Surface acoustic wave device and radio frequency filter and multiplexer including same

Abstract

The present invention relates to a surface acoustic wave (SAW) device with no spurious mode, which can be used efficiently in radio frequency (RF) filters and multiplexers (either alone or in conjunction with similar or other SAW devices), in particular to a surface acoustic wave (SAW) device with no spurious mode, which can be used in both radio frequency (RF) filters and multiplexers. Different from a traditional SAW device, the SAW device provided by the invention uses a yttrium aluminum garnet (YAG) substrate instead of a Si substrate. The dielectric layer and the piezoelectric layer are sequentially arranged on the top surface of the YAG substrate, and the IDT is arranged on the piezoelectric layer. The YAG substrate is characterized in that the rear surface thereof has an arithmetic mean roughness Ra greater than 50 nm. By using the YAG substrate (i.e., with such Ra) in the SAW device, efficient spurious mode suppression can be provided (at least) in a frequency range from 0.5 GHz to 2.7 GHz.

Description

Technical Field

[0001] The present invention generally relates to the field of surface acoustic wave (SAW) devices. In particular, the present invention relates to yttrium aluminum garnet (YAG) based multilayer SAW devices, and radio frequency (RF) filters and multiplexers using one or more of such YAG based multilayer SAW devices. Background Art

[0002] RF filters using mechanical resonators (e.g., SAW resonators) are known in the art. A SAW resonator converts an electrical signal into a mechanical oscillation (i.e., SAW) and vice versa (i.e., a mechanical oscillation or SAW is converted into an electrical signal). SAW resonators are typically used <100> or <111> Si substrate. In addition to certain SAW modes generated in such SAW resonators and expected in terms of their applicability, there may also be stray modes between the opposing faces of the piezoelectric material included in the SAW resonator. These stray modes are parasitic because they can adversely affect the operation of an RF filter that includes such a SAW resonator. More specifically, high-frequency stray modes of a given RF filter may interfere with RF filtering in different (high-frequency) communication bands. This makes it difficult to integrate different RF filters together in a communication circuit (e.g., a multiplexer). Due to the presence of undesirable stray modes, many existing SAW resonator-based RF filters and multiplexers are of limited use - they are only applicable when the stray modes are not harmful to the communication circuit. Summary of the invention

[0003] The present invention summary briefly introduces a series of concepts, which will be further described in the detailed description. The present invention summary is not intended to identify the key features of the present invention, nor is it intended to limit the scope of the present invention.

[0004] It is an object of the present invention to provide high frequency spurious mode suppression in a SAW device, thereby allowing the SAW device to be efficiently used in SAW resonators of RF filters and multiplexers.

[0005] The above objects are achieved by the features of the independent claims in the attached claims. Further embodiments and examples are apparent from the dependent claims, the detailed description and the drawings.

[0006] According to a first aspect, a SAW device is provided. The SAW device comprises: a YAG substrate having a top surface and a rear surface; a dielectric layer disposed on the top surface of the YAG substrate; a piezoelectric layer disposed on the dielectric layer; and an interdigital transducer (IDT) disposed on the piezoelectric layer. The IDT is used to convert an input RF signal into a SAW propagating in the piezoelectric layer. The rear surface of the YAG substrate has an arithmetic mean roughness Ra greater than 50 nanometers (nanometer, nm). By using the YAG substrate (i.e., having such a Ra) in the SAW device, efficient spurious mode suppression can be provided in the frequency range from 0.5 GHz to 2.7 GHz. It should also be noted that, compared with the method based on <100> Compared to existing SAW devices (eg, SAW resonators) based on Si substrates, SAW devices based on YAG substrates may be particularly beneficial (in terms of spurious mode suppression) in the frequency sub-range from 0.5 GHz to 1.8 GHz.

[0007] In an exemplary embodiment of the first aspect, the top surface of the YAG substrate has an arithmetic mean roughness Ra of less than 50 nm. By providing such a Ra of the top surface of the YAG substrate, stray mode suppression can be performed more efficiently.

[0008] In an exemplary embodiment of the first aspect, the YAG substrate has a thickness ranging from 200 micrometers (μm) to 600 μm. Preferably, the thickness of the YAG substrate is 350 μm ± 100 nm. At this thickness of the YAG substrate, the SAW device can be more compact in size, thereby enabling the SAW device (together with similar or other SAW devices) to be efficiently integrated into an RF filter or multiplexer.

[0009] In an exemplary embodiment of the first aspect, the ratio of the thickness of the piezoelectric layer to the thickness of the dielectric layer is in the range of 0.6 to 1.4. Preferably, the ratio is in the range of 0.7 to 0.85. Such thicknesses of the piezoelectric layer and the dielectric layer also make the SAW device more compact in size, thereby making the SAW device suitable for use in different RF filters and / or multiplexers.

[0010] In an exemplary embodiment of the first aspect, the piezoelectric layer is made of LiTaO3 or LiNbO3. These materials have piezoelectric properties suitable for the correct operation of the SAW device.

[0011] In an exemplary embodiment of the first aspect, the dielectric layer is made of SiO2. This material has dielectric properties suitable for the correct operation of the SAW device. In addition, compared with LiTaO3 and LiNbO3, SiO2 has an opposite temperature coefficient of elasticity (TCE), which provides efficient temperature compensation of the SAW device.

[0012] According to a second aspect, an RF filter is provided, the RF filter comprising at least one SAW resonator. Each of the at least one SAW resonator comprises at least one SAW device according to the first aspect; two SAW reflectors arranged so that the IDT of each of the at least one SAW device is located between the two SAW reflectors. The RF filter configured in this way can be integrated with one or more (similar or other) RF filters in a multiplexer in a single chip or multi-chip manner.

[0013] In an exemplary embodiment of the second aspect, the at least one SAW resonator comprises a plurality of SAW resonators, each SAW resonator comprising a single SAW device according to the first aspect. In this embodiment, the plurality of SAW resonators are arranged in a ladder scheme. By using the ladder scheme, (single-port) SAW resonators can be electrically connected in series and in parallel within the RF filter. The ladder scheme also provides a dense arrangement of SAW resonators.

[0014] In an exemplary embodiment of the second aspect, in addition to the multiple SAW resonators, the RF filter also includes an additional SAW resonator, the additional SAW resonator including: at least two SAW devices according to the first aspect; two reflectors, arranged so that the IDT of each of the at least two SAW devices is located between the two reflectors of the additional SAW resonator. In this embodiment, the RF filter consists of two filter parts: one filter part has a (single-port) SAW resonator arranged according to a ladder scheme, and the other filter part has a (multi-port) SAW resonator, including acoustically coupled IDTs of two or more SAW devices according to the first aspect. In other words, the former corresponds to a ladder SAW filter structure, while the latter corresponds to a coupled resonator filter (CRF) structure. In some RF applications, it may be beneficial to combine these filter structures in one RF filter.

[0015] In an exemplary embodiment of the second aspect, as an alternative to the plurality of SAW resonators, the at least one SAW resonator comprises a single SAW resonator comprising at least two SAW devices according to the first aspect. In this embodiment, the RF filter is configured as a CRF only.

[0016] According to a third aspect, a multiplexer is provided. The multiplexer includes a circuit board and at least two RF filters according to the second aspect. Each of the at least two RF filters is mounted on the circuit board in an inverted manner so that the IDT of each of the at least one SAW device in each of the at least one SAW resonator faces the circuit board. The multiplexer also includes: at least one impedance matching component, arranged on the circuit board, and used to provide impedance matching between the at least two RF filters and the antenna used for coupling of each of the at least two RF filters. By using a combination of two or more (similar or different) RF filters, the multiplexer can provide efficient RF filtering in different high frequency bands.

[0017] In an exemplary embodiment of the third aspect, the circuit board comprises a plurality of metal interlayers with interconnections. These interconnections can ensure correct signal routing between different parts of the circuit board. Thus, they can ensure correct (low parasitic) connections between the RF filters themselves and between one or more impedance matching components and the RF filters.

[0018] In an exemplary embodiment of the third aspect, the at least one impedance matching component comprises at least one of an inductor and a capacitor. These types of impedance matching components can provide appropriate impedance matching between the antenna and the RF filter.

[0019] Other features and advantages of the present invention will become apparent upon reading the following detailed description and upon viewing the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is explained below with reference to the accompanying drawings, in which:

[0021] Figure 1 A schematic cross-sectional view of a Si-based SAW device provided by the prior art is shown;

[0022] Figure 2 shows a schematic cross-sectional view of a YAG-based SAW device provided by an exemplary embodiment;

[0023] Figure 3 A schematic top view of a SAW resonator provided by an exemplary embodiment is shown;

[0024] Figure 4 A schematic block diagram of an RF filter provided by an exemplary embodiment is shown;

[0025] Figure 5 An exemplary embodiment provides Figure 4 A possible implementation of an RF filter on a single chip;

[0026] Figure 6 An exemplary embodiment is provided for manufacturing a Figure 4 A flow chart of a method for implementing an RF filter;

[0027] Fig. 7A and Figure 7B Different schematic diagrams of a multiplexer provided by an exemplary embodiment are shown, namely: Fig. 7A shows an isometric view of the multiplexer, and Figure 7B Shown along Fig. 7A A cross-sectional view of the multiplexer taken along line AA in FIG.

[0028] Figure 8 A flowchart of a method for manufacturing the multiplexer of FIG. 7 is shown according to an exemplary embodiment;

[0029] Fig. 9 A schematic block diagram of a duplexer provided by an exemplary embodiment is shown;

[0030] Fig.10 The frequency dependence of the transmission coefficient S21 of two duplexers is shown, namely: one duplexer with a YAG-based RF filter and the other duplexer with a Si-based RF filter. DETAILED DESCRIPTION

[0031] Various embodiments of the present invention are further described in detail in conjunction with the accompanying drawings. However, the present invention can be embodied in many other forms and should not be construed as being limited to any specific structure or function disclosed in the following description. On the contrary, these embodiments are provided to describe the present invention in detail and completely.

[0032] Based on the detailed description, it will be apparent to those skilled in the art that the scope of the present invention includes any embodiment of the present invention disclosed herein, whether the embodiment is implemented independently or in combination with any other embodiment of the present invention. For example, the apparatus disclosed herein can be implemented in practice by using any number of embodiments provided herein. In addition, it should be understood that any embodiment of the present invention can be implemented using one or more features set forth in the appended claims.

[0033] The word “exemplary” is used herein to mean “serving as an illustration.” Any embodiment described herein as “exemplary” is not to be construed as preferred or advantageous over other embodiments unless otherwise stated.

[0034] For convenience, any positioning terms such as "left", "right", "top", "bottom", "above", "below", "up", "down", "horizontal", "vertical", etc. may be used herein to describe the relationship of an element or feature to one or more other elements or features according to the accompanying drawings. It is obvious that the positioning terms are intended to include different orientations of the devices disclosed herein, as well as one or more orientations depicted in the accompanying drawings. For example, if it is imagined that the device in the figure is rotated 90 degrees clockwise, the elements or features described as "left" and "right" relative to other elements or features will be oriented "above" and "below" the other elements or features, respectively. Therefore, the positioning terms used herein should not be interpreted as any limitation to the present invention.

[0035] As used in the embodiments disclosed herein, a surface acoustic wave (SAW) device may refer to a multilayer structure comprising metal electrodes arranged in a forked form on the surface of a piezoelectric layer or substrate to form an interdigital transducer (IDT). An input radio frequency (RF) signal applied to the IDT causes a deformation wave or SAW in the piezoelectric layer or substrate. The IDT may also operate in the opposite manner, i.e., an input SAW applied to the IDT causes an output RF signal. Generally, IDTs are well known in the art and are not described herein. When a SAW device is combined with two or more reflectors, a SAW resonator is formed so that the IDT is arranged between the reflectors. Such a SAW resonator can operate the received RF signal wirelessly without the need for an additional power supply.

[0036] Figure 1 FIG. 1 shows a schematic cross-sectional view of a Si-based SAW device 100 provided in the prior art. The Si-based SAW device 100 is a multi-layer structure including <100> Si substrate 102, SiO2 layer 104 disposed on substrate 102, LiTaO3 layer 106 disposed on SiO2 layer 104, and IDT formed on the surface of LiTaO3 layer 106. For simplicity, Figure 1Only two metal (e.g., Al, Au, or Cu) trapezoidal electrodes (i.e., finger electrodes) 108 and 110 connected to separate electrical bus bars of the IDT are shown. This means that the electrodes 108 and 110 are repeated periodically on the surface of the LiTaO3 layer 106, so that there are hundreds of such electrodes along the X direction. It is known that LiTaO3 has excellent piezoelectric properties, so the input RF signal applied to the IDT will cause SAW propagation in the LiTaO3 layer 106. Preferably, LiTaO3 has the following characteristics: θY-X LiTaO3, which means that (relative to the crystal X-axis) θ is rotated in the Y direction, where θ = 20° ÷ 65°, and the SAW propagation direction is aligned with the crystal X-axis. The thickness t of the SiO2 layer 104 and the LiTaO3 layer 106 can be selected based on the inter-electrode spacing ("pitch") 112 to be obtained or the SAW wavelength λ. For example, the following relationship can be used: λ = 2×pitch, t SiO2 =0.1λ÷0.6λ, and t LiTaO3 =0.1λ÷0.6λ. The Si-based SAW device 100 can be used in RF filters and multiplexers; however, it cannot effectively suppress spurious modes that may adversely affect the operation of the RF filters and multiplexers.

[0037] The exemplary embodiments disclosed herein provide a technical solution that can alleviate or even eliminate the above-mentioned shortcomings specific to the prior art. Specifically, the exemplary embodiments disclosed herein relate to a SAW device with high-frequency spurious mode suppression, which can be efficiently used in RF filters and multiplexers (used alone or in combination with similar or other SAW devices). Unlike existing SAW devices (such as SAW device 100), the SAW device uses a yttrium aluminum garnet (YAG) substrate instead of a Si substrate. The dielectric layer and the piezoelectric layer are sequentially arranged on the top surface of the YAG substrate, and the IDT is arranged on the piezoelectric layer. The YAG substrate is characterized in that its rear surface has an arithmetic mean roughness Ra greater than 50nm. By using the YAG substrate (i.e., having such a Ra) in the SAW device, efficient spurious mode suppression can be provided (at least) in a frequency range from 0.5GHz to 2.7GHz.

[0038] Figure 2A schematic cross-sectional view of a YAG-based SAW device 200 provided by an exemplary embodiment is shown. The YAG-based SAW device 200 is a multilayer structure, which, unlike the Si-based SAW device 100, has a substrate 202 made of YAG instead of Si. The YAG substrate 202 may have a thickness in the range of 200 μm to 600 μm (preferably low, with a thickness of 350 μm ± 100 nm). The YAG substrate 202 has a top surface 204 and a rear surface 206. It is assumed that the rear surface 206 has an Ra greater than 50 nm, while the top surface 204 may optionally have an Ra less than 50 nm. The YAG-based SAW device 200 also includes a dielectric layer 208 disposed on the top surface 204 of the YAG substrate 202 and a piezoelectric layer 210 disposed on the dielectric layer 208. The dielectric layer 208 and the piezoelectric layer 210 may be implemented similarly to the dielectric layer 104 and the piezoelectric layer 106, respectively. That is, the dielectric layer 208 may be made of SiO2 and have a thickness of 0.1λ÷0.6λ, and the piezoelectric layer 210 may be made of LiTaO3 and have a thickness of 0.1λ÷0.6λ. At the same time, those skilled in the art will recognize that the present invention is not limited to these materials and thicknesses, and any other materials and thicknesses of the layers constituting the SAW device 200 may be used depending on the particular application. For example, the piezoelectric layer 210 may also be made of LiNbO3, and the thicknesses of the piezoelectric layer 210 and the dielectric layer 208 may be selected so that their ratio (i.e., t LiTaO3 / t SiO2 ) ranges from 0.6 to 1.4, preferably from 0.7 to 0.85.

[0039] like Figure 2 As shown, the YAG-based SAW device 200 further includes an IDT formed on the piezoelectric layer 210; Figure 2Only two trapezoidal electrodes (or IDT finger electrodes) 212 and 214 connected to individual electrical bus bars of the IDT are shown. Each electrode of the IDT can be made of a thin layer of electrode material (e.g., Al or Cu) deposited on the piezoelectric layer 210 through a thin adhesion Ti or Cr layer. The electrodes 212 and 214 are separated from each other by a spacing 216, which can be defined similarly to the spacing 112. The layers and electrodes included in the YAG-based SAW device 200 can be provided by using any existing manufacturing technology, such as rubbing (e.g., photolithography, electron lithography, extreme ultraviolet (EUV) lithography, etc.), 3D printing, atomic layer deposition (ALD), chemical vapor deposition (CVD), metal organic CVD (MOCVD), ultra-high vacuum CVD (UHV-CVD), chemical beam epitaxy (CBE), laser ablation, sputtering, electrolytic deposition (such as electroplating), molecular beam epitaxy (MBE), etc.

[0040] Figure 3 A schematic top view of a SAW resonator 300 provided by an exemplary embodiment is shown. The SAW resonator 300 includes a YAG-based SAW device 302 and two (e.g., distributed) reflectors 304 and 306. The YAG-based SAW device 302 can be implemented similarly to the YAG-based SAW device 200. The reflectors 304 and 306 can be manufactured as metal gratings. The reflectors 302 and 304 are formed so that the IDT 308 of the YAG-based SAW device 302 is located between the two reflectors. More specifically, the reflectors 304 and 306 are arranged along the propagation direction of the SAW excited by the IDT 308 (i.e., in the Figure 3 The left and right sides of the IDT 308 in the YAG-based SAW device 302 are arranged on the piezoelectric layer. In this configuration, the SAW excited by the IDT 308 is reflected toward the IDT 308 by each of the reflectors 304 and 306, thereby storing energy near the acoustic resonance. The SAW resonator 300 is also known in the art as a single-port SAW resonator.

[0041] It should be noted that the present invention is not limited to Figure 3The single IDT design of the SAW resonator 300 shown. In some other embodiments, the SAW resonator 300 may include two or more YAG-based SAW devices (each similar to the YAG-based SAW device 200), which are arranged so that the IDT of each of the YAG-based SAW devices is located between the reflectors 304 and 306. In this case, there is an array of two or more acoustically coupled IDTs placed between the reflectors 304 and 306, which can be used to form a coupled resonator filter (CRF) structure.

[0042] Figure 4 FIG. 4 is a schematic block diagram of an RF filter 400 provided by an exemplary embodiment. The RF filter 400 includes a plurality of SAW resonators, assuming that each of the plurality of SAW resonators is implemented as a (single-port) SAW resonator 300. The plurality of SAW resonators can be conveniently divided into two subsets: one subset has SAW resonators S1 to S5 connected in series, and the other subset has SAW resonators P1 to P6 connected in parallel. Figure 4 In the configuration shown, multiple SAW resonators are arranged according to a ladder scheme, for which reason, the RF filter 400 may also be referred to as a ladder filter. It is obvious to those skilled in the art that the number, arrangement and configuration of the SAW resonators S1 to S5, P1 to P6 are merely exemplary and should not be construed as any limitation to the present invention. In some other embodiments, the RF filter 400 may include different types of SAW resonators; for example, the RF filter 400 may include one or more SAW resonators each implemented as a SAW resonator 300 and one or more other SAW resonators each implemented as the above-mentioned CRF structure (i.e., having two or more IDTs between the reflectors 304 and 306).

[0043] Figure 5 FIG. 5 shows a possible implementation of an RF filter 400 provided by an exemplary embodiment on a single chip 500. Figure 5 As shown, the SAW resonators S1 to S5, P1 to P6 can be densely packed on the surface of the wafer 500 together with the contact pads 502 and the interconnect pads 504. The contact pads 502 are the wires between the SAW resonators toward the input and output of the RF filter 400. An additional metal layer (up to 2 μm of Al or Au) is usually deposited over the contact pads 502 and the interconnect pads 504 to reduce parasitic resistance.

[0044] Figure 61 is a flow chart of a method 600 for manufacturing an RF filter 400 on a single wafer 500 according to an exemplary embodiment. The method 600 begins with step S602, where a YAG-based multilayer substrate is manufactured. Figure 2 , step S602 includes first depositing a dielectric layer 208 on the YAG substrate 202, and then depositing a piezoelectric layer 210 on the YAG substrate 202. Then, the method 600 proceeds to step S604, where SAW resonators S1 to S5, P1 to P6 are formed on the YAG-based multilayer substrate. In other words, step 604 involves forming an IDT and a reflector on the surface of the YAG-based multilayer substrate. Step 604 also involves forming a contact pad 502 and an interconnect pad 504 between the SAW resonators S1 to S5, P1 to P6. The thickness of the finger electrodes and reflectors of the IDT can be less than 500nm. The method 600 ends with step S606, where a relatively thick metal layer is deposited over the contact pad 502 and the interconnect pad 504 to minimize parasitic resistance. The thickness of the contact pad 502 and the interconnect pad 504 can range from 500nm to 5μm.

[0045] Fig. 7A and Figure 7B 1 shows different schematic diagrams of a multiplexer 700 provided by an exemplary embodiment. More specifically, Fig. 7A An isometric view of multiplexer 700 is shown, and Figure 7B Shown along Fig. 7A 700 is a cross-sectional view of a multiplexer 700 taken along line AA in FIG. The multiplexer 700 includes a circuit board 702 and an array 704 of five RF filters RF F1 to RF F5. In one embodiment, each of the RF filters RF F1 to RF F5 may be implemented as the RF filter 400. In other embodiments, some of the RF filters RF F1 to RF F5 may be implemented as the RF filter 400, while other RF filters may be implemented as RF filters based on existing SAW devices (such as the SAW device 100). Regardless of their implementation, the RF filters RF F1 to RF F5 are mounted on the circuit board 702 in an inverted manner such that the IDT of one or more SAW devices included in each RF filter faces the circuit board 702 (see FIG. 704 ). Figure 7B ). This can be accomplished using standard flip chip technology. The multiplexer 700 also includes two impedance matching components 706 (e.g., implemented as inductors and / or capacitors) that are disposed on the circuit board 702 and are used to provide impedance matching between the RF filters RF F1 to RF F5 and the antenna to which each of the RF filters RF F1 to RFF5 is to be coupled. Figure 7BAs shown, the circuit board 702 may optionally include a plurality of metal interlayers 708 with interconnections and contact pads 710 on its rear surface. These interconnections may ensure proper signal routing between different portions of the circuit board 702.

[0046] Figure 8 A flow chart of a method 800 for manufacturing a multiplexer 700 provided by an exemplary embodiment is shown. The method 800 begins with steps S802 to S806, which can be performed in parallel or sequentially. Step S802 includes manufacturing RF filters RF F1 to RF F5 on a YAG-based substrate. Step S804 is optional and can be performed if there is at least one RF filter based on an existing Si-based SAW device (such as the SAW device 100). Step S806 includes manufacturing a circuit board 702 (optionally having a metal interlayer 708). Then, the method 800 enters step S808, wherein the RF filters RF F1 to RF F5 and the impedance matching component 706 are mounted on the circuit board 702, thereby forming the multiplexer 700. The method 800 ends with step S810, wherein the resulting multiplexer 700 is packaged.

[0047] Fig. 9 A schematic block diagram of a duplexer 900 provided by an exemplary embodiment is shown. The duplexer 900 includes two ladder-shaped RF filters 902 and 904, assuming that each of the two ladder-shaped RF filters 902 and 904 is implemented as the above-mentioned YAG-based RF filter (i.e., RF filter 400, wherein each SAW resonator uses only one or more YAG-based SAW devices 200). The RF filter 902 is used to operate at a lower frequency (e.g., band B75), while the RF filter 904 is used to operate at a higher frequency (e.g., band B1). The input RF signal is fed to port 1, filtered by the RF filters 902 and 904, and output via port 2 and port 3, respectively.

[0048] In order to demonstrate the advantages of YAG-based RF filters over conventional Si-based RF filters (i.e., RF filters in which each SAW resonator uses only Si-based SAW devices 100), two duplexers have been fabricated, one using Si-based RF filters and the other using YAG-based RF filters. Both duplexers have similar Fig. 9 Design shown.

[0049] Fig.10 The dependence of the transmission coefficient S21 of each of the two duplexers on the frequency is shown. More specifically, Fig.10The dashed curve involves <100> The solid line curve relates to a duplexer with a Si-based RF filter, while the solid line curve relates to a duplexer with a YAG-based RF filter. It can be seen that the use of a YAG-based RF filter at a lower frequency (i.e., the B75 band) can mitigate the impact of spurious mode effects better than a Si-based RF filter.

[0050] Although exemplary embodiments of the present invention are described herein, it should be noted that any various changes and modifications may be made in the embodiments of the present invention without departing from the scope of legal protection defined by the appended claims. In the appended claims, the word "comprising" does not exclude other elements or operations, and the term "a" or "an" does not exclude a plurality. The listing of certain measures in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A surface acoustic wave (SAW) device, characterized in that: include: A yttrium aluminum garnet (YAG) substrate having a top surface and a back surface; a dielectric layer disposed on the top surface of the YAG substrate; a piezoelectric layer, disposed on the dielectric layer; An interdigital transducer (IDT) is disposed on the piezoelectric layer, and the IDT is used to convert an input radio frequency (RF) signal into a SAW propagating in the piezoelectric layer; The rear surface of the YAG substrate has an arithmetic mean roughness greater than 50 nanometers (nm).

2. The SAW device according to claim 1, characterized in that: The top surface of the YAG substrate has an arithmetic mean roughness of less than 50 nm.

3. The SAW device according to claim 1 or 2, characterized in that: The YAG substrate has a thickness ranging from 200 micrometers (μm) to 600 μm.

4. The SAW device according to any one of claims 1 to 3, characterized in that: The ratio of the thickness of the piezoelectric layer to the thickness of the dielectric layer ranges from 0.6 to 1.

4.

5. The SAW device according to any one of claims 1 to 4, characterized in that: The piezoelectric layer is made of LiTaO3 or LiNbO3.

6. The SAW device according to any one of claims 1 to 5, characterized in that: The dielectric layer is made of SiO2.

7. A radio frequency (RF) filter, characterized in that: include: At least one surface acoustic wave (SAW) resonator, each SAW resonator comprising: At least one SAW device according to any one of claims 1 to 6; Two SAW reflectors are arranged such that an IDT of each of the at least one SAW device is located between the two SAW reflectors.

8. The RF filter according to claim 7, characterized in that: The at least one SAW resonator comprises a plurality of SAW resonators, each SAW resonator comprising a single SAW device according to any one of claims 1 to 6, the plurality of SAW resonators being arranged in a ladder scheme.

9. The RF filter according to claim 8, characterized in that: Also included is an additional SAW resonator, the additional SAW resonator comprising: At least two SAW devices according to any one of claims 1 to 6; Two reflectors are arranged such that an IDT of each of the at least two SAW devices is located between the two reflectors of the additional SAW resonator.

10. The RF filter according to claim 7, characterized in that: The at least one SAW resonator comprises a single SAW resonator comprising at least two SAW devices according to any one of claims 1 to 6.

11. A multiplexer, characterized in that: include: Circuit boards; At least two RF filters according to any one of claims 7 to 10, each of the at least two RF filters being mounted on the circuit board in an inverted manner such that an IDT of each of the at least one SAW device in each of the at least one SAW resonator faces the circuit board; At least one impedance matching component is arranged on the circuit board and is used to provide impedance matching between the at least two RF filters and an antenna to which each of the at least two RF filters is coupled.

12. The multiplexer according to claim 11, characterized in that The circuit board includes a plurality of metal interlayers having interconnections.

13. The multiplexer according to claim 11 or 12, characterized in that: The at least one impedance matching component includes at least one of an inductor and a capacitor.

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