Piezoelectric transducer manufacturing method and piezoelectric transducer

Abstract

The present application relates to a method for manufacturing a piezoelectric transducer and a piezoelectric transducer. The method includes first manufacturing a bottom acoustic reflection layer on a support wafer, then manufacturing a top acoustic reflection layer on a piezoelectric wafer, then bonding the side of the bottom acoustic reflection layer away from the support wafer to the side of the top acoustic reflection layer away from the piezoelectric wafer, and finally thinning the piezoelectric wafer to form a piezoelectric transducer. The support wafer serves as a support, and the piezoelectric wafer is thinned to form a piezoelectric film that can be excited to acoustically vibrate, and the top and bottom acoustic reflection layers can limit the acoustic vibration, so that the resulting piezoelectric transducer can operate at a high frequency. The piezoelectric transducer manufactured by the method has a specific stacking combination and piezoelectric film, so that it can excite and support high-performance acoustic vibration modes, has relatively low intrinsic loss, and can obtain a higher unit area capacitance while maintaining a unit area, so that the manufactured piezoelectric transducer has excellent operating performance.

Description

[Technical Field]

[0001] The present application relates to the technical field of transducers, and more particularly to a method for manufacturing a piezoelectric transducer and a piezoelectric transducer. [Background technology]

[0002] A transducer is a device that converts electrical energy into acoustic energy and vice versa. Piezoelectric transducers are a type of transducer that converts electrical energy into acoustic energy and vice versa by utilizing the piezoelectric effect of certain single crystal materials and the electrostrictive effect of certain polycrystalline materials. They have high electroacoustic efficiency, large power capacity, and can be designed to fit various structures and shapes for different applications, making them widely used in the field of power ultrasound.

[0003] Conventional piezoelectric transducers are made by bonding a piezoelectric wafer to another support wafer. In the case of silicon substrates, many single-crystal films are bonded to a support wafer (mainly silicon) directly or via a bonding interface layer. The support wafer bonded in this way can be used as a piezoelectric transducer. However, piezoelectric transducers manufactured in this way have low maximum operating frequencies, low capacitance densities, low power thresholds, and the possibility of having unresolved impurity modes, resulting in poor operational performance. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of this, there is a need to provide a piezoelectric transducer manufacturing method and a piezoelectric transducer that address the problem of poor operating performance of conventional piezoelectric transducers. [Means for solving the problem]

[0005] A method for manufacturing a piezoelectric transducer includes providing a support wafer and fabricating a bottom acoustically reflective layer on the support wafer; providing a piezoelectric wafer and fabricating a top acoustically reflective layer on the piezoelectric wafer, wherein both the top and bottom acoustically reflective layers are used to limit acoustic vibrations; bonding a side of the bottom acoustically reflective layer away from the support wafer to a side of the top acoustically reflective layer away from the piezoelectric wafer; and thinning the piezoelectric wafer to form a piezoelectric transducer.

[0006] The piezoelectric transducer is manufactured by the above method.

[0007] According to the above-mentioned piezoelectric transducer manufacturing method and piezoelectric transducer, first, a support wafer is provided, a bottom acoustic reflection layer is formed on the support wafer, a piezoelectric wafer is provided, and a top acoustic reflection layer is formed on the piezoelectric wafer, both of which serve to limit acoustic vibrations, then the side of the bottom acoustic reflection layer facing away from the support wafer is bonded to the side of the top acoustic reflection layer facing away from the piezoelectric wafer, and finally, the piezoelectric wafer is thinned to form a piezoelectric transducer. In the piezoelectric transducer manufactured by this piezoelectric transducer manufacturing method, the piezoelectric wafer, the top acoustic reflection layer, the bottom acoustic reflection layer, and the support wafer are stacked together, the support wafer provides support, the piezoelectric film formed by thinning the piezoelectric wafer can be excited to acoustically vibrate, and the top and bottom acoustic reflection layers can limit the acoustic vibrations, so that the resulting piezoelectric transducer can operate at high frequencies. The piezoelectric transducer manufactured by this method has a specific laminate combination and piezoelectric film, which can excite and support high-performance acoustic vibration modes, has relatively low intrinsic loss, and can achieve a higher unit area capacitance while maintaining a unit area, thereby providing the manufactured piezoelectric transducer with excellent operating performance.

[0008] In one embodiment, the steps of providing a piezoelectric wafer and fabricating a top acoustically reflective layer on the piezoelectric wafer include providing a piezoelectric wafer, fabricating a bottom electrode layer on the piezoelectric wafer, and fabricating a top acoustically reflective layer on the piezoelectric wafer overlying the bottom electrode layer.

[0009] In one embodiment, the bottom acoustic reflection layer includes a bottom high acoustic impedance layer and a bottom low acoustic impedance layer, and the sum of the number of the bottom high acoustic impedance layers and the number of the bottom low acoustic impedance layers is an odd number, and the step of providing a support wafer and fabricating a bottom acoustic reflection layer on the support wafer includes providing a support wafer and fabricating the bottom high acoustic impedance layers and the bottom low acoustic impedance layers alternately on one side of the support wafer.

[0010] In one embodiment, the top acoustically reflective layer comprises a top low acoustic impedance layer, and the step of providing a piezoelectric wafer and fabricating a top acoustically reflective layer on the piezoelectric wafer comprises providing a piezoelectric wafer and fabricating the top low acoustic impedance layer on the piezoelectric wafer.

[0011] In one embodiment, the top acoustically reflective layer further includes a top low acoustic impedance layer and a top high acoustic impedance layer, and the sum of the number of the top high acoustic impedance layers and the number of the top low acoustic impedance layers is an odd number, and the step of providing a piezoelectric wafer and fabricating a top acoustically reflective layer on the piezoelectric wafer includes providing a piezoelectric wafer and fabricating the top low acoustic impedance layers and the top high acoustic impedance layers alternately on the piezoelectric wafer.

[0012] In one embodiment, the layer of the bottom acoustic reflecting layer farthest from the support wafer is the bottom low acoustic impedance layer, and the layer of the top acoustic reflecting layer farthest from the piezoelectric wafer is the top low acoustic impedance layer; or the layer of the bottom acoustic reflecting layer farthest from the support wafer is the bottom high acoustic impedance layer, and the layer of the top acoustic reflecting layer farthest from the piezoelectric wafer is the top high acoustic impedance layer.

[0013] In one embodiment, after providing the piezoelectric wafer and fabricating a top acoustic reflection layer on the piezoelectric wafer, and before bonding the side of the bottom acoustic reflection layer away from the support wafer to the side of the top acoustic reflection layer away from the piezoelectric wafer, the method further includes performing a planarization process on the side of the bottom acoustic reflection layer away from the support wafer and the side of the top acoustic reflection layer away from the piezoelectric wafer.

[0014] In one embodiment, the step of bonding the side of the bottom acoustic reflection layer away from the support wafer to the side of the top acoustic reflection layer away from the piezoelectric wafer includes providing a bonding interface layer and bonding the side of the bottom acoustic reflection layer away from the support wafer to the side of the top acoustic reflection layer away from the piezoelectric wafer by the bonding interface layer.

[0015] In one embodiment, the step of providing a piezoelectric wafer and fabricating a top acoustic reflection layer on the piezoelectric wafer includes providing a piezoelectric wafer, implanting the piezoelectric wafer with ions, and fabricating a top acoustic reflection layer on the implanted piezoelectric wafer. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a flow diagram of a method for manufacturing a piezoelectric transducer according to an embodiment. [Figure 2] FIG. 10 is a flow diagram of a method for manufacturing a piezoelectric transducer according to another embodiment. [Figure 3] FIG. 10 is a flow diagram of a method for manufacturing a piezoelectric transducer according to yet another embodiment. [Figure 4] FIG. 10 is a flow diagram of a method for manufacturing a piezoelectric transducer according to yet another embodiment. [Figure 5] FIG. 10 is a flow diagram of a method for manufacturing a piezoelectric transducer according to another embodiment. [Figure 6] 1A and 1B are a top view and a cross-sectional view of a piezoelectric transducer. [Figure 7] FIG. 1 is a schematic diagram of alternating low and high acoustic impedance layers being deposited and patterned on a support wafer. [Figure 8] FIG. 1 is a schematic diagram of a piezoelectric wafer with a low acoustic impedance layer deposited on the bottom. [Figure 9] 1 is a schematic diagram of a piezoelectric wafer having a bottom electrode layer deposited thereon and a low acoustic impedance layer deposited thereon. [Figure 10] FIG. 1 is a schematic diagram of alternating low and high acoustic impedance layers being deposited and patterned on a piezoelectric wafer. [Figure 11] 10A and 10B are schematic diagrams illustrating the planarization of the outermost layer of the support wafer and the outermost layer of the piezoelectric wafer. [Figure 12] FIG. 1 is a schematic diagram of a bonding process. [Figure 13] 1A and 1B are schematic diagrams illustrating thinning and polishing of a piezoelectric wafer. [Figure 14] 1A and 1B are schematic diagrams illustrating ion implantation and exfoliation of a piezoelectric wafer. DETAILED DESCRIPTION OF THE INVENTION

[0017] In order to make the purpose, technical solution and advantages of the present application clearer, the present application will be described more comprehensively below through examples and with reference to the drawings. It should be understood that the specific examples described herein are only for the purpose of interpreting the present application, and are not intended to limit the present application.

[0018] In one embodiment, referring to FIG. 1, there is provided a method for manufacturing a piezoelectric transducer, including the following steps.

[0019] In step S200, a support wafer is provided, and a bottom acoustic reflection layer is fabricated on the support wafer.

[0020] 6 and 7, the support wafer 100 is a support device for the piezoelectric transducer and serves as a carrier for other structures in the piezoelectric transducer, providing support and fixing. The structure of the support wafer 100 is not limited. In this embodiment, the support wafer 100 is a wafer made of silicon, glass, sapphire, silicon carbide, quartz, or other materials. After providing the support wafer 100, the bottom acoustic reflection layer 200 can be formed on the support wafer 100 in a non-limiting manner. For example, the bottom acoustic reflection layer 200 can be deposited on the support wafer 100 using a physical vapor deposition method, which has a high deposition rate. Alternatively, the bottom acoustic reflection layer 200 can be formed on the support wafer 100 using an oxide film formation method or an epitaxial film formation method, which results in a highly dense and stable structure.

[0021] Furthermore, after the bottom acoustic reflection layer 200 is fabricated on the support wafer 100, the bottom acoustic reflection layer 200 can be patterned to form a specific shape according to the required characteristics of the piezoelectric transducer. There are various ways to pattern the bottom acoustic reflection layer 200, and in this embodiment, photoetching is used to pattern the bottom acoustic reflection layer 200. The shape of the bottom acoustic reflection layer 200 can be designed as needed to meet various requirements. The structure of the bottom acoustic reflection layer 200 is not limited to a single layer or a multi-layer structure, and can be any structure that can limit acoustic vibrations and is feasible for those skilled in the art.

[0022] In step S400, a piezoelectric wafer is provided and a top acoustic reflection layer is fabricated on the piezoelectric wafer.

[0023] The structure of the piezoelectric wafer 400 is not unique. Lithium tantalate, lithium niobate, aluminum nitride, quartz, and other similar doping materials may be used. Referring to FIGS. 6 to 8, after providing a piezoelectric wafer 400, fabricating the top acoustic reflecting layer 300 on the piezoelectric wafer 400 may involve depositing or growing the top acoustic reflecting layer 300 on the piezoelectric wafer 400. Furthermore, after fabricating the top acoustic reflecting layer 300 on the piezoelectric wafer 400, the top acoustic reflecting layer 300 may be further patterned to form a specific shape. The patterning of the top acoustic reflecting layer 300 is not limited to a specific method. In this embodiment, photoetching is used to pattern the top acoustic reflecting layer 300. The shape of the top acoustic reflecting layer 300 can be designed as needed to meet various requirements. The structure of the top acoustic reflecting layer 300 is not limited to a specific method and may be a single-layer or multi-layer structure, as long as it can limit acoustic vibrations and is feasible for those skilled in the art. Ion implantation may be performed on the piezoelectric wafer 400 before fabricating the top acoustic reflecting layer 300. Thus, in the subsequent process of thinning the piezoelectric wafer 400, ion implantation and film peeling transfer techniques can be adopted to thin the piezoelectric wafer 400 with better selectivity. The ion implantation process for the piezoelectric wafer 400 is performed before the deposition and patterning of the top acoustic reflection layer 300, and after ion implantation, the piezoelectric wafer may undergo a series of heating, slicing, and polishing steps, leaving a thin layer of piezoelectric material on the support wafer 100 to form a piezoelectric film.

[0024] In step S600, the side of the bottom acoustically reflective layer away from the support wafer is bonded to the side of the top acoustically reflective layer away from the piezoelectric wafer.

[0025] 6 or 12, after the bottom acoustic reflection layer 200 and the top acoustic reflection layer 300 are fabricated, the side of the bottom acoustic reflection layer 200 away from the support wafer 100 is bonded to the side of the top acoustic reflection layer 300 away from the piezoelectric wafer 400, i.e., the bottom acoustic reflection layer 200 is bonded to the top acoustic reflection layer 300. The specific manner of bonding is not limited to the above, and for example, bonding can be adopted to integrally form the bottom acoustic reflection layer 200 and the top acoustic reflection layer 300 by Van der Waals forces, molecular forces, or even atomic forces, thereby ensuring the operational performance of the piezoelectric transducer.

[0026] In step S800, the piezoelectric wafer is thinned to form piezoelectric transducers.

[0027] After bonding the side of the bottom acoustically reflective layer 200 away from the support wafer 100 to the side of the top acoustically reflective layer 300 away from the piezoelectric wafer 400, referring to FIG. 13 , the piezoelectric wafer 400 is further thinned to a desired thickness to form a piezoelectric film. The piezoelectric transducer includes the support wafer 100, the bottom acoustically reflective layer 200, the thinned piezoelectric wafer 400, and the top acoustically reflective layer 300. The piezoelectric wafer 400, the top acoustically reflective layer 300, the bottom acoustically reflective layer 200, and the support wafer 100 are stacked together, with the support wafer 100 providing support and allowing the piezoelectric film formed by thinning the piezoelectric wafer 400 to be excited to acoustically vibrate, while the top acoustically reflective layer 300 and the bottom acoustically reflective layer 200 limit the acoustic vibration, allowing the resulting piezoelectric transducer to operate at high frequencies. The piezoelectric transducer manufactured by this method has a specific laminate combination and piezoelectric film, which can excite and support high-performance acoustic vibration modes, has relatively low intrinsic loss, and can achieve a higher unit area capacitance while maintaining a unit area, thereby providing the manufactured piezoelectric transducer with excellent operating performance.

[0028] In one embodiment, referring to FIG. 2, step S400 includes step S420 and step S440.

[0029] In step S420, a piezoelectric wafer is provided and a bottom electrode layer is fabricated on the piezoelectric wafer 400.

[0030] Specifically, the bottom electrode layer 500 can be used to transmit electrical signals and generally has a layered structure. Referring to FIG. 9 , the bottom electrode layer 500 is deposited on a piezoelectric wafer 400 to form a bottom electrode of a piezoelectric transducer. After the bottom electrode layer 500 is deposited on the piezoelectric wafer 400, the bottom electrode layer 500 can be further patterned to adjust the shape, area, and thickness of the bottom metal to meet specific needs. The shape of the bottom electrode layer 500 is not limited to a single shape and can be any geometry derived from a square, rectangle, trapezoid, or any polygon with n sides. The structure of the bottom electrode layer 500 is not limited to a single shape and can be a metal layer made of Al, Pt, or Cu, or an alloy of these metals. This can be specified according to actual needs and can be implemented by those skilled in the art. Fabricating the bottom electrode layer 500 on the piezoelectric wafer 400 can change the direction of the electric field introduced into the piezoelectric material by the electrode, thereby forming a new vibration mode and improving the performance of the piezoelectric transducer. Ion implantation may be performed on the piezoelectric wafer 400 before fabricating the bottom electrode layer 500. In this way, the subsequent thinning process of the piezoelectric wafer 400 can employ a transfer technique of ion implantation and film peeling to thin the piezoelectric wafer 400 with better selectivity.

[0031] In step S440, a top acoustic reflection layer covering the bottom electrode layer is fabricated on the piezoelectric wafer.

[0032] After the bottom electrode layer 500 is fabricated, referring to FIG. 9 , a top acoustic reflection layer 300 is fabricated on the piezoelectric wafer 400 to cover the bottom electrode layer 500. It can be seen that the bottom electrode layer 500 does not completely cover the piezoelectric wafer 400. Instead, a portion of the top acoustic reflection layer 300 covers the side of the bottom electrode layer 500 facing away from the piezoelectric wafer 400, and another portion of the top acoustic reflection layer 300 covers the piezoelectric wafer 400. Thus, the top acoustic reflection layer 300 is in contact with not only the piezoelectric wafer 400 but also the bottom electrode layer 500. The top acoustic reflection layer 300 typically has a layered structure and is provided on the other side of the bottom electrode layer 500 to limit acoustic vibrations. The type of the top acoustic reflection layer 300 is not limited, and the material of the top acoustic reflection layer 300 can be selected according to specific needs. After fabricating the top acoustically reflective layer 300 on the side of the piezoelectric wafer 400 adjacent to the bottom electrode layer 500, the top acoustically reflective layer 300 can be further patterned so that the shape, size, etc. of the top acoustically reflective layer 300 can be tailored to meet needs.

[0033] In one embodiment, the bottom acoustically reflective layer 200 includes a bottom high acoustic impedance layer 220 and a bottom low acoustic impedance layer 210, and the sum of the number of the bottom high acoustic impedance layers 220 and the number of the bottom low acoustic impedance layers 210 is an odd number. Referring to FIG. 2, step S200 includes step S220.

[0034] 7 , the bottom acoustic reflecting layer 200 includes a bottom high acoustic impedance layer 220 and a bottom low acoustic impedance layer 210. The bottom high acoustic impedance layer 220 may be a layered structure made of aluminum nitride, tungsten, platinum, molybdenum, ruthenium, or oxides of these materials. The bottom low acoustic impedance layer 210 may be a layered structure made of other oxides, including silica, spin-on glass, tellurium oxide, and other materials. The bottom high acoustic impedance layer 220 and the bottom low acoustic impedance layer 210 form a stack. For example, if one bottom acoustic reflecting layer 200 includes one bottom high acoustic impedance layer 220 and one bottom low acoustic impedance layer 210, the number of layers in the stack is one bottom acoustic reflecting layer 200, which is easy to manufacture. Alternatively, one bottom acoustic reflecting layer 200 may include two or more bottom acoustic reflecting layers 200, thereby improving the operating performance of the piezoelectric transducer. Furthermore, when the sum of the number of bottom high acoustic impedance layers 220 and the number of bottom low acoustic impedance layers 210 is an odd number, the stack ends with one layer, which may be the bottom high acoustic impedance layer 220 or the bottom low acoustic impedance layer 210. The terminating layer is the layer in the bottom acoustic reflecting layer 200 that is farthest from the support wafer 100, and this layer provides a surface that easily adheres to itself, i.e., other layers made of the same material, thereby facilitating bonding with subsequent layers.

[0035] In step S220, a support wafer is provided, and bottom high acoustic impedance layers and bottom low acoustic impedance layers are fabricated alternately on one side of the support wafer.

[0036] When the bottom acoustic reflection layer 200 includes a bottom high acoustic impedance layer 220 and a bottom low acoustic impedance layer 210, after providing the support wafer 100, the bottom high acoustic impedance layer 220 and the bottom low acoustic impedance layer 210 are deposited one by one and alternately arranged on one side of the support wafer 100, thereby better limiting acoustic vibration. In other embodiments, once the alternating bottom high acoustic impedance layer 220 and bottom low acoustic impedance layer 210 are fabricated, this alternating layered structure may be fabricated on the support wafer 100, as long as it is feasible for those skilled in the art. The thicknesses of the bottom high acoustic impedance layer 220 and the bottom low acoustic impedance layer 210 are not unique, and the bottom high acoustic impedance layer 220 and the bottom low acoustic impedance layer 210 may have different thicknesses, and the different thicknesses will result in better performance of the fabricated piezoelectric transducer. The bottom high acoustic impedance layer 220 and the bottom low acoustic impedance layer 210 may have the same thickness, which makes the subsequent processes easier to perform and can be adjusted according to actual needs.

[0037] Furthermore, after the bottom high acoustic impedance layer 220 and the bottom low acoustic impedance layer 210 are fabricated alternately on one side of the support wafer 100, the bottom high acoustic impedance layer 220 can be patterned, or the bottom low acoustic impedance layer 210 can be patterned, or the bottom high acoustic impedance layer 220 and the bottom low acoustic impedance layer 210 can be patterned together. Thereby, the bottom high acoustic impedance layer 220 and / or the bottom low acoustic impedance layer 210 can be formed into a specific shape to better meet demands. The shape of the bottom high acoustic impedance layer 220 and / or the bottom low acoustic impedance layer 210 is not unique and can be adjusted according to actual demands.

[0038] In one embodiment, referring to FIG. 3, top acoustically reflective layer 300 includes top low acoustic impedance layer 310, and step S400 includes step S410.

[0039] In step S410, a piezoelectric wafer is provided and a top low acoustic impedance layer is fabricated on the piezoelectric wafer.

[0040] 6, the top acoustic reflecting layer 300 includes a top low acoustic impedance layer 310, which may be a layered structure made of other oxides, including silica, spin-on glass, tellurium oxide, and other materials. Generally, when the top acoustic reflecting layer 300 includes a top low acoustic impedance layer 310, the number of the top low acoustic impedance layer 310 is one, and the top low acoustic impedance layer 310 is fabricated on the piezoelectric wafer 400 to limit acoustic vibration. Furthermore, if the bottom electrode layer 500 has already been fabricated on one side of the piezoelectric wafer 400, it can be understood that the bottom electrode layer 500 does not completely cover the piezoelectric wafer 400, but rather a portion of the top low acoustic impedance layer 310 covers the side of the bottom electrode layer 500 away from the piezoelectric wafer 400, and another portion of the top low acoustic impedance layer 310 covers the piezoelectric wafer 400, so that the top low acoustic impedance layer 310 not only contacts the piezoelectric wafer 400 but also contacts the bottom electrode layer 500, and the top low acoustic impedance layer 310 can cover the bottom electrode layer 500. Furthermore, after fabricating the top low acoustic impedance layer 310 on the piezoelectric wafer 400, the top low acoustic impedance layer 310 can be patterned, so that the top low acoustic impedance layer 310 has a specific shape to meet demands.

[0041] In one embodiment, the top acoustically reflective layer 300 includes a top low acoustic impedance layer 310 and a top high acoustic impedance layer 320, and the sum of the number of the top high acoustic impedance layers 320 and the number of the top low acoustic impedance layers 310 is an odd number. Referring to FIG. 4, step S400 includes step S430.

[0042] In step S430, a piezoelectric wafer is provided, and alternating top low acoustic impedance layers and top high acoustic impedance layers are fabricated on the piezoelectric wafer.

[0043] In this embodiment, referring to FIGS. 11 to 14 , the top acoustic reflecting layer 300 includes a top high acoustic impedance layer 320 in addition to a top low acoustic impedance layer 310. The top high acoustic impedance layer 320 may be a layered structure made of aluminum nitride, tungsten, platinum, molybdenum, ruthenium, or an oxide of one of these materials. The top high acoustic impedance layer 320 and the top low acoustic impedance layer 310 form a stack. For example, if one top acoustic reflecting layer 300 includes one top high acoustic impedance layer 320 and one top low acoustic impedance layer 310, the number of layers in the stack may be one, i.e., one top acoustic reflecting layer 300, which is easy to manufacture. Alternatively, one top acoustic reflecting layer 300 may include two or more top acoustic reflecting layers 300, thereby improving the performance of the piezoelectric transducer. Furthermore, when the sum of the number of top high acoustic impedance layers 320 and the number of top low acoustic impedance layers 310 is odd, the stack ends with one layer, which may be either the top high acoustic impedance layer 320 or the top low acoustic impedance layer 310, and the terminating layer is the layer in the top acoustic reflecting layer 300 that is farthest from the support wafer 100.

[0044] 12a, the bonding between the bottom acoustic reflection layer 200 and the top acoustic reflection layer 300 can occur at an interface between the acoustic reflection layers, thereby achieving high bonding strength and preventing the bonded films from falling off during subsequent processing. The specific bonding location, whether it is a high-impedance layer or a low-impedance layer, can be implemented by those skilled in the art. Note that if the bottom electrode layer 500 has already been fabricated on one side of the piezoelectric wafer 400, the top low acoustic impedance layer 310 typically covers the bottom electrode layer 500, and then the top high acoustic impedance layer 320 is subsequently fabricated on the side of the top low acoustic impedance layer 310 away from the bottom electrode layer 500, so that the top low acoustic impedance layer 310 and the top high acoustic impedance layer 320 are alternately arranged.

[0045] Fabricating the alternating top low acoustic impedance layers 310 and top high acoustic impedance layers 320 on the piezoelectric wafer 400 may be done by depositing the alternating top low acoustic impedance layers 310 and top high acoustic impedance layers 320 on the piezoelectric wafer one layer at a time to form the alternating top low acoustic impedance layers 310 and top high acoustic impedance layers 320. In other embodiments, after the alternating top low acoustic impedance layers 310 and top high acoustic impedance layers 320 are fabricated, this alternating layered structure may be fabricated on the piezoelectric wafer 400, as would be feasible to one skilled in the art.

[0046] In one embodiment, the layer of the bottom acoustically reflective layer 200 farthest from the support wafer 100 is the bottom low acoustic impedance layer 210, and the layer of the top acoustically reflective layer 300 farthest from the piezoelectric wafer 400 is the top low acoustic impedance layer 310; alternatively, the layer of the bottom acoustically reflective layer 200 farthest from the support wafer 100 is the bottom high acoustic impedance layer 220, and the layer of the top acoustically reflective layer 300 farthest from the piezoelectric wafer 400 is the top high acoustic impedance layer 320.

[0047] In this embodiment, the layer of the bottom acoustic reflecting layer 200 that is farthest from the support wafer 100 is the bottom low acoustic impedance layer 210, and the layer of the top acoustic reflecting layer 300 that is farthest from the piezoelectric wafer 400 is the top low acoustic impedance layer 310, i.e., the layers used for bonding in the support wafer 100 and the layers used for bonding in the piezoelectric wafer 400 are both low acoustic impedance layers; alternatively, the layer of the bottom acoustic reflecting layer 200 that is farthest from the support wafer 100 is the bottom high acoustic impedance layer 220, and the layer of the top acoustic reflecting layer 300 that is farthest from the piezoelectric wafer 400 is the top high acoustic impedance layer 320, i.e., the layers used for bonding in the support wafer 100 and the layers used for bonding in the piezoelectric wafer 400 are both high acoustic impedance layers. The last layer in the piezoelectric wafer 400 and the top layer in the stack of layers of the support wafer 100 are made of the same material, which can provide a better bonding interface and make the bond between the bottom acoustic reflecting layer 200 and the top acoustic reflecting layer 300 stronger.

[0048] In one embodiment, referring to FIG. 4, after step S400 and before step S600, the method for manufacturing a piezoelectric transducer further includes step S500.

[0049] In step S500, a planarization process is performed on the side of the bottom acoustically reflective layer facing away from the support wafer and the side of the top acoustically reflective layer facing away from the piezoelectric wafer.

[0050] The planarization process may include steps such as thinning and polishing. Referring to Figure 11, before bonding the bottom acoustic reflective layer 200 to the top acoustic reflective layer 300, a planarization process is first performed on the side of the bottom acoustic reflective layer 200 facing away from the support wafer 100 and the side of the top acoustic reflective layer 300 facing away from the piezoelectric wafer 400, thereby providing a flat and smooth bonding interface and strengthening the bonding between the bottom acoustic reflective layer 200 and the top acoustic reflective layer 300. Furthermore, if one or more layers of the support wafer 100 and the bottom acoustic reflective layer 200 are patterned, or one or more layers of the piezoelectric wafer 400 and the top acoustic reflective layer 300 are patterned, or one or more layers of the support wafer 100, the bottom acoustic reflective layer 200, the piezoelectric wafer 400, and the top acoustic reflective layer 300 are patterned, a planarization step is performed on each patterned structure before bonding to ensure effective interfacial bonding.

[0051] In one embodiment, referring to FIG. 5, step S600 includes step S620.

[0052] In step S620, a bonding interface layer is provided, and the side of the bottom acoustically reflective layer away from the support wafer is bonded to the side of the top acoustically reflective layer away from the piezoelectric wafer by the bonding interface layer.

[0053] Specifically, referring to FIG. 12( b), when bonding the bottom acoustic reflecting layer 200 to the top acoustic reflecting layer 300, a bonding interface layer 700 is provided, and the side of the bottom acoustic reflecting layer 200 facing away from the support wafer 100 is bonded to the side of the top acoustic reflecting layer 300 facing away from the piezoelectric wafer 400 via the bonding interface layer 700. For example, when the bonding between the bottom acoustic reflecting layer 200 and the top acoustic reflecting layer 300 is performed by bonding, the bonding process may be hot pressing bonding, surface activation direct bonding, or any other method for adhering semiconductor wafers. Bonding may occur at the bottom or top of an acoustic reflecting layer. When the layer used for bonding the bottom acoustic reflecting layer 200 is of a different type from the layer used for bonding the top acoustic reflecting layer 300, for example, when one layer is a high acoustic impedance layer and the other is a low acoustic impedance layer, the bonding interface layer 700 can be used to bond the two different types of layers and ensure smooth bonding. The thickness of the bonding interface layer 700 is typically small and does not significantly affect the dimensions of the piezoelectric transducer. The type of bonding interface layer 700 is not limited to a single type and may be, for example, a silica layer, and the bonding interface layer 700 may also be considered as part of the top acoustic reflecting layer 300 or the bottom acoustic reflecting layer 200.

[0054] In one embodiment, referring to FIG. 5, step S400 includes step S450.

[0055] In step S450, a piezoelectric wafer is provided, ion implantation is performed on the piezoelectric wafer, and a top acoustic reflection layer is fabricated on the ion-implanted piezoelectric wafer.

[0056] 14, before fabricating the top acoustic reflection layer 300, ion implantation is first performed on the piezoelectric wafer 400. In this way, in the subsequent process of thinning the piezoelectric wafer 400, ion implantation and film peeling transfer techniques can be used to thin the piezoelectric wafer 400, with better selectivity. The ion implantation process on the piezoelectric wafer 400 is performed before the deposition and patterning of the top acoustic reflection layer 300. After the ion implantation, the bonding wafer undergoes a series of heating, slicing, and polishing steps, leaving a thin layer of piezoelectric material on the support wafer 100 to form a piezoelectric film.

[0057] Extendibly, the piezoelectric transducer further includes a top electrode layer 600, which is fabricated on the side of the piezoelectric wafer 400 away from the top acoustic reflection layer 300 after thinning the piezoelectric wafer 400, and a conductive wire is connected to the top electrode layer 600 as a lead wire of the top electrode, which realizes the function of the piezoelectric transducer together with other devices.

[0058] To better understand the above embodiments, the following detailed description will be given with reference to specific examples: In one embodiment, the bottom acoustically reflective layer 200 includes a low acoustic impedance layer and a high acoustic impedance layer, the top acoustically reflective layer 300 includes a low acoustic impedance layer or both a low acoustic impedance layer and a high acoustic impedance layer, and the bottom electrode layer 500 is a metal layer.

[0059] The method for manufacturing a piezoelectric transducer includes processes performed on the support wafer 100, processes performed on the piezoelectric wafer 400, and all specific process steps performed on the bonding wafer. Specifically, the flow performed on the support wafer 100 includes the following steps and overall order. Referring to FIG. 7, alternating layers of low acoustic impedance and high acoustic impedance layers are deposited on the support wafer 100 and finally patterned. These layers can be deposited by different physical vapor deposition methods, or they can be grown using oxidation or epitaxial methods. The layers forming the high and low acoustic impedances can have different thicknesses and can be patterned into specific shapes by photoetching according to the required characteristics of the piezoelectric transducer. The number of layers in the formed stack can be any number, with a minimum of two. The stack must end with one layer (which can be a high or low acoustic impedance layer), which provides a surface that is easy to adhere to itself (i.e., another layer of the same material). The support wafer 100 may be a wafer made of silicon, glass, sapphire, silicon carbide, quartz, or other materials. The low acoustic impedance layer may be formed of any material selected from the oxide family, including silica, sapphire, tellurium oxide, and other materials. The high acoustic impedance layer may be formed of any material selected from aluminum nitride, tungsten, platinum, molybdenum, ruthenium, and oxides of these materials.

[0060] Referring to FIG. 8, the process performed on the piezoelectric wafer 400 includes depositing or growing a thin low acoustic impedance layer on the piezoelectric wafer 400, which is the bonding interface with the acoustic mirror fabricated on the carrier substrate. In another embodiment, referring to FIG. 9, a metal layer is deposited and patterned on the piezoelectric wafer 400, and then a thin low acoustic impedance layer is deposited. In another embodiment, referring to FIG. 10, one or more acoustically reflective layers may be deposited or grown on the piezoelectric wafer 400. For example, one, two, or three pairs of alternating high and low acoustic impedance layers may be deposited or grown on the piezoelectric wafer 400. The last layer on the piezoelectric wafer 400 is made of the same material as the top layer in the layer stack of the support wafer 100, thereby providing a good bonding interface. It should be noted that the material of the piezoelectric wafer 400 may be: Lithium tantalate, lithium niobate , aluminum nitride and any of the same versions of quartz may be doped.

[0061] The process for bonding the piezoelectric wafer 400 and the support wafer 100 to obtain a piezoelectric film includes the following steps. If one or more layers of the support wafer 100 are patterned, or if one or more layers of the piezoelectric wafer 400 are patterned, or if one or more layers of the piezoelectric wafer 400 and the support wafer 100 are patterned, referring to FIG. 11 , a planarization step must be performed on each patterned wafer before bonding to ensure a flat and smooth interface for wafer bonding. Bonding between the support wafer 100 and the piezoelectric wafer 400 can occur at a) a high acoustic impedance layer or a low acoustic impedance layer, which is an interface between an acoustic reflector layer ( FIG. 12(a) ), or b) the bottom or top of an acoustic reflector layer. In such cases, the bonding interface between the support wafer 100 and the piezoelectric wafer 400 has different acoustic impedance layers on both sides. In this embodiment, after forming the acoustic reflector layer, a thin layer of material can be deposited on the two wafers, thereby providing a suitable bonding interface layer 700 ( FIG. 12(b) ). Such an ultra-thin material layer used for bonding purposes can be present in a portion of the acoustic reflector layer. Referring to FIG. 12, the piezoelectric wafer 400 and the support wafer 100 are bonded together by establishing a bonding interface. The bonding process can be hot press bonding, surface activation direct bonding, or any other method for adhering semiconductor wafers. Referring to FIG. 13, the piezoelectric wafer 400 is then thinned and polished to the required thickness.

[0062] If the method for obtaining the piezoelectric film is not mechanical polishing but ion implantation and film peeling transfer technology, the process performed on the piezoelectric wafer 400 needs to be slightly modified and the following steps added. Referring to FIG. 14(a), the process of ion implantation on the piezoelectric wafer 400 needs to be performed before metal electrode and lamination deposition and patterning, and the arrow shown in FIG. 14(a) indicates the ion implantation. Referring to FIG. 14(b), after the ion implantation, the process follows the above-mentioned explanation: the bonding wafer goes through a series of heating, slicing and polishing steps, leaving a thin layer of piezoelectric material on the support wafer 100 (FIG. 14(c)). The material of the piezoelectric wafer 400 is Lithium tantalate, lithium niobate , aluminum nitride and doped versions of any of the same versions of quartz.

[0063] Figures 6(a) and 6(b) show two different structures of piezoelectric transducers fabricated with the present invention. In Figure 6(a), a lithium niobate piezoelectric transducer is fabricated on top of a patterned reflector formed of silica and tungsten layers, and one piezoelectric film transducer is fabricated on top of the patterned acoustic reflector layers. In Figure 6(b), a lithium niobate piezoelectric transducer is fabricated on top of an unpatterned silica and aluminum nitride reflector, and one piezoelectric film transducer is fabricated on the patterned acoustic reflector layer, with a thin metal layer directly contacting the bottom surface of the piezoelectric layer.

[0064] The drawings are further described as follows: FIG. 6 shows a top view and a cross-sectional view of a piezoelectric transducer on a patterned acoustic reflector layer group. In the cases of FIGS. 6(b) and 6(d), the bottom of one piezoelectric layer is directly in contact with an electrode and incorporated into the device structure by bonding the two wafers. In the example shown, two pairs of low-impedance and high-impedance layers (only the high-impedance layer is patterned) are used in the support wafer 100, and cross-section BB' is used in all subsequent figures to illustrate the manufacturing flow of the piezoelectric transducer. The dotted lines in the drawings indicate the bonding interface in this example (in this example, the piezoelectric wafer 400 does not have a group of low- and high-acoustic impedance layers deposited on it before bonding). FIG. 7 is a schematic diagram of alternating low- and high-acoustic impedance layers being deposited and patterned on the support wafer 100. FIG. 8 is a schematic diagram of a low-acoustic impedance layer being deposited on the bottom of the piezoelectric wafer 400. FIG. 9 is a schematic diagram of a piezoelectric wafer 400 having a thin metal (bottom electrode layer 500) deposited and patterned thereon, followed by a low acoustic impedance layer. FIG. 10 is a schematic diagram of a piezoelectric wafer 400 having alternating low and high acoustic impedance layers deposited and patterned thereon. FIG. 11 is a schematic diagram of planarizing the top layer of the support wafer 100 and the top layer of the piezoelectric wafer 400 to achieve wafer-to-wafer bonding. FIG. 12 is a schematic diagram of the bonding process, where FIG. 12(a) is a schematic diagram of bonding two wafers at an interface between an acoustic reflector layer, and FIG. 12(b) is a schematic diagram of bonding two wafers at the bottom or top of an acoustic reflector layer. In FIG. 12(a), the dotted line indicates the bonding interface, and FIG. 12(b) includes an ultra-thin material layer used for bonding purposes, i.e., a bonding interface layer 700. 13 is a schematic diagram of thinning and polishing the piezoelectric wafer 400. FIG. 14 is a schematic diagram of ion implantation and peeling of the piezoelectric wafer 400.

[0065] The manufacturing method of the above piezoelectric transducer is as follows: first, a support wafer 100 is provided, and a bottom acoustic reflection layer 200 is fabricated on the support wafer 100; then, a piezoelectric wafer 400 is provided, and a top acoustic reflection layer 300 is fabricated on the piezoelectric wafer 400, where the top acoustic reflection layer 300 and the bottom acoustic reflection layer 200 are both used to limit acoustic vibration; then, the side of the bottom acoustic reflection layer 200 away from the support wafer 100 is bonded to the side of the top acoustic reflection layer 300 away from the piezoelectric wafer 400; and finally, the piezoelectric wafer 400 is thinned to form a piezoelectric transducer. In a piezoelectric transducer manufactured by this piezoelectric transducer manufacturing method, a piezoelectric wafer 400, a top acoustic reflection layer 300, a bottom acoustic reflection layer 200, and a support wafer 100 are stacked together, with the support wafer 100 providing support and the piezoelectric wafer 400 being thinned to form a piezoelectric film that can be excited to produce acoustic vibrations, while the top acoustic reflection layer 300 and the bottom acoustic reflection layer 200 can limit the acoustic vibrations, allowing the resulting piezoelectric transducer to operate at high frequencies. Because the piezoelectric transducer manufactured by this method has a specific stacking combination and piezoelectric film, it can excite and support high-performance acoustic vibration modes, has relatively low intrinsic loss, and can achieve a higher capacitance per unit area while maintaining a unit area, resulting in excellent operating performance.

[0066] In one embodiment, there is provided a piezoelectric transducer manufactured by the above method.

[0067] The above piezoelectric transducer Manufacturing methodfirst, a support wafer 100 is provided, and a bottom acoustic reflection layer 200 is fabricated on the support wafer 100; then, a piezoelectric wafer 400 is provided, and a top acoustic reflection layer 300 is fabricated on the piezoelectric wafer 400, where the top acoustic reflection layer 300 and the bottom acoustic reflection layer 200 are both used to limit acoustic vibration; then, the side of the bottom acoustic reflection layer 200 away from the support wafer 100 is bonded to the side of the top acoustic reflection layer 300 away from the piezoelectric wafer 400; and finally, the piezoelectric wafer 400 is thinned to form a piezoelectric transducer. In a piezoelectric transducer manufactured by this piezoelectric transducer manufacturing method, a piezoelectric wafer 400, a top acoustic reflection layer 300, a bottom acoustic reflection layer 200, and a support wafer 100 are stacked together, with the support wafer 100 providing support and the piezoelectric wafer 400 being thinned to form a piezoelectric film that can be excited to produce acoustic vibrations, while the top acoustic reflection layer 300 and the bottom acoustic reflection layer 200 can limit the acoustic vibrations, allowing the resulting piezoelectric transducer to operate at high frequencies. Because the piezoelectric transducer manufactured by this method has a specific stacking combination and piezoelectric film, it can excite and support high-performance acoustic vibration modes, has relatively low intrinsic loss, and can achieve a higher capacitance per unit area while maintaining a unit area, resulting in excellent operating performance.

[0068] The technical features of the above embodiments can be combined in any way, and for the sake of brevity, not all possible combinations of the technical features of the above embodiments are described, but as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0069] The above embodiments only represent some implementation modes of the present invention, and the descriptions are relatively specific and detailed, but this should not be understood as a limitation on the scope of the patent claims of the invention. It should be noted that those skilled in the art may make some modifications and improvements without departing from the concept of the present invention, and all of these fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention should be determined based on the appended claims.

Claims

1. providing a support wafer and fabricating a bottom acoustically reflective layer on the support wafer, the bottom acoustically reflective layer including a bottom high acoustic impedance layer and a bottom low acoustic impedance layer; providing a piezoelectric wafer and fabricating a top acoustically reflective layer on the piezoelectric wafer, wherein the top acoustically reflective layer and the bottom acoustically reflective layer are both used to limit acoustic vibrations; bonding a side of the bottom acoustically reflective layer away from the support wafer to a side of the top acoustically reflective layer away from the piezoelectric wafer; thinning the piezoelectric wafer to form a piezoelectric transducer; the top acoustic reflection layer includes a top low acoustic impedance layer and a top high acoustic impedance layer, the sum of the number of the top high acoustic impedance layers and the number of the top low acoustic impedance layers is odd, and the layer of the top acoustic reflection layer farthest from the piezoelectric wafer and the layer of the bottom acoustic reflection layer farthest from the support wafer are made of the same material.

2. The step of providing a piezoelectric wafer and fabricating a top acoustically reflective layer on the piezoelectric wafer may include providing a piezoelectric wafer and fabricating a bottom electrode layer on the piezoelectric wafer; 10. The method of claim 1, further comprising fabricating a top acoustically reflective layer on the piezoelectric wafer overlying the bottom electrode layer.

3. the sum of the number of the bottom high acoustic impedance layers and the number of the bottom low acoustic impedance layers is an odd number; 2. The method for manufacturing a piezoelectric transducer according to claim 1, wherein the step of providing a support wafer and manufacturing a bottom acoustic reflection layer on the support wafer includes providing a support wafer and manufacturing the bottom high acoustic impedance layer and the bottom low acoustic impedance layer alternately on one side of the support wafer.

4. 4. The method of claim 3, wherein the step of providing a piezoelectric wafer and fabricating a top acoustically reflective layer on the piezoelectric wafer comprises providing a piezoelectric wafer and fabricating the top low acoustic impedance layer on the piezoelectric wafer.

5. 4. The method of claim 3, wherein the step of providing a piezoelectric wafer and fabricating a top acoustically reflective layer on the piezoelectric wafer comprises providing a piezoelectric wafer and fabricating alternating top low acoustic impedance layers and top high acoustic impedance layers on the piezoelectric wafer.

6. 6. The method for manufacturing a piezoelectric transducer according to claim 5, wherein the layer of the bottom acoustic reflection layer farthest from the support wafer is the bottom low acoustic impedance layer and the layer of the top acoustic reflection layer farthest from the piezoelectric wafer is the top low acoustic impedance layer, or the layer of the bottom acoustic reflection layer farthest from the support wafer is the bottom high acoustic impedance layer and the layer of the top acoustic reflection layer farthest from the piezoelectric wafer is the top high acoustic impedance layer.

7. After providing the piezoelectric wafer and fabricating a top acoustically reflective layer on the piezoelectric wafer, and before bonding the side of the bottom acoustically reflective layer away from the support wafer to the side of the top acoustically reflective layer away from the piezoelectric wafer, further comprising:

2. The method of claim 1, further comprising: performing a planarization process on a side of the bottom acoustic reflection layer facing away from the support wafer and a side of the top acoustic reflection layer facing away from the piezoelectric wafer.

8. bonding a side of the bottom acoustically reflective layer away from the support wafer to a side of the top acoustically reflective layer away from the piezoelectric wafer, 2. The method of claim 1, further comprising providing a bonding interface layer and bonding a side of the bottom acoustically reflective layer away from the support wafer to a side of the top acoustically reflective layer away from the piezoelectric wafer by the bonding interface layer.

9. 2. The method for manufacturing a piezoelectric transducer according to claim 1, wherein the step of providing a piezoelectric wafer and fabricating a top acoustic reflection layer on the piezoelectric wafer comprises providing a piezoelectric wafer, implanting ions into the piezoelectric wafer, and fabricating a top acoustic reflection layer on the implanted piezoelectric wafer.

10. A piezoelectric transducer manufactured by the method according to any one of claims 1 to 9.

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