Abstract:
A sense amplifier for use with a dynamic random access memory is formed in a silicon integrated circuit. The pitch of an array of such sense amplifiers is equal to the pitch of pairs of bit lines of a memory array. Each array of sense amplifiers is formed from four rows of transistors of a given n or p-channel type Metal Oxide Semiconductor (MOS) transistor having a U-shaped gate electrode. The gate electrode of the transistors in each row of transistors of the sense amplifier is offset from those in a previous row by a preselected amount. The bit lines passing through the sense amplifier are straight, with no offsets to affect photolithographic performance, and no protuberances to increase the capacitance of the bit lines. Such an array of sense amplifiers has a size equivalent to the minimum size of the pairs of bit lines, and thus does not cause any increase in the width of the array of memory cells.

Description:
FIELD OF THE INVENTION 
     This invention relates to the design and manufacture of integrated circuit devices including memory and random access memory, and more particularly, to the design of transistors in a support area of the memory which allows support circuits, such as sense amplifiers, to be designed with a width commensurate with the width of the memory cells. 
     BACKGROUND OF THE INVENTION 
     There is a continuing trend towards increasing the capacity and speed, and decreasing the cost of dynamic random access memory (DRAM) fabricated in semiconductor integrated circuits. Such an increase in capacity and decrease in cost is best achieved by decreasing the area of the memory cells, and by decreasing the size of the support circuitry, sense amplifiers and addressing circuitry, to be commensurate with the smaller size of the memory cells. 
     In a typical DRAM memory cells are arranged in an array, which in most designs consumes a major portion of the area of the DRAM semiconductor integrated circuit. FIG. 1 shows a schematic block diagram of a prior art memory  100  having individual memory cells  110  arranged in a top array  120  and a bottom array  130 . Word lines  140  run horizontally, and pairs of bit lines  150  run vertically, across the arrays  120 ,  130  of memory cells  110 , and are coupled to the memory cells  110 . When one of the word lines  140  is selected, the memory cells  110  in a given row are accessed and connected to the corresponding pair of bit lines  150 . The pairs of bit lines  150  run vertically through both the top array  120  and the bottom array  130  of memory cells  110  and connect to the sense amplifiers  160 , which are typically located centrally between the two arrays  120  and  130 . The largest portion of the surface area of a memory circuit  100  is devoted to the two arrays  120  and  130  of memory cells  110 . The size of a memory circuit  100  is thus directly proportional to the size of the arrays  120  and  130  of memory cells  110 . The size of the memory cells  110  can be characterized by the horizontal pitch, or distance from cell-to-cell, of the memory cells  110 . If the size or pitch of the sense amplifiers  160  is greater than that of the memory cells  110 , the sense amplifier  160 , rather than the memory cell  110 , will be the determining factor in the size of the complete memory circuit  100 . 
     Various techniques have been used to decrease the size of the memory cells, including the use of exotic high dielectric constant insulator materials in the storage capacitors, the use of vertical structures for the storage capacitors and access transistors, and the use of particular shapes and layouts for the active area of the memory cell. By the use of these techniques the horizontal size of an individual memory cell  110  has been reduced to the point where it is comparable with the size of the pair of bit lines  150 . It is incumbent upon the circuit designer to be able to produce a sense amplifier  160  of equivalent width. 
     It is common practice to describe the size of a memory cell or sense amplifier in terms of the size of the smallest features which can be produced using the available photolithographic and pattern definition techniques. Such a minimum size feature is commonly denoted as F. The minimum pitch of the bit lines is denoted herein as P. If one assumes that the minimum width of a bit line, F, is equal to the space between the bit lines, then the pitch of a pair of bit lines will be 4F. Thus the size of the smallest memory cells described above is said to be 4F, or more generally, 2P, or less. The goal of the designers of sense amplifiers is to achieve a sense amplifier with a width of 2P, or less. 
     FIG. 2A shows a schematic circuit diagram a of prior art sense amplifier  200  fabricated in Complementary Metal Oxide Semiconductor (CMOS) transistor technology. The details of the operation of the circuit depicted in FIG. 2A is described in the existing literature. The circuit contains three n-channel Metal Oxide Semiconductor (MOS) transistors N 1 , N 2 , and N 3 , and three p-channel MOS transistors, P 1 , P 2 , and P 3 , connected as shown in FIG.  2 A. Two of the p-channel MOS transistors, P 2  and P 3 , and two of the n-channel MOS transistors, N 2  and N 3 , are connected to form a latch circuit. The remaining p-channel MOS transistor P 1  is connected as a switch from a positive power supply  230  to sources of the two p-channel MOS latch transistors P 2  and P 3 , and the remaining n-channel MOS transistor N 1  is connected as a switch from the sources of the two n-channel MOS latch transistors N 2  and N 3  to a reference potential which is shown as ground  280 . The switch transistors P 1  and N 1 , respectively, are switched off and on by p-enable/disable and n-enable/disable signals (not shown) applied to gates  240  and  250 , respectively, of transistors P 1  and N 1 , respectively. The gates of the transistors P 2  and N 2 , and P 3  and N 3 , are connected to a Data Bit Line  260  and Reference Bit Line  270 , respectively, as is shown. While one switch transistor, P 1  or N 1 , is shown connected to a single pair of latch transistors, P 2  and P 3  or N 2  and N 3 , respectively, the circuit can alternatively be implemented with a single pair of switch transistors supplying power and ground to multiple pairs of transistors of the latch circuit. The number of pairs of transistors of the latch circuit connected to a single switch transistor (P 1  or N 1 ) is a design parameter and is typically determined by the resistance of the interconnection (not shown) between the switch transistors and transistors of the latch circuit. 
     FIG. 2B is a representation of the circuit of FIG. 2A in which the circuit has been redrawn to segregate the p-channel MOS transistors (P 1 , P 2 , and P 3 ) into one p-channel region  211  (shown in dashed lines), and the n-channel MOS transistors (N 1 , N 2 , and N 3 ) into a second n-channel region  221  (shown in dashed lines). The reference numbers of the elements of FIG. 2A have been incremented by  1  for similar elements in FIG.  2 B. The p-channel  211  and n-channel  221  portions of the circuit are symmetric. In the discussion of the layout of transistors herein below, we focus on a generic layout applicable to both the p-channel  211  and n-channel  221  sections of the sense amplifier. The depiction of a sense amplifier circuit as shown in FIG. 2B is more representative of the physical layout of an actual silicon integrated circuit than is the depiction shown in FIG. 2A, which is more related to the logical representation of the sense amplifier circuit. 
     If the size of the DRAM silicon integrated circuit is to be primarily determined by the size of the major component of the integrated circuit, i.e., the array of memory cells, it is incumbent upon the designers of the peripheral components, in this case the sense amplifiers, to make the peripheral component equal or smaller in size than the memory cell. Thus, one seeks ways to make the width of the sense amplifiers no larger that the width of the memory cell, or no larger than the size of a pair of bit lines. 
     Prior art describes the design of a sense amplifier which uses rows of field effect transistors having a U-shaped gate. Typically such sense amplifiers have a width of greater than 3.5P. This is significantly greater than the size of memory cells which can be fabricated using present memory cell technology, which, as described above, is approximately 2P. 
     It is desirable to have a sense amplifier which has a width, or pitch, comparable to that of the smallest memory cells which can be produced. Further, it is desirable to have a sense amplifier which does not introduce extra capacitance onto the bit lines. Furthermore, it is desirable to have a sense amplifier which has a simple repetitive, structure, and which does not significantly compromise the cost of the integrated circuits by negatively impacting the photolithographic yield of the integrated circuit. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a sense amplifier used in semiconductor integrated circuit memory devices in which the pitch (lateral size) of the sense amplifiers is made to match the pitch of the smallest memory cells. This is made possible through the use in the sense amplifier of a U-shaped gate design and the innovative use of four rows of transistors which are laterally offset from one another by a unique amount described herein below. In addition to the small size of the sense amplifiers resulting from the use of the methods described in this invention other advantages which accrue from the use of the described layout are: the use of highly replicated shapes which allow for advantages in the lithography; the ability to fabricate the bit lines using a single level of metal which has the ability to improve the yield of the fabricated integrated circuits; and the ability to design the bit lines as straight, non-meandering, lines, reducing the area of the bit lines and reducing the capacitance of the bit lines and allowing for advantages in photolithography. 
     From one aspect the present invention is directed to a semiconductor structure. The semiconductor structure comprises two rows of field effect transistors and first and second isolation regions. In the two rows of field effect transistors each transistor has output regions of a first conductivity type separated by portions of a semiconductor body of a second opposite conductivity type and having a U-shaped gate electrode separated from a top surface of the semiconductor body by a dielectric layer. The first and second isolation regions extend from the top surface of the semiconductor body into same and are separated by a first portion of the semiconductor body in which active portions of the transistors exist. Each U-shaped gate electrode has right and left arms and a central portion which connects a right arm portion to a left arm portion. Each of the right and left arms has an end portion and a middle portion with the middle portion being adjacent the central portion. The end portions of the right and left arms of the U-shaped gate electrodes of the first row are located over portions of the first isolation region, and the middle portions of the right and left arms of the first row and the central portions of the first row being located over the first portion of the semiconductor body. The end portions of the right and left arms of the U-shaped gate electrodes of the second row being located over portions of the second isolation region, and the middle portions of the right and left arms of the second row and the central portions of the second row being located over the first portion of the semiconductor body. The U-shaped gate electrodes of the second row of transistors are displaced from the U-shaped gate electrodes of the first row with a left arm of a gate electrode of a transistor of the second row being located below a right arm of a gate electrode of a transistor of the first row and a right arm of a gate electrode of a transistor of the second row being located below a left arm of a gate electrode of a transistor of the first row. 
     From a second aspect, the present invention is directed to a semiconductor structure. The semiconductor structure comprises a semiconductor body of a first conductivity type, a semiconductor region of a second opposite conductivity type being located within a portion of the semiconductor body, a first set of four rows of field effect transistors, first, second, and third isolation regions, a second set of four rows of field effect transistors, fourth, fifth, and sixth isolation regions, conductive lines, and an array of memory cells. The first set of four rows of field effect transistors is located in a portion of the semiconductor body not occupied by the semiconductor region with each transistor of the first set of four rows having output regions of the second conductivity type separated by portions of the semiconductor body and having a U-shaped gate electrode separated from a top surface of the semiconductor body by a dielectric layer. The first, second, and third isolation regions extend from the top surface of the semiconductor body into same and being separated by first and second portions of the semiconductor body in which active portions of the transistors exist. Each U-shaped gate electrode of the first four rows has right and left arms and a central portion which connects a right arm portion to a left arm portion; and each of the right and left arms having an end portion and a middle portion with the middle portion being adjacent the central portion. The end portions of the right and left arms of the U-shaped gate electrodes of the first row are located over portions of the first isolation region, and the middle portions of the right and left arms of the first row and the central portions of the first row are located over the first portion of the semiconductor body. The end portions of the right and left arms of the U-shaped gate electrodes of the second row are located over portions of the second isolation region, and the middle portions of the right and left arms of the second row and the central portions of the second row are located over the first portion of the semiconductor body. A second portion of the semiconductor body is located between the second isolation region and a third isolation region. The third and fourth rows of transistors are essentially the same as the transistors of the first and second rows. The third and fourth rows of transistors have the same orientation of left and right arms of their U-shaped gate electrodes as in the U-shaped gate electrodes of the transistors of the first and second rows of transistors. The end portions of the right and left arms of the U-shaped gate electrodes of the third row are located over portions of the second isolation region, and the middle portions of the right and left arms of the third row and the central portions of the third row are located over the second portion of the semiconductor body. The end portions of the right and left arms of the U-shaped gate electrodes of the fourth row are located over portions of the third isolation region, and the middle portions of the right and left arms of the fourth row and the central portions of the fourth row are located over the second portion of the semiconductor body. A center of a left arm of a U-shaped gate electrode of a transistor of the third row of transistors is located below a center of a central portion of a U-shaped gate electrode of a transistor of the second row of transistors, and a center of a right arm of a U-shaped gate electrode of a transistor of the third row of transistors is located beneath a center of a space between adjacent U-shaped gate electrodes of the second row of transistors. A second set of four rows of field effect transistors is located in a portion of the semiconductor region with each transistor of the second set of four rows having output regions of the first conductivity type separated by portions of the semiconductor region and having a U-shaped gate electrode separated from a top surface of the semiconductor region by a dielectric layer. The fourth, fifth, and sixth isolation regions extending from the top surface of the semiconductor region into same and being separated by first and second portions of the semiconductor region in which active portions of the transistors are located. The second set of four rows of transistors is essentially the same as the first set of four rows of transistors and having the same orientation relative to the fourth, fifth, and sixth isolation regions and the first and second portions of the semiconductor region as the first set of four rows has to the first, second, and third isolation regions and the first and second portions of the semiconductor body. The conductive lines selectively contact gate electrodes and output regions of the field effect transistors of the first and second set of four rows so as to facilitate the semiconductor structure serving as a plurality of latch circuits of sense amplifiers. An array of memory cells having bit lines coupled thereto and to the conductive lines which contact the latch circuits. 
     From a third aspect, the present invention is directed to a semiconductor structure. The semiconductor structure comprises a semiconductor body of a first conductivity type, a set of four rows of field effect transistors, first, second, and third isolation regions, conductive lines, and an array of memory cells. The set of four rows of field effect transistors is located in a portion of the semiconductor body with each transistor of the set of four rows having output regions of the second conductivity type separated by portions of the semiconductor body and having a U-shaped gate electrode separated from a top surface of the semiconductor body by a dielectric layer. The first, second, and third isolation regions extend from the top surface of the semiconductor body into same and being separated by first and second portions of the semiconductor body in which active portions of the transistors exist. Each U-shaped gate electrode of the four rows has right and left arms and a central portion which connects a right arm portion to a left arm portion; and each of the right and left arms having an end portion and a middle portion with the middle portion being adjacent the central portion. The end portions of the right and left arms of the U-shaped gate electrodes of the first row are located over portions of the first isolation region, and the middle portions of the right and left arms of the first row and the central portions of the first row are located over the first portion of the semiconductor body. The end portions of the right and left arms of the U-shaped gate electrodes of the second row are located over portions of the second isolation region, and the middle portions of the right and left arms of the second row and the central portions of the second row are located over the first portion of the semiconductor body. A second portion of the semiconductor body is located between the second isolation region and a third isolation region. The third and fourth rows of transistors are essentially the same as the transistors of the first and second rows. The third and fourth rows of transistors have the same orientation of left and right arms of their U-shaped gate electrodes as in the U-shaped gate electrodes of the transistors of the first and second rows of transistors. The end portions of the right and left arms of the U-shaped gate electrodes of the third row are located over portions of the second isolation region, and the middle portions of the right and left arms of the third row and the central portions of the third row are located over the second portion of the semiconductor body. The end portions of the right and left arms of the U-shaped gate electrodes of the fourth row are located over portions of the third isolation region, and the middle portions of the right and left arms of the fourth row and the central portions of the fourth row are located over the second portion of the semiconductor body. A center of a left arm of a U-shaped gate electrode of a transistor of the third row of transistors is located below a center of a central portion of a U-shaped gate electrode of a transistor of the second row of transistors, and a center of a right arm of a U-shaped gate electrode of a transistor of the third row of transistors is located beneath a center of a space between adjacent U-shaped gate electrodes of the second row of transistors. The conductive lines selectively contact gate electrodes and output regions of the field effect transistors of the first and second set of four rows so as to facilitate the semiconductor structure serving as a plurality of latch circuits of sense amplifiers. An array of memory cells having bit lines coupled thereto and to the conductive lines which contact the latch circuits. 
     The invention will be better understood from the following more detailed description in conjunction with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a schematic block diagram of a prior art memory circuit which can be used in conjunction with the present invention; 
     FIG. 2A shows a circuit diagram of a prior art sense amplifier which can be used in conjunction with the present invention; 
     FIG. 2B shows the prior art circuit of FIG. 2A in a manner so as to separate n-channel MOS and p-channel MOS transistors thereof into separate regions; 
     FIG. 3 shows a top view of a portion of a sense amplifier in accordance with the present invention; 
     FIG. 4 shows a sectional view of the portion of a sense amplifier shown in FIG. 3; 
     FIG. 5 shows a top view of offset regions of a sense amplifier along with the overlying bit lines in accordance with the present invention; 
     FIG. 6 shows a top view of a portion of a sense amplifier which includes switch transistors in accordance with the present invention; and 
     FIG. 7 shows a top view of a portion of a sense amplifier which includes switch transistors along with the overlying bit lines, enable/disable signal lines, and power or ground lines in accordance with the present invention. 
    
    
     The drawing may not be to scale. 
     DETAILED DESCRIPTION 
     FIGS. 3 and 4 show a top view of a portion  300 , and a cross-sectional view through a dashed line  4 — 4  of FIG. 3, of a portion of a sense amplifier which utilizes the principles of the present invention. FIG. 3 shows a portion of an array of insulated gate field effect transistors [also denoted as Metal-Oxide-Semiconductor (MOS) transistors] which can be used to form the latch circuits (transistors P 2 , P 3 , N 2 , and N 3  of FIG. 2A) and switching transistors (P 1  and N 1 ) of FIG.  2 A. Portion  300  comprises a semiconductor body  310  of a first conductivity type. A layer with portions  340   a  and  340   b , typically of thick silicon dioxide, has been formed on selected portions of semiconductor body  310  and forms shallow trench isolated regions. Between these portions  340   a  and  340   b  transistors are formed in semiconductor body  310 . No transistor action will take place in the portion of the semiconductor body  310  where silicon dioxide layers  340   a  and  340   b  have been formed. The silicon dioxide layer  340   a  has a vertical edge  341  (see FIG.  4 ), and the silicon dioxide layer  340   b  has a vertical edge  342  (see FIG.  4 ). A portion  345  of the semiconductor body  310  is bounded by the edges  341  and  342 . A layer  380  of a gate dielectric, typically silicon dioxide, has been formed on an upper surface  344  of portion  345  of the semiconductor body  310 . Transistor action can occur in portion  345 . Portions of the region  345  are covered by a first row of conductive gate electrodes comprising individual gate electrodes  350   a ,  350   b ,  350   c , and  350   d , and a second row of conductive gate electrodes comprising individual gate electrodes  360   a ,  360   b ,  360   c , and  360   d . These electrodes will be the gates of the transistors which are to be formed in the region  345 . Each gate electrode  350   a-d  or  360   a-d  comprises a first edge, a second edge, a left portion, and a right portion. For example, gate electrode  350   a  has a first edge  351   a , a second edge  352   a , a left portion  353   a , and a right portion  354   a . Gate electrode  360   a  has a first edge  361   a , a second edge  362   a , a left portion  363   a , and a right portion  364   a . The portions of region  345  which are not covered by gate electrodes  350   a-d  or  360   a-d  have had formed in them regions of a second, opposite, conductivity type, to form common output region  320  and discrete output regions  355   a-d  and  365   a-d . Output region  355   d , for example, is adjacent to gate electrode  350   d.    
     The common region  320  and discrete regions  355   a-d  and  365   a-d  are designated as output regions rather than using the more common source and drain nomenclature since the designation of drain or source is a function of the direction of current flow through a field effect transistor, and the source and drain designation reverses if the current flow reverses. In the usage, described herein below, of the transistors containing gate electrodes  350   a-d  and  360   a-d  some of the transistors may have current flowing from one of the discrete output regions  355   a-d  or  365   a-d  into the common output region  320 , and others of the transistors may have current flowing from the common output region  320  into one or more of the discrete output regions  355   a-d  or  365   a-d.    
     The gate electrodes  350   a-d  and  360   a-d  which comprise the first and second rows, respectively, of gate electrodes, are unique in several ways. For example, the gate electrode  350   a  is of a U-shape. An end  351   a  of gate electrode  350   a  terminates on the silicon dioxide region  340   a . An output region  355   a  is defined by a portion of an edge  352   a  of the gate electrode  350   a  and a portion of the edge  341  of the silicon dioxide region  340 . The gate electrodes  350   a-d  and  360   a-d  are further unique in that the first row of gate electrodes  350   a-d  are laterally displaced with respect to the second row of gate electrodes  360   a-d  so that, for example, the left arm  363   a  of gate  360   a  is coincident with the right arm  354   a  of gate electrode  350   a  (see FIG.  3 ), and the left arm  353   d  of gate electrode  350   d  is coincident with the right arm  364   c  of gate electrode  360   c  (see FIG.  3 ). 
     FIG. 5 shows a top view of a portion of a semiconductor structure  400  comprising two sets of the features of the portion of a sense amplifier  300  shown in FIG.  3 . Features of FIG. 5 which have a function equivalent to similar features in FIGS. 3 and 4 have a reference number which is 100 greater than the reference number of the similar feature in FIGS. 3 and 4. The two sets of a portion  300  of a sense amplifier will be used to form transistors of a single type, n-channel MOS transistors or p-channel MOS transistors. Thus we are only implementing in FIG. 5 either the p-channel MOS transistors, P 2  and P 3  shown in FIGS. 2A and 2B, of the latch circuit, or the n-channel MOS transistors, N 2  and N 3  shown on FIGS. 2A and 2B. In order to form the complete CMOS latch circuit as shown in FIGS. 2A and 2B a second, similar, portion of the sense amplifier as shown in FIG. 5 must be implemented but with the opposite type of transistor. If it is desired to fabricate a CMOS latch circuit as shown in FIGS. 2A and 2B, and the transistors formed in FIG. 5 are, for example, p-channel MOS transistors, then a second portion must also be implemented, identical to the first portion except that the transistors must be n-channel MOS transistors, and vice versa. 
     Three regions of silicon dioxide, comprising regions  440   a ,  440   b , and  440   c , are shown. Lying between these three regions of silicon dioxide  440   a ,  440   b , and  440   c  are two regions  445  and  446  of the semiconductor body where transistors may be formed. First and second rows of gate electrodes, comprising gate electrodes  450   a-d  and  460   a-d  have been formed in region  445 , and third and fourth rows of gate electrodes, comprising gate electrodes  470   a-d  and  480   a-d , have been formed in region  446 . The gate electrodes  470   a-d  and  480   a-d  are further laterally displaced from the gate electrodes  450   a-d  and  460   a-d  so that, for example, the left arm  473   a  of gate electrode  470   d  is coincident with the center of gate  460   a , and the right arm  474   a  of a gate electrode  470   a  is coincident with the center of a gate  450   b . The gate electrodes  480   a-d  have the same lateral relationship with respect to gate electrodes  470   a-d  as do gate electrodes  460   a-d  with respect to gate electrodes  450   a-d , and gate electrodes  460   a-d  have the same lateral relationship with respect to gate electrodes  450   a-d  as gate electrodes  360   a-d  have to  350   a-d.    
     Also shown in schematic form in FIG. 5 are pairs of bit lines comprising Data Bit Lines and Reference Bit Lines. A Data Bit Line  491   a  of bit line pair  490   a  is shown making contact  456   c  to gate electrode  450   c  and contact  477   b  to an output region of a transistor formed by gate electrode  470   b . Reference Bit Line  492   a  is shown making contact to an output region of a transistor formed by gate electrode  450   c  and to a gate electrode  470   b . The transistors which include the gate electrodes  450   c  and  470   b  are two of the transistors forming a latch circuit, for example, p-channel MOS transistors P 2  and P 3  of FIG. 2B, connected to the bit line pair  490   a . Similarly, Data Bit Line  491   b  of a bit line pair  490   b  is shown making contact to gate electrode  460   c  and to an output region of a transistor containing gate electrode  480   b . Reference Bit Line  492   b  is shown making contact to an output region of the transistor formed by gate electrode  460   c  and to gate electrode  480   b . The transistors containing the gate electrodes  460   c  and  480   b  are two of the transistors connected to the bit line pair  490   b . Because of the manner in which the gate electrodes  450   a-d ,  460   a-d ,  470   a-d  and  480   a-d  have been laterally offset with respect to one another, the bit lines  491   a ,  492   a ,  491   b , and  492   b  can be fabricated on a single level of conductor, and with no lateral displacements or protuberances required in order to be able to contact the individual gates and output regions of the latch transistors. This means that each of the bit lines  491   a ,  492   a ,  491   b , and  492   b  is essentially a straight rectangular conductor of minimum width. This reduces the capacitive loading of the bit lines  491   a ,  492   a ,  491   b , and  492   b.    
     Additional pairs of bit lines may be added to form an array of bit lines which mate with the rows of transistors  450   a-d ,  460   a-d ,  470   a-d , and  480   a-d , until all the bit line pairs emanating from the memory cell arrays have been mated to the appropriate latch transistors of a sense amplifier. 
     The portion of a sense amplifier shown schematically in FIG. 5 has achieved a width equal to the width of one bit line pair, or 2P. This sense amplifier layout achieves the goal of being equivalent in size to the smallest memory cell arrays. 
     FIG. 6 is a top view of a portion of a semiconductor structure  500  showing the layout of a portion of an array of transistors, similar to that shown in FIG. 3, in which a portion of the transistors have been dedicated to the switch transistor function of transistors N 1  or P 1  shown in FIGS. 2A and 2B. Features of FIG. 6 which have a function equivalent to similar features in FIGS. 3 and 4 have a reference number which is 200 greater than the reference number of the similar feature in FIGS. 3 and  4 . In FIG. 6 gate electrodes  550   a ,  550   c ,  550   d ,  560   a ,  560   c , and  560   d  remain similar to their counterparts in FIG. 3, i.e.,  350   a ,  350   c ,  350   d ,  360   a ,  360   c , and  360   d , respectively. Gate electrodes  550   b  and  560   b  have been connected together by a gate electrode conductor  559  and function as a gate electrode of a switch transistor. Output regions  555   b  and  565   b  are connected together (not shown) such that two separate transistors, i.e., one in the top row and one in the bottom row act as a single transistor. Conductor  559  separates a common output region (see common output region  320  in FIGS. 3 and 4) of the transistors  550   a-d  and  560   a-d  into two common output  520   a  and  520   b . If an appropriate potential is applied to the gate conductor comprising gate conductors  550   b ,  560   b , and  559  to invert the semiconductor surface underneath these gate conductors, then the discrete output regions  555   b  and  565   b  will be connected through an inversion layer created underneath the gate conductors  550   b ,  560   b , and  559  to the common output regions  520   a  and  520   b . Thus, if the gate conductors  550   b ,  560   b , and  559  are connected to an enable/disable signal, and the regions  555   b  and  565   b  of the transistors formed by gate electrodes  550   b  and  560   b  are connected to power, the transistors formed by gate electrodes  550   b  and  560   b  can function as the switch transistors P 1 , or if the regions  555   b  and  565   b  of the transistors formed by gate electrodes  550   b ,  560   b , and  559  are connected to ground, the transistors formed by gate electrodes  550   b  and  560   b  can function as the switch transistors N 1  of FIGS. 2A and  2 B. The coupling together of the two transistors having gate electrodes  350   b  and  360   b  provides more current drive capability than if a single transistor having gate electrode  350 b were used to accomplish the function of the switch transistor N 1  or P 1  in FIGS. 2A and 2B. This is particularly useful since the layout provided would typically not use the transistor having gate electrode  560   b  unless it is specifically coupled to the transistor having gate electrode  550   b.    
     FIG. 7 shows a top view of a portion of a semiconductor structure  600  comprising two sets of the features of the portion of a sense amplifier  500  shown in FIG.  6 . Features of FIG. 7 which have a function equivalent to similar features in FIGS. 3 and 4, FIG. 5, or FIG. 6 have a reference number which is 300, 200, or 100, respectively, greater than the reference number of the similar feature in FIGS. 3 and 4, FIG. 5, or FIG.  6 . Two sets of a portion  500  of a sense amplifier will be used to form transistors of a single type, n-channel MOS transistors or p-channel MOS transistors. Thus we are only implementing in FIG. 7 either the p-channel MOS transistors, P 1 , P 2 , and P 3  shown in FIGS. 2A and 2B, of the sense amplifier, or the n-channel MOS transistors, N 1 , N 2 , and N 3  shown on FIGS. 2A and 2B, of the sense amplifier. In order to form the complete CMOS sense amplifier as shown in FIGS. 2A and 2B, a second, similar, portion of the sense amplifier shown in FIG. 7 must be implemented, but with the opposite conductivity type transistor. If it is desired to fabricate a CMOS sense amplifier as shown in FIGS. 2A and 2B, and the transistors formed in FIG. 7 are, for example, p-channel MOS transistors, then a second portion must also be implemented, identical to the first portion except that the transistors must be n-channel MOS transistors, and vice versa. 
     Three regions of silicon dioxide, comprising regions  640   a ,  640   b , and  640   c , are shown. Lying between these three regions of silicon dioxide  640   a ,  640   b , and  640   c  are two regions  645  and  646  of the semiconductor body where transistors may be formed. First and second rows of gate electrodes, comprising gate electrodes  650   a-d  and  660   a-d  have been formed in region  645 , and third and fourth rows of gate electrodes, comprising gate electrodes  670   a-d  and  680   a-d , have been formed in region  646 . The gate electrodes  670   a-d  and  680   a-d  have been further laterally displaced from the gate electrodes  650   a-d  and  660   a-d  so that, for example, the left arm  673   b  of a gate electrode  670   b  is coincident with the center (or middle portion) of a gate  660   a  and the right arm  674   a  of a gate electrode  670   a  is coincident with the center (or middle portion) of a gate  650   a . The gate electrodes  680   a-d  have the same lateral relationship with respect to gate electrodes  670   a-d  as do gate electrodes  660   a-d  with respect to gate electrodes  650   a-d , and gate electrodes  660   a-d  have the same lateral relationship with respect to gate electrodes  650   a-d  as gate electrodes  360   a-d  have to  350   a-d.    
     A conductor  640  which is connected to the switch enable/disable signal (not shown) contacts gate electrodes  650   b  and  660   b  at contacts  641   a  and  641   b . The conductor  640  also contacts gate electrodes  670   b  and  680   b  at contacts  641   c  and  641   d . The conductor  640  may be connected to a second level metal conductor (not shown) to facilitate the distribution of the switch enable/disable signal. A conductor  645   a , which is connected to either the power source or ground, contacts the output region of the transistor formed by gate electrode  650   b  at contact  646   a . A conductor  645   b , which is also connected to the same reference potential as the conductor  645   a , either the power source or ground, contacts the output region of transistor  680   b  at contact  646   b . Conductors  646   a  and  646   b  may be connected to the power source or ground through a second level metal conductor (not shown) to facilitate the distribution of power and ground on the circuit. Although not shown in FIG. 7, the output regions of transistors  660   b  and  670   b  may also be contacted by conductors which are connected to the appropriate reference potential, either the power source or ground. 
     Four pairs of bit lines,  690   a ,  690   b ,  690   c , and  690   d , are shown in FIG.  7 . Each pair of bit lines consists of a Data Bit Line and a Reference Bit Line, e.g.,  691   a  and  692   a , respectively. The pairs of bit lines  690   a-d  make contact with the appropriate gate electrode and output regions to form the latch circuits of the sense amplifiers, as described above and shown in FIG.  5 . For example, Data Bit Line  691 a makes contact with a gate electrode  650   a  at a contact  656   a , and makes contact with an output region of the transistor formed by a gate electrode  670   a  at a contact  677   a , and Reference Bit Line  692   a  makes contact with an output region of the transistor formed by a gate electrode  650   a  at a contact  657   a , and makes contact with a gate electrode  670   a  at a contact  676   a.    
     The use, for example, of one of the transistors  650   b  of the array of transistors  650   a-d  to perform the function of the switch transistor N 1  or P 1  of FIGS. 2A and 2B increases the average pitch of the sense amplifiers formed in the arrangement depicted in FIG.  7 . For this reason, a minimal number of transistors, as determined by the performance of the circuit, should be dedicated to the switch transistor function. To obtain the absolute minimum pitch of the sense amplifiers, the use of the arrangement of FIG. 5 is preferred, with the switch transistors being fabricated in another portion of the circuit. For example, the switch transistors could be fabricated in the regions  440   a ,  440   b , or  440   c  of FIG. 5, and appropriate connection made to the output regions of the transistors of FIG.  5 . 
     It is to be understood that the specific embodiments described herein are illustrative of the general principles of the invention and that various modifications may be devised in the apparatus without departing from the spirit and scope of the present invention. For example, while the present invention has been described within the context of a memory circuit fabricated using a CMOS technology and embodying both p-channel and n-channel MOS transistors, the principles of the invention could also be applied to a memory circuit employing a single type of transistor, either n-channel or p-channel MOS transistors. Further, while one method of laterally offsetting the rows of transistors has been describe in the present embodiments, other structural arrangements of laterally offsetting the transistors, or even no lateral offset of the transistors, might be employed to facilitate the desired layout of the pairs of bit lines. Furthermore, while one structural arrangement of interconnecting the transistors to perform the switch transistor function has been described, other methods may be devised to achieve this function. Additionally, while the gates of the transistors have been shown schematically with the width of the gate conductor similar in size to the space between different gate conductors and between portions of the same conductor, it is to be understood that these three feature sizes may be varied to optimize both the size and the manufacturing yield of the circuit. Specifically, the space between edges of a gate conductor in which a contact to an output region is to be made may be different than the space between edges of a gate conductor in which no such contact is made.