Patent Publication Number: US-8111112-B2

Title: Semiconductor device and method of forming compact coils for high performance filter

Description:
CLAIM TO DOMESTIC PRIORITY 
     The present application is a continuation of U.S. patent application Ser. No. 11/734,410, now U.S. Pat. No. 7,688,160, filed Apr. 12, 2007, and claims priority to the foregoing parent application pursuant to 35 U.S.C. §120. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates in general to electronic devices and, more particularly, to a semiconductor device and method of forming compact coils for a high performance filter. 
     BACKGROUND OF THE INVENTION 
     Electrical components, such as inductors, capacitors, computer chips, and the like, are increasingly in demand for a broad range of applications. Along with an increased overall need for these components has been a drive to make the components more miniaturized in size and footprint. Smaller electrical components carry through to smaller electrical devices, such as telephones and portable music player devices. 
     Electrical devices known as filters/diplexers are typically comprised of lumped LC networks or distributed-line resonators. The inductor components in typical LC type circuits are not magnetically coupled. Moreover, the size of such inductor components is usually large, particularly for low-frequency applications such as a Global System for Mobile communications (GSM) implementation in devices such as mobile phones. 
     Distributed-line topologies require the length of the respective “line” to be in the order of one-fourth (¼) of the wavelength at the operating frequency. As a result, line length requirements also limit a low frequency application for distributed-line topologies. 
     A need exists for an inductive component that realizes a compact design yet is usable in low-frequency applications. The design would benefit from compatibility with existing semiconductor technologies that allow for integration of electrical components in semiconductor devices. 
     SUMMARY OF THE INVENTION 
     Accordingly, in, one embodiment, the present invention is a method of forming a semiconductor device comprising the steps of providing a substrate, forming a first coil structure over the substrate, forming a second coil structure over the substrate adjacent to the first coil structure, and forming a third coil structure over the substrate adjacent to the second coil structure. The first, second, and third coil structures each have a height greater than a skin current depth of the coil structure defined as a depth which current reduces to 1/(complex permittivity) of a surface current value. 
     In another embodiment, the present invention is a method of forming a semiconductor device comprising the steps of providing a substrate, forming a first coil structure over the substrate, and forming a second coil structure over the substrate adjacent to the first coil structure. The first and second coil structures each have a height greater than a skin current depth of the coil structure. 
     In still another embodiment, the present invention is a method of forming a semiconductor device comprising the steps of providing a substrate, forming a first coil structure over the substrate, and forming a second coil structure over the substrate adjacent to the first coil structure. A first end of the first coil structure is placed 90 degrees from a first end of the second coil structure. 
     In still another embodiment, the present invention is a semiconductor device comprising a substrate and first coil structure formed over the substrate. A second coil structure is formed over the substrate adjacent to the first coil structure. The first and second coil structures each have a height greater than a skin current depth of the second coil structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary prior art diplexer topology using distributed lines; 
         FIGS. 2 and 3  illustrate an exemplary prior art diplexer topology using lumped LC circuits; 
         FIG. 4  illustrates an exemplary coil structure; 
         FIG. 5  illustrates a schematic of an exemplary filter device incorporating a coil structure; 
         FIG. 6  illustrates an exemplary layout of a filter device incorporating a coil structure and a plurality of capacitor devices deposited over a substrate; 
         FIG. 7  illustrates the layout depicted in  FIG. 6  in a three-dimensional view; 
         FIG. 8  illustrates an exemplary electromagnetic (EM) response of the filter device depicted in  FIGS. 6 and 7 ; 
         FIGS. 9A and 9B  illustrate an exemplary coil structure, including exemplary dimensions; 
         FIG. 10A  illustrates a conceptual depiction of a capacitor device in a side-view; 
         FIG. 10B  illustrates a three-dimensional view of a capacitor device incorporated into a filter device; 
         FIG. 10C  illustrates a side view of the capacitor device of  FIG. 10B ; and 
         FIG. 10D  illustrates a larger side view of the capacitor device of  FIG. 10B . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The present invention is described in one or more embodiments in the following description with reference to the Figures, in which like numerals represent the same or similar elements. While the invention is described in terms of the best mode for achieving the invention&#39;s objectives, it will be appreciated by those skilled in the art that it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims and their equivalents as supported by the following disclosure and drawings. 
     Turning to  FIG. 1 , an exemplary diplexer topology  10  of the prior art is shown incorporating a distributed lines methodology. A comb-line transmission filter  12  and a comb-line reception filter  14  are coupled to a transmitter  16  and receiver  18 , respectively, and an antenna  20  as shown through electrodes  54  and  56 . Transmission filter  12  includes three strip line resonators  22 ,  24 , and  26 . Likewise, reception filter  14  includes three strip line resonators  28 ,  30 , and  32  as shown. 
     A coupling capacitor  34  is formed between a coupling electrode and a strip line resonator electrode, and is electrically connected to the antenna  20  through an antenna terminal  52 . Likewise, coupling capacitor  44  is positioned as shown in the reception filter  14 . The strip line resonators are lowered in resonance frequency by loading capacitors  38 ,  40 ,  42 ,  46 ,  48 , and  50 . The strip line resonators  22 ,  24 , and  26  are magnetically coupled  62  as shown. 
     Because topology  10  uses a distribution-line methodology to perform the filtering functionality, it is limited in low-frequency (e.g., less than 2 gigahertz) applications, due to the previously described line length requirement which adds size to the component as the operating frequency of the respective device moves lower. 
       FIG. 2  shows an exemplary diplexer topology  64  of the prior art to illustrate incorporating the alternative, lumped LC circuit components methodology. A laminate  70  has a transmitter terminal electrode  66  and a receiver terminal electrode  68  provided on the left and right ends, respectively. An antenna terminal electrode is shown positioned between grounding terminal electrodes  72  and  76 , which are provided on the rear surface of the laminate  70 . Grounding terminal electrodes  74  and  78  are provided on the front surface. 
       FIG. 3  shows an electrical circuit equivalent to the prior art laminated type duplexer topology  64  shown in  FIG. 2  comprising two band pass filter components (e.g., BPF 1  and BPF 2 ). Each band pass filter incorporates nine (9) LC components (e.g., C 1 , L 1 ; C 2 , L 2 ; etc.). While the topology  64  can be used in lower frequency applications, the size and footprint of the respective topology are again prohibitively large. Further, inductor subcomponents L 1 , L 2 , L 3 , L 4 , L 5 , and L 6  are not magnetically coupled. 
     The present invention achieves a compact design which would normally be larger in size using a conventional technique as found in either of the described lumped LC or distributed-line prior art implementations. A series of tube structures is deposited on a substrate and formed into a coil structure. The coil structures can be adapted in various ways to suit a particular application. The coil structures can be easily integrated with other miniaturized electrical components such as capacitor devices using substrates, as will be seen, to perform the filtering and diplexing functionality previously seen in the prior art but using a much smaller size and footprint. 
     A series of coil structures can be used for designs of integrated passive devices (IPD) that use silicon and semiconductor technologies as will be described. Individual coil structures can be combined into a series of integrated coil structures. A series of coil structures can include two, three, four or more single coil structures. The integrated coil structures form spiral inductor devices which are magnetically coupled together. Beyond the inductive property from a single coil structure, a series of integrated coil structures has an associated mutual inductance which helps to realize a more compact design. In addition, the coil structures are efficient and cost-effective to manufacture. 
     Turning to  FIG. 4 , a conceptual diagram of a plurality of coil structures  82  is shown. Three coil structures are depicted, but again, two, three, or more coil structures can be realized in any given implementation. Coil structures  84 ,  86 , and  88  are formed by depositing metal tube-like structures over a substrate. 
     The metal tube-like structures, or “tubes” can be arranged in the round shape as shown. Additionally, the tubes can be configured in other geometrical patterns, such as an octagonal geometrical design, to suit a particular need. The tube structures can have a square, round, or rectangular cross section. In one embodiment, the tube structures are comprised of a copper (Cu) or copper alloy metal material, although additional metals and metal alloy materials can be utilized as required. The tubes can be deposited in a metallization process, accordingly, the tube structures can also be referred to as “metallizations.” The coil structures  82  are magnetically coupled to each other. 
     Coils  84 ,  86 , and  88  include respective ends  90 ,  92 , and  94  which can be adapted to provide an electrode-like function. Ends  90 ,  92 , and  94  can be positioned as shown. In the present illustration, the coil  86  having end  92  is rotated ninety (90) degrees with respect to the coil  84  having end  90 . Similarly, coil  88  having end  94  is rotated ninety (90) degrees with respect to the coil  86  having end  92 , and one-hundred eighty (180) degrees in respect to the coil  84  having end  90 . 
     The coils  84 ,  86 , and  88  can be rotated similarly having degrees of angle between 0 and 360 degrees in various embodiments. In other words, the coils  84 ,  86 , and  88  can be in any degree of angle with respect to another coil. Again, any number of coils (e.g., 2, 3, 4 or above) can be combined in a variety of embodiments. 
     Turning to  FIG. 5 , a schematic diagram of a filter device  100  incorporating a plurality of coil structures is depicted. The device  100  consists of six (6) capacitors and three (3) compact coil structures. A first capacitor (C 13 ) is coupled between an input terminal  102  and an output terminal  104 . Coils  106 ,  108 , and  110  are coupled to ground  112  at a first end. Again, the coils  106 ,  108 , and  110  are magnetically coupled as illustrated by dotted line  114 . Capacitors C 1 , C 2 , and C 3  are coupled to coils  106 ,  108 , and  110  at nodes  116 ,  118 , and  120 , and coupled to ground  122  as shown. Finally capacitors C 12  and C 23  are coupled in series between nodes  118  and  120  as depicted. C 13  is coupled between the input terminal  102  and output terminal  104  at nodes  124  and  126 , as shown. 
     In one embodiment, the capacitance of C 1 , C 2 , and C 3  is 1 picofarad (pF), while the capacitance of C 12  and C 23  are 10 picofarads (pF) and the capacitance of C 13  is 2.62 picofarads (pF). As one skilled in the art would anticipate, however, the capacitance of the depicted capacitors can be varied in any respect to suit a particular application and provide an appropriate filter response. 
       FIG. 6  illustrates a filter device incorporating an embodiment of the coil structure of the present invention in a layout view. The various subcomponents depicted share the appropriate figure numbers from  FIG. 5 , including an input terminal  102  and output terminal  104 . Coils  106 ,  108 , and  110  are positioned as shown. A portion of coil  106  is positioned interiorly to coil  108 . Similarly, a portion of coil  108  is positioned interiorly to coil  110 . Again, the coils  106 ,  108 , and  110  are magnetically coupled. 
     Coils  106 ,  108 , and  110  are each coupled to a ground bar  112  as shown at a first end. Capacitors C 12  and C 23  are coupled together through node  116 . Similarly, capacitors C 1 , C 2 , and C 3  are coupled between the ground bar  112  and nodes  116 ,  118 , and  120 . Nodes  124  and  126  are coupled as shown between capacitor C 13  and input  102  and output  104 . 
     Coils  106 ,  108 ,  110 , as well as the various capacitors, leads, and ground bar structures are deposited over and extend horizontally across a substrate, while maintaining a substantially flat vertical profile.  FIG. 7  illustrates the layout shown in  FIG. 6  in a three-dimensional view. Here again, the respective figure numbers from  FIGS. 5 and 6  are shown. Input terminal  104 , connecting leads to the various capacitors (e.g., capacitor C 12 ), and output terminal  104  are deposited over the substrate  127 . Coils  106 ,  108 , and  110 , ground bar  112 , and the various capacitor structures are deposited over the terminals  102  and  104  and connecting leads. Coils  106 ,  108 , and  110  extend horizontally across substrate  127  as shown. 
     As previously described, coils  106 ,  108 , and  110  can form an inductive device which is consistent with other so-called “integrated passive devices” (IPD). A wide variety of the passive devices such as an inductor or filter device, but also including resistors, capacitors, BALUNs, transceivers, receivers, and other interconnects are placed on a substrate such as substrate  127 . The substrate  127  can include silicon, glass, laminate, or ceramic materials. 
     Integration of an inductor or filter device as described results in a high performance system level solution, which provides a significant reduction in die size, weight, number of interconnections and system board space requirements, and can be used for many applications. 
     A wide variety of filter designs can be constructed which include coils  106 ,  108 ,  110  to suit particular applications. The filter designs can be based on differing technologies, including silicon, printed circuit board (PCB) (laminate) or low temperature co-fired ceramic (LTCC) technologies. Again, as a result, substrate  127  can include materials such as silicon or silicon-like materials, laminate materials, glass and ceramic materials. 
     Coils  106 ,  108 , and  110 , as well as filter device  100  and accompanying subcomponentry can be constructed using materials, techniques, and manufacturing equipment known in the art, including various thin-film deposition methods and techniques and incorporating the use of known manufacturing tools and equipment. 
     Turning to  FIG. 8 , an exemplary electromagnetic (EM) response curve  128  for a filter device  100  incorporating coils  106 ,  108 , and  110 , is depicted.  FIG. 8  illustrates a band pass filter (BPF) performance in the 1.5 GHz band, where a control signal  130  and filtered signal  132  are depicted. 
     As one skilled in the art would expect, filtered signal  132  is attenuated outside of the band pass range. Further, one skilled in the art will appreciate that a wide range of frequency curves having different rejection levels can be achieved by adjustment of the various capacitor devices of filter  100 . 
       FIGS. 9A and 9B  further illustrate the coil structures in a three-dimensional view. Again, coils  84 ,  86  and  88  are shown, having electrodes  90 ,  92 , and  94  which are oriented at 90 degree angles.  FIG. 9B  illustrates various dimensional aspects of coil structure  88 , including height (H)  134 , width (W)  136 , coil spacing (S)  138 , and inner opening diameter (d)  140 . 
     When an electromagnetic wave interacts with a conductive material, mobile charges within the material are made to oscillate back and forth with the same frequency as the impinging fields. The movement of these charges, usually electrons, constitutes an alternating electric current, the magnitude of which is greatest at the conductor&#39;s surface. The decline in current density versus depth is known as the “skin effect.” 
     So-called “skin depth” is a measure of the distance over which the current falls to 1/e of its original value. A gradual change in phase accompanies the change in magnitude, so that, at a given time and at appropriate depths, the current can be flowing in the opposite direction to that at the surface. 
     The skin depth is a property of the material that varies with the frequency of the applied wave. A respective skin depth can be calculated from the relative permittivity and conductivity of the material and frequency of the wave. First, the material&#39;s complex permittivity, ε c  is found such that 
                     ɛ   c     =     ɛ   ⁡     (     1   -     j   ⁢           ⁢     σ     ω   ⁢           ⁢   ɛ           )               (   1   )               
where:
         ε=permittivity of the material of propagation,   ω=angular frequency of the wave, and   σ=electrical conductivity of the material of propagation.       

     In one embodiment, to overcome the skin effect and minimize metal loss, a respective thickness of the coil structures  84 ,  86 , and  88  is maintained to be larger than the respective skin depth. 
     Again, in one embodiment, copper (Cu) is utilized as a metal material for coil  88 . A thickness of eight (8) micrometers exceeds the skin depth for copper (taking into account the electrical conductivity of the copper metal). A thickness greater than five (5) micrometers is recommended, with, again, a preferable thickness of eight (8) micrometers. 
     The total length of coil  88  is related to the operating frequency of coil  88 . In one embodiment, the coil width  136  is eight (8) micrometers. The coil height  134  is also eight (8) micrometers. The coil spacing  140  is eighty (80) micrometers. The number of turns (T) is three (3). The inner opening diameter  140  is 240 micrometers. Total area is approximately 0.7×0.7=0.49 mm 2 . The estimated inductance for the coil  88  is estimated to be approximately 6.5 nanohenrys (nH). 
     Again, as one skilled in the art would anticipate, the various dimensions of coil  88 , as well as coils  86 , and  84  can be optimized using tools such as a computer program to suit differing space requirements and/or differing specification requirements. 
       FIG. 10A  illustrates the concept of a thin film capacitor design which is integrated with the present invention in one embodiment. Terminal electrodes  144  and  148  are located on a top portion of the device  142 . A first thin metal or metal or metal alloy material  146  is separated by a dielectric material  152  and forms the bottom capacitor plate  146 . A top capacitor plate structure  150  is deposited above the dielectric  152 . 
       FIG. 10B  illustrates a thin film capacitor device  154  which can be deposited over a substrate  160  and coupled to coils  106 ,  108 , or  110 . Capacitor  154  includes the top electrodes  144  and  148 , which are deposited over the top capacitor plate  156 . A dielectric material  152 , which is thin relative to the top capacitor plate  156  and thereby not illustrated for conceptual purposes, separates the plate  156  from the bottom plate  158 . 
       FIG. 10C  illustrates the capacitor device  154  in a side view, with the substrate  160  removed for purposes of illustration. In Example A manufacturing technique, the bottom capacitor plate  158  is deposited over the substrate  160 . A thin-film dielectric  152  is deposited over the bottom plate  158 . The top capacitor plate  156  is then deposited over the dielectric material  152 . 
     An additional layer is formed over the top plate  156  to provide structural support. A first via  162  allows for electrical connectivity between the bottom electrode  144  and the bottom plate  158 . Electrodes  144  and  148  are then formed. As one skilled in the art will expect, coils  106 ,  108  and  110  can be deposited consistent with Example A manufacturing technique at an appropriate step in the deposition processes. 
       FIG. 10D  illustrates the exemplary side view depiction of  FIG. 10C  in a larger sense, and includes the second view via structure  164  which allows electrical connectivity from electrode  144  through via  162 , through plate  156  and via  164  to bottom plate  158 . 
     In one embodiment, exemplary dimensions can include one (1) micrometer in thickness for bottom plate  158 . Via  164  can be 0.2 um thick. The thin-film dielectric can also be 0.2 um thick. Top plate  156  can be 2 um thick. Via  162  can be 3 um in thickness. Finally, electrodes  144  and  148  can be 8 um in thickness. Again, however, as one skilled in the art will appreciate, various additional and differing thicknesses can be achieved for specific applications and implementations. 
     Coil structures such as coils  106 ,  108 , and  110  in implementations over a substrate as depicted can provide conventional filtering and diplexing functionality in a dramatically decreased size and footprint. 
     While one or more embodiments of the present invention have been illustrated in detail, the skilled artisan will appreciate that modifications and adaptations to those embodiments may be made without departing from the scope of the present invention as set forth in the following claims.