Patent Publication Number: US-2022237428-A1

Title: Rfid tag

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of PCT/JP2020/031307 filed Aug. 19, 2020, which claims priority to Japanese Patent Application No. 2020-012662, filed Jan. 29, 2020, the entire contents of each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a radio frequency identifier (RFID) tag including a radio frequency integrated circuit (RFIC) and an antenna. 
     BACKGROUND 
     International Publication No. 2016/084658 (hereinafter “Patent Literature 1”) discloses an example of an RFID tag including an RFIC module. This RFID tag is configured by mounting an RFIC module on an antenna base material on which an antenna is formed. The RFIC module includes an RFIC and an impedance matching circuit that matches impedance between the RFIC and the antenna. 
     In the RFIC module having the structure described in Patent Literature 1, depending on arrangement of a plurality of coils constituting the impedance matching circuit, unnecessary coupling between the coils and the antenna may occur. When this unnecessary coupling occurs, the RFIC module and the antenna cannot be independently designed, and the design of the entire RFID tag becomes complicated. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide an RFID tag in which unnecessary coupling between an antenna and a coil forming an impedance matching circuit of an RFIC module is suppressed to improve independence between the RFIC module and the antenna. 
     Accordingly, in an exemplary embodiment, an RFID tag is provided that includes an RFIC, an antenna, and an impedance matching circuit that matches impedance between the RFIC and the antenna. The impedance matching circuit includes a coil, and is connected between the RFIC and the antenna. A main plane of a magnetic flux loop generated in the vicinity of the coil by the antenna is not parallel to a main plane of a magnetic flux loop generated in the coil. 
     According to the e International Publication No. 2016/084658lary embodiments of the present invention, an RFID tag is provided in which unnecessary coupling between an antenna and a coil forming an impedance matching circuit of an RFIC module is suppressed to improve independence between the RFIC module and the antenna. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partially enlarged plan view of an RFID tag  201  according to a first exemplary embodiment. 
         FIG. 2  is a circuit diagram of an RFIC module  101 . 
         FIG. 3A  is a plan view of an RFID tag  202  according to a second exemplary embodiment.  FIG. 3B  is an enlarged plan view of a mounting portion of an RFIC module  102  included in the RFID tag  202 . 
         FIG. 4  is a plan view illustrating a conductor pattern formed on a substrate  1  of the RFIC module  102 . 
         FIG. 5  is a plan view of an RFID tag  203  according to a third exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a plurality of exemplary aspects of the present invention will be shown with examples with reference to the drawings. In each figure, the same parts are designated by the same reference signs. In consideration of the description of the main points or ease of understanding, the embodiment is divided into a plurality of exemplary embodiments for convenience of description, but partial replacement or combination of configurations shown in different embodiments is possible. In second and subsequent embodiments, description of matters common to a first embodiment will be omitted, and only different points will be described. In particular, similar actions and effects obtained by the same configuration will not be sequentially described for each embodiment. 
     First Exemplary Embodiment 
       FIG. 1  is a partially enlarged plan view of an RFID tag  201  according to the first exemplary embodiment. The RFID tag  201  includes an insulator film  60 , antenna conductor patterns  61  and  62  formed (or otherwise disposed) on the insulator film  60 , and an RFIC module  101  mounted on the insulator film  60 . 
     In an exemplary aspect, the antenna conductor patterns  61  and  62  form a dipole antenna. In  FIG. 1 , the vicinities of feeding units of the dipole antenna by the antenna conductor patterns  61  and  62  appear. A conductor pattern  61 P is a feeding unit (e.g., a feeding end) of the antenna conductor pattern  61 , and a conductor pattern  62 P is a feeding unit (e.g., a feeding end) of the antenna conductor pattern  62 . 
     The RFIC module  101  includes a substrate  1 , an RFIC  2  mounted on the substrate  1 , and an impedance matching circuit formed on the substrate  1  and matching impedance between the RFIC  2  and an antenna. 
     The impedance matching circuit includes a first inductor L 1 , a second inductor L 2 , a third inductor L 3 , a fourth inductor L 4 , and a fifth inductor L 5 . 
     According to an exemplary aspect, the insulator film  60  is, for example, a polyethylene terephthalate (PET) film, and the antenna conductor patterns  61  and  62  are, for example, patterns of aluminum foil. 
     In the RFIC module  101 , an RFIC-side first terminal electrode  31 , an RFIC-side second terminal electrode  32 , an antenna-side first terminal electrode  11 , and an antenna-side second terminal electrode  12  are formed. 
     When the RFIC module  101  is mounted on the insulator film  60 , the antenna-side first terminal electrode  11  of the RFIC module  101  is connected to the conductor pattern  61 P, and the antenna-side second terminal electrode  12  of the RFIC module  101  is connected to the conductor pattern  62 P. 
       FIG. 2  is a circuit diagram of the RFIC module  101 . The RFIC module  101  includes the RFIC  2  and an impedance matching circuit  7 . The impedance matching circuit  7  includes the first inductor L 1 , the second inductor L 2 , the third inductor L 3 , the fourth inductor L 4 , and the fifth inductor L 5 . For purposes of this disclosure, a dot symbol in  FIG. 2  indicates a coil winding direction of each inductor. 
     Moreover, each of the first inductor L 1 , the second inductor L 2 , the third inductor L 3 , and the fourth inductor L 4  illustrated in  FIG. 1  includes a spiral coil conductor pattern. A coil opening of the coil conductor pattern forming the first inductor L 1  and a coil opening of the coil conductor pattern forming the third inductor L 3  overlap with each other. Similarly, a coil opening of the coil conductor pattern forming the second inductor L 2  and a coil opening of the coil conductor pattern forming the fourth inductor L 4  overlap with each other. 
     The coils forming the first inductor L 1  and the third inductor L 3  correspond to a first coil LA according to the present invention, and the coils forming the second inductor L 2  and the fourth inductor L 4  correspond to a second coil LB according to the present invention. That is, the first coil LA and the second coil LB each have a winding axis of the coil in a direction perpendicular to the surface of the substrate  1 , and the winding direction of the first coil LA and the winding direction of the second coil LB have a relationship in which the direction of the magnetic flux generated in the coil opening of the first coil LA and the direction of the magnetic flux generated in the coil opening of the second coil LB are reverse when the current is applied from the RFIC-side first terminal electrode  31  to the RFIC-side second terminal electrode  32 . Therefore, as indicated by a magnetic flux φ 3  in  FIG. 1 , a plane of the main loop of the magnetic flux interlinking the coil openings of the first coil LA and the second coil LB is parallel to the X-Z plane. 
     On the other hand, as further shown in  FIG. 1 , as indicated by a magnetic flux φ 1 , the main plane of the magnetic flux loop generated around the antenna conductor pattern  61  is parallel to the Y-Z plane. Similarly, as indicated by a magnetic flux φ 2 , the main plane of the magnetic flux loop generated around the antenna conductor pattern  62  is also parallel to the Y-Z plane. 
     Therefore, the main planes of the magnetic flux loops generated in the vicinities of the first coil LA and the second coil LB by the antenna conductor patterns  61  and  62  (e.g., magnetic fluxes φ 1  and φ 2 ) are orthogonal to the main planes of the magnetic flux loops generated in the first coil LA and the second coil LB (e.g., magnetic flux φ 3 ). Moreover, the first coil LA and the second coil LB of the impedance matching circuit are not (or minimally) unnecessarily coupled to the antenna conductor patterns  61  and  62 . 
     Second Exemplary Embodiment 
     In the second exemplary embodiment, in particular, an RFID tag in which the configuration of the antenna is different from that of the example shown in the first embodiment is now described. 
       FIG. 3A  is a plan view of an RFID tag  202  according to the second exemplary embodiment.  FIG. 3B  is an enlarged plan view of a mounting portion of an RFIC module  102  included in the RFID tag  202 . 
     The RFID tag  202  includes an antenna  6  and an RFIC module  102  coupled to the antenna  6 . Moreover, the antenna  6  includes an insulator film  60  and antenna conductor patterns  61  and  62  formed on the insulator film  60 . 
     As shown, the antenna conductor pattern  61  includes conductor patterns  61 P,  61 L, and  61 C, and the antenna conductor pattern  62  similarly includes conductor patterns  62 P,  62 L, and  62 C. The antenna conductor patterns  61  and  62  form a dipole antenna in this exemplary aspect. 
     In addition, the RFIC module  102  is mounted on the conductor patterns  61 P and  62 P. The conductor patterns  61 L and  62 L each have a meander line shape and act as a region having a high inductance component. In addition, the conductor patterns  61 C and  62 C each have a planar shape and act as a region having a high capacitance component. As a result, the formation regions of the antenna conductor patterns  61  and  62  are reduced by increasing the inductance component in the region with high current intensity and increasing the capacitance component in the region with high voltage intensity. 
       FIG. 4  is a plan view illustrating a conductor pattern formed on the substrate  1  of the RFIC module  102 . As shown in  FIG. 4 , the upper part is a plan view of a conductor pattern formed on the upper surface of the substrate  1 , and the lower part is a plan view of a conductor pattern formed on the lower surface of the substrate  1 . 
     On the upper surface of the substrate  1 , the RFIC-side first terminal electrode  31 , the RFIC-side second terminal electrode  32 , a conductor pattern L 11  of the main part of the first inductor L 1 , and a conductor pattern L 21  of the main part of the second inductor L 2  are formed. The RFIC-side first terminal electrode  31  is connected to one end of the conductor pattern L 11 , and the RFIC-side second terminal electrode  32  is connected to one end of the conductor pattern L 21 . These conductor patterns are obtained by patterning a copper foil by photolithography, for example. 
     Moreover, the antenna-side first terminal electrode  11  and the antenna-side second terminal electrode  12  are formed on the lower surface of the substrate  1 . On the lower surface of the substrate  1 , a conductor pattern L 12  of a part of the first inductor L 1 , a conductor pattern L 22  of a part of the second inductor L 2 , a conductor pattern of the third inductor L 3 , a conductor pattern of the fourth inductor L 4 , and a conductor pattern of the fifth inductor L 5  (i.e., the conductor patterns surrounded by two-dot chain lines) are formed. These conductor patterns are also obtained by patterning a copper foil by photolithography, for example. 
     An insulating layer is formed between the conductor pattern  61 P and the antenna-side first terminal electrode  11 , and the conductor pattern  61 P and the antenna-side first terminal electrode  11  are capacitively coupled. Similarly, an insulating layer is formed between the conductor pattern  62 P and the antenna-side second terminal electrode  12 , and the conductor pattern  62 P and the antenna-side second terminal electrode  12  are capacitively coupled. 
     One end of the conductor pattern L 12  of a part of the first inductor L 1  and one end of the conductor pattern of the third inductor L 3  are connected to the antenna-side first terminal electrode  11 . Similarly, one end of the conductor pattern L 22  of a part of the second inductor L 2  and one end of the conductor pattern of the fourth inductor L 4  are connected to the antenna-side second terminal electrode  12 . The conductor pattern of the fifth inductor L 5  is connected between the other end of the conductor pattern of the third inductor L 3  and the other end of the conductor pattern of the fourth inductor L 4 . 
     The other end of the conductor pattern of the third inductor L 3  and the other end of the conductor pattern L 11  of the main part of the first inductor L 1  are connected via a via conductor V 1 . Similarly, the other end of the conductor pattern of the fourth inductor L 4  and the other end of the conductor pattern L 21  of the main part of the second inductor L 2  are connected via a via conductor V 2 . 
     As further shown, the RFIC  2  is mounted on the RFIC-side first terminal electrode  31  and the RFIC-side second terminal electrode  32 . That is, an RFIC terminal electrode  21  of the RFIC  2  is connected to the RFIC-side first terminal electrode  31 , and an RFIC terminal electrode  22  of the RFIC  2  is connected to the RFIC-side second terminal electrode  32 . 
     The first inductor L 1  and the third inductor L 3  are formed in different layers of the substrate  1 , and are arranged in a relationship in which coil openings overlap with each other. Similarly, the second inductor L 2  and the fourth inductor L 4  are formed in different layers of the substrate  1 , and are arranged in a relationship in which coil openings overlap with each other. The second inductor L 2  and the fourth inductor L 4 , and the first inductor L 1  and the third inductor L 3  are disposed in a positional relationship of sandwiching the mounting position of the RFIC  2  along the surface of the substrate  1 . 
     The winding direction from the RFIC-side first terminal electrode  31  to the other end of the third inductor L 3  is the same as the winding direction from the RFIC-side second terminal electrode  32  to the other end of the fourth inductor L 4 . 
     It is noted that the circuit of the RFIC module  102  is the same as the circuit illustrated in  FIG. 2 . The first inductor L 1  illustrated in  FIG. 2  includes the conductor patterns L 11  and L 12  illustrated in  FIG. 4 , and the second inductor L 2  includes the conductor patterns L 21  and L 22  illustrated in  FIG. 4 . The first inductor L 1  is connected between the antenna-side first terminal electrode  11  and the RFIC-side first terminal electrode  31 . The second inductor L 2  is connected between the antenna-side second terminal electrode  12  and the RFIC-side second terminal electrode  32 . One end of the third inductor L 3  is connected to the antenna-side first terminal electrode  11 , one end of the fourth inductor L 4  is connected to the antenna-side second terminal electrode  12 , and the fifth inductor L 5  is connected between the other end of the third inductor L 3  and the other end of the fourth inductor L 4 . 
     As illustrated in  FIGS. 4 and 3B , the first coil LA includes coils forming the first inductor L 1  and the third inductor L 3 , and the second coil LB includes coils forming the second inductor L 2  and the fourth inductor L 4 . The direction of the magnetic flux generated in the coil opening of the first coil LA and the direction of the magnetic flux generated in the coil opening of the second coil LB are in a reverse relationship when the current is applied from the RFIC-side first terminal electrode  31  to the RFIC-side second terminal electrode  32 . 
     As indicated by a magnetic flux φ 3  in  FIG. 3B , the plane of the main loop of the magnetic flux interlinking the coil openings of the first coil LA and the second coil LB is parallel to the X-Z plane. 
     In the present embodiment, the antenna conductor patterns  61  and  62  have the meander line-shaped conductor patterns  61 L and  62 L, but the overall extending direction for each conductor pattern is the X direction illustrated in  FIG. 3A . Therefore, in  FIG. 3A , as indicated by a magnetic flux φ 1 , the main plane of the magnetic flux loop generated around the antenna conductor pattern  61  is parallel to the Y-Z plane. Similarly, as indicated by a magnetic flux φ 2 , the main plane of the magnetic flux loop generated around the antenna conductor pattern  62  is also parallel to the Y-Z plane. 
     Therefore, the main planes of the magnetic flux loops generated in the vicinities of the first coil LA and the second coil LB by the antenna conductor patterns  61  and  62  are orthogonal to the main planes of the magnetic flux loops generated in the first coil LA and the second coil LB. Therefore, the first coil LA and the second coil LB of the impedance matching circuit are hardly unnecessarily coupled to the antenna conductor patterns  61  and  62 . 
     Third Exemplary Embodiment 
     In a third exemplary embodiment, in particular, an RFID tag in which a configuration of an antenna near an RFIC module is different from that in the first embodiment is shown. 
       FIG. 5  is a plan view of an RFID tag  203  according to the third exemplary embodiment. As shown, the RFID tag  203  includes an insulator film  60 , antenna conductor patterns  61  and  62  formed on the insulator film  60 , and an RFIC module  103  mounted on the insulator film  60 . 
     The antenna conductor patterns  61  and  62  form a dipole antenna. In  FIG. 5 , the vicinities of feeding units of the dipole antenna by the antenna conductor patterns  61  and  62  appear. A conductor pattern  61 P is a feeding unit (e.g., a feeding end) of the antenna conductor pattern  61 , and a conductor pattern  62 P is a feeding unit (e.g., a feeding end) of the antenna conductor pattern  62 . 
     The RFIC module  103  includes a substrate  1 , an RFIC  2  mounted on the substrate  1 , and an impedance matching circuit formed on the substrate  1  and matching impedance between the RFIC  2  and an antenna. The impedance matching circuit includes a first inductor L 1 , a second inductor L 2 , a third inductor L 3 , a fourth inductor L 4 , and a fifth inductor L 5 . A basic configuration of the RFIC module  103  is the same as that of the RFIC module  101  described in the first embodiment described above. 
     In the present embodiment, the antenna conductor pattern  61  has a drawing portion  61 E extending from the conductor pattern  61 P. The main direction of the drawing direction of the drawing portion  61 E is a direction parallel to the Y axis. Similarly, the antenna conductor pattern  62  has a drawing portion  62 E extending from the conductor pattern  62 P. The main direction of the drawing direction of the drawing portion  62 E is a direction parallel to the Y axis. These drawing portions  61 E and  62 E are portions close to the first coil LA and the second coil LB. 
     As indicated by a magnetic flux φ 3  in  FIG. 5 , the plane of the main loop of the magnetic flux interlinking the coil openings of the first coil LA and the second coil LB is parallel to the Y-Z plane. In addition, as indicated by a magnetic flux φ 1 , the main plane of the magnetic flux loop generated around the drawing portion  61 E in the antenna conductor pattern  61  is parallel to the X-Z plane. Similarly, as indicated by a magnetic flux φ 2 , the main plane of the magnetic flux loop generated around the drawing portion  62 E in the antenna conductor pattern  62  is parallel to the X-Z plane. 
     Therefore, the main planes of the magnetic flux loops generated in the vicinities of the first coil LA and the second coil LB by the drawing portions  61 E and  62 E of the antenna conductor patterns  61  and  62  are orthogonal to the main planes of the magnetic flux loops generated in the first coil LA and the second coil LB. Therefore, the first coil LA and the second coil LB of the impedance matching circuit are not (or minimally) unnecessarily coupled to the antenna conductor patterns  61  and  62 . 
     As described in each embodiment, according to the present invention, unnecessary coupling between the antenna and the coil forming the impedance matching circuit of the RFIC module is suppressed, and the RFID tag having high independence between the RFIC module and the antenna is obtained. 
     Finally, it is noted that the above description of the embodiments is illustrative in all respects and not restrictive. Those skilled in the art can appropriately make modifications and changes. 
     For example, in any of the embodiments described above, an example has been described in which the main planes of the magnetic flux loops generated in the vicinities of the first coil LA and the second coil LB by the antenna conductor patterns  61  and  62  and the main planes of the magnetic flux loops generated in the first coil LA and the second coil LB are “orthogonal” to each other. However, when the main planes are “non-parallel” in that they intersect each other, for example, there is an effect of suppressing unnecessary coupling between the first coil LA and the second coil LB, and the antenna conductor patterns  61  and  62 . That is, when the main planes of the magnetic flux loops generated in the vicinities of the first coil LA and the second coil LB and the main planes of the magnetic flux loops generated in the first coil LA and the second coil LB are orthogonal to each other, it can be said that this is a typical example in which the unnecessary coupling is most suppressed. For example, when the main planes of the magnetic flux loops generated in the vicinities of the first coil LA and the second coil LB intersect with the main planes of the magnetic flux loops generated in the first coil LA and the second coil LB within the range of the intersection angle of 90°±45°, a good effect of suppressing unnecessary coupling can be obtained. 
     In addition, for example, in any of the embodiments described above, an example in which the RFIC  2  is mounted on the upper surface of the substrate  1  has been described, but the RFIC  2  can be disposed inside the substrate  1  in an alternative aspect. For example, the RFIC-side first terminal electrode  31  and the RFIC-side second terminal electrode  32  can be formed in the first layer, and the RFIC  2  can be provided in the first layer. In this case, an opening (cavity) can be formed in the second layer to avoid structural interference with the RFIC  2  according to an exemplary aspect. 
     REFERENCE SIGNS LIST 
     
         
         
           
             L 1  first inductor 
             L 2  second inductor 
             L 3  third inductor 
             L 4  fourth inductor 
             L 5  fifth inductor 
             L 11 , L 12 , L 21 , L 22  conductor pattern 
             LA first coil 
             LB second coil 
             V 1 , V 2  via conductor 
               1  substrate 
               2  RFIC 
               6  antenna 
               7  impedance matching circuit 
               11  antenna-side first terminal electrode 
               12  antenna-side second terminal electrode 
               21 ,  22  RFIC terminal electrode 
               31  RFIC-side first terminal electrode 
               32  RFIC-side second terminal electrode 
               60  insulator film 
               61 ,  62  antenna conductor pattern 
               61 P,  61 L,  61 C,  62 P,  62 L,  62 C conductor pattern 
               101 ,  102 ,  103  RFIC module 
               201 ,  202 ,  203  RFID tag