antenna

Abstract

A loop circuit (21) that is electrically connected to an IC chip (30) is formed on a film (20). The loop circuit (21) has metal wiring (20b) disposed in a recessed section (21a) of the film (20). The metal wiring (20b) has: a first terminal section (21b1) that is electrically connected to the IC chip (30); a second terminal section (21b2) that is electrically connected to the first terminal section (21b1) via the IC chip (30); and a wiring section (21b3) that connects the first terminal section (21b1) and the second terminal section (21b2). The wiring section (21b3) has a thickness of 10 μm or less and a line width of 0.2 mm or less.

Description

antenna

[0001] The present disclosure relates to an antenna, and more particularly to an antenna for an IC tag used in an RFID (Radio Frequency Identification) system.

[0002] An RFID system is a system that reads an IC tag, on which information about an item is recorded, by using radio waves or an induction magnetic field generated by a reader / writer, and is used for inventory management and sales of items.

[0003] An IC tag used in an RFID system includes a substrate on which an antenna circuit is formed and a film attached to the substrate. The film includes an IC chip and a loop circuit that is electrically connected to the IC chip and magnetically coupled to the antenna circuit. An example of such an IC tag is disclosed in Japanese Patent No. 4525869.

[0004] Patent No. 4525869

[0005] Incidentally, the magnetic field is inversely proportional to the cube of the distance. Therefore, when attaching a film to a substrate, the relative positions of the antenna circuit and loop circuit of a conventional IC tag can become misaligned, weakening the magnetic coupling between the antenna circuit and loop circuit. This makes conventional IC tags prone to malfunction.

[0006] The present disclosure aims to provide an antenna that is less likely to malfunction even when the positional relationship between the antenna circuit and the loop circuit is misaligned.

[0007] The antenna of the present disclosure includes a film and an IC chip. The film has a loop circuit formed therein that is electrically connected to the IC chip. The loop circuit has a recess formed in the film and metal wiring disposed within the recess. The metal wiring has a first terminal electrically connected to the IC chip, a second terminal electrically connected to the first terminal via the IC chip, and a wiring portion connecting the first terminal and the second terminal. Here, the wiring portion has a thickness of 10 μm or less and a line width of 0.2 mm or less.

[0008] The antenna of the present disclosure can strengthen the magnetic field generated in the loop circuit, thereby suppressing malfunctions.

[0009] FIG. 1 is a schematic diagram of antenna 100 in a plan view according to the first embodiment. FIG. 2 is a schematic diagram showing an enlarged view of film 20 used in antenna 100. FIG. 3 is a cross-sectional view of antenna 100 taken along line A-A in FIG. 1. FIG. 4 is a partially enlarged view of antenna 100 in region B shown in FIG. 3. FIG. 5 is a schematic diagram showing an enlarged view of antenna 100A in a plan view according to the second embodiment. FIG. 6 is a schematic diagram of film 20A used in antenna 100A. FIG. 7 is a cross-sectional view of film 20A taken along line C-C in FIG. 6. FIG. 8 is a diagram corresponding to FIG. 2, showing an enlarged view of film 20B in a plan view according to the third embodiment. FIG. 9 is a cross-sectional view of film 20B taken along line D-D in FIG. 8. FIG. 10 is a graph (calculated by electromagnetic field simulation) showing the relationship between the size (Lx) of the loop circuit and inductance in the antenna according to the first embodiment.

[0010] The antenna of the present disclosure will be described below with reference to specific embodiments.

[0011] The embodiments (embodiments 1 to 3) described below are merely examples of embodiments of the present disclosure. The present disclosure is not limited to the following embodiments, and various modifications are possible depending on the design, etc., as long as the effects of the present disclosure can be achieved.

[0012] 1 to 4, an antenna 100 will be described. The antenna 100 includes a substrate 10, a film 20, and an IC chip 30.

[0013] An example of the material of the substrate 10 is paper. Fig. 3 shows an example of a cross-sectional structure of the substrate 10 made of paper. Note that the material of the base material 10 may be a material other than paper, such as a PET film or a polycarbonate film.

[0014] The substrate 10 has an antenna circuit 11. The antenna circuit 11 is formed of, for example, a paste material containing silver.

[0015] The film 20 is disposed on the substrate 10 (see FIGS. 1 and 3). For example, the film 20 is fixed to the substrate 10 by thermocompression bonding, bonding to the substrate 10 using an adhesive, or crimping to the substrate 10.

[0016] The film 20 is provided with a loop circuit 21. The loop circuit 21 can be used, for example, as an IC tag used in an RFID system. The loop circuit 21 is not electrically connected to the antenna circuit 11. In other words, the loop circuit 21 is electrically insulated from the antenna circuit 11.

[0017] Note that, here, the above-mentioned "not electrically connected" means that the loop circuit 21 is not directly connected to the antenna circuit 11 via a conductor (not shown), and does not mean that there is no electromagnetic coupling with the antenna circuit 11.

[0018] The loop circuit 21 has a recess 21a formed in the film 20 and a metal wiring 21b disposed in the recess 21a (see FIGS. 3 and 4).

[0019] The metal wiring 21b has a ring shape with a portion cut out in a plan view, and includes a first terminal portion 21b1, a second terminal portion 21b2, and a wiring portion 21b3 connecting the first terminal portion 21b1 and the second terminal portion 21b2 (see FIG. 2).

[0020] Here, the entire wiring portion 21b3 is disposed within the recess 21a (see FIGS. 3 and 4). The wiring portion 21b3 is formed to have a thickness t of 10 μm or less and a line width w of 0.2 mm or less (see FIG. 4).

[0021] 2, the IC chip 30 is electrically connected to the first terminal 21b1 and the second terminal 21b2. In other words, the first terminal 21b1 and the second terminal 21b2 are electrically connected via the IC chip 30.

[0022] As shown in Figures 3 and 4, the metal wiring 21b is disposed in a recess 21a formed in the film 20. In other words, the line width w and thickness t of the metal wiring 21b are regulated by the width and depth of the recess 21a. That is, the thickness t of the wiring portion 21b3 of the metal wiring 21b can be formed to be 10 μm or less, and the line width w to be 0.2 mm or less. Therefore, the antenna 100 can generate a strong magnetic field generated by the loop circuit 21. As a result, the antenna 100 is less likely to malfunction even if the film 20 is attached to the substrate 10 with the antenna circuit 11 and the loop circuit 21 misaligned.

[0023] Furthermore, in the antenna 100, the wiring portion 21b3 of the metal wiring 21b is disposed in the recess 21a formed in the film 20. The presence of the sidewall of the recess 21a makes it possible to suppress variations in the line width w of the wiring portion 21b3 during mass production. Therefore, the antenna 100 can suppress individual differences in communication distance.

[0024] The thickness t of the wiring portion 21b3 of the metal wiring 21b is preferably 0.5 μm or more. By setting the thickness t of the wiring portion 21b3 of the metal wiring 21b to 0.5 μm or more, it is possible to suppress variations in the thickness t of the wiring portion 21b3 during mass production. Therefore, the antenna 100 can suppress individual differences in communication distance.

[0025] Furthermore, the line width w of the wiring portion 21b3 of the metal wiring 21b is preferably 5 μm or more. By setting the line width w of the wiring portion 21b3 of the metal wiring 21b to 5 μm or more, it is possible to suppress variations in the line width w of the wiring portion 21b3 during mass production. Therefore, the antenna 100 can suppress individual differences in communication distance.

[0026] Furthermore, it is preferable that the line width w of each of the first terminal portion 21b1 and the second terminal portion 21b2 is larger than the line width w of the wiring portion 21b3, which makes it easier to mount an IC chip.

[0027] 5 to 7, an antenna 100A according to a second embodiment will be described. In the following, in order to simplify the description of the second embodiment, the same reference numerals will be used for the contents described in the first embodiment, and detailed description thereof will be omitted.

[0028] If it is desired to increase the communication distance of the antenna, it is preferable to widen the wiring width of the metal wiring. However, if the wiring width of the metal wiring is widened, malfunctions are likely to occur if the positional relationship between the antenna circuit and the loop circuit is misaligned.

[0029] Furthermore, when the line width of the wiring portion is increased as described above, the distance between the center of the wiring portion and the sidewall of the recess increases, and the thickness of the wiring portion at the center tends to be thinner than the thickness of the metal wiring at the outside, or the thickness of the wiring portion at the center tends to be thicker than the thickness of the metal wiring at the outside. In other words, it becomes difficult to suppress variations in the thickness of the wiring portion.

[0030] Therefore, as shown in Figures 5 to 7, in the antenna 100A, a film 20A is used instead of the film 20. The film 20A has the metal wiring 21b shown in Figures 5 to 7. Specifically, the metal wiring 21b exemplified in the second embodiment includes a plurality of wiring portions 21b3 (two in the illustrated example) that connect the first terminal portion 21b1 and the second terminal portion 21b2 in parallel. Furthermore, the plurality of wiring portions 21b3 are arranged side by side in a plan view.

[0031] The antenna 100A has multiple wiring portions 21b3 each having a thickness t of 10 μm or less and a line width w of 0.2 mm or less, which makes it less likely to malfunction even if the positional relationship between the antenna circuit and the loop circuit is misaligned.

[0032] Furthermore, the antenna 100A can increase the communication distance while suppressing individual differences in the communication distance.

[0033] 8 and 9, an antenna 100B according to a third embodiment will be described. In the following, in order to simplify the description of the third embodiment, the contents described in the first and second embodiments will be omitted.

[0034] As shown in FIGS. 8 and 9, in an antenna 100B, a film 20B is used instead of the film 20 or the film 20A.

[0035] The film 20B has the metal wiring 21b shown in Figures 8 and 9. Specifically, the metal wiring 21b exemplified in the third embodiment includes a plurality of wiring portions 21b3 (two in the illustrated example) that connect the first terminal portion 21b1 and the second terminal portion 21b2 in parallel. The plurality of wiring portions 21b3 are arranged in the thickness direction of the film 20B. Furthermore, the plurality of wiring portions 21b3 are arranged so as to overlap each other in a plan view.

[0036] The antenna 100B has multiple wiring sections 21b3 each having a thickness t of 10 μm or less and a line width w of 0.2 mm or less, which makes it less likely to malfunction even if the positional relationship between the antenna circuit and the loop circuit is misaligned.

[0037] In addition, the antenna 100B has a plurality of wiring portions 21b3 arranged in the thickness direction of the film, which allows the antenna 100B to be small while increasing the communication distance.Furthermore, the antenna 100B has a plurality of wiring portions 21b3 arranged so as to overlap in a plan view, which allows the antenna 100B to be even smaller.

[0038] The plurality of wiring portions 21b3 may be connected by vias 21b4 extending in the thickness direction of the film at a predetermined portion of the loop circuit 21 extending from the first terminal portion 21b1 to the second terminal portion 21b2. This makes it possible to prevent malfunction of the antenna 100B even if one of the plurality of wiring portions 21b3 is broken.

[0039] The antenna 100B has a structure in which a plurality of wiring portions 21b3 are formed on both sides of a film. However, the antenna may be formed by preparing a plurality of films each having a wiring portion and stacking them.

[0040] The antenna may also have metal wiring including a plurality of wiring portions arranged in the thickness direction of the film and arranged side by side in a plan view, thereby enabling the antenna to realize a loop circuit with higher wiring density.

[0041] (Regarding the relationship between loop circuit and inductance) Next, in the antenna 100 (Figures 1 to 4) according to the above-mentioned embodiment 1, the relationship between the configuration of the loop circuit 21 and the inductance will be explained based on the calculation results (see Figure 10) of a predetermined electromagnetic field simulation (hereinafter simply referred to as "simulation").

[0042] In the graph of Figure 10, the horizontal axis represents the size of the loop circuit 21 (a value corresponding to the dimension Lx shown in Figure 2 [unit: mm]), and the vertical axis represents the inductance of the loop circuit 21 [unit: nH] calculated by the above simulation.

[0043] For example, in order to generate a strong magnetic field in the loop circuit 21 (IC tag) applied to an RFID system, the optimum inductance value required for the loop circuit 21 is preferably 19.5 nH (see the dashed line RL shown in FIG. 10 ). The configuration of the loop circuit 21 that satisfies this optimum inductance value was derived based on the calculation results of the above simulation (see FIG. 10 ).

[0044] Table 1 below shows examples of the configuration of the loop circuit 21 (samples No. 1 to No. 4) used in the above simulation.

[0045]

[0046] Here, the thickness t of the wiring portion 21b3 was set to "3 μm" in all of Samples No. 1 to No. 4. That is, Samples No. 1 to No. 4 differ from one another in the line width w of the wiring portion 21b3 and the size (Lx (Ly) value) of the loop circuit 21.

[0047] The thickness t of the wiring portion 21b3 shown in Table 1 corresponds to the dimension t shown in Fig. 4. The line width w of the wiring portion 21b3 shown in Table 1 corresponds to the dimension w shown in Fig. 4. Furthermore, Lx (Ly) shown in Table 1 corresponds to the dimension Lx (dimension Ly) shown in Fig. 2. Note that the dimensions Lx and Ly shown in Table 1 are set to the same value.

[0048] 10 and Table 1, in sample No. 1, when Lx (Ly) of loop circuit 21 was 5.0 mm (the lower limit value shown in FIG. 10 and Table 1), the inductance value of loop circuit 21 was 23.8 nH. Thus, in sample No. 1, by setting the line width w of wiring portion 21b3 to 0.002 μm, it was found that the inductance exceeded the appropriate value (19.5 nH) described above even when the size (Lx (Ly) value) of loop circuit 21 was relatively small.

[0049] In sample No. 2, when Lx (Ly) of loop circuit 21 was 5.0 mm (the lower limit value shown in FIG. 10 and Table 1), the inductance value of loop circuit 21 was 20.2 nH. Thus, in sample No. 2, by setting the line width w of wiring portion 21b3 to 0.01 μm, it was found that the inductance exceeded the appropriate value (19.5 nH) described above even when the size (Lx (Ly) value) of loop circuit 21 was relatively small.

[0050] In sample No. 3, when Lx (Ly) of loop circuit 21 was 6.7 mm, the inductance value of loop circuit 21 was 19.5 nH. Thus, in sample No. 3, by setting the line width w of wiring portion 21b3 to 0.1 μm, it was found that the inductance exceeded the appropriate value (19.5 nH) described above even when the size (Lx (Ly) value) of loop circuit 21 was relatively small.

[0051] In sample No. 4, when Lx (Ly) of loop circuit 21 was 11.3 mm, the inductance value of loop circuit 21 was 19.5 nH. As described above, it was found that in sample No. 4, by setting the line width w of wiring portion 21b3 to 0.2 μm, the inductance exceeded the appropriate value (19.5 nH) described above. In other words, even when the line width w of wiring portion 21b3 was 0.2 μm, as in sample No. 4, the inductance exceeded the appropriate value (19.5 nH) described above.

[0052] In this way, if the loop circuit 21 in the antenna 100 is configured in the same manner as any of samples No. 1 to No. 4, a strong magnetic field is generated in the loop circuit 21, and the magnetic field coupling force between the antenna circuit 11 and the loop circuit 21 is strong even when the film 20 is attached to the substrate 10 with the antenna circuit 11 and the loop circuit 21 misaligned. As a result, an operational effect can be achieved in which malfunctions in the antenna 100 are less likely to occur.

[0053] Here, in Sample No. 4, when the inductance exceeds the appropriate value, the size of the loop circuit 21 (the value of Lx (Ly)) becomes relatively large compared to Samples No. 1 to No. 3. Therefore, from the viewpoint of reducing the size of the loop circuit 21 (the value of Lx (Ly)), it is preferable to make the line width w of the wiring portion 21b3 smaller than 0.2 mm.

[0054] 10: Substrate 11: Antenna circuit 20, 20A, 20B: Film 21: Loop circuit 21a: Recess 20b: Metal wiring 21b1: First terminal portion 21b2: Second terminal portion 21b3: Wiring portion 21b4: Via 30: IC chip 100, 100A, 100B: Antenna

Claims

1. A film and an IC chip, wherein a loop circuit electrically connected to the IC chip is formed in the film, the loop circuit having a recess formed in the film and a metal wiring disposed in the recess, the metal wiring having a first terminal portion electrically connected to the IC chip, a second terminal portion electrically connected to the first terminal portion via the IC chip, and a wiring portion connecting the first terminal portion and the second terminal portion, the wiring portion being an antenna having a thickness of 10 μm or less and a line width of 0.2 mm or less.

2. The antenna according to claim 1, wherein the thickness of the wiring portion is 0.5 μm or more.

3. The antenna according to claim 1 or 2, wherein the line width of the wiring portion is 5 μm or more.

4. The antenna according to any one of claims 1 to 3, wherein the line width of each of the first terminal portion and the second terminal portion is larger than the line width of the wiring portion.

5. The antenna according to claim 1, wherein a plurality of the wiring portions of the metal wiring are provided, the plurality of wiring portions being connected in parallel between the first terminal portion and the second terminal portion, and the plurality of wiring portions being arranged side by side in a plan view.

6. The antenna according to claim 1, wherein a plurality of the wiring portions of the metal wiring are provided, the plurality of wiring portions being connected in parallel between the first terminal portion and the second terminal portion, and the plurality of wiring portions being arranged in the thickness direction of the film.

7. The antenna according to claim 6, wherein the plurality of wiring portions are arranged overlapping each other in a plan view.

8. The antenna according to claim 6 or 7, wherein the metal wiring further has a via extending in the thickness direction of the film, and the plurality of wiring portions are connected by the via in the loop circuit extending from the first terminal portion to the second terminal portion.

Images