LU100594B1 - Piezoelectric device with a sensor and method for measuring the behaviour of said peizoelectric device - Google Patents

Abstract

The first object of the invention is directed to a piezoelectric device (10) shaped as a tridimensional object with at least two surfaces, wherein said piezoelectric device (10) comprises a first set of two or more electrodes (8a, 8b). Said piezoelectric device (10) is remarkable in that at least one of the surfaces which is free of electrodes from said first set of two or more electrodes (8a, 8b) is covered with at least a second set of electrodes. The second object of the invention is directed to a method for measuring the behaviour of a piezoelectric device.

Description

PIEZOELECTRIC DEVICE WITH A SENSOR AND METHOD FOR MEASURING THE BEHAVIOR OF SAID PIEZOELECTRIC DEVICE

description

Technical field [0001] The invention is directed to the field of the piezoelectric material. More particularly, the invention is directed to the field of the measurement of the deformation of the piezoelectric actuator.

Background art [0002] In the field of piezoelectric device, it is known to be a sensor to an actuator by bonding or gluing, thus requiring different material to manufacture a sensor. This therefore increases the number of steps for the fabrication of search material, as well as the step for activating the bonding. For instance, US patent application published US 2007/0165333 A1 discloses a piezoelectric sensor bonded by a non-conductive adhesive to a piezoelectric actuator to determine the pressure and / or the temperature.

[0003] One example of a piezoelectric device is the surface acoustic wave (SAW) device. A SAW device is a piezoelectric device in which an input transducer and output transducer are on the same outer surface of the device. The input transducer (also known as the actuator) and the output transducer (s) are or are being used in a mechanical energy system of SAWs. Therefore, no galvanic isolation is achieved. Moreover, the interdigitated electrodes are deposited on a piezoelectric device.

[0004] US patent application published US 2009/0009193 A1 describes a moisture-sensitive element which is formed on a printed circuit board (PCB). This moisture-sensitive element works by applying to an electric field between the two electrodes composing the interdigital capacitor. Thus, if moisture (water) enters the electric field, the total dielectric constant of the interdigital capacitor is increased.

[0005] In the case of SAW device, as explained above, the sensor is embedded in a device (in the case of the moisture-sensitive element). The adhesion between the actuator and the sensor is therefore required.

Summary of invention

Technical Problem [0006] The invention has a technical problem at least one of the drawbacks present in the prior art. A piezoelectric sensor in a piezoelectric actuation device has been fabricated without changing the manufacturing process.

Technical solution [0007] The first object of the invention is a piezoelectric device as a tridimensional object. Said piezoelectric device is at least one second of the electrodes.

According to a preferred embodiment, said second set of electrodes is at least two interdigitated electrodes.

According to a preferred embodiment, said second set of electrodes is at least two electrodes distributed along a single conductive line.

According to a preferred embodiment, said interdigitated electrodes are on two distinct surfaces of said piezoelectric device.

[0011] According to a preferred embodiment, said piezoelectric device is made of a ceramic material, preferably of the perovskite structure and even more preferably made of lead zirconate titanate or LiNbCb.

Nanoparticles, preferably nanoparticles made of silver, gold, copper, aluminum or indium tin oxide, also known as ITO, according to a second aspect of the invention.

According to a preferred embodiment, said interdigitated electrodes are spaced from each other with a gap between 10 pm and 100 pm.

According to a preferred embodiment, the electric conductors have an interdigitated size between 5 pm and 1 mm, preferably between 20 pm and 100 pm.

According to a preferred embodiment, said piezoelectric device is a pyroelectric device.

According to a preferred embodiment, said piezoelectric device is a multi-layer piezoelectric device, comprising alternating dielectric layers and metallic layers, the number of metallic layers being equal to n + 1, n being to integer.

According to a preferred embodiment, said metallic layers are made of metallic electrodes, more preferably interdigitated nickel or platinum of palladium electrodes.

According to a preferred embodiment, said electrodes of said second set of electrodes are planar.

The second object of the invention is directed to a method for measuring the behavior of a piezoelectric device, said method comprising the steps of a. providing a piezoelectric device having a first set of two or more electrodes, said piezoelectric device being shaped as a tridimensional object having at least two surfaces, b. printing at least one second of the electrodes. determining the variation of the electrical charges on said second set of electrodes.

According to a preferred embodiment, said second set of electrode is at least two interdigitated electrodes.

According to a preferred embodiment, said second set of electrode is at least two electrodes distributed along a single conductive line.

According to a preferred embodiment, said printing is performed on at least two distinct surfaces of said piezoelectric device.

According to a preferred embodiment, said step (b) is performed by inkjet printing.

[0024] According to a preferred embodiment, said step (b) is performed by aerosol printing.

According to a preferred embodiment, said step (b) is performed with an ink made of electrically conductive nanoparticies.

According to a preferred embodiment, said ink made of electrically conductive nanoparticies is an ink made of silver, gold, copper, aluminum or indium tin oxide, also known as ITO.

Advantages of the invention The invention is particularly interesting in that the piezoelectric actuator can be functionalized with the piezoelectric sensor by simple deposition of the sensor on the piezoelectric actuator, namely by inkjet printing or aerosol printing. This enables the functionalization of any type of piezoelectric device without adding any material to it.

Isolation galvanic can be because the second set of electrodes is not necessarily in contact with the first set of electrodes.

The space occupation of the printed sensor is negligible compared to the size of the piezoelectric actuator, due to the low thickness of the second set of electrodes.

Moreover, the outer surface of the piezoelectric layer, since it is the same dielectric material, as it requires any kind of activation in order to bond or glue any further element is now which is printed by the interdigitated electrodes.

Brief Description of the Drawing Figure 1 shows a representation of a mechanical deformation sensor with a cylindrical shape and with an interdigital capacitor as a deposited sensor, in accordance with the present invention.

[0032] FIG. 1A shows a representation of a mechanical deformation sensor with a cuboid shape and a piece of conductor as a deposited sensor, in accordance with the present invention.

[0033] FIG. 2 shows a representation of a mechanical deformation sensor with a cuboid shape and with an interdigital capacitor as a deposited sensor, in accordance with the present invention.

Figure 2A shows a representation of a mechanical deformation sensor with a cylindrical shape and with a piece of conductor as a deposited sensor, in accordance with the present invention.

Figure 3 shows a representation of a multilayer capacitor device in accordance with the present invention.

Description: The principle of the invention is to deposit on a piezoelectric actuator a sensor, so-called deposited sensor, which is used to measure the deformation of the piezoelectric actuator.

The piezoelectric actuator 10 is typically a device made of piezoelectric material, preferably ceramic material. Those materials therefore have dielectric properties. The crystal structure of the ceramic material can be the perovskite structure. For example, search material can be lead zirconate titanate (PZT) or lithium niobate (LiNbCb). Two electrodes (8a, 8b), which are used to actuate said piezoelectric actuators, are connected to one piece of a piezoelectric actuator, or on the same face (not shown) ,

As shown in figure 1 or 2, the two electrodes (8a, 8b) consist respectively of a positive electrode and a negative electrode. The positive electrode 8a can be interchanged with the negative electrode 8b.

The piezoelectric actuator (when electric charges are displaced in response to an applied mechanical stress) can thus be a pyroelectric sensor (when electric charges are displaced in a solid in response to a variation of temperature).

The deposited sensor can be attached to an interdigital capacitor 6 (see figures 1 and 2), or piece of conductor 60 (see figures 1A and 2A), preferentially planar, which is deposited on a face of the piezoelectric device which is free of electrode, preferably on the outer surface of the piezoelectric actuator, by a special deposition method, which is printing, preferably inkjet printing or aerosol printing. This particular deposition method allows for every kind of shape of the piezoelectric actuator, since printing, or inkjet printing, or aerosol printing, can be used on any kind of tri-dimensional shape.

When the piezoelectric actuator has been used, the mechanical deformation sensor has been developed.

When the piezoelectric actuator has a printed sensor, so has been developed.

The deposited sensor can be realized on every free surface of the piezoelectric actuator as it functions itself independently of the electrodes of the piezoelectric actuator. Isolation galvanic is as reached when the electrodes of the piezoelectric actuator are not connected to any of the electrodes of the deposited sensor.

[0044] In the case of an interdigitated capacitor, it has two electrodes, a first electrode 6a and a second electrode 6b, each of which is interdigitated with the other (see figures 1 or 2). Each is said to have a high electrical conductivity (6.30 * 107 S / m at 20 ° C). Alternatively, gold (4.10 * 107 S / m at 20 ° C) or copper (5.96 * 107 S / m at 20 ° C) can be used. Alternatively, each of the conductive components which has a conductivity superior to 106 S / m and is printable may be used.

Each of the two electrodes (6a, 6b) has a synthesis of the optional electrodes (6c and 6d). The first electrode 6c of the first electrode 6a of the second electrode 6b.

The two electrodes (6a, 6b) are formed by a gap which is between 10 pm and 100 pm, i.e. The pitch between a first extending electrode 6c and a second extending electrode 6d is between 10 pm and 100 pm.

The width / size of the two electrodes forming the interdigital capacitor, i. The interlaced overlapping length of the first extending electrode 6c and the second extending electrode 6d is between 5 pm and 1 mm. Preferentially, the width is between 20 pm and 100 pm.

The thickness of the interdigital capacitor is as low as 1 pm, the space occupation of the sensing structure compared to the size of the piezoelectric device. This has the advantages of allowing for the wide use of such device.

In the case of the deposited sensor, it is a conductor line 60 that can be made of a straight line of conducting material with two or four pads 65 (see figure 1A). The conductive line 60 and the contact pads 65 are made of silver, which is a highly conductive component (6.30 * 107 S / m at 20 ° C). Alternatively, gold (4.10 * 107 S / m at 20 ° C) or copper (5.96 * 107 S / m at 20 ° C) can be used. Alternatively, each of the conductive components which has a conductivity superior to 106 S / m and is printable may be used. This conductive line 60 can thus be a meander, as displayed in figure 2A.

The width of the conductive line 60 can be between 10 and 1 mm, preferably between 10 and 100 pm. The length of the line can be between 50 pm and 1 cm, preferably between 200 pm and 1 mm.

The thickness of the conductive line can be as low as 1 pm, thus reducing the space occupation of the sensing structure to the size of the piezoelectric device. This has the advantages of allowing for the wide use of such device.

The piezoelectric device can thus be multilayer capacitor device 100 (MLC), where metallic electrodes 2 and piezoelectric layers 4 alternate (see figure 3). The metallic layer or layers (eg, electrodes in silver) remains electrically isolated from the inner electrodes of the MLC. N the inside of the MLC, the metallic layers alternate with the dielectric layers and the number of metallic layers is equal to n while the number of dielectric layers is equal to n + 1 (n being an integer).

In a practical case, let's consider the top layer (which is a free surface) of the piezoelectric actuator 100. The dimensions of the piezoelectric device 100 are 5 mm × 5 mm × 2.4 mm in the case where the piezoelectric device is with a shape of a polyhedron with six faces. The piezoelectric device comprises two electrodes (8a, 8b) on two distinct faces. The electrodes (8a, 8b) can thus be presented on two distinct faces, which are not necessarily opposed faces (not shown on figure 3). The inkjet / aerosol printing of silver electrode (s) is performed on the free surface (see figure 3). The pattern of these electrodes (6, 60) can be either interdigitated, similar to figures 1 and 2, or a conductive line 60 similar to figures 1A or 2A. This deposition is then followed by an annealing step that is used to dry and sinter the metallic nanoparticies of silver ink (this can also be achieved with gold or copper nanoparticies). This annealing step enables electrical conductivity. The annealing step has been performed at 200 ° C during 30 minutes at atmospheric pressure.

The electric field applied between the two electrodes (8a, 8b) of the piezoelectric actuator 100 induces a mechanical deformation into the whole actuator. This deformation is detected by the deposited sensor. Via the piezoelectric effect that is induced by the electrodes (6a, 6b) of the LCR-meter or an oscilloscope (6a, 6b) of the interdigitated capacitor. If the sensor is a conductive line 60, the deformation is sensed via the variation of resistance of the conductive line (piezoresistive effect). This resistance can be measured when a current is applied to the two external pads 65a in Figures 1A or 2A, and then one measures the resulting voltage between the two inner pads 65b displayed in Figures 1A or 2A. This gives information on the actuator device 100.

[0055] The displacement of an object on the micrometer scale, a piezoelectric transformer. Fatigue monitoring system, strain sensor, temperature sensor and humidity sensor are achievable thanks to the functionalization of a piezoelectric device.

Claims (20)

1) A piezoelectric device (10, 100) in the form of a three-dimensional object with at least two surfaces, wherein said piezoelectric device (10, 100) comprises a first set of two or more electrodes (8a, 8b), characterized in that at least one of the surfaces which is devoid of electrodes from said first set of two or more electrodes (8a, 8b) is covered by at least a second set of electrodes (6, 60). 2) piezoelectric device (10, 100) according to claim 1, characterized in that said second set of electrodes consists of at least two interdigital electrodes (6a, 6b). 3) piezoelectric device (10, 100) according to claim 1, characterized in that said second set of electrodes consists of at least two electrodes distributed along a single conductive line (60). 4) piezoelectric device (10, 100) according to claim 2, characterized in that said interdigital electrodes (6a, 6b) are on two separate surfaces of said piezoelectric device (10). 5) Piezoelectric device (10, 100) according to any one of claims 1 to 4, characterized in that said piezoelectric device (10, 100) is made of a ceramic material, preferably the perovskite structure and even more preferably zirconate titanate lead or in LiNbCh. 6) piezoelectric device (10, 100) according to any one of claims 1 to 5, characterized in that said second set of electrodes (6, 60) consists of at least one electrical conductor comprising electrically conductive nanoparticles, preferentially nanoparticles made of silver, gold, copper, aluminum or indium tin oxide, aka ITO. 7) piezoelectric device (10, 100) according to any one of claims 2 or 4 to 6, characterized in that said interdigital electrodes (6a, 6b) are spaced from each other with an interval between 10 pm and 100 pm. 8) piezoelectric device (10, 100) according to any one of claims 6 to 7, characterized in that the electrical conductors constituting said interdigital electrodes (6a, 6b) have a width between 5 pm and 1 mm, preferably between 20 pm and 100 pm. 9) piezoelectric device (10, 100) according to any one of claims 1 to 8, characterized in that said piezoelectric device (10, 100) is a pyroelectric device. 10) piezoelectric device (100) according to any one of claims 1 to 9, characterized in that said piezoelectric device (100) is a multilayer piezoelectric device comprising alternating dielectric layers and metal layers, the number of metal layers being equal to "and the number of piezoelectric layers being equal to n + 1, n being an integer. 11) piezoelectric device (100) according to claim 10, characterized in that said metal layers consist of metal electrodes, preferably of interdigital metal electrodes, more preferably interdigital electrodes of nickel or platinum or palladium . 12) piezoelectric device (10, 100) according to any one of claims 1 to 11, characterized in that said electrodes (6, 60) of said second set of electrodes are planar. 13) A method of measuring the behavior of a piezoelectric device (10, 100), said method comprising the steps of: a) providing a piezoelectric device with a first set of two or more electrodes, said piezoelectric device being shape of a three-dimensional object with at least two surfaces, b) printing of at least a second set of electrodes on at least one of the faces which is devoid of electrodes, c) determination of the variation of the electrical charges on said second set of electrodes. 14) Method according to claim 13, characterized in that said second set of electrodes consists of at least two interdigital electrodes (6a, 6b). 15) Method according to claim 13, characterized in that said second set of electrodes consists of at least two electrodes distributed along a single conductive line (60). The method of claims 13-14, wherein said printing is performed on at least two distinct surfaces of said piezoelectric device. 17) Method according to any one of claims 13 to 16, wherein said step (b) is performed by inkjet printing. 18) Method according to any one of claims 13 to 16, wherein said step (b) is performed by aerosol printing. The method of any one of claims 13 to 18, wherein said step (b) is performed with an ink made of electrically conductive nanoparticles. The method of claim 19, wherein said electrically conductive nanoparticle ink is an ink made of silver, gold, copper, aluminum, or indium tin oxide, aka ITO.