Bulk acoustic wave resonator, method of manufacturing bulk acoustic wave resonator, filter, and electronic device

Abstract

The present invention relates to a bulk acoustic wave resonator comprising: a substrate; an acoustic mirror; a bottom electrode; a piezoelectric layer comprising at least a first layer and a second layer stacked adjacent to each other in a thickness direction, the first layer having a first thickness, the second layer having a second thickness; and a top electrode, wherein: at least one of the first layer and the second layer is a single-crystal piezoelectric layer, the resonator having an electromechanical coupling coefficient Kt 2 , and Kt 2 > 10%. The present invention also relates to a method of manufacturing a bulk acoustic wave resonator, a filter and an electronic device.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the field of semiconductor, and in particular, to a bulk acoustic wave resonator, a manufacturing method of a bulk acoustic wave resonator, a filter and an electronic device. BACKGROUND

[0002] With the development of 5G communication technology, the emerging frequency band is not only higher in frequency, but also larger in bandwidth. Communication technology puts forward higher and higher requirements on the large bandwidth of the filter. Under this premise, the design of the filter puts forward an urgent demand for the resonator with a larger effective electromechanical coupling coefficient (kt 2 ). For example, the demand for kt 2 of the resonator in the Wifi6 frequency band has reached about 17%.

[0003] As a new type of MEMS device, the thin film bulk acoustic resonator (FBAR) has the advantages of small size, light weight, low insertion loss, wide frequency band, and high quality factor, which well adapts to the upgrading of wireless communication systems.

[0004] In the prior art, there is still a demand to improve the Q value of the resonator while maintaining a large kt 2 of the resonator. SUMMARY

[0005] To alleviate or solve at least one aspect of the above problems in the prior art, the present application is proposed.

[0006] According to an aspect of an embodiment of the present application, a bulk acoustic wave resonator is provided, comprising:

[0007] a substrate;

[0008] an acoustic mirror;

[0009] a bottom electrode;

[0010] a piezoelectric layer comprising at least a first layer and a second layer stacked adjacent to each other in a thickness direction, the first layer having a first thickness and the second layer having a second thickness; and

[0011] a top electrode,

[0012] wherein:

[0013] at least one of the first layer and the second layer is a single-crystal piezoelectric layer, and the first layer and the second layer are different in material;

[0014] the resonator has an electromechanical coupling coefficient Kt 2 , and Kt 2 > 10%.

[0015] Embodiments of the present application also relate to a method for manufacturing a bulk acoustic wave resonator, comprising the steps of:

[0016] providing a resonator membrane layer structure comprising at least a top electrode, a piezoelectric layer and a bottom electrode of the resonator,

[0017] wherein:

[0018] the piezoelectric layer comprises at least a first layer and a second layer stacked adjacent to each other in a thickness direction, the first layer having a first thickness and the second layer having a second thickness, at least one of the first layer and the second layer being a single-crystal piezoelectric layer, and the first layer and the second layer being different in material;

[0019] the method comprises the step of selecting at least the material of the first layer and the second layer such that an electromechanical coupling coefficient Kt 2 of the resonator has a value of Kt 2 > 10%.

[0020] Embodiments of the present application also relate to a filter comprising the resonator described above.

[0021] Embodiments of the present application also relate to an electronic device comprising the filter described above or the resonator described above. BRIEF DESCRIPTION OF DRAWINGS

[0022] The following description and drawings can better help understand these and other features and advantages of various embodiments disclosed by the present application, in which like reference numerals refer to like parts throughout the several views of the drawings in which:

[0023] Figure 1 a graph showing a relationship between a quality factor Qmax value of the resonator and a kt 2 of the resonator is shown for example;

[0024] Figure 2 a graph showing a relationship between a K 33 and a K 34 of a single-crystal lithium niobate Z direction electromechanical coupling coefficient as a function of an X-axis rotation angle is shown for example;

[0025] Figure 3 a graph showing a relationship between an E / P value and a parallel resonant impedance Rp of the resonator is shown for example;

[0026] Figure 4 a graph showing a relationship between an E / P value and a Qmax value of the resonator is shown for example;

[0027] Figure 5 a graph showing a relationship between an E / P value and a Kt 2 of the resonator is shown for example;

[0028] Figures 6-9A schematic cross-sectional view of a bulk acoustic resonator according to different exemplary embodiments of the present invention;

[0029] Figures 10-20 For example, it is shown Figure 7 The diagram shows a series of cross-sectional schematics illustrating the manufacturing process of a bulk acoustic resonator. Detailed Implementation

[0030] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In this specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation thereof. These are only some embodiments of the invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0031] Figure 1 The quality factor Qmax of the resonator and the kt of the resonator 2 Relationship diagram, such as Figure 1 As shown, for a resonator utilizing a Sc-doped AlN piezoelectric layer, the kt is increased. 2 The proposed solution has certain drawbacks, namely, with the development of KT... 2 Increasing the doping concentration of the resonator leads to a decrease in Q-value. That is, as the concentration of Sc doping in the piezoelectric material AlN increases, the fabrication of high-quality thin films becomes increasingly difficult, resulting in increased piezoelectric material losses during device operation and consequently a decrease in Q-value. Therefore, continuously increasing the Sc doping concentration in AlN can improve kt. 2 The method for larger kt 2 Demands, such as those exceeding 10%, are no longer considered good solutions.

[0032] Compared to AlN-doped Sc-doped polycrystalline piezoelectric materials, which face the challenge of increasing Kt through doping... 2 However, the Q value of the resonator decreases. Single-crystal piezoelectric materials, such as lithium niobate, can improve the Kt value of the resonator. 2 For example, in implementing large Kt 2 Even with a concentration >10%, it still maintains single-crystal characteristics, thus preserving low material loss during device operation. However, as... Figure 2 As shown, single-crystal lithium niobate in most crystal tangential directions (X-axis) K 33 and K 34 To ensure coexistence and avoid mutual interference between the two while satisfying K... 33 or K 34For the state greater than 10%, the X-axis rotation angle can usually be selected as 130° or about 253°, and the two cut types are called (yxl) 40° and (yxl) 163°, which correspond to Kt 2 , respectively, about 29% and 53%. Therefore, although Kt 2 of the single crystal lithium niobate is high, the range of Kt 2 changes with the cut direction is large, and the actual Kt 2 is limited.

[0033] Figure 3 A graph showing the relationship between the layer thickness ratio E / P value (defined later) and the parallel resonance impedance Rp of the resonator is shown as an example, Figure 3 where the ordinate is the parallel resonance impedance Rp value of the resonator, and the abscissa is the layer thickness ratio E / P of the resonator. Figure 4 A graph showing the relationship between the E / P value and the Qmax value of the resonator is shown as an example, Figure 4 where the ordinate is the Qmax value of the resonator, and the abscissa is the layer thickness ratio E / P of the resonator.

[0034] As shown in Figure 3 and Figure 4 , when the layer thickness ratio E / P value of the resonator is about 1, the parallel resonance impedance Rp and the quality factor Qmax of the resonator both reach a peak value. When the E / P value deviates further from 1, both parameters show a downward trend. In addition, as shown in Figure 3 , the parallel resonance impedance Rp decreases relatively slowly on the side where E / P is greater than 1. Based on the above, in an embodiment of the present application, the range of the layer thickness ratio E / P value is 0.75≤E / P≤3, further 0.75≤E / P≤1.25, still further 0.85≤E / P≤1.15, and still further 0.95≤E / P≤1.05.

[0035] Figure 5 A graph showing the relationship between the E / P value and the Kt 2 of the resonator is shown as an example, where the abscissa is the E / P value, and the ordinate is the Kt 2 . More specifically, Figure 5 A graph showing the change of kt 2 with the layer thickness ratio E / P is shown as an example when the piezoelectric layer is a piezoelectric layer of aluminum nitride doped with a metal scandium element, and the doping concentration is 8.2%. It can be seen that as the layer thickness ratio E / P decreases, kt 2 increases. However, under the premise of ensuring that the performance of the resonator is not severely deteriorated, kt 2 cannot be improved by infinitely reducing the E / P value.

[0036] The Kt 2 of the two preferred cut directions of the single crystal lithium niobate is about 29% and 53%, respectively. If you want to use it to do something similar to the Kt2 For a 17% resonator, it is necessary to increase the E / P value (as shown in Figure 5 2 Therefore, the Rp and Qmax of the resonator are deteriorated.

[0037] To solve the above technical problems, the present application proposes a scheme of using a single-crystal piezoelectric layer and other piezoelectric layers or non-piezoelectric dielectric layers of different materials, so as to meet a relatively optimal E / P value and not to lose the Q value of the resonator due to too much doping of rare earth elements (such as Sc elements) in the polycrystal piezoelectric layer.

[0038] The following will be described with reference to the drawings to exemplarily illustrate the bulk acoustic wave resonator according to different embodiments of the present application. The description of the reference numerals in the drawings is as follows: Figures 6-10

[0039] 101: substrate, which can be made of single-crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.

[0040] 102: acoustic mirror, which can be a cavity, a Bragg reflection layer or other equivalent forms. In the embodiments of the present application, the cavity form is adopted.

[0041] 103: bottom electrode (including bottom electrode pin), which can be made of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or a composite of the above metals or an alloy thereof, etc.

[0042] 104a: polycrystal piezoelectric layer, which can be polycrystal aluminum nitride, zinc oxide, PZT, etc., or a rare earth element doping material containing the above materials in a certain atomic ratio, for example, doped aluminum nitride containing at least one rare earth element, such as scandium (Sc), yttrium (Y), magnesium (Mg), titanium (Ti), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), etc. It should be noted that in other embodiments of the present application, the layer 104a can also be replaced by a dielectric layer of non-piezoelectric material, for example, polycrystal silicon dioxide.

[0043] ​​104b: single crystal piezoelectric layer, such as single crystal aluminum nitride, single crystal gallium nitride, single crystal lithium niobate, single crystal lithium tantalate, single crystal lead zirconate titanate (PZT), single crystal potassium niobate, single crystal quartz film, etc. It can also be a rare earth element doped material with a certain atomic ratio of the above-mentioned materials, for example, it can be doped aluminum nitride, doped aluminum nitride contains at least one rare earth element, such as scandium (Sc), yttrium (Y), magnesium (Mg), titanium (Ti), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and the like.

[0044] 105: top electrode (including top electrode pin), material can be selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or composite of the above metals or their alloys, etc.

[0045] 106: passivation layer or process layer, which can be aluminum nitride, silicon nitride or silicon dioxide, etc.

[0046] 107: metal pad or electrode electrical connection part, which can be selected from gold, copper, aluminum and other high conductivity materials.

[0047] 108: via hole or electrical connection hole, which is arranged in the piezoelectric layer. In a specific embodiment, a conductive material is deposited to lead out the bottom electrode 103 to the same plane as the top electrode 105.

[0048] 111: support layer, which can be made of aluminum nitride, silicon nitride, polysilicon, silicon dioxide, amorphous silicon, boron-doped silicon dioxide and other silicon-based materials, etc.

[0049] 201: auxiliary substrate, which can be made of silicon, silicon carbide, sapphire, silicon dioxide or other silicon-based materials.

[0050] 202: insulating layer, which serves to protect the piezoelectric layer or separate the electrode connection end from the piezoelectric layer, such as silicon dioxide, silicon nitride, silicon carbide, sapphire, etc.

[0051] For bulk acoustic wave resonators, the electromechanical coupling coefficient Kt 2 is related to the value of the layer thickness ratio E / P. In addition, the Q value of the bulk acoustic wave resonator is related to the value of the layer thickness ratio E / P.

[0052] First, the layer thickness ratio E / P is briefly described below.

[0053] As Figure 6As shown, the thickness of the bottom electrode 103 is t1, the thickness of the dielectric layer 104a is t2, the thickness of the piezoelectric layer 104b is t3, the thickness of the top electrode 105 is t4, and the thickness of the passivation layer 106 above the top electrode is t5. In addition, the influence of the bottom electrode 103 on the resonant frequency Fs of the resonator is V1 nm / MHz, the influence of the dielectric layer 104a on the resonant frequency Fs of the resonator is V2 nm / MHz, the influence of the piezoelectric layer 104b on the resonant frequency Fs of the resonator is V3 nm / MHz, the influence of the top electrode 105 on the resonant frequency Fs of the resonator is V4 nm / MHz, and the influence of the passivation layer 106 above the top electrode on the resonant frequency Fs of the resonator is V5 nm / MHz, then the layer thickness ratio E / P is (t1 / V1 + t4 / V4 + t5 / V5) / (t2 / V2 + t3 / V3).

[0054] As can be understood, in the case where the passivation layer is not provided, the layer thickness ratio E / P is (t1 / V1 + t4 / V4) / (t2 / V2 + t3 / V3).

[0055] For other film layer structures, the layer thickness ratio E / P can be determined in a similar manner as described above.

[0056] The doping concentration of the doped element in the piezoelectric layer will be briefly described below.

[0057] Doping means that part of one or more elements in the piezoelectric material that was originally not doped is replaced by a doped element. At this time, the doping concentration is defined as the ratio of the number of atoms of the doped element to the sum of the total number of atoms of the one or more elements that are partially replaced by the doped element. For example, in the case where the piezoelectric layer is aluminum nitride and the doped element is scandium, part of the aluminum atoms is replaced by scandium atoms, and the doping concentration is the ratio of the number of scandium atoms to the sum of the number of aluminum atoms and the number of scandium atoms (Sc / Al+Sc) per unit volume.

[0058] In Figure 6 , the piezoelectric layer includes two layers, namely the piezoelectric layer 104a and the piezoelectric layer 104b, which are stacked on each other. The piezoelectric layer 104a is a polycrystalline piezoelectric layer as described above, for example a doped aluminum nitride piezoelectric layer, while 104b is a single crystal piezoelectric layer as described above, for example a single crystal lithium niobate piezoelectric layer, and the cut type of the single crystal lithium niobate piezoelectric layer is (yxl) 40° or (yxl) 163°.

[0059] The following will briefly explain how to adjust the Kt 2 of the resonator by selecting the thickness of the piezoelectric layer 104a and the piezoelectric layer 104b. 2 For example, the Kt 229%,

[0060] Assuming that the piezoelectric layer 104a is doped aluminum nitride and has a thickness dl, its corresponding Kt 2 8% (determined based on the doping concentration), and the piezoelectric layer 104b is a single crystal lithium niobate with a cut of (yxl) 40°, its corresponding Kt 2 29% and has a thickness d2, in order to achieve a Kt 2 17% for the resonator, the ratio of dl to d2 can be selected to achieve a Kt 2 17%, and a suitable E / P value is selected.

[0061] In the present application, by mixing single crystal piezoelectric layers and polycrystal piezoelectric layers, the layer thickness ratio E / P of the resonator can be made to satisfy 0.75 ≤ E / P ≤ 1.25; and the electromechanical coupling coefficient Kt 2 of the resonator can be made to satisfy Kt 2 > 10%.

[0062] In the embodiments of the present application, in the case of using a polycrystal piezoelectric layer doped with a rare earth element, the doping concentration is less than 20% to minimize the impact of the loss of the Q value of the resonator due to the excessively high concentration of the rare earth element.

[0063] In Figure 6 the illustrated embodiment, the single crystal piezoelectric layer 104b is disposed on the upper surface of the polycrystal piezoelectric layer 104a, so that the polycrystal piezoelectric layer 104a is disposed between the single crystal piezoelectric layer 104b and the support layer 111.

[0064] The single crystal piezoelectric layer 104b can also be disposed on the lower surface of the polycrystal piezoelectric layer 104a, so that the single crystal piezoelectric layer 104b is disposed between the polycrystal piezoelectric layer 104a and the support layer 111, as shown in Figure 7 .

[0065] In Figures 6-7 the illustrated embodiment, the piezoelectric layer includes only one polycrystal piezoelectric layer and one single crystal piezoelectric layer, but the present application is not limited thereto, and more layers can also be provided. Figures 8-9 are cross-sectional schematic views of bulk acoustic wave resonators according to other different exemplary embodiments of the present application, in which three piezoelectric layers are shown.

[0066] As shown in Figure 8 , the piezoelectric layer includes a single crystal piezoelectric layer 104b, and two polycrystal piezoelectric layers 104a disposed on the upper and lower sides of the single crystal piezoelectric layer 104b. In Figure 8 , the thicknesses of the two polycrystal piezoelectric layers are different, but in different embodiments, they can also be the same. In addition, in Figure 8 , the materials of the two polycrystal piezoelectric layers can be the same or different. In Figure 8In the case of two polycrystalline piezoelectric layers made of different materials, they can also be adjacent to each other.

[0067] like Figure 9 As shown, the piezoelectric layer includes a polycrystalline piezoelectric layer 104a and two monocrystalline piezoelectric layers 104b disposed on the upper and lower sides of the polycrystalline piezoelectric layer 104a. Figure 9 In this example, the two single-crystal piezoelectric layers have different thicknesses; however, they can also be the same in different embodiments. Furthermore, in... Figure 9 In this process, the two single-crystal piezoelectric layers can be made of the same or different materials. Figure 9 In the case of two single-crystal piezoelectric layers made of different materials, they can also be adjacent to each other.

[0068] Although not shown, a piezoelectric layer can also be a piezoelectric layer formed by combining more layers of piezoelectric film.

[0069] In reference Figures 6-9 In the described embodiments, one layer of the piezoelectric layer is a single-crystal piezoelectric layer, and the other layers include single-crystal piezoelectric layers of different materials or polycrystalline piezoelectric layers. However, the present invention is not limited to this, and the other layers may also be dielectric layers of non-piezoelectric materials.

[0070] The following reference Figures 10-20 For illustrative purposes only Figure 7 The manufacturing process of the bulk acoustic resonator is shown.

[0071] In this invention, a bulk acoustic wave resonator is fabricated based on a POI (Piezoelectrics on Insulator) wafer. The POI wafer includes an auxiliary substrate, a single-crystal piezoelectric layer, and an insulating layer disposed between the single-crystal piezoelectric layer and the auxiliary substrate.

[0072] As mentioned later, during the resonator transfer process, the insulating layer can better protect the single-crystal piezoelectric film (i.e., the single-crystal piezoelectric layer), thereby reducing or even avoiding damage to the single-crystal piezoelectric film during the subsequent removal of the auxiliary substrate, so as to obtain a high-performance bulk acoustic resonator.

[0073] In addition, the presence of the insulating layer also facilitates the diversification of substrate removal methods and simplifies device fabrication processes.

[0074] Figure 10 The POI wafer is shown. Figure 10 As shown, the POI wafer includes an auxiliary substrate or auxiliary base 201, an insulating layer 202, and a single-crystal piezoelectric layer 104b. As mentioned earlier, the single-crystal piezoelectric layer can be a piezoelectric single-crystal thin film such as lithium niobate or lithium tantalate.

[0075] The crystal orientation of the piezoelectric single crystal thin film in the POI wafer is various and is not limited by the growth conditions of the piezoelectric thin film. Therefore, piezoelectric single crystal thin films with special crystal orientations can be selected to produce resonators and filters with various properties. For example, in one embodiment of the present application, the piezoelectric layer 104b can be a single crystal lithium niobate piezoelectric layer with a cut type of (yxl) 163°.

[0076] Figure 11 An exemplary process of depositing an electrode film layer on the surface of the piezoelectric layer 104b and forming a pattern of the bottom electrode 103 is shown.

[0077] The piezoelectric layer 104b can be first deposited with a uniform electrode film layer, and then the patterned bottom electrode 103 can be formed by wet or dry etching. Alternatively, the pattern of the bottom electrode can be directly formed by lift-off or printing processes.

[0078] Figure 12 An exemplary state of depositing a support material layer on the bottom electrode 103 and the single crystal piezoelectric layer 104b and planarizing the support material layer to form a support material layer corresponding to the support layer 111 is shown. The thickness of the support material layer is greater than the thickness of the bottom electrode 103. The planarized support material layer is formed by a polishing process, such as CMP (chemical mechanical polishing).

[0079] Figure 13 An exemplary state of patterning (e.g., by etching) the support material layer to form the cavity 102 and the patterned support layer 111 is shown.

[0080] In Figure 14 , the substrate 101 is bonded to the support layer 111.

[0081] Although not shown, the planar surface of the support layer 111 can also be provided with a dedicated bonding layer via which the substrate 101 can be bonded to the support layer 111. The substrate 101 and the support layer 111 can be bonded by physical or chemical means, and the material of the dedicated bonding layer can be provided on the substrate 101 or the support layer 111 alone, or on both surfaces.

[0082] The substrate 101 and the support layer 111 can also be directly bonded without a dedicated bonding layer, i.e., a chemical bond can be formed between the substrate 101 and the support layer 111, or a physical bond can be formed by intermolecular forces when the surfaces are polished to a very low surface roughness. In this case, the support layer 111 is directly used for bonding and can also be referred to as a bonding layer.

[0083] Next is the process of reversing the device in Figure 14 , and removing the auxiliary substrate 201 and the insulating layer 202.

[0084] The etching processes of the auxiliary substrate 201 and the insulating layer 202 (barrier layer) are different, for example, the auxiliary substrate 201 is silicon and the insulating layer 202 is silicon dioxide. The insulating layer 202 can act as a termination layer or a barrier layer during the removal of the auxiliary substrate 201. The removal process of the insulating layer 202 is gentle, which reduces or even avoids the damage to the other surface of the piezoelectric single crystal thin film during the removal of the auxiliary substrate 201.

[0085] The surface release process of the piezoelectric single crystal thin film can be achieved by completely removing the auxiliary substrate 201 and completely removing the insulating layer 202.

[0086] The overall removal of the auxiliary substrate 201 can be achieved by grinding, polishing, polishing, wet or dry etching, or a combination of these processes. The overall removal process of the insulating layer 202 can be achieved by wet or dry etching.

[0087] After the removal of the insulating layer 202, if the surface of the piezoelectric single crystal thin film is partially damaged, especially the effective area of the resonator or the filter formed by the resonator is damaged, the surface of the piezoelectric thin film can be polished by a polishing process.

[0088] As shown in Figure 15 , the auxiliary substrate 201 and the insulating layer 202 have been removed to expose the side of the piezoelectric layer 104b covered thereby.

[0089] As shown in Figure 16 , a polycrystalline piezoelectric layer 104a, for example, doped aluminum nitride, is deposited on the structure shown in Figure 15 , thereby forming a hybrid piezoelectric layer structure composed of the single-crystal piezoelectric layer 104b and the polycrystalline piezoelectric layer 104a.

[0090] The piezoelectric layer formed in Figure 16 includes the piezoelectric layer 104a and the piezoelectric layer 104b stacked adjacent to each other in the thickness direction. The piezoelectric layer 104a has a first thickness and the piezoelectric layer 104b has a second thickness. The values of the first thickness and the second thickness can be selected in cooperation with the thicknesses of other film layers of the resonator stacked structure so that the resonator layer thickness ratio E / P has a value of 0.75≤E / P≤1.25, and at least the materials of the piezoelectric layer 104a and the piezoelectric layer 104b are selected so that the electromechanical coupling coefficient Kt 2 of the resonator has a value of Kt 2 >10%.

[0091] Referring to Figure 17 , a polycrystalline piezoelectric layer 104a is deposited on the structure shown in Figure 16The surface of the structure shown is deposited with a top electrode thin film and a passivation layer film layer, and a pattern of the top electrode and the passivation layer is formed. The top electrode and the passivation layer can be formed by first depositing a uniform electrode film layer and a passivation layer film layer, and then forming a patterned top electrode 105 and a passivation layer 106 by wet or dry etching.

[0092] The passivation layer 106 can also not be provided, and then Figure 16 The surface of the structure shown is deposited with a top electrode thin film, and then a patterned top electrode 105 is formed by wet or dry etching.

[0093] As shown in the figure, Figure 18 The patterned passivation layer 106 can be removed from part of the top electrode for subsequent signal lead-out.

[0094] Referring to Figure 19 The bottom electrode connecting part of the electric connection hole 108 formed on the piezoelectric layer, which exposes the bottom electrode by penetrating the piezoelectric layer 104a and the piezoelectric layer 104b, can be obtained by wet or dry etching, laser ablation, or a combination of these processes.

[0095] Referring to Figure 20 The patterned electrode connecting part 107 for electric connection of the top electrode 105, and the electrode connecting part 107 for electric connection with the bottom electrode can be formed by first depositing a uniform conductive film layer and then by wet or dry etching, or by a stripping process or printing process.

[0096] In the above embodiments, the mixed piezoelectric layer formed by a single crystal piezoelectric layer and a polycrystalline piezoelectric layer is described as an example. However, alternatively, different single crystal piezoelectric layers can also constitute the piezoelectric mixed layer.

[0097] It should be noted that in the present application, each numerical range, in addition to the end point value, can also be the median value of the numerical range, unless it is explicitly stated that the end point value is not included, which is within the protection scope of the present application.

[0098] In the present application, up and down are relative to the bottom surface of the substrate of the resonator, and for a component, the side close to the bottom surface is the lower side, and the side away from the bottom surface is the upper side.

[0099] In the present application, inner and outer are in relation to the center of the effective area (the effective area is composed of the overlapping area of the piezoelectric layer, the top electrode, the bottom electrode and the acoustic mirror in the thickness direction of the resonator) of the resonator (i.e. the center of the effective area) in the lateral direction or the radial direction, the side or the end of a component close to the center of the effective area is the inner side or the inner end, and the side or the end of the component away from the center of the effective area is the outer side or the outer end. For a reference position, the inner side of the position means between the position and the center of the effective area in the lateral direction or the radial direction, and the outer side of the position means further away from the center of the effective area than the position in the lateral direction or the radial direction.

[0100] As can be understood by those skilled in the art, the bulk acoustic wave resonator according to the present application can be used to form a filter or an electronic device.

[0101] Based on the above, the present application proposes the following technical solutions:

[0102] 1. A bulk acoustic wave resonator, comprising:

[0103] a substrate;

[0104] an acoustic mirror;

[0105] a bottom electrode;

[0106] a piezoelectric layer comprising at least a first layer and a second layer stacked adjacent to each other in the thickness direction, the first layer having a first thickness and the second layer having a second thickness; and

[0107] a top electrode,

[0108] wherein:

[0109] at least one of the first layer and the second layer is a single-crystal piezoelectric layer, and the first layer and the second layer are different in material;

[0110] the resonator has an electromechanical coupling coefficient Kt 2 , and Kt 2 > 10%.

[0111] 2. The resonator according to 1, wherein:

[0112] one of the first layer and the second layer is a single-crystal piezoelectric layer, and the other is a dielectric layer of non-piezoelectric material.

[0113] 3. The resonator according to 1, wherein:

[0114] the first layer is a single-crystal piezoelectric layer, and the second layer is a polycrystal piezoelectric layer.

[0115] 4. The resonator according to 3, wherein:

[0116] The first layer is a single-crystal lithium niobate piezoelectric layer, and a cut type of the single-crystal lithium niobate piezoelectric layer is (yxl) 40° or (yxl) 163°.

[0117] 5. The resonator according to 3, wherein:

[0118] The second layer is a doped aluminum nitride piezoelectric layer or a doped silicon nitride piezoelectric layer or a doped zinc oxide piezoelectric layer, and a doping concentration is less than 20%; and / or

[0119] The first layer is a single-crystal lithium niobate piezoelectric layer or a single-crystal lithium tantalate piezoelectric layer.

[0120] 6. The resonator according to 5, wherein:

[0121] The cut type of the single-crystal lithium niobate piezoelectric layer is (yxl) 40°; or

[0122] The cut type of the single-crystal lithium niobate piezoelectric layer is (yxl) 163°.

[0123] 7. The resonator according to 1, wherein:

[0124] The first layer is a single-crystal piezoelectric layer, and the second layer is a polycrystal piezoelectric layer or a non-piezoelectric dielectric layer; and

[0125] The first layer is arranged between the second layer and the top electrode, or the second layer is arranged between the first layer and the top electrode.

[0126] 8. The resonator according to 1, wherein:

[0127] The piezoelectric layer includes at least the first layer, the second layer and a third layer stacked in a thickness direction, and the third layer has a third thickness.

[0128] The first layer is a single-crystal piezoelectric layer, and the second layer and the third layer are polycrystal piezoelectric layers or non-piezoelectric dielectric layers;

[0129] Materials of two adjacent layers are different.

[0130] 9. The resonator according to 8, wherein:

[0131] The first layer is closer to the top electrode than the second layer and the third layer; or

[0132] The first layer is closer to the bottom electrode than the second layer and the third layer.

[0133] 10. The resonator according to 1, wherein:

[0134] The first layer, the second layer and the third layer are all single-crystal piezoelectric layers, and materials of adjacent layers are different.

[0135] 11. The resonator according to 1, wherein:

[0136] The first layer and the second layer are both single-crystal piezoelectric layers.

[0137] 12. The resonator according to 11, wherein:

[0138] The first layer is a single-crystal lithium niobate piezoelectric layer with a cut of (yxl) 40°; or

[0139] The second layer is a single-crystal lithium niobate piezoelectric layer with a cut of (yxl) 163°.

[0140] 13. The resonator according to any one of 1-14, wherein:

[0141] The resonator has a layer thickness ratio E / P, 0.75≤E / P≤3.

[0142] 14. The resonator according to 13, wherein:

[0143] The resonator has a layer thickness ratio E / P, 0.75≤E / P≤1.25.

[0144] 15. The resonator according to 14, wherein:

[0145] 0.85≤E / P≤1.15.

[0146] 16. The resonator according to 15, wherein:

[0147] 0.95≤E / P≤1.05.

[0148] 17. A method of manufacturing a bulk acoustic wave resonator, comprising the steps of:

[0149] providing a resonator membrane layer structure, the resonator membrane layer structure comprising at least a top electrode, a piezoelectric layer and a bottom electrode of the resonator,

[0150] wherein:

[0151] the piezoelectric layer comprises at least a first layer and a second layer stacked adjacent to each other in a thickness direction, the first layer having a first thickness and the second layer having a second thickness, at least one of the first layer and the second layer being a single-crystal piezoelectric layer, and the first layer and the second layer being different in material;

[0152] the method comprising the step of selecting at least the material of the first layer and the second layer such that an electromechanical coupling coefficient Kt 2 of the resonator has a value Kt 2 > 10%.

[0153] 18. The method according to 17, further comprising the step of:

[0154] The first thickness and the second thickness are selected to have values such that the resonator layer thickness ratio E / P has a value of 0.75≤E / P≤3 in cooperation with the thicknesses of the other film layers of the resonant film layer structure.

[0155] 19. A filter comprising a plurality of bulk acoustic wave resonators according to any one of claims 1-16.

[0156] 20. An electronic device comprising the filter according to claim 19, or the bulk acoustic wave resonator according to any one of claims 1-16.

[0157] Here, the electronic device includes, but is not limited to, intermediate products such as radio frequency front ends, filter amplification modules, and terminal products such as mobile phones, WIFI, and unmanned aerial vehicles.

[0158] Although embodiments of the present application have been shown and described, it is to be understood that various modifications can be made to these embodiments without departing from the principles and spirit of the application, the scope of which is to be determined by the appended claims and their equivalents.

Claims

1. A bulk acoustic wave resonator, comprising: a substrate; an acoustic mirror; a bottom electrode; a piezoelectric layer including at least a first layer and a second layer stacked adjacent to each other in a thickness direction, the first layer having a first thickness, the second layer having a second thickness; and a top electrode, wherein: at least one of the first layer and the second layer is a single-crystal piezoelectric layer, and the first layer and the second layer are of different materials; The resonator has a electromechanical coupling coefficient Kt 2 , and Kt 2 > 10%. the first layer and the second layer are stacked adjacent to each other in the thickness direction within an effective area of the resonator. 2.The resonator of claim 1, wherein: one of the first layer and the second layer is a single-crystal piezoelectric layer, and the other is a dielectric layer of a non-piezoelectric material. 3.The resonator of claim 1, wherein: the first layer is a single-crystal piezoelectric layer, and the second layer is a polycrystalline piezoelectric layer. 4.The resonator of claim 3, wherein: the first layer is a single-crystal lithium niobate piezoelectric layer, and a cut type of the single-crystal lithium niobate piezoelectric layer is (yxl) 40° or (yxl) 163°. 5.The resonator of claim 3, wherein: the second layer is a doped aluminum nitride piezoelectric layer or a doped silicon nitride piezoelectric layer or a doped zinc oxide piezoelectric layer, and a doping concentration is less than 20%; and / or the first layer is a single-crystal lithium niobate piezoelectric layer or a single-crystal lithium tantalate piezoelectric layer. 6.The resonator of claim 5, wherein: a cut type of the single-crystal lithium niobate piezoelectric layer is (yxl) 40°; or a cut type of the single-crystal lithium niobate piezoelectric layer is (yxl) 163°. 7.The resonator of claim 1, wherein: the first layer is a single-crystal piezoelectric layer, and the second layer is a polycrystalline piezoelectric layer or a non-piezoelectric dielectric layer; and the first layer is disposed between the second layer and the top electrode, or the second layer is disposed between the first layer and the top electrode. 8.The resonator of claim 1, wherein: the piezoelectric layer includes at least the first layer, the second layer, and a third layer stacked in the thickness direction, the third layer having a third thickness; the first layer is a single-crystal piezoelectric layer, and the second layer and the third layer are polycrystalline piezoelectric layers or non-piezoelectric dielectric layers; materials of two adjacent layers are different. 9.The resonator of claim 8, wherein: the first layer is closer to the top electrode than the second layer and the third layer; or the first layer is closer to the bottom electrode than the second layer and the third layer. 10.The resonator of claim 1, wherein: the first layer, the second layer, and the third layer are all single-crystal piezoelectric layers, and materials of adjacent layers are different. 11.The resonator of claim 1, wherein: the first layer and the second layer are both single-crystal piezoelectric layers. 12.The resonator of claim 11, wherein: the first layer is a single-crystal lithium niobate piezoelectric layer with a cut type of (yxl) 40°; or the second layer is a single-crystal lithium niobate piezoelectric layer with a cut type of (yxl) 163°. 13.The resonator of any one of claims 1-12, wherein: the resonator has a layer thickness ratio E / P, 0.75≤E / P≤3; in a case where a passivation layer is provided, E / P=(t1 / V1+t4 / V4+t5 / V5) / (t2 / V2+t3 / V3). E / P = (t1 / V1 + t4 / V4) / (t2 / V2 + t3 / V3) in the case where the passivation layer is not provided; In the above two formulas, t1 is the thickness of the bottom electrode, t2 is the thickness of the dielectric layer, t3 is the thickness of the piezoelectric layer, t4 is the thickness of the top electrode, and t5 is the thickness of the passivation layer; V1 is the influence of the bottom electrode on the resonance frequency Fs of the resonator, V2 is the influence of the dielectric layer on the resonance frequency Fs of the resonator, V3 is the influence of the piezoelectric layer on the resonance frequency Fs of the resonator, V4 is the influence of the top electrode on the resonance frequency Fs of the resonator, and V5 is the influence of the passivation layer on the resonance frequency Fs of the resonator.

14. The resonator according to claim 13, wherein: 0.75 ≤ E / P ≤ 1.

25.

15. The resonator according to claim 14, wherein: 0.85 ≤ E / P ≤ 1.

15.

16. The resonator according to claim 15, wherein: 0.95 ≤ E / P ≤ 1.

05.

17. A method of manufacturing a bulk acoustic wave resonator, comprising the steps of: providing a resonator membrane layer structure including at least a top electrode, a piezoelectric layer, and a bottom electrode of the resonator, wherein: the piezoelectric layer includes at least a first layer and a second layer stacked adjacent to each other in a thickness direction, the first layer having a first thickness and the second layer having a second thickness, at least one of the first layer and the second layer being a single-crystal piezoelectric layer, and the first layer and the second layer being different in material; The method includes the steps of: selecting at least the materials of the first and second layers such that the electromechanical coupling coefficient Kt of the resonator is such that... 2 The value is Kt 2 >10%; in a range of an effective area of the resonator, the first layer and the second layer are stacked adjacent to each other in the thickness direction.

18. The method according to claim 17, further comprising the step of: selecting values of the first thickness and the second thickness in cooperation with thicknesses of other membrane layers of the resonator membrane layer structure such that a resonator layer thickness ratio E / P has a value of 0.75 ≤ E / P ≤ 3; E / P = (t1 / V1 + t4 / V4 + t5 / V5) / (t2 / V2 + t3 / V3) in the case where the passivation layer is provided; E / P = (t1 / V1 + t4 / V4) / (t2 / V2 + t3 / V3) in the case where the passivation layer is not provided; In the above two formulas, t1 is the thickness of the bottom electrode, t2 is the thickness of the dielectric layer, t3 is the thickness of the piezoelectric layer, t4 is the thickness of the top electrode, and t5 is the thickness of the passivation layer; V1 is the influence of the bottom electrode on the resonance frequency Fs of the resonator, V2 is the influence of the dielectric layer on the resonance frequency Fs of the resonator, V3 is the influence of the piezoelectric layer on the resonance frequency Fs of the resonator, V4 is the influence of the top electrode on the resonance frequency Fs of the resonator, and V5 is the influence of the passivation layer on the resonance frequency Fs of the resonator.

19. A filter including a plurality of the bulk acoustic wave resonators according to any one of claims 1 to 16.

20. An electronic device including the filter according to claim 19 or the bulk acoustic wave resonator according to any one of claims 1 to 16.

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