CN111193489B - Bulk acoustic wave resonator, filter, and electronic device - Google Patents
Bulk acoustic wave resonator, filter, and electronic device Download PDFInfo
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- CN111193489B CN111193489B CN201811355093.4A CN201811355093A CN111193489B CN 111193489 B CN111193489 B CN 111193489B CN 201811355093 A CN201811355093 A CN 201811355093A CN 111193489 B CN111193489 B CN 111193489B
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Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
- H03H9/02007—Details of bulk acoustic wave devices
- H03H9/02015—Characteristics of piezoelectric layers, e.g. cutting angles
- H03H9/02039—Characteristics of piezoelectric layers, e.g. cutting angles consisting of a material from the crystal group 32, e.g. langasite, langatate, langanite
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
- H03H9/02244—Details of microelectro-mechanical resonators
Landscapes
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
Abstract
The invention relates to a bulk acoustic wave resonator comprising: a substrate; an acoustic mirror; a bottom electrode disposed over the substrate; a top electrode facing the bottom electrode, the top electrode having a main body portion and a connection portion connected to the main body portion; the piezoelectric layer is arranged above the bottom electrode and between the bottom electrode and the top electrode, and rare earth elements are doped in the piezoelectric layer; and a passivation layer disposed over the top electrode, wherein: the area where the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode overlap in the thickness direction of the substrate is an effective area of the resonator, the passivation layer is adjacent to the boundary of the effective area, at least one first fracture structure is arranged above the connecting part, and rare earth elements are doped in the piezoelectric layer. The invention also relates to a filter with the resonator, and an electronic device with the filter.
Description
Technical Field
Embodiments of the present invention relate to acoustic wave resonators, and more particularly, to a bulk acoustic wave resonator and a method of manufacturing the same, a filter having the resonator, and an electronic apparatus having the filter.
Background
With the rapid development of wireless communication technology, there is an increasing demand for multi-passband transceivers capable of simultaneously processing large amounts of data. In recent years, multi-passband transceivers have been widely used in positioning systems and multi-standard systems that require processing of signals in different frequency bands simultaneously to improve the overall performance of the system. Although the number of frequency bands in a single chip is increasing, consumer demand for miniaturized, multifunctional portable devices is increasing, and miniaturization is becoming a trend of chip development, which puts higher demands on the size of the filter.
For this reason, a thin film bulk acoustic resonator (Film Bulk Acoustic Resonator, abbreviated as FBAR) has been used in the prior art to replace the conventional waveguide technology for realizing a multiband filter.
The FBAR mainly utilizes the piezoelectric effect and the inverse piezoelectric effect of the piezoelectric material to generate bulk acoustic waves, so that resonance is formed in the device, and the FBAR has a series of inherent advantages of high quality factor, large power capacity, high frequency (up to 2-10GHz or even higher), good compatibility with a standard Integrated Circuit (IC) and the like, and can be widely applied to radio frequency application systems with higher frequency.
The structural body of the FBAR is a sandwich structure consisting of an electrode, a piezoelectric film and an electrode, namely a layer of piezoelectric material is sandwiched between two metal electrode layers. By inputting a sinusoidal signal between the two electrodes, the FBAR converts an input electrical signal into mechanical resonance using an inverse piezoelectric effect, and converts the mechanical resonance into an electrical signal output using a piezoelectric effect. The FBAR mainly uses the longitudinal piezoelectric coefficient (d 33) of the piezoelectric film to generate a piezoelectric effect, so that its main operation mode is a longitudinal wave mode (Thickness Extensional Mode, abbreviated as TE mode) in the thickness direction. Electromechanical coupling coefficient Kt 2 The value is an important parameter of the resonator, which represents the ability of the resonator to convert mechanical and electrical energy. Kt under the condition that other performance indexes of the resonator are the same 2 The larger the value the better the performance of the resonator.
Ideally, a thin film bulk acoustic resonator excites only the thickness-wise (TE) mode, but in addition to the desired TE mode, a transverse parasitic mode is created, such as a rayleigh-lamb mode that is a mechanical wave perpendicular to the direction of the TE mode. These transverse mode waves will be lost at the boundaries of the resonator, resulting in a loss of energy in the longitudinal mode required by the resonator, ultimately leading to a drop in the Q value of the resonator. By forming a fracture structure at the step of the passivation layer of the resonator or at the edge of the piezoelectric layer and the top electrode, the acoustic wave at the edge can be reflected back into the resonator, and at the same time, a part of energy can be converted into a mode of vibration in the vertical direction, so that the Q value of the resonator can be improved.
However, the existence of the fracture structure can lead the Q value of the resonator to be improved and simultaneously lead the electromechanical coupling coefficient of the resonator to be Kt 2 Is a drop in (c). For example, as the depth of the fracture structure increases, the energy of the transverse mode wave reflected back into the resonator increases due to the fracture structure, therebyResulting in a relatively reduced acoustic wave energy in the vertical mode in the resonator such that the electromechanical coupling coefficient of the resonator is reduced.
Disclosure of Invention
To alleviate or solve the electromechanical coupling coefficient of resonator, kt, caused by the arrangement of fracture structure in FBAR 2 The invention proposes to dope the piezoelectric layer material with rare earth elements.
According to an aspect of an embodiment of the present invention, there is provided a bulk acoustic wave resonator including: a substrate; an acoustic mirror; a bottom electrode disposed over the substrate; a top electrode facing the bottom electrode, the top electrode having a main body portion and a connection portion connected to the main body portion; a piezoelectric layer disposed above the bottom electrode and between the bottom electrode and the top electrode, the piezoelectric layer being doped with rare earth elements; and a passivation layer disposed over the top electrode, wherein: the area where the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode overlap in the thickness direction of the substrate is an effective area of the resonator, and the passivation layer is adjacent to the boundary of the effective area and is provided with at least one first fracture structure above the connecting part.
When the piezoelectric material is doped with rare earth element, the atomic radius of rare earth element is relatively large, so that the stress in the piezoelectric material is changed, and the electric dipole in the piezoelectric material is changed, and when an electric field is applied to the piezoelectric material, a larger mechanical response is generated in the piezoelectric material, and the resonator can obtain a higher electromechanical coupling coefficient (Kt 2 )。
Optionally, the connecting portion has an inclined surface, and the first breaking structure is disposed at the inclined surface. Further, the connection portion forms a bridge structure, an air gap is formed between the bridge structure and the piezoelectric layer, the inclined surface includes a first inclined surface of the bridge structure adjacent to the boundary and a second inclined surface adjacent to the top electrode lead, and the first breaking structure is disposed at the first inclined surface. Further, the passivation layer further includes at least one second breaking structure disposed at the second inclined surface.
Optionally, the connection portion is a horizontal connection portion.
Optionally, the top electrode is further provided with a bridge wing structure on a side opposite to the connecting portion, the bridge wing structure is provided with a bridge wing inclined plane, and an air gap is formed between the bridge wing structure and the piezoelectric layer. Further, the passivation layer further includes at least one third fracture structure disposed over the bridge wing bevel.
In the above resonator, optionally, the depth of the fracture structure is smaller than the thickness of the passivation layer. Further, the depth of the fracture structure is 5% -30% of the thickness of the passivation layer. Optionally, the depth of the fracture structure is in the range of
In the resonator, optionally, at least part of the fracture structure has a depth equal to the thickness of the passivation layer. Optionally, the passivation layer has a thickness ranging from
In the above resonator, optionally, at least one fourth fracture structure is provided in the piezoelectric layer below the top electrode or laterally outside the top electrode, adjacent to a boundary of the effective region. Further, the width of the fourth fracture structure is 1-10% of the lateral width of the effective area. Further, the depth of the fourth fracture structure is 1-15% of the thickness of the piezoelectric layer. Optionally, the depth of the fourth fracture structure is in the range of
In the above resonator, optionally, the width of the fracture structure may have a value ranging from 0.1um to 10um.
In the resonator, the fracture structure may have a cross-sectional shape selected from a circular arc shape, an inclined shape, a stepped shape, and a fan shape.
The above-mentioned harmonicsIn the vibrator, optionally, the doped rare earth element includes one or more elements of 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 yttrium (Y) and scandium (Sc). In an alternative embodiment, the doped rare earth element comprises scandium (Sc). In an alternative embodiment, the piezoelectric layer material is aluminum nitride (ALN), and Al is formed after doping 1-a X a N or Al 1-a- b X a Y b N structure, wherein X, Y represents any two elements among the rare earth elements, and a and b represent the content of the doping element X, Y, respectively. Alternatively, the atomic fraction of doping element X or Y may be 0.5% -30%.
The embodiment of the invention also relates to a filter comprising the bulk acoustic wave resonator.
The embodiment of the invention also relates to electronic equipment comprising the filter.
Drawings
These and other features and advantages of the various embodiments of the disclosed invention will be better understood from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate like parts throughout the several views, and wherein:
FIGS. 1A and 1B are a schematic top view and a cross-sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
fig. 1C, 1D, 1E, 1F schematically illustrate cross-sectional shapes of fracture structures, respectively, as exemplary embodiments of the present invention;
FIGS. 2A and 2B are a schematic top view and a cross-sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
fig. 3A and 3B are a schematic top view and a sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
fig. 4A and 4B are a schematic top view and a sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
FIGS. 5A and 5B are a schematic top view and a cross-sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
fig. 6A and 6B are a schematic top view and a sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
fig. 7 is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the invention;
fig. 8 is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention.
Detailed Description
The technical scheme of the invention is further specifically described below through examples and with reference to the accompanying drawings. In the specification, the same or similar reference numerals denote the same or similar components. The following description of embodiments of the present invention with reference to the accompanying drawings is intended to illustrate the general inventive concept and should not be taken as limiting the invention.
According to the invention, the fracture structure is formed at the edge of the effective area of the resonator, and the acoustic impedance of the fracture structure is not matched with that of the effective area of the resonator, so that the acoustic wave is reflected back into the resonator at the edge, and the leakage of the energy in the resonator is effectively prevented.
A bulk acoustic wave resonator according to an embodiment of the present invention is described below with reference to fig. 1 to 8.
Fig. 1A is a top view of a thin film bulk acoustic resonator in accordance with an exemplary embodiment of the present invention. Referring to fig. 1a, the fbar includes a bottom electrode 105, a piezoelectric layer 107, a top electrode 109, a passivation layer 111, and a breaking structure 113 in the passivation layer above the step where the top electrode 109 and its electrodes are connected.
In all embodiments of the invention, the piezoelectric layer material is doped with rare earth elements.
A typical piezoelectric material is aluminum nitride (AlN), which is a wurtzite structure, i.e., hexagonal system, with a polarization axis direction of (0001).
The doped rare earth elements include: 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 one or more of yttrium (Y) and scandium (Sc). In an alternative embodiment, the doped rare earth element comprises scandium (Sc).
For the piezoelectric material being aluminum nitride (AlN), the doping mode can be that one or any two rare earth elements X and/or Y replace Al atoms in an AlN crystal structure to form Al 1-a X a N or Al 1-a-b X a Y b N structure, wherein X, Y represents any two elements among the above rare earth elements, and a and b represent the content of the doping atoms X, Y. Alternatively, the atomic fraction of the rare earth element X or Y may be 0.5% to 30%, wherein the content of the doped rare earth element X and Y may be the same or different.
The above description of doping may be applied to all embodiments of the invention.
FIG. 1B is a cross-sectional view taken along line 1B-1B of FIG. 1A. As shown in fig. 1B, the resonator sequentially includes a substrate 101 in the thickness direction; an acoustic mirror 103 located on the upper surface of the substrate or embedded within the substrate, the acoustic mirror being formed as a cavity embedded in the substrate in fig. 1B, but any other acoustic mirror structure such as a bragg reflector is equally suitable; a bottom electrode 105; a piezoelectric layer 107 doped with any two rare earth elements; a top electrode 109; a passivation layer 111. The passivation layer can play a role in protecting the electrode, prevents the material from being adsorbed on the surface of the resonator, and eliminates or reduces oxidation and corrosion of devices caused by the influence of ambient air or humid environment, so that the frequency of the resonator is shifted; meanwhile, the passivation layer can be processed, so that the effect of fine tuning the frequency of the resonator can be achieved; and the existence of the passivation layer can reduce the requirement on the closed encapsulation of the resonator, so that the manufacturing cost of the device is reduced.
As shown in fig. 1A and 1B, the passivation layer above the step where the top electrode and its electrode are connected has a fracture structure 113 therein that breaks only partially (i.e., not completely). The cross-sectional shape of the fracture structure 113 may be an inclined shape in fig. 1D or a step in fig. 1E, in addition to the circular arc shape in fig. 1CThe fracture structure has a fixed width w and depth h, as well as other shapes such as the fan shape of fig. 1F. In alternative embodiments, the depth of the fracture structure is less than the thickness of the passivation layer, for example 5% -30% of the thickness of the passivation layer, typically in the w range of 0.1-10um, with h being in depth
In the present invention, w may be 0.1um, 5um, 10um for a quasi-fracture structure that is not completely fractured; h may be
The fracture structure can be obtained through wet etching or dry etching and the like, the width and the depth of the fracture structure can be controlled by controlling the time of wet etching and regulating and controlling the proportion of liquid medicine, or the width and the depth of the fracture structure can be controlled by controlling the time, the power of dry etching and the flow and the proportion of etching gas.
The region where the acoustic mirror 103, the bottom electrode 105, the piezoelectric layer 107, and the top electrode 109 overlap in the thickness direction is an effective region of the resonator, and has a first acoustic impedance and a second acoustic impedance in the break structure 113 of the passivation layer 111. Since the second acoustic impedance in the fracture structure 113 of the passivation layer 111 is not matched with the first acoustic impedance, and meanwhile, due to a certain depth in the fracture structure, the acoustic wave can form local oscillation at the fracture structure, and strong reflection is formed by repeated reflection and superposition of the acoustic wave in the local oscillation area, the unmatched degree can be further increased, so that the acoustic wave is discontinuously transmitted at the boundary of the effective area, and therefore, a part of acoustic energy is coupled and reflected into the effective excitation area at the boundary of the effective area and converted into a piston acoustic wave mode perpendicular to the surface of the piezoelectric layer, and the Q value of the resonator is improved. However, the existence of the fracture structure can bring Kt while increasing the Q value of the resonator 2 Problem of degradation to remedy this defect, we have used to increase the Kt of the piezoelectric layer material by doping it with rare earth elements 2 To make up for the failure of the fracture structureFeet. The shape, depth and width of the fracture structure may be selected for a particular acoustic wavelength to adjust the ability and degree of local oscillation.
Fig. 2A and 2B are a schematic top view and a sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention. Another exemplary embodiment of a bulk acoustic wave resonator is described below with reference to fig. 2A and 2B.
As shown in fig. 2A, the FBAR includes a bottom electrode 205, a piezoelectric layer 207, a top electrode 209, a passivation layer 211, and a breaking structure 213 in the passivation layer above the step where the top electrode and its electrodes are connected.
The piezoelectric resonator structure shown in fig. 2B is similar to the structure of the embodiment shown in fig. 1B, and is a sectional view taken along the plan view 1B-1B. The difference is the broken structure 213 of the passivation layer located over the top electrode and the step where its electrodes are connected. The cross-sectional shape of the fracture structure 213 may be an arc shape in fig. 1C, or may be another shape such as an inclined shape in fig. 1D, a stepped shape in fig. 1E, or a fan shape in fig. 1F, and the fracture structure is broken in such a manner that it is broken to the bottom top electrode and the depth is deep. The depth of the fracture structure 213 is the same as the thickness of the passivation layer, typically w ranges from 0.1 to 10um, and the depth h is
In the present invention, w may be 0.1um, 5um, 10um for a fully broken structure; h may be
The depth of the fracture structure is deeper, so that the degree of mismatch between the second acoustic impedance and the first acoustic impedance of the fracture structure of the passivation layer can be further improved, the transmission discontinuity of the sound wave at the boundary is enhanced, and therefore, more sound energy is coupled and reflected into the effective excitation area at the boundary of the effective area and converted into a piston sound wave mode perpendicular to the surface of the piezoelectric layer, so that the Q value of the resonator is further improved. But is broken offThe existence of the split structure can bring Kt while improving the Q value of the resonator 2 Problem of degradation, in order to compensate for the defect, the piezoelectric layer material is doped with rare earth elements to improve the Kt 2 To make up for the defect of the fracture structure.
Fig. 3A and 3B are a schematic top view and a sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention. Still another exemplary embodiment of a bulk acoustic wave resonator is described below with reference to fig. 3A and 3B.
As shown in fig. 3A, the FBAR includes a bottom electrode 305, a piezoelectric layer 307, a top electrode 309, a passivation layer 311, and a passivation layer having a fracture structure 313 and 315 therein over the step where the top electrode and its electrodes are connected.
The piezoelectric resonator structure shown in fig. 3B is similar to the structure of the embodiment shown in fig. 1B, and is a sectional view taken along the plane of view 1B-1B. The difference is that the breaking portion of the passivation layer above the step where the top electrode and the electrode are connected includes 313 and 315, and the cross-sectional shape of the breaking structure may be circular arc shape in fig. 1C, or may be other shapes such as inclined shape in fig. 1D, stepped shape in fig. 1E, and fan shape in fig. 1F, and the breaking manner is multiple positions including but not limited to two positions, and the breaking depth is shallow. The breaking portion has two fixed widths w1 and w2 and two breaking depths h1 and h2. In alternative embodiments, the depth of the fracture structure is less than the thickness of the passivation layer, for example 5% -30% of the passivation layer thickness, typically w1 and w2 in the range 0.1-10um, and h1 and h2 in depthTherefore, the Q value of the resonator is further improved, and the passivation layer covers the resonant electrode part completely, so that the passivation layer protects the resonator more comprehensively, the adsorption of materials on the surface of the resonator can be effectively prevented, the oxidization and corrosion of devices caused by the influence of surrounding air or humid environment are eliminated or reduced, and the frequency of the resonator is shifted. However, the existence of the fracture structure can bring Kt while increasing the Q value of the resonator 2 Problem of degradation, in order to compensate for the defect, the piezoelectric layer material is doped with rare earth elements to improve the Kt 2 To make up for the defect of the fracture structure.
It is to be noted that, in the present invention, the rare earth elements may be doped one kind or two or more kinds.
Based on the above, the present invention proposes a bulk acoustic wave resonator including: a substrate; an acoustic mirror; a bottom electrode disposed over the substrate; a top electrode facing the bottom electrode, the top electrode having a main body portion and a connection portion connected to the main body portion; the piezoelectric layer is arranged above the bottom electrode and between the bottom electrode and the top electrode, and rare earth elements are doped in the piezoelectric layer; and a passivation layer disposed over the top electrode, wherein: the area where the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode overlap in the thickness direction of the substrate is an effective area of the resonator, and the passivation layer is adjacent to the boundary of the effective area and is provided with at least one first fracture structure above the connecting part.
In fig. 1B, 2B and 3B above, the connection portion may be a junction of the top electrode and its electrode lead, embodied as an inclined surface. The fracture structure is disposed at the inclined surface.
It is to be noted that, in the present invention, the provision of the breaking structure above the connecting portion includes not only the provision of the breaking structure just above the connecting portion (between two vertical boundaries of the connecting portion in the lateral direction) but also the provision of the breaking structure obliquely above the connecting portion.
In the present invention, the fracture structure is provided at the inclined surface, including not only the case of being provided in the range of the inclined surface but also the case of being provided in the vicinity of the inclined surface.
Although not shown, the connection may also be a horizontal connection.
It should be noted that in the passivation layer, the fracture structure may be provided at other locations than above the connection portion.
In the present invention, the electrode constituent material may be gold (Au), tungsten (W), molybdenum (Mo), platinum (Pt), ruthenium (Ru), iridium (Ir), titanium Tungsten (TiW), aluminum (Al), titanium (Ti), or the like.
In the present invention, the piezoelectric layer material may be a material such as aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO 3), quartz (Quartz), potassium niobate (KNbO 3), or lithium tantalate (LiTaO 3).
In the present invention, the passivation layer material may be aluminum nitride (AlN), silicon carbide (SiC), aluminum oxide (Al 2O 3), silicon oxide (SiO 2), silicon nitride (Si 3N 4), or a combination thereof.
Fig. 7 is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention. As shown in fig. 7, the resonator includes a substrate 701 in order in the thickness direction; an acoustic mirror 703 located on the upper surface of the substrate or embedded within the substrate, the acoustic mirror being formed as a cavity embedded in the substrate in fig. 7, but any other acoustic mirror structure such as a bragg reflector is equally suitable; a bottom electrode 705; a piezoelectric layer 707 in which rare earth elements are doped; a top electrode 709 including two parts, namely a main body part and a connecting part, wherein the connecting part is of a bridge wing structure, and an air gap is formed between the connecting part of the top electrode and the piezoelectric layer; the passivation layer 711 includes the breaking structures 715 and 713 at the steps, and the cross-sectional shape of the breaking structures may be arc-shaped in fig. 1C, or may be other shapes such as a slope shape in fig. 1D, a step shape in fig. 1E, and a fan shape in fig. 1F, in which the breaking manner is a partial breaking, and have fixed widths w1, w2 and breaking depths h1, h2. In alternative embodiments, the depth of the fracture structure is less than the thickness of the passivation layer, for example 5% -30% of the passivation layer thickness, typically w1 and w2 are in the range of 0.1-10um, and h1 and h2 are in depth
At the bridge wing structure and the fracture structure, the acoustic impedance of the bridge wing structure and the fracture structure is mismatched with that of the effective area of the resonator due to the existence of the air gap and the fracture structure, so that the acoustic wave is discontinuously transmitted at the boundary, and therefore, a part of acoustic energy is coupled and reflected into the effective excitation area at the boundary of the effective area,and converted into a piston acoustic mode perpendicular to the surface of the piezoelectric layer, so that the Q value of the resonator is increased. However, the existence of the bridge wing structure and the fracture structure can bring Kt while improving the Q value of the resonator 2 Problem of degradation, in order to compensate for the defect, the piezoelectric layer material is doped with rare earth elements to improve the Kt 2 To make up for the defect of the fracture structure.
Fig. 8 is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention. As shown in fig. 8, the resonator includes a base 801 in order in the thickness direction; an acoustic mirror 803, which is located on the upper surface of the substrate or embedded within the substrate, and which in fig. 8 is formed as a cavity embedded in the substrate, but any other acoustic mirror structure such as a bragg reflector is equally suitable; a bottom electrode 805; a piezoelectric layer 807 in which rare earth elements are doped; a top electrode 809 comprising a main body portion and a connection portion, wherein the connection portion is of a bridge structure, and an air gap is provided between the connection portion of the top electrode and the piezoelectric layer; a passivation layer 811 includes the fracture structures 815 and 813 at the steps.
Thus, in the example of fig. 8, for example, the connection forms a bridge structure, an air gap is formed between the bridge structure and the piezoelectric layer, the inclined surfaces comprise a first inclined surface of the bridge structure adjacent to the boundary and a second inclined surface adjacent to the top electrode lead, the fracture structure being provided at the first inclined surface, optionally also at the second inclined surface.
The cross-sectional shape of the fracture structure may be an arc shape in fig. 1C, or may be another shape such as an inclined shape in fig. 1D, a stepped shape in fig. 1E, or a fan shape in fig. 1F, in which the fracture mode is a partial fracture, and has fixed widths w1, w2 and fracture depths h1, h2. In alternative embodiments, the depth of the fracture structure is less than the thickness of the passivation layer, for example 5% -30% of the passivation layer thickness, typically w1 and w2 are in the range of 0.1-10um, and h1 and h2 are in depth
At the bridge structure and the fracture structure, the acoustic impedance of the bridge structure is not matched with that of the effective area of the resonator due to the existence of the air gap and the fracture structure, so that the transmission of sound waves at the boundary of the effective area is discontinuous, and therefore, at the boundary of the effective area, a part of sound energy is coupled and reflected into the effective excitation area and converted into a piston sound wave mode perpendicular to the surface of the piezoelectric layer, and the Q value of the resonator is improved. However, the existence of the bridge structure and the fracture structure can bring Kt while improving the Q value of the resonator 2 Problem of degradation, in order to compensate for the defect, the piezoelectric layer material is doped with rare earth elements to improve the Kt 2 To make up for the defect of the fracture structure.
Fig. 4A and 4B are a schematic top view and a sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention.
As shown in fig. 4A, the FBAR includes a bottom electrode 405, a piezoelectric layer 407, a top electrode 409, a passivation layer 411, and a fracture structure 413 between the top electrode and the piezoelectric layer inside the top electrode and a fracture structure 415 in the passivation layer above the step (corresponding to the connection) where the top electrode and its electrode are connected.
As shown in fig. 4B, the resonator includes a substrate 401 in order in the thickness direction; an acoustic mirror 403 on the upper surface of the substrate or embedded within the substrate, the acoustic mirror being formed as a cavity embedded in the substrate in fig. 4B, but any other acoustic mirror structure such as a bragg reflector is equally suitable; a bottom electrode 407; a piezoelectric layer 407 in which rare earth elements are doped; a top electrode 409; a passivation layer 411; and a fracture structure 413 located inside the top electrode between the top electrode and the piezoelectric layer and a fracture structure 415 in the passivation layer located above the step (corresponding to the connection) where the top electrode and its electrode are connected.
The cross-sectional shapes of the fracture structures 413 and 415 may be circular arc shapes in fig. 1C, or other shapes such as a slope shape in fig. 1D, a step shape in fig. 1E, and a fan shape in fig. 1F, and have fixed widths w1, w2 and fracture depths h1, h2. In alternative embodimentsWherein the ratio of the width w2 of the fracture structure to the transverse width of the effective area of the resonator is 1% -10%, the ratio of the depth of the fracture structure to the thickness of the piezoelectric layer is 1% -15%, the typical ranges of w1 and w2 are 0.1-10um, and the depths of h1 and h2 areThe mechanical strength of the resonator is stronger because the depth of the fracture structure is shallower.
The fracture structure can be obtained through wet etching or dry etching and the like, the width and the depth of the fracture structure can be controlled by controlling the time of wet etching and regulating and controlling the proportion of liquid medicine, or the width and the depth of the fracture structure can be controlled by controlling the time, the power of dry etching and the flow and the proportion of etching gas.
In the embodiment of fig. 4A and 4B, the region where the acoustic mirror, bottom electrode, piezoelectric layer, top electrode overlap in the thickness direction is the active region of the resonator, having a first acoustic impedance, a second acoustic impedance in the break structure 415 of the passivation layer, and a third acoustic impedance in the break structure 413 in the piezoelectric layer. Since the second acoustic impedance of the broken structure of the passivation layer and the third acoustic impedance of the broken structure of the piezoelectric layer are not matched with the first acoustic impedance of the effective area of the resonator, the transmission of sound waves at the boundary is discontinuous, and therefore, at the boundary, a part of sound energy is coupled and reflected into the effective excitation area and converted into a piston sound wave mode perpendicular to the surface of the piezoelectric layer, so that the Q value of the resonator is improved. Meanwhile, the depth of the fracture structure is shallow, so that the piezoelectric layer is not damaged, the main mode of the resonator is not affected, and the Q value of the resonator can be improved while the mechanical strength of the resonator is effectively improved. However, the existence of the fracture structure can bring Kt while increasing the Q value of the resonator 2 Problem of degradation, in order to compensate for the defect, the piezoelectric layer material is doped with rare earth elements to improve the Kt 2 To make up for the defect of the fracture structure.
Fig. 5A and 5B are a schematic top view and a sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention.
As shown in fig. 5A, the FBAR includes a bottom electrode 505, a piezoelectric layer 507, a top electrode 509, a passivation layer 511, and a break structure 513 between the top electrode and the piezoelectric layer outside the top electrode and a break structure 515 in the passivation layer above the step (corresponding to the connection) where the top electrode and its electrode are connected.
The piezoelectric resonator structure shown in fig. 5B is similar to the structure of the embodiment shown in fig. 4B, and is a sectional view taken along the top view 1B-1B, except that: in fig. 4B, the fracture structure is below or covered by the top electrode or is laterally inboard of the boundary of the active area, while in fig. 5B, the fracture structure between the piezoelectric layer and the top electrode is located outside of the top electrode or is laterally outboard of the boundary of the active area. In this embodiment, the cross-sectional shape of the fracture structures 513 and 515 may be circular arc shape in fig. 1C, or may be other shapes such as inclined shape in fig. 1D, stepped shape in fig. 1E, and fan shape in fig. 1F, having fixed widths w1, w2 and fracture depths h1, h2. In an alternative embodiment, the width w2 of the fracture structure is in a proportional range of 1% -10% to the lateral width of the resonator active area, and the depth of the fracture structure is in a proportional range of 1% -15% to the thickness of the piezoelectric layer, and in a further embodiment w1 and w2 are in the range of 0.1-10um, and the depths h1 and h2 are in the range of
The depth of the fracture structure on the piezoelectric layer is shallow, so that the mechanical strength of the resonator is strong, and meanwhile, the fracture structure is shallow, the piezoelectric layer is not damaged, and the main mode of the resonator is not affected.
In addition, the second acoustic impedance of the passivation layer fracture structure 515 and the third acoustic impedance of the piezoelectric layer fracture structure 513 do not match the first acoustic impedance of the resonator active area, which causes the acoustic wave to be transmitted discontinuously at the boundary, so that a portion of the acoustic energy is transmitted at the boundary of the active areaCoupled and reflected into the active excitation region and converted into a piston acoustic mode perpendicular to the surface of the piezoelectric layer, resulting in an increase in the Q-value of the resonator. However, the existence of the fracture structure can bring Kt while increasing the Q value of the resonator 2 Problem of degradation to remedy this defect, we have used to increase the Kt of the piezoelectric layer material by doping it with rare earth elements 2 To make up for the defect of the fracture structure.
Fig. 6A and 6B are a schematic top view and a sectional view in the direction of 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention.
As shown in fig. 6A, the FBAR includes a bottom electrode 605, a piezoelectric layer 607, a top electrode 609, a passivation layer 611, and fracture structures 615 and 617 between the top electrode and the piezoelectric layer inside the top electrode having multiple fracture sites, including but not limited to two sites, with shallow fracture depths.
The piezoelectric resonator structure shown in fig. 6B is similar to the structure of the embodiment shown in fig. 4B, and is a sectional view taken along the top view 1B-1B, except that:
the fracture structure between the top electrode and the piezoelectric layer is located inside (covered by) the top electrode and the fracture structure comprises two parts, 615 and 617, in a number of locations including, but not limited to, two. The fracture depth of the fracture structure between the top electrode and the piezoelectric layer is shallow. In this embodiment, the cross-sectional shapes of the fracture structures 613, 615, and 617 may be circular arc shapes in fig. 1C, or may be other shapes such as an inclined shape in fig. 1D, a stepped shape in fig. 1E, and a fan shape in fig. 1F. In the embodiment of fig. 6B, the fracture structure has fixed widths w1, w2, w3 and fracture depths h1, h2, h3, optionally with a ratio between the widths w2 and w3 of the fracture structure and the lateral width of the active area of the resonator ranging from 1% to 10%, and a ratio between the depth of the fracture structure and the thickness of the piezoelectric layer ranging from 1% to 15%, further with w1, w2 and w3 ranging from 0.1-10um, h1, h2 and h3 having a depth ofLeft and right.
The depth of the fracture structure between the top electrode and the piezoelectric layer is shallow, so that the mechanical strength of the resonator is strong, and meanwhile, the piezoelectric layer is not damaged due to the fact that the depth of the fracture structure is shallow, and therefore the main mode of the resonator is not affected.
Moreover, since the fracture structure in the piezoelectric layer is multiple, the acoustic impedance mismatch degree between the fracture structure and the acoustic impedance in the effective area of the resonator is further increased, so that the transmission discontinuity of the acoustic wave at the boundary is further enhanced, and therefore, at the boundary of the effective area, more acoustic energy is coupled and reflected into the effective excitation area and converted into a piston acoustic wave mode perpendicular to the surface of the piezoelectric layer, so that the Q value of the resonator is further improved. However, the existence of the fracture structure can bring Kt while increasing the Q value of the resonator 2 Problem of degradation, in order to compensate for the defect, the piezoelectric layer material is doped with rare earth elements to improve the Kt 2 To make up for the defect of the fracture structure.
The embodiment of the invention also relates to a filter comprising the bulk acoustic wave resonator.
The embodiment of the invention also relates to electronic equipment comprising the filter. It should be noted that, the electronic devices herein include, but are not limited to, intermediate products such as a radio frequency front end, a filtering and amplifying module, and end products such as a mobile phone, a WIFI, and an unmanned aerial vehicle.
In the present invention, the electrode constituent material may be formed of gold (Au), tungsten (W), molybdenum (Mo), platinum (Pt), ruthenium (Ru), iridium (Ir), titanium Tungsten (TiW), aluminum (Al), titanium (Ti), or the like.
In the present invention, the passivation layer material may be aluminum nitride (AlN), silicon carbide (SiC), aluminum oxide (Al 2O 3), silicon oxide (SiO 2), silicon nitride (Si 3N 4), or a combination thereof.
Although embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
Claims (24)
1. A bulk acoustic wave resonator comprising:
a substrate;
an acoustic mirror;
a bottom electrode disposed over the substrate;
a top electrode facing the bottom electrode, the top electrode having a main body portion and a connection portion connected to the main body portion;
the piezoelectric layer is arranged above the bottom electrode and between the bottom electrode and the top electrode; and
a passivation layer disposed over the top electrode,
wherein:
the area where the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode overlap in the thickness direction of the substrate is an effective area of the resonator, and at least one first fracture structure is arranged at a position, adjacent to the boundary of the effective area, above the connecting part, of the passivation layer; and is also provided with
The piezoelectric layer is doped with rare earth elements.
2. The resonator of claim 1, wherein:
the connecting portion has an inclined surface, and the first breaking structure is disposed at the inclined surface.
3. The resonator of claim 2, wherein:
the connection portion forms a bridge structure, an air gap is formed between the bridge structure and the piezoelectric layer, the inclined surface comprises a first inclined surface of the bridge structure adjacent to the boundary and a second inclined surface adjacent to the top electrode lead, and the first fracture structure is arranged at the first inclined surface.
4. A resonator as claimed in claim 3, wherein:
the passivation layer further includes at least one second fracture structure disposed at the second inclined surface.
5. The resonator of claim 1, wherein:
the connecting part is a horizontal connecting part.
6. The resonator of claim 1, wherein:
the top electrode is further provided with a bridge wing structure on one side opposite to the connecting portion, the bridge wing structure is provided with a bridge wing inclined plane, and an air gap is formed between the bridge wing structure and the piezoelectric layer.
7. The resonator of claim 6, wherein:
the passivation layer further includes at least one third fracture structure disposed over the bridge wing ramp.
8. The resonator according to any of claims 1-7, wherein:
the depth of the fracture structure is less than the thickness of the passivation layer.
9. The resonator of claim 8, wherein:
the depth of the fracture structure is 5% -30% of the thickness of the passivation layer.
10. The resonator of claim 9, wherein:
the depth of the fracture structure has the value range of
11. The resonator according to any of claims 1-7, wherein:
at least a portion of the fracture structure has a depth equal to the thickness of the passivation layer.
12. The resonator of claim 11, wherein:
the thickness of the passivation layer has a value range of
13. The resonator according to any of claims 1-7, wherein:
at least one fourth fracture structure is provided in the piezoelectric layer below the top electrode or laterally outside the top electrode, adjacent to the boundary of the active area.
14. The resonator of claim 13, wherein:
the width of the fourth fracture structure is 1-10% of the transverse width of the effective area.
15. The resonator of claim 13, wherein:
the depth of the fourth fracture structure is 1-15% of the thickness of the piezoelectric layer.
16. The resonator of claim 15, wherein:
the depth of the fourth fracture structure is in the range of
17. The resonator according to any of claims 1-7, wherein:
the width of the fracture structure is 0.1-10um.
18. The resonator according to any of claims 1-7, wherein:
the section shape of the fracture structure is one of arc shape, inclined shape, ladder shape and fan shape.
19. The resonator of claim 1, wherein:
the doped rare earth elements include one or any of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y), and scandium (Sc).
20. The resonator of claim 19, wherein:
the piezoelectric layer is made of aluminum nitride (ALN) and is doped to form Al 1-a X a N or Al 1-a-b X a Y b N structure, wherein X, Y represents any two elements among the rare earth elements, and a and b represent the content of the doping element X, Y, respectively.
21. The resonator of claim 20, wherein:
the atomic fraction of the doping element X or Y is 0.5% -30%.
22. The resonator of claim 19, wherein:
the doped rare earth element includes scandium (Sc).
23. A filter comprising a bulk acoustic wave resonator according to any of claims 1-22.
24. An electronic device comprising the filter of claim 23.
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| CN111510092B (en) * | 2020-05-28 | 2023-11-21 | 苏州汉天下电子有限公司 | Bulk acoustic wave resonator and method of manufacturing the same |
| CN115051679A (en) * | 2021-03-08 | 2022-09-13 | 诺思(天津)微系统有限责任公司 | Resonator, method of manufacturing the same, filter, and electronic apparatus |
| CN115241622B (en) * | 2021-04-23 | 2024-05-03 | 诺思(天津)微系统有限责任公司 | Resonator, filter and electronic device |
| CN113364423B (en) * | 2021-05-27 | 2023-11-10 | 广州乐仪投资有限公司 | Piezoelectric MEMS resonator, forming method thereof and electronic equipment |
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