JP2003187207A - Electrode structure of tag for rfid and method for adjusting resonance frequency using the same electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode structure of a tag for RFID (radio frequency identification) by which a resonance frequency of a resonant circuit to be formed on the tag for RFID can be easily adjusted after formation of the circuit and a method for adjusting the resonance frequency using the electrode. <P>SOLUTION: In an RFID system for communicating data between a reader/ writer and the tag by using electromagnetic induction, a comb-line electrode 7 of a capacitor constituting the resonant circuit of the tag and a counter electrode 8 to be formed on the opposite side by sandwiching a substrate are formed so that area of an overlapped part between each finger 7b of the comb-line electrode 7 and the counter electrode 8 gradually becomes small from the tip side to the root side of the comb-line electrode 7, for example, the counter electrode 8 is formed like a taper and shift quantity of the resonance frequency when the fingers 7b are successively cut off is set as approximately equivalent values. Thus, the number of fingers to be cut off is directly determined from the shift quantity from desired resonant frequency and an adjustment work of the resonant frequency is facilitated. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure of a capacitor forming a resonance circuit and a resonance frequency adjusting method using the electrode, and more particularly to an RFID (Radio Frequency Identification) which can easily adjust the resonance frequency. TECHNICAL FIELD The present invention relates to the shape of a comb-shaped electrode of a tag for use and a method of adjusting resonance frequency using the comb-shaped electrode.

[0002]

2. Description of the Related Art In recent years, an R which performs data communication between a tag equipped with an IC chip and a reader / writer (or reader).
FID systems are widespread. Since this RFID system uses a tag and an antenna provided in each of the reader / writer to communicate data, it is possible to communicate even if the tag is several cm to several tens of cm away from the reader / writer, and there is no contamination or dirt. Because of its strength against static electricity, it has come to be used in various fields such as factory production control, logistics control, and room access control.

The basic circuit elements of this tag are a resonance circuit consisting of an antenna coil and a capacitor, and an IC chip, which has a desired frequency band (for example, 13.56 MH).
In order to perform data communication in z), it is necessary to accurately adjust the resonance frequency f set by the inductance L of the antenna coil and the capacitance C of the capacitor forming the resonance circuit to the above frequency.

Here, when a label-type tag is used as the tag, an antenna coil is formed on one surface of a flexible sheet-shaped substrate, and an electrode facing the antenna coil is formed on the other surface of the substrate to form the substrate. A capacitor as a dielectric is formed. Then, the inductance is adjusted by the number of turns and the area of the antenna coil, and the electrostatic capacitance is adjusted by the area of the overlapping portion of the opposing electrodes and the distance between the electrodes.

The number of turns and the area of these antenna coils, the area of the overlapping portion of the electrodes facing each other, etc. are basically set at the design stage of the tag, and the antenna coil and the capacitor are formed as designed. For example, a tag having a desired resonance frequency can be manufactured.

[0006]

In these antenna coils and capacitors, the conductive film previously formed on both surfaces of a flexible sheet-like substrate is removed by wet etching, or a conductive paste is printed by screen printing or the like. However, for example, in wet etching, the electrode end portion under the etching mask is gradually etched, so that some error occurs in the pattern dimension. Further, due to various factors such as the dimensional accuracy of screen printing and the thickness of the substrate, the shape and structure of the antenna coil and the capacitor are changed, and a desired resonance circuit cannot be formed.

Therefore, there is a demand for a structure and an adjusting method capable of correcting the deviation of the inductance of the antenna coil and the electrostatic capacity of the capacitor, that is, the deviation of the resonance frequency due to manufacturing factors. −
In Japanese Patent No. 216494, an antenna coil formed on one surface of a substrate has the same shape, and an electrode provided on the other surface is screen-printed with a conductive paste so that the area thereof is gradually reduced. The capacitance is adjusted to obtain the optimum resonance frequency.

Further, in Japanese Unexamined Patent Publication No. 10-84075, one electrode forming a capacitor has a comb structure in which a large number of fingers extend from a base portion, and the fingers of the comb electrodes are sequentially cut to obtain an electrode area of the capacitor. That is, it describes a method of adjusting the resonance frequency by changing the capacitance. This Japanese Patent Laid-Open No. 10-
The adjustment method of Japanese Patent No. 84075 will be described with reference to the drawings.

FIG. 9 is a diagram schematically showing the structure of the capacitor portion of the above-described conventional resonance circuit, in which (a) is a plan view,
(B) is a sectional view taken along the line BB 'of (a). As shown in FIG. 9, the comb-shaped electrode 7 (solid line in (a)) and the stem electrode 9 are provided on one surface with the substrate 6 made of an insulator interposed therebetween.
The counter electrode 8 (broken line of (a)) is formed on the other surface. The comb-shaped electrode 7 is formed by arranging fingers 7b having the same width side by side on the base portion 7a, while the counter electrode 8 is formed on the substrate 6.
The rectangular electrodes are formed so as to overlap the fingers 7b when viewed from the normal direction. Comb-shaped electrode 7 having the above structure
A method of adjusting the resonance frequency using the counter electrode 8 will be described below.

First, the resonance frequency f of the resonance circuit is determined by the inductance L of the coil and the electrostatic capacitance C of the sheet capacitor, and is represented by the following equation.

[0011]

Further, the capacitance C is proportional to the area of the portion where the electrodes (finger 7b and the counter electrode 8 in the figure) which face each other overlap, and is inversely proportional to the distance between the electrodes. Therefore, by cutting the cut portion 7c at the base of the finger 7b, the electrode area of the capacitor can be reduced, the capacitance C can be reduced, and the resonance frequency f can be increased according to Equation 1. Therefore, the capacitance of the capacitor before the finger 7b is cut is made large beforehand, and the finger 7b
The resonance frequency f can be adjusted to a desired value by cutting.

However, in the conventional electrode structure, the fingers 7b of the comb-shaped electrode 7 have a constant width, and the counter electrode 8 has a rectangular shape.
The areas of the electrodes formed by, that is, the electrostatic capacitance C are the same. Therefore, the shift amount of the resonance frequency when the fingers 7b are sequentially cut off is not constant from the relationship of Equation 1,
As the number of fingers 7b to be cut increases, the amount of change in the denominator of Expression 1 increases, so that the amount of shift of the resonance frequency increases.

In such a structure, in order to adjust the resonance frequency f to a target value, the desired resonance frequency f is preset.
Calculate the capacitance C of the capacitor corresponding to
It is necessary to perform a two-step procedure of obtaining the number of fingers to be cut so as to have the capacitance, and the number of fingers 7b to be cut cannot be easily calculated directly from the measured value of the resonance frequency. That is, in the actual work, even if the resonance frequency including the coil and the capacitor is formed on the substrate 6 and then the resonance frequency is measured using the inspection device, the number of cuts of the fingers 7b cannot be directly determined from the measured value. It was necessary to adjust the resonance frequency by repeating the operation of cutting the finger and performing the measurement many times.

The present invention has been made in view of the above problems, and its main object is to make it possible to easily adjust the resonance frequency of a device having a resonance circuit such as an RFID tag. Another object of the present invention is to provide an electrode structure and a method of adjusting a resonance frequency using the electrode.

[0016]

In order to achieve the above object, in the electrode structure of the RFID tag of the present invention, the electrodes of the capacitor forming the resonance circuit of the RFID tag are connected to the base of a plurality of fingers. The comb-shaped electrode and the stem electrode, and the counter electrode formed on the opposite surface across the substrate, and the area of the overlapping portion of each finger of the comb-shaped electrode and the counter electrode is the comb-shaped electrode. The shape of the electrode is set so as to gradually change from one end side to the other end side in the longitudinal direction of the base portion of the electrode.

In the present invention, the area of the overlapping portion has a substantially constant shift amount of the resonance frequency of the resonance circuit when the fingers are separated from the base in order from the one end side of the comb-shaped electrode. Thus, the shape of the electrode is preferably set.

Further, in the present invention, the capacitance ΔCn formed by the n-th finger (n is a positive number) counted from the one end side of the comb-shaped electrode and the counter electrode is a constant C and k. Then, the shape of the electrode can be set so as to satisfy the relationship represented by ΔCn = C × (1-kn).

Further, in the present invention, the counter electrode may have a taper shape that gradually narrows toward the other end side of the comb-shaped electrode or a step shape that gradually narrows. When the width on the one end side of the counter electrode is W1 and the width on the other end side is W2, W1: W2 =
It is preferable that (1-k) :( 1-kn).

Further, according to the present invention, the comb-shaped electrode may be formed such that the width of the fingers gradually decreases toward the other end side. When the width of the fingers on the one end side is Wf1 and the width on the other end side is Wf2, Wf
It is preferable that 1: Wf2 = (1-k) :( 1-kn).

In the present invention, the substrate is P
The electrode may be formed of any one of an ET sheet, a polyethylene sheet, and a polyimide sheet, and the electrode may be formed of an etching pattern of a conductive film using Al or Cu as a material, and a combination of the substrate and the material of the electrode may be used. , PET sheet and Al or Cu, polyethylene sheet and Al, polyimide sheet and Cu.

The resonance frequency adjusting method of the present invention is
A method of adjusting a resonance frequency in an RFID tag having the above electrode structure, which comprises forming the resonance circuit once on the substrate and then measuring the resonance frequency of the resonance circuit, the measured resonance frequency and a desired frequency. And a step of setting the number of the fingers to be cut by dividing the deviation amount by the resonance frequency shift amount of each finger, and cutting the fingers by the set number of fingers from the capacitor. And cutting the predetermined cut portion of the base portion at one place to adjust the resonance frequency to the desired frequency.

As described above, according to the present invention, the counter electrode forming the capacitor of the resonance circuit of the RFID tag is formed in a stepped shape or a tapered shape so that the area of the overlapping portion with the fingers of the comb-shaped electrode changes, or By changing the width of the fingers themselves of the comb-shaped electrode and setting the shape of the counter electrode and the width of the fingers so as to satisfy a predetermined relational expression (ΔCn = C × (1-kn)), The shift amount of the resonance frequency can be made substantially constant. With this, the number of fingers to be cut can be easily calculated, so that the predetermined cut portion of the base is cut at only one place, and the necessary number of fingers can be separated from the capacitor, and the resonance frequency can be easily adjusted. It becomes possible to

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION An electrode structure of an RFID tag according to the present invention is, in a preferred embodiment thereof, a comb-shaped capacitor which constitutes a resonance circuit of an RFID tag for communicating data with a reader / writer. The electrode and the counter electrode formed on the opposite side of the substrate are arranged such that the area of the overlapping portion of each finger of the comb-shaped electrode and the counter electrode is from the tip side of the comb-shaped electrode toward the root side. It is formed so as to be gradually smaller so that the shift amount of the resonance frequency becomes substantially constant when the fingers are sequentially cut.

That is, in order to make the amount of shift of the resonance frequency per finger constant regardless of the position of the finger to be cut, the minute capacitance value ΔC formed between the finger and the counter electrode is set. As a setting example, for example, ΔCn = C × (1-kn) may be set. here,
k is a proportional constant, ΔCn is a minute capacitance formed by the nth finger from the tip of the comb-shaped electrode with the counter electrode, and C is a constant. However, the value of k needs to be set to an optimum value based on the values of C ₀ (capacitance of the tag before finger cut) and C. For example, the width of fingers and the interval between fingers are constant. This can be realized by forming the intersecting counter electrodes in a tapered shape or a staircase shape with a thin root, and by narrowing the width of the fingers toward the root of the comb-shaped electrode.

[0026]

EXAMPLES Examples of the present invention will be described with reference to the drawings in order to describe the above-described embodiments of the present invention in more detail.

[Embodiment 1] First, an electrode structure of an RFID tag according to a first embodiment of the present invention and a resonance frequency adjusting method using the electrode will be described with reference to FIGS. 1 to 6. . FIG. 1 is a diagram schematically showing the overall configuration of an RFID system. In addition, FIG. 2 shows the RFID of this embodiment.
It is a figure which shows an example of the structure of the label label for, and FIG. 3 is an enlarged view of the capacitor part of a resonance circuit. 4 and 5 are diagrams for explaining the effect of this embodiment,
FIG. 6 is a diagram showing another structure of the counter electrode.

As shown in FIG. 1, the RFID system 1
Is a reader / device that communicates data using the antenna 3a.
The reader / writer 3 includes a writer 3 and a tag 2 having various shapes such as a label type, a coin type, and a sheet type. The reader / writer 3 includes a communication circuit unit 3b for converting a transmission / reception signal and a transmission / reception signal for decoding. The arithmetic processing unit 3c is connected. Further, the tag 2 includes a resonance circuit 2a including a coil and a capacitor therein, and when the tag 2 side also generates a signal, an IC 2b for calculating and storing data is connected to the resonance circuit 2a. It is driven by using a built-in power supply or a power supply supplied from the reader / writer 3.

Reader / in this RFID system 1
Since data communication between the writer 3 and the tag 2 is performed at a desired communication frequency (for example, 13.56 MHz), it is necessary to accurately adjust the resonance frequency of the resonance circuit 2a of the tag 2 to the communication frequency. Here, the structure of the tag 2 will be described with reference to FIG. 2A and 2B are views showing an example of the structure of the label-type tag, where FIG. 2A is a plan view and FIG.
3 is a cross-sectional view taken along the line AA ′ of FIG.

As shown in FIG. 2, in general, a label type tag has a substrate 6 and a conductive film pattern formed on both surfaces thereof and an IC 2
b, and the conductive film such as Al or Cu provided on both sides of the substrate 6 made of a flexible insulating sheet is removed by etching, or a conductive paste is applied by screen printing to form the coil 4 or Patterns of the comb-shaped electrode 7 and the counter electrode 8 are formed, but individual differences occur in the pattern shape depending on manufacturing conditions such as the accuracy of etching and screen printing in this pattern formation.

Therefore, in order to adjust the deviation of the resonance frequency of each tag 2 due to the individual difference in the pattern formation, the inductance L of the coil 4 forming the resonance circuit 2a or the capacitance C of the capacitor 5 is formed after the pattern formation. Although it is necessary to adjust the inductance, the inductance L is proportional to the number of turns and the area of the coil, and it is difficult to adjust these after pattern formation. On the other hand, the capacitance C of the capacitor 5 correlates with the area of the overlapping portion of the electrodes (the comb-shaped electrode 7 and the trunk electrode 9 and the counter electrode 8) formed with the insulating layer (substrate 6) sandwiched between them and the distance between the electrodes. However, it is easy to adjust the electrode area.

Therefore, as shown in the conventional example, one electrode has a comb-shaped structure in which a large number of fingers 7b are arranged in parallel on the base portion 7a, and the fingers 5b are cut by the cut portion 7c at the base to form the capacitor 5 The area of the electrode of, that is, the electrostatic capacitance C is reduced, so that the resonance frequency f is secondarily adjusted. However, in the conventional electrode structure, the counter electrode 8 has a rectangular shape and the fingers 7b of the comb-shaped electrode 7 have the same width. Therefore, no matter which finger is cut, the area reduction amount, that is, the capacitance is reduced. Since the amount of change is constant, the amount of shift of the resonance frequency f is not constant due to the relationship of Equation 1, and its adjustment is difficult.

In view of this, the present embodiment proposes an electrode shape in which the amount of change in the resonance frequency itself is substantially constant, rather than making the amount of change in capacitance constant for each finger 7b. The electrode shape designing method described below is based on the novel knowledge obtained by the inventor of the present application empirically,
This is devised in consideration of the deviation amount of the resonance frequency allowed in the RFID system 1 and the adjustment work of the actual resonance frequency. The specific design method will be described in detail below.

FIG. 3 is a diagram schematically showing the structure and positional relationship between the comb-shaped electrode 7 and the counter electrode 8 which form the capacitor 5 of the resonance circuit 2a of the present embodiment. The comb-shaped electrode 7 has a base portion 7a.
N fingers 7b (n is an arbitrary integer) are arranged on one side in parallel with each other at equal intervals, and on the opposite side with the substrate 6 sandwiched therebetween, a tapered counter electrode 8a shown by a dotted line is formed.
Is thicker on the tip side (right side in the figure) and thinner on the root side (left side in the figure). Here, the fingers 7b are arranged at equal intervals and in parallel, but as long as the area of the overlapping portion of each finger 7b and the counter electrode 8 satisfies the relationship described later, it is not limited to the shape shown in the drawing.

First, a relational expression for making the shift amount of the resonance frequency per finger substantially constant is determined. As a result of examining various relational expressions, the inventor of the present application found that the deviation of the resonance frequency in the RFID system 1 It has been found that when the variation amount ΔCn of the capacitance of the capacitor 5 is set to the relational expression of Equation 2 in consideration of the allowable value and the ease of electrode formation, the variation in the shift amount of the resonance frequency is suppressed. Hereinafter, a method of obtaining the proportionality constant k in Expression 2 will be described.

[0036]

When ΔCn is expressed by the equation 2, k is calculated so that the shift amounts Δf of the resonance frequencies at the finger cut of the first finger and the n-th finger are equal. First, Delta] f ₁ in the case of cutting a single plane fingers, when the electrostatic capacity before cutting the C _0, the capacitance after cut C ₀ -C (1-
k), it is expressed by the following equation.

[0038]

Similarly, Δf _n in the case of cutting the n- _th finger is the amount of decrease in the capacity when cutting the 1st to n−1th fingers, and the amount of decrease in the capacity when cutting the 1st to the n- _th fingers in Equation 4. Since the amount becomes the formula 5, it is expressed by the formula 6.

[0040]

Here, if Δf ₁ and Δf _n are equal, k is represented by the following equation using C, C ₀ , and n.

[0042]

That is, when the number of fingers of the comb-shaped electrode is given, by setting the initial capacitance C ₀ and the constant C, k can be obtained by using the equation 7, and this k can be obtained.
By setting Eq. 2 to set the shape of the counter electrode, the shift amount of the resonance frequency can be made substantially constant regardless of the number of fingers to be cut. This allows
It is no longer necessary to perform a two-step operation such as once converting the deviation amount of the resonance frequency into capacitance and then setting the number of fingers to be cut, and it is possible to directly cut the finger from the deviation amount of the resonance frequency. Can be determined, and the adjustment work of the resonance frequency can be significantly facilitated.

The results of concrete calculations are shown below. For example, capacitance C ₀ before cutting = 100 (pF), constant C
= 1 and the number of fingers n = 20 is substituted into Equation 7, k
Can be obtained, and k is a real number and a positive number is given in the parentheses of Expression 2, so that k = 0.0124184. If the shape of the counter electrode 8 is determined so as to satisfy the relationship of ΔCn = 1−kn≈1−n / 80 using this k, the shift amount of the resonance frequency for each finger can be made substantially constant.

In order to confirm the validity of the above calculation, the resonance frequency shift amount was simulated using the solution obtained by the above method and an arbitrarily set value. The results are shown in Table 1.
~ Shown in Table 3 and FIG. Tables 1 to 3 show the shift amounts of the resonance frequency when the nth finger is cut (that is, when the nth finger is further cut from the state where the n-1th finger is cut). Is a value obtained by the method of the present embodiment for the value of k (k = 0.012418).
4), when Table 2 is set to k = 0.01,
Table 3 shows the simulation results when k = 0.015 is set.

From FIG. 4, which summarizes Tables 1 to 3, when k is set appropriately without calculation (marked by Δ or □), the resonance frequency shifts as the number of fingers 7b cut increases. The amount has changed, but when the solution calculated by the above method is used (○ in the figure), the shift amount Δ of the resonance frequency
f was substantially constant, and the validity of the above calculation method could be confirmed.

From the results of Table 1 and FIG. 4, the resonance frequency shift amount cannot be made completely constant even with the value of k set by the method of this embodiment, but the error ((maximum value-minimum The value) / average value) is as small as about 1%, and is a numerical value that does not pose any problem in consideration of the usage form of the RFID system, and the resonance frequency can be adjusted with sufficient accuracy by the method of this embodiment.

[0048]

[Table 1] In the case of k = 0.0124184

[0049]

[Table 2] When k = 0.01

[0050]

[Table 3] When k = 0.015

Next, in order to judge the validity of the relational expression of the expression 2, the relationship in which the variation amount ΔCn of the capacitance for each finger is set to a constant value and the variation amount of the capacitance gradually decreases. Similar simulations were performed for the case of using the formula. The results are shown in Tables 4 to 6 and FIG.

Specifically, the fingers 7b of the comb-shaped electrode 7
In the label tag having the electrostatic capacitance C ₀ = 100 pF before cutting, the constant C is 1, the number n of fingers is 20, and the n-th finger from the tip of the comb-shaped electrode 7 forms the counter electrode 8 with a small capacitance. Is ΔCn = 1-n / 80 (p
The comb-shaped electrode 7 was designed so as to be F). That is, the width of the fingers and the spacing between the fingers are constant,
The width (W1) of the tip of the opposing electrodes 8 and the width (W
The ratio of 2) is W1: W2 = 1-1 / 80: 1-20 / 80.
A label label for RFID having a tapered shape of = 79: 60 was produced. Table 4 shows the shift amount of the resonance frequency when the fingers 7b are cut in order from the tip of the comb-shaped electrode 7.

As a comparative example, all fingers 7
The counter electrode 8 is formed so that the minute capacitance ΔC formed by the finger 7b and the counter electrode 8 with respect to b becomes ΔC = 1 (pF).
(Table 5), the minute capacitance ΔC _n formed by the n-th finger 7b from the tip of the comb-shaped electrode 7 and the counter electrode 8 is ΔC _n = 0.99 × C _n-1 (pF). The same calculation was applied to the case where the comb-shaped electrode was designed so that (where C ₁ = 1) (Table 6).

[0054]

[Table 4] When ΔCn = 1-n / 80

[0055]

[Table 5] When ΔCn = 1

[0056]

[Table 6] In the case of ΔCn = 0.99 × C _n-1 (pF) (however, C ₁ = 1)

The results of Tables 4 to 6 are shown in a graph in FIG. From FIG. 5, when ΔCn has a constant value (marked by □ in the figure), the amount of change in capacitance is the same as the number of fingers 7b to be cut increases.
Since the denominator of is gradually decreased, the shift amount of the resonance frequency is gradually increased, and is increased by about 37% in the first and twentieth lines. Further, when the change amount of the electrostatic capacitance is gradually reduced (marked by Δ in the figure), the shift amount of the resonance frequency is alleviated, but the difference between the first and twentieth lines is still 10%.
% Has increased.

On the other hand, in the case of designing with the relational expression of this embodiment (marked with a circle in the figure), the shift amount of the resonance frequency is substantially constant, and the minimum value (right end) and the maximum value (10th line) are set. The deviation is a little over 1%, and it can be seen that the relational expression of the present embodiment is effective for making the shift amount of the resonance frequency constant. As a result, when the resonance frequency is deviated in the inspection after the resonance circuit is formed, the deviation amount of the resonance frequency is the correction amount of the resonance frequency per finger (about 0.065 HMz in the case of FIG. 4). By cutting the divided number of fingers 7b, the desired resonance frequency can be adjusted easily and reliably. Further, in the conventional method of adjusting the resonance frequency, since the amount of change in the resonance frequency per finger is not constant, the cut portion 7c at the base of the finger 7b is
It was necessary to cut (see Fig. 9) in order and adjust.
In the method of this embodiment, since the amount of change in the resonance frequency per finger is constant, the finger 7 to be cut is
The number of b can be easily calculated, and as a result, the cut portion 7c of the base portion 7a is not the root of the finger 7b.
By directly cutting (see FIG. 3, the case of cutting two fingers in FIG. 3) can be adjusted to a desired resonance frequency with only one cutting operation, and work efficiency can be improved. You can

In this embodiment, the shape of the counter electrode 8 is
Although the taper shape is gradually thickened toward the tip as shown in FIG. 3, the shape may be gradually increased toward the tip as shown in FIG. 6A. With such a stepped shape, even if the comb-shaped electrode 7 and the counter electrode 8 are misaligned (particularly in the direction orthogonal to the fingers 7b), the overlapping portion of each finger is The change in area can be suppressed. The shape to be used can be appropriately selected in consideration of the accuracy of the resonance frequency required for the tag 2, the positional accuracy at the time of electrode formation, the ease of manufacturing, and the like. Further, the shape of the counter electrode is not limited to the tapered shape or the stepped shape described above, and may be any shape as long as the capacitance change amount ΔCn for each finger is represented by the relational expression of Expression 2. The shape is also shown in Figure 6.
As shown in (b), the finger 7b may be arranged on both sides of the base 7a.

In order to form an electrode designed by using the method of the present embodiment on a tag, for example, a PET sheet is used as an insulating film to be the substrate 6, and Al foils formed on both sides thereof are etched. The coil 4 (upper surface coil 4a and lower surface coil 4b) and the capacitor 5 (comb-shaped electrode 7, stem electrode 9 and counter electrode 8) are formed by removing the upper surface coil 4a and the lower surface coil 4b by through holes. Can be electrically conducted to produce a sheet coil, and then the IC chip 2b is mounted to produce an inlet. Then, the resonance frequency is measured using an inspection device, the resonance frequency is adjusted by trimming a desired number of fingers 7b by the method described above, and label processing is performed on both sides of the inlet to complete the label-type tag 2.

The insulating film is not limited to the PET sheet, but a polyethylene sheet or a polyimide sheet can be used, and the conductive film is Cu instead of Al.
Can be used. Among them, PET sheet and Al
It has been confirmed that a combination with Cu, a combination of a polyethylene sheet and Al, or a combination of a polyimide sheet and Cu foil is preferable in use. Furthermore,
For the purpose of use, it is preferable that the IC mounted after forming the resonance circuit is flip-chip mounted.

[Embodiment 2] Next, a comb type electrode structure of an RFID tag according to a second embodiment of the present invention and a resonance frequency adjusting method using the electrode will be described with reference to FIG. . FIG. 7 is a diagram showing a comb-shaped electrode structure of a capacitor portion which constitutes a resonance circuit of the RFID label tag of the second embodiment.

In the first embodiment described above, the method of making the shape of the counter electrode 8 forming the capacitor of the resonance circuit tapered or stepwise has been described. Conversely, the shape of the finger 7b of the comb electrode 7 is described. Can be adjusted to make the shift amount of the resonance frequency substantially constant. Therefore, in the present embodiment, the width of each finger is set to gradually increase toward the tip end so that the electrostatic capacitance, that is, the area of the electrode changes based on the equation 2.

Specifically, in the label tag having the capacitance C ₀ = 100 pF before the finger 7b is cut,
The minute capacitance ΔCn formed by the n-th finger 7b from the tip of the comb-shaped electrode 7 with the counter electrode 8 is ΔCn = 1−n / 80.
The comb-shaped electrode 7 was designed to have (pF). That is, the counter electrode 8 intersecting the fingers has a rectangular shape, and the width of the n-th finger from the tip of the comb-shaped electrode 7 is Wfn = W.
RFI having a comb-shaped electrode 7 of f ₁ × (1-n / 80)
A label tag for D was produced. However, the number of fingers is 2
There are zero, and ΔC ₁ = 1-1 / 80 (pF). The shift amount of the resonance frequency when the fingers 7b were sequentially cut from the tip of the comb-shaped electrode 7 was obtained by simulation.

Even in the above structure, the amount of change in capacitance for each finger is the same as in Table 4 and FIG.
By setting the width of the finger 7b on the basis of the relationship, the shift amount of the resonance frequency can be kept substantially constant as in the first embodiment, and when the resonance frequency shifts in actual manufacturing, Adjustment can be easily performed.

Although the shape of the counter electrode 8 was set in the first embodiment and the shape of the comb-shaped electrode 7 was set in the second embodiment, as shown in FIG. You can also do it. In this case, each electrode may be formed so that the product of the width of the counter electrode 8 and the width of the finger 7b of the comb-shaped electrode 7 satisfies the relationship of Expression 2. Further, in each of the above embodiments, the structure of the resonance circuit of the tag used in the RFID system is described, but the present invention is not limited to the above embodiments, and any circuit that requires adjustment of the capacitance of the capacitor And can be applied to the device.

[0067]

As described above, the RFID of the present invention
The electrode structure of the tag for use and the resonance frequency adjusting method using the electrode have the following effects.

The first effect of the present invention is that the shift amount of the resonance frequency per finger can be made substantially constant regardless of the position of the finger to be cut.

The reason for this is that the amount of change in capacitance for each finger is set by tapering or stepping the counter electrode or setting the width of each finger of the comb-shaped electrode based on equation (2). This is because it is being adjusted.

The second effect of the present invention is that the number of cuts necessary for adjusting the resonance frequency to a target value can be calculated in the capacitance, and as a result, the number of cuts necessary for adjusting the resonance frequency of the base is not the root of the finger. By directly cutting the cut part,
This means that the desired resonance frequency can be adjusted by only one cutting operation, and the work efficiency can be improved.

The reason for this is that, conventionally, since the electrodes are formed so that the areas of the fingers are the same, that is, the amount of change in the capacitance is the same, the capacitor is temporarily changed from the difference between the target resonance frequency and the measured frequency. It was necessary to calculate the displacement of the capacitance of, and to obtain the number of fingers to be cut from the result, but in the present invention, the shape of the counter electrode or the shape of the counter electrode so that the shift amount of the resonance frequency for each finger is substantially equal. Since the width of the fingers of the comb-shaped electrode is set, the number of fingers to be cut can be directly obtained from the shift amount of the resonance frequency.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an overall configuration of an RFID system.

2A and 2B are diagrams showing the configuration of the label-type tag according to the first embodiment of the present invention, in which FIG. 2A is a plan view and FIG. 2B is a sectional view.

FIG. 3 is a plan view showing a configuration of a comb electrode according to the first embodiment of the present invention.

FIG. 4 is a diagram for explaining the effect of the first embodiment of the present invention, showing a change in the resonance frequency shift amount per finger when the value of k in Expression 2 is changed.

FIG. 5 is a diagram for explaining the effect of the first embodiment of the present invention, showing a change in the resonance frequency shift amount per finger when the relational expression of ΔCn is changed.

FIG. 6 is a plan view showing another configuration of the counter electrode of the capacitor according to the first embodiment of the present invention.

FIG. 7 is a plan view showing a configuration of comb electrodes of a capacitor according to a second embodiment of the present invention.

FIG. 8 is a plan view showing another configuration of the comb electrodes of the capacitor according to the second embodiment of the present invention.

FIG. 9 is a plan view showing a comb-shaped electrode structure of a conventional capacitor.

[Explanation of symbols]

1 RFID system 2 tags 2a Resonant circuit 2b IC 3 Reader / Writer 3a antenna 3b Communication circuit section 3c arithmetic processing unit 4 coils 4a Top coil 4b Bottom coil 5 capacitors 6 substrate 7 Comb type electrode 7a base 7b finger 7c cut part 8 Counter electrode 8a Counter electrode (taper shape) 8b Counter electrode (step shape) 8c Counter electrode (rectangular shape) 9 Executive electrodes

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koichi Ishiyama             1-12-14 Koishikawa, Bunkyo-ku, Tokyo Mitsubishi Mate             Real Co., Ltd. RFID Business Center F term (reference) 5B035 BA01 BA03 BB09 CA11 CA23                 5B058 CA15

Claims (11)

[Claims] 1. An electrode of a capacitor constituting a resonance circuit of an RFID tag, a comb-shaped electrode and a trunk electrode to which a plurality of fingers are connected to a base, and a counter electrode formed on the opposite surface with a substrate sandwiched therebetween. So that the area of the overlapping portion of each of the fingers of the comb-shaped electrode and the counter electrode gradually changes from one end side to the other end side in the longitudinal direction of the base portion of the comb-shaped electrode. The electrode structure of the RFID tag is characterized in that the shape of the electrode is set. 2. The area of the overlapping portion is such that when the fingers are sequentially separated from the base portion from the one end side of the comb-shaped electrode, the shift amount of the resonance frequency of the resonance circuit becomes substantially constant. The electrode structure of the RFID tag according to claim 1, wherein the shape of the electrode is set. 3. N counted from the one end side of the comb-shaped electrode
The capacitance ΔCn formed by the (n is a positive number) finger and the counter electrode satisfies the relation represented by ΔCn = C × (1-kn) when C and k are constants. The electrode structure of the RFID tag according to claim 1 or 2, wherein the shape of the electrode is set. 4. The counter electrode according to claim 1, wherein the counter electrode has a tapered shape that gradually narrows toward the other end side of the comb-shaped electrode or a step shape that gradually narrows toward the other end. The electrode structure of the RFID tag according to 1 above. 5. When there are n fingers having constant widths and intervals and the width of the one end of the counter electrode is W1 and the width of the other end is W2, W1: W2 = (1- k):
5. R according to claim 4, which is (1-kn).
Electrode structure of FID tag. 6. The comb-shaped electrode is formed so that the width of each of the fingers gradually decreases toward the other end side. Electrode structure of RFID tag. 7. When the width of the finger on the one end side of the comb-shaped electrode having n fingers is Wf1 and the width on the other end side is Wf2, Wf1: Wf2 = (1-
k): (1-kn), The electrode structure of the RFID tag according to claim 6, wherein: 8. The method according to claim 1, wherein the substrate is made of any one of a PET sheet, a polyethylene sheet and a polyimide sheet, and the electrode is made of an etching pattern of a conductive film made of Al or Cu. 7. The electrode structure of the RFID tag described in any one of 7. 9. The RFID according to claim 8, wherein the combination of the material of the substrate and the electrode is any one of PET sheet and Al or Cu, polyethylene sheet and Al, and polyimide sheet and Cu. Electrode structure for tags. 10. The electrode structure for an RFID tag according to claim 1, wherein an IC is flip-chip mounted on the substrate. 11. A method of adjusting a resonance frequency in an RFID tag having an electrode structure according to claim 1, wherein the resonance circuit is formed on the substrate and then the resonance circuit is formed. A step of measuring the resonance frequency, obtaining a deviation amount between the measured resonance frequency and a desired frequency, dividing the deviation amount by the resonance frequency shift amount of each finger, and setting the number of fingers to be cut. And adjusting the resonance frequency to the desired frequency by cutting one predetermined cut portion of the base portion such that the finger can be cut by the set number of fingers from the capacitor. A method for adjusting the resonance frequency of a characteristic RFID tag.