Resonant mode control method for bulk acoustic wave resonator, and radio-frequency front end

Abstract

Provided in the present invention are a resonant mode control method for a bulk acoustic wave resonator, and a radio-frequency front end. A unipolar direct-current pulse is applied between a bottom electrode and a top electrode to change the polarity of a ferroelectric thin film in a piezoelectric layer, thereby realizing controllable switching of the resonant frequency of a resonator; and it is not necessary to provide a polycrystalline electrode modulation layer between a first thin film layer and a second thin film layer, thereby reducing the cost and improving the performance of a device. In a radio-frequency front end, a unipolar direct-current pulse is applied between the bottom electrode and the top electrode, thereby realizing controllable switching of the resonant frequency between different frequency bands, and meeting application requirements for different frequency bands; the piezoelectric layer is configured to include areas having the same polarity and areas having opposite polarities, the areas having the same polarity excite first-order resonance, and the areas having opposite polarities excite high-order resonance, such that the radio-frequency front end can operate in different frequency bands at the same time, thereby meeting the application requirements for different frequency bands; in addition, adjacent thin film layers in the piezoelectric layer are configured to have opposite polarities, so as to excite high-order resonance, thereby increasing an operating frequency band.

Description

Resonant mode control method of bulk acoustic resonator and radio frequency front end TECHNICAL FIELD

[0001] The present application belongs to the field of microelectronics, and relates to a resonant mode control method of a bulk acoustic resonator and a radio frequency front end. BACKGROUND

[0002] At present, the filters applied to 5G communication are mainly bulk acoustic wave filters (BAW) and surface acoustic wave filters (SAW). The BAW device has an extremely high Q value (4000 or more), a working frequency band from 100MHz to 20GHz, and advantages of high working frequency, low insertion loss, high frequency selection characteristic, high power capacity and strong anti-static ability, etc., and is the best solution for future radio frequency front ends.

[0003] At present, the sub-6G (3.3-4.2GHz) frequency band is generally used in 5G communication. With the development of application demand, microwave acoustics not only needs to expand the working frequency range to Ku, Ka frequency band or even millimeter wave (mm-Wave) frequency band, but also needs to meet the requirement of ultra-wideband. In a traditional single-layer piezoelectric thin film resonator, the resonant frequency of the bulk acoustic resonator is positively correlated with the ratio of the longitudinal acoustic velocity and the thickness of the thin film, which means that the thickness of the piezoelectric thin film of the filter applied to a higher frequency band 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, electromechanical coupling coefficient and Q value of the resonator will sharply decrease. In addition, the resonant mode of the single-layer piezoelectric thin film resonator is single, and only can meet the application demand of a certain frequency band, which has great application limitation.

[0004] Therefore, how to provide a resonant mode control method of a bulk acoustic resonator and a radio frequency front end to realize the switching of different resonant modes and meet the application demand of different frequency bands and improve the working frequency has become a technical problem to be solved by those skilled in the art. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a resonant mode control method of a bulk acoustic resonator and a radio frequency front end, which is used to solve the problem of low working frequency band and single resonant mode of the radio frequency front end in the prior art.

[0006] To achieve the above-mentioned purpose and other related purposes, the present application provides a resonant mode control method of a bulk acoustic resonator, which comprises a piezoelectric layer, a bottom electrode located below the piezoelectric layer and a top electrode located above the piezoelectric layer:

[0007] The piezoelectric layer comprises first thin film layers and second thin film layers which are alternately stacked, the interfaces of adjacent first thin film layers and second thin film layers are directly contacted, and the lowermost layer of the piezoelectric layer is the first thin film layer, wherein the first thin film layer is a piezoelectric thin film layer, and the second thin film layer is a ferroelectric thin film layer, or the first thin film layer is a ferroelectric thin film layer, and the second thin film layer is a piezoelectric thin film layer.

[0008] A unipolar direct current pulse is applied between the bottom electrode and the top electrode to reverse the polarity of the ferroelectric thin film layer, so as to switch the bulk acoustic wave resonator between a first order vibration mode and a high order vibration mode, wherein the high order vibration mode is a vibration mode higher than the first order.

[0009] Optionally, the unipolar direct current pulse is applied between the bottom electrode and the top electrode by a pulse generator.

[0010] Optionally, the unipolar direct current pulse shape comprises a triangular waveform and a square waveform.

[0011] Optionally, a substrate is arranged below the bottom electrode, and an air cavity is arranged between the substrate and the bottom electrode.

[0012] Optionally, a substrate is arranged below the bottom electrode, and a Bragg reflection layer is arranged between the substrate and the bottom electrode.

[0013] Optionally, the material of the piezoelectric thin film layer 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, Ga2O3.

[0014] Optionally, the material of the ferroelectric thin film layer comprises one or more of Al 1-x Sc x N (0.2 ≤ x ≤ 0.5), BST, PZT, PbTiO3.

[0015] Optionally, the thickness of a single layer of the piezoelectric thin film layer is not less than 0.01 μm, the thickness of a single layer of the ferroelectric thin film layer is not less than 0.01 μm, and the total thickness of the piezoelectric layer is not more than 2 μm.

[0016] Optionally, the material of the bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, and the material of the top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf.

[0017] Optionally, a thickness of the bottom electrode is no more than 0.3 μm, and a thickness of the top electrode is no more than 0.3 μm.

[0018] The application further provides a radio frequency front end with switchable working frequency bands, comprising:

[0019] at least one frequency-adjustable bulk acoustic resonator, the bulk acoustic resonator comprising, from bottom to top, a substrate, a bottom electrode, a piezoelectric layer, and a top electrode, the piezoelectric layer comprising first thin film layers and second thin film layers alternately stacked, one of the first thin film layers and the second thin film layers being a ferroelectric thin film layer, and the other of the first thin film layers and the second thin film layers being a piezoelectric thin film layer;

[0020] a pulse generation unit connected between the top electrode and the bottom electrode, the pulse generation unit being configured to apply a unipolar direct current pulse to the piezoelectric layer through the top electrode and the bottom electrode.

[0021] Optionally, a shape of the unipolar direct current pulse comprises a triangular waveform and a square waveform.

[0022] Optionally, a material of the piezoelectric thin film layer comprises at least one 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 a material of the ferroelectric thin film layer comprises at least one of Al 1-x Sc x N (0.2 < x < 0.5), BST, PZT, PbTiO3, wherein a thickness of a single layer of the first thin film layers is no less than 0.01 μm, a thickness of a single layer of the second thin film layers is no less than 0.01 μm, and a total thickness of the piezoelectric layer is no more than 2 μm; a material of the bottom electrode comprises at least one of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, and a material of the top electrode comprises at least one of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, wherein a thickness of the bottom electrode is no more than 0.3 μm, and a thickness of the top electrode is no more than 0.3 μm.

[0023] Optionally, a total number of layers of the first thin film layers and the second thin film layers is two, the piezoelectric thin film layer is an AlN layer, a thickness of the piezoelectric thin film layer is 210 nm, the ferroelectric thin film layer is an Al 0.7 Sc 0.3N layers, the thickness of the ferroelectric thin film layer is 220nm, the bottom electrode is a Mo metal layer, the thickness of the bottom electrode is 86nm, the top electrode is a Mo metal layer, the thickness of the top electrode is 86nm, wherein when a unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency switches between the N79 frequency band and the Ku frequency band.

[0024] Optionally, the total number of layers of the first thin film layer and the second thin film layer is two layers, the piezoelectric thin film layer is an AlN layer, the thickness of the piezoelectric thin film layer is 130nm, the ferroelectric thin film layer is an Al 0.7 Sc 0.3 N layers, the thickness of the ferroelectric thin film layer is 130nm, the bottom electrode is a Mo metal layer, the thickness of the bottom electrode is 72nm, the top electrode is a Mo metal layer, the thickness of the top electrode is 72nm, wherein when a unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency switches between the UWB frequency band and the K frequency band.

[0025] Optionally, the total number of layers of the first thin film layer and the second thin film layer is two layers, the piezoelectric thin film layer is an AlN layer, the thickness of the piezoelectric thin film layer is 140nm, the ferroelectric thin film layer is an Al 0.7 Sc 0.3 N layers, the thickness of the ferroelectric thin film layer is 100nm, the bottom electrode is a Mo metal layer, the thickness of the bottom electrode is 50nm, the top electrode is a Mo metal layer, the thickness of the top electrode is 50nm, wherein when a unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency switches between the SHF frequency band and the N258 frequency band.

[0026] Optionally, the total number of layers of the first thin film layer and the second thin film layer is two layers, the piezoelectric thin film layer is an AlN layer, the thickness of the piezoelectric thin film layer is 150nm, the ferroelectric thin film layer is an Al 0.7 Sc 0.3 N layers, the thickness of the ferroelectric thin film layer is 140nm, the bottom electrode is a Mo metal layer, the thickness of the bottom electrode is 85nm, the top electrode is a Mo metal layer, the thickness of the top electrode is 85nm, wherein when a unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency switches between the N104 frequency band and the Ku frequency band.

[0027] Optionally, an air cavity is arranged between the substrate and the bottom electrode.

[0028] Optionally, a Bragg reflection layer is arranged between the substrate and the bottom electrode.

[0029] Optionally, the substrate comprises a Si substrate, a SiC substrate, a Ge substrate or a sapphire substrate.

[0030] The application further provides a radio frequency front end with different working frequencies, comprising:

[0031] a substrate;

[0032] a first bulk acoustic resonator located above the substrate, the first bulk acoustic resonator comprising a first bottom electrode, a first piezoelectric layer and a first top electrode arranged from bottom to top, the first piezoelectric layer comprising not less than two first piezoelectric thin film layers, adjacent first piezoelectric thin film layers having the same polarity;

[0033] a second bulk acoustic resonator located above the substrate, the second bulk acoustic resonator comprising a second bottom electrode, a second piezoelectric layer and a second top electrode arranged from bottom to top, the second piezoelectric layer comprising not less than two second piezoelectric thin film layers, adjacent second piezoelectric thin film layers having opposite polarities;

[0034] wherein the working frequency of the first bulk acoustic resonator is less than the working frequency of the second bulk acoustic resonator.

[0035] Optionally, a first air cavity is arranged between the first bottom electrode and the substrate, and a second air cavity is arranged between the second bottom electrode and the substrate.

[0036] Optionally, a first Bragg reflection structure is arranged between the first bottom electrode and the substrate, and a second Bragg reflection structure is arranged between the second bottom electrode and the substrate.

[0037] Optionally, a bonding layer is further included, the bonding layer being located between the bulk acoustic resonator and the substrate, a first air cavity being arranged between the first bottom electrode and the bonding layer, and a second air cavity being arranged between the second bottom electrode and the bonding layer.

[0038] Optionally, adjacent first piezoelectric thin film layers directly contact at an interface, an interface modulation layer being arranged between adjacent second piezoelectric thin film layers, the interface modulation layer comprising 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 ranging from 0.1 to 100 nm.

[0039] Optionally, the material of the first bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, the thickness of the first bottom electrode is not more than 0.3 pm, the material of the first top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, the thickness of the first top electrode is not more than 0.3 pm, the material of the first piezoelectric layer comprises one or more of AlN, AlxGa 1-x N (0 < x < 1), Al 1-x Sc x N (0 < x < 1), Ba x Sr 1-x TiO3 (0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3, the thickness of the first piezoelectric layer is not more than 3 pm; the material of the second bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, the thickness of the second bottom electrode is not more than 0.3 pm, the material of the second top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, the thickness of the second top electrode is not more than 0.3 pm, the material of the second piezoelectric layer comprises one or more of AlN, AlxGa 1-x N (0 < x < 1), Al 1-x Sc x N (0 < x < 1), Ba x Sr 1-x TiO3 (0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, Ga a2 O3, the thickness of the second piezoelectric layer is not more than 3 pm.

[0040] Optionally, the first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of two N-polar AlN layers with a thickness of 192 nm, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, the working frequency of the first bulk acoustic resonator is in the WIFI6E frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an N-polar AlN layer with a thickness of 192 nm and an Al-polar AlN layer with a thickness of 192 nm, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, the working frequency of the second bulk acoustic resonator is in the Ku frequency band.

[0041] Optionally, the first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 198 nm and an Al 0.7 Sc 0.3N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, the working frequency of the first bulk acoustic resonator is in the WIFI6E frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 198 nm and an Al 0.7 Sc 0.3 N layers, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the Ku frequency band.

[0042] Optionally, the first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 336 nm and an Al 0.7 Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, the working frequency of the first bulk acoustic resonator is in the N79 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 336 nm and an Al 0.7 Sc 0.3 N layers, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the X wave frequency band.

[0043] Optionally, the first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 418 nm and an Al 0.7 Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, the working frequency of the first bulk acoustic resonator is in the N77 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 418 nm and an Al 0.7 Sc 0.3 N layers, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the UWB frequency band.

[0044] Optionally, the first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 785 nm and an Al 0.7 Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, the working frequency of the first bulk acoustic resonator is in the N41 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 785 nm and an Al 0.7Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic wave resonator is in the N3 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the second piezoelectric layer is composed of an AlN layer with a thickness of 1284 nm and an Al

[0045] Optionally, the first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the first piezoelectric layer is composed of an AlN layer with a thickness of 1164 nm and an Al 0.7 Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic wave resonator is in the N3 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the second piezoelectric layer is composed of an AlN layer with a thickness of 1284 nm and an Al 0.7 Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic wave resonator is in the N3 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the second piezoelectric layer is composed of an AlN layer with a thickness of 1284 nm and an Al

[0046] Optionally, the first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the first piezoelectric layer is composed of an AlN layer with a thickness of 1164 nm and an Al 0.7 Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic wave resonator is in the N3 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the second piezoelectric layer is composed of an AlN layer with a thickness of 1284 nm and an Al 0.7 Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic wave resonator is in the N3 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the second piezoelectric layer is composed of an AlN layer with a thickness of 1284 nm and an Al

[0047] Optionally, the first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the first piezoelectric layer is composed of an AlN layer with a thickness of 1112 nm and an Al 0.7 Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic wave resonator is in the N3 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the second piezoelectric layer is composed of an AlN layer with a thickness of 1284 nm and an Al 0.7 Sc 0.3 N layers, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic wave resonator is in the N3 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, and the second piezoelectric layer is composed of an AlN layer with a thickness of 1284 nm and an Al

[0048] The application also provides a radio frequency front end for 5G millimeter wave communication, the communication frequency band is in the n257 frequency band and the n258 frequency band, the radio frequency front end comprises at least one bulk acoustic resonator structure, the bulk acoustic resonator structure comprises:

[0049] a substrate;

[0050] a first electrode located above the substrate, an acoustic mirror is arranged between the substrate and the first electrode;

[0051] a piezoelectric layer located above the first electrode, the piezoelectric layer comprises first thin film layers and second thin film layers which are alternately stacked, at least one of the first thin film layers and the second thin film layers is a ferroelectric thin film layer, wherein the polarities of adjacent first thin film layers and second thin film layers are opposite to each other, so as to suppress a first order resonance mode and excite an Nth order resonance mode, N is an integer greater than 1;

[0052] a second electrode located above the piezoelectric layer.

[0053] Optionally, the piezoelectric layer comprises ferroelectric thin film layers / piezoelectric thin film layers which are alternately stacked.

[0054] Optionally, the material of the ferroelectric thin film layer comprises Sc x Al 1-x N(0.2<x<0.5), BST, PZT, PbTiO3, and the material of the piezoelectric thin film layer comprises AlN, Al x Ga 1-x N(0<x<1), Al 1-x Sc x N(0<x<1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3.

[0055] Optionally, the piezoelectric layer comprises ferroelectric thin film layers / ferroelectric thin film layers which are alternately stacked.

[0056] Optionally, the total number of layers of the first thin film layers and the second thin film layers is three, so as to suppress a first order thickness extension mode resonance and excite a third order thickness extension mode resonance.

[0057] Optionally, the thickness of a single layer of the first thin film layer is not less than 0.01 μm, and the thickness of a single layer of the second thin film layer is not less than 0.01 μm.

[0058] Optionally, the material of the first electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, and the material of the second electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf.

[0059] Optionally, the substrate is provided with an upwardly open groove, and the first electrode and the groove jointly form a cavity.

[0060] Optionally, a Bragg reflection layer is arranged between the substrate and the first electrode, and the Bragg reflection layer comprises stacked high acoustic impedance material layers and low acoustic impedance material layers.

[0061] Optionally, a support layer is arranged between the substrate and the first electrode, and the support layer is provided with an opening, and the substrate, the opening and the first electrode jointly form a cavity.

[0062] As described above, in the present application, the polarity of the ferroelectric thin film in the piezoelectric layer is changed by applying a unipolar direct current pulse between the bottom electrode and the top electrode, the resonant frequency of the resonator is controllably switched, a polycrystalline electrode modulation layer does not need to be arranged between the first thin film layer and the second thin film layer, the cost is reduced, and the device performance is improved; the polarity of all ferroelectric thin films in the piezoelectric layer can be reversed by one voltage modulation, and the voltage modulation efficiency is high; in the radio frequency front end, a unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency is controllably switched between different frequency bands, and the application requirements of different frequency bands are met; the piezoelectric layer is arranged to contain regions with the same polarity and regions with opposite polarity, the regions with the same polarity excite first-order resonance, and the regions with opposite polarity excite high-order resonance, so that the radio frequency front end can work in different frequency bands at the same time, and the application requirements of different frequency bands are met; in addition, the adjacent thin film layers in the piezoelectric layer are arranged to have opposite polarity, high-order resonance is excited, and the working frequency band is improved. BRIEF DESCRIPTION OF DRAWINGS

[0063] FIG. 1 shows a schematic diagram of an electrode modulation layer arranged between adjacent first thin film layers and second thin film layers in a piezoelectric layer.

[0064] FIG. 2 shows a schematic diagram of resonant mode control of a bulk acoustic wave resonator in an embodiment of the present application.

[0065] FIG. 3 shows a schematic diagram of polarization direction control of a piezoelectric layer in an embodiment of the present application.

[0066] FIG. 4 shows a schematic diagram of a radio frequency front end with switchable working frequency band in an embodiment of the present application.

[0067] FIG. 5 shows a simulation result diagram of adjacent first thin film layers and second thin film layers with the same polarity in an embodiment of the present application.

[0068] FIG. 6 shows a simulation result diagram of adjacent first thin film layers and second thin film layers with opposite polarity in an embodiment of the present application.

[0069] FIG. 7 shows a simulation result diagram of adjacent first thin film layers and second thin film layers with the same polarity in an embodiment of the present application.

[0070] Figure 8 shows simulation results for the case where the polarity of the adjacent first and second thin film layers is opposite in the third embodiment of the present application.

[0071] Figure 9 shows simulation results for the case where the polarity of the adjacent first and second thin film layers is the same in the fourth embodiment of the present application.

[0072] Figure 10 shows simulation results for the case where the polarity of the adjacent first and second thin film layers is opposite in the fourth embodiment of the present application.

[0073] Figure 11 shows simulation results for the case where the polarity of the adjacent first and second thin film layers is the same in the fifth embodiment of the present application.

[0074] Figure 12 shows simulation results for the case where the polarity of the adjacent first and second thin film layers is opposite in the fifth embodiment of the present application.

[0075] Figure 13 shows a structure diagram of a radio frequency front end with different operating frequencies in the sixth embodiment of the present application.

[0076] Figure 14 shows simulation results for the sixth embodiment of the present application.

[0077] Figure 15 shows simulation results for a first bulk acoustic wave resonator in the seventh embodiment of the present application.

[0078] Figure 16 shows simulation results for a second bulk acoustic wave resonator in the seventh embodiment of the present application.

[0079] Figure 17 shows simulation results for a first bulk acoustic wave resonator in the eighth embodiment of the present application.

[0080] Figure 18 shows simulation results for a second bulk acoustic wave resonator in the eighth embodiment of the present application.

[0081] Figure 19 shows simulation results for a first bulk acoustic wave resonator in the ninth embodiment of the present application.

[0082] Figure 20 shows simulation results for a second bulk acoustic wave resonator in the ninth embodiment of the present application.

[0083] Figure 21 shows simulation results for a first bulk acoustic wave resonator in the tenth embodiment of the present application.

[0084] Figure 22 shows simulation results for a second bulk acoustic wave resonator in the tenth embodiment of the present application.

[0085] Figure 23 shows simulation results for a first bulk acoustic wave resonator in the eleventh embodiment of the present application.

[0086] Figure 24 shows simulation results for a second bulk acoustic wave resonator in the eleventh embodiment of the present application.

[0087] Figure 25 shows simulation results of a first bulk acoustic resonator in Example Twelve of the present application.

[0088] Figure 26 shows simulation results of a second bulk acoustic resonator in Example Twelve of the present application.

[0089] Figure 27 shows a schematic diagram of a bulk acoustic resonator structure in Example Thirteen of the present application.

[0090] Figure 28 shows a schematic diagram of a piezoelectric layer composed of three thin film layers in Example Thirteen of the present application.

[0091] Figure 29 shows a schematic diagram of a piezoelectric layer composed of three thin film layers in a comparative example of Example Thirteen of the present application.

[0092] Figure 30 shows simulation results of Example Thirteen of the present application.

[0093] Figure 31 shows simulation results of a comparative example of Example Thirteen of the present application.

[0094] Element Number Description: 01 - first thin film layer, 02 - second thin film layer, 03 - electrode modulation layer, 04 - modulation layer lead-out port, 05 - top electrode, 06 - top electrode lead-out port, 07 - bottom electrode, 08 - bottom electrode lead-out port; 1 - piezoelectric layer, 100 - first thin film layer, 101 - second thin film layer, 2 - bottom electrode, 3 - top electrode, 4 - substrate, 5 - air cavity, 6 - bottom electrode pad, 7 - top electrode pad, 8 - pulse generator, 9 - substrate, 10 - bonding layer, 11 - first air cavity, 12 - second air cavity, 13 - first bulk acoustic resonator, 130 - first bottom electrode, 131 - first piezoelectric layer, 1310 - lower first piezoelectric thin film layer, 1311 - upper first piezoelectric thin film layer, 132 - first top electrode, 14 - second bulk acoustic resonator, 140 - second bottom electrode, 141 - second piezoelectric layer, 1410 - lower second piezoelectric thin film layer, 1411 - upper second piezoelectric thin film layer, 1412 - interface modulation layer, 142 - second top electrode, 15 - polarization direction, 16 - resonance mode. DETAILED DESCRIPTION

[0095] As shown in FIG. 1, a schematic diagram is shown in which an electrode modulation layer 03 is arranged between adjacent first thin film layer 01 and second thin film layer 02 in a piezoelectric layer, wherein the electrode modulation layer 03 is provided with a modulation layer lead port 04, a top electrode 05 is provided with a top electrode lead port 06, a bottom electrode 07 is provided with a bottom electrode lead port 08, and a bias voltage is applied to the electrode modulation layer 03 and the top electrode 05 / bottom electrode 07 to achieve polarity modulation of ferroelectric thin films in the first thin film layer 01 and the second thin film layer 02, thereby achieving switching of different frequencies of the resonator. However, the presence of the electrode modulation layer 03 will reduce the crystal quality of the first thin film layer 01 and the second thin film layer 02, thereby increasing the device loss; and each ferroelectric thin film needs to be provided with a voltage modulation once, and the voltage modulation efficiency is low.

[0096] The embodiments of the present application will be described in detail hereinafter with specific reference to certain embodiments, but the skilled in the art will understand that other advantages and effects of the present application can be easily understood from the content disclosed in the specification. The present application can also be implemented or applied by other different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0097] Please refer to FIGS. 2 to 31. It is to be noted that the diagrams provided in the embodiments only schematically illustrate the basic concept of the present application, and thus the diagrams only show the components related to the present application, not the components number, shape and size when actually implemented. The actual implementation of each component type, number and proportion can be arbitrarily changed, and the component layout type can be more complex.

[0098] Embodiment one

[0099] The embodiment provides a resonant mode control method of a bulk acoustic wave resonator. Please refer to FIG. 2. The bulk acoustic wave resonator includes a piezoelectric layer 1, a bottom electrode 2 and a top electrode 3. The piezoelectric layer 1 includes first thin film layers 100 and second thin film layers 101 which are alternately stacked. The interfaces of adjacent first thin film layers 100 and second thin film layers 101 directly contact. The lowermost layer of the piezoelectric layer 1 is the first thin film layer 100. One of the first thin film layers 100 and the second thin film layers 101 is a piezoelectric thin film layer, and the other is a ferroelectric thin film layer. The bottom electrode 2 is located below the piezoelectric layer 1, and the top electrode 3 is located above the piezoelectric layer 1. A unipolar current pulse is applied between the bottom electrode 2 and the top electrode 3 to flip the polarity of the ferroelectric thin film layer, thereby switching the bulk acoustic wave resonator between a first-order vibration mode and a high-order vibration mode. The high-order vibration mode is a vibration mode greater than the first-order vibration mode.

[0100] As an example, the total number of layers of the first thin film layer 100 and the second thin film layer 101 in the piezoelectric layer 1 is not less than 2 layers, when the total number of layers of the first thin film layer 100 and the second thin film layer 101 is 2 layers, the piezoelectric layer 1 is composed of the first thin film layer 100 / the second thin film layer 101; when the total number of layers of the first thin film layer 100 and the second thin film layer 101 is 3 layers, the piezoelectric layer 1 is composed of the first thin film layer 100 / the second thin film layer 101 / the first thin film layer 100; when the total number of layers of the first thin film layer 100 and the second thin film layer 101 is 4 layers, the piezoelectric layer 1 is composed of the first thin film layer 100 / the second thin film layer 101 / the first thin film layer 100 / the second thin film layer 101; and so on, according to the requirement, the total number of layers of the first thin film layer 100 and the second thin film layer 101 is set.

[0101] As an example, the piezoelectric thin film layer refers to a thin film layer with piezoelectric properties, and the ferroelectric thin film layer refers to a thin film layer with both piezoelectric properties and ferroelectric properties. The first thin film layer 100 can be set as a piezoelectric thin film layer, and the second thin film layer 101 can be set as a ferroelectric thin film layer; or the first thin film layer 100 can be set as a ferroelectric thin film layer, and the second thin film layer 101 can be set as a piezoelectric thin film layer, according to the requirement. The material of the piezoelectric thin film layer includes one or more of AlN, Al x Ga 1-x N(0<x<1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3; and the material of the ferroelectric thin film layer includes one or more of Al 1-x Sc x N(0<x<1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3; and the material of the ferroelectric thin film layer includes one or more of Al 1-x Sc x N(0.2≤x≤0.5), BST, PZT, PbTiO3.

[0102] As an example, the thickness of a single layer of the first thin film layer 100 is not less than 0.01 μm, and the thickness of a single layer of the second thin film layer 101 is not less than 0.01 μm, so as to avoid the thickness of the first thin film layer 100 and the second thin film layer 101 being too thin to deteriorate the quality of the thin film crystal; and the total thickness of the piezoelectric layer 1 is not more than 2 μm.

[0103] Specifically, in the present embodiment, the first thin film layer 100 is a piezoelectric thin film layer, and the first thin film layer 100 adopts a single crystal AlN thin film layer; the second thin film layer 101 is a ferroelectric thin film layer, and the second thin film layer 101 adopts an Al 0.7 Sc 0.3 N layer.

[0104] 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 material of the top electrode 3 includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf; the thickness of the bottom electrode 2 is not more than 0.3 μm, and the thickness of the top electrode 3 is not more than 0.3 μm.

[0105] In particular, in the embodiment, the bottom electrode 2 is a Mo metal layer, and the top electrode 3 is a Mo metal layer.

[0106] As an example, a substrate 4 is arranged below the bottom electrode 2, and an air cavity 5 is arranged between the substrate 4 and the bottom electrode 2, which serves as an acoustic mirror structure for limiting acoustic waves in the piezoelectric layer 1 and avoiding acoustic wave leakage to the substrate 4, thereby reducing energy loss and helping to achieve high Q value and low insertion loss. In particular, the substrate 4 includes a Si substrate, a SiC substrate, a Ge substrate, or a sapphire substrate.

[0107] In another example, the substrate 4 is arranged below the bottom electrode 2, and a Bragg reflection layer is arranged between the bottom electrode 2 and the substrate 4 as an acoustic mirror, which includes alternately stacked high acoustic impedance layers and low acoustic impedance layers, the material of the high acoustic impedance layers includes one or more of W, Mo, Pt, Au, Ni, Ir, etc., and the material of the low acoustic impedance layers includes one or more of AlN, Si3N4, SiO2, and the thickness of each layer is 1 / 4 or 3 / 4 of the wavelength of the acoustic wave corresponding to the resonator resonant frequency.

[0108] As an example, the bulk acoustic wave resonator further includes a bottom electrode pad 6 and a top electrode pad 7, the bottom electrode pad 6 is connected with the bottom electrode 2 through the piezoelectric layer 1 to electrically lead out the bottom electrode 2, and the top electrode pad 7 is connected with the top electrode 3 to electrically lead out the top electrode 3; the bottom electrode pad 6 and the top electrode pad 7 adopt a stacked Ti / Au.

[0109] As an example, a unipolar direct current pulse is applied between the bottom electrode 2 and the top electrode 3 by a pulse generator 8, wherein the pulse generator 8 is electrically connected with the bottom electrode pad 6 and the top electrode pad 7 through wires.

[0110] As an example, the unipolar direct current pulse shape includes a triangular waveform and a square waveform, and the triangular waveform is preferred.

[0111] As an example, as shown in FIG. 3, assuming that the polarization directions of the adjacent first thin film layer 100 and the second thin film layer 101 are opposite at the initial stage, a unipolar direct current pulse is applied between the bottom electrode 2 and the top electrode 3, the polarity of the first thin film layer 100 (piezoelectric thin film layer) remains unchanged, the polarization of the second thin film layer 101 (ferroelectric thin film layer) is reversed, and the polarization directions of the adjacent first thin film layer 100 and the second thin film layer 101 are the same; a reverse unipolar direct current pulse is applied between the bottom electrode 2 and the top electrode 3, the second thin film layer 101 is again polarized to reverse, and the polarization directions of the adjacent first thin film layer 100 and the second thin film layer 101 are opposite. That is, by applying a unipolar direct current pulse between the bottom electrode 2 and the top electrode 3, the adjacent first thin film layer 100 and the second thin film layer 101 can be switched between the polarization directions being opposite and the polarization directions being the same.

[0112] As an example, the ferroelectricity of the ferroelectric thin film layer causes the phenomenon of spontaneous polarization inside, the polarization state can be changed by applying a unipolar direct current pulse between the bottom electrode 2 and the top electrode 3, the polarity is reversed, and the polarization state can be maintained after the unipolar direct current pulse is removed.

[0113] As an example, when the polarization directions of the adjacent first thin film layer 100 and the second thin film layer 101 are the same, the basic first-order vibration mode is excited, and the resonator works in the low frequency band; when the polarization directions of the adjacent first thin film layer 100 and the second thin film layer 101 are opposite, the first-order vibration mode is suppressed, the high-order vibration mode is excited, and the resonator works in the high frequency band. That is, by applying a unipolar direct current pulse between the bottom electrode 2 and the top electrode 3, the resonator can be switched between the basic first-order vibration mode and the high-order vibration mode, thereby switching the resonant frequency of the resonator to meet the application requirements of different frequency bands.

[0114] As an example, when the polarization directions of the first thin film layer 100 and the second thin film layer 101 are opposite, there is a 180° phase difference in the piezoelectric response of the electric signal, the inverse piezoelectric effect causes one of the adjacent first thin film layer 100 and the second thin film layer 101 to be subjected to compressive stress, and the other to be subjected to tensile stress, thereby suppressing the first-order vibration mode and exciting the high-order vibration mode with a higher corresponding frequency.

[0115] As an example, the total number of layers of the first thin film layer 100 and the second thin film layer 101 is set according to requirements, which is not specifically limited in the embodiment.

[0116] As an example, the first thin film layer 100 and the second thin film layer 101 in the present application are in direct contact, without a polycrystalline electrode modulation layer between the first thin film layer 100 and the second thin film layer 101, which can significantly improve the crystal quality of the first thin film layer 100 and the second thin film layer 101, thereby reducing the loss of the device, improving the out-of-band rejection capability and power capacity of the device; and the thin film growth and device manufacturing process is simple, with cost advantage.

[0117] As an example, the voltage modulation efficiency in the present application is high, and a single voltage modulation can realize the polarity inversion of all ferroelectric thin film layers in the piezoelectric layer 1.

[0118] As described above, in the resonant mode control method of the bulk acoustic wave resonator of the present embodiment, the polarity of the ferroelectric thin film in the piezoelectric layer is changed by applying a single-polarity direct current pulse between the bottom electrode and the top electrode, realizing controllable switching of the resonant frequency of the resonator; and a single voltage modulation can realize the polarity inversion of all ferroelectric thin films in the piezoelectric layer, with high voltage modulation efficiency.

[0119] Embodiment two

[0120] The present embodiment provides a radio frequency front end with switchable operating frequency band, please refer to FIG. 4, the radio frequency front end includes at least one frequency adjustable bulk acoustic wave resonator as described in embodiment one.

[0121] As an example, in FIG. 4, the cavity 5 is used as an acoustic mirror structure. In another example, a Bragg reflection layer is provided between the substrate 4 and the bottom electrode 2 as an acoustic mirror.

[0122] As an example, the single-polarity direct current pulse shape applied by the pulse generating unit 8 includes triangular waveform and square waveform, and the triangular waveform is preferred.

[0123] As an example, in the present embodiment, the first thin film layer 100 is set as a piezoelectric thin film layer, and the second thin film layer 101 is set as a ferroelectric thin film layer. Specifically, the bottom electrode 2 adopts a 86nm Mo metal layer, the first thin film layer 100 adopts a 210nm AlN layer, the second thin film layer 101 adopts a 220nm Al 0.7 Sc 0.3 N layer, and the top electrode 3 adopts a 86nm M oThe metal layer, please refer to Fig. 5, when the polarization directions of the adjacent first thin film layer 100 and the second thin film layer 101 are the same, a first order vibration mode is excited, and the working frequency is near 4.85 GHz; please refer to Fig. 6, when the polarization directions of the adjacent first thin film layer 100 and the second thin film layer 101 are opposite, a high order vibration mode is excited, and the working frequency is near 12.5 GHz, that is, by applying a single polarity direct current pulse between the bottom electrode 2 and the top electrode 3, the polarity of the ferroelectric thin film in the piezoelectric layer 1 is changed, thereby realizing the switching of the radio frequency front end between the N79 frequency band (4.8-4.9 GHz) and the Ku frequency band (12-18 GHz) downlink bands to meet the application requirements of different frequency bands.

[0124] As described above, in the working frequency band switchable radio frequency front end of the embodiment, the resonant frequency is realized to be controllably switched between the N79 frequency band and the Ku frequency band, and the application requirements of different frequency bands are met.

[0125] Embodiment three

[0126] The difference between the embodiment and the embodiment two is that: the bottom electrode 2 is provided with a 72nm Mo metal layer, the first thin film layer 100 is provided with a 130nm AlN layer, the second thin film layer 101 is provided with a 130nm AlN layer, and the top electrode 3 is provided with a 72nm Mo metal layer, please refer to Fig. 7, when a first order vibration mode is excited, the working frequency is near 7.8 GHz; please refer to Fig. 8, when a high order vibration mode is excited, the working frequency is near 18.2 GHz, and the radio frequency front end is realized to be controllably switched between the UWB frequency band (7.7-8.1 GHz) and the K frequency band (12-18 GHz) downlink bands. 0.7 Sc 0.3

[0127] Embodiment four

[0128] The difference between the embodiment and the embodiment two is that: the bottom electrode 2 is provided with a 85nm Mo metal layer, the first thin film layer 100 is provided with a 150nm AlN layer, the second thin film layer 101 is provided with a 140nm AlN layer, and the top electrode 3 is provided with a 85nm Mo metal layer, please refer to Fig. 9, when a first order vibration mode is excited, the working frequency is near 6.6 GHz; please refer to Fig. 10, when a high order vibration mode is excited, the working frequency is near 17.25 GHz, and the radio frequency front end is realized to be controllably switched between the N104 frequency band (6.425-7.125 GHz) and the Ku frequency band (12-18 GHz) uplink bands. 0.7 Sc 0.3

[0129] Embodiment five

[0130] ​​The difference between this embodiment and embodiment two is that the bottom electrode 2 is provided with a 50 nm Mo metal layer, the first thin film layer 100 is provided with a 140 nm AlN layer, the second thin film layer 101 is provided with a 100 nm AlN layer, and the top electrode 3 is provided with a 50 nm Mo metal layer. Please refer to FIG. 11, when a first-order vibration mode is excited, the working frequency is near 10.25 GHz; please refer to FIG. 12, when a high-order vibration mode is excited, the working frequency is near 24.8 GHz, and the radio frequency front end is controlled to switch between the SHF frequency band (10-10.5 GHz) and the N258 frequency band (24.25-27.5 GHz). 0.7 Sc 0.3 N layer, and the top electrode 3 is provided with a 50 nm Mo metal layer. Please refer to FIG. 11, when a first-order vibration mode is excited, the working frequency is near 10.25 GHz; please refer to FIG. 12, when a high-order vibration mode is excited, the working frequency is near 24.8 GHz, and the radio frequency front end is controlled to switch between the SHF frequency band (10-10.5 GHz) and the N258 frequency band (24.25-27.5 GHz).

[0131] It should be noted that embodiments two to five only list the case that the total number of layers of the first thin film layer 100 and the second thin film layer 101 is two, and in other examples, the total number of layers of the first thin film layer 100 and the second thin film layer 101 can be more than two, which is not limited by this embodiment; in addition, in other examples, the thickness of the bottom electrode 2, the piezoelectric layer 1 and the top electrode 3 can be adjusted to control the radio frequency front end to switch between other frequency bands, which is set according to actual needs.

[0132] Embodiment six

[0133] This embodiment provides a radio frequency front end with different working frequencies. Please refer to FIG. 13, the radio frequency front end with different working frequencies includes a substrate 9, a first bulk acoustic resonator 13 and a second bulk acoustic resonator 14. The first bulk acoustic resonator 13 is located above the substrate 9. The first bulk acoustic resonator 13 includes a first bottom electrode 130, a first piezoelectric layer 131 and a first top electrode 132 arranged from bottom to top. The first piezoelectric layer 131 includes not less than two first piezoelectric thin film layers, and adjacent first piezoelectric thin film layers have the same polarity. The second bulk acoustic resonator 14 is located above the substrate 1. The second bulk acoustic resonator 14 includes a second bottom electrode 140, a second piezoelectric layer 141 and a second top electrode 142 arranged from bottom to top. The second piezoelectric layer 141 includes not less than two second piezoelectric thin film layers, and adjacent second piezoelectric thin film layers have opposite polarities. The working frequency of the first bulk acoustic resonator 13 is less than the working frequency of the second bulk acoustic resonator 14.

[0134] As an example, a bonding layer 10 is provided between the substrate 9 and the bulk acoustic resonator, and the bonding layer 10 is also located between the first bottom electrode 130 and the second bottom electrode 140. The material of the bonding layer 10 includes SiO2, Si3N4, etc. dielectric material or PI (polyimide), BCB (benzocyclobutene) polymer material, which is selected according to needs.

[0135] As an example, the area where the first bottom electrode 130, the first piezoelectric layer 131 and the first top electrode 132 overlap constitutes a resonance region of the first bulk acoustic wave resonator 13, wherein a first air cavity 11 is arranged between the first bottom electrode 130 and the bonding layer 10, the size of the first air cavity 11 is larger than the size of the resonance region of the first bulk acoustic wave resonator 13, and the first air cavity 11 acts as an acoustic mirror.

[0136] As an example, the first piezoelectric layer 131 comprises a lower first piezoelectric thin film layer 1310 and an upper first piezoelectric thin film layer 1311, the interface between the lower first piezoelectric thin film layer 1310 and the upper first piezoelectric thin film layer 1311 directly contacts, and the polarities of the lower first piezoelectric thin film layer 1310 and the upper first piezoelectric thin film layer 1311 are the same.

[0137] As an example, in the first bulk acoustic wave resonator 13, a first order resonance is excited.

[0138] As an example, in the second bulk acoustic wave resonator 14, the area where the second bottom electrode 140, the second piezoelectric layer 141 and the second top electrode 142 overlap constitutes a resonance region of the second bulk acoustic wave resonator 14, wherein a second air cavity 12 is arranged between the second bottom electrode 140 and the bonding layer 10, the size of the second air cavity 12 is larger than the size of the resonance region of the second bulk acoustic wave resonator 14, and the second air cavity 4 acts as an acoustic mirror.

[0139] As an example, the second piezoelectric layer 141 comprises a lower second piezoelectric thin film layer 1410 and an upper second piezoelectric thin film layer 1411, an interface modulation layer 1412 is arranged between the lower second piezoelectric thin film layer 1410 and the upper second piezoelectric thin film layer 1411, the interface modulation layer 1412 is beneficial to change the surface chemical bond state of the lower second piezoelectric thin film layer 1410, so that the polarities of the upper second piezoelectric thin film layer 1411 and the lower second piezoelectric thin film layer 1410 are opposite (the arrow in the figure represents the polarization direction, and the opposite polarity represents the opposite polarization direction).

[0140] As an example, the material and thickness of the piezoelectric thin film layer, the bottom electrode and the top electrode are described in Embodiment One, which will not be described in detail here.

[0141] As an example, the material of the interface modulation layer 1412 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 1412 ranges from 0.1 to 100 nm, preferably 2 to 5 nm.

[0142] Preferably, the lower first piezoelectric thin film layer 1310 and the lower second piezoelectric thin film layer 1410 are formed in the same process, then the interface modulation layer 1412 is formed, and then the upper first piezoelectric thin film layer 1311 and the upper second piezoelectric thin film layer 1411 are formed in the same process.

[0143] As an example, in the second bulk acoustic wave resonator 14, a high-order resonance with a higher excitation frequency is excited.

[0144] In another example, a first Bragg reflection structure is arranged between the first bottom electrode 130 and the substrate 9 as an acoustic mirror, and a second Bragg reflection structure is arranged between the second bottom electrode 140 and the substrate 9 as an acoustic mirror. The acoustic mirror is described in Embodiment 1, which will not be described in detail here.

[0145] Specifically, in the present embodiment, the first bottom electrode 130 adopts a Mo metal layer with a thickness of 100 nm, the lower first piezoelectric thin film layer 1310 adopts an N-polar AlN layer with a thickness of 192 nm, the upper first piezoelectric thin film layer 1311 adopts an N-polar AlN layer with a thickness of 192 nm, and the first top electrode 132 adopts a Mo metal layer with a thickness of 100 nm; the second bottom electrode 140 adopts a Mo metal layer with a thickness of 100 nm, the lower second piezoelectric thin film layer 1410 adopts an N-polar AlN layer with a thickness of 192 nm, the upper second piezoelectric thin film layer 1411 adopts an A1-polar AlN layer with a thickness of 192 nm, and the second top electrode 142 adopts a Mo metal layer with a thickness of 100 nm. Please refer to FIG. 14, which shows the simulation result graph of Embodiment 6. The working frequency of the first bulk acoustic wave resonator is 6.15 GHz, which is located in the WIFI6E frequency band (5.925-7.125 GHz); the working frequency of the second bulk acoustic wave resonator is 14.8 GHz, which is located in the Ku frequency band (12-18 GHz), which can meet the application requirements of different frequency bands.

[0146] In other examples, by adjusting the electrode material, thickness, and piezoelectric layer material, thickness, the working frequency of the radio frequency front end with different working frequencies can also be in the WIFI6E frequency band and the Ku frequency band, for example, the bottom electrode is arranged to adopt a Mo metal layer with a thickness of 100 nm, the lower piezoelectric thin film layer is arranged to adopt an AlN layer with a thickness of 198 nm, the upper piezoelectric thin film layer is arranged to adopt an AlN layer with a thickness of 198 nm, and the top electrode is arranged to adopt a Mo metal layer with a thickness of 100 nm. The working frequency of the first bulk acoustic wave resonator is in the WIFI6E frequency band, and the working frequency of the second bulk acoustic wave resonator is in the Ku frequency band. 0.7 Sc 0.3 N layer, the working frequency of the first bulk acoustic wave resonator is in the WIFI6E frequency band, and the working frequency of the second bulk acoustic wave resonator is in the Ku frequency band.

[0147] As described above, in the radio frequency front end with different operating frequencies of the embodiment, the radio frequency front end can operate in the WIFI6E frequency band and the Ku frequency band at the same time, so as to meet the application requirements of different frequency bands.

[0148] Embodiment seven

[0149] The difference between the embodiment and embodiment six is that the bottom electrode is made of a Mo metal layer with a thickness of 100 nm, the lower piezoelectric thin film layer is made of an AlN layer with a thickness of 418 nm, the upper piezoelectric thin film layer is made of an Al 0.7 Sc 0.3 N layer with a thickness of 418 nm, and the top electrode is made of a Mo metal layer with a thickness of 100 nm. Referring to FIGS. 17 and 18, the operating frequency of the first bulk acoustic wave resonator is 3.53 GHz, and the operating frequency of the second bulk acoustic wave resonator is 7.53 GHz, so that the radio frequency front end can operate in the N77 frequency band (3.3-4.2 GHz) and the UWB frequency band (7.163-8.812 GHz) at the same time.

[0150] Embodiment eight

[0151] The difference between the embodiment and embodiment six is that the bottom electrode is made of a Mo metal layer with a thickness of 100 nm, the lower piezoelectric thin film layer is made of an AlN layer with a thickness of 418 nm, the upper piezoelectric thin film layer is made of an Al 0.7 Sc 0.3 N layer with a thickness of 418 nm, and the top electrode is made of a Mo metal layer with a thickness of 100 nm. Referring to FIGS. 17 and 18, the operating frequency of the first bulk acoustic wave resonator is 3.53 GHz, and the operating frequency of the second bulk acoustic wave resonator is 7.53 GHz, so that the radio frequency front end can operate in the N77 frequency band (3.3-4.2 GHz) and the UWB frequency band (7.163-8.812 GHz) at the same time.

[0152] Embodiment nine

[0153] The difference between the embodiment and embodiment six is that the bottom electrode is made of a Mo metal layer with a thickness of 100 nm, the lower piezoelectric thin film layer is made of an AlN layer with a thickness of 785 nm, the upper piezoelectric thin film layer is made of an Al 0.7 Sc 0.3 N layer with a thickness of 785 nm, and the top electrode is made of a Mo metal layer with a thickness of 100 nm. Referring to FIGS. 19 and 20, the operating frequency of the first bulk acoustic wave resonator is 2.61 GHz, and the operating frequency of the second bulk acoustic wave resonator is 5.4 GHz, so that the radio frequency front end can operate in the N41 frequency band (2.496-2.69 GHz) and the WIFI6 frequency band (5.15-5.85 GHz) at the same time.

[0154] Embodiment ten

[0155] The difference between the embodiment and embodiment six is that the bottom electrode is made of a Mo metal layer with a thickness of 100 nm, the lower piezoelectric thin film layer is made of an AlN layer with a thickness of 1284 nm, the upper piezoelectric thin film layer is made of an Al 0.7 Sc 0.3 N layer with a thickness of 1284 nm, and the top electrode is made of a Mo metal layer with a thickness of 100 nm. Referring to FIGS. 21 and 22, the working frequency of the first bulk acoustic wave resonator is 1.73 GHz, and the working frequency of the second bulk acoustic wave resonator is 3.51 GHz, so that the radio frequency front end can work in the N3 frequency band (1.710-1.785 GHz) and the N77 frequency band (3.3-4.2 GHz) at the same time.

[0156] Embodiment eleven

[0157] The difference between the embodiment and embodiment six is that the bottom electrode is made of a Mo metal layer with a thickness of 100 nm, the lower piezoelectric thin film layer is made of an AlN layer with a thickness of 1164 nm, the upper piezoelectric thin film layer is made of an Al 0.7 Sc 0.3 N layer with a thickness of 1164 nm, and the top electrode is made of a Mo metal layer with a thickness of 100 nm. Referring to FIGS. 23 and 24, the working frequency of the first bulk acoustic wave resonator is 1.88 GHz, and the working frequency of the second bulk acoustic wave resonator is 3.8 GHz, so that the radio frequency front end can work in the N2 frequency band (1.85-1.91 GHz) and the N77 frequency band (3.3-4.2 GHz) at the same time.

[0158] Embodiment twelve

[0159] The difference between the embodiment and embodiment six is that the bottom electrode is made of a Mo metal layer with a thickness of 100 nm, the lower piezoelectric thin film layer is made of an AlN layer with a thickness of 1112 nm, the upper piezoelectric thin film layer is made of an Al 0.7 Sc 0.3 N layer with a thickness of 1112 nm, and the top electrode is made of a Mo metal layer with a thickness of 100 nm. Referring to FIGS. 25 and 26, the working frequency of the first bulk acoustic wave resonator is 1.95 GHz, and the working frequency of the second bulk acoustic wave resonator is 3.96 GHz, so that the radio frequency front end can work in the N1 frequency band (2.496-2.69 GHz) and the N77 frequency band (3.3-4.2 GHz) at the same time.

[0160] It should be noted that the electrode material, thickness, and piezoelectric layer material and thickness can be adjusted so that the radio frequency front end can work in other frequency bands at the same time, and be set according to actual needs.

[0161] Embodiment thirteen

[0162] The embodiment provides a radio frequency front end for 5G millimeter wave communication, the communication frequency band is in an n257 (26.5-29.5GHz) frequency band and an n258 (24.25-27.5GHz) frequency band, the radio frequency front end comprises at least one bulk acoustic resonator structure, referring to FIG. 27, the bulk acoustic resonator structure comprises a substrate 4, a bottom electrode 2 (a first electrode), a piezoelectric layer 1 and a top electrode 3 (a second electrode), the position and structure of the substrate 4, the bottom electrode 2 and the top electrode 3 are described in Embodiment 1, and will not be described in detail here.

[0163] As an example, the polarities of the adjacent first thin film layer 100 and the second thin film layer 101 are opposite, so as to suppress a first-order resonance mode and excite an N-order resonance mode, N is an integer greater than 1.

[0164] As an example, at least one of the first thin film layer 100 and the second thin film layer 101 is a ferroelectric thin film layer, the piezoelectric layer 1 can be an alternately stacked ferroelectric thin film layer / piezoelectric thin film layer or an alternately stacked ferroelectric thin film layer / ferroelectric thin film layer. Wherein, the piezoelectric thin film layer refers to a thin film layer with piezoelectric properties, and the ferroelectric thin film layer refers to a thin film layer with both piezoelectric properties and ferroelectric properties.

[0165] As an example, the material and thickness of the piezoelectric thin film layer and the ferroelectric thin film layer are described in Embodiment 1, and will not be described in detail here.

[0166] Specifically, referring to FIG. 28, the total number of layers of the first thin film layer 100 and the second thin film layer 101 is set to 3 layers, and an alternately stacked ferroelectric thin film layer / piezoelectric thin film layer / ferroelectric thin film layer is adopted, wherein the ferroelectric thin film layer adopts Al 0.7 Sc 0.3 N layer, the piezoelectric thin film layer adopts an AlN layer, that is, the piezoelectric layer 1 adopts an alternately stacked Al 0.7 Sc 0.3 N layer / AlN layer / Al 0.7 Sc 0.3 N layer, the thickness of the single-layer Al 0.7 Sc 0.3 N layer is 50nm, the thickness of the single-layer AlN layer is 150nm, and the thickness of the adjacent Al 0.7 Sc 0.3The N layer and the AlN layer have opposite polarities (opposite polarization direction 15), and the bottom electrode 2 and the top electrode 3 are both Mo metal layers with a thickness of 100 nm. Referring to FIG. 29, a comparative example is provided, which has the same material and thickness of the bottom electrode 2, the piezoelectric layer 1, and the top electrode 3 as in the example, but the difference is that the polarities of the adjacent first thin film layer 100 and the second thin film layer 101 are the same (the polarization direction 15 is the same), and the example and the comparative example have different resonance modes 16. Referring to FIGS. 30 and 31, which respectively show simulation results of the example and the comparative example, it can be seen from FIG. 30 that when the polarization directions of the adjacent first thin film layer 100 and the second thin film layer 101 are opposite, a third-order (TE3) thickness extension mode with a higher corresponding frequency is excited, the working frequency band is 28 GHz, and the communication frequency band is within the n257 frequency band. It can be seen from FIG. 31 that when the polarization directions of the adjacent first thin film layer 100 and the second thin film layer 101 are the same, a first-order thickness extension mode (TE1) is excited, the working frequency band is 7 GHz.

[0167] In another example, the thickness of the piezoelectric layer 1 is adjusted so that the communication frequency band is in the n258 frequency band, which can be selected according to requirements.

[0168] As an example, the piezoelectric layer 1 with a larger thickness in the present application is used to realize an ultra-high frequency resonator, 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 and low-interference wireless communication applications; and in order to ensure the manufacturing yield of the resonator, the thickness uniformity of the piezoelectric layer 1 needs to be better than 0.5%, and the thicker piezoelectric layer 1 can significantly improve the manufacturing yield and stability; in addition, the thickness of the piezoelectric layer 1 does not need to be reduced to realize the frequency increase of the resonator, which is particularly suitable for 5G new high frequency bands, high frequency satellite communication, 5G millimeter wave frequency bands, and 6G ultra-high frequency bands.

[0169] As an example, compared with existing low-temperature co-fired ceramic (LTCC) resonators and integrated passive device (IPD) resonators and other dielectric resonators for high frequency and ultra-high frequency, the present application has excellent out-of-band suppression and in-band insertion loss characteristics, and significantly reduces signal interference and operating power of wireless communication.

[0170] As an example, in a 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 resonator at a high order is very small, and the bandwidth of the corresponding filter is very small, which is difficult to meet the actual communication application requirements. In the present application, the electromechanical coupling coefficient of the high-order mode is independent of the order, and the electromechanical coupling coefficient and the bandwidth can be maintained at a high level at high frequency, which is very suitable for high frequency and large bandwidth application scenarios.

[0171] In summary, in the application, the polarity of the ferroelectric thin film in the piezoelectric layer is changed by applying unipolar direct current pulse between the bottom electrode and the top electrode, the resonant frequency of the resonator is controllable switched, the polycrystalline electrode modulation layer does not need to be arranged between the first thin film layer and the second thin film layer, the cost is reduced, and the device performance is improved; the polarity of all ferroelectric thin films in the piezoelectric layer can be reversed by one voltage modulation, the voltage modulation efficiency is high; in the radio frequency front end, the unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency is controllable switched between different frequency bands, and the application requirements of different frequency bands are met; the piezoelectric layer is arranged to include regions with the same polarity and regions with opposite polarity, the regions with the same polarity excite first-order resonance, and the regions with opposite polarity excite high-order resonance, so that the radio frequency front end can work in different frequency bands at the same time, and the application requirements of different frequency bands are met; in addition, the adjacent thin film layers in the piezoelectric layer are arranged to have opposite polarity, high-order resonance is excited, and the working frequency band is improved. Therefore, the application effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0172] 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 of the application should be covered by the claims of the application.

Claims

1. A method for controlling a resonance mode of a bulk acoustic resonator, the bulk acoustic resonator comprising a piezoelectric layer, a bottom electrode below the piezoelectric layer, and a top electrode above the piezoelectric layer, the method comprising: the piezoelectric layer comprising first thin film layers and second thin film layers alternately stacked, an interface between adjacent first thin film layers and second thin film layers directly contacting, and a lowermost layer of the piezoelectric layer being the first thin film layer, wherein the first thin film layer is a piezoelectric thin film layer, and the second thin film layer is a ferroelectric thin film layer, or the first thin film layer is a ferroelectric thin film layer, and the second thin film layer is a piezoelectric thin film layer; and applying a unipolar direct current pulse between the bottom electrode and the top electrode to flip a polarity of the ferroelectric thin film layer, and to switch the bulk acoustic resonator between a first order vibration mode and a higher order vibration mode, wherein the higher order vibration mode is a vibration mode higher than the first order vibration mode; wherein a thickness of a single layer of the piezoelectric thin film layer is not less than 0.01 μm, a thickness of a single layer of the ferroelectric thin film layer is not less than 0.01 μm, and a total thickness of the piezoelectric layer is not more than 2 μm; wherein a thickness of the bottom electrode is not more than 0.3 μm, and a thickness of the top electrode is not more than 0.3 μm; wherein the unipolar direct current pulse is applied between the bottom electrode and the top electrode by a pulse generator; wherein a shape of the unipolar direct current pulse comprises a triangular waveform and a square waveform; wherein a substrate is arranged below the bottom electrode, and an air cavity is arranged between the substrate and the bottom electrode; wherein a substrate is arranged below the bottom electrode, and a Bragg reflection layer is arranged between the substrate and the bottom electrode; wherein a material of the bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, and a material of the top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf; comprising: at least one frequency tunable bulk acoustic resonator comprising, from bottom to top, a substrate, a bottom electrode, a piezoelectric layer, and a top electrode, the piezoelectric layer comprising first thin film layers and second thin film layers alternately stacked, one of the first thin film layers and the second thin film layers being a ferroelectric thin film layer, and the other of the first thin film layers and the second thin film layers being a piezoelectric thin film layer; and a pulse generating unit connected between the top electrode and the bottom electrode, the pulse generating unit being configured to apply a unipolar direct current pulse to the piezoelectric layer through the top electrode and the bottom electrode; wherein a shape of the unipolar direct current pulse comprises a triangular waveform and a square waveform; wherein an air cavity is arranged between the substrate and the bottom electrode; wherein a Bragg reflection layer is arranged between the substrate and the bottom electrode; wherein the substrate comprises a Si substrate, a SiC substrate, a Ge substrate, or a sapphire substrate; comprising: a substrate; a first bulk acoustic resonator above the substrate, the first bulk acoustic resonator comprising, from bottom to top, a first bottom electrode, a first piezoelectric layer, and a first top electrode, the first piezoelectric layer comprising not less than two first piezoelectric thin film layers, adjacent first piezoelectric thin film layers having a same polarity; and a second bulk acoustic resonator above the substrate, the second bulk acoustic resonator comprising, from bottom to top, a second bottom electrode, a second piezoelectric layer, and a second top electrode, the second piezoelectric layer comprising not less than two second piezoelectric thin film layers, adjacent second piezoelectric thin film layers having a same polarity. ​ ​ ​ ​ 2. The method of claim 1, wherein: ​ 3. The method of claim 1, wherein: ​ 4. The method of claim 1, wherein: ​ 5. The method of claim 1, wherein: ​ 6. The method of claim 1, 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.

7. The method of claim 1, 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, PbTiO3.

8. The method of claim 1, wherein: ​ 9. A frequency band switchable radio frequency front end, characterized by ​ ​ ​ 10. The working frequency band switchable radio frequency front end of claim 9, characterized by: ​ 11. The working frequency band switchable radio frequency front end of claim 9, wherein: The material of the piezoelectric thin film layer includes at least one of AlN, Al x Ga 1-x N (0 1-x Sc x N (0 1-x Sc x N (0.2≤x≤0.5), BST, PZT, PbTiO3, wherein the thickness of the single first thin film layer is not less than 0.01 μm, the thickness of the single second thin film layer is not less than 0.01 μm, and the total thickness of the piezoelectric layer is not more than 2 μm; the material of the bottom electrode includes at least one of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, and the material of the top electrode includes at least one of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, wherein the thickness of the bottom electrode is not more than 0.3 μm, and the thickness of the top electrode is not more than 0.3 μm.

12. The working frequency band switchable radio frequency front end of claim 11, characterized by: The total number of layers of the first thin film layer and the second thin film layer is two, the piezoelectric thin film layer is an AlN layer, the thickness of the piezoelectric thin film layer is 210 nm, the ferroelectric thin film layer is an Al 0.7 Sc 0.3 N layer, the thickness of the ferroelectric thin film layer is 220 nm, the bottom electrode is a Mo metal layer, the thickness of the bottom electrode is 86 nm, the top electrode is a Mo metal layer, the thickness of the top electrode is 86 nm, wherein when a unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency switches between the N79 frequency band and the Ku frequency band.

13. The operating band switchable radio frequency front end of claim 11, wherein: The total number of layers of the first thin film layer and the second thin film layer is two, the piezoelectric thin film layer is an AlN layer, the thickness of the piezoelectric thin film layer is 130 nm, the ferroelectric thin film layer is an Al 0.7 Sc 0.3 N layer, the thickness of the ferroelectric thin film layer is 130 nm, the bottom electrode is a Mo metal layer, the thickness of the bottom electrode is 72 nm, the top electrode is a Mo metal layer, the thickness of the top electrode is 72 nm, wherein when a unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency switches between the UWB frequency band and the K frequency band.

14. The operating band switchable radio frequency front end of claim 11, wherein: The total number of layers of the first thin film layer and the second thin film layer is two, the piezoelectric thin film layer is an AlN layer, the thickness of the piezoelectric thin film layer is 140 nm, the ferroelectric thin film layer is an Al 0.7 Sc 0.3 N layer, the thickness of the ferroelectric thin film layer is 100 nm, the bottom electrode is a Mo metal layer, the thickness of the bottom electrode is 50 nm, the top electrode is a Mo metal layer, the thickness of the top electrode is 50 nm, wherein when a unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency switches between the SHF frequency band and the N258 frequency band.

15. The operating frequency band switchable radio frequency front end of claim 11, wherein: The total number of layers of the first thin film layer and the second thin film layer is two, the piezoelectric thin film layer is an AlN layer, the thickness of the piezoelectric thin film layer is 150 nm, the ferroelectric thin film layer is an Al 0.7 Sc 0.3 N layer, the thickness of the ferroelectric thin film layer is 140 nm, the bottom electrode is a Mo metal layer, the thickness of the bottom electrode is 85 nm, the top electrode is a Mo metal layer, the thickness of the top electrode is 85 nm, wherein when a unipolar direct current pulse is applied between the bottom electrode and the top electrode, the resonant frequency switches between the N104 frequency band and the Ku frequency band.

16. The work band switchable radio frequency front end of claim 9, wherein: ​ 17. The work band switchable radio frequency front end of claim 9, wherein: ​ 18. The working frequency band switchable radio frequency front end of claim 9, wherein: ​ 19. A radio frequency front end having different operating frequencies, the radio frequency front end comprising: ​ ​ ​ A second bulk acoustic resonator is located above the substrate, the second bulk acoustic resonator comprises a second bottom electrode, a second piezoelectric layer and a second top electrode arranged from bottom to top, the second piezoelectric layer comprises a second piezoelectric thin film layer of no less than two layers, the polarities of adjacent second piezoelectric thin film layers are opposite; The working frequency of the first bulk acoustic resonator is less than the working frequency of the second bulk acoustic resonator.

20. The radio frequency front end having different operating frequencies of claim 19, wherein: A first air cavity is arranged between the first bottom electrode and the substrate, and a second air cavity is arranged between the second bottom electrode and the substrate.

21. The radio frequency front end having different operating frequencies of claim 19, wherein: A first Bragg reflection structure is arranged between the first bottom electrode and the substrate, and a second Bragg reflection structure is arranged between the second bottom electrode and the substrate.

22. The radio frequency front end having different operating frequencies of claim 19, wherein: A bonding layer is further included, the bonding layer is located between the bulk acoustic resonator and the substrate, a first air cavity is arranged between the first bottom electrode and the bonding layer, and a second air cavity is arranged between the second bottom electrode and the bonding layer.

23. The radio frequency front end having different operating frequencies of claim 19, wherein: The interfaces of adjacent first piezoelectric thin film layers are directly contacted, an interface modulation layer is arranged between adjacent second piezoelectric thin film layers, 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 0.1 to 100 nm.

24. The radio frequency front end having different operating frequencies of claim 19, wherein: The material of the first bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, the thickness of the first bottom electrode is not more than 0.3 μm, the material of the first top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, the thickness of the first top electrode is not more than 0.3 μm, the material of the first piezoelectric layer comprises one or more of AlN, Al x Ga 1-x N(0 < x < 1), Al x < 1), Al 1-x Sc x N(0 < x < 1), Ba x Sr 1-x TiO3(0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3, the thickness of the first piezoelectric layer is not more than 3 μm; the material of the second bottom electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, the thickness of the second bottom electrode is not more than 0.3 μm, the material of the second top electrode comprises one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, the thickness of the second top electrode is not more than 0.3 μm, the material of the second piezoelectric layer comprises one or more of AlN, Al x Ga 1-x N(0 < x < 1), Al 1-x Sc x N(0 < x < 1), Ba x Sr 1-x TiO3(0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3, the thickness of the second piezoelectric layer is not more than 3 μm.

25. The radio frequency front end having different operating frequencies of claim 24, wherein: The first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of two layers of N-polar AlN layers with a thickness of 192 nm, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic resonator is in the WIFI6E frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an N-polar AlN layer with a thickness of 192 nm and an Al-polar AlN layer with a thickness of 192 nm, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the Ku frequency band.

26. The radio frequency front end having different operating frequencies of claim 24, wherein: The first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 198 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 198 nm, and the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic resonator is in the WIF16E frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 198 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 198 nm, and the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the Ku frequency band.

27. The radio frequency front end having different operating frequencies of claim 24, wherein: The first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 336 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 336 nm, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic resonator is in the N79 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 336 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 336 nm, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the X wave frequency band.

28. The radio frequency front end having different operating frequencies of claim 24, wherein: The first bottom electrode adopts a 100nm-thick Mo metal layer o The first piezoelectric layer is composed of a 418nm-thick AlN layer and a 418nm-thick Al 0.7 Sc 0.3 The first top electrode adopts a 100nm-thick Mo metal layer, and the working frequency of the first bulk acoustic wave resonator is in the N77 frequency band; the second bottom electrode adopts a 100nm-thick Mo metal layer, the second piezoelectric layer is composed of a 418nm-thick AlN layer and a 418nm-thick Al 0.7 Sc 0.3 The second top electrode adopts a 100nm-thick Mo metal layer, and the working frequency of the second bulk acoustic wave resonator is in the UWB frequency band.

29. The radio frequency front end having different operating frequencies of claim 24, wherein: The first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 785 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 785 nm, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic resonator is in the N41 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 785 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 785 nm, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the WIFI6 frequency band.

30. The radio frequency front end having different operating frequencies of claim 24, wherein: The first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 1284 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 1284 nm, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic resonator is in the N3 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 1284 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 1284 nm, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the N77 frequency band.

31. The radio frequency front end having different operating frequencies of claim 24, wherein: The first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 1164 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 1164 nm, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic resonator is in the N2 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 1164 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 1164 nm, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the N77 frequency band.

32. The radio frequency front end having different operating frequencies of claim 24, wherein: The first bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the first piezoelectric layer is composed of an AlN layer with a thickness of 1112 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 1112 nm, the first top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the first bulk acoustic resonator is in the N1 frequency band; the second bottom electrode adopts a Mo metal layer with a thickness of 100 nm, the second piezoelectric layer is composed of an AlN layer with a thickness of 1112 nm and an Al 0.7 Sc 0.3 N layer with a thickness of 1112 nm, the second top electrode adopts a Mo metal layer with a thickness of 100 nm, and the working frequency of the second bulk acoustic resonator is in the N77 frequency band. 33.A radio frequency front end for 5G millimeter wave communication, the communication frequency band is in n257 frequency band and n258 frequency band, characterized in that, The radio frequency front end comprises at least one bulk acoustic resonator structure, the bulk acoustic resonator structure comprises: a substrate; a first electrode located above the substrate, an acoustic mirror is arranged between the substrate and the first electrode; a piezoelectric layer located above the first electrode, the piezoelectric layer comprises first thin film layers and second thin film layers alternately stacked, at least one of the first thin film layers and the second thin film layers is a ferroelectric thin film layer, wherein 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 Nth order resonance mode, N being an integer greater than 1; a second electrode located above the piezoelectric layer.

34. The radio frequency front end for 5G millimeter wave communications of claim 33, wherein: The piezoelectric layer comprises ferroelectric thin film layers / piezoelectric thin film layers alternately stacked.

35. The radio frequency front end for 5G millimeter wave communications of claim 34, wherein: The material of the ferroelectric thin film layer includes Sc x Al 1-x N(0.2≤x≤0.5), BST, PZT, PbTiO3, and the material of the piezoelectric thin film layer includes AlN, Al x Ga 1-x N(0<x<1), Al 1-x Sc x N(0<x<1), LiNbO3, ZnO, PZT, PbTiO3, Ga2O3.

36. The radio frequency front-end for 5G millimeter wave communications of claim 33, wherein: The piezoelectric layer comprises ferroelectric thin film layers / ferroelectric thin film layers alternately stacked.

37. The radio frequency front-end for 5G millimeter wave communications of claim 33, wherein: The total number of the first thin film layers and the second thin film layers is three, a first order thickness extension mode resonance is suppressed, and a third order thickness extension mode resonance is excited.

38. The radio frequency front-end for 5G millimeter wave communications of claim 33, wherein: The thickness of a single layer of the first thin film layer is not less than 0.01 μm, and the thickness of a single layer of the second thin film layer is not less than 0.01 μm.

39. The RF front end for 5G millimeter wave communications of claim 33, 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.

40. The radio frequency front-end for 5G millimeter wave communications of claim 33, wherein: The substrate is provided with an upwardly open groove, and the first electrode and the groove jointly form a cavity.

41. The RF front end for 5G millimeter wave communications of claim 33, wherein: A Bragg reflection layer is arranged between the substrate and the first electrode, and the Bragg reflection layer comprises stacked high acoustic impedance material layers and low acoustic impedance material layers.

42. The radio frequency front-end for 5G millimeter wave communications of claim 33, wherein: A support layer is arranged between the substrate and the first electrode, and the support layer is provided with an opening, and the substrate, the opening, and the first electrode jointly form a cavity.

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