Film cavity acoustic resonator and preparation method thereof

Abstract

The invention discloses a film cavity acoustic resonator and a preparation method thereof. The film cavity acoustic resonator comprises a substrate; the multi-layer structure is positioned on the substrate; the multi-layer structure comprises a supporting layer and a functional layer from bottom to top; the functional layer comprises a bottom electrode layer, a piezoelectric layer and a top electrode layer from bottom to top; wherein the supporting layer is in partial contact with the substrate, and the non-contact part forms a cavity between the supporting layer and the substrate; the cavity is obtained by arranging a sacrificial layer on the substrate and removing the sacrificial layer after the multilayer structure is prepared in the process of preparing the film cavity acoustic wave resonator; the sacrificial layer is a nano-porous film prepared by adopting a sol-gel method. According to the invention, the soaking time of the device in the corrosive liquid is effectively shortened, and the side effect of the corrosive liquid on the device is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of acoustic wave resonators, and particularly relates to a thin-film cavity acoustic wave resonator and a preparation method thereof. Background Art

[0002] An FBAR (thin-film cavity acoustic wave resonator) is usually a sandwich structure composed of upper and lower metal electrodes and a middle piezoelectric thin film layer. The resonator mainly utilizes the piezoelectric characteristics of the piezoelectric thin film to realize the conversion between signals. Under the action of an RF (radio frequency) bias voltage, the piezoelectric thin film excites a bulk acoustic wave, and the acoustic wave reflects back and forth between the upper and lower air interfaces, thus forming a standing wave oscillation. Under the action of mechanical vibration, the piezoelectric thin film generates a piezoelectric effect, thereby completing the conversion between acoustic wave signals and electrical signals.

[0003] The air cavity type FBAR is based on the MEMS (microelectromechanical system) silicon surface processing technology. A closed cavity is etched on the upper surface of the silicon substrate, and the upper electrode interface and this closed cavity together confine the acoustic wave in the resonance region. There are two ways to form the cavity. One is to sequentially grow the functional layer materials on the silicon wafer surface, and then remove part of the silicon material in the set area under the bottom electrode through a release via to form an air cavity. The removal method mainly uses dry etching, that is, the gas etching method. This method has high cost, poor repeatability, and the used gas is highly toxic and difficult to control. The second is to prepare a sacrificial layer in the set area on the silicon wafer surface, then prepare other material layers, and finally remove the sacrificial layer through a release via to form an air cavity structure. The sacrificial layer material mostly uses silicon dioxide, and the release method mostly uses wet etching with lower cost and better repeatability.

[0004] In the existing solutions for forming cavities based on sacrificial layers, most sacrificial layer materials use silicon dioxide as the sacrificial layer material. The preparation methods of silicon dioxide include high-temperature thermal oxidation method, magnetron sputtering method or chemical vapor deposition (CVD) method. For example, the patent document with the publication number CN110868186A discloses a "bulk acoustic wave resonator, its preparation method and semiconductor device". The bulk acoustic wave resonator includes a substrate; a multilayer structure formed on the substrate, and the multilayer structure sequentially includes a lower electrode layer, a piezoelectric layer and an upper electrode layer from bottom to top; wherein, a cavity is formed between the substrate and the multilayer structure. The cavity is first filled with silicon dioxide as a sacrificial material, then a multilayer structure is formed on the sacrificial material layer, and finally the sacrificial material part is removed to form a resonator with a special cavity structure. The manufacturing method of silicon dioxide adopts the high-temperature thermal oxidation method. In an environment with a process temperature in a preset range (1000 - 1200 °C), high-purity oxygen is introduced into the substrate so that an oxide layer is generated on the part of the substrate corresponding to the preset area; after a first preset time, the introduction of high-purity oxygen into the substrate is stopped, and the thickness of the oxide layer on the substrate is made to reach the preset thickness by means of wet oxygen oxidation or hydrogen-oxygen synthesis oxidation; the introduction of wet oxygen into the substrate is stopped and high-purity oxygen is introduced into the substrate, and after a second preset time, the oxidation treatment of the substrate is completed. The oxidized part of the substrate is used as the sacrificial layer. The silicon dioxide sacrificial layer grown by the high-temperature thermal oxidation method is easier to control the surface roughness of the working area of the resonator compared with the traditional preparation method, but the material is relatively dense.

[0005] However, the sacrificial layer prepared by the above method has a high density. When removing the sacrificial layer material, due to the surface tension, the etching liquid is difficult to penetrate, resulting in a long cavity release time and low efficiency. Moreover, the device is easily affected by side effects when immersed in the etching liquid for a long time, such as the etching liquid penetrating through the cross-section of the through hole to damage other functional layers, resulting in breakage, curling, and collapse, thus weakening the performance of the resonator. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a thin-film cavity bulk acoustic wave resonator and its preparation method.

[0007] The technical problems to be solved by the present invention are realized through the following technical solutions:

[0008] A thin-film cavity bulk acoustic wave resonator, comprising:

[0009] A substrate;

[0010] A multilayer structure located above the substrate; the multilayer structure includes a support layer and a functional layer from bottom to top; the functional layer includes a bottom electrode layer, a piezoelectric layer and a top electrode layer from bottom to top;

[0011] Wherein, the support layer is in partial contact with the substrate, and the non-contact part forms a cavity between the support layer and the substrate; the cavity is obtained by setting a sacrificial layer on the substrate and removing the sacrificial layer after preparing the multi-layer structure during the preparation of the thin film bulk acoustic wave resonator; the sacrificial layer is a nano-porous film prepared by the sol-gel method.

[0012] Optionally, the nano-porous film is a nano-porous SiO 2 thin film.

[0013] Optionally, the functional layer is provided with a groove; the groove and the cavity are vertically corresponding; the support layer is below the bottom of the groove, and the support layer is provided with a through hole; the through hole is used to introduce an etching solution to the sacrificial layer when removing the sacrificial layer;

[0014] The thin film bulk acoustic wave resonator further includes: a passivation layer; the passivation layer respectively covers the functional layer on both sides of the through hole, and contacts the support layer on both sides of the through hole at the bottom of the groove to form a closed structure.

[0015] Optionally, the thickness of the sacrificial layer is 400 nm to 600 nm.

[0016] The present invention also provides a preparation method of a thin film bulk acoustic wave resonator, including:

[0017] Step 1: Provide a substrate;

[0018] Step 2: Prepare a nano-porous film on the substrate by the sol-gel method as a sacrificial layer;

[0019] Step 3: Etch the sacrificial layer to form an air cavity pattern made of a nano-porous film material;

[0020] Step 4: Deposit a support layer, a bottom electrode layer, a piezoelectric layer, and a top electrode layer on the substrate with the air cavity pattern in sequence; wherein, the bottom electrode layer, the piezoelectric layer, and the top electrode layer constitute a functional layer;

[0021] Step 5: Introduce an etching solution to the sacrificial layer to remove the sacrificial layer.

[0022] Optionally, between Step 4 and Step 5, the method further includes:

[0023] Etch a groove on the functional layer to expose the support layer below the bottom of the groove; the groove and the air cavity pattern are vertically corresponding;

[0024] Deposit a passivation layer on the surface of the functional layer and the groove;

[0025] A through hole is formed by etching the passivation layer and the support layer at the bottom of the groove; wherein, the diameter of the through hole is smaller than the diameter of the bottom of the groove, so that the passivation layer and the support layer on each side of the through hole can be in contact to form a closed structure;

[0026] The fifth step includes: introducing the etching solution to the sacrificial layer through the through hole to remove the sacrificial layer.

[0027] Optionally, the nanoporous film is a nanoporous SiO 2 film prepared by the sol-gel method.

[0028] Optionally, step two includes:

[0029] Adding tetraethyl orthosilicate to absolute ethanol and stirring evenly to obtain solution A;

[0030] Adding ammonia water and deionized water to absolute ethanol and stirring evenly to obtain solution B;

[0031] Adding solution B to solution A, stirring and refluxing, and standing to obtain a transparent SiO 2 sol;

[0032] Using the SiO 2 sol, preparing a nanoporous SiO 2 film on the substrate by the dipping method.

[0033] Optionally, when preparing solution A, the molar ratio of tetraethyl orthosilicate to absolute ethanol is 1:5 to 1:50; when preparing solution B, the molar ratio of ammonia water to deionized water is 1:5 to 1:50.

[0034] Optionally, using the SiO 2 sol to prepare a nanoporous SiO 2 film on the substrate by the dipping method, including:

[0035] Using the SiO 2 sol to prepare a SiO 2 wet film on the substrate by the dipping method, and controlling the pulling speed at 13 cm / min to 25 cm / min during this period;

[0036] Putting the substrate with the SiO 2 wet film into a quartz glass tube for heat treatment and drying to obtain a nanoporous SiO 2 film.

[0037] The thin-film bulk acoustic wave resonator provided by the present invention uses the sol-gel method to prepare a nanoporous thin film as a sacrificial layer. The prepared nanoporous thin film has the advantages of controllable structure and high porosity, which is conducive to the penetration of the etching solution during cavity release, greatly shortens the cavity release time, effectively shortens the time for the device to be immersed in the etching solution, and thus reduces the side effects of the etching solution on the device.

[0038] The present invention will be further described in detail below with reference to the accompanying drawings. Description of the Drawings

[0039] Figure 1 is a schematic structural diagram of a thin-film bulk acoustic wave resonator provided by an embodiment of the present invention;

[0040] Figure 2 is a schematic structural diagram of another thin-film bulk acoustic wave resonator provided by an embodiment of the present invention;

[0041] Figures 3 to 12 Schematically shows the process of preparing a thin-film bulk acoustic wave resonator according to an embodiment of the present invention. Detailed Embodiments

[0042] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0043] In view of the side effects brought to the device by the long-term immersion of the etching solution due to the high density of the sacrificial layer prepared by the existing method for preparing a thin-film bulk acoustic wave resonator, an embodiment of the present invention provides a thin-film bulk acoustic wave resonator, as Figure 1 shown, the device includes: a substrate 101 and a multi-layer structure located on the substrate 101; the multi-layer structure includes, from bottom to top: a support layer 103 and a functional layer; the functional layer includes, from bottom to top: a bottom electrode layer 104, a piezoelectric layer 105, and a top electrode layer 106. The thin-film bulk acoustic wave resonator further includes: a cavity A located between the support layer 103 and the substrate 101.

[0044] Specifically, the support layer 103 is in partial contact with the substrate 101, and the non-contact part forms the above-mentioned cavity A; the cavity A is obtained by setting a sacrificial layer 102 on the substrate 101 and removing the sacrificial layer 102 after preparing the multi-layer structure during the process of preparing the thin-film bulk acoustic wave resonator. Among them, the sacrificial layer 102 is a nanoporous thin film prepared by the sol-gel method. The nanoporous thin film structure contains a large number of nanoscale holes, and the structure material is loose. It has the advantages of controllable structure and high porosity, which is conducive to the penetration of the etching solution during cavity release, greatly shortens the cavity release time, effectively shortens the time for the device to be immersed in the etching solution, and thus reduces the side effects of the etching solution on the device.

[0045] In one embodiment, the nanoporous film is a nanoporous SiO prepared by the sol-gel method 2 film, but is not limited thereto.

[0046] In one embodiment, as shown in Figure 2 the functional layer is provided with a groove 107; the groove 107 and the cavity A are vertically corresponding; below the bottom of the groove 107 is a support layer 103, and the support layer 103 is provided with a through hole 109; the through hole 109 is used to introduce an etching solution into the sacrificial layer 102 when removing the sacrificial layer 102; on this basis, the thin film bulk acoustic resonator further includes: a passivation layer 108; the passivation layer 108 covers the functional layer on both sides of the through hole 109 respectively, and contacts the support layer 103 on both sides of the through hole 109 at the bottom of the groove 107 to form a closed structure.

[0047] It can be understood that after the sacrificial layer 102, the support layer 103 and the functional layer are prepared on the substrate 101, if a hole is directly etched in the functional layer and the etching solution is introduced into the sacrificial layer 102 through the hole, the etching solution may enter the gap between the electrode layer and the piezoelectric layer 105 through the cross section inside the hole, thereby damaging the overall structure of the device and causing the collapse of the device. To solve this problem, in the embodiment of the present invention, a groove 107 is provided in the functional layer, so that the bottom of the groove 107 exposes the support layer 103, and a passivation layer 108 is introduced, so that the passivation layer 108 and the support layer 103 contact each other at the bottom of the groove 107 to form a sealing structure. In this way, when the etching solution is introduced into the sacrificial layer 102 through the through hole 109, the electrode layer and the piezoelectric layer 105 in the functional layer are protected by the sealing structure and can be isolated from the etching solution, avoiding direct contact between the etching solution and the electrode layer or the piezoelectric layer 105, improving the yield of the device, and reducing the wafer cost.

[0048] Based on the same inventive concept, the embodiment of the present invention also provides a method for manufacturing a thin film bulk acoustic resonator, including the following steps:

[0049] Step 1: Provide a substrate 101.

[0050] Specifically, a silicon wafer substrate (100-800 microns thick) is taken, and is ultrasonically cleaned with acetone, ethanol and deionized water in sequence for about 5 minutes, and dried with nitrogen for standby.

[0051] Step 2: Use the sol-gel method to prepare a nanoporous film on the substrate 101 as the sacrificial layer 102, such as Figure 3 .

[0052] Preferably, the nanoporous film is a nanoporous SiO prepared by the sol-gel method 2 film. On this basis, this step 2 may specifically include:

[0053] (2-1) Add tetraethyl orthosilicate to absolute ethanol and stir evenly to obtain Solution A.

[0054] Specifically, add a certain amount of tetraethyl orthosilicate (C 8 H 20 O 4 Si) to an appropriate amount of absolute ethanol (C 2 H 5 OH) (the molar ratio of the two is 1:5 to 1:50), and stir magnetically at room temperature for about 30 minutes to obtain Solution A.

[0055] (2-2) Add ammonia water and deionized water to absolute ethanol and stir evenly to obtain Solution B.

[0056] Specifically, add a certain amount of ammonia water (NH 3 ·H 2 O) and deionized water to an appropriate amount of absolute ethanol (the ratio of the two is 1:5 to 1:50), and stir magnetically at room temperature for 10 to 60 minutes to obtain Solution B.

[0057] (2-3) Add Solution B to Solution A, stir and reflux, and then let it stand to obtain a transparent SiO 2 sol.

[0058] Under stirring at a certain temperature (10 - 100 °C), add Solution B to Solution A, stir and reflux at a certain temperature (50 - 100 °C) for 4 - 20 hours, and then let it stand for 24 - 72 hours to obtain a transparent SiO 2 sol, store it at room temperature for subsequent thin film preparation.

[0059] (2-4) Use the SiO 2 sol to prepare a nano-porous SiO 2 thin film on the substrate 101 by the dip-coating method.

[0060] Specifically, use the SiO 2 sol to prepare a SiO 2 wet film on the substrate 101 by the dip-coating method, and control the pulling speed at 13 cm / min - 25 cm / min during this process; then, put the substrate 101 with the SiO 2 wet film into a quartz glass tube for heat treatment and drying to obtain a nano-porous SiO 2 thin film.

[0061] Preferably, prepare the SiO 2The film is formed with the pulling speed controlled at 13 - 25 cm / min. After the film is formed, the substrate 101 is placed in a quartz glass tube and heat-treated in air at a certain temperature (200 - 400 °C) for a certain period of time (1 - 2 hours). The above dipping process can be repeated until a film with a certain thickness is obtained.

[0062] Step 3: Etch the sacrificial layer 102 to form an air cavity pattern made of a nano-porous thin film material, as Figure 4 .

[0063] Specifically, a thin layer of adhesive (HDMS, hexamethyldisilazane) is evenly sprayed on the substrate 101, and a layer of photoresist (1 - 3 microns) is evenly applied using a spin coater. Then it is pre-baked on a hot plate (80 - 110 °C, 80 - 110 seconds), exposed under a mask with an air cavity pattern (2 - 3 seconds), the exposed wafer is developed in a developer (30 - 40 seconds), post-baked on a hot plate (80 - 110 °C, 80 - 110 seconds), the post-baked wafer is placed in an ICP (inductively coupled plasma etcher), and etched using a mixed gas until the substrate 101 is exposed (etching depth 400 - 600 nm). The etched wafer is respectively placed in acetone, ethanol, and water to wash away the residual photoresist, obtaining a substrate 101 with an air cavity pattern.

[0064] Step 4: Deposit a support layer 103, a bottom electrode layer 104, a piezoelectric layer 105, and a top electrode layer 106 on the substrate 101 with an air cavity pattern in sequence, as Figures 5 to 8 ; among them, the bottom electrode layer 104, the piezoelectric layer 105, and the top electrode layer 106 constitute the functional layer.

[0065] Specifically, a thin layer (50 - 100 nm) of material is deposited on the above substrate 101 with an air cavity pattern as the support layer 103 (one or more of TiN, SiO 2 , Si 3 N 4 and AlN). Then, on the above support layer 103, the bottom electrode layer 104, the piezoelectric layer 105, and the top electrode layer 106 are deposited in sequence from bottom to top. Among them, the electrode layer material is one or more of Mo, Pt, W, Cu, Al, Au, and Ag, and the thickness is preferably 50 - 200 nm. The material of the piezoelectric layer 105 is one or more of AlN, AlScN, ZnO, LiNbO 3 and LiTaO 3 , and the thickness is preferably 300 - 1000 nm.

[0066] Step 5: Introduce the etching solution to the sacrificial layer 102 to remove the sacrificial layer 102.

[0067] Here, holes can be drilled in the functional layer and the support layer 103 to lead the etching solution to the sacrificial layer 102. For the effect after removing the sacrificial layer 102, refer to Figure 1 .

[0068] In one embodiment, between step four and step five, the above preparation method further includes:

[0069] (1) Etch a groove 107 in the functional layer to expose the support layer 103 below the bottom of the groove 107, as Figure 9 ; wherein, the groove 107 and the air cavity pattern correspond to each other up and down.

[0070] Specifically, spray a thin layer of adhesive (HDMS, hexamethyldisilazane) evenly on the above functional layer material, and use a spin coater to evenly apply a layer of photoresist (1 - 3 microns). Place it on a hot plate for pre-baking (80 - 110 °C, 80 - 110 seconds). After aligning with the alignment marks under the mask, expose (2 - 3 seconds). Put the exposed wafer into the developer for development (30 - 40 seconds). Place it on a hot plate for hardening (80 - 110 °C, 80 - 110 seconds). Put the hardened wafer into an ICP (Inductively Coupled Plasma Etching Machine), and use a mixed gas for etching until the support layer 103 below the bottom of the groove 107 is exposed (etching depth 400 - 600 nm). The etched wafer is respectively put into acetone, ethanol, and water to wash away the residual photoresist, obtaining the groove 107. Among them, since the functional layer and the support layer 103 are made of different materials, the etching can be controlled to stop on the upper surface of the support layer 103.

[0071] (2) Deposit a passivation layer 108 on the surfaces of the functional layer and the groove 107, as Figure 10 .

[0072] Specifically, deposit a thin layer (50 - 100 nm) of material (one or more of TiN, SiO 2 , Si 3 N4, and AlN) as the passivation layer 108 on the etched functional layer. The passivation layer 108 should be able to cover the entire device and the cross-section generated by etching at the edge of the device.

[0073] (3) Form a through hole 109 by etching the passivation layer 108 and the support layer 103 at the bottom of the groove 107, as Figure 11 ; wherein, the diameter of the through hole 109 is smaller than the diameter of the bottom of the groove 107, so that the passivation layer 108 and the support layer 103 on each side of the through hole 109 can contact each other to form a closed structure;

[0074] Specifically, a thin layer of adhesive (HDMS, hexamethyldisilazane) is evenly sprayed on the above-mentioned passivation layer 108, and a layer of photoresist (1 - 3 microns) is evenly applied using a spin coater. Then, it is pre-baked (80 - 110 °C, 80 - 110 seconds) on a hot plate. After aligning with the alignment marks under the mask, it is exposed (2 - 3 seconds). The exposed wafer is developed in a developer (30 - 40 seconds), and then post-baked (80 - 110 °C, 80 - 110 seconds) on a hot plate. The post-baked wafer is placed in an ICP (Inductively Coupled Plasma Etcher), and etched using a mixed gas until the sacrificial layer 102 is exposed (etching depth 400 - 600 nm). The etched wafer is respectively placed in acetone, ethanol, and water to wash away the residual photoresist, forming a through hole 109.

[0075] In this step, the diameter of the through hole 109 is smaller than the diameter of the bottom of the groove 107, so that the passivation layer 108 and the support layer 103 on each side of the through hole 109 can come into contact to form a closed structure, thereby using this closed structure to completely cover the sidewall cross-section of the through hole 109.

[0076] Correspondingly, step five specifically includes: introducing the etching solution to the sacrificial layer 102 through the through hole 109 to remove the sacrificial layer 102, such as Figure 12 .

[0077] Specifically, the front side (the side with the grown material) of the sample prepared in step four is facing up, and it is placed in the etching solution (a mixture of 49% hydrofluoric acid aqueous solution and ammonium fluoride buffer solution in a certain proportion). After 10 - 30 minutes, the sacrificial layer 102 is completely corroded. The sample is taken out of the etching solution, and is successively washed with acetone, ethanol, and deionized water, and then dried to obtain the prepared thin-film bulk acoustic resonator.

[0078] It is worth mentioning that, under the etching solution with the same ratio (1:7), the etching duration of the sacrificial layer in the present invention is 10 - 30 minutes, while the etching duration of the sacrificial layer in the existing solution is about 60 minutes. Moreover, when observed by slicing under FIB (Focused Ion Beam), comparing the etching effect of 10 - 30 minutes in the present invention with the etching effect of 60 minutes in the existing solution, the etching effect of the sacrificial layer in the present invention is more thorough.

[0079] The preparation method of the thin-film bulk acoustic resonator provided by the embodiment of the present invention uses the sol-gel method to prepare a silica film as the sacrificial layer, and prepares a nanoporous SiO 2The thin film has the advantages of controllable structure and high porosity. In the embodiments of the present invention, a passivation layer is used to cover the etched cross-section of the functional layer, preventing the etching solution from penetrating into the gap between the electrode layer and the piezoelectric layer and damaging the device structure. Thus, the functional layer material is "wrapped" by the passivation layer and the support layer, avoiding direct contact between the etching solution and the metal layer or the piezoelectric layer, improving the yield of the device, and reducing the wafer cost.

[0080] It should be noted that the terms "first", "second", etc. are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. On the contrary, they are only examples of devices and methods consistent with some aspects of the present invention.

[0081] In the description of this specification, the description referring to terms such as "an embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0082] Although the present invention has been described in connection with various embodiments herein, however, in the process of implementing the claimed invention, those skilled in the art can understand and achieve other variations of the disclosed embodiments by viewing the accompanying drawings and the disclosure. In the description of the present invention, the term "including" does not exclude other components or steps, the word "a" or "an" does not exclude a plurality of cases, and the meaning of "plurality" is two or more unless otherwise specifically defined. In addition, certain measures are described in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0083] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention.

[0084] In the present invention, unless otherwise clearly specified and defined, the terms "installed", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0085] In the present invention, unless otherwise clearly specified and defined, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features therebetween. Moreover, the first feature being "above", "over" and "on" the second feature includes that the first feature is directly above and obliquely above the second feature, or simply means that the horizontal height of the first feature is higher than that of the second feature. The first feature being "below", "under" and "beneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or simply means that the horizontal height of the first feature is lower than that of the second feature.

[0086] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A thin film cavity acoustic wave resonator, characterized in that: include: substrate; a multilayer structure located on the substrate; The multilayer structure comprises, from bottom to top: a support layer and a functional layer; the functional layer comprises, from bottom to top, a bottom electrode layer, a piezoelectric layer and a top electrode layer; The support layer is in partial contact with the substrate, and the uncontacted portion forms a cavity between the support layer and the substrate; the cavity is obtained by setting a sacrificial layer on the substrate during the preparation of the thin film cavity acoustic wave resonator and removing the sacrificial layer after the multilayer structure is prepared; the sacrificial layer is a nanoporous film prepared by a sol-gel method.

2. The thin film cavity acoustic wave resonator according to claim 1, characterized in that: The nanoporous film is a nanoporous SiO2 film prepared by a sol-gel method.

3. The thin film cavity acoustic wave resonator according to claim 1, characterized in that: The functional layer is provided with a groove; the groove corresponds to the cavity up and down; the support layer is below the bottom of the groove, and the support layer is provided with a through hole; the through hole is used to introduce a corrosive liquid into the sacrificial layer when removing the sacrificial layer; The thin film cavity acoustic wave resonator further includes: a passivation layer; the passivation layer covers the functional layers on both sides of the through hole respectively, and contacts the support layers on both sides of the through hole at the bottom of the groove respectively to form a closed structure.

4. The thin film cavity acoustic wave resonator according to claim 1, characterized in that: The thickness of the sacrificial layer is 400nm-600nm.

5. A method for preparing a thin film cavity acoustic wave resonator, characterized in that: include: Step 1: providing a substrate; Step 2: preparing a nanoporous film as a sacrificial layer on the substrate by a sol-gel method; Step 3: etching the sacrificial layer to form an air cavity pattern of a nanoporous film material; Step 4: depositing a support layer, a bottom electrode layer, a piezoelectric layer and a top electrode layer in sequence on the substrate with the air cavity pattern; wherein the bottom electrode layer, the piezoelectric layer and the top electrode layer constitute a functional layer; Step 5: introducing a corrosive liquid to the sacrificial layer to remove the sacrificial layer.

6. The method for preparing a thin film cavity acoustic wave resonator according to claim 5, characterized in that: Between step 4 and step 5, the method further comprises: Etching a groove on the functional layer to expose the support layer below the bottom of the groove; the groove and the air cavity pattern correspond to each other up and down; Depositing a passivation layer on the surface of the functional layer and the groove; A through hole is formed by etching the passivation layer and the support layer at the bottom of the groove; wherein the diameter of the through hole is smaller than the diameter of the bottom of the groove, so that the passivation layer and the support layer on each side of the through hole can contact each other to form a closed structure; The step five includes: introducing a corrosive liquid to the sacrificial layer through the through hole to remove the sacrificial layer.

7. The method for preparing a thin film cavity acoustic wave resonator according to claim 5, characterized in that: The nanoporous film is a nanoporous SiO2 film prepared by a sol-gel method.

8. The method for preparing a thin film cavity acoustic wave resonator according to claim 7, characterized in that: Step 2 includes: Add tetraethyl orthosilicate into anhydrous ethanol and stir evenly to obtain solution A; Add ammonia water and deionized water into anhydrous ethanol and stir evenly to obtain solution B; Solution B is added to solution A, stirred and refluxed, and allowed to stand to obtain a transparent SiO2 sol; The SiO2 sol is used to prepare a nanoporous SiO2 film on the substrate by an immersion method.

9. The method for preparing a thin film cavity acoustic wave resonator according to claim 8, characterized in that: When preparing the solution A, the molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:5 to 1:50; when preparing the solution B, the molar ratio of ammonia water to deionized water is 1:5 to 1:

50.

10. The method for preparing a thin film cavity acoustic wave resonator according to claim 8, characterized in that: The SiO2 sol is used to prepare a nanoporous SiO2 film on the substrate by an immersion method, comprising: Using the SiO2 sol, a SiO2 wet film is prepared on the substrate by an immersion method, during which the pulling speed is controlled at 13 cm / min to 25 cm / min; The substrate with the SiO2 wet film is placed in a quartz glass tube for heat treatment and drying to obtain a nanoporous SiO2 film.

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