Abstract:
An RFID tag includes: a base portion in a plate shape made of dielectric material; a loop antenna formed by etching and including a first antenna element and a second antenna element disposed in a loop shape along an outer periphery of the base portion; and an IC chip inserted to the loop antenna in series and including a first electrode and a second electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2016-080489, filed on Apr. 13, 2016, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to an RFID tag and a high frequency circuit. 
       BACKGROUND 
       [0003]    In the related art, there is a resonator including a pattern coil formed on a surface or inner layer surface of a printed circuit board and a pattern capacitor connected to the pattern coil in parallel or in series. Such pattern capacitor is configured to have a plurality of small area patterns formed on the surface or inner layer surface of the printed circuit board. 
         [0004]    Examples of the related art include Japanese Laid-open Patent Publication No. 2002-198763. 
       SUMMARY 
       [0005]    According to an aspect of the invention, an RFID tag includes: a base portion in a plate shape made of dielectric material; a loop antenna formed by etching and including a first antenna element and a second antenna element disposed in a loop shape along an outer periphery of the base portion; and an IC chip inserted to the loop antenna in series and including a first electrode and a second electrode. 
         [0006]    In the aspect, the first antenna element includes a first base portion disposed along the outer periphery of the base portion, a first wiring portion protruding from the first base portion and being connected to the first electrode, and a plurality of first protruding portions protruding from the first base portion in a comb shape along the first wiring portion. 
         [0007]    In the aspect, the second antenna element includes a second base portion disposed along the outer periphery of the base portion, a second wiring portion protruding from the second base portion toward a first terminal and being connected to the second electrode, and a plurality of second protruding portions protruding from the second base portion in a comb shape along the second wiring portion and being disposed alternately with the plurality of first protruding portions. In the above aspect, the second antenna element further includes one of a connection portion in a linear shape formed by the etching such that the connection portion is disposed along the first protruding portion and the second protruding portion and the first base portion and the second base portion are connected to each other and a third protruding portion formed by the etching in which the connection portion is separated. 
         [0008]    In the aspect, the connection portion includes a first connection portion and a second connection portion disposed in series between the first base portion and the second base portion and a line width of the first connection portion is narrower than a line width of the second connection portion. 
         [0009]    In the aspect, the third protruding portion protrudes from the second base portion along the plurality of second protruding portions. 
         [0010]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0011]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a diagram illustrating an RFID tag of Embodiment 1; 
           [0013]      FIG. 2  is a diagram illustrating a configuration in which a cover portion is removed from the RFID tag illustrated in  FIG. 1 ; 
           [0014]      FIG. 3  is a diagram illustrating a configuration in which an IC chip and the cover portion are removed from the RFID tag illustrated in  FIG. 1 ; 
           [0015]      FIGS. 4A and 4B  are diagrams illustrating a base portion, a sheet portion, an antenna element, and the IC chip; 
           [0016]      FIG. 5  is a diagram illustrating an inlay; 
           [0017]      FIG. 6  is a diagram illustrating an element obtained by removing the IC chip from the inlay illustrated in  FIG. 5 ; 
           [0018]      FIG. 7  is a diagram illustrating an equivalent circuit of the RFID tag; 
           [0019]      FIGS. 8A and 8B  are diagrams illustrating the RFID tag in which a tapered portion is separated from the element; 
           [0020]      FIG. 9  is a diagram illustrating an equivalent circuit of the RFID tag immediately after the tapered portion is separated from the element; 
           [0021]      FIG. 10  is a diagram illustrating frequency characteristics regarding a reading distance of the RFID tag; 
           [0022]      FIG. 11  is a characteristic diagram illustrating a relationship between an amount of etching and an amount of variation of a resonance frequency; 
           [0023]      FIG. 12  is a diagram illustrating a simulation model of the RFID tag; 
           [0024]      FIG. 13  is a diagram illustrating a result of a simulation of resonance frequency characteristics regarding the reading distance; 
           [0025]      FIG. 14  is a characteristic diagram illustrating a relationship between an amount of etching and an amount of variation of the resonance frequency; 
           [0026]      FIG. 15  is a diagram illustrating an inlay according to a modification example of an embodiment; 
           [0027]      FIG. 16  is a characteristic diagram illustrating a relationship between an amount of etching and an amount of variation of the resonance frequency in the RFID tag using the inlay; 
           [0028]      FIGS. 17A and 17B  are diagrams illustrating a high frequency circuit; and 
           [0029]      FIG. 18  is a diagram illustrating an implementation example of the high frequency circuit. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0030]    Typically, in the related art, it is described that a size of a pattern coil and a pattern capacitor may be selected in a resonator so that increase and decrease of capacitance of the pattern capacitor offset each other and an LC product is not changed, but it is actually very difficult to make the LC product unchanged. 
         [0031]    When the pattern coil and the pattern capacitor are formed by etching, the LC product changes and a resonance frequency may be fluctuated actually due to variation of an etching rate. 
         [0032]    A resonance circuit in the related art, there is a problem that a deviation of the resonance frequency is increased as variation in the etching rate is increased, and thus there is a possibility that an appropriate operation may not be performed. 
         [0033]    As an aspect of the following disclosure, provided are solutions for an RFID tag and a high frequency circuit which may perform an appropriate operation. 
         [0034]    Hereinafter, embodiments to which the RFID tag and the high frequency circuit of the present disclosure are applied will be described. 
         [0035]      FIG. 1  is a diagram illustrating an RFID tag  100  of Embodiment 1. 
         [0036]    The RFID tag  100  of Embodiment 1 includes a base portion  101 , a sheet portion  105 , antenna elements  110  and  120 , an IC chip  130 , and a cover portion  140 . 
         [0037]    Hereinafter, a configuration of the RFID tag  100  will be described using  FIGS. 2 to 6  in addition to  FIG. 1 . In  FIGS. 1 to 6 , an XYZ coordinate system is defined. 
         [0038]      FIG. 2  is a diagram illustrating a configuration in which the cover portion  140  is removed from the RFID tag  100  illustrated in  FIG. 1 .  FIG. 3  is a diagram illustrating a configuration in which the IC chip  130  and the cover portion  140  are removed from the RFID tag  100  illustrated in  FIG. 1 .  FIGS. 4A and 4B  are diagrams illustrating the base portion  101 , the sheet portion  105 , the antenna elements  110  and  120 , and the IC chip  130 .  FIG. 4A  is a diagram illustrating a configuration in which the cover portion  140  is removed from the RFID tag  100  and  FIG. 4B  illustrates a cross section taken along a line IVB-IVB in  FIG. 4A .  FIG. 5  is a diagram illustrating an inlay  150 .  FIG. 6  is a diagram illustrating an element  150 A obtained by removing the IC chip  130  from the inlay  150  illustrated in  FIG. 5 . The element  150 A may be treated as an antenna device. 
         [0039]    The inlay  150  is configured to have the sheet portion  105 , the antenna elements  110  and  120 , and the IC chip  130 . 
         [0040]    Hereinafter, an overall configuration of the RFID tag  100  will be described using  FIGS. 1 to 3 . The RFID tag  100  is illustrated to be transparent in  FIGS. 1 to 3  so that an internal configuration is easy to understand. In addition, a detailed configuration of the antenna elements  110  and  120 , the IC chip  130 , the inlay  150 , and the like will be descried using  FIGS. 4A to 6 . 
         [0041]    In addition, a surface of the RFID tag  100  in a thin plate shape on which the IC chip  130  is mounted is referred to as an upper surface and a surface opposite to the upper surface is referred to as a bottom surface. The bottom surface is an attachment surface for attaching the RFID tag  100  to a metal object or a nonmetal object or the like using, for example, an adhesive. 
         [0042]    Hereinafter, as an example, the RFID tag  100  having a resonance frequency of 892 MHz will be described. That is, in the RFID tag  100  of Embodiment 1, dimensions, inductance, capacitance, and the like of each of parts are optimized so that the resonance frequency of the RFID tag  100  is 892 MHz. In a case where the resonance frequency is a frequency other than 892 MHz, dimensions, inductance, capacitance, and the like of each of the parts may be optimized so that the resonance frequency of the RFID tag  100  is a desired resonance frequency. 
         [0043]    As illustrated in  FIGS. 1 to 4B , the base portion  101  is a member in a thin plate shape (rectangular shape). The base portion  101  may be made of dielectric material and may be made of, for example, ABS resin, polyethylene terephthalate (PET) resin, polycarbonate resin, polyvinyl chloride (PVC) resin, or the like. 
         [0044]    As illustrated in  FIG. 1 , the inlay  150  (see  FIG. 5 ) is wound around the base portion  101  in the X-axis direction. A length of the base portion  101  in the X-axis direction is approximately 31 mm, a width in the Y-axis direction is approximately 23 mm, and a thickness in the Z-axis direction is approximately 1.2 mm. 
         [0045]    Here, end portions of the base portion  101  in the X-axis direction are referred to as end portions  101 A and  101 B. 
         [0046]    As illustrated in  FIG. 5 , the sheet portion  105  is a rectangular film in plan view, and antenna elements  110  and  120  are formed on one surface of the sheet portion  105 . The sheet portion  105  is an example of a sheet member. The sheet portion  105  is, for example, a member in a film shape made of PET film, PET resin, or paper. 
         [0047]    The antenna elements  110  and  120  are formed on one surface of the sheet portion  105  and the sheet portion  105  is wound around and bonded to the base portion  101  in a state where further the IC chip  130  is mounted. That is, the sheet portion  105  is wound around and bonded to the base portion  101  in a state where the inlay  150  (see  FIG. 6 ) is completed and the IC chip  130  is mounted. 
         [0048]    As illustrated in  FIG. 5  and  FIG. 6 , the antenna element  110  is formed within an area of approximately one half of one surface of the sheet portion  105  in the longitudinal direction (X-axis direction). The antenna element  110  is an example of a first antenna element. 
         [0049]    The antenna element  110  includes an element  111 , a protruding portion  112 , and a wiring portion  113 . The antenna element  110  and the antenna element  120  constitute a loop antenna  180 . The loop antenna  180  is provided to wind around the base portion  101  in the X-axis direction. A length of the loop antenna  180  in the X-axis direction is approximately 31 mm, a width of the loop antenna  180  in the Y-axis direction is approximately 21 mm, and a height of the loop antenna  180  in the Z-axis direction is approximately 1.2 mm. 
         [0050]    The antenna element  110  may be made of metal and may be aluminum, copper, or the like. The antenna element  110  may be made by, for example, wet etching together with the antenna element  120 . The antenna elements  110  and  120  may be patterned by providing a metal foil such as a copper foil on one surface of the sheet portion  105  and performing wet etching. 
         [0051]    Before the wet etching is performed, a mask is opened according to a shape of the antenna elements  110  and  120 , and used to expose a resist formed on the metal foil by photolithography. 
         [0052]    The element  111  is a radiation portion in a rectangular shape in plan view. The protruding portion  112 , the wiring portion  113 , and a tapered portion  124 A 1  of a tip of a connection portion  124 A of the antenna element  120  described below are connected to an end portion  111 A of the positive X-axis direction side of the element  111 . The element  111  includes an end portion  111 B opposite the end portion  111 A. The element  111  is an example of a first base portion. 
         [0053]    The element  111  is provided in the range from the end portion  111 A positioned on an upper surface side of the base portion  101  to the end portion  111 B positioned on a bottom surface side of the base portion  101 , and is bent at the end portion  101 A of the base portion  101 . 
         [0054]    As illustrated in  FIG. 4B , the end portion  111 B is overlapped with an end portion  121 B of an element  121  described below on the bottom surface side of the base portion  101  in a state where the inlay  150  is wound around the base portion  101 . 
         [0055]    A part in which the end portion  111 B and the end portion  121 B are overlapped with each other in plan view constitutes an overlapped portion  160 . In the overlapped portion  160 , the end portion  111 B and the end portion  121 B are insulated by the sheet portion  105 . 
         [0056]    As illustrated  FIGS. 4A to 6 , the protruding portion  112  extends from the end portion  111 A of the element  111  so as to protrude in the positive X-axis direction. Three protruding portions  112  are provided on a positive Y-axis direction side with respect to the wiring portion  113  and the three protruding portions  112  are provided on a negative Y-axis direction side with respect to the wiring portion  113 . Lengths of six protruding portions  112  in the X-axis direction are all equal to each other. The protruding portion  112  is an example of a first protruding portion. Note that since  FIG. 1  to  FIG. 3  are illustrated based on a simulation model described below, twelve protruding portions  112  are provided. 
         [0057]    Widths (widths in the Y-axis direction) of the six protruding portions  112  are equal to each other and each of the six protruding portions  112  has a uniform width (width in the Y-axis direction) from a side connected to the element  111  to a tip of a positive X-axis direction side of the protruding portion  112 . The protruding portion  112  and a protruding portion  122  of the antenna element  120  are arranged alternately in plan view. 
         [0058]    The protruding portion  112 , the wiring portion  113 , the protruding portion  122 , and a wiring portion  123  constitute an interdigital portion  170 . The interdigital portion  170  functions as a capacitor having a predetermined capacitance. The interdigital portion  170  may be treated as a capacitor connected in parallel to the loop antenna  180  constituted by the antenna elements  110  and  120 . 
         [0059]    Each of dimensions such as lengths in the X-axis direction, widths in the Y-axis direction, heights in the Z-axis direction, intervals in the X-axis direction, intervals in the Y-axis direction, and the like of the protruding portion  112 , the wiring portion  113 , the protruding portion  122 , and the wiring portion  123  may be set to optimum values in order to set capacitance of the interdigital portion  170  to a desired value. 
         [0060]    The wiring portion  113  extends from the end portion  111 A of the element  111  so as to protrude in the positive X-axis direction. The wiring portion  113  is an example of a first wiring portion. The wiring portion  113  has a uniform width (width in the Y-axis direction) from a side connected to the element  111  to a tip of a positive X-axis direction side of the wiring portion  113 . The width of the wiring portion  113  is, for example, approximately twice the width of the protruding portion  112 . 
         [0061]    Since a current flows through the wiring portion  113  during communication of the RFID tag  100 , it is preferable to increase the width of the wiring portion  113  in order to reduce a resistance value of the wiring portion  113 . Accordingly, in the RFID tag  100  of Embodiment 1, the width of the wiring portion  113  is larger than that of the protruding portion  112 . The width of the wiring portion  113  is equal to the width of the wiring portion  123  connected to the wiring portion  113  with the IC chip  130  in between. 
         [0062]    The wiring portion  113  is positioned between the three protruding portions  112  and the three protruding portions  112 . The wiring portion  113  includes a terminal  113 A at a tip and the IC chip  130  is connected to the terminal  113 A. As an example, the wiring portion  113  is disposed on a central axis of the antenna element  120  parallel to the X-axis. 
         [0063]    As illustrated in  FIG. 6 , in a state before connecting the IC chip  130 , the wiring portion  113  is formed such that a space is provided in the X-axis direction between the wiring portion  113  and a terminal  123 A at a tip of the wiring portion  123 . One of two terminals of the IC chip  130  is connected to the terminal  113 A by solder or the like. Here, although the wiring portion  113  is shorter than the wiring portion  123  and the IC chip  130  is offset toward a negative X-axis direction side in plan view in  FIGS. 4A and 4B  as an example, the wiring portion  113  may be longer than the wiring portion  123  or may be equal to the wiring portion  123 . A position of the IC chip  130  in the X-axis direction is determined according to the lengths of the wiring portion  113  and the wiring portion  123 . 
         [0064]    The tapered portion  124 A 1  at a tip of the connection portion  124 A of the antenna element  120  is provided on a positive Y-axis direction side of the protruding portion  112  positioned on a most positive side in the Y-axis direction. The connection portion  124 A and the tapered portion  124 A 1  will be described below. 
         [0065]    As illustrated in  FIG. 5  and  FIG. 6 , the antenna element  120  is formed within an area of approximately one half in the longitudinal direction of one surface of the sheet portion  105 . The antenna element  120  is an example of a second antenna element. 
         [0066]    The antenna element  120  includes the element  121 , the protruding portion  122 , the wiring portion  123 , and the connection portion  124 A. The antenna element  120  and the antenna element  110  constitute the loop antenna  180 . 
         [0067]    The antenna element  120  may be made of metal and may be aluminum, copper, or the like. The antenna element  120  may be made by, for example, wet etching together with the antenna element  110 . The antenna elements  110  and  120  may be patterned by providing a metal foil such as a copper foil on one surface of the sheet portion  105  and performing wet etching. 
         [0068]    The element  121  is a radiation portion in a rectangular shape in plan view. The protruding portion  122 , the wiring portion  123 , and the connection portion  124 A are connected to an end portion  121 A of a negative X-axis direction side of the element  121 . The element  121  includes the end portion  121 B opposite the end portion  121 A. The element  121  is an example of a second base portion. 
         [0069]    The element  121  is provided in the range from the end portion  121 A positioned on an upper surface side of the base portion  101  to the end portion  121 B positioned on a bottom surface side of the base portion  101 , and is bent at the end portion  101 B side of the base portion  101 . 
         [0070]    The element  121  is overlapped with the element  111  in the end portion  121 B. 
         [0071]    As illustrated in  FIG. 4B , the end portion  121 B is overlapped with an end portion  111 B of an element  111  on the bottom surface side of the base portion  101  in a state where the inlay  150  is wound around the base portion  101 . 
         [0072]    A part in which the end portion  121 B and the end portion  111 B are overlapped with each other in plan view constitutes the overlapped portion  160  and in the overlapped portion  160 , the end portion  121 B and the end portion  111 B are insulated by the sheet portion  105 . 
         [0073]    As illustrated  FIGS. 4A to 6 , the protruding portion  122  extends from the end portion  121 A of the element  121  so as to protrude in the negative X-axis direction. Two protruding portions  122  are provided on a positive Y-axis direction side with respect to the wiring portion  123  and the three protruding portions  122  are provided on a negative Y-axis direction side with respect to the wiring portion  123 . Lengths of five protruding portions  122  in the X-axis direction are all equal to each other. The protruding portion  122  is an example of a second protruding portion. Note that since  FIG. 1  to  FIG. 3  are illustrated based on a simulation model described below, eleven protruding portions  122  are provided. 
         [0074]    Widths (widths in the Y-axis direction) of the five protruding portions  122  are equal to each other and each of the five protruding portions  122  has a uniform width (width in the Y-axis direction) from a side connected to the element  121  to a tip of a negative X-axis direction side of the protruding portion  122 . The width of the protruding portion  122  is equal to a width of the protruding portion  112 . Five protruding portions  122  and the six protruding portions  112  are arranged alternately in plan view. 
         [0075]    The wiring portion  123  extends from the end portion  121 A of the element  121  so as to protrude in the negative X-axis direction. The wiring portion  123  is an example of a second wiring portion. 
         [0076]    The width (width in the Y-axis direction) of the wiring portion  123  is uniform from a side connected to the element  121  to a tip of a negative X-axis direction side of the protruding portion  123 . The width of the wiring portion  123  is equal to the width of the wiring portion  113  and is approximately twice the width of the protruding portion  122 . 
         [0077]    Since a current flows through the wiring portion  123  during communication of the RFID tag  100 , it is preferable to increase the width of the wiring portion  123  in order to reduce a resistance value of the wiring portion  123 . Accordingly, in the RFID tag  100  of Embodiment 1, the width of the wiring portion  123  is larger than that of the protruding portion  122 . 
         [0078]    The wiring portion  123  is positioned between the two protruding portions  122  of a positive Y-axis direction side and the three protruding portions  122  of a negative Y-axis direction side. The terminal  123 A is provided at a tip of the wiring portion  123 . As illustrated in  FIG. 1 , the IC chip  130  is connected to the terminal  123 A. As an example, the wiring portion  123  is disposed on a central axis of the antenna element  120  parallel to the X-axis. 
         [0079]    As illustrated in  FIG. 6 , in a state before connecting the IC chip  130 , the wiring portion  123  is formed such that a space is provided in the X-axis direction between the wiring portion  123  and the terminal  113 A at a tip of the wiring portion  113 . The other of the two terminals of the IC chip  130  is connected to the terminal  123 A by solder or the like. 
         [0080]    The wiring portion  123 , the protruding portion  122 , the protruding portion  112 , and the wiring portion  113  constitute the interdigital portion  170 . 
         [0081]    The connection portion  124 A is disposed on a positive Y-axis direction side than the protruding portion  112  disposed on a most positive side in the Y-axis direction, and on a positive Y-axis direction side of the protruding portion  122  disposed on a most positive side in the Y-axis direction. 
         [0082]    The connection portion  124 A extends from the end portion  121 A of the element  121  so as to protrude in the negative X-axis direction and includes the tapered portion  124 A 1  at a tip. A width in the Y-axis direction at an end portion of a positive X-axis direction side of the tapered portion  124 A 1  is equal to a width of the connection portion  124 A other than the tapered portion  124 A 1 . The tapered portion  124 A 1  has a tapered shape in which a width in the Y axis direction becomes narrow toward a tip on a negative X-axis direction side. The tip on a negative X-axis direction side of the tapered portion  124 A 1  is connected to the element  111  of the antenna element  110 . 
         [0083]    In a case where the antenna elements  110  and  120  are patterned by the wet etching, as an amount of etching increases, the widths of the protruding portions  112 , the wiring portion  113 , the five protruding portions  122 , the wiring portion  123 , and the connection portion  124 A become narrow. When the widths of the protruding portions  112 , the wiring portion  113 , the five protruding portions  122 , the wiring portion  123 , and the connection portion  124 A become narrow, a capacitance value of the interdigital portion  170  is decreased. 
         [0084]    When the capacitance value of the interdigital portion  170  is decreased, the resonance frequency of the RFID tag  100  is shifted to a high frequency side. Since a frequency bandwidth which the RFID tag  100  may use is determined for each country or region in which the RFID tag  100  is used, if the resonance frequency of the RFID tag  100  deviates from a predetermined frequency band, there is a possibility that the RFID tag  100  may not be used. 
         [0085]    Therefore, the RFID tag  100  includes the connection portion  124 A having the tapered portion  124 A 1 . When the amount of etching is within a range between a design value and a value obtained by adding a certain allowable value to the design value, the tapered portion  124 A 1  is connected to the element  111  of the antenna element  110 . When the amount of etching exceeds the value obtained by adding the certain allowable value to the design value, a tip of the tapered portion  124 A 1  is separated from the element  111 . 
         [0086]    The amount of etching is determined by the etching rate and a period of time for performing etching and is the amount to remove metal foil or the like. In addition, the design value of the amount of etching is the amount of etching which realizes the design value of the antenna elements  110  and  120 . As an example, the design values of the antenna elements  110  and  120  are values in the case where the RFID tag  100  includes the connection portion  124 A having the tapered portion  124 A 1  of an ideally designed shape. 
         [0087]    When the tapered portion  124 A 1  is separated from the element  111 , since a capacitor is constituted between the protruding portion  112  disposed on a most positive side in the Y-axis direction and the connection portion  124 A, capacitance of the interdigital portion  170  is increased. 
         [0088]    When the capacitance of the interdigital portion  170  is increased, it is possible to reduce the resonance frequency of the RFID tag  100 . 
         [0089]    The RFID tag  100  includes the connection portion  124 A having the tapered portion  124 A 1 , so that even if variation of the amount of etching occurs in the wet etching, the resonance frequency of the RFID tag  100  is within a certain range. When the certain range is set so as to be within a frequency bandwidth determined for each country or region in which the RFID tag  100  is used, even if variation of the amount of etching occurs, it is possible to manufacture the RFID tag  100  capable of communicating at a predetermined frequency bandwidth. 
         [0090]    Accordingly, the RFID tag  100  includes the connection portion  124 A having the tapered portion  124 A 1 . 
         [0091]    Furthermore, intervals between adjacent two of the six protruding portions  112 , the wiring portion  113 , the five protruding portions  122 , the wiring portion  123 , and the connection portion  124 A in the Y-axis direction are, for example, all equal to each other. 
         [0092]    The IC chip  130  includes two terminals  131  and  132  and is mounted on a surface of the sheet portion  105 . The two terminals  131  and  132  of the IC chip  130  are respectively connected to the terminals  113 A and  123 A by solder or the like. The IC chip  130  is electrically connected to the antenna elements  110  and  120 . Data representing a unique ID is stored in a memory chip inside of the IC chip  130 . 
         [0093]    When the IC chip  130  receives a signal for reading a radio frequency (RF) bandwidth from a reader/writer for the RFID tag  100  through the antenna elements  110  and  120 , the IC chip  130  operates by a power of the received signal and transmits the data representing the ID through the antenna elements  110  and  120 . As a result, it is possible to read the ID of the RFID tag  100  by the reader/writer. 
         [0094]    The overlapped portion  160  is the part in which the end portion  111 B of the antenna element  110  and the end portion  121 B of the antenna element  120  are overlapped with each other. A current with a high frequency of 892 MHz flows through the antenna elements  110  and  120 . The overlapped portion  160  is connected in an AC manner and the antenna elements  110  and  120  constitute the loop antenna  180 . 
         [0095]    In addition, the overlapped portion  160  may be used for modulating the resonance frequency of the RFID tag  100 . Capacitance of the overlapped portion  160  is determined by an area in which the end portions  111 B and  121 B are overlapped with each other and an interval between the end portions  111 B and  121 B. 
         [0096]    In addition, the overlapped portion  160  includes a part in which the overlapped portion  160  and the interdigital portion  170  are overlapped with each other. With this, since the overlapped portion  160  and the interdigital portion  170  are overlapped with each other in the Z-axis direction, it is also possible to secure capacitance between the overlapped portion  160  and the interdigital portion  170 . It is possible to adjust the resonance frequency of the RFID tag  100  also by adjusting capacitance related to the overlapped portion  160 . 
         [0097]    The interdigital portion  170  is composed by alternately arranging in plan view the protruding portions  112 , the wiring portion  113 , the protruding portions  122 , and the wiring portion  123 . 
         [0098]    The interdigital portion  170  is provided to adjust the resonance frequency of the loop antenna  180  of the RFID tag  100  by saving capacitance generated by arranging the protruding portion s 112 , the wiring portion  113 , the protruding portions  122 , and the wiring portion  123  close to each other. 
         [0099]    The interdigital portion  170  is formed over the antenna elements  110  and  120 . Furthermore, in a case where a tip of the tapered portion  124 A 1  of the connection portion  124 A is separated from the element  111 , the connection portion  124 A is also included in the interdigital portion  170 . 
         [0100]      FIG. 7  is a diagram illustrating an equivalent circuit of the RFID tag  100 . 
         [0101]    The loop antenna  180  constituted by the antenna elements  110  and  120  may be represented by a resistor Rap and an inductor Lap. In the RFID tag  100  of the present embodiment, since the overlapped portion  160  and the interdigital portion  170  are provided in the loop antenna  180 , a capacitor Cap is connected in parallel to the resistor Rap and the inductor Lap in  FIG. 7 . The capacitor Cap is a combination of the overlapped portion  160  and the interdigital portion  170  and is represented as one capacitor. 
         [0102]    Furthermore, the antenna elements  110  and  120  include a loop having the wiring portions  113  and  123 , the elements  111  and  121 , and the connection portion  124 A, but the loop is shorter than the loop antenna  180  and inductance of the loop is larger than that of the loop antenna  180 . Accordingly, inductance of the loop antenna  180  occupies most of total inductance of the loop antenna  180  and the loop having the wiring portions  113  and  123 , the elements  111  and  121 , and the connection portion  124 A. 
         [0103]    In the embodiment, the antenna elements  110  and  120  are designed so that inductance of the loop having the wiring portions  113  and  123 , the elements  111  and  121 , and the connection portion  124 A is sufficiently larger than inductance of the loop antenna  180 . 
         [0104]    In addition, the IC chip  130  of the RFID tag  100  is represented by a resistor Rcp and a capacitor Ccp. 
         [0105]    That is, the loop antenna  180  includes a resistance component and an inductance component, and a capacitance component is connected to the loop antenna  180 . The IC chip  130  may be represented by a resistance component and a capacitance component. 
         [0106]    Here, the resistor Rap is a resistor of a resistance value Rap, the inductor Lap is an inductor of inductance Lap, and the capacitor Cap is a capacitor of capacitance Cap. In addition, the resistor Rcp is a resistor of a resistance value Rcp and the capacitor Ccp is a capacitor of capacitance Ccp. 
         [0107]    For example, the Rcp is 2000Ω and the Ccp is approximately 1.0 pF. This is an average value obtained in a typical IC chip. 
         [0108]    The RFID tag  100  performs communication by generating resonance in the equivalent circuit illustrated in  FIG. 7 . That is, when the RFID tag  100  receives a signal for reading and transmits data representing the ID, a current due to resonance flows through the IC chip  130  and the antenna elements  110  and  120 . 
         [0109]    The resonance frequency of the resonance current is mainly determined by capacitance of the IC chip  130 , inductance of the antenna elements  110  and  120 , capacitance of the overlapped portion  160 , and capacitance of the interdigital portion  170 . 
         [0110]    Here, the resonance frequency of the RFID tag  100  may be obtained by expression (1). 
         [0000]    
       
         
           
             
               
                 
                   
                     f 
                      
                     
                         
                     
                      
                     0 
                   
                   = 
                   
                     1 
                     
                       2 
                        
                       π 
                        
                       
                         
                           Lap 
                            
                           
                             ( 
                             
                               Ccp 
                               + 
                               Cap 
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0111]    In the expression (1), Lap is the inductance Lap of the antenna elements  110  and  120 , Ccp is the capacitance Ccp of the IC chip  130 , and Cap is the capacitance Cap of the overlapped portion  160  and the interdigital portion  170 . 
         [0112]    With this, the resonance frequency of the RFID tag  100  is not determined only by the loop antenna  180  (antenna elements  110  and  120 ), but by the loop antenna  180  (antenna elements  110  and  120 ), the overlapped portion  160 , the interdigital portion  170 , and the IC chip  130 . 
         [0113]    At this point, the loop antenna  180  included in the RFID tag  100  is different from a so-called loop antenna generating resonance by setting a loop length of the loop antenna to a length of one wavelength at the resonance frequency. 
         [0114]    The resonance frequency of the resonance current in the RFID tag  100  of the present embodiment is a frequency (communication frequency) at which the RFID tag  100  performs communication and is set to, for example, 892 MHz. A loop length of the loop antenna  180  constituted by the antenna elements  110  and  120  is approximately 65 mm and is set to be shorter than a wavelength at the resonance frequency. 
         [0115]    As an example, in a case where a resonance frequency is 892 MHz, a wavelength at the resonance frequency is 336.1 mm and a loop length of the loop antenna  180  of the RFID tag  100  is approximately 65 mm. 
         [0116]    With this, since the loop length of the loop antenna  180  is shorter than the length of one wavelength at the resonance frequency, unlike a so-called loop antenna in which the loop length is set to one wavelength at the resonance frequency, the antenna elements  110  and  120  constituting the loop antenna  180  function as an inductor. 
         [0117]    However, since a combined length (loop length) of the antenna elements  110  and  120  is relatively short as described above and inductance of the antenna elements  110  and  120  is proportional to a length of the antenna elements  110  and  120 , inductance of the loop antenna  180  is relatively small. Therefore, in the RFID tag  100 , in order to compensate for small inductance, the resonance frequency is adjusted by providing the loop antenna  180  with the overlapped portion  160  and the interdigital portion  170 . 
         [0118]    Impedance of an antenna obtained by adding the overlapped portion  160  and the interdigital portion  170  to the loop antenna  180  constituted by the antenna elements  110  and  120  is determined by a resistance value (Rap) of the resistor Rap, inductance (Lap) of the inductor Lap, and capacitance (Cap) of the capacitor Cap illustrated in  FIG. 7 . 
         [0119]    In addition, impedance of the IC chip  130  is determined by a resistance value (Rcp) of the resistor Rcp and the capacitance (Ccp) of the capacitor Ccp. 
         [0120]    In order to obtain appropriate impedance matching between the loop antenna  180  and the IC chip  130 , the resistance value Rap and the resistance value Rcp may be adjusted in addition to adjustment of the inductance Lap, the capacitance Cap, and the capacitance Ccp. 
         [0121]    Next, the RFID tag  100  in which the amount of etching is large when patterning the antenna elements  110  and  120  and the tapered portion  124 A 1  is separated from the element  111  will be described. 
         [0122]      FIGS. 8A and 8B  are diagrams illustrating the RFID tag  100  in which the tapered portion  124 A 1  is separated from the element  111 .  FIGS. 8A and 8B  correspond to  FIGS. 4A and 4B  and illustrate a configuration in which the cover portion  140  is removed from the RFID tag  100 .  FIG. 8A  illustrates a configuration in plan view and  FIG. 8B  illustrates a cross section taken along a line VIIIB-VIIIB in  FIG. 8A . 
         [0123]    In  FIG. 8A , since the amount of etching is larger than in a case of patterning the tapered portion  124 A 1  illustrated in  FIG. 4A , a tapered portion  124 B 1  is separated from the element  111 . Accordingly, the connection portion  124 A illustrated in  FIG. 4A  is a protruding portion  124 B and the tapered portion  124 B 1  is provided at a tip of the protruding portion  124 B. The protruding portion  124 B is an example of a third protruding portion. 
         [0124]    In addition, since the amount of etching is larger than in the case illustrated in  FIG. 4A , protruding portions  112  and  122  and wiring portions  113  and  123  become narrower than in  FIG. 4A . 
         [0125]    When the protruding portions  112  and  122  and the wiring portions  113  and  123  become narrow, an interval between the protruding portions  112  and  122  and the wiring portions  113  and  123  increases, so that capacitance obtained between the protruding portions  112  and  122  and the wiring portions  113  and  123  is decreased. 
         [0126]    However, since the protruding portion  124 B is added to the interdigital portion  170 , combined capacitance Cap  1  of the overlapped portion  160  and the interdigital portion  170  is lower than capacitance Cap immediately before the tapered portion  124 A 1  is separated from the element  111 . 
         [0127]    In the embodiment, the antenna elements  110  and  120  is designed so that combined capacitance Cap1 of the overlapped portion  160  and the interdigital portion  170  in a state immediately after the tapered portion  124 A 1  is separated from the element  111  is set to be equal to capacitance Cap in a case where the amount of etching is a design value. 
         [0128]    Here, the state immediately after the tapered portion  124 A 1  is separated from the element  111  is a state where the amount of etching is increased and the tapered portion  124 A 1  is separated from the element  111  and the etching has not progressed as compared with a state where the connection portion  124 A is changed to the protruding portion  124 B. 
         [0129]    Furthermore, since the elements  111  and  121  and the wiring portions  113  and  123  have a sufficient thickness even though the amount of etching is larger than in the case illustrated in  FIG. 4A , the resistance value Rap and the inductance Lap of the loop antenna  180  are substantially unchanged. 
         [0130]      FIG. 9  is a diagram illustrating an equivalent circuit of the RFID tag  100  immediately after the tapered portion  124 A 1  is separated from the element  111 . 
         [0131]    Capacitance Cap of the antenna elements  110  and  120  is changed to the capacitance Cap1 compared to the diagram of the equivalent circuit of  FIG. 7 . The capacitance Cap1 is combined capacitance Cap1 of the overlapped portion  160  and the interdigital portion  170  in a state where the tapered portion  124 A 1  is separated from the element  111 . 
         [0132]    In addition, since a resistance value Rap and inductance Lap of the loop antenna  180  are substantially unchanged, the resistance value Rap and the inductance Lap are maintained. 
         [0133]    Accordingly, a resonance frequency f0 of the RFID tag  100  immediately after the tapered portion  124 A 1  is separated from the element  111  is obtained by expression (2). 
         [0000]    
       
         
           
             
               
                 
                   
                     f 
                      
                     
                         
                     
                      
                     0 
                   
                   = 
                   
                     1 
                     
                       2 
                        
                       π 
                        
                       
                         
                           Lap 
                            
                           
                             ( 
                             
                               Ccp 
                               + 
                               
                                 Cap 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0134]    In the expression (2), since capacitance Cap1 in the RFID tag  100  immediately after the tapered portion  124 A 1  is separated from the element  111  is equal to capacitance Cap in a case where the amount of etching is a design value, a resonance frequency f0 expressed by the expression (2) is equal to a resonance frequency f0 expressed by the expression (1). 
         [0135]      FIG. 10  is a diagram illustrating frequency characteristics regarding a reading distance of the RFID tag  100 . In  FIG. 10 , a horizontal axis illustrates a frequency when reading the RFID tag  100  with a reader/writer and a vertical axis illustrates a maximum value (Read Range) which the reader/writer may read. The frequency characteristics regarding the reading distance illustrated in  FIG. 10  is obtained by an electromagnetic field simulation. 
         [0136]    The characteristic indicated by a solid line is the design value and a resonance frequency f0 at which the reading distance becomes the maximum is set to 892 MHz. 
         [0137]    The characteristic indicated by an one-dot chain line is a characteristic obtained by the RFID tag  100  immediately after the tapered portion  124 A 1  is separated from the element  111 , and a resonance frequency at which the reading distance becomes the maximum is a value which is approximately equal to the resonance frequency f0 of the characteristic indicated by the solid line. 
         [0138]    The characteristic indicated by a broken line is a characteristic indicated for comparison and is a characteristic obtained in a case where the amount of etching of the RFID tag  100  not including the connection portion  124 A is an amount of predetermined over etching. Here, the amount of etching of predetermined over etching is more than an amount of etching by which the tapered portion  124 A 1  is separated. 
         [0139]    The resonance frequency at which the reading distance is maximum in the characteristic indicated by the broken line is greatly deviated from the resonance frequency f0 of the characteristic indicated by the solid line. If the resonance frequency largely deviates in this manner, the readable distance at the resonance frequency f0 is greatly shortened, and there is a possibility that the RFID tag  100  may not be used as an RFID tag. 
         [0140]    In the wet etching, there is a case where the amount of etching varies due to distribution of concentration of etching solution. Specifically, there is a case where variation may occur in the amount of etching between a plurality of the antenna elements  110  and  120  when simultaneously patterning the plurality of the antenna elements  110  and  120  of the element  150 A before the element  150 A (see  FIG. 6 ) is made into a chip. 
         [0141]    The RFID tag  100  of the embodiment includes the connection portion  124 A of the design value in order to suppress such individual difference due to variation of the amount of etching. 
         [0142]    Before the wet etching for patterning the antenna elements  110  and  120  is performed, a mask used when exposing a resist by photolithography is opened according to a shape of the antenna elements  110  and  120 . That is, the mask includes an opening corresponding to the connection portion  124 A. 
         [0143]      FIG. 11  is a characteristic diagram illustrating a relationship between an amount of etching and an amount of variation of a resonance frequency. In  FIG. 11 , a horizontal axis illustrates an amount of variation ΔW (mm) with respect to a design value of the amount of etching. It may be seen that an amount of etching is a design value in that a value on a horizontal axis is 0 (right end) and the amount of variation ΔW of the amount of etching increases (becomes over-etching) as moved to the left. 
         [0144]    Here, the amount of variation ΔW has the largest influence on widths of the protruding portions  112  and  122  and the wiring portions  113  and  123  in the Y-axis direction. Accordingly, as the horizontal axis is moved to the left, the widths of the protruding portions  112  and  122  and the wiring portions  113  and  123  become narrow. 
         [0145]    Furthermore, here, as an example, a case is considered where the amount of variation ΔW of the amount of etching is larger than the design value with reference to a case where the amount of etching is the design value. In addition, in a case where the amount of variation ΔW is negative, since the amount of etching is not sufficient for the design value and the antenna elements  110  and  120  are incomplete, the case where the amount of variation ΔW is negative is not considered. 
         [0146]    A vertical axis of  FIG. 11  illustrates an amount of variation Δf0 (MHz) with respect to a design value of a resonance frequency f0. The amount of variation Δf0 is 0 when the resonance frequency f0 is the design value. In addition, when the amount of etching increases (becomes over-etching) than the design value, since capacitance of the interdigital portion  170  decreases and the resonance frequency increases, the amount of variation Δf0 is equal to or more than 0. 
         [0147]    In addition, a vertical axis of  FIG. 11  illustrates an allowable value Δf0A of the amount of variation Δf0. The allowable value Δf0A is approximately 15 MHz, for example. 
         [0148]    As illustrated in  FIG. 11 , when the amount of variation ΔW of the amount of etching increases, the amount of variation Δf0 of the resonance frequency f0 increases. This is because capacitance of the interdigital portion  170  decreases and the resonance frequency increases. 
         [0149]    When the amount of variation ΔW of the amount of etching becomes ΔW1, the tapered portion  124 A 1  at a tip of the connection portion  124 A is separated from the element  111  and the protruding portion  124 B appears. When the protruding portion  124 B appears, since capacitance between the protruding portion  112  on a most positive side in the Y-axis direction and the protruding portion  124 B is added to the interdigital portion  170 , capacitance of the interdigital portion  170  increases and the resonance frequency decreases. Accordingly, when the amount of variation ΔW of the amount of etching becomes ΔW1, the amount of variation Δf0 of the resonance frequency f0 becomes approximately 0. 
         [0150]    Furthermore, immediately before the amount of variation ΔW of the amount of etching reaches ΔW1, the amount of variation Δf0 of the resonance frequency f0 does not reach the allowable value Δf0A. This may be realized, for example, by setting a width of the tapered portion  124 A 1 . 
         [0151]    Since the amount of variation Δf0 increases again in an area in which the amount of variation ΔW of the amount of etching exceeds ΔW1, it is possible to use an area until the amount of variation Δf0 reaches the allowable value Δf0A with respect to the amount of etching. 
         [0152]      FIG. 12  is a diagram illustrating a simulation model of the RFID tag  100 . The simulation model of the RFID tag  100  illustrated in  FIG. 12  includes two connection portions  124 A. More specifically, the simulation model is configured to have the connection portion  124 A instead of the protruding portion  122  positioned on a most negative direction side in the Y-axis direction of the RFID tag  100  illustrated in  FIGS. 1 to 6 . 
         [0153]    Accordingly, in the simulation model of the RFID tag  100 , an antenna element  110  includes an element  111 , six protruding portions  112 , and a wiring portion  113 , and the antenna element  120  includes an element  121 , four protruding portions  122 , a wiring portion  123 , and the two connection portions  124 A. A tapered portion  124 A 1  is provided at each of tips of the two connection portion  124 A. Sizes of the two tapered portions  124 A 1  are the same. 
         [0154]    In addition, in the simulation model of the RFID tag  100 , a length of a loop antenna  180  in the X-axis direction is approximately 31 mm, a width of the loop antenna  180  in the Y-axis direction is approximately 21 mm, and a height of the loop antenna  180  in the Z-axis direction is approximately 1.2 mm. 
         [0155]    An interdigital portion  170  includes the twelve protruding portions  112  and the twelve protruding portions  122 . In addition, a width of the protruding portions  112  and  122  and the connection portion  124 A is set to 0.2 mm and an interval in the Y-axis direction between the protruding portion  112 , the wiring portion  113 , the protruding portion  122 , and the connection portion  124 A is set to 0.62 mm. 
         [0156]    A cover portion  140  is made of a flame retardant resin, a relative permittivity of the flame retardant resin is 3.2, a dielectric loss tangent tan δ is 0.02, a length in the X-axis direction is approximately 35 mm, a width in the Y-axis direction is approximately 25 mm, and a thickness in the Z-axis direction is approximately 2 mm. 
         [0157]    Under such a condition of this simulation, resonance frequency characteristics regarding a reading distance in a case where an amount of variation ΔW with respect to a design value of the amount of etching is 0 mm, a case where the amount of variation ΔW is 0.01 mm, and a case where the amount of variation ΔW is 0.02 mm are obtained. Widths W of the protruding portions  112 , the wiring portion  113 , the protruding portions  122 , the wiring portion  123 , and the connection portions  124 A are respectively 0.2 mm, 0.19 mm, and 0.18 mm when each of the amount of variation ΔW is 0 mm, 0.01 mm, and 0.02 mm. 
         [0158]    In a case where the amount of variation ΔW is 0 mm and a case where the amount of variation ΔW is 0.01 mm, the tapered portion  124 A 1  is connected to the element  111 . In a case where the amount of variation ΔW is 0.02 mm, the tapered portion  124 A 1  is separated from the element  111  and a protruding portion  124 B appears. These are the same for the two connection portions  124 A. 
         [0159]      FIG. 13  is a diagram illustrating a result of a simulation of resonance frequency characteristics regarding the reading distance. In  FIG. 13 , a triangular marker illustrates a case where an amount of variation ΔW is 0 mm and a width W is 0.2 mm. This case is a case of a design value and a case where the tapered portion  124 A 1  is connected to the element  111 . 
         [0160]    A circle marker illustrates a case where the amount of variation ΔW is 0.01 mm, the width W is 0.19 mm, and the tapered portion  124 A 1  is connected to the element  111 . A square marker illustrates a case where the amount of variation ΔW is 0.02 mm, the width W is 0.18 mm, the tapered portion  124 A 1  is separated from the element  111 , and the protruding portion  124 B appears. 
         [0161]    In addition, the resonance frequency at the design value is 892 MHz, which is one of communication frequencies of RFID tags in Japan. A horizontal axis illustrates a communication frequency in European Union (EU) and USA (US). A communication frequency bandwidth of EU is 865 MHz to 868 MHz and a communication frequency bandwidth of US is 902 MHz to 928 MHz. As an example, such frequency bandwidth is provided to verify how much the reading distance may be obtained in the RFID tag  100  of which resonance frequency is adjusted for domestic use at the communication frequencies of EU and US. 
         [0162]    In addition, a lower limit of the reading distance illustrated by a vertical axis is set to 0.8 m. 
         [0163]    As a result of the simulation, in a case of the design value (triangular marker), the resonance frequency is 892 MHz and the reading distance at 892 MHz is approximately 1.7 m. In addition, in a case where the amount of variation ΔW is approximately 0.01 mm and the width W is 0.19 mm (circle marker), the resonance frequency is 900 MHz and the reading distance at 892 MHz is approximately 1.6 m. In addition, in a case where the amount of variation ΔW is approximately 0.02 mm and the width W is 0.18 mm (square marker), the resonance frequency is 893 MHz and the reading distance at 892 MHz is approximately 1.8 m. 
         [0164]    In addition, in either case, the reading distance exceeds 0.8 m in the communication frequency bandwidth (865 MHz to 868 MHz) of EU and the communication frequency (902 MHz to 928 MHz) of US, and it is confirmed that one RFID tag  100  of the design value may correspond to three destinations. 
         [0165]    From above results, it is understood that even if over-etching of 0.01 mm occurs, deviation of the resonance frequency is 8 MHz, which is within an allowable range, and a sufficient reading distance may be obtained. In addition, it is understood that if over-etching of 0.02 mm occurs, deviation of the resonance frequency is approximately 1 MHz in the RFID tag  100  in which the protruding portion  124 B appears and which is the same as the design value, and the sufficient reading distance may be obtained. 
         [0166]      FIG. 14  is a characteristic diagram illustrating a relationship between an amount of etching and an amount of variation of a resonance frequency. The characteristic diagram illustrated in  FIG. 14  is made based on the result of the simulation illustrated in  FIG. 13 . 
         [0167]    In  FIG. 14 , a horizontal axis illustrates an amount of variation ΔW with respect to a design value of the amount of etching and a vertical axis illustrates an amount of variation Δf0 with respect to a design value of a resonance frequency f0. These are the same as  FIG. 11 . 
         [0168]    In addition, in the same manner as  FIG. 13 , a triangular marker illustrates a case of the design value, a circle marker illustrates a case where the amount of variation ΔW is 0.01 mm, a width W is 0.19 mm, and a square marker illustrates a case where the amount of variation ΔW is 0.02 mm, the width W is 0.18 mm. 
         [0169]    When the amount of variation ΔW of the amount of etching increases from zero (0) and reaches 0.01 mm, the amount of variation Δf0 of the resonance frequency f0 reaches 8 MHz. In addition, immediately before the amount of variation ΔW of the amount of etching further increases and reaches 0.02 mm, the amount of variation Δf0 of the resonance frequency f0 reaches approximately 12 MHz. This value is a value equal to or less than an allowable value Δf0A (15 MHz). 
         [0170]    When the amount of variation ΔW of the amount of etching reaches 0.02 mm, the tapered portion  124 A 1  at a tip of the connection portion  124 A is separated from the element  111  and the protruding portion  124 B appears, capacitance of the interdigital portion  170  increases, the resonance frequency decreases, and the amount of variation Δf0 of the resonance frequency f0 becomes approximately 1 MHz. 
         [0171]    When the amount of variation ΔW of the amount of etching further increases, the amount of variation Δf0 of the resonance frequency f0 increases again. Even if the amount of variation ΔW of the amount of etching is equal to or more than 0.02 mm, it is possible to use an area until the amount of variation Δf0 reaches the allowable value Δf0A. 
         [0172]    As described above, in the RFID tag  100  of the embodiment, even if the resonance frequency increases as the amount of variation ΔW of the amount of etching increases, when the amount of variation ΔW reaches a certain value, capacitance of the interdigital portion  170  increases by the connection portion  124 A being changed to the protruding portion  124 B. As a result, the resonance frequency decreases to a value close to the design value. 
         [0173]    Thus, even if the amount of etching increases exceeding the design value (over-etching), the amount of variation Δf0 is within the certain range. 
         [0174]    Accordingly, if a relationship between the tapered portion  124 A 1  and an etching rate is designed so that a maximum value of the amount of variation Δf0 is equal to or less than the allowable value Δf0A, it is possible to provide the RFID tag  100  capable of performing an appropriate operation at a desired communication frequency even if the antenna elements  110  and  120  are patterned in the wet etching. 
         [0175]    Specifically, there is a case where variation may occur in the amount of etching between a plurality of the antenna elements  110  and  120  when simultaneously patterning the plurality of the antenna elements  110  and  120  of the element  150 A (see  FIG. 6 ). The element  150 A having a small amount of etching may include the connection portion  124 A and the element  150 A having a large amount of etching may include the protruding portion  124 B. 
         [0176]    In this case, if the relationship between the tapered portion  124 A 1  and the etching rate is designed so that the maximum value of the amount of variation Δf0 is equal to or less than the allowable value Δf0A, it is possible to manufacture the element  150 A including the connection portion  124 A and the element  150 A including the protruding portion  124 B even if the antenna elements  110  and  120  are patterned in the wet etching. 
         [0177]    Both of the RFID tag  100  manufactured using the element  150 A including the connection portion  124 A and the RFID tag  100  manufactured using the element  150 A including the protruding portion  124 B have an amount of variation Δf0 equal to or less than the allowable value Δf0A and may communicate at a desired communication frequency bandwidth. 
         [0178]    Accordingly, even if variation occurs in the amount of etching, a plurality of RFID tags  100  in which a plurality of elements  150 A simultaneously manufactured in the wet etching are made into chips may perform an appropriate operation. 
         [0179]    As described above, according to the embodiment, it is possible to provide the RFID tag  100  capable of performing an appropriate operation at a desired communication frequency. 
         [0180]    In above descriptions, the antenna elements  110  and  120  are provided on a surface of the sheet portion  105  and the loop antenna  180  is constituted by winding the sheet portion  105  around the base portion  101 . 
         [0181]    However, instead of using the base portion  101  and the sheet portion  105 , following descriptions may be used. For example, in addition to providing a part illustrated in  FIG. 4A  among the elements  111  and  121 , that is, the protruding portions  112  and  122 , the wiring portions  113  and  123 , and the connection portion  124 A on the upper surface of the wiring substrate, a metal foil is provided on a lower surface of a wiring substrate and a via hole penetrating through the wiring substrate in the thickness direction is provided, so that the elements  111  and  121  of an upper surface of the wiring substrate may be connected to the metal foil on the lower surface via the wiring substrate. 
         [0182]    In this way, it is possible to constitute a loop antenna in the same manner as a case where the antenna elements  110  and  120  are provided on the surface of the sheet portion  105  and the sheet portion  105  is wound around the base portion  101 . 
         [0183]    In addition, instead of the via hole, a plating layer may be provided on a side surface of the wiring substrate to connect the elements  111  and  121  on the upper surface of the wiring substrate and the metal foil on the lower surface. 
         [0184]    In addition, in the above descriptions, a width of the tapered portion  124 A 1  provided at a tip of the connection portion  124 A becomes narrow toward the element  111 . However, the width of the tapered portion  124 A 1  may be equal to a width of the connection portion  124 A on the element  111  side and may be thinner toward the connection portion  124 A. That is, a tapered shape illustrated in  FIGS. 4A to 6  and the like may be reversed in the X-axis direction. In addition, a shape of the tapered portion  124 A 1  may be any shape as long as the shape of the tapered portion  124 A 1  is a tapered shape in plan view. 
         [0185]    In addition, in the above descriptions, although the tapered portion  124 A 1  is provided at the tip of the connection portion  124 A, the connection portion  124 A may include a section (narrow section) having a width narrower than a width of the connection portion  124 A instead of the tapered portion  124 A 1 . This narrow section may be provided at any portion in the connection portion  124 A in the X-axis direction. 
         [0186]    If this narrow section is used, as in a case of using the tapered portion  124 A 1 , when an amount of variation ΔW of the amount of etching exceeds a predetermined amount, the connection portion  124 A is separated and a capacitance value of the interdigital portion  170  may be increased. 
         [0187]    In addition, in the above descriptions, the RFID tag  100  includes the one connection portion  124 A. As only one exception, the RFID tag  100  of the simulation model illustrated in  FIG. 12  includes the two connection portion  124 A, but sizes of the two tapered portion  124 A 1  are the same. 
         [0188]    The RFID tag  100  may include the connection portion  124 A having a plurality of tapered portions  124 A 1  with different sizes. 
         [0189]      FIG. 15  is a diagram illustrating an inlay  150 B according to a modification example of the embodiment. In  FIG. 15 , component elements similar to those of the RFID tag  100  and the inlay  150  of the embodiment are denoted by the same reference numerals, and description thereof is omitted. 
         [0190]    The inlay  150 B includes the sheet portion  105 , antenna elements  110 A and  120 A, and the IC chip  130 . 
         [0191]    The antenna element  110 A includes the element  111 , the protruding portions  112 , the wiring portion  113 , and connection portions  114 A and  114 C. The connection portions  114 A and  114 C are similar to the connection portion  124 A illustrated in  FIGS. 4A to 6  and extend from the element  111  in the positive X-axis direction. 
         [0192]    The connection portion  114 A is positioned between the protruding portion  122  positioned on a most positive side in the Y-axis direction and the connection portion  124 A. The connection portion  114 C is positioned between the protruding portion  122  positioned on a most negative direction side in the Y-axis direction and a connection portion  124 C. 
         [0193]    The connection portions  114 A and  114 C include tapered portions  114 A 1  and  114 C 1  at tips of the connection portions  114 A and  114 C, and the tapered portions  114 A 1  and  114 C 1  are connected to the element  121 . The tapered portions  114 A 1  and  114 C 1  have tapered shapes in which widths thereof decrease in the positive X-axis direction. 
         [0194]    The antenna element  120 A includes the element  121 , the protruding portions  122 , the wiring portion  123 , and the connection portions  124 A and  124 C. The connection portion  124 A is similar to the connection portion  124 A illustrated in  FIGS. 4A to 6 . The connection portion  124 C is similar to the connection portion  124 A illustrated in  FIGS. 4A to 6  and extends from the element  121  in the negative X-axis direction. 
         [0195]    The connection portion  124 A is positioned on a positive Y-axis side than the connection portion  114 A. That is, the connection portion  124 A is positioned on a most positive side in the Y-axis direction. The connection portion  124 C is positioned on a negative Y-axis side than the connection portion  114 C. That is, the connection portion  124 C is positioned on a most negative side in the Y-axis direction. 
         [0196]    The connection portions  124 A and  124 C include tapered portions  124 A 1  and  124 C 1  at tips of the connection portions  124 A and  124 C, and the tapered portions  124 A 1  and  124 C 1  are connected to the element  111 . The tapered portions  124 A 1  and  124 C 1  have tapered shapes in which widths thereof decrease in the negative X-axis direction. 
         [0197]    These antenna elements  110 A and  120 A is wound around the base portion  101  to constitute the loop antenna in the same manner as the antenna elements  110  and  120 . 
         [0198]    Here, the tapered portions  114 A 1 ,  114 C 1 ,  124 A 1 , and  124 C 1  are different in thickness from each other. Thicknesses at tips of the tapered portions  114 A 1 ,  114 C 1 ,  124 A 1 , and  124 C 1  are respectively set to d 1 , d 2 , d 3 , and d 4  (d 1 &lt;d 2 &lt;d 3 &lt;d 4 ). 
         [0199]    The thicknesses at the tips of the tapered portions  114 A 1 ,  114 C 1 ,  124 A 1 , and  124 C 1  are as follows. The thicknesses of the tapered portions  114 A 1  and  114 C 1  are widths in the Y-axis direction of parts (thinnest portions of tapered portions  114 A 1  and  114 C 1 ) connected to the element  121  at end portions in the positive X-axis direction. The thicknesses of the tapered portions  124 A 1  and  124 C 1  are widths in the Y-axis direction of parts (thinnest portions of tapered portions  124 A 1  and  124 C 1 ) connected to the element  111  at end portions in the negative X-axis direction. 
         [0200]    The thicknesses d 1 , d 2 , d 3 , and d 4  of the tapered portions  114 A 1 ,  114 C 1 ,  124 A 1 , and  124 C 1  are set so as to satisfy a relationship of d 1 &lt;d 2 &lt;d 3 &lt;d 4 . This is because the tapered portions  114 A 1 ,  114 C 1 ,  124 A 1 , and  124 C 1  are separated in this order and capacitance of the interdigital portion  170  is increased in this order of the tapered portions  114 A 1 ,  114 C 1 ,  124 A 1 , and  124 C 1  in the wet etching. 
         [0201]    In addition, the connection portion  114 A is disposed on an inner side than the connection portion  124 A. This is because the tapered portion  114 A 1  is separated before the tapered portion  124 A 1  and capacitance is obtained between the connection portion  114 A and the protruding portion  122  on a negative Y-axis direction side. 
         [0202]    This is because if the tapered portion  124 A 1  is separated before the tapered portion  114 A 1 , capacitance is not included in the interdigital portion  170  due to the protruding portion  124 B (see  FIG. 8 ) appeared when the tapered portion  114 A 1  is not separated and the tapered portion  124 A 1  is separated. 
         [0203]    In addition, this is because if the tapered portion  124 A 1  is separated after the tapered portion  114 A 1  is separated and a protruding portion appears, capacitance obtained between the protruding portion appeared when the tapered portion  114 A 1  is separated and the protruding portion  124 B when the tapered portion  124 A 1  is separated is included in the interdigital portion  170 . 
         [0204]    For the same reason, the connection portion  114 C is disposed on an inner side than the connection portion  124 C. This is because the tapered portion  114 C 1  is separated before the tapered portion  124 C 1  and capacitance is combined between the protruding portions  122  on a negative Y-axis direction side. 
         [0205]    The thicknesses d 1 , d 2 , d 3 , and d 4  are set so as to satisfy the relationship of d 1 &lt;d 2 &lt;d 3 &lt;d 4  and the connection portions  114 A and  114 C are respectively disposed on the inner side than the connection portions  124 A and  124 C, so that it is possible to separate the tapered portions  114 A 1 ,  114 C 1 ,  124 A 1 , and  124 C 1  in this order and to increase capacitance of the interdigital portion  170  in this order. 
         [0206]      FIG. 16  is a characteristic diagram illustrating a relationship between an amount of etching and an amount of variation of the resonance frequency in the RFID tag  100  using the inlay  150 B. In  FIG. 16 , a horizontal axis illustrates an amount of variation ΔW with respect to a design value of the amount of etching. In addition, a vertical axis illustrates an amount of variation Δf0 with respect to a design value of a resonance frequency f0. The horizontal axis and vertical axis of  FIG. 16  are the same as the horizontal axis and vertical axis of  FIG. 11  and  FIG. 14 . 
         [0207]    When the amount of variation ΔW with respect to the design value of the amount of etching is increased from zero (0), since capacitance of the interdigital portion  170  is decreased, the resonance frequency f0 is increased. With this, the amount of variation Δf0 is increased. 
         [0208]    When the amount of variation ΔW reaches d 1 , since the tapered portion  114 A 1  is separated, the connection portion  114 A replaces a protruding portion, and capacitance obtained by the protruding portion based on the connection portion  114 A is added to the interdigital portion  170 , the resonance frequency is decreased. With this, the amount of variation Δf0 is decreased. In  FIG. 16 , although the amount of variation Δf0 is below zero (0), even if the amount of variation Δf0 falls below zero (0) as described above, if the frequency is equal to or higher than a frequency obtained by subtracting the allowable value Δf0A from the resonance frequency f0, there is no hindrance in communication. 
         [0209]    Similarly, when the amount of variation ΔW is increased from d 1  and reaches d 2 , since the tapered portion  114 C 1  is separated, the connection portion  114 C is changed to a protruding portion, and capacitance obtained by the protruding portion based on the connection portion  114 C is added to the interdigital portion  170 , the resonance frequency is decreased. With this, the amount of variation Δf0 is decreased. 
         [0210]    In addition, when the amount of variation ΔW is further increased from d 2  and reaches d 3 , since the tapered portion  124 A 1  is separated, the connection portion  124 A is changed to the protruding portion  124 B (see  FIG. 8 ), and capacitance obtained by the protruding portion  124 B is added to the interdigital portion  170 , the resonance frequency is decreased. With this, the amount of variation Δf0 is decreased. 
         [0211]    In addition, when the amount of variation ΔW is further increased from d 3  and reaches d 4 , since the tapered portion  124 C 1  is separated, the connection portion  124 C is changed to a protruding portion, and capacitance obtained by the protruding portion based on the connection portion  124 C is added to the interdigital portion  170 , the resonance frequency is decreased. With this, the amount of variation Δf0 is decreased. 
         [0212]    When the amount of variation ΔW is further increased from d 4  and reaches d 5 , the amount of variation Δf0 reaches the allowable value Δf0A. 
         [0213]    The RFID tag  100  using the inlay  150 B of the modification example of the embodiment may perform an appropriate operation even if the amount of variation ΔW is changed from zero (0) to d 5  in the wet etching for patterning the antenna elements  110 A and  120 A. 
         [0214]    As described above, according to the modification example of the embodiment, it is possible to provide the RFID tag  100  capable of performing an appropriate operation at a desired communication frequency. In addition, it is possible to provide the RFID tag  100  which is particularly effective in a case where variation of the amount of etching is large by including the four the connection portions  114 A,  114 C,  124 A, and  124 C with different widths of the tapered portions  114 A 1 ,  114 C 1 ,  124 A 1 , and  124 C 1 . 
         [0215]    Furthermore, in the modification of the embodiment, although the RFID tag  100  includes the four the connection portions  114 A,  114 C,  124 A, and  124 C with different widths of the tapered portions  114 A 1 ,  114 C 1 ,  124 A 1 , and  124 C 1 , in a case of providing a plurality of connection portions having such tapered portions, the RFID tag  100  may include any number of the connection portions as long as the number of the connection portions is equal to or more than two. 
         [0216]    In the above descriptions, although the inlay  150  or  150 B is wound around the base portion  101  and the RFID tag  100  is covered with the cover portion  140 , the element  150 A (see  FIG. 6 ) before attaching the IC chip  130  is wound around the base portion  101  and it may be used as a high frequency circuit. 
         [0217]      FIGS. 17A and 17B  are diagrams illustrating a high frequency circuit  200 .  FIG. 18  is a diagram illustrating an implementation example of the high frequency circuit  200 .  FIG. 17A  illustrates a configuration of the high frequency circuit  200  in plan view and  FIG. 17B  illustrates a cross section taken along arrows of XVIIB-XVIIB in  FIG. 17A . 
         [0218]    The high frequency circuit  200  includes the element  150 A and the base portion  101  and the element  150 A is wound around the base portion  101 . The high frequency circuit  200  is a circuit having one of the terminals  113 A and  123 A as an input terminal and the other as an output terminal. 
         [0219]    As illustrated in  FIG. 18 , the high frequency circuit  200  is connected to, for example, a branch line  203 A branched from a microstrip line  203  connecting an antenna  201  and a power amplifier (PA)  202 . A communication device  204  includes the antenna  201 , the PA  202 , the microstrip line  203 , and the branch line  203 A. The communication device  204  is, for example, a smartphone terminal, a mobile phone terminal, a tablet computer, a portable game machine, and the like. 
         [0220]    The antenna  201  is built in a case of the communication device  204  and communicates, for example, with a communication bandwidth of 1.5 GHz. Although a duplexer may be provided between the PA  202  and the antenna  201 , the duplexer is omitted here. In addition, although a central processing unit (CPU) chip is connected to the PA  202  via, for example, a modulator/demodulator, the CPU chip is omitted here. 
         [0221]    The microstrip line  203  is provided on a surface of the wiring substrate. This wiring substrate includes a ground plane overlapping with the microstrip line  203  in plan view. 
         [0222]    The branch line  203 A is a microstrip line overlapping with the ground plane and is connected to the terminal  113 A (see  FIGS. 17A and 17B ) of the high frequency circuit  200 . The terminal  123 A (see  FIGS. 17A and 17B ) of the high frequency circuit  200  is connected to the ground plane of the wiring substrate in which the branch line  203 A is provided through the via hole or the like. 
         [0223]    The resonance frequency f0 of the high frequency circuit  200  is set to, for example, 2.5 GHz and an allowable range of the resonance frequency f0 is set to 2.5 GHz±15%. For example, 2.5 GHz is a communication bandwidth used for a wireless local area network (LAN). 
         [0224]    Although the communication device  204  performs communication at a communication bandwidth of 1.5 GHz through the antenna  201 , there is a case where a signal of 2.5 GHz is received through the antenna  201 . That is, there is a case the communication device  204  receives the signal of 2.5 GHz in addition to a signal of 1.5 GHz through the antenna  201 . 
         [0225]    In this case, since the resonance frequency f0 of the high frequency circuit  200  is set to 2.5 GHz, the signal of 2.5 GHz received by the antenna  201  is input from the antenna  201  to the high frequency circuit  200  through the microstrip line  203  and the branch line  203 A and resonates. Accordingly, the signal of 2.5 GHz received by the antenna  201  is not transmitted to the PA  202 . 
         [0226]    This uses a notch function of the high frequency circuit  200 , and the signal of 2.5 GHz is cut by the notch function of the high frequency circuit  200 . 
         [0227]    If the high frequency circuit  200  is manufactured in the wet etching, there is a case where the resonance frequency of the high frequency circuit  200  is shift due to variation in the amount of etching when the antenna elements  110  and  120  are patterned. 
         [0228]    In this case, since the allowable range of the resonance frequency f0 (2.5 GHz)±15% is realized by the connection portion  124 A, it is possible to provide the high frequency circuit  200  with an appropriate operation even if variation of the amount of etching occurs. 
         [0229]    Here, in a case where the allowable range of the resonance frequency f0 (2.5 GHz)±15% is realized using the connection portion  124 A, for example, the design value described with reference to  FIGS. 1 to 16  may be set to a level of −15%, the allowable value Δf0A may be set to a level of +15%, and a level of 0% may be set to a median value between the level of −15% and the level of +15%. 
         [0230]    Furthermore, although the notch function for the high frequency circuit  200  has been described here, the notch function may be used for other purposes. 
         [0231]    All examples and conditional language recited herein of the RFID tag and the high frequency circuit are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.