Abstract:
An integrated circuit including a field effect transistor (FET) is provided in which the gate conducter has an even number of fingers disposed between alternating source and drain regions of a substrate. The fingers are disposed in a pattern over an area of the substrate having a length in a horizontal direction, the area equaling the length multiplied by a width in a vertical direction that is occupied by an odd number of the fingers.

Description:
BACKGROUND OF INVENTION 
     The present invention relates to semiconductor integrated circuits and more specifically to the layout of semiconductor devices, especially for a semiconductor memory. 
     Operational performance and conservation of integrated circuit “chip” area are considerable in the design of circuits. It is desirable to reduce chip area because circuit designs that occupy smaller chip areas generally offer higher interconnect performance and speed. Circuit designs that occupy large chip areas typically have longer interconnect wiring which degrades performance. Longer wires have higher parasitic capacitance and resistance, either of which increases delay. 
     Because of their high integration density, dynamic random access memories are a favored way of storing large amounts of information for ready access within a computing system. A typical dynamic random access memory (DRAM)  10  consists of a data storage array  12 , a bit line access system  14 , a word line select system  16 , control logic  18 , and an external interface  20 , as shown in FIG.  1 . 
     FIG. 2 provides a detailed illustration of a DRAM  110  corresponding to DRAM  10  shown in FIG.  1 . As shown in FIG. 2, data storage array  112  corresponds to data storage array  12  shown in FIG.  1  and block  116  corresponds to wordline select system  16  shown in FIG.  1 . The bitline (data) access system  14 , control logic  18  and external interface  20  are not shown in FIG.  2 . 
     As used herein, the terms “horizontal” and “horizontally”, “vertical” and “vertically” describe directions generally parallel to the main surface of a semiconductor substrate, horizontal being the direction in which wordlines extend across the substrate, and vertical being the direction in which bitlines extend across the substrate. As shown in FIG. 2, the bitlines  100 ,  102  and  104  run vertically in columns across the data storage array  112 , traversing the wordlines  120 ,  122  and  124  which run horizontally in rows across the data storage array  112 . Data storage cells (e.g. Data Cell ( 0 , 0 ) ) are provided at the intersections between the bitlines and the wordlines. The wordlines of the data storage array  112  have a pitch  130 . Pitch is defined as the dimension occupied by a recurring feature and its spacing to the next recurring feature in a line of such features. 
     It is desirable that the pitch  130  of wordlines in the data storage array  112  be kept as small as possible for the following reasons. First, the data storage array  112  should store as much information as possible within a given area of an integrated circuit (hereinafter, a “chip”). Accordingly, data storage cells and the wordlines and bitlines that provide access to the data stored therein should be packed as closely together as possible. 
     Second, the wordline pitch  130  should be made small because the length of the bitlines in the data storage array  112  is directly controlled by the wordline pitch. The length of the bitlines spanning a data storage array  112  should be made as short as possible in order to best transfer signals on each bitline, e.g. bitline  100 , to and from a data cell (e.g. Data Cell ( 0 , 0 )  106 ) of the data storage array  112 . Parasitic bitline capacitance, which affects both the speed and the validity of signals transferred on a bitline, increases with the length of the bitline. Keeping bitlines short reduces the parasitic capacitance and improves the quality of the bitline signal. 
     As further shown in FIG. 2, the word lines in the data storage array  112  are driven by a word line select system  116 . Each wordline is activated by a corresponding driver, upon the driver receiving an enabling decoded input from wordline select decoder  117  and decoded power supply input for the particular bank. For example, wordline  120  is activated by a driver  150  when enabling decoded input  119  is received from wordline select decoder  117  together with a decoded power supply input BK 2  for a bank  2  of the data storage array  112 . 
     FIG. 3 is a diagram illustrating the timing of operations within the data storage array  112 . As illustrated in FIG. 3, an operation to read a data bit from or write a data bit to a data cell is provided in three phases. In a first phase,  300 , bitlines are precharged and equalized by signal EQ to a desirable voltage. Thereafter, at the start of the next phase  310 , EQ is lowered and the wordline is activated, as indicated by the rising signal WL. During this phase, the activated wordline turns on transistors of data cells, which results in the transfer of stored charge from storage capacitors of the data cells to bitlines. The bitlines, in turn, transfer the charge retrieved from data cells as data bit signals to sense amplifiers. 
     At the start of the next phase  320 , the transfer of the data bit signal from the data cell to sense amplifier is about complete. During this phase  320 , which commences with the rising SET signal, each sense amplifier amplifies a data bit signal for the purpose of outputting the data bit from the DRAM, and/or for restoring the data bit to the data cell of the data storage array  112 . 
     During phase  320 , the data bits accessed from data cells by the activated wordline are written back, i.e. restored to the data cells. The data access cycle is now completed. Accordingly, the wordline is now deactivated, as marked by the falling signal WL, and a precharge phase  330  begins for a new data access cycle. 
     The cycle time for accessing the data stored in a data cell is the sum of the length of phases  300 ,  310  and  320 . As apparent from the above description, two factors contribute heavily to the cycle time. 
     The first is the length of time, i.e., the duration of the phase  310 , that is required to transfer data bit signals from storage capacitors of data cells to sense amplifiers. The duration of this phase  310  is influenced heavily by the amount of parasitic capacitance of the bitline. The time delay for a data bit signal to be transferred from a data cell to a sense amplifier is measured in terms of an “RC” delay determined by the resistance “R” of the bitline multiplied by the capacitance “C” of the bitline. The resistance and parasitic capacitance of a bitline are directly proportional to the length of the bitline. Accordingly, the length of bitlines must be kept as small as practicable in order to provide desirably short cycle time. 
     In addition to determining the RC delay, the amount of the bitline capacitance also affects the maximum voltage which appears on the bitline at the sense amplifier during the phase  310  in which charge is transferred from data cell to sense amplifier. The greater the bitline capacitance, the smaller the voltage appears at the sense amplifier. Thus, high bitline capacitance increases the chance that the data bit signal is amplified incorrectly, for example, that a signal from a data cell storing a value of “1” is amplified as a “0” or vice versa. To counteract signal loss due to increased bitline capacitance, the voltage stored in the data cell must be increased. Such increase typically requires increasing the duration of phase  320  in order to lengthen the write-back time for storing a data bit signal from sense amplifier to data cell. This also increases cycle time. 
     A second factor contributing to the length of the cycle time is the transition time of the wordline WL. As shown in FIG. 3, at the beginning of the signal development phase  310 , the wordline WL rises from an deactivated level to an activated level over a rising transition time  340 . The wordline remains at the activated level throughout phases  310  and  320  and then falls back to the deactivated level over a falling transition time  350 . These transition times represent wasted time because the voltage level of the wordline is then intermediate between activated and deactivated levels and therefore cannot be relied upon for operations. Thus, the rising and falling transition times of the wordline represent wasted time that contributes directly to the overall cycle time of the memory. 
     Accordingly, it would be desirable to reduce the transition times of the wordline in order to shorten the memory access cycle time. However, the wordlines themselves have parasitic capacitive loads  140  (FIG. 2) that must be driven in order for the wordline to transition between inactive and active levels. For a given amount of capacitance, the speed at which the wordline transitions is directly related to the amount of current that the driver circuit for that wordline can source or sink. Therefore, for fast switching, it is desirable that the wordline driver circuit (hereinafter, “wordline driver”) be able to source and sink a large amount of current. 
     The amount of drive current output by a wordline driver is determined by the width to length ratio of the FET channel that makes up the wordline driver. The width of the FET channel corresponds to the length of the gate conductor of the FET, and the length of the FET channel is determined by the width of the gate conductor. Since the length of the FET channel is already fixed at a desirably small dimension by the particular technology employed in a given generation, width is the only parameter capable of being changed to increase the drive current. Because the wordline drivers already occupy a given area of the chip outside the data storage array  112 , it would be desirable to increase the width of the FET channel without increasing the amount of chip area occupied by each driver. 
     A typical layout of a word line driver FET  400  is shown in FIG. 4. A wordline driver typically includes both a p-type FET (PFET) and an n-type FET. In the following description, reference will be made to both PFET and NFET simply as a “FET,” with the understanding that the description applies to both transistor types of the driver. Only one such FET  400  is illustrated in FIG.  4 . The FET  400  includes a gate conductor  410  operated by decoded input from a wordline select decoder ( 117  of FIG. 2) and a source region  420  and a drain region  430  on each side of the gate conductor  410 . A plurality of contacts  422  are provided to source region  420  and a plurality of contacts  424  are provided to drain region  430 . When the FET  400  is an NFET, the source region  420  is connected to ground and the drain region  430  provides the output current of the FET  400 . Otherwise, when the FET  400  is a PFET, the source region  420  is connected to a wordline power supply, for example, a boosted wordline driver power supply, which may be provided thereto as a decoded bank power supply voltage input. In such case, the drain region  430  provides the output current of the FET  400 . 
     The particular layout of the wordline driver FET  400  in FIG. 4 is not optimized to conserve chip area. The source region  420  and the drain region  430  of each FET  400  lie along respective edges  440  and  450  of the FET  400 . Because of that, when FETs  400  are placed next to each other in a layout, neither the source region  420  nor the drain region  430  of the FETs  500  can be shared, as the sources of all FETs is maintained at a fixed potential while the drains provide the drive current. Moreover, the juxtaposition of the source region  420  of a first FET  400  to the drain region  430  of a second FET  400  requires that there be an isolating gap in the semiconductor area between the two FETs, thus wasting valuable chip area. 
     As shown in FIG. 5, if space is available for the wordline driver within the pitch of wordlines of the data storage array  112 , the FET  500  can be fabricated with a plurality of fingers to increase the drive current, as represented by a plurality of gate conductors  510 ,  512 . 
     In a multiple-fingered FET  500 , the width of the transistor channel W channel  is increased to an amount equal to: W channel =N finger  *I diffusion  where Nfinger equals the number of fingers of the transistor and I diffusion  equals the current output from each source region or each drain region of the transistor. 
     The FET  500  shown in FIG. 5 has two fingers in which a central source region  514  is shared between two FETs having gate conductors  510  and  512 . Thus, the channel width is increased to two times the amount of I diffusion . In this arrangement, the FET  500  has a pair of drain regions  516  and  518  lying along the outside edges. Because of that, FETs  500  that are placed adjacent to each other in a layout can share drain regions. This, in turn, helps maximize the utilization of chip area along a direction of the width  520  of the semiconductor area for each FET  500 . 
     SUMMARY OF INVENTION 
     According to an aspect of the invention, an integrated circuit including a field effect transistor (FET) is provided in which the gate conductor has an even number of fingers disposed between alternating source and drain regions of a substrate. The fingers are disposed in a pattern over an area of the substrate having a length in a horizontal direction, the area equaling the length multiplied by a width in a vertical direction that is occupied by an odd number of the fingers. 
     According to another aspect of the invention, an integrated circuit is provided which includes a plurality of wordline drivers. Each wordline driver includes a first field effect transistor (FET) that is conductively connected to a wordline of a data storage array for driving a voltage on the wordline. The first FET is arranged in a column of FETs including the first FET and a second FET disposed adjacent to the first FET, such that a source region of the first FET is shared with a source region of the second FET. The first FET includes a gate conductor having an even number of fingers disposed between alternating source and drain regions of a substrate, wherein the fingers are disposed in an L-shaped pattern over an area of the substrate having a length in a horizontal direction, in which the area further equals that length multiplied by a width in a vertical direction that is occupied by an odd number of fingers. 
     According to another aspect of the invention, a method of is provided for making a field effect transistor (FET) of an integrated circuit. The method includes forming a gate conductor having an even number of fingers, the fingers being disposed in a pattern over an area of a substrate having a length in a horizontal direction, wherein the area equals that length multiplied by a width in a vertical direction that is occupied by an odd number of fingers. The method further includes forming a plurality of source regions and drain regions in the substrate alternating with the fingers. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a functional block diagram illustrating the organization of a dynamic random access memory (DRAM) according to the prior art. 
     FIG. 2 is a block and schematic diagram illustrating the organization and interconnection of circuit elements within a DRAM according to the prior art. 
     FIG. 3 is a diagram illustrating the timing of operations in a DRAM according to the prior art. 
     FIG. 4 is a plan view illustrating the structure of a field effect transistor (FET) of a wordline driver according to the prior art. 
     FIG. 5 is a plan view illustrating the structure of a two-finger field effect transistor (FET) of a wordline driver according to the prior art. 
     FIG. 6 is a plan view illustrating the structure of a three finger field effect transistor (FET) of a wordline driver which is background to the invention but which is not admitted to be prior art. 
     FIG. 7 is a block and schematic diagram illustrating placement and interconnection of wordline drivers relative to wordlines in a DRAM according to an embodiment of the invention. 
     FIG. 8 is a plan view illustrating size and placement of gate conductor fingers of a wordline driver FET in relation to the wordlines in a DRAM according to an embodiment of the invention. 
     FIG. 9 is a plan view illustrating the structure of a three finger folded wordline driver FET having open gate conductor patterns according to an embodiment of the invention. 
     FIG. 10 is a plan view illustrating the structure of a three finger folded wordline driver FET having closed gate conductor patterns according to another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     According to embodiments of the invention described herein, a field effect transistor (FET) is provided for a wordline driver which takes advantage of available chip area to increase the effective width of the FET. In such manner, greater drive current can be obtained in a FET formed in the same chip area. 
     Circumstances exist in which available chip area supports a wordline driver FET having only an odd number of gate conductor fingers. In order to maximize the output current of the wordline driver FET, it is desirable to fabricate wordline driver FETs having as many fingers as can be fitted within the available vertical space allotted thereto in the DRAM. FIG. 6 illustrates a three-fingered FET  600 , which is background to the invention but which is not admitted to be prior art. As shown in FIG. 6, the three-fingered FET  600  is provided over an active area  650  having a width  620  in a vertical direction (the direction transverse to the wordlines) and a length  640  in a horizontal direction (the direction parallel to the wordlines). The FET  600  has three gate conductor fingers  610 ,  612 , and  614 , and corresponding source regions  620 ,  622  and drain regions  630 ,  632 . 
     Assume that the horizontal length  640  of the active area  650  of the FET  600  is the same as that of the FET  500 . Because the FET  600  has more fingers than the prior art FET  500 , the FET  600  has a larger transistor channel width, and therefore, a higher output drive current, for the same horizontal length of the active area. However, FET  600  has the same disadvantage as FET  400  in that source regions or drain regions of FETs in a layout adjacent to each other cannot be shared, and therefore, an area-wasting isolation gap must be provided between such FETs. Moreover, especially in newer transistor technologies, an isolation gap may create a physical stress on the silicon and reduce the current drive of the FET. Hence, it is more desirable than ever to maintain a continuous strip of active area without any isolation gaps. 
     Thus, fabrication of a wordline driver FET having an odd number of gate conductor fingers is problematic because of the inability of adjacent FETs in such arrangement to share transistor regions (e.g. source regions). Such problem is resolved in the embodiments of the present invention by providing interleaved L-shaped wordline driver FETs having an even number of gate conductor fingers which are provided in an L-shape. 
     According to the embodiments of the invention described herein, a FET is provided having an even number of gate conductor fingers disposed between alternating source and drain regions of a single-crystal semiconductor region of a substrate. The even number of gate conductor fingers are disposed at a pitch corresponding to an odd number of gate conductor fingers occupying the vertical space allotted to the FET. In such manner, source regions of the FET are able to be shared between neighboring ones of the FETs. The even number is obtained by “folding” the layout of the FET into an L-shape such that a first horizontal portion of the FET has a first even number of fingers, for example two, and a second horizontal portion of the FET has a different even number of fingers, for example four. Two such adjacent L-shaped FETs are interleaved such that the FETs each effectively have a pitch of three, without there being an isolation gap between the two FETs. 
     FIG. 7 illustrates a preferred interconnection of wordline drivers  720 - 726  to wordlines WL 0 -WL 3  of a data storage array and of wordline drivers  730 - 736  to wordlines WL 4 -WL 7  of a data storage array. Each set of four wordline drivers, e.g.  720 - 726 , are horizontally stacked to the side of the data storage array  712 . The drivers thus occupy area of the chip extending outward from the edge of the data storage array  712 . The wordlines of the data storage array  712  have fixed pitch, which is desirably small for the reasons discussed above. In order to provide consistent operation and to avoid possible differences in the timing of wordline operation from one wordline to another, the capacitive load on each word line is made uniform from one wordline to another. To achieve this, the pitch of the wordline drivers, e.g. the pitch of drivers  720 - 726 , is provided in a way to match exactly the pitch of wordlines in the data storage array  712 , e.g., the pitch of wordlines WL 0 -WL 3 . In such manner, physical interconnections between the wordline drivers and the wordlines are provided at uniform pitch for the whole data storage array  712 . This also poses constraints on the physical layout of the field effect transistors (FETs) that make up the driver, as well as the wiring of the driver. 
     In the embodiments of the invention described herein, the drive current output by wordline drivers is increased by increasing the width of the channels of field effect transistors (FETs) used in the wordline drivers. Width, as a parameter, is specifically increased because the drive current output by the wordline driver can only be increased by increasing the width to length ratio of the FET channel, and the length of the FET channel is already fixed by transistor processing technology. Further, because the pitch of wordlines WL 0 , etc. in the data storage array  712  provides sufficient space to increase the number of fingers of the wordline driver FET in a direction of the wordline pitch, as described below, the width of the transistor channel of the FET can be increased without requiring an increase in the amount of chip area occupied by each FET. This is described as follows. 
     FIG. 8 illustrates the placement of wordlines  810  within a data storage array  812  of a dynamic random access memory (DRAM), in relation to gate conductor fingers  820  of a FET  814  of a wordline driver provided according to an embodiment of the invention. This example assumes an arrangement as shown in FIG. 7 in which four wordline drivers are horizontally stacked. Each FET  814  of each of the four drivers has a width  830  in the vertical direction equivalent to the width  830  of the data storage array  812  over which four wordlines  810  are provided. Because of the different technologies involved in fabricating transistors of the data storage array  812  and those of the FET  814 , the wordlines  810  are formed at a tighter pitch than the gate conductor fingers  820  of the FET  814 . As shown in FIG. 8, the pitch of the word lines supports a pitch of three for the gate conductor fingers of the FET  814 . 
     This is illustrated in FIG. 8 as follows. Four wordlines  810  are provided within a given width  830  of the data storage array  812 . The four wordlines  810  each has a given width X LA  and spacing X SA  between wordlines  810 . In addition, a contact  811  is provided to the data storage array  812  having width X CA , that contact providing an interconnection of one of the wordlines  810  to a FET  814 . The contact is spaced from the wordline  810  by a spacing X CSA . Therefore, within the vertical dimension  830 , wordlines, a contact and associated spacings are provided having a combined width of 4X LA +3X SA+ 2X CSA +X CA . 
     On the other hand, in the FET  814 , the minimum width of each gate conductor finger is X LD , the minimum width of each contact  821  is X CD , and the minimum spacing from gate conductor finger to contact is X CSD . As shown in FIG. 8, three such gate conductor fingers  820  can be accommodated within the allotted vertical dimension  830 . The combined width of the gate conductor fingers, contacts and associated spacings within width  830  is 3X LD +6X CSD +3X CD . 
     Therefore, in an arrangement in which four wordline drivers are horizontally stacked, each FET  814  can be provided having three gate conductor fingers  820  whenever the following relation is satisfied: 3X LD +6X CSD +3X CD  (FET)&lt;4X LA +3X SA +2X CSA +X CA  (Array). 
     However, as noted above with respect to FIG. 6, there is a problem implementing an. FET  600  having three parallel gate conductor fingers  610 ,  612 ,  614 . The source region  620  and the drain region  632  on the outside edges of the FET  600  cannot be shared, therefor requiring an isolating structure to be formed between adjacent FETs  600 . 
     This problem is resolved according to embodiments of the invention, as will be described relative to FIGS. 9 and 10, as follows. As illustrated in FIG. 9, in an embodiment of the invention, the FETs  900 ,  910  of two adjacent wordline drivers are interleaved and are each formed in the shape of an L, each FET having width effectively equal to that provided by three parallel gate conductors. In these embodiments, because the FET now has the effective width of three gate conductor fingers, it is estimated that the drive current output from a FET  900  is increased by 50% above that output by a two-fingered FET  500  such as that shown and described above with respect to FIG.  5 . 
     As shown in FIG. 9, two interleaved L-shaped FETs  900  and  910  are provided within an active area  950  having a width  930  in a vertical direction, which preferably corresponds to the vertical width occupied by eight adjacent wordlines of a data storage array  712  (FIG.  7 ). An FET  910  is rotated  180  degrees relative to the other FET  900 . As shown in FIG. 9, each FET  900 ,  910  has two fingers  912  which run the length  940  in the horizontal direction of the allotted active area  950 . Each FET  900 ,  910  also has two additional parallel fingers  914  that run only over a portion of the horizontal length of the active area  950 . 
     In the arrangement shown in FIG. 9, source regions  920  are provided both in the interior of the active area  950  and along the outer edges  916 ,  918  of the vertical width  930 . Because the transistor regions provided at the outer edges  916 ,  918  of the active area  950  are both the same type, i.e. they are source regions  920 , they can be shared with other FETs (not shown) of other wordline drivers that are located adjacent to each edge  916  and  918 . In such manner, efficient use can be made of the active area  950  because there is no need for an isolating gap between the active area  950  and neighboring active areas (not shown) for other FETs. In addition to the source regions  920 , drain regions  922  are provided in the active area  950  on opposite sides of each gate conductor finger  912  from each source region  920 . A set of contacts  924  to the drain regions  922  of each of the FETs  900 ,  910  provide the current drive output from the FETs. 
     In another embodiment, as illustrated in FIG. 10, the FETs  1000 ,  1010  of two adjacent wordline drivers have gate conductor fingers  1012  connected by vertical connections  1002  to provide interleaved ring-shaped gate conductors of the FETs. Each FET  1000 ,  1010  is further formed in the shape of an L, each FET having width effectively equal to that provided by three parallel gate conductors. In this embodiment, because the FET  1000 ,  1010  now has the effective width of three gate conductor fingers, it is estimated that the drive current output from a FET  1000  is increased by 50% above that output by a two-fingered FET  500  such as that shown and described above with respect to FIG.  5 . 
     As shown in FIG. 10, two interleaved L-shaped FETs  1000  and  1010  are provided within an active area  1050  having a width  1030  in a vertical direction, which preferably corresponds to the vertical width occupied by eight adjacent wordlines of a data storage array  712  (FIG.  7 ). 
     As described above relative to FIG. 9, FET  1010  is rotated 180 degrees relative to the other FET  1000 . As further shown in FIG. 10, each FET  1000 ,  1010  has two fingers  1012  which run the length  1040  in the horizontal direction of the allotted active area  1050 . Each FET  1000 ,  1010  also has two additional parallel fingers  1014  that run only over a portion of the horizontal length  1040  of the active area  1050 . 
     In the arrangement shown in FIG. 10, source regions  1020  are provided both in the interior of the active area  1050  and along the outer edges  1016 ,  1018  of the vertical width  1030 . Because the transistor regions provided at the outer edges  1016 ,  1018  of the active area  1050  are both the same type, i.e. they are source regions  1020 , they can be shared with other FETs (not shown) of other wordline drivers that are located adjacent to each edge  1016  and  1018 . In such manner, efficient use can be made of the active area  1050  because there is no need for an isolating gap between the active area  1050  and neighboring active areas (not shown) for other FETs. In addition to the source regions  1020 , drain regions  1022  are provided in the active area  1050  on opposite sides of each gate conductor finger  1012  from each source region  1020 . A set of contacts  1024  to the drain regions  1022  of each of the FETs  1000 ,  1010  provide the current drive output from the FETs. 
     Various modifications and enhancements of the invention can be made without departing from the scope of the invention. In another embodiment, a greater number of FETs, e.g. three FETs, each having an L-shaped structure as shown in FIGS. 9 or  10 , can be fitted into a given active area having a vertical width. The vertical width of the active area, in turn, corresponds to a different number of wordlines, for example, six wordlines or eight wordlines of the data storage array  712 . In such manner, the L-shaped FET structures shown in either FIG. 9 or FIG. 10 would be implemented to increase the channel width of such FET under circumstances other than the particular situation above in which the FET is provided within an active area having the vertical array width in which four wordlines are vertically disposed. 
     The principles of the invention apply equally to the structure and fabrication of FETs having a pitch equivalent to any odd number of gate conductor fingers, for example, FETs having a pitch of five, seven or nine fingers. In an embodiment, a FET having a pitch equivalent to five gate conductor fingers is arranged in a manner similar to that described above. In such embodiment, the. FET has four fingers which run the horizontal length of the device and a fifth finger which is folded into two fingers which run only about half the length of the device. In such embodiment, the current drive of the FET is increased by 25% over a FET having only four fingers. Similarly, in another embodiment, a FET having a pitch equivalent to seven gate conductor fingers is provided. In that embodiment, six fingers run the horizontal length of the device and a seventh finger is folded into two fingers which run only about half the length of the device. The current drive of such FET having a seven-finger pitch is increased by 16% over a FET having only six fingers. 
     While the invention has been described in accordance with certain preferred embodiments thereof, those skilled in the art will understand the many modifications and enhancements which can be made thereto without departing from the true scope and spirit of the invention, which is limited only by the claims appended below.