire. Further, in a semiconductor integrated circuit, a circuit wire in a second metal wiring layer is placed along grid points with a fixed pitch, and is connected to a terminal connection point of a transistor terminal, which is displaced from the grid points, through a terminal wire provided in the first metal wiring layer.

Abstract: A semiconductor device having a shallow trench isolation (STI) structure, which is capable of reducing leakage current in a P-FET and improving the device characteristics of a memory device, and a manufacturing method thereof, including a semiconductor substrate having a first area with a first trench formed therein and a second area with a second trench formed therein; a first sidewall oxide layer formed on the inner surface of the first trench; a second sidewall oxide layer, which is thinner than the first sidewall oxide layer, formed on the inner surface of the second trench; a liner formed on the surfaces of the first and second sidewall oxide layers; and a dielectric material that fills the first and second trenches.

Abstract: There is provided a semiconductor integrated circuit device which has realized high speed operation, high integration density and highly efficient layout of the RAM macro, in which a memory array which is divided into four sections in the X and Y coordinates directions is disposed, a first input circuit for receiving a signal which requires optimization for a signal delay is disposed to the center of such four memory arrays, a second input circuit for receiving a data input and control signals thereof is disposed to the center of Y coordinate corresponding to the extending direction of the word line and a signal line for transferring an input signal from the external circuit of the RAM macro to the first and second input circuits is formed using an upper layer wiring for the wiring to form the memory array.

Abstract: A semiconductor device having self-aligned contact pads and a method for manufacturing the same are provided. The semiconductor device includes a semiconductor substrate and an isolation layer formed on the semiconductor substrate. The semiconductor substrate defines a plurality of active regions that each have a major axis and a minor axis. A plurality of gates are formed to cross the plurality of active regions and extend in the direction of the minor axis. First and second source/drain regions are formed in active regions at either side of each of the gates. First and second self-aligned contact pads (SACs) are formed to contact the top surfaces of the first and second source/drain regions, respectively.

Abstract: A semiconductor memory device has a reference section which includes a first reference cell block and second reference cell blocks. The first reference cell block includes a second contact diffusion region which is arranged under a virtual ground line and is connected to this virtual ground line via a contact hole. The second reference cell blocks include first and third contact diffusion regions which are arranged under a bit line and can be connected to the bit line via contact holes as needed. Thereby, the number of reference cell blocks to be connected in series can be selected freely, allowing finer settings of a reference current value.