KR102381743B1 - Multilayer actuator and display device comprising the same - Google Patents

Abstract

A multilayer variable device according to an embodiment of the present invention is a multilayer variable device including three or more electroactive layers, wherein each of the three or more electroactive layers is made of a ferroelectric polymer, and the polarization of all three or more electroactive layers is direction is the same

Description

Multilayer variable element and display device including same

The present invention relates to a multi-layer variable element and a display device including the same, and more particularly, to a multi-layer variable element capable of greater displacement even at a constant voltage and a display device including the same.

Recently, in response to the demand of users who want to conveniently use various display devices, including liquid crystal displays and organic light emitting displays, the use of a touch type display device in which a user touches the display device to input has become common. Accordingly, research using a variable actuator to provide direct and various touch feedback to a user is continuing. In addition, research to implement various displacements of the flexible display panel by attaching a variable element to a flexible display panel that has been actively developed in recent years is also being conducted.

In general, a conventional display device uses a vibration motor such as an eccentric rotating mass (ERM) or a linear resonance motor (LRA) as a variable element. Since the vibration motor is designed to vibrate the entire display device, there is a problem that the size of the mass needs to be increased in order to increase the vibration force, it is difficult to modulate the frequency to control the degree of vibration, the response speed is very slow, and the flexible display The disadvantage was that it was not suitable for use in the device.

In order to improve this problem, shape memory alloy (SMA) and piezoelectric ceramics (EAC) have been developed as variable element materials, but shape memory alloy (SMA) has a slow reaction rate and lifespan. This short, opaque, and brittle piezoelectric ceramic is difficult to apply to a display device, particularly a flexible display device.

Accordingly, a variable actuator technology using an electro-active polymer (EAP) has attracted many people's attention. An electro-active polymer (EAP) is a polymer that can be deformed by electrical stimulation, and refers to a polymer that can be repeatedly expanded, contracted, and bent by electrical stimulation. Research is being conducted to fabricate a variable device including such an electroactive polymer as an electroactive layer, and to attach the variable device to a flexible display panel to implement various bending of the display.

However, a variable device including only one electroactive layer has a limitation in bending performance due to its thickness and a problem in that a driving voltage is high. In order to solve this problem, a multi-layer variable device in which a plurality of unit variable devices including one electroactive layer are stacked has been introduced. It has been demonstrated that a multi-layer variable device including a plurality of electroactive layers can realize a larger driving displacement at the same thickness as compared to a variable device including only one electroactive layer.

In the conventional multi-layer variable device, the electroactive layer of the unit variable device is generally formed of a dielectric elastomer. Since the dielectric elastomer does not maintain a polarization state in a natural state, conventional researchers have not considered the polarization state of the plurality of electroactive layers at all, and accordingly, it is natural that the polarization directions of the plurality of electroactive layers should be arranged in what form. I didn't even consider it at all.

However, the implementation of an electroactive layer of a ferroelectric polymer that can secure a higher driving displacement than a dielectric elastomer is being visualized, and in essence, the ferroelectric polymer maintains a polarization state in a specific direction. The need to consider how the polarization directions of a plurality of electroactive layers made of Accordingly, in consideration of the expansion and contraction of the electroactive layer according to the direction of application of the electric field, a method of adjusting the direction of application of the electric field to each of the plurality of electroactive layers has been partially introduced, but it is not yet very effective.

The inventors of the present invention found that in a multilayer variable device including three or more electroactive layers made of a ferroelectric polymer, when the polarization directions of all three or more electroactive layers are the same, the driving displacement of the multilayer variable device regardless of the direction of application of the electric field was found to be maximized.

Accordingly, an object of the present invention is to provide a multi-layer variable device including three or more electroactive layers made of a ferroelectric polymer and maximizing driving displacement when a constant voltage is applied, and a display device including the same.

Another object to be solved by the present invention is to provide a multilayer variable element in which the polarization directions of three or more electroactive layers are arranged in an optimized form in terms of voltage and displacement, and a display device including the same.

Another object of the present invention is to provide a multilayer variable element capable of being driven even with a low voltage and a display device including the same.

The problems of the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

A multilayer variable device according to an embodiment of the present invention for achieving the above object is a multilayer variable device including three or more electroactive layers, wherein each of the three or more electroactive layers is made of a ferroelectric polymer, and three The polarization directions of all of the above electroactive layers are the same.

According to another feature of the present invention, the three or more electroactive layers may be made of the same material.

According to another feature of the present invention, each of the three or more electroactive layers may be formed of a polyvinylidenefluoride (PVDF)-based polymer.

According to another feature of the present invention, a stretching process or a polling process may be applied to each of the three or more electroactive layers.

According to another feature of the present invention, the multi-layer variable element includes three or more unit variable elements having one electroactive layer, and each of the three or more variable unit variable elements includes a lower electrode facing each other with an electroactive layer interposed therebetween. and an upper electrode.

According to another feature of the present invention, in three or more unit variable elements, the directions of the electric field formed by the upper electrode and the lower electrode may all be the same.

According to another feature of the present invention, two or more adhesive layers disposed between three or more unit variable elements may be further included.

According to another feature of the present invention, each of the two or more adhesive layers may include a dielectric elastomer and a high dielectric filler.

A display device according to an embodiment of the present invention for achieving the above object is a display device including a multilayer variable element including three or more electroactive layers, and a display panel, wherein each of the three or more electroactive layers is ferroelectric It is made of a polymer, and the polarization directions of all three or more electroactive layers are the same.

According to another feature of the present invention, the display panel may include a flexible substrate.

The present invention has an effect that a multilayer variable device including three or more electroactive layers made of a ferroelectric polymer can realize maximum vibration acceleration under a constant voltage.

The present invention has the effect of providing a clear standard regarding the shape in which the polarization directions of the plurality of electroactive layers constituting the multi-layer variable device should be arranged.

The present invention has the effect of providing a multilayer variable device suitable for a portable mobile device by having a low driving voltage.

Effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a schematic exploded perspective view illustrating a structure of a display device according to an exemplary embodiment.
2 is a schematic cross-sectional view of a multilayer variable element of a display device according to an exemplary embodiment.
3 is a view showing the polarization direction of the first electroactive layer composed of a polyvinylidene fluoride-based polymer.
4 is a graph of measuring the vibration acceleration of the multilayer variable elements of Examples 1, 2, Comparative Examples 1 and 2;
5 is an exemplary state diagram for explaining various modified forms of a display device according to an embodiment of the present invention.
6 is a view showing examples in which a multi-layer variable device according to an embodiment of the present invention can be advantageously utilized.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention belongs It is provided to fully inform the possessor of the scope of the invention, and the present invention is only defined by the scope of the claims.

Reference to a device or layer “on” another device or layer includes any intervening layer or other device directly on or in the middle of the other device or layer.

Although first, second, etc. are used to describe various elements, these elements are not limited by these terms. These terms are only used to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the spirit of the present invention.

Like reference numerals refer to like elements throughout.

The size and thickness of each component shown in the drawings are illustrated for convenience of description, and the present invention is not necessarily limited to the size and thickness of the illustrated component.

Each feature of the various embodiments of the present invention may be partially or wholly combined or combined with each other, technically various interlocking and driving are possible, and each of the embodiments may be independently implemented with respect to each other or implemented together in a related relationship. may be

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic exploded perspective view illustrating a structure of a display device according to an exemplary embodiment.

Referring to FIG. 1 , a display device 10 according to an exemplary embodiment includes an upper cover 100 , a lower cover 200 , a flexible display panel 300 , and a multilayer variable element 400 .

The upper cover 100 is disposed on the flexible display panel 300 and the multilayer variable element 400 to cover the flexible display panel 300 and the multilayer variable element 400 . The upper cover 100 protects the components inside the display device 10 from external impact and penetration of foreign substances or moisture. The upper cover 100 may be made of a material having high ductility, for example, plastic, so that the multilayer variable element 400 can be displaced together when it is displaced by an electric field.

The lower cover 200 is disposed to face the upper cover 100 , and is disposed under the flexible display panel 300 and the multilayer variable device 400 to cover the flexible display panel 300 and the multilayer variable device 400 . . The lower cover 200 also protects the components inside the display device 10 from external impact and penetration of foreign substances or moisture. The lower cover 200 may also be made of a material having high ductility, for example, plastic, so that the multilayer variable element 400 can be displaced together when it is displaced.

The flexible display panel 300 is disposed between the upper cover 100 and the lower cover 200 . The flexible display panel 300 is a panel having flexibility to be bent like paper, and refers to a panel in which a display element for displaying an image is disposed. Since the flexible display panel 300 has flexibility, when the multilayer variable element 400 is displaced by an electric field, it may be displaced together. The flexible display panel 300 may include at least a flexible substrate in order to secure flexibility. The flexible display panel 300 may be, for example, an organic light emitting display panel. The organic light emitting display panel is a display panel in which the organic light emitting layer emits light by flowing a current through the organic light emitting layer, and emits light of a specific wavelength using the organic light emitting layer. The organic light emitting display panel includes at least a cathode, an organic light emitting layer, and an anode.

The multi-layer variable element 400 is disposed between the upper cover 100 and the lower cover 200 . The multilayer variable element 400 is disposed under the flexible display panel 300 and is attached to the flexible display panel 300 by an adhesive such as optical clear adhesive (OCA) or optical clear resin (OCR). The multilayer variable element 400 may be displaced as each of the three or more electroactive layers expands or contracts. As the multilayer variable element 400 is displaced, the upper cover 100 , the lower cover 200 , and the flexible display panel 300 are displaced, and thus the entire display device 10 may be displaced.

2 is a schematic cross-sectional view of a multilayer variable element of a display device according to an exemplary embodiment.

Referring to FIG. 2 , the multilayer variable element 400 according to an embodiment of the present invention includes a first unit variable element 410 , a first adhesive layer 420 , a second unit variable element 430 , and a second adhesive layer ( 440 , a third unit variable element 450 , a third adhesive layer 460 , and a fourth unit variable element 470 .

The first unit variable element 410 is one unit variable element constituting the multilayer variable element 400 and is configured to be displaced by an electric field. 2 , the first unit variable element 410 includes a first lower electrode 412 , a first upper electrode 414 , and between the first lower electrode 412 and the first upper electrode 414 . and a first electroactive layer 416 disposed on the

The first lower electrode 412 and the first upper electrode 414 serve to form an electric field in the first electroactive layer 416 when a voltage is applied from the outside. In order to form an electric field in the first electroactive layer 416 , a potential difference must exist between the first lower electrode 412 and the first upper electrode 414 . Accordingly, voltages of different magnitudes are applied to the first lower electrode 412 and the first upper electrode 414 . For example, a ground voltage may be applied to the first upper electrode 414 while a positive voltage is applied to the first lower electrode 412 , and a negative voltage may be applied to the first lower electrode 412 while the first A ground voltage may be applied to the upper electrode 414 .

The direction of the electric field formed in the first electroactive layer 416 may be different depending on the magnitude of the voltage applied to each of the first lower electrode 412 and the first upper electrode 414 . For example, when the voltage applied to the first upper electrode 414 is lower than the voltage applied to the first lower electrode 412 , an electric field in an upward direction may be formed in the first electroactive layer 416 . Also, when the voltage applied to the first upper electrode 414 is higher than the voltage applied to the first lower electrode 412 , an electric field in a downward direction may be formed in the first electroactive layer 416 .

An alternating voltage AC or a direct current voltage DC may be applied to the first lower electrode 412 and the first upper electrode 414 . When an alternating voltage (AC) is applied to the first lower electrode 412 and the first upper electrode 414 , the first unit variable element 410 may be periodically displaced, and the first lower electrode 412 and the first unit variable element 410 may be periodically displaced. When the DC voltage DC is applied to the first upper electrode 414 , the first unit variable element 410 may be maintained in a bent state.

The first lower electrode 412 and the first upper electrode 414 may be formed of a conductive material, but are not limited thereto. For example, the first lower electrode 412 and the first upper electrode 414 may be formed of a conductive material. Formed from a metal material such as gold (Au), copper (Cu), titanium (Ti), chromium (Cr), molybdenum (Mo), aluminum (Al), aluminum-Cu alloy, or PEDOT [ Poly(3,4-EthyleneDiOxyThiophene)]:PSS [Poly(4-StyreneSulfonic acid)], polypyrrole, polyaniline, etc. may be formed of a conductive polymer. The first lower electrode 412 and the first upper electrode 414 may be made of the same material or different materials.

As the thickness of the electrodes disposed on the lower surface and the upper surface of the electroactive layer increases, the number of electroactive layers included in the multilayer variable device having a constant thickness decreases. Considering that as the number of electroactive layers increases, the driving displacement of the multilayer variable element also increases, in order to arrange a larger number of electroactive layers in the multilayer variable element having a constant thickness, the electrode disposed on the lower surface and upper surface of the electroactive layer The thickness is preferably as thin as possible. For example, the thickness of the first lower electrode 412 and the first upper electrode 414 respectively disposed on the lower surface and the upper surface of the first electroactive layer 416 is preferably 50 nm to 100 nm.

When the same voltage is applied to the first lower electrode 412 and the first upper electrode 414, the lower the sheet resistance of the first lower electrode 412 and the first upper electrode 414, the lower the first electroactive layer 416 The electric field formed in the Accordingly, the first lower electrode 412 and the first upper electrode 414 preferably have a sheet resistance as low as possible, for example, a sheet resistance of 200 Ω/sq or less.

The first lower electrode 412 and the first upper electrode 414 may be disposed on both surfaces of the first electroactive layer 416 in various ways. For example, the first lower electrode 412 and the first upper electrode 414 are formed on both sides of the first electroactive layer 416 in a manner such as sputtering, printing, slit coating, or the like. can be placed. In particular, when the first lower electrode 412 and the first upper electrode 414 are formed of the same material, the first lower electrode 412 and the first upper electrode 414 may be simultaneously disposed in the same process.

The first electroactive layer 416 is disposed between the first lower electrode 412 and the first upper electrode 414 by the electric field formed by the first lower electrode 412 and the first upper electrode 414 . can be displaced.

The first electroactive layer 416 is made of a ferroelectric polymer maintaining a polarization state in a natural state. For example, the first electroactive layer 416 may be formed of a polyvinylidenefluoride (PVDF)-based polymer such as polyvinylidenefluoride homopolymer or polyvinylidenefluoride co-polymer. is done Displacement of the first electroactive layer 416 may be caused by applying an electric field to the first electroactive layer 416 maintaining a polarization state in a specific direction, for example, an upper direction or a lower direction.

The polarization direction of the first electroactive layer 416 may be determined according to an arrangement state of atoms constituting the first electroactive layer 416 . In FIG. 3 , it is assumed that the first electroactive layer 416 is made of a polyvinylidene fluoride-based polymer, and the polarization direction of the first electroactive layer 416 will be described.

3 is a view showing the polarization direction of the first electroactive layer composed of a polyvinylidene fluoride-based polymer.

Referring to FIG. 3A , in the first electroactive layer 416 , fluorine (F) atoms having a large number of electrons are disposed at the bottom, and hydrogen (H) atoms having a small number of electrons are disposed at the top Therefore, it can be seen that the polarization direction of the first electroactive layer 416 is an upward direction. In the polyvinylidene fluoride-based polymer, the polarization direction may be defined as a direction from a fluorine (F) atom to a hydrogen (H) atom.

Referring to FIG. 3B , in the first electroactive layer 416 , fluorine (F) atoms having a large number of electrons are disposed on the upper portion, and hydrogen (H) atoms having a small number of electrons are disposed on the lower portion. Therefore, it can be seen that the polarization direction of the first electroactive layer 416 is a downward direction.

The first electroactive layer 416 may be manufactured using a co-extrusion method instead of a solution casting method. When the electroactive layer is manufactured from a dielectric elastomer such as polydimethyl siloxane (PDMS), a solution casting method in which a solution is applied on a substrate and dried is generally used. This is because the dielectric elastomer can secure a certain level of permittivity even with a simple solution wire casting method. However, since a ferroelectric polymer such as a polyvinylidene fluoride-based polymer cannot secure a high dielectric constant by a solu wire casting method, a high dielectric constant is secured by a coextrusion method, and furthermore, a stretching process or a falling process.

In this sense, the first electroactive layer 416 may be a film to which a stretching process or a palling process has been applied. The stretching process refers to a process of pulling and orienting polymer chains in a heated state, and the poling process refers to a process of arranging atoms having a specific charge in one direction by applying a high DC voltage to the polymer. As the stretching process or the poling process is applied to the first electroactive layer 416 , the first electroactive layer 416 may function as an electroactive layer by securing a high dielectric constant. For example, PVDF (Poly VinyliDene Fluoride), a polyvinylidene fluoride homopolymer, can be stretched and folded to function as an electroactive layer, and a polyvinylidene fluoride copolymer P (VDF-TrFE) (Poly (VinyliDene Fluoride) )-TriFlurorEtylene can be poled to function as an electroactive layer.

When the first electroactive layer 416 is manufactured using a co-extrusion method, furthermore, a stretching process or a poling process, as shown in FIG. 2 , the first unit variable element 410 is formed by a first lower electrode 412, The configuration of the first upper electrode 414 and the first electroactive layer 416 may be advantageous in terms of driving displacement, rather than simply configuring the first unit variable element 410 with one electrode and the first electroactive layer. . Because the closer the distance between the two electrodes, the stronger the electric field can be generated with the same driving voltage. In the former case, between the two electrodes, that is, the first lower electrode 412 and the second upper electrode 414 In the latter case, only the first electroactive layer 416 exists, but in the latter case, not only the first electroactive layer but also an adhesive layer for adhering two unit variable elements to each other is further present between the two electrodes, so that in the former case, the latter This is because the distance between the two electrodes becomes closer than the case.

The thickness of the first electroactive layer 416 may be determined by those skilled in the art in consideration of power consumption and driving voltage required to operate as the first unit variable element 410 and whether a normal operation can be performed as the first unit variable element 410 . can be freely chosen. Preferably, the thickness of the first electroactive layer 416 may be 50 μm to 400 μm. More preferably, the thickness of the first electroactive layer 416 may be 100 μm to 300 μm. Here, when the thickness of the first electroactive layer 416 is less than 50 μm, a sufficient voltage required for the first unit variable element 410 to operate normally may not be applied. Accordingly, the first unit variable element 410 may not operate normally. In addition, when the thickness of the first electroactive layer 416 is greater than 400 μm, a high driving voltage is required to generate Maxwellian stress required for normal driving of the first unit variable element 410 , and thus power consumption is excessively high. can be increased.

The first adhesive layer 420 is disposed between the first unit variable element 410 and the second unit variable element 430 , and serves to bond the first unit variable element 410 and the second unit variable element 430 to each other. do Optical clear adhesive (OCA) or optical clear resin (OCR) may be used as the first adhesive layer 420 , and preferably, a high dielectric adhesive layer obtained by adding a ferroelectric filler to a dielectric elastomer may be used. Here, the dielectric elastomer may be one or more materials selected from the group consisting of an acrylic polymer, a urethane-based polymer, and a silicone-based polymer, preferably polydimethyl siloxane (PDMS). The ferroelectric filler may be one or more materials selected from the group consisting of piezoelectric ceramics, carbon nanoparticles, metal nanoparticles and conductive polymers, and preferably barium titanate (BaTiO ₃ ) It may be a piezoelectric ceramic such as.

Since the high dielectric adhesive layer has a high dielectric constant, it can serve not only as an adhesive layer but also as another electroactive layer. Specifically, the high dielectric adhesive layer not only serves as an adhesive layer for bonding the first unit variable element 410 and the second unit variable element 430 , but also serves as an adhesive layer for adjacent electrodes, that is, the first variable element of the first unit variable element 410 . The lower electrode 412 and the second upper electrode 434 of the second unit variable element 430 may serve as another electroactive layer that is deformed by an electric field applied thereto. Accordingly, when a high dielectric adhesive layer obtained by adding a ferroelectric filler to a dielectric elastomer is employed as the first adhesive layer 420, the driving displacement of the multilayer variable element 400 in the same electric field can be improved, and the multilayer variable element 400 can be improved. The overall permittivity of can be increased.

Each of the second unit variable element 430 , the third unit variable element 450 , and the fourth unit variable element 470 is one unit variable element constituting the multilayer variable element 400 , and is configured to be displaced by an electric field. do.

As shown in FIG. 2 , the second unit variable element 430 includes a second lower electrode 432 , a second upper electrode 434 , and a second electroactive layer 436 , and a third variable element unit 430 . Reference numeral 450 includes a third lower electrode 452 , a third upper electrode 454 , and a third electroactive layer 456 , and the fourth unit variable element 470 includes a fourth lower electrode 472 , a second 4 upper electrodes 474 , and a fourth electroactive layer 476 .

Here, each of the second electroactive layer 436, the third electroactive layer 456, and the fourth electroactive layer 476 is made of a ferroelectric polymer that maintains a polarized state in a natural state, and is configured to be displaced by an electric field. Furthermore, the polarization directions of all of the first electroactive layer 416 , the second electroactive layer 436 , the third electroactive layer 456 , and the fourth electroactive layer 476 are the same as each other. For example, as shown in FIG. 2 , the polarization directions of the first electroactive layer 416 , the second electroactive layer 436 , the third electroactive layer 456 , and the fourth electroactive layer 476 are all upward. am.

When the multilayer variable device includes only two electroactive layers, the driving displacement of the multilayer variable device is greatly affected by the direction of the electric field applied to each of the plurality of electroactive layers rather than the arrangement of the polarization directions of the plurality of electroactive layers. However, when the multilayer variable device includes three or more electroactive layers, the driving displacement of the multilayer variable device is greatly affected by the arrangement of the polarization directions of the electroactive layers rather than the direction of the electric field applied to the electroactive layers.

In this context, in the multilayer variable device 400 according to an embodiment of the present invention, the first electroactive layer 416 , the second electroactive layer 436 , the third electroactive layer 456 , and the fourth electroactive layer 476 . ) to maximize the driving displacement of the multilayer variable element 400 by making the polarization directions of all of them the same. When the multi-layer variable element 400 includes three or more electroactive layers 416, 436, 456, and 476, the plurality of electroactive layers 416, 436, 456, and 476 all have the same polarization direction. It exhibits a higher driving displacement at a constant voltage than different polarization directions of the electroactive layers 416, 436, 456, and 476 of Such a result is derived irrespective of how the direction of the electric field applied to each of the plurality of electroactive layers 416, 436, 456, and 476 is adjusted.

Of course, even when the polarization directions of all three or more electroactive layers 416 , 436 , 456 , and 476 are arranged in the same manner, the driving displacement of the multilayer variable element 400 is partially affected by the direction of the electric field. Specifically, even when the polarization directions of all three or more electroactive layers 416, 436, 456, and 476 are arranged in the same way, the direction of the electric field applied to the three or more electroactive layers 416, 436, 456, 476 is determined. Doing the same represents a higher drive displacement at a constant voltage than differentiating the direction of the electric field applied to the three or more electroactive layers 416 , 436 , 456 , 476 . This will be further described later with reference to Table 1 and FIG. 4 .

The first electroactive layer 416 , the second electroactive layer 436 , the third electroactive layer 456 , and the fourth electroactive layer 476 may be made of the same material, for example, a polyvinylidene fluoride-based polymer. . When the first electroactive layer 416, the second electroactive layer 436, the third electroactive layer 456, and the fourth electroactive layer 476 are made of the same material, the coextrusion process, the grinding process, and the palling process are performed at once. Since it can proceed, it is possible to simplify the manufacturing process of the multi-layer variable element 400 . In addition, since the first electroactive layer 416 , the second electroactive layer 436 , the third electroactive layer 456 , and the fourth electroactive layer 476 behave the same as each other at a constant voltage, the multilayer variable element 400 . It is advantageous for predicting the driving displacement of

The thickness of the second electroactive layer 436 , the third electroactive layer 456 , and the fourth electroactive layer 476 , the forming method, and the like may adopt the contents described above with respect to the first electroactive layer 416 as they are. , and overlapping descriptions are omitted. In addition, the second lower electrode 432 , the third lower electrode 452 , and the fourth lower electrode 472 may have substantially the same configuration as the first lower electrode 412 , and the second upper electrode 434 . , the third upper electrode 454 , and the fourth upper electrode 474 may have substantially the same configuration as the first upper electrode 414 , and thus overlapping descriptions will be omitted.

The second adhesive layer 440 is disposed between the second unit variable element 430 and the third unit variable element 450 , and the third adhesive layer 460 is formed between the third unit variable element 450 and the fourth unit variable element 450 . 470 is placed between. Since the second adhesive layer 440 and the third adhesive layer 460 may have substantially the same configuration as the first adhesive layer 420 , overlapping descriptions will be omitted.

For convenience of description, the multi-layer variable element 400 of FIG. 2 is disposed between the four unit variable elements 410 , 430 , 450 , 470 and the four unit variable elements 410 , 430 , 450 , 470 . Although it has been described as having three adhesive layers 420, 440, and 460, the multilayer variable element of the present invention basically includes three or more unit variable elements, and two or more adhesive layers disposed between three or more unit variable elements. Note that it can be configured.

In order to examine the effects of the present invention, as shown in FIG. 2 , a multilayer variable device including four electroactive layers arranged in the same polarization direction is applied to the four electroactive layers while attached to the flexible display panel. The radius of curvature and vibration acceleration of the multilayer variable device were measured by changing the direction of the electric field. In a state in which a multilayer variable device including four electroactive layers arranged in different polarization directions is attached to the flexible display panel, the directions of electric fields applied to the four electroactive layers are changed to increase the radius of curvature and vibration acceleration of the multilayer variable device. measured.

In Example 1, a multilayer variable device in which the polarization directions of all four electroactive layers are arranged in an upward direction is attached to the flexible display panel, an electric field in a downward direction is applied to the first electroactive layer and the third electroactive layer, and the second electric field is applied An experiment was conducted so that an electric field in an upward direction was applied to the active layer and the fourth electroactive layer. To this end, a positive voltage is applied to the first upper electrode, the second lower electrode, the third upper electrode, and the fourth lower electrode, and the first lower electrode, the second upper electrode, the third lower electrode, and the fourth upper electrode are applied with a positive voltage. A negative voltage was applied.

In Example 2, in a state in which multilayer variable elements in which the polarization directions of all four electroactive layers are arranged in an upward direction are attached to the flexible display panel, the first electroactive layer, the second electroactive layer, the third electroactive layer, and the fourth electroactive layer The experiment was conducted so that the electric field in the downward direction was applied to all. To this end, a positive voltage is applied to the first upper electrode, the second upper electrode, the third upper electrode, and the fourth upper electrode, and the first lower electrode, the second lower electrode, the third lower electrode, and the fourth lower electrode are applied with a positive voltage. A negative voltage was applied.

In Comparative Example 1, a multilayer variable device in which the polarization directions of the four electroactive layers are alternately arranged differently was prepared. Specifically, a multilayer variable device was prepared in which the polarization directions of the first electroactive layer and the third electroactive layer were arranged in the upper direction, and the polarization directions of the second electroactive layer and the fourth electroactive layer were arranged in the lower direction. In a state in which the multilayer variable element is attached to the flexible display panel, a downward electric field is applied to the first electroactive layer and the third electroactive layer, and an upward electric field is applied to the second electroactive layer and the fourth electroactive layer. The experiment was carried out as much as possible.

In Comparative Example 2, an electric field in a downward direction is applied to all of the first electroactive layer, the second electroactive layer, the third electroactive layer, and the fourth electroactive layer in a state in which the multilayer variable device as in Comparative Example 1 is attached to the flexible display panel. The experiment was carried out.

In Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the same conditions were applied except for the polarization directions of the four electroactive layers and the direction of application of the electric field to the four electroactive layers. Specifically, in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the polyvinylidene fluoride homopolymer was laminated after the stretching process and the falling process were performed on the polyvinylidene fluoride homopolymer. ) to prepare four electroactive layers, and by depositing metal electrodes on both sides of each electroactive layer, four unit variable devices were manufactured. The polarization directions of the four electroactive layers were measured using a polarization direction measuring device (APC International, 90-2030), and the maximum radius of curvature and the minimum radius of curvature were measured under the condition of 4.2 kVpp, and the condition of 100 kHz and 1.4 kVpp. Vibration acceleration was measured under

Table 1 below is a table showing the maximum radius of curvature, the minimum radius of curvature, and the change in curvature values of Examples 1, 2, Comparative Examples 1 and 2;

4 is a graph of measuring the vibration acceleration of the multilayer variable device of Examples 1, 2, Comparative Examples 1 and 2;

4 , Example 1 has a vibration acceleration of about 0.19 G, Example 2 has a vibration acceleration of about 0.27 G, Comparative Example 1 has a vibration acceleration of about 0.10 G, and Comparative Example 2 has a vibration acceleration of about 0.06 G It can be seen that the vibration acceleration is represented.

From the results of Table 1 and FIG. 4, it is consistent to arrange and drive as in Example 2, that is, to make the direction of the electric field applied to the four electroactive layers the same in a state where the displacement directions of the four electroactive layers are the same. It was confirmed that the driving displacement of the multi-layer variable device can be maximized at voltage.

And, from the results of Table 1 and FIG. 4, disposing and driving as in Example 1, that is, in a state in which the displacement directions of the four electroactive layers are the same, change the directions of the electric fields applied to the four electroactive layers Rather than disposing and driving as in Example 3, that is, making the direction of the electric field applied to the four electroactive layers the same in a state where the displacement directions of the four electroactive layers are different, multilayer variableness at a constant voltage It was confirmed that the driving displacement of the device could be increased. From this fact, it was confirmed that, regardless of the direction of the electric field applied to each of the four electroactive layers, making the directions of three or more electroactive layers the same is an effective way to increase the driving displacement of the multilayer variable device.

5 is an exemplary state diagram for explaining various modified forms of a display device according to an embodiment of the present invention. In FIG. 5 , it is assumed that the display device 500 is a smartphone for convenience of explanation.

Referring to FIG. 5 , a portion of the display device 500 may be bent upward or downward. Specifically, in the display device 500 , the multilayer variable element is fixed to the rear surface of the display screen 510 , and the multilayer variable element and the entire display device 500 are deformed by driving the multilayer variable element. That is, as a portion of the multilayer variable element is bent upward or downward, a portion of the display device 500 may also be bent upward or downward. Here, as a portion of the multilayer variable element is bent upward or downward with a predetermined period, a portion of the display device 500 may also be bent upward or downward. Also, as a portion of the multilayer variable element is maintained in a bent upper or lower state, a portion of the display device 500 may also be maintained in an upper or lower bent state.

For example, as an output corresponding to a user's touch input input to the display device 500 , a portion of the display device 500 may be bent upward or downward. That is, when a message is received from the display device 500 or a voice call is made to the display device 500 , a portion of the display device 500 may be bent upward or downward as an output.

In the display device 500 , a bending portion, a bending direction, a bending time, and a period in which the bending direction is changed may be variously set through the display device 500 . That is, the change in the shape of the display device 500 by the multi-layer variable element may be variously set by the user, and is not limited to the example change of the shape presented above.

In the display device 500 including the multi-layer variable element according to the exemplary embodiment of the present invention, the multi-layer variable element is differently deformed according to the input corresponding to various inputs. Specifically, the deformable portion, the deformed direction, the duration of the deformation, the period during which the deformation direction is changed, etc. may be set differently for each input applied to the display device 500 . Accordingly, the display device 500 may be deformed into various shapes by the multilayer variable element, and various types of outputs may be provided to the user.

6 is a view showing examples in which a multi-layer variable device according to an embodiment of the present invention can be advantageously utilized.

6A is an exemplary external view of an electronic newspaper 600 including a multi-layer variable element according to an embodiment of the present invention. Referring to FIG. 6A , the electronic newspaper 600 includes a display panel 610 and a multilayer variable element bonded to the rear surface of the display panel 610 .

In the electronic newspaper 600 including the multi-layer variable element according to an embodiment of the present invention, a feeling similar to viewing an actual paper newspaper may be provided by the multi-layer variable element. When a page turning signal is input through the display panel 610 of the electronic newspaper 600 , the multilayer variable element of a portion to which the signal is input may be deformed. Accordingly, as the multi-layer variable element is deformed, a portion of the electronic newspaper 600 is temporarily bent to provide a feeling of turning pages like a paper newspaper.

In addition, when a new article is uploaded and displayed in the electronic newspaper 600 including the multi-layer variable element according to an embodiment of the present invention, the fact that a part of the electronic newspaper 600 is modified and the article is uploaded is provided. For example, when an article with a new headline is uploaded, the multilayer variable element of the part where the article is uploaded is deformed, so that the fact of uploading the article is immediately displayed.

6B is an exemplary diagram of a watch 700 including a multi-layer variable element according to an embodiment of the present invention. Referring to FIG. 11B , the watch 700 includes a display panel 710 and a multilayer variable element bonded to the lower portion of the display panel 710 . Here, for convenience of description, the watch 700 is assumed to be a smart watch.

In the watch 700 including the multi-layer variable element according to an embodiment of the present invention, various functions of the watch 700 may be implemented by the multi-layer variable element. General time information is displayed through the display panel 710 of the watch 700 . In addition, weather, news, etc. may be displayed through the display panel 710 of the watch 700 . In addition, the watch 700 may include a simple call function, and may determine the heart rate of a user wearing the watch 700 . Here, the multi-layer variable element inside the watch 700 may be contracted to notify the hour on the hour or to notify the specified alarm time. Accordingly, time information may be provided by tightening the user's wrist. In addition, even when new weather information or news is displayed, the multilayer variable element inside the watch 700 is contracted, or when a call is received, a protrusion is formed on a part of the display panel 710 of the watch 700 to provide information can be In addition, when the user's heart rate measured through a part of the watch 700 is at a dangerous level, a warning notification may be provided to the user by contracting or changing the shape of the multilayer variable element inside the watch 700 .

6C is an exemplary view of a curtain including a multi-layer variable element according to an embodiment of the present invention. Referring to FIG. 6C , the curtain 800 includes a display panel 810 and a multilayer variable element bonded to the lower portion of the display panel 810 .

In the curtain 800 including the multi-layer variable element according to an embodiment of the present invention, information on the external environment may be expressed in various ways by the variable element. Specifically, the external weather may be displayed on a predetermined screen through the display panel 810 of the curtain 800 , and the shape of the curtain 800 may be changed to express specific weather conditions. For example, when wind blows in cloudy weather, clouds are displayed through the display panel 810 of the curtain 800, and a portion of the curtain 800 is displayed by a multi-layer variable element according to the wind direction and speed of the wind. is bent, and the area of the bent portion may also be different. That is, the direction in which the actual curtain can be folded or shaken according to the direction of the wind may be expressed as the bending direction of the curtain 800 , and the stronger the wind, the greater the area of the bent portion of the curtain 800 may be. In addition, when the amount of illuminance incident through the glass window is less than or equal to a predetermined illuminance, the curtain 800 may be automatically rolled up or folded in the left or right direction.

Although embodiments of the present invention have been described in more detail with reference to the accompanying drawings, the present invention is not necessarily limited to these embodiments, and various modifications may be made within the scope without departing from the technical spirit of the present invention. . Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

10, 500: display device
100: upper cover
200: lower cover
300: display panel
400: multi-layer variable element
410: first unit variable element
412: first lower electrode
414: first upper electrode
416: first electroactive layer
420: first adhesive layer
430: second unit variable element
432: second lower electrode
434: second upper electrode
436: second electroactive layer
440: second adhesive layer
450: third unit variable element
452: third lower electrode
454: third upper electrode
456: third electroactive layer
460: third adhesive layer
470: fourth unit variable element
472: third lower electrode
474: third upper electrode
476: third electroactive layer
600: electronic newspaper
700: clock
800: curtain

Claims (10)

a plurality of unit variable elements; and
A plurality of adhesive layers each disposed between two adjacent unit variable elements,
Each of the plurality of unit variable elements includes an electroactive layer and a lower electrode and an upper electrode facing each other with the electroactive layer interposed therebetween,
Each of the plurality of electroactive layers included in each of the plurality of unit variable elements is made of a ferroelectric polymer,
The polarization directions of all of the plurality of electroactive layers are the same as each other,
wherein the plurality of adhesive layers have a high dielectric constant to be another electroactive layer deformed by an electric field applied by an adjacent electrode. According to claim 1,
The plurality of electroactive layers are made of the same material as each other, a multi-layer variable device. According to claim 1,
Each of the plurality of electroactive layers is made of a polyvinylidenefluoride (PVDF)-based polymer. According to claim 1,
A stretching process or a polling process is applied to each of the plurality of electroactive layers, a multilayer variable device. delete According to claim 1,
In the plurality of unit variable elements, the directions of the electric fields formed by the upper electrode and the lower electrode are all the same. delete According to claim 1,
wherein each of the plurality of adhesive layers includes a dielectric elastomer and a high dielectric filler. A display device having a multilayer variable element and a display panel, comprising:
The multi-layer variable element may include a plurality of unit variable elements; and
A plurality of adhesive layers each disposed between two adjacent unit variable elements,
Each of the plurality of unit variable elements includes an electroactive layer and a lower electrode and an upper electrode facing each other with the electroactive layer interposed therebetween,
Each of the plurality of electroactive layers included in each of the plurality of unit variable elements is made of a ferroelectric polymer, and the polarization directions of all of the plurality of electroactive layers are the same as each other,
The plurality of adhesive layers have a high dielectric constant so as to be another electroactive layer deformed by an electric field applied by an adjacent electrode. 10. The method of claim 9,
The display panel includes a flexible substrate.

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