Abstract:
A resonant element is provided with a multilayer board, comprising a plurality of conductor layers isolated by a dielectric, a signal via conductor, penetrating through the multilayer board, and a plurality of ground vias, penetrating thought the multilayer board and disposed around the signal via conductor. The multilayer board comprises a first conductor layer, a second conductor layer, and a corrugated conductor layer disposed between the first and the second conductor layers. The corrugated conductor layer comprises a corrugated signal plate, connected to the signal via conductor, and a corrugated ground plate, connected to the plurality of ground vias, isolated from the corrugated signal plate by the dielectric.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to resonant elements, resonators, and filters based on multilayer board technologies. 
       BACKGROUND ART 
       [0002]    Miniaturization and cost-effectiveness are key directions in development of modern and next-generation networking and computing systems. Multilayer boards serve as main interconnect technologies in electronics devices constructed by means of chip, package and printed circuit board components. Besides that, interconnections are a base in forming passive components. Open-circuited and short-circuited planar transmission line segments of different forms and dimensions act as stubs, resonators, and other elements of passive components. A reason why the transmission lines have been used for such purposes is that these structures are well wave-guiding structures which can provide operation on a fundamental mode (for example, TEM or Quasi-TEM) with defined propagation constant and characteristic impedance in a wide frequency band. 
         [0003]    Via structures formed by signal and ground vias conjointly can be not only vertical interconnections between planar transmission lines disposed at different conductor layers of the multilayer board but also as building blocks of passive components. 
         [0004]    Japanese Laid Open Application JP 2008-507858 (US 2008/0093112A1) discloses composite via structures which can be used to design both open-circuited and short-circuited stubs and, as result, compact filtering components based on multilayer boards. 
         [0005]    However, further dimensional reductions of passive components including filtering structures are necessary in a cost-effective manner for their application in next-generation computing and networking systems. 
         [0006]    Also, it is important to obtain methods which can be used to control a bandwidth of filters. 
       CITATION LIST 
       [0007]    Patent Literature: Japanese Laid Open Application JP 2008-507858 (US 2008/0093112A1). 
       SUMMARY OF INVENTION 
       [0008]    It is an object of the present invention to provide compact resonant elements in a multilayer board by means of via structures. 
         [0009]    In an aspect of the present invention, such a resonant element is provided by forming a specific coaxial transmission line structure in a multilayer board. In this specific coaxial transmission line, inner and outer conductive boundaries are constructed as followings. The inner conductive boundary comprises a signal via and conductive plates connected to the signal via, wherein conductive plates have corrugated edges. The outer conductive boundary of the coaxial transmission line comprises ground vias and ground conductive plates connected to ground vias. Edges of ground conductive plates disposed in the area between signal and ground vias are corrugated. As result, signal and ground plates disposed at the same conductor layer form double corrugated surface in which signal and ground parts are separated by an isolating slit. 
         [0010]    Due to such double corrugations at the conductive layers in the area between signal and ground vias, the effective relative permittivity with the magnitude larger than the relative permittivity of the board isolating material is established and, as result, resonant conditions are achieved in a short via structure segment. 
         [0011]    It is another object of this invention to provide open-circuited and short-circuited resonant stubs, resonators, and filtering components, using invented resonant elements, as a result, to reduce their transverse dimensions. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1A  is a vertical cross-sectional view illustrating a resonant element in an exemplary embodiment of the present invention; 
           [0013]      FIG. 1B  is a horizontal cross-sectional view of the resonant element shown in  FIG. 1A  on the  1 B section; 
           [0014]      FIG. 1C  is a horizontal cross-sectional view of the resonant element shown in  FIG. 1A  on the  1 C section; 
           [0015]      FIG. 1D  is top and bottom views of the resonant element shown in  FIG. 1A ; 
           [0016]      FIG. 2A  is a vertical cross-sectional view illustrating a relating art structure; 
           [0017]      FIG. 2B  is a horizontal cross-sectional view of the relating art structure shown in  FIG. 2A  on the  2 B section; 
           [0018]      FIG. 2C  is top and bottom views of the relating art structure shown in  FIG. 2A ; 
           [0019]      FIG. 3A  is a vertical cross-sectional view illustrating another relating art structure; 
           [0020]      FIG. 3B  is a horizontal cross-sectional view of the relating art structure shown in  FIG. 3A  on the  3 B section; 
           [0021]      FIG. 3C  is top and bottom views of the relating art structure shown in  FIG. 3A ; 
           [0022]      FIG. 4A  is a vertical cross-sectional view illustrating a resonant element in another exemplary embodiment of the present invention; 
           [0023]      FIG. 4B  is a horizontal cross-sectional view of the resonant element shown in  FIG. 4A  on the  4 B section; 
           [0024]      FIG. 4C  is top and bottom views of the resonant element shown in  FIG. 4A ; 
           [0025]      FIG. 5  is a graph showing the effect of the double-corrugated plates on the electrical performance of the resonant element by means of simulated return losses; 
           [0026]      FIG. 6  is a graph showing the effect of the double-corrugated plates on the electrical performance of the resonant element by means of simulated insertion losses; 
           [0027]      FIG. 7A  is a vertical cross-sectional view illustrating a filter with a resonant stub element in an exemplary embodiment of the present invention; 
           [0028]      FIG. 7B  is a horizontal cross-sectional view of the filter shown in  FIG. 7A  on the  7 B section; 
           [0029]      FIG. 7C  is a horizontal cross-sectional view of the filter shown in  FIG. 7A  on the  7 C section; 
           [0030]      FIG. 7D  is top and bottom views of the filter shown in  FIG. 7A ; 
           [0031]      FIG. 8A  is a vertical cross-sectional view illustrating a filter with a resonant stub element in an exemplary embodiment of the present invention; 
           [0032]      FIG. 8B  is a horizontal cross-sectional view of the filter shown in  FIG. 8A  on the  8 B section; 
           [0033]      FIG. 8C  is a horizontal cross-sectional view of the filter shown in  FIG. 8A  on the  8 C section; 
           [0034]      FIG. 8D  is top and bottom views of the filter shown in  FIG. 8A ; 
           [0035]      FIG. 9  is a graph showing the effect of the double-corrugated plates on the electrical performance of the filter by means of simulated return losses; and 
           [0036]      FIG. 10  is a graph showing the effect of the double-corrugated plates on the electrical performance of the filter by means of simulated insertion losses. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0037]    Hereinafter, several types of resonant elements, short-circuited and open-circuited stubs, and filters based on these resonant elements disposed in multilayer boards according to the present invention will be described in detail with reference to attached drawings. But, it would be well understood that this description should not be viewed as narrowing the appended claims. 
         [0038]    In  FIGS. 1A to 1D , an exemplary embodiment of a resonant element in a twelve-conductor-layer board is shown. 
         [0039]    It should be noted that this twelve conductor layer board is only an example of multilayer boards and a number of conductor layers, filling material and other board parameters can be different that depends on applications. 
         [0040]    In present exemplary embodiment, the resonant element is disposed in the vertical direction from the pad  104  at the top conductor layer of the 12-conductor-layer board to pad  104  of the bottom layer of this board. Conductor layers  1 L 1 ,  1 L 2 ,  1 L 3 ,  1 L 4 ,  1 L 5 ,  1 L 6 ,  1 L 7 ,  1 L 8 ,  1 L 9 ,  1 L 10 ,  1 L 11 , and  1 L 12  are isolated by a dielectric  109 . The resonant element comprises a signal via  101  surrounded by ground vias  102 , pads  104  isolated from other conductors by clearance area  103  and a double corrugated surface  110 . This double corrugated surface  110  is formed in the area between the signal via  101  and ground vias  102  and comprises a corrugated signal plate  105  connected to the signal via  101  and a corrugated ground plate  107  connected to ground vias  102 . The signal plate  105  is separated from ground plate  107  by an isolating slit  106  in the double corrugated surface  110 . 
         [0041]    In fixed multilayer board, the resonant frequency is dependent on dimensions of both signal and ground corrugated conductive plates in the area between signal and ground vias and number of conductive layers in which double corrugated surfaces  110  are formed. 
         [0042]    Consider physical mechanisms which are in the base of invented resonant elements. If there are no conductive plates in the area between signal and ground vias, then such structure acts as a coaxial transmission line disposed vertically in a multilayer board. In this coaxial transmission line, the inner conductive boundary is the signal via while ground vias connected to the ground planes act as the outer conductive boundary. 
         [0043]    The relative permittivity, ε r , of a material filling area between inner and outer conductive boundary in this transmission line can be defined as following: 
         [0000]      ε r   =C /(2·π· F ( a, b ))  (1)
 
         [0000]    where C is the capacitance per unit length, F(a, b) is a function of the transverse dimensions of the inner conductive boundary and the distance between inner conductive boundary and outer conductive boundary. 
         [0044]    To form the resonant element, the length, 1, of the coaxial line transmission line segment (shown in  FIG. 1A ) has to satisfy following condition: 
         [0000]      1=( n·π·λ   0 )/(2√ε r )  (2)
 
         [0000]    where n is an integer number, λ 0  is wavelength in free space. 
         [0045]    As one can conclude from Eq. 2, the reduction of the resonant element length can be achieved, if the relative permittivity of the filling material will be increased. In this invention it has been obtained by the creation of an artificial medium in the area between inner and outer conductive boundaries of the coaxial transmission line. This artificial medium is obtained by means of the double-corrugated surface at conductor layers of the multilayer board. Due to this double-corrugated surface, the effective capacitance, ε eff , between inner and outer conductive boundaries increases and, as result, the effective permittivity, ε eff , of the artificial medium between these boundaries is increased. 
         [0046]    Obtained effect can be traced by following equation: 
         [0000]      ε eff   C   eff /(2·π· F ( a, b ))  (3)
 
         [0047]    As result, the length of the resonant element in the case of the double-corrugated surface can be defined as: 
         [0000]      1=( n·π·λ   0 )/(2√ε eff )  (4)
 
         [0048]    Thus as follows from Eq. 4, the increase of the effective permittivity of the filling medium in the coaxial transmission line gives the shorter length of the resonant element, that is, its more compact dimensions. 
         [0049]    To show advantages of invented resonant elements full-wave simulations for typical configurations were carried out by the Finite-Difference Time-Domain (FDTD) technique. 
         [0050]    These configurations include two cases of relating art structures and one case of the resonant element of present invention. 
         [0051]    Consider these cases in details. 
         [0052]    In  FIGS. 2A to 2C , the coaxial transmission line of the length  1  in the twelve-conductor-layer board is shown. This transmission line comprises a signal via conductor  201 , ground vias  202  connected to ground plates  207 , pads  204  connected to the signal via conductor  201 , and clearance area  203  isolating signal conductors from ground conductors. Conductor layer in the board are isolated by a dielectric  209 . 
         [0053]    Another relating art structure is shown in  FIGS. 3A to 3C . This structure presents the coaxial transmission line of the length  1  in the twelve-conductor-layer board. Similarly to above-mentioned case of the relating art, the coaxial transmission line comprises a signal via conductor  301 , ground vias  302  connected to ground plates  307 , pads  304  connected to the signal via conductor  301 , and clearance area  303  isolating signal conductors from ground conductors. However in this case, additional conductor plates  305  are connected to signal via conductor  301  at conductor layers. These plates  305  are isolated from ground conductors by isolating slits  306 . 
         [0054]    The resonant element of present invention is shown in  FIGS. 4A to 4C . This resonant element is formed as a segment of the coaxial transmission line comprising a signal via conductor  401 , ground vias  402  connected to ground plates  407 , pads  404  connected to the signal via conductor  401 , and clearance area  403  isolating signal conductors from ground conductors. In this resonant element, the double corrugated surface is formed in the area between signal via conductor and ground vias by the signal corrugated plate  405  and ground corrugated plate  407  which are separated by an isolating slit  406 . 
         [0055]    Dimensions of three considered structures were as following: the thickness of the twelve-conductor-layer board was 2.944 mm; the thickness of copper conductor layers was 0.035 mm; the diameter of the signal via conductor was 0.65 mm; the pad diameter was 0.95 mm; ground vias in the structures were arranged as the square with the side of 3.32 mm; conductive plates connected to the signal via had the square form with the side of 2.8 mm; the isolating slits separating these plates from the ground conductors had the width of 0.1 mm; the ground plate corrugations had the rectangular form with the depth of 0.8 mm and width of 0.3 mm; the signal plate corrugations had the rectangular form with the depth of 0.8 mm and width of 0.3 mm. 
         [0056]    In  FIGS. 5 and 6 , simulation data for presented three cases are shown by means of return and insertion losses, spectively, in the frequency band up to 10 GHz. 
         [0057]    Thus, if there is only the coaxial transmission line (this case is shown in  FIGS. 2A-2C ), then signal is propagating between top and bottom pads with low losses, that is, there are no resonance effects in this coaxial transmission line segment (corresponding curve is marked as “without plate” in  FIGS. 5 and 6 ). 
         [0058]    The application of the plates connected to the signal via conductor leads to another behavior of the coaxial transmission line segment. This effect is presented in  FIGS. 5 and 6  by the curve indicated as “smooth plate.” As one can see, resonance effect appears for the structure shown in  FIGS. 3A-3C  at the frequency of about 4.7 GHz. The electrical performance of the invented resonant element shown in  FIGS. 4A-4C  is presented in  FIGS. 5 and 6  by the curve marked as “double-corrugated.” For this element, the first resonance frequency is at about 3.7 GHz. 
         [0059]    As follows from simulation results, the application of the double-corrugated surface shifts the position of the resonant frequency to the lower frequency. This means that the shorter length of the coaxial transmission line is required for the case of the double-corrugated surfaces to satisfy the same resonance conditions as for the smooth conductor plates. 
         [0060]    Thus, the application of a double-corrugated surface in the area between signal and ground vias gives more compact resonant elements. 
         [0061]    Here an exemplary embodiment of a filter which comprises an invented resonant element is presented in  FIGS. 7A to 7D . 
         [0062]    In this filter, the invented resonant element is used to obtain a resonance stub. 
         [0063]    In  FIGS. 7A-7D , the filter comprises the coaxial transmission line, planar transmission line  711  and resonant element  712  forming the stub as a part of the coaxial transmission line in a fourteen-conductor-layer board. 
         [0064]    The coaxial transmission line comprises a signal via conductor  701 , pads  704  connected to the signal via conductor  701 , ground vias  702  connected to ground plates  707 , and clearance area  703  isolating signal conductors from ground conductors. 
         [0065]    A planar transmission line  711  is formed as a coplanar waveguide in which the signal trace is shielded by ground plates at the same conductor layer  7 L 3 . One end of the planar transmission line is connected to the coaxial transmission line by means of the pad  704  and another end is a terminal of the filter. It should be noted that pad  704  formed at top conductor layer  7 L 1  is another terminal of the filter. 
         [0066]    The stub is formed by means of the resonant element  712  which is obtained in the part of the coaxial transmission line disposed in the vertical direction from the planar transmission line to the pad  704  at the bottom conductor layer  7 L 14 . This resonant element includes the signal via conductor  701 , ground vias  702  connected to ground plates  707 , pad  704  disposed at the bottom conductor layer  7 L 14 , and double-corrugated surfaces  710  arranged in the area between signal via  701  and ground vias  702 . This double-corrugated surface comprises ground plates  707  and signal plates  705  which are separated by isolating slits  706 . 
         [0067]    It should be noted that the form of corrugations in the double-corrugated surface can be different that is dependent on applications. In  FIGS. 7A-7D , both rectangular and trapezoidal shapes of corrugations are used. 
         [0068]    In  FIGS. 8A to 8D , another exemplary embodiment of the filter using invented resonant element is shown. The construction of this filter similar to that shown in  FIGS. 7A-7D  but the resonant element comprises the same double corrugated surfaces  810  disposed at conductor layers  8 L 4 ,  8 L 5 ,  8 L 6 ,  8 L 7 ,  8 L 8 ,  8 L 9 ,  8 L 10 ,  8 L 11 ,  8 L 12 , and  8 L 13 . Ground plates  807  have corrugations of the rectangular form and signal plates  805  have also corrugations of the rectangular form. These plates are separated by isolating slits  806 . 
         [0069]    The electrical performance of the filter shown in  FIGS. 8A-8D  is presented in  FIGS. 9 and 10  by means of return and insertion losses, respectively. The characteristics of this filter are indicated as “10 layers with double-corrugation.” 
         [0070]    To show effect of a number of double-corrugated surfaces on the frequency response, the parameters of another filter were calculated and are marked in  FIGS. 9 and 10  as “5 layers with double-corrugation.” The structure and dimensions of this filter are the same as in previous case but only five conductor layers, instead ten conductor layers, are used in the resonant element. 
         [0071]    Also in  FIGS. 9 and 10 , the structure in which there are no conductor plates connected to the signal vias is presented and indicated as “stub without plates.” The stub in this structure is similar to the configuration shown in  FIGS. 2A-2C . 
         [0072]    As one can conclude from  FIGS. 9 and 10 , the use of the double corrugated surfaces in the resonant element forming the stub is an important factor to obtain resonance effect and, as result, the filter. If there are no double-corrugated surfaces, then the structure loses the filtering properties. 
         [0073]    Also a number of double-corrugated surfaces are a clearly-expressed parameter to control the position of the resonance in the frequency domain. 
         [0074]    It is well understandable that different types of multilayer boards such as printed circuit boards, packages, interposers for example can be used to form presented resonant elements. Moreover, these resonant elements can be applied as both open-circuited stubs and short-circuited stubs to obtain a required filtering component. 
         [0075]    While the present invention has been described in relation to some exemplary embodiments, it is to be understood that these exemplary embodiments are for the purpose of description by example, and not of limitation. While it will be obvious to those skilled in the art upon reading the present specification that various changes and substitutions may be easily made by equal components and art, it is obvious that such changes and substitutions lie within the true scope and spirit of the presented invention as defined by the claims.