WO2020133002A1 - 谐振器和梯形滤波器 - Google Patents

谐振器和梯形滤波器 Download PDF

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Publication number
WO2020133002A1
WO2020133002A1 PCT/CN2018/124083 CN2018124083W WO2020133002A1 WO 2020133002 A1 WO2020133002 A1 WO 2020133002A1 CN 2018124083 W CN2018124083 W CN 2018124083W WO 2020133002 A1 WO2020133002 A1 WO 2020133002A1
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Prior art keywords
resonator
filter
piezoelectric layer
top electrode
convex structure
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PCT/CN2018/124083
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English (en)
French (fr)
Inventor
张孟伦
庞慰
杨清瑞
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Tianjin University
ROFS Microsystem Tianjin Co Ltd
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Tianjin University
ROFS Microsystem Tianjin Co Ltd
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Priority to PCT/CN2018/124083 priority Critical patent/WO2020133002A1/zh
Publication of WO2020133002A1 publication Critical patent/WO2020133002A1/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 elements; Electromechanical resonators
    • H03H9/02—Details
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/56—Monolithic crystal filters

Definitions

  • the invention relates to the technical field of communication, and in particular to a resonator and a ladder filter.
  • FBAR Thin film bulk acoustic resonator
  • a typical FBAR structure is shown in FIG. 1 and includes a top electrode 101, a bottom electrode 103, a piezoelectric layer 102 sandwiched therebetween, an acoustic wave reflection structure 104 on the bottom electrode 103, and a substrate 105.
  • FBAR uses the inverse piezoelectric effect to convert the input sinusoidal electrical signal into mechanical resonance, and then uses the piezoelectric effect to convert the mechanical resonance into electrical signal output.
  • the frequency filter device can be constructed by connecting the resonators according to a certain topological structure, and the most common topological structure of the resonators constituting the filter is the ladder structure (ie, ladder structure).
  • each stage of the ladder filter is composed of a series resonator (X1, X2... or Xn) and a parallel resonator (Y1, Y2... or Yn).
  • the external electrical properties of the entire device are basically in the form of capacitors, so the electrical transmission characteristics of the entire network are consistent with the ladder-shaped capacitor network.
  • the frequency of parallel resonators is lower than that of series resonators.
  • FBAR mainly uses the longitudinal piezoelectric coefficient of the piezoelectric film to generate the piezoelectric effect, so its main working mode is the longitudinal wave mode (Thickness, Extensional Mode, TE mode for short) in the thickness direction.
  • Thin film bulk acoustic resonators only excite the thickness direction (TE) mode, but in addition to the desired TE mode, lateral parasitic modes can also be generated.
  • TE thickness direction
  • Rayleigh-Ram mode is a mechanical wave perpendicular to the direction of the TE mode. The waves of these transverse modes will be lost at the boundary of the resonator, so that the energy of the longitudinal mode required by the resonator will be lost, and eventually the Q value of the resonator will decrease.
  • a common method is to add a convex structure around the edge of the upper electrode of the resonator. Since the acoustic impedance in the convex structure does not match the acoustic impedance in the effective area of the resonator, the acoustic wave at the edge can be reflected back into the resonator, so that the energy loss in the resonator can be reduced.
  • the added convex structure will cause the series resonator to have a spurious peak 301 on the left side of the impedance frequency curve, resulting in a defect 302 in the passband of the filter, which in turn makes the performance of the filter decline.
  • the present invention provides a resonator and a ladder filter, which increases the Q value of the resonator by adding a convex structure, and at the same time, through the design of the convex structure in the resonator, the impedance frequency characteristic curve of the series resonator is left The side peaks move to the left to move the defects in the filter passband to the filter stopband, thereby improving the filter performance.
  • embodiments of the present invention provide a resonator, a plurality of the resonators are used to form a filter in cascade;
  • the resonator includes: a substrate, a bottom electrode, a piezoelectric layer, a top electrode, an acoustic wave A reflective structure and a convex structure for adjusting the passband performance of the filter;
  • the piezoelectric layer is located between the top electrode and the bottom electrode, and the convex structure is located on the top electrode away from the piezoelectric One side of the layer, either the surface of the piezoelectric layer below the top electrode, or the upper surface of the bottom electrode below the piezoelectric layer, or below the bottom electrode;
  • the acoustic wave reflection structure is located between the substrate and the bottom electrode.
  • An embodiment of the present invention further provides a ladder filter including a plurality of the above-mentioned resonators, and a plurality of the resonators are cascaded to form the filter.
  • the convex structure design of the resonator of the present invention can move the stray peak in the left side of the impedance frequency characteristic curve of the series resonator to the left while improving the Q value of the resonator, so that the The defect moves into the filter stop band, so that the pass band performance of the filter can be improved.
  • the material composition of the piezoelectric layer is doped with rare earth elements. Doping rare-earth elements in the piezoelectric layer can compensate for the decrease in the resonator electromechanical coupling coefficient caused by the convex structure design.
  • the material composition of the piezoelectric layer is aluminum nitride, and the aluminum nitride is doped with rare earth elements.
  • the rare earth element is any one or more of the following: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium, and scandium .
  • the acoustic wave reflection structure is located on the upper surface of the substrate.
  • the substrate has a structure corresponding to the acoustic wave reflection structure, and a part of the acoustic wave reflection structure is embedded in the substrate.
  • the sound wave reflection structure is an acoustic mirror.
  • the acoustic mirror is an air cavity or a Bragg reflection layer.
  • the noise peaks in the passband of the filter are moved into the stopband.
  • the distance between the raised structure and the edge of the top electrode is a predetermined distance.
  • the material density of the raised structure is greater than the material density of the top electrode.
  • the top electrode has a concave structure corresponding to the position of the convex structure, and the concave structure is located inside the convex structure.
  • the top electrode has a bridge wing structure and the bridge wing structure is located outside the raised structure, there is an air gap between the bridge wing structure and the piezoelectric layer, and the bridge wing structure Corresponding to the sound wave reflection structure.
  • the top electrode has a bridge structure, and the bridge structure is located outside of the convex structure, and the bridge structure has a portion between the piezoelectric layer and a portion of the bridge structure close to the convex structure Air gap.
  • FIG. 1 is a schematic structural diagram of a prior art acoustic wave resonator
  • FIG. 3 is a schematic diagram comparing the impedance curve of the resonator in the prior art filter with the transmission characteristic curve of the filter;
  • FIG. 4 is a schematic diagram of the structure of the resonator in the first embodiment
  • FIG. 5 is a cross-sectional view of FIG. 4 taken along the direction of top views 1B-1B;
  • FIG. 6 is a schematic diagram comparing the impedance curve of the resonator and the transmission characteristic curve of the filter in the first embodiment
  • FIG. 7 is a schematic diagram of the structure of the resonator in the second embodiment
  • FIG. 8 is a cross-sectional view of FIG. 7 taken along the direction of the top views 1B-1B;
  • FIG. 9 is a schematic structural view of a resonator in a third embodiment
  • FIG. 10 is a cross-sectional view of FIG. 9 taken along the direction of top views 1B-1B;
  • FIG. 11 is a schematic structural view of the resonator in the fourth embodiment.
  • FIG. 12 is a cross-sectional view of FIG. 11 taken along the direction of the top views 1B-1B;
  • FIG. 13 is a schematic structural view of a resonator in a fifth embodiment
  • FIG. 14 is a cross-sectional view of FIG. 13 taken along the direction of top views 1B-1B;
  • 15 is a schematic diagram of the structure of the resonator in the sixth embodiment.
  • FIG. 16 is a cross-sectional view of FIG. 15 taken along the direction of FIGS. 1B-1B from above.
  • the first embodiment of the invention relates to a resonator.
  • a plurality of the resonators are used in cascade to form a filter.
  • the resonator includes a substrate 401, a bottom electrode 402, a piezoelectric layer 403 doped with rare earth elements, a top electrode 404, an acoustic wave reflection structure 405, and a filter for adjusting the passband performance of the filter ⁇ 406.
  • the piezoelectric layer 403 is located between the top electrode 404 and the bottom electrode 402, and the convex structure 406 is located on a side of the top electrode 404 facing away from the piezoelectric layer 403, but is not limited thereto, It can also be located elsewhere.
  • the top electrode 404 and the bottom electrode 402 can be composed of gold (Au), tungsten (W), molybdenum (Mo), platinum (Pt), ruthenium (Ru), iridium (Ir), titanium tungsten (TiW), aluminum (Al), titanium (Ti) and other similar metals are formed.
  • the material composition of the raised structure may be the same as or different from the top electrode.
  • the material density of the raised structure is greater than the material density of the top electrode, so that the stray peaks in the pass band of the filter can be moved into the stop band.
  • the processing method of the raised structure 406 is as follows: First, a thin film of a specific thickness is deposited on the surface of the top electrode by a thin film deposition process such as PVD, CVD, or PECVD; then, a layer of photoresist is spin-coated on the surface of the thin film , The pattern on the photoresist plate is transferred to the photoresist by the method of ultraviolet exposure; finally, the process method of dry etching or wet etching will not affect the film deposited on the top electrode. The required parts are etched away, and after removing the photoresist, the designed raised structure is formed.
  • a thin film deposition process such as PVD, CVD, or PECVD
  • the acoustic wave reflection structure 405 is located between the substrate 401 and the bottom electrode 402. Wherein, the sound wave reflection structure 405 is an acoustic mirror. In practical applications, the acoustic wave reflection structure 405 may be located on the upper surface of the substrate 401 or inside the substrate 401. In the figure, an acoustic mirror is used as an example in the air cavity embedded in the substrate 401, but it is worth noting that any other acoustic mirror structure such as a Bragg reflector is also applicable.
  • the area where the top electrode 404, the piezoelectric layer 403, the bottom electrode 402, and the acoustic mirror overlap in the thickness direction is generally defined as the effective area of the resonator. It has a first acoustic impedance in the effective area of the resonator and a second acoustic impedance in the raised structure 406.
  • the first acoustic impedance in the effective area of the resonator does not match the second acoustic impedance in the raised structure 406, As a result, the laterally propagating acoustic waves are reflected back at the edge of the convex structure 406, reducing the loss of acoustic wave energy in the resonator, thus improving the quality factor value of the resonator, that is, the Q value.
  • the added raised structure 406 will cause the series resonator to have a spurious peak 601 on the left side of the impedance frequency curve, resulting in a defect 602 in the passband of the filter, which in turn will degrade the performance of the filter, as shown in FIG. 6 Show.
  • the resonance frequency in the convex structure can be lowered, and then the stray peak 601 on the left side of the impedance frequency characteristic curve of the series resonator can be moved to the left to far
  • the defect structure 602 in the passband of the filter is moved to 604 in the stopband that is not required by the filter index.
  • the acoustic wave energy reflected back to the transverse mode in the resonator can be further increased, so that the Q value of the resonator is further improved.
  • the electromechanical coupling coefficient of the resonator will be greatly reduced.
  • the increase in the thickness D of the convex structure 406 will increase the energy of the acoustic wave reflected back to the transverse mode in the resonator, so that the energy of the acoustic wave in the vertical mode of the resonator is relatively reduced, which in turn causes the electromechanical coupling system of the resonator to decrease significantly .
  • the distance between the series resonance point 605 and the parallel resonance point 606 becomes smaller. For a series resonator, it has two resonance points at resonance, which are the series resonance point and the parallel resonance point, respectively.
  • the phase of the applied electric field is the same as the phase of the polarization vector inside the piezoelectric film.
  • the electrical impedance of the resonator is a minimum, as shown at 605 in FIG. 6; the phase of the applied electric field is opposite to the phase of the internal polarization vector during parallel resonance, and the electrical impedance of the resonator is at a maximum value, as shown in FIG. 6 ⁇ 606.
  • the size of the distance between the series resonance point and the parallel resonance point represents the size of the resonator electromechanical coupling coefficient.
  • the piezoelectric layer 403 material may be doped with rare earth elements to increase the resonator electromechanical coupling coefficient.
  • a typical piezoelectric layer 403 material composition may be aluminum nitride, etc., and this type of material is a piezoelectric thin film with a thickness of less than 10 microns.
  • the aluminum nitride film is in a polycrystalline or single crystal form, and the growth method is thin film sputtering (sputtering) or organic metal chemical vapor deposition (MOCVD).
  • the rare earth element can be any one or more of the following: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd) ), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y), scandium (Sc), etc.
  • the typical doping element is scandium (Sc).
  • the AlN piezoelectric layer 403 material is doped with a rare earth element, due to the relatively large atomic radius of the rare earth element, the stress in the piezoelectric material changes, which in turn causes the electric dipole in the piezoelectric material to change.
  • an electric field is applied to the piezoelectric layer 403, a larger mechanical response is generated in the piezoelectric layer 403.
  • the series resonance point moves from 605 to 607 after doping, and the distance between the series resonance point and the parallel resonance point becomes larger, so that the resonator can obtain a higher electromechanical coupling coefficient.
  • the material of the convex structure 406 can be selected to move the stray peak on the left side of the series-resonator impedance frequency characteristic curve to the left.
  • the material density of the raised structure 406 can be selected to be greater than the density of the top electrode 404, so that the resonance frequency in the raised structure becomes lower.
  • the stray peak on the left side of the impedance frequency characteristic curve of the series resonator can also be turned to the left Move to a distance, thereby moving the defective structure in the filter passband formed by the resonator cascade with raised structures 406 out of the passband.
  • the second embodiment of the present invention relates to a resonator.
  • this embodiment has also been improved on the basis of the first embodiment.
  • the main improvement lies in:
  • the distance between the raised structure and the edge of the top electrode has a predetermined distance.
  • the size of the preset distance is adjusted according to different performance indexes of the filter to move the noise peaks in the pass band of the filter to the stop band.
  • the distance of the convex structure 406 from the edge of the resonator top electrode 404 is W1.
  • the size of the preset distance W1 is adjusted according to the specific performance index of the filter, so that the noise peak in the passband of the filter can be moved to the stopband, that is, the raised structure 406 can be adjusted to the top of the resonator
  • the distance W1 of the edge of the electrode 404 can make the resonance frequency in the convex structure lower than the main resonance frequency in the effective area of the resonator, and then move the stray peak on the left side of the impedance frequency characteristic curve of the series resonator to the left to the distance .
  • the stray peak on the left side of the impedance frequency characteristic curve of the series resonator can be moved to the left to the
  • the defective structure in the filter passband formed by the resonator cascade with raised structures 406 moves out of the passband.
  • the third embodiment of the present invention relates to a resonator.
  • this embodiment has also been improved on the basis of the first embodiment.
  • the main improvement lies in:
  • the top electrode has a concave structure corresponding to the position of the convex structure, and the concave structure is located inside the convex structure.
  • the top electrode 404 has a concave structure 901 corresponding to the position of the convex structure 406, and the concave structure 901 is located inside the convex structure 406.
  • the convex structure 406 can increase the Qp value of the resonator (Qp value refers to the quality factor value of the parallel resonance point), and the concave structure 901 can increase the Qs value of the resonator (Qs value refers to the quality factor value of the series resonance point ), so that the total quality factor Q value of the resonator can be increased.
  • the resonance frequency in the convex structure can be lowered, and then the left peak in the impedance frequency characteristic curve of the series resonator can be moved to the left to make the filter passband The defects are moved into the stop band of the filter, thereby improving the performance of the filter.
  • the fourth embodiment of the present invention relates to a resonator.
  • this embodiment has also been improved on the basis of the first embodiment.
  • the main improvement lies in:
  • the top electrode has a bridge wing structure.
  • the top electrode 404 has a bridge wing structure 111 and the bridge wing structure 11 is located outside the convex structure 406. There is an air gap 112 between the bridge wing structure 111 and the piezoelectric layer 403, and the bridge wing structure 111 is correspondingly located inside the acoustic wave reflection structure 405.
  • the resonator in addition to the convex structure 406, also has a bridge wing structure 111. There is an air gap 112 between the bridge wing structure 111 and the piezoelectric layer 403. And in combination with the direction shown in FIG. 12, the projection of the bridge wing structure 111 in the thickness direction is within the acoustic wave reflection structure 405 of the resonator.
  • the acoustic impedance in the air gap 112 does not match the acoustic impedance in the effective area of the resonator, and it can further reflect the acoustic wave of the transverse mode in the resonator back to the resonator Inside, there is a part of the sound wave energy converted into a wave in a mode perpendicular to the resonator, which further increases the Q value of the resonator.
  • the resonance frequency in the convex structure can be lowered, and then the left peak in the impedance frequency characteristic curve of the series resonator can be moved to the left to make the filter passband The defects are moved into the stop band of the filter, thereby improving the performance of the filter.
  • the fifth embodiment of the present invention relates to a resonator.
  • this embodiment has also been improved on the basis of the first embodiment.
  • the main improvements are:
  • the top electrode has a bridge structure.
  • the top electrode 404 has a bridge structure 131, and the bridge structure 131 is located outside the raised structure 406, and the bridge structure 131 is close to the raised structure 406
  • the resonance frequency in the convex structure can be lowered, and then the left peak in the impedance frequency characteristic curve of the series resonator can be moved to the left to make the filter passband The defects are moved into the stop band of the filter, thereby improving the performance of the filter.
  • the sixth embodiment of the present invention relates to a resonator.
  • this embodiment has also been improved on the basis of the first embodiment.
  • the main improvement lies in:
  • the top electrode has both a bridge wing structure and a bridge structure. Meanwhile, the top electrode has a concave structure corresponding to the position of the convex structure.
  • the top electrode 404 has a bridge wing structure 111 and the bridge wing structure 111 is located outside the convex structure 406.
  • the bridge wing structure 111 and the piezoelectric layer 403 There is an air gap 112 between them, and the bridge wing structure 111 is correspondingly located inside the acoustic wave reflection structure 405.
  • the acoustic impedance in the air gap 112 does not match the acoustic impedance in the effective area of the resonator, and it can further reflect the acoustic wave of the transverse mode in the resonator back to the resonator Inside, there is a part of the sound wave energy converted into a wave in a mode perpendicular to the resonator, which further increases the Q value of the resonator.
  • the top electrode 404 has a bridge structure 131, and the bridge structure 131 is located outside the raised structure 406, the bridge structure 131 is close to a portion of the raised structure 406 and the piezoelectric layer 403 There is an air gap 112 between. Since the acoustic impedance in the air gap 112 under the bridge structure 131 does not match the acoustic impedance in the effective area of the resonator, it can further reflect the sound waves in the transverse mode of the resonator back into the resonator, and a part of the sound wave energy is converted into resonance The vertical mode wave of the resonator makes the Q value of the resonator further increase. There is a third acoustic impedance in the concave structure 901.
  • the reflection effect of the resonator on the lateral mode wave at the edge of the top electrode 404 will be further improved .
  • a part of the transverse mode wave is converted into a wave in the vertical vibration mode with the resonator, so that the Q value of the resonator is further increased.
  • the convex structure 406 can increase the Qp value of the resonator (Qp value refers to the quality factor value of the parallel resonance point), and the concave structure 901 can increase the Qs value of the resonator (Qs value refers to the quality factor value of the series resonance point ), so that the total quality factor Q value of the resonator can be increased.
  • the resonance frequency in the convex structure can be lowered, and then the left peak in the impedance frequency characteristic curve of the series resonator can be moved to the left to make the filter passband The defects are moved into the stop band of the filter, thereby improving the performance of the filter.
  • the seventh embodiment of the present invention relates to a ladder filter.
  • the ladder filter includes a plurality of resonators according to the first, second, third, fourth, fifth, or sixth embodiments, and a plurality of the resonators are cascaded to form the ladder filter.

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  • Chemical & Material Sciences (AREA)
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Abstract

本发明涉及通信领域，提供一种谐振器和梯形滤波器。本发明中，谐振器包括：基底、底电极、压电层、顶电极、声波反射结构以及用以调节滤波器通带性能的凸起结构；其中，压电层位于顶电极和底电极之间，凸起结构位于顶电极上背离压电层的一面，或者位于所述顶电极之下的所述压电层的表面，或者位于所述压电层之下的所述底电极的上表面，或者位于所述底电极之下；声波反射结构位于基底和底电极之间。本发明与现有技术相比，通过凸起结构设计将串联谐振器阻抗频率特性曲线中左侧的杂峰向左移动，以使滤波器通带中的缺陷移至滤波器阻带中，从而提高滤波器的性能，而且压电层掺杂稀土元素，能够弥补因凸起结构设计所导致的谐振器机电耦合系数的降低。

Description

谐振器和梯形滤波器 技术领域
本发明涉及通信技术领域，特别地涉及一种谐振器和梯形滤波器。
背景技术
随着无线通讯系统的快速发展，人们对无线终端的滤波器件提出微型化、集成化、高频化等新的要求。薄膜体声波谐振器(简称FBAR)，因其高谐振频率、高品质因数、高功率承受能力、低功耗、低价格等诸多优点，可以级联而成具有高工作频率、低插入损耗、高陡降特性、高功率承受能力的滤波器、双工器，被普遍认为是替代声表面波器件解决无线通信高密集频段双工器的最佳方案而受到广泛关注。
典型的FBAR结构如图1所示，包括顶电极101、底电极103、夹在中间的压电层102、位于底电极103的声波反射结构104以及基底105。通过顶电极101和底电极103间输入正弦电信号，FBAR利用逆压电效应将输入的正弦电信号转换为机械谐振，然后再利用压电效应将机械谐振转换为电信号输出。将谐振器按照一定的拓扑结构连接就可以构建频率滤波器件，其中最常见的组成滤波器的谐振器连接拓扑结构为Ladder结构(即梯形结构)。如图2所示，梯形滤波器的每一级由一个串联谐振器(X1、X2…或Xn)和一个并联谐振器(Y1、Y2…或Yn)组成。在谐振器的谐振频率之外，整个器件对外的电学性质基本上表现为电容的形式，因此整个网络的电学传输特性与阶梯形的电容网络一致。Ladder结构中并联的谐振器频率比串联的谐振器频率要低。
FBAR主要利用压电薄膜的纵向压电系数产生压电效应，所以其主要工作模式为厚度方向上的纵波模式(Thickness Extensional Mode，简称TE模式)。薄膜体声波谐振器仅激发厚度方向(TE)模，但是除了期望的TE模式之外，还会产生横向的寄生模式，如瑞利-拉姆模是与 TE模的方向相垂直的机械波。这些横向模式的波会在谐振器的边界处损失掉，从而使得谐振器所需的纵模的能量损失，最终导致谐振器Q值下降。为了解决在谐振器边缘处能量的损失，常用的一种方法是在谐振器上电极边缘的周围增加一凸起结构。由于凸起结构中的声阻抗与谐振器有效区域中的声阻抗不匹配，从而可以将边缘处的声波反射回谐振器内，从而可以减少谐振器中能量的损耗。
但是，如图3所示，加入的凸起结构，会使得串联谐振器在阻抗频率曲线的左侧存在杂峰301，从而导致在滤波器的通带中存在缺陷302，进而使得滤波器的性能下降。
发明内容
有鉴于此，本发明提供一种谐振器和梯形滤波器，通过增加凸起结构来提高谐振器Q值的同时，通过谐振器中的凸起结构设计，将串联谐振器阻抗频率特性曲线中左侧的杂峰向左移动，以使滤波器通带中的缺陷移至滤波器阻带中，从而提高滤波器的性能。
为解决上述技术问题，本发明的实施例提供了一种谐振器，多个所述谐振器用于级联形成滤波器；所述谐振器包括：基底、底电极、压电层、顶电极、声波反射结构以及用以调节滤波器通带性能的凸起结构；所述压电层位于所述顶电极和所述底电极之间，所述凸起结构位于所述顶电极上背离所述压电层的一面，或者位于所述顶电极之下的所述压电层的表面，或者位于所述压电层之下的所述底电极的上表面，或者位于所述底电极之下；所述声波反射结构位于所述基底和所述底电极之间。
本发明的实施例还提供了一种梯形滤波器，所述滤波器包括多个上述谐振器，多个所述谐振器级联形成所述滤波器。
本发明谐振器的凸起结构设计，在提高谐振器Q值的同时，能够将所述串联谐振器阻抗频率特性曲线左侧中的杂峰向左移动，以使所述滤波器通带中的缺陷移至所述滤波器阻带中，从而可以提高滤波器的通带性能。
可选的，所述压电层的材料成分中掺杂稀土元素。在压电层掺杂 稀土元素，能够弥补因凸起结构设计所导致的谐振器机电耦合系数的降低。
可选的，所述压电层的材料成分为氮化铝，所述氮化铝中掺杂稀土元素。
可选的，所述稀土元素为以下任意一种或几种：镧、铈、镨、钕、钷、钐、铕、钆、铽、镝、钬、铒、铥、镱、镥、钇以及钪。
可选的，所述声波反射结构位于所述基底的上表面。
可选的，所述基底具有对应于所述声波反射结构的，所述声波反射结构的其中一部分嵌于所述基底内。
可选的，所述声波反射结构为声学镜。
可选的，所述声学镜为空气腔或者布拉格反射层。
可选的，通过增加凸起结构厚度，将滤波器通带中的杂峰移动到阻带中。
可选的，所述凸起结构与所述顶电极边缘的距离有一预设距离。
可选的，凸起结构的材料密度大于所述顶电极的材料密度。
可选的，所述顶电极对应于所述凸起结构的位置具有凹陷结构，且所述凹陷结构位于所述凸起结构的内部。
可选的，所述顶电极具有桥翼结构且所述桥翼结构位于所述凸起结构的外部，所述桥翼结构与所述压电层之间具有空气隙，并且所述桥翼结构对应于所述声波反射结构。和/或，所述顶电极具有桥部结构，且所述桥部结构位于所述凸起结构的外部，所述桥部结构靠近所述凸起结构的一部分与所述压电层之间具有空气隙。
附图说明
附图用于更好地理解本发明，不构成对本发明的不当限定。其中：
图1是现有技术声波谐振器的结构示意图；
图2是现有技术滤波器的结构示意图；
图3是现有技术滤波器中谐振器的阻抗曲线与滤波器的传输特性曲线对比示意图；
图4是第一实施方式中谐振器的结构示意图；
图5是图4沿俯视图1B-1B方向所取的截面图；
图6是第一实施方式中谐振器的阻抗曲线与滤波器的传输特性曲线对比示意图；
图7是第二实施方式中谐振器的结构示意图；
图8是图7沿俯视图1B-1B方向所取的截面图；
图9是第三实施方式中谐振器的结构示意图；
图10是图9沿俯视图1B-1B方向所取的截面图；
图11是第四实施方式中谐振器的结构示意图；
图12是图11沿俯视图1B-1B方向所取的截面图；
图13是第五实施方式中谐振器的结构示意图；
图14是图13沿俯视图1B-1B方向所取的截面图；
图15是第六实施方式中谐振器的结构示意图；
图16是图15沿俯视图1B-1B方向所取的截面图。
具体实施方式
为使本发明实施例的目的、技术方案和优点更加清楚，下面将结合附图对本发明的各实施例进行详细的阐述。然而，本领域的普通技术人员可以理解，在本发明各实施例中，为了使读者更好地理解本申请而提出了许多技术细节。但是，即使没有这些技术细节和基于以下各实施例的种种变化和修改，也可以实现本申请所要求保护的技术方案。
本发明的第一实施例涉及一种谐振器。多个所述谐振器用于级联形成滤波器。如图4和图5所示，所述谐振器包括：基底401、底电极402、压电层403并掺杂有稀土元素、顶电极404、声波反射结构405以及用于调节滤波器通带性能的凸起结构406。所述压电层403位于所述顶电极404和所述底电极402之间，所述凸起结构406位于所述顶电极404上背离所述压电层403的一面，但不限定于此，还可以位于其他位置。比如，位于所述顶电极404之下的所述压电层403的表面，或者位于所述压电层403之下的所述底电极402的上表面，或者位于所述底电极402之下。此外，顶电极404和底电极402组成材料可以 由金(Au)、钨(W)、钼(Mo)、铂(Pt)，钌(Ru)、铱(Ir)、钛钨(TiW)、铝(Al)、钛(Ti)等类似金属形成。凸起结构的材料组成可以与顶电极相同也可以不同。优选的，所述凸起结构的材料密度大于所述顶电极的材料密度，这样可以使得将滤波器通带中的杂峰移动到阻带中。
凸起结构406的加工方法为：首先，在顶电极的表面，通过PVD、CVD或PECVD等类似的薄膜沉积工艺沉积一层特定厚度的薄膜；然后，在薄膜的表面旋涂一层光刻胶，通过紫外线曝光的方法将光刻板上的图案转移到光刻胶上形成刻蚀阻挡层；最后，通过干法刻蚀或者湿法刻蚀的工艺方法，将在顶电极上沉积的薄膜中不需要的部分刻蚀掉，去掉光刻胶之后，就形成了设计的凸起结构。
所述声波反射结构405位于所述基底401和所述底电极402之间。其中，所述声波反射结构405为声学镜。于实际应用中，所述声波反射结构405可以位于所述基底401的上表面，也可以位于基底401的内部。图中以声学镜为嵌入基底401的空气腔内为例，但是值得说明的是，任何其它的声学镜结构如布拉格反射器也同样适用。
通常将顶电极404、压电层403、底电极402和声学镜在厚度方向上重叠的区域定义为谐振器的有效区域。在谐振器的有效区域内具有第一声阻抗，而在凸起结构406中具有第二声阻抗，由于谐振器有效区域内的第一声阻抗与凸起结构406中第二声阻抗不匹配，从而使得横向传播的声波在凸起结构406的边缘处被反射回来，减小了谐振器内声波能量的损失，因而提高了谐振器的品质因数值即Q值。但是增加的凸起结构406，会使得串联谐振器在阻抗频率曲线的左侧存在杂峰601，从而导致在滤波器的通带中存在缺陷602，进而使得滤波器的性能下降，如图6所示。在本发明实施例中，通过增加凸起结构406的厚度D，可以使得凸起结构中的谐振频率变低，进而可以将串联谐振器阻抗频率特性曲线左侧的杂峰601向左移动到远处603处，从而将滤波器通带中的缺陷结构602移动到滤波器指标所不需要的阻带中604处。而且，在增加凸起结构的同时，能够进一步增加反射回谐振器内横向模式的声波能量，使得谐振器的Q值进一步得到提升。
但是于实际的应用中，在增加凸起结构406厚度D的同时，会导 致谐振器的机电耦合系数大幅下降。原因为：凸起结构406厚度D的增加，会使得反射回谐振器中横向模式的声波能量增加，从而使得谐振器中垂直模式的声波能量相对减小，进而导致谐振器的机电耦合系大幅下降。在图6所示中，会导致串联谐振点605与并联谐振点606之间的距离变小。对于串联谐振器而言，其在谐振时有两个谐振点，分别为串联谐振点和并联谐振点，在串联谐振时外加电场的相位与压电薄膜内部极化向量的相位相同，此时谐振器的电学阻抗为极小值，如图6所示的605；在并联谐振时外加电场的相位与内部极化向量的相位相反，此时谐振器的电学阻抗为极大值，如图6所示的606。其中，串联谐振点与并联谐振点之间距离的大小即表示谐振器机电耦合系数的大小。
为了弥补因调节凸起结构406的厚度D，而导致谐振器机电耦合系数的降低，可以通过对压电层403材料进行掺杂稀土元素，来提高谐振器的机电耦合系数。其中典型的压电层403材料成分可以为氮化铝等，且该类材料为压电薄膜，厚度小于10微米。氮化铝薄膜为多晶形态或者单晶形态，生长方式为薄膜溅射(sputtering)或者有机金属化学气相沉积法(MOCVD)。稀土元素可以为以下任意一种或者几种：镧(La)、铈(Ce)、镨(Pr)、钕(Nd)、钷(Pm)、钐(Sm)、铕(Eu)、钆(Gd)、铽(Tb)、镝(Dy)、钬(Ho)、铒(Er)、铥(Tm)、镱(Yb)、镥(Lu)、钇(Y)、钪(Sc)等。其中，典型的掺杂元素为钪(Sc)。当对AlN压电层403材料掺杂稀土元素时，由于稀土元素的原子半径比较大，从而引起压电材料中的应力发生变化，进而导致压电材料中的电偶极子发生改变，此时对压电层403施加一电场时，压电层403中就会产生更大的机械响应。在图6所示中，掺杂后串联谐振点从605处移动到607处，串联谐振点与并联谐振点之间的距离变大，从而可以使得谐振器获得更高的机电耦合系数。
优选的，可以通过选择凸起结构406的材料来实现将串联谐振器阻抗频率特性曲线左侧的杂峰向左移动到远处。比如，可以选择凸起结构406的材料密度比顶电极404的密度较大，使得凸起结构中的谐振频率变低，此时也可以将串联谐振器阻抗频率特性曲线左侧的杂峰 向左移动到远处，从而将以带有凸起结构406的谐振器级联形成的滤波器通带中的缺陷结构移出到通带以外。
本发明的第二实施例涉及一种谐振器，本实施例除包含第一实施例中所有的技术特征之外，还在第一实施例的基础上做了改进，主要改进之处在于：所述凸起结构与所述顶电极边缘的距离有一预设距离。预设距离的大小，根据滤波器不同的性能指标来调节，以将滤波器通带中的杂峰移到阻带中。
如图7和图8所示，凸起结构406距离谐振器顶电极404边缘的距离为W1。所述预设距离W1的大小，为根据滤波器特定的性能指标来调节的，可以使得将滤波器通带中的杂峰移到阻带中，即可以通过调节凸起结构406距离谐振器顶电极404边缘的距离W1，可以使得凸起结构中的谐振频率相对于谐振器有效区域中的主谐振频率较低，进而将串联谐振器阻抗频率特性曲线左侧的杂峰向左移动到远处。比如，可以通过增大W1也就是将凸起结构406移向靠近谐振器的中心区域，以此可以实现将串联谐振器阻抗频率特性曲线左侧的杂峰向左移动到远处，从而将带有凸起结构406的谐振器级联形成的滤波器通带中的缺陷结构移出到通带以外。
本发明的第三实施例涉及一种谐振器，本实施例除包含第一实施例中所有的技术特征之外，还在第一实施例的基础上做了改进，主要改进之处在于：所述顶电极对应于所述凸起结构的位置具有凹陷结构，且所述凹陷结构位于所述凸起结构的内部。
如图9和图10所示，所述顶电极404对应于所述凸起结构406的位置具有凹陷结构901，且所述凹陷结构901位于所述凸起结构406的内部。在凹陷结构901中有着第三声阻抗。由于谐振器有效区域中的声阻抗与凸起结构406中的声阻抗以及凹陷结构901中的第三声阻抗不匹配，所以会进一步提高谐振器在顶电极404边缘处对横向模式波的反射作用。并且横向模式波一部分转换成了与谐振器垂直震动模式的波，使得谐振器的Q值进一步增加。其中凸起结构406能够增加谐 振器的Qp值(Qp值指的是并联谐振点的品质因数值)，凹陷结构901能够增加谐振器的Qs值(Qs值指的是串联谐振点的品质因数值)，从而可以增加谐振器总的品质因数值Q值。在本实施例中，通过凸起结构设计，可以使得凸起结构中的谐振频率变低，进而将串联谐振器阻抗频率特性曲线中左侧的杂峰向左移动，以使滤波器通带中的缺陷移至滤波器阻带中，从而提高滤波器的性能。
本发明的第四实施例涉及一种谐振器，本实施例除包含第一实施例中所有的技术特征之外，还在第一实施例的基础上做了改进，主要改进之处在于：所述顶电极具有桥翼结构。
如图11和图12所示，所述顶电极404具有桥翼结构111且所述桥翼结构11位于所述凸起结构406的外部。所述桥翼结构111与所述压电层403之间具有空气隙112，并且所述桥翼结构111对应位于所述声波反射结构405内侧。
在图12中谐振器除了有凸起结构406以外，还存在桥翼结构111。其中所述桥翼结构111与所述压电层403之间具有空气隙112。并且结合图12所示的方向，所述桥翼结构111在厚度方向上的投影位于谐振器的声波反射结构405以内。由于桥翼结构111与压电层403之间具有空气隙112，空气隙112中的声阻抗与谐振器有效区域中的声阻抗不匹配，能够进一步将谐振器中横向模式的声波反射回谐振器内，并有一部分声波能量转成与谐振器垂直模式的波，从而使得谐振器的Q值进一步提高。在本实施例中，通过凸起结构设计，可以使得凸起结构中的谐振频率变低，进而将串联谐振器阻抗频率特性曲线中左侧的杂峰向左移动，以使滤波器通带中的缺陷移至滤波器阻带中，从而提高滤波器的性能。
本发明的第五实施例涉及一种谐振器，本实施例除包含第一实施例中所有的技术特征之外，还在第一实施例的基础上做了改进，主要改进之处在于：所述顶电极具有桥部结构。
如图13和图14所示，所述顶电极404具有桥部结构131，且所述 桥部结构131位于所述凸起结构406的外部，所述桥部结构131靠近所述凸起结构406的一部分与所述压电层403之间具有空气隙112。由于桥部结构131下空气隙112中的声阻抗与谐振器有效区域中的声阻抗不匹配，能够进一步将谐振器中横向模式的声波反射回谐振器内，并有一部分声波能量转成与谐振器垂直模式的波，从而使得谐振器的Q值进一步提高。在本实施例中，通过凸起结构设计，可以使得凸起结构中的谐振频率变低，进而将串联谐振器阻抗频率特性曲线中左侧的杂峰向左移动，以使滤波器通带中的缺陷移至滤波器阻带中，从而提高滤波器的性能。
本发明的第六实施例涉及一种谐振器，本实施例除包含第一实施例中所有的技术特征之外，还在第一实施例的基础上做了改进，主要改进之处在于：所述顶电极既具有桥翼结构又具有桥部结构。同时，所述顶电极对应于所述凸起结构的位置具有凹陷结构。
如图15和图16所示，所述顶电极404具有桥翼结构111且所述桥翼结构111位于所述凸起结构406的外部，所述桥翼结构111与所述压电层403之间具有空气隙112，并且所述桥翼结构111对应位于所述声波反射结构405内侧。由于桥翼结构111与压电层403之间具有空气隙112，空气隙112中的声阻抗与谐振器有效区域中的声阻抗不匹配，能够进一步将谐振器中横向模式的声波反射回谐振器内，并有一部分声波能量转成与谐振器垂直模式的波，从而使得谐振器的Q值进一步提高。所述顶电极404具有桥部结构131，且所述桥部结构131位于所述凸起结构406的外部，所述桥部结构131靠近所述凸起结构406的一部分与所述压电层403之间具有空气隙112。由于桥部结构131下空气隙112中的声阻抗与谐振器有效区域中的声阻抗不匹配，能够进一步将谐振器中横向模式的声波反射回谐振器内，并有一部分声波能量转成与谐振器垂直模式的波，从而使得谐振器的Q值进一步提高。在凹陷结构901中有着第三声阻抗。由于谐振器有效区域中的声阻抗与凸起结构406中的声阻抗以及凹陷结构901中的第三声阻抗不匹配，所以会进一步提高谐振器在顶电极404边缘处对横向模式波的反射作 用。并且横向模式波一部分转换成了与谐振器垂直震动模式的波，使得谐振器的Q值进一步增加。其中凸起结构406能够增加谐振器的Qp值(Qp值指的是并联谐振点的品质因数值)，凹陷结构901能够增加谐振器的Qs值(Qs值指的是串联谐振点的品质因数值)，从而可以增加谐振器总的品质因数值Q值。在本实施例中，通过凸起结构设计，可以使得凸起结构中的谐振频率变低，进而将串联谐振器阻抗频率特性曲线中左侧的杂峰向左移动，以使滤波器通带中的缺陷移至滤波器阻带中，从而提高滤波器的性能。
本发明的第七实施例涉及梯形滤波器。所述梯形滤波器包括多个第一、第二、第三、第四、第五或第六实施例所述的谐振器，多个所述谐振器级联形成所述梯形滤波器。
上述具体实施方式，并不构成对本发明保护范围的限制。本领域技术人员应该明白的是，取决于设计要求和其他因素，可以发生各种各样的修改、组合、子组合和替代。任何在本发明的精神和原则之内所作的修改、等同替换和改进等，均应包含在本发明保护范围之内。

Claims (12)

  1. 一种谐振器，其特征在于，多个所述谐振器用于级联形成滤波器；
    所述谐振器包括：基底、底电极、压电层、顶电极、声波反射结构以及能够将串联谐振器阻抗频率特性曲线中左侧的杂峰向左移动以使滤波器通带中的缺陷移至滤波器阻带中的凸起结构。
    所述压电层位于所述顶电极和所述底电极之间，所述凸起结构位于所述顶电极上背离所述压电层的一面，或者位于所述顶电极之下的所述压电层的表面，或者位于所述压电层之下的所述底电极的上表面，或者位于所述底电极之下；
    所述声波反射结构位于所述基底和所述底电极之间。
  2. 根据权利要求1所述的谐振器，其特征在于，所述压电层的材料成分中掺杂稀土元素。
  3. 根据权利要求1所述的谐振器，其特征在于，所述压电层的材料成分为氮化铝，所述氮化铝中掺杂稀土元素。
  4. 根据权利要求1所述的谐振器，其特征在于，所述声波反射结构位于所述基底的上表面。
  5. 根据权利要求1所述的谐振器，其特征在于，所述声波反射结构为声学镜。
  6. 根据权利要求1所述的谐振器，其特征在于，所述凸起结构的厚度可调；
    所述凸起结构厚度的大小，为根据滤波器特定的性能指标来调节，使得将滤波器通带中的杂峰移到阻带中。
  7. 根据权利要求1所述的谐振器，其特征在于，所述凸起结构与所述顶电极边缘的距离为一预设距离；
    所述预设距离的大小，为根据滤波器特定的性能指标来调节，使得将滤波器通带中的杂峰移到阻带中。
  8. 根据权利要求1所述的谐振器，其特征在于，所述凸起结构的材料与所述顶电极的材料不同。
  9. 根据权利要求8所述的谐振器，其特征在于，所述凸起结构的材料密度大于所述顶电极的材料密度；
    所述凸起结构的材料密度，为根据滤波器特定的性能指标来选择，使得将滤波器通带中的杂峰移动到阻带中。
  10. 根据权利要求1所述的谐振器，其特征在于，所述顶电极对应于所述凸起结构的位置具有凹陷结构，且所述凹陷结构位于所述凸起结构的内部。
  11. 根据权利要求1所述的谐振器，其特征在于，所述顶电极具有桥翼结构且所述桥翼结构位于所述凸起结构的外部，所述桥翼结构与所述压电层之间具有空气隙，并且所述桥翼结构对应位于所述声波反射结构内部；
    和/或，所述顶电极具有桥部结构，且所述桥部结构位于所述凸起结构的外部，所述桥部结构靠近所述凸起结构的一部分与所述压电层之间具有空气隙。
  12. 一种梯形滤波器，其特征在于，所述梯形滤波器包括多个如权利要求1至11中任意一项所述的谐振器，多个所述谐振器级联形成所述梯形滤波器，其中，所述梯形滤波器的每一级包括一个串联谐振器和一个并联谐振器。
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