WO2021248572A1 - 一种薄膜体声波谐振器及其制作工艺 - Google Patents

一种薄膜体声波谐振器及其制作工艺 Download PDF

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Publication number
WO2021248572A1
WO2021248572A1 PCT/CN2020/098557 CN2020098557W WO2021248572A1 WO 2021248572 A1 WO2021248572 A1 WO 2021248572A1 CN 2020098557 W CN2020098557 W CN 2020098557W WO 2021248572 A1 WO2021248572 A1 WO 2021248572A1
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Prior art keywords
piezoelectric layer
resonator
reflection structure
acoustic wave
film bulk
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PCT/CN2020/098557
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English (en)
French (fr)
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李林萍
盛荆浩
江舟
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Hangzhou Jwl Technology Inc
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Hangzhou Jwl Technology Inc
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Priority to US18/007,994 priority Critical patent/US11901872B2/en
Priority to KR1020227045935A priority patent/KR20230007552A/ko
Priority to JP2022574755A priority patent/JP2023522485A/ja
Priority to EP20939534.2A priority patent/EP4164126A4/en
Publication of WO2021248572A1 publication Critical patent/WO2021248572A1/zh
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    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02086—Means for compensation or elimination of undesirable effects
    • H03H9/02125—Means for compensation or elimination of undesirable effects of parasitic elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; 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
    • H03H9/171—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator implemented with thin-film techniques, i.e. of the film bulk acoustic resonator [FBAR] type
    • H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
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    • 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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    • H03H9/02015—Characteristics of piezoelectric layers, e.g. cutting angles
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    • H03H2009/02165—Tuning
    • H03H2009/02173—Tuning of film bulk acoustic resonators [FBAR]
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    • H03H9/05—Holders or supports
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    • H03H9/605—Electric coupling means therefor consisting of a ladder configuration

Definitions

  • This application relates to the field of communication devices, and mainly relates to a thin-film bulk acoustic resonator and its manufacturing process.
  • the filter is one of the radio frequency front-end modules, which can improve the transmission and reception of signals. It is mainly composed of multiple resonators connected through a topological network structure. Fbar (Thin film bulk acoustic resonator) is a bulk acoustic wave resonator.
  • the filter composed of it has the advantages of small size, strong integration capability, high quality factor Q during high-frequency operation, and strong power tolerance. It is used as a radio frequency front-end The core device.
  • Fbar is a basic structure composed of upper and lower electrodes and a piezoelectric layer sandwiched between the electrodes.
  • the piezoelectric layer mainly realizes the conversion of electrical energy and mechanical energy.
  • the piezoelectric layer converts electrical energy into mechanical energy, and the mechanical energy exists in the form of sound waves.
  • Acoustic waves have two vibration modes: transverse wave and longitudinal wave. Longitudinal wave is the main mode in Fbar working state, and transverse wave is easy to leak from the edge of the resonator and take away energy.
  • the Q value is an important index to measure the performance of the resonator, which is equal to the ratio of the energy stored by the resonator to the energy lost by the resonator. Therefore, the energy taken away by the transverse wave will inevitably attenuate the Q value and degrade the performance of the device.
  • the air gap at the cavity boundary reflects the transverse wave to suppress the energy taken by the transverse wave.
  • the air gap is made by a process of releasing the internal sacrificial layer. The process is more complicated and the mechanical stability of the top electrode connection part on the upper part of the cavity needs to be ensured. .
  • the arrangement of interlaced electrode structures on the effective resonance region of the resonator can suppress parasitic oscillations to a certain extent, but cannot suppress the energy carried by transverse waves from passing out of the resonator.
  • the grooves are made by an etching process, which will cause the piezoelectric layer at the bottom and sidewalls of the grooves to have a crystal lattice Defects and micro-holes affect the performance of the resonator; on the other hand, reducing the area of the resonance area on the upper part of the cavity increases the size of the filter to a certain extent.
  • the mass load layer on the top of the top electrode can form a sudden change in acoustic impedance to suppress the energy taken by the transverse wave, but the piezoelectric layer on the edge of the cavity will copy the lattice defects and micropores caused by the etching process of the bottom electrode. .
  • the present invention proposes a thin film bulk acoustic wave resonator and The manufacturing process is used to solve the above-mentioned problems.
  • a thin-film bulk acoustic resonator which includes a bottom electrode layer, a piezoelectric layer, and a top electrode layer disposed on a substrate where the acoustic wave reflection structure is located, wherein the piezoelectric layer and the acoustic wave reflection structure
  • the part corresponding to the boundary of is depolarized to form a depolarized part.
  • the depolarization portion is partially depolarized. Setting partial depolarization according to device performance requirements can facilitate the production of devices that meet the expected performance requirements at a minimum cost.
  • the depolarization portion is fully depolarized. With all the depolarization of the depolarization part, a perfect isolation effect and minimal parasitic effects can be achieved.
  • the projection area of the depolarization portion on the substrate spans at least from the area outside the acoustic wave reflection structure to the inside of the acoustic wave reflection structure.
  • the depolarization portion is formed by subjecting the piezoelectric layer to selective depolarization treatment.
  • the selective depolarization process can facilitate the control of depolarization.
  • the depolarization treatment includes ion implantation and annealing of the piezoelectric material in the piezoelectric layer. Through ion implantation, different annealing processes can be used to achieve depolarization of the piezoelectric layer.
  • the resonator includes a plurality of resonators disposed on the same substrate, and the piezoelectric layer in the region between the plurality of resonators is depolarized. This setting can achieve the overall technical effect of suppressing parasitic oscillations.
  • the acoustic wave reflecting structure is a cavity.
  • the cavity structure can enhance the reflection effect of sound waves and improve the Q value of the device.
  • the acoustic wave reflection structure is a Bragg reflection structure.
  • a manufacturing process of a thin film bulk acoustic resonator which includes the following steps:
  • the transverse wave can be suppressed from taking energy away from the resonance region of the resonator, thereby ensuring the mechanical vibration strength of the resonance region and suppressing parasitics Oscillate and increase the Q value of the resonator.
  • step S3 specifically includes:
  • the S33 step further includes applying an annealing process to the piezoelectric layer after ion implantation.
  • the piezoelectricity of the piezoelectric layer can be eliminated by the annealing process.
  • step S33 specifically includes controlling the type and/or concentration of doped ions during ion implantation so that the Curie point of the piezoelectric layer material after ion implantation is lower than the manufacturing process of the resonator after ion implantation The highest process temperature.
  • This setting can select appropriate doping ion species and/or concentration according to the highest process temperature to meet the depolarization operation at different process temperatures.
  • the acoustic wave reflection structure is a cavity or a Bragg reflection structure.
  • Acoustic reflection structure can choose cavity or Bragg reflection structure according to different application effects.
  • a thin-film bulk acoustic resonator is provided, which is manufactured through the above-mentioned manufacturing process.
  • the piezoelectric layer in a specific area of a thin film bulk acoustic wave resonator of the present invention is depolarized to make it non-piezoelectric, which can suppress parasitic oscillations and suppress transverse waves from taking away energy, thereby increasing the Q value and improving the performance of the device.
  • the process is simpler, and there is no need to worry about the mechanical stability of the top electrode connection part.
  • ion implantation is performed on the exposed part of the piezoelectric layer, and an annealing process is applied to make the part of the piezoelectric layer corresponding to the boundary of the acoustic wave reflection structure
  • the depolarization part is formed, and partial or full depolarization is realized according to the device performance requirements and cost requirements of different frequency bands, and thin film bulk acoustic wave resonators with different costs or performance requirements can be fabricated.
  • Figure 1 shows a cross-sectional view of a thin film bulk acoustic resonator according to an embodiment of the present invention
  • Figure 2 shows a top view of a filter according to an embodiment of the present invention
  • Figure 3 shows a cross-sectional view of a thin film bulk acoustic resonator in a series connection state according to a specific embodiment of the present invention
  • Figure 4 shows a partially polarized cross-sectional view of a thin film bulk acoustic wave resonator in a series connection state according to a specific embodiment of the present invention
  • FIG. 5 shows a cross-sectional view of a thin film bulk acoustic resonator with SMR structure according to another embodiment of the present invention
  • Figures 6a-o show a process flow diagram of a thin film bulk acoustic resonator according to an embodiment of the present invention.
  • Figure 1 shows a cross-sectional view of a thin film bulk acoustic resonator according to an embodiment of the present invention.
  • the thin film bulk acoustic resonator includes a substrate 101, a support layer 102, a bottom electrode 103, and a piezoelectric layer. 104 and the top electrode 105, wherein the support layer 102 connects the substrate 101 and the bottom electrode 103 and forms a cavity 106 between the two.
  • the piezoelectric layer 104 outside the cavity 106 and the longitudinal region of the electrode depolarize to form a depolarization
  • the arrangement of the depolarized piezoelectric layer 107 and the depolarized piezoelectric layer 107 can restrain the energy of the resonator from being carried away by the transverse wave, thereby increasing the Q value of the device.
  • the depolarized piezoelectric layer 107 can be fully depolarized or partially depolarized. Setting local depolarization according to device performance requirements can facilitate the production of devices that meet the expected performance requirements at a minimum cost, while all depolarization A perfect isolation effect and minimal parasitic effects can be achieved.
  • the projection area of the depolarized piezoelectric layer 107 on the substrate 101 can span from the area outside the cavity 106 to the edge of the cavity 106 or within the cavity 106, where the depolarization
  • the piezoelectric layer 107 is formed by subjecting the piezoelectric layer 104 to a selective depolarization process.
  • the depolarization process includes ion implantation and annealing of the piezoelectric material in the piezoelectric layer 104.
  • the arrangement of the depolarized piezoelectric layer 107 can better suppress the energy taken away by the transverse wave from the resonator. Through ion implantation, different annealing processes can be used to achieve the depolarization of the piezoelectric layer 104 and facilitate the control of the depolarization. .
  • the top electrode 105 of the general thin film bulk acoustic wave resonator extends to the right side, and the piezoelectric layer 104 outside the cavity 106 and the longitudinal region of the electrode will form parasitic oscillations, which will affect the performance of the device and make the The loss of piezoelectricity of the piezoelectric layer can suppress parasitic oscillations.
  • the bottom electrode 103 has lattice defects and micropores due to the etching process.
  • the piezoelectric layer 104 in the vertical direction will replicate the defects of the bottom electrode 103 during the film formation process. Defects in the electrical layer 104 will cause the transverse waves to scatter here and take away energy.
  • the arrangement of the depolarized piezoelectric layer 107 can avoid the energy loss caused by the defects of the piezoelectric layer 104, regardless of whether the top electrode 105 extends outward or not, the depolarization
  • the arrangement of the piezoelectric layer 107 can suppress the transverse wave from taking away the energy of the resonator and improve the Q value of the device.
  • multiple groups of resonators are connected in parallel on the same substrate (the right side of the resonator in Figure 1 is only partially shown), and the top electrode 105 of the previous group of resonators is connected to the top electrode of the next resonator.
  • the area 1071 and the area 1072 must be set as the depolarized piezoelectric layer 107 to suppress the parasitic oscillation and improve the performance of the device.
  • the process is more complicated and the mechanical stability of the top electrode connection part on the upper part of the cavity needs to be ensured.
  • the invention only needs to remove the piezoelectricity of the piezoelectric layer at the cavity boundary to achieve the effect of suppressing the energy carried by the transverse wave, the process is simpler, and there is no need to worry about the mechanical stability of the top electrode connection part.
  • Fig. 2 shows a top view of a filter according to a specific embodiment of the present invention. As shown in Fig. 2, it includes four sets of resonators 201, 202, 203, 204 and a connecting plate 205.
  • the supporting layers 2011, 2021, 2031, 2041 of, 203, 204 and the electrodes 2012, 2022, 2032, and 2042 can have any shape, which can be set according to the shape of the filter.
  • the connection plate 205 is the connection of the electrode 2042 of the resonator 204 Department.
  • the cavities of the four groups of resonators are connected to the outside of the resonator, so that the edges can be released through interconnected channels, so as to achieve the effect of cavity release without destroying the piezoelectric layer at the edge of the resonator, which is improved to a certain extent.
  • Device performance is improved.
  • FIG. 3 shows a cross-sectional view of a thin film bulk acoustic resonator in a series connection state according to a specific embodiment of the present invention.
  • the top electrode 105 of the former resonator and the latter The bottom electrode 103 of the resonator is connected to realize the series connection of the resonators, and a depolarized piezoelectric layer 307 is respectively arranged on the piezoelectric layer 104 where the two resonators are connected in series.
  • the regions 3071 and 3072 must be set as depolarized piezoelectric layers 307. If the depolarized piezoelectric layer 307 is not provided, parasitic oscillations will occur and affect device performance.
  • the resonator energy suppresses the technical effect of parasitic oscillation.
  • FIG. 5 shows a cross-sectional view of a thin film bulk acoustic resonator with an SMR structure according to another embodiment of the present invention. As shown in FIG.
  • the SMR structure thin film bulk acoustic resonator includes a substrate 501, a bottom electrode 502, and a piezoelectric
  • the layer 503 and the top electrode 504, the substrate 501 is provided with a Bragg reflection structure 506, and the piezoelectric layer 503 is provided with a depolarized piezoelectric layer 505 at both ends of the upper part of the reflection area of the Bragg reflection structure 506, which can also suppress the transverse band
  • Fig. 6 shows a manufacturing process of a thin film bulk acoustic resonator according to an embodiment of the present invention. As shown in Fig. 6, the process includes the following processes:
  • a silicon layer 602 is grown on a substrate 601, where the substrate 601 can be Si, SiC, sapphire, spinel, etc., preferably, the thickness of the silicon layer grown by PVD is 1.5-3 ⁇ m.
  • the required cavity pattern of the resonator is generated on the silicon layer 602 by photolithography, as shown in FIG. 6b.
  • a sacrificial layer 603 is grown in the cavity, where the material of the sacrificial layer may be PSG (P-doped SiO 2 ), and the sacrificial layer 603 is chemically mechanically polished, as shown in FIG. 6c.
  • a bottom electrode 604 is fabricated on the silicon layer 602 and the sacrificial layer 603, wherein the material of the bottom electrode 604 can be molybdenum, and a piezoelectric layer 605 is fabricated on the basis of the bottom electrode 604, wherein the piezoelectric layer 605 is aluminum nitride.
  • the specific structure As shown in Figures 6d and 6e.
  • a hard mask 606 is deposited on the surface of the piezoelectric layer 605 by CVD.
  • the hard mask 606 is an inorganic thin film material.
  • the main components include TiN, SiN, SiO 2 and so on.
  • the shape of the hard mask area is the same as the shape of the subsequent top electrode, and the blocking area is the effective area of the resonator.
  • ion implantation is performed on the area of the piezoelectric layer 605 exposed to the hard mask 606, where the implanted atoms can be Ni/Fe/Cr/Mn/Co/V/Y/Si, etc.
  • the implanted piezoelectric layer 605 is subjected to an annealing process.
  • the annealing temperature in the annealing process should be higher than the Curie point of the piezoelectric layer 605 material after ion implantation, so that the ion implanted region of the piezoelectric layer 605 is depolarized Department 607.
  • the type and/or concentration of doped ions in the ion implantation process can be controlled so that the Curie point of the piezoelectric layer material after ion implantation is lower than the maximum process temperature of the manufacturing process of the resonator after ion implantation.
  • ion implantation is performed on the piezoelectric layer 605, followed by selective depolarization to eliminate the piezoelectricity of the piezoelectric layer 605.
  • the Curie point of the aluminum nitride piezoelectric layer 605 is 673.15K (400°C) as the critical point.
  • the operating temperature of the multiple processes after the ion implantation process exceeds 673.15K, and the operating temperature>the Curie point of the piezoelectric layer 605 causes the piezoelectric layer 605 film
  • the molecules and atoms inside the layer move violently and are arranged randomly.
  • the chromium piezoelectric layer 605 can be cited.
  • the chromium doping concentration is 1-3%
  • the Curie point is slightly higher than 350K
  • the doping concentration is 15%
  • the Curie point is slightly higher than 400K.
  • the Curie point is lower than the critical point set earlier (673.15K) Therefore, there is no need to anneal; when the doping concentration is 7%, the Curie point is slightly higher than 900K, and the Curie point is higher than the critical point at this time. Therefore, it is necessary to set an annealing temperature higher than 900K to make the depolarization part 607 lose its piezoelectricity.
  • the vanadium piezoelectric layer 605 can be used.
  • the doping concentration of vanadium is 1.58%, the piezoelectric layer 605 can obtain a Curie point 300K close to room temperature at this time, and the piezoelectricity of the depolarization portion 607 can be eliminated in the subsequent process without annealing.
  • the hard mask 606 is removed with a hydrofluoric acid etching solution. It should be noted that no matter what shape the ion implantation area, the ion implantation area on each side does not exceed the range of the cavity, that is, the ion implantation area is vertical The projection in the direction can partially overlap the cavity boundary or extend slightly into the cavity.
  • the region defined in the horizontal direction of ion implantation may be all projected outside the cavity (as shown in FIG. 6j), or it may be projected on a part of the periphery of the cavity (as shown in FIG. 6k);
  • the range of the ion implantation in the vertical direction is limited, and it can be through the piezoelectric layer (as shown in FIG. 6j) or local implantation (as shown in FIG. 61).
  • the area range in the horizontal direction can be realized by adjusting the topography of the opening pattern of the hard mask 606, and the vertical direction can be realized by adjusting the process parameters of ion implantation. It should be noted that the larger the ion implantation area, the better the performance improvement of the device, but the greater the increase in cost. Therefore, the cost and device performance requirements can be weighed to select a suitable ion implantation area.
  • ion implantation can be used in the non-resonant region to make the piezoelectric layer 605 lose its piezoelectricity, and only the piezoelectricity of the piezoelectric layer 605 in the resonator region can be retained to realize the device function and achieve perfect isolation. Effects and minimal parasitic effects. As shown in Figure 6m. All regions except for the piezoelectric layer 605 region corresponding to the top electrode 608 are doped.
  • the basis for the setting of the doped region is to produce the depolarization region that can achieve the predetermined requirement with the effect of suppressing the parasitic oscillation at the minimum cost.
  • the area of the piezoelectric layer 605 to be doped, the position between the resonators, the area size and depth, and the doped area outside the resonators can be arbitrarily selected and set.
  • a top electrode 608 is fabricated on the surface of the piezoelectric layer 605, wherein the material of the top electrode 608 is molybdenum.
  • the sacrificial layer 603 is released by the hydrofluoric acid etchant to obtain a cavity 609, and the manufacturing process of the thin film bulk acoustic wave resonator is completed.
  • This process exposes the piezoelectric layer that needs to be depolarized through the deposition of the hard mask 606.
  • the depolarization can be performed in a selective manner to eliminate the piezoelectricity of part of the piezoelectric layer.
  • the corresponding ion implantation area can be selected comprehensively according to the cost and the performance of the device to meet the manufacturing process of different types of thin-film bulk acoustic wave resonators.
  • the thin film bulk acoustic resonator produced by the manufacturing process shown in Figures 6a-6o through the depolarization of the piezoelectric layer in a specific area or a specific depth, when an electric field is applied to the top electrode and the bottom electrode, the piezoelectric layer transfers electrical energy Converted into mechanical energy including two vibration modes of transverse wave and longitudinal wave, the depolarized region can restrain the transverse wave from taking energy away from the resonance region on the upper part of the resonator cavity, thereby ensuring the mechanical vibration strength of the resonance region, thereby increasing the Q value of the resonator .
  • the piezoelectric layer in a specific area is depolarized so that it does not have piezoelectricity, which can suppress parasitic oscillations and suppress transverse waves from taking away energy, thereby increasing the Q value and improving the performance of the device.
  • the manufacturing process is simple, the manufacturing cost is low, and it is convenient for large-scale industrial production.

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Abstract

公开了一种薄膜体声波谐振器，包括设置在声波反射结构所在衬底的上部的底电极层、压电层和顶电极层，其中压电层的与声波反射结构的边界对应的部位经过退极化处理以形成退极化部。还公开了一种薄膜体声波谐振器的制作工艺，包括在形成或将要形成声波反射结构的衬底上制作底电极层以覆盖声波反射结构；在底电极层上制作压电层；对压电层的与声波反射结构的边界对应的部位进行退极化处理以形成退极化部；在压电层上制作顶电极层。该薄膜体声波谐振器及其制作工艺可以抑制横波从谐振器的空腔上部的谐振区域带走能量，从而保证谐振区域的机械振动强度，抑制寄生振荡，并提升谐振器Q值。

Description

一种薄膜体声波谐振器及其制作工艺 技术领域
本申请涉及通信器件领域，主要涉及一种薄膜体声波谐振器及其制作工艺。
背景技术
随着电磁频谱的日益拥挤、无线通讯设备的频段与功能增多，无线通讯使用的电磁频谱从500MHz到5GHz以上高速增长，因此对性能高、成本低、功耗低、体积小的射频前端模块需求也日益增长。滤波器是射频前端模块之一，可改善发射和接收信号，主要由多个谐振器通过拓扑网络结构连接而成。Fbar(Thin film bulk acoustic resonator)是一种体声波谐振器，由它组成的滤波器具有体积小、集成能力强、高频工作时保证高品质因素Q、功率承受能力强等优势而作为射频前端的核心器件。
Fbar是由上下电极和夹在电极之间的压电层组成的基本结构。压电层主要实现电能与机械能的转化。当Fbar的上下电极施加电场时，压电层将电能转换为机械能，机械能则以声波的形式存在。声波有横波和纵波两种振动模式，纵波是Fbar工作状态下的主要模式，横波易从谐振器边缘泄露而带走能量。Q值是衡量谐振器性能的重要指标，等于谐振器储存能量与谐振器所损失能量的比值。因此横波带走能量必然会衰减Q值，使器件性能下降。
现有技术通过空腔边界的air gap反射横波而抑制横波带走能量，air gap以释放内部牺牲层的工艺制成，工艺较为复杂，且需要保证空腔上部的顶电极连接部的机械稳定性。或者通过在谐振器的有效谐振区域上交错的电极结构上的设置可一定程度上抑制寄生振荡，但无法抑制横波携带能量传出谐振器。或者通过在压电层上制作凹槽来抑制横波带走能量，从而提升器件Q值，但是凹槽通过蚀刻工艺制成，此工艺会造成凹槽底部及侧壁的的压电层的晶格缺陷及微孔洞，影响谐 振器性能；另一方面减小空腔上部的谐振区域面积，一定程度增加了滤波器的尺寸。又或者通过顶电极上部的质量负载层来形成声阻抗突变而抑制横波带走能量，但空腔边缘上部的压电层会复制其底电极经刻蚀工艺所带来的晶格缺陷及微孔。
发明内容
为了解决现有技术谐振器空腔上部的谐振区域处横波易从谐振器边缘泄露而带走能量，难以抑制寄生振荡，影响器件性能的技术问题，本发明提出了一种薄膜体声波谐振器及其制作工艺，用以解决上述问题。
根据本发明的一方面，提出了一种薄膜体声波谐振器，包括设置在声波反射结构所在衬底的上部的底电极层、压电层和顶电极层，其中压电层的与声波反射结构的边界对应的部位经过退极化处理以形成退极化部。凭借退极化部的设置，可以抑制横波从谐振器的谐振区域带走能量，进而保证谐振区域的机械振动强度，抑制寄生振荡，提升谐振器的Q值。
在一些实施例中，退极化部被部分退极化。根据器件性能需求设置局部退极化可以便于以最小成本制作出满足预期性能需求的器件。
在一些实施例中，退极化部被全部退极化。凭借退极化部的全部退极化可以实现完美的隔离效果和最小的寄生效应。
在一些实施例中，退极化部在衬底上的投影区域至少从声波反射结构之外的区域跨越到声波反射结构之内。凭借该设置能够更好地抑制横波带走谐振器的能量。
在一些实施例中，退极化部是通过将压电层进行选择性退极化处理后形成的。凭借选择性退极化的处理可以便于实现对退极化的控制。
在一些实施例中，退极化处理包括对压电层中的压电材料进行离子注入以及退火。通过离子注入可以实现利用不同的退火工艺实现压电层的退极化。
在一些实施例中，谐振器包括设置在同一衬底上的多个谐振器，其中在多个谐振器之间的区域所具有的压电层被退极化处理。通过该 设置可以实现整体抑制寄生振荡的技术效果。
在一些实施例中，声波反射结构为空腔。空腔结构可以增强声波的反射效果，提高器件的Q值。
在一些实施例中，声波反射结构为布拉格反射结构。
根据本发明的第二方面，提出了一种薄膜体声波谐振器的制作工艺，其中包括以下步骤：
S1、在形成或将要形成声波反射结构的衬底上制作底电极层以覆盖声波反射结构；
S2、在底电极层上制作压电层；
S3、对压电层的与声波反射结构的边界对应的部位进行退极化处理以形成退极化部；以及
S4、在压电层上制作顶电极层。
凭借对压电层与声波反射结构的边界对应的部位进行退极化处理以形成退极化部，可以抑制横波从谐振器的谐振区域带走能量，从而保证谐振区域的机械振动强度，抑制寄生振荡，并提升谐振器Q值。
在一些实施例中，步骤S3具体包括：
S31、在压电层上沉积硬掩膜或涂覆光刻胶，
S32、将所述硬掩模或所述光刻胶图形化以使得压电层的至少与声波反射结构的边界对应的部位暴露出，
S33、对压电层的暴露部位进行离子注入，
S34、去除硬掩膜或光刻胶。
在一些实施例中，S33步骤还包括在离子注入后，对压电层施加退火工艺。通过退火工艺可以消除压电层的压电性。
在一些实施例中，S33步骤具体包括控制离子注入过程中的掺杂离子的种类和/或浓度以使得被离子注入后的压电层材料的居里点低于离子注入后谐振器的制作工艺的最高工艺温度。该设置可以根据最高工艺温度选择合适的掺杂离子种类和/或浓度，以满足不同工艺温度下的去极化操作。
在一些实施例中，声波反射结构为空腔或者布拉格反射结构。声波反射结构可以根据不同的应用效果选择空腔或布拉格反射结构。
根据本发明的第三方面，提出了一种薄膜体声波谐振器，通过上述制作工艺制成。
本发明的一种薄膜体声波谐振器的特定区域的压电层被退极化使其不具有压电性，可以抑制寄生振荡，抑制横波带走能量从而提升Q值，提升器件的性能。相较于现有技术中利用air gap等工艺反射横波抑制横波带走能量的方式，工艺更加简单，无需顾虑顶电极连接部的机械稳定性。同时根据本发明的另一方面的一种薄膜体声波谐振器的制作工艺，对压电层的暴露部位进行离子注入，并施加退火工艺，使得压电层的与声波反射结构的边界对应的部位形成退极化部，并根据不同频段的器件性能需求以及成本要求实现部分或全部退极化，可以制作不同成本或性能要求的薄膜体声波谐振器。
附图说明
包括附图以提供对实施例的进一步理解并且附图被并入本说明书中并且构成本说明书的一部分。附图图示了实施例并且与描述一起用于解释本发明的原理。将容易认识到其它实施例和实施例的很多预期优点，因为通过引用以下详细描述，它们变得被更好地理解。附图的元件不一定是相互按照比例的。同样的附图标记指代对应的类似部件。
图1示出了根据本发明的一个实施例的薄膜体声波谐振器的截面图；
图2示出了根据本发明的一个实施例的滤波器的俯视图；
图3示出了根据本发明的一个具体的实施例的薄膜体声波谐振器的串联状态下的截面图；
图4示出了根据本发明的一个具体的实施例的薄膜体声波谐振器的串联状态下部分极化的截面图；
图5示出了根据本发明的另一个实施例的SMR结构薄膜体声波谐振器的截面图；
图6a-o示出了根据本发明的一个实施例的薄膜体声波谐振器的制作工艺流程图。
具体实施方式
下面结合附图和实施例对本申请作进一步的详细说明。可以理解的是，此处所描述的具体实施例仅仅用于解释相关发明，而非对该发明的限定。另外还需要说明的是，为了便于描述，附图中仅示出了与有关发明相关的部分。
需要说明的是，在不冲突的情况下，本申请中的实施例及实施例中的特征可以相互组合。下面将参考附图并结合实施例来详细说明本申请。
图1示出了根据本发明的一个实施例的薄膜体声波谐振器的截面图，如图1所示，该薄膜体声波谐振器包括衬底101、支撑层102、底电极103、压电层104和顶电极105，其中支撑层102连接衬底101和底电极103并在二者之间形成空腔106，在空腔106外部的压电层104与电极的纵向区域退极化形成退极化压电层107，退极化压电层107的设置可以抑制横波带走谐振器的能量进而提升器件的Q值。优选的，退极化压电层107可以为全部退极化或局部退极化，根据器件性能需求设置局部退极化可以便于以最小成本制作出满足预期性能需求的器件，而全部退极化可以实现完美的隔离效果和最小的寄生效应。
在具体的实施例中，退极化压电层107在衬底101上的投影区域可以从空腔106之外的区域跨越到空腔106的边缘或空腔106之内，其中，退极化压电层107是通过将压电层104进行选择性退极化处理后形成的，退极化处理包括对压电层104中的压电材料进行离子注入以及退火。退极化压电层107的设置能够更好地抑制横波带走谐振器的能量，通过离子注入可以实现利用不同的退火工艺实现压电层104的退极化且便于实现对退极化的控制。
在具体的实施例中，一般的薄膜体声波谐振器的顶电极105右侧往外延伸，空腔106外部的压电层104与电极纵向区域会形成寄生振荡，影响器件性能，令该区域内的压电层失去压电性可以抑制寄生振荡，底电极103因刻蚀工艺而出现晶格缺陷及微孔，垂直方向上的压电层104在成膜过程中会复制底电极103的缺陷，压电层104缺陷会导致横波在此处散射而带走能量，通过退极化压电层107的设置可以 避免压电层104缺陷所导致的能量损失，无论顶电极105是否向外延伸，退极化压电层107的设置都能够抑制横波带走谐振器能量而提升器件Q值。
在具体的实施例中，同一衬底上多组谐振器并联(图1中谐振器右侧仅局部示意)，前一组谐振器的顶电极105与下一谐振器的顶电极连接，应当注意的是，区域1071与区域1072必须设置为退极化压电层107，才能够抑制寄生振荡提升器件性能。
对比于现有技术中利用在空腔边界释放内部牺牲层形成的air gap来反射横波，工艺较为复杂且需要保证空腔上部的顶电极连接部的机械稳定性。本发明只需去除空腔边界的压电层的压电性即可实现抑制横波带走能量的效果，工艺更加简单，且无需顾虑顶电极连接部的机械稳定性能。
图2示出了根据本发明的一个具体的实施例的滤波器的俯视图，如图2所示，包括四组谐振器201、202、203、204和连接板205，其中，谐振器201、202、203、204的支撑层2011、2021、2031、2041与电极2012、2022、2032、2042可以为任意形状，具体可以依滤波器形状进行设定，连接板205为谐振器204的电极2042的连接部。四组谐振器的空腔与谐振器外部相互连通，使得边缘可以通过互通互联的通道实现释放，从而达到不破坏谐振器边缘的压电层就可以进行空腔释放的效果，一定程度上提升了器件性能。
继续参考图3，图3示出了根据本发明的一个具体的实施例的薄膜体声波谐振器的串联状态下的截面图，如图3所示，前一谐振器的顶电极105与后一谐振器的底电极103连接实现谐振器的串联，并分别在两谐振器串联处的压电层104上设置退极化压电层307，区域3071和区域3072必须设置为退极化压电层307，如未设置退极化压电层307会产生寄生振荡影响器件性能。
在另一具体的实施例中，退极化压电层的设置区域越大性能提升越好，但成本更高，因此可以根据成本以及器件的性能调整退极化压电层的范围，例如图4中示出的一个具体的实施例的薄膜体声波谐振器的串联状态下部分极化的截面图，区域4071和区域4072必须设置 为退极化压电层407，同样能够实现抑制横波带走谐振器能量，抑制寄生振荡的技术效果。
虽然图1-3中示出的均为空腔结构的谐振器结构的退极化压电层设置方案，但应当认识到，该退极化的压电层结构同样适用于SMR结构，同样能够实现本发明的技术效果。图5示出了根据本发明的另一个实施例的SMR结构薄膜体声波谐振器的截面图，如图5所示，该SMR结构薄膜体声波谐振器包括衬底501、底电极502、压电层503和顶电极504，衬底501上设置有布拉格反射结构506，压电层503在布拉格反射结构506的反射区域上部的两端设置有退极化压电层505，同样能够实现抑制横波带走谐振器能量的技术效果。
图6示出了根据本发明的一个实施例的薄膜体声波谐振器的制作工艺，如图6所示，该工艺包括以下流程：
首先如图6a所示，在衬底601上生长硅层602，其中，衬底601可以为Si、SiC、蓝宝石、尖晶石等，优选的，通过PVD生长硅层的厚度为1.5-3μm。利用光刻在硅层602上生成所需的谐振器空腔图形，如图6b所示。在空腔中生长牺牲层603，其中，牺牲层材料可以为PSG(掺杂P的SiO 2)，并对牺牲层603进行化学机械抛光，如图6c所示。在硅层602以及牺牲层603上制作底电极604，其中底电极604的材料可以为钼，并在底电极604的基础上制作压电层605，其中压电层605为氮化铝，具体结构如图6d和6e所示。
继续参考图6f和6g，通过CVD在压电层605表面沉积硬掩模606，硬掩模606为无机薄膜材料，主要成分包括TiN、SiN、SiO 2等，利用光刻与刻蚀将硬掩模开口，应当注意的是，硬掩模区域的形状与后续顶电极的形状相同，阻挡区域为谐振器的有效区域。可替代的，也可以直接采用光刻胶显影制作开口图形的技术(即将硬掩模换做光刻胶)，同样能够实现本发明的技术效果。
如图6h和6i所示，对压电层605暴露于硬掩模606的区域进行离子注入，其中，注入原子可以为Ni/Fe/Cr/Mn/Co/V/Y/Si等，对离子注入后的压电层605施加退火工艺，退火工艺中的退火温度应当高于被离子注入后的压电层605材料的居里点，以使得压电层605被离子 注入的区域形成退极化部607。优选的，可以控制离子注入过程中的掺杂离子的种类和/或浓度以使得被离子注入后的压电层材料的居里点低于离子注入后谐振器的制作工艺的最高工艺温度。
在具体的实施例中，对压电层605进行离子注入，随后进行选择性处理的方式退极化以消除压电层605的压电性。以氮化铝压电层605的居里点为673.15K(400℃)作临界点。当压电层605的居里点低于673.15K时，因离子注入工艺后的多个工序温度作业温度超673.15K，此作业温度＞压电层605的居里点而致使压电层605膜层内部分子和原子剧烈运动而无规则排布，这些相对高温工艺可使压电层605压电性消除；当压电层605的居里点高于673.15K时，此时没有工艺超过673.15K，因此在压电层605离子注入后添加一道额外的退火工艺，退火温度需高于压电层605的居里点，最佳温度可设定为高于压电层605居里点约10-20℃，保温时间约0.5h。
在一个具体的实施例中，可以引用铬压电层605。铬掺杂浓度为1-3％时居里点略高于350K，掺杂浓度为15％时居里点略高于400K，此时居里点低于前文所设置的临界点(673.15K)，因此无需退火；掺杂浓度为7％时居里点略高于900K，此时居里点高于临界点，因此需要设置高于900K的退火温度使退极化部607失去压电性。
在另一具体的实施例中，可引用钒压电层605。当钒的掺杂浓度为1.58％时，此时压电层605可获得接近于室温的居里点300K，无需退火即可在后续的工艺中使退极化部607的压电性消除。
继续参考图6j，利用氢氟酸蚀刻液去除硬掩模606，应当注意的是，无论何种形貌的离子注入区域，各侧离子注入区域均不超出空腔的范围，即离子注入区域垂直方向上的投影可以局部与空腔边界重叠，也可稍延伸至空腔内部。
在具体的实施例中，离子注入水平方向的区域限定，可以是投影于空腔外的全部(如图6j所示)，也可以是投影于空腔外围的局部(如图6k所示)；离子注入垂直方向区域范围限定，可以是贯穿压电层(如图6j所示)，也可以是局部注入(如图6l所示)。水平方向的区域范围可通过调整硬掩模606开口图形的形貌来实现，垂直方向可以通过 调节离子注入的工艺参数来实现。应当注意的是，离子注入区域越大对于器件的性能提升更好，但成本增加越大，因此可以权衡成本和器件性能需求来选择合适的离子注入的区域。
在另一具体的实施例中，非谐振区域可以全部使用离子注入使得压电层605失去压电性，只保留谐振器区域的压电层605的压电性以实现器件功能，实现完美的隔离效果和最小的寄生效应。如图6m所示。除了顶电极608对应的压电层605区域以外的所有区域全部掺杂。
在优选的实施例中，掺杂区域的设定依据是以最小成本制作可达到预定要求的抑制寄生震荡效果的退极化部区域。应当注意的是，所掺杂的压电层605的区域，所在谐振器之间的位置，面积大小和深度以及谐振器之外的掺杂区域都是可以任意选择和设定的。
最后参考图6n和图6o，在压电层605表面制作顶电极608，其中，顶电极608材料为钼。利用氢氟酸蚀刻剂释放牺牲层603获得空腔609，完成薄膜体声波谐振器的制作工艺。该工艺通过硬掩模606的沉积将需要退极化的压电层暴露，通过对压电层605进行离子注入，可以进行选择性处理的方式退极化来消除部分压电层的压电性，可以根据成本以及器件的性能综合选择相应的离子注入区域，满足不同类型的薄膜体声波谐振器的制作工艺。
利用如图6a-6o所示的制作工艺制作获得的薄膜体声波谐振器，通过特定区域或特定深度的压电层的退极化，当顶电极和底电极施加电场时，压电层将电能转换为包括横波和纵波两种振动模式的机械能，退极化的区域可以抑制横波从谐振器空腔上部的谐振区域带走能量，从而保证谐振区域的机械振动强度，进而提升谐振器的Q值。
以上描述了本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到变化或替换，都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。
在本申请的描述中，需要理解的是，术语“上”、“下”、“内”、“外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本申请和简化描述，而不是指示或暗示所指的装置 或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本申请的限制。措词‘包括’并不排除在权利要求未列出的元件或步骤的存在。元件前面的措词‘一’或‘一个’并不排除多个这样的元件的存在。在相互不同从属权利要求中记载某些措施的简单事实不表明这些措施的组合不能被用于改进。在权利要求中的任何参考符号不应当被解释为限制范围。
工业实用性
本发明实施例在特定区域的压电层被退极化使其不具有压电性，可以抑制寄生振荡，抑制横波带走能量从而提升Q值，提升器件的性能。制造工艺简单、制造成本低、便于大规模工业化生产。

Claims (15)

  1. 一种薄膜体声波谐振器，其特征在于，包括设置在声波反射结构所在衬底的上部的底电极层、压电层和顶电极层，其中所述压电层的与所述声波反射结构的边界对应的部位经过退极化处理以形成退极化部。
  2. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述退极化部被部分退极化。
  3. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述退极化部被全部退极化。
  4. 根据权利要求1-3中任一项所述的薄膜体声波谐振器，其特征在于，所述退极化部在所述衬底上的投影区域至少从所述声波反射结构之外的区域跨越到所述声波反射结构之内。
  5. 根据权利要求1-3中任一项所述的薄膜体声波谐振器，其特征在于，所述退极化部是通过将所述压电层进行选择性退极化处理后形成的。
  6. 根据权利要求5所述的薄膜体声波谐振器，其特征在于，所述退极化处理包括对压电层中的压电材料进行离子注入以及退火。
  7. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述谐振器包括设置在同一衬底上的多个谐振器，其中在所述多个谐振器之间的区域所具有的压电层被退极化处理。
  8. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述声波反射结构为空腔。
  9. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述声波反射结构为布拉格反射结构。
  10. 一种薄膜体声波谐振器的制作工艺，其特征在于，包括以下步骤：
    S1、在形成或将要形成声波反射结构的衬底上制作底电极层以覆盖所述声波反射结构；
    S2、在所述底电极层上制作压电层；
    S3、对所述压电层的与所述声波反射结构的边界对应的部位进行退极化处理以形成退极化部；以及
    S4、在所述压电层上制作顶电极层。
  11. 根据权利要求10所述的制作工艺，其特征在于，所述步骤S3具体包括：
    S31、在所述压电层上沉积硬掩膜或涂覆光刻胶，
    S32、将所述硬掩模或所述光刻胶图形化以使得所述压电层的至少与所述声波反射结构的边界对应的部位暴露出，
    S33、对所述压电层的暴露部位进行离子注入，
    S34、去除所述硬掩膜或光刻胶。
  12. 根据权利要求11所述的制作工艺，其特征在于，所述S33步骤还包括在离子注入后，对所述压电层施加退火工艺。
  13. 根据权利要求11所述的制作工艺，其特征在于，所述S33步骤具体包括控制离子注入过程中的掺杂离子的种类和/或浓度以使得被离子注入后的压电层材料的居里点低于所述离子注入后的所述谐振器的制作工艺的最高工艺温度。
  14. 根据权利要求10-13中任一项所述的制作工艺，其特征在于，所述声波反射结构为空腔或者布拉格反射结构。
  15. 一种薄膜体声波谐振器，其特征在于，通过权利要求10-14中任一项所述的制作工艺制成。
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