CN114584097A - Surface acoustic wave resonator, method for manufacturing the same, and surface acoustic wave filter - Google Patents
Surface acoustic wave resonator, method for manufacturing the same, and surface acoustic wave filter Download PDFInfo
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- H—ELECTRICITY
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/08—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of resonators or networks using surface acoustic waves
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
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- H03H9/46—Filters
- H03H9/64—Filters using surface acoustic waves
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Abstract
The invention provides a surface acoustic wave resonator, a method for manufacturing the same, and a surface acoustic wave filter, which have high quality factor Q, high electromechanical coupling coefficient, good TCF characteristic and power resistance. The surface acoustic wave resonator of the present invention comprises: a composite piezoelectric substrate having: an LGS base layer formed of a single crystal LGS, and a ZnO piezoelectric layer formed over the LGS base layer, the ZnO piezoelectric layer being formed of a single crystal ZnO having a c-axis preferred orientation; and interdigital electrodes formed on the ZnO piezoelectric layer.
Description
Technical Field
The invention relates to the technical field of surface acoustic wave devices. And more particularly, to a surface acoustic wave resonator using a composite piezoelectric substrate, a method of manufacturing the same, and a surface acoustic wave filter
Background
With the rapid development of information technology, especially in the field of wireless communication, it is becoming more important to apply the radio frequency front end widely to various communication devices, data transmission devices, audio-visual devices, positioning navigation devices, and the like. The radio frequency front end is a functional area between a radio frequency transceiver and an antenna and consists of devices such as a power amplifier, an antenna switch, a filter, a duplexer, a low noise amplifier and the like. In order to adapt to the rapid development of the communication field, higher requirements are put forward on various performances of the radio frequency front end.
A Surface Acoustic Wave (SAW) filter is used as a key device of a radio frequency front end, works based on the piezoelectric effect of a piezoelectric material and through the SAW, converts an input electric signal into an acoustic wave signal or converts the acoustic wave signal into the electric signal by using an interdigital transducer (IDT) formed on the surface of the piezoelectric material so as to extract and process the signal, and has the advantages of small size, low cost, light weight, good consistency and semiconductor process compatibility, and is suitable for mass production.
The type of piezoelectric material, electromechanical coupling coefficient, temperature coefficient, high-temperature resistivity, surface acoustic wave velocity and the like all determine the performance of the surface acoustic wave filter. The piezoelectric materials commonly used at present are a wafer made of single quartz, lithium niobate or lithium tantalate crystal, an aluminum nitride film, and the like. Wherein, quartz loses piezoelectric property when the temperature reaches 573 ℃, and cannot be used in high-temperature environment; the Curie temperature of the lithium niobate crystal is 1210 ℃, but the low resistivity of the lithium niobate crystal also limits the application of the lithium niobate crystal in a high-temperature environment at the temperature of over 600 ℃; aluminum nitride is a non-ferroelectric material, and the thin film thereof has good piezoelectric characteristics at 1150 ℃ or less, but it is difficult to prepare a high-quality and large-sized aluminum nitride thin film. In addition, piezoelectric single crystal materials of Lanthanum Gallium Silicate (LGS) are also used. The langasite has good temperature characteristic, the electromechanical coupling coefficient is 2 to 3 times of that of quartz, the wave velocity of the surface acoustic wave is less than that of the quartz, the loss is reduced, the working bandwidth of the surface acoustic wave device is improved, and the size of the device is reduced. In addition, the lanthanum gallium silicate does not have phase change between room temperature and the melting point of 1470 ℃, has good temperature stability and is very suitable for working in a high-temperature environment.
When the piezoelectric material is used, the passband characteristics of the prepared surface acoustic wave filter are not good due to high sensitivity to temperature and weak electromechanical coupling. With the development of communication technology, especially the improvement of 5G communication technology, higher requirements are put forward on the performance of the surface acoustic wave filter and corresponding structures and materials, for example, indexes such as quality factor Q, effective electromechanical coupling coefficient, insertion loss, bandwidth, TCF, and power durability need to be improved and promoted.
Disclosure of Invention
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter; nor is it intended to be used as an aid in determining or limiting the scope of the claimed subject matter.
In order to solve the above problems, an object of the present invention is to provide a surface acoustic wave resonator using a composite piezoelectric substrate, a method of manufacturing the same, and a surface acoustic wave filter, in which a composite piezoelectric substrate is formed of an LGS (lanthanum gallium silicate) and ZnO composite layer, and a high-performance surface acoustic wave filter having a low TCF and a low loss is obtained by combining characteristics of the LGS such as a low temperature coefficient, a high resistivity, a low acoustic velocity, and excellent piezoelectricity and high acoustic velocity of ZnO.
The surface acoustic wave resonator of the present invention includes: a composite piezoelectric substrate having: an LGS base layer formed of a single crystal LGS, and a ZnO piezoelectric layer formed over the LGS base layer, the ZnO piezoelectric layer being formed of a single crystal ZnO having a c-axis preferred orientation; and interdigital electrodes formed on the ZnO piezoelectric layer.
In the present invention, a surface acoustic wave resonator is manufactured using a composite piezoelectric substrate formed by combining Lanthanum Gallium Silicate (LGS) and zinc oxide (ZnO). First, a conventional single-crystal piezoelectric material LGS is used as a base layer of the composite piezoelectric substrate. The electromechanical coupling coefficient of the single-crystal LGS was 17%, which was about quartz (SiO)2) 2-3 times of the crystal volume, while having the same temperature stability as quartz, and the LGS has a temperature coefficient of 0 at a specific tangential direction (e.g., a crystal slab at euler angles (0 °,138.5 °,26.5 °)) of the acoustic wave propagation direction. Next, single crystal ZnO was used as a piezoelectric layer, and combined with single crystal LGS to form a composite piezoelectric substrate. Single-crystal ZnO has a smaller thermal expansion coefficient than lithium tantalate (LiTaO3) or lithium niobate (LiNbO3), and the like, and it can realize a surface acoustic wave resonator having a temperature characteristic close to 0 ppm/deg.c in combination with the above-mentioned specific tangential LGS. Moreover, a single crystal or C-axis oriented ZnO piezoelectric material has a high electromechanical coupling coefficient, and a surface acoustic wave resonator produced therefrom also has a high effective electromechanical coupling coefficient. In addition, the difference in victory concern between the single-crystal LGS and the single-crystal ZnO is large, and electricity is generatedThe resistivity is also high, so that the energy is difficult to be taken away by the sound wave leaked from the substrate, and the quality factor Q of the surface acoustic wave resonator is ensured. Moreover, the high electromechanical coupling coefficient and the low dielectric constant of the single crystal ZnO play a role in inhibiting energy loss and further improving quality factors.
Preferably, in the surface acoustic wave resonator of the present invention, the LGS base layer has a temperature coefficient of 0 at an euler angle (0 °,138.5 °,26.5 °) in a direction of propagation of an acoustic wave.
By utilizing the 0 temperature coefficient of the single crystal LGS under Euler angles (0 degrees, 138.5 degrees and 26.5 degrees), surface acoustic wave resonators and filters with temperature characteristics close to 0 ppm/DEG C can be prepared, so that the requirements of 5G communication technology can be met.
Preferably, in the surface acoustic wave resonator of the present invention, after the LGS base layer and the ZnO piezoelectric layer are bonded, the ZnO piezoelectric layer is thinned to a predetermined thickness by a semiconductor thinning process and a chemical mechanical polishing process, thereby forming the composite piezoelectric substrate.
The LGS base layer and the original substrate of the ZnO piezoelectric layer are bonded and then thinned and polished until the thickness of the piezoelectric layer meets the design requirement, so that the large-size ultrathin single crystal ZnO piezoelectric layer with the thickness of 15-20 mu m can be manufactured, and the single crystal property of the ZnO piezoelectric layer cannot be damaged.
Preferably, in the surface acoustic wave resonator of the present invention, the ZnO piezoelectric layer is formed on the LGS base layer by any one of PVD, MOCVD, MBE, and ALD.
In addition to the bonding thinning method, a ZnO thin film layer having a desired thickness may be formed or grown on the LGS base layer as the ZnO piezoelectric layer by a film formation technique such as Physical Vapor Deposition (PVD), Metal Oxide Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), or Atomic Layer Deposition (ALD).
Preferably, in the surface acoustic wave resonator of the present invention, the thickness of the ZnO piezoelectric layer is 20 λ or less, where λ is a surface acoustic wave wavelength excited by the interdigital electrode.
The thickness of the ZnO piezoelectric layer influences the performance of the surface acoustic wave resonator, and the thickness of the ZnO piezoelectric layer is controlled within 20 times of the wavelength of the sound wave transmitted in the surface acoustic wave resonator, so that noise waves can be effectively reduced, and the performance of the device is improved. The thickness of the ZnO piezoelectric layer is preferably set to 1 λ.
In the surface acoustic wave resonator according to the present invention, the interdigital electrode is preferably made of any one of metals of Ti, Al, Cu, Au, Pt, Ag, and Pd, an alloy thereof, and a laminate thereof.
In order to enhance the bonding force between the interdigital electrode and the ZnO piezoelectric layer to improve the power resistance of the surface acoustic wave resonator and obtain excellent conductivity, the interdigital electrode preferably adopts the structure of the above laminated body, for example, the first layer is Ti/Ni and the second layer is Al/pt from bottom to top.
Preferably, the surface acoustic wave resonator of the present invention further comprises a protective layer formed on the surface of the interdigital electrode.
As a protective layer, the interdigital electrode can be protected from being corroded or damaged, the working frequency of the resonator can be properly adjusted to the actually required frequency band in the process, temperature compensation can be carried out, the resonator can normally work at a certain temperature, and the TCF coefficient of the resonator is reduced to-15-25 ppm/DEG C.
Preferably, in the surface acoustic wave resonator of the present invention, the protective layer is made of SiO2、Si3N4SiFO, and SiOC.
The method for manufacturing a surface acoustic wave resonator of the present invention includes: preparing an LGS base layer formed of a single-crystal LGS; forming a ZnO piezoelectric layer over the LGS base layer to obtain a composite piezoelectric substrate, the ZnO piezoelectric layer being formed of single crystal ZnO having a preferred c-axis orientation; and forming an interdigital electrode on the ZnO piezoelectric layer.
Preferably, in the method for manufacturing a surface acoustic wave resonator of the present invention, the LGS base layer has a temperature coefficient of 0 at an euler angle (0 °,138.5 °,26.5 °) in a direction of propagation of an acoustic wave.
Preferably, in the method for manufacturing a surface acoustic wave resonator of the present invention, the LGS base layer and the ZnO piezoelectric layer form the composite piezoelectric substrate by bonding, and after the bonding, the ZnO piezoelectric layer is thinned to a prescribed thickness by a semiconductor thinning process and a chemical mechanical polishing process.
Preferably, in the method for manufacturing a surface acoustic wave resonator of the present invention, before the bonding, a cleaning pretreatment is performed on bonding surfaces of the LGS base layer and the ZnO piezoelectric layer, respectively.
By cleaning and pretreating the bonding surface before bonding, good cleanliness and roughness can be obtained, and good adhesion and bonding property of the substrate and the piezoelectric layer after subsequent bonding can be ensured.
Preferably, in the method for manufacturing a surface acoustic wave resonator of the present invention, the ZnO piezoelectric layer is formed on the LGS base layer by any one of PVD, MOCVD, MBE, and ALD.
Preferably, in the method for manufacturing a surface acoustic wave resonator of the present invention, the thickness of the ZnO piezoelectric layer is 20 λ or less, λ being a surface acoustic wave wavelength excited by the interdigital electrode.
The surface acoustic wave filter of the present invention includes at least one of the surface acoustic wave resonators.
According to the surface acoustic wave resonator, the manufacturing method thereof and the surface acoustic wave filter of the present invention, the composite piezoelectric substrate composed of the LGS base layer and the ZnO piezoelectric layer is used to realize the surface acoustic wave resonator and the surface acoustic wave filter having a high quality factor Q, a high electromechanical coupling coefficient, a good TCF characteristic and a good power durability.
The composite piezoelectric substrate formed by the LGS base layer and the single crystal ZnO piezoelectric layer is adopted, so that the high-performance surface acoustic wave resonator with high quality factors, good TCF (thermal conductivity field effect) characteristics and power resistance can be prepared. The surface acoustic wave resonator and the surface acoustic wave filter with the temperature characteristics close to 0 ppm/DEG C are prepared by using the single crystal ZnO which has a smaller thermal expansion coefficient compared with the traditional material and is easier to combine with LGS with a positive temperature coefficient, and the single crystal ZnO piezoelectric material with the preferred orientation of the C axis has a high electromechanical coupling coefficient, so that the prepared surface acoustic wave resonator and the prepared surface acoustic wave filter have high effective electromechanical coupling coefficients. On the other hand, a single crystal LGS itself is a piezoelectric material and is applied to a surface acoustic wave device, and in the present invention, a surface acoustic wave filter having a temperature characteristic close to 0 ppm/deg.c can be manufactured by combining the single crystal LGS as a base layer of a composite pressure-point substrate, using a characteristic that the LGS has a temperature coefficient of 0 at a specific tangential direction (e.g., a crystal slice at an euler angle (0 deg., 138.5 deg., 26.5 deg.) in the acoustic wave propagation direction) with single crystal ZnO. Moreover, the characteristics of larger difference of acoustic velocity and high resistivity of the LGS compared with zinc oxide enable signals to be difficult to leak from the substrate to take away energy, and quality factors of the device are improved.
These and other features and advantages will become apparent upon reading the following detailed description and upon reference to the accompanying drawings. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of aspects as claimed.
Drawings
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which specific embodiments of the invention are shown. The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to embodiments of the present application. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to refer to like parts throughout the drawings. The drawings are only schematic and are not to be construed as limiting the actual dimensional proportions.
Fig. 1 is a schematic diagram of the structure of a surface acoustic wave resonator 10 according to the present invention.
Fig. 2 is an admittance diagram of a surface acoustic wave resonator 10 according to the present invention.
Fig. 3 is a flowchart of a method of manufacturing the surface acoustic wave resonator 10 according to the present invention.
Fig. 4 is a process flow diagram of one embodiment of a method of manufacturing the surface acoustic wave resonator 10 according to the present invention.
Fig. 5 is a plan view of the electrode 103 of the surface acoustic wave resonator 10 according to the present invention.
Fig. 6 is a top view of the surface acoustic wave resonator 10 according to the present invention.
Detailed Description
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which specific embodiments of the invention are shown. Various advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading the following detailed description of the specific embodiments. It should be understood, however, that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. The following embodiments are provided so that the invention may be more fully understood. Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meaning as understood by those of skill in the art to which this application belongs.
Fig. 1 is a schematic diagram of the structure of a surface acoustic wave resonator 10 according to the present invention. As shown in the figure, the surface acoustic wave resonator 10 includes a base layer 101, a piezoelectric layer 102, an electrode 103, and a protective layer 104, wherein the base layer 101 and the piezoelectric layer 102 constitute a composite substrate 100 of the present invention.
The composite substrate 100 of the surface acoustic wave resonator 10 is a composite substrate in which a base layer 101 and a piezoelectric layer 102 are bonded to each other. Among them, Lanthanum Gallium Silicate (LGS) is used for the base layer 101. The LGS is hardly soluble in acid and alkali, has good chemical stability, and has a temperature coefficient of 0 at a specific tangential direction (e.g., a crystal slice at an euler angle (0 °,138.5 °,26.5 °) in a propagation direction of an acoustic wave), thereby contributing to improvement of the TCF characteristic of the surface acoustic wave resonator 10, i.e., ensuring temperature stability. Moreover, the LGS has a low acoustic surface propagation velocity (about 2740 m/s), and is suitable as a substrate material with high acoustic impedance. Moreover, since the LGS single crystal is not ferroelectric, there is no pyroelectric effect, there is no need for polarization and no domain inversion problem, and phase transition does not occur until the melting point temperature (1470 ℃), thereby eliminating the possibility of device performance degradation or complete failure due to incomplete polarization or inversion. In addition, the LGS single crystal has moderate hardness, Mohs hardness of 5.5, is not deliquescent and is not easy to dissolve in common acid and alkali, thus being very beneficial to wafer processing and device manufacturing. Meanwhile, the LGS single crystal has the characteristics of low acoustic scattering and small interference, which is very beneficial to the design and manufacture of surface acoustic wave devices and the full play of surface acoustic wave performance, and reduces the noise of the devices. The LGS single crystal also has the insensitivity of the surface acoustic wave device process, and the material has the self-stability of the temperature characteristic of the surface acoustic wave device, so that the repeatability and the consistency of the performance of the surface acoustic wave device are greatly facilitated, for example, the film thickness of an interdigital transducer in the surface acoustic wave device can be allowed to have larger errors, and the reliability of the device is also greatly improved.
In the present embodiment, the LGS base layer 101 has a thickness ranging from 50 to 1000 μm. Under the condition of high power, if the heat dissipation effect of the substrate is not good, the working temperature of the device can be continuously increased to cause acoustic migration of electrode atoms to finally damage the device, but the langasite serving as the substrate layer can enable the device to stably work by virtue of good heat dissipation performance of the langasite.
The material of the piezoelectric layer 102 is C-axis oriented single crystal ZnO. ZnO is one of the most widely used piezoelectric materials for surface acoustic wave filters, and has excellent piezoelectric properties, such as high electromechanical coupling coefficient, low dielectric constant, high acoustic velocity and the like, due to the preferred orientation of the lattice C axis. In addition, the resistivity of single crystal ZnO is also high. These characteristics satisfy the low loss requirements of surface acoustic wave filters. Further, the difference in acoustic impedance between the ZnO piezoelectric layer 102 and the LGS base layer 101 can suppress leakage of a surface acoustic wave excited by an electrode 103 described later from the composite substrate 100.
On the other hand, single crystal ZnO has a wurtzite-type crystal structure and a lattice constant
LGS is a trigonal system with a lattice constant
In the case where the single crystal C axis is preferentially oriented, both can achieve good bonding (e.g., bonding), and thus, the bonding surface between the LGS base layer 101 and the ZnO piezoelectric layer 102 has good adhesion and bondability, ensuring the quality of the resulting composite substrate 10.
The temperature characteristics of the surface acoustic wave resonator 10 prepared by combining the ZnO piezoelectric layer 102 of the present embodiment with the LGS base layer 101 described above can be close to 0 ppm/deg.c. The thickness of the single crystal ZnO piezoelectric layer 102 is 0.5-20 μm.
The piezoelectric layer 102 is provided with an electrode 103, i.e., an interdigital electrode (IDT electrode), and is made of a metal or an alloy such as Ti, Al, Cu, Cr, Au, Pt, Ag, Pd, and Ni, or a laminate of these metals or alloys. In order to enhance the bonding force between the electrode 103 and the piezoelectric layer 102, to improve the power resistance of the surface acoustic wave resonator 10, and to enhance the conductivity, the electrode 103 in this embodiment is preferably a laminate structure in which, for example, the first layer is Ti or Ni and the second layer is Al or pt from the bottom to the top. The thickness of the electrode 103 is 0.1 to 0.6 μm. In fig. 1, the electrode 103 is provided on the surface of the piezoelectric layer 102, and may be formed by a patterning process including photoresist patterning, evaporation coating, peeling, and the like. Although not shown, the electrode 103 may be completely buried in the piezoelectric layer 102 by etching or the like.
The protective layer 104 functions to protect the electrode 103 from erosion or damage, and also functions as a frequency adjustment layer to appropriately adjust the frequency to an actually required frequency band, and a temperature compensation layer to lower the TCF coefficient of the resonator to, for example, -15 to 25 ppm/deg.c. The material of the protective layer 104 may be selected from, for example, SiO2、Si3N4SiFO, SiOC, etc., the thickness and material selection of which depend on the type of resonator.
Fig. 2 is an admittance characteristics diagram of the surface acoustic wave resonator 10 according to the present invention. As shown in the figure, the curve is smooth without burrs, and the surface acoustic wave resonator 10 embodying the present invention effectively suppresses parasitic oscillation of the device. The difference between the resonant frequency fs and the anti-resonant frequency fp is about 40MHz, which facilitates the manufacture of a high bandwidth bandpass filter. Further, as shown in FIG. 2, the electromechanical coupling coefficient k is shown29.77%, the surface acoustic wave resonator 10 can realize a high electromechanical coupling coefficient.
Next, a method for manufacturing a surface acoustic wave resonator according to the present invention will be specifically described with reference to fig. 3 and 4. Fig. 3 is a flowchart of a method of manufacturing the surface acoustic wave resonator 10 according to the present invention. Fig. 4 is a process flow diagram of one embodiment of a method of manufacturing a surface acoustic wave resonator 10 according to the present invention.
As shown in fig. 3, at stepIn S1001, the composite piezoelectric substrate 100 is prepared. As described above, the composite piezoelectric substrate 100 of the present invention is composed of the LGS base layer 101 and the ZnO piezoelectric layer 102. There are various methods for manufacturing the composite piezoelectric substrate 100, and a bonding method is adopted in this embodiment, as shown in fig. 4. First, a single-crystal langasite LGS substrate for forming the LGS base layer 101 and a single-crystal ZnO substrate for forming the ZnO piezoelectric layer 102 are prepared. The thickness of the LGS substrate herein is in the range of 50-1000 μm. Subsequently, using a plasma, e.g. H2And cleaning and pretreating the bonding surface, namely the surface to be bonded of the LGS substrate and the ZnO substrate by using plasma of/Ar/He and the like to obtain good cleanliness and roughness, and ensure that the LGS substrate and the ZnO substrate after subsequent bonding have good adhesion and bonding property.
Then, most of the ZnO substrate is removed by a semiconductor thinning process, and a small portion of the ZnO substrate is removed by a CMP (chemical mechanical polishing) process, thereby obtaining a desired thickness and flatness of the ZnO piezoelectric layer 102. The thickness of the ZnO piezoelectric layer 102, which is the thinned ZnO substrate, is 0.5 to 20 μm, for example. The thickness of the ZnO piezoelectric layer 102 affects the performance of the surface acoustic wave resonator 10, and by controlling the thickness of the ZnO piezoelectric layer 102 within 20 times of the wavelength of an acoustic wave propagating in the surface acoustic wave resonator, noise waves can be effectively reduced, and the performance of the device is improved. The thickness of the ZnO piezoelectric layer 102 is preferably set to 1 λ. Through step S1001, the composite piezoelectric substrate 100 is obtained.
In addition to the bonding method described above, the ZnO piezoelectric layer 102 may be formed by PVD, MOCVD, MBE, ALD, or the like. For example, a single crystal ZnO thin film of a predetermined thickness may be grown on the LGS base layer 101 by a PVD (physical vapor deposition) process, or a single crystal ZnO thin film may be epitaxially grown on the LGS base layer 101 by an MOCVD (metal organic chemical vapor deposition) process.
Returning to fig. 3, in step S1002, a patterned interdigital electrode, i.e., electrode 103, is formed. As described above, the electrode (IDT electrode) 103 may be made of a metal or alloy such as Ti, Al, Cu, Cr, Au, Pt, Ag, Pd, Ni, or a laminate of these metals or alloys, and in the present embodiment, it is preferably made of a laminate, and for example, the first layer may be Ti/Ni and the second layer may be Al/Pt from the bottom to the top, and the structure of the laminate can enhance the bonding force between the electrode 103 and the ZnO piezoelectric layer 102, thereby improving the power durability of the surface acoustic wave resonator 10 and obtaining excellent conductivity. In this embodiment mode, the electrode 103 can be formed by a process of patterning a photoresist → evaporating a plating → peeling. As shown in fig. 4, electrodes 103 are arranged at equal intervals on the surface of the ZnO piezoelectric layer 102. In the present embodiment, the thickness of the electrode 103 is 0.1 to 0.6. mu.m.
Fig. 5 is a top view of the electrode 103 of the surface acoustic wave resonator 10 according to the present invention. As shown, the electrode 103 is a periodic structure of metal electrodes shaped like a two-handed cross. The side view thereof is as shown in fig. 1 and 4, and is composed of a plurality of electrodes arranged at intervals. The duty cycle of the electrode 103 is 0.5. In the figure, the width of the electrodes 103 and the spacing between the electrodes are the same, both 0.25 λ, and the thickness of the electrodes is 180 nm.
In step S1003, the protective layer 104 is produced. In this embodiment, SiO is selected2The material of the protective layer 104 may be formed by sputtering, CVD, or the like. As described above, the protective layer 104 may also function as a frequency modulation layer or a temperature compensation layer. For example, in the case of manufacturing a temperature compensated surface acoustic wave (TC-SAW) device, the thickness of the protective layer 104 (e.g., within 2.5 μm) can be adjusted to serve as a temperature compensation layer, so that the device can work normally at a certain temperature, and the TCF coefficient can be reduced to-15 to 25 ppm/degree c. If a conventional surface acoustic wave device (Normal-SAW) is prepared, the thickness can be controlled within the range
Within. SiO is chosen here2As the material of the protective layer 104, Si may be selected3N4The specific thickness and material selection of the materials such as SiFO and SiOC depend on the kind and requirements of the device.
In step S1004, a lead (connection wire) is manufactured. The lead can be manufactured by photoetching, dry etching, evaporation coating and stripping processes. The lead wires may electrically connect the plurality of resonators to form a filter using a high conductivity metal, such as Au/Ag/Cu/Ag, etc. Fig. 6 is a top view of a surface acoustic wave resonator 10 according to the present invention, in which an electrode 103 and a lead 105 are included. In the present embodiment, the thickness of the lead 105 is 0.5 to 2.5 μm.
According to the surface acoustic wave resonator, the manufacturing method thereof and the surface acoustic wave filter of the present invention, the composite piezoelectric substrate composed of the LGS base layer and the ZnO piezoelectric layer is used to realize the surface acoustic wave resonator and the surface acoustic wave filter having a high quality factor Q, a high electromechanical coupling coefficient, a good TCF characteristic and a good power durability. The composite piezoelectric substrate formed by the LGS base layer and the single crystal ZnO piezoelectric layer is adopted, so that the high-performance surface acoustic wave resonator with high quality factor, good TCF (thermal conductive film) characteristic and power resistance can be prepared. The surface acoustic wave resonator and the filter with the temperature characteristics close to 0 ppm/DEG C are prepared by using the single crystal ZnO which has a smaller thermal expansion coefficient compared with the traditional material and is easier to combine with the LGS with the positive temperature coefficient, and the single crystal ZnO piezoelectric material with the preferred orientation of the C axis has a high electromechanical coupling coefficient, so that the prepared surface acoustic wave resonator and the prepared filter have high effective electromechanical coupling coefficients. On the other hand, a single crystal LGS itself is a piezoelectric material and is applied to a surface acoustic wave device, and in the present invention, a surface acoustic wave filter having a temperature characteristic close to 0 ppm/deg.c can be manufactured by combining the single crystal LGS as a base layer of a composite pressure-point substrate, using a characteristic that the LGS has a temperature coefficient of 0 at a specific tangential direction (e.g., a crystal slice at an euler angle (0 deg., 138.5 deg., 26.5 deg.) in the acoustic wave propagation direction) with single crystal ZnO. Moreover, the characteristics of larger difference of acoustic velocity of LGS compared with zinc oxide and high resistivity enable signals to be difficult to leak from a substrate to take away energy, and quality factors of devices are improved.
The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present disclosure, and the present disclosure should be construed as being covered by the claims and the specification.
Reference numerals
10 surface acoustic wave resonator
100 composite substrate
101 base layer
102 piezoelectric layer
103 electrode
104 protective layer
105 lead wires.
Claims (17)
1. A surface acoustic wave resonator, comprising:
a composite piezoelectric substrate having: a Langasite (LGS) base layer formed of a single crystal LGS, and a ZnO piezoelectric layer formed on the LGS base layer, the ZnO piezoelectric layer being formed of a single crystal ZnO having a c-axis preferred orientation; and
interdigital electrodes formed on the ZnO piezoelectric layer.
2. A surface acoustic wave resonator as set forth in claim 1,
the LGS substrate layer has a temperature coefficient of 0 at euler angles (0 °,138.5 °,26.5 °) in the direction of acoustic wave propagation.
3. A surface acoustic wave resonator as set forth in claim 1,
and the LGS base layer and the ZnO piezoelectric layer are bonded, and then the ZnO piezoelectric layer is thinned to a specified thickness, so that the composite piezoelectric substrate is formed.
4. A surface acoustic wave resonator as set forth in claim 1,
the ZnO piezoelectric layer is formed on the LGS base layer by any one of PVD, MOCVD, MBE, ALD.
5. A surface acoustic wave resonator as set forth in claim 1,
the thickness of the ZnO piezoelectric layer is less than 20 lambda, and lambda is the wavelength of surface acoustic waves excited by the interdigital electrode.
6. A surface acoustic wave resonator as set forth in claim 1,
the interdigital electrode is made of any one of metals of Ti, Al, Cu, Au, Pt, Ag and Pd, or an alloy thereof, or a laminate thereof.
7. A surface acoustic wave resonator as set forth in claim 1,
the protective layer is formed on the surface of the interdigital electrode.
8. A surface acoustic wave resonator as set forth in claim 7,
the protective layer is made of SiO2、Si3N4SiFO, SiOC.
9. A method for manufacturing a surface acoustic wave resonator, comprising:
preparing an LGS base layer formed of a single-crystal LGS;
forming a ZnO piezoelectric layer over the LGS base layer to obtain a composite piezoelectric substrate, the ZnO piezoelectric layer being formed of single crystal ZnO having a preferred c-axis orientation;
and forming interdigital electrodes on the ZnO piezoelectric layer.
10. The method of claim 9,
the LGS substrate layer has a temperature coefficient of 0 at euler angles (0 °,138.5 °,26.5 °) in the direction of acoustic wave propagation.
11. The method of claim 9,
LGS stratum basale with the ZnO piezoelectric layer forms through the bonding mode compound piezoelectric substrate the bonding back attenuate ZnO piezoelectric layer to regulation thickness.
12. The method of claim 11,
the thinning is performed by a semiconductor thinning process and a chemical mechanical polishing process.
13. The method of claim 11,
and before bonding, cleaning and pretreating bonding surfaces of the LGS base layer and the ZnO piezoelectric layer respectively.
14. The method of claim 9,
the ZnO piezoelectric layer is formed on the LGS base layer by any one of PVD, MOCVD, MBE, ALD.
15. The method of claim 9,
the thickness of the ZnO piezoelectric layer is below 20 lambda, and lambda is the surface acoustic wave wavelength excited by the interdigital electrode.
16. A surface acoustic wave filter, characterized in that,
comprising at least one surface acoustic wave resonator as claimed in any one of claims 1 to 8.
17. A surface acoustic wave filter as set forth in claim 16,
the surface acoustic wave filter is any one of a Normal-SAW (traditional surface acoustic wave) filter, a TC-SAW (temperature compensation surface acoustic wave) filter and an IHP-SAW (ultra high performance surface acoustic wave) filter.
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| JPH1084248A (en) * | 1996-09-10 | 1998-03-31 | Murata Mfg Co Ltd | Surface acoustic wave device and its production |
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| US20210111689A1 (en) * | 2019-10-10 | 2021-04-15 | Skyworks Solutions, Inc. | Method of manufacturing acoustic wave device with multi-layer piezoelectric substrate |
| CN113300683A (en) * | 2021-05-25 | 2021-08-24 | 中国科学院上海微系统与信息技术研究所 | Surface acoustic wave resonator and preparation method thereof |
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| JPH1084248A (en) * | 1996-09-10 | 1998-03-31 | Murata Mfg Co Ltd | Surface acoustic wave device and its production |
| US6121713A (en) * | 1996-10-18 | 2000-09-19 | Tdk Corporation | Surface acoustic wave device |
| US20210111689A1 (en) * | 2019-10-10 | 2021-04-15 | Skyworks Solutions, Inc. | Method of manufacturing acoustic wave device with multi-layer piezoelectric substrate |
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