Abstract:
According to one exemplary embodiment, a transistor includes a channel region situated adjacent to a field oxide region. The transistor further includes a gate have a first portion situated over the channel region and a second portion situated over the field oxide region. The transistor further includes at least one gate contact situated on the second portion of the gate, where the second portion of the gate does not reduce a channel width of the channel region, and where the second portion of the gate does not increase gate resistance. According to this exemplary embodiment, the transistor further includes a drain active region, where the drain active region is surrounded by the gate. The transistor further includes a source active region surrounding the gate. The transistor further includes a well, where the channel region is situated between the well and the source active region.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is generally in the field of semiconductors. More particularly, the invention is in the field of semiconductor transistor design. 
         [0003]    2. Background Art 
         [0004]    In a high voltage transistor, such as a high voltage lateral diffusion (LD) Metal Oxide Semiconductor Field Effect Transistors (MOSFET), a large channel width can be utilized to achieve a high drive current. In a high voltage transistor, such as a high voltage MOSFET, a large channel width can be achieved by, for example, forming a drain region within an inner perimeter of a racetrack-shaped polysilicon (poly) gate and forming a source region along an outer perimeter of the poly gate. In a conventional high voltage transistor, such as a conventional high voltage MOSFET, gate contacts are generally prohibited from being placed directly on the poly gate by applicable process design rules. As a result, gate contacts are typically formed on a segment of poly that extends a considerable distance from the poly gate to outside of the active transistor area. 
         [0005]    However, since they are formed on an extended poly segment, the gate contacts are separated from the poly gate directly on the transistor channel, which can undesirably increase gate resistance and, thereby, undesirably increase gate charge and discharge time. Also, the extended poly segment can cause an undesirable reduction in drive current in the conventional high voltage MOSFET by reducing channel width. 
       SUMMARY OF THE INVENTION 
       [0006]    A transistor, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  illustrates a top view of an exemplary structure including a conventional exemplary high voltage transistor. 
           [0008]      FIG. 2A  illustrates a top view of an exemplary structure including an exemplary high voltage transistor in accordance with one embodiment of the present invention. 
           [0009]      FIG. 2B  illustrates a cross sectional view of the exemplary structure in  FIG. 2A . 
           [0010]      FIG. 3  illustrates a diagram of an exemplary electronic system including an exemplary chip or die utilizing one or more high voltage transistors in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    The present invention is directed to a high voltage transistor. The following description contains specific information pertaining to the implementation of the present invention. One skilled in the art will recognize that the present invention may be implemented in a manner different from that specifically discussed in the present application. Moreover, some of the specific details of the invention are not discussed in order not to obscure the invention. 
         [0012]    The drawings in the present application and their accompanying detailed description are directed to merely exemplary embodiments of the invention. To maintain brevity, other embodiments of the present invention are not specifically described in the present application and are not specifically illustrated by the present drawings. 
         [0013]    The present invention achieves an innovative high voltage transistor. As will be discussed in detail below, the present invention advantageously achieves a high voltage transistor having substantially reduced gate resistance, increased drive current, and reduced size. It is noted that although an NMOS transistor is utilized to illustrate the invention, the invention can also be applied to a PMOS transistor. 
         [0014]      FIG. 1  shows a top view of a portion of a semiconductor die including a conventional exemplary high voltage transistor. Certain details and features have been left out of  FIG. 1 , which are apparent to a person of ordinary skill in the art. Structure  100  includes conventional transistor  102 , which includes gate region  104 , drain active region  106 , source active region  108 , channel region  110 , extended poly segment  112 , drain contacts, such as contacts  114  and  116 , source contacts, such as contacts  118  and  120 , gate contacts, such as contacts  122  and  124 , and field oxide region  126 . Transistor  102  can be a high voltage MOSFET, such as a high voltage LD (lateral diffusion) NMOS transistor, for example. Structure  100  also includes field oxide region  128 , wells  130  and  132 , and substrate  133 , which in one embodiment can be a P type substrate. 
         [0015]    As shown in  FIG. 1 , gate region  104  is situated over a substrate  133  and has inner perimeter  134  and outer perimeter  136 . Gate region  104  can have a hexagonal “racetrack” shape, for example. Gate region  104  can comprise polycrystalline silicon (polysilicon or poly), which can be heavily doped with a suitable N type dopant, for example. Also shown in  FIG. 1 , extended poly segment  112  extends from outer perimeter  136  of gate  104  and can comprise polysilicon, which can be heavily doped with a suitable N type dopant. Extended poly segment  112  has width  138  and length  140 , which corresponds to the distance between edge  142  of extended poly segment  112  and outer perimeter  136  of gate region  104 . Further shown in  FIG. 1 , gate contacts  122  and  124  and other gate contacts not specifically numbered are situated on extended poly segment  112  adjacent to edge  142 . The gate contacts are also situated over a field oxide region (not shown in  FIG. 1 ), which is situated under a portion of extended poly segment  112 . 
         [0016]    Also shown in  FIG. 1 , source region  108  is situated in substrate  133  and can be a heavily doped N type region. Source region  108  extends from edge  146  of extended poly segment  112  along outer perimeter  136  of gate  104  to edge  148  of extended poly segment  112  and also extends between broken line  144  and outer perimeter  136  of gate region  104 . Further shown in  FIG. 1 , source contacts  118  and  120  and other source contacts not specifically numbered are situated on source active region  108 . Also shown in  FIG. 1 , field oxide region  128 , which can comprise silicon oxide, is situated in substrate  133  and surrounds source active region  108 . Further shown in  FIG. 1 , drain active region  106 , which can be heavily doped N type region, is situated in substrate  133 . Drain active region  106  is enclosed by inner perimeter  134  of gate region  104 . Also shown in  FIG. 1 , drain contacts  114  and  116  and other drain contacts not specifically numbered are situated on drain active region  106 . 
         [0017]    Further shown in  FIG. 1 , field oxide region  126 , which can comprise silicon oxide, is situated in substrate  133  and surrounds drain active region  106 . Also shown in  FIG. 1 , well  130  is situated in substrate  133  and also situated under a portion of gate region  104 . Well  130  is further situated under field oxide region  126  and drain active region  106  and can be implanted with a suitable N type dopant, for example. Further shown in  FIG. 1 , well  132  is situated in substrate  133  and is also situated under source active region  108  and field oxide region  128  and can be implanted with a suitable P type dopant. Also shown in  FIG. 1 , channel region  110  is situated in substrate  133  between well  130  and source active region  108  and is also situated under a gate oxide layer (not shown in  FIG. 1 ), which is situated under a portion of gate region  104 . Channel region  110  has an effective channel width that extends along the portion of outer perimeter  136  of gate region  104  that is adjacent to source active region  108 . However, the effective channel width excludes width  138  which is occupied and blocked by extended poly segment  112 . 
         [0018]    In conventional transistor  102 , gate contacts (e.g. gate contacts  122  and  124 ) are situated on extended poly segment  112  because applicable design rules prevent gate contacts from being situated directly on gate poly. However, since channel region  110  is not formed between extended poly segment  112  and well  130 , extended poly segment  112  causes a reduction in the effective channel width of channel region  110  by an amount equivalent to width  138 , since there can be no current flow between the source and drain through the portion blocked by width  138 . By reducing the effective channel width of channel region  110 , extended poly segment  112  causes a reduction in drive current of conventional transistor  102 , which is undesirable. Also, extended poly segment  112  separates the gate contacts from the gate by length  140  of poly segment  112 , which undesirably increases the series resistance between the gate contacts and the poly gate directly over channel region  110 . Furthermore, extended poly segment  112  increases the amount of semiconductor die area that conventional transistor  102  consumes while reducing transistor performance by increasing gate resistance and decreasing drive current. 
         [0019]      FIG. 2A  shows a top view of a portion of a semiconductor die including an exemplary high voltage transistor in accordance with one embodiment of the present invention. Certain details and features have been left out of  FIG. 2A , which are apparent to a person of ordinary skill in the art. Structure  200  includes transistor  202 , which includes channel gate region  204 , drain active region  206 , source active region  208 , channel region  210 , drain contacts  212  and  214 , source contacts  216  and  218 , gate contacts  220  and  222 , and field oxide region  224 . Transistor  202  can be a high voltage transistor, such as a high voltage LD (lateral diffusion) NMOS transistor. In one embodiment, transistor  202  can be a high voltage LD PMOS transistor. Structure  200  also includes field oxide region  226 , wells  228  and  230 , and substrate  232 , which can be a P type substrate. In the present embodiment, transistor  202  is situated on substrate  232 . In another embodiment, transistor  202  can be situated on a P type epitaxial layer, which can be situated on a substrate. It is noted that the shapes, geometries, dimensions, and sizes of various regions, for example, the active regions, the field oxide regions, the wells, the transistor channel region, and the poly gate region are merely for the purpose of illustration by way of specific examples, and other alternative shapes, geometries, dimensions, and sizes are possible and can be used. Moreover, the number of contacts shown is also for the purpose of illustration by way of a specific example, and a greater or smaller number of contacts can be used. 
         [0020]    As shown in  FIG. 2A , drain active region  206  is situated in substrate  232  and can be a heavily doped N type region, for example. Also shown in  FIG. 2A , drain contacts  212  and  214  and other drain contacts not specifically numbered are situated on substrate  232  and situated in drain region  206 . Further shown in  FIG. 2A , field oxide region  224  is situated in substrate  232  and surrounds drain active region  206 . Field oxide region  224  can comprise a thick layer of thermally grown silicon oxide, for example. 
         [0021]    Also shown in  FIG. 2A , channel gate region  204  is situated over channel region  210  and can comprise polysilicon, which can be heavily doped with a suitable N type dopant, for example. Channel gate region  204  has outer perimeter  234 , which surrounds source active region  208 . Source active region  208  is situated in substrate  232 , extends between dashed line  235  and outer perimeter  234  of channel gate region  204 , and can comprise a heavily doped N type region, for example. A thin gate oxide layer (not shown in  FIG. 2A ) is situated between channel region  210  and channel gate region  204  and is also situated on substrate  232 . Channel gate region  204  has inner perimeter  236 , which surrounds the outer perimeter of drain active region  206 . Thus, inner perimeter  236  of channel gate region  204  extends along the outer perimeter of drain active region  206  and, thereby, surrounds drain active region  206 . In the present embodiment, channel gate region  204  has a hexagonal “racetrack” shape. In other embodiments, channel gate region  204  can have other types of geometries or shapes. 
         [0022]    Further shown in  FIG. 2A , channel gate region  204  forms gate extension  238 , which is situated over field oxide region  224 . Thus, a portion of channel gate region  204  is situated over channel region  210  and another portion of channel gate region  204  (i.e. gate extension  238 ) is situated over field oxide region  224 . Also shown in  FIG. 2A , gate contacts  220  and  222  and other gate contacts not specifically numbered are situated on gate extension  238 . Field oxide region  224  comprises a sufficiently thick layer of silicon oxide so as to allow the gate contacts to be situated on an overlying portion of channel gate region  204  (i.e. gate extension  238 ). Further shown in  FIG. 2A , well  228  is situated in substrate  232  and can be an N well, for example. Well  228  is also situated under gate extension  238 , field oxide region  224 , drain active region  206 , and the gate and the drain contacts. Also shown in  FIG. 2A , well  230  is situated in substrate  232  and can be a P well, for example. Well  230  is also situated under source active region  208  and field oxide region  226 . 
         [0023]    Further shown in  FIG. 2A , channel region  210  is situated in substrate  232  and also situated between well  228  and source active region  208 . Channel region  210  is further situated under a thin gate oxide layer (not shown in  FIG. 1 ), which is situated under a portion of channel gate region  204 . Channel region  210 , which forms a transistor channel between drain active region  206  and source active region  208 , has an effective channel width that extends along outer perimeter  234  of channel gate region  204 . Also shown in  FIG. 2A , source contacts  216  and  218  and other source contacts not specifically numbered are situated on substrate  232  and situated on source active region  208 . Further shown in  FIG. 2A , field oxide region  226 , which can comprise a thick layer of silicon oxide, for example, is situated in substrate  232  and surrounds source active region  208 . It is noted that in  FIG. 2A , only drain contacts  212  and  214 , source contacts  216  and  218 , and gate contacts  220  and  222  are specifically numbered and discussed herein to preserve brevity. 
         [0024]      FIG. 2B  shows a cross-sectional view of structure  200  in  FIG. 2A  along line  2 B- 2 B in  FIG. 2A . In particular, transistor  202 , channel gate region  204 , drain active region  206 , source active region  208 , channel region  210 , drain contacts  212  and  214 , source contacts  216  and  218 , gate contacts  220  and  222 , field oxide regions  224  and  226 , wells  228  and  230 , substrate  232 , outer perimeter  234 , inner perimeter  236 , and correspond to the same elements in  FIG. 2A  and  FIG. 2B . 
         [0025]    As shown in  FIG. 2B , source active region  208  is situated in well  230 , which is situated in substrate  232  and drain active region  206  is situated in well  228 , which is also situated in substrate  232 . Also shown in  FIG. 2B , field oxide region  226  is situated in substrate  232  and is also situated adjacent the outer perimeter of source active region  208 . Further shown in  FIG. 2B , field oxide region  224 , which forms a very thick gate oxide layer, surrounds drain active region  206 . Also shown in  FIG. 2B , channel gate region  204  is situated over channel region  210 , which is formed in substrate  232  between well  228  and source active region  208 . Further shown in  FIG. 2B , channel gate region  204  forms gate extension  238 , which is situated over field oxide region  224 . Thus, a portion of channel gate region  204  (i.e. gate extension  238 ) is situated over a very thick gate oxide layer (i.e. field oxide region  224 ) and a remaining portion of channel gate region  204  is situated over a thin gate oxide layer (not shown in  FIG. 2B ), which is situated over channel region  210 . 
         [0026]    Also shown in  FIG. 2B , outer perimeter  234  of channel gate region  204  surrounds the inner perimeter of source active region  208  while inner perimeter  236  of channel gate region  204  surrounds the outer perimeter of drain active region  206 . Further shown in  FIG. 2B , source contacts  216  and  218  are situated over source active region  208  and drain contact  212  is situated over drain active region  206 . Also shown in  FIG. 2B , gate contacts  220  and  222  are situated directly on gate extension  238 , which is the portion of channel gate region  204  that is situated over field oxide region  224 . 
         [0027]    As discussed above, the invention discloses and teaches a transistor, such as a high voltage transistor, having a channel region with an effective channel width that extends along the entire and complete outer perimeter of a channel gate region. In contrast, channel region  110  of conventional transistor  102  in  FIG. 1  has an effective channel width that does not extend along a portion of outer perimeter  136  of gate region  104  that is adjacent to extended poly segment  112 . Accordingly, the present invention achieves a transistor having a greater effective channel width compared to conventional transistor  102  in  FIG. 1 . As a result, the invention&#39;s transistor advantageously achieves increased drive current compared to conventional transistor  102 . 
         [0028]    Also, in conventional transistor  102 , gate contacts (e.g. gate contacts  122  and  124 ) are situated on extended poly segment  112 , which extends from gate region  104  of conventional transistor  102 . As a result, extended poly segment  112  increases the series resistance between the gate contacts and gate region  104 . In contrast, the invention&#39;s transistor provides gate contacts (e.g. gate contacts  220  and  222 ) are situated directly on a portion of channel gate region  202  (i.e. gate extension  238 ), which is situated over field oxide region  224 . By placing gate contacts directly on a portion of the channel gate region, the invention substantially reduces the series resistance between the gate contacts and the channel gate region. Additionally, the invention can provide a large number of gate contacts situated adjacent to inner perimeter of the channel gate region, which form “parallel resistors” that further reduce the series resistance between the gate contacts and the channel gate region. As a result, the invention advantageously achieves a transistor, such as a high voltage MOSFET, having a substantially reduced gate resistance compared to conventional transistor  102  in  FIG. 1 . 
         [0029]    Furthermore, the invention achieves a transistor, such as a high voltage MOSFET, that does not require an extended poly segment coupled to a gate region to provide gate contacts. As a result, the invention&#39;s high voltage transistor advantageously consumes less area on a semiconductor die compared to a conventional high voltage transistor. Thus, the invention advantageously achieves a high voltage transistor with increased performance and reduced die area consumption compared to a conventional high voltage transistor. 
         [0030]      FIG. 3  illustrates a diagram of an exemplary electronic system including an exemplary chip or die utilizing one or more high voltage transistors in accordance with one embodiment of the present invention. Electronic system  300  includes exemplary modules  302 ,  304 , and  306 , IC chip  308 , discrete components  310  and  312 , residing in and interconnected through printed circuit board (PCB)  314 . In one embodiment, electronic system  300  may include more than one PCB. IC chip  308  includes circuit  316 , such as a power amplifier circuit, which utilizes one or more high voltage transistors designated by numeral  318 . 
         [0031]    As shown in  FIG. 3 , modules  302 ,  304 , and  306  are mounted on PCB  314  and can each be, for example, a central processing unit (CPU), a graphics controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a video processing module, an audio processing module, an RF receiver, an RF transmitter, an image sensor module, a power control module, an electro-mechanical motor control module, or a field programmable gate array (FPGA), or any other kind of module utilized in modern electronic circuit boards. PCB  314  can include a number of interconnect traces (not shown in  FIG. 3 ) for interconnecting modules  302 ,  304 , and  306 , discrete components  310  and  312 , and IC chip  308 . 
         [0032]    Also shown in  FIG. 3 , IC chip  308  is mounted on PCB  314  and can be, for example, any chip or die utilizing an embodiment of the invention&#39;s high voltage transistor. In one embodiment, IC chip  308  may not be mounted on PCB  314 , and may be interconnected with other modules on different PCBs. Circuit  316  is situated in IC chip  308  and includes one or more high voltage transistors  318 . High voltage transistor(s)  318  can comprise, for example, a high voltage transistor as specified in one of the embodiments of the invention described above. Further shown in  FIG. 3 , discrete components  310  and  312  are mounted on PCB  314  and can each be, for example, an active filter discrete component, such as one including a BAW or SAW filter or the like, a power amplifier or an operational amplifier, a semiconductor device, such as a transistor or a diode or the like, an antenna element, an inductor, a capacitor, or a resistor. Discrete components  310  and  312  may themselves utilize one embodiment of the invention&#39;s high voltage transistor described above. 
         [0033]    Electronic system  300  can be, for example, a wired or wireless communications device, a cell phone, a switching device, a router, a repeater, a codec, a LAN, a WLAN, a Bluetooth enabled device, a digital camera, a digital audio player and/or recorder, a digital video player and/or recorder, a computer, a monitor, a television set, a satellite set top box, a cable modem, a digital automotive control system, a digitally-controlled home appliance, a printer, a copier, a digital audio or video receiver, an RF transceiver, a personal digital assistant (PDA), a digital game playing device, a digital testing and/or measuring equipment, digital avionics equipment, or a digitally-controlled medical equipment, or in any other kind of module utilized in modern electronics applications. 
         [0034]    From the above description of the invention it is manifest that various techniques can be used for implementing the concepts of the present invention without departing from its scope. Moreover, while the invention has been described with specific reference to certain embodiments, a person of ordinary skill in the art would appreciate that changes can be made in form and detail without departing from the spirit and the scope of the invention. Thus, the described embodiments are to be considered in all respects as illustrative and not restrictive. It should also be understood that the invention is not limited to the particular embodiments described herein but is capable of many rearrangements, modifications, and substitutions without departing from the scope of the invention. 
         [0035]    Thus, a high voltage transistor has been described.