Bulk Acoustic Wave Resonator

Abstract

The present disclosure provides a bulk acoustic wave resonator. The bulk acoustic wave resonator includes: a first electrode disposed on the upper side of a substrate; a piezoelectric layer disposed on the upper surface of the first electrode; and a second electrode disposed on the upper surface of the piezoelectric layer, wherein the upper surface of at least one of the first electrode and the second electrode has a concave region, wherein the depth of the concave region is D, the width of the concave region is W, and the resonant frequency is F, and ln is a natural logarithm, and wherein [{ln(D×W)} / (‑0.59×F)] is greater than or equal to [[ln{0.008(μm) 2}] / {‑0.59×(3.5GHz)}] and less than or equal to [[ln{0.022(μm) 2}] / {‑0.59×(3.5GHz)}].

Description

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2021-0010053 filed on January 25, 2021, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety for all purposes by reference. Technical Field

[0002] The present disclosure relates to a bulk acoustic wave resonator. Background Art

[0003] As the performance of mobile devices improves, demand for bulk acoustic wave (BAW) filters using BAW resonators is increasing, and such filters may have advantages of high power handling characteristics and high frequency compared to surface acoustic wave (SAW) filters.

[0004] Low loss is crucial for the performance required of mobile devices. To this end, designing filters with low losses across the entire frequency band is crucial, and the use of low-loss resonators is most effective. Losses in BAW resonators are caused by various factors, including dielectric loss in the piezoelectric body, imperfect crystallinity within the piezoelectric body itself, and resistance in the electrode material. Furthermore, spurious noise (SN), a physical phenomenon associated with BAW resonance, generated in the region near the resonant frequency before reaching resonant frequency, is also a major contributor to resonator losses.

[0005] The above information is presented as background information only to help understand the present disclosure. The above description should not be interpreted as these contents belonging to the prior art of the present disclosure. Summary of the Invention

[0006] This summary is provided to introduce selected concepts in a simplified form and further describe these concepts in the following detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0007] In one general aspect, a bulk acoustic wave resonator includes: a first electrode disposed on an upper side of a substrate; a piezoelectric layer disposed on an upper surface of the first electrode; and a second electrode disposed on an upper surface of the piezoelectric layer, wherein the upper surface of at least one of the first electrode and the second electrode has a concave region, wherein the concave region has a depth D, a width W, and a resonant frequency F, and ln is a natural logarithm, and wherein [{ln(D×W)} / (−0.59×F)] is greater than or equal to [[ln{0.008(μm) 2}] / {-0.59×(3.5GHz)}] and less than or equal to [[ln{0.022(μm) 2}] / {-0.59×(3.5GHz)}].

[0008] D×W can be greater than or equal to 0.008 (μm) 2 And less than or equal to 0.022 (μm) 2 .

[0009] D×W can be greater than or equal to 0.010 (μm) 2 And less than or equal to 0.016 (μm) 2 .

[0010] D may be greater than or equal to 5 nm.

[0011] D may be greater than or equal to 1% of the thickness of the piezoelectric layer.

[0012] The concave region may be located on an upper surface of the second electrode, and D may be greater than or equal to 5 / 174 times the thickness of the second electrode and less than the thickness of the second electrode.

[0013] Each of the first electrode and the second electrode may include molybdenum (Mo).

[0014] The upper surface of the piezoelectric layer may have a concave area, and a product of a depth and a width of the concave area of ​​at least one of the first electrode and the second electrode may be smaller than a product of a depth and a width of the concave area of ​​the piezoelectric layer.

[0015] The BAW resonator may further include a protective layer disposed on the upper surface of the second electrode, wherein the upper surface of the protective layer may have a concave area, and a product of a depth and a width of the concave area of ​​the piezoelectric layer may be smaller than a product of a depth and a width of the concave area of ​​the protective layer.

[0016] The BAW resonator may further include a seed layer disposed on a lower surface of the first electrode, wherein an upper surface of the seed layer may have a recessed area, and a product of a depth and a width of the recessed area of ​​the protective layer may be smaller than a product of a depth and a width of the recessed area of ​​the seed layer.

[0017] The seed layer may include AlN, and the protection layer may include SiO 2 .

[0018] In another general aspect, a bulk acoustic wave resonator includes: a first electrode disposed on an upper side of a substrate; a piezoelectric layer disposed on an upper surface of the first electrode; and a second electrode disposed on an upper surface of the piezoelectric layer, wherein the upper surface of the piezoelectric layer has a concave region, wherein the concave region has a depth D, a width W, a resonant frequency F, and ln is a natural logarithm, wherein D is greater than or equal to 1% and less than 100% of the thickness of the piezoelectric layer, and wherein [{ln(D×W)} / (−0.412×F)] is greater than or equal to [[ln{0.015 (μm) 2}] / {-0.412×(3.5GHz)}] and less than or equal to [[ln{0.03(μm) 2}] / {-0.412×(3.5GHz)}].

[0019] D×W can be greater than or equal to 0.015 (μm) 2 And less than or equal to 0.03 (μm) 2 .

[0020] The BAW resonator may further include a seed layer disposed on a lower surface of the first electrode, wherein an upper surface of the seed layer may have a concave region, and a product of a depth and a width of the concave region of the piezoelectric layer may be smaller than a product of a depth and a width of the concave region of the seed layer.

[0021] In another general aspect, a bulk acoustic wave resonator includes: a seed layer; a first electrode disposed on the upper surface of the seed layer; a piezoelectric layer disposed on the upper surface of the first electrode; a second electrode disposed on the upper surface of the piezoelectric layer; and a protective layer disposed on the upper surface of the second electrode, wherein the upper surfaces of at least two of the seed layer, the first electrode, the piezoelectric layer, the second electrode and the protective layer respectively have a first concave region and a second concave region, and the product of the depth and width of the first concave region is different from the product of the depth and width of the second concave region.

[0022] The first concave region may be located on the upper surface of at least one of the first electrode and the second electrode, the second concave region may be located on the upper surface of at least one of the seed layer, the piezoelectric layer and the protective layer, and the product of the depth and width of the first concave region may be smaller than the product of the depth and width of the second concave region.

[0023] Each of the first electrode and the second electrode may include molybdenum (Mo), and at least one of the seed layer, the piezoelectric layer, and the protection layer may include at least one of AlN, ScAlN, and SiO 2 .

[0024] The first concave region may be located on the upper surface of at least one of the first electrode, the piezoelectric layer and the second electrode, the second concave region may be located on the upper surface of at least one of the seed layer and the protective layer, and the product of the depth and width of the first concave region may be smaller than the product of the depth and width of the second concave region.

[0025] The first concave region may be located on the upper surface of at least one of the first electrode, the piezoelectric layer, the second electrode and the protective layer, the second concave region may be located on the upper surface of the seed layer, and the product of the depth and width of the first concave region may be smaller than the product of the depth and width of the second concave region.

[0026] The first concave region and the second concave region may have different depths.

[0027] Other features and aspects will be readily apparent from the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a diagram illustrating a concave region of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0029] Figure 2 is a diagram illustrating the width and depth of a concave region of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0030] Figures 3A to 3E is a diagram illustrating a concave region of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0031] Figures 4A to 4E is a diagram illustrating depth differences between a plurality of concave regions of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0032] Figure 5 is a graph showing that the number of acoustic waves increases as the depth of the plurality of concave regions increases.

[0033] Figure 6A and Figure 6B is a graph showing an optimal area curve of a concave region located on the upper surface of the second electrode;

[0034] Figure 6C and Figure 6D is a graph showing optimal area curves of the concave regions located on the upper surfaces of the seed layer, the first electrode, the piezoelectric layer, the second electrode, and the protective layer.

[0035] Figure 7A and Figure 7Bis a graph showing a difference in dispersion curves when a concave region having the same depth is formed in each of the seed layer, the first electrode, the piezoelectric layer, the second electrode, and the protective layer, compared to an active region.

[0036] Figure 8A and Figure 8B is a graph showing an optimal area curve in which a thickness variation of the piezoelectric layer is added to the optimal area curve of the concave region located on the upper surfaces of the seed layer, the first electrode, the piezoelectric layer, the second electrode, and the protective layer.

[0037] Figure 9A and Figure 9B is a graph showing that optimal areas vary according to depths of recessed regions respectively located on upper surfaces of the seed layer, the first electrode, the piezoelectric layer, the second electrode, and the protective layer.

[0038] Figure 10A and Figure 10B is a graph showing a difference in spurious noise in a frequency range lower than a resonance frequency according to the presence or absence of a concave region.

[0039] Figure 11A is a graph showing spurious noise according to the product of the width and depth of a concave region.

[0040] Figure 11B is a graph showing an optimal area according to a resonance frequency of a concave region of a first electrode and / or a second electrode.

[0041] Figure 12A is a graph showing spurious noise according to the width of a concave region.

[0042] Figure 12B is a graph showing the optimum area of ​​the concave region of the piezoelectric layer according to the resonance frequency.

[0043] Figure 13 is a diagram illustrating a specific form of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0044] Throughout the drawings and detailed description, like reference numerals refer to like elements. The drawings may not be drawn to scale, and the relative sizes, proportions, and depictions of elements in the drawings may be exaggerated for clarity, illustration, and convenience. DETAILED DESCRIPTION

[0045] Hereinafter, although example embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, it should be noted that the examples are not limited to the example embodiments of the present disclosure.

[0046] The following detailed description is provided to help the reader gain a comprehensive understanding of the methods, apparatuses, and / or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and / or systems described herein will be readily understood after an understanding of the present disclosure. For example, the order of operations described herein is merely an example and is not limited to the order set forth herein, but rather, except for operations that must occur in a particular order, changes may be made that will be readily understood after an understanding of the present disclosure. Furthermore, descriptions of functions and configurations that would be well known to one of ordinary skill in the art may be omitted for clarity and brevity.

[0047] The features described herein may be implemented in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein are provided merely to illustrate some of the many possible ways to implement the methods, devices, and / or systems described herein that will be readily understood after understanding the present disclosure.

[0048] It is noted here that the use of the term "may" with respect to an example or embodiment (e.g., with respect to what an example or embodiment may include or implement) means that there is at least one example or embodiment that includes or implements such feature, and is not limited to all examples or embodiments including or implementing such feature.

[0049] Throughout this specification, when an element, such as a layer, region, or substrate, is described as being “on,” “connected to,” or “coupled to” another element, the element may be directly “on,” “connected to,” or “coupled to” another element, or one or more other elements may be present between them. In contrast, when an element is described as being “directly on,” “directly connected to,” or “directly coupled to” another element, there are no other elements present. As used herein, “a portion” of an element may include the entire element or less than the entire element.

[0050] As used herein, the term "and / or" includes any one of the relevant listed items or any combination of any two or more items. Similarly, "at least one of / at least one of" includes any one of the relevant listed items or any combination of any two or more items.

[0051] Although terms such as "first," "second," and "third" may be used herein to describe various members, components, regions, layers, or portions, these members, components, regions, layers, or portions are not limited by these terms. Rather, these terms are used solely to distinguish one member, component, region, layer, or portion from another member, component, region, layer, or portion. Thus, what is referred to as a first member, first component, first region, first layer, or first portion in the examples described herein may also be referred to as a second member, second component, second region, second layer, or second portion without departing from the teachings of the examples.

[0052] For ease of description, spatially relative terms such as "above," "above," "below," and "below" may be used herein to describe the relationship of one element to another element as shown in the accompanying drawings. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the accompanying drawings. For example, if the device in the accompanying drawings is turned over, an element described as being "above" or "above" relative to another element would then be "below" or "below" relative to the other element. Thus, the term "above" includes both "above" and "below" orientations depending on the spatial orientation of the device. The device may also be positioned in other ways (e.g., rotated 90 degrees or in other orientations), and the spatially relative terms used herein will be interpreted accordingly.

[0053] The terms used herein are only used to describe various examples and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. The terms "comprising," "including," and "having" list the presence of the stated features, quantities, operations, components, elements, and / or combinations thereof, but do not preclude the presence or addition of one or more other features, quantities, operations, components, elements, and / or combinations thereof.

[0054] Due to manufacturing techniques and / or tolerances, the shapes shown in the drawings may vary. Therefore, the examples described herein are not limited to the specific shapes shown in the drawings but include changes in shape that occur during manufacturing.

[0055] The features of the examples described herein can be combined in various ways that will be readily understood after understanding this disclosure. In addition, although the examples described herein have multiple configurations, other configurations that will be readily understood after understanding this disclosure are feasible.

[0056] One aspect of the present disclosure is to provide a bulk acoustic wave resonator.

[0057] Figure 1 is a diagram illustrating a concave region of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0058] Reference Figure 1 The bulk acoustic wave resonator according to an embodiment of the present disclosure may include a resonator 135 , and the resonator 135 may include a first electrode 140 , a piezoelectric layer 150 , and a second electrode 160 .

[0059] The first electrode 140 may be disposed on an upper side of the substrate 110 , the piezoelectric layer 150 may be disposed on an upper surface of the first electrode 140 , and the second electrode 160 may be disposed on an upper surface of the piezoelectric layer 150 .

[0060] Each of the first electrode 140 and the second electrode 160 may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof to improve coupling efficiency with the piezoelectric layer 150, but is not limited thereto. Each of the first electrode 140 and the second electrode 160 may be formed using a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or an alloy thereof.

[0061] The piezoelectric layer 150 may include a piezoelectric material to produce a piezoelectric effect (converting electrical energy into mechanical energy in the form of elastic waves). For example, the piezoelectric material may include at least one of aluminum nitride (AlN), zinc oxide (ZnO), and lead zirconate titanate (PZT, PbZrTiO). It may also include rare earth metals and transition metals, and may also include divalent metals such as magnesium (Mg). For example, the rare earth metal may include at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). The transition metal may include at least one of titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb).

[0062] Resonator 135 can convert the electrical energy of a radio frequency (RF) signal into mechanical energy, and vice versa, through the piezoelectric properties of piezoelectric layer 150. When the frequency of the RF signal is closer to the resonant frequency of the BAW resonator, the energy transfer rate between first electrode 140 and second electrode 160 can be greatly increased. When the frequency of the RF signal is closer to the antiresonant frequency of the BAW resonator, the energy transfer rate between first electrode 140 and second electrode 160 can be greatly reduced. Due to the piezoelectric properties, the antiresonant frequency can be higher than the resonant frequency.

[0063] Reference Figure 1 The BAW resonator according to an embodiment of the present disclosure may be a film bulk acoustic resonator (FBAR) in which the air cavity 112 is located between the substrate 110 and the resonator 135, but is not limited thereto. For example, the BAW resonator according to an embodiment of the present disclosure may be a solid-state mount resonator (SMR) in which a support portion composed of alternating stacks of at least one insulating layer and at least one metal layer is located between the substrate 110 and the resonator 135.

[0064] Reference Figure 1 The BAW resonator according to an embodiment of the present disclosure may further include a substrate 110 , an insulating layer 120 , a sacrificial layer 130 , a protective layer 170 , and at least one of metal layers 181 and 182 .

[0065] The substrate 110 may be formed using a conventional silicon substrate or a silicon substrate having a high specific resistance, and the insulating layer 120 may be provided on the upper surface of the substrate 110 to electrically isolate the substrate 110 from the resonator 135. The insulating layer 120 may be formed by forming at least one of silicon dioxide (SiO2) and aluminum oxide (Al2O3) on the substrate 110 by any one of chemical vapor deposition, RF magnetron sputtering, and evaporation.

[0066] Air cavity 112 may be provided on insulating layer 120. Air cavity 112 may be located below resonator 135 so that resonator 135 can vibrate in a predetermined direction. Air cavity 112 may be formed by forming sacrificial layer 130 on insulating layer 120, forming a film on sacrificial layer 130, and then etching and removing a portion of sacrificial layer 130.

[0067] A seed layer for improving the crystal orientation of the piezoelectric layer 150 may be additionally provided under the first electrode 140. For example, the seed layer may be formed using one of aluminum nitride (AlN), zinc oxide (ZnO), and lead zirconate titanate (PZT, PbZrTiO) having the same crystallinity as that of the piezoelectric layer 150.

[0068] The protective layer 170 may be disposed on the second electrode 160 of the resonator 135 to prevent the second electrode 160 from being exposed to the outside. The protective layer 170 may be formed using one of a silicon oxide-based insulating material, a silicon nitride-based insulating material, and an aluminum nitride-based insulating material.

[0069] The metal layers 181 and 182 may be electrical connection nodes between a plurality of BAW resonators or electrical connection nodes between a BAW resonator and a connection port, and may be implemented with a material having a relatively low specific resistance, such as gold (Au), a gold-tin (Au-Sn) alloy, copper (Cu), a copper-tin (Cu-Sn) alloy, aluminum (Al), an aluminum alloy, etc., but are not limited thereto.

[0070] An upper surface of at least one of the first electrode 140 and the second electrode 160 of the BAW resonator according to an embodiment of the present disclosure may include at least one concave region.

[0071] Figure 2 is a diagram illustrating the width and depth of a concave region of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0072] Reference Figure 2One surface (inner surface or outer surface) of the BAW resonator according to an embodiment of the present disclosure may include a concave region and an effective region, and may further include a convex region.

[0073] The concave region may have a vertical depth D and a horizontal width W. For example, the depth D may be an average depth of the concave region, and the width W may be an average distance between one side surface of the active region and one side surface of the convex region.

[0074] For example, the concave region may have a groove shape surrounding the active region in a top view. When the concave region has a groove shape, the two concave regions in a cross section obtained by vertically cutting the BAW resonator may correspond to a single three-dimensional concave region. Here, the depth D and width W of the concave region may be the average values ​​of the depth and width of each of the two concave regions in a cross section obtained by vertically cutting the BAW resonator.

[0075] The side surface of the raised region may provide a portion of the vertical boundary surface of the recessed region. The raised region may be the same component as the component (e.g., an electrode) in which the recessed region is formed, and may correspond to the remaining portion of one surface of the BAR, excluding the recessed region and the active region. Depending on the design, the raised region may also be a component (e.g., an electrode) different from the component (e.g., a metal layer) in which the recessed region is formed.

[0076] The side surface of the active area may provide a portion of a vertical boundary surface of the concave area. The height of the active area may be lower than that of the convex area, but is not limited thereto.

[0077] For example, a type II BAW resonator may have a structure in which the concave region is adjacent to and outside the effective region, and the convex region is adjacent to and outside the concave region, and a type I BAW resonator may have a structure in which the convex region is adjacent to and outside the effective region, and the concave region is adjacent to and outside the convex region.

[0078] The magnitude relationship of the resonant frequencies of the concave area, the convex area, and the effective area (the cutoff frequency corresponding to kx=0 in the dispersion curve) can be the following relationship: [Fcutoff_recessed]>[Fcutoff_active]>[Fcutoff_raised], where Fcutoff_recessed represents the cutoff frequency of the concave area, Fcutoff_active represents the cutoff frequency of the effective area, and Fcutoff_raised represents the cutoff frequency of the convex area. Therefore, the convex area and the concave area can be defined as the difference in physical thickness from the effective area, but more basically, they can also be defined as areas with different resonant frequencies for each type. For example, although the concave area, the convex area, and the effective area have the same thickness in appearance, by stacking different types of materials, the concave area, the convex area, and the effective area can be distinguished from each other by having different resonant frequencies or different cutoff frequencies.

[0079] Reference Figure 2 The BAW resonator according to an embodiment of the present disclosure may include a seed layer 138a, a first electrode 140a, a piezoelectric layer 150a, a second electrode 160a, and a protective layer 170a. A concave region may be formed in at least one of the seed layer 138a, the first electrode 140a, the piezoelectric layer 150a, the second electrode 160a, and the protective layer 170a.

[0080] Figures 3A to 3E is a diagram illustrating a concave region of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0081] Reference Figure 3A , a concave region having a depth D may be formed only on the protective layer 170b among the seed layer 138b, the first electrode 140b, the piezoelectric layer 150b, the second electrode 160b, and the protective layer 170b.

[0082] Reference Figure 3B , the concave region having a depth D may be formed only on the protective layer 170c and the second electrode 160c among the seed layer 138c, the first electrode 140c, the piezoelectric layer 150c, the second electrode 160c, and the protective layer 170c. For example, the protective layer 170c may be deposited with a uniform thickness over the entire region of the second electrode 160c in which the concave region is formed.

[0083] Reference Figure 3C , a concave region having a depth D may be formed only on the protective layer 170d, the second electrode 160d, and the piezoelectric layer 150d among the seed layer 138d, the first electrode 140d, the piezoelectric layer 150d, the second electrode 160d, and the protective layer 170d.

[0084] Reference Figure 3D, a concave region having a depth D may be formed only on the protective layer 170e, the second electrode 160e, the piezoelectric layer 150e, and the first electrode 140e among the seed layer 138e, the first electrode 140e, the piezoelectric layer 150e, the second electrode 160e, and the protective layer 170e.

[0085] Reference Figure 3E , a concave region having a depth D may be formed on each of the seed layer 138f, the first electrode 140f, the piezoelectric layer 150f, the second electrode 160f, and the protective layer 170f.

[0086] For example, the first electrode 140f, the piezoelectric layer 150f, the second electrode 160f, and the protective layer 170f may be deposited with uniform thickness over the entire region of the seed layer 138f where the recessed region is formed. That is, the BAW resonator according to an embodiment of the present disclosure may have a plurality of recessed regions formed in different surfaces.

[0087] Figures 4A to 4E is a diagram illustrating a depth difference between a plurality of concave regions of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0088] Reference Figure 4A A recessed region having a deeper depth 2D may be formed on the protective layer 170g among the seed layer 138g, the first electrode 140g, the piezoelectric layer 150g, the second electrode 160g, and the protective layer 170g. A recessed region having a depth D may be formed in the second electrode 160g. For example, the protective layer 170g may be deposited on the second electrode 160g having the recessed region having the depth D with a thickness difference of the depth D.

[0089] Reference Figure 4B , a recessed region having a deeper depth 2D may be formed on the seed layer 138h, the first electrode 140h, the piezoelectric layer 150h, the second electrode 160h, and the protective layer 170h, and a recessed region having a depth D may be formed in each of the second electrode 160h and the piezoelectric layer 150h.

[0090] Reference Figure 4C , a recessed region having a deeper depth 2D may be formed in each of the seed layer 138i, the first electrode 140i, the piezoelectric layer 150i, the second electrode 160i and the protective layer 170i, and a recessed region having a depth D may be formed in the piezoelectric layer 150i.

[0091] Reference Figure 4D, a recessed region having a deeper depth 2D may be formed in each of the seed layer 138j, the first electrode 140j, the piezoelectric layer 150j, the second electrode 160j and the protective layer 170j, and a recessed region having a depth D may be formed in each of the piezoelectric layer 150j and the first electrode 140j.

[0092] Reference Figure 4E , a concave region having a deeper depth 2D may be formed in the protective layer 170k, and concave regions having a depth D may be formed in the seed layer 138k, the first electrode 140k, the piezoelectric layer 150k, and the second electrode 160k, respectively. For example, each of the first electrode 140k, the piezoelectric layer 150k, and the second electrode 160k may be deposited with a uniform thickness over the entire region of the seed layer 138k in which the concave region having the depth D is formed, and the protective layer 170k may be deposited on the second electrode 160k with a thickness difference of the depth D.

[0093] That is, the BAW resonator according to an embodiment of the present disclosure may have a plurality of recessed regions formed in different surfaces, and the plurality of recessed regions may have different depths. Therefore, the product of the depth and width of each of the plurality of recessed regions formed in different surfaces and having different depths may be different from each other.

[0094] Return to reference Figure 2 According to an embodiment of the present disclosure, the sound waves of the convex area of ​​the BAW resonator may have a vibration displacement according to the following Formula 1 according to the wave equation, and the sound waves of the concave area may have a vibration displacement according to the following Formula 2 according to the wave equation, and the sound waves of the effective area may have a vibration displacement according to the following Formula 3.

[0095] Formula 1

[0096]

[0097] Formula 2

[0098]

[0099] Formula 3

[0100]

[0101] β1 is kx(1 / μm) (the propagation number (or wave number) of the convex area), β2 is kx(1 / μm) (the propagation number (or wave number) of the concave area), U is the vibration displacement constant, is a phase constant, and x is a coordinate in a direction corresponding to the width.

[0102] The vibration displacement and stress (including the slope component of the vibration displacement) may be continuous at the interface between the convex region and the concave region and at the interface between the concave region and the effective region.

[0103] The following Equation 4 represents a combination of Equations 1 and 2, and a wave equation in a state where the x value at the interface between the convex region and the concave region is defined as 0.

[0104] Formula 4

[0105]

[0106] The following Equation 5 represents a combination of Equation 2, Equation 3, and a wave equation in a state where the value of x at the interface between the recessed region and the effective region is defined as W.

[0107] Formula 5

[0108]

[0109] According to Equation 4 and Equation 5, the width W can be 2 and β2 as the resulting values ​​of the functions of the variables, and 2 may be a result value of a function to which β1 and β2 are applied as variables.

[0110] When the width of the concave area is closer to the width according to Equations 4 and 5, the effective area is in a piston mode state with basically no surface acoustic waves, thereby suppressing parasitic resonance. In the convex area, energy leakage can be suppressed by attenuating the acoustic waves, and the concave area can also be smoothly connected between the effective area and the convex area.

[0111] For example, when the width of the concave region is closer to the width according to Equations 4 and 5, spurious noise in a frequency range below the resonant frequency of the BAW resonator can be reduced, the resonant frequency can be formed more sharply, and the insertion loss near the resonant frequency can be reduced. Therefore, the roll-off characteristics of the filter including the BAW resonator can be improved, and energy loss (e.g., insertion loss and return loss) can be reduced.

[0112] Figure 5 is a graph showing that the number of acoustic waves increases as the depth of the plurality of concave regions increases.

[0113] Figure 5D09 represents a dispersion curve, i.e., a curve of change of the wave number (β1) according to the frequency (Freq) of the convex region, D10 represents a dispersion curve, i.e., a curve of change of the wave number according to the frequency (Freq) of the effective region, D11 represents a dispersion curve, i.e., a curve of change of the wave number (β2) according to the frequency (Freq) when the depth D of the concave region is the shortest, D12 represents a dispersion curve, i.e., a curve of change of the wave number (β2) according to the frequency (Freq) when the depth D of the concave region is the second shortest, D13 represents a dispersion curve, i.e., a curve of change of the wave number (β2) according to the frequency (Freq) when the depth D of the concave region is the third shortest, D14 represents a dispersion curve, i.e., a curve of change of the wave number (β2) according to the frequency (Freq) when the depth D of the concave region is the fourth shortest, and D15 represents a dispersion curve, i.e., a curve of change of the wave number (β2) according to the frequency (Freq) when the depth D of the concave region is the fifth shortest.

[0114] The wave number is a physical value determined by the physical properties and thickness of the corresponding region and corresponds to kx (propagation number). When kx is negative, it represents the imaginary value of a complex number (real number + imaginary number). In other words, the real value of kx represents the vibration of the sound wave, the imaginary value of kx represents the attenuation of the sound wave, and the complex value of kx represents the attenuation of the sound wave during vibration.

[0115] Reference Figure 5 , the wave number of the effective area at 3.5 GHz may be 0, the wave number of the convex area at 3.5 GHz may be a negative number, and the wave number of the concave area at 3.5 GHz may be a positive number, and the wave number may increase as the depth of the concave area increases.

[0116] Figure 6A and Figure 6B is a graph showing an optimal area curve of a concave region located on the upper surface of the second electrode.

[0117] When the general Figure 5 When the wave number at a specific frequency (e.g., 3.5 GHz) is applied to Equations 4 and 5, it can be seen that the optimal width and depth of the concave region are inversely proportional to each other, and an equation such as Figure 6A Here, the optimal area refers to the product of width and depth.

[0118] Reference Figure 6B , since the optimal area (depth × width) in the optimal area curve R24 can be around 0.015 (μm) 2 Therefore, the middle value of the optimal area range of the concave region can be 0.015 (μm) 2 , and since the maximum deviation of the optimal area range of the concave region can be about 0.007 (μm) 2, so the optimal area range of the concave region can be greater than or equal to 0.008 (μm) 2 And less than or equal to 0.022 (μm) 2 .

[0119] Figure 6A and Figure 6B , but since the physical properties and thicknesses of the first and second electrodes may be similar, the optimal area curve for the structure in which the recessed region is formed in the first electrode may also be similar to Figure 6A and 6B The optimal area curve.

[0120] Therefore, in the BAW resonator according to the embodiment of the present disclosure, the BAW resonator according to the embodiment of the present disclosure can have improved performance (e.g., parasitic noise reduction, sharpness of (anti-)resonance frequency, etc.) based on the width of the concave region (close to the width according to Formula 5) by including the following structure: the product (D×W) of the depth D and the width W of the concave region formed in the first electrode and the second electrode is greater than or equal to 0.008 (μm) 2 And less than or equal to 0.022 (μm) 2 .

[0121] Reference Figure 6B , when the depth D of the concave region is less than 1% of the thickness of the piezoelectric layer, the slope of the optimal area (depth×width) in the optimal area curve R24 may be relatively steep.

[0122] The depth D of the recessed region can be greater than or equal to 1% of the thickness of the piezoelectric layer. Therefore, since the optimal area (depth × width) can be stable, the influence of dispersion in the manufacturing process of the BAW resonator can be minimized. However, depending on the structure, shape, material, and required standards of the BAW resonator, the depth D of the recessed region can be designed to be less than 1% of the thickness of the piezoelectric layer.

[0123] Alternatively, the depth of the concave region may be greater than or equal to 5 nm. Therefore, it is possible to prevent the depth of the concave region from being greatly affected by dispersion in the process of manufacturing the BAW resonator when the depth of the concave region is too thin.

[0124] Figure 6C and Figure 6D is a graph showing optimal area curves of the concave regions located on the upper surfaces of the seed layer, the first electrode (lower electrode), the piezoelectric layer, the second electrode (upper electrode), and the protective layer.

[0125] Reference Figure 6C and Figure 6D, the optimal area curves R31 and R41 of the seed layer may be different from each other, the optimal area curves R32 and R42 of the first electrode may be different from each other, the optimal area curves R33 and R43 of the piezoelectric layer may be different from each other, the optimal area curves R34 and R44 of the second electrode may be different from each other, and the optimal area curves R35 and R45 of the protective layer may be different from each other.

[0126] The optimal area curves R31 and R41 for the seed layer can be based on values ​​for a seed layer containing AlN, the optimal area curves R33 and R43 for the piezoelectric layer can be based on values ​​for a piezoelectric layer containing ScAlN, the optimal area curves R35 and R45 for the protective layer can be based on values ​​for a protective layer containing SiO2, and the optimal area curves R32 and R42 for the first electrode and R34 and R44 for the second electrode, respectively, can be based on values ​​for the first electrode and the second electrode containing molybdenum (Mo). Depending on the design, the seed layer or protective layer can be replaced with the same or different materials, such as AlN or SiO2, and in this case, the relative positions of the curves can also be changed. Furthermore, depending on the design, the scandium (Sc) concentration of the piezoelectric layer ScAlN can be increased from 0 at.%.

[0127] The overall optimal area (depth × width) of the seed layer may be greater than the overall optimal area (depth × width) of the protective layer, the overall optimal area (depth × width) of the protective layer may be greater than the overall optimal area (depth × width) of the piezoelectric layer, and the overall optimal area (depth × width) of the piezoelectric layer may be greater than the overall optimal area (depth × width) of the first electrode and / or the second electrode.

[0128] Therefore, the BAW resonator according to an embodiment of the present disclosure may include a plurality of recessed regions, and the optimal area (depth × width) of the recessed region formed in the seed layer among the plurality of recessed regions may be greater than the optimal area (depth × width) of the recessed region formed in the protective layer, the optimal area (depth × width) of the recessed region formed in the protective layer among the plurality of recessed regions may be greater than the optimal area (depth × width) of the recessed region formed in the piezoelectric layer, and the optimal area (depth × width) of the recessed region formed in the piezoelectric layer among the plurality of recessed regions may be greater than the optimal area (depth × width) of the recessed region formed in the first electrode and / or the second electrode. For example, one of the depth and width of each component may be the same, and the other may be different.

[0129] Therefore, in the BAW resonator according to the embodiment of the present disclosure, since each of the plurality of recessed regions can have a structure close to the optimal area (depth×width), the BAW resonator can have improved performance (e.g., parasitic noise reduction, sharpness of (anti-)resonance frequency, etc.) based on the width of the recessed region (close to the width according to Equations 4 and 5).

[0130] Figure 7A and Figure 7B is a graph showing a difference in dispersion curves when a concave region having the same depth is formed in each of the seed layer, the first electrode, the piezoelectric layer, the second electrode, and the protective layer, compared to an active region.

[0131] Reference Figure 7A and Figure 7B , kx according to the frequency (Freq) of the active area, kx according to the frequency (Freq) of the seed layer, kx according to the frequency (Freq) of the protective layer, kx according to the frequency (Freq) of the piezoelectric layer PZL, and kx according to the frequency (Freq) of the first electrode BE and the second electrode TE may be different from each other. Figure 6C and Figure 6D The optimal area curve shown in can be a value based on this. The amount of shift in the dispersion curve varies depending on which layer the concave region is formed on, so the value of kx that satisfies the cutoff frequency of the effective region can differ from layer to layer. Due to this effect, the optimal area of ​​the concave region can be different for each layer.

[0132] Figure 7A and Figure 7B The specific value of kx shown in may vary slightly depending on the position, material, density, stiffness, and thickness of each of the seed layer, first electrode, piezoelectric layer, second electrode, and protective layer, and is a value when the depth of the recessed region is 10 nm. A BAW resonator according to an embodiment of the present disclosure may be in either the TE1 mode or the SE2 mode depending on the frequency of the RF signal. The TE1 mode is a first-order thickness longitudinal vibration mode and may be the primary mode of the BAW resonator. The SE2 mode is a second-order shear horizontal mode.

[0133] Figure 8A and Figure 8B is a graph showing an optimal area curve in which a thickness variation of the piezoelectric layer is added to the optimal area curve of the concave region located on the upper surfaces of the seed layer, the first electrode, the piezoelectric layer, the second electrode, and the protective layer.

[0134] Figure 8A shows the optimal area curve when the thickness of the piezoelectric layer is 345 nm, and Figure 8B The optimum area curve is shown when the thickness of the piezoelectric layer is 600 nm.

[0135] Reference Figure 8A and Figure 8BThe optimal area curves R51 and R61 of the seed layer, the optimal area curves R52 and R62 of the first electrode, the optimal area curves R53 and R63 of the piezoelectric layer, the optimal area curves R54 and R64 of the second electrode, and the optimal area curves R55 and R65 of the protective layer may have steep slopes when the depth D of the recessed area is less than 1% of the thickness of the piezoelectric layer, and may have gentle slopes when the depth D of the recessed area is greater than or equal to 1% of the thickness of the piezoelectric layer.

[0136] That is, regardless of the location or number of recessed regions in a BAW resonator according to embodiments of the present disclosure, the depth D of the recessed regions can be greater than or equal to 1% of the thickness of the piezoelectric layer. Therefore, since the optimal area (depth × width) can be stable, the effect of variations in the BAW resonator manufacturing process can be minimized. However, depending on the structure, shape, material, and required standards of the BAW resonator, the depth D of the recessed regions can also be designed to be less than 1% of the thickness of the piezoelectric layer.

[0137] Figure 9A and Figure 9B is a graph showing changes in optimal areas according to depths of concave regions located on upper surfaces of the seed layer, the first electrode, the piezoelectric layer, the second electrode, and the protective layer.

[0138] Figure 9A shows the optimal area curve when the thickness of the piezoelectric layer is 345 nm, and Figure 9B The optimum area curve is shown when the thickness of the piezoelectric layer is 600 nm.

[0139] Reference Figure 9A and Figure 9B , the optimal area curves R72 and R82 of the first electrode, the optimal area curves R73 and R83 of the piezoelectric layer, and the optimal area curves R74 and R84 of the second electrode may have saturated characteristics in a specific optimal area, and the optimal area curves R71 and R81 of the seed layer and the optimal area curves R75 and R85 of the protective layer may not have the characteristics of saturating the optimal area, and may be saturated when the depth is deeper.

[0140] The optimum area curves of the piezoelectric layer R73 and R83 have an optimum area (depth × width) of approximately 0.02 (μm). 2 and 0.024 (μm) 2 and the maximum deviation of the optimal area range of the concave region can be about 0.008 (μm). 2 Therefore, the optimal area range of the concave region of the piezoelectric layer can be greater than or equal to 0.012 (μm) 2 And less than or equal to 0.032 (μm) 2For example, the optimal area range (D×W) of the concave region of the piezoelectric layer may be greater than or equal to 0.015 (μm) 2 And less than or equal to 0.03 (μm) 2 .

[0141] The piezoelectric layer of the BAW resonator according to an embodiment of the present disclosure may have a concave region, and a product (D×W) of a depth D and a width W of the concave region may be greater than or equal to 0.012 (μm). 2 And less than or equal to 0.032 (μm) 2 , so that the BAW resonator can have improved performance (eg, spurious noise reduction, sharpness of (anti-)resonance frequency, etc.) based on the width of the concave region (close to the width according to Equations 4 and 5).

[0142] also, Figure 9A The values ​​of the optimal area curve are based on the values ​​of the protective layer having a thickness of 130 nm, the second electrode having a thickness of 174 nm, the first electrode having a thickness of 215 nm, and the seed layer having a thickness of 57 nm, and Figure 9B The values ​​of the optimal area curve are based on a protective layer having a thickness of 130 nm, a second electrode having a thickness of 120 nm, a first electrode having a thickness of 161 nm, and a seed layer having a thickness of 57 nm.

[0143] For example, since the thickness of the second electrode can be 174 nm or less, the depth D of the recessed region formed in the upper surface of the second electrode can be 5 / 174 times or greater and less than the thickness of the second electrode. Therefore, since the optimal area (depth × width) can be stable, the effect of variations in the process of manufacturing the BAW resonator can be minimized.

[0144] Figure 10A and Figure 10B is a graph showing a difference in spurious noise in a frequency range below the resonance frequency according to the presence or absence of a concave region.

[0145] Reference Figure 10A and Figure 10B Since the ripple of the S parameter (S11) SR of the BAW resonator having the recessed region may be smaller than the ripple of the S parameter (S11) SW of the BAW resonator not having the recessed region, the BAW resonator having the recessed region may have lower spurious noise.

[0146] Figure 11A is a graph showing spurious noise according to the product of the width and depth of a concave region.

[0147] Reference Figure 11A , when the product of the width and depth of the concave region of the first electrode and / or the second electrode is greater than or equal to 0.010 (μm)2 And less than or equal to 0.016 (μm) 2 When , the parasitic noise can be the lowest. Figure 11A The values ​​in are based on a recessed region having a depth of 8 nm.

[0148] Therefore, the BAW resonator according to an embodiment of the present disclosure may have a concave region in which the product of the width and the depth of the concave region of the first electrode and / or the second electrode is greater than or equal to 0.010 (μm). 2 And less than or equal to 0.016 (μm) 2 , which can also reduce parasitic noise.

[0149] Figure 11B is a graph showing an optimal area according to a resonance frequency of a concave region of a first electrode and / or a second electrode.

[0150] Reference Figure 11B The curve SN of the optimal area (width×depth) of the concave region of the first electrode and / or the second electrode may be an exponential function of the resonance frequency and may be an approximate curve based on a plurality of points (according to fabricated data). Figure 11B The values ​​in the table are based on 4900 (μm) 2 The value of the resonator's width in the horizontal direction.

[0151] Therefore, [{ln(D×W)} / {−0.59×F}] of the concave region of the first electrode and / or the second electrode of the BAW resonator according to an embodiment of the present disclosure may be greater than or equal to [[ln{0.008(μm) 2}] / {-0.59×(3.5GHz)}] and less than or equal to [[ln{0.022(μm) 2}] / {-0.59×(3.5 GHz)}]. Here, F may represent the resonant frequency of the BAW resonator and may be determined based on the size of the BAW resonator. ln is a natural logarithm. Therefore, the BAW resonator according to an embodiment of the present disclosure may have improved performance (e.g., reduced spurious noise, sharpness of (anti-)resonance frequency, etc.) over a wide frequency range.

[0152] FIG. 12 is a graph showing spurious noise according to the width of a concave region.

[0153] Reference Figure 12A When the depth D2 of the concave region of the first electrode and / or the second electrode is 8 nm and the width of the concave region is 1.4 μm, the parasitic noise can be minimized. When the concave region has a large depth D1, the width of the concave region corresponding to the lowest parasitic noise can be shortened, and when the concave region has a small depth D3, the width of the concave region corresponding to the lowest parasitic noise can be lengthened.

[0154] For example, when the depth of the concave region of the first electrode and / or the second electrode is 10 nm, the optimal width of the concave region may be 3.6 μm. For example, when the depth of the concave region of the first electrode and / or the second electrode is 20 nm, the optimal width of the concave region may be 1.8 μm.

[0155] Figure 12B is a graph showing the optimum area of ​​the concave region of the piezoelectric layer according to the resonance frequency.

[0156] Reference Figure 12B , a curve SN of the optimal area (width×depth) of the concave region of the piezoelectric layer may be an exponential function of the resonance frequency and may be an approximate curve based on a plurality of points (according to fabricated data). Figure 12B The value is based on 4900 (μm) 2 The value of the resonant frequency of the width in the horizontal direction.

[0157] Therefore, the [{ln(D×W)} / {−0.412×F}] of the concave region of the BAW resonator according to an embodiment of the present disclosure may be greater than or equal to [[ln{0.015(μm) 2}] / {-0.412×(3.5GHz)}] and less than or equal to [[ln{0.015(μm) 2}] / {-0.412×(3.5 GHz)}]. Therefore, the BAW resonator according to the embodiment of the present disclosure may have improved performance (eg, spurious noise reduction, sharpness of (anti-)resonance frequency, etc.) over a wide frequency range.

[0158] Figure 13 is a diagram illustrating a specific form of a bulk acoustic wave resonator according to an embodiment of the present disclosure.

[0159] Reference Figure 13 The bulk acoustic wave resonator according to an embodiment of the present disclosure may include at least a portion of a substrate 110, a cavity (or air cavity) 112, an insulating layer 120, a sacrificial layer 130, an etch stop layer 132, a seed layer 138, a first electrode 140, a piezoelectric layer 150, a second electrode 160, a protective layer 170, an insertion layer 172, and a metal pad 180. Figure 13 At least a portion of the structure shown may have Figure 1 The structure of the bulk acoustic wave resonator shown is at least partially the same material, or can be formed by Figure 1 At least a portion of the structure of the BAW resonator shown is formed using the same or similar process.

[0160] The piezoelectric layer 150 , the second electrode 160 , and / or the protective layer 170 may include a concave region, and may also include a convex region and an active region.

[0161] The insertion layer 172 may be formed on the upper surface of the first electrode 140 so that the piezoelectric layer 150, the second electrode 160, and / or the protective layer 170 have a recessed area. For example, the insertion layer 172 and the etch stop layer 132 may have an insulating material that is the same as or similar to that of the insulating layer 120 and may be formed using a process that is the same as or similar to the process for forming the insulating layer 120.

[0162] As described above, according to one or more embodiments of the present disclosure, a BAW resonator can reduce parasitic noise of the BAW resonator, more sharply form the resonant frequency of the BAW resonator, and reduce insertion loss near the resonant frequency. Consequently, the roll-off characteristics of a filter including the BAW resonator can be improved, and energy loss (e.g., insertion loss and return loss) can be reduced.

[0163] Although specific example embodiments have been shown and described above, it will be readily understood after understanding this disclosure that various changes may be made to these examples in form and detail without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only and not for purposes of limitation. The description of the features or aspects in each example will be considered to be applicable to similar features or aspects in other examples. Suitable results may be obtained if the described techniques are performed in a different order, and / or if the components in the described systems, architectures, devices, or circuits are combined in different ways, and / or if the components in the described systems, architectures, devices, or circuits are replaced or added by other components or their equivalents. Therefore, the scope of this disclosure is not limited by the specific embodiments, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents will be interpreted as being included in this disclosure.

Claims

1. A bulk acoustic wave resonator, comprising: a first electrode disposed on an upper side of the substrate; a piezoelectric layer, disposed on an upper surface of the first electrode; as well as a second electrode disposed on the upper surface of the piezoelectric layer, wherein the upper surface of at least one of the first electrode and the second electrode has a concave area, Wherein, the depth of the concave region is D, the width of the concave region is W, and the resonant frequency is F, and ln is the natural logarithm, and Where, [{ln(D×W)} / (-0.59×F)] is greater than or equal to [[ln{0.008(μm) 2 }] / {-0.59×(3.5GHz)}] and less than or equal to [[ln{0.022(μm) 2 }] / {-0.59×(3.5GHz)}].

2. The bulk acoustic wave resonator according to claim 1, wherein D×W greater than or equal to 0.008 (μm) 2 And less than or equal to 0.022 (μm) 2 .

3. The bulk acoustic wave resonator according to claim 2, wherein D×W is greater than or equal to 0.010 (μm) 2 And less than or equal to 0.016 (μm) 2 .

4. The bulk acoustic wave resonator according to any one of claims 1 to 3, wherein: D is greater than or equal to 5nm.

5. The bulk acoustic wave resonator according to any one of claims 1 to 3, wherein: D is greater than or equal to 1% of the thickness of the piezoelectric layer.

6. The bulk acoustic wave resonator according to any one of claims 1 to 3, wherein: The recessed area is located on the upper surface of the second electrode, and Wherein, D is greater than or equal to 5 / 174 times the thickness of the second electrode and less than the thickness of the second electrode.

7. The bulk acoustic wave resonator according to any one of claims 1 to 3, wherein: Each of the first electrode and the second electrode includes molybdenum.

8. The bulk acoustic wave resonator according to any one of claims 1 to 3, wherein: The upper surface of the piezoelectric layer has a concave area, and A product of a depth and a width of the concave region of at least one of the first electrode and the second electrode is smaller than a product of a depth and a width of the concave region of the piezoelectric layer.

9. The BAW resonator according to claim 8, further comprising a protective layer provided on the upper surface of the second electrode, in, The upper surface of the protective layer has a concave area, and The product of the depth and width of the concave region of the piezoelectric layer is smaller than the product of the depth and width of the concave region of the protective layer.

10. The BAW resonator according to claim 9, further comprising a seed layer provided on a lower surface of the first electrode, in, The upper surface of the seed layer has a concave area, and The product of the depth and width of the concave region of the protection layer is smaller than the product of the depth and width of the concave region of the seed layer.

11. The bulk acoustic wave resonator according to claim 10, wherein The seed layer includes AlN, and Wherein, the protective layer includes SiO2.

12. A bulk acoustic wave resonator, comprising: a first electrode disposed on an upper side of the substrate; a piezoelectric layer, disposed on an upper surface of the first electrode; as well as a second electrode disposed on the upper surface of the piezoelectric layer, wherein the upper surface of the piezoelectric layer has a concave area, Wherein, the depth of the concave region is D, the width of the concave region is W, the resonant frequency is F, and ln is the natural logarithm, wherein D is greater than or equal to 1% of the thickness of the piezoelectric layer and less than 100% of the thickness of the piezoelectric layer, and Where, [{ln(D×W)} / (-0.412×F)] is greater than or equal to [[ln{0.015(μm) 2 }] / {-0.412×(3.5GHz)}] and less than or equal to [[ln{0.03(μm) 2 }] / {-0.412×(3.5GHz)}].

13. The BAW resonator according to claim 12, wherein: D×W greater than or equal to 0.015 (μm) 2 And less than or equal to 0.03 (μm) 2 .

14. The BAW resonator according to claim 12 or 13, further comprising a protective layer provided on the upper surface of the second electrode, in, The upper surface of the protective layer has a concave area, and The product of the depth and width of the concave region of the piezoelectric layer is smaller than the product of the depth and width of the concave region of the protective layer.

15. The BAW resonator according to claim 12 or 13, further comprising a seed layer provided on a lower surface of the first electrode. in, The upper surface of the seed layer has a concave area, and The product of the depth and width of the concave region of the piezoelectric layer is smaller than the product of the depth and width of the concave region of the seed layer.

16. A bulk acoustic wave resonator, comprising: seed layer; a first electrode disposed on an upper surface of the seed layer; a piezoelectric layer, disposed on an upper surface of the first electrode; a second electrode disposed on the upper surface of the piezoelectric layer; as well as a protective layer disposed on the upper surface of the second electrode, In which, the upper surfaces of at least two of the seed layer, the first electrode, the piezoelectric layer, the second electrode and the protective layer respectively have a first concave area and a second concave area, and the product of the depth and width of the first concave area is different from the product of the depth and width of the second concave area.

17. The BAW resonator according to claim 16, wherein: The first concave region is located on an upper surface of at least one of the first electrode and the second electrode, wherein the second concave region is located on an upper surface of at least one of the seed layer, the piezoelectric layer, and the protective layer, and The product of the depth and width of the first concave region is smaller than the product of the depth and width of the second concave region.

18. The BAW resonator according to claim 17, wherein Each of the first electrode and the second electrode includes molybdenum, and Wherein, at least one of the seed layer, the piezoelectric layer and the protective layer includes at least one of AlN, ScAlN and SiO2.

19. The BAW resonator according to claim 16, wherein: The first concave region is located on an upper surface of at least one of the first electrode, the piezoelectric layer, and the second electrode, wherein the second concave region is located on an upper surface of at least one of the seed layer and the protective layer, and The product of the depth and width of the first concave region is smaller than the product of the depth and width of the second concave region.

20. The BAW resonator of claim 16, wherein: The first concave region is located on an upper surface of at least one of the first electrode, the piezoelectric layer, the second electrode, and the protective layer. wherein the second concave region is located on the upper surface of the seed layer, and The product of the depth and width of the first concave region is smaller than the product of the depth and width of the second concave region.

21. The bulk acoustic wave resonator according to any one of claims 16 to 20, wherein: The seed layer includes AlN, and Wherein, the protective layer includes SiO2.

22. The bulk acoustic wave resonator according to any one of claims 16 to 20, wherein: The first concave region and the second concave region have different depths.

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