Patent Publication Number: US-2019196589-A1

Title: Mobile terminal

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Pursuant to 35 U.S.C. § 119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2017-0178628, filed on Dec. 22, 2017, the contents of which is incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mobile terminal having a piezoelectric actuator. 
     2. Description of the Related Art 
     Electronic devices may be divided into mobile/portable terminals and stationary terminals according to mobility. Also, the mobile terminals may be classified into handheld types and vehicle mount types according to whether or not a user can directly carry. 
     The electronic device (or the terminal) has various functions according to development of technologies. For example, an electronic device can be allowed to capture still images or moving images, play music or video files, play games, receive broadcast and the like, so as to be implemented as an integrated multimedia player. Efforts are ongoing to support and increase the functionality of electronic devices. Such efforts include software improvements, as well as changes and improvements in the structural components. 
     In recent years, studies have been conducted to provide a user with various haptic feedbacks. An exemplary haptic feedback is transfer of vibration. In the past, a linear resonant actuator (LRA) has been generally used to generate vibration. However, as compared with a piezoelectric actuator described later, the linear resonant actuator has limitations such as a slow response speed and a narrow operating frequency range. 
     The piezoelectric actuator is an actuator driven using a piezoelectric element having a size or shape instantaneously changed by an electric field. The piezoelectric actuator has an advantage of being capable of implementing various haptic effects because of a high response speed and a wide operating frequency range. In addition, there is another advantage in that the piezoelectric actuator has no limitation in size or thickness and thus is more freely formed than the linear resonant actuator. 
     Meanwhile, in recent years, a mobile terminal equipped with a fingerprint sensor has become popular to improve security. Previously, the fingerprint sensor was generally disposed on a bezel. With the release of an almost bezel-less mobile terminal for the implementation of a large screen, studies have been conducted to dispose the fingerprint sensor under a display part. 
     SUMMARY OF THE INVENTION 
     The first object of the present invention is to provide a structure capable of effectively supplying vibration feedback to a user during a fingerprint recognition process, when a fingerprint sensor is disposed below a display part. 
     The second object of the present invention is to provide a structure capable of supplying fingerprint recognition and vibration feedback through a rear key disposed on a rear surface of a mobile terminal. 
     The third object of the present invention is to provide various user interfaces using a plurality of vibration elements, such as a piezoelectric actuator, and other sensors (touch sensor, grip sensor). 
     In order to achieve the first object, a mobile terminal of the present invention includes: a window; a display disposed on the underside of the window to output visual information through the window and including an organic light emitting diode; a fingerprint sensor disposed on the underside of the display to sense a fingerprint of a user on the window; and a piezoelectric actuator formed in an annular shape with a hollow portion to receive the fingerprint sensor in the hollow portion and configured to transfer vibration to the window or sense a force applied to the window. 
     The mobile terminal may further include: a buffer sheet attached to the underside of the display; and a thermal sheet attached to the underside of the buffer sheet to diffuse heat generated in the display, wherein the fingerprint sensor may be attached to the underside of the display, and the piezoelectric actuator may be attached to the underside of the thermal sheet. 
     The mobile terminal may further include a flexible circuit disposed between the thermal sheet and the piezoelectric actuator, formed in an annular shape to receive the fingerprint sensor therein, and electrically connected to the piezoelectric actuator. 
     First and second electrodes may be disposed on the both-side top surfaces of the piezoelectric actuator, respectively, with the fingerprint sensor therebetween, and the flexible circuit may be electrically connected to the first and second electrodes and attached to the underside of the thermal sheet. 
     The mobile terminal may further include: a flexible circuit electrically connected to the first and second electrodes provided on the one-side top surface of the piezoelectric actuator; and a vibration transfer member formed in an annular shape to receive the fingerprint sensor therein, disposed to cover the flexible circuit, and attached to the underside of the thermal sheet. 
     The vibration transfer member may include: a first portion disposed between the flexible circuit and the thermal sheet; and a second portion extended from the first portion and disposed between the piezoelectric actuator and the thermal sheet, with a greater thickness than that of the first portion, wherein the first portion and the second portion may be formed in an annular shape to receive the fingerprint sensor therein. 
     The vibration transfer member may further include a support portion extending downwardly from the second portion and supported by a frame on which the piezoelectric actuator is supported. 
     The flexible circuit and the support portion may be disposed at both sides, respectively, with the fingerprint sensor therebetween. 
     The mobile terminal may further include a FPCB electrically connected to the fingerprint sensor and extended in one direction from the fingerprint sensor, wherein the FPCB may be electrically connected to the first and second electrodes provided on the top surface of the piezoelectric actuator. 
     The mobile terminal may further include a controller for controlling a voltage applied to the piezoelectric actuator based on the fingerprint sensed by the fingerprint sensor. 
     The mobile terminal may further include a controller for controlling the driving of the display based on the fingerprint sensed by the fingerprint sensor and the force applied to the window and sensed by the piezoelectric actuator. 
     In addition, in order to achieve the second object, a mobile terminal of the present invention includes: a display part for outputting visual information to the front surface; a rear key including a fingerprint sensor for sensing a fingerprint of a user and disposed on the rear surface to overlap with the display part in the thickness direction; a piezoelectric actuator disposed on the underside of the rear key to transfer vibration to the rear key or sense a force applied to the rear key; and a frame supporting the piezoelectric actuator and including a recess portion in the top surface to define a cavity with the underside of the piezoelectric actuator. 
     The mobile terminal may further include a flexible circuit disposed between the rear key and the piezoelectric actuator and electrically connected to first and second electrodes of the piezoelectric actuator. 
     Further, in order to achieve the third object, a mobile terminal of the present invention includes: a touch screen having an organic light emitting diode; a fingerprint sensor; a piezoelectric actuator; and a controller for controlling the driving of the touch screen and the piezoelectric actuator, wherein the controller is configured to: use the piezoelectric actuator to sense a force applied to a preset region of the touch screen, when the touch screen is turned off; switch the preset region into the on state; sense a fingerprint of a user on the preset region; and control the driving of the touch screen based on the fingerprint sensed by the fingerprint sensor. 
     The controller may be further configured to display a graphic object on the preset region of the touch screen, when the touch screen is turned off. 
     The controller may be further configured to control a voltage applied to the piezoelectric actuator based on the fingerprint sensed by the fingerprint sensor. 
     Furthermore, the third object of the present invention can be achieved by a mobile terminal including: a touch screen for outputting visual information; a plurality of vibration elements; and a controller for controlling the driving of the touch screen and the plurality of vibration elements, wherein the controller is configured to: sense the touch position of the touch screen; drive any one of the plurality of vibration elements to generate vibration based on the sensed touch position; sense the movement of the touch; and change the vibration element generating vibration to another vibration element based on the moved touch position. 
     The controller may drive the vibration element, which is adjacent to the touch position, of the plurality of vibration elements. 
     The controller may control a current applied to the vibration element adjacent to the touch position, based on a distance between the touch position and the adjacent vibration element. 
     At least one of the plurality of vibration elements may be a piezoelectric actuator. 
     Still furthermore, the third object of the present invention can be achieved by a mobile terminal including: a plurality of vibration elements; a grip sensor part for sensing the grip of the terminal body; and a controller for controlling the driving of the plurality of vibration elements, wherein the controller is configured to: use the grip sensor part to sense the grip of the terminal body; and control the driving of each of the plurality of vibration elements to output one of a plurality of vibration patterns based on the sensed grip position. 
     The grip sensor part may include a first grip sensor and a second grip sensor that are disposed on the left side and the right side of the terminal body, respectively, and the controller may drive any one of the plurality of vibration elements, when the grips of the first and second grip sensors are all sensed, and drive all the vibration elements, when the grip of any one of the first and second grip sensors is sensed. 
     Still furthermore, the third object of the present invention can be achieved by a mobile terminal including: a display part for outputting visual information; a plurality of vibration elements; a grip sensor part for sensing the grip of the terminal body; and a controller for controlling the driving of the plurality of vibration elements, wherein the controller is configured to: use the grip sensor part to sense the grip of the terminal body; sense the movement of the grip; and drive any one of the plurality of vibration elements to generate vibration based on the moved grip position. 
     The controller may drive the vibration element, which is adjacent to the sensed grip position, of the plurality of vibration elements. 
     The controller may control a current applied to the adjacent vibration element based on the moved grip position. 
     The effects of the present invention obtained through the above-described solutions are as follows. 
     First, the fingerprint sensor is disposed on the underside of the display part including the OLED display and the piezoelectric actuator is formed in an annular shape to surround the fingerprint sensor and attached to the underside of the display part, as a result of which the vibration feedback can be effectively supplied to the user during the fingerprint recognition process. 
     In particular, the vibration (or force) transfer structure between the piezoelectric actuator and the display part is different depending on the arrangement type of the electrodes provided on the piezoelectric actuator and the connection structure of the electrodes and the flexible circuit, as a result of which the vibration feedback can be clearly transferred to the display part and the force applied to the display part by the user can be clearly transferred to the piezoelectric actuator. 
     Second, the fingerprint sensor is built in the rear key, the piezoelectric actuator is disposed on the underside of the rear key, and the recess portion for the vibration of the piezoelectric actuator is defined in the frame supporting the piezoelectric actuator, as a result of which it is possible to implement the mobile terminal capable of supplying fingerprint recognition and vibration feedback. 
     Third, various user interfaces can be provided using the plurality of vibration elements, such as the piezoelectric actuator, and other sensors (touch sensor, grip sensor), as a result of which it is possible to implement the mobile terminal satisfying the sensibility of the user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  is a block diagram showing a mobile terminal related to the present invention. 
         FIGS. 2 and 3  are concept views showing the mobile terminal according to one embodiment of the present invention, when viewed in different directions. 
         FIG. 4  includes a plan view showing one example of a piezoelectric actuator applied to the mobile terminal of the present invention, and a concept view showing a structure in which the piezoelectric actuator of  FIG. 4 ( a )  is disposed together with a fingerprint sensor. 
         FIG. 5  includes a plan view showing another example of a piezoelectric actuator applied to the mobile terminal of the present invention, and a concept view showing a structure in which the piezoelectric actuator of  FIG. 5 ( a )  is disposed together with a fingerprint sensor. 
         FIG. 6  is a concept view showing a structure in which the piezoelectric actuator applied to the mobile terminal of the present invention is electrically connected to an FPCB of the fingerprint sensor. 
         FIG. 7  is a concept view showing a structure in which the piezoelectric actuator is applied to an operation unit applied to the mobile terminal of the present invention. 
         FIG. 8  is a concept view showing the force-voltage characteristics of the piezoelectric actuator. 
         FIG. 9  is a concept view showing one example of a method of controlling a mobile terminal using a piezoelectric actuator and a fingerprint sensor. 
         FIG. 10  is a concept view showing one example of a method of controlling a mobile terminal using a plurality of vibration elements. 
         FIG. 11  is a concept view showing one example of a method of controlling a mobile terminal using a grip sensor and a plurality of vibration elements. 
         FIG. 12  is a concept view showing another example of the method of controlling the mobile terminal using the grip sensor and the plurality of vibration elements. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Description will now be given in detail according to exemplary embodiments disclosed herein, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components may be provided with the same or similar reference numbers, and description thereof will not be repeated. In general, a suffix such as “module” and “unit” may be used to refer to elements or components. Use of such a suffix herein is merely intended to facilitate description of the specification, and the suffix itself is not intended to give any special meaning or function. In describing the present disclosure, if a detailed explanation for a related known function or construction is considered to unnecessarily divert the gist of the present disclosure, such explanation has been omitted but would be understood by those skilled in the art. The accompanying drawings are used to help easily understand the technical idea of the present disclosure and it should be understood that the idea of the present disclosure is not limited by the accompanying drawings. The idea of the present disclosure should be construed to extend to any alterations, equivalents and substitutes besides the accompanying drawings. 
     It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are generally only used to distinguish one element from another. 
     It will be understood that when an element is referred to as being “connected with” another element, the element can be connected with the another element or intervening elements may also be present. In contrast, when an element is referred to as being “directly connected with” another element, there are no intervening elements present. 
     A singular representation may include a plural representation unless it represents a definitely different meaning from the context. 
     Terms such as “include” or “has” are used herein and should be understood that they are intended to indicate an existence of several components, functions or steps, disclosed in the specification, and it is also understood that greater or fewer components, functions, or steps may likewise be utilized. 
     Mobile terminals presented herein may be implemented using a variety of different types of terminals. Examples of such terminals include cellular phones, smart phones, user equipment, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigators, portable computers (PCs), slate PCs, tablet PCs, ultra books, wearable devices (for example, smart watches, smart glasses, head mounted displays (HMDs)), and the like. 
     By way of non-limiting example only, further description will be made with reference to particular types of mobile terminals. However, such teachings apply equally to other types of terminals, such as those types noted above. In addition, these teachings may also be applied to stationary terminals such as digital TV, desktop computers, and the like. 
       FIG. 1A  is a block diagram of a mobile terminal in accordance with the present invention. 
     The mobile terminal  100  may be shown having components such as a wireless communication unit  110 , an input unit  120 , a sensing unit  140 , an output unit  150 , an interface unit  160 , a memory  170 , a controller  180 , and a power supply unit  190 .  FIG. 1  shows the mobile terminal  100  having various components, but it may be understood that implementing all of the illustrated components is not a requirement. Greater or fewer components may alternatively be implemented. 
     In more detail, the wireless communication unit  110  may typically include one or more modules which permit communications such as wireless communications between the mobile terminal  100  and a wireless communication system, communications between the mobile terminal  100  and another mobile terminal, or communications between the mobile terminal  100  and an external server. Further, the wireless communication unit  110  may typically include one or more modules which connect the mobile terminal  100  to one or more networks. 
     The wireless communication unit  110  may include one or more of a broadcast receiving module  111 , a mobile communication module  112 , a wireless Internet module  113 , a short-range communication module  114 , and a location information module  115 . 
     The input unit  120  may include a camera  121  or an image input unit for obtaining images or video, a microphone  122 , which is one type of audio input device for inputting an audio signal, and a user input unit  123  (for example, a touch key, a mechanical key, and the like) for allowing a user to input information. Data (for example, audio, video, image, and the like) may be obtained by the input unit  120  and may be analyzed and processed according to user commands. 
     The sensing unit  140  may typically be implemented using one or more sensors configured to sense internal information of the mobile terminal  100 , the surrounding environment of the mobile terminal  100 , user information, and the like. For example, the sensing unit  140  may include at least one of a proximity sensor  141 , an illumination sensor  142 , a touch sensor, an acceleration sensor, a magnetic sensor, a G-sensor, a gyroscope sensor, a motion sensor, an RGB sensor, an infrared (IR) sensor, a fingerprint sensor (a finger scan sensor)  143 , a grip sensor  145 , a ultrasonic sensor, an optical sensor (for example, camera  121 ), a microphone  122 , a battery gauge, an environment sensor (for example, a barometer, a hygrometer, a thermometer, a radiation detection sensor, a thermal sensor, and a gas sensor, among others), and a chemical sensor (for example, an electronic nose, a health care sensor, a biometric sensor, and the like). The mobile terminal disclosed herein may be configured to utilize information obtained from one or more sensors of the sensing unit  140 , and combinations thereof. 
     The output unit  150  may typically be configured to output various types of information, such as audio, video, tactile output, and the like. The output unit  150  may be shown having at least one of a display unit  151 , an audio output module  152 , a haptic module  153 , and an optical output module  154 . The display unit  151  may have an inter-layered structure or an integrated structure with a touch sensor in order to implement a touch screen. The touch screen may function as the user input unit  123  which provides an input interface between the mobile terminal  100  and the user and simultaneously provide an output interface between the mobile terminal  100  and a user. 
     The interface unit  160  serves as an interface with various types of external devices that are coupled to the mobile terminal  100 . The interface unit  160 , for example, may include any of wired or wireless ports, external power supply ports, wired or wireless data ports, memory card ports, ports for connecting a device having an identification module, audio input/output (I/O) ports, video I/O ports, earphone ports, and the like. In some cases, the mobile terminal  100  may perform assorted control functions associated with a connected external device, in response to the external device being connected to the interface unit  160 . 
     The memory  170  is typically implemented to store data to support various functions or features of the mobile terminal  100 . For instance, the memory  170  may be configured to store application programs executed in the mobile terminal  100 , data or instructions for operations of the mobile terminal  100 , and the like. Some of these application programs may be downloaded from an external server via wireless communication. Other application programs may be installed within the mobile terminal  100  at time of manufacturing or shipping, which is typically the case for basic functions of the mobile terminal  100  (for example, receiving a call, placing a call, receiving a message, sending a message, and the like). It is common for application programs to be stored in the memory  170 , installed in the mobile terminal  100 , and executed by the controller  180  to perform an operation (or function) for the mobile terminal  100 . 
     The controller  180  typically functions to control an overall operation of the mobile terminal  100 , in addition to the operations associated with the application programs. The controller  180  may provide or process information or functions appropriate for a user by processing signals, data, information and the like, which are input or output by the aforementioned various components, or activating application programs stored in the memory  170 . 
     Also, the controller  180  may control at least some of the components illustrated in  FIG. 1A , to execute an application program that have been stored in the memory  170 . In addition, the controller  180  may control at least two of those components included in the mobile terminal to activate the application program. 
     The power supply unit  190  may be configured to receive external power or provide internal power in order to supply appropriate power required for operating elements and components included in the wearable device  100 , under the control of the controller  180 . The power supply unit  190  may include a battery, and the battery may be configured as an embedded battery or a detachable battery. 
     At least part of the components may cooperatively operate to implement an operation, a control or a control method of the mobile terminal  100  according to various embodiments disclosed herein. Also, the operation, the control or the control method of the mobile terminal  100  may be implemented on electronic device by an activation of at least one application program stored in the memory  170 . 
     Hereinafter, description will be given in more detail of the aforementioned components with reference to  FIG. 1A , prior to describing various embodiments implemented through the mobile terminal  100 . 
     First, regarding the wireless communication unit  110 , the broadcast receiving module  111  is typically configured to receive a broadcast signal and/or broadcast associated information from an external broadcast managing entity via a broadcast channel. The broadcast channel may include a satellite channel, a terrestrial channel, or both. In some embodiments, two or more broadcast receiving modules  111  may be utilized to facilitate simultaneous reception of two or more broadcast channels, or to support switching among broadcast channels. 
     The mobile communication module  112  may transmit and/or receive wireless signals to and from one or more network entities. Typical examples of a network entity include a base station, an external mobile terminal, a server, and the like. Such network entities form part of a mobile communication network, which is constructed according to technical standards or communication methods for mobile communications (for example, Global System for Mobile Communication (GSM), Code Division Multi Access (CDMA), CDMA2000 (Code Division Multi Access 2000), EV-DO (Enhanced Voice-Data Optimized or Enhanced Voice-Data Only), Wideband CDMA (WCDMA), High Speed Downlink Packet access (HSDPA), HSUPA (High Speed Uplink Packet Access), Long Term Evolution (LTE), LTE-A (Long Term Evolution-Advanced), and the like). 
     The wireless signal may include various types of data depending on a voice call signal, a video call signal, or a text/multimedia message transmission/reception. 
     The wireless Internet module  113  refers to a module for wireless Internet access. This module may be internally or externally coupled to the mobile terminal  100 . The wireless Internet module  113  may transmit and/or receive wireless signals via communication networks according to wireless Internet technologies. 
     Examples of such wireless Internet access include Wireless LAN (WLAN), Wireless Fidelity (Wi-Fi), Wi-Fi Direct, Digital Living Network Alliance (DLNA), Wireless Broadband (WiBro), Worldwide Interoperability for Microwave Access (WiMAX), High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), Long Term Evolution (LTE), LTE-advanced (LTE-A) and the like. The wireless Internet module  113  may transmit/receive data according to one or more of such wireless Internet technologies, and other Internet technologies as well. 
     When the wireless Internet access is implemented according to, for example, WiBro, HSDPA, HSUPA, GSM, CDMA, WCDMA, LTE, LTE-A and the like, as part of a mobile communication network, the wireless Internet module  113  performs such wireless Internet access. As such, the Internet module  113  may cooperate with, or function as, the mobile communication module  112 . 
     The short-range communication module  114  is configured to facilitate short-range communications. Suitable technologies for implementing such short-range communications include BLUETOOTH™, Radio Frequency IDentification (RFID), Infrared Data Association (IrDA), Ultra-WideBand (UWB), ZigBee, Near Field Communication (NFC), Wireless-Fidelity (Wi-Fi), Wi-Fi Direct, Wireless USB (Wireless Universal Serial Bus), and the like. The short-range communication module  114  in general supports wireless communications between the mobile terminal  100  and a wireless communication system, communications between the mobile terminal  100  and another mobile terminal  100 , or communications between the mobile terminal and a network where another mobile terminal  100  (or an external server) is located, via wireless area networks. One example of the wireless area networks is a wireless personal area networks. 
     Here, another electronic device may be a wearable device, for example, a smart watch, a smart glass or a head mounted display (HMD), which is able to exchange data with the mobile terminal  100  (or otherwise cooperate with the mobile terminal  100 ). The short-range communication module  114  may sense or recognize the wearable device, and permit communication between the wearable device and the mobile terminal  100 . In addition, when the sensed wearable device is a device which is authenticated to communicate with the mobile terminal  100 , the controller  180 , for example, may cause transmission of at least part of data processed in the mobile terminal  100  to the wearable device via the short-range communication module  114 . Hence, a user of the wearable device may use the data processed in the mobile terminal  100  on the wearable device. For example, when a call is received in the mobile terminal  100 , the user may answer the call using the wearable device. Also, when a message is received in the mobile terminal  100 , the user can check the received message using the wearable device. 
     The location information module  115  is generally configured to detect, calculate, derive or otherwise identify a position (or current position) of the mobile terminal  100 . As an example, the location information module  115  includes a Global Position System (GPS) module, a Wi-Fi module, or both. For example, when the mobile terminal  100  uses a GPS module, a position of the mobile terminal  100  may be acquired using a signal sent from a GPS satellite. As another example, when the mobile terminal  100  uses the Wi-Fi module, a position of the mobile terminal  100  may be acquired based on information related to a wireless access point (AP) which transmits or receives a wireless signal to or from the Wi-Fi module. If desired, the location information module  115  may alternatively or additionally perform a function of any of the other modules of the wireless communication unit  110  to obtain data related to the position of the mobile terminal  100 . The location information module  115  is a module used for acquiring the position (or the current position) of the mobile terminal  100 , and may not be limited to a module for directly calculating or acquiring the position of the electronic device. 
     Next, the input unit  120  is for inputting image information (or signal), audio information (or signal), data, or information input from a user. For inputting image information, the mobile terminal  100  may be provided with a plurality of cameras  121 . Such cameras  121  may process image frames of still pictures or video obtained by image sensors in a video or image capture mode. The processed image frames can be displayed on the display unit  151  or stored in memory  170 . Meanwhile, the cameras  121  provided in the mobile terminal  100  may be arranged in a matrix configuration to permit a plurality of image information having various angles or focal points to be input to the mobile terminal  100 . Also, the cameras  121  may be located in a stereoscopic arrangement to acquire left and right images for implementing a stereoscopic image. 
     The microphone  122  processes an external audio signal into electric audio (sound) data. The processed audio data can be processed in various manners according to a function being executed in the mobile terminal  100 . If desired, the microphone  122  may include assorted noise removing algorithms to remove unwanted noise generated in the course of receiving the external audio signal. 
     The user input unit  123  is a component that permits input by a user. Such user input may enable the controller  180  to control operation of the mobile terminal  100 . The user input unit  123  may include one or more of a mechanical input element (for example, a mechanical key, a button located on a front and/or rear surface or a side surface of the mobile terminal  100 , a dome switch, a jog wheel, a jog switch, and the like), or a touch-sensitive input element, among others. As one example, the touch-sensitive input element may be a virtual key, a soft key or a visual key, which is displayed on a touch screen through software processing, or a touch key which is located on the electronic device at a location that is other than the touch screen. On the other hand, the virtual key or the visual key may be displayed on the touch screen in various shapes, for example, graphic, text, icon, video, or a combination thereof. 
     The sensing unit  140  is generally configured to sense one or more of internal information of the mobile terminal  100 , surrounding environment information of the mobile terminal  100 , user information, or the like, and generates a corresponding sensing signal. The controller  180  generally cooperates with the sending unit  140  to control operations of the mobile terminal  100  or execute data processing, a function or an operation associated with an application program installed in the mobile terminal based on the sensing signal. The sensing unit  140  may be implemented using any of a variety of sensors, some of which will now be described in more detail. 
     The proximity sensor  141  refers to a sensor to sense presence or absence of an object approaching a surface, or an object located near a surface, by using an electromagnetic field, infrared rays, or the like without a mechanical contact. The proximity sensor  141  may be arranged at an inner region of the mobile terminal  100  covered by the touch screen, or near the touch screen. 
     The proximity sensor  141 , for example, may include any of a transmissive type photoelectric sensor, a direct reflective type photoelectric sensor, a mirror reflective type photoelectric sensor, a high-frequency oscillation proximity sensor, a capacitance type proximity sensor, a magnetic type proximity sensor, an infrared rays proximity sensor, and the like. When the touch screen is implemented as a capacitance type, the proximity sensor  141  can sense proximity of a pointer relative to the touch screen by changes of an electromagnetic field, which is responsive to an approach of an object with conductivity. In this case, the touch screen (touch sensor) may also be categorized as a proximity sensor. 
     The term “proximity touch” will often be referred to herein to denote the scenario in which a pointer is positioned to be proximate to the touch screen without contacting the touch screen. The term “contact touch” will often be referred to herein to denote the scenario in which a pointer makes physical contact with the touch screen. For the position corresponding to the proximity touch of the pointer relative to the touch screen, such position will correspond to a position where the pointer is perpendicular to the touch screen. The proximity sensor  141  may sense proximity touch, and proximity touch patterns (for example, distance, direction, speed, time, position, moving status, and the like). In general, the controller  180  may process data corresponding to proximity touches and proximity touch patterns sensed by the proximity sensor  141 , and cause visual information corresponding to the processed data to be output on the touch screen. In addition, the controller  180  can control the mobile terminal  100  to execute different operations or process different data (or information) according to whether a touch with respect to a point on the touch screen is either a proximity touch or a contact touch. 
     A touch sensor can sense a touch (or a touch input) applied to the touch screen, such as display unit  151 , using any of a variety of touch methods. Examples of such touch methods include a resistive type, a capacitive type, an infrared type, and a magnetic field type, among others. 
     As one example, the touch sensor may be configured to convert changes of pressure applied to a specific part of the display unit  151 , or convert capacitance occurring at a specific part of the touch screen, into electric input signals. The touch sensor may also be configured to sense not only a touched position and a touched area, but also touch pressure and/or touch capacitance. A touch object is generally used to apply a touch input to the touch sensor. Examples of typical touch objects include a finger, a touch pen, a stylus pen, a pointer, or the like. 
     When a touch input is sensed by a touch sensor, corresponding signals may be transmitted to a touch controller. The touch controller may process the received signals, and then transmit corresponding data to the controller  180 . Accordingly, the controller  180  may sense which region of the display unit  151  has been touched. Here, the touch controller may be a component separate from the controller  180 , the controller  180 , and combinations thereof. 
     Meanwhile, the controller  180  may execute the same or different controls according to a type of touch object that touches the touch screen or a touch key provided in addition to the touch screen. Whether to execute the same or different control according to the object which provides a touch input may be decided based on a current operating state of the mobile terminal  100  or a currently executed application program, for example. 
     The touch sensor and the proximity sensor may be implemented individually, or in combination, to sense various types of touches. Such touches includes a short (or tap) touch, a long touch, a multi-touch, a drag touch, a flick touch, a pinch-in touch, a pinch-out touch, a swipe touch, a hovering touch, and the like. 
     If desired, an ultrasonic sensor may be implemented to recognize location information relating to a touch object using ultrasonic waves. The controller  180 , for example, may calculate a position of a wave generation source based on information sensed by an illumination sensor and a plurality of ultrasonic sensors. Since light is much faster than ultrasonic waves, the time for which the light reaches the optical sensor is much shorter than the time for which the ultrasonic wave reaches the ultrasonic sensor. The position of the wave generation source may be calculated using this fact. For instance, the position of the wave generation source may be calculated using the time difference from the time that the ultrasonic wave reaches the sensor based on the light as a reference signal. 
     The camera  121 , which has been depicted as a component of the input unit  120 , typically includes at least one a camera sensor (CCD, CMOS etc.), a photo sensor (or image sensors), and a laser sensor. 
     Implementing the camera  121  with a laser sensor may allow detection of a touch of a physical object with respect to a 3D stereoscopic image. The photo sensor may be laminated on, or overlapped with, the display device. The photo sensor may be configured to scan movement of the object in vicinity of the touch screen. In more detail, the photo sensor may include photo diodes and transistors (TRs) at rows and columns to scan content received at the photo sensor using an electrical signal which changes according to the quantity of applied light. Namely, the photo sensor may calculate the coordinates of the physical object according to variation of light to thus obtain location information of the physical object. 
     The display unit  151  is generally configured to output information processed in the mobile terminal  100 . For example, the display unit  151  may display execution screen information of an application program executing at the mobile terminal  100  or user interface (UI) and graphic user interface (GUI) information in response to the execution screen information. 
     Also, the display unit  151  may be implemented as a stereoscopic display unit for displaying stereoscopic images. 
     A typical stereoscopic display unit may employ a stereoscopic display scheme such as a stereoscopic scheme (a glass scheme), an auto-stereoscopic scheme (glassless scheme), a projection scheme (holographic scheme), or the like. 
     The audio output module  152  may receive audio data from the wireless communication unit  110  or output audio data stored in the memory  170  during modes such as a signal reception mode, a call mode, a record mode, a voice recognition mode, a broadcast reception mode, and the like. The audio output module  152  can provide audible output related to a particular function (e.g., a call signal reception sound, a message reception sound, etc.) performed by the mobile terminal  100 . The audio output module  152  may also be implemented as a receiver, a speaker, a buzzer, or the like. 
     A haptic module  153  can be configured to generate various tactile effects that a user feels, perceives, or otherwise experiences. A typical example of a tactile effect generated by the haptic module  153  is vibration. The strength, pattern and the like of the vibration generated by the haptic module  153  can be controlled by user selection or setting by the controller. For example, the haptic module  153  may output different vibrations in a combining manner or a sequential manner. 
     Besides vibration, the haptic module  153  can generate various other tactile effects, including an effect by stimulation such as a pin arrangement vertically moving to contact skin, a spray force or suction force of air through a jet orifice or a suction opening, a touch to the skin, a contact of an electrode, electrostatic force, an effect by reproducing the sense of cold and warmth using an element that can absorb or generate heat, and the like. 
     The haptic module  153  can also be implemented to allow the user to feel a tactile effect through a muscle sensation such as the user&#39;s fingers or arm, as well as transferring the tactile effect through direct contact. Two or more haptic modules  153  may be provided according to the particular configuration of the mobile terminal  100 . 
     An optical output module  154  may output a signal for indicating an event generation using light of a light source of the mobile terminal  100 . Examples of events generated in the mobile terminal  100  may include message reception, call signal reception, a missed call, an alarm, a schedule notice, an email reception, information reception through an application, and the like. 
     A signal output by the optical output module  154  may be implemented in such a manner that the mobile terminal  100  emits monochromatic light or light with a plurality of colors to a front or rear surface. The signal output may be terminated as the mobile terminal  100  senses that a user has checked the generated event, for example. 
     The interface unit  160  serves as an interface for external devices to be connected with the mobile terminal  100 . For example, the interface unit  160  can receive data transmitted from an external device, receive power to transfer to elements and components within the mobile terminal  100 , or transmit internal data of the mobile terminal  100  to such external device. The interface unit  160  may include wired or wireless headset ports, external power supply ports, wired or wireless data ports, memory card ports, ports for connecting a device having an identification module, audio input/output (I/O) ports, video I/O ports, earphone ports, or the like. 
     The identification module may be a chip that stores various information for authenticating authority of using the mobile terminal  100  and may include a user identity module (UIM), a subscriber identity module (SIM), a universal subscriber identity module (USIM), and the like. In addition, the device having the identification module (also referred to herein as an “identifying device”) may take the form of a smart card. Accordingly, the identifying device can be connected with the mobile terminal  100  via the interface unit  160 . 
     When the mobile terminal  100  is connected with an external cradle, the interface unit  160  can serve as a passage to allow power from the cradle to be supplied to the mobile terminal  100  or may serve as a passage to allow various command signals input by the user from the cradle to be transferred to the mobile terminal therethrough. Various command signals or power input from the cradle may operate as signals for recognizing that the mobile terminal is properly mounted on the cradle. 
     The memory  170  can store programs to support operations of the controller  180  and store input/output data (for example, phonebook, messages, still images, videos, etc.). The memory  170  may store data related to various patterns of vibrations and audio which are output in response to touch inputs on the touch screen. 
     The memory  170  may include one or more types of storage mediums including a flash memory type, a hard disk type, a solid state disk (SSD) type, a silicon disk drive (SDD) type, a multimedia card micro type, a card-type memory (e.g., SD or DX memory, etc), a Random Access Memory (RAM), a Static Random Access Memory (SRAM), a Read-Only Memory (ROM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a Programmable Read-Only memory (PROM), a magnetic memory, a magnetic disk, an optical disk, and the like. The mobile terminal  100  may also be operated in relation to a network storage device that performs the storage function of the memory  170  over a network, such as the Internet. 
     The controller  180  may typically control operations relating to application programs and the general operations of the mobile terminal  100 . For example, the controller  180  may set or release a lock state for restricting a user from inputting a control command with respect to applications when a status of the mobile terminal  100  meets a preset condition. 
     The controller  180  can also perform the controlling and processing associated with voice calls, data communications, video calls, and the like, or perform pattern recognition processing to recognize a handwriting input or a picture drawing input performed on the touch screen as characters or images, respectively. In addition, the controller  180  can control one or a combination of those components in order to implement various exemplary embodiments disclosed herein. 
     The power supply unit  190  receives external power or provides internal power and supply the appropriate power required for operating respective elements and components included in the wearable device  100  under the control of the controller  180 . The power supply unit  190  may include a battery, which is typically rechargeable or be detachably coupled to the terminal body for charging. 
     The power supply unit  190  may include a connection port. The connection port may be configured as one example of the interface unit  160  to which an external charger for supplying power to recharge the battery is electrically connected. 
     As another example, the power supply unit  190  may be configured to recharge the battery in a wireless manner without use of the connection port. In this example, the power supply unit  190  can receive power, transferred from an external wireless power transmitter, using at least one of an inductive coupling method which is based on magnetic induction or a magnetic resonance coupling method which is based on electromagnetic resonance. 
     Various embodiments described herein may be implemented in a computer-readable medium, a machine-readable medium, or similar medium using, for example, software, hardware, or any combination thereof. 
     Hereinafter, an embodiment of the mobile terminal  100  having the above-described configurations will be described with reference to  FIGS. 2 and 3 . 
     Referring to  FIGS. 2 and 3 , the mobile terminal  100  includes a bar-like terminal body. However, the mobile terminal  100  may alternatively be implemented in any of a variety of different configurations. Examples of such configurations include watch type, clip-type, glasses-type, or a folder-type, flip-type, slide-type, swing-type, and swivel-type in which two and more bodies are combined with each other in a relatively movable manner, and combinations thereof. Discussion herein will often relate to a particular type of mobile terminal. However, such teachings with regard to a particular type of mobile terminal will generally be applied to other types of mobile terminals as well. 
     Here, considering the mobile terminal  100  as at least one assembly, the terminal body may be understood as a conception referring to the assembly. 
     The mobile terminal  100  will generally include a case (for example, frame, housing, cover, and the like) forming the appearance of the terminal. In this embodiment, the case is formed using a front case  101  and a rear case  102 . Various electronic components are interposed into a space formed between the front case  101  and the rear case  102 . At least one middle case may be additionally positioned between the front case  101  and the rear case  102 . 
     The display unit  151  is shown located on the front side of the terminal body to output information. As illustrated, a window  151   a  of the display unit  151  may be mounted to the front case  101  to form the front surface of the terminal body together with the front case  101 . 
     In some embodiments, electronic components may also be mounted to the rear case  102 . Examples of such electronic components include a detachable battery  191 , an identification module, a memory card, and the like. In this case, a rear cover  103  is shown covering the electronic components, and this cover may be detachably coupled to the rear case  102 . Therefore, when the rear cover  103  is detached from the rear case  102 , the electronic components mounted on the rear case  102  are exposed to the outside. 
     As illustrated, when the rear cover  103  is coupled to the rear case  102 , a side surface of the rear case  102  may partially be exposed. In some cases, upon the coupling, the rear case  102  may also be completely shielded by the rear cover  103 . Meanwhile, the rear cover  103  may include an opening for externally exposing a camera  121   b  or an audio output module  152   b.    
     The cases  101 ,  102 ,  103  may be formed by injection-molding synthetic resin or may be formed of a metal, for example, stainless steel (STS), aluminum (Al), titanium (Ti), or the like. 
     As an alternative to the example in which the plurality of cases form an inner space for accommodating components, the mobile terminal  100  may be configured such that one case forms the inner space. In this case, a mobile terminal  100  having a uni-body is formed in such a manner that synthetic resin or metal extends from a side surface to a rear surface. 
     Meanwhile, the mobile terminal  100  may include a waterproofing unit (not shown) for preventing introduction of water into the terminal body. For example, the waterproofing unit may include a waterproofing member which is located between the window  151   a  and the front case  101 , between the front case  101  and the rear case  102 , or between the rear case  102  and the rear cover  103 , to hermetically seal an inner space when those cases are coupled. 
     The mobile terminal  100  may include a display unit  151 , first and second audio output module  152   a  and  152   b , a proximity sensor  141 , an illumination sensor  142 , an optical output module  154 , first and second cameras  121   a  and  121   b , first and second manipulation units  123   a  and  123   b , a microphone  122 , an interface unit  160 , and the like. 
     Hereinafter, as illustrated in  FIGS. 1B and 1C , description will be given of the exemplary mobile terminal  100  in which the front surface of the terminal body is shown having the display unit  151 , the first audio output module  152   a , the proximity sensor  141 , the illumination sensor  142 , the optical output module  154 , the first camera  121   a , and the first manipulation unit  121   a , the side surface of the terminal body is shown having the second manipulation unit  123   b , the microphone  122 , and the interface unit  160 , and the rear surface of the terminal body is shown having the second audio output module  152   b  and the second camera  121   b.    
     However, those components may not be limited to the arrangement. Some components may be omitted or rearranged or located on different surfaces. For example, the first manipulation unit  123   a  may be located on another surface of the terminal body, and the second audio output module  152   b  may be located on the side surface of the terminal body other than the rear surface of the terminal body. 
     The display unit  151  is generally configured to output information processed in the mobile terminal  100 . For example, the display unit  151  may display execution screen information of an application program executed on the mobile terminal  100  or user interface (UI) and graphic user interface (GUI) information in response to the execution screen information. 
     The display unit  151  may be implemented using one or more suitable display devices. Examples of such suitable display devices include a liquid crystal display (LCD), a thin film transistor-liquid crystal display (TFT-LCD), an organic light emitting diode (OLED), a flexible display, a 3-dimensional (3D) display, an e-ink display, and combinations thereof. 
     The display unit  151  may be implemented using two display devices, according to the configuration type thereof. For instance, a plurality of the display units  151  may be arranged on one side, either spaced apart from each other, or these devices may be integrated, or these devices may be arranged on different surfaces. 
     The display unit  151  may include a touch sensor that senses a touch with respect to the display unit  151  so as to receive a control command in a touch manner. Accordingly, when a touch is applied to the display unit  151 , the touch sensor may sense the touch, and a controller  180  may generate a control command corresponding to the touch. Contents input in the touch manner may be characters, numbers, instructions in various modes, or a menu item that can be designated. 
     On the other hand, the touch sensor may be configured in a form of a film having a touch pattern and disposed between a window and a display (not illustrated) on a rear surface of the window, or may be a metal wire directly patterned on the rear surface of the window. Alternatively, the touch sensor may be formed integrally with the display. For example, the touch sensor may be disposed on a substrate of the display, or may be provided inside the display. 
     In this way, the display unit  151  may form a touch screen together with the touch sensor, and in this case, the touch screen may function as the user input unit ( 123 , see  FIG. 1A ). In some cases, the touch screen may replace at least some of functions of a first manipulation unit  123   a . Hereinafter, for the sake of explanation, the display unit (display module) for outputting the image and the touch sensor are collectively referred to as a touch screen  151 . 
     The first audio output module  152   a  may be implemented as a receiver for transmitting a call sound to a user&#39;s ear and the second audio output module  152   b  may be implemented as a loud speaker for outputting various alarm sounds or multimedia playback sounds. 
     The window  151   a  of the display unit  151  may include a sound hole for emitting sounds generated from the first audio output module  152   a . However, the present invention is not limited thereto, and the sounds may be released along an assembly gap between the structural bodies (for example, a gap between the window  151   a  and the front case  101 ). In this case, a hole independently formed to output audio sounds may not be seen or may otherwise be hidden in terms of appearance, thereby further simplifying the appearance of the mobile terminal  100 . 
     The optical output module  154  may be configured to output light for indicating an event generation. Examples of such events may include a message reception, a call signal reception, a missed call, an alarm, a schedule alarm, an email reception, information reception through an application, and the like. When a user has checked a generated event, the controller  180  may control the optical output module  154  to stop the light output. 
     The first camera  121   a  may process image frames such as still or moving images obtained by the image sensor in a capture mode or a video call mode. The processed image frames can then be displayed on the display unit  151  or stored in the memory  170 . 
     The first and second manipulation units  123   a  and  123   b  are examples of the user input unit  123 , which may be manipulated by a user to provide input to the mobile terminal  100 . The first and second manipulation units  123   a  and  123   b  may also be commonly referred to as a manipulating portion. The first and second manipulation units  123   a  and  123   b  may employ any method if it is a tactile manner allowing the user to perform manipulation with a tactile feeling such as touch, push, scroll or the like The first and second manipulation units  123   a  and  123   b  may also be manipulated through a proximity touch, a hovering touch, and the like, without a user&#39;s tactile feeling. 
     The drawings are illustrated on the basis that the first manipulation unit  123   a  is a touch key, but the present disclosure may not be necessarily limited to this. For example, the first manipulation unit  123   a  may be configured with a mechanical key, or a combination of a touch key and a push key. 
     The content received by the first and second manipulation units  123   a  and  123   b  may be set in various ways. For example, the first manipulation unit  123   a  may be used by the user to input a command such power on/off, start, end, switching to a touch recognition mode of the display unit  151  or the like, and the second manipulation unit  123   b  may be used by the user to input a command, such as controlling a volume level being output from the first or second audio output module  152   a  or  152   b , switching into a touch recognition mode of the display unit  151 , or the like. 
     The first manipulation unit  123   a  may be disposed to overlap the display unit  151  of the front surface in a thickness direction of the terminal body. As one example, the first manipulation unit  123   a  may be disposed on an upper end portion of the rear surface of the terminal body such that the user can easily manipulate it using a forefinger when the user grabs the terminal body with one hand. However, the present invention may not be limited to this, and the position of the first manipulation unit  123   a  may be changeable. 
     When the first manipulation unit  123   a  is disposed on the rear surface of the terminal body, a new user interface may be implemented using the first manipulation unit  123   a . In addition, the display unit  151  may be configured as a larger screen. 
     On the other hand, the mobile terminal  100  may include a finger scan sensor which scans a user&#39;s fingerprint. The controller  180  may use fingerprint information sensed by the finger scan sensor as an authentication means. The finger scan sensor may be installed in the display unit  151  or the user input unit  123 . 
     The microphone  122  may be configured to receive the user&#39;s voice, other sounds, and the like. The microphone  122  may be provided at a plurality of places, and configured to receive stereo sounds. 
     The interface unit  160  may serve as a path allowing the mobile terminal  100  to interface with external devices. For example, the interface unit  160  may be at least one of a connection terminal for connecting to another device (for example, an earphone, an external speaker, or the like), a port for near field communication (for example, an Infrared DaAssociation (IrDA) port, a Bluetooth port, a wireless LAN port, and the like), or a power supply terminal for supplying power to the mobile terminal  100 . The interface unit  160  may be implemented in the form of a socket for accommodating an external card, such as Subscriber Identification Module (SIM), User Identity Module (UIM), or a memory card for information storage. 
     The second camera  121   b  may be further mounted to the rear surface of the terminal body. The second camera  121   b  may have an image capturing direction, which is substantially opposite to the direction of the first camera unit  121   a.    
     The second camera  121   b  may include a plurality of lenses arranged along at least one line. The plurality of lenses may be arranged in a matrix form. The cameras may be referred to as an ‘array camera.’ When the second camera  121   b  is implemented as the array camera, images may be captured in various manners using the plurality of lenses and images with better qualities may be obtained. 
     The flash  124  may be disposed adjacent to the second camera  121   b . When an image of a subject is captured with the camera  121   b , the flash  124  may illuminate the subject. 
     The second audio output module  152   b  may further be disposed on the terminal body. The second audio output module  152   b  may implement stereophonic sound functions in conjunction with the first audio output module  152   a , and may be also used for implementing a speaker phone mode for call communication. 
     At least one antenna for wireless communication may be disposed on the terminal body. The antenna may be embedded in the terminal body or formed in the case. For example, an antenna which configures a part of the broadcast receiving module  111  (see  FIG. 1A ) may be retractable into the terminal body. Alternatively, an antenna may be formed in a form of film to be attached onto an inner surface of the rear cover  103  or a case including a conductive material may serve as an antenna. 
     The terminal body is provided with a power supply unit  190  (see  FIG. 1A ) for supplying power to the mobile terminal  100 . The power supply unit  190  may include a batter  191  which is mounted in the terminal body or detachably coupled to an outside of the terminal body. 
     The battery  191  may receive power via a power cable connected to the interface unit  160 . Also, the battery  191  may be (re)chargeable in a wireless manner using a wireless charger. The wireless charging may be implemented by magnetic induction or electromagnetic resonance. 
     On the other hand, the drawing illustrates that the rear cover  103  is coupled to the rear case  102  for shielding the battery  191 , so as to prevent separation of the battery  191  and protect the battery  191  from an external impact or foreign materials. When the battery  191  is detachable from the terminal body, the rear case  103  may be detachably coupled to the rear case  102 . 
     An accessory for protecting an appearance or assisting or extending the functions of the mobile terminal  100  may further be provided on the mobile terminal  100 . As one example of the accessory, a cover or pouch for covering or accommodating at least one surface of the mobile terminal  100  may be provided. The cover or pouch may cooperate with the display unit  151  to extend the function of the mobile terminal  100 . Another example of the accessory may be a touch pen for assisting or extending a touch input onto a touch screen. 
     Meanwhile, a piezoelectric actuator  153   a  is provided in the mobile terminal  100  of the present invention to apply vibration to the mobile terminal  100  or sense a force applied to the mobile terminal  100 . The piezoelectric actuator  153   a  can be understood as one example of the haptic module  153 . 
     A structure in which the piezoelectric actuator  153   a  is disposed together with the fingerprint sensor  143  will now be described. 
       FIG. 4 ( a )  is a plan view showing one example of the piezoelectric actuator  153   a  applied to the mobile terminal  100  of the present invention, and  FIG. 4 ( b )  is a concept view showing a structure in which the piezoelectric actuator  153   a  of  FIG. 4 ( a )  is disposed together with the fingerprint sensor  143 . 
     Referring to  FIG. 4 ( a ) , the piezoelectric actuator  153   a  is formed in an annular shape with a hollow portion  153   a ′. As shown, the piezoelectric actuator  153   a  may be formed in a square pillar shape, and the hollow portion  153   a ′ may also be formed in a square shape. 
     First and second electrodes  153   a   1  and  153   a   2  for electrical connection may be provided on the top surface of the piezoelectric actuator  153   a . The first and second electrodes  153   a   1  and  153   a   2  can be understood as +/−electrodes, respectively. In the drawing, the first and second electrodes  153   a   1  and  153   a   2  are disposed on the two top surfaces disposed in parallel, with the hollow portion  153   a ′ therebetween, of the four top surfaces of the piezoelectric actuator  153   a  disposed orthogonal to each other. 
     As shown, the first and second electrodes  153   a   1  and  153   a   2  may be formed in mutual positions relative to the center of the piezoelectric actuator  153   a . Alternatively, the first and second electrodes  153   a   1  and  153   a   2  may be formed in mutual asymmetric positions relative to the center of the piezoelectric actuator  153   a  so that they can be easily distinguished from each other. 
     Referring to  FIG. 4 ( b ) , the piezoelectric actuator  153   a  is positioned on the underside of the display part  151 . That is, the piezoelectric actuator  153   a  is disposed to overlap with the display part  151  in the thickness direction of the mobile terminal  100 . With this arrangement, the piezoelectric actuator  153   a  is configured to transfer vibration to the display part  151  or sense a force applied to the display part  151 . 
     The fingerprint sensor  143  is received in the hollow portion  153   a ′ of the piezoelectric actuator  153   a . That is, the fingerprint sensor  143  is also positioned on the underside of the display part  151 . That is, the fingerprint sensor  143  is disposed to overlap with the display part  151  in the thickness direction of the mobile terminal  100  so as to sense a fingerprint of a finger brought into contact with the display part  151  on the fingerprint sensor  143 . 
     The fingerprint sensor  143  may be operated in a ultrasonic manner or optical manner. Taking into account the structure in which the fingerprint sensor  143  is disposed on the underside of the display part  151 , it is preferable for this structure to be applied to the OLED display  151   d . If the fingerprint sensor  143  is disposed on the underside of the LCD display  151   d , reflection or refraction of light or refraction or interception of ultrasonic waves may occur due to the LCD inner structure. 
     In the drawing, the display part  151  includes a window  151   a  and the OLED display  151   d.    
     The window  151   a  is formed in a light-transmitting type to define one surface of the mobile terminal  100  (the front surface in the drawing). The window  151   a  may be made of a glass material, a synthetic resin material, etc. 
     The display part  151  may include a light-transmitting region R1 (see  FIG. 2 ) corresponding to the OLED display  151   d  and a light-blocking region R2 (see  FIG. 2 ) surrounding the light-transmitting region R1. In order to define the light-transmitting region R1 and the light-blocking region R2, a deco layer  151   b  may be disposed on one surface of the window  151   a.    
     The deco layer  151   b  is made of a light-blocking material and printed on the underside of the window  151   a  to define the light-blocking region R2. Alternatively, the deco layer  151   b  may be formed in a film type and attached to one surface of the window  151   a . For example, the film-type deco layer  151   b  may include a light-transmitting portion for defining the light-transmitting region R1 and a light-blocking portion for defining the light-blocking region R2. 
     Hereinafter, for convenience, the window  151   a  with the deco layer  151   b  formed or attached thereon is referred to as a window part. 
     The OLED display  151   d  is disposed on the underside of the window part to output visual information through the window part. Here, examples of the OLED display  151   d  may include a typical OLED display as well as a plastic OLED display  151   d.    
     The OLED display  151   d  may be attached to the underside of the window part. For the attachment, a light-transmitting adhesive layer  151   c , for example, an optically clear adhesive (OCA) or an optically clear resin (OCR) may be disposed between the OLED display  151   d  and the window part. 
     A buffer sheet  151   e  may be attached to the underside of the OLED display  151   d . The buffer sheet  151   e  can protect the OLED display  151   d  from external shocks. As an example, the buffer sheet  151   e  may be made of a polyurethane material and formed in a foam type. 
     A thermal sheet  151   f  may be attached to the underside of the buffer sheet  151   e  to diffuse heat generated in the OLED display  151   d . The thermal sheet  151   f  may be made of a material with high thermal conductivity, such as graphite, copper, aluminum, etc. 
     The fingerprint sensor  143  and the piezoelectric actuator  153   a  are disposed on the underside of the display part  151 . The fingerprint sensor  143  and the piezoelectric actuator  153   a  may be disposed to overlap with the aforementioned light-transmitting region R1 in the thickness direction of the mobile terminal  100 . 
     As the fingerprint sensor  143  is operated in a ultrasonic manner or optical manner to sense a fingerprint of a finger brought into contact with the window  151   a , a structure causing reflection or refraction of light or refraction or interception of ultrasonic waves should not be interposed between the window  151   a  and the fingerprint sensor  143 . 
     Therefore, it is preferable for the fingerprint sensor  143  to be attached to the underside of the OLED display  151   d . For the attachment, a light-transmitting adhesive layer  144   a , for example, an optically clear adhesive (OCA) or an optically clear resin (OCR) may be disposed between the OLED display  151   d  and the fingerprint sensor  143 . 
     With this arrangement, portions of the aforementioned buffer sheet  151   e  and thermal sheet  151   f  that correspond to the fingerprint sensor  143  may be cut out. That is, the fingerprint sensor  143  may be received in the cutout portions and surrounded by the buffer sheet  151   e  and the thermal sheet  151   f . It is preferable for the contours of the cutout portions to correspond to the contour of the fingerprint sensor  143 . For example, if the fingerprint sensor  143  is formed in a square pillar shape, the cutout portions may be formed in a square shape. 
     The fingerprint sensor  143  may be electrically connected to the controller  180  through an FPCB  144   b . In the drawing, the FPCB  144   b  is disposed on the underside of the fingerprint sensor  143 . 
     The fingerprint sensor  143  may be supported by the frame  104  or an adjacent component (for example, the battery  191 ). In the drawing, the fingerprint sensor  143  is supported by the battery  191 . A reinforcement  144   c  may be disposed between the fingerprint sensor  143  and the battery  191 . The reinforcement  144   c  may be attached to the underside of the FPCB  144   b.    
     The piezoelectric actuator  153   a  is formed in an annular shape to surround the fingerprint sensor  143 . It is preferable for the contour of the hollow portion  153   a ′ for receiving the fingerprint sensor  143  to correspond to the contour of the fingerprint sensor  143 . For example, if the fingerprint sensor  143  is formed in a square pillar shape, the hollow portion  153   a ′ may be formed in a square shape. 
     The piezoelectric actuator  153   a  is attached to the underside of the thermal sheet  151   f  to transfer vibration to the display part  151  or sense a force applied to the display part  151 . 
     The first and second electrodes  153   a   1  and  153   a   2  are disposed on the top surface of the piezoelectric actuator  153   a , respectively. The first and second electrodes  153   a   1  and  153   a   2  may be disposed on the both-side top surfaces relative to the hollow portion  153   a , respectively. The first and second electrodes  153   a   1  and  153   a   2  are electrically connected to the controller  180  through a flexible circuit  155   b.    
     The flexible circuit  155   b  is disposed between the thermal sheet  151   f  and the piezoelectric actuator  153   a  and electrically connected to the first and second electrodes  153   a   1  and  153   a   2 . The flexible circuit  155   b  is bendable to some extent without being damaged. The flexible circuit  155   b  may be a conductive foil, a flexible printed circuit (FPC), or a flexible flat cable (FFC). 
     For the electrical connection of the flexible circuit  155   b  and the first and second electrodes  153   a   1  and  153   a   2 , conductive adhesives  155   c   1  and  155   c   2  may be disposed between the flexible circuit  155   b  and the first and second electrodes  153   a   1  and  153   a   2 . The conductive adhesives  155   c   1  and  155   c   2  may be made of various materials such as Ag, Cu, C, etc. 
     Taking into account the structure in which the first and second electrodes  153   a   1  and  153   a   2  are disposed at both sides of the hollow portion  153   a ′, the flexible circuit  155   b  may be formed in an annular shape to receive the fingerprint sensor  143  in its hollow portion. The contour of the hollow portion of the flexible circuit  155   b  may correspond to the contour of the hollow portion  153   a ′ of the piezoelectric actuator  153   a.    
     The flexible circuit  155   b  is attached to the underside of the thermal sheet  151   f  For the attachment, an adhesive layer  155   a  may be disposed between the thermal sheet  151   f  and the flexible circuit  155   b . The adhesive layer  155   a  may be made of an optically clear adhesive (OCA) or an optically clear resin (OCR) as well as a known adhesive film or adhesive which does not have a light-transmitting characteristic. Because of the attachment, vibration generated in the piezoelectric actuator  153   a  can be transferred to the window  151   a , and pressure applied to the window  151   a  can be transferred to the piezoelectric actuator  153   a.    
     The piezoelectric actuator  153   a  may be supported by the frame  104  or an adjacent component (for example, the battery  191 ). In the drawing, the piezoelectric actuator  153   a  is supported by the frame  104  in the mobile terminal  100 . The frame  104  may be made of a metal material (for example, SUS, aluminum, etc.) or a synthetic resin material. 
     As shown, the frame  104  may have a hollow portion corresponding to the fingerprint sensor  143 . The aforementioned reinforcement  144   c  may be disposed in the hollow portion, and a damper  155   d  may be provided to surround the reinforcement  144   c . The damper  155   d  may be formed of a polyurethane material in a foam type. 
     The damper  155   d  may be configured to support at least part of the piezoelectric actuator  153   a . That is, part of the piezoelectric actuator  153   a  can be supported by the frame  104  and the other part thereof can be supported by the damper  155   d.    
     As described above, in the structure in which the first and second electrodes  153   a   1  and  153   a   2  are provided on the both-side top surfaces of the piezoelectric actuator  153   a  relative to the hollow portion  153   a ′, the flexible circuit  155   b  is disposed to cover the both-side top surfaces, without causing a step difference. Therefore, vibration generated in the piezoelectric actuator  153   a  can be transferred to the window  151   a , and pressure applied to the window  151   a  can be transferred to the piezoelectric actuator  153   a , without using a separate component. 
       FIG. 5 ( a )  is a plan view showing another example of a piezoelectric actuator  253   a  applied to the mobile terminal of the present invention, and  FIG. 5 ( b )  is a concept view showing a structure in which the piezoelectric actuator  253   a  of  FIG. 5 ( a )  is disposed together with a fingerprint sensor  243 . 
     In this example, first and second electrodes  253   a   1  and  253   a   2  are provided on the one-side top surface relative to a hollow portion  253   a ′. As such, a structure for electrically connecting the piezoelectric actuator  253   a  to a flexible circuit  255   b  and a structure for solving a step difference caused by such an electrical connection structure are different from the structure of  FIG. 4 . 
     Referring to  FIG. 5 ( a ) , the piezoelectric actuator  253   a  is formed in an annular shape with a hollow portion  253   a ′. As shown, the piezoelectric actuator  253   a  may be formed in a square pillar shape, and the hollow portion  253   a ′ may also be formed in a square shape. 
     The first and second electrodes  253   a   1  and  253   a   2  may be provided on the one-side top surface of the piezoelectric actuator  253   a . In the drawing, the first and second electrodes  253   a   1  and  253   a   2  are disposed on one of the four top surfaces of the piezoelectric actuator  253   a  disposed orthogonal to each other. 
     Referring to  FIG. 5 ( b ) , the piezoelectric actuator  253   a  is positioned on a underside of a display part  251 . That is, the piezoelectric actuator  253   a  is disposed to overlap with the display part  251  in the thickness direction of the mobile terminal. With this arrangement, the piezoelectric actuator  253   a  is configured to transfer vibration to the display part  251  or sense a force applied to the display part  251 . 
     A fingerprint sensor  243  is received in the hollow portion  253   a ′ of the piezoelectric actuator  253   a . That is, the fingerprint sensor  243  is also positioned on the underside of the display part  251 . That is, the fingerprint sensor  243  is disposed to overlap with the display part  251  in the thickness direction of the mobile terminal so as to sense a fingerprint of a finger brought into contact with the display part  251  on the fingerprint sensor  243 . 
     The fingerprint sensor  243  may be operated in a ultrasonic manner or optical manner. Taking into account the structure in which the fingerprint sensor  243  is disposed on the underside of the display part  251 , it is preferable for this structure to be applied to the OLED display  251   d . If the fingerprint sensor  243  is disposed on the underside of the LCD display  251   d , reflection or refraction of light or refraction or interception of ultrasonic waves may occur due to the LCD inner structure. 
     In the drawing, the display part  251  includes a window  251   a  and the OLED display  251   d.    
     The window  251   a  is formed in a light-transmitting type to define one surface of the mobile terminal (the front surface in the drawing). The window  251   a  may be made of a glass material, a synthetic resin material, etc. 
     The display part  251  may include a light-transmitting region R1 (see  FIG. 2 ) corresponding to the OLED display  251   d  and a light-blocking region R2 (see  FIG. 2 ) surrounding the light-transmitting region R1. In order to define the light-transmitting region R1 and the light-blocking region R2, a deco layer  251   b  may be disposed on one surface of the window  251   a.    
     The deco layer  251   b  is made of a light-blocking material and printed on the underside of the window  251   a  to define the light-blocking region R2. Alternatively, the deco layer  251   b  may be formed in a film type and attached to one surface of the window  251   a . For example, the film-type deco layer  251   b  may include a light-transmitting portion for defining the light-transmitting region R1 and a light-blocking portion for defining the light-blocking region R2. 
     Hereinafter, for convenience, the window  251   a  with the deco layer  251   b  formed or attached thereon is referred to as a window part. 
     The OLED display  251   d  is disposed on the underside of the window part to output visual information through the window part. Here, examples of the OLED display  251   d  may include a typical OLED display as well as a plastic OLED display  251   d.    
     The OLED display  251   d  may be attached to the underside of the window part. For the attachment, a light-transmitting adhesive layer, for example, an optically clear adhesive (OCA) or an optically clear resin (OCR) may be disposed between the OLED display  251   d  and the window part. 
     A buffer sheet  251   e  may be attached to the underside of the OLED display  251   d . The buffer sheet  251   e  can protect the OLED display  251   d  from external shocks. As an example, the buffer sheet  251   e  may be made of a polyurethane material and formed in a foam type. 
     A thermal sheet  251   f  may be attached to the underside of the buffer sheet  251   e  to diffuse heat generated in the OLED display  251   d . The thermal sheet  251   f  may be made of a material with high thermal conductivity, such as graphite, copper, aluminum, etc. 
     The fingerprint sensor  243  and the piezoelectric actuator  253   a  are disposed on the underside of the display part  251 . The fingerprint sensor  243  and the piezoelectric actuator  253   a  may be disposed to overlap with the aforementioned light-transmitting region R1 in the thickness direction of the mobile terminal. 
     As the fingerprint sensor  243  is operated in a ultrasonic manner or optical manner to sense a fingerprint of a finger brought into contact with the window  251   a , a structure causing reflection or refraction of light or refraction or interception of ultrasonic waves should not be interposed between the window  251   a  and the fingerprint sensor  243 . 
     Therefore, it is preferable for the fingerprint sensor  243  to be attached to the underside of the OLED display  251   d . For the attachment, a light-transmitting adhesive layer, for example, an optically clear adhesive (OCA) or an optically clear resin (OCR) may be disposed between the OLED display  251   d  and the fingerprint sensor  243 . 
     With this arrangement, portions of the aforementioned buffer sheet  251   e  and thermal sheet  251   f  that correspond to the fingerprint sensor  243  may be cut out. That is, the fingerprint sensor  243  may be received in the cutout portions and surrounded by the buffer sheet  251   e  and the thermal sheet  251   f . It is preferable for the contours of the cutout portions to correspond to the contour of the fingerprint sensor  243 . For example, if the fingerprint sensor  243  is formed in a square pillar shape, the cutout portions may be formed in a square shape. 
     The fingerprint sensor  243  may be electrically connected to the controller  180  through an FPCB  244   b . In the drawing, the FPCB  244   b  is disposed on the underside of the fingerprint sensor  243 . 
     The fingerprint sensor  243  may be supported by a frame  204  or an adjacent component (for example, a battery  291 ). In the drawing, the fingerprint sensor  243  is supported by the battery  291 . A reinforcement  244   c  may be disposed between the fingerprint sensor  243  and the battery  291 . The reinforcement  244   c  may be attached to the underside of the FPCB  244   b.    
     The piezoelectric actuator  253   a  is formed in an annular shape to surround the fingerprint sensor  243 . It is preferable for the contour of the hollow portion  253   a ′ for receiving the fingerprint sensor  243  to correspond to the contour of the fingerprint sensor  243 . For example, if the fingerprint sensor  243  is formed in a square pillar shape, the hollow portion  253   a ′ may be formed in a square shape. 
     The first and second electrodes  253   a   1  and  253   a   2  are disposed on the top surface of the piezoelectric actuator  253   a , respectively. The first and second electrodes  253   a   1  and  253   a   2  may be disposed on the one-side top surface of the hollow portion  253   a . The first and second electrodes  253   a   1  and  253   a   2  are electrically connected to the controller  180  through a flexible circuit  255   b.    
     The flexible circuit  255   b  is disposed between the thermal sheet  251   f  and the piezoelectric actuator  253   a  and electrically connected to the first and second electrodes  253   a   1  and  253   a   2 . The flexible circuit  255   b  is bendable to some extent without being damaged. The flexible circuit  255   b  may be a conductive foil, a flexible printed circuit (FPC), or a flexible flat cable (FFC). 
     For the electrical connection of the flexible circuit  255   b  and the first and second electrodes  253   a   1  and  253   a   2 , conductive adhesives  255   c   1  and  255   c   2  may be disposed between the flexible circuit  255   b  and the first and second electrodes  253   a   1  and  253   a   2 . The conductive adhesives  255   c   1  and  255   c   2  may be made of various materials such as Ag, Cu, C, etc. 
     Taking into account the structure in which the first and second electrodes  253   a   1  and  253   a   2  are disposed on the one-side top surface relative to the hollow portion  253   a ′, the flexible circuit  255   b  may be formed to cover only the one-side top surface for the electrical connection to the first and second electrodes  253   a   1  and  253   a   2 . That is, the flexible circuit  255   b  may not be disposed on the top surfaces other than the one-side top surface. For example, as shown, if the first and second electrodes  253   a   1  and  253   a   2  are provided on one of the four top surfaces of the piezoelectric actuator  253   a  disposed orthogonal to each other, the flexible circuit  255   b  may be disposed to cover only the one top surface and not to cover the other three top surfaces. 
     With this arrangement, a distance from the underside of the thermal sheet  251   f  to the flexible circuit  255   b  is different from a distance from the underside of the thermal sheet  251   f  to the other three top surfaces without the flexible circuit  255   b  thereon. This difference in distance, i.e., the step difference makes it difficult to attach the flexible circuit  255   b  to the underside of the thermal sheet  251   f , unlike the above embodiment. 
     Thus, this embodiment discloses a structure in which a vibration transfer member  255   d  is interposed between the thermal sheet  251   f  and the piezoelectric actuator  253   a . The vibration transfer member  255   d  may be referred as a bracket because it serves to fix the piezoelectric actuator  253   a  to the underside of the thermal sheet  251   f    
     Specifically, the vibration transfer member  255   d  is formed in an annular shape with a hollow portion to receive the fingerprint sensor  243  therein and disposed to cover the flexible circuit  255   b  and the three top surfaces of the piezoelectric actuator  253   a  on which the flexible circuit  255   b  is not disposed. 
     The vibration transfer member  255   d  includes a first portion  255   d   1  and a second portion  255   d   2 . The first portion  255   d   1  is disposed between the flexible circuit  255   b  and the thermal sheet  251   f . The second portion  255   d   2  is extended from the first portion  255   d   1  and disposed between the piezoelectric actuator  253   a  and the thermal sheet  251   f , with a greater thickness than that of the first portion  255   d   1 . The first portion  255   d   1  and the second portion  255   d   2  are formed in an annular shape with the hollow portion  253   a ′ to receive the fingerprint sensor  243  therein. 
     The vibration transfer member  255   d  may further include a support portion  255   d   3  extending downwardly from the second portion  255   d   2 . The support portion  255   d   3  is supported by the frame  204 , which supports the piezoelectric actuator  253   a , or an adjacent component. As shown in  FIG. 5 ( b ) , the flexible circuit  255   b  and the support portion  255   d   3  are disposed at both sides, respectively, with the fingerprint sensor  243  therebetween. 
     The piezoelectric actuator  253   a  may be supported by the frame  204  or the adjacent component (for example, the battery  291 ). In the drawing, the piezoelectric actuator  253   a  is supported by the frame  204  in the mobile terminal. The frame  204  may be made of a metal material (for example, SUS, aluminum, etc.) or a synthetic resin material. 
     As shown, the frame  204  may have a hollow portion corresponding to the fingerprint sensor  243 . The aforementioned reinforcement  244   c  may be disposed in the hollow portion, and a damper  255   d  may be provided to surround the reinforcement  244   c . The damper  255   d  may be formed of a polyurethane material in a foam type. 
     The damper  255   d  may be configured to support at least part of the piezoelectric actuator  253   a . That is, part of the piezoelectric actuator  253   a  can be supported by the frame  204  and the other part thereof can be supported by the damper  255   d.    
     The above-described embodiments show a structure in which the FPCB  144   b  and  244   b  connected to the fingerprint sensor  143  and  243  and the flexible circuit  155   b  and  255   b  connected to the piezoelectric actuator  153   a  and  253   a  are separately provided. A structure in which a fingerprint sensor  343  and a piezoelectric actuator  353   a  are electrically connected to the controller  180  through one FPCB  344   b  will now be described. 
       FIG. 6  is a concept view showing a structure in which the piezoelectric actuator  353   a  applied to the mobile terminal  300  of the present invention is electrically connected to the FPCB  344   b  of the fingerprint sensor  343 . 
     Referring to  FIG. 6 , the fingerprint sensor  343  is electrically connected to the controller  180  through the FPCB  344   b . The FPCB  344   b  is extended from one side of the fingerprint sensor  343 . 
     The piezoelectric actuator  353   a  is formed in an annular shape to surround the fingerprint sensor  343 . It is preferable for the contour of the hollow portion  353   a ′ for receiving the fingerprint sensor  343  to correspond to the contour of the fingerprint sensor  343 . For example, if the fingerprint sensor  343  is formed in a square pillar shape, the hollow portion  353   a ′ may be formed in a square shape. 
     First and second electrodes  353   a   1  and  353   a   2  are provided on the one-side top surface of the piezoelectric actuator  353   a , respectively. The first and second electrodes  353   a   1  and  353   a   2  may be disposed on the one-side top surface relative to the hollow portion  353   a ′. The first and second electrodes  353   a   1  and  353   a   2  are electrically connected to the controller  180  through a flexible circuit  355   b.    
     When the fingerprint sensor  343  is received in the hollow portion  353   a ′ of the piezoelectric actuator  353   a , the FPCB  344   b  is extended in the lateral direction of the piezoelectric actuator  353   a  past the one-side top surface thereof. Here, the first and second electrodes  353   a   1  and  353   a   2  are provided on the one-side top surface, and first and second terminals  344   b   1  and  344   b   2  for the electrical connection to the first and second electrodes  353   a   1  and  353   a   2  are provided on the underside of the FPCB  344   b  that faces the one-side top surface. 
     In other words, when the fingerprint sensor  343  is received in the hollow portion  353   a ′ of the piezoelectric actuator  353   a , the first terminal  344   b   1  is disposed to face the first electrode  353   a   1  and the second terminal  344   b   2  is disposed to face the second electrode  353   a   2 . For the electrical connection of the first and second electrodes  353   a   1  and  353   a   2  to the first and second terminals  344   b   1  and  344   b   2 , a conductive adhesive (not shown) may be disposed therebetween. The conductive adhesive may be made of various materials such as Ag, Cu, C, etc. 
     With this structure, the fingerprint sensor  343  and the piezoelectric actuator  353   a  can be electrically connected to the controller  180  through one FPCB  344   b . Therefore, the flexible circuit  355   b  for the electrical connection of the piezoelectric actuator  353   a  is not necessary, which makes the structure for electrical connection more simple. 
       FIG. 7  is a concept view showing a structure in which a piezoelectric actuator  453   a  is applied to an operation unit applied to the mobile terminal of the present invention. 
     As described above in relation to  FIG. 3 , the display part  151  for outputting visual information is provided on the front surface of the mobile terminal  100 , and the first operation unit  123   a  is provided on the rear surface thereof.  FIG. 7  shows a structure in which the piezoelectric actuator  453   a  is applied to the first operation unit  123   a.    
     Referring to  FIG. 7 , the first operation unit  123   a  may be referred to as a rear key  423   a  in consideration of its position. The rear key  423   a  may also be referred to as a type of key in that it provides a user with a similar haptic effect to that of a mechanical button, although it is not a typical push-type mechanical button. 
     The rear key  423   a  is configured to sense a fingerprint of a user and to transfer vibration to the user or sense a force applied by the user. The rear key  423   a  is exposed to the rear surface of the mobile terminal and disposed to overlap with the display part in the thickness direction of the mobile terminal. 
     A fingerprint sensor  443  may be built in the rear key  423   a . The fingerprint sensor  443  may be operated in a ultrasonic manner or optical manner. The fingerprint sensor  443  may be electrically connected to the controller  180  through an FPCB  444   b.    
     It is preferable for the rear key  423   a  to be made of a light-transmitting material to reduce reflection or refraction of light or refraction or interception of ultrasonic waves when the fingerprint sensor  443  recognizes the fingerprint of the finger brought into contact with the rear key  423   a . The rear key  423   a  may be made of a glass material, a synthetic resin material, etc. 
     The piezoelectric actuator  453   a  is disposed on the underside of the rear key  423   a  to transfer vibration to the rear key  423   a  or sense a force applied to the rear key  423   a . The piezoelectric actuator  453   a  may be formed in various shapes. That is, the piezoelectric actuator  453   a  is not always formed in an annular shape as in the above-described embodiments. In the drawing, the piezoelectric actuator  453   a  does not have a hollow portion, first and second electrodes being provided on the top surface thereof 
     The piezoelectric actuator  453   a  may be supported by a frame  404  or an adjacent component (for example, a battery). In the drawing, the piezoelectric actuator  453   a  is supported by the frame  404 . The frame  404  may be made of a metal material (for example, SUS, aluminum, etc.) or a synthetic resin material. 
     A recess portion  404   a  is formed in the top surface of the frame  404  for supporting the piezoelectric actuator  453   a . When the piezoelectric actuator  453   a  is supported on the top surface of the frame  404 , the recess portion  404   a  defines a cavity with the underside of the piezoelectric actuator  453   a . The cavity serves to secure a deformable space of the piezoelectric actuator  453   a  and suppress transfer of vibration in the rearward direction, i.e., to the underside of the frame  404 , upon vibration of the piezoelectric actuator  453   a.    
     Accordingly, the depth of the recess portion  404   a  should be designed in consideration of the downward displacement amount of the piezoelectric actuator  453   a  upon vibration of the piezoelectric actuator  453   a . For example, the recess portion  404   a  may be designed to have a depth such that it does not contact the piezoelectric actuator  453   a  when the displacement amount of the piezoelectric actuator  453   a  is maximum. 
     In this structure, the rear key  423   a , the piezoelectric actuator  453   a  and the recess portion  404   a  of the frame  404  are disposed to overlap with each other in the thickness direction of the mobile terminal. 
     The piezoelectric actuator  453   a  is attached to the underside of the rear key  423   a  to transfer vibration to the rear key  423   a  or sense a force applied to the rear key  423   a.    
     First and second electrodes are disposed on the piezoelectric actuator  453   a , respectively. For example, the first and second electrodes may be provided on the top surface of the piezoelectric actuator  453   a . In this case, the first and second electrodes may be formed on the same plane, or on the two top surfaces of different heights, respectively, as shown. 
     The first and second electrodes are electrically connected to the controller  180  through a flexible circuit  455   b . The flexible circuit  455   b  is disposed between the rear key  423   a  and the piezoelectric actuator  453   a  and electrically connected to the first and second electrodes. 
     The flexible circuit  455   b  is bendable to some extent without being damaged. The flexible circuit  455   b  may be a conductive foil, a flexible printed circuit (FPC), or a flexible flat cable (FFC). 
     For the electrical connection of the flexible circuit  455   b  and the first and second electrodes, conductive adhesives  455   c   1  and  455   c   2  may be disposed between the flexible circuit  455   b  and the first and second electrodes. The conductive adhesives  455   c   1  and  455   c   2  may be made of various materials such as Ag, Cu, C, etc. 
     The flexible circuit  455   b  is attached to the underside of the rear key  423   a . For the attachment, an adhesive layer  455   a  may be disposed between the rear key  423   a  and the flexible circuit  455   b . The adhesive layer  455   a  may be made of an optically clear adhesive (OCA) or an optically clear resin (OCR) as well as a known adhesive film or adhesive which does not have a light-transmitting characteristic. Because of the attachment, vibration generated in the piezoelectric actuator  453   a  can be transferred to the rear key  423   a , and pressure applied to the rear key  423   a  can be transferred to the piezoelectric actuator  453   a.    
       FIG. 8  is a concept view showing the force-voltage characteristics of the piezoelectric actuator  153   a.    
     The piezoelectric actuator  153   a  has a characteristic that a potential difference (voltage) is generated when a force is applied thereto, and on the contrary, physical displacement (vibration) occurs when a potential difference (voltage) is applied thereto. The piezoelectric actuator  153   a  may be made of quartz, Rochelle salt, barium titanate, artificial ceramic, etc. 
     As seen from the graph of  FIG. 8 , the force and voltage exhibit linear characteristics within a certain range. With these characteristics, the controller  180  can sense the intensity of the applied force based on the generated potential difference and control the voltage (or current) applied to the piezoelectric actuator  153   a  to regulate the intensity of the vibration. 
     For example, when a force of 6 N is applied to the piezoelectric actuator  153   a , a voltage of 90 mV is generated. Therefore, the controller can sense the voltage generated in the piezoelectric actuator  153   a  to calculate the force applied to the piezoelectric actuator  153   a.    
     Meanwhile, when a voltage of 90 mV is applied to the piezoelectric actuator  153   a , a force of 6 N is generated. Thus, the controller can control the voltage applied to the piezoelectric actuator  153   a  to regulate the intensity of the vibration. 
     Combining the piezoelectric actuator  153   a  having these characteristics with the fingerprint sensor  143  can provide a novel user interface. 
       FIG. 9  is a concept view showing one example of a method of controlling the mobile terminal  100  using the piezoelectric actuator  153   a  and the fingerprint sensor  143 . 
     Referring to  FIG. 9  together with  FIG. 8 , the controller  180  is configured to control the driving of the display part  151  based on the force applied to the display part  151  sensed by the piezoelectric actuator  153   a  and on the fingerprint sensed by the fingerprint sensor  143 . 
     In  FIG. 9 ( a ) , when the mobile terminal  100  enters a sleep mode, the display part  151  is also put into the sleep mode to reduce power consumption. The sleep mode can be understood as a power saving mode, a low power mode, a standby mode, etc. 
     In the sleep mode of the display part  151 , the display part  151  is turned off or set to output only the preset visual information. As an example, a graphic object G 1  for indicating the position of the user&#39;s finger for fingerprint recognition may be displayed on the display part  151 . It is preferable for the graphic object G 1  to be positioned above the fingerprint sensor  143 , i.e., to overlap with the fingerprint sensor  143  in the thickness direction of the mobile terminal  100 . 
     It is noted that the fingerprint sensor  143  may be received in the hollow portion of the piezoelectric actuator  153   a , as described above. That is, the piezoelectric actuator  153   a  may be disposed to surround the fingerprint sensor  143 . 
     Here, as shown in  FIGS. 9B and 9C , when the user puts his/her finger on a portion of the display part  151  having the graphic object G 1  displayed thereon, that graphic object G 1 -displayed portion is contacted and pressed. The controller  180  uses the touch sensor and the piezoelectric actuator  153   a  to sense that the graphic object G 1 -displayed portion has been contacted and pressed and controls the display part  151  based on the sensing result. 
     For example, when the touch sensor of the display part  151  senses that the graphic object G 1 -displayed portion has been contacted and the piezoelectric actuator  153   a  senses that the display part  151  has been pressed above a preset force, the controller  180  may switch a first region of the display part  151  into the on state, for fingerprint recognition. Therefore, when portions other than the graphic object G 1 -displayed portion are contacted and pressed, the controller  180  does not switch at least some portion of the display part  151  into the on state. 
     The first region switched into the on state may include the graphic object G 1 -displayed portion. That is, the display part  151  supplies light to the graphic object G 1 -displayed portion so that the fingerprint sensor  143  can recognize the fingerprint of the finger brought into contact with the graphic object G 1 -displayed portion. In order to supply light to the first region as described, it is preferable for the display part  151  to include the OLED display  151   d.    
     In turn, as shown in  FIG. 9 ( d ) , when the fingerprint sensed by the fingerprint sensor  143  corresponds to the preset fingerprint, the controller  180  switches a second region of the display part  151  into the on state. Here, the second region may include the first region and may be larger than the first region. As an example, the second region may be the entire region of the display part  151 . 
     As the second region of the display part  151  is switched into the on state, the display part  151  is switched from the sleep mode to a driving mode. Further, the mobile terminal  100  is also switched from the sleep mode to the driving mode. 
     The controller  180  may be configured to transfer vibration to the display part  151  through the piezoelectric actuator  153   a , when the second region of the display part  151  is switched into the on state. To this end, the controller  180  can change a voltage applied to the piezoelectric actuator  153   a.    
     When the fingerprint sensed by the fingerprint sensor  143  does not correspond to the preset fingerprint, the controller  180  maintains the display part  151  in the sleep mode. In this case, the display part  151  may output visual information indicating that the sensed fingerprint does not correspond to the preset fingerprint. 
     Meanwhile, the controller  180  can control a voltage applied to the piezoelectric actuator  153   a  based on the fingerprint sensed by the fingerprint sensor  143 . That is, the controller  180  can change a voltage so that the piezoelectric actuator  153   a  can generate different patterns of vibration depending on the fingerprint recognition results. 
     For example, when the fingerprint sensed by the fingerprint sensor  143  corresponds to the preset fingerprint, the controller  180  may apply a first pattern voltage to the piezoelectric actuator  153   a  to apply first pattern vibration to the display part  151 . On the contrary, when the fingerprint sensed by the fingerprint sensor  143  does not correspond to the preset fingerprint, the controller  180  may apply a second pattern voltage to the piezoelectric actuator  153   a  to apply second pattern vibration to the display part  151 . Here, the first pattern voltage is different from the second pattern voltage, and the first pattern vibration is different from the second pattern vibration. 
       FIG. 10  is a concept view showing one example of a method of controlling the mobile terminal  100  using a plurality of vibration elements  153   a  and  153   b.    
     Referring to  FIG. 10 , the mobile terminal  100  is equipped with the plurality of vibration elements  153   a  and  153   b . For example, the plurality of vibration elements  153   a  and  153   b  may be provided on the lower side and the upper side in the longitudinal direction with respect to the center C of the display part  151 , respectively. 
     At least one of the plurality of vibration elements  153   a  and  153   b  can be the piezoelectric actuator  153   a . As an example, a linear resonant actuator  153   b  may be disposed on the upper side of the display part  151 , and the piezoelectric actuator  153   a  may be disposed on the lower side thereof. As another example, of course, the piezoelectric actuators may be disposed on the upper and lower sides of the display part  151 . 
     The controller  180  uses the touch sensor of the display part  151  to sense the touch position of the display part  151  and drives any one of the plurality of vibration elements  153   a  and  153   b  to generate vibration based on the sensed touch position. For example, the controller  180  can drive the vibration element adjacent to the touch position. 
     As shown in  FIG. 10 ( a ) , when the upper region of the display part  151  is touched, the controller  180  drives the vibration element  153   b  positioned on the upper side of the display part  151 . Here, the vibration element  153   a  positioned on the lower side of the display part  151  is not driven. 
     Here, when the touch is moved, the controller  180  drives the vibration element  153   a , instead of the vibration element  153   b , to generate vibration based on the moved touch position. For example, the controller  180  can drive the vibration element  153   a  adjacent to the touch position. 
     As shown in  FIGS. 10B and 10C , when the touch is moved from the upper region to the lower region of the display part  151 , the controller  180  drives the vibration element  153   a  positioned on the lower side of the display part  151 . Here, when the vibration element  153   a  positioned on the lower side is driven, the vibration element  153   b  positioned on the upper side of the display part  151  is not driven. 
     In addition, the controller  180  can control a voltage (or current) applied to the vibration element  153   a  and  153   b  adjacent to the touch position, based on a distance between the touch position and the adjacent vibration element  153   a  and  153   b . That is, the controller  180  can control a voltage applied to the vibration element  153   a  and  153   b  to change the frequency, intensity, pattern, etc. of the vibration generated in the vibration element  153   a  and  153   b . Therefore, the user may feel different whenever moving the finger touching the display part  151 . 
     For example, when the distance between the touch position and the vibration element  153   a  and  153   b  adjacent to the touch position becomes smaller, the controller  180  can increase a current applied to the adjacent vibration element  153   a  and  153   b  to increase the intensity of the vibration. 
       FIG. 11  is a concept view showing one example of a method of controlling the mobile terminal  100  using a grip sensor  145  and a plurality of vibration elements  153   a  and  153   b.    
     Referring to  FIG. 11 , the mobile terminal  100  is equipped with the plurality of vibration elements  153   a  and  153   b . For example, the vibration elements may be spaced apart in the longitudinal direction of the display part  151 . 
     At least one of the plurality of vibration elements  153   a  and  153   b  can be the piezoelectric actuator  153   a . As an example, a linear resonant actuator may be disposed on the upper side of the display part  151 , and the piezoelectric actuator  153   a  may be disposed thereunder. As another example, of course, the piezoelectric actuators  153   a  may be spaced apart vertically along the longitudinal direction the display part  151 . 
     The mobile terminal  100  may be equipped with a grip sensor part for sensing the grip of the terminal body. The grip sensor part may include a first grip sensor  145   a  and a second grip sensor  145   b  that are disposed vertically on the left side and the right side of the terminal body, respectively. The first and second grip sensors  145   a  and  145   b  may be configured to sense a pressure or touch during the grip. 
     When the user grips the terminal body with one hand, the user&#39;s finger or palm is brought into contact with at least some portion of the grip sensor part disposed vertically. For example, as shown in  FIGS. 11A to 11C , portions of the first and second grip sensors  145   a  and  145   b  which the user&#39;s finger or palm contacts may vary depending on the grip type. 
     The controller  180  uses the grip sensor part to sense the grip of the terminal body and controls the driving of each of the plurality of vibration elements  153   a  and  153   b  to output one of the plurality of vibration patterns depending on the sensed grip position. 
     The controller  180  may use the first and second grip sensors  145   a  and  145   b  to calculate the grip positions or the distribution of the grip positions to distinguish grip states. As an example, as shown in  FIGS. 11A to 11C , the grip states may be divided into first to third grip states. 
     When the grips of the first and second grip sensors  145   a  and  145   b  are all sensed, the controller  180  can distinguish the grip state into the first or second grip state based on the grip positions or the distribution of the grip positions of the first or second grip sensor  145   a  or  145   b.    
     For example, as shown in  FIG. 11 ( a ) , when the grips of the upper side and the lower side of the first grip sensor  145   a  are all sensed, the controller  180  can determine the grip state as the first grip state and drive any one of the plurality of vibration elements  153   a  and  153   b . Meanwhile, as shown in  FIG. 11 ( b ) , when only the grip of the lower side of the first grip sensor  145   a  is sensed, the controller  180  can determine the grip state as the second grip state and drive a different one of the plurality of vibration elements  153   a  and  153   b.    
     When only the grip of one of the first and second grip sensors  145   a  and  145   b  is sensed, the controller  180  can determine the grip state as the third grip state and drive the plurality of vibration elements  153   a  and  153   b . It can be understood that this using aspect occurs when the user grips the terminal body less than  FIGS. 11A and 11B . Accordingly, it is possible to transfer vibration through the plurality of vibration elements  153   a  and  153   b  to clearly transfer haptic feedback to the user. 
       FIG. 12  is a concept view showing another example of the method of controlling the mobile terminal  100  using a grip sensor  145  and the plurality of vibration elements  153   a  and  153   b.    
     Referring to  FIG. 12 , the mobile terminal  100  is equipped with the plurality of vibration elements  153   a  and  153   b . For example, the plurality of vibration elements  153   a  and  153   b  may be spaced apart in the longitudinal direction of the display part  151 . 
     At least one of the plurality of vibration elements  153   a  and  153   b  can be the piezoelectric actuator  153   a . As an example, a linear resonant actuator may be disposed on the upper side of the display part  151 , and the piezoelectric actuator  153   a  may be disposed thereunder. As another example, of course, the piezoelectric actuators  153   a  may be spaced apart vertically along the longitudinal direction the display part  151 . 
     It is noted that, in the drawing, the mobile terminal  100  is rotated by 90 degrees to be placed in the transverse direction. Therefore, in the drawing, it can be understood that the plurality of vibration elements  153   a  and  153   b  are spaced apart along the transverse direction of the display part  151 . 
     The mobile terminal  100  may be equipped with the grip sensor  145  for sensing the grip of the terminal body. The grip sensor  145  may be disposed vertically on one side (at least one of the left side and the right side) of the terminal body. The grip sensor  145  may be configured to sense a pressure or touch during the grip. 
     For example, the grip sensor  145  may be disposed on the right side of the terminal body. When the mobile terminal  100  is rotated by 90 degrees, the grip sensor  145  is disposed on the upper side of the mobile terminal  100 . 
     When the user grips the terminal body in the transverse direction with both hands, the left and right fingers (generally, index fingers) of the user are brought into contact with the grip sensor  145 , respectively. As shown, the left index finger contacts the left side of the grip sensor  145  and the right index finger contacts the right side of the grip sensor  145 . 
     The controller  180  uses the grip sensor  145  to sense the grip of the terminal body and outputs a graphic object G 2  to the display part  151  when the grip is sensed. The controller  180  may be configured to display the graphic object G 2  only when the multi-contact is made to the grip sensor  145 , which makes it possible for this function to be performed only when the user grips the terminal body in the transverse direction with both hands. 
     The graphic object G 2  may be displayed adjacent to one side of the terminal body on which the grip sensor  145  is disposed. The graphic object G 2  may be a type of indicator informing the user of the function capable of changing visual information outputted to the display part  151  depending on the movement of the grip. 
     The portion of the display part  151  with the graphic object G 2  displayed thereon may be changed according to the setting. For example, when the right-hander is set, the controller can display the graphic object G 2  on the display part  151  adjacent to the right side of the grip sensor  145 . On the contrary, when the left-hander is set, the controller can display the graphic object G 2  on the display part  151  adjacent to the left side of the grip sensor  145 . 
     When the movement of the grip is sensed, the controller  180  drives any one of the plurality of vibration elements  153   a  and  153   b  to generate vibration based on the moved grip position. The controller  180  may drive the vibration element  153   a , which is adjacent to the movement-sensed grip position, of the plurality of vibration elements  153   a  and  153   b . For example, as shown, when the right index finger contacting the grip sensor  145  is moved to the left and right, the vibration element  153   a  disposed on the right side in the drawing is driven to generate vibration. 
     The controller  180  can control a current applied to the adjacent vibration element  153   a  and  153   b  based on the moved grip position. That is, the controller  180  can control a current applied to the vibration element  153   a  and  153   b  to change the frequency, intensity, pattern, etc. of the vibration generated in the vibration element  153   a  and  153   b . Therefore, the user may feel different whenever moving the finger touching the grip sensor  145 . 
     For example, when the right index finger contacting the grip sensor  145  is moved to the left side, the controller  180  can increase a current applied to the adjacent vibration element  153   a  to increase the intensity of the vibration. 
     In addition, the controller  180  may change visual information outputted to the display part  151  depending on the moved grip position. For example, when the grip position is moved, the controller  180  can enlarge or reduce visual information outputted to the display part  151 . Here, the aforementioned graphic object G 2  may be changed corresponding to the movement of the grip position. 
     While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.