CN111049495B - Optimized structure of film bulk acoustic resonator with high quality factor - Google Patents
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- 229910052769 Ytterbium Inorganic materials 0.000 claims description 4
- OGPBJKLSAFTDLK-UHFFFAOYSA-N europium atom Chemical compound [Eu] OGPBJKLSAFTDLK-UHFFFAOYSA-N 0.000 claims description 4
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 4
- NAWDYIZEMPQZHO-UHFFFAOYSA-N ytterbium Chemical compound [Yb] NAWDYIZEMPQZHO-UHFFFAOYSA-N 0.000 claims description 4
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- H—ELECTRICITY
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- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
- H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
- H03H9/171—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator implemented with thin-film techniques, i.e. of the film bulk acoustic resonator [FBAR] type
- H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
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- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
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- 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
- H03H9/02086—Means for compensation or elimination of undesirable effects
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- 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
- H03H9/125—Driving means, e.g. electrodes, coils
- H03H9/13—Driving means, e.g. electrodes, coils for networks consisting of piezoelectric or electrostrictive materials
- H03H9/131—Driving means, e.g. electrodes, coils for networks consisting of piezoelectric or electrostrictive materials consisting of a multilayered structure
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
- H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
- H03H9/171—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator implemented with thin-film techniques, i.e. of the film bulk acoustic resonator [FBAR] type
- H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
- H03H9/174—Membranes
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- 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
- H03H2009/02165—Tuning
- H03H2009/02173—Tuning of film bulk acoustic resonators [FBAR]
Abstract
The invention relates to a preferable structure of a film bulk acoustic resonator with a high quality factor, which comprises a substrate with a groove on the upper surface, a bottom electrode layer positioned above the substrate, and a piezoelectric layer, and is characterized by also comprising a top electrode layer with a special-shaped air bridge structure, wherein an acoustic rebound structure capable of playing a role in rebounding transverse acoustic waves is arranged in the air bridge structure; the acoustic resilience structure is a convex or trapezoidal polyhedron opposite to a bridge cavity of the special-shaped air bridge structure and is horizontally arranged above the bridge cavity of the special-shaped air bridge structure, the top end face of the acoustic resilience structure is embedded and tightly attached to a top face groove of the special-shaped air bridge structure, an air gap is reserved between the bottom end face of the acoustic resilience structure and a suspension structure below the bridge cavity of the special-shaped air bridge structure, and the left side face and the right side face of the acoustic resilience structure are respectively embedded and tightly attached to a groove of the inner side face adjacent to a bridge cavity supporting structure of the special-shaped air bridge structure. The invention can obviously improve the quality factor of the film bulk acoustic resonator.
Description
Technical Field
The invention relates to a film bulk acoustic wave device, in particular to a preferable structure of a film bulk acoustic wave resonator with high quality factor.
Background
With the development of wireless communication technology and smart phones, the requirements of the radio frequency front end on the performance index and the integration level of components are higher and higher. The radio frequency front-end filter, the duplexer and the multiplexer based on the film bulk acoustic wave device have been widely used in smart phones, communication terminals and communication base stations due to the advantages of small size, low insertion loss, fast roll-off, low power consumption and the like, and are applied to communication equipment of internet of things terminals such as internet of vehicles and industrial control in the future. In addition, the oscillator based on the film bulk acoustic wave device has great application value in high-speed serial data equipment such as SATA hard disk drives, USB3.0 standard PC peripherals, C-type interfaces, optical transceivers and the like.
A typical thin film bulk acoustic resonator includes an acoustic rebound layer located over a substrate, a bottom electrode layer located over the acoustic rebound layer, a piezoelectric layer located over the bottom electrode layer, and a top electrode layer located over the piezoelectric layer. Two common configurations of acoustically resilient layers are, respectively, an air cavity structure or a multi-layer composite structure of overlapping high and low acoustic impedance layers. The conventional method for forming the air cavity structure is to deposit a layer of sacrificial material, and release the sacrificial material after processing other layers of the device, so that the remaining space can form a cavity.
When alternating voltage is applied to the upper electrode and the lower electrode of the film bulk acoustic resonator, the piezoelectric layer film can generate longitudinal deformation under the action of an external electric field, and bulk acoustic waves which are longitudinally propagated and vibrated are generated. The bulk acoustic wave is rebounded back on the upper and lower surfaces of the film bulk acoustic resonator to form a standing wave in the piezoelectric layer, so that resonance is generated. The acoustic resonance forms a measurable electric signal between the upper and lower electrode layers, namely a resonance electric signal of the bulk acoustic wave resonator, through the piezoelectric effect of the piezoelectric layer film. The signal contains information on the resonance frequency, amplitude, phase, etc. In addition, in order to improve the surface oxidation resistance, power tolerance, mechanical strength, frequency and temperature stability and other performances of the film bulk acoustic resonator, an additional material layer and structure can be added on the basis of the basic structure.
The arrangement of the air bridge structure in the laminated structure of the film bulk acoustic resonator, especially at the boundary of the overlapping region of the bottom acoustic reflection cavity and the upper and lower electrode layers, is beneficial to reducing the leakage of acoustic energy to the substrate, thereby improving the quality factor of the resonator, see US20140225683a 1. However, in this solution, a part of the acoustic energy may leak to the external area through the air bridge structure, and the quality factor of the resonator is still greatly damaged. Therefore, how to overcome the defects of the prior art has become one of the key problems to be solved urgently in the technical field of the thin film bulk acoustic wave device.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a preferable structure of a film bulk acoustic resonator with a high quality factor.
The preferable structure (scheme 1) of the film bulk acoustic resonator with the high quality factor comprises a substrate with a groove on the upper surface, a bottom electrode layer and a piezoelectric layer, wherein the bottom electrode layer and the piezoelectric layer are positioned above the substrate; the boundary of one direction of the special-shaped air bridge structure is positioned in the groove, and the boundary of the other direction extends out of the boundary of the groove; the acoustic resilience structure is tightly attached to the special-shaped air bridge structure to form an acoustic impedance mismatching interface in the horizontal propagation direction; the material of the acoustic resilience structure is a thin film medium formed by combining SiC and perovskite or a thin film medium formed by combining SiN and perovskite; the special-shaped air bridge structure is characterized in that a groove is formed in the inner side face of a bridge cavity supporting structure of the special-shaped air bridge structure, and protrusions with the same size as the groove are arranged on the outer side faces which are symmetrical oppositely; the acoustic resilience structure is tightly attached to the special-shaped air bridge structure, the acoustic resilience structure is a convex polyhedron opposite to a bridge cavity of the special-shaped air bridge structure and is horizontally arranged above the bridge cavity of the special-shaped air bridge structure, the top end face of the acoustic resilience structure is embedded and is tightly attached to a top face groove of the special-shaped air bridge structure, an air gap is reserved between the bottom end face of the acoustic resilience structure and a suspension structure below the bridge cavity of the special-shaped air bridge structure, and the left side face and the right side face of the acoustic resilience structure are respectively embedded and are tightly attached to grooves of inner side faces adjacent to a bridge cavity supporting structure of the special-shaped air bridge structure.
According to the preferred structure of the film bulk acoustic resonator with high quality factor (scheme 2), the scheme 2 is different from the scheme 1 in that: the acoustic resilience structure is a trapezoidal polyhedron opposite to a bridge cavity of the air bridge structure and is horizontally arranged in an area above the bridge cavity of the air bridge structure, an air gap is reserved between the bottom end face of the acoustic resilience structure and a suspension structure in an area below the bridge cavity of the air bridge structure, and the top end face, the left side face and the right side face of the acoustic resilience structure are respectively embedded and are tightly attached to bridge cavity grooves which are opposite and symmetrical to the air bridge structure.
The preferred structure (scheme 1 or scheme 2) of the film bulk acoustic resonator with the high quality factor provided by the invention is a further improvement on the basic structure of the film bulk acoustic resonator with the high quality factor, wherein no groove is formed on the inner side surface of the bridge cavity supporting structure of the air bridge structure. The basic structure and the optimum structure (scheme 1 or scheme 2) of the present invention will be described in detail in examples 1 to 3 of the present invention.
Compared with the prior art, the invention has the remarkable advantages that:
firstly, the basic structure of the film bulk acoustic resonator with high quality factor of the invention is to apply a horizontal acoustic rebound structure in the air bridge structure, the acoustic rebound structure forms an additional acoustic impedance interval in the horizontal direction of the air bridge structure, and the acoustic impedances in different intervals are different due to the introduction of the horizontal acoustic rebound structure, so that a rebound effect is generated on the acoustic waves which are transmitted in the horizontal direction of the air bridge structure, the transmission and leakage of the acoustic waves to the areas outside the air bridge structure are greatly reduced, and the quality factor of the film bulk acoustic resonator is remarkably improved.
Secondly, in the basic structure of the film bulk acoustic resonator with high quality factor, the product of the thickness of the acoustic resilience structure and the acoustic impedance of the material of the film bulk acoustic resonator is larger than the product of the thickness of the air bridge structure and the acoustic impedance of the material of the film bulk acoustic resonator, and at the moment, the acoustic wave energy leaked through the air bridge structure is reduced to be within 33 percent of the original acoustic wave energy.
Thirdly, the basic structure of the film bulk acoustic resonator with high quality factor of the invention is determined as the film medium of the combination of SiC and perovskite or the film medium of the combination of SiN and perovskite, and the film medium has low loss, high Q value and good piezoelectricity.
Fourth, the preferred structure of the high-quality-factor film bulk acoustic resonator of the present invention has not only all the advantages of the basic structure of the present invention described above but also a more excellent high-quality factor. The preferred structure (scheme 1 or scheme 2) of the film bulk acoustic resonator with the high quality factor is based on the arrangement scheme of the acoustic rebound structure in the basic structure, when partial end faces of the convex polyhedron or the trapezoidal polyhedron of the acoustic rebound structure in the preferred structure are embedded and respectively attached to the end face grooves adjacent to the special-shaped air bridge structure or the air bridge structure, the side wall of the air bridge structure can be changed to form the side wall of the air bridge structure with discontinuous thickness, namely a first-level transverse acoustic rebound structure is added, and the acoustic wave energy leaked through the air bridge structure can be reduced to be within 20% of the original acoustic wave energy. Meanwhile, the acoustic resilience structure is tightly attached to the thinned side wall part of the air bridge structure, so that the structural strength of the air bridge reduced due to thinning can be compensated, and the air bridge structure still keeps good structural strength.
Drawings
Fig. 1A is a schematic diagram of a basic structure of a film bulk acoustic resonator.
FIG. 1B is a schematic diagram of the acoustic impedance of the basic structure of the film bulk acoustic resonator shown in FIG. 1A.
Fig. 2A is a schematic diagram of a basic structure of a film bulk acoustic resonator with a high q factor according to the present invention.
FIG. 2B is a schematic diagram of the acoustic impedance of the basic structure of the film bulk acoustic resonator with high Q-factor shown in FIG. 2A.
Fig. 3A is a schematic diagram of a preferred structure (scheme 1) of a film bulk acoustic resonator with a high quality factor according to the present invention.
FIG. 3B is a schematic diagram of the acoustic impedance path of the preferred structure (case 1) of a high Q film bulk acoustic resonator as shown in FIG. 3A.
Fig. 4A is a schematic diagram of a preferred structure (scheme 2) of a film bulk acoustic resonator with a high quality factor according to the present invention.
FIG. 4B is a schematic diagram of the acoustic impedance path of the preferred structure (case 2) of a high Q film bulk acoustic resonator as shown in FIG. 4A.
Fig. 5 is a schematic diagram of performance test parameters of a film bulk acoustic resonator without an air bridge structure.
Fig. 6 is a schematic diagram of performance test parameters of a film bulk acoustic resonator provided with an air bridge structure.
Fig. 7 is a schematic diagram of performance test parameters of a basic structure of a high-quality-factor film bulk acoustic resonator according to the present invention.
Fig. 8 is a schematic diagram of performance test parameters of a preferred structure (scheme 1) of the film bulk acoustic resonator with a high quality factor according to the present invention.
Fig. 9 is a schematic diagram of performance test parameters of a preferred structure (scheme 2) of the film bulk acoustic resonator with a high quality factor according to the present invention.
The symbol A, B, C, D or E in the drawings represents the acoustic impedance, the definition of which is explained below:
and A is the acoustic impedance of a two-layer composite structure formed by the top electrode layer 5 and the partial surface of the piezoelectric layer 4.
B is the acoustic impedance of the air bridge structure 6 single layer structure.
And C is the acoustic impedance of a three-layer composite structure consisting of the air bridge structure 6, the acoustic rebound structure 7 and part of the surface of the piezoelectric layer 4.
D is the acoustic impedance of a two-layer composite structure consisting of the special-shaped air bridge structure 12 and the convex polyhedron acoustic rebound structure 7.
And E is the acoustic impedance of a two-layer composite structure consisting of the air bridge structure 6 and the acoustic resilience structure 7 of the trapezoid polyhedron.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples.
With reference to fig. 1A and 1B, a basic structure of a film bulk acoustic resonator includes a top electrode layer 5 having an air bridge structure 6, and in a path of an acoustic wave in the top electrode layer 5 propagating outward from a central region of a bridge cavity, the acoustic wave propagates from an acoustic impedance a to an acoustic impedance B of the air bridge structure 6, and then propagates to an acoustic impedance a region outside the film bulk acoustic resonator. In the path of the acoustic wave propagation, the acoustic impedance value, the thickness, and the structure of the material of the top electrode layer 5 as the propagation medium and the piezoelectric layer 4 adjacent to the propagation medium affect the acoustic impedance in the propagation structure. The method comprises the following steps: the propagation structures of the bridge cavity suspension area of the air bridge structure 6 are a top electrode layer 5 and a piezoelectric layer 4 positioned below the top electrode layer 5, and the acoustic impedance value in the structure is defined as A; when sound waves are transmitted into the air bridge structure 6 from the top electrode layer 5, the acoustic impedance of the air bridge structure 6 is only formed by the top electrode layer 5, and the acoustic impedance value is defined as B; therefore, an impedance mismatching interface is formed at the junction S1 between the air bridge structure 6 and the suspension area of the bridge cavity, the sound wave can form rebound in the horizontal direction on the interface, and part of the energy which originally enters the air bridge structure 6 can be rebounded to the suspension effective resonance area of the bridge cavity, so that the quality factor of the film bulk acoustic resonator can be increased. Similarly, at the interface S2 where the acoustic wave is transmitted from the air bridge structure 6 to the peripheral region, the acoustic wave will rebound to the air bridge structure 6, reducing the energy transmission to the external region, so that the quality factor of the film bulk acoustic resonator will increase. However, a part of the acoustic wave energy in this basic structure scheme still leaks to the external area through the air bridge structure 6, which still has a large damage to the quality factor of the film bulk acoustic resonator.
In order to overcome the defects in the prior art, the film bulk acoustic resonator with high quality factor provided by the invention has three structural schemes different from the basic structures shown in fig. 1A and 1B, and the three structural schemes are as follows:
example 1. With reference to fig. 2A and fig. 2B, the basic structure of a film bulk acoustic resonator with a high quality factor according to the present invention includes a substrate 1 having a groove 2 on an upper surface thereof, a bottom electrode layer 3 located above the substrate 1, a piezoelectric layer 4, and a top electrode layer 5 having an air bridge structure 6, where an acoustic rebound structure 7 capable of playing a role of rebounding a transverse acoustic wave and improving the quality factor of the film bulk acoustic resonator is disposed in the air bridge structure 6; the boundary of one direction of the air bridge structure 6 is positioned in the groove 2, and the boundary of the other direction extends out of the boundary of the groove 2; the acoustic resilience structure 7 is tightly attached to the air bridge structure 6 to form an acoustic impedance mismatching interface in the horizontal propagation direction; the acoustic resilience structure 7 is made of a thin film medium; the acoustic rebound structure 7 is tightly attached to the air bridge structure 6, namely, the acoustic rebound structure 7 is horizontally arranged in an area above a bridge cavity in the air bridge structure 6, an air gap 8 is reserved between the bottom end surface of the rebound structure 7 and a suspended structure in an area below the bridge cavity of the air bridge structure 6, the top end surface of the acoustic rebound structure 7 is tightly attached to the overhead surface of the bridge cavity of the air bridge structure 6, and the left side surface and the right side surface of the acoustic rebound structure 7 are respectively tightly attached to the inner side surfaces adjacent to a bridge cavity supporting structure of the air bridge structure 6; the thin film medium is a thin film medium formed by combining SiC and perovskite or a thin film medium formed by combining SiN and perovskite.
Example 2. With reference to fig. 3A and 3B, the present invention provides a preferred structure of a film bulk acoustic resonator with a high quality factor (scheme 1). The optimized structure (scheme 1) comprises a substrate 1 with a groove 2 on the upper surface, a bottom electrode layer 3 and a piezoelectric layer 4 which are positioned above the substrate 1, and further comprises a top electrode layer 5 with a special-shaped air bridge structure 12, wherein an acoustic rebound structure 7 which can play a role in rebounding transverse sound waves and improve the quality factor of the film bulk acoustic wave resonator is arranged in the special-shaped air bridge structure 12; the boundary of one direction of the special-shaped air bridge structure 12 is positioned in the groove 2, and the boundary of the other direction extends out of the boundary of the groove 2; the acoustic resilience structure 7 is tightly attached to the special-shaped air bridge structure 12 to form an acoustic impedance mismatching interface in the horizontal propagation direction; the material of the acoustic resilience structure 7 is a thin film medium formed by combining SiC and perovskite or a thin film medium formed by combining SiN and perovskite; the special-shaped air bridge structure (12) is characterized in that a groove (9) is formed in the inner side face of the bridge cavity supporting structure, and protrusions with the same size as the groove (9) are formed in the outer side faces which are symmetrical in opposite directions; the acoustic resilience structure 7 is tightly attached to the special-shaped air bridge structure 12, namely, the acoustic resilience structure 7 is a convex polyhedron opposite to a bridge cavity of the special-shaped air bridge structure 12 and is horizontally arranged in the upper area of the bridge cavity of the special-shaped air bridge structure 12, the top end face of the acoustic resilience structure 7 is embedded and tightly attached to a groove 8 in the overhead side of the bridge cavity of the special-shaped air bridge structure 12, an air gap 11 is reserved between the bottom end face of the acoustic resilience structure 7 and a suspended structure in the lower area of the bridge cavity of the special-shaped air bridge structure 12, and the left side face and the right side face of the acoustic resilience structure 7 are respectively embedded and tightly attached to a groove 9 in the inner side face adjacent to a bridge cavity supporting structure of the air bridge structure 12.
Example 3. With reference to fig. 4A and 4B, the present invention provides a preferred structure of a film bulk acoustic resonator with high quality factor (scheme 2). The optimal structure (scheme 2) comprises a substrate 1 with a groove 2 on the upper surface, a bottom electrode layer 3 positioned above the substrate 1, a piezoelectric layer 4 and a top electrode layer 5 with an air bridge structure 6, wherein an acoustic rebound structure 7 which can play a role in transverse acoustic wave rebound and improve the quality factor of the film bulk acoustic resonator is arranged in the air bridge structure 6; the boundary of one direction of the air bridge structure 6 is positioned in the groove 2, and the boundary of the other direction extends out of the boundary of the groove 2; the acoustic resilience structure 7 is tightly attached to the air bridge structure 6 to form an acoustic impedance mismatching interface in the horizontal propagation direction; the material of the acoustic resilience structure 7 is a thin film medium formed by combining SiC and perovskite or a thin film medium formed by combining SiN and perovskite; the acoustic rebound structure 7 is a trapezoid polyhedron facing the bridge cavity of the air bridge structure 6 and horizontally arranged above the bridge cavity of the air bridge structure 6, an air gap 11 is reserved between the bottom end face of the acoustic rebound structure 7 and a suspension structure below the bridge cavity of the air bridge structure 6, and the top end face, the left side face and the right side face of the acoustic rebound structure 7 are respectively embedded and tightly attached to a bridge cavity groove 10 facing and symmetrical to the air bridge structure 6.
The basic structure and the preferred structure of the film bulk acoustic resonator with high quality factor (scheme 1 or scheme 2) provided by the invention are further preferred in the following aspects:
the mass ratio of SiC to perovskite in the thin film medium is 4: 1.
The mass ratio of SiN to perovskite in the thin film medium is 4: 1.
The film medium formed by combining SiC and perovskite is doped with one or two of rare earth elements ytterbium (Yb) and europium (Eu).
The film medium formed by the combination of SiN and perovskite is doped with one or two of rare earth elements ytterbium (Yb) and europium (Eu).
The material of the piezoelectric layer 4 is the same as that of the acoustic rebound structure 7.
The bridge cavity height of dysmorphism air bridge structure 12 or air bridge structure 6 is 10nm to 2um (if select 10nm, 50nm, 150nm, 200nm, 300nm, 1um or 2um etc.), the bridge cavity width of dysmorphism air bridge structure 12 or air bridge structure 6 is 1um to 15um (if select 1um, 5um, 8um, 10um or 15um etc.).
The product of the thickness of the acoustic resilience structure 7 and the acoustic impedance of the material of the acoustic resilience structure is larger than the product of the thickness of the special-shaped air bridge structure 12 or the air bridge structure 6 and the acoustic impedance of the material of the air bridge structure. Wherein: the thickness of the acoustically resilient structure 7 is: the thickness of the thin film medium constituting the acoustic rebound structure 7, i.e., the distance from the uppermost surface to the lowermost surface thereof.
The shape of the special-shaped air bridge structure 12 or the air bridge structure 6 is directly formed by the top electrode layer 5.
The basic structure and the preferred structure (scheme 1 or scheme 2) of the invention have the following realization principles and beneficial effects: as shown in fig. 2A and 2B, in the basic structure of the present invention, the top electrode layer 5 with the air bridge structure 6 is included, and further, the structure 7 of acoustic rebound is closely attached to the piezoelectric layer 4, two end faces of the structure 7 of acoustic rebound are closely attached to the support structures on two sides of the air bridge structure 6, but an air gap is still left between the structure and the central suspended structure of the air bridge structure 6. Due to the introduction of acoustic rebound structure 7, a region with acoustic impedance different from A, B is generated above air bridge structure 6, the value of acoustic impedance is defined as C, and two impedance discontinuity boundaries S31 and S41 are further divided on the basis of the two boundaries S11/S21, and when the sound wave propagates to the boundaries S31 and S41, acoustic rebound is generated. Compared with the basic structure shown in fig. 1A and 1B, the basic structure of the present invention has more acoustic energy rebounded to the central effective resonance area, so that the quality factor of the film bulk acoustic resonator is increased. For example, when the product of the thickness of the acoustic rebound structure 7 and the acoustic impedance of the material thereof is greater than the product of the thickness of the air bridge structure 6 and the acoustic impedance of the material thereof, the acoustic energy leaking through the air bridge structure 6 is reduced to 33% of the original energy.
Based on the arrangement scheme of the acoustic rebound structure 7 in the basic structure, when the preferred structure (scheme 1) of the invention is adopted, the convex polyhedron part end face of the acoustic rebound structure 7 is embedded and closely attached to the end face groove adjacent to the special-shaped air bridge structure 12 in fig. 3A and 3B; or when the preferred structure (scheme 2) of the invention is adopted, the end face of the trapezoidal polyhedron part of the acoustic resilience structure 7 is embedded and closely attached to the end face groove adjacent to the air bridge structure 6 in fig. 4A and 4B; the side wall of the special-shaped air bridge structure 12 or the air bridge structure 6 can be changed to form the side wall of the special-shaped air bridge structure 12 or the air bridge structure 6 with discontinuous thickness, which is equivalent to adding a one-level transverse acoustic rebound structure. Specifically, the method comprises the following steps: with reference to fig. 3A and 3B, due to the introduction of acoustic rebound structure 7, a region with acoustic impedance different from A, B, C is generated above shaped air bridge structure 12, the value of acoustic impedance is defined as D, and two impedance discontinuity boundaries S51 and S61 are further divided based on two boundaries S12/S22, when the acoustic wave propagates to the boundary S51 and S61, acoustic rebound occurs, so that the acoustic wave energy leaking through shaped air bridge structure 12 or air bridge structure 6 can be reduced to within 20% of the original acoustic wave energy. Similarly, in conjunction with FIGS. 4A and 4B, a region of acoustic impedance different from A, B, C, D is created over the air cavity structure 6, the value of acoustic impedance being defined as E, and further divided into two impedance discontinuity boundaries S71 and S81 based on the two boundaries S12/S22. When the sound wave propagates to the boundary between S71 and S81, the sound wave rebounds, so that the sound wave energy leaking through the air bridge structure 6 can be reduced to be within 20% of the original energy. Meanwhile, the acoustic resilience structure 7 is tightly attached to the thinned side wall part of the special-shaped air bridge structure 12 or the air bridge structure 6, so that the structural strength of the air bridge reduced due to thinning can be compensated, and the air bridge structure still keeps good structural strength.
The effect of suppressing the lateral leakage of acoustic energy on the improvement of the Q value is further analyzed in principle below.
The Q value of the film bulk acoustic resonator is the reciprocal of the total energy percentage of the acoustic wave energy leakage. For example, before the air bridge structure 6 is not provided, about 1/2000 acoustic wave energy leaks to the substrate 1, about 1/2000 acoustic wave energy leaks laterally outward from the edge of the top electrode 5, and the sum of the two is about 1/1000 acoustic wave energy, so that the Q value of the thin film bulk acoustic resonator without the air bridge structure 6 is about 1000.
After the air bridge structure 6 of the film bulk acoustic resonator shown in fig. 1A and 1B is provided, the energy leaked laterally from the edge of the top electrode 5 is reduced to about 1/2, i.e., about 1/4000 acoustic wave energy, so that the total acoustic wave energy leaked is about 1/4000+1/2000 — 1/1333, and therefore the Q value of the film bulk acoustic resonator shown in fig. 1A and 1B is about 1333, which is increased by about 333 and by more than 30% compared with the film bulk acoustic resonator without the air bridge structure 6.
After the basic structure of the present invention as shown in fig. 2A and fig. 2B is configured, the energy leaked laterally from the edge of the top electrode 5 is reduced to about 1/3, i.e. about 1/6000 acoustic wave energy, so that the total leaked acoustic wave energy is about 1/6000+1/2000 ═ 1/1500, and therefore the Q value of the film bulk acoustic resonator as shown in fig. 2 is about 1500, which is improved by about 500 and 50% compared with the film bulk acoustic resonator without the air bridge structure 6.
After the preferred structure of the present invention (embodiment 1) shown in fig. 3A and 3B is configured, the energy leaking laterally from the edge of the top electrode 5 is reduced to within about 1/5, i.e. less than about 1/10000 sound wave energy, so that the total sound wave energy leaking is about 1/10000+1/2000 to 1/1667, and therefore the Q value of the film bulk acoustic resonator shown in fig. 3A and 3B is about 1667, which is at least 667 higher and at least 66.7 higher than that of the film bulk acoustic resonator without the air bridge structure 6.
Similarly, after the preferred structure of the present invention (embodiment 2) shown in fig. 4A and 4B is configured, the energy leaked laterally from the edge of the top electrode 5 is reduced to within about 1/5, i.e. less than about 1/10000 sound wave energy, so that the total sound wave energy leaked is about 1/10000+1/2000 ═ 1/1667, and thus the Q value of the film bulk acoustic resonator shown in fig. 4A and 4B is about at least 1667, which is at least 667 higher and at least 66.7 higher than that of the film bulk acoustic resonator without the air bridge structure 6.
Example 4. Taking a specific 2.6GHz film bulk acoustic resonator as an example, the practical effect of the invention on improving the Q value of the film bulk acoustic resonator is verified and analyzed through a simulation design result by using each embodiment of the structure.
Fig. 5 is a schematic diagram of performance test parameters of a film bulk acoustic resonator without an air bridge structure. Fig. 6 is a schematic diagram of performance test parameters of a film bulk acoustic resonator provided with an air bridge structure. Fig. 7 is a schematic diagram of performance test parameters of a basic structure of a high-quality-factor film bulk acoustic resonator according to the present invention. Fig. 8 is a schematic diagram of performance test parameters of a preferred structure (scheme 1) of the film bulk acoustic resonator with a high quality factor provided by the invention. Fig. 9 shows a preferred structure of a film bulk acoustic resonator with a high quality factor (scheme 2). In the simulation design result of the film bulk acoustic resonator without the air bridge structure shown in fig. 5, the Q value of the film bulk acoustic resonator is 1065.762; FIG. 6 shows that the Q value of the film bulk acoustic resonator with the air bridge structure in FIGS. 1A and 1B is 1430.836, which is improved by 34%; fig. 7 shows that the Q value of the basic structure of the film bulk acoustic resonator with high quality factor shown in fig. 2A and 2B is 1685.933, which is improved by 58%; fig. 8 shows that the Q value of the preferred structure (scheme 1) of the film bulk acoustic resonator with high quality factor as shown in fig. 3A and 3B is 1832.814, which is 72% higher; fig. 9 shows that the Q value of the preferred structure (case 2) of the film bulk acoustic resonator with high Q factor as shown in fig. 4A and 4B is 1758.426, which is 63% higher. Compared with the performance test parameters in the prior art, the acoustic rebound structure 7 is arranged to form an additional acoustic impedance mismatching interface in the horizontal direction, so that the transverse acoustic wave transmitted through the special-shaped air bridge structure 12 or the air bridge structure 6 is rebounded, and the quality factor of the film bulk acoustic wave resonator can be remarkably improved.
Descriptions not related to the embodiments of the present invention are well known in the art, and may be implemented by referring to the well-known techniques.
The invention obtains satisfactory performance improvement effect through simulation test verification.
The above embodiments and examples are specific supports for the technical idea of the preferred structure of the film bulk acoustic resonator with high quality factor, which is proposed by the present invention, and the protection scope of the present invention is not limited thereby, and any equivalent changes or equivalent modifications made on the basis of the technical scheme according to the technical idea proposed by the present invention still belong to the protection scope of the technical scheme of the present invention.
Claims (10)
1. A film bulk acoustic resonator with a high quality factor comprises a substrate (1) with a groove (2) on the upper surface, a bottom electrode layer (3) positioned above the substrate (1), and a piezoelectric layer (4), and is characterized by further comprising a top electrode layer (5) with a special-shaped air bridge structure (12), wherein an acoustic rebound structure (7) which can play a role in rebounding transverse acoustic waves and improving the quality factor of the film bulk acoustic resonator is arranged in the special-shaped air bridge structure (12); the boundary of one direction of the special-shaped air bridge structure (12) is positioned in the groove (2), and the boundary of the other direction extends out of the boundary of the groove (2); the acoustic resilience structure (7) is tightly attached to the special-shaped air bridge structure (12) to form an acoustic impedance mismatching interface in the horizontal propagation direction; the material of the acoustic resilience structure (7) is a thin film medium formed by combining SiC and perovskite or a thin film medium formed by combining SiN and perovskite; the special-shaped air bridge structure (12) is characterized in that a groove (9) is formed in the inner side face of the bridge cavity supporting structure, and protrusions with the same size as the groove (9) are formed in the outer side faces which are symmetrical in opposite directions; the acoustic resilience structure (7) is tightly attached to the special-shaped air bridge structure (12), the acoustic resilience structure (7) is a convex polyhedron opposite to the bridge cavity of the special-shaped air bridge structure (12) and is horizontally arranged in the region above the bridge cavity of the special-shaped air bridge structure (12), the top end face of the acoustic resilience structure (7) is embedded into the recess (8) in the top face of the bridge cavity of the special-shaped air bridge structure (12) and is tightly attached to the recess (8), an air gap (11) is reserved between the bottom end face of the acoustic resilience structure (7) and the piezoelectric layer (4) in the region below the special-shaped air bridge structure (12), and the left side face and the right side face of the acoustic resilience structure (7) are respectively embedded into the recess (9) of the inner side face adjacent to the bridge cavity supporting structure of the special-shaped air bridge structure (12) and are tightly attached.
2. A film bulk acoustic resonator with a high quality factor comprises a substrate (1) with a groove (2) on the upper surface, a bottom electrode layer (3) positioned above the substrate (1), a piezoelectric layer (4) and a top electrode layer (5) with an air bridge structure (6), and is characterized in that an acoustic rebound structure (7) which can play a role in rebounding transverse acoustic waves and improve the quality factor of the film bulk acoustic resonator is arranged in the air bridge structure (6); the boundary of one direction of the air bridge structure (6) is positioned inside the groove (2), and the boundary of the other direction extends out of the boundary of the groove (2); the acoustic resilience structure (7) is tightly attached to the air bridge structure (6) to form an acoustic impedance mismatching interface in the horizontal propagation direction; the material of the acoustic resilience structure (7) is a thin film medium formed by combining SiC and perovskite or a thin film medium formed by combining SiN and perovskite; the acoustic resilience structure (7) is tightly attached to the air bridge structure (6), namely, the acoustic resilience structure (7) is a trapezoidal polyhedron opposite to the bridge cavity of the air bridge structure (6) and is horizontally arranged in the area above the bridge cavity of the air bridge structure (6), an air gap (11) is reserved between the bottom end face of the acoustic resilience structure (7) and the piezoelectric layer (4) in the area below the air bridge structure (6), and the top end face, the left side face and the right side face of the acoustic resilience structure (7) are respectively embedded into and tightly attached to the bridge cavity grooves (10) which are symmetrical to the air bridge structure (6).
3. A high quality factor thin film bulk acoustic resonator according to any of claims 1-2, wherein the mass ratio of SiC to perovskite in the thin film dielectric is 4: 1.
4. A high quality factor thin film bulk acoustic resonator according to any of claims 1-2, wherein the mass ratio of SiN to perovskite in the thin film dielectric is 4: 1.
5. The high quality factor film bulk acoustic resonator according to any one of claims 1-2, wherein the thin film medium of the combination of SiC and perovskite is doped with one or both of the rare earth elements ytterbium (Yb), europium (Eu).
6. The high quality factor film bulk acoustic resonator according to any one of claims 1-2, wherein the thin film dielectric of the combination of SiN and perovskite is doped with one or both of the rare earth elements ytterbium (Yb), europium (Eu).
7. A high quality factor film bulk acoustic resonator according to any of claims 1-2, characterized in that the piezoelectric layer (4) is made of the same material as the acoustically resilient structure (7).
8. A high quality factor film bulk acoustic resonator according to any of claims 1-2, characterized in that the height of the bridge cavity of the shaped air bridge structure (12) or the air bridge structure (6) is 10nm to 2um, and the width of the bridge cavity of the shaped air bridge structure (12) or the air bridge structure (6) is 1um to 15 um.
9. The film bulk acoustic resonator with high quality factor according to claim 8, characterized in that the product of the thickness of the acoustically resilient structure (7) and the acoustic impedance of the material is larger than the product of the thickness of the special-shaped air bridge structure (12) or the air bridge structure (6) and the acoustic impedance of the material.
10. A high-quality-factor film bulk acoustic resonator according to claim 9, characterized in that the shape of the shaped air bridge structure (12) or the air bridge structure (6) is directly formed by the top electrode layer (5).
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