Bulk acoustic wave filter and preparation method thereof

Abstract

The invention discloses a bulk acoustic wave filter and a preparation method thereof.The bulk acoustic wave filter comprises a substrate, a Bragg reflection layer used for reflecting acoustic waves, a bottom electrode, a piezoelectric layer and a top electrode, the substrate is provided with a groove, the Bragg reflection layer is arranged on the substrate in a stacked mode and covers a groove opening of the groove, the bottom electrode is arranged on the Bragg reflection layer, and the piezoelectric layer is arranged on the bottom electrode. The bottom electrode is arranged on the side, away from the substrate, of the Bragg reflection layer in a stacked mode, at least part of the bottom electrode is opposite to a groove opening of the groove, and the piezoelectric layer is arranged on the side, away from the Bragg reflection layer, of the bottom electrode in a stacked mode. The top electrode is arranged on the side, away from the bottom electrode, of the piezoelectric layer in a stacked mode. According to the scheme, the problem that a bulk acoustic wave filter in the related technology cannot well consider the miniaturization design and the filtering performance improvement of the bulk acoustic wave filter can be solved.

Description

Technical Field

[0001] This invention relates to the field of filter technology, and in particular to a bulk acoustic wave filter and its fabrication method. Background Technology

[0002] Filters are important devices in modern communications used to extract or block signals in specific frequency bands and improve the signal-to-noise ratio. They are typically implemented using resonant circuits. With the advent of the 5G era, bulk acoustic wave (BAW) filters are widely used due to their advantages, such as higher operating frequencies and smaller size as frequency increases.

[0003] In related technologies, bulk acoustic wave (SAW) filters are employed based on the principle of Bragg reflectors to reflect bulk acoustic waves. These filters utilize metal layers on opposite sides of a piezoelectric thin film layer. A Bragg reflector is formed on one side of this metal layer by stacking thin layers of different materials, thus reflecting the sound waves back and forth within the piezoelectric thin film layer to create oscillations. However, given the chosen material for the Bragg reflector, its reflectivity is primarily determined by the number of layers. A higher number of layers hinders miniaturization and increases manufacturing costs, while a lower number of layers limits reflectivity and reduces filtering performance. Therefore, related technologies for bulk acoustic wave filters suffer from the inability to effectively balance miniaturization and improved filtering performance. Summary of the Invention

[0004] This invention discloses a bulk acoustic wave filter and its fabrication method, in order to solve the problem that bulk acoustic wave filters in related technologies cannot effectively balance miniaturization design and improved filtering performance.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0006] In a first aspect, this application discloses a bulk acoustic wave filter, which includes a substrate, a Bragg reflector layer for reflecting sound waves, a bottom electrode, a piezoelectric layer, and a top electrode, wherein:

[0007] The substrate has a groove, the Bragg reflective layer is stacked on the substrate and covers the groove opening, the bottom electrode is stacked on the side of the Bragg reflective layer away from the substrate, and at least a portion of the bottom electrode is opposite to the groove opening, the piezoelectric layer is stacked on the side of the bottom electrode away from the Bragg reflective layer, and the top electrode is stacked on the side of the piezoelectric layer away from the bottom electrode.

[0008] Secondly, this application also discloses a method for fabricating a bulk acoustic wave filter, wherein the bulk acoustic wave filter is the bulk acoustic wave filter described in the first aspect, and the disclosed fabrication method includes:

[0009] The groove is etched onto the substrate;

[0010] The Bragg reflective layer is stacked on the substrate, and the Bragg reflective layer covers the groove opening;

[0011] The bottom electrode is stacked on the side of the Bragg reflector layer away from the substrate, and at least a portion of the bottom electrode is opposite to the groove opening of the groove.

[0012] The piezoelectric layer is stacked and disposed on the side of the bottom electrode opposite to the Bragg reflector layer;

[0013] The top electrode is stacked on the side of the piezoelectric layer opposite to the bottom electrode.

[0014] The technical solution adopted in this invention can achieve the following technical effects:

[0015] The bulk acoustic wave filter disclosed in this application has a groove formed on the substrate, and a Bragg reflector layer is placed over the groove opening, creating a cavity between the Bragg reflector layer and the inner wall of the groove. When an alternating current is input to the bottom and top electrodes to excite the piezoelectric layer to generate sound waves, part of the sound waves are reflected by the Bragg reflector layer and return to the space between the bottom and top electrodes, while the remaining sound waves are reflected at the interface between the Bragg reflector layer and the air in the cavity and return to the space between the bottom and top electrodes. This creates a standing wave oscillation between the bottom and top electrodes, thereby achieving piezoelectric conversion. Since the reflection of sound waves at the interface between the Bragg reflector layer and the air in the cavity is stronger than the reflection capability of the Bragg reflector layer itself, this method further enhances the sound wave reflection capability of the bulk acoustic wave filter compared to related technologies that only use a Bragg reflector layer, thus improving the filtering performance of the bulk acoustic wave filter. Moreover, since the reflection of sound waves at the interface between the Bragg reflector and the air in the cavity is stronger than that of the Bragg reflector itself, the Bragg reflector does not need to have many material layers, which is conducive to the design of a thinner Bragg reflector and thus to the miniaturization of the bulk acoustic wave filter. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the bulk acoustic wave filter disclosed in an embodiment of the present invention;

[0017] Figure 2 This is a flowchart illustrating the fabrication process of a bulk acoustic wave filter according to an embodiment of the present invention;

[0018] Figure 3 This is a flowchart illustrating the fabrication process of another bulk acoustic wave filter disclosed in an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of the lanthanum nickelate layer and the lead zirconate titanate piezoelectric ceramic layer prepared by the preparation method disclosed in the embodiments of this application;

[0020] Figure 5 and Figure 6 This is a schematic diagram of a piezoelectric layer prepared using related techniques (not the preparation method disclosed in the embodiments of this application).

[0021] Explanation of reference numerals in the attached figures:

[0022] 100 - base, 101 - groove

[0023] 200-Bragg reflector layer, 210-tungsten layer, 220-silicon oxide layer,

[0024] 300-bottom electrode,

[0025] 400-Piezoelectric layer, 410-Lead zirconate titanate piezoelectric ceramic layer, 420-Lanium nickelate layer,

[0026] 500-top electrode,

[0027] 600 - First epitaxial electrode

[0028] 700 - Second epitaxial electrode

[0029] 810 - First substrate, 820 - First adhesive layer, 830 - Second adhesive layer, 840 - Third adhesive layer, 850 - Fourth adhesive layer. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] The technical solutions disclosed in the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] Please refer to Figure 1 This invention discloses a bulk acoustic wave filter, which includes a substrate 100, a Bragg reflector layer 200 for reflecting sound waves, a bottom electrode 300, a piezoelectric layer 400, and a top electrode 500.

[0033] A groove 101 is formed in the substrate 100. A Bragg reflector layer 200 is stacked on the substrate 100 and covers the groove opening of the groove 101. A bottom electrode 300 is stacked on the side of the Bragg reflector layer 200 away from the substrate 100, and at least a portion of the bottom electrode 300 is opposite to the groove opening of the groove 101. A piezoelectric layer 400 is stacked on the side of the bottom electrode 300 away from the Bragg reflector layer 200. A top electrode 500 is stacked on the side of the piezoelectric layer 400 away from the bottom electrode 300.

[0034] The bulk acoustic wave filter disclosed in this application has a groove 101 formed on the substrate, and a Bragg reflector layer 200 is placed over the groove 101. This creates a cavity between the Bragg reflector layer 200 and the inner wall of the groove 101. When an alternating current is input to the bottom electrode 300 and the top electrode 500 to excite the piezoelectric layer 400 to generate sound waves, part of the sound waves are reflected by the Bragg reflector layer 200 and return to the space between the bottom electrode 300 and the top electrode 500. The remaining part of the sound waves are reflected at the interface between the Bragg reflector layer 200 and the air in the cavity and return to the space between the bottom electrode 300 and the top electrode 500. As a result, a standing wave oscillation is formed between the bottom electrode 300 and the top electrode 500, thereby achieving piezoelectric conversion. Because the interface between the Bragg reflector layer 200 and the air inside the cavity has a stronger reflection capability for sound waves than the Bragg reflector layer 200 itself, the reflection capability of the bulk acoustic wave filter can be further improved compared to related technologies that only use the Bragg reflector layer 200, thereby enhancing the filtering performance of the bulk acoustic wave filter. Furthermore, since the interface between the Bragg reflector layer 200 and the air inside the cavity has a stronger reflection capability for sound waves than the Bragg reflector layer 200 itself, the Bragg reflector layer 200 does not need to have a large number of material layers, which facilitates a thinner and lighter design of the Bragg reflector layer 200, and consequently, a smaller design for the bulk acoustic wave filter.

[0035] Specifically, the substrate 100 can be made of sapphire, silicon carbide, silicon, etc., and this application embodiment does not impose specific restrictions on the material of the substrate 100. The bottom electrode 300 and the top electrode 500 can be made of metal materials such as molybdenum, platinum, tungsten, aluminum, etc., and this application embodiment does not impose specific restrictions on the materials of the bottom electrode 300 and the top electrode 500.

[0036] In one optional embodiment, the Bragg reflector layer 200 may include stacked tungsten layers 210 and silicon oxide layers 220. Both tungsten layers 210 and silicon oxide layers 220 can be multiple layers, and the multiple tungsten layers 210 and multiple silicon oxide layers 220 are alternately distributed. The two outermost layers of the Bragg reflector layer 200 can both be silicon oxide layers 220; the two outermost layers refer to the top and bottom layers of the Bragg reflector layer 200. The bulk acoustic filter disclosed in this application, by setting the Bragg reflector layer 200 to a structure with alternating multiple tungsten layers 210 and multiple silicon oxide layers 220, allows the alternating distribution of silicon oxide layers 220 with low acoustic impedance and tungsten layers with high acoustic impedance, thereby inducing strong capacitive coupling generated by the structure formed by the conductor and dielectric, which in turn enhances the reflection capability of the Bragg reflector layer 200 of sound waves.

[0037] Of course, the Bragg reflector layer 200 can also be formed by alternating distribution of molybdenum layer and silicon oxide layer 220, or by alternating distribution of other metals and silicon oxide layer 220. The embodiments of this application do not impose specific restrictions on the type of Bragg reflector layer 200.

[0038] It should be noted that, while meeting the strength requirements, the tungsten layer 210 can be a single layer and the silicon oxide layer 220 can be two layers, which helps to further reduce the thickness of the Bragg reflector layer 200. Moreover, with fewer layers of tungsten layer 210 and silicon oxide layer 220, the cavity formed by the Bragg reflector layer 200 and the inner wall of the groove 101 is closer to the bottom electrode 300, thus preventing sound waves from reaching the interface between the Bragg reflector layer 200 and the air in the cavity, which would result in significant sound wave attenuation. Since the sound wave reflection at the interface between the Bragg reflector layer 200 and the air in the cavity is stronger than that of the Bragg reflector layer 200, the sound wave reflection capability of the bulk acoustic wave filter can be improved.

[0039] Optionally, the piezoelectric layer 400 may include a lead zirconate titanate piezoelectric ceramic layer 410 or a scandium-doped aluminum nitride layer. Lead zirconate titanate piezoelectric ceramic materials or scandium-doped aluminum nitride materials have high piezoelectric coefficients and high structural strength, and relatively low thermal conductivity. Therefore, when the piezoelectric layer 400 is configured to include a lead zirconate titanate piezoelectric ceramic layer 410 or a scandium-doped aluminum nitride layer, the piezoelectric coefficient and structural strength of the piezoelectric layer 400 can be improved, while the thermal conductivity of the piezoelectric layer 400 can be reduced.

[0040] Of course, the material of the piezoelectric layer 400 can also be cadmium sulfide, zinc sulfide, zinc oxide, aluminum nitride, etc. This application embodiment does not impose specific restrictions on the material of the piezoelectric layer 400.

[0041] Optionally, when the piezoelectric layer 400 includes a lead zirconate titanate piezoelectric ceramic layer 410, the piezoelectric layer 400 may further include a lanthanum nickelate layer 420, which may be disposed between the lead zirconate titanate piezoelectric ceramic layer 410 and the bottom electrode 300. Disposing of the lanthanum nickelate layer 420 between the lead zirconate titanate piezoelectric ceramic layer 410 and the bottom electrode 300 helps to improve the cycle characteristics of the bulk acoustic wave filter and extend its service life.

[0042] In one optional embodiment, the bulk acoustic wave filter may further include a first epitaxial electrode 600 and a second epitaxial electrode 700, wherein the first epitaxial electrode 600 may be electrically connected to the bottom electrode 300 and the second epitaxial electrode 700 may be electrically connected to the top electrode 500.

[0043] The bulk acoustic wave filter disclosed in this application provides a first epitaxial electrode 600 and a second epitaxial electrode 700, such that the first epitaxial electrode 600 is electrically connected to the bottom electrode 300 and the second epitaxial electrode 700 is electrically connected to the top electrode 500, thereby facilitating the electrical connection of external devices of the bulk acoustic wave filter.

[0044] Please refer to Figure 3 This application also discloses a method for fabricating a bulk acoustic wave filter. The disclosed bulk acoustic wave filter is the bulk acoustic wave filter disclosed in the above embodiments. The disclosed fabrication method includes:

[0045] S101, a groove 101 is etched on the substrate 100.

[0046] Specifically, before etching the groove 101 on the substrate 100, the substrate 100 needs to be cleaned. The RCA standard cleaning method is usually used, which involves mixing 98% concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 7:3, placing the mixture into the substrate 100, and heating it to 110 degrees Celsius until the bubbles disappear (at least 30 minutes). The substrate 100 is then removed and cleaned with ultrapure water.

[0047] After cleaning the substrate 100, a first adhesive layer 820 is spin-coated onto the surface of the substrate 100 where the etched grooves 101 are to be formed. The thickness of the first adhesive layer 820 can be 0.5–10 micrometers, preferably 3 micrometers. The first adhesive layer 820 is then patterned by exposure and development. The exposure time can be between 3 and 20 seconds, preferably 6 seconds; the development time can be between 45 and 120 seconds, preferably 75 seconds; and the fixing time can be between 60 and 300 seconds, preferably 120 seconds.

[0048] After patterning the first adhesive layer 820, the substrate 100 is etched to form the groove 101.

[0049] After etching the groove 101, the first adhesive layer 820 is removed. Specifically, a wet removal method (e.g., using an organic solvent, such as acetone) can be used. The soaking time is not limited, but should end when most of the first adhesive layer 820 has detached from the surface of the substrate 100. Then, rinse with a flowing organic solvent until the first adhesive layer 820 is completely detached from the surface of the substrate 100, removing the first adhesive layer 820 and any remaining etching byproducts. Of course, a dry removal method can also be used to remove the first adhesive layer 820. This application embodiment does not impose specific limitations on the method for removing the first adhesive layer 820.

[0050] S102, the Bragg reflective layer 200 is stacked on the substrate 100, and the Bragg reflective layer 200 covers the groove of the groove 101.

[0051] S103, the bottom electrode 300 is stacked on the side of the Bragg reflector layer 200 away from the substrate 100, and at least a portion of the bottom electrode 300 is opposite to the groove opening of the groove 101.

[0052] Specifically, when preparing the bottom electrode 300, the bottom electrode 300 can be deposited on the side of the Bragg reflector layer 200 away from the substrate 100 by physical vapor deposition. The material of the bottom electrode 300 can be a metal such as molybdenum, platinum, tungsten, or aluminum. The thickness of the bottom electrode 300 can be between 0.05 and 0.2 micrometers, preferably 0.1 micrometers. When the bottom electrode 300 is deposited in the reaction chamber, the process conditions can be that the pressure in the reaction chamber is between 10 and 100 mTorr, the power of the upper electrode is between 750 and 3000 W, the power of the lower electrode is between 5 and 500 W, and the argon flow rate is between 50 and 500 sccm.

[0053] After the bottom electrode 300 is deposited, a second adhesive layer 830 needs to be spin-coated on the side of the bottom electrode 300 facing away from the Bragg reflector layer 200. The second adhesive layer 830 is then patterned through exposure and development. The exposure and development conditions for the second adhesive layer 830 can refer to those for the first adhesive layer 820. After patterning the second adhesive layer 830, the bottom electrode 300 is etched. The etching process for the bottom electrode 300 can use chlorine-based gases, such as chlorine and boron trichloride. The upper electrode power range can be between 100 and 10000 W, the lower electrode power range can be between 0 and 1000 W, the argon flow rate range can be between 1 and 1000 sccm, the chlorine flow rate range can be between 1 and 1000 sccm, and the boron trichloride flow rate range can be between 1 and 1000 sccm.

[0054] After etching the bottom electrode 300, the second adhesive layer 830 is removed. The method for removing the second adhesive layer 830 can refer to the method for removing the first adhesive layer 820.

[0055] S104, the piezoelectric layer 400 is stacked and disposed on the side of the bottom electrode 300 away from the Bragg reflector layer 200.

[0056] S105, the top electrode 500 is stacked on the side of the piezoelectric layer 400 away from the bottom electrode 300.

[0057] Specifically, when preparing the top electrode 500, the top electrode 500 can be deposited on the side of the piezoelectric layer 400 away from the substrate 100 by physical vapor deposition. The material of the top electrode 500 can be a metal such as molybdenum, platinum, tungsten, or aluminum. The thickness of the top electrode 500 can be between 0.05 and 0.2 micrometers, preferably 0.1 micrometers. When depositing the bottom and top electrodes 500 in the reaction chamber, the process conditions can be that the pressure in the reaction chamber is between 10 and 100 mTorr, the power of the upper electrode is between 750 and 3000 W, the power of the lower electrode is between 5 and 500 W, and the argon flow rate is between 50 and 500 sccm.

[0058] After the top electrode 500 is deposited, a third adhesive layer 840 needs to be spin-coated on the side of the top electrode 500 away from the piezoelectric layer 400. Then, the third adhesive layer 840 is patterned by exposure and development. The exposure and development conditions for the third adhesive layer 840 can refer to the exposure and development conditions for the first adhesive layer 820.

[0059] After patterning the third adhesive layer 840, the top electrode 500 is etched. The etching process formulation for the top electrode 500 can be a mixture of chlorine-based gas and fluorine-based gas. Adding fluorine-based gas can improve the selectivity of etching the piezoelectric layer 400 below the top electrode 500. The power range of the upper electrode can be between 100 and 10000 W, the power range of the lower electrode can be between 0 and 1000 W, the flow rate of argon can be between 1 and 1000 sccm, the flow rate of sulfur hexafluoride can be between 1 and 1000 sccm, the flow rate of chlorine can be between 1 and 1000 sccm, and the flow rate of boron trichloride can be between 1 and 1000 sccm.

[0060] The bulk acoustic wave filter fabrication method disclosed in this application involves etching a groove 101 on a substrate 100, stacking a Bragg reflector layer 200 on the substrate 100 such that the Bragg reflector layer 200 covers the opening of the groove 101, stacking a bottom electrode 300 on the side of the Bragg reflector layer 200 away from the substrate 100 such that at least a portion of the bottom electrode 300 faces the opening of the groove 101, stacking a piezoelectric layer 400 on the side of the bottom electrode 300 away from the Bragg reflector layer 200, and stacking a top electrode 500 on the side of the piezoelectric layer 400 away from the bottom electrode 300. The bulk acoustic wave filter fabricated on one side creates a cavity between the Bragg reflector layer 200 and the inner wall of the groove 101. When an alternating current is input to the bottom electrode 300 and the top electrode 500 to excite the piezoelectric layer 400 to generate sound waves, part of the sound waves are reflected back between the bottom electrode 300 and the top electrode 500 by the Bragg reflector layer 200, while another part is reflected back between the bottom electrode 300 and the top electrode 500 at the interface between the Bragg reflector layer 200 and the air in the cavity. This creates a standing wave oscillation between the bottom electrode 300 and the top electrode 500, thus achieving piezoelectric conversion. Since the reflection of sound waves at the interface between the Bragg reflector layer 200 and the air in the cavity is stronger than the reflection capability of the Bragg reflector layer 200 itself, this method further enhances the sound wave reflection capability of the bulk acoustic wave filter compared to related technologies that only use the Bragg reflector layer 200, thereby improving the filtering performance of the bulk acoustic wave filter. Moreover, since the reflection of sound waves at the interface between the Bragg reflector layer 200 and the air in the cavity is stronger than that of the Bragg reflector layer 200, the Bragg reflector layer 200 does not need to have a large number of material layers, which is conducive to the thinner and lighter design of the Bragg reflector layer 200, and thus conducive to the miniaturization design of the bulk acoustic wave filter.

[0061] Optionally, before depositing the Bragg reflector layer 200 onto the substrate 100, the fabrication method may further include:

[0062] Step A1: A Bragg reflector layer 200 is grown on the first substrate 810 by thermal oxidation, chemical vapor deposition, or physical vapor deposition.

[0063] The Bragg reflector layer 200 is stacked on the substrate 100, and the Bragg reflector layer 200 covers the groove opening of the recess, including:

[0064] Step A2: Bond the side of the Bragg reflector layer 200 away from the first substrate 810 to the substrate 100.

[0065] Step A3: Remove the first substrate 810 by polishing.

[0066] The preparation method disclosed in this application involves growing the Bragg reflective layer 200 on the first substrate 810 using a thermal oxidation process, a chemical vapor deposition process, or a physical vapor deposition process before stacking the Bragg reflective layer 200 on the substrate 100. Then, the side of the Bragg reflective layer 200 facing away from the first substrate 810 is bonded to the substrate 100. Finally, the first substrate 810 is removed by polishing. This method avoids filling the groove 101 with a sacrificial layer compared to directly preparing the Bragg reflective layer 200 on the substrate 100 using a thermal oxidation process, a chemical vapor deposition process, or a physical vapor deposition process. Since the process of removing the sacrificial layer is relatively complex, this application embodiment simplifies the process flow by growing the Bragg reflective layer 200 on the first substrate 810 and then bonding it to the substrate 100.

[0067] Optionally, in the preparation method disclosed in the embodiments of this application, a Bragg reflective layer 200 is grown on the first substrate 810 by a thermal oxidation process, a chemical vapor deposition process, or a physical vapor deposition process, including:

[0068] Step B1: A tungsten layer 210 and a silicon oxide layer 220 are alternately grown on the first substrate 810 by thermal oxidation, chemical vapor deposition, or physical vapor deposition to form a Bragg reflector layer 200, wherein the two outermost layers of the Bragg reflector layer 200 are silicon oxide layers 220.

[0069] It should be noted that during the alternating growth of tungsten layer 210 and silicon oxide layer 220 on the first substrate 810, the thickness of each tungsten layer 210 and silicon oxide layer 220 is one-quarter of the wavelength of the sound wave to be reflected. There can be 1-4 tungsten layers 210, and the silicon oxide layer 220 is always one more layer than the tungsten layer 210. Preferably, there are 3 tungsten layers 210 and 4 silicon oxide layers 220. The first substrate 810 can be made of materials such as silicon or organic substrates.

[0070] In an optional embodiment, after the top electrode 500 is stacked on the piezoelectric layer 400, the disclosed fabrication method may further include:

[0071] Step C1 involves etching the piezoelectric layer 400. During the etching process, the upper electrode power ranges from 100W to 10000W, the lower electrode power ranges from 0 to 1000W, the argon flow rate ranges from 1 to 1000 sccm, the hydrogen flow rate ranges from 1 to 1000 sccm, the chlorine flow rate ranges from 1 to 1000 sccm, and the boron trichloride flow rate ranges from 1 to 1000 sccm. Specific preferred process parameters can be found in the etching steps in Table 1.

[0072] The specific etching process time can vary depending on the thickness of the etching.

[0073] Step C2: After etching the piezoelectric layer 400, turn off the lower electrode power, shut off all gas inlets, and perform a vacuum operation. Specific preferred process parameters can be found in step 1 of Table 1.

[0074] Table 1 Plasma Etching Process Formulation

[0075]

[0076] The preparation method disclosed in this application involves turning off the lower electrode power and all gas inlets after etching the piezoelectric layer 400, and performing a vacuum operation. This allows the byproducts to evaporate quickly under the vacuum, thereby reducing the deposition of byproducts during etching.

[0077] Optionally, after the vacuuming operation is completed, the disclosed preparation method may further include:

[0078] Step D1: Open the cooling gas supply channel to cool the substrate 100, Bragg reflector layer 200, bottom electrode 300, piezoelectric layer 400 and top electrode 500.

[0079] The preparation method disclosed in this application involves opening a cooling gas supply channel after the vacuuming operation is completed. This channel allows argon gas to be introduced, carrying away heat and cooling the substrate 100, Bragg reflector layer 200, bottom electrode 300, piezoelectric layer 400, and top electrode 500, thus ensuring the uniformity of subsequent etching. Preferred process parameters are detailed in step 2 of Table 1.

[0080] In an optional embodiment, after cooling the substrate 100, Bragg reflector layer 200, bottom electrode 300, piezoelectric layer 400, and top electrode 500, the disclosed fabrication method may further include:

[0081] Step E1 involves etching the byproducts generated during the etching of the piezoelectric layer 400.

[0082] Specifically, the byproducts are further etched in the etching step, which can have a selectivity for the bottom electrode 300 material and reduce damage to the bottom electrode 300.

[0083] The preparation method disclosed in this application can alleviate the problem of severe byproduct accumulation during the etching of the piezoelectric layer 400 by etching the byproducts generated during the etching process.

[0084] Optionally, when the piezoelectric layer 400 includes a lead zirconate titanate piezoelectric ceramic layer 410 and a lanthanum nickelate layer 420, in the preparation method disclosed in the embodiments of this application, the piezoelectric layer 400 is stacked and disposed on the bottom electrode 300, including:

[0085] Step F1: Spin-coat a lanthanum nickelate layer 420 onto the bottom electrode 300.

[0086] Step F2: Spin-coat lead zirconate titanate piezoelectric ceramic layer 410 onto lanthanum nickelate layer 420.

[0087] The piezoelectric layer 400 includes a lanthanum nickelate layer 420 and a lead zirconate titanate piezoelectric ceramic layer 410.

[0088] The preparation method disclosed in this application improves the cycle characteristics of the bulk acoustic wave filter and extends its service life by setting a lanthanum nickelate layer 420 between the lead zirconate titanate piezoelectric ceramic layer 410 and the bottom electrode 300.

[0089] It should be noted that the piezoelectric layer 400 can be prepared using the sol-gel method. First, the lanthanum nickelate layer 420 is prepared using lanthanum nitrate and nickel acetate as precursors. These precursors are dissolved in organic solvents such as ethanol and then spin-coated onto the bottom electrode 300 prepared in the previous step. The layer is heated at 150°C for ten minutes to remove residual organic matter, then at 350°C for ten minutes, and finally at 750°C for five minutes. Finally, it is rapidly annealed in an oxygen atmosphere to fully remove organic matter and prevent the formation of oxides. Next, the lead zirconate titanate piezoelectric ceramic layer 410 is prepared using isopropyl titanate, zirconium n-propoxide, and lead acetate as precursors (making the volume ratio Zr:Ti = 53:47). These precursors are dissolved in organic solvents such as ethanol (concentration 0.6 mol / L). -1 Spin-coating onto lanthanum nickelate layer 420, heating at 110°C for 10 minutes to remove residual organic matter, heating at 420°C for 10 minutes, heating at 600°C for 5 minutes, and then rapid thermal annealing to fully remove organic matter and generate oxides.

[0090] It should be noted that the specific effects of the lanthanum nickelate layer 420 and the lead zirconate titanate piezoelectric ceramic layer 410 prepared by the preparation method disclosed in the embodiments of this application can be referred to Figure 4 However, when preparing piezoelectric layer 400 using the methods described in related technologies, there is a serious problem of byproduct accumulation. For details on the prepared piezoelectric layer 400, please refer to... Figure 5 and Figure 6 .

[0091] In another embodiment, where the piezoelectric layer 400 comprises only a scandium-doped aluminum nitride layer, stacking the piezoelectric layer 400 on the bottom electrode 300 includes:

[0092] Step G1: Spin-coat a scandium-doped aluminum nitride layer onto the bottom electrode 300.

[0093] Please refer to Figure 2 This application discloses a specific method for fabricating a bulk acoustic wave filter, comprising:

[0094] S201, Clean the substrate 100.

[0095] S202, spin-coating a first adhesive layer 820 onto the surface of the substrate 100 where the groove 101 to be etched is to be formed.

[0096] S203, through exposure and development, patterns the first adhesive layer 820.

[0097] S204, etching is performed on the substrate 100 to form the groove 101.

[0098] S205, Select the first substrate 810 and clean the first substrate 810.

[0099] S206, a silicon oxide layer 220 is grown on the first substrate 810 by thermal oxidation, chemical vapor deposition, or physical vapor deposition.

[0100] S207, a tungsten layer 210 is grown on the silicon oxide layer 220 by thermal oxidation, chemical vapor deposition, or physical vapor deposition, and then a silicon oxide layer 220 is grown on the tungsten layer 210.

[0101] It should be noted that the silicon oxide layer 220 and the tungsten layer 210 can be multiple layers, and the silicon oxide layer 220 and the tungsten layer 210 can be grown alternately. The silicon oxide layer 220 and the tungsten layer 210 form the Bragg reflector layer 200.

[0102] S208, remove the first adhesive layer 820.

[0103] S209, the side of the Bragg reflector layer 200 facing away from the first substrate 810 is bonded to the substrate 100.

[0104] S210, the first substrate 810 is removed by polishing.

[0105] S211, a bottom electrode 300 is deposited on the side of the Bragg reflector layer 200 away from the substrate 100 by physical vapor deposition.

[0106] S212, spin-coating a second adhesive layer 830 onto the side of the bottom electrode 300 opposite to the Bragg reflective layer 200.

[0107] S213, the second adhesive layer 830 is patterned by exposure and development.

[0108] S214, etching the bottom electrode 300.

[0109] S215, remove the second adhesive layer 830.

[0110] S216, the piezoelectric layer 400 is stacked on the bottom electrode 300. Specifically, when the piezoelectric layer 400 is disposed, a lanthanum nickelate layer 420 can be spin-coated onto the bottom electrode 300 first, and then a lead zirconate titanate piezoelectric ceramic layer 410 can be spin-coated onto the lanthanum nickelate layer 420 to form the piezoelectric layer 400.

[0111] S217, a top electrode 500 is deposited on the side of the piezoelectric layer 400 away from the substrate 100 by physical vapor deposition.

[0112] S218, a third adhesive layer 840 is spin-coated on the side of the top electrode 500 away from the piezoelectric layer 400.

[0113] S219, the third adhesive layer 840 is patterned by exposure and development.

[0114] S220, etching the top electrode 500.

[0115] S221, etch the piezoelectric layer 400.

[0116] S222, remove the third adhesive layer 840.

[0117] S223, spin-coating the fourth adhesive layer 850 to cover the top electrode 500, the piezoelectric layer 400 and the bottom electrode 300.

[0118] S224, the fourth adhesive layer 850 is patterned by exposure and development.

[0119] S225, prepare a first epitaxial electrode 600 and a second epitaxial electrode 700, wherein the first epitaxial electrode 600 is electrically connected to the bottom electrode 300 and the second epitaxial electrode 700 is electrically connected to the top electrode 500.

[0120] S226, remove the fourth adhesive layer 850.

[0121] It should be noted that, in the embodiments of this application, regarding the numerical range, if the end value of the numerical range is 0, then the end value with a value of 0 is not included; if the end value of the numerical range is not 0, then the end value with a value that is not 0 is included.

[0122] The above embodiments of the present invention focus on describing the differences between the various embodiments. As long as the different optimization features between the various embodiments are not contradictory, they can be combined to form a better embodiment. For the sake of brevity, they will not be described in detail here.

[0123] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these modifications are within the protection scope of the present invention.

Claims

1. A bulk acoustic wave filter, characterized in that, It includes a substrate (100), a Bragg reflector layer (200) for reflecting sound waves, a bottom electrode (300), a piezoelectric layer (400), and a top electrode (500), wherein: The substrate (100) has a groove (101), the Bragg reflector layer (200) is stacked on the substrate (100) and covers the opening of the groove (101), the bottom electrode (300) is stacked on the side of the Bragg reflector layer (200) away from the substrate (100), and at least a portion of the bottom electrode (300) is opposite to the opening of the groove (101), the piezoelectric layer (400) is stacked on the side of the bottom electrode (300) away from the Bragg reflector layer (200), and the top electrode (500) is stacked on the side of the piezoelectric layer (400) away from the bottom electrode (300).

2. The bulk acoustic wave filter according to claim 1, characterized in that, The Bragg reflector layer (200) includes a stacked tungsten layer (210) and a silicon oxide layer (220), both of which are multilayered and the multilayers of tungsten layer (210) and silicon oxide layer (220) are alternately distributed. The two outermost layers of the Bragg reflector layer (200) are both silicon oxide layers (220).

3. The bulk acoustic wave filter according to claim 1, characterized in that, The piezoelectric layer (400) may include only a lead zirconate titanate piezoelectric ceramic layer (410), or only a scandium-doped aluminum nitride layer, or the lead zirconate titanate piezoelectric ceramic layer (410) and a lanthanum nickelate layer (420). In the case where the piezoelectric layer (400) includes the lead zirconate titanate piezoelectric ceramic layer (410) and the lanthanum nickelate layer (420), the lanthanum nickelate layer (420) is disposed between the lead zirconate titanate piezoelectric ceramic layer (410) and the bottom electrode (300).

4. The bulk acoustic wave filter according to claim 1, characterized in that, The bulk acoustic wave filter further includes a first epitaxial electrode (600) and a second epitaxial electrode (700), wherein the first epitaxial electrode (600) is electrically connected to the bottom electrode (300) and the second epitaxial electrode (700) is electrically connected to the top electrode (500).

5. A method for fabricating a bulk acoustic wave filter, characterized in that, The bulk acoustic wave filter is the bulk acoustic wave filter according to claim 1, and the disclosed preparation method includes: The groove (101) is etched on the substrate (100); The Bragg reflector layer (200) is stacked on the substrate (100) and the Bragg reflector layer (200) covers the groove opening of the groove (101); The bottom electrode (300) is stacked on the side of the Bragg reflector layer (200) away from the substrate (100), and at least a portion of the bottom electrode (300) is opposite to the opening of the groove (101). The piezoelectric layer (400) is stacked and disposed on the side of the bottom electrode (300) opposite to the Bragg reflector layer (200); The top electrode (500) is stacked on the side of the piezoelectric layer (400) opposite to the bottom electrode (300).

6. The preparation method according to claim 5, characterized in that, Before the Bragg reflective layer (200) is stacked and disposed on the substrate (100), the fabrication method further includes: The Bragg reflector layer (200) is grown on the first substrate (810) by thermal oxidation, chemical vapor deposition or physical vapor deposition. The step of stacking the Bragg reflective layer (200) on the substrate (100) and making the Bragg reflective layer (200) cover the groove opening of the recess includes: The side of the Bragg reflector layer (200) facing away from the first substrate (810) is bonded to the substrate (100); The first substrate (810) is removed by polishing.

7. The preparation method according to claim 6, characterized in that, The growth of the Bragg reflector layer (200) on the first substrate (810) by thermal oxidation, chemical vapor deposition, or physical vapor deposition includes: The Bragg reflector layer (200) is formed by alternately growing a tungsten layer (210) and a silicon oxide layer (220) on the first substrate (810) through the thermal oxidation process, the chemical vapor deposition process, or the physical vapor deposition process, wherein the two outermost layers of the Bragg reflector layer (200) are both silicon oxide layers (220).

8. The preparation method according to claim 7, characterized in that, After the top electrode (500) is stacked on the piezoelectric layer (400), the fabrication method further includes: The piezoelectric layer (400) is etched, wherein during the etching process, the upper electrode power ranges from 100W to 10000W, the lower electrode power ranges from 0 to 1000W, the argon flow rate ranges from 1 to 1000 sccm, the hydrogen flow rate ranges from 1 to 1000 sccm, the chlorine flow rate ranges from 1 to 1000 sccm, and the boron trichloride flow rate ranges from 1 to 1000 sccm. After etching the piezoelectric layer (400), the lower electrode power is turned off, all air intakes are shut off, and a vacuum operation is performed.

9. The preparation method according to claim 8, characterized in that, After the vacuuming operation is completed, the preparation method further includes: Open the cooling gas supply channel to cool the substrate (100), the Bragg reflector layer (200), the bottom electrode (300), the piezoelectric layer (400), and the top electrode (500); The byproducts generated during the etching of the piezoelectric layer (400) are etched.

10. The preparation method according to claim 5, characterized in that, The piezoelectric layer (400) is stacked and disposed on the bottom electrode (300), including: A lanthanum nickelate layer (420) is spin-coated onto the bottom electrode (300); A lead zirconate titanate piezoelectric ceramic layer (410) is spin-coated onto the lanthanum nickelate layer (420); The piezoelectric layer (400) includes the lanthanum nickelate layer (420) and the lead zirconate titanate piezoelectric ceramic layer (410).

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