Piezoelectric layer structure, bulk acoustic wave resonator, bulk acoustic wave filter, and manufacturing method

Abstract

The present invention provides a piezoelectric layer structure, a bulk acoustic wave resonator, a bulk acoustic wave filter, and a manufacturing method. In a piezoelectric layer, adjacent first and second thin-film layers have opposite polarities, breaking the conventional inverse constraint relationship between the resonance frequency of a bulk acoustic wave resonator and the thickness of a piezoelectric layer, so that a high-order resonant mode of the resonator is excited while maintaining a relatively thick piezoelectric layer, thereby significantly increasing the resonance frequency of the bulk acoustic wave resonator. There is no need to insert an electrode material layer between the first thin-film layer and the second thin-film layer, so that the manufacturing method is simple, and the device performance is high. In addition, the piezoelectric layer is divided into two regions, a first region in which adjacent piezoelectric thin-film layers have the same polarity, and a second region in which adjacent piezoelectric thin-film layers have opposite polarities, so that the bulk acoustic wave filter has two frequencies, enabling application requirements of different frequency bands to be met.

Description

Piezoelectric layer structure, bulk acoustic wave resonator, bulk acoustic wave filter and manufacturing method TECHNICAL FIELD

[0001] The present application belongs to the field of microelectronics technology, and relates to a piezoelectric layer structure, a bulk acoustic wave resonator, a bulk acoustic wave filter and a manufacturing method. BACKGROUND

[0002] Currently, radio frequency filters need to have a working frequency of 5GHz or higher for wireless data transmission, and the filters applied in 5G communication are mainly bulk acoustic wave filters (BAW) and surface acoustic wave filters (SAW). BAW devices have an extremely high Q value (4000 or more), a working frequency band of 100MHz-20GHz, and advantages such as high working frequency, low insertion loss, high frequency selection characteristics, high power capacity and strong anti-static ability, and are the best solution for future radio frequency front ends.

[0003] With the increasing application requirements, microwave acoustics not only needs to expand the working frequency range to Ku, Ka bands and even mm-wave (mm-Wave) bands, but also needs to meet the application requirements of ultra-wideband. In a traditional single-layer piezoelectric thin film resonator, the resonant frequency of the bulk acoustic wave resonator is positively correlated with the ratio of the longitudinal acoustic velocity and the film thickness, which means that the thickness of the piezoelectric thin film of the filter applied in higher frequency bands such as 5G will be smaller. For example, the piezoelectric thin film thickness corresponding to a working frequency of more than 10GHz is less than 100nm, the quality of the piezoelectric thin film crystal will be seriously deteriorated, and at the same time, the power handling capacity, the electromechanical coupling coefficient and the Q value of the resonator will sharply decrease.

[0004] In addition, the working frequency of the existing bulk acoustic wave filter is single, and can only meet the application requirements of a certain frequency band, which has great limitations.

[0005] Therefore, how to improve the resonant frequency of the resonator to meet the requirements of different frequency bands has become a technical problem to be solved by those skilled in the art. SUMMARY

[0006] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a piezoelectric layer structure, a bulk acoustic wave resonator, a bulk acoustic wave filter and a manufacturing method, which are used to solve the problems of performance degradation when the resonant frequency of the bulk acoustic wave resonator is improved and single working frequency of the device in the prior art.

[0007] To achieve the above-mentioned purpose and other related purposes, the present application provides a bulk acoustic wave resonator structure, which comprises:

[0008] a substrate;

[0009] a bottom electrode located above the substrate;

[0010] a piezoelectric layer located above the bottom electrode, the piezoelectric layer comprising first ferroelectric thin film layers and second ferroelectric thin film layers stacked alternately from bottom to top, wherein adjacent first ferroelectric thin film layers and second ferroelectric thin film layers are in direct contact at interfaces, and adjacent first ferroelectric thin film layers and second ferroelectric thin film layers have opposite polarization directions to excite N-order mode resonance, N being an integer no less than the total number of layers of the first ferroelectric thin film layers and the second ferroelectric thin film layers;

[0011] a top electrode located above the piezoelectric layer.

[0012] Optionally, the total number of layers of the first ferroelectric thin film layers and the second ferroelectric thin film layers is 3, 1-order thickness expansion mode resonance is suppressed, and 3-order thickness expansion mode resonance is excited.

[0013] Optionally, the material of the first ferroelectric thin film layers comprises one or more of Al 1-x Sc x N (0.2≤x≤0.5), BST, PZT and PbTiO3, and the material of the second ferroelectric thin film layers comprises one or more of Al 1-x Sc x N (0.2≤x≤0.5), BST, PZT and PbTiO3.

[0014] Optionally, the thickness of the first ferroelectric thin film layers is no less than 0.01 μm, and the thickness of the second ferroelectric thin film layers is no less than 0.01 μm.

[0015] Optionally, the material of the bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf, and the material of the top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf.

[0016] Optionally, the thickness of the bottom electrode is no more than 0.3 μm, and the thickness of the top electrode is no more than 0.3 μm.

[0017] Optionally, an upwardly open groove is provided in the substrate, and the bottom electrode and the groove jointly form a cavity.

[0018] Optionally, a Bragg reflection layer is provided between the substrate and the bottom electrode, the Bragg reflection layer comprising layers of high acoustic impedance material and low acoustic impedance material stacked alternately.

[0019] Optionally, the substrate comprises a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate or a diamond substrate.

[0020] The application further provides a high-frequency bulk acoustic wave resonator structure, comprising:

[0021] a substrate;

[0022] a bottom electrode above the substrate;

[0023] a piezoelectric layer above the bottom electrode, the piezoelectric layer being composed of piezoelectric thin film layers and ferroelectric thin film layers stacked alternately, adjacent piezoelectric thin film layers and ferroelectric thin film layers being in direct contact at their interfaces, and adjacent piezoelectric thin film layers and ferroelectric thin film layers having opposite polarities to excite N-order mode resonance, N being an integer no less than the total number of the piezoelectric thin film layers and the ferroelectric thin film layers;

[0024] a top electrode above the piezoelectric layer.

[0025] Optionally, the total number of the piezoelectric thin film layers and the ferroelectric thin film layers is 3, and a 3-order thickness-extended mode resonance is excited.

[0026] Optionally, the material of the piezoelectric thin film layers comprises one or more of AlN, Al x Ga 1-x N (0 < x < 1), Al 1-x Sc x N (0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, and Ga2O3.

[0027] Optionally, the material of the ferroelectric thin film layers comprises one or more of Al 1-x Sc x N (0.2 ≤ x ≤ 0.5), BST, PZT, and PbTiO3.

[0028] Optionally, the thickness of the piezoelectric thin film layers is no less than 0.01 μm, and the thickness of the ferroelectric thin film layers is no less than 0.01 μm.

[0029] Optionally, the material of the bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, and the material of the top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf.

[0030] Optionally, the thickness of the bottom electrode is no more than 0.3 μm, and the thickness of the top electrode is no more than 0.3 μm.

[0031] Optionally, the substrate is provided with a groove opening upward, and the bottom electrode and the groove jointly form a cavity.

[0032] Optionally, a Bragg reflection layer is arranged between the substrate and the bottom electrode, and the Bragg reflection layer comprises layers of high acoustic impedance material and layers of low acoustic impedance material stacked alternately.

[0033] Optionally, the substrate comprises a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate or a diamond substrate.

[0034] The application further provides a method for manufacturing a high-frequency bulk acoustic wave resonator, comprising the following steps:

[0035] A first substrate is provided, and a piezoelectric layer is formed on the first substrate, the piezoelectric layer comprising first thin film layers and second thin film layers stacked alternately, at least one of the first thin film layers and the second thin film layers being a ferroelectric thin film layer;

[0036] A first electrode is formed on a side of the piezoelectric layer away from the first substrate, and a dielectric layer is formed on the side of the piezoelectric layer away from the first substrate, the dielectric layer covering the first electrode;

[0037] An opening is formed in the dielectric layer, the opening exposing part of the first electrode;

[0038] A second substrate is provided, the dielectric layer is bonded to the second substrate, and the first substrate is removed;

[0039] A second electrode is formed on a side of the piezoelectric layer away from the second substrate;

[0040] A first electrode pad and a second electrode pad are formed on a side of the piezoelectric layer away from the second substrate, the first electrode pad electrically connected through the piezoelectric layer and the first electrode, and the second electrode pad electrically connected to the second electrode;

[0041] Among them, the polarities of adjacent first thin film layers and second thin film layers are opposite, so as to suppress a first-order resonance mode and excite an N-order resonance mode, N being an integer greater than 1.

[0042] Optionally, after the first electrode pad and the second electrode pad are formed, a voltage or a voltage pulse is further applied between the first electrode and the second electrode, so as to control the polarity direction of the ferroelectric thin film layer, and the polarities of adjacent first thin film layers and second thin film layers are opposite.

[0043] Optionally, the piezoelectric layer comprises a first piezoelectric layer and a second piezoelectric layer, the first piezoelectric layer comprising at least one of the first thin film layers and the second thin film layers stacked alternately, the second piezoelectric layer comprising at least one of the first thin film layers and the second thin film layers stacked alternately, and the step of forming the piezoelectric layer comprises:

[0044] forming the first piezoelectric layer on the first substrate;

[0045] forming the first electrode on a side of the first piezoelectric layer away from the first substrate;

[0046] forming the first electrode, the dielectric layer and the opening on a side of the first piezoelectric layer away from the first substrate;

[0047] bonding the dielectric layer to the second substrate and removing the first substrate;

[0048] forming the second piezoelectric layer on a side of the first piezoelectric layer away from the second substrate.

[0049] Optionally, after removing the first substrate, the method further comprises the step of thinning a side of the first piezoelectric layer away from the second substrate.

[0050] Optionally, the piezoelectric layer comprises piezoelectric thin film layers / ferroelectric thin film layers stacked alternately.

[0051] Optionally, the piezoelectric layer comprises ferroelectric thin film layers / ferroelectric thin film layers stacked alternately.

[0052] Optionally, the ferroelectric thin film layer is made of one or more of Sc x Al 1-x N(0.2≤x≤0.5), BST, PZT, PbTiO3.

[0053] Optionally, the thickness of the first thin film layer is not less than 0.01 μm, and the thickness of the second thin film layer is not less than 0.01 μm.

[0054] Optionally, the first electrode is made of one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, and the second electrode is made of one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf.

[0055] Optionally, the method of forming the piezoelectric layer comprises one or more of physical vapor deposition, chemical vapor deposition and spin coating.

[0056] The application further provides a method for manufacturing a cavity type bulk acoustic wave resonator, comprising the following steps:

[0057] providing a first substrate, wherein a piezoelectric layer is formed on the first substrate, and the piezoelectric layer comprises first thin film layers and second thin film layers stacked alternately, and at least one of the first thin film layers and the second thin film layers is a ferroelectric thin film layer;

[0058] forming a first electrode on the piezoelectric layer, and forming a barrier layer on the piezoelectric layer covering the first electrode, forming a sacrificial layer on the barrier layer, the sacrificial layer partially overlaps with a projection of the first electrode on the piezoelectric layer;

[0059] forming a support layer on the barrier layer, the support layer covering the sacrificial layer;

[0060] providing a second substrate, bonding the support layer to the second substrate, and removing the first substrate;

[0061] forming a second electrode on a side of the piezoelectric layer away from the second substrate;

[0062] forming a first electrode pad and a second electrode pad on a side of the piezoelectric layer away from the second substrate, the first electrode pad electrically connected through the piezoelectric layer and the first electrode, and the second electrode pad electrically connected with the second electrode;

[0063] removing the sacrificial layer to form a cavity;

[0064] wherein polarities of adjacent first thin film layers and second thin film layers are opposite to each other to suppress a 1st order resonance mode and excite an Nth order resonance mode, N being an integer greater than 1.

[0065] Optionally, before forming the first electrode pad and the second electrode pad, the method further comprises forming a contact via vertically through the piezoelectric layer, the contact via exposing the first electrode, the first electrode pad extending into the contact via to electrically connect with the first electrode, wherein a projection of the contact via on the second substrate does not overlap with a projection of the cavity on the second substrate.

[0066] Optionally, before removing the sacrificial layer, the method further comprises applying a voltage or a voltage pulse between the first electrode and the second electrode to control a polarity direction of the ferroelectric thin film layer, so that polarities of adjacent first thin film layers and second thin film layers are opposite to each other.

[0067] Optionally, the piezoelectric layer comprises a first piezoelectric layer and a second piezoelectric layer, the first piezoelectric layer comprises at least one of the first thin film layers and the second thin film layers stacked alternately, the second piezoelectric layer comprises at least one of the first thin film layers and the second thin film layers stacked alternately, and the step of forming the piezoelectric layer comprises:

[0068] forming the first piezoelectric layer on the first substrate;

[0069] forming the first electrode on a side of the first piezoelectric layer away from the first substrate;

[0070] forming the first electrode, the support layer and the opening on a side of the first piezoelectric layer away from the first substrate;

[0071] bonding the support layer to the second substrate and removing the first substrate;

[0072] forming the second piezoelectric layer on a side of the first piezoelectric layer away from the second substrate.

[0073] Optionally, after removing the first substrate, the method further comprises the step of thinning a side of the first piezoelectric layer away from the second substrate.

[0074] Optionally, before forming the cavity, the method further comprises forming a sacrificial layer etching hole penetrating through the piezoelectric layer, the sacrificial layer etching hole exposing the sacrificial layer, etching and removing the sacrificial layer based on the sacrificial layer etching hole, wherein the sacrificial layer etching hole avoids the first electrode and the second electrode.

[0075] Optionally, the piezoelectric layer comprises piezoelectric thin film layers / ferroelectric thin film layers stacked alternately.

[0076] Optionally, the piezoelectric layer comprises ferroelectric thin film layers / ferroelectric thin film layers stacked alternately.

[0077] Optionally, the material of the ferroelectric thin film layer comprises one or more of Sc x Al 1-x N (0.2≤x≤0.5), BST, PZT, PbTiO3.

[0078] Optionally, the thickness of the first thin film layer is not less than 0.01 μm, and the thickness of the second thin film layer is not less than 0.01 μm.

[0079] The application further provides a method for manufacturing a Bragg reflection type bulk acoustic wave resonator, comprising the following steps:

[0080] providing a first substrate, the first substrate being provided with a piezoelectric layer, the piezoelectric layer comprising first thin film layers and second thin film layers stacked alternately, at least one of the first thin film layers and the second thin film layers being a ferroelectric thin film layer;

[0081] forming a first electrode on the piezoelectric layer and forming a Bragg reflection structure covering the first electrode on the piezoelectric layer, the Bragg reflection structure comprising low acoustic impedance layers and high acoustic impedance layers stacked alternately;

[0082] forming a dielectric layer on the Bragg reflection structure;

[0083] providing a second substrate, bonding the dielectric layer to the second substrate and removing the first substrate;

[0084] forming a second electrode on a side of the piezoelectric layer distal to the second substrate;

[0085] forming a first electrode pad and a second electrode pad on a side of the piezoelectric layer distal to the second substrate, the first electrode pad electrically connected through the piezoelectric layer and the first electrode, and the second electrode pad electrically connected to the second electrode;

[0086] wherein polarities of adjacent ones of the first thin film layers and the second thin film layers are opposite to each other to suppress a 1st order resonance mode and to excite an Nth order resonance mode, N being an integer greater than 1.

[0087] Optionally, the number of the Bragg reflection structures is multiple, and the multiple Bragg reflection structures are stacked in sequence from bottom to top.

[0088] Optionally, a material of the low acoustic impedance layer includes one or more of AlN, Si3N4, and SiO2, and a material of the high acoustic impedance layer includes one or more of W, Mo, Pt, Au, Ni, and Ir.

[0089] Optionally, after forming the first electrode pad and the second electrode pad, the method further comprises applying a voltage or a voltage pulse between the first electrode and the second electrode to control a polarity direction of the ferroelectric thin film layer, so that polarities of adjacent ones of the first thin film layers and the second thin film layers are opposite to each other.

[0090] Optionally, the piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer, the first piezoelectric layer includes at least one of the first thin film layers and the second thin film layers stacked alternately, the second piezoelectric layer includes at least one of the first thin film layers and the second thin film layers stacked alternately, and the step of forming the piezoelectric layer comprises:

[0091] forming the first piezoelectric layer on the first substrate;

[0092] forming the first electrode and the Bragg reflection structure on a side of the first piezoelectric layer distal to the first substrate;

[0093] forming the dielectric layer on the Bragg reflection structure;

[0094] bonding the dielectric layer to the second substrate and removing the first substrate;

[0095] forming the second piezoelectric layer on a side of the first piezoelectric layer distal to the second substrate.

[0096] Optionally, after removing the first substrate, the method further comprises a step of thinning a side of the first piezoelectric layer distal to the second substrate.

[0097] Optionally, the piezoelectric layer comprises an alternating stack of piezoelectric thin film layers / ferroelectric thin film layers.

[0098] Optionally, the piezoelectric layer comprises an alternating stack of ferroelectric thin film layers / ferroelectric thin film layers.

[0099] Optionally, the material of the ferroelectric thin film layer comprises Sc x Al 1-x N (0.2≤x≤0.5), BST, PZT, PbTiO3.

[0100] Optionally, the thickness of the first thin film layer is not less than 0.01 μm, and the thickness of the second thin film layer is not less than 0.01 μm.

[0101] The application also provides an aluminum nitride-based piezoelectric layer structure, comprising:

[0102] a substrate;

[0103] a piezoelectric layer located above the substrate, the piezoelectric layer comprising a first aluminum nitride-based piezoelectric thin film layer and a second aluminum nitride-based piezoelectric thin film layer, the second aluminum nitride-based piezoelectric thin film layer being located above the first aluminum nitride-based piezoelectric thin film layer;

[0104] In the horizontal direction, the piezoelectric layer is divided into a first region and a second region, in the first region, the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer are in direct contact, and in the second region, an interface modulation layer is provided between the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer.

[0105] Wherein, in the first region, the polarities of the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer are the same, and in the second region, the polarities of the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer are opposite.

[0106] Optionally, the material of the interface modulation layer comprises at least one of TiN, Ti2O3, SiO2, SiC, SiN, AlN, Al2O3, AlON, SiON, HfO2, Mo, Mg, MgO, W, Pt, and the thickness of the interface modulation layer ranges from 0.1 to 100 nm.

[0107] Optionally, the material of the first aluminum nitride-based piezoelectric thin film layer comprises aluminum nitride and / or doped aluminum nitride, and the material of the second aluminum nitride-based piezoelectric thin film layer comprises aluminum nitride and / or doped aluminum nitride, wherein the doping elements in the doped aluminum nitride comprise one or more of Ga, Sc, Mg, Hf, Zr, B, Er, Be, Ce, Ti, Si, Ge, Li, As, Nb, Sb, Sn, Sr.

[0108] Optionally, the first aluminum nitride-based piezoelectric thin film layer has a thickness ranging from 0.01 to 2 μm, and the second aluminum nitride-based piezoelectric thin film layer has a thickness ranging from 0.01 to 2 μm.

[0109] Optionally, the substrate comprises a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate, and a diamond substrate.

[0110] The present application also provides a method for manufacturing an aluminum nitride-based piezoelectric layer structure, comprising the following steps:

[0111] providing a substrate, and forming a first aluminum nitride-based piezoelectric thin film layer on the substrate;

[0112] forming an interface modulation layer on the first aluminum nitride-based piezoelectric thin film layer, wherein the interface modulation layer exposes the first aluminum nitride-based piezoelectric thin film layer at a preset region;

[0113] forming a second aluminum nitride-based piezoelectric thin film layer on the first aluminum nitride-based piezoelectric thin film layer, wherein the second aluminum nitride-based piezoelectric thin film layer covers the interface modulation layer.

[0114] Optionally, the step of forming the interface modulation layer comprises:

[0115] forming an interface modulation material layer on the first aluminum nitride-based piezoelectric thin film layer;

[0116] forming a photoresist layer on the interface modulation material layer and patterning the photoresist layer, removing the interface modulation material layer at a preset position with the patterned photoresist layer as a mask, and the remaining interface modulation material layer constituting the interface modulation layer;

[0117] removing the photoresist layer.

[0118] Optionally, the method for removing the interface modulation material layer at a preset position comprises at least one of dry etching and wet etching.

[0119] Optionally, the step of forming the interface modulation layer comprises:

[0120] forming a hard mask layer on the first aluminum nitride-based piezoelectric thin film layer and patterning the hard mask layer, wherein the patterned hard mask layer exposes the first aluminum nitride-based piezoelectric thin film layer at a preset position;

[0121] forming an interface modulation material layer on the first aluminum nitride-based piezoelectric thin film layer, wherein the interface modulation material layer covers the hard mask layer;

[0122] stripping off the hard mask layer, wherein when the hard mask layer is stripped off, the interface modulation material layer above the hard mask layer is removed, and the remaining interface modulation material layer constitutes the interface modulation layer.

[0123] Optionally, the hard mask layer is a dielectric mask layer or a metal mask layer.

[0124] The present invention also provides a dual - frequency bulk acoustic wave filter structure, comprising:

[0125] A substrate;

[0126] A bottom electrode located above the substrate, the bottom electrode includes a first bottom electrode and a second bottom electrode, and in the horizontal direction, the first bottom electrode and the second bottom electrode are spaced apart by a preset distance;

[0127] A piezoelectric layer located above the bottom electrode, the piezoelectric layer includes a piezoelectric thin film layer stacked from bottom to top, and in the horizontal direction, the piezoelectric layer is divided into a first region and a second region. In the first region, adjacent piezoelectric thin film layers have the same polarity, and in the second region, adjacent piezoelectric thin film layers have opposite polarities;

[0128] A top electrode located above the piezoelectric layer, the top electrode includes a first top electrode and a second top electrode, and in the horizontal direction, the first top electrode and the second top electrode are spaced apart by a preset distance;

[0129] Wherein, in the projection in the vertical direction, the first bottom electrode, the first region and the first top electrode overlap, and the second bottom electrode, the second region and the second top electrode overlap.

[0130] Optionally, the piezoelectric layer includes a first piezoelectric thin film layer and a second piezoelectric thin film layer stacked from bottom to top. In the first region, the first piezoelectric thin film layer and the second piezoelectric thin film layer are in direct contact, and in the second region, an interface modulation layer is provided between the first piezoelectric thin film layer and the second piezoelectric thin film layer.

[0131] Optionally, the material of the interface modulation layer includes one or more of TiN, Ti2O3, SiO2, SiC, SiN, AlN, Al2O3, AlON, SiON, HfO2, Mo, Mg, MgO, W and Pt, and the thickness range of the interface modulation layer is 1 - 100 nm.

[0132] Optionally, the material of the piezoelectric thin film layer includes one or more of AlN, Al x Ga 1-x N(0 < x < 1), Al 1-x Sc x N(0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3. The thickness of a single piezoelectric thin film layer is not less than 0.01 μm, and the thickness of the piezoelectric layer does not exceed 2 μm.

[0133] Optionally, the substrate is provided with a first groove and a second groove, at least a part of the first groove is located below the first bottom electrode, and at least a part of the second groove is located below the second bottom electrode.

[0134] Optionally, a bonding layer is arranged between the substrate and the bottom electrode, the bonding layer is provided with a first groove and a second groove, at least a part of the first groove is located below the first bottom electrode, and at least a part of the second groove is located below the second bottom electrode.

[0135] Optionally, a Bragg reflection layer is arranged between the substrate and the bottom electrode.

[0136] Optionally, the Bragg reflection layer comprises a stack of high acoustic impedance material layers and low acoustic impedance material layers, the material of the high acoustic impedance material layers comprises one or more of W, Mo, Pt, Au, Ni and Ir, and the material of the low acoustic impedance material layers comprises one or more of AlN, Si3N4 and SiO2.

[0137] Optionally, the material of the bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf, and the material of the top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf.

[0138] Optionally, the substrate comprises a Si substrate, a SiC substrate, a Ge substrate and a sapphire substrate.

[0139] As described above, in the piezoelectric layer of the present application, the polarities of the adjacent first thin film layer and the second thin film layer are opposite, breaking the inverse proportional relationship between the resonant frequency of the traditional bulk acoustic wave resonator and the thickness of the piezoelectric layer, maintaining the high-order resonant mode of the resonator under a relatively thick piezoelectric layer, and significantly improving the resonant frequency of the bulk acoustic wave resonator; without inserting an electrode material layer between the first thin film layer and the second thin film layer, the manufacturing method is simple, and the device performance is high. In addition, the piezoelectric layer is divided into two regions, the polarities of the adjacent piezoelectric thin film layers in the first region are the same, and the polarities of the adjacent piezoelectric thin film layers in the second region are opposite, so that the bulk acoustic wave filter has two frequencies, which can meet the application requirements of different frequency bands. BRIEF DESCRIPTION OF DRAWINGS

[0140] FIG. 1 shows a structure schematic diagram of a bulk acoustic wave resonator in an embodiment of the present application.

[0141] FIG. 2 shows a schematic diagram of a piezoelectric layer composed of three thin film layers in an embodiment of the present application.

[0142] FIG. 3 shows a schematic diagram of a piezoelectric layer composed of three thin film layers in a comparative example of an embodiment of the present application.

[0143] Figure 4 shows simulation results of an embodiment of the present application.

[0144] Figure 5 shows simulation results of a comparative example of an embodiment of the present application.

[0145] Figure 6 shows a schematic diagram of a high-frequency bulk acoustic wave resonator of an embodiment of the present application.

[0146] Figure 7 shows a schematic diagram of a high-frequency bulk acoustic wave resonator of an embodiment of the present application.

[0147] Figure 8 shows a schematic diagram of a high-frequency bulk acoustic wave resonator of a comparative example of an embodiment of the present application.

[0148] Figure 9 shows simulation results of an embodiment of the present application.

[0149] Figure 10 shows simulation results of a comparative example of an embodiment of the present application.

[0150] Figure 11 shows a flow chart of a method of fabricating a high-frequency bulk acoustic wave resonator of an embodiment of the present application.

[0151] Figure 12 shows a schematic diagram of providing a first substrate and forming a first piezoelectric layer on the first substrate of an embodiment of the present application.

[0152] Figure 13 shows a schematic diagram of forming a first electrode of an embodiment of the present application.

[0153] Figure 14 shows a schematic diagram of forming a dielectric layer of an embodiment of the present application.

[0154] Figure 15 shows a schematic diagram of planarizing the dielectric layer of an embodiment of the present application.

[0155] Figure 16 shows a schematic diagram of forming an opening of an embodiment of the present application.

[0156] Figure 17 shows a schematic diagram of providing a second substrate and bonding the dielectric layer to the second substrate of an embodiment of the present application.

[0157] Figure 18 shows a schematic diagram of removing the first substrate of an embodiment of the present application.

[0158] Figure 19 shows a schematic diagram of thinning the exposed first piezoelectric layer of an embodiment of the present application.

[0159] Figure 20 shows a schematic diagram of forming a second piezoelectric layer of an embodiment of the present application.

[0160] Figure 21 shows a schematic diagram of forming a second electrode of an embodiment of the present application.

[0161] Figure 22 shows a schematic diagram of forming a contact via of an embodiment of the present application.

[0162] FIG. 23 shows a schematic diagram of forming the first electrode pad and the second electrode pad in the third embodiment of the present application.

[0163] FIG. 24 shows a schematic diagram of forming the barrier layer and the sacrificial layer in the fourth embodiment of the present application.

[0164] FIG. 25 shows a schematic diagram of forming the support layer in the fourth embodiment of the present application.

[0165] FIG. 26 shows a schematic diagram of forming the first electrode pad and the second electrode pad in the fourth embodiment of the present application.

[0166] FIG. 27 shows a schematic diagram of removing the sacrificial layer in the fourth embodiment of the present application.

[0167] FIG. 28 shows a schematic diagram of forming the Bragg reflection structure and the dielectric layer in the fifth embodiment of the present application.

[0168] FIG. 29 shows a schematic diagram of forming the first electrode pad and the second electrode pad in the fifth embodiment of the present application.

[0169] FIG. 30 shows a schematic diagram of the aluminum nitride-based piezoelectric layer structure in the sixth embodiment of the present application.

[0170] FIG. 31 shows a schematic diagram of providing a substrate and forming a first aluminum nitride-based piezoelectric thin film layer in the seventh embodiment of the present application.

[0171] FIG. 32 shows a schematic diagram of forming an interface modulation material layer in the seventh embodiment of the present application.

[0172] FIG. 33 shows a schematic diagram of forming a photoresist layer on the interface modulation material layer and patterning in the seventh embodiment of the present application.

[0173] FIG. 34 shows a schematic diagram of etching the interface modulation material layer in the seventh embodiment of the present application.

[0174] FIG. 35 shows a schematic diagram of removing the photoresist layer in the seventh embodiment of the present application.

[0175] FIG. 36 shows a schematic diagram of forming a hard mask layer and patterning in the eighth embodiment of the present application.

[0176] FIG. 37 shows a schematic diagram of forming an interface modulation material layer in the eighth embodiment of the present application.

[0177] FIG. 38 shows a schematic diagram of stripping and removing the hard mask layer in the eighth embodiment of the present application.

[0178] FIG. 39 shows a schematic diagram of the structure of the dual-frequency bulk acoustic wave filter in the ninth embodiment of the present application.

[0179] FIG. 40 shows a simulation result diagram of the ninth embodiment of the present application.

[0180] Element No. 1 - substrate, 2 - bottom electrode, 3 - piezoelectric layer, 3A - first ferroelectric thin film layer, 3B - second ferroelectric thin film layer, 300 - piezoelectric thin film layer, 301 - ferroelectric thin film layer, 4 - polarization direction, 5 - top electrode, 6 - cavity, 7 - resonance mode, 8 - first substrate, 9A - first thin film layer, 9B - second thin film layer, 10 - first electrode, 11 - dielectric layer, 12 - opening, 13 - second substrate, 14 - second electrode, 15 - contact via, 16 - first electrode pad, 17 - second electrode pad, 18 - barrier layer, 19 - sacrificial layer, 20 - support layer, 21A - low acoustic impedance layer, 21B - high acoustic impedance layer, 22 - substrate, 23 - piezoelectric layer, 2300 - first aluminum nitride-based piezoelectric thin film layer, 2301 - second aluminum nitride-based piezoelectric thin film layer, 24 - interface modulation layer, 25 - interface modulation material layer, 26 - photoresist layer, 27 - hard mask layer, 28 - substrate, 29 - bonding layer, 2900 - first recess, 2901 - second recess, 3000 - first bottom electrode, 3001 - second bottom electrode, 31 - piezoelectric layer, 3100 - first piezoelectric thin film layer, 3101 - second piezoelectric thin film layer, 32 - interface modulation layer, 3300 - first top electrode, 3301 - second top electrode, 3400 - first bottom electrode pad, 3401 - second bottom electrode pad, 3500 - first top electrode pad, 3501 - second top electrode pad. DETAILED DESCRIPTION

[0181] The present application is herein described, by way of example only, with the assistance of the accompanying drawings detailed description. As will be realized by those skilled in the art, the application is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from the spirit and scope of the application. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

[0182] Reference will now be made to the drawings wherein like numerals refer to like parts throughout the several views. It is also noted that the various figures of the drawing may not be drawn to scale since such a detailed depiction can obscure important aspects of the application. In this regard, the drawings provide merely illustrations of the application, which is not limiting of the present application. They are schematic illustrations of idealized embodiments of the application, and the conceptions may be applied to other embodiments or implementations of the application, in addition to those illustrated.

[0183] Example 1

[0184] The embodiment provides a bulk acoustic wave resonator structure. Referring to FIG. 1, the bulk acoustic wave resonator structure comprises a substrate 1, a bottom electrode 2, a piezoelectric layer 3 and a top electrode 5, the bottom electrode 2 is located above the substrate 1; the piezoelectric layer 3 is located above the bottom electrode 2, the piezoelectric layer 3 comprises first ferroelectric film layers 3A and second ferroelectric film layers 3B which are alternately stacked from bottom to top, wherein adjacent first ferroelectric film layers 3A and second ferroelectric film layers 3B are in direct contact at an interface, and the polarization directions 4 of adjacent first ferroelectric film layers 3A and second ferroelectric film layers 3B are opposite to each other, so as to excite N-order mode resonance, N is an integer not less than the total number of layers of the first ferroelectric film layers 3A and the second ferroelectric film layers 3B; the top electrode 5 is located above the piezoelectric layer 3.

[0185] As an example, the substrate 1 comprises a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate or a diamond substrate, the substrate 1 is provided with a groove opening upward, the bottom electrode 2 and the groove jointly form a cavity 6 as an acoustic wave reflection structure. In other examples, a Bragg reflection layer is arranged between the substrate 1 and the bottom electrode 2 as an acoustic wave reflection structure, the Bragg reflection layer comprises stacked high acoustic impedance material layers and low acoustic impedance material layers, the material of the high acoustic impedance material layers comprises one or more of W, Mo, Pt, Au, Ni and Ir, the material of the low acoustic impedance material layers comprises one or more of AlN, Si3N4 and SiO2, and the thickness of each layer in the Bragg reflection layer is 1 / 4 or 3 / 4 of the wavelength of the acoustic wave corresponding to the resonator resonance frequency.

[0186] As an example, the first ferroelectric film layers 3A and the second ferroelectric film layers 3B refer to film layers which simultaneously have piezoelectric properties and ferroelectric properties.

[0187] As an example, the material of the first ferroelectric film layers comprises Al 1-x Sc x N (0.2≤x≤0.5), BST, PZT and PbTiO3, and the thickness of a single first ferroelectric film layer 3A is not less than 0.01 μm; the material of the second ferroelectric film layers comprises Al 1-x Sc x N (0.2≤x≤0.5), BST, PZT and PbTiO3, and the thickness of a single second ferroelectric film layer 3B is not less than 0.01 μm; and the total thickness of the piezoelectric layer 3 is not more than 2 μm. In the embodiment, the first ferroelectric film layers 3A are Al 1-x Sc x N layers, and the second ferroelectric film layers 3B are Al 1-x Sc x N layers.

[0188] As an example, the material of the bottom electrode 2 includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, and the thickness of the bottom electrode 2 is not more than 0.3 μm; the material of the top electrode 5 includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, and the thickness of the top electrode 5 is not more than 0.3 μm. In the embodiment, the bottom electrode 2 adopts a Mo metal layer, and the top electrode 5 adopts a Mo metal layer.

[0189] Specifically, referring to FIG. 2, the total number of layers of the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B in the piezoelectric layer 3 is set to 3 layers, and the piezoelectric layer 3 is composed of the first ferroelectric thin film layer 3A / the second ferroelectric thin film layer 3B / the first ferroelectric thin film layer 3A stacked together, wherein the first ferroelectric thin film layer 3A adopts an Al 0.7 Sc 0.3 N layer, the second ferroelectric thin film layer 3B adopts an Al 0.7 Sc 0.3 N layer, the thickness of the first ferroelectric thin film layer 3A is 50 nm, the thickness of the second ferroelectric thin film layer 3B is 100 nm, the polarization directions 4 of the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B are opposite, and the bottom electrode 2 and the top electrode 5 both adopt a Mo metal layer with a thickness of 100 nm. In addition, referring to FIG. 3, a comparative example is provided, which is different from the embodiment in that the polarization directions 4 of the adjacent first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B are the same, and the embodiment and the comparative example have different resonance modes 7. Referring to FIGS. 4 and 5, simulation results of the embodiment and the comparative example are shown respectively. As shown in FIG. 4, when the polarization directions of the adjacent first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B are opposite, there is a phase difference of 180° in the piezoelectric response to the electric signal, the inverse piezoelectric effect causes one of the adjacent first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B to be subjected to a compressive stress, and the other to be subjected to a tensile stress, thereby inhibiting the first-order asymmetric thickness expansion mode and exciting the third-order (TE3) thickness expansion mode with a higher corresponding frequency, and the working frequency band is 28 GHz. As shown in FIG. 5, when the polarization directions of the adjacent first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B are the same, the excited resonance mode is the first-order thickness expansion mode (TE1), and the working frequency band is 7 GHz.

[0190] It should be noted that in the embodiment, the total number of layers of the first ferroelectric film layer 3A and the second ferroelectric film layer 3B is three, and in other examples, more layers of the first ferroelectric film layer 3A and the second ferroelectric film layer 3B can be provided, and the thickness of the first ferroelectric film layer 3A and the second ferroelectric film layer 3B is adjusted until the first-order thickness expansion mode is close to complete suppression, and the order of the excited thickness expansion mode is equal to the total number of layers of the first ferroelectric film layer 3A and the second ferroelectric film layer 3B.

[0191] As an example, in the embodiment, the thicker piezoelectric layer 3 is used to realize the ultra-high frequency of the filter, the crystal quality of the piezoelectric layer 3 is high, the defect density is small, the Q value of the corresponding device is high, the loss is small, the power capacity is higher, and it is more suitable for low-power mobile communication, low-interference demand wireless communication application; and in order to guarantee the manufacturing yield of the resonator, the thickness uniformity of the piezoelectric layer 3 needs to be better than 0.5%, the thicker piezoelectric layer 3 can significantly improve the manufacturing yield and manufacturing stability; in addition, the thickness of the piezoelectric layer 3 does not need to be reduced to realize the frequency increase of the resonator, which is particularly suitable for 5G new high frequency band, high frequency satellite communication, 5G millimeter wave frequency band, 6G ultra-high frequency band.

[0192] As an example, compared with existing low-temperature co-fired ceramic (LTCC) filter and integrated passive device (IPD) filter and other medium filters for high frequency and ultra-high frequency, the resonator of the present application has excellent out-of-band suppression, in-band insertion loss and other characteristics, which significantly reduces signal interference and operating power of wireless communication.

[0193] As an example, in the conventional single-layer piezoelectric material bulk acoustic wave resonator, the electromechanical coupling coefficient of the excited high-frequency mode is inversely proportional to the order of the high-order mode, so the electromechanical coupling coefficient of the high-order resonator is very small, and the bandwidth of the corresponding filter is small, which is difficult to meet the actual communication application demand. In the present application, the electromechanical coupling coefficient of the high-order mode of the device is independent of the order, which can maintain high electromechanical coupling coefficient and large bandwidth at high frequency, and is very suitable for high frequency and large bandwidth application scenarios.

[0194] As an example, in the prior art, when a high-frequency mode is excited by using a piezoelectric thin film layer and a ferroelectric thin film layer with opposite polarities, an electrode material layer needs to be inserted between the piezoelectric thin film layer and the ferroelectric thin film layer, and a very high bias voltage is applied through the electrode material layer to realize polarity reversal control. However, the insertion of the electrode material layer will seriously affect the crystal quality of the piezoelectric thin film layer and the ferroelectric thin film layer, worsen the characteristics such as out-of-band rejection and in-band loss of the device, and greatly challenge the cost, controllability and integration. In the present application, the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B are in direct contact. The ferroelectricity of the ferroelectric thin film layer causes the phenomenon of spontaneous polarization. The polarization reversal voltage between different ferroelectric thin films is different due to the influence of deposition conditions, material type, doping concentration, etc. By applying an external voltage between the bottom electrode 2 and the top electrode 5, the polarization state of one of the adjacent first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B remains unchanged, and the polarization state of the other layer is reversed, realizing the opposite polarity control of the adjacent first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B. No electrode material layer needs to be inserted between the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B. The device structure is simple, and the device performance is high.

[0195] In another example, by adjusting the thickness of the bottom electrode 2, the piezoelectric layer 3 and the top electrode 5, the 3rd order thickness expansion mode can be suppressed, and the 4th order overtone thickness mode resonance can be excited.

[0196] As described above, in the bulk acoustic wave resonator of the present embodiment, the polarities of the adjacent first ferroelectric thin film layer and the second ferroelectric thin film layer are opposite, breaking the inverse proportionality relationship between the resonant frequency and the thickness of the piezoelectric layer in the traditional bulk acoustic wave resonator. The high-order resonant mode of the resonator is excited under the condition of maintaining a relatively thick piezoelectric layer, and the resonant frequency of the bulk acoustic wave resonator is significantly improved. In addition, no electrode material layer needs to be inserted between the first ferroelectric thin film layer and the second ferroelectric thin film layer. The device structure is simple, and the device performance is high.

[0197] Embodiment Two

[0198] The present embodiment provides a high-frequency bulk acoustic wave resonator structure. Referring to FIG. 6, the high-frequency bulk acoustic wave resonator structure of the present embodiment is different from that of embodiment one in that the piezoelectric layer 3 is composed of piezoelectric thin film layers 300 and ferroelectric thin film layers 301 stacked alternately, and adjacent piezoelectric thin film layers 300 and ferroelectric thin film layers 301 have opposite polarities.

[0199] As an example, the piezoelectric thin film layer 300 refers to a thin film layer with piezoelectric properties, and the ferroelectric thin film layer 301 refers to a thin film layer with both piezoelectric properties and ferroelectric properties.

[0200] As an example, the material of the piezoelectric thin film layer 300 includes AlN, Al x Ga1-x N (0 < x < 1), Al 1-x Sc x N (0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3, and the thickness of the single piezoelectric thin film layer 300 is not less than 0.01 μm; the material and thickness of the ferroelectric thin film layer 301 are described in Embodiment One and will not be described in detail here.

[0201] For example, the bottom layer of the piezoelectric layer 3 is the piezoelectric thin film layer 300, or the bottom layer of the piezoelectric layer 3 is the ferroelectric thin film layer 301, which is set according to requirements.

[0202] Specifically, referring to FIG. 7, the ferroelectric thin film layer 301 in this embodiment adopts Al 0.7 Sc 0.3 N layer, the piezoelectric thin film layer 300 adopts an AlN layer, and the piezoelectric layer 3 adopts a stacked Al 0.7 Sc 0.3 N layer / AlN layer / Al 0.7 Sc 0.3 N layer, the thickness of the single Al 0.7 Sc 0.3 N layer is 50 nm, the thickness of the single AlN layer is 150 nm, the polarities of the adjacent Al 0.7 Sc 0.3 N layers and AlN layers are opposite (the polarization direction 4 is opposite), and the bottom electrode 2 and the top electrode 5 both adopt a Mo metal layer with a thickness of 100 nm. Referring to FIG. 8, the bottom electrode 2, the piezoelectric layer 3, and the top electrode 5 in the comparative example and the embodiment have the same material and thickness, and the difference lies in that the polarities of the adjacent ferroelectric thin film layer 301 and piezoelectric thin film layer 300 are the same (the polarization direction 4 is the same), and the embodiment and the comparative example have different resonance modes 7. Referring to FIGS. 9 and 10, which respectively show the simulation results of the embodiment and the comparative example, it can be seen from FIG. 9 that the embodiment excites a third-order (TE3) thickness extension mode corresponding to a higher frequency, the working frequency band is 28 GHz, and the electromechanical coupling coefficient K eff 2 is 17.24%; it can be seen from FIG. 10 that the comparative example excites a first-order thickness extension mode (TE1), the working frequency band is 7 GHz, and the electromechanical coupling coefficient K eff 2 is 14.67%.

[0203] As an example, the piezoelectric thin film layer 300 and the ferroelectric thin film layer 301 are in direct contact in the embodiment, the ferroelectric property of the ferroelectric thin film layer 301 causes the phenomenon of spontaneous polarization inside, the polarization state can be changed by applying an external voltage between the bottom electrode 2 and the top electrode 5, and the polarization state can be maintained after the external voltage is removed, realizing the opposite polarity control of the adjacent piezoelectric thin film layer 300 and the ferroelectric thin film layer 301, without inserting an electrode material layer between the piezoelectric thin film layer 300 and the ferroelectric thin film layer 301, the device structure is simple, and the device performance is high.

[0204] As described above, the piezoelectric thin film layer and the ferroelectric thin film layer adjacent to each other have opposite polarities in the embodiment, the high-order resonant mode of the excitation resonator is excited under the condition of maintaining a relatively thick piezoelectric layer, and the resonant frequency of the bulk acoustic wave resonator is significantly improved. In addition, no electrode material layer needs to be inserted between the piezoelectric thin film layer and the ferroelectric thin film layer, the device structure is simple, and the device performance is high.

[0205] Embodiment three

[0206] The embodiment provides a manufacturing method of a high-frequency bulk acoustic wave resonator. Referring to FIG. 11, the manufacturing method of the high-frequency bulk acoustic wave resonator comprises the following steps:

[0207] S1: providing a first substrate, forming a piezoelectric layer on the first substrate, the piezoelectric layer comprising first thin film layers and second thin film layers stacked alternately, at least one of the first thin film layers and the second thin film layers being a ferroelectric thin film layer;

[0208] S2: forming a first electrode on a side of the piezoelectric layer away from the first substrate, and forming a dielectric layer on the side of the piezoelectric layer away from the first substrate, the dielectric layer covering the first electrode;

[0209] S3: forming an opening in the dielectric layer, the opening exposing part of the first electrode;

[0210] S4: providing a second substrate, bonding the dielectric layer to the second substrate, and removing the first substrate;

[0211] S5: forming a second electrode on a side of the piezoelectric layer away from the second substrate;

[0212] S6: forming a first electrode pad and a second electrode pad on a side of the piezoelectric layer away from the second substrate, the first electrode pad being electrically connected through the piezoelectric layer and the first electrode, and the second electrode pad being electrically connected with the second electrode.

[0213] The manufacturing method of the high-frequency bulk acoustic wave resonator of the embodiment will be described in detail below in combination with specific drawings.

[0214] First, referring to Fig. 12, a step S1 is performed: providing a first substrate 8, and forming a piezoelectric layer on the first substrate 8, the piezoelectric layer comprising first thin film layers 9A and second thin film layers 9B stacked alternately, at least one of the first thin film layers 9A and the second thin film layers 9B being a ferroelectric thin film layer.

[0215] As an example, the material of the first substrate 8 includes, but is not limited to, monocrystalline silicon, silicon carbide, germanium, sapphire, gallium nitride, etc.

[0216] As an example, at least one of the first thin film layers 9A and the second thin film layers 9B being a ferroelectric thin film layer, the piezoelectric thin film layers / ferroelectric thin film layers can be stacked alternately, or the ferroelectric thin film layers / ferroelectric thin film layers can be stacked alternately.

[0217] As an example, the description of the piezoelectric thin film layers and the ferroelectric thin film layers can refer to Embodiment One, which will not be described in detail here.

[0218] As an example, in this embodiment, the piezoelectric layer is composed of piezoelectric thin film layers / ferroelectric thin film layers stacked alternately, the first thin film layers 9A are piezoelectric thin film layers, and the second thin film layers 9B are ferroelectric thin film layers; specifically, in this embodiment, the first thin film layers 9A are monocrystalline AlN layers, and the second thin film layers 9B are Sc 0.3 Al 0.7 N layers.

[0219] As an example, the method for forming the first thin film layers 9A and the second thin film layers 9B includes one or more of physical vapor deposition, chemical vapor deposition, or spin coating. Preferably, in this embodiment, MOCVD, MBE, ALD, or PLD is used to form the first thin film layers 9A and the second thin film layers 9B.

[0220] Next, referring to Figs. 13-14, a step S2 is performed: forming a first electrode 10 on the side of the piezoelectric layer away from the first substrate 8, and forming a dielectric layer 11 on the side of the piezoelectric layer away from the first substrate 8, the dielectric layer 11 covering the first electrode 10.

[0221] As an example, as shown in Fig. 13, after forming a first electrode material layer and patterning, the first electrode 10 is obtained.

[0222] As an example, as shown in Fig. 14, the dielectric layer 11 covering the first electrode 10 is formed. Since the dielectric layer 11 is thick and the surface is not flat, referring to Fig. 15, a step of planarizing the surface of the dielectric layer 11 is further included, for example, chemical mechanical polishing (CMP) can be used to planarize the surface of the dielectric layer 4.

[0223] As an example, the material of the dielectric layer 11 includes but is not limited to silicon dioxide, silicon nitride, aluminum oxide, etc., preferably silicon dioxide.

[0224] Next, referring to FIG. 16, step S3 is performed: forming an opening 12 in the dielectric layer 11, the opening 12 exposing part of the first electrode 10.

[0225] As an example, the opening 12 is formed by etching or other suitable method, wherein the opening 12 exposes part of the first electrode 10, and another part of the first electrode 10 is covered by the dielectric layer 11.

[0226] Next, referring to FIGS. 17-18, step S4 is performed: providing a second substrate 13, bonding the dielectric layer 11 to the second substrate 13, and removing the first substrate 8.

[0227] As an example, the material of the second substrate 13 includes but is not limited to single crystal silicon, silicon carbide, germanium, sapphire, or gallium nitride, etc., and the structure formed by the opening 12 is inverted so that the dielectric layer 11 and the second substrate 13 are bonded together.

[0228] As an example, the second substrate 13 and the opening 12 enclose a cavity, which serves as an acoustic mirror structure.

[0229] As an example, the method of removing the first substrate 8 includes but is not limited to one or more of ion implantation stripping, mechanical grinding, polishing, wet etching, dry etching, etc.

[0230] As an example, after the first substrate 8 is removed, the bottom surface of the first thin film layer 9A is exposed, and during the process of removing the first substrate 8, the quality of the bottom surface of the first thin film layer 9A is damaged to some extent. Referring to FIG. 19, the step of thinning the bottom surface of the first thin film layer 9A is further included to remove the first thin film layer 9A with poor quality. The method of thinning the first thin film layer 9A includes etching, polishing, or other suitable methods.

[0231] As an example, referring to FIG. 20, after the bottom surface of the first thin film layer 9A is thinned, the second thin film layer 9B is further formed on the side of the first thin film layer 9A away from the second substrate 13; that is, in this application, the piezoelectric layer is formed in two steps, and the piezoelectric layer can be regarded as being composed of a first piezoelectric layer and a second piezoelectric layer. The first piezoelectric layer is first formed on the first substrate 8, then the first electrode 10, the dielectric layer 11, the opening 12 are formed on the first piezoelectric layer, and then the second substrate 13 is bonded, and the first substrate 8 is removed. Finally, the second piezoelectric layer is formed on the side of the first piezoelectric layer away from the second substrate 13, and thus the piezoelectric layer is completed.

[0232] As an example, in the present embodiment, the piezoelectric layer is composed of a second thin film layer 9B / first thin film layer 9A / second thin film layer 9B of a three-layer structure, wherein the first thin film layer 9A is a single-crystal material layer, and the second thin film layers 9B on both sides of the first thin film layer 9A are deposited based on the first thin film layer 9A as a substrate, so that the piezoelectric layer formed by growth has better overall quality; in other examples, the number of layers of the piezoelectric layer is not limited to three layers, and the number of layers is set according to requirements, without being limited by the present embodiment.

[0233] It should be noted that, in another example, a piezoelectric layer with a required number of layers can also be formed on the first substrate 8, and the first substrate 8 is removed without forming a piezoelectric layer, which also belongs to the protection scope of the present application.

[0234] Next, referring to FIG. 21, step S5 is performed: forming a second electrode 14 on the side of the piezoelectric layer away from the second substrate 13.

[0235] As an example, a second electrode material layer is formed on the side of the piezoelectric layer away from the second substrate 13 and is patterned to obtain the second electrode 14.

[0236] As an example, for the description of the electrode, please refer to Embodiment 1, which will not be described in detail here.

[0237] Next, referring to FIGS. 22-23, step S6 is performed: forming a first electrode pad 16 and a second electrode pad 17 on the side of the piezoelectric layer away from the second substrate 13, the first electrode pad 16 penetrating the piezoelectric layer and electrically connected to the first electrode 10, and the second electrode pad 17 electrically connected to the second electrode 14.

[0238] As an example, as shown in FIG. 22, before forming the first electrode pad 16 and the second electrode pad 17, a contact via hole 15 penetrating the piezoelectric layer is formed in the piezoelectric layer, and the projection of the contact via hole 15 on the second substrate 13 does not overlap with the projection of the opening 12 on the second substrate 13.

[0239] As an example, as shown in FIG. 23, the first electrode pad 16 extends into the contact via hole 15 and is electrically connected to the first electrode 10, and the first electrode pad 16 and the second electrode pad 17 are used for electrode lead-out of the first electrode 10 and the second electrode 14.

[0240] As an example, the contact via 15 is located outside the projection of the opening 12 on the second substrate 13, i.e. the contact via 15 is located outside the periphery of the opening 12, which can avoid introducing acoustic obstacles in the resonance region, prevent the occurrence of spurious waves and energy loss, and avoid the occurrence of spurious waves near the resonance peak.

[0241] As an example, after forming the first electrode pad 16 and the second electrode pad 17, a voltage or voltage pulse is applied between the first electrode 10 and the second electrode 14 to control the polarity direction of the ferroelectric thin film layer, so that the polarities of the adjacent first thin film layer 9A and the second thin film layer 9B are opposite (the polarization directions are opposite).

[0242] It should be noted that in other examples, the first thin film layer 9A and the second thin film layer 9B formed by deposition are layers of materials with opposite polarities, and no external voltage needs to be applied between the first electrode 10 and the second electrode 14 to regulate the polarity of the ferroelectric thin film layer. Although the formation of the piezoelectric layer with opposite polarities by the deposition process has high requirements on the deposition conditions, material types, and doping concentrations, it still falls within the scope of protection of the present application.

[0243] As an example, in the present embodiment, the piezoelectric layer is composed of a three-layer structure, which suppresses the first-order asymmetric thickness extension mode and excites the third-order thickness extension mode, so that the operating frequency of the resonator can reach more than 24 GHz; in another example, the piezoelectric layer is composed of a three-layer structure, and by adjusting the thicknesses of the first electrode 10, the piezoelectric layer, and the second electrode 14, the third-order thickness extension mode can be suppressed and the fourth-order overtone thickness mode can be excited. When the total number of layers of the first thin film layer 9A and the second thin film layer 9B is N layers, and the polarities of adjacent first thin film layers 9A and second thin film layers 9B are opposite, the N-th order thickness extension mode or the N+1-th order overtone thickness mode can be excited, thereby improving the operating frequency band.

[0244] As described above, in the present embodiment, the polarities of the adjacent first thin film layer and the second thin film layer are opposite, which can excite high-order resonance modes of the resonator while maintaining a relatively thick piezoelectric layer, thereby significantly improving the resonance frequency of the bulk acoustic wave resonator; in addition, no electrode material layer needs to be inserted between the first thin film layer and the second thin film layer, and the manufacturing method is simple and the device performance is high.

[0245] Embodiment Four

[0246] The present embodiment provides a manufacturing method of a cavity bulk acoustic wave resonator, which is different from the manufacturing method of the cavity bulk acoustic wave resonator in Embodiment Three in that:

[0247] (1) As shown in Fig. 24, after forming the first electrode 10, a barrier layer 18 covering the first electrode 10 is formed on the piezoelectric layer, and a sacrificial layer 19 is formed on the barrier layer 18, the projection of the sacrificial layer 19 on the piezoelectric layer partially overlaps the projection of the first electrode 10 on the piezoelectric layer;

[0248] (2) As shown in Fig. 25, after forming the sacrificial layer 19, a support layer 20 covering the sacrificial layer 19 is formed on the barrier layer 18, and the support layer 20 and the subsequent second substrate 13 are bonded;

[0249] (3) As shown in Figs. 26-27, after forming the first electrode pad 16 and the second electrode pad 17, the sacrificial layer 19 is removed, and a cavity is formed.

[0250] As an example, the steps of removing the first substrate 8, thinning the exposed first thin film layer 9A, continuing to form the second thin film layer 9B, forming the second electrode 14, and forming the first electrode pad 16 and the second electrode pad 17 can refer to Embodiment Three, which will not be described in detail here.

[0251] As an example, the material of the barrier layer 18 includes SiN, and the barrier layer 18 is used to protect the first electrode 10 and the piezoelectric layer when the sacrificial layer 19 is subsequently released and removed.

[0252] As an example, the material of the sacrificial layer 19 includes Si or SiO2, and the sacrificial layer 19 has a high etching selectivity with the barrier layer 18.

[0253] As an example, the material of the support layer 20 includes Si3N4, SiN, or amorphous AlN, which has a large performance difference with the sacrificial layer 19, so that the support layer 20 will not react when the sacrificial layer 19 is subsequently removed by a release liquid or a release gas.

[0254] As described above, in the present embodiment, the polarities of the adjacent first thin film layer and the second thin film layer are opposite, the high-order resonant mode of the resonator is excited while maintaining a relatively thick piezoelectric layer, and the resonant frequency of the bulk acoustic wave resonator is significantly improved; in addition, there is no need to insert an electrode material layer between the first thin film layer and the second thin film layer, the manufacturing method is simple, and the device performance is high.

[0255] Embodiment Five

[0256] The present embodiment provides a manufacturing method of a Bragg reflection type bulk acoustic wave resonator, which is different from Embodiment Three in that:

[0257] As shown in Fig. 28, after forming the first electrode 10, a Bragg reflection structure covering the first electrode 10 is formed on the piezoelectric layer, the Bragg reflection structure includes a low acoustic impedance layer 21A and a high acoustic impedance layer 21B stacked alternately, and then a dielectric layer 11 is formed on the Bragg reflection structure.

[0258] For example, the low acoustic impedance layer 21A is made of one or more of AlN, Si3N4 and SiO2, and the high acoustic impedance layer 21B is made of one or more of W, Mo, Pt, Au, Ni and Ir, wherein the thickness of each layer in the Bragg reflection structure is 1 / 4 or 3 / 4 of the wavelength of the acoustic wave corresponding to the resonant frequency of the resonator.

[0259] For example, the Bragg reflection structure is provided in multiple layers, and the multiple layers are stacked in turn from bottom to top. In this embodiment, the Bragg reflection structure is stacked three times, i.e., the low acoustic impedance layer 21A and the high acoustic impedance layer 21B are stacked alternately three times. In other examples, the low acoustic impedance layer 21A and the high acoustic impedance layer 21B can be stacked alternately less than three times or more than three times according to requirements, and the embodiment is not limited in this way.

[0260] For example, after the deposition of the low acoustic impedance layer 21A as the bottom layer, the surface of the low acoustic impedance layer 21A is uneven due to the presence of the first electrode 10. The surface of the low acoustic impedance layer 21A is planarized by grinding, polishing or other methods, and then the high acoustic impedance layer 21B is formed.

[0261] For example, the steps of bonding the dielectric layer 11 and the second substrate 13, removing the first substrate 8, thinning the exposed first thin film layer 9A, continuing to form the second thin film layer 9B, forming the second electrode 14, and forming the first electrode pad 16 and the second electrode pad 17 are described in Embodiment Three, and will not be described in detail here. The structure shown in Fig. 29 is obtained.

[0262] For example, the Bragg reflection structure is used to confine the acoustic wave in the piezoelectric layer, avoid the acoustic wave leaking to the second substrate 6, thereby reducing the energy loss and improving the performance of the resonator, which is helpful to achieve high Q value and low insertion loss.

[0263] As described above, in this embodiment, the polarities of the adjacent first thin film layer and the second thin film layer are opposite, which can maintain a relatively thick piezoelectric layer to excite high-order resonant modes of the resonator, thereby significantly improving the resonant frequency of the bulk acoustic wave resonator. In addition, the electrode material layer does not need to be inserted between the first thin film layer and the second thin film layer, the manufacturing method is simple, and the device performance is high.

[0264] Embodiment Six

[0265] The embodiment provides an aluminum nitride-based piezoelectric layer structure. Referring to FIG. 30, the aluminum nitride-based piezoelectric layer structure comprises a substrate 22 and a piezoelectric layer 23, the piezoelectric layer 23 is located above the substrate 22, the piezoelectric layer 23 comprises a first aluminum nitride-based piezoelectric thin film layer 2300 and a second aluminum nitride-based piezoelectric thin film layer 2301, the second aluminum nitride-based piezoelectric thin film layer 2301 is located above the first aluminum nitride-based piezoelectric thin film layer 2300; in the horizontal direction, the piezoelectric layer 23 is divided into a first region and a second region, in the first region, the second aluminum nitride-based piezoelectric thin film layer 2301 and the first aluminum nitride-based piezoelectric thin film layer 2300 are in direct contact, and in the second region, an interface modulation layer 24 is arranged between the second aluminum nitride-based piezoelectric thin film layer 2301 and the first aluminum nitride-based piezoelectric thin film layer 2300; wherein, in the first region, the second aluminum nitride-based piezoelectric thin film layer 2301 and the first aluminum nitride-based piezoelectric thin film layer 2300 have the same polarity, and in the second region, the second aluminum nitride-based piezoelectric thin film layer 2301 and the first aluminum nitride-based piezoelectric thin film layer 2300 have opposite polarities.

[0266] As an example, the substrate 22 can be a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate, a diamond substrate or any other suitable substrate, which is selected according to requirements.

[0267] As an example, the arrow direction in the figure is represented as the polarization direction, the same polarity is represented as the same polarization direction, and the opposite polarity is represented as the opposite polarization direction. In the first region, the second aluminum nitride-based piezoelectric thin film layer 2301 and the first aluminum nitride-based piezoelectric thin film layer 2300 have the same polarity, when an alternating voltage is applied to both sides of the piezoelectric layer 23 in the first region, a basic first-order resonance is excited, and the resonance frequency is low; in the second region, the second aluminum nitride-based piezoelectric thin film layer 2301 and the first aluminum nitride-based piezoelectric thin film layer 2300 have opposite polarities, when an alternating voltage is applied to both sides of the piezoelectric layer 23 in the second region, the first-order resonance is suppressed, a high-order resonance is excited, and the resonance frequency is high; that is, the piezoelectric layer 23 simultaneously has regions with the same polarity and regions with opposite polarities, can excite different resonances, and meets different requirements.

[0268] As an example, the material of the first aluminum nitride-based piezoelectric thin film layer 2300 comprises aluminum nitride and / or doped aluminum nitride, and the material of the second aluminum nitride-based piezoelectric thin film layer 2301 comprises aluminum nitride and / or doped aluminum nitride, wherein, in the doped aluminum nitride, the doping elements comprise one or more of Ga, Sc, Mg, Hf, Zr, B, Er, Be, Ce, Ti, Si, Ge, Li, As, Nb, Sb, Sn, Sr, and the doping concentration is ≤50%.

[0269] As an example, in the first region, the first aluminum nitride-based piezoelectric thin film layer 2300 is an N-polar AlN layer, and the second aluminum nitride-based piezoelectric thin film layer 2301 is an N-polar AlN layer; in the second region, the first aluminum nitride-based piezoelectric thin film layer 2300 is an N-polar AlN layer, and the second aluminum nitride-based piezoelectric thin film layer 2301 is an A1-polar AlN layer.

[0270] As an example, the thickness of the first aluminum nitride-based piezoelectric thin film layer 2300 ranges from 0.01 to 2 μm, and the thickness of the second aluminum nitride-based piezoelectric thin film layer 2301 ranges from 0.01 to 2 μm.

[0271] As an example, the material of the interface modulation layer 24 includes one or more of TiN, Ti2O3, SiO2, SiC, SiN, AlN, Al2O3, AlON, SiON, HfO2, Mo, Mg, MgO, W, and Pt. Due to the presence of the interface modulation layer 24, the surface chemical bond state of the first aluminum nitride-based piezoelectric thin film layer 2300 can be changed, so that the polarity of the second aluminum nitride-based piezoelectric thin film layer 3021 in the second region is opposite to that of the first aluminum nitride-based piezoelectric thin film layer 2300. The thickness of the interface modulation layer 24 ranges from 0.1 to 100 nm, and preferably ranges from 2 to 5 nm.

[0272] As an example, the number of the first regions can be one or more, and the number of the second regions can be one or more, which can be selected according to actual needs.

[0273] As described above, in the present embodiment, the polarities of the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer in the first region are the same, and the polarities of the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer in the second region are opposite, so that regions with the same polarity and regions with opposite polarity coexist in the piezoelectric layer, different resonances can be excited, and different needs can be met.

[0274] Embodiment Seven

[0275] The present embodiment provides a manufacturing method of an aluminum nitride-based piezoelectric layer structure, which is used for manufacturing the aluminum nitride-based piezoelectric layer structure described in Embodiment Six, and includes the following steps:

[0276] S1: providing a substrate, and forming a first aluminum nitride-based piezoelectric thin film layer on the substrate;

[0277] S2: forming an interface modulation layer on the first aluminum nitride-based piezoelectric thin film layer, wherein the interface modulation layer exposes the first aluminum nitride-based piezoelectric thin film layer in a preset region;

[0278] S3: forming a second aluminum nitride-based piezoelectric thin film layer on the first aluminum nitride-based piezoelectric thin film layer, wherein the second aluminum nitride-based piezoelectric thin film layer covers the interface modulation layer.

[0279] The method for manufacturing the aluminum nitride-based piezoelectric layer structure of the embodiment will be described in detail below with reference to the specific drawings.

[0280] First, referring to FIG. 31, step S1 is performed: a substrate 22 is provided, and a first aluminum nitride-based piezoelectric thin film layer 2300 is formed on the substrate 22.

[0281] Next, referring to FIG. 35, step S2 is performed: an interface modulation layer 24 is formed on the first aluminum nitride-based piezoelectric thin film layer 2300, and the interface modulation layer 24 exposes the first aluminum nitride-based piezoelectric thin film layer 2300 in a preset region.

[0282] Specifically, the interface modulation layer 24 exposes the first aluminum nitride-based piezoelectric thin film layer 2300 in a first region, and the step of forming the interface modulation layer 24 includes:

[0283] (1) As shown in FIG. 32, an interface modulation material layer 25 is formed on the first aluminum nitride-based piezoelectric thin film layer 2300;

[0284] (2) As shown in FIG. 33, a photoresist layer 26 is formed on the interface modulation material layer 25 and is patterned;

[0285] (3) As shown in FIG. 34, the interface modulation material layer 25 in the first region is removed by dry etching or wet etching using the patterned photoresist layer 26 as a mask, and the remaining interface modulation material layer 25 constitutes the interface modulation layer 24;

[0286] (4) As shown in FIG. 35, the photoresist layer 26 is removed, and the step of forming the interface modulation layer 24 on the first aluminum nitride-based piezoelectric thin film layer 2300 is completed.

[0287] As an example, a second aluminum nitride-based piezoelectric thin film layer 2301 covering the interface modulation layer 24 is then formed on the first aluminum nitride-based piezoelectric thin film layer 2300, obtaining the structure shown in FIG. 30.

[0288] Embodiment Eight

[0289] The embodiment provides a method for manufacturing an aluminum nitride-based piezoelectric layer structure, which is used to manufacture the aluminum nitride-based piezoelectric layer structure described in Embodiment Six, and differs from Embodiment Seven in that:

[0290] (1) As shown in FIG. 36, after the first aluminum nitride-based piezoelectric thin film layer 2300 is formed, a hard mask layer 27 is formed on the first aluminum nitride-based piezoelectric thin film layer 2300 and is patterned, and the patterned hard mask layer 27 exposes the first aluminum nitride-based piezoelectric thin film layer 2300 at a preset position (second region), wherein the hard mask layer 27 includes a dielectric mask layer or a metal mask layer;

[0291] (3) As shown in FIG. 37, an interface modulation material layer 25 covering the hard mask layer 27 is formed on the first aluminum nitride-based piezoelectric thin film layer 2300, wherein a portion of the interface modulation material layer 25 is in contact with the first aluminum nitride-based piezoelectric thin film layer 2300, and a portion of the interface modulation material layer 25 is in contact with the hard mask layer 27;

[0292] (4) As shown in FIG. 38, the hard mask layer 27 is removed by peeling, wherein when the hard mask layer 27 is removed by peeling, the interface modulation material layer 25 above the hard mask layer 27 is removed, and the remaining interface modulation material layer 25 constitutes the interface modulation layer 24;

[0293] As an example, then a second aluminum nitride-based piezoelectric thin film layer 2301 covering the interface modulation layer 24 is formed on the first aluminum nitride-based piezoelectric thin film layer 2300, and the structure shown in FIG. 30 is obtained.

[0294] Embodiment Nine

[0295] This embodiment provides a dual-frequency bulk acoustic wave filter structure. As shown in FIG. 39, the dual-frequency bulk acoustic wave filter structure includes a substrate 28, a bottom electrode, a piezoelectric layer 31, and a top electrode. The bottom electrode is located above the substrate 1, and the bottom electrode includes a first bottom electrode 3000 and a second bottom electrode 3001. In the horizontal direction (X direction), the first bottom electrode 3000 and the second bottom electrode 3001 are spaced apart by a preset distance. The piezoelectric layer 31 is located above the bottom electrode, and the piezoelectric layer 31 includes piezoelectric thin film layers stacked from bottom to top. In the horizontal direction, the piezoelectric layer 31 is divided into a first region and a second region. In the first region, adjacent piezoelectric thin film layers have the same polarity (in the figure, the arrow represents the polarization direction, and the same polarity means the same polarization direction). In the second region, adjacent piezoelectric thin film layers have opposite polarity. The top electrode is located above the piezoelectric layer 31, and the top electrode includes a first top electrode 3300 and a second top electrode 3301. In the horizontal direction (X direction), the first top electrode 3300 and the second top electrode 3301 are spaced apart by a preset distance. In the vertical direction (Z direction), the first bottom electrode 3000, the first region, and the first top electrode 3300 overlap, and the second bottom electrode 3001, the second region, and the second top electrode 3301 overlap.

[0296] As an example, a bonding layer 29 is arranged between the substrate 28 and the bottom electrode, and the bonding layer 29 is also arranged between the first bottom electrode 3000 and the second bottom electrode 3001, and the material of the bonding layer 29 includes a dielectric material such as SiO2, Si3N4, or a polymer material such as PI (polyimide) and BCB (benzocyclobutene), which is selected according to requirements.

[0297] As an example, the bonding layer 29 is provided with a first groove 2900 and a second groove 2901, and the first groove 2900 and the second groove 2901 are spaced apart by a predetermined distance in the horizontal direction (X direction), at least a part of the first groove 2900 is located below the first bottom electrode 3000, and at least a part of the second groove 2901 is located below the second bottom electrode 3001, and in the projection in the vertical direction (Z direction), the first groove 2900 covers the overlapping area of the first bottom electrode 3000, the first area, and the first top electrode 3300, and the second groove 2901 covers the overlapping area of the second bottom electrode 3001, the second area, and the second top electrode 3301.

[0298] It should be noted that in other examples, the bonding layer 29 is not arranged between the substrate 28 and the bottom electrode, and the first groove 2900 and the second groove 2901 are arranged in the substrate 28, which also belongs to the protection scope of the present application.

[0299] As an example, the piezoelectric layer 31 includes a first piezoelectric thin film layer 3100 and a second piezoelectric thin film layer 3101 stacked from bottom to top, and in the first area, the first piezoelectric thin film layer 3100 and the second piezoelectric thin film layer 3101 are in direct contact, and in the second area, an interface modulation layer 32 is arranged between the first piezoelectric thin film layer 3100 and the second piezoelectric thin film layer 3101.

[0300] As an example, for the description of the piezoelectric thin film layer, please refer to Embodiment One, which will not be described in detail here.

[0301] As an example, for the description of the interface modulation layer, please refer to Embodiment Eight, which will not be described in detail here.

[0302] As an example, in this embodiment, the first groove 2900 and the second groove 2901 are air cavity acoustic mirrors, and in another example, a Bragg reflection layer acoustic mirror can also be arranged between the bottom electrode and the substrate 28, and for the description of the acoustic mirror, please refer to Embodiment One, which will not be described in detail here.

[0303] As an example, a first bottom electrode pad 3400 is provided, which is electrically connected through the piezoelectric layer 31 and the first bottom electrode 3000, and is used for electrically leading out the first bottom electrode 3000. A first top electrode pad 3500 is also provided, which is electrically connected with the first top electrode 3300, and is used for electrically leading out the first top electrode 3300. A second bottom electrode pad 3401 is also provided, which is electrically connected through the piezoelectric layer 31 and the second bottom electrode 3001, and is used for electrically leading out the second bottom electrode 3001. A second top electrode pad 3501 is also provided, which is electrically connected with the second top electrode 3301, and is used for electrically leading out the second top electrode 3301.

[0304] As an example, the dual-frequency bulk acoustic wave filter structure of the embodiment includes a first resonator and a second resonator. The polarities of adjacent piezoelectric thin film layers in the piezoelectric layer 31 of the first resonator are the same, a first-order resonance is excited, and the working frequency is f1. The polarities of adjacent piezoelectric thin film layers in the piezoelectric layer 31 of the second resonator are opposite, a first-order resonance is suppressed, a high-order resonance is excited, and the working frequency is f2. The working frequency f1 of the first resonator is less than the working frequency f2 of the second resonator.

[0305] Specifically, in the embodiment, a Mo metal layer with a thickness of 100 nm is used as the bottom electrode, and a Mo metal layer with a thickness of 100 nm is used as the top electrode. In the first region, the first piezoelectric thin film layer 43100 is an N-polar AlN layer with a thickness of 192 nm, and the second piezoelectric thin film layer 3101 is an N-polar AlN layer with a thickness of 192 nm. In the second region, the first piezoelectric thin film layer 3100 is an N-polar AlN layer with a thickness of 192 nm, and the second piezoelectric thin film layer 3101 is an Al-polar AlN layer with a thickness of 192 nm. Please refer to FIG. 40, which shows a simulation result diagram of the ninth embodiment of the application. The working frequency of the first resonator is 6.15 GHz, and the working frequency of the second resonator is 14.8 GHz. That is, the dual-frequency bulk acoustic wave filter structure of the application has two working frequencies, which can meet the application requirements of different frequency bands.

[0306] In summary, in the piezoelectric layer of the application, the adjacent first thin film layer and the second thin film layer have opposite polarities, breaking the inverse proportional relationship between the resonant frequency of the traditional bulk acoustic wave resonator and the thickness of the piezoelectric layer, maintaining the high-order resonant mode of the resonator under the thicker piezoelectric layer, and significantly improving the resonant frequency of the bulk acoustic wave resonator; without inserting an electrode material layer between the first thin film layer and the second thin film layer, the manufacturing method is simple, and the device performance is high. In addition, the piezoelectric layer is divided into two regions, the polarities of the adjacent piezoelectric thin film layers in the first region are the same, and the polarities of the adjacent piezoelectric thin film layers in the second region are opposite, so that the bulk acoustic wave filter has two frequencies and can meet the application requirements of different frequency bands. Therefore, the application effectively overcomes the various shortcomings in the prior art and has high industrial utilization value.

[0307] The above embodiments only exemplarily illustrate the principles and effects of the application, and are not used to limit the application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the application should be covered by the claims of the application.

Claims

1. A bulk acoustic resonator structure, characterized by, The application relates to a piezoelectric resonator, comprising: a substrate; a bottom electrode above the substrate; a piezoelectric layer above the bottom electrode, the piezoelectric layer comprising first ferroelectric thin film layers and second ferroelectric thin film layers stacked alternately from bottom to top, wherein adjacent first ferroelectric thin film layers and second ferroelectric thin film layers are in direct contact at the interface, and adjacent first ferroelectric thin film layers and second ferroelectric thin film layers have opposite polarization directions to excite N-order mode resonance, N being an integer not less than the total number of the first ferroelectric thin film layers and the second ferroelectric thin film layers; and a top electrode above the piezoelectric layer. The total number of the first ferroelectric thin film layers and the second ferroelectric thin film layers is 3, 1-order thickness expansion mode resonance is suppressed, and 3-order thickness expansion mode resonance is excited. The thickness of the first ferroelectric thin film layers is not less than 0.01 mu m, and the thickness of the second ferroelectric thin film layers is not less than 0.01 mu m. The material of the bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf, and the material of the top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf. The thickness of the bottom electrode is not more than 0.3 mu m, and the thickness of the top electrode is not more than 0.3 mu m.

2. The bulk acoustic resonator structure of claim 1, wherein: The substrate is provided with an upwardly-opened groove, and the bottom electrode and the groove jointly form a cavity.

3. The bulk acoustic resonator structure of claim 1, wherein: The material of the first ferroelectric thin film layer includes Al 1-x Sc x one or more of NiO, CoO, FeO, MnO, CrO, V2O3, Cr2O3, MoO2, WO2, RuO2, RhO2, IrO2, PtO2, PdO, CuO, AgO, AuO, ZnO, CdO, HgO, Al2O3, Ga2O3, In2O3, Tl2O3, SnO2, GeO2, PbO2, Bi2O3, and Sb2O3 1-x Sc x one or more of NiO, CoO, FeO, MnO, CrO, V2O3, Cr2O3, MoO2, WO2, RuO2, RhO2, IrO2, PtO2, PdO, CuO, AgO, AuO, ZnO 4. The bulk acoustic resonator structure of claim 1, wherein: The substrate and the bottom electrode are provided with a Bragg reflection layer, and the Bragg reflection layer comprises high acoustic impedance material layers and low acoustic impedance material layers stacked alternately.

5. The bulk acoustic resonator structure of claim 1, wherein: The substrate comprises a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate or a diamond substrate.

6. The bulk acoustic resonator structure of claim 1, wherein: The application relates to a piezoelectric resonator, comprising: a substrate; a bottom electrode above the substrate; a piezoelectric layer above the bottom electrode, the piezoelectric layer comprising first ferroelectric thin film layers and second ferroelectric thin film layers stacked alternately from bottom to top, wherein adjacent first ferroelectric thin film layers and second ferroelectric thin film layers are in direct contact at the interface, and adjacent first ferroelectric thin film layers and second ferroelectric thin film layers have opposite polarization directions to excite N-order mode resonance, N being an integer not less than the total number of the first ferroelectric thin film layers and the second ferroelectric thin film layers; and a top electrode above the piezoelectric layer.

7. The bulk acoustic resonator structure of claim 1, wherein: The total number of the first ferroelectric thin film layers and the second ferroelectric thin film layers is 3, 1-order thickness expansion mode resonance is suppressed, and 3-order thickness expansion mode resonance is excited.

8. The bulk acoustic resonator structure of claim 1, wherein: The thickness of the first ferroelectric thin film layers is not less than 0.01 mu m, and the thickness of the second ferroelectric thin film layers is not less than 0.01 mu m.

9. The bulk acoustic resonator structure of claim 1, wherein: The material of the bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf, and the material of the top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf.

10. A high frequency bulk acoustic resonator structure, characterized by, The thickness of the bottom electrode is not more than 0.3 mu m, and the thickness of the top electrode is not more than 0.3 mu m. The substrate is provided with an upwardly-opened groove, and the bottom electrode and the groove jointly form a cavity. The substrate and the bottom electrode are provided with a Bragg reflection layer, and the Bragg reflection layer comprises high acoustic impedance material layers and low acoustic impedance material layers stacked alternately. ​ ​ 11. The high-frequency bulk acoustic resonator structure of claim 10, wherein: ​ 12. The high-frequency bulk acoustic resonator structure of claim 10, wherein: The material of the piezoelectric thin film layer includes one or more of AlN, Al x Ga 1-x N(0 < x < 1), Al 1-x Sc x N(0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3.

13. The high-frequency bulk acoustic resonator structure of claim 10, wherein: The material of the ferroelectric thin film layer includes Al 1-x Sc x one or more of N (0.2≤x≤0.5), BST, PZT and PbTiO3.

14. The high-frequency bulk acoustic resonator structure of claim 10, wherein: ​ 15. The high-frequency bulk acoustic resonator structure of claim 10, wherein: ​ 16. The high-frequency bulk acoustic resonator structure of claim 15, wherein: ​ 17. The high-frequency bulk acoustic resonator structure of claim 10, wherein: ​ 18. The high-frequency bulk acoustic resonator structure of claim 10, wherein: ​ 19. The high-frequency bulk acoustic resonator structure of claim 10, wherein: The substrate comprises a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate or a diamond substrate.

20. A method of fabricating a high frequency bulk acoustic wave resonator, comprising: The method comprises the following steps: providing a first substrate, forming a piezoelectric layer on the first substrate, the piezoelectric layer comprising first thin film layers and second thin film layers stacked alternately, at least one of the first thin film layers and the second thin film layers being a ferroelectric thin film layer; forming a first electrode on a side of the piezoelectric layer away from the first substrate, and forming a dielectric layer on the side of the piezoelectric layer away from the first substrate, the dielectric layer covering the first electrode; forming an opening in the dielectric layer, the opening exposing part of the first electrode; providing a second substrate, bonding the dielectric layer to the second substrate, and removing the first substrate; forming a second electrode on a side of the piezoelectric layer away from the second substrate; forming a first electrode pad and a second electrode pad on a side of the piezoelectric layer away from the second substrate, the first electrode pad being electrically connected through the piezoelectric layer and the first electrode, and the second electrode pad being electrically connected to the second electrode; applying a voltage or a voltage pulse between the first electrode and the second electrode to control the polarity direction of the ferroelectric thin film layer, so that the polarity of adjacent first thin film layers and second thin film layers is opposite, thereby suppressing a first-order resonance mode and exciting an N-order resonance mode, N being an integer greater than 1.

21. The method of claim 20, wherein The piezoelectric layer comprises a first piezoelectric layer and a second piezoelectric layer, the first piezoelectric layer comprising at least one of the first thin film layers and the second thin film layers stacked alternately, the second piezoelectric layer comprising at least one of the first thin film layers and the second thin film layers stacked alternately, the step of forming the piezoelectric layer comprising: forming the first piezoelectric layer on the first substrate; forming the first electrode on a side of the first piezoelectric layer away from the first substrate; forming the first electrode, the dielectric layer and the opening on a side of the first piezoelectric layer away from the first substrate; bonding the dielectric layer to the second substrate, and removing the first substrate; forming the second piezoelectric layer on a side of the first piezoelectric layer away from the second substrate.

22. The method of claim 21, wherein: After removing the first substrate, the method further comprises the step of thinning a side of the first piezoelectric layer away from the second substrate.

23. The method of claim 20, wherein: The piezoelectric layer comprises piezoelectric thin film layers / ferroelectric thin film layers stacked alternately.

24. The method of claim 20, wherein: The piezoelectric layer comprises ferroelectric thin film layers / ferroelectric thin film layers stacked alternately.

25. The method of claim 20, wherein: The material of the ferroelectric thin film layer includes Sc x Al 1-x N (0.2≤x≤0.5), BST, PZT, PbTiO3, or one or more thereof.

26. The method of claim 20, wherein: The thickness of the first thin film layers is not less than 0.01 μm, and the thickness of the second thin film layers is not less than 0.01 μm.

27. The method of claim 20, wherein: The material of the first electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf; and the material of the second electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf.

28. The method of claim 20, wherein: The method of forming the piezoelectric layer comprises one or more of physical vapor deposition, chemical vapor deposition and spin coating.

29. A method of fabricating a cavity bulk acoustic resonator, the method comprising: The method comprises the following steps: A first substrate is provided, on which a piezoelectric layer is formed, the piezoelectric layer comprising first thin film layers and second thin film layers stacked alternately, at least one of the first thin film layers and the second thin film layers being a ferroelectric thin film layer; A first electrode is formed on the piezoelectric layer, and a barrier layer covering the first electrode is formed on the piezoelectric layer, a sacrificial layer is formed on the barrier layer, the projection of the sacrificial layer on the piezoelectric layer partially overlaps the projection of the first electrode on the piezoelectric layer; A support layer is formed on the barrier layer, the support layer covering the sacrificial layer; A second substrate is provided, the support layer is bonded to the second substrate, and the first substrate is removed; A second electrode is formed on the side of the piezoelectric layer away from the second substrate; A contact via is formed in the piezoelectric layer, the contact via penetrating through the piezoelectric layer, the contact via exposing the first electrode, the projection of the contact via on the second substrate does not overlap the projection of the cavity on the second substrate; A first electrode pad and a second electrode pad are formed on the side of the piezoelectric layer away from the second substrate, the first electrode pad penetrating through the piezoelectric layer and the first electrode to be electrically connected, the second electrode pad being electrically connected to the second electrode; A voltage or a voltage pulse is applied between the first electrode and the second electrode to control the polarity direction of the ferroelectric thin film layer, so that the polarity of adjacent first thin film layers and second thin film layers is opposite; The sacrificial layer is removed to form a cavity; Wherein, the polarity of adjacent first thin film layers and second thin film layers is opposite to suppress the 1st order resonance mode and excite the Nth order resonance mode, N being an integer greater than 1.

30. The method of claim 29, wherein: The piezoelectric layer comprises a first piezoelectric layer and a second piezoelectric layer, the first piezoelectric layer comprising at least one of the first thin film layers and the second thin film layers stacked alternately, the second piezoelectric layer comprising at least one of the first thin film layers and the second thin film layers stacked alternately, the step of forming the piezoelectric layer comprising: The first piezoelectric layer is formed on the first substrate; The first electrode is formed on the side of the first piezoelectric layer away from the first substrate; The first electrode, the support layer and the opening are formed on the side of the first piezoelectric layer away from the first substrate; The support layer is bonded to the second substrate, and the first substrate is removed; The second piezoelectric layer is formed on the side of the first piezoelectric layer away from the second substrate.

31. The method of claim 30, wherein: After the first substrate is removed, the step of thinning the side of the first piezoelectric layer away from the second substrate is further included.

32. The method of claim 29, wherein: Before the cavity is formed, the step of forming a sacrificial layer etching hole penetrating through the piezoelectric layer is further included, the sacrificial layer etching hole exposing the sacrificial layer, the sacrificial layer is etched and removed based on the sacrificial layer etching hole, wherein the sacrificial layer etching hole avoids the first electrode and the second electrode.

33. The method of claim 29, wherein: The piezoelectric layer comprises piezoelectric thin film layers / ferroelectric thin film layers stacked alternately.

34. The method of claim 29, wherein: The piezoelectric layer comprises ferroelectric thin film layers / ferroelectric thin film layers stacked alternately.

35. The method of claim 29, wherein: The material of the ferroelectric thin film layer includes Sc x Al 1-x N (0.2≤x≤0.5), BST, PZT, PbTiO3, or one or more thereof.

36. The method of claim 29, wherein: The thickness of the first thin film layer is not less than 0.01 μm, and the thickness of the second thin film layer is not less than 0.01 μm.

37. A method of fabricating a Bragg reflector bulk acoustic resonator, the method comprising: The method comprises the following steps: A first substrate is provided, and a piezoelectric layer is formed on the first substrate, the piezoelectric layer comprising first thin film layers and second thin film layers stacked alternately, at least one of the first thin film layers and the second thin film layers being a ferroelectric thin film layer; A first electrode is formed on the piezoelectric layer, and a Bragg reflection structure covering the first electrode is formed on the piezoelectric layer, the Bragg reflection structure comprising low acoustic impedance layers and high acoustic impedance layers stacked alternately, and the number of the Bragg reflection structures is plural, and the plural Bragg reflection structures are stacked in turn from bottom to top; A dielectric layer is formed on the Bragg reflection structure; A second substrate is provided, the dielectric layer is bonded to the second substrate, and the first substrate is removed; A second electrode is formed on a side of the piezoelectric layer away from the second substrate; A first electrode pad and a second electrode pad are formed on a side of the piezoelectric layer away from the second substrate, the first electrode pad is electrically connected through the piezoelectric layer and the first electrode, and the second electrode pad is electrically connected with the second electrode; A voltage or a voltage pulse is applied between the first electrode and the second electrode to control the polarity direction of the ferroelectric thin film layer, so that the polarity of adjacent first thin film layers and second thin film layers is opposite, thereby suppressing a first-order resonance mode and exciting an N-order resonance mode, N being an integer greater than 1.

38. The method of claim 37, wherein: The material of the low acoustic impedance layer comprises one or more of AlN, Si3N4 and SiO2, and the material of the high acoustic impedance layer comprises one or more of W, Mo, Pt, Au, Ni and Ir.

39. The method of claim 37, wherein: The piezoelectric layer comprises a first piezoelectric layer and a second piezoelectric layer, the first piezoelectric layer comprises at least one of the first thin film layers and the second thin film layers stacked alternately, the second piezoelectric layer comprises at least one of the first thin film layers and the second thin film layers stacked alternately, and the step of forming the piezoelectric layer comprises: The first piezoelectric layer is formed on the first substrate; The first electrode and the Bragg reflection structure are formed on a side of the first piezoelectric layer away from the first substrate; The dielectric layer is formed on the Bragg reflection structure; The dielectric layer is bonded to the second substrate, and the first substrate is removed; The second piezoelectric layer is formed on a side of the first piezoelectric layer away from the second substrate.

40. The method of claim 39, wherein: After the first substrate is removed, a step of thinning a side of the first piezoelectric layer away from the second substrate is further included.

41. The method of claim 37, wherein: The piezoelectric layer comprises piezoelectric thin film layers / ferroelectric thin film layers stacked alternately.

42. The method of claim 37, wherein: The piezoelectric layer comprises ferroelectric thin film layers / ferroelectric thin film layers stacked alternately.

43. The method of claim 37, wherein: The material of the ferroelectric thin film layer includes Sc x Al 1-x N (0.2≤x≤0.5), BST, PZT, PbTiO3, or one or more thereof.

44. The method of claim 37, wherein: The thickness of the first thin film layer is not less than 0.01 μm, and the thickness of the second thin film layer is not less than 0.01 μm.

45. An aluminum nitride-based piezoelectric layer structure, characterized by, It comprises: a substrate; a piezoelectric layer above the substrate, the piezoelectric layer comprising a first aluminum nitride-based piezoelectric thin film layer and a second aluminum nitride-based piezoelectric thin film layer, the second aluminum nitride-based piezoelectric thin film layer being above the first aluminum nitride-based piezoelectric thin film layer; In the horizontal direction, the piezoelectric layer is divided into a first region and a second region, in the first region, the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer are in direct contact, and in the second region, an interface modulation layer is arranged between the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer. Wherein, in the first region, the polarity of the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer is the same, and in the second region, the polarity of the second aluminum nitride-based piezoelectric thin film layer and the first aluminum nitride-based piezoelectric thin film layer is opposite.

46. The aluminum nitride-based piezoelectric layer structure of claim 45, wherein: The material of the interface modulation layer includes at least one of TiN, Ti2O3, SiO2, SiC, SiN, AlN, Al2O3, AlON, SiON, HfO2, Mo, Mg, MgO, W, Pt, and the thickness of the interface modulation layer ranges from 0.1 to 100 nm.

47. The aluminum nitride-based piezoelectric layer structure of claim 45, wherein: The material of the first aluminum nitride-based piezoelectric thin film layer includes aluminum nitride and / or doped aluminum nitride, and the material of the second aluminum nitride-based piezoelectric thin film layer includes aluminum nitride and / or doped aluminum nitride, wherein the doping elements in the doped aluminum nitride include one or more of Ga, Sc, Mg, Hf, Zr, B, Er, Be, Ce, Ti, Si, Ge, Li, As, Nb, Sb, Sn, Sr.

48. The aluminum nitride-based piezoelectric layer structure of claim 45, wherein: The thickness of the first aluminum nitride-based piezoelectric thin film layer ranges from 0.01 to 2 μm, and the thickness of the second aluminum nitride-based piezoelectric thin film layer ranges from 0.01 to 2 μm.

49. The aluminum nitride-based piezoelectric layer structure of claim 45, wherein: The substrate includes Si substrate, SiC substrate, Ge substrate, sapphire substrate and diamond substrate.

50. A method of fabricating an aluminum nitride-based piezoelectric layer structure as claimed in any one of claims 45-49, characterized by, The method comprises the following steps: providing a substrate, forming a first aluminum nitride-based piezoelectric thin film layer on the substrate; forming an interface modulation layer on the first aluminum nitride-based piezoelectric thin film layer, the interface modulation layer exposing the first aluminum nitride-based piezoelectric thin film layer in a preset region; forming a second aluminum nitride-based piezoelectric thin film layer covering the interface modulation layer on the first aluminum nitride-based piezoelectric thin film layer.

51. The method of fabricating an aluminum nitride-based piezoelectric layer structure of claim 50, wherein, The step of forming the interface modulation layer comprises: forming an interface modulation material layer on the first aluminum nitride-based piezoelectric thin film layer; forming a photoresist layer on the interface modulation material layer and patterning, using the patterned photoresist layer as a mask to remove the interface modulation material layer at a preset position, and the remaining interface modulation material layer constitutes the interface modulation layer; removing the photoresist layer.

52. The method of fabricating an aluminum nitride-based piezoelectric layer structure of claim 51, wherein: The method for removing the interface modulation material layer at a preset position comprises at least one of dry etching and wet etching.

53. The method of claim 50, wherein: The step of forming the interface modulation layer comprises: forming a hard mask layer on the first aluminum nitride-based piezoelectric thin film layer and patterning, the patterned hard mask layer exposing the first aluminum nitride-based piezoelectric thin film layer at a preset position; forming an interface modulation material layer covering the hard mask layer on the first aluminum nitride-based piezoelectric thin film layer; stripping the hard mask layer, wherein when the hard mask layer is stripped, the interface modulation material layer above the hard mask layer is removed, and the remaining interface modulation material layer constitutes the interface modulation layer.

54. The method of fabricating an aluminum nitride-based piezoelectric layer structure of claim 53, wherein: The hard mask layer is a dielectric mask layer or a metal mask layer.

55. A dual frequency bulk acoustic wave filter structure, comprising: Comprise: a substrate; a bottom electrode above the substrate, the bottom electrode comprising a first bottom electrode and a second bottom electrode, the first bottom electrode and the second bottom electrode being spaced apart by a preset distance in the horizontal direction; a piezoelectric layer above the bottom electrode, the piezoelectric layer comprising piezoelectric thin film layers stacked from bottom to top, the piezoelectric layer being divided into a first region and a second region in the horizontal direction, adjacent piezoelectric thin film layers in the first region having the same polarity, and adjacent piezoelectric thin film layers in the second region having opposite polarities, the piezoelectric layer comprising a first piezoelectric thin film layer and a second piezoelectric thin film layer stacked from bottom to top, the first piezoelectric thin film layer and the second piezoelectric thin film layer being in direct contact in the first region, and an interface modulation layer being arranged between the first piezoelectric thin film layer and the second piezoelectric thin film layer in the second region; a top electrode above the piezoelectric layer, the top electrode comprising a first top electrode and a second top electrode, the first top electrode and the second top electrode being spaced apart by a preset distance in the horizontal direction; wherein, in the vertical direction, the first bottom electrode, the first region and the first top electrode overlap, and the second bottom electrode, the second region and the second top electrode overlap.

56. The dual-band bulk acoustic wave filter structure of claim 55, wherein: The material of the interface modulation layer comprises one or more of TiN, Ti2O3, SiO2, SiC, SiN, AlN, Al2O3, AlON, SiON, HfO2, Mo, Mg, MgO, W and Pt, and the thickness of the interface modulation layer ranges from 1 to 100 nm.

57. The dual-band bulk acoustic wave filter structure of claim 55, wherein: The material of the piezoelectric thin film layer includes one or more of AlN, Al x Ga 1-x N (0 < x < 1), Al 1-x Sc x N (0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3, and the thickness of the single piezoelectric thin film layer is not less than 0.01 μm, and the thickness of the piezoelectric layer is not more than 2 μm.

58. The dual-band bulk acoustic wave filter structure of claim 55, wherein: The substrate is provided with a first recess and a second recess, at least a part of the first recess being below the first bottom electrode, and at least a part of the second recess being below the second bottom electrode.

59. The dual-band bulk acoustic wave filter structure of claim 55, wherein: A bonding layer is arranged between the substrate and the bottom electrode, the bonding layer being provided with a first recess and a second recess, at least a part of the first recess being below the first bottom electrode, and at least a part of the second recess being below the second bottom electrode.

60. The dual-band bulk acoustic wave filter structure of claim 55, wherein: A Bragg reflection layer is arranged between the substrate and the bottom electrode.

61. The dual-band bulk acoustic wave filter structure of claim 60, wherein: The Bragg reflection layer comprises stacked high acoustic impedance material layers and low acoustic impedance material layers, the material of the high acoustic impedance material layers comprising one or more of W, Mo, Pt, Au, Ni and Ir, and the material of the low acoustic impedance material layers comprising one or more of AlN, Si3N4 and SiO2.

62. The dual-band bulk acoustic wave filter structure of claim 55, wherein: The material of the bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf, and the material of the top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf.

63. The dual-band bulk acoustic wave filter structure of claim 55, wherein: The substrate comprises a Si substrate, a SiC substrate, a Ge substrate and a sapphire substrate.

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