Elastic wave device and method for manufacturing same

Abstract

The present invention relates to an elastic wave device and a method for manufacturing the same, and the elastic wave device according to one embodiment of the present invention comprises: a piezoelectric substrate having a first surface and a second surface; a support substrate having a third surface adjacent to or in contact with the first surface of the piezoelectric substrate to form a cavity defined as a space; the first bonding layer is arranged between the supporting substrate and the piezoelectric substrate and forms a bonding interface, so that the first surface of the supporting substrate is bonded with the third surface of the piezoelectric substrate; a second adhesive layer which is formed on at least one of the third surface of the support substrate and the first surface of the piezoelectric substrate on which the bonding interface is not formed, and which is exposed in the cavity; and the interdigital transducer electrode is formed on the second surface of the piezoelectric substrate, and the thickness of the first bonding layer is larger than that of the second bonding layer.

Description

Technical Field

[0001] This invention relates to filter technology, and more specifically, to bulk elastic wave devices and methods for manufacturing the same. Background Technology

[0002] A radio frequency (RF) filter is a device that allows certain frequencies to pass through while blocking others. It is used in wireless communication systems, such as cellular base stations, mobile phones, and computing devices. "Passing through" means transmitting signals with relatively low loss, while "blocking" means attenuating the signal during transmission. The frequency range that an RF filter passes through is called its "passband," and the frequency range that it blocks is called its "stopband." Typically, an RF filter has at least one passband and at least one stopband. Specific requirements for the passband or stopband can vary depending on the application. For example, a "passband" can be defined as the frequency range where the filter's insertion loss is less than a specified value such as 1dB, 2dB, or 3dB. A "stopband" can be defined, depending on the application, as the filter's insertion loss is greater than a specified value such as 20dB, 30dB, or 40dB or more.

[0003] Research and development are underway for 6G mobile communication, the next generation of mobile communication. 6G utilizes ultra-high frequency bands and THz frequencies to support faster data transmission speeds at the Tbps level, minimizing latency (e.g., 0.1ms) to provide real-time interaction between connected devices. Currently, high-performance radio frequency filters used in communication systems typically employ surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, and film bulk acoustic wave resonators (FBARs). However, these existing technologies are not suitable for next-generation mobile communication using ultra-high frequency bands and THz frequencies.

[0004] Therefore, it is necessary to study elastic wave devices suitable for high-frequency bands and high frequencies that can meet the required characteristics of the device through a simple structure without performance degradation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an elastic wave device suitable for high frequency bands and high frequencies that meets the required characteristics of the device through a simple manufacturing process without performance degradation.

[0006] Furthermore, the technical problem to be solved by the present invention is to provide a method for manufacturing the elastomer device.

[0007] The problems to be solved by the present invention are not limited to those mentioned above. Those skilled in the art to which this invention pertains may understand other problems not mentioned from the following description.

[0008] According to a first embodiment of the present invention, the present invention may include: a piezoelectric substrate having a first surface and a second surface; a support substrate having a third surface, the third surface being adjacent to or in contact with the first surface of the piezoelectric substrate to form a cavity defined as a space; a first adhesive layer disposed between the support substrate and the piezoelectric substrate to form a bonding interface, thereby bonding the first surface of the support substrate with the third surface of the piezoelectric substrate; a second adhesive layer formed on at least one of the third surface of the support substrate and the first surface of the piezoelectric substrate where the bonding interface is not formed, exposed within the cavity; and an interdigital transducer (IDT) electrode formed on the second surface of the piezoelectric substrate, wherein the thickness of the first adhesive layer is greater than the thickness of the second adhesive layer.

[0009] According to one embodiment, the first and second adhesive layers may include inorganic materials. The inorganic material may be a metal selected from the element group Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, Pt, Au, W, or an alloy or oxide thereof including one or more elements selected from these element groups. Preferably, the inorganic material may include one of silicon oxide (SiO2), titanium oxide (TiO2), and aluminum oxide (Al2O3). The second adhesive layer does not possess chemical bonds formed by atomic diffusion or atomic rearrangement, but can form a structure with the same shape as the cavity.

[0010] According to one embodiment, the first adhesive layer may include: a first sub-adhesive layer deposited on one side of the piezoelectric substrate, comprising a first metal atomic layer or a first ceramic atomic layer; a second sub-adhesive layer deposited on one side of the supporting substrate, comprising a second metal atomic layer or a second ceramic atomic layer; and a bonding interface layer having chemical bonds formed by atomic diffusion or atomic rearrangement between the first sub-adhesive layer and the second sub-adhesive layer. The chemical bonds may include at least one of ionic bonds, metallic bonds, covalent bonds, and coordination bonds.

[0011] According to one embodiment, all or part of the third surface of the support substrate may further include a trap-rich layer, the trap-rich layer being disposed between the support substrate and the piezoelectric substrate, the trap-rich layer being formed of at least one of polycrystalline silicon, amorphous silicon or porous silicon.

[0012] According to one embodiment, the piezoelectric substrate may have a thickness ranging from 10 nm to 500 nm, and the second adhesive layer may have a thickness ranging from 0.3 nm to 10 nm. Alternatively, the second adhesive layer may have a thickness ranging from 0.1 μm to 10 nm. The first adhesive layer may be 1.2 to less than 2.0 times the thickness of the second adhesive layer.

[0013] According to one embodiment, the piezoelectric substrate may be composed of one of lithium niobate (LiNbO3), lithium tantalate, lanthanum gallium silicate, gallium nitride, aluminum nitride, zinc oxide, or lead zirconate titanate (PZT). The interdigital transducer electrodes may be alloys primarily composed of Al (aluminum), Cu (copper), Pt (platinum), Au (gold), Ag (silver), Ti (titanium), Ni (nickel), Cr (chromium), Mo (molybdenum), W (tungsten), or one of these metals. The support substrate may be composed of one of silicon (Si), quartz, glass, silicon carbide (SiC), sapphire, or aluminum nitride (AlN).

[0014] According to a second embodiment of the present invention, the present invention provides a method for manufacturing an elastic wave device, the method comprising the following steps: preparing a first support substrate having a first surface on which a piezoelectric layer is formed; preparing a second support substrate having a second surface on which an open cavity is formed; forming atomic layers on the exposed surface of the piezoelectric layer formed on the first surface of the first support substrate and on the second surface of the second support substrate respectively; forming an adhesive layer by tightly adhering or folding the exposed surface of the piezoelectric layer to the second surface of the second support substrate to form a space by closing the open cavity of the second support substrate; removing the first support substrate to expose the other surface opposite to the exposed surface of the piezoelectric layer; and forming interdigitated transducer electrodes on the exposed other surface of the piezoelectric layer.

[0015] According to one embodiment, the step of forming atomic layers on the exposed surface of the piezoelectric layer formed on the first side of the first support substrate and on the second side of the second support substrate may include the following steps: depositing an inorganic material on at least one of the exposed surface of the piezoelectric layer and the second side of the second support substrate.

[0016] According to one embodiment, the step of forming a space by sealing the open cavity of the piezoelectric layer by forming an adhesive layer by tightly adhering or folding the exposed surface of the piezoelectric layer to the second surface of the second support substrate may include the step of forming a bonding interface layer by atomic diffusion between the first atomic layer and the second atomic layer. The steps of forming the atomic layers and forming the adhesive layer by tightly adhering or folding the exposed surface of the piezoelectric layer to the second surface of the second support substrate can be performed under vacuum conditions.

[0017] According to one embodiment, the step of preparing the second support substrate may further include the following step: forming a trap-rich layer on all or part of the second surface of the second support substrate. The step of preparing the first support substrate may include the following step: forming a dielectric layer between the first support substrate and the piezoelectric layer. The space formed by closing the open cavity of the second support substrate can be in a vacuum state.

[0018] In an embodiment of the elastic wave device of the present invention, a sealed cavity is formed between the support substrate and the piezoelectric substrate, thereby preventing one side of the piezoelectric substrate from being exposed through the cavity, thereby preventing impurities from flowing into one side of the piezoelectric substrate. An adhesive layer is provided on one side of the piezoelectric substrate adjacent to the cavity, thereby being protected by an adhesive.

[0019] Furthermore, in another embodiment of the present invention, an elastic wave device can be additionally formed between the support substrate and the piezoelectric substrate to form a trap-rich layer or trap-rich region, thereby improving the insertion loss and distortion (linearity) of the radio frequency signal.

[0020] Furthermore, in another embodiment of the manufacturing method of the elastic wave device of the present invention, there is no need for the complex and precise etching process of forming etching holes and removing the sacrificial layer corresponding to the cavity through the etching holes. The elastic wave device can be manufactured simply and at low cost by bonding a support substrate having a cavity and a piezoelectric substrate. Moreover, the bonding process using bonding materials is performed under vacuum conditions, thereby maintaining the vacuum state of the cavity and improving the performance degradation of the piezoelectric layer caused by impurities or foreign matter.

[0021] Furthermore, by performing the bonding process using bonding materials under vacuum conditions, the cavity can maintain a vacuum state, thereby improving the performance degradation of the piezoelectric layer caused by impurities or foreign matter.

[0022] However, the effects of the present invention are not limited to those described, and can be extended in various ways without exceeding the technical concept and field of the present invention. Attached Figure Description

[0023] Figure 1aThis is a partially exploded perspective view of the elastic wave device according to the first embodiment of the present invention.

[0024] Figure 1b This is a cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0025] Figure 2a and Figure 2b This is a cross-sectional view of the elastic wave device according to the second embodiment of the present invention.

[0026] Figures 3a to 3e This is a diagram illustrating a method for manufacturing an elastic wave device according to a first embodiment of the present invention.

[0027] Figures 4a to 4e This is a diagram illustrating a method for manufacturing an elastic wave device according to a second embodiment of the present invention.

[0028] Figure 5a and Figure 5b This is a diagram illustrating the effect of the manufacturing method of the elastic wave device according to an embodiment of the present invention.

[0029] Explanation of reference numerals in the attached figures

[0030] 100, 100', 100'': Elastic wave devices

[0031] 110: Support substrate

[0032] 120: Piezoelectric substrate, piezoelectric layer

[0033] 130, 131, 132: Adhesive layer

[0034] 140: Interdigital transducer electrode

[0035] 141: Finger electrode

[0036] 142: Busbar

[0037] 150, 151, 152: Reflectors

[0038] 160: Rich Trap Layer Detailed Implementation

[0039] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0040] The embodiments of the present invention described below are provided to more clearly illustrate the present invention to those skilled in the art. The present invention is not limited to the following embodiments, and the following embodiments can be modified into various forms.

[0041] The terminology used in this specification is for describing specific embodiments and is not intended to limit the invention. Unless otherwise expressly indicated in the context, the singular form of the term as used in this specification may include multiple forms. Furthermore, the terms "comprise" and / or "comprising" as used in this specification are used to specify the presence of the mentioned shapes, steps, numbers, actions, components, elements, and / or combinations thereof, and do not presuppose the presence or addition of more than one other shape, step, number, action, component, element, and / or combination thereof. Moreover, the term "connected" as used in this specification means that some components are directly connected, and also includes indirect connections between multiple components that form other components.

[0042] Furthermore, in this specification, when referring to a component being "on" other components, this includes situations where a component is in contact with other components and situations where other components exist between two components. The term "and / or" as used in this specification includes one or more of the listed items in combination. Moreover, the terms of degree such as "about," "substantially," etc., used in this specification are to take into account inherent manufacturing and material tolerances, and refer to a range of numerical values ​​or degrees or meanings close to those, and are used to prevent unauthorized use by infringers of disclosures that mention precise or absolute numerical values ​​provided to aid in understanding the invention.

[0043] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions or thicknesses of the areas or portions shown in the drawings may be enlarged to improve clarity and ease of explanation. Throughout the detailed description, the same reference numerals denote the same structural elements.

[0044] Recently, a high-frequency, high-bandwidth laterally excited bulk wave resonator (XBAR) has been developed. This XBAR comprises a thin floating layer of piezoelectric material or an interdigital transducer (IDT) formed on a diaphragm. A microwave signal applied to the IDT excites a shear-based fundamental acoustic wave within the piezoelectric diaphragm, causing the acoustic wave energy to flow orthogonally to the direction of the generated electric field or laterally, i.e., substantially perpendicular to the surface of the layer. Furthermore, this XBAR can provide higher electromechanical coupling and high-frequency capability than existing resonators.

[0045] The resonant frequency of this transverse exciter acoustic resonator can be determined by the thickness of the piezoelectric diaphragm suspended in the cavity. One side of the piezoelectric diaphragm can be exposed or sealed by the cavity. Specifically, when one side of the piezoelectric diaphragm is exposed through the cavity, after forming a piezoelectric layer on one side of the support substrate, an open cavity is formed on the other side of the support substrate by an etching process. Alternatively, an open cavity can be formed on one side of the support substrate first by an etching process, and then a piezoelectric layer is formed on the support substrate having the open cavity. When one side of the piezoelectric diaphragm is sealed by the cavity, after forming a piezoelectric layer on one side of the support substrate where a sacrificial layer has been deposited, an etch hole is formed. The sacrificial layer of the support substrate is removed through the etch hole, thereby forming a sealed cavity between the support substrate and the piezoelectric layer.

[0046] However, in a structure where one side of the piezoelectric film is exposed through a cavity, impurities may flow in through the exposed surface of the piezoelectric film, thereby potentially reducing the performance of the filter or damaging the piezoelectric film due to the exposed surface.

[0047] Furthermore, in the structure where one side of the piezoelectric film is enclosed by a cavity, after forming the piezoelectric layer on the support substrate, and after forming etch holes on the support substrate and the piezoelectric layer, the cavity is formed by etching the sacrificial layer of the support substrate through the formed etch holes. Therefore, the process becomes complex, requiring high precision during etching, and a portion of the piezoelectric layer may also be etched along with the sacrificial layer. In this case, the resonant frequency of the resonator is determined by the thickness of the piezoelectric film, making it difficult to meet the required characteristics of the resonator.

[0048] Therefore, there is a need to develop elastic wave devices suitable for high-frequency bands and high frequencies that can meet the required characteristics of the device through simple manufacturing processes without performance degradation.

[0049] Figure 1a This is a partially exploded perspective view of the elastic wave device according to the first embodiment of the present invention. Figure 1b This is a cross-sectional view of the elastic wave device 100.

[0050] Reference Figure 1a and Figure 1b The elastic wave device 100 may be composed of a support substrate 110, a piezoelectric substrate 120, an adhesive layer 130, and interdigital transducer electrodes 140. The interdigital transducer electrodes 140 may include finger electrodes 141 and bus electrodes 142.

[0051] The piezoelectric substrate 120 has a first side and a second side, and preferably, it can be made of lithium niobate (LiNbO3). However, the material of the piezoelectric substrate 120 is not limited to this; for example, lithium tantalate, lanthanum gallium silicate, gallium nitride, aluminum nitride, zinc oxide, or lead zirconate titanate (PZT) can be used. The thickness of the piezoelectric substrate 120, which is bonded to one side of the support substrate 110, ranges from 10 nm to 500 nm. When the thickness of the piezoelectric substrate 120 is less than 10 nm, it is difficult to process during manufacturing and breakage may occur. When the thickness is greater than 1500 nm, it is difficult to realize a filter that operates at high frequencies and in high-frequency bands. The support substrate 110 may have a coefficient of thermal expansion smaller than that of the piezoelectric substrate 120. A support substrate 110 with a coefficient of thermal expansion smaller than that of the piezoelectric substrate 120 is attached to the piezoelectric substrate 120. This allows for suppression of changes in the frequency characteristics of the elastic wave device 100 by suppressing dimensional changes in the piezoelectric substrate 120 due to temperature variations. Furthermore, the piezoelectric substrate 120 is preferably a single-crystal layer.

[0052] The support substrate 110 serves as the substrate supporting the piezoelectric substrate 120 and has a third surface forming a cavity that is adjacent to or in contact with the first surface of the piezoelectric substrate 120. The support substrate 110 can be, but is not limited to, silicon, quartz, glass, silicon carbide (SiC), sapphire, aluminum nitride (AlN), or other materials. For example, the support substrate 110 may have a thermal oxide (TOX) layer and a crystalline silicon layer.

[0053] The adhesive layer 130 includes a first adhesive layer 131 and a second adhesive layer 132, disposed between the support substrate 110 and the piezoelectric substrate 120 and bonding them together. The first adhesive layer 131 can form a bonding interface such that the third surface of the support substrate 110 is bonded to the first surface of the piezoelectric substrate 120. The second adhesive layer 132 can be defined as a region where the bonding interface is not formed, preventing the third surface of the support substrate 110 from bonding to the first surface of the piezoelectric substrate 120 through the cavity C. This second adhesive layer 132 is present on at least one of the third surface of the support substrate 110 and the first surface of the piezoelectric substrate 120, and can be exposed in the cavity C. The thickness of the first adhesive layer 131 can be greater than the thickness of the second adhesive layer 132.

[0054] In the manufacturing method of the elastic wave device 100 described later, after forming sub-adhesive layers on the third surface of the support substrate 110 and the first surface of the piezoelectric substrate 120, the two surfaces of the support substrate 110 and the piezoelectric substrate 120 are joined. In the region where the two surfaces of the support substrate 110 and the piezoelectric substrate 120 are in contact, a bonding interface is formed by the sub-adhesive layers of the support substrate 110 and the piezoelectric substrate 120. In the region where the two surfaces of the support substrate 110 and the piezoelectric substrate 120 are not in contact, the adhesive layer remains separately within the support substrate 110 or the piezoelectric substrate 120. Therefore, the thickness of the first adhesive layer 131 forming the bonding interface can be at least equal to or greater than the thickness of the second adhesive layer 132.

[0055] In one embodiment, the first adhesive layer 131 and the second adhesive layer 132 comprise inorganic materials. These inorganic materials may include oxide- and silicate-based ceramic or metallic materials. Specifically, the inorganic material may be a metal selected from the element group Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, Pt, Au, and W, or an alloy or oxide thereof comprising one or more elements selected from these element groups. Preferably, the inorganic material may include one of silicon oxide (SiO2), titanium oxide (TiO2), and aluminum oxide (Al2O3).

[0056] The second adhesive layer 132 may have a thickness ranging from 0.3 nm to 10 nm and may have the same shape as the cavity C. Specifically, the second adhesive layer 132 may cover the shape of the cavity C. Stable bonding strength can be achieved within the thickness range of 0.3 nm to 10 nm, which is also advantageous in terms of manufacturing cost. Furthermore, the thickness of the first adhesive layer 131 is in the range of 1.2 to 2.0 times the thickness of the second adhesive layer 132.

[0057] In one embodiment, the first adhesive layer may include: a first sub-adhesive layer deposited on one side of the piezoelectric substrate 120, comprising a first metal atomic layer or a first ceramic atomic layer; a second sub-adhesive layer deposited on one side of the support substrate 110, comprising a second metal atomic layer or a second ceramic atomic layer; and a bonding interface layer formed by atomic diffusion or atomic rearrangement between multiple metal atomic layers, multiple ceramic atomic layers, or metal atomic layers and ceramic atomic layers between the first and second sub-adhesive layers. The bonding interface layer has chemical bonds, through which a strong atomic diffusion bonding is achieved between the piezoelectric substrate 120 and the support substrate 110. The chemical bonds may include at least one of ionic bonds, metallic bonds, covalent bonds, and coordinate bonds.

[0058] The atomic diffusion bonding method achieves bonding of two substrates with deposited atomic layers under the same vacuum or pressure conditions, enabling bonding accompanied by atomic diffusion and rearrangement at the bonding interface. While solid-phase metal atoms are almost immobile at room temperature, the atomic diffusion bonding process utilizes the high surface energy of the bonding layer deposited in the vacuum chamber as the bonding driving force. The high atomic diffusion performance on the surface of the bonding layer and the atomic rearrangement phenomenon at the contact interface allow the atoms constituting the bonding layer to move at room temperature, thereby achieving bonding. In this surface, atomic diffusion or atomic rearrangement refers to the phenomenon where atomic defects (vacancies) on the surface and at the bonding interface can move at high speeds even at low energies. This phenomenon allows metal atoms to move at room temperature to achieve bonding. In this atomic diffusion bonding method, bonding can be achieved at room temperature using bonding layers of all metals. In particular, metals with higher self-diffusion coefficients, such as Ti and Au, exhibit more active atomic movement at the bonding interface and are more prone to atomic rearrangement, thus achieving higher bonding performance.

[0059] The metal atomic layer or the ceramic atomic layer can be deposited on the support substrate 110 and the piezoelectric substrate 120 respectively by one of atomic layer deposition (ALD), chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), and physical vapor deposition (PVD). Preferably, the metal atomic layer or the ceramic atomic layer can be deposited by physical vapor deposition. The thickness and type of the metal atomic layer or the ceramic atomic layer deposited on the support substrate 110 and the piezoelectric substrate 120 respectively can be the same or different. Specifically, the thickness of the piezoelectric substrate 120 is relatively smaller than the thickness of the support substrate 110. Preferably, the thickness of the atomic layer deposited on the piezoelectric substrate 120 is greater than the thickness of the atomic layer deposited on the support substrate 110, thereby improving the stability of the piezoelectric substrate 120.

[0060] In another embodiment, the first adhesive layer may be composed of a first sub-adhesive layer bonded to the piezoelectric substrate 120, a second sub-adhesive layer bonded to the support substrate 110, and an amorphous layer between the first and second sub-adhesive layers. The first and second sub-adhesive layers have Si... （1-x） O xThe composition is (0.01≤x≤0.5). The oxygen ratio of the amorphous layer may be higher than that of the first sub-adhesive layer or the second sub-adhesive layer. Oxygen diffusion occurs from the sub-adhesive layers of the support substrate 110 or piezoelectric substrate 120 to the amorphous layer, thereby increasing the oxygen ratio of the amorphous layer formed between them compared to the oxygen ratio in the sub-adhesive layers. Furthermore, with oxygen diffusion, the bonding strength between the support substrate 110 and the piezoelectric substrate 120 increases, making it less prone to peeling of the piezoelectric substrate 120. Moreover, the stacked structure of the amorphous layer between the first and second sub-adhesive layers can function as a trap-rich layer (described later) by improving the insulation of the adhesive layer to suppress the transfer of electrons from the support substrate 110 to the piezoelectric substrate 120.

[0061] Interdigitated transducer electrodes 140 can be disposed on the second surface of the piezoelectric substrate 120. A plurality of finger electrodes 141 of the interdigitated transducer electrodes 140 extend apart from each other along an orthogonal direction in the electric field direction (X-axis direction), with one end of each finger electrode 141 connected to a busbar electrode 142 to form a comb-like pattern. The finger electrodes 141 can be an alloy with Al (aluminum), Cu (copper), Pt (platinum), Au (gold), Ag (silver), Ti (titanium), Ni (nickel), Cr (chromium), Mo (molybdenum), W (tungsten), or one of these metals as the main body. The upper and lower finger electrodes 141 can be arranged intersectingly. The invention may also include an offset electrode (not shown) in a direction orthogonal to the other end of the finger electrodes 141. The finger electrodes 141 are connected to the upper busbar electrode 142, and the offset electrode (not shown) is connected to the lower busbar electrode 142, thus allowing them to be arranged facing each other. The offset electrode has a range smaller than the length of the finger electrode 141.

[0062] The intersection regions between the multiple finger electrodes and the intersection regions between the multiple offset electrodes, as well as the regions corresponding to the thickness of the bus electrode, can have different electric field velocities. Non-limitingly, reflectors 151 and 152 can be respectively disposed at both ends of the interdigital transducer electrode 140. That is, the interdigital transducer electrode 140 can be disposed between reflectors 151 and 152. Reflectors 151 and 152 can be designed to have high reflection coefficients within a defined frequency band including the resonant frequency of the elastic wave device 100, to prevent the propagation of elastic waves undergoing total internal reflection to the outside. Depending on the type of metal, the thickness of the interdigital transducer electrode 140 can be varied, and the width of the interdigital transducer electrode 140 can be determined according to the performance requirements of the desired filter.

[0063] As described above, a cavity is formed between the support substrate 110 and the piezoelectric substrate 120, thereby preventing one side of the piezoelectric substrate 120 from being exposed through the cavity and thus preventing impurities from flowing into one side of the piezoelectric substrate 120. Furthermore, an adhesive layer is provided on one side of the piezoelectric substrate 120 adjacent to the cavity, thereby serving as a protective layer. Moreover, the resonant frequency of the elastic wave device 100 can be adjusted by the size of the cavity C of the piezoelectric substrate 120, thereby easily realizing an elastic wave device 100 that operates at multiple resonant frequencies. The shape of the cavity C can be implemented in various forms, including rectangular.

[0064] To explain the operation of the elastic wave device 100 of the present invention, when a radio frequency (RF) signal is applied to the interdigital transducer electrode 140, the RF signal can generate a time-varying electric field between the finger electrodes 141. In this case, the direction of the electric field can be the X-axis direction or a direction parallel to the piezoelectric substrate 120. Due to the higher dielectric constant of the piezoelectric substrate, the electric field is more concentrated in the piezoelectric substrate compared to air. The electric field in the X-axis direction can induce shear deformation. Therefore, a strong fundamental shear acoustic wave mode can be excited within the piezoelectric substrate 120. In the present invention, "shear deformation" is defined as the deformation in which multiple parallel surfaces within a material remain parallel and maintain a specified distance during the deformation. "Shear acoustic wave mode" is defined as the acoustic wave vibration mode of the medium that causes shear deformation of the medium. Although the atomic motion caused by the shear deformation of the elastic wave device 100 is mostly in the X-axis direction, the direction of acoustic wave energy flow of the excited fundamental shear acoustic wave mode can be the thickness direction of the piezoelectric substrate 120.

[0065] Shear wave resonators can exhibit superior performance compared to state-of-the-art thin-film bulk acoustic resonators (FBARs) and solidly-mounted resonator bulk acoustic wave (SMRBAW) devices where the electric field is applied along the thickness direction. In this type of resonator, the acoustic modes are compressed along the thickness direction by atomic movement, resulting in acoustic energy flow along the thickness direction. Additionally, the piezoelectric coupling for transverse excitation of the resonance in the shear wave in the FBAR can be higher (>20%) compared to other acoustic resonators. This higher piezoelectric coupling enables the design and implementation of microwave and millimeter-wave resonators with significantly wider bandwidths.

[0066] On the other hand, even if the support substrate 110 has high resistivity, it can still contain free charge carriers, which in particular increases the insertion loss and distortion (linearity) of the radio frequency signal to the solid piezoelectric substrate 120, thereby affecting the performance of the device. To improve this problem, in a variation of the invention, such as... Figure 2a and Figure 2b As shown, a trap-rich layer or trap-rich region may be added between the support substrate 110 and the piezoelectric substrate 120.

[0067] A trap-rich layer is formed within a silicon substrate by irradiating the substrate surface with seeds, protons, or various ions (silicon, argon, nitrogen, neon, oxygen, etc.) that generate defects within the substrate's crystalline structure. Alternatively, trap-rich regions can be formed within the silicon substrate by introducing deep trap impurities such as gold, copper, or other metal ions. These impurities can be formed through ion implantation, diffusion, and several other methods. The trap-rich regions can be formed through a combination of these techniques.

[0068] Figure 2a and Figure 2b This is a cross-sectional view of the elastic wave device according to the second embodiment of the present invention.

[0069] Reference Figure 2a and Figure 2b The elastic wave devices 100' and 100'' may include a support substrate 110, a piezoelectric substrate 120, an adhesive layer 130, and interdigital transducer electrodes 140. The interdigital transducer electrodes 140 may include finger electrodes 141 and bus electrodes 142. The support substrate 110, piezoelectric substrate 120, adhesive layer 130, and interdigital transducer electrodes 140 of the elastic wave devices 100' and 100'' are... Figure 1a and Figure 1b The support substrate 110, piezoelectric substrate 120, adhesive layer 130, and interdigital transducer electrode 140 of the elastic wave device 100 described herein are similar. Therefore, as long as there is no contradiction, the descriptions of the elastic wave devices 100' and 100'' can be referred to the descriptions in [the original text]. Figure 1a and Figure 1b Explanation

[0070] Reference Figure 2a Furthermore, a rich trap layer 160 can be provided that covers the entire side of the support substrate 110. Moreover, when the rich trap layer 160 has a sufficient thickness to accommodate the cavity C, the cavity C can be accommodated within the rich trap layer 160.

[0071] Reference Figure 2b Furthermore, a trap-rich layer 160' can be provided covering a portion of one side of the support substrate 110. Figure 2bIn this case, the rich trap layer 160' is not disposed in a portion of the support substrate 110 exposed through the cavity C of the piezoelectric substrate 120, but can be disposed in the region where the support substrate 110 and the piezoelectric substrate 120 are joined on both sides. Figure 2b In the case where the trap-rich layer 160' has a relatively thin thickness that cannot accommodate the cavity C, the cavity C can be formed within the support substrate 110.

[0072] The trap-rich layers 160 and 160' electrically isolate the support substrate 110 from the piezoelectric substrate 120 to improve performance (e.g., linearity and stray suppression). The term "trap-rich" refers to a layer that can absorb charge even without forming a conductive layer. The trap-rich layers can be formed from at least one of polycrystalline, amorphous, or porous materials such as polycrystalline silicon, amorphous silicon, or porous silicon, but the invention is not limited to such materials. Furthermore, without limitation, the trap-rich layers 160 and 160' can be formed by ion implantation into the surface layer of the support substrate 110 or by etching and structuring the surface layer of the support substrate 110.

[0073] Figures 3a to 3e This is a diagram illustrating a method for manufacturing an elastic wave device according to a first embodiment of the present invention.

[0074] First, such as Figure 3a As shown, a first support substrate SS can be prepared, having a first surface S1, on which a piezoelectric layer 120 is formed. Non-limitingly, the first support substrate SS can be silicon, sapphire, AlN, quartz, SiC, or other materials. The piezoelectric layer 120 may be made of lithium niobate (LiNbO3), lithium tantalate, lanthanum gallium silicate, gallium nitride, aluminum nitride, zinc oxide, or lead zirconate titanate. Furthermore, a second support substrate 110 can be prepared, having a second surface S2 with an open cavity on the second surface. The step of preparing the second support substrate 110 with the open cavity OC may include forming the open cavity OC on the second support substrate 110 through photolithography and etching processes. The material of the second support substrate 110 may be the same as that of the first support substrate SS.

[0075] Next, as Figure 3b As shown, sub-adhesive layers AD1 and AD2 are deposited on one side S1 of the piezoelectric layer 120 formed on the first support substrate SS and the other side S2 of the second support substrate 110, respectively.

[0076] The first sub-adhesive layer AD1 is deposited on one side of the piezoelectric substrate 120 using a corresponding deposition method and is composed of a first metal atomic layer or a first ceramic atomic layer. The second sub-adhesive layer AD2 is deposited on one side of the support substrate 110 using a corresponding deposition method and can be composed of a second metal atomic layer or a second ceramic atomic layer. The corresponding deposition method may include one of atomic layer deposition (ALD), chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), and physical vapor deposition (PVD). Preferably, the metal atomic layer or the ceramic atomic layer can be deposited using physical vapor deposition.

[0077] Furthermore, preferably, the first sub-adhesive layer AD1 and the second sub-adhesive layer AD2 are deposited under high vacuum to achieve an active state (activation) that allows chemical bonds to easily form at the bonding surface. However, the invention is not limited to this; the first sub-adhesive layer AD1 and the second sub-adhesive layer AD2 can also be deposited under atmospheric pressure, provided they also possess an active state under atmospheric pressure. The active state of the first sub-adhesive layer AD1 and the second sub-adhesive layer AD2 allows for easy bonding and diffusion based on atomic rearrangement through a high self-diffusion coefficient.

[0078] The first adhesive layer 131 and the second adhesive layer 132 comprise inorganic materials, which may include ceramic or metallic materials based on oxides or silicates. Specifically, the inorganic materials may be metals selected from the group consisting of Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, Pt, Au, and W, or alloys or oxides thereof comprising one or more elements selected from these groups.

[0079] After that, as Figure 3cAs shown, the exposed surface of the piezoelectric layer 120 and the second surface S2 of the second support substrate 110 can be closely attached or overlapped to form adhesive layers 131 and 132, thereby forming a sealed space C by closing the open cavity OC of the second support substrate 110. Within the adhesive layer 131, chemical or metallic bonds are formed through atomic diffusion and double bonding between the first sub-adhesive layer AD1 and the second sub-adhesive layer AD2. For example, atoms from the first sub-adhesive layer AD1 move towards the second sub-adhesive layer AD2, or atoms from the second sub-adhesive layer AD2 move towards the first sub-adhesive layer AD1, thereby causing atomic diffusion and double bonding. Due to the chemical bonds formed through these atomic diffusions and double bondings, the piezoelectric layer 120 and the second support substrate 110 can be strongly bonded. Furthermore, in the adhesive layer 132, the first sub-adhesive layer AD1 and the second sub-adhesive layer AD2 do not contact each other through the cavity C; therefore, it is possible that chemical bonds formed through atomic diffusion and double bonding in the adhesive layer 131, etc., will not occur. Thus, the adhesive layer 132 does not include a bonding interface based on chemical bonds.

[0080] The second adhesive layer 132 may have a thickness ranging from 0.3 nm to 10 nm, within which it can maintain stable bonding strength and is also advantageous in terms of manufacturing cost. The thickness of the second adhesive layer 132 may be less than the thickness of the first adhesive layer 131.

[0081] In another embodiment, the steps of forming adhesive layers 131 and 132 may include: a first oxide layer forming step, forming a first oxide layer on the bonding surface side of the piezoelectric layer 120; a first metal layer forming step, forming a first metal layer on the bonding surface side of the piezoelectric layer 120; a second oxide layer forming step, forming a second oxide layer on the bonding surface side of the second support substrate 110; a second metal layer forming step, forming a second metal layer on the bonding surface side of the second support substrate 110; a metal bonding layer forming step, overlapping the first metal layer and the second metal layer, rearranging the crystals of the first metal layer and the second metal layer to form a metal bonding layer; and a metal oxide layer forming step, forming a metal oxide layer by oxidizing the metal bonding layer. Preferably, the first metal layer forming step, the second metal layer forming step, and the metal bonding layer forming step can be performed continuously under an inert gas atmosphere or under vacuum.

[0082] After that, as Figure 3d As shown, the first support substrate SS can be removed, exposing one side S3 of the piezoelectric layer 120 that is in contact with the adhesive layers 131 and 132, and the other side of the opposing piezoelectric layer 120. The first support substrate SS can be removed by a grinding or etching process. Afterwards, as... Figure 3e As shown, interdigitated transducer electrodes 140 and reflectors 151 and 152 can be formed on the other side S4 of the exposed piezoelectric layer 120.

[0083] Figures 4a to 4e This is a diagram illustrating a method for manufacturing an elastic wave device according to a second embodiment of the present invention.

[0084] First, such as Figure 4a As shown, a first support substrate SS2 having a first surface S1 and a piezoelectric layer 120 formed on the first surface S1 can be prepared. The first support substrate SS2 and the piezoelectric layer 120 are... Figure 3a The first supporting substrate SS is similar to the piezoelectric layer 120; therefore, it can be referenced to the... Figure 3a Description of the first support substrate SS and the piezoelectric layer 120. The steps of preparing the first support substrate SS2 on which the piezoelectric layer 120 is formed may include forming the piezoelectric layer 120 on the first support substrate SS by a film forming process or a deposition process. Optionally, a dielectric layer (not shown) (e.g., SiO2) may also be formed between the first support substrate SS2 and the piezoelectric layer 120.

[0085] The present invention can also prepare a second support substrate 110 having a second surface S2 and having a trap-rich layer 160 having an open cavity on the second surface. The steps of preparing the second support substrate 110 may include: forming the trap-rich layer 160 on the second support substrate 110 by a deposition process or a film-forming process; and forming the open cavity OC in the trap-rich layer 160 by a photolithography process and an etching process. The material of the second support substrate 110 may be the same as that of the first support substrate SS2. The trap-rich layer 160' can improve the performance of electrically isolating the support substrate 110 from the piezoelectric substrate 120 (e.g., linearity and stray suppression).

[0086] Next, as Figure 4b As shown, sub-adhesive layers AD1 and AD2 are deposited on one side of the piezoelectric layer 120 formed on the first support substrate SS2 and on one side of the trap-rich layer 160 formed on the second support substrate 110, respectively.

[0087] The first sub-adhesive layer AD1 can be deposited on one side of the piezoelectric substrate 120 using a corresponding deposition method, and is composed of a first metal atomic layer or a first ceramic atomic layer. The second sub-adhesive layer AD2 can be deposited on one side of the support substrate 110 using a corresponding deposition method, and is composed of a second metal atomic layer or a second ceramic atomic layer. Preferably, the first sub-adhesive layer AD1 and the second sub-adhesive layer AD2 are deposited under a high vacuum state so that the surfaces have an active state (activation) where multiple atoms can easily form chemical or metallic bonds at the bonding surface. The active state of the first sub-adhesive layer AD1 and the second sub-adhesive layer AD2 allows for easy bonding and diffusion based on atomic rearrangement through the self-diffusion coefficient.

[0088] The first adhesive layer 131 and the second adhesive layer 132 comprise inorganic materials, which may include oxide- or silicate-based ceramic or metallic materials. Specifically, the inorganic material may be a metal selected from the element group Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, Pt, Au, W, or an alloy or oxide thereof comprising one or more elements selected from these element groups. Preferably, the inorganic material may include silicon oxide (SiO2), titanium oxide (TiO2), aluminum oxide (Al2O3), or alloys thereof.

[0089] After that, as Figure 4c As shown, the exposed surface L1 of the piezoelectric layer 120 and the exposed surface L2 of the trap-rich layer 160 can be closely adhered to each other to form adhesive layers 131 and 132, so as to close the open cavity OC of the piezoelectric layer 120 to form a sealed space C. The first adhesive layer 131 can have a thickness ranging from 0.3 nm to 10 nm, within which it can have stable bonding strength and is also advantageous in terms of manufacturing cost. The thickness of the second adhesive layer 132 can be less than the thickness of the first adhesive layer 131.

[0090] In another embodiment, sub-adhesive layers can be formed on one side of the piezoelectric layer 120 and one side of the second support substrate 110, respectively. A neutralizing beam is irradiated onto the surface of the first sub-adhesive layer formed on one side of the piezoelectric layer 120 and the surface of the second sub-adhesive layer formed on one side of the trap-rich layer 160, thereby activating the first and second sub-adhesive layers. Then, the activated first and second sub-adhesive layers are brought into direct contact and pressure is applied, thereby obtaining adhesive layers 131 and 132. An amorphous layer can be formed between the activated first and second sub-adhesive layers. Furthermore, the amount of oxygen introduced can be changed by introducing oxygen, thereby adjusting the voltage and oxygen partial pressure of the atmosphere within the chamber, and thus regulating the oxygen ratio x of the first and second sub-adhesive layers.

[0091] After that, as Figure 4d As shown, the first support substrate SS2 and the dielectric layer SS1 can be removed, exposing the other side S4 of the piezoelectric layer 120, which faces one side S3 of the piezoelectric layer 120 that is in contact with the adhesive layers 131 and 132. The first support substrate SS2 and the dielectric layer SS1 can be removed by a polishing or etching process. Afterwards, as... Figure 4e As shown, interdigitated transducer electrodes 140 and reflectors 151 and 152 can be formed on the other side S4 of the exposed piezoelectric layer 120.

[0092] As described above, unlike the prior art where a sacrificial layer corresponding to the cavity is formed on a support substrate, and the sacrificial layer of the support substrate is removed by etching holes after the support substrate and the piezoelectric substrate are joined together, the elastic wave device manufacturing method of the present invention does not require a complex and precise process of forming etching holes and removing the sacrificial layer corresponding to the cavity through the etching holes. The support substrate and the piezoelectric substrate with the cavity can be simply joined together to manufacture the elastic wave device.

[0093] Furthermore, when the bonding process using bonding materials is performed under vacuum conditions, the cavity can maintain a vacuum state, where there are no impurities or foreign matter. Therefore, by maintaining a vacuum state in the cavity, the performance degradation of the piezoelectric layer caused by impurities or foreign matter can be mitigated.

[0094] Figure 5a and Figure 5b This is a diagram illustrating the effect of the manufacturing method of the elastic wave device according to an embodiment of the present invention.

[0095] Reference Figure 5a In the past, to form a cavity, a sacrificial layer was formed on a support substrate, and then a piezoelectric layer was formed on the surface where the sacrificial layer was formed. Therefore, the piezoelectric layer had uneven, protruding areas due to the sacrificial layer. Subsequently, after forming the etch hole RH, etching gas or etching solution was introduced into the etch hole to remove the sacrificial layer, thereby forming a cavity defined as a sealed space. As described above, the conventional method required a complex and precise etching process to remove the sacrificial layer through the etch hole RH.

[0096] Furthermore, in order to form elastic wave devices operating at multiple different resonant frequencies on the support substrate, it is necessary to form multiple different sacrificial layers corresponding to different resonant frequencies. For example, in Figure 5a The example illustrates elastic wave devices operating at different resonant frequencies, but the present invention is not limited thereto. Specifically, in Figure 5a In this process, when the height of the sacrificial layer is H1 and H2 is less than H1, the dimensions of the protruding portions of the piezoelectric layer differ. A separate polishing process is required to remove these protruding portions, but it is difficult to achieve the required piezoelectric layer thickness corresponding to the desired resonant frequency through polishing alone. Furthermore, it is difficult to maintain a vacuum state in the cavity due to the etched holes RH.

[0097] On the contrary, such as Figure 5b As shown, in this invention, a simple process of bonding the piezoelectric substrate and the support substrate with the cavity using an adhesive layer prevents the formation of protrusions on the piezoelectric layer. Therefore, a planarization process to remove the protrusions is unnecessary. Furthermore, in the manufacturing process of this invention, the formation is controllable, thus the cavity can be maintained in a vacuum state.

[0098] Preferred embodiments of the invention are disclosed in this specification. Although specific terminology is used, these are merely general terms used to readily illustrate the technical content of the invention and to aid in understanding it, and are not intended to limit the scope of the invention. Other modifications based on the technical concept of the invention, in addition to the embodiments disclosed herein, will be readily apparent to those skilled in the art. References to this specification will be readily understood by those skilled in the art. Figures 1a to 4e The elastic wave device and its manufacturing method described in the embodiments can be substituted, modified, and transformed in various ways without departing from the technical concept of the present invention. Therefore, the scope of the invention should be defined by the technical concept described in the claims, and not by the described embodiments.

Claims

1. An elastic wave device, characterized in that, include: A piezoelectric substrate having a first side and a second side; A support substrate having a third surface, the third surface being adjacent to or in contact with the first surface of the piezoelectric substrate to form a cavity defined as a space; A first adhesive layer is disposed between the support substrate and the piezoelectric substrate to form a bonding interface, so that the first surface of the support substrate is bonded to the third surface of the piezoelectric substrate. A second adhesive layer is formed on at least one of the third surface of the support substrate where the bonding interface is not formed and the first surface of the piezoelectric substrate, and is exposed within the cavity; as well as Interdigitated transducer electrodes are formed on the second surface of the piezoelectric substrate. The thickness of the first adhesive layer is greater than the thickness of the second adhesive layer.

2. The elastic wave device according to claim 1, characterized in that, The first adhesive layer and the second adhesive layer comprise inorganic materials. The inorganic materials include ceramic materials or metallic materials. The inorganic material is a metal selected from the element group Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, Pt, Au, W, or an alloy or oxide thereof including one or more elements selected from these element groups.

3. The elastic wave device according to claim 1, characterized in that, The second adhesive layer forms a structure with the same shape as the cavity.

4. The elastic wave device according to claim 1, characterized in that, The first adhesive layer includes: The first sub-adhesive layer is deposited on one side of the piezoelectric substrate and is composed of a first metal atomic layer or a first ceramic atomic layer; A second sub-adhesive layer, deposited on one side of the supporting substrate, is composed of a second metal atomic layer or a second ceramic atomic layer; and The bonding interface layer has chemical bonds formed by atomic diffusion or atomic rearrangement between the first sub-adhesive layer and the second sub-adhesive layer.

5. The elastic wave device according to claim 1, characterized in that, The third surface of the supporting substrate also includes a trap-rich layer in whole or in part. The trap-rich layer is disposed between the support substrate and the piezoelectric substrate. The trap-rich layer is formed from at least one of polycrystalline silicon, amorphous silicon, or porous silicon.

6. The elastic wave device according to claim 1, characterized in that, The piezoelectric substrate has a thickness ranging from 10 nm to 500 nm.

7. The elastic wave device according to claim 1, characterized in that, The second adhesive layer has a thickness ranging from 0.3 nm to 10 nm. The first adhesive layer has a thickness ranging from 1.2 to 2.0 times that of the second adhesive layer.

8. The elastic wave device according to claim 1, characterized in that, The piezoelectric substrate is composed of one of lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride, aluminum nitride, zinc oxide, or lead zirconate titanate.

9. The elastic wave device according to claim 1, characterized in that, The interdigital transducer electrode is an alloy with Al, Cu, Pt, Au, Ag, Ti, Ni, Cr, Mo, W, or one of these metals as the main component.

10. The elastic wave device according to claim 1, characterized in that, The supporting substrate is made of one of silicon, glass, silicon carbide, or sapphire.

11. A method for manufacturing an elastic wave device, characterized in that, Includes the following steps: Prepare a first support substrate having a first surface, on which a piezoelectric layer is formed; Prepare a second support substrate having a second surface and an open cavity on the second surface; Atomic layers are formed on the exposed surface of the piezoelectric layer formed on the first surface of the first support substrate and on the second surface of the second support substrate, respectively; An adhesive layer is formed by closely adhering to or folding the exposed surface of the piezoelectric layer with the second surface of the second support substrate, thereby forming a space by closing the open cavity of the second support substrate; Remove the first support substrate to expose the other side facing the exposed surface of the piezoelectric layer; as well as Interdigitated transducer electrodes are formed on the other side of the exposed piezoelectric layer.

12. The method for manufacturing an elastic wave device according to claim 11, characterized in that, The step of forming atomic layers on the exposed surface of the piezoelectric layer formed on the first side of the first support substrate and on the second side of the second support substrate includes the following steps: depositing an inorganic material on at least one of the exposed surface of the piezoelectric layer and the second side of the second support substrate.

13. The method for manufacturing an elastic wave device according to claim 11, characterized in that, The step of forming a space by forming an adhesive layer by adhering or folding the exposed surface of the piezoelectric layer to the second surface of the second support substrate includes the following steps: forming a bonding interface layer by atomic diffusion between the first atomic layer and the second atomic layer.

14. The method for manufacturing an elastic wave device according to claim 11, characterized in that, The steps of forming the atomic layer and forming the adhesive layer by adhering or folding the exposed surface of the piezoelectric layer to the second surface of the second support substrate are performed under vacuum conditions.

15. The method for manufacturing an elastic wave device according to claim 11, characterized in that, The step of preparing the second support substrate further includes the following step: forming a trap-rich layer on all or part of the second side of the second support substrate.

16. The method for manufacturing an elastic wave device according to claim 11, characterized in that, The steps for preparing the first support substrate include the following steps: a dielectric layer is also formed between the first support substrate and the piezoelectric layer.

17. The method for manufacturing an elastic wave device according to claim 11, characterized in that, The space formed by closing the open cavity of the second support substrate is in a vacuum state.

18. The method for manufacturing an elastic wave device according to claim 11, characterized in that, It also includes the step of oxidizing the atomic layer.

Images