Piezoelectric device and electronic device including the same

CROSS-REFERENCE TO RELATED APPLICATION

0001This application claims priority to Korean Patent Application No. 10-2014-0107855 filed on Aug. 19, 2014 and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which are incorporated by reference in their entirety.

BACKGROUND

0002The present disclosure relates to a piezoelectric device, and more particularly, to a piezoelectric device available as a piezoelectric sound device and piezoelectric vibration device and an electronic device including the same.

0003A wireless call function itself such as voice or message transmission and reception is a main purpose in a typical mobile terminal. However, as recently a smart phone is developed, the wireless call function is merely a simple function and performance of various functions such as internet, applications, TV, navigation, and SNS becomes the main purpose.

0004Accordingly, in order to conveniently use various functions of a smart phone, as a display unit of a smart phone is enlarged and the size thereof gets larger, a user may more conveniently use a smart phone terminal with rapidly developed techniques including internet speed, operation, or pupil recognition. In addition, in the market, a smart phone terminal to which various functions are added is rapidly released due to fierce competition between companies.

0005However, as the display is enlarged and accordingly the size of the smart phone terminal gets larger in order to realize various functions of a smart phone, when wearing casual dress for taking a walk or exercising, it is inconvenient to carry and a robbery or loss case may occur. In addition, when possessing the smart phone in a bag, it is inconvenient to take the smart phone out of the bag for an incoming or outgoing call, or using a messaging function. There is also a limitation in that since vibration or a ring tone of the smart phone in the bag is not heard by a user, the user may not receive an incoming call or message.

0006In order to address that limitation, a technique enabling a device to be mounted on a human body, namely, a wearable technique is being developed. As a typical example, Korean Patent Application Laid-open Publication Nos. 10-2009-0046306 and 10-2012-0083804 respectively disclose “Band type mobile terminal” and “Mobile terminal modifiable to bracelet type”. In addition, Korean Patent Application Laid-Open Publication No. 10-2013-0054309 also discloses “Human body-mounted auxiliary mobile device assembly”. Such a typical technique enables the wearable device, namely, an auxiliary mobile device to be carried in a watch, or necklace type.

0007The auxiliary mobile device notifies a user of message reception with a notification sound or vibration. To this end, a speaker for generating the notification sound and an actuator for generating vibration are required to be mounted in the auxiliary mobile device. In other words, both the speaker and actuator are required to be mounted in the auxiliary mobile device. However, since the speaker and actuator are all mounted, an area occupied by them in the auxiliary device becomes large and accordingly there is a limitation in making the size of the auxiliary mobile device small.

SUMMARY

0008The present disclosure provides a piezoelectric device available as at least any one of a piezoelectric sound device and piezoelectric vibration device.

0009The present disclosure also provides a piezoelectric device capable of generating a sound and vibration by being mounted in an electronic device and operating as at least any one of the piezoelectric sound device and piezoelectric vibration device according to an applied signal.

0010The present disclosure also provides an electronic device including a piezoelectric device available as at least any one of the piezoelectric sound device and piezoelectric vibration device mounted therein to reduce an area occupied by the piezoelectric device.

0011In accordance with an exemplary embodiment, a piezoelectric device includes at least two piezoelectric plates configured to include at two contact points, wherein the at least two piezoelectric plates include at least two resonant frequencies.

0012At least one intermediate plate may be disposed between the at least two piezoelectric plates and the at least two piezoelectric plates may be separated by a predetermined interval.

0013The at least two piezoelectric plates may include at least two shapes.

0014At least one first piezoelectric plate may include one surface, another surface, and side surfaces therebetween.

0015The at least one intermediate plate may be provided in a frame shape including an empty inner part.

0016At least one second piezoelectric plate may include a support plate including a shape of the intermediate plate and at least one extension plate formed from at least one area of the support plate to an inner area of the support plate.

0017One end portion of the extension unit contacts one surface of the support plate.

0018The extension plate may include a protrusion part formed on a predetermined area thereof and the protrusion part may be connected to at least one surface of the support plate.

0019The piezoelectric device may further include a dummy plate disposed on a predetermined area on the support plate and the extension plate is connected to a top surface or side surface of the dummy plate.

0020The piezoelectric device may further include a load disposed on at least one area on the extension plate.

0021The piezoelectric device may further include a load disposed on at least one area on the support plate.

0022The piezoelectric device may further include a vibration plate disposed between at least one area on the extension plate and at least one area on the support plate.

0023The piezoelectric device may operate as at least any one of a piezoelectric sound device or a piezoelectric vibration device according to a signal applied to the at least two piezoelectric plates.

0024The signal may be applied to the extension plate of the second piezoelectric plate or to the extension and support plates.

0025A signal is applied to the intermediate plate to vibrate the intermediate plate.

0026In accordance with another exemplary embodiment, an electronic device includes a piezoelectric device configured to include at least two piezoelectric plates configured to include at two contact points, wherein the at least two piezoelectric plates include at least two resonant frequencies and the piezoelectric device operates as at least any one of a piezoelectric sound device and a piezoelectric vibration device according to a signal applied to the at least two piezoelectric devices.

0027The electronic device may be separated from a mobile terminal body to perform an auxiliary function of the mobile terminal, and is wearable.

0028At least one intermediate plate may be disposed between the at least two piezoelectric plates and the at least two piezoelectric plates are separated by a predetermined interval.

0029The at least two piezoelectric plates may include at least two shapes.

0030At least a first piezoelectric plate may be provided in a plate shape, the at least one intermediate plate may be provided in a frame shape including an empty inner part.

0031At least one second piezoelectric plate includes a support plate including a shape of the intermediate plate and at least one extension plate formed from at least one area from the support plate to an inner area of the support plate.

0032The electronic device may further include a load disposed on at least one area on the extension plate.

0033The electronic device may further include a load disposed on at least one area on the support plate.

0034The electronic device may further include a vibration plate provided between at least one area of the extension plate and at least one area of the support plate.

0035A signal may be applied to at least any one of the extension plate and support plate of the second piezoelectric plate.

0036A signal may be further applied to the intermediate plate to vibrate the intermediate plate.

BRIEF DESCRIPTION OF THE DRAWINGS

0037Exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which:

0038<figref idref="DRAWINGS">FIG. 1</figref> is an exploded perspective view of a piezoelectric device according to an exemplary embodiment;

0039<figref idref="DRAWINGS">FIGS. 2 to 4</figref> are exploded perspective views of piezoelectric devices according to other exemplary embodiments;

0040<figref idref="DRAWINGS">FIGS. 5A to 9D</figref> are plan views of piezoelectric devices according to various modification examples of an embodiment;

0041<figref idref="DRAWINGS">FIGS. 10A to 12B</figref> are graphs representing impedance and sound pressure characteristics of each part of an piezoelectric device according to an exemplary embodiment;

0042<figref idref="DRAWINGS">FIGS. 13A to 15B</figref> are graphs representing impedance and sound pressure characteristics of a piezoelectric device according to a signal application scheme according to an exemplary embodiment;

0043<figref idref="DRAWINGS">FIG. 16</figref> is a comparison graph of sound pressure characteristic of a piezoelectric device according to a signal application scheme; and

0044<figref idref="DRAWINGS">FIG. 17</figref> is a vibration characteristic graph of a piezoelectric device according to an exemplary embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

0045Hereinafter, specific embodiments will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

0046<figref idref="DRAWINGS">FIG. 1</figref> is an exploded perspective view of a piezoelectric device according to an exemplary embodiment.

0047Referring to <figref idref="DRAWINGS">FIG. 1</figref>, a piezoelectric device according to an exemplary embodiment may include a first piezoelectric plate <b>100</b> having a predetermined plate form, an intermediate plate <b>200</b> disposed to contact an edge of one surface of the first piezoelectric plate <b>100</b>, a second piezoelectric plate <b>300</b> disposed to make a contact on the intermediate plate <b>200</b> and having a different resonant frequency from the first piezoelectric plate <b>100</b>. In other words, in the piezoelectric device according to an embodiment, the intermediate plate <b>200</b> is disposed on an edge of the first and second piezoelectric plates <b>100</b> and <b>300</b> having different resonant frequencies and the central portions of the first and second piezoelectric plates <b>100</b> and <b>300</b> are separated by a predetermined interval with the intermediate plate <b>200</b> disposed therebetween. In addition, the first and second piezoelectric plates <b>100</b> and <b>300</b> may be differed in shape.

0048The first piezoelectric plate <b>100</b> may be provided to have a predetermined thickness and, for example, in a rectangular plate shape. In other words, in the piezoelectric device <b>100</b>, one surface and the other surface opposite to each other are provided and four side surfaces may be provided along edges of the top and bottom surfaces. The first piezoelectric plate <b>100</b> may be provided in various forms such as a square, ellipse, or polygon as well as the rectangle. The first piezoelectric plate <b>100</b> may include a substrate and a piezoelectric layer in which the substrate is formed on at least one surface. For example, the first piezoelectric plate <b>100</b> may be formed in a bimorph type in which piezoelectric layers are formed on both sides of a substrate, or in a unimorph type in which a piezoelectric layer is formed on one side of a substrate. The piezoelectric layer may be formed by stacking at least one layer, or a plurality of layers. In addition, electrodes may be respectively formed on the top and bottom portions of the piezoelectric layer. In other words, a plurality of piezoelectric layers and a plurality of electrodes may be alternately stacked to realize the first piezoelectric plate <b>100</b>. The first piezoelectric plate <b>100</b> may be manufactured by forming electrodes in a frame shape on the top portion of the piezoelectric layer to stack a plurality of layers on which the electrodes are formed in this shape and then removing predetermined areas of the piezoelectric layers on which the electrodes are not formed. Here, the piezoelectric layer may be formed of a piezoelectric material, for example, PZT (Pb, Zr, Ti), NKN (Na, K, Nb), or BNT (Bi, Na, Ti)-based material. In addition, the piezoelectric layer may be polarized in different directions or an identical direction and stacked. In other words, when a plurality of piezoelectric layers are formed on one surface of a substrate, polarizations of each of the plurality of piezoelectric layers may be alternately formed in different directions or in an identical direction. Furthermore, the substrate may use a material, for example, a metal or plastics, having a characteristic that vibration may be generated while a structure in which the piezoelectric layers are stacked may be maintained. However, the first piezoelectric plate <b>100</b> may not employ a substrate of a different material from that of the piezoelectric layer. In other words, in the first piezoelectric plate <b>100</b>, an unpolarized piezoelectric layer may be provided at the central portion and a plurality of piezoelectric layers polarized in different directions may be stacked at the top and bottom portions thereof. Furthermore, an electrode pattern (not illustrated) to which a driving signal is applied may be formed on one surface of the first piezoelectric plate <b>100</b>, for example, a surface facing the second piezoelectric plate <b>300</b>. At least two electrode patterns may be formed separately from each other and connected to an electronic device, for example, an auxiliary mobile device through connection to connection terminals (not illustrated). The first piezoelectric plate <b>100</b> may be driven as a piezoelectric sound device or a piezoelectric vibration device according to a signal applied through an electronic device, namely, AC power. For example, power having a polarity identical to a polarization direction may be applied to drive the first piezoelectric plate <b>100</b> as the piezoelectric vibration device, or power having a polarity opposite to the polarization direction may be applied to drive as the piezoelectric sound device.

0049The intermediate plate <b>200</b> contacts an edge of one surface of the first piezoelectric plate <b>100</b>. In other words, the intermediate plate <b>200</b> is provided in an approximately rectangular frame shape having a predetermined width and an empty inner part in order to correspond to the edge of the first piezoelectric plate <b>100</b>. The intermediate plate <b>200</b> may be provided in various forms such as a square, ellipse, or polygon as well as the rectangular frame shape. At this point, the intermediate plate <b>200</b> may be provided in an identical shape to or in a different shape from that of the first and second piezoelectric plates <b>200</b>. For example, the first and second piezoelectric plates <b>100</b> may be provided in rectangle and the intermediate plate <b>200</b> may be prepared in square. Furthermore, the intermediate plate <b>200</b> may be provided in a smaller size than that of the first piezoelectric plate <b>100</b>. In other words, the intermediate plate <b>200</b> may contact from an edge into the inside of the first piezoelectric plate <b>100</b> and accordingly the edge of the first piezoelectric plate <b>100</b> may be exposed to the outside of the intermediate plate <b>200</b>. In addition, the intermediate plate <b>200</b> may have the thickness identical to or different from the first piezoelectric plate <b>100</b>. The intermediate plate <b>200</b> may include a substrate and at least one piezoelectric layer formed on at least one surface of the substrate. In other words, the intermediate plate <b>200</b> may be formed in an identical stacked structure to that of the first piezoelectric plate <b>100</b>. In addition, electrodes may be respectively formed on the top and bottom portions of the piezoelectric layer. In other words, a plurality of piezoelectric layers and a plurality of electrodes may be alternately stacked to realize the intermediate piezoelectric plate <b>200</b>. Here, the piezoelectric layer may be polarized in different directions or an identical direction and stacked. In other words, when a plurality of piezoelectric layers are formed on at least one surface of a substrate, polarizations of each of the plurality of piezoelectric layers may be alternately formed in different directions or in an identical direction. At this point, a predetermined electrode pattern may be formed for signal application at a predetermined area. Accordingly, the intermediate plate <b>200</b> may generate vibration by a predetermined signal and accordingly be functioned as a piezoelectric sound device or a piezoelectric vibration device. However, the intermediate plate <b>200</b> may not receive a signal and then not generate the vibration, and to this end, an electrode may be formed between the piezoelectric layers and the piezoelectric layer may not be polarized.

0050The second piezoelectric plate <b>300</b> may contact the intermediate plate <b>200</b> and be provided thereon. In other words, the central portion of the second piezoelectric plate <b>300</b> may be separated from the central portion of the first piezoelectric plate <b>100</b> by a predetermined interval with the intermediate plate <b>200</b> disposed therebetween. At this point, the interval between the first and second piezoelectric plates <b>100</b> and <b>300</b> may be adjusted according to the thickness of the intermediate plate <b>200</b>. The second piezoelectric plate <b>300</b> may be formed in a different shape from that of the first piezoelectric plate <b>100</b> and have a different resonant frequency from the first piezoelectric plate <b>100</b>. For example, the second piezoelectric plate <b>300</b> may include a support plate <b>310</b> having an identical shape to the intermediate layer <b>200</b> and an extended plate <b>320</b> contacting at least one area of the support plate <b>310</b> and disposed at an area inside the support plate <b>310</b>. In other words, the second piezoelectric plate <b>300</b> may include the support plate <b>310</b> having two long sides and two short sides opposite to each other in an approximately rectangular frame shape and the extension plate <b>320</b> contacting at least one area of the support plate <b>310</b> and disposed inside the support plate <b>310</b>. Here, the thickness of the extension plate <b>320</b> may be identical to that of the support plate <b>310</b>. In other words, the second piezoelectric plate <b>300</b> may be realized by removing an area between the extension plate <b>320</b> and the support plate <b>310</b> on the approximately rectangular plate. The thickness of the extension plate <b>320</b> may be thinner than that of the support plate <b>310</b>. In other words, after the support plate <b>310</b> is formed in an identical shape to that of the intermediate plate <b>200</b> on the approximately rectangle plate, the extension plate <b>320</b> may be disposed inside the support plate <b>310</b> by bonding the extension plate <b>320</b> to at least one area on the support plate <b>310</b>. Here, an area of a space between the support plate <b>310</b> and the extension plate <b>320</b> and an area of the extension plate <b>320</b> may have a ratio of 5:1 to 1:5. The resonant frequency of the second piezoelectric plate <b>300</b> may be adjusted by adjusting a ratio of an area of a space between the support plate <b>310</b> and the extension plate <b>320</b> and an area of the extension plate <b>320</b>. The second piezoelectric plate <b>300</b> may be provided in various forms such as a square, ellipse, or polygon as well as the rectangle. In other words, the second piezoelectric plate <b>300</b> may be disposed in an identical shape as those of the first piezoelectric plate <b>100</b> and the intermediate layer <b>200</b>. However, the second piezoelectric plate <b>300</b> may have a different shape from those of the first piezoelectric plate <b>100</b> and the intermediate layer <b>200</b>. In addition, the second piezoelectric plate <b>300</b> may have the identical thickness to or a different thickness from those of the first piezoelectric plate <b>100</b> and the intermediate layer <b>200</b>. For example, the first and second piezoelectric plates <b>100</b> and <b>300</b> may be formed to have the identical thickness and the intermediate plate <b>200</b> may be formed to have the different thickness from those of them. Furthermore, the second piezoelectric plate <b>300</b> may include a substrate and a piezoelectric layer formed on at least one surface of the substrate. In other words, the support plate <b>310</b> and the extension plate <b>320</b> may include a substrate and a piezoelectric layer formed on at least one surface of the substrate. For example, the second piezoelectric plate <b>300</b> may be formed in a bimorph type in which piezoelectric layers are formed on both sides of the substrate, or in a unimorph type in which a piezoelectric layer is formed on one side of the substrate. The piezoelectric layer may be formed by stacking at least one layer, or a plurality of layers. In addition, electrodes may be respectively formed on the top and bottom portions of the piezoelectric layer. In other words, a plurality of piezoelectric layers and a plurality of electrodes may be stacked to realize the second piezoelectric plate <b>300</b>. The second piezoelectric plate <b>300</b> may be manufactured by forming electrodes in a shape of the support plate <b>310</b> and extension plate <b>320</b> on the top portion of the piezoelectric layer, stacking a plurality of layers on which the electrodes are formed in this shape and then removing predetermined areas of the piezoelectric layers on which the electrodes are not formed. The second piezoelectric plate <b>300</b> may be manufactured by bonding the extension plate <b>320</b> in which a plurality of piezoelectric layers, each of which has an electrode therein, are stacked to a predetermined area of the support plate <b>310</b> in which a plurality of piezoelectric plates, each of which has an electrode thereon, are stacked. In addition, the piezoelectric layers may be polarized in different directions or an identical direction and stacked. In other words, when a plurality of piezoelectric layers are formed on one surface of the substrate, polarization of each of the plurality of piezoelectric layers may be alternately formed in different directions or in an identical direction. Furthermore, the substrate may use a material, for example, a metal or plastics, having a characteristic that vibration may be generated while a structure in which the piezoelectric layers are stacked may be maintained However, the second piezoelectric plate <b>300</b> may not employ a substrate having a different material from the piezoelectric layer. In other words, in the second piezoelectric plate <b>300</b>, an unpolarized piezoelectric layer may be provided at the central portion and a plurality of piezoelectric layers polarized in different directions may be stacked at the top and bottom portions thereof. Furthermore, an electrode pattern (not illustrated) to which a driving signal is applied may be formed on a predetermined area of the second piezoelectric plate <b>300</b>, for example, on the top surface of the extension plate <b>320</b>. At least two electrode patterns may be formed separately from each other and connected to an electronic device, for example, an auxiliary mobile device through connection to connection terminals (not illustrated). In addition, an electrode pattern (not illustrated) may be formed on a predetermined area of the support plate <b>310</b> as well as the extension plate <b>320</b>, and connected to an electronic device, for example, an auxiliary mobile device through connection to connection terminals (not illustrated). The second piezoelectric plate <b>300</b> like this may be driven as a piezoelectric sound device or a piezoelectric vibration device according to a signal applied through an electronic device, namely, AC power. For example, power having a polarity identical to a polarization direction may be applied to drive the second piezoelectric plate <b>300</b> as the piezoelectric vibration device, or power having a polarity opposite to the polarization direction may be applied to drive as the piezoelectric sound device.

0051As described above, a piezoelectric device according to an embodiment includes a first piezoelectric plate <b>100</b>, an intermediate plate <b>200</b> formed at an edge of one surface of the first piezoelectric plate <b>100</b> to have an approximate frame shape, and a second piezoelectric plate <b>300</b> including a support plate <b>310</b> disposed on the intermediate plate <b>200</b> to have an approximate frame shape, and an extension plate <b>320</b> contacting one area of the support plate <b>310</b> and disposed in the support plate <b>310</b>. In other words, a piezoelectric device may include at least two piezoelectric plates <b>100</b> and <b>300</b> having at least two contact points. Here, the intermediate plate <b>200</b> contacts edges of the first and second piezoelectric plates <b>100</b> and <b>300</b> to operate as contact points of the first and second piezoelectric plates <b>100</b> and <b>300</b>, and since the second piezoelectric plate <b>300</b> includes the support plate <b>310</b> and the extension plate <b>320</b>, a part of the support plate <b>310</b> operates as a contact point of the extension plate <b>320</b>. Accordingly, since a piezoelectric device of an embodiment has at least two contact points, the at least two piezoelectric plates <b>100</b> and <b>300</b> may have different resonant frequencies. In addition, in a piezoelectric device of an embodiment, the at least two piezoelectric plates <b>100</b> and <b>300</b> may have different shapes. Such a piezoelectric device is separated from an electronic device, for example, a smart phone to be disposed in an auxiliary mobile device performing an auxiliary function of the smart phone, namely, a wearable device mountable on a body and may operate as at least any one of a piezoelectric speaker and a piezoelectric actuator according to a signal provided from the auxiliary mobile device. In other words, the first and second piezoelectric plates <b>100</b> and <b>300</b> may selectively operate as a piezoelectric sound device or a piezoelectric vibration device at the same time, or any one of the first and second piezoelectric plates <b>100</b> and <b>300</b> may operate as the piezoelectric sound device and the other may operate as the piezoelectric vibration device. Typically, a piezoelectric actuator oscillates at a frequency of 300 Hz to generate vibration and a piezoelectric speaker oscillates at a frequency of 500 Hz or higher to output a sound. However, a piezoelectric device of an embodiment operates at a frequency of 300 Hz to 1.2 kHz to output a vibration or sound. In other words, a piezoelectric device of an embodiment is a complex device including the first and second piezoelectric plates <b>100</b> and <b>300</b> having different shapes and resonant frequencies, and applied to an electronic device such as an auxiliary mobile device to generate the sound and vibration. Accordingly, a piezoelectric device of an embodiment may function as the piezoelectric sound device or the piezoelectric vibration device, and when applied to an electronic device such as an auxiliary mobile device, may reduce an occupied area in the auxiliary mobile device in comparison to a typical device that both of sound and vibration devices are necessary. In addition, when a piezoelectric device of an embodiment is used as a piezoelectric sound device, medium and high frequency band characteristics as well as low frequency characteristic may be improved. In other words, characteristic of a frequency of 1 kHz or lower and characteristic of a frequency higher than 1 kHz may be improved.

0052<figref idref="DRAWINGS">FIGS. 2 to 4</figref> are exploded perspective views of piezoelectric devices according to other exemplary embodiments.

0053Referring to <figref idref="DRAWINGS">FIG. 2</figref>, a piezoelectric device according to another embodiment includes a first piezoelectric plate <b>100</b> having an approximately rectangular plate shape, an intermediate plate <b>200</b> formed at an edge of one surface of the first piezoelectric plate <b>100</b> to have an approximately rectangular frame shape, and a second piezoelectric plate <b>300</b> including a support plate <b>310</b> disposed on the intermediate plate <b>200</b> to have an identical shape to the intermediate plate <b>200</b> and an extension plate <b>320</b> contacting two areas of the support plate <b>310</b> and disposed in the support plate <b>310</b>. In other words, the extension plate <b>320</b> of the second piezoelectric plate <b>300</b> is disposed in a space formed by the support plate <b>310</b> and two protrusion parts <b>322</b> are formed from the central portion of a long side of the extension plate <b>320</b> and contact long sides of the support plate <b>310</b>. Compared to the embodiment of <figref idref="DRAWINGS">FIG. 1</figref>, while one short side of the extension unit <b>320</b> contacts the support plate <b>310</b> in the embodiment of <figref idref="DRAWINGS">FIG. 1</figref>, two long side areas of the extension plate <b>320</b> contact the support plate <b>310</b> in the other embodiment of <figref idref="DRAWINGS">FIG. 2</figref>.

0054Referring to <figref idref="DRAWINGS">FIG. 3</figref>, a piezoelectric device according to still another embodiment includes a first piezoelectric plate <b>100</b> having an approximately rectangular plate shape, an intermediate plate <b>200</b> formed at an edge of one surface of the first piezoelectric plate <b>100</b> to have an approximately rectangular frame shape, and a second piezoelectric plate <b>300</b> including a support plate <b>310</b> disposed on the intermediate plate <b>200</b> to have an identical shape to the intermediate plate <b>200</b>, and first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>contacting one area of the support plate <b>310</b> and disposed in the support plate <b>310</b>. In other words, the first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>of the second piezoelectric plate <b>300</b> are disposed to be separated from each other at the long side central portions of the support plate <b>310</b>and two area protrusion units <b>322</b><i>a </i>and <b>322</b><i>b </i>are formed from areas corresponding to the long side central portions of the support plate <b>310</b> to contact the support plate <b>310</b>. Compared to the other embodiment of <figref idref="DRAWINGS">FIG. 2</figref>, in the still other embodiment of <figref idref="DRAWINGS">FIG. 3</figref>, the central portion of the area contacting the support plate <b>310</b> is cut to form first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b. </i>

0055Referring to <figref idref="DRAWINGS">FIG. 4</figref>, a piezoelectric device according to still another embodiment includes a first piezoelectric plate <b>100</b> having an approximately circular plate shape, an intermediate plate <b>200</b> formed at an edge of a side of the first piezoelectric plate <b>100</b> to have an approximately circular frame shape, and a second piezoelectric plate <b>300</b> including a support plate <b>310</b> disposed on the intermediate plate <b>200</b> to have an identical shape to the intermediate plate <b>200</b> and an extension plate <b>320</b> contacting one area of the support plate <b>310</b> and disposed in the support plate <b>310</b>. In other words, a piezoelectric device of an embodiment may be provided in a circular shape. In addition, in the second piezoelectric plate <b>300</b>, the extension plate <b>320</b> is provided in a circular shape and one area of the extension plate <b>320</b> is extended to contact a predetermined area of the support plate <b>310</b>.

0056Furthermore, in the piezoelectric device of an embodiment, the shape of the second piezoelectric plate <b>300</b> may be diversely changed and accordingly various frequency characteristics can be obtained. <figref idref="DRAWINGS">FIGS. 5A to 5D</figref> illustrate the second piezoelectric plates according to various modification examples of an embodiment.

0057As illustrated in <figref idref="DRAWINGS">FIG. 5A</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape and an extension plate <b>320</b> contacting one short side of the support plate <b>310</b> and disposed in the support plate <b>310</b> in a long side direction of the support plate <b>310</b>. In addition, at least two electrode patterns <b>321</b> and <b>322</b> may be formed on the top surface of the extension plate <b>320</b> and AC power having different polarities may be applied to the two electrode pattern <b>321</b> and <b>322</b>.

0058As illustrated in <figref idref="DRAWINGS">FIG. 5B</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape, a dummy plate <b>315</b> disposed between predetermined areas of two opposite long sides of the support plate <b>310</b>, and an extension plate <b>320</b> contacting the top surface of the dummy plate <b>315</b> and disposed in a long side direction of the support plate <b>310</b>. The dummy plate <b>315</b> may be formed to have a predetermined width between, for example, central portions of two opposite long sides. Here, the dummy plate <b>315</b> may be formed to have an identical width to, or a wider or narrower width than the support plate <b>310</b>. In addition, the central portion of the extension plate <b>320</b> may make a contact on the dummy plate <b>315</b>. In other words, the central portion of the extension unit <b>320</b> makes a contact on the dummy plate <b>315</b> to be disposed in a space formed by the support plate <b>310</b> in a long side direction of the support plate <b>310</b>. In addition, at least two electrode patterns <b>321</b> and <b>322</b> may be formed on the top surface of the extension plate <b>320</b> and AC power having different polarities may be applied to the two electrode pattern <b>321</b> and <b>322</b>.

0059As illustrated in <figref idref="DRAWINGS">FIG. 5C</figref>, the second piezoelectric plate <b>300</b> may include a support plate <b>310</b> having an approximately rectangular frame shape, a dummy plate <b>315</b> disposed between predetermined areas, for example, central portions, of two opposite long sides of the support plate <b>310</b>, and first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>disposed in opposite directions from the dummy plates <b>315</b>. In other words, the first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>may be separated and contact two side surfaces or the top surface of the dummy plate <b>315</b>. In addition, at least two electrode patterns <b>321</b><i>a </i>and <b>322</b><i>a </i>may be formed on the top surface of the first extension plate <b>320</b><i>a </i>and at least two electrode patterns <b>321</b><i>b </i>and <b>322</b><i>b </i>may also be formed on the top surface of the second extension plate <b>320</b><i>b. </i>AC power having different polarities may be applied to each electrode pattern.

0060As illustrated in <figref idref="DRAWINGS">FIG. 5D</figref>, the second piezoelectric plate <b>300</b> may include a support plate <b>310</b> having an approximately rectangular frame shape, and first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>extended along a long side direction of the support plate <b>310</b> from two opposite short sides of the support plate <b>310</b>. In other words, the first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>are formed in a long side direction of the support plate <b>310</b> from the top surface of the opposite two short sides or side surfaces of the support plated <b>310</b> and disposed to be separated by a predetermined interval at the central area inside the support plate <b>310</b>. Here, at least two electrode patterns <b>321</b><i>a </i>and <b>322</b><i>a </i>may be formed on the top surface of the first extension plate <b>320</b><i>a </i>and at least two electrode patterns <b>321</b><i>b </i>and <b>322</b><i>b </i>may also be formed on the top surface of the second extension plate <b>320</b><i>b. </i>AC power having different polarities may be applied to each electrode pattern.

0061Furthermore, in a piezoelectric vibration device of an embodiment, AC power may also be applied to the support plate <b>310</b> as well as the extension plate <b>320</b> of the second piezoelectric plate <b>300</b>, and accordingly frequency characteristic may be diversely changed. <figref idref="DRAWINGS">FIGS. 6A to 6D</figref> illustrate the second piezoelectric plate <b>300</b> according to various modification examples according to an embodiment.

0062As illustrated in <figref idref="DRAWINGS">FIG. 6A</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape and an extension plate <b>320</b> contacting one short side of the support plate <b>310</b> and disposed in the support plate <b>310</b> in a long side direction of the support plate <b>310</b>. In addition, at least two electrode patterns <b>311</b> and <b>312</b> are formed on the top surface of the support plate <b>310</b> and at least two electrode patterns <b>321</b> and <b>322</b> are formed on the top surface of the extension plate <b>320</b>. AC power having different polarities may be applied to each of the electrode patterns <b>311</b> and <b>312</b> of the support plate <b>310</b> and the electrode patterns <b>321</b> and <b>322</b> of the extension plate <b>320</b>.

0063As illustrated in <figref idref="DRAWINGS">FIG. 6B</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape, a dummy plate <b>315</b> disposed between the central portions of two opposite long sides of the support plate <b>310</b>, and an extension plate <b>320</b> making a contact on the dummy plate <b>315</b> and disposed in a long side direction of the support plate <b>310</b>. In addition, at least two electrode patterns <b>311</b> and <b>312</b> are formed on the top surface of the support plate <b>310</b> and at least two electrode patterns <b>321</b> and <b>322</b> are formed on the top surface of the extension plate <b>320</b>. AC power having different polarities may be applied to each of the electrode patterns <b>311</b> and <b>312</b> of the support plate <b>310</b> and the electrode patterns <b>321</b> and <b>322</b> of the extension plate <b>320</b>.

0064As illustrated in <figref idref="DRAWINGS">FIG. 6C</figref>, the second piezoelectric plate <b>300</b> may include a support plate <b>310</b> having an approximately rectangular frame shape, a dummy plate <b>315</b> disposed between predetermined areas, for example, the central portions, of two opposite long sides of the support plate <b>310</b>, and first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>disposed in opposite directions from the dummy plates <b>315</b>. In other words, the first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>may be separated and contact two side surfaces or the top surface of the dummy plate <b>315</b> in a long side direction of the support plate <b>310</b>. In addition, at least two electrode patterns <b>321</b><i>a </i>and <b>322</b><i>a </i>may be formed on the top surface of the first extension plate <b>320</b><i>a </i>and at least two electrode patterns <b>321</b><i>b </i>and <b>322</b><i>b </i>may also be formed on the top surface of the second extension plate <b>320</b><i>b. </i>AC power having different polarities may be applied to each electrode pattern. In addition, at least two electrode patterns <b>311</b> and <b>312</b> may be formed on the top surface of the support plate <b>310</b> and AC power having different polarities may be applied thereto.

0065As illustrated in <figref idref="DRAWINGS">FIG. 6D</figref>, the second piezoelectric plate <b>300</b> may include a support plate <b>310</b> having an approximately rectangular frame shape, and first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>extended along a long side direction of the support plate <b>310</b> from two opposite short sides of the support plate <b>310</b>. In other words, the first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>are formed in a long side direction of the support plate <b>310</b> from the top surface of the opposite two short sides or side surfaces of the support plated <b>310</b> and disposed to be separated by a predetermined interval at the central area inside the support plate <b>310</b>. Here, at least two electrode patterns <b>321</b><i>a </i>and <b>322</b><i>a </i>may be formed on the top surface of the first extension plate <b>320</b><i>a </i>and at least two electrode patterns <b>321</b><i>b </i>and <b>322</b><i>b </i>may also be formed on the top surface of the second extension plate <b>320</b><i>b. </i>AC power having different polarities may be applied to each electrode pattern. In addition, at least two electrode patterns <b>311</b> and <b>312</b> may be formed on the top surface of the support plate <b>310</b> and AC power having different polarities may be applied thereto.

0066In addition, in a piezoelectric device of an embodiment, a load is disposed on at least one area of the second piezoelectric plate <b>300</b> to increase a vibration force and accordingly frequency characteristic may be diversely changed. Weight, position, and form of the load may be diversely modified and accordingly various vibration forces may be realized. <figref idref="DRAWINGS">FIGS. 7A to 7D</figref> illustrate the second piezoelectric plate <b>300</b> according to various modification examples according to an embodiment.

0067As illustrated in <figref idref="DRAWINGS">FIG. 7A</figref>, the second piezoelectric plate <b>300</b> may include a support plate <b>310</b> having an approximately rectangular frame shape and an extension plate <b>320</b> contacting a predetermined area of one short side of the support plate <b>310</b> and disposed in a long side direction of the support plate <b>310</b>, and a load <b>350</b> may be disposed on one end portion of the extension plate <b>320</b>, which does not contact the support plate <b>310</b>. In addition, at least two electrode patterns <b>320</b> and <b>321</b> may be formed on the top surface of the extension plate <b>320</b> and AC power having different polarities may be applied thereto.

0068As illustrated in <figref idref="DRAWINGS">FIG. 7B</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape and having a dummy plate <b>315</b> formed between one long side and the other long side opposite to each other, an extension plate <b>320</b> making a contact on the dummy plate <b>135</b> and disposed in a long side direction of the support plate <b>310</b>, and loads <b>350</b><i>a </i>and <b>350</b><i>b </i>respectively disposed on two opposite end portions of the extension plate <b>320</b>. In other words, the load <b>350</b><i>a </i>may be disposed on an area to which AC power is applied.

0069As illustrated in <figref idref="DRAWINGS">FIG. 7C</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape and having a dummy plate <b>315</b> formed between one long side and the other long side opposite to each other, first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>contacting two side surfaces of the dummy plate <b>315</b> and disposed in a long side direction of the support plate <b>310</b>, and loads <b>350</b><i>a </i>and <b>350</b><i>b </i>disposed on two opposite end portions of the first and second extension plate <b>320</b><i>a </i>and <b>320</b><i>b, </i>which do not contact the dummy plate <b>315</b>. In other words, the loads <b>350</b><i>a </i>and <b>350</b><i>b </i>may be disposed on areas of the first and second <b>320</b><i>a </i>and <b>320</b><i>b, </i>to which AC power is applied.

0070As illustrated in <figref idref="DRAWINGS">FIG. 7D</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape, first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>formed in a long side direction of the support plate <b>310</b> from two opposite short sides of the support plate <b>310</b> and separated by a predetermined interval at the central area inside the support plate <b>310</b>, and loads <b>350</b><i>a </i>and <b>350</b><i>b </i>formed on end portions of the first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b. </i>In other words, the loads <b>350</b><i>a </i>and <b>350</b><i>b </i>may be disposed on areas of the first and second <b>320</b><i>a </i>and <b>320</b><i>b, </i>to which AC power is applied.

0071In addition, the load may also be formed on predetermined areas of the support plate <b>310</b> as well as on the extension plate <b>320</b>, and <figref idref="DRAWINGS">FIGS. 8A to 8D</figref> illustrate the second piezoelectric plate <b>300</b> on which the loads are formed on the support pate <b>310</b> and the extension plate <b>320</b>.

0072As illustrated in <figref idref="DRAWINGS">FIG. 8A</figref>, the second piezoelectric plate <b>300</b> may include a support plate <b>310</b> having an approximately rectangular frame shape, an extension plate <b>320</b> disposed in a predetermined area of one short side of the support plate <b>310</b> in a long side direction of the support plate <b>310</b> in the support plate <b>310</b>, and a load <b>350</b> on one end portion of the extension plate <b>320</b>, which does not contact the support plate <b>310</b>. In addition, a plurality of loads <b>351</b>, <b>352</b>, <b>353</b>, and <b>354</b> are disposed at corner areas of the support plate <b>310</b>.

0073As illustrated in <figref idref="DRAWINGS">FIG. 8B</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape and having a dummy plate <b>315</b> formed between one long side and the other long side opposite to each other, an extension plate <b>320</b> making a contact on the dummy plate <b>135</b> and disposed in a long side direction of the support plate <b>310</b>, and loads <b>350</b><i>a </i>and <b>350</b><i>b </i>disposed on two end portions of the extension plate <b>320</b>. In addition, a plurality of loads <b>351</b>, <b>352</b>, <b>353</b>, and <b>354</b> are disposed at corner areas of the support plate <b>310</b>.

0074As illustrated in <figref idref="DRAWINGS">FIG. 8C</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape and having a dummy plate <b>315</b> formed between one long side and the other long side opposite to each other, first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>contacting two side surfaces of the dummy plate <b>315</b> and disposed in a long side direction of the support plate <b>310</b> in an area inside the support plate <b>310</b>, and loads <b>350</b><i>a </i>and <b>350</b><i>b </i>respectively disposed on two end portions of the first and second extension plate <b>320</b><i>a </i>and <b>320</b><i>b. </i>In addition, a plurality of loads <b>351</b>, <b>352</b>, <b>353</b>, and <b>354</b> are disposed at corner areas of the support plate <b>310</b>.

0075As illustrated in <figref idref="DRAWINGS">FIG. 8D</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape, first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>formed in a long side direction of the support plate <b>310</b> from two opposite short sides of the support plate <b>310</b> and separated by a predetermined interval at the central area inside the support plate <b>310</b>, and loads <b>350</b><i>a </i>and <b>350</b><i>b </i>formed on end portions of the first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b. </i>In addition, a plurality of loads <b>351</b>, <b>352</b>, <b>353</b>, and <b>354</b> are disposed at corner areas of the support plate <b>310</b>.

0076Furthermore, in a piezoelectric device of an embodiment, a vibration plate is disposed on at least one area of the second piezoelectric plate <b>300</b> to increase a vibration force and accordingly frequency characteristic may be diversely changed. The vibration plate may use a material such as a polymer, a metal, or silicon, the size thereof may be diversified, and accordingly the vibration force may be diversely realized. <figref idref="DRAWINGS">FIGS. 9A to 9D</figref> illustrate the second piezoelectric plate according to various modification examples of an embodiment.

0077As illustrated in <figref idref="DRAWINGS">FIG. 9A</figref>, the second piezoelectric plate <b>300</b> may include a support plate <b>310</b> having an approximately rectangular frame shape, an extension plate <b>320</b> disposed in a predetermined area of one short side of the support plate <b>310</b> in a long side direction of the support plate <b>310</b> in the support plate <b>310</b>, and a vibration plate <b>360</b> between one end portion of the extension plate <b>320</b>, which does not contact the support plate <b>310</b>, and a short side of the support plate <b>310</b>.

0078As illustrated in <figref idref="DRAWINGS">FIG. 9B</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape and having a dummy plate <b>315</b> formed between one long side and the other long side opposite to each other, an extension plate <b>320</b> making a contact on the dummy plate <b>315</b> and disposed in a long side direction of the support plate <b>310</b> in an area inside the support plate <b>310</b>, and vibration plates <b>360</b><i>a </i>and <b>350</b><i>b </i>respectively disposed between two end portions of the extension plate <b>320</b> and the support plate <b>310</b>.

0079As illustrated in <figref idref="DRAWINGS">FIG. 9C</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape and having a dummy plate <b>315</b> formed between one long side and the other long side opposite to each other, first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>contacting two side surfaces of the dummy plate <b>315</b> and disposed in a long side direction of the support plate <b>310</b>, and vibration plates <b>360</b><i>a </i>and <b>350</b><i>b </i>disposed between end portions of the first and second extension plate <b>320</b><i>a </i>and <b>320</b><i>b </i>and the support plate <b>310</b>.

0080As illustrated in <figref idref="DRAWINGS">FIG. 9D</figref>, the second piezoelectric plate <b>300</b> includes a support plate <b>310</b> having an approximately rectangular frame shape, first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b </i>formed in a long side direction of the support plate <b>310</b> from two opposite short sides of the support plate <b>310</b> and separated by a predetermined interval at the central area inside the support plate <b>310</b>, and a vibration plate <b>360</b> provided between end portions of the first and second extension plates <b>320</b><i>a </i>and <b>320</b><i>b. </i>

0081When such a piezoelectric device of an embodiment is used as a piezoelectric sound device, medium and higher frequency band characteristics as well as low frequency band characteristic can be improved.

0082<figref idref="DRAWINGS">FIGS. 10A to 12B</figref> are graphs representing impedance and sound pressure characteristics of each part of a piezoelectric device according to an exemplary embodiment. In other words, <figref idref="DRAWINGS">FIGS. 10A and 10B</figref> are impedance and sound pressure characteristic graphs when only the extension plate of the second piezoelectric plate is used, <figref idref="DRAWINGS">FIGS. 11A and 11B</figref> are impedance and sound pressure characteristic graphs of the second piezoelectric plate, and <figref idref="DRAWINGS">FIGS. 12A and 12B</figref> are impedance and sound pressure characteristic graphs of the first piezoelectric plate.

0083The extension plate exhibits impedance characteristic at approximately 3.215 kHz as illustrated in <figref idref="DRAWINGS">FIG. 10A</figref>, and a resonant frequency of approximately 0.4 kHz and sound pressure characteristic of approximately 75 dB as illustrated in <figref idref="DRAWINGS">FIG. 10B</figref>. In addition, the second piezoelectric plate exhibits impedance characteristic at approximately 0.1889 kHz as illustrated in <figref idref="DRAWINGS">FIG. 11A</figref>, and a resonant frequency of approximately 0.15 kHz and sound pressure characteristic of approximately 60 dB as illustrated in <figref idref="DRAWINGS">FIG. 11B</figref>. In addition, the first piezoelectric plate exhibits impedance characteristic at approximately 1.3772 kHz as illustrated in <figref idref="DRAWINGS">FIG. 12A</figref>, and a resonant frequency of approximately 1.12 kHz and sound pressure characteristic of approximately 82 dB as illustrated in <figref idref="DRAWINGS">FIG. 12B</figref>. However, when the piezoelectric device is typically used as a sound device, a form of the first piezoelectric plate is used and since a resonant frequency is approximately 1.12 kHz at this point, sound pressure characteristic in a lower frequency band of approximately 1 kHz or lower gets lowered.

0084In addition, <figref idref="DRAWINGS">FIGS. 13A to 15B</figref> are graphs representing impedance and sound pressure characteristics of a piezoelectric device according to a signal application scheme according to an exemplary embodiment. In other words, <figref idref="DRAWINGS">FIGS. 13A and 13B</figref> are impedance and sound pressure characteristic graphs when a signal is applied only to the second piezoelectric plate is used, <figref idref="DRAWINGS">FIGS. 14A and 14B</figref> are impedance and sound pressure characteristic graphs when a signal is applied only to the first piezoelectric plate, and <figref idref="DRAWINGS">FIGS. 15A and 15B</figref> are impedance and sound pressure characteristic graphs when a signal is applied to the first and second piezoelectric plates.

0085When the signal is applied only to the second piezoelectric plate, the piezoelectric device exhibits impedance characteristic at approximately 2.7425 kHz as illustrated in <figref idref="DRAWINGS">FIG. 13A</figref>, and a resonant frequency of approximately 0.4 kHz and sound pressure characteristic of approximately 89 dB as illustrated in <figref idref="DRAWINGS">FIG. 13B</figref>. In addition, when the signal is applied only to the first piezoelectric plate, the piezoelectric device exhibits impedance characteristic at approximately 0.836 kHz as illustrated in <figref idref="DRAWINGS">FIG. 14A</figref>, and a resonant frequency of approximately 0.9 kHz and sound pressure characteristic of approximately 104 dB as illustrated in <figref idref="DRAWINGS">FIG. 14B</figref>. In addition, when the signal is simultaneously applied to the first and second piezoelectric plates, the piezoelectric device exhibits impedance characteristic at approximately 0.8326 kHz as illustrated in <figref idref="DRAWINGS">FIG. 15A</figref>, and resonant frequencies of approximately 0.4 kHz and 0.9 kHz and sound pressure characteristics of approximately 88 dB and 100 dB as illustrated in <figref idref="DRAWINGS">FIG. 15B</figref>. Accordingly, when the piezoelectric device of embodiments is used as a piezoelectric sound device, resonant frequencies may be approximately 0.4 kHz and 0.9 kHz by simultaneously applying a signal to first and second piezoelectric plates, and accordingly sound pressure characteristic can be improved from a low frequency band to a high frequency band. In other words, as illustrated in <figref idref="DRAWINGS">FIG. 16</figref>, a case C where a signal is simultaneously applied to the first and second piezoelectric plate may improve sound pressure characteristics from the low frequency band to the high frequency band than a case A where a signal is applied to the second piezoelectric plate and a case B where a signal is applied to the first piezoelectric plate. In addition, <figref idref="DRAWINGS">FIG. 17</figref> is a graph representing vibration characteristic of a piezoelectric device of an embodiment, which exhibits an output of approximately 2.2 G at a resonant frequency of 228 Hz.

0086A piezoelectric device according to embodiments includes at least two piezoelectric plates and at least two contact points to have at least two resonant frequencies. The piezoelectric device according to embodiments is disposed in an electronic device such as an auxiliary mobile device to operate as at least any one of the piezoelectric sound device and piezoelectric vibration device according to a signal provided from the electronic device. In other words, the piezoelectric device may operate as a piezoelectric sound device or a piezoelectric vibration device, or may simultaneously operate as the piezoelectric sound device and piezoelectric vibration device. Accordingly, an area occupied in the auxiliary mobile device can be reduced and accordingly the size and weight of the auxiliary mobile device can also be reduced by applying the piezoelectric device according to embodiments to the auxiliary mobile device in comparison to a typical technique that a sound device and vibration device are separately applied. In addition, when used as a piezoelectric sound device, the piezoelectric device can improve sound pressure characteristic from a lower frequency band to a higher frequency band.

0087Although the piezoelectric device and the electronic device including the same have been described with reference to the specific embodiments, they are not limited thereto. Therefore, it will be readily understood by those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the present invention defined by the appended claims.