Microcircuit device including means for amplifying the gain of an antenna

The electronic device (10) comprising a microcircuit (18) module (20), a near-field communication antenna (36) electrically connected to the microcircuit (18) of the module (20), delimiting an antenna surface (S), and a body (12) incorporating the module (20). More precisely, the antenna (36) is arranged within the module (20) and the body (12) incorporates means (40) of amplifying the gain of the antenna (36) comprising an electrically conductive element (42) electrically isolated from the microcircuit (18) and the antenna (36), of an annular general shape arranged around an area (R) of the body (12) forming a volume generated by the projection of the antenna surface (S) along a direction (Z) substantially orthogonal to the surface (S).

RELATED APPLICATIONS

This application claims the priority of French application no. 10/55886 filed Jul. 20, 2010, the entire content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the technical field of portable electronic devices of the contactless type comprising a near-field communication antenna connected to a microcircuit, allowing contactless communication to be established with an external device.

The invention applies more particularly but not exclusively to chip cards equipped with an antenna, such as the so-called contactless cards allowing contactless communication to be established at a predefined operating frequency, for example 13.56 MHz defined by the ISO 14443 standard, or the so-called hybrid or dual cards allowing both the establishment of contactless communication and communication with contact through an external contact interface capable of making contact with a matching reader.

The invention also applies to any type of portable or pocket-sized electronic device incorporating such an antenna, such as a USB key, an RFID (Radio Frequency IDentification) tag, a passport, etc.

BACKGROUND OF THE INVENTION

The near-field communication antenna is generally made up of an electrically conducting wire wound in a plurality of electrically conductive coils, incorporated into the periphery of the card body in order to optimize the dimensions of the antenna and thus the range of the electronic device.

An electronic device such as a dual type chip card comprising an antenna connected to a microcircuit is already known in the state of the art, particularly from document WO 2008/129526. The card comprises a body provided with a cavity for receiving a module bearing the microcircuit. The body also incorporates the antenna which is connected to the microcircuit through two metal lands carried on the substrate.

Such a connection has the disadvantage of being relatively complex to make, particularly due to the fact of the presence of the junction between the antenna and the microcircuit. The manufacture of this junction requires the use of specific equipment which is relatively costly.

In addition, the junction obtained is more or less reliable, particularly because it can be weakened during bending or torsion of the card body which can lead to bad contacts and short-circuits between the internal circuits of the microcircuit and the antenna.

SUMMARY OF THE INVENTION

One object of the invention is to provide a contactless card comprising a near-field communication antenna allowing a reliable connection of the antenna and the microcircuit while being simple to make.

To this end, one aspect of the invention is directed to an electronic device comprising a microcircuit module, a near-field communication antenna electrically connected to the module's microcircuit delimiting an antenna surface, and a body incorporating the module. The antenna is arranged on a substrate of the module and the body incorporates means of amplifying the gain of the antenna comprising an electrically conductive element, electrically isolated from the microcircuit and from the antenna, of generally annular shape, arranged around an area of the body constituting a volume generated by the projection of the antenna surface along a direction substantially orthogonal to the surface.

The arrangement of the antenna within the module makes it possible to facilitate the manufacture of the junction between the microcircuit and the antenna. Such an arrangement of the antenna also makes it possible to dispense with the conventional drawbacks connected with positioning of this antenna within the body of the device. Thanks to the invention, various printing, embossing and magnetic striping operations are independent of the position of the antenna in the device, which has many advantages, particularly in the case of special applications such as in the field of chip cards.

To maintain satisfactory performance of the antenna despite a reduction in its dimensions due to incorporation in the module, one embodiment of the invention includes an antenna gain amplification element to the body. The addition of such an electrically conductive element significantly increases the performance of the antenna by channeling the lines of the magnetic field emitted by an external terminal into the antenna surface.

Indeed, the element constitutes an antenna gain amplifier improving the level of the current induced in the latter as well as the level of back-modulation of the antenna when the device is placed in the magnetic field of the external terminal.

Further, the positioning within the body of this element does not have the aforementioned drawbacks relating to the arrangement of the antenna within the body.

In conformity with an embodiment of the invention, the element extends around the antenna outside of an area defined by the projection of the antenna along a direction substantially orthogonal to the antenna surface. Thus, the antenna and the ring must not extend facing one another so as not to mask the magnetic field flux through the antenna surface.

In other words, the element extends outside the outer perimeter of the antenna in a plane parallel to that containing the antenna or part of the antenna, or possibly in the same plane. However, when the element extends within the same plane as the antenna or part of the antenna, a minimum spacing is provided between the element and the antenna to ensure electrical isolation.

In a preferred embodiment, the element delimits an internal peripheral edge surrounding the area at a minimum distance, for example less than or equal to five millimeters. It has in fact been discovered that the smaller the distance separating the element from the antenna, the better the performance. Thus, the distance can be substantially nil in the case where the antenna and the element are in separate planes.

Preferably, the distance is minimized to within the limit of a positioning tolerance of the antenna within the module.

In a preferred embodiment, the antenna consisting of a winding of electrically conductive coils, the positioning tolerance of the antenna within the module corresponds substantially to one interval between coils. Generally, the space between two coils is limited by the accuracy of manufacture of the antenna, for example the accuracy of the etching that allows the two coils to be insulated from each other.

Preferably, the module including a substrate bearing the microcircuit and the antenna, the positioning tolerance of the antenna within the module corresponds substantially to the positioning tolerance of the antenna on the substrate.

A device according to an embodiment of the invention may also include one or more of the following features:the antenna extending along the periphery of at least one of the faces of the substrate or of the two opposite faces of the module substrate;the element extending in a plane containing the antenna or at least part of the antenna;the body being provided with a cavity for receiving the module, the element delimiting an inner peripheral edge surrounding the module which is at least partly flush with the surface of a peripheral wall of the cavity;the cavity including a deep central area for receiving the microcircuit and a peripheral area, raised with respect to the central area, supporting a module substrate, the element surrounds the peripheral area;the element forming a ring that is closed, or broken at least once;the device is a chip card of the contactless type or of the dual type;the element is made of a metallic material with magnetic permeability less than or equal to one;the metallic material is an electrically conductive ink.

Another aspect of the invention is directed to a manufacturing method for a device according to the invention, comprising a body forming step and a step for forming the cavity within the body. During the body forming step, an electrically conductive layer is arranged in the body such that, during the cavity forming step, the cavity passes through the electrically conductive layer to form the ring.

A method according to an embodiment of the invention can also comprise one or another of the features wherein:the layer extends transversely over the entire surface of the body;the body consisting of a multilayer structure, the electrically conductive layer is interleaved between two layers of the body;the electrically conductive layer is printed on one of the layers of the body with an electrically conductive ink, for example by silkscreen printing on one of the layers of the body.

DETAILED DESCRIPTION OF THE DRAWINGS

A microcircuit device according to the invention is shown inFIG. 1. This device is designated with the general reference number10.

In the example described, the microcircuit device10is a chip card. As a variation, the device10can be a page of a passport such as the cover of the passport or a self-adhesive tag such as a “sticker.”

As shown inFIG. 1, the device10comprises a body12in the general shape of a card delimiting the first12A and second12B opposite faces.

In this embodiment, the body12delimits the outside dimensions of the card10. In this example and by preference, the dimensions of the card are defined by the ID-1 format of the ISO 7816 standard which is the format conventionally used for bank cards with dimensions of 86 mm by 54 mm and with a thickness substantially equal to eight hundred micrometers. Of course, other card formats can also be used.

Preferably, the card body12is formed by lamination, that is by formation, for example by means of a press and in a hot laminating operation, of a stack of laminated layers of sheets made for example of thermoplastic material.

Preferably, the body12comprises a stack of at least three layers: a central layer14forming a data printing layer interleaved between two external transparent layers16A,16B. In the embodiment illustrated inFIG. 2, the central layer14for data printing is itself made up of three sublayers, a central sublayer14C forming an “inlay,” interleaved between two other sublayers for data printing14A,14B. The two outside layers16A,16B are called “overlay,” and have the function for example of protecting the data printed on the central layer14C. For example, the body has a thickness of eight hundred micrometers and the outside layers16A,16B have a thickness substantially comprised between forty and eighty micrometers. The sublayers14A,14B,14C have thicknesses comprised between 200 and 300 micrometers.

In the variation illustrated byFIG. 8, the body12can include a central layer14comprising two sublayers14A and14B, the two layers together being interleaved between two transparent layers16A,16B. More generally, the central layer14can comprise one sublayer or more than two sublayers.

For example, the layers14,16are made of a material consisting essentially of a plastic such as polycarbonate, PVC, etc.

As a variation, the body12can be formed by casting, for example from plastic.

In conventional fashion, the device comprises a microcircuit18capable of exchanging data with an external terminal, of processing and/or storing data in memory. In conformity with the invention, the body12incorporates a microcircuit module20comprising the microcircuit18.

In the example described, the module20includes a substrate22bearing the microcircuit18. Thus, as illustrated inFIG. 2, the substrate22delimits the first22A and second22B opposite faces, called respectively the outer face and the inner face, the outer face22A being oriented toward the outside of the card10. The substrate22is, for example, made of epoxy type glass fiber, of polyester or of paper and has a thickness comprised for example between fifty and two hundred micrometers. Preferably, the substrate22is made of plastic based essentially on polyimide with a thickness of about seventy micrometers.

In addition, in this example, as illustrated byFIG. 2, the body12includes a cavity24for housing the module20. This cavity24is preferably formed within the body12and opens onto one of the faces12A,12B of the body12, for example the first face12A.

In a variation not illustrated in the figures, the module20can be incorporated into the body12, for example to constitute a contactless type device. In this case, the module20can be made invisible from the outside by opacification, for example with opaque ink, of the layers surrounding it.

As illustrated inFIG. 5, the cavity comprises for example a deep central area26provided with a bottom28for housing the microcircuit18and a peripheral area30raised with respect to the central area26delimiting a step29with the bottom28. This peripheral area30comprises a supporting surface raised with respect to the bottom of the cavity24on which rest the edges of the substrate22of the module20(FIG. 2).

Such a cavity24is generally obtained by machining, typically by milling or spot facing, in two operations:a large spot facing to form the peripheral area30corresponding to the depth of the step,a small spot facing to form the deeper central area26.

In order to communicate with an external terminal, the card10comprises for example an external interface32of contact pads34electrically connected to the microcircuit18. This interface32allows communication to be established by contact between the card10and another external terminal, for example when the card10is inserted into a matching card reader.

In the example described, the interface32comprises a series of metal electrical contact pads34, complying with a predefined chip card standard. For example, the contact pads comply with the ISO7816 standard. In this embodiment, the contacts34of the interface32correspond to the contacts C1, C2, C3, C5, C6, C7of the ISO7816 standard.

The interface32of the card10is preferably made of a layer of metallic material such as copper but may also be made, as a variation, by silkscreen printing of conductive ink of the epoxy ink filled with particles of silver or gold type or by silkscreen printing of an electrically conductive polymer. Conventionally, the pads are electrically connected to the microcircuit18by electrically conductive wires such as for example gold wires running through vias provided in the module substrate, connected in their turn to electrically conductive connecting traces extending over the inner face of the substrate.

In this embodiment, the card10is of the dual type, that is it includes both a contactless interface capable of establishing near-field communication with an external terminal and an interface with contact capable of establishing communication with another external terminal by contact. However, in a variation not illustrated, the card can be solely of the contactless type. In that case, the card10is preferably not equipped with the interface32having external contacts34.

To this end, for establishing contactless communication with an external terminal, such as an external reader, the device10still comprises a near-field communication antenna36electrically connected to the microcircuit18. The antenna36has an outside perimeter delimiting an antenna surface S.

In conformity with the invention, the antenna36is arranged within the module20.

Preferably, the antenna36consists of a winding of electrically conductive coils. For example, the antenna36consists of a copper trace. The antenna36preferably comprises a plurality of coils each with a width on the order of fifty to three hundred microns and the spacing between two contiguous coils is on the order of fifty to two hundred micrometers. The minimum spacing between two coils of the antenna36will be denoted coil interval.

Preferably, the antenna36extends over the substrate22and consists of a winding of electrically conductive coils extending along the periphery of one of the faces of the substrate22, for example the inner face22B.

The antenna36is for example made by depositing a metal, using an etching or a silk-screening technology. Possibly, as a variation, the antenna36can also consist of an electrically conductive wire in an insulating sleeve.

In the embodiment of the invention, as illustrated byFIGS. 3 and 4, the antenna36extends in two parts36A,36B and along the periphery of the two opposite faces22A,22B of the substrate22of the module20, the two parts36A,36B being electrically interconnected by at least one via V1, V2passing through the substrate22of the module20.

For example, the part36A of the antenna extends over the face22A opposite face22B bearing the microcircuit18and surrounds the interface34. The substrate22of the module20has for example a rectangular general shape and the antenna36runs along the periphery of the substrate22. As a variation, the substrate22can have any oblong shape. Preferably, the substrate22has dimensions compatible with known manufacturing processes used for manufacturing chip cards, whether in length, in width or in thickness.

In this embodiment the antenna36consists of a winding of electrically conductive coils extending along the periphery of one of the faces22A,22B of the substrate22of the module20.

Preferably, the distance separating the antenna36from an outside perimeter of the face22A,22B of the substrate22is less than or equal to a coil interval, that is the minimum spacing distance between two coils of the antenna36.

In conformity with the invention, the body12also incorporates means40for amplifying the gain of the antenna36, comprising an electrically conductive element42electrically insulated from the microcircuit18and the antenna36. The skilled person understands that the function of the element42is to concentrate or to direct the field lines from the reader toward the antenna36.

This element42has, in conformity with the invention and as illustrated inFIGS. 1 and 2, an annular general shape and is arranged so as to surround a region R of the body12constituting a volume generated by the projection of the antenna surface along a direction substantially orthogonal to the antenna surface S. Preferably, the volume is also limited by the perimeter of the body12. In the example described, the surface S extends parallel to the two opposite faces22A,22B of the substrate22and the orthogonal direction Z corresponds substantially to the vertical direction of the substrate22and therefore of the body12of the card10.

In the example described, the element42forms a closed ring. The ring thus constitutes means of channeling the magnetic flux generated by the external terminal within the antenna26in order to increase the gain of the antenna. As a variation and as illustrated inFIGS. 11 to 15, the element42can form a ring that is broken at least once. Indeed, it has been discovered that making an open ring further improved the performance of the antenna36.

In the example described, the ring is shaped so that the device10operates at a communication frequency with an external terminal for example of 13.56 MHz. Thus, the presence of the ring is taken into account in adjusting the resonance frequency of the device.

As the antenna36lies along the outside perimeter of the substrate22of the module16, the antenna surface S corresponds substantially to the surface of the substrate22and the region R consequently has a transverse section corresponding substantially to the surface of the substrate22. The ring42has preferably a shape generally surrounding the substrate, and therefore substantially rectangular.

The element42is preferably made of a metallic material with a relative magnetic permeability less than or equal to one. For example, the element42is made of a material such as an electrically conductive ink. In the example described, the ink includes a binder with an essentially polymeric base and metal pigments (silver for example). This ink is intended to be applied preferably by silkscreen to form a film with a thickness substantially comprised between ten and twenty micrometers.

In order to optimize the performance of the antenna36, the element42extends preferably as close as possible to the antenna along a direction substantially transverse to the body12which corresponds to a horizontal direction of the body12. This improvement of performance as a function of the transverse distance between the antenna36and the element42is brought out by the curve C2of the graphic inFIG. 10.

It is seen in this curve C2that the more the distance D is reduced, the better is the range P, that is the reading distance expressed in millimeters.

Preferably, the element42delimits an inner peripheral edge48surrounding the region R with a minimized distance, for example less than or equal to five millimeters. For example, this distance is minimized to the limit of the positioning accuracy of the antenna36within the module16.

In this example, the positioning tolerance of the antenna36within the module16corresponds to the positioning tolerance of the antenna36on the substrate22.

In the example described, the antenna36, consisting of a winding of electrically conductive coils, and the element42extending within the same plane as that containing the antenna36or at least a part36A,36B of the antenna36, the minimized distance is selected to ensure electrical isolation of the antenna26and the element42.

For example, in this case, the minimized distance is greater than or equal to one coil interval.

Preferably, the element42delimits an inner peripheral edge48surrounding the module20, the inner edge48is at least partly flush with the surface of a peripheral wall of the cavity24.

This makes it possible to limit the distance, along a direction transverse to the body12, between the antenna36and the ring42, to the distance separating the outer perimeter of the antenna36from the edge of the substrate22of the module20in the case where the dimensions of the substrate22are substantially fitted to those of the cavity24.

Thus, when the substrate22is substantially in contact with the peripheral wall of the cavity24, that is when the dimensions of the substrate22are substantially fitted to the dimensions of the cavity24, the ring42surrounds the region R at a distance corresponding to the distance between the edge of the substrate22and the outer perimeter of the antenna36.

The element42extends, in this example, substantially in a plane of the device that includes the antenna36or a plane including at least one of the parts36A,36B of the antenna36when the latter is in two parts.

However, in the illustrated variation, the element42can extend in a plane substantially parallel to that or those containing the antenna36, for example to satisfy volume constraints specific to the device10. Thus, inFIG. 8, different possible positions of the element42in the body12are shown, the element42being able in particular to be in a position visible from the outside of the device, for example by being printed on a face that is visible through the outside layer16A or15B, of a data printing layer14. To vary the position of the element42within the body12, for example, the thickness of the layers is varied, for example that of the sublayers of the central layer14.

In this example, the element42surrounds the lateral area30of the cavity24wherein the substrate22extends.

In addition, increasing the width L of the annular element42also makes it possible to improve the performance of the antenna36and in particular the range P (seeFIG. 9).FIG. 9shows a graphic comprising a curve C1of the change in the range P expressed in millimeters as a function of the width L of the element42.

In this embodiment, the element42has a full pattern. In the variation presented onFIGS. 12 to 15, the element42can also have a non-full pattern. For example, the ring42forms a grid or even a series of concentric rings with increasing circumference, etc.

This variation presents the interest of reducing the quantity of conductive ink while keeping RF performances equivalent to that of a full pattern. This variation also presents the advantage of improving the connection between the layers, a grid pattern allowing increasing the facing plastic surface.

OnFIGS. 12 and 13, the element42is designed to be used in a passport. It presents a dimension equivalent to that of a passport and a rectangular main opening of 27.2 mm×17.8 mm dimension compatible with the dimension of a module for passport. The position of the opening onFIG. 12allows obtaining optimal contactless RF performances. The position of this opening onFIG. 13allows, by moving the antenna closer to the seam of the passport, reducing the mechanical constrains supported by the antenna during the homologation tests and during use of the passport.

OnFIGS. 14 and 15, the element42is designed to be used in ID1 format card. It presents a dimension equivalent to that of an ID1 card and a rectangular main opening of 27.2 mm×17.8 mm or 27.2 mm×13.1 mm dimension compatible with the dimension of a module of an ID1 format card. The skill person will understand that the larger dimension improves the contactless RF performances.

A manufacturing method for the device ofFIGS. 1 through 4will now be described with reference toFIG. 5.

Firstly, the method comprises for example a step for forming the substrate22of the device10. This forming step can constitute either a step of laminating a plurality of layers together, or an operation of casting the body in plastic.

During this step of forming the body12, an electrically conductive layer is arranged within the body12. This arrangement is designed in such a way that, during the step of forming the cavity24, the cavity24passes through the electrically conductive layer to form the ring42. Preferably, during the forming step, the body12is made up of a multilayer structure, and the electrically conductive layer is interleaved between two layers of the body12.

For example, the electrically conductive layer is printed on one of the layers of the body12with electrically conductive ink, for example by silk-screening or by etching.

Preferably, the electrically conductive layer is printed on a data printing layer14. This data printing layer14is delimited by a face visible from the outside of the device bearing data such as the name of a bank or the identification number of a card or any personal or informational data held by the card, and an opposite, hidden face hidden in the body12, and the electrically conductive layer is carried on this hidden face, for esthetic reasons for example.

An electronic device according to a second embodiment of the invention is shown inFIGS. 6 and 7. In these figures, the elements corresponding to those inFIGS. 1 through 5have identical reference numbers.

In this second embodiment, the layer extends transversely over the entire surface of the body as illustrated inFIG. 7. This embodiment makes it possible to obtain an element42with the greatest possible width L and therefore to further improve performance.

Due to the fact that the cavity24is formed after deposition of the electrically conductive layer, the element42obtained extends as closely as possible to the peripheral wall of the cavity24and therefore to the antenna36along a direction transverse to the body12. It is then possible to obtain a precise fit of the position of the ring42with respect to the antenna36. Indeed, the antenna36extends along the periphery of the substrate22of the module20for example with a positioning tolerance less than or equal to one coil interval.

The element42extends around, the cavity24at a substantially zero distance as the ring42is flush with the wall of the cavity24. Thus, in the case where the dimensions of the substrate22of the module20are substantially fitted to the dimensions of the cavity24, the distance along a direction transverse to the body12separating the element42and the antenna36can be less than or equal to the positioning tolerance of the antenna36on the substrate42, and thus less than or equal to one coil interval.

In addition, the device obtained is more resistant to folding due to the combining of sensitive components such as the antenna and the microcircuit in the module.

The invention has been described more particularly for a card of the ID-1 format. It can apply to any pocket-sized, portable or other electronic device using a near-field field communication antenna the gain whereof it is desired to increase. For example, the device constitutes an inlay having a thickness comprised for example between 300 and 400 micrometers.

It is well understood that the embodiments that have just been described are not of a limiting nature and that they can undergo any desirable modification without thereby departing from the scope of the invention.