MULTILAYER INDUCTOR

Abstract

The invention provides an inductor (1) comprising at least one first conductive layer (4a) comprising at least one first turn (5) of conductive material and at least one second conductive layer (4b) comprising at least one second turn (5) of conductive material, at least one conductive bridge (7) connecting the first and second turns (5), a layer of insulating material (6a) being interposed at least partially between the first and second turns (5), the first and second turns (5) being at least partially superimposed in the stacking direction (Z) of said layers (4a, 4b, 6a), characterized in that, in the area of superimposition of said turns, the width (I1) of the section of the first turn (5, 4a) is greater than the width (I2) of the section of the second turn (5, 4b).

Claims

1. An inductor (1) comprising at least one first conductive layer (4a) comprising at least one first turn (5) of conductive material and at least one second conductive layer (4b) comprising at least one second turn (5) of conductive material, at least one conductive bridge (7) connecting the first and second turns (5), a layer of insulating material (6a) being interposed at least partially between the first and second turns (5), the first and second turns (5) being superimposed at least partly in the stacking direction (Z) of said layers (4a, 4b, 6a), characterized in that, in the area of superimposition of said turns, the width (I1) of the section of the first turn (5), 4a) is greater than the width (I2) of the section of the second turn (5, 4b), one of the conductive layers (4a, 4b) being formed on a substrate (3) made of paper, synthetic paper, polyethylene terephthalate, polyethylene naphthalate or polyimide.

2. Inductor (1) according to claim 1, characterised in that the difference in width between the corresponding sections of two turns (5) of two consecutive layers (4a, 4b) is between 50 and 500 m, preferably between 100 and 300 m.

3. Inductor (1) according to claim 1 or 2, characterized in that each conductive layer (4a, 4b) is made with a conductive ink.

4. Inductor (1) according to claim 3, characterized in that the conductive ink is selected from the following inks: a carbon-based ink, e.g. based on graphite or graphene, carbon nanotubes (CNT), an ink based on a conductive polymeric material, for example polyaniline, poly(3,4-ethylenedioxythiophene), more commonly known as PEDOT, polythiophenes or polypyrrole, an ink based on metal, for example metal microparticles or nanoparticles, for example based on silver, copper, nickel, platinum, tin or gold, in particular an ink based on silver in the form of microparticles or nanoparticles.

5. Inductor (1) according to claim 3 or 4, characterized in that the conductive ink is deposited by a printing process of the screen, flexographic, rotogravure, offset or inkjet type.

6. Inductor (1) according to one of claims 1 to 5, characterized in that the insulating layer (6a) is made with a UV dielectric ink.

7. Radio identification transponder (2) characterized in that it comprises an inductor (1) according to one of claims 1 to 6 forming an antenna (1), and a chip or printed circuit (9) connected to the antenna (1).

8. Method for manufacturing an inductor (1) according to one of claims 1 to 6, characterised in that it includes the following steps: forming at least a first conductive layer (4a) comprising at least a first turn (5) of conductive material, forming a layer of insulating material (6a) on at least part of the first conductive layer (4a), forming at least one second conductive layer (4b) comprising at least one second turn (5) of conductive material, on the layer of insulating material (6a) and/or on the first layer (4a), the first and second turns (5) being superimposed at least partly in the stacking direction (Z) of said layers, the turns (5) being dimensioned and positioned in such a way that, in the region of superimposition of said turns (5), the width of the section (I1) of the first turn (5, 4a) is greater than the width (I2) of the section of the second turn (5, 4b), and in such a way that the turns (5) are connected by at least one conductive bridge (7).

9. Method according to claim 8, characterized in that the steps of forming the conductive layers (4a, 4b) are carried out by printing with a conductive ink.

10. Method according to claim 9, characterized in that it comprises at least one step of annealing at least one of the conductive layers (4a, 4b).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0109] FIG. 1 is an exploded perspective view, illustrating an antenna in a first embodiment of the invention, intended to equip a radio-identification transponder, the antenna having two conductive layers;

[0110] FIG. 2 is a top view of a part of the conductive layers of the antenna of FIG. 1,

[0111] FIG. 3 is a sectional view of a part of a transponder having an antenna of FIG. 1,

[0112] FIG. 4 is a diagram representing the characteristic curve of a transponder equipped with the antenna of FIG. 1, representing the evolution of impedance as a function of frequency;

[0113] FIG. 5 is an exploded perspective view, illustrating an antenna in a second embodiment of the invention, intended to equip a radio-identification transponder, the antenna having four conductive layers;

[0114] FIG. 6 is a sectional view of a part of a transponder having an antenna of FIG. 5.

DETAILED DESCRIPTION

[0115] An antenna 1 intended to equip a transponder 2 with radio identification according to a first embodiment of the invention is illustrated in FIGS. 1 and 2, transponder 2 being illustrated in FIG. 3. Antenna 1 comprises a substrate 3 (FIG. 3) on which a first conductive layer 4a printed with a conductive ink is deposited. The first layer 4a is generally planar, said plane being defined by two orthogonal X and Y axes. The first conductive layer 4a has generally rectangular turns 5, here four turns 5. Each turn 5 thus comprises straight portions 5a extending along the X-axis and straight portions 5b extending along the Y-axis. Each turn 5 may also have straight zones 5c oblique to the X and Y axes.

[0116] A layer 6a of dielectric or insulating material is imprinted on most of the first conductive layer 4a. Some areas of the first conductive layer 4a are not covered with dielectric material 6a. A second conductive layer 4b is applied by printing with a conductive ink. The second conductive layer 4b has generally rectangular turns 5, here five turns 5. As afore mentioned, each turn 5 thus comprises straight portions 5a extending along the X-axis and straight portions 5b extending along the Y-axis. Each turn 5 may also have straight zones 5c oblique to the X and Y axes.

[0117] The turns 5 of the second conductive layer 4b are superimposed on the turns 5 of the first conductive layer 4a. The stacking axis of layers 4a, 4b is defined by Z. The X, Y and Z axes are orthogonal. In other words, turns 5 of the first conductive layer 4a are located opposite, along the axis Z, to turns 5 of the second conductive layer 4b.

[0118] At least one turn 5 of the second conductive layer 4b is located in an area free of insulating material so that, in this area, the turn 5 of the second conductive layer 4b is in contact with the corresponding turn 5 of the first conductive layer 4a so as to form a conductive bridge 7. The two layers of turns 5 thus form a continuous coil with a total number of turns 5 corresponding to the sum of the turns 5 of the first conductive layer 4a and the turns 5 of the second conductive layer 4b. Conductive layers 4a, 4b are preferably only connected in series, not in parallel. The coil is open in that it has two free ends 8 which are electrically connected to a chip or integrated circuit 9 of transponder 2. The chip 9 can be located in an area free of a layer of dielectric material 6a and free of turns 5 of the second conductive layer 4b, so as to be housed or embedded, at least partially, in a cavity of the insulating layer 6a and of the second conductive layer 4b.

[0119] Chip 9 is glued and electrically connected to the corresponding ends 8 of the coil, e.g. by means of a conductive adhesive 10.

[0120] In this example, turns 5 of the first conductive layer 4a have a section width I1 (also called line width) of the order of 500 m, the interval i1 between turns 5 (also called line spacing) being of the order of 300 m. The turns 5 of the second conductive layer 4b have a section width I2 of the order of 300 m, the interval i2 between the turns 5 being of the order of 500 m. It is to be noted that I1+i1=I2+i2, so as to respect the superposition of turns 5 of the different conductive layers 4a, 4b, along the axis Z of stacking of layers 4a, 4b, 6a.

[0121] The turns 5 of the first conductive layer 4a are thus wider than the turns 5 of the second conductive layer 4b, the difference in width being here in the order of 200 m. This ensures that the turns 5 of the second conductive layer 4b are aligned with the turns 5 of the first conductive layer 4a, with a positioning tolerance to a desired nominal position of +/100 m. Such a tolerance can be achieved with the majority of the usual printing processes used in the printing industry, such as screen printing, flexography, rotogravure, offset or inkjet.

[0122] The turns 5 of the first conductive layer 4a and the second conductive layer 4b have a thickness e of between 1 and 40, preferably between 2 and 20.

[0123] The dielectric material layer 6a has a thickness ranging from 5 to 50 m, preferably from 10 to 30 m.

[0124] The transponder has a width I of about 10 mm and a length L of about 20 mm, i.e. an area of about 200 mm.sup.2.

[0125] FIG. 4 is a diagram representing the characteristic curve of a transponder equipped of FIGS. 1 and 2, representing the evolution of impedance Z as a function of frequency f. It can be seen that the transponder is perfectly tuned since the resonant frequency f0 is of the order of 13.56 MHz, even with a slight shift of tracks 5 of the second conductive layer 4b with respect to tracks 5 of the first conductive layer 4a. In this case, the offset can be of the order of +/100 m both along the X and Y axes, without affecting the resonant frequency f0.

[0126] For a transponder having only one conductive layer, with a width I of the order of 10 mm and a length L of the order of 20 mm, and for a line width I1 of 300 m and an interval i1 between the turns of 300 m, and a number of turns of seven, the resonant frequency f0 obtained after transfer from a 50 pF chip is of the order of 26 MHz, i.e. much higher than the desired frequency of 13.56 MHz.

[0127] By comparison, in order to obtain a resonant frequency of 13.56 MHz, after carrying a 50 pF NFC chip, with the same performance, in the case of an antenna comprising a single layer of turns with a section width of the turns and identical intervals between the turns, the transponder should have a width I of the order of 15 mm and a length L of the order of 30 mm, i.e. an area of the order of 450 mm.sup.2.

[0128] It should also be noted that, in the case of an offset of conductive layers with sections of the same width, there is also an increase in the actual resonant frequency, compared to the desired resonant frequency of 13.56 MHz.

[0129] An antenna 1 intended to equip a transponder with radio identification according to a second embodiment of the invention is illustrated in FIG. 5, transponder 2 being illustrated in FIG. 6. Antenna 1 comprises a substrate 3 on which a first conductive layer 4a printed with a conductive ink is deposited. The first conductive layer 4a is generally planar, said plane being defined by two orthogonal X and Y axes. The first conductive layer 4a has generally rectangular turns 5, here four turns 5. Each turn 5 thus comprises straight portions 5a extending along the X-axis and straight portions 5b extending along the Y-axis. Each turn may also have straight zones 5c oblique to the X and Y axes.

[0130] A first layer of dielectric or insulating material 6a is imprinted on most of the first conductive layer 4a. Some areas of the first conductive layer 4a are not covered with dielectric material 6a. A second conductive layer 4b is applied by printing with a conductive ink. The second conductive layer 4b has generally rectangular turns 5, here four turns. As afore mentioned, each turn 5 thus comprises straight portions 5a extending along the X-axis and straight portions 5b extending along the Y-axis. Each turn 5 may also have straight zones 5c oblique to the X and Y axes.

[0131] At least one turn 5 of the second conductive layer 4b is located in an area free of insulating material 6a so that, in this area, the turn 5 of the second conductive layer 4b is in contact with the corresponding turn 5 of the first conductive layer 4a so as to form a conductive bridge 7.

[0132] A second layer of dielectric or insulating material 6b is imprinted on most of the second conductive layer 4b. Some areas of the second conductive layer 4b are not covered with dielectric material 6b. A third conductive layer 4c is applied by printing with a conductive ink. The third conductive layer 4c has generally rectangular turns 5, here four turns. As afore mentioned, each turn 5 thus comprises straight portions 5a extending along the X-axis and straight portions 5b extending along the Y-axis. Each turn 5 may also have straight zones 5c oblique to the X and Y axes.

[0133] As above mentioned, at least one turn 5 of the third conductive layer 4c is located in an area free of insulating material 6b so that, in this area, the turn 5 of the third conductive layer 4c is in contact with the corresponding turn 5 of the second conductive layer 4b so as to form a conductive bridge 7.

[0134] A third layer of dielectric or insulating material 6c is imprinted on most of the third conductive layer 4c. Some areas of the third conductive layer 4c are not covered with dielectric material 6c. A fourth conductive layer 4d is applied by printing with a conductive ink. The fourth conductive layer 4d has generally rectangular turns 5, here four turns 5. As afore mentioned, each turn 5 thus comprises straight portions 5a extending along the X-axis and straight portions 5b extending along the Y-axis. Each turn 5 may also have straight zones 5c oblique to the X and Y axes.

[0135] As above mentioned, at least one turn 5 of the fourth conductive layer 4d is located in an area free of insulating material 6c so that, in this area, the turn 5 of the fourth conductive layer 4c is in contact with the corresponding turn 5 of the third conductive layer 4d so as to form a conductive bridge 7. A conductive bridge also connects the first conductive layer 4a and the fourth conductive layer 4d.

[0136] Turns 5 of the different conductive layers 4a, 4b, 4c, 4d are superimposed. The stacking axis of layers 4a, 4b, 4c, 4d, 6a, 6b, 6c is defined by Z. The X, Y and Z axes are orthogonal. In other words, the turns 5 of the different conductive layers 4a, 4b, 4c, 4d are located opposite each other along the axis Z, at least partially.

[0137] The stack of conductive layers is located on only one side of the substrate, which avoids the need to create a via between the two sides, allows the stacking of as many layers as desired or allows thinner insulating layers.

[0138] The four layers 4a, 4b, 4c, 4d of turns 5 thus form a continuous coil having a total number of turns 5 corresponding to the sum of the turns 5 of the first conductive layer 4a, the turns 5 of the second conductive layer 4b, the turns 5 of the third conductive layer 4c and the turns 5 of the fourth conductive layer 4d. The coil is open in that it has two free ends 8 which are electrically connected to a chip or integrated circuit 9 of transponder 2. Chip 9 is glued and electrically connected to the corresponding ends 8 of the coil, e.g. by means of a conductive adhesive 10.

[0139] In this example, the turns 5 of the first conductive layer 4a have a section width I1 of the order of 900 m, the interval i1 between the turns 5 being of the order of 300 m. The turns 5 of the second conductive layer 4b have a section width I2 of the order of 700 m, the interval i2 between the turns 5 being of the order of 500 m. The turns of the third conductive layer 4c have a section width I3 of the order of 500 m, the interval i3 between the turns 5 being of the order of 700 m. The turns 5 of the fourth conductive layer 4d have a section width I4 of the order of 300 m, the interval i3 between the turns 5 being of the order of 900 m. It is to be noted that I1+i1=I2+i2=I3+i3=I4+i4, so as to respect the superposition of turns 5 of the different conductive layers 4a, 4b, 4c, 4d, along the axis Z of stacking of layers.

[0140] The turns 5 of the first conductive layer 4a are thus wider than the turns 5 of the second conductive layer 4b. The turns 5 of the second conductive layer 4b are thus wider than the turns 5 of the third conductive layer 4c. Finally, the turns 5 of the third conductive layer 4c are wider than the turns 5 of the fourth conductive layer 4d. The difference in section width of turns 5 between two adjacent conductive layers is of the order of 200 m. As before, this ensures that the turns 5 of the individual conductor layers 4a, 4b, 4c, 4d are aligned with each other, despite positioning tolerances of +/100 m between the individual conductor layers 4a, 4b, 4c, 4d.

[0141] The turns 5 of the first conductive layer 4a, of the second conductive layer 4b, of the third conductive layer 4c and of the fourth conductive layer 4d have a thickness e of between 1 and 40, preferably between 2 and 20.

[0142] The dielectric material layers 6a, 6b, 6c have a thickness e ranging from 5 to 50 m, preferably from 10 to 30 m.

[0143] The transponder has a width I of about 8 mm and a length L of about 16 mm, i.e. an area of about 128 mm.sup.2.

[0144] Of course, the shape of the turns of each conductive layer may be different from the one presented above. For example, the turns may have a rounded shape or any polygonal shape.