CN116233709A - High-performance acoustic device based on longitudinal acoustic surface wave - Google Patents
High-performance acoustic device based on longitudinal acoustic surface wave Download PDFInfo
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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
- H03H9/25—Constructional features of resonators using surface acoustic waves
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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
- H03H9/02535—Details of surface acoustic wave devices
- H03H9/02543—Characteristics of substrate, e.g. cutting angles
- H03H9/02559—Characteristics of substrate, e.g. cutting angles of lithium niobate or lithium-tantalate substrates
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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
- H03H9/02535—Details of surface acoustic wave devices
- H03H9/02614—Treatment of substrates, e.g. curved, spherical, cylindrical substrates ensuring closed round-about circuits for the acoustical waves
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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
- H03H9/05—Holders; Supports
- H03H9/08—Holders with means for regulating temperature
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Abstract
The invention provides a high-performance acoustic device based on longitudinal acoustic surface waves, and belongs to the technical field of acoustic devices. The acoustic device comprises a substrate, a temperature compensation layer, a piezoelectric film and an interdigital transducer which are sequentially overlapped, wherein the substrate adopts a silicon carbide single crystal substrate or a diamond substrate, the piezoelectric film adopts an X-Y cut lithium niobate single crystal piezoelectric film, the rotation cutting angle of the X-Y cut lithium niobate single crystal piezoelectric film is phi, the propagation angle is phi, phi is more than or equal to 25 degrees and less than or equal to +18 degrees, and +19 degrees and less than or equal to +52 degrees. The acoustic device has the characteristics of high sound velocity, high electromechanical coupling coefficient and stable temperature frequency characteristic, so that the acoustic device can meet the application environment of a 5G communication system.
Description
Technical Field
The invention belongs to the technical field of acoustic devices, and particularly relates to a high-performance acoustic device based on longitudinal acoustic surface waves.
Background
The surface acoustic wave device is a solid state device that performs various processes on acoustic signals propagating on the surface of a piezoelectric material substrate by utilizing the characteristics of an acoustic-electric transducer, and performs various functions, including a surface acoustic wave filter, a surface acoustic wave resonator, and the like. The surface acoustic wave device is mainly composed of a substrate material with piezoelectric characteristics and interdigital transducers which are made of metal thin films and are mutually staggered on a polished surface of the substrate material. If a high frequency electrical signal is applied across the interdigital transducers, the surface of the piezoelectric material will produce mechanical vibrations and simultaneously excite Surface Acoustic Waves (SAW) at the same frequency as the applied electrical signal, which will propagate along the surface of the substrate material. If the receiving interdigital transducer is reproduced on the SAW propagation path, the SAW can be detected and converted to an electrical signal. Processing is performed in the electro-acoustic-electric conversion transfer process, so that an output electric signal for analog processing of the input electric signal is obtained. However, the conventional surface acoustic wave device has the following problems.
First, current saw devices cannot achieve high frequencies. The working principle of the surface acoustic wave device is that interdigital electrodes are etched on a piezoelectric film, and surface acoustic waves in different modes are excited in a piezoelectric substrate by applying alternating current signals to the interdigital electrodes. The resonance frequency of the surface acoustic wave resonator is the ratio of the phase velocity to the interdigital period, so the resonance frequency can be increased by reducing the electrode linewidth. However, too small an electrode linewidth limits the device fabrication process and electrode lifetime. It is therefore critical to increase the phase velocity of each acoustic mode in the substrate material. The piezoelectric single crystal substrate materials used in the traditional acoustic device are lithium tantalate and lithium niobate, the Rayleigh wave mode sound velocity is about 3300m/s and 3900m/s, and high frequency is difficult to achieve.
Second, the requirement of large bandwidth in the 5G band presents a significant challenge to current rf saw filter design technology. The current surface acoustic wave filter is composed of surface acoustic wave resonators in series and parallel. The operating frequency of the filter is determined by the resonant frequency of the resonator and the maximum relative bandwidth of the filter is determined by the electromechanical coupling coefficient of the resonator. To design a ladder filter with a relative bandwidth of 4%, it is necessary to achieve an electromechanical coupling coefficient of the resonator of 10% or more. However, the electromechanical coupling coefficients of the lithium tantalate and lithium niobate rayleigh wave modes are about 0.7% and 5.4% respectively at present, which cannot meet the design requirements of the filter.
Third, temperature performance is poor. The temperature stability is determined by the frequency temperature coefficient TCF of the saw resonator and requires that the TCF of the resonator be as small as possible. In general, when the electromechanical coupling coefficient is high, the substrate material is sensitive to external interference, and the frequency temperature coefficient TCF of the substrate material is poor, so that temperature drift is caused, and the bandwidth of the filter is smaller than that of the actual design.
Therefore, in order to enable the surface acoustic wave device to meet the demands of miniaturization, high frequency, large bandwidth, low temperature stability, and the like of high frequency communication systems and apparatuses, it is necessary to optimize piezoelectric materials and structures and design a high performance surface acoustic wave device.
The highest frequency of the resonator manufactured by using the IHP-SAW technology in village and field is 3.5GHz [1-2] Since SAW sound velocity is low, researchers have been turning to a research on a surface acoustic wave (LLSAW) mode in order to develop a resonator and a filter of a 5GHz band.
In 2013, the S.Kakio research group at Japanese sorbitol university found that in IDT/LiNbO by theoretical and experimental study 3 The substrate surface is covered with a high sonic velocity dielectric film (such as an amorphous AlN film) with proper thickness, so that the bulk wave loss of LLSAW can be reduced, and the frequency temperature coefficient TCF is improved, but the electromechanical coupling coefficient of the device is reduced along with the increase of the AlN film thickness [3] . In 2018, S.Kakio research group researches the influence of scandium (Sc) -doped AlN film on LLSAW propagation characteristics through theory and experiment, and discovers that the film has larger electromechanical coupling coefficient but improves LiNbO 3 The LLSAW characteristic of the substrate is similar to that of the amorphous AlN film studied before, namely, the bulk wave loss of the LLSAW can be reduced properly, but the electromechanical coupling coefficient of the LLSAW is reduced obviously along with the increase of the film thickness [4 -5]. Thus, this approach is useful for improving LiNbO 3 The effect of LLSAW propagation characteristics in a substrate is relatively limited.
In addition, in recent years, the S.Kakio research group has also studied LiTaO 3 And LiNbO 3 The single crystal film is bonded to high sonic velocity AT cut or X cut quartz and sapphire (Al 2 O 3 ) On a substrate to improve LLSAW propagation characteristics in both substrates [6-9] . However, from the results of the study, although the bulk wave loss of LLSAW was reduced, resonance was observedThe Q value of the filter is still not high. For example, they have studied best at present as LLSAW resonators (X31-YLiTaO 3 a/X32-Y quartz substrate) at 200MHz, 282 and 404 respectively, and an effective electromechanical coupling coefficient of 5.6%. Those skilled in the art recognize that this is because the slow shear-bulk wave sound velocity of both quartz (5100 m/s) and sapphire (5700 m/s) substrates are higher than LiTaO 3 And LiNbO 3 The LLSAW acoustic velocity (6300 m/s) in the substrate is low, so that it is impossible to completely eliminate the loss caused by bulk wave radiation by using both substrates as bonding substrates, which restricts further improvement of the Q value thereof.
In 2018, village field (Murata) corporation of japan was utilized in LiNbO 3 The technology of adding a reflecting layer between the monocrystalline film and the Si substrate greatly improves the performance of the LLSAW resonator. The principle is to use a material (SiO) with low acoustic impedance 2 ) Acoustic reflection layers (SiO) alternately formed with high acoustic impedance material (Pt) 2 Pt) to reflect bulk wave energy radiated by LLSAW during propagation back to LiNbO 3 Piezoelectric thin film to reduce its energy leakage in Si substrate [10-11] . By using the method, by using LiNbO 3 Five layers of SiO are added between the monocrystalline film and the Si substrate 2 An acoustic reflection layer made of Pt, and the Q values of LLSAW resonators manufactured by the acoustic reflection layer reach 664 and 565 at 3.5GHz and 5GHz respectively, which benefit from SiO 2 The temperature compensation characteristic of the film, the frequency temperature coefficient TCF of the device is also reduced to 21 ppm/DEG C. However, the technology is complex, and for the acoustic reflection layer SiO 2 The precision requirements of the film thickness of each Pt layer are very strict, so that the mass production of devices with consistent performance is difficult. In addition, those skilled in the art recognize that a certain number of acoustic reflecting layers reflect a substantial portion of the bulk wave energy back to LiNbO 3 In the piezoelectric layer, however, there is still a problem of leakage of some of the acoustic energy because the slow shear bulk wave acoustic velocity (5800 m/s) of the Si substrate is still less than the LLSAW acoustic velocity.
It can be seen that the problems of the LLSAW energy leakage and the larger propagation loss of the vertical surface acoustic wave device reported in the related art will result in the lower Q value of the vertical surface acoustic wave device, thereby affecting the performance of the vertical surface acoustic wave device, such as small electromechanical coupling coefficient and insufficient temperature stability.
[1]Ruppel,Clemens.Acoustic Wave Filter Technology-A Review[J].IEEE Transactions on Ultrasonics,Ferroelectrics,and Frequency Control,2017:1390-1400.
[2]Amelie Hagelauer,Gernot Fattinger,Clemens C.W.Ruppel,et al.Microwave Acoustic Wave Devices:Recent Advances on Architectures,Modeling,Materials,and Packaging[J].IEEE Transactions on Microwave Theory and Techniques,2018,66(10):4548-4562.
[3]Matsukura F,Kakio S.Loss Reduction of Longitudinal-type Leaky Surface Acoustic Wave by Loading with High-velocity Thin Film[J].Japanese Journal of Applied Physics,2014,53(7S):07KD04.
[4]Suzuki M,Gomi M,Kakio S.Propagation Characteristics of Longitudinal-type Leaky Surface Acoustic Wave on Layered Structure Consisting of Scx Al1-x N film/LiNbO3 substrate[J].Japanese Journal of Applied Physics,2018,57(7S1):07LD06.
[5]Suzuki M,Kakio S.Theoretical Analysis and Design of Longitudinal Leaky SAW Device Consisting of ScA1N Film/Piezoelectric Single Crystal Substrate[C].Proc.2018IEEE International Ultrasonics Symposium(IUS),2018:1-9.
[6]Hayashi J,Gomi M,Suzuki M,et al.High-coupling leaky SAWs on LiTaO3 thin plate bonded to quartz substrate[C].2017IEEE International Ultrasonics Symposium(IUS),2017:1-4.
[7]Gomi M,Kataoka T,Hayashi J,et al.High-coupling Leaky Surface Acoustic Waves on Li Nb O3 or Li TaO3 Thin Plate bonded to High-velocity Substrate[J].Japanese Journal of Applied Physics,2017,56(7S1):07JD13.
[8]Hayashi J,Yamaya K,Suzuki M,et al.High Coupling and Highly Stable Leaky Surface Acoustic Waves on LiTaO3 Thin Plate bonded to Quartz Substrate[J].Japanese Journal of Applied Physics,2018,57(7S1):07LD21.
[9]Hayashi J,Suzuki M,Yonai T,et al.Longitudinal Leaky Surface Acoustic Wave with Low Attenuation on LiTaO3 Thin Plate Bonded to Quartz Substrate[C].Proc.2018IEEE International Ultrasonics Symposium(IUS),2018:1-4.
[10]Kimura Tetsuya,Omura Masashi,Kishimoto Yutaka,et al.Comparative Study of Acoustic Wave Devices Using Thin Piezoelectric Plates in the 3–5-GHz Range[J].IEEE Transactions on Microwave Theory and Techniques,2019,67(3):915-921.
[11]Kimura T,Kishimoto Y,Omura M,et al.3.5GHz longitudinal leaky surface acoustic wave resonator using a multilayered waveguide structure for high acoustic energy confinement[J].Japanese Journal of Applied Physics,2018,57(7S1):07LD15.
Disclosure of Invention
The present invention has been made based on the findings and knowledge of the inventors regarding the following facts and problems: aiming at the problems of small Q value, small electromechanical coupling coefficient and insufficient temperature stability caused by large LLSAW energy leakage and large propagation loss in the application of the prior acoustic surface wave device in a high frequency band, further research is needed to provide a high-performance acoustic device based on longitudinal acoustic surface waves, which has the characteristics of high sound velocity, high electromechanical coupling coefficient and stable temperature frequency characteristic and meets the application environment of a 5G communication system.
The present invention aims to solve at least one of the technical problems in the related art to some extent. Therefore, the embodiment of the invention provides a high-performance acoustic device based on longitudinal acoustic surface waves, which has the characteristics of high sound velocity, high electromechanical coupling coefficient and stable temperature frequency characteristic, so that the acoustic device can meet the application environment of a 5G communication system.
The high-frequency longitudinal surface acoustic wave acoustic device provided by the embodiment of the invention comprises a substrate, a temperature compensation layer, a piezoelectric film and an interdigital transducer which are sequentially overlapped, and is characterized in that the substrate adopts a silicon carbide single crystal substrate or a diamond substrate, the piezoelectric film adopts an X-Y cut lithium niobate single crystal piezoelectric film, and the spin cutting angle of the X-Y cut lithium niobate single crystal piezoelectric film is
Propagation angle is psi->
+19°≤ψ≤+52°。
The high-frequency longitudinal surface acoustic wave acoustic device provided by the embodiment of the invention has the following advantages and technical effects:
(1) The sound velocity of the longitudinal surface acoustic wave in the lithium niobate single crystal piezoelectric film is as high as 6300m/s, and the upper limit of the frequency of an acoustic device manufactured by using the longitudinal surface acoustic wave mode is improved by 1.5 times compared with that of a common SAW acoustic device, so that the lithium niobate single crystal piezoelectric film is suitable for a high-frequency communication system;
(2) The slow shear bulk wave sound velocity of the silicon carbide single crystal substrate is about 7200m/s, the slow shear bulk wave sound velocity of the diamond single crystal substrate is about 10000m/s, the longitudinal leakage surface wave sound velocity in the lithium niobate single crystal piezoelectric film is as high as 6300m/s, and the lithium niobate single crystal piezoelectric film is bonded on the silicon carbide single crystal substrate or the diamond substrate, so that sound waves can be guided to propagate in a low sound velocity area (piezoelectric surface area), and a longitudinal leakage surface wave mode can be converted into a non-leakage guided wave mode, namely a longitudinal acoustic surface wave (LSAW), thereby reducing acoustic energy loss, obtaining a high Q value and improving the performance of an acoustic device;
(3) By adjusting the chamfer and the film thickness of the lithium niobate single crystal piezoelectric film, the sound velocity of the longitudinal leakage wave short-circuit gate and the open-circuit gate is smaller than that of the slow shear bulk wave in the substrate, so that sound waves can be guided to propagate in a low sound velocity region (piezoelectric surface region), the loss of sound energy is further reduced, a high Q value is obtained, and the performance of an acoustic device is improved; meanwhile, the electromechanical coupling coefficient of the longitudinal acoustic surface wave mode in the lithium niobate single crystal piezoelectric film is not less than 13.5%, and the lithium niobate single crystal piezoelectric film is suitable for the application environment of a 5G communication system;
(4) The temperature compensation layer is arranged on the silicon carbide monocrystalline substrate or the diamond substrate, so that the frequency temperature coefficient TCF of the acoustic device can be reduced, higher temperature stability is achieved, the acoustic device is prevented from generating temperature drift, the bandwidth of the acoustic device is large, and the application environment of a 5G communication system can be met.
In some embodiments of the present invention, in some embodiments,
ψ＝+37°。
in some embodiments, the piezoelectric film has a thickness of 0.16λ -2λ.
In some embodiments, the piezoelectric film has a thickness of 0.18λ.
In some embodiments, the silicon carbide single crystal substrate employs SiC-6H or SiC-4H.
In some embodiments, the polycrystalline silicon dioxide film is grown using a plasma enhanced chemical vapor deposition process.
In some embodiments, the temperature compensation layer has a thickness of 0.16λ -2λ.
In some embodiments, the temperature compensation layer has a thickness of 0.18λ.
In some embodiments, the thickness of the temperature compensation layer is equal to the thickness of the piezoelectric film.
In some embodiments, the interdigitated electrodes are aluminum electrodes.
In some embodiments, the device has an electromechanical coupling coefficient of not less than 13.5%.
Drawings
Fig. 1 is a schematic structural view of a high-frequency longitudinal surface acoustic wave acoustic device of embodiment 1 of the present invention;
FIG. 2 is a graph showing the electromechanical coupling coefficient, sound velocity with the spin angle of the high-frequency longitudinal surface acoustic wave acoustic device according to example 1 of the present invention
And a two-dimensional plot of the propagation angle ψ change;
fig. 3 is an admittance curve of a high-frequency longitudinal surface acoustic wave acoustic device of embodiment 1 of the present invention;
reference numerals illustrate:
1-a substrate; 2-a temperature compensation layer; 3-a piezoelectric film; 4-interdigital transducers.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below by referring to the drawings are illustrative and intended to explain the present invention and should not be construed as limiting the invention.
The embodiment of the invention provides a high-performance acoustic device based on longitudinal acoustic surface waves, which comprises a substrate 1, a temperature compensation layer 2, a piezoelectric film 3 and an interdigital transducer 4 which are sequentially overlapped, wherein the substrate 1 adopts a silicon carbide single crystal substrate or a diamond substrate, the piezoelectric film 3 adopts an X-Y cut lithium niobate single crystal piezoelectric film, and the spin cutting angle of the X-Y cut lithium niobate single crystal piezoelectric film is
Propagation angle is psi->
+19°≤ψ≤+52°。
Working principle: lithium niobate, as a piezoelectric material, has anisotropy, and its acoustic properties are affected by different tangential and propagation directions. The electromechanical coupling coefficient of the lithium niobate longitudinal surface wave mode is larger, and the electromechanical coupling coefficient of the lithium niobate longitudinal surface wave mode can be enhanced by optimizing the tangential direction and the film thickness to enable energy to be concentrated in the piezoelectric film 3 as much as possible. In the specific lithium niobate chamfer and a certain film thickness range, when the longitudinal leakage surface wave (LLSAW) is smaller than the slow shear bulk wave sound velocity in the substrate 1, the longitudinal leakage surface wave (LLSAW) mode is converted into a longitudinal surface wave (LSAW) mode, so that the energy loss is reduced, the Q value is improved, the electromechanical coupling coefficient reaches more than 13.5%, the frequency temperature coefficient TCF is reduced, and the longitudinal surface wave device is suitable for the application environment of a 5G communication system.
Specifically, the slow shear bulk wave sound velocity (about 7200 m/s) of the silicon carbide substrate is greater than the sound velocity (about 6300 m/s) of a longitudinal leakage wave mode in the lithium niobate single crystal piezoelectric film, so when sound waves propagate near the boundary between a low sound velocity region and a high sound velocity region, through accurate design, the embodiment of the invention adjusts the cut angle and the film thickness of the lithium niobate single crystal piezoelectric film, so that the sound velocity of the longitudinal leakage wave short-circuit gate and the open-circuit gate is smaller than the sound velocity of the slow shear bulk wave in the silicon carbide single crystal substrate, the sound waves can be guided to propagate in the low sound velocity region (piezoelectric surface region), and the acoustic surface wave of a non-leakage guided wave mode is excited in the high-frequency piezoelectric substrate.
The vertical surface acoustic wave (LSAW) is a special case of a vertical surface acoustic wave (LLSAW), and the difference between the vertical surface acoustic wave (LSAW) and the vertical surface acoustic wave (LLSAW) is that: the propagation of the surface acoustic wave (LSAW) is mainly concentrated on the piezoelectric surface as compared with the surface acoustic wave (LLSAW), and therefore the energy of the surface acoustic wave (LSAW) is not partially leaked into the substrate 1 like the surface acoustic wave (LLSAW), and the Q value of the surface acoustic wave device is higher.
In addition, the silicon carbide substrate also has a smaller coefficient of thermal expansion (about 4.7 ppm/. Degree.C.) than the lithium niobate substrate (about 15.4 ppm/. Degree.C.), which also helps to reduce the frequency temperature coefficient TCF of the surface acoustic wave device. The thermal conductivity of the silicon carbide substrate is nearly 100 times that of the traditional lithium niobate substrate, and the excellent heat dissipation performance is also beneficial to the future application of the silicon carbide substrate in high-power user equipment (HPUE) of a mobile terminal.
Likewise, the diamond substrate also has an ultra-high sound velocity (about 10000 m/s), and can be substituted for a silicon carbide single crystal substrate. However, the present invention preferably uses a silicon carbide single crystal as the substrate 1 because of complexity of the diamond manufacturing process and excessive cost, making mass production of diamond difficult.
FIG. 2 (a) depicts the electromechanical coupling coefficient K 2 And rotation angle
And the propagation angle ψ; FIG. 2 (b) depicts the sound velocity Vp and the rotation angle +.>
And the propagation angle ψ; fig. 2 (b) corresponds to fig. 2 (a). It can be seen in conjunction with FIGS. 2 (a) and (b)And (3) out: the electromechanical coupling coefficient and the sound velocity are in inverse proportion, and the sound velocity is lower as the electromechanical coupling coefficient is larger, so that in practical application, the electromechanical coupling coefficient and the sound velocity can be selected according to practical conditions, and an acoustic device with better comprehensive performance is further preferred. In some embodiments, when->
When the phi is = +37 degrees, the electromechanical coupling coefficient is 18.95 percent, the sound velocity is as high as 5626.41m/s, and the acoustic device obtained under the condition is the optimal scheme of the invention.
In some embodiments, the thickness of the piezoelectric film 3 is 0.16λ -2λ, and under the above optimized film thickness conditions, energy can be concentrated in the piezoelectric film 3 as much as possible, so as to further enhance the electromechanical coupling coefficient thereof. Lambda is the period of the interdigital transducer, lambda is determined according to the center frequency of the device, and lambda is the ratio of the sound velocity of the longitudinal surface acoustic wave to the center frequency. Preferably, in some embodiments, the thickness of the piezoelectric film 3 is 0.18λ.
In some embodiments, the silicon carbide single crystal substrate may be a SiC-3C substrate, a SiC-4H substrate, a SiC-6H substrate, or the like. Preferably, in some embodiments, the silicon carbide single crystal substrate is a SiC-6H substrate or a SiC-4H substrate.
In addition, in order to further reduce the frequency temperature coefficient TCF of the surface acoustic wave device and increase the temperature stability of the surface acoustic wave device, the embodiment of the present invention provides polycrystalline silicon dioxide on a silicon carbide single crystal substrate as the temperature compensation layer 2. The polycrystalline silicon dioxide film has an elastic temperature coefficient opposite to that of lithium niobate, which is helpful for reducing the frequency temperature coefficient TCF of the longitudinal surface acoustic wave device, thereby achieving higher temperature stability, avoiding temperature drift of the longitudinal surface acoustic wave device, leading the bandwidth of the longitudinal surface acoustic wave device to be larger and meeting the application environment of a 5G communication system.
In some embodiments, the temperature compensation layer 2 is a polycrystalline silicon dioxide film grown by a Plasma Enhanced Chemical Vapor Deposition (PECVD) method, the PECVD method adopts a low-temperature process, and large-area deposition can be performed, so that the obtained polycrystalline silicon dioxide film is more uniform.
The longitudinal wave sound velocity (about 5700 m/s) of the polycrystalline silicon dioxide film is smaller than the slow shear wave sound velocity (about 7200 m/s) of the silicon carbide single crystal substrate, so that the polycrystalline silicon dioxide film and the lithium niobate single crystal piezoelectric film form a waveguide layer together, and the propagation characteristic parameters such as sound velocity, electromechanical coupling coefficient, frequency temperature coefficient TCF and the like of a high sound velocity guided wave mode can be optimized by regulating and controlling the thicknesses of the lithium niobate single crystal piezoelectric film and the polycrystalline silicon dioxide film.
In some embodiments, the temperature compensation layer 2 has a thickness of 0.16λ -2λ. Under the above conditions of optimizing the film thickness, the temperature compensation effect of the temperature compensation layer 2 is relatively remarkable. Preferably, the thickness of the temperature compensation layer 2 is 0.18λ.
The thickness of the piezoelectric film 3 is 0.16λ -2λ, and the thickness of the temperature compensation layer 2 is 0.16λ -2λ. When the thicknesses of the piezoelectric film 3 and the temperature compensation layer 2 are too high, that is, the total thickness of the waveguide layer is too high, the sound velocity is lowered, and the bandwidth becomes small. When the thickness of the piezoelectric thin film 3 and the temperature compensation layer 2 is too low, i.e., the total thickness of the waveguide layer is too low, LSAW is caused to be converted into other modes, and the bandwidth becomes small.
In some embodiments, the thickness of the piezoelectric film 3 and the temperature compensation layer 2 are substantially comparable. When the ratio of the thickness of the piezoelectric film 3 and the temperature compensation layer 2 is too high, a mode transition is caused, and furthermore, the temperature compensation effect is not obvious because the temperature compensation layer 2 is thin. When the ratio of the thickness of the piezoelectric film 3 to that of the temperature compensation layer 2 is too low, a mode transition is caused, the sound velocity is lowered, and the bandwidth becomes small.
In some embodiments, the interdigital electrode 4 is an aluminum electrode. The Al electrode thickness ranges from 0.06λ to 0.09 λ, preferably 0.08λ. The aluminum electrode width was 0.25λ.
The present invention will be described in detail with reference to the following examples and drawings.
Example 1
A5G SAW filter has a structure shown in figure 1, and comprises a substrate 1, a temperature compensation layer 2, a piezoelectric film 3 and an interdigital transducer 4 which are sequentially overlapped, wherein the substrate 1 adopts a SiC-6H single crystal substrate, the temperature compensation layer 2 adopts an amorphous silicon dioxide film grown by a PECVD method, the piezoelectric film 3 adopts an X-Y cut lithium niobate single crystal piezoelectric film, and the interdigital transducer 4 adopts an aluminum electrode. The aluminum electrode width is 0.25 lambda (i.e., the metallization ratio is 0.5, lambda being the interdigital transducer period).
In XY-LN multilayer structure, electromechanical coupling coefficient, sound velocity with spin angle
And a two-dimensional graph of the change in propagation angle ψ as shown in fig. 2, in order to make XY-LN general in SiC-based SAW in the simulation of acoustic characteristics of different tangential LNs in a multilayer film structure, the temperature compensation layer 2 under the lithium niobate single crystal piezoelectric thin film was not added because the temperature compensation layer 2 does not affect the trend of the change between the electromechanical coupling coefficient and the tangential angle. />
From the analysis of fig. 2, it is known that: the X-cut lithium niobate has a Y plane rotation of not less than-25 DEG and not more than +18 DEG, a surface acoustic wave propagation direction along the Y axis direction, and a propagation angle in the range of not more than +52 DEG and not less than +19 DEG, in which the electromechanical coupling coefficient K is obtained 2 The method comprises the following steps: 13.5%<K 2 <18％。
Specific cases: in XY-LN, the optimal tangential direction of lithium niobate is X37 DEG Y-LN, namely the rotation angle, is obtained through finite element FEM analysis
Rotated by 0 deg., the propagation angle is 37 deg.. When the wavelength λ is 1.12um, the thickness of the interdigital transducer 4 is 0.08λ, the thickness of the piezoelectric film 3 is 0.18λ, and the thickness of the temperature compensation layer 2 is 0.18λ, an admittance curve is obtained as shown in fig. 3, where the acoustic wave mode is: longitudinal Surface Acoustic Wave (LSAW). Results: the electromechanical coupling coefficient is 18.95%, the sound velocity is as high as 5626.41m/s, and the frequency temperature coefficient is-45.04 ppm/DEG C; in addition, the admittance diagram shows that the resonance frequency of LSAW reaches 5GHz, and the transverse high-order mode between the LSAW resonance frequency and the anti-resonance frequency in the multi-layer structure can be well restrained through simulation optimization. So that it can be applied to the design of high-frequency large-bandwidth SAW filter application.
Advantageous effects for the 5G SAW filter of embodiment 1:
(1) The SiC high sound velocity substrate is used, so that the LSAW mode sound velocity reaches more than 5000m/s, and the SAW filter breaks through the low-frequency defect and reaches a frequency band of more than 5GHz under the condition of reasonably controlling the wavelength.
(2) Under the new cut-off proposed by the embodiment, the material structure is reasonably designed, so that the LSAW resonator with large electromechanical coupling coefficient, high Q value and low frequency temperature coefficient can be obtained, and the SAW filter with large bandwidth, high temperature stability and high power tolerance can be obtained.
Example 2
In this example, a diamond substrate was used as the substrate 1, and the other conditions were the same as in example 1. Diamond replaces silicon carbide, and a SAW filter of higher frequency is obtained due to the ultra high sound velocity of diamond.
For purposes of this disclosure, the terms "one embodiment," "some embodiments," "example," "a particular example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (10)
1. A high-performance acoustic device based on longitudinal surface acoustic wave comprises a substrate, a temperature compensation layer, a piezoelectric film and an interdigital transducer which are sequentially overlapped, and is characterized in thatThe substrate adopts a silicon carbide monocrystal substrate or a diamond substrate, the piezoelectric film adopts an X-Y cut lithium niobate monocrystal piezoelectric film, and the spin cutting angle of the X-Y cut lithium niobate monocrystal piezoelectric film is
Propagation angle is psi->
+19°≤ψ≤+52°。
2. The high performance acoustic device based on longitudinal surface acoustic waves as set forth in claim 1,
ψ＝+37°。
3. the high performance acoustic device based on longitudinal surface acoustic waves of claim 1, wherein the piezoelectric film has a thickness of 0.16λ -2λ.
4. The high performance acoustic device based on longitudinal surface acoustic waves of claim 3 wherein the piezoelectric film has a thickness of 0.18λ.
5. The high performance acoustic device based on longitudinal acoustic surface waves according to claim 1, wherein the silicon carbide single crystal substrate is SiC-6H or SiC-4H.
6. The high performance acoustic device based on longitudinal surface acoustic waves of claim 1 wherein the temperature compensation layer is comprised of polycrystalline silicon dioxide.
7. The high performance acoustic device based on longitudinal acoustic surface waves of claim 6, wherein the polycrystalline silicon dioxide thin film is grown by a plasma enhanced chemical vapor deposition method.
8. The high performance acoustic device based on longitudinal surface acoustic waves of claim 1 or 6, wherein the thickness of the temperature compensation layer is 0.16λ -2λ.
9. The high performance acoustic device based on longitudinal acoustic surface waves of claim 1, wherein the thickness of the temperature compensation layer is equal to the thickness of the piezoelectric film.
10. The high performance acoustic device based on longitudinal surface acoustic waves of claim 1, wherein the interdigital electrode is an aluminum electrode.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117013984A (en) * | 2023-08-21 | 2023-11-07 | 天通瑞宏科技有限公司 | Bonding wafer and film surface acoustic wave device |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117013984A (en) * | 2023-08-21 | 2023-11-07 | 天通瑞宏科技有限公司 | Bonding wafer and film surface acoustic wave device |
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