Patent Description:
The present disclosure relates to a display device.

Patent Document <NUM> discloses a display device including a display panel and an actuator. The display device of Patent Document <NUM> has a function of vibrating the display panel by controlling the actuator.

[Related Art Documents] Patent Document <NUM>, Patent Publication No. <CIT>.

<CIT> presents a display device including a piezoelectric element capable of reproducing sound by securing a sufficient sound pressure even in a low frequency range.

<CIT> presents a display apparatus that includes a display panel which displays an image and a vibration member attached to a surface of the display panel, where the vibration member receives a sound signal, generates a vibration in response to the sound signal, and transfers the vibration to the display panel to allow the display panel to output a sound.

<CIT> presents a display device that includes-a display panel, a piezoelectric member and an elastic member connected to a portion of the piezoelectric element and to the display panel.

In order to improve a sense of realism or the like, a display device, which emits a sound by allowing a display panel itself to function as a speaker, is being considered. However, although a display panel is allowed to function as a speaker through a structure disclosed in Patent Document <NUM>, sound quality may not be sufficient.

The present disclosure is directed to a display device having improving sound quality by emitting a sound from a display panel. One or more of the abovementioned objectives are achieved by subject-matter of the independent claim.

According to an aspect of the present disclosure, there is provided a display device including a piezoelectric element vibrated according to input audio signals, a display panel configured to display an image. An elastic member is provided which is configured to connect a portion of the piezoelectric element and the display panel so as to transmit a vibration of the piezoelectric element to the display panel.

According to another aspect of the present disclosure, there is provided a display device including a piezoelectric element which includes a first vibration part and a second vibration part extending in different directions when viewed from above. The piezoelectric element is vibrated according to input audio signals. The display panel is configured to display an image. An elastic member is provided which is configured to connect a portion of the piezoelectric element and the display panel so as to transmit a vibration of the piezoelectric element to the display panel.

According to still another aspect of the present disclosure, there is provided a display device including a plurality of piezoelectric elements vibrated according to one or more input audio signals, and a display panel configured to display an image, wherein each of the plurality of piezoelectric elements is connected to the display panel to transmit a vibration to the display panel.

Preferably, a first piezoelectric element and a second piezoelectric element among the plurality of piezoelectric elements have different frequency characteristics.

In some or more embodiments, the piezoelectric element may have a flat plate shape.

In some or more embodiments, the elastic member may be connected to a main surface of the piezoelectric element.

In some or more embodiments, the piezoelectric element may have a rectangular shape having a long side direction and a short side direction when viewed from above.

In some or more embodiments, the elastic member is connected at a position including a center of the piezoelectric element in the long side direction.

The area wherein the elastic member is fixed to the piezoelectric element is smaller than area of the piezoelectric element, preferably the area of the main surface, being spaced apart from the rear surface of the display panel.

In some embodiments, the elastic member may be fixed to the piezoelectric element and/or to the display panel by an adhesive.

In some embodiments the elastic element may have a thickness equal or smaller than the thickness of the piezoelectric element.

The surface of the elastic element facing the piezoelectric element is smaller than the opposing surface of the piezoelectric element.

An end of the piezoelectric element in the long side direction is not connected to the elastic member and the piezoelectric element is spaced apart from the rear surface of the display panel. There is a gap between the piezoelectric element and the rear surface of the display panel. The gap or distance might surround the position of the elastic member.

In some or more embodiments, the long side direction may be perpendicular to at least a part of ends of the display panel.

In some or more embodiments, the long side direction may be not perpendicular or diagonally or inclined to any one of ends of the display panel or to an edge of the display panel.

In some or more embodiments not covered by the scope of the claims, the piezoelectric element may have a circular shape when viewed from above and the elastic member may be connected at a position including a center of the circular shape of the piezoelectric element.

In some or more embodiments, the piezoelectric element may be vibrated so as to bend in a thickness direction thereof.

In some or more embodiments, the piezoelectric element may include a first piezoelectric layer, a first electrode, and a second electrode which are stacked on each other.

Preferably, the first electrode and the second electrode may be disposed such that the first piezoelectric layer is interposed therebetween in a thickness direction thereof.

In some or more embodiments, the piezoelectric element may include a first piezoelectric layer, a second piezoelectric layer, a first electrode, a second electrode, and a third electrode which are stacked on each other.

Preferably, the first electrode and the second electrode may be disposed such that the first piezoelectric layer is interposed therebetween in a thickness direction thereof, and the second electrode and the third electrode are disposed such that the second piezoelectric layer is interposed therebetween in a thickness direction thereof.

In some or more embodiments, polarization directions of the first piezoelectric layer and the second piezoelectric layer may be the same.

In some or more embodiments, the audio signals may have the same phase and may be input to the first electrode and the second electrode.

In some or more embodiments, the piezoelectric element may include a first piezoelectric layer, a second piezoelectric layer, a first electrode, a second electrode, a third electrode, and a fourth electrode which are stacked on each other.

Preferably, the first electrode and the second electrode may be disposed such that the first piezoelectric layer is interposed therebetween in a thickness direction thereof, and the third electrode and the fourth electrode may be disposed such that the second piezoelectric layer is interposed therebetween in a thickness direction thereof.

Preferably, polarization directions of the first piezoelectric layer and the second piezoelectric layer may be opposite.

Preferably, the audio signals having the same phase may be input to the first electrode and the third electrode.

Preferably, the audio signals having the same phase may be input to the second electrode and the fourth electrode.

In another aspect the piezoelectric element may include a first vibration part and a second vibration part extending in different directions when viewed from above and is vibrated according to input audio signals; a display panel configured to display an image; and an elastic member configured to connect a portion of the piezoelectric element and the display panel so as to transmit a vibration of the piezoelectric element to the display panel.

Preferably, the first vibration part may have a first main surface and a second main surface, a portion of the first main surface is connected to the elastic member, and a portion of the second main surface is connected to a portion of the second vibration part.

Preferably, each of the first vibration part and the second vibration part may have a rectangular shape having a long side direction and a short side rectangular shape when viewed from above, and the long side direction of the first vibration part is different from the long side direction of the second vibration part.

Preferably, the long side direction of the first vibration part may be perpendicular to the long side direction of the second vibration part.

Preferably, the elastic member may be connected at a position including a center of the first vibration part in the long side direction.

Preferably, a position including a center of the first vibration part in the long side direction may be connected to a position including a center of the second vibration part in the long side direction.

An end of each of the first vibration part and the second vibration part in the long side direction is not connected to the elastic member.

Preferably, the long side direction of each of the first vibration part and the second vibration part may be perpendicular to any one of ends of the display panel.

Preferably, the long side direction of each of the first vibration part and the second vibration part may be not perpendicular to any one of ends of the display panel.

Preferably, the first vibration part and the second vibration part may be vibrated in the same phase according to the audio signal.

Preferably, each of the first vibration part and the second vibration part may be vibrated so as to bend in a thickness direction thereof.

In another aspect the display device comprises a plurality of piezoelectric elements vibrated according to input audio signals; and a display panel configured to display an image, wherein each of the plurality of piezoelectric elements is connected to the display panel to transmit a vibration to the display panel, and a first piezoelectric element and a second piezoelectric element among the plurality of piezoelectric elements have different frequency characteristics.

Preferably, the first piezoelectric element and the second piezoelectric element may have different natural frequencies.

Preferably, the first piezoelectric element and the second piezoelectric element may have different shapes.

Preferably, a material constituting the first piezoelectric element and a material constituting the second piezoelectric element may differ in at least one of a sound speed, elastic modulus, and density.

Preferably, the display panel may have an image display surface, on which the image is displayed, and a rear surface opposite to the image display surface, and the vibration of the piezoelectric element is transmitted to the rear surface of the display panel.

Preferably, the display panel may include an organic light-emitting diode (OLED).

The accompanying drawings, which are included to provide a further understanding of the disclosure, are incorporated in and constitute a part of this specification, illustrate implementations of the disclosure and together with the description serve to explain the principles of embodiments of the disclosure.

Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. In each drawing, the same numerals are assigned to the elements having the common function, and redundant descriptions thereof will be omitted or simplified.

<FIG> is a schematic block diagram of a display device <NUM> according to a first embodiment. The display device <NUM> of the present embodiment may be, for example, used for an image output device of a computer, a television receiver, a smartphone, a game console, and the like, but the present disclosure is not particularly limited thereto.

As shown in <FIG>, the display device <NUM> includes a piezoelectric element <NUM>, a display panel <NUM>, an elastic member <NUM>, a first controller <NUM>, a second controller <NUM>, a data driving circuit <NUM>, and a gate driving circuit <NUM>. The display device <NUM> is a device that displays an image on the display panel <NUM> on the basis of input RGB data or the like and generates a sound based on an input audio signal or the like.

The display panel <NUM> includes a plurality of pixels P arranged to form a plurality of rows and a plurality of columns. The display device <NUM> may be, for example, an organic light-emitting diode (OLED) display using an OLED as a light-emitting element of the pixel P. When the display device <NUM> is capable of displaying a color image, the pixel P may be a subpixel that displays any one of a plurality of colors (for example, red (R), green (G), and blue (B)) constituting the color image.

The piezoelectric element <NUM> is an element that is displaced by an inverse piezoelectric effect when a voltage based on an input audio signal is applied. The piezoelectric element <NUM> may be, for example, an element such as a bimorph element or a unimorph element, which is flexural-displaced according to a voltage. Since the input audio signal is usually an alternating current (AC) voltage, the piezoelectric element <NUM> functions as a vibration element that vibrates according to the input audio signal.

The elastic member <NUM> is a member made of a material having elasticity. As a material of the elastic member <NUM>, a material such as rubber having an elastic modulus smaller than that of the piezoelectric element <NUM> and the display panel <NUM> is typically used. A portion of the piezoelectric element <NUM> and a portion of the display panel <NUM> are connected by the elastic member <NUM>. As a result, a vibration of the piezoelectric element <NUM> is transmitted to the display panel <NUM>, and the display panel <NUM> emits a sound based on the input audio signal.

A host system <NUM> is a system including a device or a plurality of devices for controlling the display device <NUM> by supplying an image signal (for example, RGB data), an audio signal, and timing signals (vertical synchronization signal, horizontal synchronization signal, data enable signal, and the like). The host system <NUM> may be, for example, a television system, a set-top box, a navigation system, an optical disk player, a computer, a home theater system, a video phone system, or the like. Furthermore, the display device <NUM> and the host system <NUM> may be an integrated device or may be separate devices.

The first controller <NUM> supplies a voltage to the piezoelectric element <NUM> on the basis of the audio signal and the timing signal input from the host system <NUM>.

The second controller <NUM> controls the data driving circuit <NUM> and the gate driving circuit <NUM> on the basis of the image data and the timing signals input from the host system <NUM>. The data driving circuit <NUM> supplies a data voltage or the like to the plurality of pixels P through a driving line <NUM> disposed for each column of the plurality of pixels P. The gate driving circuit <NUM> supplies control signals to the plurality of pixels P through a driving line <NUM> disposed for each row of the plurality of pixels P. Furthermore, each of the driving line <NUM> and the driving line <NUM> may be provided with a plurality of lines.

Each of the first controller <NUM>, the second controller <NUM>, the data driving circuit <NUM>, and the gate driving circuit <NUM> may be provided as one or more semiconductor integrated circuits. In addition, some or all of the first controller <NUM>, the second controller <NUM>, the data driving circuit <NUM>, and the gate driving circuit <NUM> may be integrally provided as one semiconductor integrated circuit.

<FIG> is a plan view illustrating a schematic configuration of the piezoelectric element <NUM> according to the first embodiment. <FIG> is a schematic cross-sectional view illustrating the configuration of the piezoelectric element <NUM> according to the first embodiment. The layout of the piezoelectric element <NUM> will be described with reference to <FIG> and <FIG>. In <FIG>, a rectangular outline of the display panel <NUM> schematically shows an exterior of the display panel <NUM>.

As shown in <FIG>, a surface of the display panel <NUM> on which an image is displayed is an image display surface 20a, and a surface thereof opposite to the image display surface 20a is a rear surface 20b. In this case, <FIG> is a plan view of the display panel <NUM> viewed from the rear surface 20b. <FIG> illustrates coordinate axes in which a horizontal direction of the image display surface 20a corresponds to an x-axis, a vertical direction of the image display surface 20a corresponds to a z-axis, and a depth direction of the image display surface 20a corresponds to a y-axis. Furthermore, a direction from the rear surface 20b toward the image display surface 20a is a forward direction of the y-axis. <FIG> is a cross-sectional view taken along line A-A' in <FIG>.

The piezoelectric element <NUM> has a flat plate shape. As shown in <FIG>, the piezoelectric element <NUM> has a rectangular shape having a long side direction (z direction in the drawing) and a short side direction (x direction in the drawing) when viewed from above. As a result, deformation such as bending occurs when viewed from a cross section (line A-A') in the long side direction. The piezoelectric element <NUM> is disposed such that the long side direction is perpendicular to an end or upper or lower side edge of the display panel <NUM>.

The elastic member <NUM> is connected at a position including a center of the piezoelectric element <NUM> in the long side direction. Since the center of the piezoelectric element <NUM> in the long side direction becomes a center of a vibration, the vibration is efficiently transmitted to the display panel <NUM>.

As shown in <FIG>, the piezoelectric element <NUM> has a first main surface 10a and a second main surface 10b. The first main surface 10a faces the rear surface or back side 20b of the display panel <NUM>. Preferably, there is a gap or space between the first main surface 10a and the back side or rear surface 20b of the display panel <NUM> The elastic member <NUM> connects the first main surface 10a of the piezoelectric element <NUM> and the rear surface 20b of the display panel <NUM>. As described above, the piezoelectric element <NUM> and the elastic member <NUM> are disposed on the rear surface 20b of the display panel <NUM> so as to not interfere with when a user views the image display surface 20a. So, the piezoelectric element <NUM> is fully covered or overlapped by the display panel when view from a front surface 20a of the display panel <NUM>.

The elastic member <NUM> is connected only to a portion of the first main surface 10a of the piezoelectric element <NUM>. Since both ends of the piezoelectric element <NUM> in the long side direction are in a floating state, a displacement of a flexural vibration is great in the both ends in the long side direction, and thus, the vibration of the piezoelectric element <NUM> is difficult to disrupt.

<FIG> is a cross-sectional view illustrating a structure of the piezoelectric element <NUM> according to the first embodiment in more detail. Although the direction of <FIG> is different from that of <FIG>, like <FIG> is a cross-sectional view along line A-A' of <FIG>. In addition, <FIG> schematically illustrates a connection relationship between electrodes included in the piezoelectric element <NUM> using a circuit diagram in order to describe a method of inputting an audio signal to the piezoelectric element <NUM>.

The piezoelectric element <NUM> shown in <FIG> has a structure referred to as a bimorph in which two piezoelectric layers are stacked. The piezoelectric element <NUM> includes electrodes <NUM>, <NUM> and <NUM> and piezoelectric layers <NUM> and <NUM>. The electrode <NUM> (first electrode) installed at a side closest to the display panel <NUM> is connected to the elastic member <NUM>. The electrode <NUM> and the electrode <NUM> (second electrode) are disposed such that the piezoelectric layer <NUM> (first piezoelectric layer) is interposed therebetween in a thickness direction thereof. The electrode <NUM> and the electrode <NUM> (third electrode) are disposed such that the piezoelectric layer <NUM> (second piezoelectric layer) is interposed therebetween in a thickness direction thereof. Arrows shown inside the piezoelectric layers <NUM> and <NUM> indicate polarization directions of the piezoelectric layers <NUM> and <NUM>. That is, the polarization directions of the piezoelectric layer <NUM> and the piezoelectric layer <NUM> are the same. Furthermore, lines for applying voltages to the electrodes may be connected to the electrodes <NUM>, <NUM> and <NUM> through soldering or the like, but the illustration of the lines is omitted in <FIG>.

Since a voltage applied to the piezoelectric element <NUM> is based on an audio signal, the voltage may be considered as an AC voltage according to a frequency of a sound to be generated. In <FIG>, the AC voltage is illustrated by circuit symbol V of an AC power source. One terminal of the AC power source V is connected to the electrodes <NUM> and <NUM>, and the other terminal thereof is connected to the electrode <NUM>. In other words, voltages having the same phase are applied to the electrode <NUM> and the electrode <NUM>, voltages having opposite phases are applied to the electrode <NUM> and the electrode <NUM>, and voltages having opposite phases are also applied to the electrode <NUM> and the electrode <NUM>. Accordingly, voltages in opposite directions are applied to the piezoelectric layer <NUM> and the piezoelectric layer <NUM>.

A material of the piezoelectric layers <NUM> and <NUM> is not particularly limited, but a material having excellent piezoelectricity such as lead zirconate titanate may be used because the material may increase a displacement amount. In addition, although not shown in the configuration of <FIG>, an outer periphery of the piezoelectric element <NUM> may be covered with an insulator such as a resin in order to avoid a short circuit with other members.

<FIG> are schematic views illustrating deformation of the piezoelectric element <NUM> to which a voltage is applied according to the first embodiment. As shown in <FIG>, the polarization directions of the piezoelectric layers <NUM> and <NUM> are the same direction, and voltages in opposite directions are applied to the piezoelectric layers <NUM> and <NUM>. Accordingly, expansion and contraction directions of the piezoelectric layer <NUM> and the piezoelectric layer <NUM> are opposite.

As shown in <FIG>, at a timing when the piezoelectric layer <NUM> is deformed so as to contract in a lateral direction, the piezoelectric layer <NUM> is deformed to expand in the lateral direction. Accordingly, an end of the piezoelectric element <NUM> is bent in a direction toward the display panel <NUM>. In this case, the display panel <NUM> is deformed by receiving stress in a direction toward the piezoelectric element <NUM>.

As shown in <FIG>, at a timing when the piezoelectric layer <NUM> is deformed to expand in the short side direction, the piezoelectric layer <NUM> is deformed to contract in the short side direction. Accordingly, the end of the piezoelectric element <NUM> is bent in a direction away from the display panel <NUM>. In this case, the display panel <NUM> is deformed by receiving stress in a direction away from the piezoelectric element <NUM>.

When an AC voltage based on an audio signal is applied to the piezoelectric element <NUM>, the state of <FIG> and the state of <FIG> are alternately repeated at a frequency of a sound. As described above, a vibration of the piezoelectric element <NUM> is transmitted to the display panel <NUM>, and the display panel <NUM> vibrates. Accordingly, since a sound based on an audio signal is emitted from the display panel <NUM>, the display panel <NUM> functions as a speaker.

In the present embodiment, effects obtained by connecting the portion of the piezoelectric element <NUM> and the display panel <NUM> through the elastic member <NUM> will be described in more detail with reference to <FIG> is a cross-sectional view illustrating a configuration of a piezoelectric element <NUM> according to a comparative example. <FIG> is a schematic view illustrating a vibration model according to the comparative example. <FIG> is a schematic view illustrating a vibration model according to the first embodiment.

As shown in <FIG>, in the comparative example, a front surface of the piezoelectric element <NUM> is connected directly and fully to a display panel <NUM>. Even in such a configuration, a displacement of the piezoelectric element <NUM> is transmitted to the display panel <NUM> to allow the display panel <NUM> to function as a speaker.

In the vibration model according to the comparative example, as shown in <FIG>, springs S1 and S2 are connected to both ends of a material point showing the piezoelectric element <NUM> and the display panel <NUM>. The piezoelectric element <NUM> having mass m<NUM> and the display panel <NUM> having mass m<NUM> are directly connected.

The spring S1 having a spring constant k<NUM> is connected to the piezoelectric element <NUM>, and the spring S2 having a spring constant k<NUM> is connected to the display panel <NUM>. The spring S1 is a model of elasticity of the piezoelectric element <NUM>. The spring S2 is a model of the display panel <NUM> itself or a member such as a housing for restricting the display panel <NUM>. In addition, both ends in the present vibration model are typically fixed ends.

In the vibration model of the comparative example, the piezoelectric element <NUM> and the display panel <NUM> may be replaced with one material point having mass m<NUM>+m<NUM>. When a voltage is applied to the piezoelectric element <NUM>, a force generated by the piezoelectric element <NUM> vibrates the entirety of both of the piezoelectric element <NUM> and the display panel <NUM> having the mass m<NUM>+m<NUM>. Here, since the display panel <NUM> is much larger than the piezoelectric element <NUM>, the mass m<NUM>+m<NUM> is much greater than the mass m<NUM>. Since the force generated by the piezoelectric element <NUM> is applied to an object having very large mass, acceleration of the piezoelectric element <NUM> and the display panel <NUM> due to the force is small. Accordingly, a displacement amount of the piezoelectric element <NUM> and the display panel <NUM> is not so large, and in the configuration of the comparative example, sound pressure of a sound emitted from the display panel <NUM> may not be sufficient.

On the other hand, in the vibration model according to the present embodiment, as shown in <FIG>, a spring S3 having a spring constant k3 is connected between material points showing the piezoelectric element <NUM> and the display panel <NUM>. The spring S3 is a model of elasticity of the elastic member <NUM>. The piezoelectric element <NUM> having mass m1 and the display panel <NUM> having mass m2 are connected through the spring S3.

In the vibration model of the present embodiment, the piezoelectric element <NUM> and the display panel <NUM> are independently displaced. A force generated when a voltage is applied to the piezoelectric element <NUM> vibrates the piezoelectric element <NUM> having the mass m<NUM>. Since mass of an object to which a force is applied is small as compared with the case of the comparative example, acceleration of the piezoelectric element <NUM> due to the force is greater than that of the comparative example. As a result, the piezoelectric element <NUM> resonates in a large displacement range. Since the displacement of the piezoelectric element <NUM> is gradually transmitted to the display panel <NUM> through the spring S3, the displacement is difficult to disturb due to the mass of the display panel <NUM> as in the case of the comparative example. Therefore, in the present embodiment, when compared to the case of the comparative example, the displacement can be increased, and the sound pressure can be improved.

As described above, according to the present embodiment, when the display panel <NUM> functions as a speaker, the display device <NUM>, which is capable of improving sound quality by improving sound pressure of a sound generated by the display panel <NUM>, is provided.

In addition, in the present embodiment, a vibration source is the piezoelectric element <NUM>, but a sound source is the display panel <NUM> having large mass and a low natural frequency. Therefore, when compared to a configuration in which a sound is generated directly from the piezoelectric element <NUM> or a configuration in which a sound is generated from a member having a high natural frequency such as a configuration in which the piezoelectric element <NUM> is connected to a small diaphragm separate from the display panel <NUM>, it is possible to improve sound pressure in bass.

In the present embodiment, a modified example of the layout of the piezoelectric element <NUM> according to the first embodiment will be described. Since the basic configuration of a display device <NUM>, the structure of a piezoelectric element <NUM>, and the like are the same as those of the first embodiment, descriptions thereof will be omitted.

<FIG> is a plan view illustrating a schematic configuration of the piezoelectric element <NUM> according to a second embodiment. As shown in <FIG>, in the present embodiment, the piezoelectric element <NUM> is disposed such that a long side direction of the piezoelectric element <NUM> is not perpendicular to any one of ends or side edge of a display panel <NUM>.

When the piezoelectric element <NUM> has a rectangular shape, in a distribution of vibrations generated in the display panel <NUM>, a main component of the vibration is a component directed in the long side direction of the piezoelectric element <NUM>. As in the first embodiment, when the long side direction of the piezoelectric element <NUM> is perpendicular to the end of the display panel <NUM>, a vibration generated by the piezoelectric element <NUM> and a vibration reflected from the end of the display panel <NUM> may be reinforced to generate a resonance. The resonance may cause noise. On the other hand, in the present embodiment, since the long side direction of the piezoelectric element <NUM> is not perpendicular to any one of the ends of the display panel <NUM>, a resonance due to the above-described factors is difficult to generate, thereby reducing noise.

Accordingly, according to the present embodiment, the same effect as in the first embodiment is obtained, and simultaneously, noise due to a resonance generated by reflection from an end surface of the display panel <NUM> is reduced, thereby providing the display device <NUM> having improved sound quality.

In addition, since vibration reinforcement occurs in the configuration of the first embodiment, in some cases, sound pressure improvement, frequency characteristic adjustment, or the like are possible by using the vibration reinforcement. Therefore, according to design conditions such as required characteristics and design constraints, in some cases, it is desirable to make the long side direction or extension of the piezoelectric element <NUM> in its longer dimension perpendicular to the end of the display panel <NUM> as in the first embodiment.

In the present embodiment, a modified example of the cross-sectional structure of the piezoelectric element <NUM> according to the first embodiment will be described. Since the basic configuration of a display device <NUM>, the structure of a piezoelectric element <NUM>, and the like are the same as those of the first embodiment, descriptions thereof will be omitted.

<FIG> is a cross-sectional view illustrating the structure of the piezoelectric element <NUM> according to a third embodiment. The position of a cross section is the same as that in <FIG>.

The piezoelectric element <NUM> includes four electrodes <NUM>, <NUM>, <NUM> and <NUM>, two piezoelectric layers <NUM> and <NUM>, and one insulating layer <NUM>. The electrode <NUM> (first electrode) installed at a side closest to a display panel <NUM> is connected to an elastic member <NUM>. The electrode <NUM> and the electrode <NUM> (second electrode) are disposed such that the piezoelectric layer <NUM> (first piezoelectric layer) is interposed therebetween in a thickness direction thereof. The electrode <NUM> (third electrode) and the electrode <NUM> (fourth electrode) are disposed such that the piezoelectric layer <NUM> (second piezoelectric layer) is interposed therebetween in a thickness direction thereof. The insulating layer <NUM> is disposed between the electrode <NUM> and the electrode <NUM>. The insulating layer <NUM> is a layer that secures an insulating property between the electrode <NUM> and the electrode <NUM>. Arrows shown inside the piezoelectric layers <NUM> and <NUM> indicate polarization directions of the piezoelectric layers <NUM> and <NUM>. That is, the polarization directions of the piezoelectric layer <NUM> and the piezoelectric layer <NUM> are opposite.

One terminal of a current power source V showing a voltage based on an audio signal is connected to the electrodes <NUM> and <NUM>, and the other terminal thereof is connected to the electrodes <NUM> and <NUM>. In other words, voltages having the same phase are applied to the electrode <NUM> and the electrode <NUM>. Voltages having a phase opposite to that of the voltages input to the electrode <NUM> and the electrode <NUM> are applied to the electrode <NUM> and the electrode <NUM>. Accordingly, voltages in the same direction are applied to the piezoelectric layer <NUM> and the piezoelectric layer <NUM>.

Even in the present embodiment, when one of the two piezoelectric layers contracts in a lateral direction, a flexural vibration occurs in the same manner as in the first embodiment. Therefore, even in the present embodiment, the same effect as in the case of the first embodiment can be obtained. As described above, the structure of the piezoelectric element <NUM>, the structure of the electrodes, and the like are not limited to the structures of the first embodiment, and various structures can be applied.

For example, the piezoelectric element <NUM> may have a structure referred to as a unimorph in which one piezoelectric layer, a pair of electrodes with the piezoelectric layer interposed therebetween, and a vibration plate are stacked. However, in order to improve the conversion efficiency between a voltage and a displacement, it is desirable to adopt a bimorph structure as shown in <FIG> or <FIG>. The embodiment of <FIG> may be applied to first and second embodiment. So the alignment direction of the piezoelectric element <NUM> might by perpendicular or no perpendicular or diagonal to the edges of the display panel.

In the present embodiment, a modified example of the structure of the piezoelectric element <NUM> according to the first embodiment will be described. Since the basic configuration and the like of a display device <NUM> are the same as those of the first embodiment, descriptions thereof will be omitted.

<FIG> is a plan view illustrating a schematic configuration of a piezoelectric element <NUM> according to a fourth embodiment. <FIG> is a cross-sectional view illustrating the schematic configuration of the piezoelectric element <NUM> according to the fourth embodiment. The layout of the piezoelectric element <NUM> will be described with cross-reference to <FIG>.

As shown in <FIG>, the piezoelectric element <NUM> of the present embodiment includes a first vibration part <NUM> and a second vibration part <NUM> extending in different directions when viewed from above. A configuration of the first vibration part <NUM> is the same as that of the piezoelectric element <NUM> of the first embodiment. The first vibration part <NUM> has a rectangular shape having a long side direction (z direction in the drawing) and a short side direction (x direction in the drawing) when viewed from above. The second vibration part <NUM> extends in a direction different from that of the first vibration part <NUM>. That is, the second vibration part <NUM> has a rectangular shape having a long side direction (x direction in the drawing) and a short side direction (z direction in the drawing) when viewed from above. The long side direction of the first vibration part <NUM> and the long side direction of the second vibration part <NUM> are perpendicular to each other. In addition, the long side direction of the first vibration part <NUM> and the long side direction of the second vibration part <NUM> are both perpendicular to an end of a display panel <NUM>.

As shown in <FIG>, the first vibration part <NUM> has a first main surface 12a and a second main surface 12b. An elastic member <NUM> connects the first main surface 12a of the first vibration part <NUM> and a rear surface 20b of the display panel <NUM>. The elastic member <NUM> is connected only to a portion of the first main surface 12a of the first vibration part <NUM>. As described above, the piezoelectric element <NUM> and the elastic member <NUM> are disposed on the rear surface 20b of the display panel <NUM> so as to not interfere with when a user views an image display surface 20a.

The second vibration part <NUM> is connected only to a portion of the second main surface 12b of the first vibration part <NUM>. Thus, both ends of the first vibration part <NUM> in the long side direction are in a floating state, and also, both ends of the second vibration part <NUM> in the long side direction are in a floating state. When both ends of the piezoelectric element <NUM> in the long side direction are in a floating state, a displacement of a flexural vibration is great in the both ends in the long side direction, and thus, the vibration of the piezoelectric element <NUM> is difficult to disrupt.

<FIG> is a cross-sectional view illustrating the structure of the piezoelectric element <NUM> according to the fourth embodiment in more detail. Although the direction of <FIG> is different from that of <FIG>, like <FIG>, <FIG> is a cross-sectional view along line B-B' of <FIG>. In addition, <FIG> schematically illustrates a connection relationship between electrodes included in the piezoelectric element <NUM> using a circuit diagram in order to describe a method of inputting an audio signal to the piezoelectric element <NUM>.

The piezoelectric element <NUM> shown in <FIG> has a structure in which two bimorphs are stacked. The piezoelectric element <NUM> includes the first vibration part <NUM> and the second vibration part <NUM>. The structure of the first vibration part <NUM> is the same as that of the piezoelectric element <NUM> of the first embodiment. In <FIG>, an insulating layer <NUM> is provided between the first vibration part <NUM> and the second vibration part <NUM> but is not essential.

The second vibration part <NUM> includes electrodes <NUM>, <NUM>, and <NUM> and piezoelectric layers <NUM> and <NUM>. The electrode <NUM> installed at a side closest to the first vibration part <NUM> is connected to the insulating layer <NUM>. The electrodes <NUM> and <NUM> are disposed such that the piezoelectric layer <NUM> is interposed therebetween in a thickness direction thereof. The electrodes <NUM> and <NUM> are disposed such that the piezoelectric layer <NUM> is interposed therebetween in a thickness direction thereof. Arrows shown inside the piezoelectric layers <NUM> and <NUM> indicate polarization directions of the piezoelectric layers <NUM> and <NUM>. That is, the polarization directions of the piezoelectric layer <NUM> and the piezoelectric layer <NUM> are the same.

One terminal of an AC power source V showing a voltage based on an audio signal is connected to the electrodes <NUM>, <NUM>, <NUM>, and <NUM>, and the other terminal thereof is connected to the electrodes <NUM> and <NUM>. In other words, voltages having the same phase are applied to the electrodes <NUM>, <NUM>, <NUM>, and <NUM>. Voltages having a phase opposite to that of the voltages input to the electrodes <NUM>, <NUM>, <NUM>, and <NUM> are applied to the electrodes <NUM> and <NUM>. Accordingly, voltages in the same direction are applied to the piezoelectric layers <NUM>, <NUM>, <NUM>, and <NUM>.

Even in both of the first vibration part <NUM> and the second vibration part <NUM>, when one of the two piezoelectric layers contracts in a lateral direction, the other thereof expands in the lateral direction. Accordingly, both the first vibration part <NUM> and the second vibration part <NUM> are flexural-vibrated in the same manner as in the first embodiment. Further, by setting the polarization direction and the voltage direction as described above, the first vibration part <NUM> and the second vibration part <NUM> vibrate in the same phase according to an audio signal. As a result, a vibration generated by the first vibration part <NUM> and a vibration generated by the second vibration part <NUM> are reinforced to improve vibration efficiency.

According to the present embodiment, similarly to the first embodiment, the display device <NUM>, which is capable of improving sound quality by improving sound pressure of a sound generated by the display panel <NUM>, is provided. In addition, since the piezoelectric element <NUM> of the present embodiment uses two vibration parts, sound pressure can be further improved as compared with the configuration of the first embodiment in which one vibration part is provided.

Furthermore, in the first embodiment, since only one vibration part is provided, a vibration distribution is concentrated in the long side direction of the piezoelectric element <NUM>, that is, is concentrated one-dimensionally. Therefore, a resonance is likely to occur in the display panel <NUM>, and noise caused by the resonance may be increased. On the other hand, in the present embodiment, since the piezoelectric element <NUM> includes the first vibration part <NUM> and the second vibration part <NUM> extending in different directions, a vibration distribution is two-dimensional, and it is difficult for the vibration distribution to be concentrated on a specific part. Therefore, it is difficult for a resonance to occur in the display panel <NUM>. Accordingly, in the present embodiment, noise due to a resonance in the display panel <NUM> is reduced, and the display device <NUM> having improved sound quality is provided.

In the present embodiment, a modified example of the layout of the piezoelectric element <NUM> according to the fourth embodiment will be described. Since the basic configuration of a display device <NUM>, the structure of a piezoelectric element <NUM>, and the like are the same as those of the fourth embodiment, descriptions thereof will be omitted.

<FIG> is a plan view illustrating a schematic configuration of the piezoelectric element <NUM> according to a fifth embodiment. As shown in <FIG>, in the present embodiment, the piezoelectric element <NUM> is disposed such that long side directions of a first vibration part <NUM> and a second vibration part <NUM> are not perpendicular to any one of ends of a display panel <NUM>.

As described in the description of the second embodiment, vibrations generated by the first vibration part <NUM> and the second vibration part <NUM> and vibration reflected from the end of the display panel <NUM> may be reinforced to generate a resonance. The resonance may cause noise. On the contrary, in the present embodiment, long side directions of the first vibration part <NUM> and the second vibration part <NUM> are not perpendicular to any one of the ends of the display panel <NUM>, and thus a resonance is difficult to generate, thereby reducing noise.

Therefore, according to the present embodiment, the same effect as in the fourth embodiment is obtained, and concurrently, noise, which is caused by a resonance generated due to reflection from an end surface of the display panel <NUM>, is reduced, thereby providing a display device <NUM> having improved sound quality.

In addition, in the configuration of the fourth embodiment, in some cases, a design for sound pressure improvement, frequency characteristic adjustment, or the like is possible by using vibration reinforcement. Therefore, according to design conditions such as required characteristics and design constraints, in some cases, it is desirable to make the long side direction of the piezoelectric element <NUM> perpendicular to the end of the display panel <NUM> as in the fourth embodiment.

In the present embodiment, a modified example of the structure of the piezoelectric element <NUM> according to the fourth embodiment will be described. The basic configuration and the like of a display device <NUM> are the same as those of the fourth embodiment, and thus descriptions thereof will be omitted.

<FIG> is a plan view illustrating a schematic configuration of a piezoelectric element <NUM> according to a sixth embodiment. As shown in <FIG>, the piezoelectric element <NUM> of the present embodiment includes a first vibration part <NUM>, a second vibration part <NUM>, and a third vibration part <NUM> extending in different directions when viewed from above. Since only the number of layers is increased by adding piezoelectric layers and electrodes corresponding to the third vibration part <NUM> to the structure of <FIG>, descriptions of a cross-sectional structure of the piezoelectric element <NUM> will be omitted.

In the present embodiment, similarly to the first embodiment, a display device <NUM> capable of improving sound pressure of a sound generated by the display panel <NUM> is provided. In addition, since the piezoelectric element <NUM> of the present embodiment uses three vibration parts, sound pressure can be further improved as compared with the configuration of the fourth embodiment having two vibration parts. As described above, the number of vibration parts is not limited to one or two and may be three or more. As the number of vibration parts is increased, sound pressure is improved.

In addition, in the present embodiment, a vibration distribution is more uniform two-dimensionally as compared with the configuration of the fourth embodiment. Therefore, a vibration is more difficult to generate in the display panel <NUM>. Accordingly, according to the present embodiment, noise due to a resonance in the display panel <NUM> is further reduced, and the display device <NUM> having improved sound quality is provided.

In the present embodiment, a modified example of the structure of the piezoelectric element <NUM> according to the first embodiment will be described. The basic configuration and the like of a display device <NUM> are the same as those of the first embodiment, and thus descriptions thereof will be omitted.

<FIG> is a plan view illustrating a schematic configuration of a piezoelectric element <NUM> according to a seventh embodiment. The piezoelectric element <NUM> has a flat plate shape. As shown in <FIG>, the piezoelectric element <NUM> of the present embodiment has a circular shape when viewed from above. An elastic member <NUM> is connected at a position including a center of a circle of the piezoelectric element <NUM>. Since a cross-sectional structure of the piezoelectric element <NUM> is the same as that in <FIG>, descriptions thereof will be omitted.

In the present embodiment, similarly to the first embodiment, a display device <NUM> capable of improving sound pressure of a sound generated by a display panel <NUM> is provided.

In addition, in the present embodiment, since the piezoelectric element <NUM> has the circular shape, the vibration distribution is two-dimensionally uniform. Therefore, a resonance is difficult to generate in the display panel <NUM> for the same reason as in the case of the fourth embodiment. Therefore, according to the present embodiment, noise caused by a resonance in the display panel <NUM> is reduced, thereby providing the display device <NUM> having improved sound quality.

In the present embodiment, a modified example of the structure of the piezoelectric element <NUM> according to the fifth embodiment will be described. The basic configuration and the like of a display device <NUM> are the same as those of the fifth embodiment, and thus descriptions thereof will be omitted.

<FIG> is a plan view illustrating the layout of a piezoelectric element <NUM> according to an eighth embodiment. As shown in <FIG>, in the present embodiment, a plurality of piezoelectric elements <NUM> are disposed on a display panel <NUM>. The plurality of piezoelectric elements <NUM> are arranged in a matrix in an x direction and a z direction. The piezoelectric element <NUM> is the same as that of the fifth embodiment. The plurality of piezoelectric elements <NUM> are disposed on the display panel <NUM>, and thus, sound pressure of a sound generated by the display panel <NUM> is improved as compared to the case of one piezoelectric element.

The display panel <NUM> includes a region R1 and a region R2. The one or more piezoelectric elements <NUM> (first piezoelectric element) in the region R1 and the one or more piezoelectric elements <NUM> (second piezoelectric element) in the region R2 have different frequency characteristics. For example, the frequency characteristics of the two piezoelectric elements are made to be different from each other, thereby reducing the bias of a frequency characteristic of a sound generated by the display panel <NUM>.

Since the piezoelectric element <NUM> has a natural frequency due to a shape or the like thereof, the piezoelectric element <NUM> may have a biased frequency characteristic such as sound pressure at a specific frequency being increased. When the characteristics of all the piezoelectric elements <NUM> of the display panel <NUM> are the same, the biases of the frequency characteristics of the plurality of piezoelectric elements <NUM> overlap each other, and thus the frequency characteristics of the entire display panel <NUM> may be biased. In the present embodiment, the frequency characteristic of the piezoelectric element <NUM> in the region R1 and the frequency characteristic of the piezoelectric element <NUM> in the region R2 are made to be different from each other and be leveled off, thereby reducing the bias of the frequency characteristic that may occur due to the above-described factors.

The bias of the frequency characteristic of the piezoelectric element <NUM> is mainly caused by a natural frequency of the piezoelectric element <NUM>. Therefore, it is desirable to make the natural frequency of the piezoelectric element <NUM> in the region R1 different from the natural frequency of the piezoelectric element <NUM> in the region R2. For example, by making the natural frequency of the piezoelectric element <NUM> in the region R2 lower than the natural frequency of the piezoelectric element <NUM> in the region R1, the region R1 functions as a high-pitched tone generating region, and the region R2 functions as a low-pitched tone generating region. Therefore, the display device <NUM> capable of generating bass and treble in balance is provided.

The natural frequency of the piezoelectric element <NUM> depends on the shape or material of the piezoelectric element <NUM>. Accordingly, the piezoelectric element <NUM> in the region R1 and the piezoelectric element <NUM> in the region R2 may have different natural frequencies by making shapes or sound speeds different from each other. As examples of material properties that affect a sound speed in a material, there are an elastic modulus and density. Therefore, it is desirable to use materials that differ in any one of a sound speed, elastic modulus, and density. In addition, when the piezoelectric element <NUM> in the region R1 and the piezoelectric element <NUM> in the region R2 are made to differ only in shape, a material may be used in common, which is desirable.

As described above, according to the present embodiment, the bias of a frequency characteristic of a sound generated the display panel <NUM> is reduced, thereby providing the display device <NUM> having improved sound quality.

In addition, although the piezoelectric element <NUM> of the fifth embodiment has been described as an example of the piezoelectric element <NUM> applicable to the present embodiment, the present disclosure is not limited thereto. The piezoelectric element <NUM> having any structure or layout among the first to seventh embodiments may be used, or a piezoelectric element having a different structure or layout from that described in the first to seventh embodiments may be used.

The above-described embodiments are merely several exemplary aspects to which the present disclosure can be applied, and the technical scope of the present disclosure should not be construed as being limited by the above-described embodiments. In addition, the present disclosure may be appropriately modified and changed to be implemented in various aspects without departing from the scope of the present disclosure. For example, it should be understood that within the scope defined by the appended claims, an embodiment in which some components of one embodiment are added to another embodiment, or an embodiment in which some components of one embodiment are replaced with some components of another embodiment are also an embodiment to which the present disclosure can be applied.

In the above-described embodiment, the device configuration of the display device <NUM> or the like is merely an example and is not limited to the illustrated one. For example, the display device <NUM> may be not an OLED display but may be a liquid crystal display, a cathode ray tube (CRT) display, or the like. Since it is desirable that the display device <NUM> is a display capable of efficiently transmitting a vibration from the piezoelectric element <NUM> to the display panel <NUM>, an OLED display with few cavities is particularly desirable.

Claim 1:
A display device comprising:
a piezoelectric element (<NUM>) configured to be vibrated according to input audio signals;
a display panel (<NUM>) configured to display an image; and
an elastic member (<NUM>) connected to a portion of the piezoelectric element (<NUM>) and the display panel (<NUM>) so as to transmit a vibration of the piezoelectric element (<NUM>) to the display panel (<NUM>),
wherein both ends of the piezoelectric element (<NUM>) in a long side direction are not connected to the elastic member (<NUM>) and there is a gap between the piezoelectric element (<NUM>) and a rear surface (20b) of the display panel (<NUM>), and
characterized in that both ends of the piezoelectric element (<NUM>) in the long side direction are in a floating state.