Piezoelectric device and method for manufacturing a piezoelectric device

Abstract

Piezoelectric device (1) comprising: a first electrode (2), a second electrode (3), and a deformable insulating layer (4) between the first electrode (2) and the second electrode (3), wherein a plurality of channels (6) are formed in the insulating layer (4) which are filled with a polymer with a piezoelectric effect, characterized by a layer (5) of the polymer with piezoelectric effect, which is arranged between the first electrode (2) and the second electrode (3) on the deformable insulating layer (4).

Description

[0001] The invention relates to a piezoelectric device and a method for producing a piezoelectric device.

[0002] Force sensors are used in modern motor vehicles. Simple piezoceramics or strain gauges are often used for this purpose. Another option is to measure force using the piezoelectric effect of a film. For a few years now, the material polyvinylidene fluoride (PVDF) has been further developed for this purpose. The effect is still small, so it is desirable to increase the effect in order to obtain suitable force sensors. Since the general goal is to use force sensors where the action occurs (e.g., pressing a control element with a finger), the use of materials with high optical transmission makes sense. Furthermore, electrical conductors with high optical transmission are already being used successfully.The problem with using these piezoelectric components is that a typical application involves compression induced by pressure, in which a longitudinal effect occurs. 33 is utilized. However, the material cannot utilize its full piezoelectric coefficient here.

[0003] US 2015 / 0 357 374 A1 discloses a transistor array comprising a substrate and a plurality of transistor elements sharing the substrate. Each of the transistor elements comprises: a lower electrode arranged on the substrate and a connecting wire for the lower electrode; a piezoelectric body arranged on the lower electrode, the piezoelectric body being made of piezoelectric material; and an upper electrode arranged on the piezoelectric body. Furthermore, a method for manufacturing a transistor array is also known. The transistor array contains transistor elements that are two-terminal devices. Piezoelectric bodies with piezoelectric properties are provided between the upper and lower electrodes of the transistor array.The charge carrier transport of the transistor elements in the transistor array device can be effectively regulated or triggered by voltages applied to the transistor elements.

[0004] The invention is based on the object of improving a piezoelectric device and a method for producing a piezoelectric device, in particular with regard to force detection and energy harvesting.

[0005] The object is achieved according to the invention by a piezoelectric device having the features of patent claim 1 and a method having the features of patent claim 8. Advantageous embodiments of the invention emerge from the subclaims.

[0006] In particular, a piezoelectric device is provided, comprising a first electrode, a second electrode and a deformable insulator layer between the first electrode and the second electrode, wherein a plurality of channels are formed in the insulator layer, which channels are filled with a polymer with a piezoelectric effect.

[0007] Furthermore, in particular, a method for producing a piezoelectric device is provided, wherein a deformable insulator layer having a plurality of channels is produced, wherein the channels are filled with a polymer having a piezoelectric effect, wherein a first electrode is applied, and wherein a second electrode is applied such that the insulator layer is arranged between the first electrode and the second electrode.

[0008] The device and the method make it possible to amplify the piezoelectric effect in the polymer and thereby increase a measurable voltage between the electrodes. This can, in particular, increase a measurement signal upon compression of the piezoelectric device. This enables, in particular, use as a force sensor at the functional site, i.e., at the location where the force is applied. Furthermore, energy harvesting can be improved. This is achieved by arranging a deformable insulator layer between the electrodes. The insulator layer is, in particular, an electrical insulator. A plurality of channels are formed in the insulator layer, wherein the channels are filled with a polymer with a piezoelectric effect. This can ensure that pressure on the piezoelectric device leads to compression of the deformable insulator layer.As the deformable insulator layer deforms under pressure, the channels in the insulator layer bend. Since the channels are filled with the polymer with a piezoelectric effect, the bending intensifies the piezoelectric effect, particularly not only as a longitudinal effect (i.e., a longitudinal effect). 33 ), but also as a transverse or cross-effect (d 31 This allows a signal detectable at the electrodes to be amplified. The insulator layer also ensures, via the channels, that the polymer in the channels is returned to its original orientation after pressing by relieving the deformation of the insulator layer.

[0009] The piezoelectric device is, in particular, a piezoelectric force sensor. This force sensor is compressed when pressed, generating a measurable voltage between the electrodes. The measurable voltage is, in particular, proportional to the force acting on the piezoelectric device. Furthermore, the piezoelectric device can also be used for energy harvesting, for example, to supply sensors with energy.

[0010] It is envisaged that the device comprises a layer of the polymer with a piezoelectric effect, which is arranged between the first electrode and the second electrode on the deformable insulator layer. This allows the piezoelectric effect to be further enhanced. The polymer in the channels is in particular (electrically) connected to the polymer of the layer, or in other words: the channels merge seamlessly into the layer. During production, it can be provided that the layer of the polymer with a piezoelectric effect is applied or arranged on the deformable insulator layer in such a way that the polymer fills the channels in the insulator layer.

[0011] In one embodiment, the channels run in a direction perpendicular to the insulating layer. In other words, the channels run in a direction perpendicular to a surface formed by the insulating layer. This allows the piezoelectric effect of the device to be optimally enhanced. In particular, the electrodes are flat, and the channels run in a direction perpendicular to the flat electrodes.

[0012] In principle, however, the direction of the channels in the deformable insulator layer can be freely selected. For example, the direction in which the channels run to a surface of the insulator layer can be provided at a predetermined angle to the surface, depending on an application scenario. If, for example, the device is arranged on a vehicle windshield for energy harvesting, the airflow will hit the device at an angle of approximately 45°. This can be taken into account by appropriately selecting the angle at which the channels run in the insulator layer. The angle is then selected such that the airflow leads to a longitudinal compression of the polymer or the channels. In the example mentioned, the angle would then be approximately 45°.

[0013] In one embodiment, the first electrode, the second electrode, the insulator layer, and the layer, if present, are (optically) transparent. This allows the piezoelectric device to be used in conjunction with graphic displays. Transparent here means, in particular, that optical imaging is possible through the electrodes and the layers in accordance with the laws of geometric optics. For example, a graphic design of a button or a control panel, which can be actuated by means of an actuating element, can be arranged behind the piezoelectric device. This graphic design can then be detected through the piezoelectric device. Actuation via the piezoelectric device designed as a force sensor can then occur in a logically corresponding manner with the graphic display.

[0014] In one embodiment, the insulating layer is formed from or comprises silicone (in particular, poly(organo)siloxane). This allows, in particular, simple production of the deformable insulating layer by processing it in liquid form, which subsequently cures. For example, polydimethylsiloxane (PDMS) can be used; this can be processed in liquid form and subsequently cured.

[0015] In one embodiment, the polymer is or comprises polyvinylidene fluoride (PVDF). This allows the use of a polymer with a strong piezoelectric effect. For example, the copolymer poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) can be used. A further advantage is that PVDF can be processed in liquid form. This makes it easier to introduce the polymer into the channels, for example, by sucking it into the channels using a vacuum during production.

[0016] In one embodiment, at least one of the electrodes is formed from or comprises one of the following materials: poly-3,4-ethylenedioxythiophene (PEDOT:PSS), indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), antimony-doped tin oxide (ATO), silver nanowires, silver nanowires and carbon tubes, graphene, dodecacalcium heptaaluminate (DC12A7), and metal mesh. In particular, the electrodes can be made (optically) transparent.

[0017] In one embodiment, the insulator layer is formed from or comprises one of the following materials: leather, injection-molded plastic. This allows surfaces, for example, surfaces of a motor vehicle interior, to be functionalized with different appearances using the piezoelectric device, i.e., in particular, to be used for force sensing and / or energy harvesting. It can also be provided that the injection-molded plastic is given a visual appearance such as aluminum, leather, wood, etc. through suitable admixtures.

[0018] The process involves applying a layer of polymer with a piezoelectric effect to the deformable insulator layer.

[0019] In one embodiment of the method, a matrix is ​​used to produce the insulator layer, which matrix has a plurality of pillars and / or rods designed to form the channels in the insulator layer. This makes it possible to provide a negative mold for producing the deformable insulator layer. For example, a glass carrier or silicon carrier can be used as the matrix, into which the pillars and / or rods are etched. The deformable insulator layer is then sprayed in liquid form onto the matrix, in particular the glass carrier or silicon carrier, and hardens. The pillars and / or rods can then be removed using suitable etching processes (e.g., using hydrofluoric acid or HNA = hydrofluoric acid / HF + nitric acid / HNO3 + acetic acid / C2H4O2 or dry etching), so that the channels in the insulator layer are exposed.

[0020] In one embodiment, at least some of the plurality of channels are formed in the insulator layer by laser processing. This also allows channels to be formed in materials for which working with a matrix is ​​not possible, for example, because the material used cannot be liquefied (e.g., leather).

[0021] Further features of the method will become apparent from the description of embodiments of the device. The advantages of the method are the same as those of the device.

[0022] The invention will be explained in more detail below using preferred embodiments with reference to the figures. Fig. 1 is a schematic representation of an embodiment of the piezoelectric device; Fig. 2 a schematic flow diagram of an embodiment of the method for manufacturing a piezoelectric device.

[0023] The Fig. 1 shows a schematic representation of an embodiment of the piezoelectric device 1. The piezoelectric device 1 comprises a first electrode 2 and a second electrode 3. Furthermore, the piezoelectric device 1 comprises a deformable insulator layer 4 between the first electrode 2 and the second electrode 3.

[0024] The piezoelectric device 1 comprises a layer 5 made of the polymer with a piezoelectric effect, as shown here by way of example. The layer 5 is also arranged between the first electrode 2 and the second electrode 3 on the deformable insulator layer 4.

[0025] A plurality of channels 6 filled with the polymer are formed in the insulator layer 4. For the sake of clarity, not all channels 6 are labeled with their own reference symbols.

[0026] The piezoelectric device 1 forms in particular a force sensor or a device for generating energy by means of energy harvesting.

[0027] The insulator layer 4 can, for example, have a thickness of several hundred micrometers. For example, the insulator layer 4 can have a thickness of 300 to 500 µm, in particular 400 µm. The channels 6 have, in particular, a diameter in the range of 40 to 100 µm. A distance between the channels 6 can, for example, be half the diameter. It can be provided that a diameter of the channels 6 and a distance between adjacent channels 6 are selected with reference to a predetermined layer thickness of the insulator layer 4 and / or the layer 5 such that a piezoelectric effect is maximized, in particular upon compression of the piezoelectric device 1 along a surface normal 10.

[0028] The channels 6 are arranged in a regular pattern, in particular in a regular grid. For example, a densest packing can be selected with respect to a two-dimensional surface of the device 1.

[0029] It can be provided that the piezoelectric device 1 has a protective layer 7, which is arranged on an outer surface, in particular on the first electrode 2. The protective layer 7 serves to insulate and protect the device 1.

[0030] The electrodes 2, 3 are formed, for example, from PEDOT:PSS or indium tin oxide (ITO). The deformable insulator layer 4 can be made of silicone or comprise silicone. Layer 5 can be made of PVDF, for example. The PVDF in layer 5 and in channels 6 has been brought into the beta phase, in particular, by a polarization step during the manufacturing process.

[0031] In particular, it is provided that the electrodes 2, 3 are flat and the channels 6 run in a direction perpendicular to the insulator layer 4.

[0032] It can be provided that the first electrode 2, the second electrode 3, the insulator layer 4, and the layer 5 are transparent. This allows a graphically designed layer 8 arranged behind the piezoelectric device 1 with respect to a perception direction to be perceived through the device 1. This allows both functionalized surfaces and graphically designed buttons and keys to be provided. Furthermore, the piezoelectric device 1 can also be arranged or arranged on a display device, so that a touch-sensitive display device can be formed. For example, the electrodes 2, 3 for this purpose can be formed from PEDOT:PSS or indium tin oxide (ITO) or the materials mentioned in the following paragraph. Transparent silicone can be used as the insulator layer 4. Transparent PVDF can also be used as the polymer in the layer 5.

[0033] Alternatively, it may be provided that at least one of the electrodes is formed from or comprises one of the following materials: fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), antimony-doped tin oxide (ATO), silver nanowires, silver nanowires and carbon tubes, graphene, dodecacalcium heptaaluminate (DC12A7), metal mesh.

[0034] Alternatively, it can be provided that the insulator layer 4 is formed from or comprises one of the following materials: leather, injection-molded plastic.

[0035] The Fig. 2 shows a schematic flow diagram of an embodiment of the method for manufacturing a piezoelectric device.

[0036] In a method step 100, a deformable insulator layer with a plurality of channels is produced. For this purpose, in a method step 100a, a matrix is ​​used to produce the insulator layer, which matrix has a plurality of columns and / or rods configured to form the channels in the insulator layer. For this purpose, the plurality of columns and / or rods can be formed, for example, in a glass carrier or a silicon carrier using an etching process, so that a negative mold is created. In a method step 100b, the material for the insulator layer is introduced into this negative mold in liquid form, in particular injected or poured into it. After curing, the columns and / or rods are removed in a method step 100c, in particular by etching them away. This forms the channels in the insulator layer or can thereby be exposed.As an alternative to using a matrix, the channels can also be drilled into a silicone mat. Other methods for forming channels in the deformable insulator layer, such as electron beam bombardment, would also be possible.

[0037] In a method step 101, a layer of a polymer with a piezoelectric effect, for example PVDF, in particular P(VDF-TrFE), is applied or arranged on the deformable insulator layer such that the polymer fills the channels in the insulator layer. The PVDF is applied in particular in liquid form. It can be provided that the channels are subjected to a negative pressure so that the liquid polymer, starting from the layer, is thereby conveyed into the channels. At the end of method step 101, the insulator layer and the layer are arranged next to one another and the channels are filled with the polymer. The polymer is in particular bonded to the polymer in the layer or merges seamlessly into it. The polymer is then cured. For this purpose, introduction and heating in an oven or heating on a hot plate can be provided.

[0038] Optionally, in a process step 102, the layer is annealed at a temperature above the Curie temperature to improve polymer crystallinity. For example, this can be done in an oven at a temperature of 145°C for 5 to 15 minutes.

[0039] In a process step 103, a first electrode is applied. This can be done, for example, by printing PEDOT:PSS or another suitable material. Alternative processes that can be used depending on the selected electrode material include screen printing, physical vapor deposition (PVD), chemical vapor deposition (CVD), or roll-to-roll printing.

[0040] In a process step 104, a second electrode is applied so that the insulator layer and the layer between the first electrode and the second electrode are arranged. This can be done, for example, by printing PEDOT:PSS or another suitable material. Alternative processes that can be used depending on the selected electrode material include screen printing, physical vapor deposition (PVD), chemical vapor deposition (CVD), or roll-to-roll printing.

[0041] In a process step 105, the polymer, in particular the PVDF, is polarized using a voltage to align the crystals. For this purpose, a DC voltage of 10 V / µm to 100 V / µm is used, for example. The voltage can also be sinusoidal or rising. With a layer thickness of 400 µm and a channel length of the same order of magnitude, this results in voltages in the range of 4 kV to 40 kV, which leads to polarization of the polymer.

[0042] In an alternative embodiment, at least some of the plurality of channels may be formed in the insulator layer by laser machining. This is particularly useful when a matrix cannot be used as a negative mold because the deformable insulator layer cannot be brought into a liquid state (e.g., in leather). List of reference symbols 1 piezoelectric device 2 first electrode 3 second electrode 4 deformable insulator layer 5 layer (polymer with piezoelectric effect) 6 channel 7 Protective layer 8 graphically designed layers 10 surface normals 100-105 Procedural steps of the procedure

Claims

[1] Piezoelectric device (1) comprising: a first electrode (2), a second electrode (3), and a deformable insulator layer (4) between the first electrode (2) and the second electrode (3), wherein a plurality of channels (6) are formed in the insulator layer (4) which are filled with a polymer with a piezoelectric effect, characterized by a layer (5) of the polymer with piezoelectric effect, which is arranged between the first electrode (2) and the second electrode (3) on the deformable insulator layer (4). [2] Piezoelectric device (1) according to claim 1, characterized by that the channels (6) run in a direction perpendicular to the insulator layer (4). [3] Piezoelectric device (1) according to one of the preceding claims, characterized bythat the first electrode (2), the second electrode (3), the insulator layer (4) and the layer (5) are transparent. [4] Piezoelectric device (1) according to one of the preceding claims, characterized by that the insulating layer (4) is made of or comprises silicone. [5] Piezoelectric device (1) according to one of the preceding claims, characterized by that the polymer is or comprises polyvinylidene fluoride (PVDF). [6] Piezoelectric device (1) according to one of the preceding claims, characterized by that at least one of the electrodes (2,3) is formed from or comprises one of the following materials: poly-3,4-ethylenedioxythiophene (PEDOT:PSS), indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), antimony-doped tin oxide (ATO), silver nanowires, silver nanowires and carbon tubes, graphene, dodecacalcium heptaaluminate (DC12A7), metal mesh. [7] Piezoelectric device (1) according to one of the preceding claims, characterized by that the insulating layer (4) is made of or comprises one of the following materials: leather, injection-molded plastic. [8] Method for manufacturing a piezoelectric device (1), wherein a deformable insulator layer (4) having a plurality of channels (6) is produced, wherein the channels (6) are filled with a polymer with a piezoelectric effect, wherein a first electrode (2) is applied, and wherein a second electrode (3) is applied so that the insulator layer (4) is arranged between the first electrode (2) and the second electrode (3), characterized by that a layer (5) of the polymer with piezoelectric effect is applied to the deformable insulator layer (4). [9] Method according to claim 8, characterized bythat for producing the insulator layer (4) a matrix is used which has a plurality of columns and / or rods arranged to form the channels (6) in the insulator layer (4). [10] Method according to one of claims 8 or 9, characterized by that at least a part of the plurality of channels (6) is formed in the insulator layer (4) by means of laser processing.

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