WO2022134861A1 - 一种频率可调的薄膜体声波谐振器及其制备方法 - Google Patents

一种频率可调的薄膜体声波谐振器及其制备方法 Download PDF

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WO2022134861A1
WO2022134861A1 PCT/CN2021/127795 CN2021127795W WO2022134861A1 WO 2022134861 A1 WO2022134861 A1 WO 2022134861A1 CN 2021127795 W CN2021127795 W CN 2021127795W WO 2022134861 A1 WO2022134861 A1 WO 2022134861A1
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electrode
piezoelectric layer
layer
frequency
bulk acoustic
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PCT/CN2021/127795
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English (en)
French (fr)
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李国强
张铁林
刘红斌
衣新燕
赵利帅
欧阳佩东
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华南理工大学
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Priority to AU2021407849A priority Critical patent/AU2021407849B2/en
Priority to JP2023532676A priority patent/JP2023552179A/ja
Priority to US18/274,236 priority patent/US20240088869A1/en
Publication of WO2022134861A1 publication Critical patent/WO2022134861A1/zh

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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
    • 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
    • H03H9/173—Air-gaps
    • 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
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02015—Characteristics of piezoelectric layers, e.g. cutting angles
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02015—Characteristics of piezoelectric layers, e.g. cutting angles
    • H03H9/02031—Characteristics of piezoelectric layers, e.g. cutting angles consisting of ceramic
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02157—Dimensional parameters, e.g. ratio between two dimension parameters, length, width or thickness
    • 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
    • H03H9/178—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator of a laminated structure of multiple piezoelectric layers with inner electrodes
    • 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
    • H03H2003/021—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 the resonators or networks being of the air-gap type
    • 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
    • H03H2003/023—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 the resonators or networks being of the membrane type
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H2009/02165—Tuning
    • H03H2009/02173—Tuning of film bulk acoustic resonators [FBAR]
    • H03H2009/02188—Electrically tuning
    • H03H2009/02196—Electrically tuning operating on the FBAR element, e.g. by direct application of a tuning DC voltage
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H2009/02165—Tuning
    • H03H2009/02173—Tuning of film bulk acoustic resonators [FBAR]
    • H03H2009/02188—Electrically tuning
    • H03H2009/02204—Electrically tuning operating on an additional circuit element, e.g. applying a tuning DC voltage to a passive circuit element connected to the resonator

Definitions

  • the invention relates to the technical field of radio frequency communication, in particular to a frequency-adjustable thin-film bulk acoustic wave resonator and a preparation method thereof.
  • Thin-film bulk acoustic wave filters are widely used in RF communication front-end signal processing, and are the best filter components for high-frequency communications, especially 5G communications, sub-6G communications, and future higher-frequency communications.
  • the BAW filter plays a vital role.
  • bulk acoustic wave filters have gradually replaced surface acoustic wave devices as the mainstream filter type.
  • the traditional thin film bulk acoustic wave resonator is a sandwich structure composed of upper and lower metal electrodes and a piezoelectric film material sandwiched between them.
  • the principle is to use the piezoelectric effect.
  • the piezoelectric effect is that when a dielectric is deformed by an external force in a certain direction, polarization will occur inside it, and positive and negative opposite charges will appear on its two opposite surfaces.
  • an alternating voltage is applied to the electrodes at both ends, the piezoelectric effect causes the piezoelectric film to vibrate mechanically and generate bulk acoustic waves.
  • the frequency of the acoustic wave and the thickness of the piezoelectric film satisfy a certain mathematical relationship, resonance occurs, and the bulk acoustic wave resonates.
  • the principle of the device is to use the resonance phenomenon at a specific frequency to make frequency selection.
  • the acoustic wave For the transmission form of the acoustic wave in the piezoelectric film, when the bulk acoustic wave is transmitted to the electrode interface, the acoustic wave is reflected back by the acoustic reflection layer outside the electrode, thereby confining the bulk acoustic wave between the two electrodes to generate oscillation. Because the acoustic impedance of air is approximately zero, the solid/air interface composed of electrode material and air has a very strong ability to reflect acoustic waves.
  • a cavity is formed so that the lower electrode is in direct contact with the air, or a part of the substrate of the device is directly etched away, so that the lower electrode of the device is suspended to form a solid/gas interface, that is, a silicon etched device .
  • the purpose of the present invention is to provide a frequency-adjustable thin film bulk acoustic resonator and a preparation method thereof.
  • the purpose of the present invention is to propose a structure and preparation method of a novel frequency-adjustable thin-film bulk acoustic resonator.
  • the manufacturing process of the preparation method is simple, and the space limitation of the traditional bulk acoustic wave filter can be broken, and the functions that can only be realized by multiple bulk acoustic wave resonators in the past can be realized by one resonator, which saves space resources to a greater extent and promotes the device. progress in miniaturization.
  • the frequency-adjustable thin-film bulk acoustic resonator provided by the present invention is an air-gap thin-film bulk acoustic resonator.
  • the frequency-tunable thin film bulk acoustic wave resonator provided by the present invention has a multi-layer structure of electrode-piezoelectric layer-electrode-piezoelectric layer-electrode.
  • the composite "sandwich" structure of the electrode and the piezoelectric layer can be from 1st to Nth order.
  • all electrode layers control the resonant frequency of the resonator by applying a bias voltage through the lead-out layer and applying a bias voltage.
  • the frequency-tunable thin-film bulk acoustic wave resonator provided by the present invention includes a substrate, an air gap, a sandwich structure of electrodes and piezoelectric layers, and an electrode lead-out layer; the substrate is connected to the sandwich structure of electrodes and piezoelectric layers.
  • the connection between the substrate and the sandwich structure of the electrode and the piezoelectric layer is recessed in the substrate to form an air gap;
  • the electrode lead-out layer is connected to the sandwich structure of the electrode and the piezoelectric layer;
  • the electrode and the piezoelectric layer The sandwich structure of the layer includes a bottom electrode, a piezoelectric layer, a middle electrode and a top electrode, the electrodes and the piezoelectric layer are arranged alternately to form a sandwich structure, the piezoelectric layer is laminated on the bottom electrode, and the middle electrode is wrapped by the piezoelectric layer,
  • the top electrode is stacked on the piezoelectric layer; the number of the piezoelectric layer and the middle electrode is n, where n is an integer and the value of n is greater than or equal to 1.
  • the sandwich structure of the electrode and the piezoelectric layer may include a plurality of electrode layers and piezoelectric layers, and the electrode layers and the piezoelectric layers are arranged alternately to form a "sandwich" structure together.
  • An air gap is prepared between the substrate and the lower electrode.
  • the electrode extraction layer respectively extracts the lower electrode (bottom electrode) and the middle electrode.
  • the top electrode, the piezoelectric film, the middle electrode and the bottom electrode together form a sandwich structure, and the resonator can adjust the resonance frequency multiplication according to the applied bias voltage, and is suitable for the field of 5G high-frequency communication.
  • the bottom electrode and the middle electrode in the sandwich structure of the electrode and the piezoelectric layer are both connected to the external bias voltage source through the electrode extraction layer.
  • the potentials of different electrodes in the sandwich structure of the electrode and the piezoelectric layer are set to the same polarity or opposite polarity.
  • Each electrode layer is connected to an external bias voltage source through an electrode lead-out layer, and the potential of each electrode layer can be set to be the same or the positive and negative polarities are opposite. That is, the potential difference between all the electrodes can be made equal, or the electric field directions in the adjacent two piezoelectric layer regions can be opposite as shown in FIG. 9 and FIG. 10 .
  • the substrate is single crystal Si;
  • the piezoelectric layer is a piezoelectric film, and the piezoelectric layer is one or more of PZT, AlN, ZnO, CdS, and LiNbO 3 ;
  • the bottom electrode, the middle Both the electrode and the top electrode are metal electrode layers, and the metal electrode layer is one or more of Pt, Mo, W, Ti, Al, Au, and Ag.
  • the thickness of the piezoelectric layer is 500nm-3 ⁇ m; the thickness of the top electrode, the middle electrode and the bottom electrode is 20nm-1 ⁇ m.
  • the thickness of the electrode extraction layer is 0.3-1 ⁇ m.
  • the depth of the air gap is 0.5-2 ⁇ m.
  • the present invention provides a method for preparing the above-mentioned frequency-adjustable thin-film bulk acoustic resonator, comprising the following steps:
  • the etching method can use ICP or RIE technology to obtain grooves on a single crystal Si substrate), and deposit SiO 2 in the grooves as a filling layer (support layer);
  • step (2) Perform mechanical polishing on the filling layer described in step (1), so that the steps between the filling layer area and the surrounding area are as small as possible, deposit metal electrodes on the filling layer, and perform patterning treatment to obtain the bottom electrode (bottom). electrode);
  • n is an integer and the value of n is ⁇ 1 (n can be valued according to design needs, and can be
  • the multi-layer “electrode-piezoelectric layer-electrode” sandwich structure is obtained by depositing the electrode and the piezoelectric layer for many times), the electrode and the piezoelectric layer are alternately arranged, and the bottom electrode, the piezoelectric layer, the middle electrode and the top electrode form a sandwich structure, and the obtained the sandwich structure of the electrode and the piezoelectric layer;
  • a mask or photolithography method is used to etch out the through-holes drawn from the electrode on the piezoelectric layer and deposit metal to obtain the electrode lead-out layer;
  • the method for depositing SiO 2 in step (1) is PECVD; the method for depositing metal electrodes in step (2) is magnetron sputtering or evaporation; the method for depositing piezoelectric layer in step (3) includes: One or more of PVD (magnetron sputtering), MOCVD (metal organic compound chemical vapor deposition), PLD (pulsed laser deposition system), and ALD (atomic layer deposition).
  • PVD magnetic sputtering
  • MOCVD metal organic compound chemical vapor deposition
  • PLD pulsesed laser deposition system
  • ALD atomic layer deposition
  • the method of etching the through holes drawn from the electrodes on the piezoelectric layer is to use mask etching or photolithography; the material of the mask is SiO 2 or photoresist; deposit metal
  • the method for obtaining the electrode extraction layer is vapor deposition or magnetron sputtering.
  • the present invention has the following advantages and beneficial effects:
  • the present invention aims to propose a novel frequency-tunable thin-film bulk acoustic wave filter structure, which can change the center frequency of the resonator by adjusting the applied bias voltage; when the bias voltages applied to the electrodes all have the same
  • the sign of the equivalent piezoelectric coupling coefficient inside the piezoelectric film is the same in all parts, so that the resonator will resonate at its fundamental resonance frequency f0 ; when the bias voltage applied to the electrode
  • the equivalent piezoelectric coupling coefficient inside the corresponding piezoelectric film will also be affected, so that the phase of the transmission of the acoustic wave inside the piezoelectric film is opposite, so the resonant frequency will also change accordingly.
  • the frequency-adjustable thin-film bulk acoustic wave resonator provided by the present invention can realize the function that previously required multiple thin-film bulk acoustic wave resonators, saves space resources, and is beneficial to promoting the process of device miniaturization.
  • the preparation process is simple, the production cost is largely saved, and it is compatible with the existing MEMS/Si process.
  • Embodiment 1 is a cross-sectional view of an air cavity groove etched on a single crystal silicon substrate in Embodiment 1;
  • Example 2 is a cross-sectional view after filling the groove with SiO 2 and leveling it in Example 1;
  • Example 3 is a cross-sectional view of a metal bottom electrode grown on a single crystal silicon substrate in Example 1;
  • Example 4 is a cross-sectional view of a piezoelectric thin film grown in Example 1;
  • Example 5 is a cross-sectional view of a grown metal intermediate electrode in Example 1;
  • Example 6 is a cross-sectional view of continuing to grow a piezoelectric thin film on the intermediate electrode in Example 1;
  • Example 7 is a cross-sectional view of growing a top electrode and preparing an electrode extraction layer in Example 1;
  • Example 8 is a cross-sectional view of the air cavity obtained by releasing the filling layer under the bottom electrode in Example 1;
  • Example 9 is a schematic diagram of the frequency-adjustable thin-film bulk acoustic resonator provided in Example 1 with the same bias voltage polarity;
  • Example 10 is a schematic diagram of the frequency-adjustable thin-film bulk acoustic resonator provided in Example 1 with opposite polarity of bias voltage;
  • Example 11 is a schematic diagram of the admittance of the frequency-tunable thin-film bulk acoustic resonator provided in Example 1;
  • the figure includes: a single crystal silicon substrate 101 , a filling layer 102 , a bottom electrode 103 , a piezoelectric film 104 , a middle electrode 105 , an electrode lead-out layer 106 , an air cavity 107 , and a top electrode 108 .
  • Examples of the present invention provide a method of tuning a thin film bulk acoustic wave filter. Adjusting the frequency of the thin-film bulk acoustic wave filter commonly used in the art is achieved by adjusting the thickness and area of the mass-loading layer above the top electrode. In this example, a novel resonator structure is proposed to realize the frequency doubling adjustment of the thin-film bulk acoustic wave filter.
  • This embodiment provides an air-gap thin-film bulk acoustic wave resonator with adjustable frequency.
  • FIG. 8 from bottom to top, there are a single crystal silicon substrate 101 , a filling layer 102 , a bottom electrode 103 , and a piezoelectric film respectively.
  • 104 piezoelectric layer
  • middle electrode 105 electrode extraction layer 106
  • air cavity 107 top electrode 108
  • top electrode 108 top electrode
  • the filling layer 102 is finally released to become an air cavity 107 (air gap), so it is marked with 102 in the figure.
  • the specific structure of the filling layer 102 can be referred to FIG. 2 .
  • the frequency-tunable air-gap thin-film bulk acoustic wave resonator provided in Example 1 includes a single-crystal silicon substrate 101, an air gap 107, a sandwich structure of electrodes and piezoelectric layers, and an electrode lead-out layer 106;
  • the sandwich structure of the electrode and the piezoelectric layer is connected, and the connection between the single crystal silicon substrate 101 and the sandwich structure of the electrode and the piezoelectric layer is recessed in the substrate to form an air gap 107;
  • the electrode lead-out layer 106 is connected to the The sandwich structure of the electrode and the piezoelectric layer is connected;
  • the sandwich structure of the electrode and the piezoelectric layer includes a bottom electrode 103, a piezoelectric layer 104, a middle electrode 105 and a top electrode 108, and the electrodes and the piezoelectric layer are arranged alternately to form a sandwich structure,
  • the piezoelectric layer 104 is stacked on the bottom electrode 103, the middle electrode 105 is wrapped by
  • the substrate 101 is single crystal Si; the filling layer 102 is SiO 2 or doped P ion SiO 2 ; the piezoelectric film 104 is AlN with a thickness of 0.5 ⁇ m; the bottom electrode 103 , the top electrode 108 and the middle electrode 105 are all metal electrode layers, The thickness of the electrode layer was 200 nm, and the metal was Mo.
  • each electrode layer is connected to an external bias voltage source through an electrode lead-out layer, and the potential of each electrode layer can be set to be the same or opposite in positive and negative polarities. That is, the potential difference between all the electrodes can be made equal, or the electric field directions in the adjacent two piezoelectric layer regions can be opposite as shown in FIG. 9 and FIG. 10 .
  • U represents the applied bias voltage applied to the electrodes.
  • a frequency-adjustable air-gap thin-film bulk acoustic resonator in the present embodiment 1 is prepared by the following steps:
  • the single crystal silicon substrate 101 is etched.
  • the etching method can use ICP or RIE to obtain grooves on the single crystal Si substrate.
  • the depth of the grooves is 2 ⁇ m, as shown in FIG. 1 ;
  • the filling layer 102 and the Si surface in the surrounding area are polished by chemical mechanical polishing to obtain a surface with steps less than 20 nm; deposit on the filling layer metal electrode, and perform patterning treatment to obtain the bottom electrode 103 (refer to FIG. 3), the bottom electrode (lower electrode) 103 is made of metal Mo, and the electrode thickness is 0.2 ⁇ m;
  • n piezoelectric layers 104 on the bottom electrode 103 described in step (2) (refer to FIG. 4 , only one piezoelectric layer is depicted in FIG. 4 , but there can be multiple ones in the actual production process)
  • n intermediate electrodes 105 (refer to FIG. 5, only one intermediate electrode is depicted in FIG. 5, but there can be multiple in the actual production process)
  • a top electrode 108 n is an integer and the value of n is greater than or equal to 1 , the electrode and the piezoelectric layer are alternated, the bottom electrode 103, the piezoelectric layer 104, the middle electrode 105 and the top electrode 108 form a sandwich structure, the middle electrode is wrapped by the piezoelectric layer (refer to FIG.
  • the top electrode is stacked on the piezoelectric layer.
  • the piezoelectric layer 104 can be made of AlN material, and the thickness of the piezoelectric layer is 2 ⁇ m; the thickness of the middle electrode 105 is 0.2 ⁇ m; The area of the electrode 108 is smaller than that of the bottom electrode 103, and the thickness of the top electrode is 0.2 ⁇ m;
  • a mask or photolithography method is used to etch out the through hole of the electrode lead-out on the piezoelectric layer 104, and deposit metal to obtain the electrode lead-out layer 106, as shown in FIG. 7;
  • Example 1 the frequency-tunable thin-film bulk acoustic resonator is synthesized, and the number of piezoelectric thin-film layers and the number of intermediate electrodes are both 2, that is, the value of n is 2.
  • n is equal to 2
  • the obtained frequency-tunable thin-film bulk acoustic resonator is subjected to filter admittance test, which is tested for Anglent E50 using a network analyzer.
  • the network analyzer is connected to the probe station, and the wafers and probes are fixed and prepared on the probe station. Then calibrate the network analyzer, and then set the center frequency of the network analyzer to 1675MHz and test the bandwidth to 900MHz.
  • the BAW resonator of this example can be inferred that when the number of piezoelectric film layers is 1, 2, 3...N (N is a positive integer), and the value of N increases continuously, the BAW resonator can be realized.
  • the resonant frequency is multiplied.

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  • Acoustics & Sound (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Abstract

本发明公开了一种频率可调的薄膜体声波谐振器及其制备方法。该谐振器包括衬底、空气隙、电极和压电层的三明治结构及电极引出层；所述衬底与所述电极和压电层的三明治结构连接，衬底与所述电极和压电层的三明治结构的连接面向衬底内凹陷，形成空气隙；所述电极引出层与所述电极和压电层的三明治结构连接。所述电极和压电层的三明治结构包括底电极、压电层、中间电极及顶电极，电极与压电层相间排布形成三明治结构，所述底电极上层叠压电层，所述中间电极被压电层包裹，顶电极层叠在压电层上；所述压电层及中间电极的数量均为n个，n为整数且n的取值≥1。该谐振器可以根据外加偏置电压调整谐振倍频，适用于5G高频通信领域。

Description

一种频率可调的薄膜体声波谐振器及其制备方法 技术领域
本发明涉及射频通信技术领域，具体涉及一种频率可调的薄膜体声波谐振器及其制备方法。
 背景技术
薄膜体声波滤波器广泛应用于射频通信前端信号处理，是高频通信特别是5G通信、sub-6G通信以及未来更高频率通信的最佳滤波器件。在射频信号处理过程中，体声波滤波器发挥着至关重要的作用。例如在通信基站、WiFi路由器、个人移动便携设备等方面体声波滤波器已经逐渐替代声表面波器件成为主流的滤波器类型。
传统的薄膜体声波谐振器是由上下两层金属电极和夹于其中间的压电薄膜材料所构成的三明治结构。其原理为利用压电效应，压电效应是电介质在沿一定方向上受到外力的作用而变形时，其内部会产生极化现象，同时在它的两个相对表面上出现正负相反的电荷。当施加一个交变电压于两端电极时，压电效应使压电薄膜产生机械振动并产生体声波，当声波的频率与压电薄膜厚度满足一定数学关系时就发生谐振现象，而体声波谐振器的原理即是利用特定频率下的谐振现象做出频率选择。
对于压电薄膜内声波的传递形式，具体为当体声波传输到电极界面时，经电极外的声学反射层将声波反射回来，从而将体声波限制在两电极之间产生振荡。因为空气的声阻抗近似为零，因此在电极材料和空气组成的固/气界面具有非常强的反射声波的能力。在电极的下方制备填充层后，形成空腔使下电极直接与空气接触，或将器件的一部分衬底直接刻蚀掉，使器件的下电极悬空形成固/气界面，即硅刻蚀型器件。
对于频率可调的体声波滤波器的研究较少，大多是根据温度变化做频率补偿，或者修饰电极上方的质量负载层对谐振频率进行调整。例如诺思（天津）微系统有限公司在CN202010013002.X 调节体声波滤波器中谐振器频率的方法及体声波滤波器中提出的通过调整体声波谐振器上方的质量负载层的面积实现对谐振器中心频率的调整。上述提到的现有技术虽然起到频率调节的作用，但是其调频作用是一次性的，即在器件加工完成后频率已经固定，不能进行二次调整。这没有解决频率调节的本质问题，不能实现单个谐振器频率随外界单一变量进行改变的功能，只能作为一种频率修饰的技术手段。
 技术解决方案
为了克服现有技术存在的不足，本发明的目的是提供一种频率可调的薄膜体声波谐振器及其制备方法。
本发明的目的在于提出一种新型频率可调的薄膜体声波谐振器的结构与制备方法。采用该制备方法的制造工艺简单，而且可以突破传统体声波滤波器的空间限制，将以往多个体声波谐振器才能实现的功能使用一个谐振器实现，在更大程度上节约了空间资源，推动器件的小型化进步。
本发明的目的是通过以下技术方案之一实现的。
    本发明提供的频率可调的薄膜体声波谐振器是一种空气隙型薄膜体声波谐振器。
    本发明提供的频率可调的薄膜体声波谐振器具有电极-压电层-电极-压电层-电极的多层结构。其中电极与压电层的复合“三明治”结构可以为1阶到N阶。且所有电极层均通过引出层与施加偏置电压，外加偏执电压控制谐振器的谐振频率。
    本发明提供的频率可调的薄膜体声波谐振器，包括衬底、空气隙、电极和压电层的三明治结构及电极引出层；所述衬底与所述电极和压电层的三明治结构连接，衬底与所述电极和压电层的三明治结构的连接面向衬底内凹陷，形成空气隙；所述电极引出层与所述电极和压电层的三明治结构连接；所述电极和压电层的三明治结构包括底电极、压电层、中间电极及顶电极，电极与压电层相间排布形成三明治结构，所述底电极上层叠压电层，所述中间电极被压电层包裹，顶电极层叠在压电层上；所述压电层及中间电极的数量均为n个，n为整数且n的取值≥1。
    所述电极和压电层的三明治结构中可包含多个电极层与压电层，电极层与压电层相间排布，共同构成“三明治”结构。
    所述衬底与下电极间制备空气隙。所述电极引出层分别将下电极（底电极）与中间电极引出。所述顶电极、压电薄膜、中间电极和底电极共同构成三明治结构，该谐振器可以根据外加偏置电压调整谐振倍频，适用于5G高频通信领域。
    进一步地，所述电极和压电层的三明治结构中的底电极和中间电极均通过电极引出层与外界偏置电压源相连。
    进一步地，所述电极和压电层的三明治结构中不同的电极的电位设置为相同极性或相反极性。每一电极层通过电极引出层与外界偏置电压源相连，每一电极层的电位可以设置为相同或正负极性相反。即所有的电极之间可以令他们的电势差相等，或者令相邻两个压电层区域中的电场方向相反如图9、图10所示。
    进一步地，所述衬底为单晶Si；所述压电层为压电薄膜，所述压电层为PZT、AlN、ZnO、CdS、LiNbO 3中的一种以上；所述底电极、中间电极和顶电极均为金属电极层，所述金属电极层为Pt、Mo、W、Ti、Al、Au、Ag中的一种以上。
    进一步地，所述压电层的厚度为500nm-3μm；所述顶电极、中间电极和底电极的厚度为20nm-1μm。
    进一步地，所述电极引出层的厚度为0.3-1μm。
    进一步地，所述空气隙的深度为0.5-2μm。
    本发明提供一种制备上述的频率可调的薄膜体声波谐振器的方法，包括如下步骤：
   （1）对衬底进行刻蚀得到凹槽（刻蚀方式可以采用ICP或者RIE等技术在单晶Si衬底上得到凹槽），在凹槽中沉积SiO 2作为填充层（支撑层）；
   （2）对步骤（1）所述填充层做机械抛光处理，使填充层区域与周围区域的台阶尽量小，在填充层上沉积金属电极，并进行图形化处理，得到所述底电极（下电极）；
   （3）在步骤（2）所述底电极上沉积n个压电层、n个中间电极及一个顶电极，n为整数且n的取值≥1（n可根据设计需要进行取值，可通过多次沉积电极和压电层得到多层“电极-压电层-电极”的三明治结构），电极与压电层相间，底电极、压电层、中间电极及顶电极形成三明治结构，得到所述电极和压电层的三明治结构；
   （4）在最后一层顶电极制备完成之后，利用掩膜或者光刻方法在压电层上刻蚀出电极引出的通孔并沉积金属得到电极引出层；
   （5）利用ICP、RIE或者湿法刻蚀等方式刻蚀连通下方填充层的通孔并释放填充层得到空气隙（即空气腔结构，此处可采用腐蚀液释放填充层），得到所述频率可调的薄膜体声波谐振器。
    进一步地，步骤（1）所述沉积SiO 2的方法为PECVD；步骤（2）所述沉积金属电极的方法为磁控溅射或蒸镀；步骤（3）所述沉积压电层的方法包括PVD（磁控溅射）、MOCVD（金属有机化合物化学气相沉淀）、PLD（脉冲激光沉积系统）、ALD（原子层沉积）中的一种以上。
    进一步地，步骤（4）中，在压电层上刻蚀出电极引出的通孔的方法为利用掩膜刻蚀或光刻；所述掩膜的材料为SiO 2或者光刻胶；沉积金属得到电极引出层的方法为蒸镀或磁控溅射。  
有益效果
 与现有技术相比，本发明具有如下优点和有益效果：
   （1）本发明旨在提出一种新型频率可调薄膜体声波滤波器结构，该结构能够通过调节外加偏置电压从而改变谐振器的中心频率；当施加在电极上的偏置电压都具有相同的大小和极性时，所有部分内的压电薄膜内部的等效压电耦合系数符号是一致的，这样谐振器就会在其基础谐振频率f 0处谐振；当施加在电极上的偏执电压大小相同而极性相反时，那么同样会对相应压电薄膜内部的等效压电耦合系数产生影响，使声波在压电薄膜内部的传递的相位相反，所以谐振频率相应也发生改变。
   （2）本发明提供的频率可调的薄膜体声波谐振器，能够实现以往需要多个薄膜体声波谐振器完成的功能，节约了空间资源，有益于推进器件小型化进程。制备工艺简单，在很大程度上节约了生产成本，并与现有的MEMS/Si工艺兼容。
 附图说明
图1为实施例1中在单晶硅衬底上刻蚀出空气腔凹槽的剖视图；
图2为实施例1中在凹槽中填充SiO 2并抛平后的的剖视图；
图3为以实施例1中在单晶硅衬底上生长金属底电极的剖视图；
图4为实施例1中生长压电薄膜的剖视图；
图5为实施例1中生长金属中间电极的剖视图；
图6为实施例1中在中间电极上继续生长压电薄膜的剖视图；
图7为以实施例1生长顶电极以及制备电极引出层的剖视图；
图8为实施例1中将底电极下方填充层释放得到空气腔的剖视图；
图9为实施例1提供的频率可调的薄膜体声波谐振器加偏置电压极性相同的示意图；
图10为实施例1提供的频率可调的薄膜体声波谐振器加偏置电压极性相反的示意图；
图11为实施例1提供的频率可调的薄膜体声波谐振器的导纳示意图；
图中包括：单晶硅衬底101、填充层102、底电极103、压电薄膜104、中间电极105、电极引出层106、空气腔107、顶电极108。
 本发明的实施方式
以下结合实例对本发明的具体实施作进一步说明，但本发明的实施和保护不限于此。需指出的是，以下若有未特别详细说明之过程，均是本领域技术人员可参照现有技术实现或理解的。所用试剂或仪器未注明生产厂商者，视为可以通过市售购买得到的常规产品。
本发明示例提供了一种调节薄膜体声波滤波器的方法。通常在本技术领域中常用的调整薄膜体声波滤波器的频率是通过调整顶电极上方质量负载层的厚度后者面积实现的。而在本例中是提出一种新型谐振器结构实现薄膜体声波滤波器的倍频调整。
实施例 1
本实施例提供了一种频率可调的空气隙型薄膜体声波谐振器，如图8所示，自下而上分别为单晶硅衬底101、填充层102、底电极103、压电薄膜104（压电层）、中间电极105、电极引出层106、空气腔107、顶电极108。其中填充层102最终经过释放成为空气腔107（空气隙），故图中为标出102。填充层102具体结构可以参考图2。
    实施例1提供的频率可调的空气隙型薄膜体声波谐振器，包括单晶硅衬底101、空气隙107、电极和压电层的三明治结构及电极引出层106；所述衬底与所述电极和压电层的三明治结构连接，单晶硅衬底101与所述电极和压电层的三明治结构的连接面向衬底内凹陷，形成空气隙107；所述电极引出层106与所述电极和压电层的三明治结构连接；所述电极和压电层的三明治结构包括底电极103、压电层104、中间电极105及顶电极108，电极与压电层相间排布形成三明治结构，所述底电极103上层叠压电层104，所述中间电极105被压电层104包裹，顶电极108层叠在压电层104上；所述压电层104及中间电极105的数量均为n个，n为整数且n的取值≥1。
衬底101为单晶Si；填充层102为SiO 2或者掺杂P离子SiO 2；压电薄膜104为0.5μm厚的AlN；底电极103、顶电极108以及中间电极105均为金属电极层，电极层的厚度为200nm，所述金属为Mo。
除了顶电极以外，每一电极层通过电极引出层与外界偏置电压源相连，每一电极层的电位可以设置为相同或正负极性相反。即所有的电极之间可以令他们的电势差相等，或者令相邻两个压电层区域中的电场方向相反如图9、图10所示。图9、图10中U代表对电极施加的外加偏置电压。
    本实施例1中一种频率可调的空气隙型薄膜体声波谐振器，通过以下步骤制备：
   （1）对单晶硅衬底101进行刻蚀，刻蚀方式可以采用ICP或者RIE等技术在单晶Si衬底上得到凹槽，凹槽的深度为2μm，参照图1所示；
   （2）在凹槽中利用PECVD等技术沉积SiO 2作为填充层102（参照图2所示），填充层102与周围区域Si表面使用化学机械抛光得到台阶小于20nm的表面；在填充层上沉积金属电极，并进行图形化处理得到底电极103（参照图3所示），底电极（下电极）103材料为金属Mo，电极厚度为0.2μm；
   （3）在步骤（2）所述底电极103上沉积n个压电层104（参照图4所示，图4中的压电层只描绘出一个，但实际生产过程中可以为多个）、n个中间电极105（参照图5所示，图5中的中间电极只描绘出一个，但实际生产过程中可以为多个）及一个顶电极108，n为整数且n的取值≥1，电极与压电层相间，底电极103、压电层104、中间电极105及顶电极108形成三明治结构，所述中间电极被压电层包裹（参照图6所示），顶电极层叠在压电层上（参照图7所示），得到所述电极和压电层的三明治结构；所述压电层104可以为AlN材料，压电层厚度为2μm；中间电极105厚度为0.2μm；顶电极108面积小于底电极103，顶电极厚度为0.2μm；
   （4）在顶电极制备完成之后，利用掩摸或者光刻方法在压电层104上刻蚀出电极引出的通孔，并沉积金属得到电极引出层106，参照图7所示；
   （5）利用ICP、RIE或者湿法刻蚀等方式，刻蚀连通填充层102的通孔，使用腐蚀液释放填充层102，形成空气腔107结构（空气隙），得到所述频率可调的薄膜体声波谐振器（参照图8所示）。
作为举例，实施例1合成了所述频率可调的薄膜体声波谐振器，其压电薄膜层数和中间电极的数量均为2，即n的取值为2。当n等于2时，得到的频率可调的薄膜体声波谐振器进行滤波器导纳测试，使用网络分析仪为Anglent E50进行测试。测试流程先将网络分析仪与探针台进行连接，在探针台上固定制备晶圆以及探针。然后对网络分析仪进行校准，再设置网络分析仪的中心频率为1675MHz测试的带宽为900MHz。移动探针台使探针接触到晶圆表面的金属电极，使用扫描键进行扫描测试。如图11所示，当改变施加在电极上的偏执电压时，该谐振器出现不同的谐振峰现在，这表明：压电耦合系数受偏置电压影响，谐振频率相应也发生改变。
本实例的体声波谐振器按照同样的原理可以推知当压电薄膜层数为1,2,3……N（N为正整数），N的取值不断增大时，可以实现体声波谐振器谐振频率倍增。
以上实施例仅为本发明较优的实施方式，仅用于解释本发明，而非限制本发明，本领域技术人员在未脱离本发明精神实质下所作的改变、替换、修饰等均应属于本发明的保护范围。

Claims (10)

  1. 一种频率可调的薄膜体声波谐振器，其特征在于，包括衬底、空气隙、电极和压电层的三明治结构及电极引出层；所述衬底与所述电极和压电层的三明治结构连接，衬底与所述电极和压电层的三明治结构的连接面向衬底内凹陷，形成空气隙；所述电极引出层与所述电极和压电层的三明治结构连接；所述电极和压电层的三明治结构包括底电极、压电层、中间电极及顶电极，电极与压电层相间排布形成三明治结构，所述底电极上层叠压电层，所述中间电极被压电层包裹，顶电极层叠在压电层上；所述压电层及中间电极的数量均为n个，n为整数且n的取值≥1。
  2. 根据权利要求1所述的频率可调的薄膜体声波谐振器，其特征在于，所述电极和压电层的三明治结构中的底电极和中间电极均通过电极引出层与外界偏置电压源相连。
  3. 根据权利要求1所述的频率可调的薄膜体声波谐振器，其特征在于，所述电极和压电层的三明治结构中不同的电极的电位设置为相同极性或相反极性。
  4. 根据权利要求1所述的频率可调的薄膜体声波谐振器，其特征在于，所述衬底为单晶Si；所述压电层为压电薄膜，所述压电层为PZT、AlN、ZnO、CdS、LiNbO 3中的一种以上；所述底电极、中间电极和顶电极均为金属电极层，所述金属电极层为Pt、Mo、W、Ti、Al、Au、Ag中的一种以上。
  5. 根据权利要求1所述的频率可调的薄膜体声波谐振器，其特征在于，所述压电层的厚度为500nm-3μm；所述顶电极、中间电极和底电极的厚度为20nm-1μm。
  6. 根据权利要求1所述的频率可调的薄膜体声波谐振器，其特征在于，所述电极引出层的厚度为0.3-1μm。
  7. 根据权利要求1所述的频率可调的薄膜体声波谐振器，其特征在于，所述空气隙的深度为0.5-2μm。
  8. 一种制备权利要求1-7任一项所述的频率可调的薄膜体声波谐振器的方法，其特征在于，包括如下步骤：
       （1）对衬底进行刻蚀得到凹槽，在凹槽中沉积SiO 2作为填充层；
       （2）在步骤（1）所述填充层上沉积金属电极，并进行图形化处理，得到所述底电极；
       （3）在步骤（2）所述底电极上沉积n个压电层、n个中间电极及一个顶电极，n为整数且n的取值≥1，电极与压电层相间，底电极、压电层、中间电极及顶电极形成三明治结构，得到所述电极和压电层的三明治结构；
       （4）在压电层上刻蚀出电极引出的通孔并沉积金属得到电极引出层；
       （5）刻蚀连通下方填充层的通孔并释放填充层得到空气隙，得到所述频率可调的薄膜体声波谐振器。
  9. 根据权利要求8所述的频率可调的薄膜体声波谐振器的制备方法，其特征在于，步骤（1）所述沉积SiO 2的方法为PECVD；步骤（2）所述沉积金属电极的方法为磁控溅射或蒸镀；步骤（3）所述沉积压电层的方法包括PVD、MOCVD、PLD、ALD中的一种以上。
  10. 根据权利要求8所述的频率可调的薄膜体声波谐振器的制备方法，其特征在于，步骤（4）中，在压电层上刻蚀出电极引出的通孔的方法为利用掩膜刻蚀或光刻；所述掩膜的材料为SiO 2或者光刻胶；沉积金属得到电极引出层的方法为蒸镀或磁控溅射。
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