Patent Publication Number: US-2021167274-A1

Title: Piezoelectric device and method for manufacturing the same, and display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Chinese Patent Application No. 201911207749.2, filed on Nov. 29, 2019, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of sensing technologies, and in particular, to a piezoelectric device and a method for manufacturing the same, and a display apparatus. 
     BACKGROUND 
     Ultrasonic waves are a type of mechanical waves having advantages of high frequency, short wavelength, good directivity, directional propagation and high penetration rate. Ultrasonic sensors are sensors that convert ultrasonic signals into other energy signals (typically electrical signals). 
     Sensing materials in the ultrasonic sensors mainly are piezoelectric materials or nickel-iron-aluminum alloy materials. The piezoelectric materials includes piezoelectric crystals, piezoelectric ceramics, and a piezoelectric high polymer material. Ultrasonic sensors whose sensing materials are mainly made of the piezoelectric materials, i.e., piezoelectric sensors, are reversible sensors that are capable of converting electrical signals into mechanical oscillations to generate ultrasonic signals, and are also capable of converting received ultrasonic signals into electrical signals. Therefore, the ultrasonic sensors include transmitting sensors, receiving sensors, and transmitting-receiving ultrasonic sensors. 
     SUMMARY 
     In first aspect, a piezoelectric device is provided. The piezoelectric device includes a base having at least one hole, a heat conductive portion disposed in the at least one hole and in contact with a wall of the at least one hole, and at least one piezoelectric sensor disposed on the base. A thermal conductivity of the heat conductive portion is greater than a thermal conductivity of the base. Each piezoelectric sensor includes a first electrode, a piezoelectric pattern made of a piezoelectric material and a second electrode that are sequentially stacked in a thickness direction of the base. 
     In some embodiments, a depth of the at least one hole is less than a thickness of the base in the thickness direction of the base. 
     In some embodiments, the base further has a first surface and a second surface that are opposite to each other in the thickness direction of the base. The at least one hole is disposed in the first surface, and the at least one piezoelectric sensor is disposed on the second surface. 
     In some embodiments, a thickness of the heat conductive portion is equal to a depth of the at least one hole in the thickness direction of the base. 
     In some embodiments, the thermal conductivity of the heat conductive portion is in a range from approximately 120 W/mK to approximately 450 W/mK. 
     In some embodiments, the at least one hole includes a plurality of holes spaced apart from each other. 
     In some embodiments, an orthographic projection of one piezoelectric sensor on the base does not overlap with any hole. In some other embodiments, the orthographic projection of one piezoelectric sensor on the base overlaps with at least one of the plurality of holes. 
     In some embodiments, the heat conductive portion includes a plurality of heat conductive blocks spaced apart from each other, and each heat conductive block is disposed in a respective one of the plurality of holes. 
     In some embodiments, the piezoelectric device further includes at least one connecting electrode. The at least one piezoelectric sensor includes a plurality of piezoelectric sensors spaced apart from each other, and second electrodes in all piezoelectric sensors are electrically connected by the at least one connecting electrode. 
     In some embodiments, a size of the at least one piezoelectric pattern is in an order of micrometers or nanometers. 
     In second aspect, a display apparatus is provided. The display apparatus includes a display panel, and the piezoelectric device according to the above embodiments, disposed on a side of the display panel. 
     In some embodiments, the display panel includes a plurality of sub-pixels. An orthographic projection of one piezoelectric sensor in the piezoelectric device on the display panel has an overlapping region with M sub-pixels in the plurality of sub-pixels, M being an integer greater than zero and less than four. 
     In some embodiments, an orthographic projection of a first electrode of the piezoelectric sensor on the display panel completely overlaps with one of the M sub-pixels. An orthographic projection of a piezoelectric pattern of the piezoelectric sensor on the display panel has an overlapping region with the M sub-pixels. 
     In third aspect, a method for manufacturing the piezoelectric device according to the above embodiments. The method includes: forming the base having the at least one hole; forming the heat conductive portion in the at least one hole; wherein the heat conductive portion is in contact with the wall of the at least one hole, and the thermal conductivity of the heat conductive portion is greater than the thermal conductivity of the base; and forming the at least one piezoelectric sensor on the base. Each piezoelectric sensor includes the first electrode, the piezoelectric pattern made of the piezoelectric material and the second electrode that are sequentially formed on the base. 
     In some embodiments, the base further has a first surface and a second surface that are opposite to each other in the thickness direction of the base. Forming the base having the at least one hole, includes: forming the at least one hole in the first surface by a dry etching process, a wet etching process, or a laser drilling process. Forming the at least one piezoelectric sensor on the base, includes: forming the at least one piezoelectric sensor on the second surface. 
     In some embodiments, forming the heat conductive portion in the at least one hole, includes: forming the heat conductive portion in the at least one hole by an evaporation process or an electroplating process. 
     In some embodiments, forming the at least one piezoelectric sensor on the base, includes: forming at least one first electrode on the base; forming a piezoelectric film on the at least one first electrode; forming at least one protective pattern made of a conductive material on the piezoelectric film; wherein an area of an orthographic projection of each protective pattern on the base is less than an area of an orthographic projection of the piezoelectric film on the base; removing a portion of the piezoelectric film that is not covered by the at least one protective pattern by an etching process to form at least one piezoelectric pattern; and forming a conductive film on the at least one protective pattern. Each protective pattern and a portion of the conductive film that is in contact with the protective pattern forming a second electrode. 
     In some other embodiments, forming the at least one piezoelectric sensor on the base, includes: forming at least one first electrode on the base; forming a piezoelectric film on the at least one first electrode; forming at least one second electrode on the piezoelectric film; wherein an area of an orthographic projection of each second electrode on the base is less than an area of an orthographic projection of the piezoelectric film on the base; and removing a portion of the piezoelectric film that is not covered by the at least one second electrode by an etching process to form at least one piezoelectric pattern. 
     In yet some other embodiments, forming the at least one piezoelectric sensor on the base, includes: forming at least one first electrode on the base; forming a piezoelectric film on the at least one first electrode; forming at least one third photoresist pattern on the piezoelectric film; wherein an area of an orthographic projection of each third photoresist pattern on the base is less than an area of an orthographic projection of the piezoelectric film on the base; removing a portion of the piezoelectric film that is not covered by the at least one third photoresist pattern by an etching process to form at least one piezoelectric pattern; removing the at least one third photoresist pattern; and forming a second electrode on each piezoelectric pattern. 
     In some embodiments, forming the at least one protective pattern on the piezoelectric film, includes: forming a first conductive layer on the piezoelectric film; forming a photoresist layer on the first conductive layer; patterning the photoresist layer to form at least one first photoresist pattern; wherein an area of an orthographic projection of each first photoresist pattern on the base is less than an area of an orthographic projection of the piezoelectric film on the base; and etching a region in the first conductive layer that is not covered by the at least one first photoresist pattern to form the at least one protective pattern. 
     In some other embodiments, forming the at least one second electrode on the piezoelectric film, includes: forming a second conductive layer on the piezoelectric film; forming a photoresist layer on the second conductive layer; wherein an area of an orthographic projection of each second photoresist pattern on the base is less than an area of an orthographic projection of the piezoelectric film on the base; patterning the photoresist layer to form at least one second photoresist pattern; and etching a region in the second conductive layer that is not covered by the at least one second photoresist pattern to form the at least one second electrode. 
     In fourth aspect, a method for manufacturing a piezoelectric device is provided. The method includes: forming at least one hole in a first surface of a base, a depth of the at least one hole being less than a thickness of the base; forming a heat conductive portion in the at least one hole; wherein the heat conductive portion is in contact with a wall of the at least one hole, and a thermal conductivity of the heat conductive portion is greater than a thermal conductivity of the base; forming at least one piezoelectric sensor on a second surface of the base opposite to the first surface; wherein each piezoelectric sensor includes a first electrode, a piezoelectric pattern made of a piezoelectric material and a second electrode that are sequentially formed on the base; and thinning the base to remove the at least one hole and the heat conductive portion therein. 
     In fifth aspect, a piezoelectric device is provided, obtained by using the method according to the above embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe technical solutions in the present disclosure more clearly, accompanying drawings to be used in some embodiments of the present disclosure will be introduced briefly. However, the accompanying drawings to be described below are merely accompanying drawings of some embodiments of the present disclosure, and a person of ordinary skill in the art can obtain other drawings according to these drawings. In addition, accompanying drawings in the following description may be regarded as schematic diagrams, and are not limitations on actual sizes of products, an actual process of a method and so on that the embodiments of the present disclosure relate to. 
         FIG. 1A  is a schematic diagram of a piezoelectric device, in accordance with some embodiments; 
         FIG. 1B  is a schematic diagram of another piezoelectric device, in accordance with some embodiments; 
         FIG. 1C  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 1D  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 1E  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 2A  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 2B  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 2C  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 3  is a graph showing a relationship between the temperature and a piezoelectric constant of a piezoelectric material in a piezoelectric sensor, in accordance with some embodiments; 
         FIG. 4A  is a schematic diagram showing a method for manufacturing a piezoelectric layer of a piezoelectric device in the related art; 
         FIG. 4B  is a schematic diagram showing another method for manufacturing the piezoelectric layer of the piezoelectric device in the related art; 
         FIG. 4C  is a schematic diagram of the piezoelectric sensor in the related art; 
         FIG. 5A  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 5B  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 6  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 7  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; 
         FIG. 8A  is a schematic diagram of a display apparatus, in accordance with some embodiments; 
         FIG. 8B  is a schematic diagram of another display apparatus, in accordance with some embodiments; 
         FIG. 8C  is a schematic diagram of yet another display apparatus, in accordance with some embodiments; 
         FIG. 9A  is a schematic diagram showing a corresponding relationship between a sub-pixel and a piezoelectric sensor in a display apparatus, in accordance with some embodiments; 
         FIG. 9B  is a schematic diagram showing another corresponding relationship between a sub-pixel and a piezoelectric sensor in a display apparatus, in accordance with some embodiments; 
         FIG. 10A  is a flow diagram of a method for manufacturing a piezoelectric device, in accordance with some embodiments; 
         FIGS. 10B to 10C  are schematic diagrams showing a process of manufacturing a piezoelectric device, in accordance with some embodiments; 
         FIG. 11A  is a schematic diagram of a base in a piezoelectric device, in accordance with some embodiments; 
         FIG. 11B  is a schematic diagram of a base in another piezoelectric device, in accordance with some embodiments; 
         FIG. 12A  is a flow diagram of a method for manufacturing a piezoelectric sensor, in accordance with some embodiments; 
         FIGS. 12B to 12F  are schematic diagrams showing a process of manufacturing a piezoelectric sensor, in accordance with some embodiments; 
         FIG. 13A  is a flow diagram of a method for manufacturing another piezoelectric sensor, in accordance with some embodiments; 
         FIGS. 13B to 131  are schematic diagrams showing a process of manufacturing another piezoelectric sensor, in accordance with some embodiments; 
         FIG. 14A  is a flow diagram of a method for manufacturing yet another piezoelectric sensor, in accordance with some embodiments; 
         FIG. 14B  is a schematic diagram showing a process of manufacturing yet another piezoelectric sensor, in accordance with some embodiments; 
         FIGS. 15A to 15E  are schematic diagrams showing a process of forming a second electrode in a piezoelectric sensor, in accordance with some embodiments; 
         FIG. 16A  is a flow diagram of a method for manufacturing another piezoelectric sensor, in accordance with some embodiments; 
         FIG. 16B  is a schematic diagram of yet another piezoelectric device, in accordance with some embodiments; and 
         FIG. 17  is a scanning electron microscope (SEM) photograph of a piezoelectric pattern, in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Technical solutions in embodiments of the present disclosure will be described clearly and completely in combination with accompanying drawings in the embodiments of the present disclosure. However, the described embodiments are merely some but not all embodiments of the present disclosure. All other embodiments obtained on a basis of the embodiments of the present disclosure by a person of ordinary skill in the art without paying any creative effort shall be included in the protection scope of the present disclosure. 
     Unless the context requires otherwise, the term “comprise” and other forms thereof such as the third-person singular form “comprises” and the present participle form “comprising” in the description and the claims are construed as open and inclusive, i.e., “including, but not limited to”. In the description of the specification, the terms such as “one embodiment”, “some embodiments”, “exemplary embodiments”, “example”, “specific example” or “some examples” are intended to indicate that specific features, structures, materials or characteristics related to the embodiment(s) or the example(s) are included in at least one embodiment or example of the present disclosure. Schematic representations of the above terms do not necessarily refer to the same embodiment(s) or example(s). In addition, the specific features, structures, materials or characteristics may be included in any one or more embodiments/examples in any suitable manner. 
     In addition, the terms such as “first” and “second” are used for descriptive purposes only and are not to be construed as indicating or implying the relative importance or implicitly indicating the number of indicated technical features below. Thus, features defined as “first” and “second” may explicitly or implicitly include one or more of the features. As used in the Description and the claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. In the description of the embodiments of the present disclosure, the term “a/the plurality of” means two or more unless otherwise specified. 
     It will be understood that when a layer or element is referred to as being “on” another layer or substrate, it may be directly on the another layer or substrate, or one or more intervening layers or elements may also be present. Further, it will also be understood that when a layer or element is referred to as being “under” another layer or substrate, it may be directly under the layer or substrate, and one or more intervening layers or elements may also be present. Similarly, it will also be understood that when a layer or element is referred to as being “between” two layers or elements, it may be the only layer or element between the two layers or elements, or one or more intervening layers may also be present. 
     Some embodiments may be described using the expression “coupled” and “connected” along with their derivatives. For example, some embodiments may be described using the term “connected” to indicate that two or more elements are in direct physical or electrical contact with each other. In another example, some embodiments may be described using the term “coupled” to indicate that two or more elements are in direct physical or electrical contact. The term “coupled” or “communicatively coupled”, however, may also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other. The embodiments disclosed herein are not necessarily limited in this context. 
     Exemplary embodiments are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present claims. 
     In this Description, the term “thickness” means an average value of the thickness of each part of a layer or element, or means a general, overall thickness of the layer or element. 
     In addition, “about” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±30%, ±20%, ±10% or ±5% of the stated value. 
     In recent years, with the development of intelligent electronic products and increasing requirements of users for security and privacy of the electronic products, a biometric identification technology has developed rapidly, which is particularly represented by a fingerprint identification technology and facial identification technology. 
     An ultrasonic technology is widely used due to its advantages of good stability and high accuracy. Taking the fingerprint identification as an example, when a fingerprint is collected by using the ultrasonic technology, the collected fingerprint may be not affected by dirt (e.g., sweat, hand cream or gel) on a surface of the finger. 
     In a case where the ultrasonic technology is applied to the fingerprint identification, ultrasonic signals are generated by mechanical oscillation of a piezoelectric material in a piezoelectric sensor. After the ultrasonic signals are reflected by the finger, the piezoelectric sensor is capable of receiving the reflected ultrasonic signals, and converting the received ultrasonic signals into electrical signals to identify the fingerprint information. 
     Of course, the ultrasonic technology may be applied not only to the fingerprint identification technology and the facial identification technology, but also to technologies such as a tactile feedback technology, a medical measurement, a mechanical measurement. Therefore, the ultrasonic technology has become a current research hotspot. 
     Some embodiments of the present disclosure provide a piezoelectric device capable of generating ultrasonic signals and receiving reflected ultrasonic signals. 
     As shown in any one of  FIGS. 1A to 2C , the piezoelectric device  1  includes a base  2 , a heat conductive portion  12 , and at least one piezoelectric sensor  10 . 
     The base  2  is generally in a shape of a plate, and  FIGS. 1A to 2C  are sectional structural diagrams of the piezoelectric device  1  along a thickness direction of the base  2 . The base  2  may be a rigid base or a flexible base. The rigid base is, for example, a glass base with a thermal conductivity of approximately 1.1 W/mK (Watts per meter Kelvin). The flexible base is, for example, a polyimide (PI) base with a thermal conductivity of approximately 0.15 W/mK. 
     The base  2  is provided with at least one hole  11 . For example, the base  2  provided with the at least one hole  11  may be obtained by etching a substrate. 
     The heat conductive portion  12  is disposed in the at least one hole  11 , and in contact with a wall of the at least one hole  11 . For example, the at least one hole  11  includes a plurality of holes  11 , the heat conductive portion  12  includes a plurality of heat conductive blocks  120 , and each heat conductive block  120  is disposed in a respective one of the plurality of holes  11 . 
     A thermal conductivity of the heat conductive portion  12  is greater than the thermal conductivity of the base  2 . Herein, the thermal conductivity of the heat conductive portion  12  refers to a thermal conductivity of a material of the heat conductive portion  12 , and the thermal conductivity of the base  2  refers to a thermal conductivity of a material (e.g., glass or PI) of the base  2 . 
     The heat conductive portion  12  may be a metal heat conductive portion, an inorganic heat conductive portion, or an organic heat conductive portion, according to a type of a heat conductive material for forming the heat conductive portion  12 . The metal heat conductive portion may be made of a metal material, for example, silver (Ag), aluminum (Al), or copper (Cu). A thermal conductivity of Ag is approximately 429 W/mK, a thermal conductivity of Al is approximately 237 W/mK, and a thermal conductivity of Cu is approximately 400 W/mK. The inorganic heat conductive portion may be made of, for example, silicon with a thermal conductivity of approximately 148 W/mK. 
     The heat conductive portion  12  may be obtained by filling the at least one hole  11  with the heat conductive material by an evaporation process, an electroplating process or a coating process. 
     The at least one piezoelectric sensor  10  is disposed on the base  2 . In some examples, the at least one piezoelectric sensor  10  includes a plurality of piezoelectric sensors  10  arranged in an array. Of course, the piezoelectric sensors  10  may also be arranged in other ways according to actual needs, such as arranged in a certain pattern. 
     Each piezoelectric sensor  10  includes a first electrode  101 , a piezoelectric pattern  103  and a second electrode  102  that are sequentially stacked in the thickness direction of the base  2 , and the piezoelectric pattern  103  is made of a piezoelectric material. That is, in a same piezoelectric sensor  10 , an orthographic projection of the first electrode  101 , an orthographic projection of the piezoelectric pattern  103 , and an orthographic projection of the second electrode  102  on the base  2  have overlapping regions. 
     The first electrode  101  and the second electrode  102  in the piezoelectric sensor  10  are insulated from each other. The first electrode  101  or the second electrode  102  is made of a metal or a transparent conductive oxide. The metal includes at least one of a metal element and an alloy. The metal element may be, for example, Ag, Al or Cu, and the transparent conductive oxide may be indium tin oxide (ITO) or indium zinc oxide (IZO). 
     The piezoelectric sensor  10  may include one or more first electrodes  101 . In a case where the piezoelectric sensor  10  includes a plurality of piezoelectric sensors  10 , first electrodes  101  in different piezoelectric sensors  10  are insulated from each other. Second electrodes  102  in the plurality of piezoelectric sensors  10  may be separately disposed, or may be connected to each other to form an integrated structure, which is not limited in the embodiments of the present disclosure, as long as it may be ensured that each piezoelectric sensor  10  may be separately controlled. 
     It will be noted that, the piezoelectric sensor  10  may be disposed on a surface of the base  2 , or an insulating layer may be disposed between the piezoelectric sensor  10  and the base  2 , and the piezoelectric sensor  10  and the base  2  are in contact with two opposite surfaces of the insulating layer, respectively. In the case where there are the plurality of piezoelectric sensors  10 , as long as it is ensured that the plurality of piezoelectric sensors  10  are not short-circuited due to an existence of the heat conductive portion  12  in the at least one hole  11 . 
     The piezoelectric pattern  103  in the piezoelectric sensor  10  is made of the piezoelectric material. For example, the piezoelectric material is a ferroelectric polymer, such as poly vinyledene fluoride-trifluoroethylene (PVDF-TrFE), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), or polytetrafluoroethylene (PTFE). 
     When a piezoelectric material subjected to a polarization treatment is subjected to an external force, opposite charges are generated on two opposite surfaces of the piezoelectric material in a polarization direction. This process is referred to as a positive piezoelectric effect. In contrast, when voltages are applied to electrodes on two opposite sides of the piezoelectric material (e.g., the first electrode  101  and the second electrode  102  on two opposite sides of the piezoelectric pattern  103 ), the piezoelectric material is in an electric field, and elongated stress or compressed stress (mechanical stress) will be generated within the piezoelectric material. This process is referred to as an inverse piezoelectric effect. In this case, If high-frequency voltages are applied, high-frequency mechanical vibration, i.e., ultrasonic signals are generated. 
     The piezoelectric sensor  10  operates mainly by using the positive piezoelectric effect and the inverse piezoelectric effect of the piezoelectric material. The polarization treatment herein means that after the piezoelectric pattern  103  or a piezoelectric film for forming the piezoelectric pattern  103  is formed, the polarization treatment is performed on the piezoelectric pattern  103  or the piezoelectric film by applying an external electric field perpendicular to the base  2 , so that electric domains inside the piezoelectric pattern  103  or the piezoelectric film are arranged in order in a direction of the electric field. 
     It will be understood that, in a case where the piezoelectric material is applied to the piezoelectric sensor  10 , a structure (i.e., the piezoelectric pattern  103 ) formed by the piezoelectric material needs to be subjected to the polarization treatment, so as to make a piezoelectric performance of the piezoelectric material well embodied. 
     By taking an example in which the piezoelectric sensor  10  is used for the fingerprint identification, the piezoelectric pattern  103  generates and emits ultrasonic signals under action of an electric field generated by the first electrode  101  and the second electrode  102 . The ultrasonic signals will be reflected when blocked by a finger. After receiving the reflected ultrasonic signals, the piezoelectric pattern  103  converts the received ultrasonic signals into corresponding electrical signals. On this basis, the electrical signals may be transmitted to, for example, a processor through the first electrode  101  and the second electrode  102 . Finally, a corresponding image of a fingerprint is obtained through specific calculation by the processor. 
     However, a piezoelectric constant of the piezoelectric material is affected by temperature. By taking an example in which the piezoelectric material is PVDF, as shown in  FIG. 3 , as the temperature increases, the piezoelectric constant of PVDF decreases. Especially when the temperature is greater than 130° C., the piezoelectric constant of PVDF decreases sharply, thereby causing a decrease in a vibration frequency generated by the piezoelectric material. Thus, not only is an identification accuracy of the piezoelectric sensor  10  reduced, but also power consumption of the piezoelectric sensor  10  is increased. Herein, it is only to explain a trend of an impact of the temperature on the piezoelectric material, and not to limit the temperature at which the characteristics of the piezoelectric material change drastically. 
     It will be noted that, a relationship between the piezoelectric constant and temperature in  FIG. 3  is described by taking the example in which the piezoelectric material is PVDF. In a case where the piezoelectric material is another material, the relationship between the piezoelectric constant of the piezoelectric material and the temperature has similar change characteristics to the PVDF material. 
     Moreover, the piezoelectric material will generate heat in a process of generating high-frequency vibration to emit the ultrasonic signals by being excited by an electric field, and a large amount of heat will also be generated in a process of manufacturing the piezoelectric sensor  10 . As will be seen from the above description, if the heat cannot be transferred and dissipated in time, performances of the piezoelectric sensor  10  will be affected. 
     In the piezoelectric device  1  provided by the embodiments of the present disclosure, the base  2  is provided with the at least one hole  11 . The at least one hole  11  is filled with the heat conductive material, and the thermal conductivity of the heat conductive material is greater than the thermal conductivity of the base  2 . 
     In this way, on one hand, the heat conductive portion  12  may make the heat generated by the piezoelectric sensor  10  to be quickly conducted to an outer side of the piezoelectric device  1  toward a side away from the piezoelectric sensor  10  through the heat conductive portion  12 , without being accumulated in the base  2 . Therefore, the heat may be prevented from being continuously accumulated in the piezoelectric sensor  10 , thereby improving a heat dissipation efficiency and a heat dissipation performance of the whole piezoelectric device  1 . After a heat dissipation performance of the piezoelectric device  1  is improved, a working performance and an identification accuracy of the piezoelectric sensor  10  may be ensured, and the power consumption of the piezoelectric sensor  10  may be reduced. On another hand, the heat generated in the process of manufacturing the piezoelectric sensor  10  may also be quickly conducted to the outer side of the piezoelectric device  1  toward the side away from the piezoelectric sensor  10 . Therefore, an impact of high temperature on the piezoelectric constant of the piezoelectric sensor  10  is avoided, thereby ensuring the working performance of the piezoelectric device  1 . 
     Optionally, the thermal conductivity of the heat conductive portion  12  is in a range from approximately 120 W/mK to approximately 450 W/mK, such as, 150 W/mK, 200 W/m K, 240 W/m K, 300 W/m K, 350 W/m K, 380 W/m K, 400 W/mK, 430 W/m K, or 450 W/mK. The thermal conductivity of the heat conductive portion  12  is much greater than the thermal conductivity of the base  2  (e.g., 1.1 W/mK or 0.15 W/mK). Therefore, compared with a base of a same thickness and without the heat conductive portion  12 , the base  2  provided with the heat conductive portion  12  in the embodiments of the present disclosure may make the heat transferred to the side away from the piezoelectric sensor  10  more quickly, thereby dissipating the heat quickly. 
       FIG. 4C  shows a structure of an illustrative piezoelectric sensor in the related art. The piezoelectric sensor includes a base  2 ′, and a lower electrode  51 , a piezoelectric layer  41 , and an upper electrode  52  that are sequentially stacked on the base  2 ′. As shown in  FIG. 4C , the upper electrode  52  may include a plurality of sub-electrodes  520  spaced apart from each other, or may be one electrode. 
     In the related art, the piezoelectric sensor may be formed in the following two methods. 
     In one method, as shown in  FIG. 4A , a piezoelectric film  4  is formed on a motherboard base on which a lower electrode layer is formed by a spin coating process, and an upper electrode layer is formed on the piezoelectric film  4 . Then, a motherboard including the piezoelectric film  4  is cut into a plurality of small pieces along cutting lines  50  intersecting each other horizontally and vertically, and each small piece serves as one piezoelectric sensor, thereby obtaining the piezoelectric sensor shown in  FIG. 4C , and the piezoelectric layer  41  in the piezoelectric sensor has a whole-layer structure. 
     In the other method, as shown in  FIG. 4B , a plurality of piezoelectric layers  41  spaced apart from each other are formed on a motherboard base on which a lower electrode layer is formed by a slot blade coating process, and an upper electrode layer is formed on the piezoelectric layers  41 . Then, a motherboard region corresponding to each piezoelectric layer  41  is cut along cutting lines  50  intersecting each other horizontally and vertically, and the motherboard region after being cut serves as one piezoelectric sensor, thereby obtaining the piezoelectric sensor shown in  FIG. 4C , and the piezoelectric layer  41  in the piezoelectric sensor has a whole-layer structure. 
     In the above related art, limited by cutting technology, a size of the piezoelectric layer  41  in the cut piezoelectric sensor is at least in an order of millimeters. However, a measurement accuracy of the piezoelectric sensor including the piezoelectric layer  41  of a millimeter-scale size or even a larger size is low, Therefore, the piezoelectric sensor  1  cannot accurately measure a region of a smaller size (i.e., a size less than the size of the piezoelectric layer  41 ). 
     In some embodiments of the present disclosure, the at least one piezoelectric sensor  10  includes a plurality of piezoelectric sensors  10  spaced apart from each other. Each piezoelectric sensor  10  includes a first electrode  101 , a piezoelectric pattern  103 , and a second electrode  102 . First electrodes  101  in different piezoelectric sensors  10  are insulated from each other. Therefore, each piezoelectric sensor  10  may be separately controlled. 
     A sum of regions where all piezoelectric sensors  10  are located is a measurement region of the piezoelectric device  1 , and a region where each piezoelectric sensor  10  is located may be regarded as a measurement sub-region. Since each piezoelectric sensor  10  may be separately controlled, a measurement sub-region corresponding to each piezoelectric sensor  10  may be separately measured. That is, the piezoelectric device  1  is capable of separately measuring the measurement sub-region having a size equivalent to a size of the piezoelectric pattern  103 , thereby improving the measurement accuracy of the piezoelectric device  1 . 
     Optionally, a size of the piezoelectric pattern  103  is in an order of micrometers or nanometers. That is, a length of each side of the piezoelectric pattern  103  may be less than 1,000 micrometers, or further may be less than 1,000 nanometers. The smaller the size of the piezoelectric pattern  103  is, the smaller the size of the measurement sub-region is, the greater the number of measurement sub-regions in a measurement region of a same area, then the higher the measurement accuracy is. Therefore, in the embodiments of the present disclosure, a measurement accuracy of a piezoelectric pattern  103  of a micrometer-scale size or a nanometer-scale size is higher than a measurement accuracy of a piezoelectric pattern of a millimeter-scale size obtained by cutting in the above related art. 
     In a direction parallel to the base  2 , a shape of a section (i.e., cross-section) of any hole  11  may be a circle, an ellipse, a rectangle, a long strip or other irregular patterns, the embodiments of the present disclosure do not limit this. 
     In some embodiments, as shown in  FIGS. 1A and 2A , the holes  11  penetrate the base  2 . That is, in the thickness direction of the base  2 , a depth of the holes  11  is equal to the thickness of the base  2 . In this case, the holes  11  are through holes (i.e., openings) formed in the base  2 . 
     In some other embodiments, as shown in  FIGS. 1B to 1E, 2B and 2C , in the thickness direction of the base  2 , the depth of the hole  11  is less than the thickness of the base  2 , that is, the hole  11  does not penetrate the base  2 . In this case, the hole  11  is a blind hole (i.e., a groove) formed in the base  2 . 
     Optionally, as shown in  FIGS. 1B, 1D, 1E and 2B , the hole  11  is disposed in a first surface  21  of the base  2 , the piezoelectric sensors  10  are disposed on a second surface  22  of the base  2 . The first surface  21  and the second surface  22  are two opposite surfaces in the thickness direction of the base  2 . By arranging the piezoelectric sensors  10  and the heat conductive portion  12  at two opposite sides of the base  2  respectively, a flat bearing surface may be provided for the piezoelectric sensors  10  to ensure that different piezoelectric sensors  10  are at a same height, thereby ensuring that a distance from each piezoelectric sensor  10  to a detection surface (i.e., a surface in contact with the finger) is equal in the case where the piezoelectric device  1  is applied to the fingerprint identification. 
     In some embodiments, as shown in  FIGS. 1A to 1C, 1E and 2A to 2C , in the thickness direction of the base  2 , a thickness of the heat conductive portion  12  is equal to the depth of the hole  11 . 
     That is, in a case where the hole  11  is a through hole, the first surface  21  and a surface of the heat conductive portion  12  facing the first surface  21  are in a same plane (or approximately in a same plane), and the second surface  22  and a surface of the heat conductive portion  12  facing the second surface  22  are in a same plane (or approximately in a same plane). In a case where the hole  11  is a blind hole, a corresponding surface (i.e., the first surface  21  or the second surface  22 ) of the base  2  where the blind hole is located and a surface of the heat conductive portion  12  facing the corresponding surface are in a same plane (or approximately in a same plane). 
     The thermal conductivity of the heat conductive portion  12  is greater than the thermal conductivity of the base  2 . Therefore, the heat conductive portion  12  is disposed in the hole  11 , and the thickness of the heat conductive portion  12  is equal to the depth of the hole  11 , which is conductive to improving a heat conducting capability of the base  2 , so that the heat may be dissipated quickly. The one of two surfaces of the heat conductive portion  12  and the corresponding surface(s) of the base  2  being in the same plane facilitates subsequent manufacturing of the piezoelectric sensor  10  on the base  2 . 
     Of course, the thickness of the heat conductive portion  12  may be less than or greater than the depth of the hole  11 , which is not limited in the embodiments of the present disclosure. In a case where the thickness of the heat conductive portion  12  is less than the depth of the hole  11 , a structure of the piezoelectric device  1  is as shown in  FIG. 1D . That is, the holes  11  are not filled with the heat conductive portion  12 . In a case where the thickness of the heat conductive portion  12  is greater than the depth of the hole  11 , a part of the heat conductive portion  12  protrudes from the hole  11 . 
     In some examples, as shown in  FIGS. 1A, 1C, 2A and 2C , in the thickness direction of the base  2 , a distance between the piezoelectric sensor  10  and the heat conductive portion  12  is zero. 
     For example, as shown in  FIGS. 1A and 2A , the holes  11  penetrate the base  2 , one of the two opposite surfaces of the heat conductive portion  12  and the first surface  21  of the base  2  are in the same plane, and the other of the two opposite surfaces of the heat conductive portion  12  and the second surface  22  of the base  2  are in the same plane. The piezoelectric sensors  10  are disposed on the second surface  22  of the base  2 . 
     For another example, as shown in  FIGS. 1C and 2C , the holes  11  and the piezoelectric sensors  10  are located at a same side of the base  2 , and one surface of the heat conductive portion  12  and the second surface  22  of the base  2  are in the same plane. The distance between the piezoelectric sensor  10  and the heat conductive portion  12  is small, which is conducive to the heat dissipation. 
     In some other examples, as shown in  FIGS. 1B, 1D, 1E and 2B , the hole  11  and the piezoelectric sensors  10  are located at different sides of the base  2 . In the thickness direction of the base  2 , the distance between the piezoelectric sensor  10  and the heat conductive portion  12  is set as L, and L is greater than zero and less than the thickness of the base  2 . In this case, the thickness of a part of the base  2  provided with the hole  11  is small, and the heat conductive portion  12  in the hole  11  has a strong heat conducting capability, which is conducive to the heat dissipation. 
     It will be seen that, regardless whether the distance between the piezoelectric sensor  10  and the heat conductive portion  12  is equal to L or zero, the distance between the piezoelectric sensor  10  and the heat conductive portion  12  is less than the thickness D of the base  2 . Therefore, the heat may be quickly transferred from the piezoelectric sensor  10  to the heat conductive portion  12 , and is then conducted to the outer side of the piezoelectric device  1  in a direction away from the piezoelectric sensor  10  through the heat conductive portion  12 . 
     In some embodiments, as shown in  FIG. 1E , there is one hole  11  having a large cross-section. The one hole  11  may be disposed in a middle position of the base  2 , and the one hole  11  overlaps with orthographic projections of the plurality of piezoelectric sensors  10  on the base  2 . 
     In some other embodiments, as shown in  FIGS. 1A to 1D and 2A to 2C , there are a plurality of holes  11  spaced apart from each other. That is, there is a spacing between adjacent holes  11 . By spacing apart the plurality of holes  11  in the base  2 , a good bearing capacity of the base  2  in the process of manufacturing the piezoelectric sensor  10  may be ensured. 
     In some examples, as shown in  FIGS. 2A to 2C , the orthographic projections of the piezoelectric sensors  10  on the base  2  do not overlap with any hole  11 . For example, as shown in  FIGS. 2A to 2C , one or more holes  11  are disposed between every two adjacent piezoelectric sensors  10 . 
     The piezoelectric pattern  103  in the piezoelectric sensor  10  is manufactured by using a patterning process, and the patterning process includes processes such as exposure, development and etching. In the etching process (e.g., a dry etching process), a large amount of heat will be generated. An etched region is exactly between two adjacent piezoelectric sensors  10 , that is, a large amount of heat will be generated in the etched region between the two adjacent piezoelectric sensors  10 . Therefore, in order to reduce an impact of a temperature increase on the piezoelectric material in the manufacturing process, the holes  11  are disposed between two adjacent piezoelectric sensors  10 . Moreover, by arranging the holes  11  between two adjacent piezoelectric sensors  10 , dissipation of heat generated by the piezoelectric device  1  during operation will not be affected, that is, the heat may still be dissipated quickly through the heat conductive portion  12 . 
     In some other examples, as shown in  FIGS. 1A to 1E , the orthographic projections of the piezoelectric sensors  10  on the base  2  overlap with at least one of the plurality of holes  11 . For example, as shown in  FIGS. 1A to 1D , some of the plurality of holes  11  are disposed at positions where all piezoelectric sensors  10  face the base  2 , and the remaining holes  11  are disposed in regions of the base  2  where the piezoelectric sensors  10  are not disposed. 
     In this way, by arranging a plurality of holes  11  in regions of the base  2  facing the piezoelectric sensors  10  and regions between the piezoelectric sensors  10 , an overall heat dissipation effect of the piezoelectric device  1  may be improved, thereby better ensuring the performance of the piezoelectric device  1 . 
     In some embodiments, as shown in  FIGS. 5A and 5B , in a case where the piezoelectric device  1  includes the plurality of piezoelectric sensors  10 , the second electrodes  102  in all piezoelectric sensors  10  are electrically connected through at least one connecting electrode  104 , and all second electrodes  102  and all connecting electrodes  104  are disposed in a same layer. For example, the piezoelectric device  1  further includes a plurality of connecting electrodes  104 , second electrodes  102  in every two adjacent piezoelectric sensors  10  are electrically connected through one connecting electrode  104 , and all second electrodes  102  and all connecting electrodes  104  may form an integrated structure. Therefore, a circuit of the piezoelectric device  1  is relatively simple. 
     The term “same layer” herein refers to a layer structure formed by a same patterning process by using a same mask in which a film for forming specific patterns is formed by using a same film-forming process. Depending on the specific patterns, the same patterning process may include exposure, development and etching, and the specific patterns formed in the layer structure may be continuous or discontinuous, and these specific patterns may also be at different heights or have different thicknesses. 
     That is, the second electrodes  102  and the connecting electrodes  104  are manufactured based on a same film by the same patterning process. Therefore, a manufacturing process of the piezoelectric device  1  is simple, and circuit wiring of the piezoelectric device  1  may be simplified. 
     A part of the connecting electrode  104  is located between two adjacent piezoelectric patterns  103 , and the first electrode  101  and the second electrode  102  in the same piezoelectric sensor  10  need to be insulated from each other. Therefore, the first electrode  101  and the connecting electrode  104  also need to be insulated from each other. In order to ensure that the first electrode  101  and the connecting electrode  104  are insulated from each other, the first electrode  101  and the piezoelectric pattern  103  may be arranged in any of the following two methods. 
     In some examples, as shown in  FIG. 5A , a side edge of the piezoelectric pattern  103  in each piezoelectric sensor  10  and a side edge of the first electrode  101  located at an edge of the piezoelectric sensor  10  that is proximate to an adjacent piezoelectric sensor  10  are substantially in a same plane. 
     For example, in a case where each piezoelectric sensor  10  includes one first electrode  101 , in the thickness direction of the base  2 , the orthographic projection of the piezoelectric pattern  103  on the base  2  completely overlaps with the orthographic projection of the first electrode  101  on the base  2 . For another example, in a case where each piezoelectric sensor  10  includes two first electrodes  101 , one of two side edges of the piezoelectric pattern  103  and a side edge of one of the two first electrodes  101  that is proximate to an adjacent piezoelectric sensor  10  are substantially in a same plane, and the other of the two side edges of the piezoelectric pattern  103  and a side edge of the other of the two first electrodes  101  that is proximate to an adjacent piezoelectric sensor  10  are substantially in a same plane. 
     In this case, as shown in  FIG. 5A , the piezoelectric device  1  further includes an insulating layer  105  disposed between first electrodes  101  of adjacent piezoelectric sensors  10 , and the connecting electrode  104  is located at a side of the insulating layer  105  facing away from the base  2 . A thickness of the insulating layer  105  may be greater than or equal to a thickness of the first electrode  101 , as long as it may be ensured that the connecting electrode  104  is not in contact with the first electrode  101 . 
     Further, In the case where each piezoelectric sensor  10  includes one first electrode  101 , since the piezoelectric pattern  103  and the first electrode  101  have a same shape, the piezoelectric pattern  103  and the first electrode  101  may be separately patterned by using a same mask, thereby reducing a manufacturing cost. 
     In some other examples, as shown in  FIG. 5B , in each piezoelectric sensor  10 , in the thickness direction of the base  2 , an orthographic projection of any first electrode  101  on the base  2  is within a range of the orthographic projection of the piezoelectric pattern  103  on the base  2 , and side faces of any first electrode  101  is covered by the piezoelectric pattern  103 . In this case, the connecting electrode  104  is located between the adjacent piezoelectric patterns  103 , which ensures that the first electrode  101  and the connecting electrode  104  are insulated from each other. A large area of the piezoelectric pattern  103  enables a spacing between two adjacent piezoelectric patterns  103  to reduce. Therefore, the measurement accuracy of the piezoelectric device  1  is high. 
     Optionally, an included angle a between a plane where a sidewall of the piezoelectric pattern  103  is located and the base  2  is in a range from approximately 85° to approximately 90°, such as 85°, 87° or 90°. The sidewall of the piezoelectric pattern  103  herein refers to a side edge of the piezoelectric pattern  103 , i.e., a side that is not parallel to the second surface  22  of the base  2 . In some examples, as shown in  FIGS. 1A to 2C , the included angle a is equal to 90°. In some other examples, as shown in  FIG. 6 , the included angle a is equal to 85°. 
     The includes angle a between the plane where the sidewall of the piezoelectric pattern  103  is located and the base  2  is in the range from approximately 85° to approximately 90°, which may make a size of an upper surface (i.e., a surface facing away from the base  2  in the thickness direction of the base  2 ) of the piezoelectric pattern  103  proximate to a size of a lower surface (i.e., a surface facing the base  2  in the thickness direction of the base  2 ). 
     The smaller the spacing between two adjacent piezoelectric patterns  103  is, the more piezoelectric sensors  10  may be disposed in the piezoelectric device  1  of a certain size, and thus the higher the measurement accuracy of the piezoelectric device is. The closer the sizes of the upper surface and the lower surface of the piezoelectric pattern  103  are, the smaller the spacing between two adjacent piezoelectric patterns  103  is. Therefore, in a case where the included angle a between the plane where the sidewall of the piezoelectric pattern  103  is located and the base  2  is in the range from approximately 85° to approximately 90°, the measurement accuracy of the piezoelectric device  1  may be made high. 
     Optionally, as shown in  FIG. 7 , the piezoelectric device  1  further includes a driving circuit layer  106  disposed between the base  2  and the piezoelectric sensors  10 . The driving circuit layer  106  is configured to provide a voltage to the first electrode  101  in each piezoelectric sensor  10 , separately. A circuit connection relationship of the driving circuit layer  106  may be determined according to circuit design needs, and is not limited in the embodiments of the present disclosure herein. 
     For example, the driving circuit layer  106  includes a plurality of driving circuits each corresponding to a respective one of the plurality of piezoelectric sensors  10 , and each driving circuit includes at least one transistor (e.g., thin film transistor, TFT). For example, each driving circuit includes one TFT to which one first electrode  101  in the piezoelectric sensor  10  is electrically connected. 
     Some embodiments of the present disclosure provide a display apparatus  3 . As shown in  FIGS. 8A and 8B , the display apparatus  3  includes a display panel  31  and the above piezoelectric device  1 . The display panel  31  and the piezoelectric device  1  may be bonded together by using an adhesive layer  32 . 
     In some examples, as shown in  FIG. 8A , the piezoelectric device  1  is located at a side of the display panel  31  facing away from a light emitting surface, and the light emitting surface is one of a plurality of surfaces of the display panel  31  from which light is emitted. The piezoelectric device  1  is bonded to a surface of the display panel  31  facing away from the light emitting surface, for example, through the adhesive layer  32 . In the display apparatus  3  having such a structure, the piezoelectric device  1  may be fully transparent, or translucent or opaque, which will not affect the light emitted from the display panel  31 . Therefore, requirements for materials and processes of manufacturing the piezoelectric device  1  are low, and the manufacturing is relatively simple. 
     In some other examples, as shown in  FIG. 8B , the piezoelectric device  1  is located on the light emitting surface of the display panel  31 . The piezoelectric device  1 , for example, is bonded to the light emitting surface of the display panel  31  through the adhesive layer  32 . In the display apparatus  3  having such a structure, in order to reduce an impact on the light emitted from the display panel  31 , all layers in the piezoelectric device  1  are required to be transparent layers or approximately transparent layers. Or, in a case where an amount of the emitted light required by the display panel  31  may be ensured, some of all layers in the piezoelectric device  1  are translucent film layers, and the remaining layers are transparent layers. The piezoelectric device  1  is located at a light exit side of the display panel  31 , which may make a distance between the piezoelectric device  1  and the finger  7  more closer, thereby facilitating to improve the measurement accuracy of the piezoelectric device  1 . 
     In a case where voltages are applied to the first electrode  101  and the second electrode  102 , the piezoelectric pattern  103  formed by using the piezoelectric material may generate ultrasonic signals. This process is referred to as the inverse piezoelectric effect. 
     As shown in  FIGS. 8A and 8B , when the ultrasonic signals generated by the piezoelectric patterns  103  contact a fingerprint on the finger  7 , reflection interfaces contacted by the ultrasonic signals are different due to the presence of valleys and ridges on a surface of the fingerprint. An air interface corresponding to the valleys has a large impedance to the ultrasonic signals, which makes an amount of ultrasonic signals passing through the air interface be small, and thus an intensity of reflected ultrasonic signals be large. A solid interface corresponding to the ridges has a small impedance to the ultrasonic signals, which makes an amount of ultrasonic signals passing through the solid interface be large, and thus an intensity of reflected ultrasonic signals be small. 
     On this basis, when the ultrasonic signals reflected by the air interface and the solid interface are received by the piezoelectric patterns  103 , the piezoelectric material of the piezoelectric patterns  103  will generate the positive piezoelectric effect, and will correspondingly generate a plurality of local charges accumulated on surfaces of a plurality of first electrodes  101 , thereby generating corresponding electrical signals. An amount of each accumulated local charges is positively correlated with the intensity of the reflected ultrasonic signals that are received. Therefore, after an electrical signal generated by each first electrode  101  is processed, an image representing the fingerprint information may be obtained, thereby achieving a fingerprint identification function. 
     In some embodiments, the display panel  31  includes a plurality of sub-pixels. As shown in  FIGS. 9A and 9B , an orthographic projection of the piezoelectric sensor  10  on the display panel  31  has an overlapping region with at least one sub-pixel P. That is, the orthographic projection of the piezoelectric sensor  10  on the display panel  31  overlaps with a region where the at least one sub-pixel P is located. Overlap herein includes full overlap and partial overlap. 
     The orthographic projection of the piezoelectric sensor  10  on the display panel  31  has an overlapping region with M sub-pixels P, and M is an integer greater than zero and less than four. 
     Optionally, as shown in  FIG. 9A , the orthographic projection of the piezoelectric sensor  10  on the display panel  31  completely overlaps with a region where one sub-pixel P is located. In this case, the measurement accuracy of the piezoelectric device  1  may reach a sub-pixel level. For example, each sub-pixel P may correspond to a respective piezoelectric sensor  10 , that is, an area of the measurement region of the piezoelectric device  1  is equal to a sum of areas of regions where all sub-pixels P are located, and an area of each measurement sub-region is equal to an area of a respective sub-pixel P. 
     In the display apparatus  3  having such a structure, the piezoelectric sensor  10  corresponding to each sub-pixel P may be separately controlled, and an orthographic projection of a measurement sub-region A of the piezoelectric device  1  on the display panel  31  completely overlaps with a region B where the sub-pixel P is located. Therefore, there is no part that cannot be measured in the measurement sub-region A corresponding to each sub-pixel P of the display panel  31 , and an overall measurement accuracy of the display apparatus  3  is high. 
     Optionally, as shown in  FIG. 9B , the orthographic projection of the piezoelectric sensor  10  on the display panel  31  overlaps with regions where two adjacent sub-pixels P are located. In this case, the measurement accuracy of the piezoelectric device  1  may also reach the sub-pixel level. For example, a measurement sub-region corresponding to the piezoelectric sensor  10  is a region A, a region where each sub-pixel is located is a region B, a region where the measurement sub-region A overlaps with the region B corresponding to the sub-pixel is a region C, and a region where the measurement sub-region A dose not overlap with the region B is a region D. In a sub-pixel P, the region C may be measured, while the region D cannot be measured. Therefore, in sub-pixels P, there are some regions that cannot be measured. By controlling sizes of these regions that cannot be measured, impacts of these regions on the measurement accuracy may be reduced or even ignored. As for the region B where each sub-pixel P is located, since the region C in the region B may be measured, the region corresponding to each sub-pixel P may still be measured. 
     The display apparatus  3  has same beneficial effects as the above piezoelectric device  1 , which will not be repeated herein. 
     Some embodiments of the present disclosure provide a method for manufacturing the piezoelectric device  1 , as shown in  FIG. 10A , the method includes S 1  to S 3 . 
     In S 1 , as shown in  FIG. 10B , a base  2  having at least one hole  11  is formed. 
     For example, the base  2  is a glass base, and a thickness of the glass base is in a range from approximately 0.4 mm to approximately 0.5 mm. 
     For example, S 1  includes: forming at least one hole  11  in a substrate by a dry etching process, a wet etching process or a laser drilling process to obtain the base  2 . Taking the wet etching process as an example, an etching liquid used in the wet etching process may be hydrofluoric acid (HF). 
     In S 2 , as shown in  FIG. 10C , a heat conductive portion  12  is formed in the at least one hole  11 . A thermal conductivity of the heat conductive portion  12  is greater than a thermal conductivity of the base  2 . 
     For example, the heat conductive portion  12  is made of silver (Ag), aluminum (Al) or copper (Cu). A thermal conductivity of Ag is approximately 429 W/mK, a thermal conductivity of Al is approximately 237 W/mK, and a thermal conductivity of Cu is approximately 400 W/mK. 
     For example, S 2  includes: filling the at least one hole  11  with a heat conductive material by an evaporation process, an electroplating process or a coating process to form the heat conductive portion  12 . 
     For example, a thickness of the heat conductive portion  12  is substantially equal to a depth of the hole  11 . 
     In S 3 , as shown in  FIG. 1E , at least one piezoelectric sensor  10  is formed on the base  2 . Each piezoelectric sensor  10  includes a first electrode  101 , a piezoelectric pattern  103  and a second electrode  102  that are sequentially formed on the base  2 . 
     The piezoelectric pattern  103  is made of a piezoelectric material, such as poly vinylidene fluoride (PVDF), poly vinyledene fluoride-trifluoroethylene (PVDF-TrFE), or polytetrafluoroethylene (PTFE). 
     In the method for manufacturing the piezoelectric device  1  provided by some embodiments of the present disclosure, at least one hole  11  is formed in the base  2 , the heat conductive portion  12  is formed in the at least one hole  11 , the thermal conductivity of the heat conductive portion  12  being greater than the thermal conductivity of the base  2 , and then at least one piezoelectric sensor  10  is formed on the base  2 . 
     In this way, on one hand, compared with a base of a same thickness and without the heat conductive portion  12 , heat generated in a manufacturing process (e.g., the dry etching) of the piezoelectric sensor  10  may be quickly conducted to the outer side of the piezoelectric device  1  toward a side away from the piezoelectric pattern  103 , thereby preventing the heat from being accumulated in the piezoelectric pattern  103 , and further preventing a temperature rise from affecting a piezoelectric constant of the piezoelectric pattern  103 . On another hand, heat generated during operation of the piezoelectric device  1  may also be quickly conducted to the outer side of the piezoelectric device  1  toward the side away from the piezoelectric sensor  10  through the heat conductive portion  12 , in stead of being accumulated in the base  2  to cause heat generated by the piezoelectric sensor  10  to be accumulated, thereby improving a heat dissipation efficiency and a heat dissipation performance of the piezoelectric device  1 . After the heat dissipation performance of the piezoelectric device  1  is improved, a working performance and an identification accuracy of the piezoelectric device  1  may be ensured, and power consumption of the piezoelectric device  1  may be reduced. 
     Optionally, as shown in  FIGS. 11A and 11B , S 1  includes: forming a plurality of holes  11  in a first surface  21  of the base  2  by the dry etching process, the wet etching process or the laser drilling process. The depth of the holes  11  is less than the thickness of the base  2 , that is, the holes  11  do not penetrate the base  2 . 
     Optionally, as shown in  FIGS. 1B and 2B , S 3  includes: forming a plurality of piezoelectric sensors  10  on a second surface  22  of the base  2 . The first surface  21  and the second surface  22  are two opposite surfaces in the thickness direction of the base  2 . 
     In the process of forming the plurality of piezoelectric sensors  10 , all first electrodes  101 , all piezoelectric patterns  103  and all second electrodes  102  may be separately formed by a single patterning process. For example, a conductive material film may be formed by a magnetron sputtering, and a first patterning process may be performed on the conductive material film to form all first electrodes  101 . A piezoelectric material film may be formed by a coating process, and a second patterning process may be performed on the piezoelectric material film to form all piezoelectric patterns  103 . Another conductive material film may be formed by a magnetron sputtering, and a third patterning process may be performed on the conductive material film to form all second electrodes  102 . 
     The patterning process may include exposure, development and etching. Mask plates used for exposure in different patterning processes may be the same or different. If patterns formed by different patterning processes are different, the mask plates used are different. If the patterns formed by different patterning processes are the same, the mask plates used are the same. 
     In some examples, as shown in  FIG. 1B , orthographic projections of the piezoelectric sensors  10  on the base  2  have overlapping regions with the holes  11 . 
     In some other examples, as shown in  FIG. 2B , the orthographic projections of the piezoelectric sensors  10  on the base  2  do not overlap with any hole  11 . 
     Optionally, taking one piezoelectric sensor  10  as an example, as shown in  FIG. 12A , S 3  includes S 201  to S 205 . 
     In S 201 , as shown in  FIG. 12B , a first electrode  101  is formed on the second surface  22  of the base  2 . 
     For example, a first metal film is formed on the second surface  22  of the base  2  by a magnetron sputtering process, and a first patterning process is performed on the first metal film to form a first electrode  101  in a piezoelectric sensor  101 . 
     In S 202 , as shown in  FIG. 12B , a piezoelectric film  4  is formed on the first electrode  101 . 
     For example, the piezoelectric film  4  is formed on the first electrode  101  by a spin coating process or a slit blade coating process. Then, the piezoelectric film  4  is cured at a low temperature in an environment of 25° C. to 100° C. A curing time is in a range, for example, from 20 minutes to 6 hours. Finally, the piezoelectric film  4  is crystallized at a high temperature in an environment of 130° C. to 150° C. A crystallization time is in a range, for example, from 1 hour to 6 hours. 
     In S 203 , as shown in  FIG. 12D , a third photoresist pattern  63  is formed on the piezoelectric film  4 . 
     For example, as shown in  FIG. 12C , a photoresist layer  6  is formed on the piezoelectric film  4 , and the photoresist layer  6  is exposed by using a mask plate and developed, so as to form the third photoresist pattern  63  as shown in  FIG. 12D . 
     In S 204 , as shown in  FIG. 12E , a portion of the piezoelectric film  4  that is not covered by the third photoresist pattern  63  is removed by an etching process to form a piezoelectric pattern  103 . 
     For example, the portion of the piezoelectric film  4  that is not covered by the third photoresist pattern  63  is removed by the dry etching process. 
     In the dry etching process, the piezoelectric film  4  may be etched by using a reactive ion etching process or a plasma etching process. A gas used in the reactive ion etching process or the plasma etching process need to be selected from gases that have no etching effect on the photoresist and only have an etching effect on the piezoelectric film  4 , thereby ensuring integrity of the formed third photoresist pattern  63 , and further ensuring that a shape of the etched piezoelectric pattern  103  conforms to an expected design. 
     In S 205 , as shown in  FIG. 12F , the third photoresist pattern  63  is removed, and as shown in  FIG. 1B , a second electrode  102  is formed on the piezoelectric pattern  103 . 
     For example, the third photoresist pattern  63  is removed by using the etching process. After the third photoresist pattern  63  is removed, a second metal film is formed on the base  2  on which a plurality of piezoelectric patterns  103  are formed by using the magnetron sputtering process, and a third patterning process is performed on the second metal film to form the second electrode  102 . 
     It will be noted that, in the above embodiments, a process of forming the piezoelectric device  1  is described by taking one piezoelectric sensor  10  as an example. However, in order to clearly show the process of forming the whole piezoelectric device  1 ,  FIGS. 12B to 12F  show a plurality of piezoelectric sensors  10 . 
     Optionally, taking one piezoelectric sensor  10  as an example, as shown in  FIG. 13A , S 3  includes S 301  to S 305 . 
     In S 301 , as shown in  FIG. 12B , a first electrode  101  is formed on the second surface  22  of the base  2 . 
     As for a manner in which the first electrode  101  is formed, reference may be made to S 201  in the above embodiments. 
     In S 302 , as shown in  FIG. 12B , a piezoelectric film  4  is formed on the first electrode  101 . 
     As for a manner in which the piezoelectric film  4  is formed, reference may be made to S 202  in the above embodiments. 
     In S 303 , as shown in  FIG. 13E , a protective pattern  1070  is formed on the piezoelectric film  4 , and a material of the protective pattern  1070  is a conductive material. 
     For example, the conductive material includes a metal or a transparent conductive oxide. The metal is, for example, Ag, Al, titanium (Ti) or molybdenum (Mo). The transparent conductive oxide is, for example, indium tin oxide (ITO), indium zinc oxide (IZO), indium gallium zinc oxide (IGZO). Optionally, the protective pattern  1070  is made of Ag. 
     A process of forming the protective pattern  1070  on the piezoelectric film  4  is as follows. 
     Firstly, as shown in  FIG. 13B , a first conductive layer  107  is formed on the piezoelectric film  4  by using a screen printing process, the magnetron sputtering process, or the evaporation process. Secondly, as shown in  FIG. 13C , a photoresist layer  6  is formed on the first conductive layer  107 . Thirdly, as shown in  FIG. 13D , the photoresist layer  6  is patterned to form a first photoresist pattern  61 , the patterning process herein includes exposing the photoresist layer  6  to, for example, ultraviolet light, by using a mask plate, and developing the exposed photoresist layer  6  to transfer a pattern of the mask plate to the photoresist layer  6 . Fourthly, as shown in  FIG. 13E , the first conductive layer  107  is etched by using the first photoresist pattern  61  as a mask, that is, a region in the first conductive layer  107  that is not covered by the first photoresist pattern  61  is etched, so as to form a protective pattern  1070 , and an edge of an orthographic projection of the protective pattern  1070  on the base  2  is located outside an edge of an orthographic projection of the first electrode  101  on the base  2 . Finally, the first photoresist pattern  61  is removed, that is, a structure as shown in  FIG. 13F  is formed. 
     It will be noted that, in the above process, the protective pattern  1070  is formed by using an ultraviolet lithography process, but the protective pattern  1070  may also be formed by using other processes, such as an electron beam lithography process or a laser direct writing process, which is not limited in the embodiments of the present disclosure. 
     In S 304 , as shown in  FIG. 13G , a portion of the piezoelectric film  4  that is not covered by the protective pattern  1070  is removed by the etching process to form a piezoelectric pattern  103 . 
     In this process, the piezoelectric film  4  needs to be etched by using the protective pattern  1070  as a mask. The etching process may be the dry etching process, such as the reactive ion etching process or the plasma etching process, and a gas used in the etching process needs to be selected from gases that only have an etching effect on the piezoelectric film  4  and have no or very little etching effect on the protective pattern  1070 . For example, the gas is oxygen (O 2 ), a mixture of O 2  and argon (Ar), or a mixture of O 2  and helium (He). 
     It will be noted that, the gas that may be selected in the dry etching process is not limited to the gases listed above. The etching gas needs to be selected according to materials of films. During the selection, a principle that is followed is to select gases that have a high etching selectivity for the relevant films in the etching process. 
     For example, O 2  has a high etching rate for the piezoelectric film  4 , but does not have an etching effect on or has a very low etching rate for the protective pattern  1070 , which will not affect integrity of the piezoelectric pattern  103  formed according to the protective pattern  1070 . Therefore, O 2  is a gas having a high etching selectivity for the piezoelectric pattern  103 . 
     For example, the piezoelectric film  4  is made of PVDF, and the protective pattern  1070  is made of any of Ag, Al, Ti, or Mo. The protective pattern  1070  is used as a mask, and a sectional view of the piezoelectric pattern  103  formed by etching the piezoelectric film  4  is shown in  FIG. 17 . It will be seen from  FIG. 17  that, the gas used in the dry etching process, such as O 2 , can remove a portion of the piezoelectric film that is not covered by the protective pattern  1070  (as shown by the dashed frame A in  FIG. 17 ), and has no etching effect on the protective pattern  1070 . 
     In S 305 , as shown in  FIG. 13H , a conductive film  108  is formed on the protective pattern  1070 . The protective pattern  1070  and a portion of the conductive film  108  that is located on the protective pattern  1070  form a second electrode  102 . 
     For example, the conductive film  108  is formed on the protective pattern  1070  by using a sputtering process or the evaporation process. The conductive film  108  is made of, for example, a conductive metal material or a transparent conductive oxide. 
     It will be noted that, in the above embodiments, a process of forming the piezoelectric device  1  is described by taking one piezoelectric sensor  10  as an example. However, in order to clearly show the process of forming the whole piezoelectric device  1 ,  FIGS. 13B to 13I  show a plurality of piezoelectric sensors  10  in the piezoelectric device  1 . 
     In a case where a plurality of piezoelectric sensors  10  are formed, as shown in  FIG. 13H , the conductive film  108  has a whole-layer structure and is located on protective patterns  1070  of all piezoelectric sensors  10 . A portion of the conductive film  108  that is located between protective patterns  1070  of adjacent piezoelectric sensors  10  is a connecting electrode  104 . The connecting electrode  104  may electrically connect second electrodes  102  of the adjacent piezoelectric sensors  10 . The whole conductive film  108  covers all protective patterns  1070 , and the protective patterns  1070  are made of the conductive material. Therefore, the protective patterns  1070  and the conductive film  108  are electrically connected to each other, and all second electrodes  102  are also electrically connected to each other. 
     In each piezoelectric sensor  10 , since the first electrode  101  and the second electrode  102  need to be insulated from each other, the first electrode  101  may be wrapped inside the piezoelectric pattern  103  during forming the piezoelectric pattern  103 . By taking an example in which the piezoelectric sensor  10  includes one first electrode  101 , a size of the piezoelectric pattern  103  is greater than a size of the first electrode  101 , thereby forming the piezoelectric pattern  103  and the first electrode  101  shown in  FIG. 13H . 
     Of course, an insulating layer  105  may be formed before the conductive film  108  is formed. For example, in the case where a plurality of piezoelectric sensors  10  are formed, as shown in  FIG. 13I , the insulating layer  105  is formed between adjacent piezoelectric patterns  103 . Or, the insulating layer  105  is formed between adjacent first electrodes  101 . Or, the insulating layer  105  is formed between adjacent protective patterns  1070 . 
     The material protective pattern  1070  and the conductive film  108  may be made of the same material or different materials. For example, in a case where the protective pattern  1070  and the conductive film  108  are both made of Ag, since they are made of the same material, a contact interface between the protective pattern  1070  and the conductive film  108  may not be clearly observed in a sectional diagram as shown in  FIG. 13H . For another example, in a case where one of the protective pattern  1070  and the conductive film  108  is made of Ag, and the other of the protective pattern  1070  and the conductive film  108  is made of Al, the contact interface between the protective pattern  1070  and the conductive film  108  may be clearly observed in the sectional diagram as shown in  FIG. 13H . 
     It will be noted that, in  FIG. 13H , in order to clearly show structures and positions of the protective pattern  1070  and the conductive film  108 , the materials of the protective pattern  1070  and the conductive film  108  are distinguished, so that the contact interface between the protective pattern  1070  and the conductive film  108  may be clearly observed in  FIG. 13H . However, whether the materials of the protective pattern  1070  and the conductive film  108  are actually the same or not is not limited. 
     On a basis of the piezoelectric sensor  10  formed in S 301  to S 305 , the piezoelectric film  4  is etched by using the protective pattern  1070  as a mask, so that there are a plurality of gases that may be selected in the etching process, and a difficulty in etching the piezoelectric film  4  is reduced. Moreover, all second electrodes  102  are electrically connected together, which is conductive to reducing a difficulty in wiring of the piezoelectric device  1 , thereby improving a product yield. 
     Optionally, taking one piezoelectric sensor  10  as an example, S 3  includes S 401  to S 405 . 
     In S 401 , as shown in  FIG. 12B , a first electrode  101  is formed on the second surface  22  of the base  2 . 
     As for a manner in which the first electrode  101  is formed, reference may be made to S 201  in the above embodiment. 
     In S 402 , as shown in  FIG. 12B , a piezoelectric film  4  is formed on the first electrode  101 . 
     In S 403 , as shown in  FIG. 14B , a second electrode  102  is formed on the piezoelectric film  4 . 
     For example, a second metal film is formed on the piezoelectric film  4  by using the screen printing process, the magnetron sputtering process or the evaporation process, and a third patterning process, similar to that in S 205 , is performed on the second metal film to form the second electrode  102 . 
     A process of forming the second electrode  102  on the piezoelectric film  4  is as follows. 
     Firstly, as shown in  FIG. 15A , a second conductive layer  109  is formed on the piezoelectric film  4  by using the screen printing process, the magnetron sputtering process, or the evaporation process. Secondly, as shown in  FIG. 15B , a photoresist layer  6  is formed on the second conductive layer  109 . Thirdly, as shown in  FIG. 15C , the photoresist layer  6  is patterned to form a second photoresist pattern  62 , and the patterning process herein includes exposing the photoresist layer  6  by using a mask plate, and developing the exposed photoresist layer  6  to transfer a pattern of the mask plate to the photoresist layer  6 . Fourthly, as shown in  FIG. 15D , the second conductive layer  109  is etched by using the second photoresist pattern  62  as a mask, that is, a region in the second conductive layer  109  that is not covered by the second photoresist pattern  62  is etched to form a second electrode  102 . Finally, the second photoresist pattern  62  on the second electrode  102  is removed, that is, a structure as shown in  FIG. 15E  is formed. The second photoresist pattern  62  may be removed by using, for example, an ashing process. 
     In above process, the etching process may be the dry etching process. In the dry etching process, since gas is used for etching, an etching accuracy is higher than an etching accuracy of the wet etching process, so that the included angle between the sidewall of the piezoelectric pattern  103  and the base  2  is close to a right angle, thereby facilitating to reduce a spacing between two adjacent piezoelectric patterns  103 . In a case where the base  2  has a same size, the smaller the spacing between the piezoelectric patterns  103  is, the greater the number of the piezoelectric patterns  103  is, thereby facilitating to improve a measurement accuracy of the piezoelectric device  1 . 
     In S 404 , a portion of the piezoelectric film  4  that is not covered by the second electrode  102  is removed by the etching process to form a piezoelectric pattern  103  as shown in  FIG. 1B . 
     In S 404 , the piezoelectric film  4  is directly etched by using the second electrode  102  as a mask, and a manufacturing process is simple. That is, in a case where the protective pattern  1070  is made of the conductive material, the protective pattern  1070  may directly serve as the second electrode  102 . Therefore, the manufacturing process may be simplified, and a manufacturing efficiency of the piezoelectric device  1  may be improved. 
     It will be noted that, in the above embodiments, a process of forming the piezoelectric device  1  is described by taking one piezoelectric sensor  10  as an example. However, in order to clearly show the process of forming the whole piezoelectric device  1 ,  FIGS. 14B to 15D  show a plurality of piezoelectric sensors  10  in the piezoelectric device  1 . 
     On a basis of the piezoelectric sensor  10  formed in S 401  to S 404 , the manufacturing process is relatively simple, the manufacturing efficiency is relatively high, and the piezoelectric device  1  may be made light and thin. 
     Some embodiments of the present disclosure provide a method for manufacturing another piezoelectric device  1 . As shown in  FIG. 16A , the method includes S 10  to S 40 . 
     In S 10 , as shown in  FIG. 10B , at least one hole  11  is formed on a first surface  21  of a base  2 . 
     For example, the base  2  is a glass base, and a thickness of the glass base is in a range from approximately 0.4 mm to approximately 0.5 mm. 
     The at least one hole  11  may be formed in the first surface  21  of the base  2  by a dry etching process, a wet etching process, or a laser drilling process. 
     In S 20 , as shown in  FIG. 10C , a heat conductive portion  12  is formed in the at least one hole  11 . A thermal conductivity of the heat conductive portion  12  is greater than a thermal conductivity of the base  2 . 
     The heat conductive portion  12  is made of silver (Ag), aluminum (Al) or copper (Cu). A thermal conductivity of Ag is approximately 429 W/mK, a thermal conductivity of Al is approximately 237 W/mK, and a thermal conductivity of Cu is approximately 400 W/mK. 
     For example, S 20  includes: filling the at least one hole  11  with a heat conductive material by an evaporation process, an electroplating process or a coating process to form the heat conductive portion  12 . 
     In S 30 , as shown in  FIG. 1E , at least one piezoelectric sensor  10  is formed on a second surface  22  of the base  2 . Each piezoelectric sensor  10  includes at least one first electrode  101 , a piezoelectric pattern  103  and a second electrode  102  that are sequentially formed on the base  2 . 
     The piezoelectric pattern  103  is made of a piezoelectric material, and the piezoelectric material may be polyvinylidene fluoride (PVDF), poly vinyledene fluoride-trifluoroethylene (PVDF-TrFE), or polytetrafluoroethylene (PTFE). 
     As for a process of manufacturing the piezoelectric sensor  10 , reference may be made to the description in the foregoing embodiments, which will not be repeated herein. 
     In S 40 , the base  2  is thinned to remove the at least one hole  11  and the heat conductive portion  12  therein, so that a thinned base  2 - a  is obtained as shown in  FIG. 16B . 
     For example, after the glass base is thinned, a remaining thickness of the base  2  is approximately 0.1 mm. 
     In the process of thinning the base  2 , for example, hydrofluoric acid (HF) may be used to etch the base  2  to achieve thinning, or the base  2  may be thinned by means of mechanical grinding. By thinning the base  2 , a thickness of the piezoelectric device  1  may be reduced, which is conducive to making the piezoelectric device  1  light and thin. 
     As for details of the method for manufacturing the piezoelectric device  1 , reference may be made to contents of the above method for manufacturing the piezoelectric device  1 , which will not be repeated herein. 
     Some embodiments of the present disclosure provide a piezoelectric device  1  that is manufactured by using the above manufacturing method in S 10  to S 40 . The piezoelectric device  1  includes a base  2 - a  and the at least one piezoelectric sensor  10  disposed on the base  2 - a.    
     It will be noted that, after the piezoelectric sensor  10  is formed, the base  2 , provided with the hole  11  and the heat conductive portion  12  therein, provided in the foregoing embodiments is thinned to remove the hole  11  and the heat conductive portion  12 , so that the base  2 - a  may be obtained. That is, the thickness of the base  2 - a  is less than that of the base  2 . 
     In addition to having the same beneficial effects as the piezoelectric device  1  in the above embodiments, the piezoelectric device  1  also has an advantage of being light and thin. 
     Some embodiments of the present disclosure provide a display apparatus  3  including a display panel  31  and a piezoelectric device  1 . As shown in  FIG. 8C , the piezoelectric device  1  is the piezoelectric device  1  manufactured by using the manufacturing method in S 10  to S 40 . 
     As for an arrangement relationship between the piezoelectric device  1  and the display panel  31 , reference may be made to the embodiments of the display apparatus corresponding to  FIGS. 8A and 8B , which will not be repeated herein. 
     The foregoing descriptions are merely specific implementation manners of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any changes or replacements that a person skilled in the art could readily conceive of within the technical scope of the present disclosure shall be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.