Patent Abstract:
A MOS transistor structure for matched operation in weak-inversion or sub-threshold range (e.g. input-pair of operational amplifier, comparator, and/or current-minor) is disclosed. The transistor structure may include a well region of any impurity type in a substrate (SOI is included). The well-region can even be represented by the substrate itself. At least one transistor is located in the well region, whereby the active channel-region of the transistor is independent from lateral isolation interfaces between GOX (gate oxide) and FOX (field oxide; including STI-shallow trench isolation).

Full Description:
TECHNICAL FIELD 
       [0001]    Various embodiments relate to a transistor structure with a reduced parasitic “side wall” transistor regions. 
       BACKGROUND 
       [0002]    Certain low power analog circuits utilize various types of field effect transistors (e.g. complementary metal-oxide-semiconductor “CMOS”; metal-oxide-semiconductor field-effect transistor “MOSFET”; metal-insulation-semiconductor field-effect transistor “MISFET”; etc.). Some low power applications use matched pairs of such transistors, however the “matching” properties of these transistors begins to change for the worse at lower operating currents. This is because, in low power applications, the transistors operate in the so-called “Weak Inversion” mode (or sub-threshold region), in which a low drain current (I ds ) is flowing. Further, when operating in the sub-threshold region, various phenomena which adversely affect the performance of the transistor may become dominant. Some of these adverse phenomena are related to the mechanical structure of a typical field effect transistor. In most MOSFET devices, so-called “side wall” transistors form at the edges of the gate region and adversely affect the performance of such devices, particularly when a closely matched pair of transistors is required for a given application. 
       SUMMARY 
       [0003]    In various embodiments, a transistor structure is provided. The transistor structure may include a well region of a first impurity type in a substrate with at least one transistor in the well region, a structure of the first impurity type enclosing the well region, and a trench or a field oxide isolation layer enclosing the structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    In the drawings, like reference characters generally refer to the same parts of the disclosure throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the disclosure. In the following description, various embodiments of the disclosure are described with reference to the following drawings, in which: 
           [0005]      FIG. 1  shows, in accordance with a potential embodiment, a longitudinal cross-sectional representation of a transistor structure; 
           [0006]      FIG. 2  shows, according to an embodiment, a transverse cross-sectional representation of a transistor structure; 
           [0007]      FIG. 3  shows a planar top-down view of an embodiment of the transistor structure of  FIGS. 1 &amp; 2 ; 
           [0008]      FIG. 4  shows, according to an embodiment a planar top-down view of a quad-transistor structure; 
           [0009]      FIG. 5  shows, according to an embodiment a planar top-down view of a multi-transistor structure including eight transistors; 
           [0010]      FIG. 6  shows, according to an embodiment a planar top-down view of a ring-shaped transistor structure. 
       
    
    
     DESCRIPTION 
       [0011]    The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the disclosure may be practiced. 
         [0012]    The word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. 
         [0013]    The word “over” used with regards to a deposited material formed “over” a side or surface may be used herein to mean that the deposited material may be formed “directly on”, e.g. in direct contact with the implied side or surface. The word “over” used with regards to a deposited material formed “over” a side or surface may be used herein to mean that the deposited material may be formed “indirectly on” the implied side or surface with one or more additional layers being arranged between the implied side or surface and the deposited material. 
         [0014]    In various embodiments, a transistor with reduced parasitic “side wall” transistor regions is disclosed. 
         [0015]    The transistor structure  100 , as illustrated in  FIGS. 1-3 , may include a substrate  102 , a well region  101  of a first impurity type in the substrate  102 , at least one transistor  104  formed at least partially on the well region  101 , a portion of the well region  101  may be implemented as a transistor channel  108  of the transistor  104 . The transistor  104  may include a first diffusion region  104   a  of a second impurity type in the well region  101 , and a second diffusion region  104   b  of the second impurity type in the well region  101 . According to an embodiment, the transistor structure  100  may include a structure of the first impurity type  110  in the substrate  102  enclosing the well region  101 . According to various embodiments, the structure of the first impurity type  110  is implemented as a bulk diffusion region for connection to the well region  101 . The transistor structure  100  may further include a trench or field oxide isolation layer  112  in the substrate  102  enclosing the structure of the first impurity type  110 . In some embodiments, an impurity concentration in the structure of the first impurity type  110  is higher than an impurity concentration in the well region  101 . 
         [0016]    In various embodiments, the transistor  104  may further include an oxide layer  114  disposed over the channel  108 , a gate electrode  116  on the oxide layer  114 , a source electrode  118  on the first diffusion region  104   a,  a drain electrode  120  on the second diffusion region  104   b,  and at least one body connection electrode  122  on the structure of the first impurity type  110 . According to various embodiments, the transistor  104  may include at least one lightly doped source region  124  of the second impurity type extending from the perimeter of the first diffusion region  104   a  and into the channel  108 , and at least one lightly doped drain region  126  of the second impurity type extending from the perimeter of the second diffusion region  104   b  and into the channel  108 . 
         [0017]    According to various embodiments, the substrate  102  may include or essentially consist of various materials, e.g. a semiconductor material such as various elemental and/or compound semiconductors. The substrate  102  may include or essentially consist of, for example, glass, and/or various polymers. The substrate  102  may be a silicon-on-insulator (SOI) structure. In various embodiments, the substrate  102  may include or essentially consist of one or more of the following materials: a polyester film, a thermoset plastic, a metal, a metalized plastic, a metal foil, and a polymer. In some embodiments, the substrate  102  may be a multilayer substrate. According to various embodiments, the substrate  102  may have a thickness T 1  in the range from about 10 μm to about 700 μm. According to various embodiments, the substrate  102  may have a thickness T 1  which may be any thickness desirable for a given application. According to various embodiments, the substrate  102  may be formed into any shape that may be desired for a given application. 
         [0018]    In various embodiments, the well region  101  may be formed in and/or on the substrate  102 . The well region  101  may be an impurity doped region in the substrate  102 , e.g. an n-type or p-type region in a semiconductor substrate. In some embodiments, the well region  101  may be formed in the substrate  102  through various techniques, e.g. vapor-phase epitaxy, diffusion, and/or ion implantation, etc. In various embodiments, the well region  101  may have an impurity concentration in the range from about 10 13  cm −3 to about 10 18  cm −3 . According to various embodiments, the well region may have a thickness T 2 , in the range from about 0.5 μm to about 10 μm. According to a first example of an embodiment, the well region  101  is implemented as a p-type well region in a semiconductor substrate  102 . In a second example of an embodiment, the well region  101  is implemented as an n-type well region in a semiconductor substrate  102 . 
         [0019]    According to various embodiments, the transistor structure  100  may include a first diffusion region  104   a.  In various embodiments, the first diffusion region  104   a  may be formed in and/or on the well region  101 . In some embodiments, the first diffusion region  104   a  is implemented as an impurity doped region in the well region  101 , e.g. an n-type or p-type region in a semiconductor substrate. In some embodiments, the first diffusion region  104   a  is formed in the well region  101  through various techniques, e.g. vapor-phase epitaxy, diffusion, and/or ion implantation, etc. According to various embodiments, the first diffusion region  104   a  may have an impurity concentration in the range from about 10 18  cm −3 to 5×10 21  cm −3 . According to an embodiment, the first diffusion region  104   a  is implemented as a p-type region in the well region  101 . In another embodiment, the first diffusion region  104   a  is implemented as an n-type well region in the well region  101 . According to various embodiments, the first diffusion region  104   a  may serve as a source and/or drain region for the transistor  104 . In at least one embodiment and various other embodiments, the first diffusion region  104   a  is implemented as an n++ type doped source region for the transistor  104 . In some embodiments and various other embodiments, the first diffusion region  104   a  is implemented as a p++ type doped source or drain region  104   a  for the transistor  104 . In at least one embodiment, the second diffusion region  104   a  may be implemented as a common source or drain region for a plurality of transistors. 
         [0020]    According to various embodiments, the transistor structure  100  may include a second diffusion region  104   b,  which may be substantially similar to the first diffusion region  104   a,  described above and may contain many of the same materials. 
         [0021]    In various embodiments, the transistor channel  108  may be formed between the first diffusion region  104   a  and the second diffusion region  104   b.  The transistor channel  108  may have a length, shown in  FIGS. 1 &amp; 3  and indicated by reference character L, which is the distance between the first diffusion region  104   a  and the second diffusion region  104   b,  in the range from about 0.04 μm to about 10 μm. According to various embodiments, the length L of the transistor channel  108  may be scaled to any distance desirable for a given application. In various embodiments the transistor channel  108  may have a width, indicated by reference character W shown in  FIGS. 2 &amp; 3 , in the range from about 0.04 μm to about 10 μm. According to various embodiments, the width W of the transistor channel  108  may be scaled to any distance desirable for a given application. 
         [0022]    According to various embodiments, the structure of the first impurity type  110  enclosing the well region  101  may be formed in the substrate  102  through various techniques, e.g. vapor-phase epitaxy, diffusion, and/or ion implantation, etc. The structure of the first impurity type  110  may have a depth, indicated by reference character D, below the surface of the substrate  102 . In various embodiments the depth D is in the range from about 1 nm to about 500 nm. The depth D may be implemented as any depth desirable for a given application. According to various embodiments, the structure of the first impurity type  110  may have an impurity concentration in the range from about 10 18  cm −3  to 5×10 21  cm −3 . According to various embodiments, the structure of the first impurity type  110  may have any impurity concentration desirable for a given application. According to at least one and various other embodiments, the structure of the first impurity type  110  is implemented as a p-type or n-type region in the substrate  102  which substantially and/or completely encloses the well region  101 . According to various embodiments, the structure of the first impurity type  110  may be formed into any shape that may be desired for a given application. 
         [0023]    According to various embodiments, the transistor structure  100  includes a trench or field oxide isolation layer  112  in the substrate  102  enclosing the structure of the first impurity type  110 . In an embodiment, the trench or field oxide isolation layer completely encloses and/or surrounds the structure of the first impurity type  110  and serves to electrically isolate and/or insulate the transistor structure  100  from other electrical components which may be formed on the substrate  102 . According to various embodiments, the trench or field oxide isolation layer  112  may be implemented as a so-called shallow trench isolation (STI) layer. In various embodiments, the trench or field oxide isolation layer  112  may be implemented as a LOCOS (local oxidation of silicon) field oxide. The trench or field oxide isolation layer  112  may be composed primarily of and/or may contain various dielectric materials, e.g. a semiconductor oxide, various high-k dielectrics, etc. According to an embodiment, the trench or field oxide isolation layer  112  may be essentially consist of and/or may contain any element desirable for a given application. 
         [0024]    According to various embodiments, the transistor structure  100  includes an oxide layer  114 , e.g. a gate oxide, over the channel  108 . The oxide layer  114  may have a thickness between about  1  nm and about  50  nm. According to various embodiments, the oxide layer may have any thickness that may be desirable for a given application. The oxide layer  114  may be implemented as a semiconductor oxide layer. In at least one embodiment, the oxide layer  114  is implemented as a silicon dioxide layer. In various embodiments, the oxide layer  114  may include and/or be composed essentially of high-k dielectrics, e.g. various IVb metal silicates such as hafnium silicates and/or a zirconium silicate. According to an embodiment, the oxide layer may be essentially consist of and/or may contain any element desirable for a given application. According to an embodiment, the oxide layer  114  is implemented as a gate oxide layer situated between the transistor  104  and the channel  108 . The oxide layer, in some embodiments, serves to electrically isolate and/or insulate at least a portion of the transistor  104  from the channel  108 . In some embodiments, the oxide layer  114  does not extend past the perimeter of the gate electrode  116 , while in other embodiments the oxide layer  114  may cover and/or be formed over the entirety of the well region  101 . 
         [0025]    According to various embodiments, the transistor  104  includes a gate electrode  116  on the oxide layer  114 . The gate electrode  116  may be implemented as a stack structure formed on the oxide layer  114 . In various embodiments where the gate electrode  116  is implemented as a stack structure, the gate electrode  116  may include a semiconductor layer, such as an n-type or p-type polysilicon, formed on the oxide layer  114 . In at least one embodiment the semiconductor layer is implemented as a combination of several p-type and n-type polysilicon structures. According to various embodiments, the gate electrode may have a conductive layer  116   a  formed over the semiconductor layer. In at least one embodiment, this conductive layer may be a self-aligned silicide layer, e.g. a cobalt silicide, titanium silicide, nickel silicide, platinum silicide, and/or a tungsten silicide. In some embodiments, the conductive layer  116   a  may be formed of a metallic material, a metalized material, a metal foil, an elemental metal, and/or a metal alloy. The conductive layer  116   a  may have a thickness between about 2 nm and about 15 nm. According to various embodiments, conductive layer  116   a  may have any thickness that may be desirable for a given application. In various embodiments, the transistor  104  might include at least one spacer structure  116   c  on at least one sidewall of the stack structure. The spacer structure  116   c  may be implemented as various nitrides, in some embodiments; the spacer structure  116   c  may include or essentially consist of tetraethyl orthosilicate. According to various embodiments, the transistor structure  100  includes an electrical contact  116   b  formed and/or arranged over a top side of the gate electrode  130 . In some embodiments, the electrical contact  116   b  may be formed of a metallic material, a metalized material, a metal foil, an elemental metal, and/or a metal alloy. The electrical contact  116   b  may include or may essentially consist of cobalt silicide, titanium silicide, nickel silicide, platinum silicide, and/or a tungsten silicide. 
         [0026]    According to various embodiments, the transistor structure  100  includes a source electrode  118  formed over and/or on a surface of the first diffusion region  104   a . In some embodiments, the source electrode  118  is electrically coupled and/or in electrical contact or communication with the first diffusion region  104   a.  In some embodiments, the source electrode  118  includes a base layer  118   a  formed on a surface of the first diffusion region  104   a  and a conductive extension  118   b  formed on the base layer  118   a.  The base layer  118   a  may be a self-aligned silicide layer, e.g. a cobalt silicide, titanium silicide, nickel silicide, platinum silicide, and/or a tungsten silicide. In some embodiments, the base layer  118   a  may be formed of a metallic material, a metalized material, a metal foil, an elemental metal, and/or a metal alloy. In some embodiments, the conductive extension  118   b  may be formed of a metallic material, a metalized material, an elemental metal, and/or a metal alloy. In at least one embodiment, the base layer  118   a  and the conductive extension  118   b  may be formed together, i.e. may consist of a monolithic structure, while in other embodiments the base layer  118   a  and the conductive extension  118   b  are formed in discrete steps. 
         [0027]    According to various embodiments, the transistor structure  100  includes a drain electrode  120  formed over and/or on a surface of the second diffusion region  104   b . In some embodiments, the drain electrode  120  is electrically coupled and/or in electrical contact or communication with the second diffusion region  104   b.  In some embodiments, the drain electrode  120  includes a base layer  120   a  formed on a surface of the second diffusion region  104   b  and a conductive extension  120   b  formed on the base layer  120   a . The base layer  120   a  may be substantially similar to the base layer  118   a,  and the conductive extension  120   b  may be substantially similar to the conductive extension  118   b , described above. 
         [0028]    According to various embodiments, the transistor structure  100  includes at least one body connection electrode  122  formed on the structure of the first impurity type  110 . In some embodiments, the at least one body connection electrode  122  is electrically coupled and/or in electrical contact or communication with the structure of the first impurity type  110 . In some embodiments, the at least one body connection electrode  122  is electrically coupled and/or in electrical contact or communication with the first diffusion region  104   a,  while in other embodiments the at least one body connection is electrically coupled to the second diffusion region  104   b.  In some embodiments, the at least one body connection electrode  122  includes a base layer  122   a  formed on a surface of the structure of the first impurity type  110  and a conductive extension  122   b  formed on the base layer  122   a.  The base layer  122   a  may be substantially similar to the base layer  118   a,  and the conductive extension  122   b  may be substantially similar to the conductive extension  118   b,  described above. 
         [0029]    According to various embodiments, the transistor structure  100  includes at least one lightly doped source region  124  extending from the perimeter of the first diffusion region  104   a  and into the channel  108 . In some embodiments, the lightly doped source region  124  is implemented as a p-type impurity doped region in the well region  101 . In some embodiments, the lightly doped source region  124  is implemented as an n-type impurity doped region in the well region  101 . In some embodiments, the lightly doped source region may have an impurity concentration from about 10 16  cm −3  to about  10   19  cm −3 . The lightly doped source region  124  may be formed in the substrate  102  and/or well region  101  through various techniques, e.g. vapor-phase epitaxy, diffusion, and/or ion implantation, etc. 
         [0030]    According to various embodiments, the transistor structure  100  includes at least one lightly doped drain region  126  of the second impurity type extending from the perimeter of the second diffusion region  106  and into the channel  108 . In some embodiments, the lightly doped drain region  126  is implemented as a p-type impurity doped region in the well region  101 . In some embodiments, the lightly doped drain region  126  is implemented as an n-type impurity doped region in the well region  101 . In some embodiments, the lightly doped drain region may have an impurity concentration from about 10 16  cm −3  to about 10 19  cm −3 . The lightly doped drain region  126  may be formed in the substrate  102  and/or well region  101  through various techniques, e.g. vapor-phase epitaxy, diffusion, and/or ion implantation, etc. In various embodiments, the transistor structure  100  includes at least one defined border  128  where the oxide layer  114  stops and the trench or field oxide isolation layer  112  begins. In other words the border  128  is a well-defined transition region between the oxide layer  114  and the trench or field oxide isolation layer  112 , i.e. a border where the oxide layer  114  and the trench or field oxide isolation layer  112  are in physical contact. 
         [0031]    According to various embodiments, as illustrated in  FIG. 4 , the transistor structure  100  can be implemented as a type of multi-transistor structure  400 . In various embodiments, the multi-transistor structure  400  includes a well region  401 . The well region  401  may be substantially similar to the well region  101 , described above, and may be formed through many of the processes and may contain many of the same physical and/or electrical properties. In various embodiments, the multi-transistor structure  400  includes substrate  402 . The substrate  402  may be substantially similar to the substrate  102 , described above, and may be formed through many of the processes and may contain many of the same properties. The multi-transistor structure  400  is similar to the transistor structure  100  in many respects, differing mainly in the number of transistors  404  it contains. The illustrative embodiment of the multi-transistor structure  400 , depicted in  FIG. 4  contains four transistors, represented by reference  FIGS. 404 a -404 d   . The transistors  404   a - 404   d  may be substantially similar to the at least one transistor  104  and may be formed through many of the processes described above. According to various embodiments, the transistors  404   a - 404   d  are each implemented with independent source diffusion regions  406   a - 406   d.  The source diffusion regions  406   a - 406   d  are analogous to the first and second diffusion regions  104   a  and  104   b,  respectively, described above and may be formed using many of the same processes. According to various embodiments, the transistors  404   a - 404   d  are each implemented with source electrodes  408   a - 408   d.  The source electrodes  408   a - 408   d  are analogous to the source electrode  118  described above and may be implemented using many of the same materials and processes. According to an embodiment, the multi-transistor structure  400  contains a common drain diffusion region  410 . The common drain diffusion region  410  may be located in a central portion of the multi-transistor structure  400 . In some embodiments, the common drain diffusion region  410  is arranged between the source electrodes  408   a - 408   d.  In the embodiment depicted in  FIG. 4 , the source electrodes  408   a - 408   d  are arranged around the perimeter of the common drain diffusion region  410  in a cross-like configuration, however it should be noted that this geometry is exemplary and not intended to be limiting. The source electrodes  408   a - 408   d  may be arranged around the common drain diffusion region  410  in a variety of configurations, e.g. in some embodiments the common drain diffusion region  410  and the source electrodes  408   a - 408   d  may be parallel to each other. According to an embodiment, the common drain diffusion region  410  is analogous to the first and second diffusion regions  104   a  and  104   b , respectively, described above and may be formed using many of the same processes and materials. According to an embodiment, the multi-transistor structure  400  contains a common drain electrode  412 . The common drain electrode  412  is analogous to the drain electrode  120  described above and may be implemented using many of the same materials and processes. According to an embodiment, the common drain electrode  412  and the common drain diffusion region  410  are coextensive and/or substantially overlap one another. According to an embodiment, the multi-transistor structure  400  contains a channel region for each of the transistors it may contain. In the embodiment depicted in  FIG. 4 , the multi-transistor structure  400  is implemented with four channel regions  414   a - 414   d  for each of the transistors  404   a - 404   d.  According to various embodiments, the channel regions  414   a - 414   d  are analogous to the channel  108  described above and may be implemented using many of the same materials and processes. In various embodiments, the length and width of each of the channel regions  414   a - 414   d  are depicted by references figures W x  and L x  in  FIG. 4 , i.e. channel region  414   a  has a width W 1  and a length L 1 , etc. According to an embodiment, the multi-transistor structure  400  contains a gate oxide layer  416 . In various embodiments, the gate oxide layer  416  is formed over the common drain diffusion region  410  and extends over each of the channel regions  414   a - 414   d,  with a defined border interface  420  where the gate oxide layer  416  switches to the trench or field oxide layer  422 . According to various embodiments, the gate oxide layer  416  is analogous to the oxide layer  114  described above and may be implemented using many of the same materials and processes. According to an embodiment, the multi-transistor structure  400  contains a gate electrode structure  418 , which may be implemented as a gate base layer  418   a  and a plurality of gate contacts  418   b.  In the embodiment depicted in  FIG. 4 , the gate base layer  418   a  is shown in transparency for clarity of detail of the other elements contained in the multi-transistor structure  400 . The gate electrode structure  418  is analogous to gate electrode  116  and may be formed using many of the same processes and material and may share many of the same physical and/or electrical properties as the gate electrode  116 . According to an embodiment, the multi-transistor structure  400  contains a border interface  420  where the field oxide or shallow trench isolation layer  422  is located outside of the gate oxide layer  416 . The shallow trench or field oxide isolation layer  422  is analogous to the trench or field oxide isolation layer  112  and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties as the trench or field oxide isolation layer  112 . According to an embodiment, the multi-transistor structure  400  contains a bulk diffusion region  424  in the substrate  402  enclosing the well region  401 . According to various embodiments, the bulk diffusion region  424  is implemented as a bulk diffusion region for connection to the well region  401 . The bulk diffusion region  424  is analogous to the structure of the first impurity type  110  and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties as the structure of the first impurity type  110 . According to various embodiments, the multi-transistor structure  400  contains at least one body connection electrode  430  formed on the bulk diffusion region  424 . In some embodiments, the at least one body connection electrode  430  is analogous to the at least one body connection electrode  122 , described in detail above, and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties as the at least one body connection electrode  122 . In some embodiments, the at least one body connection electrode  430  includes a base layer  430   a  formed on a surface of the bulk diffusion region  424  and a conductive extension  430   b  formed on the base layer  430   a.  According to various embodiments, the base layer  430   a  is analogous to the base layer  122   a,  described in detail above, and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties. Similarly, conductive extension  430   b  is analogous to the conductive extension  122   b,  described in detail above, and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties. 
         [0032]    According to various embodiments, as illustrated in  FIG. 5 , the transistor structure  100  can be implemented as a type of multi-transistor structure  500 . In various embodiments, the multi-transistor structure  500  includes a well region  501 . The well region  501  may be substantially similar to the well region  101 , described above, and may be formed through many of the processes and may contain many of the same physical and/or electrical properties. In various embodiments, the multi-transistor structure  500  includes a substrate  502 . The substrate  502  may be substantially similar to the substrate  102 , described above, and may be formed through many of the processes and may contain many of the same properties. The multi-transistor structure  500  may be similar or identical to the transistor structure  100  in many respects, differing mainly in the number of transistors  504  it contains. The illustrative embodiment of the multi-transistor structure  500 , depicted in  FIG. 5  contains eight transistors, represented by reference  FIGS. 504 a   - 504   h.  The transistors  504   a - 504   h  may be substantially similar to the at least one transistor  104  and may be formed through many of the processes described above. According to various embodiments, the transistors  504   a - 504   h  are each implemented with independent source diffusion regions  506   a - 506   h.  The source diffusion regions  506   a - 506   h  are analogous to the first diffusion region  104   a,  described above and may be formed using many of the same processes. According to various embodiments, the transistors  504   a - 504   h  are each implemented with source electrodes  508   a - 508   h.  The source electrodes  408   a - 408   d  are analogous to the source electrode  118  described above and may be implemented using many of the same materials and processes. According to an embodiment, the multi-transistor structure  500  contains a common drain diffusion region  510 . The common drain diffusion region  510  may be located in a central portion of the multi-transistor structure  500 . In some embodiments, the common drain diffusion region  510  is arranged between the source electrodes  508   a - 508   h.  In the embodiment depicted in  FIG. 5 , the source electrodes  508   a - 508   h  are arranged around the perimeter of the common drain diffusion region  510  in an octagonal configuration, however it should be noted that this geometry is exemplary and not intended to be limiting. The source electrodes  508   a - 508   h  may be arranged around the common drain diffusion region  510  in a variety of configurations, e.g. in some embodiments the common drain diffusion region  510  and the source electrodes  508   a - 508   h  may be parallel to each other. According to an embodiment, the common drain diffusion region  510  is analogous to the second diffusion region  104   b,  described above and may be formed using many of the same processes and materials. According to an embodiment, the multi-transistor structure  500  contains a common drain electrode  512 . The common drain electrode  512  is analogous to the drain electrode  120  described above and may be implemented using many of the same materials and processes. According to an embodiment, the common drain electrode  512  and the common drain diffusion region  510  are coextensive and/or substantially overlap one another. According to an embodiment, the multi-transistor structure  500  contains a channel region for each of the transistors it may contain. In the embodiment depicted in  FIG. 5 , the multi-transistor structure  500  is implemented with eight channel regions  514   a - 514   h  for each of the transistors  504   a - 504   h.  According to various embodiments, the channel regions  514   a - 514   h  are analogous to the channel  108  described above and may be implemented using many of the same materials and processes. In various embodiments, the length and width of each of the channel regions  514   a - 514   h  are depicted by references figures W x  and L x  in  FIG. 5 , i.e. channel region  514   a  has a width W 1  and a length L 1 , etc. According to an embodiment, the multi-transistor structure  500  contains an oxide layer  516 . In various embodiments, the oxide layer  516  is formed over the common drain diffusion region  510  and extends over each of the channel regions  514   a - 514   h.  According to various embodiments, the oxide layer  516  is analogous to the oxide layer  114  described above and may be implemented using many of the same materials and processes. According to an embodiment, the multi-transistor structure  500  contains a gate electrode structure  518 , which may be implemented as a gate base layer  518   a  and a plurality of gate contacts  518   b.  In the embodiment depicted in  FIG. 5 , the gate base layer  518   a  is shown in transparency for clarity of detail of the other elements contained in the multi-transistor structure  500 . The gate electrode structure  518  is analogous to gate electrode  116  and may be formed using many of the same processes and material and may share many of the same physical and/or electrical properties as the gate electrode  116 . According to an embodiment, the multi-transistor structure  500  contains a boarder interface  520  with the gate oxide layer  516  inside a shallow trench or field oxide isolation layer  522  outside the transistor channel regions  514   a - 514   h.  In various embodiments, the border interface  520  is a region where the gate oxide layer  516  stops and the trench or field oxide isolation layer  522  begins. In other words the border interface  520  is a well-defined transition region between the gate oxide layer  516  and the trench or field oxide isolation layer  522 , i.e. a border where the gate oxide layer  516  and the trench or field oxide isolation layer  522  are in physical contact. The shallow trench isolation layer  522  is analogous to the trench or field oxide isolation layer  112  and may be formed from the same and/or similar materials as the trench or field oxide isolation layer  112 . Further, in an embodiment, the shallow trench isolation layer  522  serves the same purpose the trench or field oxide isolation layer  112 . According to an embodiment, the multi-transistor structure  500  contains a bulk diffusion region  524  in the substrate  502  enclosing the well region  501 . According to various embodiments, the bulk diffusion region  524  is implemented as a bulk diffusion region for connection to the well region  501 . The bulk diffusion region  524  is analogous to the structure of the first impurity type  110  and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties as the structure of the first impurity type  110 . According to various embodiments, the multi-transistor structure  500  contains at least one body connection electrode  530  formed on the bulk diffusion region  524 . In some embodiments, the at least one body connection electrode  530  is analogous to the at least one body connection electrode  122 , described in detail above, and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties as the at least one body connection electrode  122 . In some embodiments, the at least one body connection electrode  530  includes a base layer  530   a  formed on a surface of the bulk diffusion region  524  and a conductive extension  530   b  formed on the base layer  530   a.  According to various embodiments, the base layer  530   a  is analogous to the base layer  122   a,  described in detail above, and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties. Similarly, conductive extension  530   b  is analogous to the conductive extension  122   b,  described in detail above, and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties. 
         [0033]    According to various embodiments, as illustrated in  FIG. 6 , the transistor structure  100  can be implemented as a type of multi-transistor structure  600 . In various embodiments, the multi-transistor structure  600  includes a well region  601 . The well region  601  may be substantially similar to the well region  101 , described above, and may be formed through many of the processes and may contain many of the same physical and/or electrical properties. In various embodiments, the multi-transistor structure  600  includes substrate  602 . The substrate  602  may be substantially similar to the substrate  102 , described above, and may be formed through many of the processes and may contain many of the same properties. The multi-transistor structure  600  may be similar or identical to the transistor structure  100  in many respects, differing mainly in the number of transistors  604  it contains. The illustrative embodiment of the multi-transistor structure  600 , depicted in  FIG. 6  contains a continuous and/or infinitely divisible transistor  604 . The continuous transistor  604  depicted in  FIG. 6  may be substantially similar to the at least one transistor  104  and may be formed through many of the processes described above. According to various embodiments, the continuous transistor  604  is implemented with a source diffusion region  606 . The source diffusion region  606  is analogous to the first diffusion region  104   a,  described above, and may be formed using many of the same processes. In the embodiment depicted in  FIG. 6 , the source diffusion region  606  is implemented as an annular diffusion region, however it should be noted that this geometry is exemplary and not intended to be limiting. According to various embodiments, the continuous transistor is implemented with a continuous source electrode  608 . The continuous source electrode  608  is analogous to the source electrode  118  described above and may be implemented using many of the same materials and processes. In the embodiment depicted in  FIG. 6 , the continuous source electrode  608  is impended as an annular structure, however it should be noted that this geometry is exemplary and not intended to be limiting. According to an embodiment, the continuous source electrode  608  and the source diffusion region  606  are coextensive and/or substantially overlap one another, in other words the continuous source electrode  608  is formed over and/or directly on the source diffusion region  606 . According to an embodiment, the multi-transistor structure  600  contains a common drain diffusion region  610 . The common drain diffusion region  610  may be located in a central portion of the multi-transistor structure  600 . In some embodiments, the common drain diffusion region  610  is arranged between inside the annular continuous source electrode  608 . In the embodiment depicted in  FIG. 6 , the continuous source electrode  608  and the common drain diffusion region  610  are depicted as concentric annular structures, however it should be noted that this geometry is exemplary and not intended to be limiting. According to an embodiment, the common drain diffusion region  610  is analogous to the second diffusion region  104   b,  described above, and may be formed using many of the same processes and materials. According to an embodiment, the multi-transistor structure  600  contains a common drain electrode  612 . The common drain electrode  612  is analogous to the drain electrode  120  described above and may be implemented using many of the same materials and processes. According to an embodiment, the common drain electrode  612  and the common drain diffusion region  610  are coextensive and/or substantially overlap one another. According to an embodiment, the multi-transistor structure  600  contains a portion of the well region  601  implemented as a transistor channel region  614 , in  FIG. 6  the channel region  614  is obscured by the gate base layer  618   a.  In various embodiments, the length and width of each of the transistor channel region  614  is depicted by references figures W and L in  FIG. 6 . According to an embodiment, the multi-transistor structure  600  contains an oxide layer  616  disposed over the channel region  614 . The oxide layer  616  is analogous to the oxide layer  114 , described above, and may be formed from the same and/or similar materials. According to an embodiment, the multi-transistor structure  600  contains a gate electrode structure  618 , which may be implemented as a gate base layer  618   a  and a plurality of gate contacts  618   b.  The gate electrode structure  618  is analogous to gate electrode  116  and may be formed using many of the same processes and material and may share many of the same physical and/or electrical properties as the gate electrode  116 . According to an embodiment, the multi-transistor structure  600  contains a border interface  620  to separate the gate oxide layer  616  from the shallow trench or field oxide isolation layer  622 . In other words the border interface  620  is a well-defined transition region between the oxide layer  616  and the trench or field oxide isolation layer  622 , i.e. a border where the oxide layer  616  and the trench or field oxide isolation layer  622  are in physical contact. The shallow trench isolation layer  622  is analogous to the trench or field oxide isolation layer  112  and may be formed from the same and/or similar materials as the trench or field oxide isolation layer  112 . According to an embodiment, the multi-transistor structure  600  contains a bulk diffusion region  624  in the substrate  602  enclosing the well region  601 . According to various embodiments, the bulk diffusion region  624  is implemented as a bulk diffusion region for connection to the well region  601 . The bulk diffusion region  624  is analogous to the structure of the first impurity type  110  and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties as the structure of the first impurity type  110 . According to various embodiments, the multi-transistor structure  600  contains at least one body connection electrode  630  formed on the bulk diffusion region  624 . In some embodiments, the at least one body connection electrode  630  is analogous to the at least one body connection electrode  122 , described in detail above, and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties as the at least one body connection electrode  122 . In some embodiments, the at least one body connection electrode  630  includes a base layer  630   a  formed on a surface of the bulk diffusion region  624  and a conductive extension  630   b  formed on the base layer  630   a . According to various embodiments, the base layer  630   a  is analogous to the base layer  122   a,  described in detail above, and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties. Similarly, conductive extension  630   b  is analogous to the conductive extension  122   b , described in detail above, and may be formed from the same and/or similar materials and may share many of the same physical and/or electrical properties. 
         [0034]    The following examples pertain to further embodiments. 
         [0035]    In Example 1, a transistor structure, which includes a substrate; a well region of a first impurity type in the substrate; at least one transistor formed at least partially on the well region, a portion of the well region comprising a transistor channel; a structure of the first impurity type in the substrate enclosing the well region; and a trench and/or field oxide isolation layer in the substrate enclosing the structure; where a concentration of the first impurity type in the structure enclosing the well region is higher than a concentration of the first impurity type in the well region. 
         [0036]    In Example 2, the transistor structure of Example 1, where the first impurity type is a p-type dopant and the second impurity type is an n-type dopant. 
         [0037]    In Example 3, a transistor structure, which includes a substrate; a well region of a first impurity type in the substrate; at least one transistor formed at least partially on the well region, the transistor having a drain region in the well region and a plurality of source regions at least partially in the well region, said source regions being arranged around the gate region; the well region including a plurality of channels separating the drain region from the plurality of source regions; a structure of the first impurity type in the substrate enclosing the well region; and a trench and/or field oxide isolation layer in the substrate enclosing the isolation structure; where a concentration of the first impurity type in the structure enclosing the well region is higher than a concentration of the first impurity type in the well region. 
         [0038]    In Example 4, the transistor structure of Example 3, further includes an oxide layer over the well region which surrounds the drain region and extends over each of the channels from the plurality and/or overlaps the channel-regions, known from classical CMOS-transistor layouts, defined by W (channel-width); and a gate electrode on the oxide layer, e.g. the channel-width is not determined any more by the lateral interface of the oxide-layer (GOX) and the field-oxide layer (e.g. LOCOS or STI), as it is state of the art today in a classical CMOS-transistor. The definition of the channel length remains un-changed, as known from stat of the art, determined by the length of the gate-electrode between source and drain. 
         [0039]    In Example 5, the transistor structure of Example 3 &amp; 4, where a lateral extension of the oxide layer is bounded by the structure of the first impurity type. 
         [0040]    In Example 6, the transistor structure Examples 3-5, where the drain region includes a substantially square structure; and the plurality of source regions include four source regions arranged around the perimeter of the drain region in a substantially cross-shaped configuration. 
         [0041]    In Example 7, the transistor structure of Examples 3-5, where the drain region includes a substantially octagonal structure; and the plurality of source regions include eight source regions arranged around the perimeter of the drain diffusion region in a substantially octagonal configuration. Generally the drain region is determined by a 2 n -corner structure and 2 n  sources are arranged around the common drain diffusion. n=1,2,3,4 . . . ∞. 
         [0042]    In Example 8, the transistor structure of Examples 3-5, where the drain region includes a substantially circular structure; and the plurality of source regions includes a substantially annular structure concentrically arranged with the drain region. Compare to Example 7: n=∞. 
         [0043]    In Example 9, the transistor structure of Example 8, where the gate electrode includes a substantially annular structure situated concentrically with the drain region and a planar section extending over the drain region and the plurality of source regions. 
         [0044]    In Example 10, the at least one field effect transistor of Examples 3-9, where the first impurity type is a p-type dopant and the second impurity type is an n-type dopant; or or: where the first impurity type is a n-type dopant and a second impurity type is an p-type dopant. 
         [0045]    In Example 11, at least one field effect transistor includes a substrate; a gate dielectric layer on the substrate; and a trench or a field oxide isolation layer in the substrate enclosing the gate dielectric layer; where the gate dielectric layer is structured such that it does not extend over the trench isolation layer. 
         [0046]    In Example 12, the at least one field effect transistor of Example 11 further includes a well region of a first impurity type in the substrate; and at least one transistor gate formed at least partially on the well region, a portion of the well region including a least one transistor channel; where the gate dielectric layer is arranged between the at least one transistor gate and the at least one transistor channel. 
         [0047]    In Example 13, the at least one field effect transistor of Examples 11 &amp; 12 further includes a ring structure of the first impurity type arranged in the substrate between the well region and the trench and/or field oxide isolation layer; where a concentration of the first impurity type in the ring structure is higher than a concentration of the first impurity type in the well region. 
         [0048]    In Example 14, the at least one field effect transistor of Example 13, where a lateral extension of the gate dielectric layer is bounded and/or terminated by a ring structure for source or drain diffusion. 
         [0049]    In Example 15, the at least one field effect transistor of Examples 11-14 further includes a drain region in the well region and a plurality of source regions at least partially in the well region, said source regions being arranged around the at least one transistor gate. 
         [0050]    In Example 16, the at least one field effect transistor of Example 15, where the plurality of source regions include four source regions arranged around the perimeter of the drain region in a substantially cross-shaped configuration; and where the well region includes four transistor channels, one channel formed between each source region and a corresponding portion of the drain region. 
         [0051]    In Example 17, the at least one field effect transistor of Example 15, where the plurality of source regions includes eight source regions arranged around the perimeter of the drain diffusion region in a substantially octagonal configuration; and where the well region includes eight transistor channels, one channel formed between each source region and a corresponding portion of the drain region. Generally the number of transistor-channels is determined by 2n, n=1,2,3,4 . . . ∞. 
         [0052]    In Example 18, the at least one field effect transistor of Example 15, where the drain region includes a substantially circular structure; and the plurality of source regions includes a substantially annular structure concentrically arranged with the drain region. See Example 17: n=∞. 
         [0053]    In Example 19, the at least one field effect transistor of Example 18, where the gate electrode includes an annular structure situated concentrically with the drain region and a planar section extending from the annular structure over the drain region and the plurality of source regions. Optional the source region might be placed in the center as common source diffusion surrounded by a plurality of drain regions. 
         [0054]    In Example 20, the at least one field effect transistor of Examples 11-19, where the first impurity type is a p-type dopant and the second impurity type is an n-type dopant; or: where the first impurity type is a n-type dopant and a second impurity type is a p-type dopant. 
         [0055]    In Example 21, a transistor structure which includes a substrate; a well region of a first impurity type in the substrate; a first diffusion region of a second impurity type in the well region; a second diffusion region of the second impurity type in the well region, a portion of the well region forming a channel separating the first diffusion region and the second diffusion region; an isolation structure of the first impurity type in the substrate enclosing the well region; and a trench isolation layer in the substrate enclosing the isolation structure; where a concentration of the first impurity type in the isolation structure is higher than a concentration of the first impurity type in the well region. 
         [0056]    In Example 22, the transistor structure of Example 21 further includes an oxide layer over the channel; a gate electrode on the oxide layer; a source electrode on the first diffusion region; a drain electrode on the second diffusion region; and at least one body connection electrode on the isolation structure. 
         [0057]    In Example 23, the transistor structure of Examples 21 and 22 further includes at least one lightly doped drain region of the second impurity type extending from the perimeter of the first diffusion region and into the channel, the at least one lightly doped drain region having a concentration of the second impurity type which is lower than a concentration of the second impurity type in the first diffusion region; and at least one lightly doped drain region of the second impurity type extending from the perimeter of the second diffusion region and into the channel, the at least one lightly doped drain region having a concentration of the second impurity type which is lower than a concentration of the second impurity type in the second diffusion region. 
         [0058]    In Example 24, the transistor structure of Examples 21 &amp; 23, where the gate electrode includes a stack layer formed on the oxide layer and a spacer structure on at least one sidewall of the stack layer. 
         [0059]    In Example 25, the transistor structure of Examples 21-24, where the source electrode is electrically coupled to the at least one body connection electrode. 
         [0060]    In Example 26, the transistor structure of Examples 21-25, where the first impurity type includes a p-type dopant and the second impurity type includes an n-type dopant. 
         [0061]    In Example 27, a transistor structure, which includes a substrate; a well region of a first impurity type in the substrate; a primary diffusion region of a second impurity type in the well region; a plurality of secondary diffusion regions of the second impurity type in the well region arranged around the perimeter of the primary diffusion region; the well region including a plurality of channels separating the primary diffusion region from the secondary diffusion regions; an isolation structure of the first impurity type in the substrate enclosing the well region; and a trench isolation layer in the substrate enclosing the isolation structure; where a concentration of the first impurity type in the isolation structure is higher than a concentration of the first impurity type in the well region. 
         [0062]    In Example 28, the transistor structure of Example 27, further including an oxide layer over the well region which surrounds the primary diffusion region and extends over each of the channels from the plurality; a gate electrode on the oxide layer; at least one drain electrode in the primary diffusion region; at least one source electrode in each of the secondary diffusion regions; and at least one body connection electrode in the isolation structure. 
         [0063]    In Example 29, the transistor structure of Examples 27 &amp; 28, where gate electrode includes a stack layer formed on the oxide layer and a at least one gate contact formed on the gate electrode. 
         [0064]    In Example 30, the transistor structure of Examples 27-29, where at least one source electrode from each of the secondary diffusion regions is electrically coupled to the at least one body connection electrode. 
         [0065]    In Example 31, the transistor structure of Examples 27-30, where the primary diffusion region is a transistor drain region; and the plurality of secondary diffusion regions is a plurality of transistor source regions. 
         [0066]    In Example 32, the transistor structure of Examples 27-31, where the plurality of secondary diffusion regions includes four diffusion regions arranged around the perimeter of the primary diffusion region to form a substantially cross-shaped configuration. 
         [0067]    In Example 33, the transistor structure of Examples 27-32, where the plurality of secondary diffusion regions includes eight diffusion regions arranged around the perimeter of the primary diffusion region in a substantially octagonal configuration. 
         [0068]    In Example 34, the transistor structure of Examples 27-33, where the primary diffusion region includes a substantially circular structure and; where the plurality of secondary diffusion regions includes substantially annular structure concentrically arranged with the primary diffusion region. 
         [0069]    In Example 35, the transistor structure of Examples 27-34, where and the gate electrode includes a substantially annular structure situated concentrically with the primary diffusion region and a planar section extending over the primary diffusion region and the secondary diffusion region. 
         [0070]    In Example 36, a method of forming a transistor structure, the method including providing a substrate; forming a well region of a first impurity type in the substrate; forming a first diffusion region of a second impurity type in the well region; forming a second diffusion region of the second impurity type in the well region, shaping a portion of the well region to form a channel separating the first diffusion region and the second diffusion region; forming an isolation structure of the first impurity type in the substrate to enclose the well region; and forming a trench isolation layer in the substrate to enclose the isolation structure; where a concentration of the first impurity type in the isolation structure is higher than a concentration of the first impurity type in the well region. 
         [0071]    In Example 37, the method of Example 36 further includes forming an oxide layer over the channel; providing a gate electrode on the oxide layer; forming a source electrode on the first diffusion region; forming a drain electrode on the second diffusion region; and forming at least one body connection electrode on the isolation structure. 
         [0072]    In Example 38, the method of Examples 36 &amp; 37 further includes forming at least one lightly doped drain region of the second impurity type extending from the perimeter of the first diffusion region and into the channel, the at least one lightly doped drain region having a concentration of the second impurity type which is lower than a concentration of the second impurity type in the first diffusion region; and forming at least one lightly doped drain region of the second impurity type extending from the perimeter of the second diffusion region and into the channel, the at least one lightly doped drain region having a concentration of the second impurity type which is lower than a concentration of the second impurity type in the second diffusion region. 
         [0073]    In Example 39, a method for forming a transistor structure includes providing a substrate; forming a well region of a first impurity type in the substrate; forming a primary diffusion region of a second impurity type in the well region; forming a plurality of secondary diffusion regions of the second impurity type in the well region; arranging the plurality of secondary diffusion regions around the perimeter of the primary diffusion region; forming the well region into a plurality of channels separating the primary diffusion region from the secondary diffusion regions; forming an isolation structure of the first impurity type in the substrate enclosing the well region; and providing a trench isolation layer in the substrate enclosing the isolation structure; where a concentration of the first impurity type in the isolation structure is higher than a concentration of the first impurity type in the well region. 
         [0074]    In Example 40, the method of Example 39 further includes forming an oxide layer over the well region and shaping the oxide layer to surround the primary diffusion region and extend over each of the channels from the plurality; providing a gate electrode on the oxide layer; forming at least one drain electrode in the primary diffusion region; forming at least one source electrode in each of the secondary diffusion regions; and forming at least one body connection electrode in the isolation structure.

Technology Classification (CPC): 7