CN111147040A - Air gap type film bulk acoustic resonator and preparation method thereof - Google Patents
Air gap type film bulk acoustic resonator and preparation method thereof Download PDFInfo
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
- H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
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- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
Abstract
The invention discloses an air-gap type film bulk acoustic resonator and a preparation method thereof, wherein a transfer substrate, a bonding layer, a bottom electrode, a piezoelectric film and a top electrode are sequentially distributed on the resonator from bottom to top; the bonding layer, the bottom electrode and the transfer substrate are enclosed to form an air gap structure, the upper surface and the lower surface of the piezoelectric film are respectively connected with a top electrode and a bottom electrode which are opposite, the bottom electrode is positioned in the air gap structure, the top electrode, the piezoelectric film and the bottom electrode form a sandwich structure, and the orthographic projections of the top electrode and the bottom electrode are not completely overlapped; and a filling and leveling layer is also arranged between the bonding layer and the piezoelectric film, is positioned at the outer side of the bottom electrode and has the same thickness as the bottom electrode. The cavity is formed by bonding, a sacrificial layer is not required to be introduced, the structure is simple and stable, the controllability is high, the production cost is reduced, and the preparation process is simplified.
Description
Technical Field
The invention relates to the technical field of film bulk acoustic resonators, in particular to an air gap type film bulk acoustic resonator and a preparation method thereof.
Background
With the development of modern wireless communication technologies like high frequency and high speed, higher requirements are put forward on the front-end filter commonly used in radio frequency communication. While the working frequency is continuously improved, the requirements on the size, the use performance, the stability and the integration of the device are higher, and the Surface Acoustic Wave (SAW) filter used in the past can not meet the requirements of the existing high-frequency communication any more due to the problems of larger size, compatible process and working frequency band.
The Film Bulk Acoustic Resonator (FBAR) is a new type of filter, and compared with the surface Acoustic wave filter, it not only has small volume, large power capacity, integratable performance and high working frequency, but also has better out-of-band rejection and insertion loss, and has a wide application in the current 5G communication. The film bulk acoustic resonator mainly has three structures of a diaphragm type, an air gap type and a solid assembly type, and the three structures all have a sandwich structure of 'electrode-piezoelectric film-electrode'.
In order to reduce the loss of the sound wave, the sound wave should be made to be capable of forming total reflection as much as possible. The acoustic impedance of air can be considered to be approximately zero, so that the top electrode and the surface of the bottom electrode need to be in contact with the air during manufacturing, the top electrode is in contact with the air, the bottom electrode grows on the substrate, and the substrate material at the bottom electrode needs to be removed by using an etching method, so that the substrate material can form solid/air interface contact with the air, and sufficient mechanical strength is ensured, namely the air gap type film bulk acoustic resonator is manufactured. The preparation method of the mainstream air gap type film bulk acoustic resonator is that a silicon cavity is etched through a silicon cavity, then a sacrificial layer is filled in the silicon cavity, other materials are continuously grown after chemical mechanical polishing, and finally the materials are released and removed. The first disadvantage is that the release of the sacrificial layer needs to use corrosive solution, which can corrode other structures of the device to a certain extent, the second is that the sacrificial layer becomes gas when released, the control rate is not appropriate, the pressure in the cavity is too high, the device structure is damaged, and the third is that the release of the sacrificial layer may not be thorough, thereby introducing other influences. Due to these factors, the yield of the mainstream FBAR device is low.
In order to improve various problems existing in a mainstream process, a recent patent proposes a method for preparing a cavity by metal bonding, but in the metal bonding process, the metal has high fluidity, bonding pressure and bonding temperature are difficult to control, and the metal easily generates an electromagnetic effect.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide an air-gap type film bulk acoustic resonator and a preparation method thereof, which have the advantages of simple and stable structure, strong controllability and reduced production cost.
One of the purposes of the invention is realized by adopting the following technical scheme:
an air gap type film bulk acoustic resonator is characterized in that a transfer substrate, a bonding layer, a bottom electrode, a piezoelectric film and a top electrode are sequentially distributed on the resonator from bottom to top; the bonding layer, the bottom electrode and the transfer substrate are enclosed to form an air gap structure, the upper surface and the lower surface of the piezoelectric film are respectively connected with a top electrode and a bottom electrode which are opposite, the bottom electrode is positioned in the air gap structure, the top electrode, the piezoelectric film and the bottom electrode form a sandwich structure, and the orthographic projections of the top electrode and the bottom electrode are not completely overlapped; and a filling and leveling layer is also arranged between the bonding layer and the piezoelectric film, is positioned at the outer side of the bottom electrode and has the same thickness as the bottom electrode.
Furthermore, the top surface of the transfer substrate is provided with a groove, the bonding layer and part of the transfer substrate form a groove wall, the filling and leveling layer is positioned on the upper surface of the groove wall, and the groove, the bonding layer and the bottom electrode enclose an air gap structure.
Further, the bonding layer comprises a first bonding layer and a second bonding layer, the first bonding layer is arranged on the bottom surface of the filling and leveling layer, and the second bonding layer is arranged on the bottom surface of the first bonding layer; the first bonding layer adopts titanium dioxide TiO2The second bonding layer adopts aluminum oxide Al2O3。
Further, the transfer substrate is monocrystalline silicon, and the piezoelectric film is one or more of piezoelectric ceramic, aluminum nitride AlN and zinc oxide ZnO; the bottom electrode and the top electrode are made of metal materials, and the metal materials comprise one or more of platinum Pt, molybdenum Mo, tungsten W, titanium Ti, aluminum Al, gold Au and silver Ag.
Further, the depth of the groove is 500 nm-3 μm; the depth of an air gap structure formed by the bonding layer, the bottom electrode and the groove is 900 nm-8 mu m.
Further, the thickness of the bonding layer is 400 nm-5 μm; the thickness of the piezoelectric film is 200 nm-3 mu m; the thickness of the top electrode and the bottom electrode is 50 nm-500 nm.
The second purpose of the invention is realized by adopting the following technical scheme:
the preparation method of the air-gap type film bulk acoustic resonator comprises the following steps:
s1, selecting a monocrystalline silicon base as an epitaxial substrate, and cleaning and thermally oxidizing the surface of the epitaxial substrate; sequentially growing a piezoelectric film and a bottom electrode on the upper surface of the epitaxial substrate, wherein the piezoelectric film is exposed out of the bottom electrode, and obtaining a pattern of the bottom electrode through photoetching and wet etching; growing a filling and leveling layer on the upper surface of the bottom electrode and the area of the piezoelectric film exposed on the bottom electrode, and removing the filling and leveling layer on the surface of the bottom electrode by photoetching and wet method; growing a first bonding layer on the upper surface of the bottom electrode and the upper surface of the filling layer, removing the first bonding layer on the surface of the bottom electrode through photoetching and a wet method, and carrying out surface activation treatment on the first bonding layer to obtain a first wafer;
s2, selecting monocrystalline silicon as a transfer substrate, and cleaning the surface of the transfer substrate; etching a groove on the top surface of the transfer substrate, growing a second bonding layer on the upper surface of the transfer substrate, removing the second bonding layer in the groove through photoetching and a wet method, and carrying out surface activation treatment on the second bonding layer to obtain a second wafer;
s3, pre-bonding the first wafer and the second wafer respectively by taking the first bonding layer and the second bonding layer as contact surfaces, annealing, bonding the first wafer and the second wafer, and transferring the piezoelectric film to form an air gap;
s4, separating the epitaxial substrate of the first wafer from the piezoelectric film;
s5, cleaning the surface of the piezoelectric film, depositing a top electrode on the upper surface of the piezoelectric film, and carrying out imaging processing, wherein the top electrode is opposite to the bottom electrode, and the orthographic projection of the top electrode and the orthographic projection of the bottom electrode are not completely overlapped.
Further, the surfaces of the epitaxial substrate and the transfer substrate are cleaned to make the epitaxial substrate or the transfer substrate pass through the concentrated H2SO4：H2O2：H2Cleaning SPM solution with O1.5: 1.5:4 at 60 deg.C for 10min, and using H2O: rinse with BOE solution of HF 20:1 for 5 min.
Further, the surface of the first bonding layer or the second bonding layer is subjected to activation treatment by using H2O: HF ═ 5:1, treating the surface of the first bonding layer or the second bonding layer by hydrofluoric acid (HF) acid solution, entering the ICP-RIE system to perform surface activation on the first bonding layer or the second bonding layer, and performing surface activation on the first bonding layer or the second bonding layer at 200W of power and N with the concentration of 99.99%2The atmosphere was maintained for 2 minutes.
Further, a radio frequency magnetron sputtering platform is used for growing a first bonding layer or a second bonding layer, the radio frequency magnetron sputtering platform is used, aluminum Al or titanium Ti with the purity of 99.99% is used as a sputtering target material, and sputtering gas Ar (50sccm) with the concentration of 99.99% and reaction gas oxygen O with the concentration of 99.99% are introduced during sputtering2(0.8sccm) and a vacuum degree of 9.9X 10- 4Pa, working pressure of 2.0-4.0 Pa, substrate temperature of 200 ℃ and growth thickness of 400nm of aluminum oxide Al2O3First bonding layer or titanium dioxide TiO with thickness of 400nm2And removing the first bonding layer on the surface of the bottom electrode or the second bonding layer on the surface of the transfer substrate by photoetching and wet etching.
Further, a piezoelectric film is grown through one or more of PVD, MOCVD and PLD; growing a bottom electrode through magnetron sputtering, growing a filling layer through PECVD, and generating a first bonding layer and a second bonding layer through PVD.
Compared with the prior art, the invention has the beneficial effects that:
the invention discloses an air-gap type film bulk acoustic resonator and a preparation method thereof. And bonding is carried out through the bonding layer, so that the introduction of extra parasitic capacitance is avoided, the bonding strength is high, the mechanical stability is good, the response speed of the acoustic wave resonator is improved, the electric leakage risk is reduced, and the method is compatible with the existing MEMS/Si process.
Drawings
FIG. 1 is a schematic structural diagram of an embodiment of the present invention;
FIG. 2 is a cross-sectional view of a first wafer after patterning in accordance with an embodiment of the present invention;
FIG. 3 is a cross-sectional view of a second wafer after patterning in accordance with an embodiment of the present invention;
FIG. 4 is a cross-sectional view of a first wafer bonded to a second wafer in accordance with an embodiment of the present invention;
FIG. 5 is a schematic illustration of epitaxial substrate lift-off in an embodiment provided by the present invention;
in the figure: 101. an epitaxial substrate; 102. a piezoelectric film; 103. filling and leveling the layer; 104. a bottom electrode; 105. a first bonding layer; 106. transferring the substrate; 107. a second bonding layer; 108. a top electrode.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and the detailed description, and it should be noted that any combination of the embodiments or technical features described below can be used to form a new embodiment without conflict.
The invention discloses an air-gap type film bulk acoustic resonator, which is characterized in that a transfer substrate 106, a bonding layer, a bottom electrode 104, a piezoelectric film 102 and a top electrode 108 are sequentially distributed on the resonator from bottom to top; the bonding layer, the bottom electrode 104 and the transfer substrate 106 enclose an air gap structure, the upper surface and the lower surface of the piezoelectric film 102 are respectively connected with the top electrode 108 and the bottom electrode 104 which are opposite, the bottom electrode 104 is located in the air gap structure, the top electrode 108, the piezoelectric film 102 and the bottom electrode 104 form a sandwich structure, and orthographic projections of the top electrode 108 and the bottom electrode 104 are not completely overlapped.
As shown in fig. 1, the top surface of the transfer substrate 106 has a recess, and the bonding layer and a portion of the transfer substrate 106 form a wall of the recess. A filling and leveling layer 103 is further arranged between the bonding layer and the piezoelectric film 102, and the filling and leveling layer 103 is located on the outer side of the bottom electrode 104, has the same thickness as the bottom electrode 104, and is used for filling a gap between the piezoelectric film 102 and the bonding layer. And the bottom electrode 104 is located at the top of the groove, the width of the bottom electrode 104 being the same as the width of the groove.
The bonding layer includes a first bonding layer 105 and a second bonding layer 107, the first bonding layer 105 is disposed on the bottom surface of the leveling layer 103, and the second bonding layer 107 is disposed on the bottom surface of the first bonding layer 105. The first bonding layer 105 adopts titanium dioxide TiO2The second bonding layer 107 is made of alumina Al2O3. In the process of bonding the first bonding layer 105 and the second bonding layer 107, the second bonding layer 107 is made of an insulating material, namely, aluminum oxide (Al)2O3The first bonding layer 105 is made of titanium dioxide TiO with poor conductivity2The bonding temperature is low and the cost is low. Compared with the traditional metal bonding, the method can effectively avoid the introduction of extra parasitic capacitance, has high bonding strength and good mechanical stability, improves the response speed and reduces the electric leakage risk. An air gap structure is formed by the bonding layer, the bottom electrode 104 and the transfer substrate 106 in a surrounding mode, a sacrificial layer is not required to be introduced, and the production and preparation process is simplified.
The main material of the epitaxial substrate 101 is single-crystal high-resistance silicon, the piezoelectric film 102 is made of zinc oxide ZnO, aluminum nitride AlN or piezoelectric ceramic, and the top electrode 108 and the bottom electrode 104 are made of metal materials including one or more of platinum Pt, molybdenum Mo, tungsten W, titanium Ti, aluminum Al, gold Au and silver Ag. In the present embodiment, since the piezoelectric film 102 determines the resonant frequency, and the sound velocity and the temperature coefficient have a large influence on the resonant frequency of the device, the piezoelectric film 102 uses the aluminum nitride AlN, and the resonant frequency is high and the temperature coefficient is low. The electrode material needs to have lower resistivity and density to reduce the electrical loss and mechanical loss of the acoustic wave resonator, respectively, so the top electrode 108 and the bottom electrode 104 use molybdenum Mo as a metal material.
The depth of the groove is 500 nm-3 μm. The depth of an air gap structure formed by the bonding layer, the bottom electrode 104 and the groove is 900 nm-8 μm. The thickness of the top electrode 108 and the bottom electrode 104 may be 50nm to 500nm, and the thickness of the piezoelectric film 102 is 200nm to 3 um. In this embodiment, the thickness of the first bonding layer 105 and the second bonding layer 107 is 400nm, the thickness of the top electrode 108 and the thickness of the bottom electrode 104 are both 300nm, and the thickness of the piezoelectric film 102 is 1.2 μm.
The invention also provides a method for preparing the air gap film bulk acoustic resonator, which comprises the following steps:
s1, selecting a monocrystalline silicon base as the epitaxial substrate 101, and cleaning and thermally oxidizing the surface of the epitaxial substrate; sequentially growing a piezoelectric film 102 and a bottom electrode 104 on the upper surface of the epitaxial substrate 101, wherein the piezoelectric film 102 is exposed out of the bottom electrode 104, and obtaining a pattern of the bottom electrode 104 through photoetching and wet etching; growing a filling-up layer 103 on the upper surface of the bottom electrode 104 and the area of the piezoelectric film 102 exposed on the bottom electrode 104, and removing the filling-up layer 103 on the surface of the bottom electrode 104 by photolithography and wet process; and growing a first bonding layer 105 on the upper surface of the bottom electrode 104 and the upper surface of the filling layer 103, removing the first bonding layer 105 on the surface of the bottom electrode 104 by photolithography and wet process, and performing surface activation treatment on the first bonding layer 105 to obtain a first wafer.
Specifically, as shown in FIG. 2, the epitaxial substrate 101 is cleaned by passing it through a concentrated H2SO4：H2O2：H2Cleaning SPM solution with O1.5: 1.5:4 at 60 deg.C for 10min, and using H2O: and cleaning with BOE solution of HF (20: 1) for 5min to remove organic matters and dirt on the surface of the epitaxial substrate 101. After cleaning, a layer of piezoelectric film 102 is grown on the epitaxial substrate 101 by one or more of PVD, MOCVD and PLD (pulsed mechanical deposition) by using a metal-organic chemical vapor deposition system and a radio frequency magnetron sputtering system, wherein the reaction gas is trimethylaluminum C3H9Al with a volume flow of 50sccm, ammonia NH3The flow rate was 3slm, the flow rate of Ar was 1slm as a carrier gas, the substrate temperature was about 900 deg.C, the total pressure in the reaction chamber was about 40Torr, and 1.2 μm of single crystal aluminum nitride AlN was grown.
Growing a bottom electrode 104 on the upper surface of the piezoelectric film 102, using a radio frequency magnetron sputtering machine, taking molybdenum Mo with the purity of 99.99% as a sputtering target material, introducing high-purity argon gas as a sputtering gas during sputtering, wherein the total working pressure is 3-10 Pa, the target base distance is 60mm, the vacuum degree is 4.0 multiplied by 10 < -4 > Pa, and the substrate temperature is 200 ℃ to grow the molybdenum Mo with the thickness of 300nm, namely the bottom electrode 104. The bottom electrode 104 does not completely cover the piezoelectric film 102, and the outer side of the piezoelectric film 102 is exposed to the bottom electrode 104. After the bottom electrode 104 is patterned, a filling layer 103 is grown on the area of the piezoelectric film 102 exposed to the bottom electrode 104 and the upper surface of the bottom electrode 104 by a Plasma Enhanced Chemical Vapor Deposition (PECVD) method, and the filling layer 103 on the surface of the bottom electrode 104 is removed by photolithography and wet etching. The thickness of the remaining filling-up layer 103 is consistent with that of the bottom electrode 104, and is used for filling up the area of the piezoelectric film 102 exposed on the bottom electrode 104.
After the growth of the fill-and-level layer 103 is completed, a first bonding layer 105 is grown using a radio frequency magnetron sputtering station. Aluminum Al with the purity of 99.99 percent is taken as a sputtering target material, and argon Ar (50sccm) with the concentration of 99.99 percent and reaction gas O with the concentration of 99.99 percent are introduced during sputtering2(0.8sccm) and a vacuum degree of 9.9X 10-4Pa, working pressure of 2.0-4.0 Pa, substrate temperature of 200 ℃ and growth thickness of 400nm of aluminum oxide Al2O3I.e., the first bonding layer 105, and the bonding layer on the surface of the bottom electrode 104 is removed by photolithography and wet etching, leaving the first bonding layer 105 on the planarization layer 103.
The bottom electrode 104 is protected by photoresist, and the first bonding layer 105 is subjected to surface activation treatment using H2O: HF ═ 5:1, and then sending the first bonding layer 105 into an ICP-RIE system (reactive ion etching machine) to carry out surface activation treatment on the first bonding layer 105, wherein nitrogen N with the concentration of 99.99% is adopted under the power of 200W2The atmosphere was maintained for 2 minutes to obtain a first wafer.
S2, selecting monocrystalline silicon as the transfer substrate 106, and cleaning the surface of the transfer substrate; etching a groove on the top surface of the transfer substrate 106, growing a second bonding layer 107 on the upper surface of the transfer substrate 106, removing the second bonding layer 107 in the groove by photolithography and wet method, and performing surface activation treatment on the second bonding layer 107 to obtain a second wafer.
As shown in FIG. 3, high-resistance single-crystal silicon is selected as the transfer substrate 106, and the surface of the transfer substrate 106 is cleaned in the same step as the epitaxial substrate 101, and then is subjected to a concentrated H process2SO4：H2O2：H2SPM solution (SPM solution: Surfuric/Peroxide Mi) with O1.5: 1.5:4 was washed at 60 deg.C for 10min, and then H was used2O: and cleaning with BOE solution of HF (20: 1) for 5min to remove organic matters and dirt on the surface of the epitaxial substrate 101. On the upper surface of the transfer substrate 106, a groove having a depth of 800nm was formed on the transfer substrate 106 by an inductively coupled plasma etcher. Using a radio frequency magnetron sputtering machine, taking titanium Ti with the purity of 99.99 percent as a sputtering target material, and introducing a sputtering gas Ar with the concentration of 99.99 percent (50sccm) and a reaction gas O with the concentration of 99.99 percent during sputtering2(4sccm) and a vacuum degree of 2X 10-6Torr, the working pressure is 0.5-1.5 Pa, and the substrate temperature is 100 ℃ to grow titanium dioxide TiO with the thickness of 400nm2I.e. second bonding layer 107, and the second bonding layer 107 is removed in the recess of the transfer substrate 106 by means of photolithography and wet etching, leaving the second bonding layer 107 on the top surface of the wall of said recess.
The second bonding layer 107 is subjected to a surface activation treatment, i.e. using H2O: HF ═ 5:1, and then sending the second bonding layer 107 into an ICP-RIE system (reactive ion etching machine) to carry out surface activation treatment on the second bonding layer 107, wherein nitrogen N with the concentration of 99.99% is adopted under the power of 200W2The atmosphere was maintained for 2 minutes to obtain a second wafer.
And S3, pre-bonding the first wafer and the second wafer respectively by taking the first bonding layer 105 and the second bonding layer 107 as contact surfaces, annealing, bonding the first wafer and the second wafer, and transferring the piezoelectric film 102 to form an air gap. Using insulating material Al2O3And TiO with poor conductivity2The film transfer is carried out, the bonding temperature is low, the cost is low, and compared with the metal bonding, the method can be used forThe method effectively avoids the introduction of extra parasitic capacitance, has high bonding strength and good mechanical stability, improves the response speed of the FBAR device, reduces electric leakage, and is compatible with the existing MEMS/Si process.
As shown in fig. 4, in the bonding process, pressure is applied from the center of the transfer substrate 106 of the second wafer and gradually expands towards the edge, after the bonding pressure reaches 2MPa, bonding is performed for 2h at 300 ℃, annealing is performed, the bonding is performed after the bonding is taken out, the bonding is performed in an annealing furnace at 200 ℃ for 30min, firm bonding is formed between the pre-bonded wafers, the piezoelectric film 102 is transferred, and an air gap structure is formed. The depth of an air gap structure formed by the bonding layer, the bottom electrode 104 and the groove is 900 nm-8 μm.
S4, separating the epitaxial substrate 101 of the first wafer from the piezoelectric film 102; as shown in fig. 5, the epitaxial substrate 101 is separated from the piezoelectric film 102 by mechanical thinning, chemical polishing, and chemical etching, and the volume ratio is 5:1, mixing 30 mass percent of KOH potassium hydroxide and IPA indole propionic acid to prepare a corrosive liquid, and corroding the piezoelectric film 102 at 80 ℃ until the piezoelectric film stops, as shown in figure 4;
s5, cleaning the surface of the piezoelectric film 102, depositing a top electrode 108 on the surface of the piezoelectric film 102, and performing an imaging process, where the top electrode 108 is opposite to the bottom electrode 104, and the orthographic projections of the top electrode 108 and the bottom electrode 104 are not completely overlapped, and the top electrode 108, the piezoelectric film 102, and the bottom electrode 104 form a sandwich structure, such as the structure shown in fig. 1.
The preparation method provided by the invention is used for preparing the aluminum oxide Al of the first bonding layer 1052O3Titanium dioxide, TiO, of the second bonding layer 1072After surface active treatment, the surface of the material has higher surface energy, and Al is used for the treatment2O3-TiO2The film transfer is realized by bonding, a high-quality piezoelectric film 102 of single crystal aluminum nitride AlN is extended on an extension substrate 101, a metal electrode is deposited on the piezoelectric film 102 of single crystal aluminum nitride AlN and is patterned, a cavity is formed under the piezoelectric film 102 of single crystal aluminum nitride AlN by a transfer substrate 106, finally the pattern of the piezoelectric film 102 of aluminum nitride AlN is modified and is patterned after the metal is deposited, and a sandwich composite structure of the electrode-the piezoelectric film 102-the electrode is formedThe cavity is formed by bonding, a sacrificial layer is not required to be introduced, and the high-quality single-crystal AlN piezoelectric film 102 can be applied to the FBAR, so that the preparation process is greatly simplified.
The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.
Claims (10)
1. An air gap type film bulk acoustic resonator is characterized in that a transfer substrate, a bonding layer, a bottom electrode, a piezoelectric film and a top electrode are sequentially distributed on the resonator from bottom to top; the bonding layer, the bottom electrode and the transfer substrate are enclosed to form an air gap structure, the upper surface and the lower surface of the piezoelectric film are respectively connected with a top electrode and a bottom electrode which are opposite, the bottom electrode is positioned in the air gap structure, the top electrode, the piezoelectric film and the bottom electrode form a sandwich structure, and the orthographic projections of the top electrode and the bottom electrode are not completely overlapped; and a filling and leveling layer is also arranged between the bonding layer and the piezoelectric film, is positioned at the outer side of the bottom electrode and has the same thickness as the bottom electrode.
2. The air gap type thin film bulk acoustic resonator according to claim 1, wherein the top surface of the transfer substrate has a recess, the bonding layer and a portion of the transfer substrate form a recess wall, the filling layer is located on the upper surface of the recess wall, and the recess, the bonding layer and the bottom electrode form an air gap structure.
3. The air gap type thin film bulk acoustic resonator according to claim 2, wherein the bonding layer comprises a first bonding layer and a second bonding layer, the first bonding layer is disposed on the bottom surface of the filling layer, and the second bonding layer is disposed on the bottom surface of the first bonding layer; the first bonding layer adopts titanium dioxide TiO2The second bonding layer adopts aluminum oxide Al2O3。
4. The air gap type thin film bulk acoustic resonator according to claim 1, wherein the transfer substrate is single crystal silicon, and the piezoelectric thin film is one or more of piezoelectric ceramic, aluminum nitride AlN, and zinc oxide ZnO; the bottom electrode and the top electrode are made of metal materials, and the metal materials comprise one or more of platinum Pt, molybdenum Mo, tungsten W, titanium Ti, aluminum Al, gold Au and silver Ag.
5. The air gap type thin film bulk acoustic resonator according to claim 2, wherein the depth of the groove is 500nm to 3 μm; the depth of an air gap structure formed by the bonding layer, the bottom electrode and the groove is 900 nm-8 mu m; the thickness of the bonding layer is 400 nm-5 μm; the thickness of the piezoelectric film is 200 nm-3 mu m; the thickness of the top electrode and the bottom electrode is 50 nm-500 nm.
6. A preparation method of an air-gap film bulk acoustic resonator is characterized in that the preparation method of the air-gap film bulk acoustic resonator according to any one of claims 1 to 5 comprises the following steps:
s1, selecting a monocrystalline silicon base as an epitaxial substrate, and cleaning and thermally oxidizing the surface of the epitaxial substrate; sequentially growing a piezoelectric film and a bottom electrode on the upper surface of the epitaxial substrate, wherein the piezoelectric film is exposed out of the bottom electrode, and obtaining a pattern of the bottom electrode through photoetching and wet etching; growing a filling and leveling layer on the upper surface of the bottom electrode and the area of the piezoelectric film exposed on the bottom electrode, and removing the filling and leveling layer on the surface of the bottom electrode by photoetching and wet method; growing a first bonding layer on the upper surface of the bottom electrode and the upper surface of the filling layer, removing the first bonding layer on the surface of the bottom electrode through photoetching and a wet method, and carrying out surface activation treatment on the first bonding layer to obtain a first wafer;
s2, selecting monocrystalline silicon as a transfer substrate, and cleaning the surface of the transfer substrate; etching a groove on the top surface of the transfer substrate, growing a second bonding layer on the upper surface of the transfer substrate, removing the second bonding layer in the groove through photoetching and a wet method, and carrying out surface activation treatment on the second bonding layer to obtain a second wafer;
s3, pre-bonding the first wafer and the second wafer respectively by taking the first bonding layer and the second bonding layer as contact surfaces, annealing, bonding the first wafer and the second wafer, and transferring the piezoelectric film to form an air gap;
s4, separating the epitaxial substrate of the first wafer from the piezoelectric film;
s5, cleaning the surface of the piezoelectric film, depositing a top electrode on the upper surface of the piezoelectric film, and carrying out imaging processing, wherein the top electrode is opposite to the bottom electrode, and the orthographic projection of the top electrode and the orthographic projection of the bottom electrode are not completely overlapped.
7. The method of claim 6, wherein the cleaning of the surfaces of the epitaxial substrate and the transfer substrate is performed by passing the epitaxial substrate or the transfer substrate through concentrated H2SO4：H2O2：H2Cleaning SPM solution with O1.5: 1.5:4 at 60 deg.C for 10min, and using H2O: rinse with BOE solution of HF 20:1 for 5 min.
8. The method for manufacturing an air-gap film bulk acoustic resonator according to claim 6, wherein the surface of the first bonding layer or the second bonding layer is activated by using H2O: HF ═ 5:1, treating the surface of the first bonding layer or the second bonding layer by hydrofluoric acid (HF) acid solution, entering the first bonding layer or the second bonding layer in an Inductively Coupled Plasma (ICP) -Reactive Ion Etching (RIE) system for surface activation, and performing surface activation on the first bonding layer or the second bonding layer by nitrogen (N) with the power of 200W and the concentration of 99.99 percent2The atmosphere was maintained for 2 minutes.
9. The method for manufacturing an air-gap thin film bulk acoustic resonator according to claim 6, wherein a radio frequency magnetron sputtering station is used to grow the first bonding layer or the second bonding layer, the radio frequency magnetron sputtering station is used, aluminum Al or titanium Ti with a purity of 99.99% is used as a sputtering target, and argon Ar (50sccm) as a sputtering gas with a concentration of 99.99% and oxygen as a reaction gas with a concentration of 99.99% are introduced during sputteringGas O2(0.8sccm) and a vacuum degree of 9.9X 10-4Pa, working pressure of 2.0-4.0 Pa, substrate temperature of 200 ℃ and growth thickness of 400nm of aluminum oxide Al2O3First bonding layer or titanium dioxide TiO with thickness of 400nm2And removing the first bonding layer on the surface of the bottom electrode or the second bonding layer on the surface of the transfer substrate by photoetching and wet etching.
10. The method of manufacturing an air-gap thin film bulk acoustic resonator according to claim 6, wherein the piezoelectric thin film is grown by one or more of PVD, MOCVD, PLD; growing a bottom electrode through magnetron sputtering, growing a filling layer through PECVD, and generating a first bonding layer and a second bonding layer through PVD.
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| CN113285688A (en) * | 2021-05-14 | 2021-08-20 | 中国科学技术大学 | Bonding type high-resistivity silicon substrate with groove, piezoelectric resonator and preparation method thereof |
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| CN111786647A (en) * | 2020-08-07 | 2020-10-16 | 展讯通信（上海）有限公司 | Wafer-level surface acoustic wave filter and packaging method |
| TWI797704B (en) * | 2020-08-07 | 2023-04-01 | 大陸商展訊通信（上海）有限公司 | Wafer level surface acoustic wave filter and package method |
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| CN113285688A (en) * | 2021-05-14 | 2021-08-20 | 中国科学技术大学 | Bonding type high-resistivity silicon substrate with groove, piezoelectric resonator and preparation method thereof |
| CN114221631A (en) * | 2021-12-21 | 2022-03-22 | 武汉敏声新技术有限公司 | Resonator, preparation method thereof and filter |
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