Surface acoustic wave resonator and method for manufacturing the same, and surface acoustic wave filter

Abstract

The present invention provides a surface acoustic wave resonator and a manufacturing method thereof, and a surface acoustic wave filter, which have high quality factor Q, high electromechanical coupling coefficient, good TCF characteristics and power resistance. The surface acoustic wave resonator of the present invention comprises: a composite piezoelectric substrate, the composite piezoelectric substrate having: an LGS base layer, the LGS base layer is formed of single crystal LGS, and a GaN piezoelectric layer formed on the LGS base layer, the thickness of the GaN piezoelectric layer does not exceed 20 times the wavelength of the acoustic wave propagating in the surface acoustic wave resonator; and interdigital electrodes formed on the GaN piezoelectric layer.

Description

Technical Field

[0001] The present invention relates to the technical field of surface acoustic wave devices. More specifically, it relates to a surface acoustic wave resonator using a composite substrate and a method for manufacturing the same, as well as a surface acoustic wave filter. Background Art

[0002] With the rapid development of information technology, especially in the field of wireless communications, the RF front end, which is widely used in various communication equipment, data transmission equipment, audio-visual equipment, and positioning and navigation equipment, has become increasingly important. The RF front end refers to the functional area between the RF transceiver and the antenna, and is composed of devices such as power amplifiers, antenna switches, filters, duplexers, and low-noise amplifiers. In order to adapt to the rapid development of the communication field, higher requirements are placed on the various performance of the RF front end.

[0003] As a key component of the RF front-end, the surface acoustic wave (SAW) filter is based on the piezoelectric effect of piezoelectric materials and works through surface acoustic waves. It uses the interdigital transducer (IDT: interdigital transducer, a periodic metal electrode structure, shaped like crossed hands, so it is also called interdigital electrode) formed on the surface of the piezoelectric material to convert the input electrical signal into an acoustic wave signal or convert the acoustic wave signal into an electrical signal, so as to extract and process the signal. It has the advantages of small size, low cost, lightweight, good consistency, and compatibility with semiconductor processes and is suitable for mass production.

[0004] Among them, the type of piezoelectric material, electromechanical coupling coefficient, temperature coefficient, high temperature resistivity, surface acoustic wave velocity, etc. all determine the performance of the surface acoustic wave filter. Currently, the commonly used piezoelectric materials include single-piece quartz, wafers made of lithium niobate or lithium tantalate crystals, aluminum nitride films, etc. Among them, quartz loses its piezoelectric properties when the temperature reaches 573°C and cannot be used in high-temperature environments; the Curie temperature of lithium niobate crystals is 1210°C, but at temperatures above 600°C, its low resistivity also limits its application in high-temperature environments; aluminum nitride is a non-ferroelectric material, and its film has good piezoelectric properties below 1150°C, but it is difficult to prepare high-quality and large-sized aluminum nitride films. In addition, there are also piezoelectric single crystal materials using lanthanum gallium silicate (LGS). Lanthanum gallium silicate has good temperature characteristics, the electromechanical coupling coefficient is 2 to 3 times that of quartz, and the surface acoustic wave velocity is less than that of quartz, which is conducive to reducing losses, increasing the working bandwidth of surface acoustic wave devices and reducing device size. In addition, lanthanum gallium silicate does not undergo phase change between room temperature and the melting point of 1470°C, has good temperature stability, and is very suitable for working in high-temperature environments.

[0005] When using the above-mentioned piezoelectric materials, due to their high sensitivity to temperature and weak electromechanical coupling, the passband characteristics of the prepared surface acoustic wave filter are poor. With the development of communication technology, especially the advancement of 5G communication technology, higher requirements are put forward for the performance of surface acoustic wave filters and the corresponding structures and materials. For example, indicators such as quality factor Q, effective electromechanical coupling coefficient, insertion loss, bandwidth, TCF, and power resistance all need to be improved and enhanced. Summary of the invention

[0006] This Summary is provided to introduce some 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 to determine or limit the scope of the claimed subject matter.

[0007] In order to solve the above problems, the purpose of the present invention is to provide a surface acoustic wave resonator and a manufacturing method thereof, as well as a surface acoustic wave filter using a composite piezoelectric substrate, wherein the composite piezoelectric substrate is composed of LGS (lanthanum gallium silicate) and GaN (gallium nitride), thereby combining the low temperature coefficient, high resistivity, low sound velocity, and excellent piezoelectric performance of LGS with the excellent heat dissipation, high electron mobility, and low dielectric constant of GaN to obtain a high-quality and high-performance surface acoustic wave filter that can work stably at high frequency, high temperature, and high power and has good heat dissipation.

[0008] The surface acoustic wave resonator of the present invention is a basic unit constituting a surface acoustic wave filter, comprising: a composite piezoelectric substrate, the composite piezoelectric substrate having: an LGS base layer, the LGS base layer being formed of single crystal LGS, and a GaN piezoelectric layer formed on the LGS base layer, the thickness of the GaN piezoelectric layer not exceeding 20 times the wavelength of the acoustic wave propagating in the surface acoustic wave resonator; and interdigital electrodes formed on the GaN piezoelectric layer.

[0009] In the present invention, a composite piezoelectric substrate formed by combining lanthanum gallium silicate (LGS) and gallium nitride (GaN) is used to prepare a surface acoustic wave resonator. Among them, a single crystal piezoelectric material LGS is used as the base layer of the composite piezoelectric substrate. The electromechanical coupling coefficient of single crystal LGS is 17%, which is about 2 to 3 times that of quartz (SiO2), but it also has the same temperature stability as quartz. Moreover, LGS has a temperature coefficient of 0 under a specific tangent (such as a crystal slice of the Euler angle (0°, 138.5°, 26.5°) in the direction of sound wave propagation). By growing a GaN piezoelectric layer on the single crystal LGS base layer, a composite piezoelectric substrate of the surface acoustic wave resonator of the present invention is formed. The crystal structure of the GaN material is a hexagonal wurtzite structure or a tetragonal metastable zinc blende structure, and the lattice symmetry is relatively low, so it has strong piezoelectricity and ferroelectricity. The GaN material also performs outstandingly in terms of stability, and has high hardness and a high melting point, with a melting point of about 1700°C. In addition, GaN material has excellent heat dissipation, with a thermal conductivity of 1.3W / (cm·K). GaN material also has a very high breakdown electric field, so it is one of the important materials for the development of high-temperature, high-power electronic devices and high-frequency microwave devices. GaN's high saturated electron mobility and low dielectric constant make it very suitable for working at high frequencies, while its good insulation and heat dissipation properties make it suitable for working at high temperatures and high powers. Therefore, the inventors selected GaN material as the piezoelectric layer in the composite piezoelectric substrate, and combined it with the single crystal LGS as the base layer to realize a surface acoustic wave resonator suitable for high frequency, high temperature and high power. On the other hand, the thickness of the GaN piezoelectric layer depends on the operating frequency of the surface acoustic wave device prepared thereby. In the present invention, the thickness of the GaN piezoelectric layer does not exceed 20 times the wavelength of the acoustic wave propagating in the surface acoustic wave resonator, which can effectively reduce noise and improve device performance.

[0010] Preferably, in the surface acoustic wave resonator of the present invention, the LGS substrate layer has a temperature coefficient of 0 at the Euler angle (0°, 138.5°, 26.5°) in the acoustic wave propagation direction.

[0011] By utilizing the 0 temperature coefficient of the single crystal LGS at the Euler angle (0°, 138.5°, 26.5°), surface acoustic wave resonators and filters with temperature characteristics close to 0ppm / °C can be prepared, thus meeting the requirements of 5G communication technology.

[0012] Preferably, in the surface acoustic wave resonator of the present invention, the GaN piezoelectric layer is an epitaxial single crystal film epitaxially grown on the LGS substrate layer. The growth of GaN requires a certain temperature and a certain NH3 partial pressure, and the epitaxial growth method can obtain high-quality and stable GaN single crystal films, which has been fully proven in semiconductor and other related fields.

[0013] Preferably, in the surface acoustic wave resonator of the present invention, the GaN piezoelectric layer is formed on the LGS substrate layer by any one of MOCVD, MBE and HVPE.

[0014] Preferably, in the surface acoustic wave resonator of the present invention, a seed layer for preparing the GaN piezoelectric layer is further formed between the GaN piezoelectric layer and the LGS substrate layer, and the thickness of the seed layer is Within.

[0015] The provision of the seed layer can make the crystal structure of the subsequently prepared GaN piezoelectric layer more uniform. The material of the seed layer can be selected by considering the compatibility of the semiconductor process and the matching degree with the GaN lattice. For example, AlN can be used as the seed layer.

[0016] Preferably, in the surface acoustic wave resonator of the present invention, the interdigital electrodes are made of any one metal of Ti, Al, Cu, Au, Pt, Ag, and Pd, or an alloy thereof, or a laminate thereof.

[0017] In order to enhance the bonding force between the interdigital electrodes and the GaN piezoelectric layer to improve the power resistance of the surface acoustic wave resonator and obtain excellent conductivity, the interdigital electrodes preferably adopt the above-mentioned stacked structure, for example, the first layer from bottom to top is Ti / Ni and the second layer is Al / pt.

[0018] Preferably, in the surface acoustic wave resonator of the present invention, the interdigital electrodes can be prepared by directly forming patterned electrodes on the GaN piezoelectric layer.

[0019] Preferably, in the surface acoustic wave resonator of the present invention, the interdigital electrodes can be prepared by patterning the GaN piezoelectric layer and then filling it with electrode material.

[0020] The interdigitated electrodes can be directly formed on the GaN single crystal piezoelectric layer, or can be arranged in a GaN single crystal piezoelectric layer with a pre-formed pattern, and can be designed and processed according to the actual needs of the device.

[0021] Preferably, the surface acoustic wave resonator of the present invention further comprises a protective layer formed on the surface of the interdigital electrodes.

[0022] As a protective layer, it can not only protect the interdigital electrodes from corrosion or damage, but also properly adjust the operating frequency of the resonator to the actual required frequency band in the process. It can also perform temperature compensation to ensure that the resonator works normally at a certain temperature, so that the TCF coefficient of the resonator is reduced to -15~25ppm / ℃.

[0023] Preferably, in the surface acoustic wave resonator of the present invention, the protective layer is formed of any one of SiO2, Si3N4, SiFO, and SiOC.

[0024] The method for manufacturing a surface acoustic wave resonator of the present invention comprises: preparing an LGS substrate layer, which is formed of single crystal LGS; forming a GaN piezoelectric layer on the LGS substrate layer to obtain a composite piezoelectric substrate, wherein the thickness of the GaN piezoelectric layer does not exceed 20 times the wavelength of the acoustic wave propagating in the surface acoustic wave resonator; and forming interdigital electrodes on the GaN piezoelectric layer.

[0025] Preferably, in the method for manufacturing a surface acoustic wave resonator of the present invention, the LGS substrate layer has a temperature coefficient of 0 at the Euler angle (0°, 138.5°, 26.5°) in the acoustic wave propagation direction.

[0026] Preferably, in the method for manufacturing a surface acoustic wave resonator of the present invention, the GaN piezoelectric layer is an epitaxial single crystal thin film epitaxially grown on the LGS substrate layer.

[0027] Preferably, in the method for manufacturing a surface acoustic wave resonator of the present invention, the GaN piezoelectric layer is formed on the LGS substrate layer by any one of MOCVD, MBE and HVPE.

[0028] Preferably, the method for manufacturing a surface acoustic wave resonator of the present invention further comprises the step of forming a seed layer on the GaN piezoelectric layer, preparing the GaN piezoelectric layer on the seed layer, and the thickness of the seed layer is Within.

[0029] Preferably, in the method for manufacturing a surface acoustic wave resonator of the present invention, the seed layer is AlN.

[0030] Preferably, in the surface acoustic wave resonator of the present invention, the interdigital electrodes can be prepared by directly forming patterned electrodes on the GaN piezoelectric layer.

[0031] Preferably, in the surface acoustic wave resonator of the present invention, the interdigital electrodes can be prepared by patterning the GaN piezoelectric layer and then filling it with electrode material.

[0032] The surface acoustic wave filter of the present invention includes at least one surface acoustic wave resonator and a lead wire connecting the at least one surface acoustic wave resonator.

[0033] According to the surface acoustic wave resonator and its manufacturing method, as well as the surface acoustic wave filter of the present invention, a composite piezoelectric substrate composed of an LGS base layer and a GaN piezoelectric layer is used to realize a surface acoustic wave resonator and a surface acoustic wave filter with high quality factor Q, high electromechanical coupling coefficient, good TCF characteristics and power resistance.

[0034] A composite piezoelectric substrate formed by an LGS substrate layer and a single-crystal GaN piezoelectric layer is used to prepare a high-performance surface acoustic wave resonator with a high quality factor, good TCF characteristics and power resistance. Among them, single-crystal LGS itself is a piezoelectric material and is used in surface acoustic wave devices. In the present invention, single-crystal LGS is used as the substrate layer of the composite piezoelectric substrate, and the characteristic of LGS having a temperature coefficient of 0 under a specific tangent (such as a crystal slice of the Euler angle (0°, 138.5°, 26.5°) in the direction of acoustic wave propagation) is utilized. GaN is more easily combined with LGS with a positive temperature coefficient to prepare a surface acoustic wave resonator and filter with a temperature characteristic close to 0ppm / ℃, and the surface acoustic wave resonator and filter thus prepared have a high effective electromechanical coupling coefficient. Moreover, the large difference in sound velocity between LGS and GaN zinc oxide and the high resistivity make it difficult for the signal to leak energy from the substrate and improve the quality factor of the device.

[0035] These and other features and advantages will become apparent by reading the following detailed description and by reference to the associated drawings.It is to be understood that the foregoing general description and the following detailed description are illustrative only and are not restrictive of the aspects of what is claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be described in more detail below with reference to the specific embodiments shown in the accompanying drawings. The flowcharts and block diagrams in the accompanying drawings show the system architecture, functions and operations that may be implemented by the systems and methods according to the embodiments of the present application. The accompanying drawings are only used for the purpose of illustrating preferred embodiments and are not considered to be limitations of the present application. Moreover, the same reference symbols are used to represent the same components throughout the accompanying drawings. Some of the drawings are for illustration only, and their dimensional ratios do not constitute a limitation on the actual dimensional ratios.

[0037] Figure 1 is a schematic diagram of the internal structure of the surface acoustic wave resonator 10 according to the present invention.

[0038] Figure 2 1 is a plan view of the surface acoustic wave resonator 10 according to the present embodiment.

[0039] Figure 3 1 is a plan view showing a surface acoustic wave filter manufactured using the surface acoustic wave resonator 10 of the present embodiment.

[0040] Figure 4This is a waveform diagram of a surface acoustic wave filter formed by cascading the surface acoustic wave resonators 10 according to the present embodiment.

[0041] Figure 5 1 is a flowchart of a method for manufacturing the surface acoustic wave resonator 10 according to the present embodiment.

[0042] Figure 6 1 is a flowchart showing a method for manufacturing the composite piezoelectric substrate 100 according to the present embodiment.

[0043] Figure 7 1 is a process flow chart of one example of a method for manufacturing the electrode 104 in the surface acoustic wave filter 10 according to the present embodiment.

[0044] Figure 8 FIG. 1 is a process flow chart of another example of a method for manufacturing the electrode 104 in the surface acoustic wave filter 10 according to the present embodiment.

[0045] Fig. 9 is a top view of a surface acoustic wave resonator 10 according to the present invention. DETAILED DESCRIPTION

[0046] The present invention will be described in more detail below by referring to the specific embodiments shown in the accompanying drawings. By reading the detailed description of the specific embodiments below, various advantages and benefits of the present invention will become clear to those of ordinary skill in the art. However, it should be understood that the present invention can be implemented in various forms and should not be limited by the various embodiments set forth herein. The following embodiments are provided in order to be able to more thoroughly understand the present invention. Unless otherwise stated, the technical terms or scientific terms used in this application should be the common meanings understood by those skilled in the art to which this application belongs.

[0047] <Basic structure>

[0048] Figure 1 is a schematic diagram of the internal structure of the surface acoustic wave resonator 10 according to the present invention. Figure 1 The cross-sectional view is shown along the thickness direction (stacked direction) of the surface acoustic wave resonator 10. As shown in the figure, the surface acoustic wave resonator 10 includes a base layer 101, a seed layer 102, a piezoelectric layer 103, an electrode 104, and a protective layer 105, wherein the base layer 101 and the piezoelectric layer 103 constitute the composite substrate 100 of the present invention.

[0049] The composite substrate 100 of the surface acoustic wave resonator 10 adopts a composite substrate formed by combining a base layer 101 and a piezoelectric layer 103. Among them, the base layer 101 uses lanthanum gallium silicate (LGS). LGS is insoluble in acid and alkali, has good chemical stability, and has a temperature coefficient of 0 under a specific tangent (such as a crystal slice with an Euler angle (0°, 138.5°, 26.5°) in the direction of acoustic wave propagation), which helps to improve the TCF characteristics of the surface acoustic wave resonator 10, that is, to ensure temperature stability. In addition, the acoustic surface propagation speed of LGS is relatively low (about 2740m / s), which is suitable as a substrate material with high acoustic impedance. In addition, since the LGS single crystal is not a ferroelectric, there is no pyroelectric effect, no polarization is required, and there is no anti-domain region problem, and no phase change occurs until the melting point temperature (1470°C), thereby eliminating the possibility of device performance degradation or complete failure due to incomplete or flipping polarization. In addition, LGS single crystal has moderate hardness, with a Mohs hardness of 5.5. It is non-deliquescent and not easily soluble in common acids and alkalis, which is very beneficial for wafer processing and device manufacturing. At the same time, LGS single crystal has the characteristics of low acoustic scattering and low interference, which is very beneficial for the design and manufacture of surface acoustic wave devices and the full play of surface acoustic wave performance, reducing device noise. LGS single crystal is also insensitive to the process of surface acoustic wave devices, and the material has the self-stability of the temperature characteristics of surface acoustic wave devices, which is very beneficial for the repeatability and consistency of surface acoustic wave device performance. For example, it can allow a large error in the film thickness of the interdigital transducer in the surface acoustic wave device, which also greatly improves the reliability of the device.

[0050] In this embodiment, the thickness of the LGS substrate layer 101 is in the range of 50-1000 μm. Under high power conditions, if the heat dissipation effect of the substrate is poor, the operating temperature of the device will continue to rise, causing the acoustic migration of electrode atoms and eventually damaging the device. However, lanthanum gallium silicate as the substrate layer can make the device work stably with its good heat dissipation performance.

[0051] The material of the piezoelectric layer 103 is GaN. The crystal structure of the GaN material is a hexagonal wurtzite structure or a tetragonal metastable zinc blende structure, and the lattice symmetry is relatively low, so it has strong piezoelectricity and ferroelectricity. The GaN material also performs outstandingly in terms of stability, and has high hardness and a high melting point, with a melting point of about 1700°C. In addition, the heat dissipation of the GaN material is very excellent, with a thermal conductivity of 1.3W / (cm·K). The GaN material also has a very high breakdown electric field, so it is one of the important materials for the development of high-temperature, high-power electronic devices and high-frequency microwave devices. The high saturation electron mobility and low dielectric constant of GaN make it very suitable for working at high frequencies, while its good insulation and heat dissipation properties make it suitable for working at high temperatures and high powers. Therefore, the inventors selected GaN material as the piezoelectric layer in the composite piezoelectric substrate, and combined it with a single crystal LGS as a substrate layer to realize a surface acoustic wave resonator suitable for high frequency, high temperature and high power. In this embodiment, the thickness of the GaN piezoelectric layer 103 does not exceed 20 times the wavelength of the acoustic wave in the surface acoustic wave resonator. The temperature characteristic of the surface acoustic wave resonator 10 manufactured by combining the GaN piezoelectric layer 103 of this embodiment with the LGS base layer 101 can be close to 0 ppm / °C.

[0052] On the other hand, due to the LGS lattice constant GaN lattice constant There is a large lattice mismatch. Therefore, in the present invention, in order to obtain a high-quality GaN film, a seed layer 102 is provided between the LGS substrate layer 101 and the GaN piezoelectric layer 103 to make the crystal structure of the subsequently prepared GaN piezoelectric layer 103 more uniform. In this embodiment, AlN is used as the seed layer 102 in consideration of the compatibility of the semiconductor process and the matching degree with the GaN lattice. The thickness of the AlN seed layer 102 is about 1000 nm. For the surface acoustic wave resonator of this embodiment, the AlN seed layer 102 is not necessary, and is only provided to improve the film quality of the subsequent GaN piezoelectric layer 103. The seed layer 102 can be omitted if the process conditions can ensure the film quality. The material of the seed layer 102 is not limited to AlN, and can be appropriately selected according to the actual process.

[0053] The piezoelectric layer 103 is provided with an electrode 104, i.e., an interdigital electrode (IDT electrode), which is composed of a metal or alloy such as Ti, Al, Cu, Cr, Au, Pt, Ag, Pd, Ni, or a laminate of these metals or alloys. In order to enhance the bonding force between the electrode 104 and the piezoelectric layer 103 and improve the power resistance and conductivity of the surface acoustic wave resonator 10, the electrode 104 in this embodiment preferably adopts a laminate structure, for example, the first layer from bottom to top is Ti or Ni, and the second layer is Al or Pt. The thickness of the electrode 104 is 0.1 to 0.6 μm.

[0054] Figure 1 In the embodiment, the electrode 104 is disposed on the surface of the piezoelectric layer 103 and can be formed by a patterning process including photoresist patterning, evaporation coating, stripping, etc. Although not shown, the electrode 104 can also be completely buried in the piezoelectric layer 103 by a process such as etching. The specific preparation method will be described later.

[0055] The protective layer 105 covers the upper surface of the electrode 104, plays a role in protecting the electrode 104 from corrosion or damage, and can also serve as a frequency modulation layer to appropriately adjust the frequency to the actual required frequency band and a temperature compensation layer to reduce the TCF coefficient of the resonator to, for example, -15 to 25 ppm / °C. The material of the protective layer 105 can be selected from materials such as SiO2, Si3N4, SiFO, SiOC, etc., and its thickness and material selection depend on the type of resonator. In this embodiment, the protective layer 105 is formed of SiO2 material. When the surface acoustic wave resonator of this embodiment is Normal-SAW, the thickness of the protective layer 105 is between 100 and 200 nm. When the surface acoustic wave resonator of this embodiment is a TC-SAW (temperature compensated SAW), the thickness of the protective layer 105 can be controlled within 2.5 μm.

[0056] In addition to the above structure, Figure 1 Although not shown in the figure, the surface acoustic wave resonator 10 of this embodiment further includes a lead wire (also called a connection wire) and a heat dissipation layer. Figure 2 1 is a top view of the surface acoustic wave resonator 10 of this embodiment. The figure shows an electrode 104 and a lead 106 electrically connected thereto. A plurality of surface acoustic wave resonators 10 are electrically connected via the lead 106, thereby forming a surface acoustic wave filter. The lead 106 is made of a metal with high electrical conductivity, and any metal with high electrical conductivity such as Au, Ag, Cu, Ag, etc. can be selected. In this embodiment, the thickness of the lead 106 is 0.5-2.5 μm.

[0057] When a plurality of surface acoustic wave resonators 10 are cascaded through leads 106 to form a surface acoustic wave filter, a heat dissipation layer 107 may be provided around the filter. Since the surface acoustic wave filter generates a large amount of heat when operating at high frequency and high power, it has high requirements for heat dissipation in order to ensure stable operation during operation. In addition to improving the heat dissipation of the composite substrate 100 in this embodiment, a heat dissipation layer 107 may be provided on the surface of the device such as Figure 3 As shown, a heat dissipation layer such as a metal heat dissipation layer is additionally provided to further improve the heat dissipation capability during the process. Figure 3 1 is a top view showing a surface acoustic wave filter fabricated from the surface acoustic wave resonator 10 of the present embodiment. In the figure, the heat dissipation layer 107 is distributed around the filter in a square structure.

[0058] The heat dissipation layer 107 is formed of a metal with good heat dissipation properties and can be formed simultaneously with the lead 106 but is not in electrical contact with the lead 106. Figure 1 The heat dissipation layer 107 can be arranged in a direction of stacking of the layers of the surface acoustic wave filter 10 and in direct contact with the GaN piezoelectric layer 103, thereby drawing the heat inside the device to the outside. Figure 2 Other than the position, you can also use different Figure 2 Circle or other arbitrary shapes.

[0059] If the surface acoustic wave resonator 10 of this embodiment is applied to TC-SAW and is covered with a thicker temperature compensation layer, for example, the protective layer 105 is a SiO2 temperature compensation layer of about 2.5μm, the provision of the metal heat dissipation layer 107 can further improve the heat dissipation performance of the surface acoustic wave resonator or surface acoustic wave filter manufactured thereby.

[0060] Figure 4 This is a waveform diagram of a surface acoustic wave filter composed of cascaded surface acoustic wave resonators 10 of this embodiment. As shown in the figure, the filter has a high center frequency (2.60 GHz), few ripples in the passband (2.53 to 2.68 GHz), a large bandwidth, low insertion loss, and excellent out-of-band suppression effect.

[0061] It can be seen that the surface acoustic wave resonator according to this embodiment includes: a composite piezoelectric substrate, the composite piezoelectric substrate having: an LGS base layer, the LGS base layer is formed of single crystal LGS, and a GaN piezoelectric layer formed on the LGS base layer, the thickness of the GaN piezoelectric layer does not exceed 20 times the wavelength of the acoustic wave propagating in the surface acoustic wave resonator; and interdigital electrodes formed on the GaN piezoelectric layer. Thus, by combining the low temperature coefficient, high resistivity, low acoustic velocity, and excellent piezoelectric performance of LGS with the excellent heat dissipation, high electron mobility, and low dielectric constant of GaN, a high-frequency heat dissipation type surface acoustic wave filter can be obtained.

[0062] <Manufacturing method>

[0063] Next, combine Figures 5 to 8 , the method for manufacturing the surface acoustic wave resonator 10 of the present invention is specifically described. Figure 5 1 is a flowchart of a method for manufacturing the surface acoustic wave resonator 10 according to the present embodiment. Figure 6 1 is a flowchart showing a method for manufacturing the composite piezoelectric substrate 100 according to the present embodiment. Figure 7 1 is a process flow chart of one example of a method for manufacturing the electrode 104 in the surface acoustic wave filter 10 according to the present embodiment. Figure 8FIG. 1 is a process flow chart of another example of a method for manufacturing the electrode 104 in the surface acoustic wave filter 10 according to the present embodiment.

[0064] like Figure 5 As shown, in step S1001, a composite piezoelectric substrate 100 is prepared. As described above, the composite piezoelectric substrate 100 of the present invention is composed of an LGS base layer 101 and a GaN piezoelectric layer 103. There are many methods for preparing the composite piezoelectric substrate 100. In this embodiment, considering the characteristics of the GaN piezoelectric layer 103, a method of epitaxially growing a GaN film is adopted. The epitaxial growth of GaN includes MOCVD (metal organic vapor phase epitaxy, including AP (normal pressure)-MOCVD, LP (low pressure)-MOCVD, PE (plasma enhanced)-MOCVD, etc.), MBE (molecular beam epitaxy, including ECR (electron cyclotron resonance)-MBE), HVPE (hydride vapor phase epitaxy) and the like. In this embodiment, it is preferred to epitaxially grow a GaN film as the piezoelectric layer 103 by MOCVD. Moreover, in this embodiment, the thickness of the GaN epitaxial film does not exceed 20 times the wavelength of the acoustic wave in the surface acoustic wave filter.

[0065] On the other hand, due to the LGS lattice constant GaN lattice constant There is a large lattice mismatch. Therefore, in the present invention, in order to obtain a high-quality GaN film, a seed layer 102 is provided between the LGS substrate layer 101 and the GaN piezoelectric layer 103, so that the crystal structure of the subsequently prepared GaN piezoelectric layer 103 is more uniform. In this embodiment, AlN is used as the seed layer 102 in consideration of the compatibility of the semiconductor process and the matching degree with the GaN lattice. However, for the surface acoustic wave resonator of this embodiment, the AlN seed layer 102 is not necessary. It is only provided to improve the film quality of the subsequent GaN piezoelectric layer 103. The seed layer 102 can also be omitted if the process conditions can guarantee the film quality. The material of the seed layer 102 is not limited to AlN, and can be appropriately selected according to the actual process. Therefore, in the subsequent Figure 7 In the process flow chart of an embodiment of a method for manufacturing the electrode 104 shown, the process flow corresponding to step S1001 only shows the structures of the LGS substrate layer 101 and the GaN piezoelectric layer 103 , while the illustration of the AlN seed layer 102 is omitted.

[0066] Figure 6The preparation method of the composite piezoelectric substrate 100 of this embodiment is shown. First, a single crystal lanthanum gallium silicate LGS substrate for forming the LGS base layer 101 is prepared. Then, an AlN film is formed on the LGS base layer 101 as a seed layer 102. There are many methods for preparing the AlN film. In this embodiment, the epitaxial growth method is also used. The thickness of the obtained AlN film, i.e., the seed layer 102, is controlled within Next, a GaN single crystal thin film is epitaxially grown on the AlN seed layer 102 by the MOCVD method. The LGS base layer 101, the AlN seed layer 102, and the GaN piezoelectric layer 103 thus obtained are subjected to post-processing such as annealing to form the composite piezoelectric substrate 100 of this embodiment.

[0067] Back to Figure 5 In step S1002, a patterned interdigital electrode, namely, electrode 104, is produced. As described above, the electrode (IDT electrode) 104 can be made of metals or alloys such as Ti, Al, Cu, Cr, Au, Pt, Ag, Pd, Ni, or a laminate of these metals or alloys. In this embodiment, it is preferably made of a laminate, for example, the first layer from bottom to top may be Ti / Ni, and the second layer may be Al / pt. Through the structure of the laminate, and the thickness is preferably 0.1 to 0.6 μm, the bonding force between the electrode 104 and the GaN piezoelectric layer 103 can be enhanced, thereby improving the power resistance of the surface acoustic wave resonator 10 and obtaining excellent conductivity.

[0068] Figure 7 , Figure 8 1 and 2 are process flow charts of two examples of a method for manufacturing the electrode 104 in the surface acoustic wave filter 10 according to the present embodiment.

[0069] Figure 7 As described above, the AlN seed layer 102 is omitted from the illustration, and only the LGS base layer 101 and the GaN piezoelectric layer 103 constituting the composite piezoelectric substrate 100 are shown. Figure 7 In the embodiment shown, the patterned interdigital electrodes 104 are directly prepared on the GaN epitaxial film. Specifically, the patterned interdigital electrodes are prepared by photolithography → evaporation coating → wet stripping process, which is relatively simple and is not easy to damage the GaN epitaxial film 103.

[0070] Figure 8 In the embodiment of the present invention, the electrode 104 is disposed in the GaN piezoelectric layer 103. Figure 8 As shown in FIG. 1 , the formation step of the electrode 104 is divided into two steps. First, the GaN piezoelectric layer 103 is subjected to photolithography and IBE (ion beam epitaxy) to selectively open the GaN piezoelectric layer 103 so that the GaN piezoelectric layer 103 is patterned. Then, Figure 7The process of the electrode 104 in the embodiment is the same, and the electrode 104 is manufactured by photolithography (which can be set as needed, or photolithography can be omitted) → evaporation coating → wet stripping process. The height (thickness) of the electrode 104 manufactured in this way is required to be not less than the height (thickness) of the GaN piezoelectric layer. Figure 8 The structure shown in FIG. 1 is a case where the electrode 104 is flush with the GaN piezoelectric layer 103 , which can be achieved by CMP (chemical mechanical polishing) and / or trimming processes.

[0071] Figure 8 The preparation process of the electrode 104 shown is compared with Figure 7 The implementation method is more complicated and the cost is higher, but through the excellent properties of the GaN piezoelectric layer 103 such as heat dissipation and insulation, the surface acoustic wave resonator, surface acoustic wave filter and other devices made therefrom can still work stably at high temperature and high power, while suppressing the atomic acoustic migration of the electrode and effectively dissipating heat, greatly improving the power resistance of the device.

[0072] Fig. 9 1 is a top view of the electrode 104 of the surface acoustic wave resonator 10 according to the present embodiment. As shown in the figure, the electrode 104 is a metal electrode periodic structure shaped like two crossed hands, and is composed of a plurality of interdigital electrodes arranged at intervals. Fig. 9 In the embodiment, the duty cycle of the electrode 104 is 0.5, and the width of the electrode 104 and the spacing between the electrodes are the same, both of which are 0.25λ (λ is the wavelength of the acoustic wave in the surface acoustic wave resonator 10), and the thickness of the electrode 104 is 180nm.

[0073] Back to Figure 5 , in step S1003, a protective layer 105 is prepared. In this embodiment, SiO2 is selected as the material of the protective layer 105, which can be prepared by sputtering or CVD. As mentioned above, the protective layer 105 can also function as a frequency modulation layer or a temperature compensation layer. For example, in the case of preparing a TC-SAW device, the thickness of the protective layer 105 can be adjusted (for example, within 2.5 μm) to serve as a temperature compensation layer to ensure that the device works normally at a certain temperature, and its TCF coefficient can be reduced to -15 to 25 ppm / °C. If a Normal-SAW is prepared, its thickness can be controlled at Here, SiO2 is selected as the material of the protective layer 105, but Si3N4, SiFO, SiOC and other materials can also be selected. The specific thickness and material selection depend on the type of device and requirements.

[0074] Although not shown in the figure, after step S1003, the process of manufacturing the lead 106, the heat dissipation layer 107, etc. is also included. The lead 106 can be made by photolithography, dry etching, evaporation coating and stripping process. The lead can electrically connect multiple resonators to form a filter, and the lead uses a metal with high conductivity, such as Au / Ag / Cu / Ag. In this embodiment, the thickness of the lead 106 is 0.5 to 2.5 μm. The heat dissipation layer 107 can be as shown in FIG. Figure 3 The heat dissipation layer 107 is formed of a metal with good heat dissipation performance and can be formed simultaneously with the lead 106 but is not in electrical contact with the lead 106. The heat dissipation layer 107 is in direct contact with the GaN piezoelectric layer 103 in the stacking direction of the device, thereby conducting the heat inside the device to the outside. The heat dissipation layer 107 can be arranged at Figure 2 Other than the position, you can also use different Figure 2 In addition to using metal materials with good heat dissipation, the heat dissipation layer 107 can also be made of other non-metal materials with high thermal conductivity.

[0075] A composite piezoelectric substrate formed by an LGS substrate layer and a single-crystal GaN piezoelectric layer is used to prepare a high-performance surface acoustic wave resonator with a high quality factor, good TCF characteristics and power resistance. Among them, single-crystal LGS itself is a piezoelectric material and is used in surface acoustic wave devices. In the present invention, single-crystal LGS is used as the substrate layer of the composite piezoelectric substrate, and the characteristic of LGS having a temperature coefficient of 0 under a specific tangent (such as a crystal slice of the Euler angle (0°, 138.5°, 26.5°) in the direction of acoustic wave propagation) is utilized. GaN is more easily combined with LGS with a positive temperature coefficient to prepare a surface acoustic wave resonator and filter with a temperature characteristic close to 0ppm / ℃, and the surface acoustic wave resonator and filter thus prepared have a high effective electromechanical coupling coefficient. Moreover, the large difference in sound velocity between LGS and GaN zinc oxide and the high resistivity make it difficult for the signal to leak energy from the substrate and improve the quality factor of the device.

[0076] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application.

[0077] Reference numerals

[0078] 10Surface Acoustic Wave Resonator

[0079] 100 Composite substrate

[0080] 101 Basal Layer

[0081] 102 seed layer

[0082] 103 Piezoelectric layer

[0083] 104 Electrodes

[0084] 105 protective layer

[0085] 106 Lead

[0086] 107 heat dissipation layer.

Claims

1. A surface acoustic wave resonator, characterized in that: include: A composite piezoelectric substrate, the composite piezoelectric substrate comprising: an LGS base layer, the LGS base layer being formed of single crystal LGS, and a GaN piezoelectric layer formed on the LGS base layer, the thickness of the GaN piezoelectric layer being no greater than 20 times the wavelength of the acoustic wave propagating in the surface acoustic wave resonator; as well as Interdigital electrodes are formed on the GaN piezoelectric layer.

2. The surface acoustic wave resonator according to claim 1, characterized in that The LGS substrate layer has a temperature coefficient of 0 at the Euler angle (0°, 138.5°, 26.5°) in the direction of sound wave propagation.

3. The surface acoustic wave resonator according to claim 1, characterized in that The GaN piezoelectric layer is an epitaxial single crystal thin film epitaxially grown on the LGS substrate layer.

4. The surface acoustic wave resonator according to claim 1, characterized in that The GaN piezoelectric layer is formed on the LGS substrate layer by any one of MOCVD, MBE and HVPE.

5. The surface acoustic wave resonator according to claim 1, characterized in that A seed layer for preparing the GaN piezoelectric layer is also formed between the GaN piezoelectric layer and the LGS substrate layer, and the thickness of the seed layer is Within.

6. The surface acoustic wave resonator according to claim 5, characterized in that The seed layer is AlN.

7. The surface acoustic wave resonator according to claim 1, characterized in that The interdigital electrodes are made of any one metal of Ti, Al, Cu, Au, Pt, Ag, and Pd, or an alloy thereof, or a laminate thereof.

8. The surface acoustic wave resonator according to claim 1, characterized in that The invention also includes a protective layer formed on the surface of the interdigital electrode.

9. The surface acoustic wave resonator according to claim 8, characterized in that The protective layer is formed of any one of SiO2, Si3N4, SiFO, and SiOC.

10. A method for manufacturing a surface acoustic wave resonator, characterized in that: include: preparing an LGS base layer, wherein the LGS base layer is formed of single crystal LGS; Forming a GaN piezoelectric layer on the LGS substrate layer to obtain a composite piezoelectric substrate, wherein the thickness of the GaN piezoelectric layer is no more than 20 times the wavelength of the acoustic wave propagating in the surface acoustic wave resonator; and Interdigital electrodes are formed on the GaN piezoelectric layer.

11. The method for manufacturing a surface acoustic wave resonator according to claim 10, characterized in that: The GaN piezoelectric layer is an epitaxial single crystal thin film epitaxially grown on the LGS substrate layer.

12. The method for manufacturing a surface acoustic wave resonator according to claim 10, characterized in that: The GaN piezoelectric layer is formed on the LGS substrate layer by any one of MOCVD, MBE and HVPE.

13. The method for manufacturing a surface acoustic wave resonator according to claim 10, characterized in that: The invention also includes the step of forming a seed layer on the GaN piezoelectric layer, preparing the GaN piezoelectric layer on the seed layer, and the thickness of the seed layer is Within.

14. The method for manufacturing a surface acoustic wave resonator according to claim 13, characterized in that: The seed layer is AlN.

15. The method for manufacturing a surface acoustic wave resonator according to claim 10, characterized in that: The interdigitated electrodes are prepared by directly forming patterned electrodes on the GaN piezoelectric layer.

16. The method for manufacturing a surface acoustic wave resonator according to claim 10, characterized in that: The interdigital electrodes can be prepared by patterning the GaN piezoelectric layer and then filling it with electrode materials.

17. A surface acoustic wave filter, characterized in that: The device comprises at least one surface acoustic wave resonator according to any one of claims 1 to 9, and a lead wire connecting at least one of the surface acoustic wave resonators.

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