Patent Publication Number: US-2021170448-A1

Title: Wafer level ultrasonic device and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This non-provisional application claims priority under 35 U.S.C. § 119(a) to Patent Application No. 108144395 in Taiwan, R.O.C. on Dec. 4, 2019, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The present invention relates to an ultrasonic transmission technology, and in particular, to a wafer level ultrasonic device and a manufacturing method thereof. 
     Related Art 
     With the development of smartphones and application programs, an increasing scope of individual life is covered. For example, smartphones are widely applied to mobile payment, electronic keys, and the like nowadays. A large amount of important individual information is stored in the smartphone. Therefore, once the smartphone is missing, the information is likely to be stolen, resulting in a great loss. 
     Therefore, in addition to setting a password generally, many functions such as face recognition, iris recognition, and fingerprint recognition, which use a personal feature to assist in encryption, have been developed. Fingerprint recognition is used most commonly at present, which, however, still has the problem of inaccurate recognition. 
     In the current fingerprint recognition technology, a finger touches an upper cover of an ultrasonic module or a screen protective layer of a smart electronic device; the ultrasonic module sends an ultrasonic signal to the finger and receives a strength of the ultrasonic signal reflected by peaks and roughs of the fingerprint, so that the fingerprint can be recognized. However, the ultrasonic signal of the ultrasonic module may be transmitted to an area not in contact with the finger through a medium. In this case, the reflected ultrasonic signal received by the ultrasonic module may not necessarily be reflected by the finger. Therefore, it is difficult to recognize the fingerprint. 
     SUMMARY 
     It should be understood that, when an element is referred to as being “connected to” another element, it may indicate that the element is directly connected to the another element, or there is a middle element. 
     In addition, it should be understood that although terms such as “first”, “second”, and “third” in this specification may be used for describing various elements, components, areas, or parts, the elements, components, areas, or parts are not limited by such terms. The terms are only used to distinguish one element, component, area, or part from another element, component, area, or part. 
     In addition, terms such as “on”, “below”, “top”, and “bottom” are used for describing a relative relationship between one element and another element. It should be understood that such relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, an element described as being “below” another element will then be “above” the other element. 
     To solve the foregoing problems, a wafer level ultrasonic device is provided herein, including a composite layer, a first conductive layer, a second conductive layer, a base, a first electrical connection region, and a second electrical connection region. The composite layer includes an ultrasonic element and a protective layer, the ultrasonic element includes a first electrode and a second electrode, and the first electrode is not connected to the second electrode. The protective layer covers the ultrasonic element and is provided with a first connecting channel and a second connecting channel, one end of the first connecting channel corresponds to the first electrode, and one end of the second connecting channel corresponds to the second electrode. The first conductive layer is in the first connecting channel and is electrically connected to the first electrode, and a part of the first conductive layer is exposed to the protective layer. The second conductive layer is in the second connecting channel and is electrically connected to the second electrode, and a part of the second conductive layer is exposed to the protective layer. The base is connected to the protective layer, and includes an opening. The opening forms a closed cavity with the protective layer. The first electrical connection region is filled with a metal material to be electrically connected to the first conductive layer. The second electrical connection region is filled with a metal material to be electrically connected to the second conductive layer. 
     In some embodiments, the ultrasonic element includes a first piezoelectric layer, the first electrode, a second piezoelectric layer, and the second electrode. The first electrode is on the first piezoelectric layer, the second piezoelectric layer is on the first electrode, the second electrode is on the second piezoelectric layer, and the second piezoelectric layer and the second electrode do not cover the first electrode completely. 
     In more detail, in some embodiments, the protective layer includes a first protective layer and a second protective layer. The first protective layer covers the ultrasonic element, and exposes a part of the first electrode and a part of the second electrode. The first conductive layer and the second conductive layer are on the first protective layer, and are connected to the first electrode and the second electrode respectively. The second protective layer covers the first conductive layer, the second conductive layer, and the first protective layer, and exposes a part of the first conductive layer and a part of the second conductive layer. 
     In some embodiments, the ultrasonic element includes a first ultrasonic unit and a second ultrasonic unit. The first ultrasonic unit includes the first piezoelectric layer and the first electrode, the first piezoelectric layer covers the first electrode, and the first piezoelectric layer is provided with a contact hole, to expose a part of the first electrode. The second ultrasonic unit does not overlap the first ultrasonic unit in a direction perpendicular to a substrate. The second ultrasonic unit includes the second piezoelectric layer, a second circuit layer, and the second electrode. The second piezoelectric layer and the first piezoelectric layer are in a same layer and are separated from each other. The second circuit layer is covered in the second piezoelectric layer. The second circuit layer and the first electrode are in a same layer and are separated from each other, and the second electrode is on the second piezoelectric layer. 
     Furthermore, in some embodiments, the protective layer includes a first protective layer and a second protective layer. The first protective layer covers the first ultrasonic unit and the second ultrasonic unit. The first protective layer is provided with a first communicating hole and a second communicating hole. The first communicating hole is in communication with a contact hole, and the second communicating hole exposes a part of the second electrode. The first conductive layer is filled into the contact hole and the first communicating hole and is connected to the first electrode. The second conductive layer is filled into a part of the second communicating hole and is connected to the second electrode. The second protective layer covers the first conductive layer, the second conductive layer, the first protective layer, and the second electrode, and exposes a part of the first conductive layer and a part of the second conductive layer. 
     In more detail, in some embodiments, the first piezoelectric layer includes a first bottom piezoelectric layer and a first top piezoelectric layer. The first electrode is on the first bottom piezoelectric layer, and is covered by the first top piezoelectric layer. The first top piezoelectric layer includes the contact hole to expose a part of the electrode, the second piezoelectric layer includes a second bottom piezoelectric layer and a second top piezoelectric layer. The second circuit layer is on the second bottom piezoelectric layer, and is covered by the second top piezoelectric layer. The second electrode is on the second top piezoelectric layer. 
     In more detail, in some embodiments, the first electrical connection region and the second electrical connection region are through holes penetrating the base. Furthermore, the wafer level ultrasonic device further includes two bonding pads. The bonding pads are on one side, away from the protective layer, of the base, and are respectively connected to the metal materials in the first electrical connection region and the second electrical connection region. 
     In some other embodiments, the first electrical connection region and the second electrical connection region are side edges on the base. 
     In some embodiments, the base is made of glass. 
     Herein, a manufacturing method of a wafer level ultrasonic device is further provided. The method includes: forming an ultrasonic element on a substrate, where the ultrasonic element includes a first electrode and a second electrode that is not connected to the first electrode; forming a first protective layer on the ultrasonic element and the substrate, and forming a first through hole and a second through hole that expose a part of the first electrode and a part of the second electrode; forming a first conductive layer and a second conductive layer on the first protective layer, where a part of the first conductive layer is in the first through hole and is connected to the first electrode, and a part of the second conductive layer is in the second through hole and is connected to the second electrode; forming a second protective layer on the ultrasonic element, the first protective layer, the first conductive layer, and the second conductive layer; providing a base, and connecting the base and the second protective layer in a vacuum environment, where the base is provided with an opening, and the opening forms a closed cavity with the protective layer; removing the substrate; forming a first electrical connection region and a second electrical connection region on the base, and forming, on the second protective layer, a first groove and a second groove that expose a part of the first conductive layer and a part of the second conductive layer, where the first electrical connection region and the second electrical connection region are in communication with the first groove and the second groove respectively; and filling the first electrical connection region, the second electrical connection region, the first groove, and the second groove with metal materials, so that the metal materials are connected to the first conductive layer and the second conductive layer. 
     In some embodiments, the step of forming the ultrasonic element includes: forming a first piezoelectric material layer, a first electrode material layer, a second piezoelectric material layer, and a second electrode material layer in sequence; and removing parts of the first piezoelectric material layer, the first electrode material layer, the second piezoelectric material layer, and the second electrode material layer, to form a first piezoelectric layer, the first electrode, a second piezoelectric layer, and the second electrode, where the second piezoelectric layer and the second electrode expose a part of the first electrode. 
     In some other embodiments, the step of forming the ultrasonic element includes: forming the first piezoelectric material layer and the first electrode material layer on the substrate in sequence; removing parts of the first piezoelectric material layer and the first electrode material layer, to form the first bottom piezoelectric layer and the second bottom piezoelectric layer that are separated from each other and the first electrode and the second circuit layer that are separated from each other; forming the second piezoelectric material layer and the second electrode material layer in sequence, where the second piezoelectric material layer covers the first bottom piezoelectric layer, the second bottom piezoelectric layer, the first electrode, and the second circuit layer; and removing parts of the second piezoelectric material layer and the second electrode material, to form a first top piezoelectric layer, a second top piezoelectric layer, and the second electrode that are separated from each other, where the first top piezoelectric layer covers the first bottom piezoelectric layer and the first electrode, the second top piezoelectric layer covers the second bottom piezoelectric layer and the second circuit layer, and the second electrode is on the second top piezoelectric layer, to form a first ultrasonic unit and a second ultrasonic unit. 
     In some embodiments, the step of forming the first electrical connection region and the second electrical connection region includes penetrating the base to form two through holes as the first electrical connection region and the second electrical connection region, and removing a part of the protective layer to form the first groove and the second groove. Furthermore, the method further includes: forming two bonding pads on one side, away from the protective layer, of the base, where the two bonding pads are respectively connected to the metal materials in the first electrical connection region and the second electrical connection region. 
     In some embodiments, the step of forming the first electrical connection region and the second electrical connection region includes removing edges of the base and the protective layer to form the first electrical connection region and the second electrical connection region. 
     Based on the foregoing, by using the closed cavity between the base and the protective layer, the speed of ultrasonic transmission through vacuum and a general medium changes obviously. Therefore, a transfer direction of a signal can be clearly distinguished. Furthermore, because a propagation direction of an ultrasonic signal may be recognized clearly, functions such as gesture sensing may be further provided, and can be applied to a tablet and a television with a large size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic cross-sectional view of a wafer level ultrasonic device according to a first embodiment. 
         FIG. 2  is schematic cross-sectional view of a wafer level ultrasonic device according to a second embodiment. 
         FIG. 3  is schematic cross-sectional view of a wafer level ultrasonic device according to a third embodiment. 
         FIG. 4  is schematic cross-sectional view of a wafer level ultrasonic device according to a fourth embodiment. 
         FIG. 5A  to  FIG. 5I  are stepwise schematic cross-sectional views of a manufacturing method of the wafer level ultrasonic device according to the first embodiment. 
         FIG. 6A  to  FIG. 6B  are stepwise schematic cross-sectional views of a manufacturing method of the wafer level ultrasonic device according to the second embodiment. 
         FIG. 7A  to  FIG. 7K  are stepwise schematic cross-sectional views of a manufacturing method of the wafer level ultrasonic device according to the third embodiment. 
         FIG. 8A  to  FIG. 8B  are stepwise schematic cross-sectional views of a manufacturing method of the wafer level ultrasonic device according to the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is schematic cross-sectional view of a wafer level ultrasonic device according to a first embodiment. As shown in  FIG. 1 , the wafer level ultrasonic device  1  of the first embodiment includes a composite layer  15 , a first conductive layer  31 , a second conductive layer  33 , a base  40 , a first electrical connection region  51 , and a second electrical connection region  53 . The composite layer  15  includes an ultrasonic element  10  and a protective layer  20 . The ultrasonic element  10  includes a first electrode  121  and a second electrode  123 . The first electrode  121  is not connected to the second electrode  123 . The protective layer  20  covers the ultrasonic element  10  and is provided with a first connecting channel  211  and a second connecting channel  213 . One end of the first connection channel  211  corresponds to the first electrode  121 , and one end of the second connection channel  213  corresponds to the second electrode  123 . The first conductive layer  31  is in the first connecting channel  211  and is electrically connected to the first electrode  121 . The second conductive layer  33  is in the second connecting channel  213  and is electrically connected to the second electrode  123 . Parts of the first conductive layer  31  and the second conductive layer  33  are exposed to the protective layer  20 . The base  40  is connected to the protective layer  20 . The base  40  includes an opening  45 , and after the base  40  is connected to the protective layer  20 , the opening  45  forms a closed cavity H with the protective layer  20 . The first electrical connection region  51  is filled with a metal material  61  to be electrically connected to the first conductive layer  31 . The second electrical connection region  53  is filled with a metal material  63  to be electrically connected to the second conductive layer  33 . 
     In more detail, in the first embodiment, the ultrasonic element  10  includes a first piezoelectric layer  111 , the first electrode  121 , a second piezoelectric layer  113 , and the second electrode  123 . The first electrode  121  is on the first piezoelectric layer  111 . The second piezoelectric layer  113  is on the first electrode  121 . The second electrode  123  is on the second piezoelectric layer  113 . The second piezoelectric layer  113  and the second electrode  123  do not cover the first electrode  121  completely. Herein, “on” indicates a stacking relationship between elements, but does not indicate an absolute direction relationship. 
     The protective layer  20  includes a first protective layer  21  and a second protective layer  23 . The first protective layer  21  covers the ultrasonic element  10 , and exposes a part of the first electrode  121  and a part of the second electrode  123 . The first conductive layer  31  and the second conductive layer  33  are on the first protective layer  21 , and are connected to the first electrode  121  and the second electrode  123  respectively. The second protective layer  23  covers the first conductive layer  31 , the second conductive layer  33 , and the first protective layer  21 , and exposes a part of the first conductive layer  31  and a part of the second conductive layer  33 . In other words, the first connecting channel  211  and the second connecting channel  213  respectively provide, between the first protective layer  21  and the second protective layer  23 , space for receiving the first conductive layer  31  and the second conductive layer  33  so as to be connected to the first electrode  121  and the second electrode  123  respectively. 
     In the first embodiment, the first electrical connection region  51  and the second electrical connection region  53  are through holes penetrating the base  40 , and correspond to the first conductive layer  31  and the second conductive layer  33  respectively. The metal materials  61  and  63  are connected to the first conductive layer  31  and the second conductive layer  33  through the first electrical connection region  51  and the second electrical connection region  53 . Herein, the first electrical connection region  51  and the second electrical connection region  53  in the figure are oblique, but are not limited thereto actually. In addition, the wafer level ultrasonic device  1  further includes two bonding pads  70 . The bonding pads  70  are on one side, away from the protective layer  20 , of the base  40  separately, and are respectively connected to the metal materials  61  and  63  in the first electrical connection region  51  and the second electrical connection region  53 . The bonding pads  70  may have a relatively large size, to be connected to a circuit board (not shown in the figure). 
     Herein, the base  40  may be made of glass. However, this is only an example, and is not intended for limitation. Other materials, for example, silicon wafers and quartz, may also be used. 
       FIG. 2  is schematic cross-sectional view of a wafer level ultrasonic device according to a second embodiment. As shown in  FIG. 2 , and with reference to  FIG. 1 , a main difference between the first embodiment and the second embodiment is a structure of the base  40 . The base  40  of the second embodiment is bowl-shaped. A first electrical connection region  55 A and a second electrical connection region  55 B are side edges at the base  40  and the protective layer  20 , and are filled with metal materials  65 A and  65 B in a lump form to be connected to the first conductive layer  31  and the second conductive layer  33 . 
       FIG. 3  is schematic cross-sectional view of a wafer level ultrasonic device according to a third embodiment. As shown in  FIG. 3 , and with reference to  FIG. 1 , a main difference between the third embodiment and the first embodiment is a structure of the composite layer  15 . As shown in  FIG. 3 , the ultrasonic element  10  of the third embodiment includes a first ultrasonic unit  10 A and a second ultrasonic unit  10 B. The first ultrasonic unit  10 A includes a first piezoelectric layer  13  and a first electrode  141 . The first piezoelectric layer  13  covers the first electrode  141 . The first piezoelectric layer  13  is provided with a contact hole  571 , to expose a part of the first electrode  141 . The second ultrasonic unit  10 B does not overlap the first ultrasonic unit  10 A in a direction perpendicular to a substrate. The second ultrasonic unit  10 B includes a second piezoelectric layer  17 , a second circuit layer  143 , and a second electrode  145 . The second piezoelectric layer  17  and the first piezoelectric layer  13  are in a same layer and are separated from each other. The second circuit layer  143  is covered in the second piezoelectric layer  17 . The second circuit layer  143  and the first electrode  141  are in a same layer and are separated from each other, and the second electrode  145  is on the second piezoelectric layer  17 . 
     In more detail, in the third embodiment, similar to the first embodiment and the second embodiment, the protective layer  20  includes the first protective layer  21  and the second protective layer  23 . The first protective layer  21  covers the first ultrasonic unit  10 A and the second ultrasonic unit  10 B. The first protective layer  21  is provided with a first communicating hole  573  and a second communicating hole  575 , and the first communicating hole  573  is in communication with the contact hole  571 . The second communicating hole  575  exposes a part of the second electrode  145 . The first conductive layer  31  is filled into the contact hole  571  and the first communicating hole  573  and is connected to the first electrode  141 . The second conductive layer  33  is filled into a part of the second communicating hole  575  and is connected to the second electrode  145 . The second protective layer  23  covers the first conductive layer  31 , the second conductive layer  33 , the first protective layer  21 , and the second electrode  145 , and exposes a part of the first conductive layer  31  and a part of the second conductive layer  33 , to be in electrical conduction with the metal materials  61  and  63  filled in the first electrical connection region  51  and the second electrical connection region  53  in the base  40 . 
     Referring to  FIG. 3  again, the first piezoelectric layer  13  includes a first bottom piezoelectric layer  131  and a first top piezoelectric layer  133 . The first electrode  141  is on the first bottom piezoelectric layer  131 , and is covered by the first top piezoelectric layer  133 . The first top piezoelectric layer  133  includes the contact hole  571  to expose a part of the first electrode  141 . The second piezoelectric layer  17  includes a second bottom piezoelectric layer  171  and a second top piezoelectric layer  173 . The second circuit layer  143  is on the second bottom piezoelectric layer  171 , and is covered by the second top piezoelectric layer  173 . The second electrode  145  is on the second top piezoelectric layer  173 . Similarly, herein, “top” and “bottom” indicate a mutual relationship of stacking, but not indicate an absolute direction relationship. 
       FIG. 4  is schematic cross-sectional view of a wafer level ultrasonic device according to a fourth embodiment. As shown in  FIG. 4 , the fourth embodiment may be a combination of the structure of the base  40  at a lower part of the second embodiment and a structure of an upper half part of the third embodiment, and details are not described herein again. 
       FIG. 5A  to FIG. SI are stepwise schematic cross-sectional views of a manufacturing method of the wafer level ultrasonic device according to the first embodiment. As shown in  FIG. 5A , the manufacturing method of the wafer level ultrasonic device according to the first embodiment includes: first, forming a first piezoelectric material layer  11 A, a first electrode material layer  12 A, a second piezoelectric material layer  11 B, and a second electrode material layer  12 B on a substrate  600  in sequence; next, as shown in  FIG. 5B , removing parts of the first piezoelectric material layer  11 A, the first electrode material  12 A, the second piezoelectric material layer  11 B, and the second electrode material layer  12 B, to form the first piezoelectric layer  111 , the first electrode  121 , the second piezoelectric layer  113 , and the second electrode  123 , where the first electrode  121  is not connected to the second electrode  123 . Lengths of the second piezoelectric layer  113  and the second electrode  123  are shorter than those of the first piezoelectric layer  111  and the first electrode  121 , so that a part of the first electrode  121  is exposed, thus completing manufacturing of the ultrasonic element  10 . 
     As shown in  FIG. 5C , the first protective layer  21  is formed on the ultrasonic element  10  and the substrate  600 . The first protective layer  21  is provided with a first through hole  215  and a second through hole  217  that expose a part of the first electrode  121  and a part of the second electrode  123 . Herein, the first protective layer  21  may be manufactured by means of lithography, and may be also manufactured by means of laser punching after coating. However, the above are only examples, and not intended for limitation. 
     Then, as shown in  FIG. 5D , the first conductive layer  31  and the second conductive layer  33  are formed on the first protective layer  21 . A part of the first conductive layer  31  is in the first through hole  215  and is connected to the first electrode  121 . A part of the second conductive layer  33  is in the second through hole  217  and is connected to the second electrode  123 . Similarly, the first conductive layer  31  and the second conductive layer  33  may be also manufactured by means of lithography. 
     As shown in  FIG. 5E , the second protective layer  23  is formed on the ultrasonic element  10 , the first protective layer  21 , the first conductive layer  31 , and the second conductive layer  33 . 
     Subsequently, as shown in  FIG. 5F , an original structure is reversed, and the base  40  is provided. The base  40  and the second protective layer  20  are connected in a vacuum environment. The base  40  is provided with the opening  45 , and the opening  45  forms the closed cavity H with the protective layer  20 . As shown in  FIG. 5G , the substrate  600  is removed. 
     As shown in  FIG. 5H , the first electrical connection region  51  and the second electrical connection region  53  are formed on the base  40 . The second protective layer  23  forms a first groove  231  and a second groove  233  that expose a part of the first conductive layer  31  and a part of the second conductive layer  33 . The first electrical connection region  51  and the second electrical connection region  53  are in communication with the first groove  231  and the second groove  233  respectively. In the state of the first embodiment, a punching technology is used. The first electrical connection region  51  and the first groove  231  are substantially completed by a same punching procedure, and the second electrical connection region  53  and the second groove  233  are substantially completed by a same punching procedure. 
     Finally, as shown in  FIG. 51 , the first electrical connection region  51 , the second electrical connection region  53 , the first groove  231 , and the second groove  233  are filled with the metal materials  61  and  63 , so that the metal materials  61  and  63  are connected to the first conductive layer  31  and the second conductive layer  33 . Further, the method further includes forming the two bonding pads  70 . The bonding pads  70  are on one side, away from the protective layer  20 , of the base  40 , and are respectively connected to the metal materials  61  and  63  in the first electrical connection region  51  and the second electrical connection region  53 . 
       FIG. 6A  to  FIG. 6B  are stepwise schematic cross-sectional views of a manufacturing method of the wafer level ultrasonic device according to the second embodiment. The manufacturing method of the second embodiment is roughly the same as  FIG. 5A  to  FIG. 5G  of the first embodiment, and details are not described herein again.  FIG. 6A  shows a first electrical connection region  55 A and a second electrical connection region  55 B formed by directly removing parts of edges of the base  40  and the protective layer  20 . In this case, regions of the first conductive layer  31  and the second conductive layer  33 , which are exposed after the protective layer  20  is removed, may be treated as the first groove and the second groove (not shown in the figure). Finally, as shown in  FIG. 6B , the first electrical connection region  55 A and the second electrical connection region  55 B are filled with metal materials  65 A and  65 B, and the wafer level ultrasonic device  1  of the second embodiment is completed. 
       FIG. 7A  to  FIG. 7K  are stepwise schematic cross-sectional views of a manufacturing method of the wafer level ultrasonic device according to the third embodiment. As shown in  FIG. 7A , first, a first piezoelectric material layer  13 A and a first electrode material layer  14 A are formed on the substrate  600  in sequence. Next, as shown in  FIG. 7B , parts of the first piezoelectric material layer  13 A and the first electrode material layer  14 A are removed, to form the first bottom piezoelectric layer  131  and the second bottom piezoelectric layer  171  that are separated from each other and the first electrode  141  and the second circuit layer  143  that are separated from each other. As shown in  FIG. 7C , a second piezoelectric material layer  13 B and a second electrode material layer  14 B are formed in sequence. The second piezoelectric material layer  13 B covers the first bottom piezoelectric layer  131 , the second bottom piezoelectric layer  171 , the first electrode  141 , and the second circuit layer  143 . 
     As shown in  FIG. 7D , parts of the second piezoelectric material layer  13 B and the second electrode material layer  14 B are removed, to form the first top piezoelectric layer  133 , the second top piezoelectric layer  173 , and the second electrode  145  that are separated from each other. The first top piezoelectric layer  133  covers the first bottom piezoelectric layer  131  and the first electrode  141 . The second top piezoelectric layer  173  covers the second bottom piezoelectric layer  171  and the second circuit layer  143 . The second electrode  145  is on the second top piezoelectric layer  173 , to form the first ultrasonic unit  10 A and the second ultrasonic unit  10 B. Then, as shown in  FIG. 7E , the first protective layer  21  is formed on the first ultrasonic unit  10 A and the second ultrasonic unit  10 B, and a first through hole (that is, the contact hole  571  and the first communicating hole  573 ) and a second through hole (that is, the second communicating hole  575 ) are form in the first protective layer  21  and the first top piezoelectric layer  133  by an opening technology. 
     Subsequently, as shown in  FIG. 7F , metal materials are formed on the first protective layer  21 , and parts of the metal materials are removed to form the first conductive layer  31  and the second conductive layer  33 . A part of the first conductive layer  31  is filled into the contact hole  571  and the first communicating hole  573  and is connected to the first electrode  141 . A part of the second conductive layer  33  is in the second communicating hole  575  and is connected to the second electrode  145 . As shown in  FIG. 7G , the second protective layer  23  is formed on the ultrasonic element  10 , the first protective layer  21 , the first conductive layer  31 , and the second conductive layer  33 . 
     As shown in  FIG. 7H, 7I, 7J, and 7K , and with reference to  FIG. 5F to 5I , the closed cavity H is formed by blocking the base  40  in the same way, the substrate  600  is removed, the first electrical connection region  51  and the second electrical connection region  53  are formed by means of punching, the metal materials  61  and  63  are then filled, and the bonding pads  70  are formed. 
       FIG. 8A  to  FIG. 8B  are stepwise schematic cross-sectional views of a manufacturing method of the wafer level ultrasonic device according to the fourth embodiment. The manufacturing method of the wafer level ultrasonic device of the fourth embodiment is the same as  FIG. 7A to 7G  of the third embodiment in general, and details are not described herein again. As shown in  FIG. 8A  to  FIG. 8B , and with reference to  FIG. 6A  to  FIG. 6B , the first electrical connection region  55 A and the second electrical connection region  55 B are also formed by directly removing parts of edges of the base  40  and the protective layer  20 ; the first electrical connection region  55 A and the second electrical connection region  55 B are then filled with the metal materials  65 A and  65 B; and the wafer level ultrasonic device  1  of the fourth embodiment is completed. 
     Based on the foregoing, by using the closed cavity H between the base  40  and the protective layer  20  of the wafer level ultrasonic device, the speed of ultrasonic transmission through vacuum and a general medium changes obviously. Therefore, a transfer direction of a signal can be clearly distinguished. In addition to fingerprint recognition, functions such as gesture sensing may be further provided though a high resolution of the wafer level ultrasonic device. In addition, a manufacturing process is simple, and a manufacturing cost may be reduced greatly. 
     Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, the disclosure is not for limiting the scope of the invention. Persons having ordinary skill in the art may make various modifications and changes without departing from the scope and spirit of the invention. Therefore, the scope of the appended claims should not be limited to the description of the preferred embodiments described above.