A cavity-type bulk acoustic resonator with a support and its fabrication method

Abstract

This invention provides a cavity-type bulk acoustic wave resonator with pillars and its fabrication method. The method includes the following steps: taking a piezoelectric single-crystal wafer that has undergone ion implantation and has a bottom electrode, forming a plurality of pillars on the side of the piezoelectric single-crystal wafer with the bottom electrode, and forming cavities in the gaps between the pillars; then taking a substrate, bonding the substrate to the cavity-containing side of the piezoelectric single-crystal wafer; after bonding, heat-treating the substrate to peel off the thin film of the piezoelectric single-crystal wafer; and then producing a top electrode on the peeled side of the piezoelectric single-crystal wafer. The technical solution provided by this invention does not require the growth of a sacrificial layer or etching of the thin film, thus improving the mechanical strength of the device and reducing the risk of damage to the thin film. The cavity structure is formed before film deposition, resulting in a high yield, and there are no residues left from etching after film deposition, eliminating the need to consider the impact of incomplete release on the device.

Description

Technical Field

[0001] This invention belongs to the field of MEMS microfabrication of single-crystal thin-film devices. Specifically, this invention relates to a cavity-type bulk acoustic resonator with a support and its fabrication method. Background Technology

[0002] A film bulk acoustic wave resonator (FBAR) is a single-crystal thin-film device. Its main structures include solid-mount (SMR), back-etched, and cavity types. Cavity FBARs are simpler than SMRs and have higher mechanical strength than back-etched types. In recent years, with advancements in fabrication technology and the rapid development of wireless communication, FBARs have seen rapid growth due to their high Q value (greater than 1000) and compatibility with CMOS processes. FBARs convert electrical energy into sound waves through the inverse piezoelectric effect of a piezoelectric thin film, thus creating resonance. The resonant cavity is supported by the piezoelectric thin film, forming a sandwich structure with the piezoelectric film sandwiched between two metal electrodes. The resonant frequency is primarily inversely proportional to the thickness of the piezoelectric thin film, but also related to the characteristics and thickness of the other layers in the sandwich structure. Ideally, total internal reflection occurs when both sides of the resonant cavity in the sandwich structure are air.

[0003] Existing thin-film bulk acoustic wave (FBAR) resonators primarily deposit piezoelectric thin films onto a bottom electrode layer via deposition, making the film quality highly dependent on the quality of the bottom electrode. This method suffers from several problems: mismatches between the electrode material and the lattice constant of the piezoelectric single-crystal wafer, as well as uneven electrode surfaces, can lead to polycrystalline formation of the piezoelectric single-crystal film, resulting in poor film growth quality and difficulty in controlling crystal axis orientation. These issues severely impact the performance of FBAR devices.

[0004] To obtain high-quality piezoelectric thin films, existing technologies employ wafer bonding and transfer methods. This method uses single-crystal wafers or wafers with high-quality epitaxial piezoelectric layers as the piezoelectric single-crystal wafer, performs high-energy ion implantation, and then combines this with wafer bonding to transfer the high-quality piezoelectric thin film onto the target substrate. However, the microfabrication method for cavity-type thin-film bulk acoustic wave resonators requires etching openings on the surface of the thin film to corrode the silicon material beneath the piezoelectric film. While this achieves good reflection effects, it requires the prior preparation of silicon material as a sacrificial layer under the piezoelectric film. Furthermore, the etching process can easily damage the film, reducing its quality. Additionally, corrosion residues can form in the cavity, affecting device performance. Therefore, the fabrication method for cavity-type bulk acoustic wave resonators still requires improvement. Summary of the Invention

[0005] This invention provides a cavity-type bulk acoustic wave resonator with a support and its fabrication method, to solve the problems of low film quality and corrosion residue formation in the cavity when fabricating cavity-type thin-film bulk acoustic wave resonators in the prior art.

[0006] To address the above problems, this invention provides a method for fabricating a cavity-type bulk acoustic resonator with a support pillar, comprising the following steps:

[0007] (1) Take a piezoelectric single crystal wafer that has been ion implanted and has a bottom electrode, and form a plurality of pillars on the side of the piezoelectric single crystal wafer with the bottom electrode, and form a cavity in the gap between the pillars. Then take a substrate and bond the substrate to the side of the piezoelectric single crystal wafer with the cavity.

[0008] (2) Heat-treat the intermediate product obtained in step (1) to peel off the thin film of the piezoelectric single crystal wafer, and then grow a top electrode on one side of the peeled piezoelectric single crystal wafer to obtain the final product.

[0009] Preferably, in step (1), bonding the substrate to the cavity-containing side of the piezoelectric single crystal wafer specifically includes the following steps: taking the substrate, coating a bonding agent on one side of the substrate, and bonding the substrate to the cavity-containing side of the piezoelectric single crystal wafer; wherein, the bonding agent is an organic insulating material; the organic insulating material includes one or more of benzocyclobutene, polyimide, silsesqui-epoxyethylene ether, and spin-coated glass; preferably, the thickness of the coated bonding agent is 100nm-4000nm; wherein, benzocyclobutene is abbreviated as BCB; polyimide is abbreviated as PI; silsesqui-epoxyethylene ether is abbreviated as HSQ; and spin-coated glass is abbreviated as SOG;

[0010] Alternatively, a substrate is taken, a bonding compound is grown on one side of the substrate, and the substrate is bonded to the cavity side of the piezoelectric single crystal wafer; wherein the bonding compound is one or more of silicon oxide, silicon nitride, aluminum oxide, and aluminum nitride; preferably, the thickness of the grown bonding compound is 100nm-4000nm.

[0011] Preferably, the piezoelectric single crystal wafer is one of quartz, lithium niobate, lithium tantalate, aluminum nitride, zinc oxide, barium titanate, potassium dihydrogen phosphate, and lead magnesium niobate-lead titanate;

[0012] Wherein, the lithium niobate is LiNbO3, abbreviated as LN; the lithium tantalate is LiTaO3, abbreviated as LT; the aluminum nitride is AlN; the zinc oxide is ZnO; the barium titanate is BaTiO3, abbreviated as BTO; the potassium dihydrogen phosphate is KH2PO4; and the lead magnesium niobate-lead titanate is (1-x)[Pb(Mg 1 / 3 Nb2 / 3 [PbTiO3]-x[PbTiO3], abbreviated as PMN-PT;

[0013] Preferably, the piezoelectric single crystal wafer with a bottom electrode after ion implantation is obtained by the following method: taking a piezoelectric single crystal wafer, performing ion implantation on the piezoelectric single crystal wafer, and growing a bottom electrode on the ion implantation surface to obtain a piezoelectric single crystal wafer with a bottom electrode after ion implantation.

[0014] Preferably, the ions implanted into the piezoelectric single crystal wafer are one or more of H ions, He ions, B ions, and As ions; the energy of the implanted ions is 100 keV-1000 keV; and the implantation dose is 2-8 × 10⁻⁶. 16 / cm 2 The ion beam current is 0.1-10 μm / cm. -2 The injection depth is 0.3-8μm.

[0015] More preferably, the piezoelectric single crystal wafer is lithium tantalate, and the ions implanted into the piezoelectric single crystal wafer are H ions; the energy of the implanted ions is 150keV-1000keV; and the implantation depth is 1.5-8μm.

[0016] Alternatively, the piezoelectric single crystal wafer is lithium tantalate, and the ions implanted into the piezoelectric single crystal wafer are As ions; the energy of the implanted ions is 150 keV-1000 keV; and the implantation depth is 0.5-1.8 μm.

[0017] Alternatively, the piezoelectric single crystal wafer is lithium niobate, and the ions implanted into the piezoelectric single crystal wafer are He ions; the energy of the implanted ions is 150 keV-1000 keV; and the implantation depth is 0.6-2.2 μm.

[0018] Alternatively, the piezoelectric single crystal wafer is lithium niobate, and the ions implanted into the piezoelectric single crystal wafer are B ions; the energy of the implanted ions is 150 keV-1000 keV; and the implantation depth is 0.3-1 μm.

[0019] Preferably, the bottom electrode of the piezoelectric single crystal wafer is grown by the following method: first, a pattern to be grown is formed on the surface of the piezoelectric single crystal wafer by photolithography, then the electrode is grown, and finally the excess part is washed away; or, the electrode is grown on the surface of the piezoelectric single crystal wafer first, then a mask is prepared, and finally the excess part is etched away.

[0020] Preferably, the electrode material for growing the bottom electrode is one of Al, Au, Mo, Pt, and W; the thickness of the bottom electrode is 50-500 nm.

[0021] The growth methods for the bottom electrode include magnetron sputtering, resistive evaporation, and electron beam deposition;

[0022] Preferably, the substrate is made of one or more of silicon, silicon-on-insulator (SOI), glass, quartz, lithium niobate, lithium tantalate, silicon carbide, gallium nitride, and gallium arsenide; wherein, silicon-on-insulator is abbreviated as SOI; lithium niobate is abbreviated as LN; and lithium tantalate is abbreviated as LT.

[0023] In step (1), several pillars are formed on one side of the piezoelectric single crystal wafer with a bottom electrode, and cavities are formed in the gaps between the pillars. Specifically, the steps include: growing a support layer on one side of the piezoelectric single crystal wafer with a bottom electrode, forming several pillars on the grown support layer, and forming cavities in the gaps between the pillars.

[0024] Preferably, in step (1), a plurality of pillars are formed on one side of the piezoelectric single crystal wafer with a bottom electrode, and cavities are formed at the gaps between the pillars. Specifically, this includes the following steps: growing a support layer on one side of the piezoelectric single crystal wafer with a bottom electrode, and then patterning and etching one side of the grown support layer to form a plurality of pillars, and forming cavities at the gaps between the pillars; preferably, the cavity depth is greater than 100 nm.

[0025] Preferably, the support layer is one or more selected from silicon oxide, silicon nitride, amorphous silicon, and metal. The metal includes, but is not limited to, aluminum, molybdenum, platinum, gold, chromium, silver, copper, and their alloys. Preferably, the etching of the grown support layer is performed using dry etching or wet etching.

[0026] Preferably, the wet etching specifically involves etching with an etchant at a temperature of 40–90°C for 5–30 minutes; the etchant is one or more of KOH solution and TMAH solution.

[0027] Preferably, in step (1), the bonding compound is coated by spin coating to form a bonding layer; the spin coating includes a low-speed stage and a high-speed stage; the low-speed stage has a speed of 200-1000 rpm / s and a rotation time of 10s-30s; the high-speed stage has a speed of 1000-8000 rpm / s and a rotation time of 15-60s.

[0028] Preferably, the process further includes a step of pre-baking the piezoelectric single crystal wafer spin-coated with the bonding compound; the pre-baking temperature is 50–120°C, and the pre-baking time is 60–600 s.

[0029] Preferably, in step (1), the substrate is first pre-bonded to the cavity side of the piezoelectric single crystal wafer, and then the bonding is performed; preferably, the bonding pressure of the pre-bonding is 1×10⁻⁶. 5 pa~5×10 6The pressure holding time is 3-30 minutes; after pre-bonding, the temperature is slowly raised to 150-500℃ and maintained at 150-500℃ to completely cure the organic insulating material and complete the bonding.

[0030] Preferably, in step (2), the bonded intermediate product obtained in step (1) is peeled off at 180-400°C, and then annealed at 180-400°C for 10-600 min to obtain the peeled film; preferably, the thickness of the piezoelectric single crystal wafer after peeling is 500-1000 nm.

[0031] Preferably, the electrode material of the grown top electrode is one of Al, Au, Mo, Pt, and W, and the thickness of the top electrode is 50–300 nm. The growth method of the top electrode includes magnetron sputtering, resistive evaporation, and electron beam deposition.

[0032] The cavity-type bulk acoustic resonator with support provided by the present invention is prepared by the method for preparing the cavity-type bulk acoustic resonator with support described above.

[0033] Preferably, the substrate comprises, from top to bottom, a top electrode, a piezoelectric thin film, a bottom electrode, a support layer, a bonding layer, and a substrate, wherein the support layer has a plurality of pillars and cavities are formed at the gaps between the pillars; preferably, the pillars are located between the bottom electrode and the bonding layer; preferably, the bonding layer has a thickness of 2-6 μm.

[0034] The present invention provides a cavity-type bulk acoustic resonator with a support pillar, the resonator comprising, from top to bottom, a top electrode, a piezoelectric thin film, a bottom electrode, a support layer, a bonding layer, and a substrate;

[0035] The support layer has a plurality of pillars, and cavities are formed between the pillars; wherein the pillars are formed by growing the support layer on one side of the piezoelectric single crystal wafer, and forming a plurality of pillars on the support layer. Preferably, the pillars are located between the bottom electrode and the bonding layer.

[0036] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0037] 1. The method for fabricating a cavity-type bulk acoustic wave resonator with a support pillar according to the present invention involves creating a cavity on the piezoelectric single-crystal wafer before bonding, with the cavity located on one side of the injection surface. This eliminates the need to first grow a sacrificial layer and then drill holes in the piezoelectric thin film layer, lower electrode, or upper electrode to release the sacrificial layer, significantly reducing process complexity. Furthermore, the absence of etching and hole openings in the thin film improves the device's mechanical strength, reduces the risk of damage to the film, and does not affect the film's quality. The cavity structure is formed before film deposition, resulting in a high yield rate and eliminating the need to consider the impact of incomplete release on the device. This significantly improves the resonator's Q-value and reduces resonator noise. High-quality single-crystal oxide thin films can be grown on polycrystalline metal bottom electrodes, and single-crystal thin-film devices can be fabricated using a film lift-off method. The present invention can use silicon substrates of any crystal orientation or any other commonly used substrate.

[0038] In particular, the cavity is formed by the gaps between the supports, and its support structure serves to support, compensate for stress, and protect the membrane. By adding supports to the cavity region, this invention can improve the strength of the membrane, reduce warping and cracking of the membrane after low-temperature self-peeling, and greatly improve the quality of the membrane.

[0039] 2. The method for fabricating a cavity-type bulk acoustic resonator with a support as described in this invention involves growing a film on one side of the piezoelectric single crystal wafer with a bottom electrode, and etching the grown film to form a shallow cavity. Compared with etching the substrate on the reverse side, the etching depth is greatly reduced, and the etching time is shortened.

[0040] 3. The method for preparing the cavity-type bulk acoustic resonator with support pillars described in this invention uses organic insulating material as the bonding agent during bonding. On the one hand, it can play a bonding role, and the organic insulating material as the bonding agent can overcome the problem of uneven bonding surface during bonding. On the other hand, it can provide support for the thin film layer. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of the piezoelectric single crystal wafer with a bottom electrode obtained in step (a) of Example 1 after ion implantation.

[0042] Figure 2 This is a schematic diagram of the structure after the support layer is grown on the piezoelectric single crystal wafer in step (b) of Example 1.

[0043] Figure 3 This is a schematic diagram of the structure of the piezoelectric single crystal wafer with pillars and cavities formed in the gaps between the pillars in step (b) of Example 1.

[0044] Figure 4 for Figure 3The diagram shows a top view of a piezoelectric single-crystal wafer with a cavity.

[0045] Figure 5 This is a schematic diagram of the structure of the substrate after coating with the bonding compound in step (c) of Example 1.

[0046] Figure 6 This is a schematic diagram of the structure of the intermediate product after bonding in step (c) of Example 1.

[0047] Figure 7 This is a schematic diagram of the structure of the peeling film in step (d) of Example 1;

[0048] Figure 8 This is a schematic diagram of the cavity-type bulk acoustic resonator with support pillars obtained in step (d) of Example 1.

[0049] Figure 9 This is a schematic diagram of the structure of the piezoelectric single crystal wafer with a bottom electrode obtained in step (b) of Example 3 after ion implantation.

[0050] Figure 10 This is a schematic diagram of the structure of the piezoelectric single crystal wafer with pillars and cavities formed at the gaps between the pillars in step (b) of Example 3;

[0051] Figure 11 This is a schematic diagram of the cavity-type bulk acoustic resonator with a support column in step (d) of Example 3;

[0052] Figure 12 This is a schematic diagram of the cavity-type bulk acoustic resonator obtained in Comparative Example 2.

[0053] In the figure, 1-substrate; 2-cavity; 3-bonding layer; 4-piezoelectric single crystal wafer; 5-ion damage layer; 6-implantation surface; 7-bottom electrode; 8-support layer; 9-top electrode; 10-pillar. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] It should be noted that, unless otherwise specified in the embodiments of the present invention, the conditions shall be performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. The use of raw materials from different manufacturers or of different models does not affect the implementation of the technical solution or the achievement of the technical effects of the present invention.

[0056] Example 1

[0057] The method for fabricating a cavity-type bulk acoustic resonator with a support pillar in this embodiment includes the following steps:

[0058] (a) Take a piezoelectric single crystal wafer, wherein the piezoelectric single crystal wafer is a lithium tantalate wafer, and perform ion implantation on the piezoelectric single crystal wafer to form an ion damage layer. The implanted ions are H ions, the energy of the implanted ions is 195 keV, and the implantation dose is 6 × 10⁻⁶. 16 / cm 2 The ion beam current is 1 μm / cm -2 A pyroelectric material was obtained by implanting it to a depth of 6 μm. Then, a pattern to be grown was formed on the implanted surface of the pyroelectric material using photolithography. An electrode was then grown using magnetron sputtering with Au as the electrode material. Finally, excess material was removed by washing with acetone to obtain a piezoelectric single-crystal wafer with a bottom electrode, which has a thickness of 100 nm. Figure 1 The figure shows a schematic diagram of the structure of the piezoelectric single crystal wafer with a bottom electrode obtained in step (a) after ion implantation.

[0059] (b) Take the piezoelectric single crystal wafer obtained in step (a), grow a film on the side of the piezoelectric single crystal wafer with the bottom electrode, the film being a support layer, and then perform patterned etching on the side where the support layer is grown to form a plurality of pillars, and form cavities in the gaps between the pillars; the support layer is one or more of silicon oxide, silicon nitride, and metal.

[0060] Specifically, a support layer, wherein the support layer is SiO2, is grown on the piezoelectric single crystal wafer. Figure 2 This is a schematic diagram of the structure after the support layer is grown on the piezoelectric single-crystal wafer in step (b). Then, the pattern to be etched is transferred onto the support layer, and a mask is prepared on the surface of the support layer. The mask pattern has convex corner compensation sections at its convex corners. Wet etching is then performed. During etching, the portion covered by the mask is retained, while the portion not covered by the mask is etched away, forming a cavity. The wet etching can perform anisotropic etching of single-crystal silicon. Because the etchant has the fastest etching rate on the support layer below the "convex corner" structure in the mask pattern when using wet etching to etch single-crystal silicon, by designing the etching pattern and setting convex corner compensation sections, the "convex corner" can be compensated for, avoiding structural loss. Figure 3-4 The figure shows a schematic diagram of the structure of the piezoelectric single crystal wafer with pillars and cavities formed in the gaps between the pillars obtained in step (b).

[0061] It should be noted that the shape, number, and arrangement of the pillars are not unique. In this embodiment, a specific design method is provided, such as... Figure 3-4 As shown, the cross-section of the support column is rectangular, and there are 6 supports arranged symmetrically in two rows.

[0062] In a preferred embodiment, a support layer, SiO2, is grown on the piezoelectric single-crystal wafer. The pattern to be etched is transferred onto the support layer. The support layer is cleaned with a cleaning solution to remove surface impurities. Photoresist is then spin-coated onto the surface of the support layer as a mask. The mask pattern is obtained through photolithography, and a corner supplement is provided at the protruding corners of the mask pattern. Then, wet etching is used to etch the target location, forming pillars and creating cavities at the gaps between the pillars. The depth of the cavities is 2000 nm, and the location of the cavities is called a cavity layer. After etching the target location, the cleaning solution is used to remove surface impurities, resulting in a piezoelectric single-crystal wafer with pillars and cavities formed at the gaps between the pillars.

[0063] As a preferred implementation of this embodiment, the cleaning solution is one or more of water, acetone, ethanol, and hydrogen fluoride. In this embodiment, it is cleaned with acetone and ethanol solutions respectively to remove impurities on its surface, then rinsed with deionized water, and then soaked in 15wt% hydrogen fluoride for 20 minutes to remove the oxide layer. Finally, it is rinsed repeatedly with deionized water.

[0064] Specifically, the wet etching process involves etching at 90°C for 30 minutes using an etchant; the etchant is a 30wt% KOH solution.

[0065] (c) Take a substrate, wherein the substrate is silicon, coat one side of the substrate with a bonding agent to form a bonding layer, and bond it to the side of the piezoelectric single crystal wafer obtained in step (b) with the bottom electrode to obtain a bonded intermediate product; such as Figure 5 The diagram shown is a schematic representation of the structure of the substrate after the bonding agent is coated in step (c). Figure 6 The diagram shown is a schematic diagram of the structure of the intermediate product after bonding in step (c).

[0066] In a preferred embodiment of this invention: the bonded compound is benzocyclobutene, and the thickness of the bonded layer is 4 μm; the bonded compound is coated by spin coating; the spin coating includes a low-speed stage and a high-speed stage; the low-speed stage has a rotation speed of 800 rpm / s and a rotation time of 10 s; the high-speed stage has a rotation speed of 3000 rpm / s and a rotation time of 30 s;

[0067] In a preferred embodiment, the substrate with the bonding compound spin-coated is placed in an oven for pre-baking at a temperature of 100°C for 4 minutes.

[0068] As a preferred implementation of this embodiment, the bonding specifically includes the following steps: first, the piezoelectric single crystal wafer, which has undergone ion implantation and has a bottom electrode, and the substrate are placed in a bonding machine or tube furnace for pre-bonding, wherein the bonding pressure of the pre-bonding is 4×10⁻⁶. 5 The pressure was maintained at 30 min for 30 min; then, the temperature was slowly raised to 200 °C and maintained at 200 °C for 2 h to allow the benzocyclobutene to be completely cured and bonded, resulting in the bonded intermediate product.

[0069] (d) The bonded intermediate product obtained in step (c) is annealed at 350°C for 2 hours to allow the film to peel off. During annealing, the lattice damage caused by ion implantation can be restored, thus obtaining the peeled film, as shown below. Figure 7 The diagram shown is a schematic representation of the structure of the peeled-off film in step (d). A patterned metal top electrode is fabricated on the surface of the peeled-off film using electron beam evaporation or magnetron sputtering to obtain a cavity-type bulk acoustic resonator with a support; wherein the electrode material of the top electrode is Al and the electrode thickness is 100 nm. Figure 8 This is a schematic diagram of the cavity-type bulk acoustic resonator with support pillars in step (d).

[0070] As a preferred implementation of this embodiment, the step of bombarding the obtained release film is further included: bombarding the obtained release film with RIE plasma to reduce its roughness to 4 nm; in the RIE plasma bombardment step, the ions used are Ar+ ions, the pressure is 20 mT, the flow rate is 30 sccm, the RIE power is 100 W, and the vacuum degree is 10 -4 Pa, processing time is 120s.

[0071] The cavity-type bulk acoustic wave resonator with pillars prepared in this embodiment includes, from top to bottom, a top electrode, a piezoelectric thin film, a bottom electrode, a support layer, a bonding layer, and a substrate. The support layer has several pillars, forming cavities between the pillars. The pillars are located between the bottom electrode and the bonding layer. The bonding layer has a thickness of 4 μm. The piezoelectric thin film is the peeled-off film. In this embodiment, the upper surface area of ​​the bottom electrode of the cavity-type bulk acoustic wave resonator with pillars is smaller than the upper surface area of ​​the cavity.

[0072] Example 2

[0073] The method for fabricating a cavity-type bulk acoustic resonator with a support pillar in this embodiment includes the following steps:

[0074] (a) Take a piezoelectric single crystal wafer, wherein the piezoelectric single crystal wafer is a lithium tantalate wafer, and perform ion implantation on the piezoelectric single crystal wafer. The implanted ions are As ions, and the energy of the implanted ions is 500 keV. The implantation depth is 1.8 μm to obtain a pyroelectric material. Then, use magnetron sputtering to grow an electrode on the implantation surface of the obtained pyroelectric material. The electrode material is Au. Then, prepare a mask. Finally, etch away the excess part to obtain a piezoelectric single crystal wafer with a bottom electrode after ion implantation. The thickness of the bottom electrode is 100 nm.

[0075] (b) Take a piezoelectric single crystal wafer that has been ion implanted and has a bottom electrode, and form a plurality of pillars on the side of the piezoelectric single crystal wafer with the bottom electrode, and form cavities in the gaps between the pillars. Then take a substrate, grow a bonding compound on one side of the substrate, and bond the substrate to the side of the piezoelectric single crystal wafer with cavities. The bonding compound is one or more of silicon oxide, silicon nitride, aluminum oxide, and aluminum nitride. In this embodiment, the bonding compound is silicon dioxide.

[0076] As a preferred implementation of this embodiment, the bonding specifically includes the following steps: first, the piezoelectric single crystal wafer, which has undergone ion implantation and has a bottom electrode, and the substrate are placed in a bonding machine or tube furnace for pre-bonding, wherein the bonding pressure of the pre-bonding is 4×10⁻⁶. 5 Pa, holding pressure for 30 min; then, slowly raise the temperature to 200℃ and maintain the temperature at 200℃ for 2 h to allow it to fully solidify and complete the bonding, resulting in the bonded intermediate product.

[0077] (c) The bonded intermediate product obtained in step (b) is annealed at 350°C for 2 hours to exfoliate the film. During the annealing process, the lattice damage caused by ion implantation can be restored, thus obtaining the exfoliated film. A patterned metal top electrode is prepared on the surface of the exfoliated film by electron beam evaporation or magnetron sputtering. The electrode material of the top electrode is Al, and the electrode thickness is 100 nm.

[0078] The cavity-type bulk acoustic resonator with pillars prepared in this embodiment includes, from top to bottom, a top electrode, a piezoelectric thin film, a bottom electrode, a support layer, a bonding layer, and a substrate. The support layer has several pillars, and cavities are formed between the pillars. The pillars are located between the bottom electrode and the bonding layer. Preferably, the bonding layer thickness is 2-6 μm. The piezoelectric thin film is the peeled-off thin film.

[0079] Example 3

[0080] The fabrication method of the cavity-type bulk acoustic resonator with support pillar in this embodiment is exactly the same as that in Embodiment 1, except that the upper surface area of ​​the bottom electrode is larger than the upper surface area of ​​the cavity.

[0081] Figure 9 This is a schematic diagram of the structure of the piezoelectric single crystal wafer obtained in step (b) after ion implantation and having a bottom electrode.

[0082] Figure 10 This is a schematic diagram of the structure of the piezoelectric single crystal wafer with pillars and cavities formed at the gaps between the pillars in step (b).

[0083] Figure 11 This is a schematic diagram of the cavity-type bulk acoustic resonator with support pillars in step (d).

[0084] Example 4

[0085] The method for fabricating a cavity-type bulk acoustic resonator with a support pillar in this embodiment includes the following steps:

[0086] (1) Take a piezoelectric single crystal wafer that has been ion implanted and has a bottom electrode, and form a plurality of pillars on the side of the piezoelectric single crystal wafer with the bottom electrode, and form cavities in the gaps between the pillars. Then take a substrate, coat a bonding compound on one side of the substrate, and bond the substrate to the side of the piezoelectric single crystal wafer with cavities. The bonding compound is an organic insulating material. The organic insulating material includes one or more of benzocyclobutene, polyimide, silsesquioxide, and spin-coated glass. The thickness of the coated bonding compound is 100nm-4000nm. In this embodiment, the organic insulating material is polyimide, and the thickness of the coated bonding compound is 2000nm.

[0087] (2) Heat-treat the intermediate product obtained in step (1) to peel off the thin film of the piezoelectric single crystal wafer, and then grow a top electrode on one side of the peeled piezoelectric single crystal wafer to obtain the final product.

[0088] Example 5

[0089] The method for fabricating a cavity-type bulk acoustic resonator with a support pillar in this embodiment includes the following steps:

[0090] (1) Take a piezoelectric single crystal wafer that has been ion implanted and has a bottom electrode, and form a plurality of pillars on the side of the piezoelectric single crystal wafer with the bottom electrode, and form a cavity in the gap between the pillars. Then take a substrate, grow a bonding compound on one side of the substrate, and bond the substrate to the side of the piezoelectric single crystal wafer with the cavity. The bonding compound is one or more of silicon oxide, silicon nitride, aluminum oxide, and aluminum nitride. In this embodiment, the bonding compound is aluminum oxide.

[0091] (2) Heat-treat the intermediate product obtained in step (1) to peel off the thin film of the piezoelectric single crystal wafer, and then grow a top electrode on one side of the peeled piezoelectric single crystal wafer to obtain the final product.

[0092] Comparative Example 1

[0093] The fabrication method of the cavity-type bulk acoustic resonator with pillars in this comparative example uses the same conditions and methods as in Example 1, except that instead of forming the pillars and cavity on the piezoelectric single crystal wafer, a substrate with a sacrificial layer is used. Specifically, the method includes the following steps:

[0094] A substrate is taken, and a sacrificial layer, which is amorphous silicon, is grown on the substrate. A piezoelectric single-crystal wafer with a bottom electrode, which has undergone ion implantation, is then taken. A bonding compound is grown on the side of the piezoelectric single-crystal wafer with the bottom electrode and bonded to the substrate with the sacrificial layer. After bonding, the composite is peeled off to obtain a piezoelectric thin film. Then, openings are etched on the upper surface of the piezoelectric single-crystal wafer. XeF2 gas is introduced through the etched openings to etch the amorphous silicon sacrificial layer, forming a cavity to obtain a cavity-type bulk acoustic resonator with support pillars.

[0095] Comparative Example 2

[0096] The fabrication method of the cavity-type bulk acoustic resonator with support pillars in this comparative example uses the same conditions and methods as in Example 1, the only difference being that instead of forming the support pillars and cavity on the piezoelectric single crystal wafer, a complete cavity is formed on the piezoelectric single crystal wafer. The resulting cavity-type bulk acoustic resonator is as follows: Figure 12 As shown.

[0097] Effect test case

[0098] To verify the technical effect of the method for preparing a single-crystal thin-film device with a cavity structure according to the present invention, the single-crystal thin film was prepared by the methods in Examples 1-5 and Comparative Examples 1-2, and the following comparative test was conducted.

[0099] Twenty single-crystal thin films were prepared according to the methods in Examples 1-5 and Comparative Examples 1-2, and the results were tested and recorded.

[0100] The single-crystal thin films prepared by the methods in Examples 1-5 and Comparative Examples 1-2 were used to measure their inductance Q values ​​and the results were recorded.

[0101] The single-crystal thin films prepared by the methods in Examples 1-5 and Comparative Examples 1-2 were used as thin-film bulk acoustic resonators. The amount of noise was measured and the results were recorded.

[0102] The experimental data obtained from the above experiments are as follows:

[0103] Group Finished Product Rate Q value How much noise Example 1 99％ 2300 none Example 2 99％ 3000 none Example 3 99％ 2500 none Example 4 99％ 1800 none Example 5 99％ 2000 small amount Comparative Example 1 76％ 300 many Comparative Example 2 98％ 2300 none

[0104] The experimental results above show that the method for fabricating single-crystal thin-film devices with cavity structures described in this invention produces devices with improved mechanical strength, and etching is less likely to damage the film, thus not affecting its quality. The cavity structure is formed before film formation, resulting in a high yield and eliminating residue left by etching after film formation. This allows for the growth of high-quality single-crystal oxide films on polycrystalline metal bottom electrodes, enabling the fabrication of single-crystal thin-film devices using a film lift-off method. In particular, by adding support pillars to the cavity region, this invention improves the film's strength, reducing warpage and cracking after low-temperature self-lifting, thus significantly improving film quality. Furthermore, in Example 2, the Q-value of the single-crystal thin film obtained by bonding with silicon dioxide as the bonding compound is superior to the Q-value of the single-crystal thin film obtained by bonding with benzocyclobutene as the bonding compound in Example 1.

[0105] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A method for fabricating a cavity-type bulk acoustic resonator with a support pillar, characterized in that, Includes the following steps: (1) Take a piezoelectric single crystal wafer, perform ion implantation on the piezoelectric single crystal wafer, and grow a bottom electrode on the ion implantation surface to obtain a piezoelectric single crystal wafer with a bottom electrode after ion implantation. Then, grow a film on the side of the piezoelectric single crystal wafer with the bottom electrode. The film is a support layer. Then, perform patterned etching on the support layer to form a plurality of pillars and form cavities at the gaps between the pillars. The pillars are formed on the surface of the bottom electrode. Then, take a substrate and bond the substrate to the side of the piezoelectric single crystal wafer with cavities. (2) Heat-treat the intermediate product obtained in step (1) to peel off the thin film of the piezoelectric single crystal wafer, and then grow a top electrode on one side of the peeled piezoelectric single crystal wafer to obtain the final product.

2. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 1, characterized in that, In step (1), bonding the substrate to the cavity side of the piezoelectric single crystal wafer specifically includes the following steps: taking the substrate, coating a bonding agent on one side of the substrate, and bonding the substrate to the cavity side of the piezoelectric single crystal wafer; wherein the bonding agent is an organic insulating material; the organic insulating material includes one or more of benzocyclobutene, polyimide, silsesquioxide, and spin-coated glass.

3. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 2, characterized in that, The coating thickness of the bonding compound is 100nm-4000nm.

4. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 1, characterized in that, In step (1), the substrate is bonded to the cavity side of the piezoelectric single crystal wafer, which specifically includes the following steps: taking the substrate, growing a bonding compound on one side of the substrate, and bonding the substrate to the cavity side of the piezoelectric single crystal wafer; wherein the bonding compound is one or more of silicon oxide, silicon nitride, aluminum oxide, and aluminum nitride.

5. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 4, characterized in that, The thickness of the grown bonded compound is 100 nm to 4000 nm.

6. The method for fabricating a cavity-type bulk acoustic resonator with a support according to any one of claims 1-5, characterized in that: The piezoelectric single crystal wafer is one of the following: quartz, lithium niobate, lithium tantalate, aluminum nitride, zinc oxide, barium titanate, potassium dihydrogen phosphate, and lead magnesium niobate-lead titanate.

7. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to any one of claims 1-5, characterized in that: The ions implanted into the piezoelectric single crystal wafer are one or more of H ions, He ions, B ions, and As ions; the energy of the implanted ions is 100keV-1000keV; the implantation dose is 2-8×10¹⁶ / cm²; the ion beam current is 0.1-10μm / cm⁻²; and the implantation depth is 0.3-8μm.

8. The method for fabricating a cavity-type bulk acoustic resonator with a support according to any one of claims 1-5, characterized in that, The bottom electrode of the piezoelectric single crystal wafer is grown by the following method: first, a pattern to be grown is formed on the surface of the piezoelectric single crystal wafer by photolithography, then the electrode is grown, and finally the excess part is washed away; or, the electrode is grown on the surface of the piezoelectric single crystal wafer first, then a mask is prepared, and finally the excess part is etched away.

9. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 8, characterized in that, The electrode material for growing the bottom electrode is one of Al, Au, Mo, Pt, and W; the thickness of the bottom electrode is 50-500 nm. The bottom electrode is grown using methods including magnetron sputtering, resistive evaporation, and electron beam deposition.

10. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 1, characterized in that, The substrate is made of one or more of the following materials: silicon, silicon-on-insulator, glass, quartz, lithium niobate, lithium tantalate, silicon carbide, gallium nitride, and gallium arsenide.

11. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 1, characterized in that, The cavity has a depth greater than 100 nm.

12. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 1, characterized in that, The support layer is one or more of silicon oxide, silicon nitride, amorphous silicon, and metal.

13. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 2 or 3, characterized in that, In step (1), the bonding compound is coated by spin coating to form a bonding layer; the spin coating includes a low speed stage and a high speed stage; the speed of the low speed stage is 200 to 1000 rpm / s and the rotation time is 10s to 30s; the speed of the high speed stage is 1000 to 8000 rpm / s and the rotation time is 15 to 60s.

14. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 13, characterized in that, Step (1) also includes a step of pre-baking the piezoelectric single crystal wafer with the bonding compound spin-coated on it; the pre-baking temperature is 50 to 120°C and the pre-baking time is 60 to 600 seconds.

15. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 13, characterized in that, In step (1), the substrate is first pre-bonded to the cavity side of the piezoelectric single crystal wafer, and then bonded.

16. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 15, characterized in that, The bonding pressure of the pre-bonding is 1×10. 5 pa~5×10 6 The pressure holding time is 3-30 minutes; after pre-bonding, the temperature is slowly raised to 150-500℃ and maintained at 150-500℃ to completely cure the organic insulating material and complete the bonding.

17. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 1, characterized in that, Step (2) further includes: peeling the bonded intermediate product obtained in step (1) at 180-400°C, and then annealing it at 180-400°C for 10-600 min to obtain the peeled film.

18. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 17, characterized in that, The thickness of the piezoelectric single crystal wafer after peeling is 500-1000 nm.

19. The method for fabricating a cavity-type bulk acoustic resonator with a support pillar according to claim 1, characterized in that, The electrode material of the grown top electrode is one of Al, Au, Mo, Pt, and W, and the thickness of the top electrode is 50–300 nm.

20. A cavity-type bulk acoustic resonator with a support pillar, characterized in that, It is prepared by the method for preparing a cavity-type bulk acoustic resonator with a support according to any one of claims 1-19.

21. The cavity-type bulk acoustic resonator with a support pillar according to claim 20, characterized in that, It includes a top electrode, a piezoelectric thin film, a bottom electrode, a support layer, a bonding layer and a substrate arranged from top to bottom. The bottom electrode is provided with a number of pillars and cavities are formed in the gaps between the pillars.

22. The cavity-type bulk acoustic resonator with a support pillar according to claim 21, characterized in that, The support is located between the bottom electrode and the bonding layer.

23. The cavity-type bulk acoustic resonator with a support column according to claim 22, characterized in that, The thickness of the bonding layer is 2-6 μm.

24. A cavity-type bulk acoustic resonator with a support pillar, characterized in that, The resonator is prepared by the method of fabricating a cavity-type bulk acoustic wave resonator with pillars according to any one of claims 1-19. The resonator includes a top electrode, a piezoelectric thin film, a bottom electrode, a support layer, a bonding layer and a substrate arranged sequentially from top to bottom. A plurality of pillars are provided on the support layer, and cavities are formed at the gaps between the pillars. The pillars are formed by growing the support layer on one side of a piezoelectric single crystal wafer and patterning the support layer to form a plurality of pillars, wherein the pillars are located between the bottom electrode and the bonding layer.

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