WO2008132379A2

WO2008132379A2 - Radio-tag fabrication method

Info

Publication number: WO2008132379A2
Application number: PCT/FR2008/050480
Authority: WO
Inventors: Joseph Tregret; Olivier Briere; Gérard Gadot
Original assignee: Microcomposants Haute Sécurité Mhs
Priority date: 2007-03-22
Filing date: 2008-03-20
Publication date: 2008-11-06
Also published as: WO2008132379A3; FR2914087A1

Abstract

The invention relates to a method of fabricating a radio-tag intended to be implemented in a radio-identification system, the method comprising the step of producing, on a substrate (1), an electronic radio-identification circuit (3), termed the RFID circuit, and being characterized in that it furthermore comprises the step of producing on said substrate (1) an antenna (4) making it possible to receive and/or to transmit radio signals. The invention also relates to a radio-tag fabricated according to this method.

Description

METHOD FOR MANUFACTURING RADIO LABEL

The present invention relates to a method for manufacturing a radio-tag, that is to say a label intended to be affixed to an object, in order to allow the implementation of a method of identifying this object by radio, generally known as RFID technology.

RFID technology is used for identifying short-range objects. The principle of this identification is as follows: it affixes, on the objects to be identified, a label capable of responding to a request from an RFID reader, this reader consisting of a radio frequency transmitter. The tags can be passive or active devices. Passive tags are devices that are activated only when passing an RFID reader.

An RFID tag is usually composed of the following elements:

an antenna capable of transmitting and / or receiving radio waves,

an electronic chip, for example made of silicon, and

a substrate or an encapsulation allowing the two previous elements to communicate. The techniques currently used for the manufacture of these labels implement several separate manufacturing steps.

Thus, the RFID electronic circuit is first produced in the form of an integrated circuit on a substrate, to form an electronic chip. Next, the radio antenna is produced, and during these assembly steps, these two elements are assembled on the same substrate or in the same housing. During the assembly step, the antenna is, for example, glued or soldered on the chip.

The disadvantage of these techniques is that they implement several successive steps, which is costly in terms of time and manufacturing costs, and in terms of space for the installation of manufacturing equipment.

The present invention aims to provide a manufacturing method for removing at least one of the above steps, to allow a reduction in the cost and / or the size of the component and / or the manufacturing time.

Thus, the invention relates to a tag manufacturing method intended to be implemented in a radio-identification system, the method comprising the step of producing on a substrate an electronic radio-identification circuit, said RFID circuit, characterized in that it further comprises the step of providing on said substrate an antenna for receiving and / or transmitting radio signals.

In this method, the antenna is directly integrated into the electronic chip containing the RFID circuit. This eliminates manufacturing steps, since it is no longer necessary to perform an assembly at the end of the manufacturing steps of the various components of the label; indeed, the elements are directly integrated in the same circuit.

The method described here implements conventional techniques for manufacturing integrated circuits. This fabrication is based on the use of masks on which we draw the electronic circuit, these masks being then used to impress several plates photographic, called reticles. The reticles are reduced to the final size of the integrated circuit, for example by a photogravure process, and are then copied onto a substrate to form the integrated circuit.

In a method according to the invention, an antenna is drawn on one of the reticles, which results in the integration of this antenna in the integrated circuit finally made.

Thus, the antenna is made of the same material as one of the interconnection levels of the integrated circuit.

Among the materials that can be used to produce this level intended to receive the antenna, mention may be made of aluminum, aluminum-silicon, aluminum-silicon-copper, aluminum-copper, copper, or any of these compounds associated with titanium.

The design of the antenna is preferably optimized according to the chosen operating frequency range, as well as the desired transmission performance. These performances are, for example, expressed in terms of range of the waves, in order to be able to use the radio-identification device in a radius ranging from a few centimeters to a few meters.

Antennas used in radio-identification systems have a relatively large area, since they have a size of the order of several square centimeters.

The constraints on the size of the antennas result from the physical laws of electromagnetism, and more particularly from those of radioelectricity. Indeed, there is a direct relationship between the frequency of use of an antenna and the length and / or diameter of the conductor used for its manufacture. The material used for this manufacture may also, to a lesser extent, have an influence on the dimensions of said antenna. However, the RFID electronic circuits are made on substrates such as silicon substrates, which are expensive materials. Consequently, the realization of antennas of this size directly integrated in an electronic circuit can sometimes be relatively expensive, because it requires the use of large silicon wafers, or other semiconductor material. It has therefore been envisaged the possibility of proposing a method in which an antenna of smaller size is manufactured than the existing conventional antennas, which therefore implies an impedance mismatch at the desired frequency of use. To alleviate this problem, the method comprises an additional step during which an impedance matching device is made, allowing a correct association of the antenna and the RFID circuit. The use of such an impedance matching device is imperative for proper operation of the assembly. This device can cause losses of a few decibels, but these losses do not affect too much the operation of the antenna.

Indeed, for a short-distance application such as that of the radio-identification, it is not useful to obtain a gain unitary or superior, since the uses are limited to a few tens or hundreds of centimeters, this taking into account the power loss due to the impedance matching circuit. Consequently, the use of the impedance matching circuit in a radio tag according to the invention makes it possible to reduce manufacturing costs, without affecting the performance of this tag.

The adaptation of the impedance of the antenna must be precisely performed, in order not to degrade the operating performance of the antenna and the RFID circuit. Thus, it is determined, depending on the size of the antenna that it is desired to obtain and the electronic circuit, the characteristics of the impedance matching circuit to achieve. However, it may be that after manufacture, the characteristics of the different elements differ slightly from the values initially planned. It is therefore useful to be able, after having performed a test of the label, to modify the parameters of the impedance adaptation. For this purpose, the method comprises a step of producing, on the substrate, a control circuit of the impedance matching device. With this control circuit, a fine adjustment can be envisaged at the end of the steps of making the assembly.

The control circuit, however, does not allow to vary the adaptation too much. It is therefore necessary that parameters of the different elements of the radio-label are chosen beforehand. Thus, the parameters of the antenna are, for example, chosen as a function of the parameters of the RFID circuit and / or the impedance matching circuit. Indeed, the electronic circuit has a fixed output impedance to which it is necessary to adapt. Consequently, from this fixed value and the possibilities offered by the adaptation device, it will be possible to determine sets of values in which the parameters of the antenna must be located.

Several embodiments have been envisaged for the implementation of the adaptation circuit.

In a first embodiment, a mechanical adaptation is used, that is to say, during a step, a branch line section is produced between the antenna and the electronic circuit.

Such a line short-circuited and placed in parallel with the line between the antenna and the circuit is known as a "stub". The impedance adaptation depends on the length of this line, as well as its position relative to the electronic circuit, here playing the role of the load. To determine the parameters of the line, one can use charts, such as the Smith chart, which make it possible to establish a relation between the dimensions of the line and the impedance adaptation carried out, according to the frequency under which one wishes to work.

In a second embodiment, the impedance matching device is in the form of an electronic circuit comprising a set of electronic components such as capacitors and / or coils. To carry out the impedance matching, switching between the coils and the capacitors is implemented. This embodiment will be illustrated later with the aid of figures.

The characteristics of the coils and / or capacitors present in the circuit depend on the impedance values that it is desired to obtain. Advantageously, the components used in such a circuit are variable components, so that they can be controlled by a control circuit as described above. In a third embodiment, the embodiment of the adaptation device consists in producing a device known as a gamma-match adaptation. An adjustable slider is positioned on the antenna power line at the location where the desired adaptation is achieved. Thus, in an advantageous embodiment, the cursor is controlled by a control circuit as described above.

The invention also relates to a label intended to be implemented in a radio-identification system, comprising an electronic radio-identification circuit, made on a substrate, and characterized in that it further comprises an antenna for receiving and / or to emit radio signals, the antenna being made on the same substrate.

In a variant, a label according to the invention comprises one or more of the following characteristics:

it comprises an impedance matching device placed on the substrate, between the antenna and the RFID circuit, it comprises a control circuit of the impedance matching device,

the adaptation device takes the form of a section of line placed in shunt between the antenna and the RFID circuit,

the adaptation device takes the form of an electronic circuit comprising a set of electronic components such as capacitors and / or coils and

- The adaptation device takes the form of a line in parallel with the connection between the antenna and the RFID circuit, this line being short-circuited at one end and having a capacitance in series at the other end.

Other characteristics and advantages of the invention will become apparent with the description of some of its embodiments, this description being made without limitation by means of the figures in which: FIG. 1 shows a block diagram of a radio tag according to the invention,

FIGS. 2, 3, 4a, 4b and 4c show exemplary embodiments of an impedance matching device used in a radio-tag according to the invention,

- Figures 5a, 5b and 5c show different configurations of an antenna made according to a method according to the invention.

A radio-tag according to the invention is formed of a silicon substrate 1, on which an RFID electronic circuit 2 and a radio antenna 4 are installed.

This radio-tag is intended to operate at a frequency of 2,450 GigaHertz. The impedance 5 at the output of the RFID circuit is of the order of 50 ohms.

The radio antenna 4 has a geometric shape, for example square, of a few millimeters on a side. The impedance 6 at its terminals, at the resonance, is different from the impedance of the RFID circuit, which is 50 Ohms. Consequently, it is necessary to adapt this impedance to be able to correctly associate the antenna and the RFID circuit. This adaptation is performed by a device 3, two embodiments of which are shown in FIGS. 2 and 3.

It is sometimes useful that this impedance matching device 3 can be controlled by a user after completion of the tag. For this purpose, the radio-tag preferably comprises a control circuit 7 of the impedance matching device.

This control circuit 7 can be directly installed on the substrate 1, as shown here, but it can also be outside the label. In the case where the impedance matching device is in the form of an electronic circuit, the control circuit is, for example, used to program certain components or the entire circuit.

In an embodiment shown in FIG. 2, the impedance matching device 3 is in the form of an open or short stub. circuit, that is to say a section of transmission line 10, shunted between the RFID circuit 2 and the radio antenna 4.

The impedance matching achieved by this method depends on the length of the line section 10, as well as the position of this line with respect to the RFID circuit.

The line section is, for example, made at the time of manufacture of the integrated circuit, being drawn on one of the reticles during a manufacturing process of the entire integrated circuit of the radio-label, as described in FIG. beginning of this application.

Another embodiment of the impedance matching device, called gamma-match, is shown in FIG.

The principle of this device is to modify the connection between the antenna and the RFID circuit by introducing a line section between the RFID circuit 2 and the antenna 4. This section comprises, at one end, a capacitor in series 12. It is further provided with a slider 11 for adjusting its length.

Impedance matching is achieved by changing the length of the line section and the capacity of the capacitor.

A third embodiment, shown in FIGS. 4a, 4b and 4c, illustrates the case in which the impedance matching device is in the form of an electronic circuit.

In these figures, it can be seen that the RFID circuit 2 and the antenna 4 are connected via an electronic circuit comprising at least one variable inductor and at least one variable capacitor.

In the example of FIG. 4a, the impedance matching electronic circuit comprises a variable inductance 13 controlled by the RFID circuit. A capacitor 14 is placed in parallel with this inductor 13 and the antenna 4. In the example of FIG. 4b, the electronic circuit is composed of a capacitor 15 connected in series of the RFID circuit 2, and an inductor 16 in parallel with the antenna 4.

In the example of Figure 4c, the electronic circuit comprises three capacitors 17, 18 and 19, and an inductor 20, each of these components being variable. Figures 5a, 5b and 5c illustrate different possible configurations for an antenna made in a label according to the invention. These different configurations are intended to be used in the case where the impedance matching device is in the form of a stub or a gamma match. Thus, in each of these figures, an antenna 21 appears, connected to an impedance matching device 22. This matching device receives, on an input, 23, an electrical signal from the RFID circuit.

It can be seen from these figures that it is possible to implement a large number of geometrical configurations for producing the antenna, these configurations generally having at least one symmetry.

Thus, on the examples shown here, the antennas have the following symmetries:

in FIG. 5a, a central symmetry,

- In Figure 5b, two axial symmetries (vertical and horizontal), and - in Figure 5c, an axial symmetry with respect to the vertical axis.

Claims

A method of manufacturing a radio tag for implementation in a radio identification system, the method comprising

the step of producing, on a substrate (1), an electronic radio-identification circuit (2), called RFID circuit,

the step of producing, on said substrate, an antenna (4) for receiving and / or transmitting radio signals, and characterized in that it comprises, in addition,

the step of producing on said substrate (1) an impedance matching device (3) between the antenna (4) and the RFID circuit (2), and

the step of producing on the substrate (1) a control circuit (7) of the impedance matching device (3).

2. Method according to claim 1 characterized in that it comprises the preliminary step of determining the parameters of the antenna (4) according to the parameters of the RFID circuit (2) and / or the impedance matching device (3).

3. Method according to one of claims 1 or 2, characterized in that the step of producing the impedance matching device (3) consists in producing a line section (10) in shunt between the RFID circuit (2) and the antenna (4).

4. Method according to claim 3, characterized in that it comprises the step of determining the length of the line section (10) as a function of the impedance (6) of the antenna (4) and the impedance (5) of the RFID circuit (2).

5. Method according to one of the preceding claims, characterized in that the step of producing the impedance matching device (3) consists in producing a set of capacitor type electronic components (14, 15, 17, 18, 19) and / or coil (13, 16, 20).

6. Method according to one of the preceding claims, characterized in that the step of producing the impedance matching device (3) consists in producing an additional connection line between the antenna (4) and the RFID circuit (2), this line being short-circuited at one end and having a capacitance (12) in series at the other end.

7. Method according to one of the preceding claims, characterized in that the different steps of realization are carried out simultaneously.

8. Radio-tag for use in a radio-identification system, comprising an electronic radio-identification circuit (2), made on a substrate (1), and an antenna (4) for receiving and / or or to emit radio signals, the antenna (4) being made on the same substrate (1)

Characterized in that it further comprises an impedance matching device (3) placed on the substrate (1), between the antenna (4) and the RFID circuit (2) and a control circuit ( 7) of the impedance matching device (3).

9. Radio tag according to claim 8, characterized in that the adaptation device (3) takes the form of a line section (10) shunted between the antenna (4) and the impedance circuit (2).

10. Radio tag according to claim 8 or 9, characterized in that the adaptation device (3) takes the form of an electronic circuit comprising a set of electronic components such as capacitors (14, 15, 17, 18 , 19) and / or coils (13, 16, 20).

Radio tag according to claim 8 or 9, characterized in that the adaptation device (3) takes the form of an additional connecting line between the antenna (4) and the RFID circuit (2), this line being short-circuited at one end and having a capacitance (12) in series at the other end.