PIEZOELECTRIC TRANSDUCER PREPARATION METHOD AND PIEZOELECTRIC TRANSDUCER

The present application relates to a piezoelectric transducer preparation method and a piezoelectric transducer. The method comprises: first, preparing a bottom acoustic reflection layer on a carrier wafer; then preparing a top acoustic reflection layer on a piezoelectric wafer; then combining the side of the bottom acoustic reflection layer that is away from the carrier wafer with the side of the top acoustic reflection layer that is away from the piezoelectric wafer; and finally, thinning the piezoelectric wafer to form a piezoelectric transducer. The carrier wafer performs a carrying function, a piezoelectric film formed by thinning the piezoelectric wafer can be excited by acoustic vibration, and the top acoustic reflection layer and the bottom acoustic reflection layer can limit the acoustic vibration, such that the resulting piezoelectric transducer can work at a high frequency. The piezoelectric transducer prepared by using the method has a specific stacking combination and a piezoelectric film, can excite and support a high-performance acoustic vibration mode, has a low inherent loss, and can obtain a higher capacitance per unit area while maintaining the unit area, such that a good working performance of the prepared piezoelectric transducer is achieved.

TECHNICAL FIELD

The present disclosure relates to transducers, in particular to a method for preparing a piezoelectric transducer and a piezoelectric transducer.

BACKGROUND

Transducers are devices that realize conversion between electrical energy and sound energy. As a specific type of transducers, piezoelectric transducers use the piezoelectric effect of certain crystalline materials to achieve the conversion between electrical energy and mechanical energy. Piezoelectric transducers are widely used due to their high electroacoustic efficiency, large power capacity, and their ability to be tailored in structure and shape to suit different applications.

Conventional piezoelectric transducers are based on bonding piezoelectric wafers to other carrier wafers, and most monocrystalline thin films on a silicon substrate are based on bonding piezoelectric wafers to carrier wafers (mostly silicon) directly or through a bonding interface layer. Such bonded carrier wafers can be used as piezoelectric transducers. However, the piezoelectric transducers prepared in this way have low maximum operating frequency, low capacitance density, low power threshold, and may have insuppressible spurious modes, resulting in poor performance of the piezoelectric transducers.

SUMMARY

Accordingly, there is a need to provide a method for preparing a piezoelectric transducer and a piezoelectric transducer.

A method for preparing a piezoelectric transducer includes following steps of:providing a carrier wafer and preparing a bottom acoustic reflection layer on the carrier wafer;providing a piezoelectric wafer and preparing a top acoustic reflection layer on the piezoelectric wafer, wherein both the top acoustic reflection layer and the bottom acoustic reflection layer are configured to confine acoustic vibrations;combining a side of the bottom acoustic reflection layer away from the carrier wafer and a side of the top acoustic reflection layer away from the piezoelectric wafer; andthinning the piezoelectric wafer, thereby achieving the piezoelectric transducer.

A piezoelectric transducer is prepared by the aforementioned method.

In an embodiment, the step of providing the piezoelectric wafer and preparing the top acoustic reflection layer on the piezoelectric wafer includes substeps of:providing the piezoelectric wafer, and preparing a bottom electrode layer on the piezoelectric wafer; andpreparing the top acoustic reflection layer covering the bottom electrode layer on the piezoelectric wafer.

In an embodiment, the bottom acoustic reflection layer includes one or more bottom high acoustic impedance layers and one or more bottom low acoustic impedance layers. The total number of the one or more bottom high acoustic impedance layers and the one or more bottom low acoustic impedance layers is an odd number. The step of providing the carrier wafer and preparing the bottom acoustic reflection layer on the carrier wafer includes substeps of:providing the carrier wafer, andalternately preparing the one or more bottom high acoustic impedance layers and the one or more bottom low acoustic impedance layers on one side of the carrier wafer.

In an embodiment, the top acoustic reflection layer includes a top low acoustic impedance layer, and the step of providing the piezoelectric wafer and preparing the top acoustic reflection layer on the piezoelectric wafer includes substeps of:providing the piezoelectric wafer, andpreparing the top low acoustic impedance layer on the piezoelectric wafer.

In an embodiment, the top acoustic reflection layer includes one or more top low acoustic impedance layers and one or more top high acoustic impedance layers. The total number of the one or more top high acoustic impedance layers and the one or more top low acoustic impedance layers is an odd number. The step of providing the piezoelectric wafer and preparing the top acoustic reflection layer on the piezoelectric wafer includes substeps of:providing a piezoelectric wafer, andalternately preparing the one or more top low acoustic impedance layers and the one or more top high acoustic impedance layers on the piezoelectric wafer.

In an embodiment, in the bottom acoustic reflection layer, the farthest from the carrier wafer is a bottom low acoustic impedance layer, and in the top acoustic reflection layer, the farthest from the piezoelectric wafer is a top low acoustic impedance layer.

In an embodiment, in the bottom acoustic reflection layer, the farthest from the carrier wafer is a bottom high acoustic impedance layer, and in the top acoustic reflection layer, the farthest from the piezoelectric wafer is a top high acoustic impedance layer.

In an embodiment, after the step of providing the piezoelectric wafer and preparing the top acoustic reflection layer on the piezoelectric wafer, and prior to the step of combining the side of the bottom acoustic reflection layer away from the carrier wafer and the side of the top acoustic reflection layer away from the piezoelectric wafer, the method further includes a step of:planarizing the side of the bottom acoustic reflection layer away from the carrier wafer and the side of the top acoustic reflection layer away from the piezoelectric wafer.

In an embodiment, the step of combining the side of the bottom acoustic reflection layer away from the carrier wafer with the side of the top acoustic reflection layer away from the piezoelectric wafer includes substeps of:providing a bonding interface layer, andcombining the side of the bottom acoustic reflection layer away from the carrier wafer and the side of the top acoustic reflection layer away from the piezoelectric wafer through the bonding interface layer.

In an embodiment, the step of providing the piezoelectric wafer and preparing the top acoustic reflection layer on the piezoelectric wafer includes substeps of:providing the piezoelectric wafer, implanting ions into the piezoelectric wafer, andpreparing the top acoustic reflection layer on the ion implanted piezoelectric wafer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to illustrate the purpose, technical solutions and advantages of the present disclosure clearer, the present disclosure will be described more fully through the following embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining the present disclosure, and not intended to limit the present disclosure.

In an embodiment, referring toFIG.1, a method for preparing a piezoelectric transducer is provided, which includes the following steps S200to S800.

Step S200: a carrier wafer is provided, and a bottom acoustic reflection layer is prepared on the carrier wafer.

Referring toFIGS.6and7, the carrier wafer100is a carrier device of the piezoelectric transducer. The carrier wafer100serves as a carrier of other structures in the piezoelectric transducer, and plays a role of carrying and fixing. The structure of the carrier wafer100is not exclusive. In the present embodiment, the carrier wafer100may be a wafer made of silicon, glass, sapphire, silicon carbide, quartz, or other materials. After the carrier wafer100is provided, the bottom acoustic reflection layer200is prepared on the carrier wafer100, and the method for preparing the bottom acoustic reflection layer200is not exclusive. For example, a physical vapor deposition method, which has a high depositing speed, may be used to deposit the bottom acoustic reflection layer200. Alternatively, an oxidation method or an epitaxial method may be used to form the bottom acoustic reflection layer200on the carrier wafer100, so that the formed bottom acoustic reflection layer200has a high density and is relatively stable.

Further, after the bottom acoustic reflection layer200is prepared on the carrier wafer100, the bottom acoustic reflection layer200may be patterned to form a specific shape as required by the piezoelectric transducer behavior. The method for patterning the bottom acoustic reflection layer200is not exclusive. In the present embodiment, the bottom acoustic reflection layer200may be patterned by photolithography, and the shape of the bottom acoustic reflection layer200may be designed as required to meet more requirements. The structure of the bottom acoustic reflection layer200is not exclusive, and may be a one-layer or multi-layer structure, as long as acoustic vibrations can be confined.

Step S400: a piezoelectric wafer is provided, and a top acoustic reflection layer is prepared on the piezoelectric wafer.

The structure of the piezoelectric wafer400is not exclusive, and can be any of the following doped versions: lithium niobate, lithium tantalate, aluminum nitride, quartz, etc. Referring toFIGS.6and8to10, after the piezoelectric wafer400is provided, the top acoustic reflection layer300on the piezoelectric wafer400may be prepared by depositing or growing the top acoustic reflection layer300on the piezoelectric wafer400. Further, after the top acoustic reflection layer300is prepared on the piezoelectric wafer400, the top acoustic reflection layer300may also be patterned, so that the top acoustic reflection layer300forms a specific shape. The method for patterning the top acoustic reflection layer300is not exclusive. In the present embodiment, the top acoustic reflection layer300may be patterned by photolithography, and the shape of the top acoustic reflection layer300may be designed as required to meet more requirements. The structure of the top acoustic reflection layer300is not exclusive, it may be a one-layer or multi-layer structure, as long as acoustic vibrations can be confined. In addition, prior to preparing the top acoustic reflection layer300, the piezoelectric wafer400may be subjected to ion implantation. In this way, the piezoelectric wafer400can be thinned by using film slicing and transfer technology in a subsequent thinning process. The process of ion implantation to the piezoelectric wafer400can be performed prior to the deposition and patterning of the top acoustic reflection layer300. After the ion implantation, the piezoelectric wafer may be subjected to a series of heating, slicing, and polishing steps to leave a thin layer of piezoelectric material on the carrier wafer100to form a piezoelectric film.

Step S600: a side of the bottom acoustic reflection layer away from the carrier wafer and a side of the top acoustic reflection layer away from the piezoelectric wafer are combined.

Referring toFIG.6orFIG.12, after the bottom acoustic reflection layer200and the top acoustic reflection layer300are prepared, the side of the bottom acoustic reflection layer200away from the carrier wafer100and the side of the top acoustic reflection layer300away from the piezoelectric wafer400are combined. In this way, the bottom acoustic reflection layer200and the top acoustic reflection layer300are combined. The specific combining method is not exclusive. For example, the bottom acoustic reflection layer200and the top acoustic reflection layer300may be bonded together through van der Waals force, molecular force, or even atomic force, which ensures the working performance of the piezoelectric transducer.

Step S800: the piezoelectric wafer is thinned to achieve the piezoelectric transducer.

The piezoelectric wafer400is thinned after the side of the bottom acoustic reflection layer200away from the carrier wafer100and the side of the top acoustic reflection layer300away from the piezoelectric wafer400are combined. Referring toFIG.13, the thickness of the piezoelectric wafer400reaches a desired value, so as to form the piezoelectric film. The piezoelectric transducer includes the carrier wafer100, the bottom acoustic reflection layer200, the top acoustic reflection layer300, and the thinned piezoelectric wafer400. The piezoelectric wafer400, the top acoustic reflection layer300, the bottom acoustic reflection layer200, and the carrier wafer100are stacked one on another. The carrier wafer100serves as a carrier. The piezoelectric wafer400is thinned to form the piezoelectric film, which can be excited to generate acoustic vibrations. The top acoustic reflection layer300and the bottom acoustic reflection layer200can confine the acoustic vibrations, so that the obtained piezoelectric transducer can work at high frequencies. Since the piezoelectric transducer prepared by the method has a specific layer group including the piezoelectric film, it can excite and support high-performance acoustic vibration modes, has relatively low inherent loss, and can obtain relatively high capacitance per unit area while maintaining unit area, so that the manufactured piezoelectric transducer has good performance.

In an embodiment, referring toFIG.2, step S400includes step S420and step S440.

Step S420: the piezoelectric wafer is provided, and a bottom electrode layer is prepared on the piezoelectric wafer400.

Specifically, the bottom electrode layer500is configured to transmit electrical signals. Typically, the bottom electrode layer500has a layered structure. Referring toFIG.9, the bottom electrode layer500is deposited on the piezoelectric wafer400to form a bottom electrode of the piezoelectric transducer. Further, after the bottom electrode layer500is deposited on the piezoelectric wafer400, the bottom electrode layer500can also be patterned to adjust the shape, the area, and the thickness of the bottom metal, etc., so as to meet specific requirements. The shape of the bottom electrode layer500is not exclusive and may be any geometry from square, rectangle, trapezoid or any polygon with n sides. The structure of the bottom electrode layer500is not exclusive and may be a metal layer made of Al, Pt, Cu, or an alloy of these metals, etc., which can be adjusted according to actual needs, as long as it can be achieved by those skilled in the art. The preparation of the bottom electrode layer500on the piezoelectric wafer400can change the direction of the electric field introduced by the electrode into the piezoelectric material, thus forming a new vibration mode, and improving the performance of the piezoelectric transducer. In addition, prior to preparing the bottom electrode layer500, the piezoelectric wafer400may be subject to ion implantation. In this way, the piezoelectric wafer400can be thinned by using film slicing and transfer technology in a subsequent thinning process.

Step S440: the top acoustic reflection layer is prepared on the piezoelectric wafer and covers the bottom electrode layer.

After the bottom electrode layer500is prepared, referring toFIG.9, the top acoustic reflection layer300is prepared on the piezoelectric wafer400and covers the bottom electrode layer500. It should be understood that the bottom electrode layer500does not completely cover the piezoelectric wafer400. A part of the top acoustic reflection layer300covers the surface of the bottom electrode layer500away from the piezoelectric wafer400, and the other part of the top acoustic reflection layer300directly covers the piezoelectric wafer400, so that the top acoustic reflection layer300is in contact with both the piezoelectric wafer400and the bottom electrode layer500. Typically, the top acoustic reflection layer300is a layered structure and is disposed on the other side of the bottom electrode layer500to confine the acoustic vibrations. The type of the top acoustic reflection layer300is not exclusive, and the material of the top acoustic reflection layer300can be selected according to specific requirements. After the top acoustic reflection layer300is prepared on the side of the piezoelectric wafer400adjacent to the bottom electrode layer500, the top acoustic reflection layer300may also be patterned, so that the shape and size of the top acoustic reflection layer300meet more requirements.

In an embodiment, the bottom acoustic reflection layer200includes a bottom high acoustic impedance layer220and a bottom low acoustic impedance layer210. The sum of the number of bottom high acoustic impedance layers220and the number of the bottom low acoustic impedance layers210is an odd number. Referring toFIG.2, step S200includes step S220.

In the present embodiment, referring toFIG.7, the bottom acoustic reflection layer200includes a bottom high acoustic impedance layer220and a bottom low acoustic impedance layer210. The bottom high acoustic impedance layer220may be a layered structure made of aluminum nitride, tungsten, platinum, molybdenum, ruthenium or oxides thereof. The bottom low acoustic impedance layer210may be a layered structure made of silicon dioxide, spin glass, tellurium oxide, or other oxide families including other materials. One bottom high acoustic impedance layer220and one bottom low acoustic impedance layer210form a stack. In an example, the number of stack may be one, which has good manufacturability. Alternatively, one bottom acoustic reflection layer200may include two or more stacks, so as to improve the performance of the piezoelectric transducer. Further, the sum of the number of the bottom high acoustic impedance layers220and the number of the bottom low acoustic impedance layers210is an odd number, which means that besides the stack(s), the bottom acoustic reflection layer200further includes one end layer, which may be a bottom high acoustic impedance layer220or a bottom low acoustic impedance layer210. The end layer is the layer farthest from the carrier wafer100in the bottom acoustic reflection layer200. This layer provides a surface that is adapted to bond to another layer made of the same material, which is convenient for subsequent combination with the other layer.

Step S220: the carrier wafer is provided, and the bottom high acoustic impedance layer(s) and the bottom low acoustic impedance layer(s) are alternately prepared on one side of the carrier wafer.

When the bottom acoustic reflection layer200includes the bottom high acoustic impedance layer(s)220and the bottom low acoustic impedance layer(s)210, after the carrier wafer100is provided, the bottom high acoustic impedance layer(s)220and the bottom low acoustic impedance layer(s)210are deposited layer by layer, alternately on one side of the wafer100, so as to better confine the acoustic vibrations. In other embodiments, after preparing the alternating bottom high acoustic impedance layer(s)220and bottom low acoustic impedance layer(s)210, this alternating layered structure can be transferred to the carrier wafer100, as long as it can be achieved by those skilled in the art. The thicknesses of the bottom high acoustic impedance layer220and the bottom low acoustic impedance layer210are not exclusive. The bottom high acoustic impedance layer220and the bottom low acoustic impedance layer210may have different thicknesses, and the different thicknesses will result in more optimized performance of the manufactured piezoelectric transducers. The bottom high acoustic impedance layer220and the bottom low acoustic impedance layer210may have the same thickness, which is convenient for performing subsequent processes, and the thicknesses can be adjusted according to actual needs.

Further, after the bottom high acoustic impedance layer(s)220and bottom low acoustic impedance layer(s)210are alternately prepared on the side of the carrier wafer100, either or both of the bottom high acoustic impedance layer(s)220and the bottom low acoustic impedance layer(s)210may be patterned, so that the bottom high acoustic impedance layer(s)220and/or the bottom low acoustic impedance layer(s)210form specific shape, so as to better meet requirements. The shape of the bottom high acoustic impedance layer(s)220and/or the bottom low acoustic impedance layer(s)210is not exclusive and can be adjusted according to actual needs.

In an embodiment, referring toFIG.3, the top acoustic reflection layer300includes a top low acoustic impedance layer310. Step S400includes step S410.

Step S410: the piezoelectric wafer is provided, and the top low acoustic impedance layer is prepared on the piezoelectric wafer.

The structure of the top acoustic reflection layer300is not exclusive. In the present embodiment, referring toFIG.6, the top acoustic reflection layer300includes the top low acoustic impedance layer310, which may be a layered structure made of silicon dioxide, spin glass, tellurium oxide, or other oxide families including other materials. When the top acoustic reflection layer300includes the top low acoustic impedance layer310, one top low acoustic impedance layer310is provided. The top low acoustic impedance layer310is prepared on the piezoelectric wafer400, which can be configured to confine acoustic vibrations. Further, in the embodiment that the bottom electrode layer500is prepared on one side of the piezoelectric wafer400, the bottom electrode layer500does not completely cover the piezoelectric wafer400. A part of the top low acoustic impedance layer310covers the surface of the bottom electrode layer500away from the piezoelectric wafer400, and the other part of the top low acoustic impedance layer310directly covers the piezoelectric wafer400, so that the top low acoustic impedance layer310is in contact with both the piezoelectric wafer400and the bottom electrode layer500. The top low acoustic impedance layer310can cover the bottom electrode layer500. Further, after the top low acoustic impedance layer310is prepared on the piezoelectric wafer400, the top low acoustic impedance layer310may also be patterned, so that the top low acoustic impedance layer310has a specific shape to meet specific requirements.

In an embodiment, the top acoustic reflection layer300includes not only the top low acoustic impedance layer310but also a top high acoustic impedance layer320. The sum of the number of the top high acoustic impedance layer(s)320and the number of the top low acoustic impedance layer(s)310is an odd number. Referring toFIG.4, step S400includes step S430.

Step S430: the piezoelectric wafer is provided, and the top low acoustic impedance layer(s) and the top high acoustic impedance layer(s) are alternately prepared on the piezoelectric wafer.

In the present embodiment, referring toFIGS.11to14, in addition to the top low acoustic impedance layer310, the top acoustic reflection layer300further includes a top high acoustic impedance layer320. The top high acoustic impedance layer320may be a layered structure made of aluminum nitride, tungsten, platinum, molybdenum, ruthenium, or oxides thereof. One top high acoustic impedance layer320and one top low acoustic impedance layer310form a stack. In an example, the number of the stack can be one, which has good manufacturability. Alternatively, one top acoustic reflection layer300may include two or more stacks to improve the performance of the piezoelectric transducer. Further, the sum of the number of the top high acoustic impedance layers320and the number of the top low acoustic impedance layers310is an odd number, which means that besides the stack(s), the top acoustic reflection layer300further includes one end layer. This layer may be a top high acoustic impedance layer320or a top low acoustic impedance layer310. The end layer is the layer furthest from the carrier wafer100in the top acoustic reflection layer300.

Further, referring toFIG.12a, the combination between the bottom acoustic reflection layer200and the top acoustic reflection layer300may occur at a certain interface between certain acoustic reflection layers, such that a relatively high strength can be achieved. In the subsequent process, the combined layers are not easy to peel off from each other. The position of the combination can be between the high impedance layers or between the low impedance acoustic layers, as long as it can be achievable by those skilled in the art. In addition, when the bottom electrode layer500has been prepared on the side of the piezoelectric wafer400, it is typically a top low acoustic impedance layer310that directly covers the bottom electrode layer500. A top high acoustic impedance layer320is prepared subsequently on the side of the top low acoustic impedance layer310away from the bottom electrode layer500, so that the top low acoustic impedance layer(s)310and the top high acoustic impedance layer(s)320can be arranged alternately.

The top low acoustic impedance layer(s)310and the top high acoustic impedance layer(s)320may be deposited layer by layer on the piezoelectric wafer to form the alternately arranged top low acoustic impedance layer(s)310and top high acoustic impedance layer(s)320. In other embodiments, after preparing the alternating top low acoustic impedance layer(s)310and top high acoustic impedance layer(s)320, the alternating layered structure may be transferred to the piezoelectric wafer400, as long as it can be achieved by those skilled in the art.

In an embodiment, in the bottom acoustic reflection layer200, the farthest from the carrier wafer100is a bottom low acoustic impedance layer210, and in the top acoustic reflection layer300, the farthest from the piezoelectric wafer400is a top low acoustic impedance layer310. Alternatively, in the bottom acoustic reflection layer200, the farthest from the carrier wafer100is a bottom high acoustic impedance layer220, and in the top acoustic reflection layer300, the farthest from the piezoelectric wafer400is a top high acoustic impedance layer320.

In the present embodiment, in the bottom acoustic reflection layer200, the farthest from the carrier wafer100is a bottom low acoustic impedance layer210, and in the top acoustic reflection layer300, the farthest from the piezoelectric wafer400is a top low acoustic impedance layer310. That is, the layer on the carrier wafer100and the layer on the piezoelectric wafer400that are to be combined together are both low acoustic impedance layers. Alternatively, in the bottom acoustic reflection layer200, the farthest from the carrier wafer100is a bottom high acoustic impedance layer220, and in the top acoustic reflection layer300, the farthest from the piezoelectric wafer400is a top high acoustic impedance layer320. That is, the layer on the carrier wafer100and the layer on the piezoelectric wafer400that are to be combined together are both high acoustic impedance layers. The outermost layer on the piezoelectric wafer400is made of the same material as the outermost layer on the carrier wafer100, which can provide a good bonding interface and make the combination between the bottom acoustic reflection layer200and the top acoustic reflection layer300more stable.

In an embodiment, referring toFIG.4, after step S400and prior to step S600, the method for preparing the piezoelectric transducer further includes step S500.

Step S500: the side of the bottom acoustic reflection layer away from the carrier wafer and the side of the top acoustic reflection layer away from the piezoelectric wafer are planarized.

The planarization may include steps such as thinning and polishing. Referring toFIG.11, prior to combining the bottom acoustic reflection layer200and the top acoustic reflection layer300, the side of the bottom acoustic reflection layer200away from the carrier wafer100and the side of the top acoustic reflection layer300away from the piezoelectric wafer400are planarized, so as to provide a flat and smooth combination interface, so that the bottom acoustic reflection layer200and the top acoustic reflection layer300can combined more firmly. Further, if any of the carrier wafer100, one or more layers of the bottom acoustic reflection layer200, the piezoelectric wafer400, and one or more layers of the top acoustic reflection layer300are patterned, each patterned structure are planarized prior to the combination step, so as to ensure the effectiveness of the interface combination.

In an embodiment, referring toFIG.5, step S600includes step S620.

Step S620: a bonding interface layer is provided, and the side of the bottom acoustic reflection layer away from the carrier wafer and the side of the top acoustic reflection layer away from the piezoelectric wafer are combined through the bonding interface layer.

Specifically, referring toFIG.12b, the bonding interface layer700is provided in the combination of the bottom acoustic reflection layer200and the top acoustic reflection layer300. The side of the bottom acoustic reflection layer200away from the carrier wafer100and the side of top acoustic reflection layer300away from the piezoelectric wafer400are combined through the bonding interface layer700. In an embodiment, the combination is by bonding of the bottom acoustic reflection layer200and the top acoustic reflection layer300together. The bonding can be such as thermo-compression bonding, surface activated direct bonding, etc. Other methods for bonding semiconductor wafers also can be used. The bonding can occur at a bottom portion or an upper portion, etc., of a certain acoustic reflection layer. When the layer in the bottom acoustic reflection layer200for combination and the layer in the top acoustic reflection layer300for combination are different in type, for example, one is a high acoustic reflection layer and the other is a low acoustic impedance layer, the two layers of different types can be combined through the bonding interface layer700, so as to ensure a stable bonding. Generally, the bonding interface layer700is relatively thin, which will not have a great impact on the size of the piezoelectric transducer. The type of the bonding interface layer700is not exclusive, for example, it may be a silicon dioxide layer, etc. The bonding interface layer700may also be regarded as a part of the top acoustic reflection layer300or the bottom acoustic reflection layer200.

In an embodiment, referring toFIG.5, step S400includes step S450.

Step S450: the piezoelectric wafer is provided, ions are implanted into the piezoelectric wafer, and the top acoustic reflection layer is prepared on the ion implanted piezoelectric wafer.

Referring toFIG.14, prior to preparing the top acoustic reflection layer300, the piezoelectric wafer400is subject to ion implantation. In this way, the piezoelectric wafer400can be thinned by using film slicing and transfer technology in the subsequent thinning process. The ion implantation to the piezoelectric wafer400is prior to the deposition and patterning of the top acoustic reflection layer300. After the ion implantation, the bonding wafer may be subjected to a series of heating, slicing, and polishing steps to leave a thin layer of piezoelectric material on the carrier wafer100to form a piezoelectric film.

Optionally, the piezoelectric transducer further includes a top electrode layer600. After the piezoelectric wafer400is thinned, the top electrode layer600is prepared on a side of the piezoelectric wafer400away from the top acoustic reflection layer300. The top electrode layer600can be connected to a top electrode lead wire, connecting to other devices to achieve the function of the piezoelectric transducer.

In order to better understand the above embodiments, a detailed example will be given below. In the example, the bottom acoustic reflection layer200includes the low acoustic impedance layers and the high acoustic impedance layers, the top acoustic reflection layer300includes the low acoustic impedance layer or both the low acoustic impedance layers and the high acoustic impedance layers, and the bottom electrode layer500is a metal layer.

The method for preparing the piezoelectric transducer includes the process performed on the carrier wafer100, the process performed on the piezoelectric wafer400, and the process for bonding the wafers. Specifically, the process performed on the carrier wafer100includes the following steps. Referring toFIG.7, the alternating low acoustic impedance layers and high acoustic impedance layers are deposited on the carrier wafer100and eventually patterned. These layers can be deposited by different physical vapor deposition methods, or they can be grown by oxidation or epitaxial methods. The high and low acoustic impedance layers can have different thicknesses and can be lithographically patterned into specific shapes as required by the piezoelectric transducer behavior. The layers forming the stack may be any number, starting from a minimum of 2. The stack needs to end in a layer (a high acoustic impedance layer or a low acoustic impedance layer), which provides a surface that is adapted to be bonded to another layer made of the same material. The carrier wafer100may be a wafer made of silicon, glass, sapphire, silicon carbide, quartz, or other materials. The low acoustic impedance layer may be made of silicon dioxide, spin glass, tellurium oxide, or other oxide families including other materials. The high acoustic impedance layer may be made of aluminum nitride, tungsten, platinum, molybdenum, ruthenium, or oxides thereof.

The process performed on the piezoelectric wafer400is as follows. Referring toFIG.8, a thin low acoustic impedance layer is deposited or grown on the piezoelectric wafer400, which is a bonding interface to an acoustic mirror formed on the carrier wafer. In another embodiment, referring toFIG.9, a metal layer is deposited and eventually patterned on the piezoelectric wafer400, and then a thin low acoustic impedance layer is deposited thereon. In other embodiments, referring toFIG.10, one or more acoustic reflection layers may also be deposited or grown on the piezoelectric wafer400. For example, one, two, or three pairs of alternating high acoustic impedance layers and low acoustic impedance layers may be deposited or grown on the piezoelectric wafer400. The outermost layer on piezoelectric wafer400is made of the same material as the outermost layer on the carrier wafer100, so as to provide a good bonding interface. The material of the piezoelectric wafer400may be any of the following doped versions: lithium niobate, lithium tantalate, aluminum nitride, and quartz.

The process performed to bond the piezoelectric wafer400and the carrier wafer100to obtain the piezoelectric film includes the following steps. In case of patterning of one or more layers on the carrier wafer100and/or on the piezoelectric wafer400, referring toFIG.11, prior to bonding, a planarization step is performed to each patterned wafer, so as to ensure a flat and smooth interface for wafer bonding. The bonding between the carrier wafer300and the piezoelectric wafer400may occur between: a. an interface in a certain acoustic reflection layer, either a high acoustic impedance layer or a low acoustic impedance layer (FIG.12a); b. a bottom portion or an upper portion of an acoustic reflection layer. In this case, two sides of the carrier wafer100and the piezoelectric wafer400in contact with the bonding interface will have different acoustic impedance layers. In this embodiment, after the acoustic reflection layers have been formed, a thin material layer may be deposited on the two wafers to provide an appropriate bonding interface layer700(FIG.12b). This ultra-thin layer of material for bonding may also be deposited in a portion of an acoustic reflection layer. Referring toFIG.12, the piezoelectric wafer400and the carrier wafer100are bonded together through the established bonding interface. The bonding process can be any method based on thermo-compression bonding, surface activated direct bonding, or other methods to bond semiconductor wafers. Referring toFIG.13, the piezoelectric wafer400is then thinned and polished to a desired thickness.

If the piezoelectric film is obtained by ion instead of mechanical polishing, the process performed to the piezoelectric wafer400needs to be slightly modified and the following steps are added. Referring toFIG.14a, the process of ion implantation to the piezoelectric wafer400is required to be performed prior to the deposition and patterning of the metal electrode and the layer stack. The arrows inFIG.14aindicate ion implantation. Referring toFIG.14b, after ion implantation, the process follows as previously described, the bonded wafer is subjected to a series of heating, slicing, and polishing steps to form a thin layer of piezoelectric material remaining on top of the carrier wafer100(FIG.14c). The material of the piezoelectric wafer400may be any of the following doped versions: lithium niobate, lithium tantalate, aluminum nitride, and quartz.

FIG.6aandFIG.6bshow two structures of piezoelectric transducers prepared by the method of the present disclosure. InFIG.6aa piezoelectric transducer is built on top of the patterned acoustic reflection layer stack. InFIG.6b, a piezoelectric transducer is formed on top of the patterned acoustic reflection layers, having a thin metal layer in contact with the bottom surface of the piezoelectric layer.

A supplementary description for the drawings is as follows.FIG.6shows top views and cross-sectional views of the piezoelectric transducers including the patterned acoustic reflection layer stack, and in the case of b) and d), also incorporating a bottom electrode in direct contact with the piezoelectric layer by means of bonding two wafers. The examples shown use two pairs of low impedance layers and high impedance layers (in which only the high impedance layers are patterned) in the carrier wafer100. The cross-section BB′ is used in all following figures to show the preparation process for the piezoelectric transducers. The dotted line in the figure represents the bonding interface in the examples (in these examples, the piezoelectric wafer400is not deposited with the low acoustic impedance layer and the high acoustic impedance layer prior to bonding).FIG.7is a schematic view of deposition and patterning of alternating low and high acoustic impedance layers on the carrier wafer100.FIG.8is a schematic view of deposition of a low acoustic impedance layer on the bottom of the piezoelectric wafer400.FIG.9is a schematic view of deposition and patterning a thin metal (the bottom electrode layer500) on the piezoelectric wafer400, and deposition of a low acoustic impedance layer on the piezoelectric wafer400.FIG.10is a schematic view of deposition and patterning of alternating low acoustic impedance layers and high acoustic impedance layers on the piezoelectric wafer400.FIG.11is a schematic view of planarization of the outermost layer on the carrier wafer100and the outermost layer on the piezoelectric wafer400, so as to achieve bonding between the wafers.FIG.12is a schematic view of a bonding process, where (a) is for bonding the two wafers at an interface in an acoustic reflection layer, and (b) is for bonding at a bottom portion or an upper portion of an acoustic reflection layer. The dotted line in (a) indicates the bonding interface, and (b) includes an ultra-thin material layer for bonding, that is, the bonding interface layer700.FIG.13is a schematic view of thinning and polishing the piezoelectric wafer400.FIG.14is a schematic view of ion implantation and slicing of the piezoelectric wafer400.

According to the aforementioned method for preparing the piezoelectric transducer, firstly, the carrier wafer100is provided, and the bottom acoustic reflection layer200is prepared on the carrier wafer100, then the piezoelectric wafer400is provided, and the top acoustic reflection layer300is prepared on the piezoelectric wafer400. The top acoustic reflection layer300and the bottom acoustic reflection layer200are configured to confine acoustic vibrations. Then, the side of the bottom acoustic reflection layer200away from the carrier wafer100and the side of the top acoustic reflection layer300away from the piezoelectric wafer400are combined, and finally the piezoelectric wafer400is thinned to achieve the piezoelectric transducer. In the piezoelectric transducer prepared by the piezoelectric transducer preparation method, the piezoelectric wafer400, the top acoustic reflection layer300, the bottom acoustic reflection layer200, and the carrier wafer100are stacked one on another. The carrier wafer100serves as a carrier. The piezoelectric wafer400is thinned to form a piezoelectric film, which can be excited to vibrate acoustically. The top acoustic reflection layer300and the bottom acoustic reflection layer200can confine acoustic vibrations, so that the obtained piezoelectric transducer can operate at high frequencies. Since the piezoelectric transducer prepared by the method has a specific layer group including the piezoelectric film, it can excite and support high-performance acoustic vibration modes, has relatively low inherent loss, and can obtain relatively high capacitance per unit area while maintaining unit area, so that the manufactured piezoelectric transducer has good performance.

In an embodiment, the piezoelectric transducer is provided, which is prepared by the above-mentioned method.

According to the piezoelectric transducer, firstly, the carrier wafer100is provided, and the bottom acoustic reflection layer200is prepared on the carrier wafer100, then the piezoelectric wafer400is provided, and the top acoustic reflection layer300is prepared on the piezoelectric wafer400. The top acoustic reflection layer300and the bottom acoustic reflection layer200are configured to confine acoustic vibrations. Then, the side of the bottom acoustic reflection layer200away from the carrier wafer100and the side of the top acoustic reflection layer300away from the piezoelectric wafer400are combined, and finally the piezoelectric wafer400is thinned to achieve the piezoelectric transducer. In the piezoelectric transducer prepared by the piezoelectric transducer preparation method, the piezoelectric wafer400, the top acoustic reflection layer300, the bottom acoustic reflection layer200, and the carrier wafer100are stacked one on another. The carrier wafer100serves as a carrier. The piezoelectric wafer400is thinned to form a piezoelectric film, which can be excited to vibrate acoustically. The top acoustic reflection layer300and the bottom acoustic reflection layer200can confine acoustic vibrations, so that the obtained piezoelectric transducer can operate at high frequencies. Since the piezoelectric transducer prepared by the method has a specific layer group including the piezoelectric film, it can excite and support high-performance acoustic vibration modes, has relatively low inherent loss, and can obtain relatively capacitance per unit area while maintaining unit area, so that the manufactured piezoelectric transducer has good performance.

The above-mentioned embodiments do not constitute a limitation on the protection scope of the technical solution. Any modifications, equivalent replacements and improvements made within the spirit and principles of the above-mentioned embodiments shall be included within the protection scope of this technical solution.