CN111193489A - Bulk acoustic wave resonator, filter, and electronic device - Google Patents
Bulk acoustic wave resonator, filter, and electronic device Download PDFInfo
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- CN111193489A CN111193489A CN201811355093.4A CN201811355093A CN111193489A CN 111193489 A CN111193489 A CN 111193489A CN 201811355093 A CN201811355093 A CN 201811355093A CN 111193489 A CN111193489 A CN 111193489A
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Images
Classifications
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- H—ELECTRICITY
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- 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
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- 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 are overlapped in the thickness direction of the substrate is an effective area of the resonator, the passivation layer is close to the boundary of the effective area, at least one first fracture structure is arranged above the connecting portion, 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 an acoustic wave resonator, 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-band transceivers capable of processing a large amount of data simultaneously. In recent years, multi-band transceivers have been widely used in positioning systems and multi-standard systems, which require simultaneous processing of signals in different frequency bands to improve the overall performance of the system. Although the number of frequency bands in a single chip is increasing, consumer demand for miniaturized and multifunctional portable devices is increasing, and miniaturization becomes a trend of chips, which puts higher demands on the size of filters.
For this reason, in the prior art, a Film Bulk Acoustic Resonator (FBAR) has been used to replace the conventional waveguide technology to implement a multiband filter.
The FBAR mainly generates bulk acoustic waves by using the piezoelectric effect and the inverse piezoelectric effect of a piezoelectric material, so that resonance is formed in a device, and the FBAR has a series of inherent advantages of high quality factor, large power capacity, high frequency (up to 2-10GHz and even higher), good compatibility with a standard Integrated Circuit (IC), and the like, and can be widely applied to a radio frequency application system with higher frequency.
The structure 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 the input electrical signal into mechanical resonance using the inverse piezoelectric effect, and converts the mechanical resonance into an electrical signal for output using the piezoelectric effect. Since the FBAR mainly generates a piezoelectric effect by using the longitudinal piezoelectric coefficient (d33) of the piezoelectric film, the main operation Mode thereof is a longitudinal wave Mode (TE Mode) in the Thickness direction. Electromechanical coupling coefficient Kt2The value is an important parameter of the resonator, which represents the capacity of the resonator to convert mechanical and electrical energy. Kt, other performance criteria of the resonator being equal2The larger the value the better the performance of the resonator.
Ideally, the thin film bulk acoustic resonator excites only a thickness direction (TE) mode, but generates a lateral parasitic mode in addition to a desired TE mode, such as a rayleigh-lamb mode which is a mechanical wave perpendicular to the direction of the TE mode. These transverse mode waves are lost at the boundaries of the resonator, thereby causing a loss of energy in the longitudinal mode required for the resonator, ultimately resulting in a decrease in the resonator Q-value. By forming the 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 sound wave at the edge can be reflected back into the resonator, and meanwhile, a part of energy can be converted into a mode of vibration in the vertical direction, so that the Q value of the resonator is improved.
However, the existence of the fracture structure can lead the electromechanical coupling coefficient, namely Kt, of the resonator to be brought while the Q value of the resonator is improved2Is reduced. For example, as the depth of the fractured structure increases, the electromechanical coupling coefficient of the resonator decreases due to a relative decrease in the acoustic wave energy of the vertical mode in the resonator as the lateral mode energy reflected back into the resonator in the fractured structure increases.
Disclosure of Invention
To mitigate or solve the problem of the electromechanical coupling coefficient, Kt, of the resonator caused by the presence of the fracture structure in the FBAR2The present invention proposes a scheme for doping the piezoelectric layer material with a rare earth element.
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; 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 are overlapped 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 layer material is doped with the rare earth element, the stress in the piezoelectric material is changed due to the larger atomic radius of the rare earth element, so that the stress is further changedWhen an electric field is applied to the piezoelectric material, a larger mechanical response is generated in the piezoelectric material, so that 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 provided at the inclined surface. Further, the connection part forms a bridge structure, an air gap is formed between the bridge structure and a piezoelectric layer, the inclined planes include a first inclined plane of the bridge structure adjacent to the boundary and a second inclined plane adjacent to a top electrode lead, and the first breaking structure is disposed at the first inclined plane. Further, the passivation layer further includes at least one second rupture structure disposed at the second inclined surface.
Optionally, the connecting portion is a horizontal connecting portion.
Optionally, a bridge wing structure is further disposed on a side of the top electrode opposite to the connecting portion, the bridge wing structure has 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 slope.
In the resonator, optionally, a depth of the fracture structure is smaller than a 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 has a value range of
In the resonator, optionally, a depth of at least a part of the fracture structure is equal to a thickness of the passivation layer. Optionally, the thickness of the passivation layer has a value range of
In the above resonator, optionally, below the top electrode or laterally outside the top electrode, adjacent to the active regionThe boundaries of the domains are provided with at least one fourth breaking structure in said piezoelectric layer. Further, the width of the fourth breaking structure is 1-10% of the lateral width of the effective area. Further, the depth of the fourth breaking structure is 1-15% of the thickness of the piezoelectric layer. Optionally, the depth of the fourth fracture structure has a value range of
In the resonator, optionally, the width of the fracture structure ranges from 0.1um to 10 um.
In the resonator, the cross-sectional shape of the fracture structure may be one of an arc shape, an inclined shape, a step shape, and a fan shape.
In the resonator, the doped rare earth element may include one or any plurality 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 is made of aluminum nitride (ALN) and doped to form Al1-aXaN or Al1-a- bXaYbAn N structure, wherein X, Y represents any two elements in the rare earth elements, and a and b respectively represent the content of a doping element X, Y. Optionally, the atomic fraction of the doping element X or Y may be 0.5% to 30%.
Embodiments of the present invention also relate to a filter comprising the bulk acoustic wave resonator described above.
Embodiments of the present invention also relate to an electronic device including the filter described above.
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, and in which:
FIGS. 1A and 1B are a schematic top view and a cross-sectional view in the direction 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
fig. 1C, 1D, 1E, 1F are schematic views each showing a sectional shape of a fracture structure as an exemplary embodiment of the present invention;
FIGS. 2A and 2B are a schematic top view and a cross-sectional view along line 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
FIGS. 3A and 3B are a schematic top view and a cross-sectional view along line 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
FIGS. 4A and 4B are a schematic top view and a cross-sectional view along line 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 along line 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
FIGS. 6A and 6B are a schematic top view and a cross-sectional view along line 1B-1B, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;
figure 7 is a schematic cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present 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 by the following embodiments and the accompanying drawings. In the specification, the same or similar reference numerals denote the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the general inventive concept of the present invention and should not be construed as limiting the invention.
According to the invention, the fracture structure is formed at the edge of the effective area of the resonator, and due to the fact that the acoustic impedance of the fracture structure is not matched with the acoustic impedance of the effective area of the resonator, acoustic waves are reflected back into the resonator at the edge, and the energy leakage 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 according to 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 fracture structure 113 in the passivation layer over a step where the top electrode 109 and its electrode are connected.
In all embodiments of the invention, the piezoelectric layer material is doped with a rare earth element.
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 any plurality of yttrium (Y) and scandium (Sc). In an alternative embodiment, the doped rare earth element comprises scandium (Sc).
For the piezoelectric material of aluminum nitride (AlN), the doping mode can be that one or two rare earth elements X and/or Y replace Al atoms in the AlN crystal structure to form Al1-aXaN or Al1-a-bXaYbAn N structure, wherein X, Y represents any two of the rare earth elements, and a and b represent the content of a doping atom X, Y. Optionally, the atomic fraction of the rare earth element X or Y may be 0.5% to 30%, wherein the contents of the doped rare earth elements X and Y may be the same or different.
The above description of doping can be applied to all embodiments of the invention.
FIG. 1B is a cross-sectional view taken along line 1B-1B in FIG. 1A. As shown in fig. 1B, the resonator includes a substrate 101 in order in the thickness direction; an acoustic mirror 103, which is located on the upper surface of the substrate or embedded inside the substrate, and which in fig. 1B is constituted by a cavity embedded in the substrate, 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, prevent the adsorption of materials on the surface of the resonator, eliminate or reduce the oxidation and corrosion of the device caused by the influence of ambient air or a humid environment, and further enable the frequency of the resonator to shift; meanwhile, the passivation layer can be processed, so that the frequency of the resonator can be finely adjusted; and the existence of the passivation layer can reduce the requirement on the closed packaging of the resonator, so that the manufacturing cost of the device is reduced.
As shown in fig. 1A and 1B, the passivation layer over the step where the top electrode and its electrode are connected has a fracture structure 113 therein, which fractures only partially (i.e., not completely). The cross-sectional shape of the fractured structure 113 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 addition to the circular arc shape in fig. 1C, and the fractured structure has a constant width w and depth h. In an alternative embodiment the depth of the fracture structure is smaller than the thickness of the passivation layer, e.g. 5-30% of the thickness of the passivation layer, with a typical w-range of 0.1-10um and a depth of h in the range of 0.1-10um
In the present invention, w may be 0.1um, 5um, 10um for quasi-fractured structures that are not completely fractured; h may be
The fracture structure can be obtained by wet etching or dry etching and other similar processes, the width and the depth of the fracture structure are controlled by controlling the time of the wet etching and regulating and controlling the proportion of liquid medicine, or the width and the depth of the fracture structure are controlled by controlling the time and the power of the 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 fracture structure 113 of the passivation layer 111. Due to passivationThe second acoustic impedance in the fracture structure 113 of the layer 111 is not matched with the first acoustic impedance, meanwhile, due to the fact that the fracture structure has a certain depth, the sound wave can form local oscillation at the fracture structure, strong reflection is formed by multiple reflection and superposition of the sound wave in a local oscillation area, the degree of mismatching can be further increased, transmission of the sound wave at the boundary of the effective area is discontinuous, therefore, at the boundary of the effective area, a part of sound energy can be coupled and reflected into an effective excitation area, and the sound wave is converted into a piston sound wave mode perpendicular to the surface of the piezoelectric layer, and therefore the Q value of the resonator is improved. However, the existence of the fracture structure can bring Kt while improving the Q value of the resonator2Problem of droop, to compensate for this deficiency, we doped the piezoelectric layer material with rare earth elements to increase its Kt2To make up for the deficiency of the fracture structure. The shape, depth and width of the fracture structure can be selected to tune the ability and extent of local oscillation formation for a particular acoustic wavelength.
Fig. 2A and 2B are a schematic top view and a sectional view in the direction 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 fracture structure 213 in the passivation layer above the step where the top electrode and its electrode are connected.
The piezoelectric resonator structure shown in fig. 2B is similar to the embodiment structure shown in fig. 1B, and both are cross-sectional views taken along top view 1B-1B. Except for a rupture structure 213 of the passivation layer over the step where the top electrode and its electrode 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 step shape in fig. 1E, or a fan shape in fig. 1F, and the fracture structure fractures in such a manner that the top electrode fractures to the bottom and has a large depth. 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 within
In the present invention, w may be 0.1um, 5um, 10um for a completely broken structure; h may be
Due to the fact that the fracture structure has a deeper depth, the degree of mismatching between the second acoustic impedance of the passivation layer fracture structure and the first acoustic impedance can be further improved, transmission discontinuity of the acoustic wave at the boundary is enhanced, and therefore more 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 further improved. However, the existence of the fracture structure can bring Kt while improving the Q value of the resonator2The problem of the drop, in order to compensate the defect, the Kt of the piezoelectric layer is increased by doping the material of the piezoelectric layer with rare earth elements2To make up for the deficiency of the fracture structure.
Fig. 3A and 3B are a schematic top view and a sectional view in the direction 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 fracture structure 313 and 315 in the passivation layer above the step where the top electrode and its electrode are connected.
The piezoelectric resonator structure shown in fig. 3B is similar to the embodiment structure shown in fig. 1B, and both are cross-sectional views taken along top view 1B-1B. The difference is that the fracture structure of the passivation layer above the step at the connection point of the top electrode and the top electrode, the fracture part of which includes 313 and 315, the cross-sectional shape of the fracture structure may be a circular arc shape in fig. 1C, or may also be other shapes such as an inclined shape in fig. 1D, a step shape in fig. 1E, and a fan shape in fig. 1F, and the fracture mode is that the fracture depth is shallow at multiple positions including but not limited to two positions. Fracture ofThe section has two fixed widths w1 and w2 and two depths of break h1 and h 2. In an alternative embodiment, 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, with typical w1 and w2 ranges from 0.1-10um, and h1 and h2 depths
Therefore, the Q value of the resonator is further improved, and meanwhile, the passivation layer covers the resonant electrode part comprehensively, so that the passivation layer can protect the resonator more comprehensively, the adsorption of materials on the surface of the resonator can be effectively prevented, the oxidation and corrosion of devices caused by the influence of ambient air or a humid environment are eliminated or reduced, and the frequency of the resonator is deviated. However, the existence of the fracture structure can bring Kt while improving the Q value of the resonator2The problem of the drop, in order to compensate the defect, the Kt of the piezoelectric layer is increased by doping the material of the piezoelectric layer with rare earth elements2To make up for the deficiency of the fracture structure.
It is to be noted that, in the present invention, the rare earth element to be doped may be one kind or two or more kinds.
Based on the above, the present invention provides 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 are overlapped 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 the above fig. 1B, 2B and 3B, the connection portion may be a connection portion of the top electrode and the electrode lead thereof, embodied as an inclined surface. The breaking structure is arranged at the inclined surface.
It should be noted specifically that, in the present invention, the fracture structure is disposed above the connecting portion, which includes not only the case where the fracture structure is disposed just above the connecting portion (between two vertical boundaries of the connecting portion in the lateral direction), but also the case where the fracture structure is disposed obliquely above the connecting portion.
In the present invention, the breaking structure is provided at the inclined surface, and includes not only the case where it is provided within the range of the inclined surface, but also the case where it is provided in the vicinity of the inclined surface.
Although not shown, the connection may also be a horizontal connection.
It is noted that in the passivation layer, the breaking structures may be provided at other locations than above the connection portions.
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 aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO3), Quartz (Quartz), potassium niobate (KNbO3), lithium tantalate (LiTaO3), or the like.
In the present invention, the passivation layer material may be aluminum nitride (AlN), silicon carbide (SiC), aluminum oxide (Al2O3), silicon oxide (SiO2), silicon nitride (Si3N4), 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 a thickness direction; an acoustic mirror 703, which is located on the upper surface of the substrate or embedded inside the substrate, and which in fig. 7 is constituted by a cavity embedded in the substrate, but any other acoustic mirror structure such as a bragg reflector is equally suitable; a bottom electrode 705; a piezoelectric layer 707 doped with a rare earth element; a top electrode 709 including two parts, a main body part and a connecting part, wherein the connecting part is a bridge wing structure, and an air gap is formed between the connecting part of the top electrode and the piezoelectric layer; passivation layer 711 including fracture structures 715 and 713 at steps, the fracture structures having a cross-sectional shape of a circular arc in fig. 1C or an inclination in fig. 1DOther shapes, such as the shape of a step in fig. 1E, and the shape of a sector in fig. 1F, are broken in a partially broken manner and have fixed widths w1, w2 and breaking depths h1, h 2. In an alternative embodiment, 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, with typical w1 and w2 ranges from 0.1-10um, and h1 and h2 depths
At the bridge wing structure and the fracture structure, the acoustic wave is not transmitted continuously at the boundary because the acoustic impedance of the air gap and the fracture structure is not matched with that of the effective area of the resonator, so that a part of the acoustic energy is coupled and reflected into the effective excitation area at the boundary of the effective area and is converted into a piston acoustic wave mode vertical to the surface of the piezoelectric layer, and the Q value of the resonator is improved. However, the existence of the bridge wing structure and the fracture structure can bring Kt while improving the Q value of the resonator2The problem of the drop, in order to compensate the defect, the Kt of the piezoelectric layer is increased by doping the material of the piezoelectric layer with rare earth elements2To make up for the deficiency 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 substrate 801 in order in the thickness direction; an acoustic mirror 803, which is located on the upper surface of the substrate or embedded inside the substrate, and which in fig. 8 is constituted by 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 doped with a rare earth element; a top electrode 809 including a main body portion and a connecting portion, wherein the connecting portion is a bridge portion structure, and an air gap is formed between the connecting portion of the top electrode and the piezoelectric layer; passivation layer 811 comprising rupture 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 planes comprising a first inclined plane of the bridge structure adjacent to the border and a second inclined plane adjacent to the top electrode lead, the breaking structure being provided at the first inclined plane and, optionally, also at the second inclined plane.
The fracture structure may have a cross-sectional shape of an arc shape in fig. 1C, or may have other shapes such as an inclined shape in fig. 1D, a step shape in fig. 1E, and a fan shape in fig. 1F, and has a fracture mode of partial fracture, and has constant widths w1, w2 and fracture depths h1, h 2. In an alternative embodiment, 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, with typical w1 and w2 ranges from 0.1-10um, and h1 and h2 depths
At the bridge part structure and the fracture structure, due to the existence of the air gap and the fracture structure, the acoustic impedance of the bridge part structure and the fracture structure is not matched with the acoustic impedance in the effective area of the resonator, so that the transmission of the acoustic wave at the boundary of the effective area is discontinuous, and therefore, at the boundary of the effective area, a part of the acoustic energy is coupled and reflected into the effective excitation area and is 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 bridge structure and the fracture structure can bring Kt while improving the Q value of the resonator2The problem of the drop, in order to compensate the defect, the Kt of the piezoelectric layer is increased by doping the material of the piezoelectric layer with rare earth elements2To make up for the deficiency of the fracture structure.
Fig. 4A and 4B are a schematic top view and a sectional view in the direction 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 breaking structure 413 between the top electrode and the piezoelectric layer inside the top electrode and a breaking structure 415 in the passivation layer above a step (corresponding to a 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, which is located on the upper surface of the substrate or embedded inside the substrate, and which in fig. 4B is constituted by a cavity embedded in the substrate, but any other acoustic mirror structure such as a bragg reflector is equally suitable; a bottom electrode 407; a piezoelectric layer 407 doped with a rare earth element; a top electrode 409; a passivation layer 411; and a breaking structure 413 between the top electrode and the piezoelectric layer inside the top electrode and a breaking structure 415 in the passivation layer above the step (corresponding to the connection) where the top electrode and its electrode are connected.
The cross-sectional shape of the rupture structures 413 and 415 may be circular arc shape in fig. 1C, or may be other shapes such as an inclined shape in fig. 1D, a step shape in fig. 1E, and a fan shape in fig. 1F, and have constant widths w1 and w2 and rupture depths h1 and h 2. In an alternative embodiment, the ratio between the width w2 of the breaking structure and the lateral width of the active area of the resonator is in the range of 1-10%, the ratio between the depth of the breaking structure and the thickness of the piezoelectric layer is in the range of 1-15%, typical w1 and w2 ranges from 0.1-10um, and the depths of h1 and h2 range from 0.1-10um
The mechanical strength of the resonator is stronger due to the shallow depth of the fracture structure.
The fracture structure can be obtained by wet etching or dry etching and other similar processes, the width and the depth of the fracture structure are controlled by controlling the time of the wet etching and regulating and controlling the proportion of liquid medicine, or the width and the depth of the fracture structure are controlled by controlling the time and the power of the dry etching and the flow and the proportion of etching gas.
In the embodiment of fig. 4A and 4B, the area where the acoustic mirror, the bottom electrode, the piezoelectric layer, and the top electrode overlap in the thickness direction is the effective area of the resonator, and has a first acoustic impedance, a second acoustic impedance in the fracture structure 415 of the passivation layer, and a third acoustic impedance in the fracture structure 413 in the piezoelectric layer. The third acoustic impedance of the fracture structure in the second acoustic impedance and the piezoelectric layer of the passivation layer is not matched with the first acoustic impedance of the effective area of the resonatorThe acoustic wave transmission is discontinued at the boundary, and therefore a portion of the acoustic energy is coupled and reflected into the active excitation area at the boundary and converted into a piston acoustic wave mode perpendicular to the surface of the piezoelectric layer, resulting in an improved Q value of the resonator. Meanwhile, the depth of the fracture structure is shallow, so that the piezoelectric layer cannot be damaged, the main mode of the resonator cannot be influenced, 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 improving the Q value of the resonator2The problem of the drop, in order to compensate the defect, the Kt of the piezoelectric layer is increased by doping the material of the piezoelectric layer with rare earth elements2To make up for the deficiency of the fracture structure.
Fig. 5A and 5B are a schematic top view and a sectional view in the direction 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 breaking structure 513 between the top electrode and the piezoelectric layer outside the top electrode and a breaking structure 515 in the passivation layer above a step (corresponding to a connection portion) where the top electrode and its electrode are connected.
The piezoelectric resonator structure shown in fig. 5B is similar to the embodiment structure shown in fig. 4B, and is a sectional view taken along top view 1B-1B, except that: in fig. 4B the fracture structure is underneath or covered by the top electrode or laterally inside the boundary of the active area, while in fig. 5B the fracture structure between the piezoelectric layer and the top electrode is outside the top electrode or laterally outside the boundary of the active area. In this embodiment, the cross-sectional shape of the breaking structures 513 and 515 may be circular in fig. 1C, 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, and have constant widths w1, w2 and breaking depths h1, h 2. In an alternative embodiment, the ratio between the width w2 of the breaking structure and the lateral width of the active area of the resonator is in the range 1% -10%, and the ratio between the depth of the breaking structure and the thickness of the piezoelectric layer is also in the rangeIn a ratio ranging between 1% and 15%, in further embodiments w1 and w2 range between 0.1-10um, and h1 and h2 are deep
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 depth of the fracture structure is shallow, so that the piezoelectric layer cannot be damaged, and the main mode of the resonator cannot be influenced.
Furthermore, the mismatch between the second acoustic impedance of the passivation layer fracture structure 515 and the third acoustic impedance of the piezoelectric layer fracture structure 513 and the first acoustic impedance of the active area of the resonator makes the transmission of the acoustic wave discontinuous at the boundary, so that at the boundary of the active area, a part of the acoustic energy is coupled and reflected into the active excitation area and converted into a piston acoustic wave mode perpendicular to the surface of the piezoelectric layer, thereby improving the Q value of the resonator. However, the existence of the fracture structure can bring Kt while improving the Q value of the resonator2Problem of droop, to compensate for this deficiency, we doped the piezoelectric layer material with rare earth elements to increase its Kt2To make up for the deficiency of the fracture structure.
Fig. 6A and 6B are a schematic top view and a sectional view in the direction 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 comprises a bottom electrode 605, a piezoelectric layer 607, a top electrode 609, a passivation layer 611, and fracture structures 615 and 617 having a plurality of fracture sites inside the top electrode between the top electrode and the piezoelectric layer, wherein the fracture sites are fractured in a manner that the fracture depth is shallow, including but not limited to two.
The piezoelectric resonator structure shown in fig. 6B is similar to the embodiment structure shown in fig. 4B, and is a sectional view taken along top view 1B-1B, except that:
the fracture structure between the top electrode and the piezoelectric layer is located inside the top electrode (covered by the top electrode) and comprises two parts, 615 and 617, which fracture in multiple waysThe site includes, but is not limited to, two sites. The fracture depth of the fracture structure between the top electrode and the piezoelectric layer is shallow. In this embodiment, the cross-sectional shape of the rupture structures 613, 615, and 617 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 the embodiment of fig. 6B, the fracture structure has fixed widths w1, w2, w3 and fracture depths h1, h2, h3, optionally, the widths w2 and w3 of the fracture structure have a ratio range between 1% and 10% with the transverse width of the resonator active area, the depth of the fracture structure has a ratio range between 1% and 15% with the thickness of the piezoelectric layer, further, the widths w1, w2, and w3 have a range between 0.1um and 10um, and the depths h1, h2, and h3 have a range between 0.1um and 10um
Left 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 depth of the fracture structure is shallow, so that the piezoelectric layer cannot be damaged, and the main mode of the resonator cannot be influenced.
Moreover, since the fracture structures in the piezoelectric layer are in multiple positions, the degree of mismatch between the acoustic impedance in the fracture structures 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, more acoustic energy is coupled and reflected into the effective excitation area at the boundary of the effective area and is 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 improving the Q value of the resonator2The problem of the drop, in order to compensate the defect, the Kt of the piezoelectric layer is increased by doping the material of the piezoelectric layer with rare earth elements2To make up for the deficiency of the fracture structure.
Embodiments of the present invention also relate to a filter comprising the bulk acoustic wave resonator described above.
Embodiments of the present invention also relate to an electronic device comprising a filter as described above. It should be noted that the electronic device herein includes, but is not limited to, intermediate products such as a radio frequency front end and a filtering and amplifying module, and terminal products such as a mobile phone, 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 (Al2O3), silicon oxide (SiO2), silicon nitride (Si3N4), 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;
a piezoelectric layer disposed 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 are overlapped 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; and is
And the piezoelectric layer is doped with rare earth elements.
2. The resonator of claim 1, wherein:
the connecting portion has an inclined surface at which the first breaking structure is provided.
3. The resonator of claim 2, wherein:
the connection part forms a bridge structure, an air gap is formed between the bridge structure and a piezoelectric layer, the inclined planes include a first inclined plane adjacent to the boundary of the bridge structure and a second inclined plane adjacent to a top electrode lead, and the first fracture structure is disposed at the first inclined plane.
4. The resonator of claim 3, wherein:
the passivation layer further includes at least one second rupture structure disposed at the second inclined face.
5. The resonator of claim 1, wherein:
the connecting part is a horizontal connecting part.
6. The resonator of claim 1, wherein:
and the top electrode is also provided with a bridge wing structure at one side opposite to the connecting part, 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 slope.
8. The resonator of any of claims 1-7, wherein:
the depth of the fracture structure is smaller 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 is in a value range of
11. The resonator of any of claims 1-7, wherein:
the depth of at least part of the fracture structure is 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 of any of claims 1-12, wherein:
at least one fourth breaking structure is provided in the piezoelectric layer adjacent to a boundary of the active area, below the top electrode or laterally outside the top electrode.
14. The resonator of claim 13, wherein:
the width of the fourth breaking structure is 1-10% of the transverse width of the effective area.
15. The resonator of claim 13 or 14, wherein:
the depth of the fourth breaking structure is 1-15% of the thickness of the piezoelectric layer.
16. The resonator of claim 15, wherein:
depth of the fourth fracture structureThe value range of the degree is
17. The resonator of any of claims 1-16, wherein:
the width of the fracture structure ranges from 0.1um to 10 um.
18. The resonator of any of claims 1-17, wherein:
the cross-sectional shape of the fracture structure is one of an arc shape, an inclined shape, a step shape and a fan shape.
19. The resonator of claim 1, wherein:
the doped rare earth element includes one or any plurality of 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), yttrium (Y), and scandium (Sc).
20. The resonator of claim 19, wherein:
the piezoelectric layer is made of aluminum nitride (ALN) and doped to form Al1-aXaN or Al1-a-bXaYbAn N structure, wherein X, Y represents any two elements in the rare earth elements, and a and b respectively represent the content of a doping element X, Y.
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 the bulk acoustic wave resonator according to any one of claims 1-22.
24. An electronic device comprising the filter of claim 23.
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| CN113364423A (en) * | 2021-05-27 | 2021-09-07 | 天津大学 | Piezoelectric MEMS resonator, forming method thereof and electronic equipment |
| WO2022188779A1 (en) * | 2021-03-08 | 2022-09-15 | 诺思(天津)微系统有限责任公司 | Resonator and manufacturing method therefor, filter, and electronic device |
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