Device for generating acoustic wave, and radio frequency filter and

Abstract

The present disclosure relates to a cubic boron arsenide (c-BAs)-based multilayer device for generating acoustic waves. The device comprises a c-BAs-based substrate (102), a piezoelectric layer (104) arranged on the c-BAs-based substrate (102), and an interdigital transducer (IDT) (108, 110) arranged on the piezoelectric layer (104), and the c-BAs-based substrate (102) and the c-BAs-based substrate (102) are arranged on the c-BAs-based substrate (102), the c-BAs-based substrate (102), the c-BAs-based substrate (102) and the c-BAs-based substrate (104). The IDT is used to excite the acoustic wave in response to an applied RF signal. The device further comprises a temperature compensation (TC) layer (106), and the temperature compensation (TC) layer (106) is arranged between the c-BAs-based substrate and the piezoelectric layer or covers the piezoelectric layer and the IDT. By using the c-BAs-based substrate, the number of stray sound waves propagating at different material interfaces in the device can be reduced to the greatest extent. Thus, in an RF circuit in which the device is to be used, suppression of stray acoustic wave modes is provided without using any external components (e.g., a combination of capacitors, inductors, transformers, etc.) or additional resonators.

Description

Technical Field

[0001] The present disclosure relates generally to the field of acoustic devices, and more particularly to cubic boron arsenide (c-BAs) based multilayer devices for generating acoustic waves, and radio frequency (RF) filters and multiplexers each using one or more of such c-BAs based multilayer devices. Background Art

[0002] Wireless communication devices (e.g., mobile phones) rely heavily on high-performance RF filters, which are used to reject any unwanted incoming RF signals and retain only the desired transmission signals. In some wireless communication applications, the RF filter must be particularly selective for the incoming RF signal, passing only a very narrow band of the incoming spectrum. More specifically, the key technical requirements of the RF filter may include, but are not limited to: high frequency, high selectivity for suppressing spurious signals, large bandwidth for high data rates, low insertion loss factor for low power consumption, and a form factor suitable for RF filters used in small handheld devices.

[0003] The above requirements have led to the use of acoustic devices, such as surface acoustic wave (SAW) devices, in the design of RF filters. In addition, acoustic devices are now not only key components for signal filtering in different wireless communication systems (such as 2G / 3G / 4G / LTE / 5G, Bluetooth, etc.), but also key components for other signal processing, frequency generation and sensing applications. In order to reduce the inherent high insertion loss of SAW devices, a variety of special low-loss technologies have been developed, each optimized for specific applications.

[0004] The latest generation of SAW devices are called layered SAW (LSAW) or film SAW (FSAW) devices. FSAW devices have a multilayer design where the piezoelectric layer is placed on a stack of layers, each made of a different material. The combination of these different materials in the stack, as well as the proper selection of their thickness and material properties, can significantly improve the acoustic energy confinement in the piezoelectric layer. This effect reduces the acoustic losses / radiation in the supporting substrate of the FSAW device and improves the overall response of the resulting RF filter.

[0005] However, the presence of multiple "buried" layers in the stack of FSAW devices also increases the number of acoustic and mechanical modes that can propagate. These waves can also include those generated at frequencies far from the main operating band of the RF filter. According to current radio communication standards, out-of-band response needs to be strictly controlled because the front-end circuits rely on strict out-of-band channel attenuation levels to prevent any interaction between different communication channels and / or standards. Therefore, it is very important to be able to minimize or even eliminate the out-of-band spurious mode content of RF filters that include such SAW devices. Summary of the invention

[0006] The present invention summary briefly introduces some 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 disclosure, nor is it intended to limit the scope of the present disclosure.

[0007] The object of the present disclosure is to provide a technical solution that can effectively guide the desired acoustic wave mode over a wide frequency range while minimizing the generation of stray acoustic wave modes.

[0008] 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 description and the drawings.

[0009] According to a first aspect, a device for generating acoustic waves is provided. The device includes a cubic boron arsenide (c-BAs)-based substrate, a piezoelectric layer disposed on the c-BAs-based substrate, and an interdigital transducer (IDT) disposed on the piezoelectric layer. The IDT is used to excite the acoustic wave in response to an applied RF signal. The device also includes a temperature compensation (TC) layer, which is disposed between the c-BAs-based substrate and the piezoelectric layer or covers the piezoelectric layer and the IDT. By using a c-BAs-based substrate, the number of stray (i.e., out-of-band) acoustic waves propagating at the interfaces of different materials in the device can be minimized, i.e., the boundary conditions required for the existence and propagation of stray acoustic wave modes in the device are destroyed. Therefore, in an RF circuit in which the device will be used, suppression or attenuation of stray acoustic wave modes is provided without using any external components (e.g., a combination of capacitors, inductors, transformers, etc.) or additional resonators. Other benefits provided by the device configured in this way are as follows:

[0010] - High mechanical quality factor (Q) due to guiding only the desired acoustic modes;

[0011] - High electromechanical coupling coefficient (k) due to fast longitudinal / shear bulk acoustic waves in the device t2 );

[0012] - The mismatch of the coefficient of thermal-expansion (CTE) of c-BAs relative to the piezoelectric material can improve the passive temperature compensation of the device due to temperature changes (or in other words, reduce frequency drift);

[0013] -The presence of the TC layer can provide additional temperature compensation, which can make the device suitable for a wide temperature range;

[0014] - Devices so configured are less susceptible to packaging / filter architecture issues and can be implemented in a wide variety of filter products and frequency bands;

[0015] - In addition, the device configured in this way can be used in different micro-electro-mechanical-system (MEMS) based phase-locked loop (PLL) timing circuits (oscillators), thereby reducing the number of available stray acoustic wave modes that the oscillator may lock onto.

[0016] In an exemplary embodiment of the first aspect, the c-BAs-based substrate has a crystal orientation <111> , <110> or <100> By using c-BAs with this crystal orientation, the core region of the device (i.e., the region with the piezoelectric layer and the IDT) can be more effectively isolated from the substrate both electrically and acoustically. This in turn may contribute to better suppression of stray acoustic wave modes.

[0017] In an exemplary embodiment of the first aspect, the c-BAs-based substrate comprises an underlying support layer and a c-BAs layer disposed on the underlying support layer. This embodiment may be beneficial when it is difficult to fabricate a thick c-BAs substrate.

[0018] In an exemplary embodiment of the first aspect, the bottom support layer in the c-BAs-based layered substrate is made of quartz, diamond, fused quartz, sapphire, yttrium aluminum garnet (YAG), silicon (Si), gallium nitride (GaN), gallium arsenide (GaAs) or silicon carbide (SiC). Any of these materials is well known in the art, and therefore, the technology for manufacturing thick substrates based on these materials is very mature.

[0019] In an exemplary embodiment of the first aspect, the c-BAs layer is a polycrystalline layer or has a crystal orientation <111> , <110> or <100> Through this c-BAs layer, the core region of the device (i.e., the region with the piezoelectric layer and the IDT) can be more effectively isolated from the substrate both electrically and acoustically. This in turn may contribute to better suppression of stray acoustic wave modes.

[0020] In an exemplary embodiment of the first aspect, the c-BAs layer has a thickness defined based on the wavelength of the main mode of the acoustic wave in the piezoelectric layer. The c-BAs layer having such a thickness value can provide the electroacoustic characteristics required by the device (e.g., acoustic energy confinement or waveguiding).

[0021] In an exemplary embodiment of the first aspect, the thickness of the c-BAs layer is in the range of 0.25λ to 2λ, where λ is the wavelength of the main mode of the acoustic wave in the piezoelectric layer. By using this thickness value range, the desired electroacoustic characteristics of the device can be achieved.

[0022] In an exemplary embodiment of the first aspect, the shear acoustic impedance of the TC layer is lower than the shear acoustic impedance of the piezoelectric layer or the c-BAs-based substrate. By using this relationship between the shear acoustic impedances of the TC layer, the piezoelectric layer and the c-BAs-based substrate, acoustic waves in the TC layer and the piezoelectric layer can be confined.

[0023] In an exemplary embodiment of the first aspect, the TC layer is disposed between the c-BAs-based substrate and the piezoelectric layer. In this embodiment, the device further comprises a passivation layer covering the piezoelectric layer and the IDT. The TC layer so arranged can provide better adhesion or bonding between the piezoelectric layer and the c-BAs-based substrate in addition to the TC. As for the passivation layer, it can protect the core area of ​​the device from the influence of the surrounding environment, thereby extending the service life of the device.

[0024] In an exemplary embodiment of the first aspect, the passivation layer is made of a dielectric material including at least one or both of silicon oxide (SiO2) and silicon nitride (Si3N4). These materials are less susceptible to the influence or corrosion of the surrounding environment.

[0025] In an exemplary embodiment of the first aspect, the acoustic wave (e.g., its main mode) is one of a surface acoustic wave (SAW), a Lamb wave, and a shear horizontal plate wave. This means that the device can be used to excite different types of acoustic waves (depending on the configuration parameters of the IDT, the thickness and crystal orientation of the piezoelectric layer, etc.), thereby making the device more flexible to use.

[0026] In an exemplary embodiment of the first aspect, the piezoelectric layer is made of lithium tantalate (LiTaO3), lithium niobate (LiNbO3), aluminum nitride (AlN), scandium (Sc) or yttrium (Y) doped AlN (AlScxN, AlN:Y), lithium iodate (LiIO3), zinc oxide (ZnO), lead zirconate titanate (PZT), potassium niobate (KNbO3), sodium niobate (NaNbO3), gadolinium doped cerium oxide (Gd:CeO2) or quartz. These materials have piezoelectric properties suitable for normal operation of the device.

[0027] In an exemplary embodiment of the first aspect, the piezoelectric layer is made of: θY-X LiTaO3, where θ = (20°–65°)∪(115°–135°); or θY-X LiNbO3, where θ = (0°–90°)∪(115°–135°). These cuts of LiTaO3 or LiNbO3 can provide different electromechanical coupling coefficients (K 2 ) and wave polarization, allowing for more flexible use of the device (e.g., if the device is intended to be used in a narrow bandwidth filter, a large K 2 There may be a problem and vice versa, so the angle θ of θY-XLiTaO3 or θY-XLiNbO3 should be appropriately selected from the angle range indicated above).

[0028] In an exemplary embodiment of the first aspect, each of the piezoelectric layer and the TC layer has a thickness defined based on the wavelength of the main mode of the acoustic wave in the piezoelectric layer. The TC layer having such a thickness value can provide suitable TC.

[0029] In an exemplary embodiment, the TC layer is disposed between the c-BAs-based substrate and the piezoelectric layer. In this embodiment, the thickness of each of the piezoelectric layer and the TC layer is in the range of 0.1λ to 0.5λ, where λ is the wavelength of the main mode of the acoustic wave in the piezoelectric layer. This combination of thicknesses of the TC layer and the piezoelectric layer can allow for a minimum temperature coefficient of frequency (TCF) (ideally equal to 0 ppm / K).

[0030] In an exemplary embodiment of the first aspect, the TC layer covers the piezoelectric layer and the IDT. In this embodiment, the thickness of the piezoelectric layer is in the range of 0.15λ to λ, and the thickness of the TC layer is in the range of 0.15λ to 0.5λ, where λ is the wavelength of the main mode of the acoustic wave in the piezoelectric layer. This combination of thicknesses of the TC layer and the piezoelectric layer can allow a minimum temperature coefficient of frequency (TCF) (ideally equal to 0 ppm / K) to be achieved.

[0031] In an exemplary embodiment of the first aspect, the TC layer is disposed between the c-BAs-based substrate and the piezoelectric layer. In this embodiment, the device further comprises a trap-rich material layer disposed between the c-BAs-based substrate and the TC layer. The trap-rich material layer can be used to prevent charge accumulation at the material interface, which may adversely affect the operation of the device.

[0032] In an exemplary embodiment of the first aspect, the TC layer covers the piezoelectric layer and the IDT. In this embodiment, the device further comprises a trap-rich material layer disposed between the c-BAs-based substrate and the piezoelectric layer. The trap-rich material layer can be used to prevent charge accumulation at the material interface, which may adversely affect the operation of the device.

[0033] In an exemplary embodiment of the first aspect, the thickness of the trap-rich material layer is in the range of 0.1λ to λ, where λ is the wavelength of the main mode of the acoustic wave in the piezoelectric layer. This thickness value range of the trap-rich material layer can provide appropriate electroacoustic characteristics of the device together with other layers of the device.

[0034] According to a second aspect, an RF filter is provided. The RF filter comprises at least one acoustic wave resonator, each acoustic wave resonator comprising: at least one device according to the first aspect; two reflectors arranged so that the IDT of each device in the at least one device is located between the two reflectors. The RF filter configured in this way can provide a broadband spurious-free response. In addition, 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.

[0035] According to a third aspect, a multiplexer is provided. The multiplexer includes a circuit card, at least two RF filters according to the second aspect, at least one first impedance matching component and at least one second impedance matching component. Each of the at least two RF filters is mounted on the circuit card. Each of the at least one first impedance matching component is arranged on the circuit card to provide impedance matching between the at least two RF filters and the antenna to which each of the at least two RF filters is coupled. Each of the at least one second impedance matching component is arranged on the circuit card to provide impedance matching between the at least two RF filters and the radiofrequency integrated circuit (RFIC) to which each of the at least two RF filters is coupled. By using a combination of two or more RF filters, the multiplexer can provide efficient RF filtering in different high frequency bands.

[0036] Other features and advantages of the present disclosure will be apparent upon reading the following detailed description and viewing the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present disclosure is explained below with reference to the accompanying drawings, in which:

[0038] Figure 1 A schematic cross-sectional view of a device for generating sound waves provided by a first exemplary embodiment is shown;

[0039] Figure 2 shows a schematic cross-sectional view of a device for generating sound waves provided by a second exemplary embodiment;

[0040] Figure 3 A schematic top view of a device for generating sound waves provided by a third exemplary embodiment is shown;

[0041] Figure 4A and Figure 4B Shows <100> FSAW devices on Si-based substrates ( Figure 4A )and Figure 1 Devices ( Figure 4B ) comparison results of simulated admittance;

[0042] Figure 5 A schematic block diagram of an acoustic wave resonator provided by an exemplary embodiment is shown;

[0043] Figure 6 A schematic block diagram of a multiplexer provided by an exemplary embodiment is shown. DETAILED DESCRIPTION

[0044] Various embodiments of the present disclosure are further described in detail in conjunction with the accompanying drawings. However, the present disclosure may be embodied in many other forms and should not be construed as limited to any specific structure or function discussed in the following description. On the contrary, these embodiments are provided to make the description of the present disclosure detailed and complete.

[0045] Based on the detailed description, it is apparent to those skilled in the art that the scope of the present disclosure includes any embodiment of the present disclosure disclosed herein, whether the embodiment is implemented independently or in combination with any other embodiment of the present disclosure. 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 disclosure can be implemented using one or more features set forth in the appended claims.

[0046] The word "exemplary" is used herein in the sense of "serving as an illustration." Any embodiment described herein as "exemplary" is not to be construed as preferred or having advantages over other embodiments unless otherwise stated.

[0047] For convenience, any positioning terms, such as "left", "right", "up", "down", "above", "below", "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 should be apparent that the positioning terms are intended to cover different orientations of the devices disclosed herein, as well as one or more orientations depicted in the accompanying drawings. As an example, if the device in the figure is imagined to be 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.

[0048] In addition, although various embodiments, elements or features may be described herein using numerical terms such as "first", "second", etc., it should be understood that these embodiments, elements or features should not be limited by such numerical terms. Such numerical terms are used herein only to distinguish one embodiment, element or feature from another embodiment, element or feature. For example, the first exemplary embodiment discussed below may be referred to as the second exemplary embodiment, and vice versa, without departing from the guidance of the present disclosure.

[0049] Currently, film surface acoustic wave (FSAW) devices are widely used in different wireless communication applications (e.g., RF filters, multiplexers, etc.). Generally, FSAW devices have a multilayer structure. The characteristics of FSAW devices depend on the piezoelectric material, support substrate, and other layers in the multilayer structure used for FSAW devices. Preferably, a piezoelectric material with a high K2 Different crystal cuts of piezoelectric materials such as lithium tantalate (LiTaO3), lithium niobate (LiNbO3) or aluminum nitride (AlN) are used. The support substrate is usually made of a high acoustic velocity support material (e.g., Si). However, the main disadvantage of using only such a substrate in the multilayer structure of the FSAW device is the natural accumulation of high-order / out-of-band spurious modes. In addition, for temperature compensation (TC) purposes, additional layers (e.g., Si, silicon oxide (SiO2), etc.) are included in the multilayer structure of the FSAW device. However, it is known that the Si (support substrate) / SiO2 (TC layer) interface will generate additional interface charges, which can significantly degrade the RF performance of the FSAW device. Optionally, a rough or thin layer of polysilicon (e.g., 1 μm thick) can be added to the multilayer structure of the FSAW device and used as a "trap-rich" layer to prevent unwanted RF coupling through the substrate, which may degrade the performance of the RF filter based on the FSAW device. However, the addition of a trap-rich layer significantly increases the overall manufacturing complexity and thus limits the choice of alternative deposition techniques / optimizations for the other layers that make up the multilayer stack.

[0050] Exemplary embodiments disclosed herein provide a technical solution that can mitigate or even eliminate the above-mentioned disadvantages that are specific to the prior art. Specifically, exemplary embodiments disclosed herein relate to a cubic boron arsenide (c-BAs)-based multilayer device for generating acoustic waves. More specifically, the device includes a c-BAs-based substrate, a piezoelectric layer disposed on the c-BAs-based substrate, and an interdigital transducer (IDT) disposed on the piezoelectric layer. The IDT is used to excite the acoustic wave in response to an applied RF signal. The device also includes a temperature compensation (TC) layer disposed between the c-BAs-based substrate and the piezoelectric layer or covering the piezoelectric layer and the IDT. By using the c-BAs-based substrate, the number of stray acoustic waves propagating at the interfaces of different materials in the device can be minimized. Therefore, in an RF circuit (e.g., an RF filter or multiplexer) in which the device is to be used, suppression or attenuation of stray acoustic wave modes is provided without using any external components (e.g., a combination of capacitors, inductors, transformers, etc.) or additional resonators.

[0051] Figure 1A schematic cross-sectional view of a device 100 for generating acoustic waves provided by a first exemplary embodiment is shown. The device 100 is intended to be used in RF filters and multiplexers. As shown in the figure, the device 100 has a multilayer structure, which includes a c-BAs-based substrate 102, a piezoelectric layer 104 disposed on the c-BAs-based substrate 102, a TC layer 106 disposed between the piezoelectric layer 104 and the c-BAs-based substrate 102, and an IDT formed on the surface of the piezoelectric layer 104.

[0052] To keep it simple, Figure 1 Only two metal trapezoidal electrodes (or in other words, finger electrodes) 108, 110 connected to separate electrical bus bars of the IDT are shown. Those skilled in the art will recognize that the IDT may include multiple (e.g., hundreds of) electrodes arranged in an interdigitated format along the X direction on the surface of the piezoelectric layer 104. The electrodes of the IDT may be made of aluminum, aluminum-copper alloy, copper, copper-aluminum alloy, chromium, titanium, tungsten, gold, palladium, molybdenum, or any combination thereof. The spacing 112 between the electrodes 108 and 110 is selected to provide the desired wavelength of the acoustic wave excited by the IDT in response to the applied RF signal. The IDT is well known in the art, so the details of its operation are omitted here. For example, the relationship between the wavelength and the spacing 112 can be expressed as follows: λ=2×spacing, where λ is the wavelength of the main mode of the acoustic wave in the piezoelectric layer 104. Typically, the shape of the electrodes and the spacing of the electrodes in an IDT are determined by the capabilities of existing manufacturing technologies, such as lithography (e.g., photolithography, electron beam lithography), 3D printing, physical vapor deposition (PVD), chemical vapor deposition (CVD), dry and wet etching, laser ablation, electrolytic deposition (e.g., electroplating), etc. IDTs can be used to excite acoustic waves in the form of surface acoustic waves (SAW), Lamb waves, or shear horizontal plate waves.

[0053] The c-BAs-based substrate 102 may be relatively thick (eg, its thickness may be defined based on the compactness, strength, and heat dissipation requirements of the device 100 and / or the capabilities of existing manufacturing technologies). Preferably, the c-BAs-based substrate 102 has a crystal orientation <111> , <110> or <100> If crystal orientation is used <111> , then the Euler angles are preferably defined as (45°, 54.74°, 0°) with a certain range around the angle (e.g., + / –15 degrees). c-BAs is a material of particular interest today in the semiconductor industry. It has high ambipolar carrier mobility and at the same time has an ultra-high thermal conductivity of 1300 W / (m·K). The main advantage of c-BAs for FSAW device applications is that its shear wave phase velocity is higher than the shear wave phase velocity of typical piezoelectric materials (LiNbO3 and LiTaO3) arranged above it in the multilayer structure of the device 100. This allows one to confine the acoustic waves to the upper layer (waveguide) of the device 100, minimize body radiation losses, and thereby improve the performance of the device. Table 1 below presents some parameters of c-BAs relevant to acoustic device applications in comparison with silicon and yttrium aluminum garnet (YAG) (in Table 1, V sh is the phase velocity, ρ is the material density, ε r is the relative dielectric constant and CTE stands for the coefficient of thermal expansion). In addition, the c-BAs-based substrate 102 can be manufactured in a practical and economical manner because B and As are abundant minerals and crystal manufacturing technology is inexpensive. In some embodiments, the c-BAs-based substrate 102 can be made n-type and p-type doped.

[0054] Table 1: Parameter comparison of Si, BAs and YAG

[0055]

[0056] The piezoelectric layer 104 may be made of any of the following piezoelectric materials: lithium tantalate (LiTaO3), lithium niobate (LiNbO3), aluminum nitride (AlN), scandium (Sc) or yttrium (Y) doped AlN (AlScxN, AlN:Y), lithium iodate (LiIO3), zinc oxide (ZnO), lead zirconate titanate (PZT), potassium niobate (KNbO3), sodium niobate (NaNbO3), gadolinium doped cerium oxide (Gd:CeO2) and quartz. Preferably, the piezoelectric layer 104 may be made of θY-X LiTaO3, where θ = (20°–65°)∪(115°–135°), or θY-X LiNbO3, where θ = (0°–90°)∪(115°–135°). Those skilled in the art will recognize that the notation "θY-XLiTaO3" or "θY-X LiNbO3" refers to LiTaO3 or LiNbO3 that is θ-rotated (relative to the crystallographic X-axis) Y-cut, and the propagation direction of the excitation acoustic wave is aligned with the crystal X-axis. The piezoelectric layer 104 may have a thickness defined based on the wavelength λ of the dominant mode of the acoustic wave.

[0057] The TC layer 106 can be made of a material having a shear acoustic impedance lower than the shear acoustic impedance of the material of the piezoelectric layer 104 or the c-BAs-based substrate 102. For example, the TC layer 106 can be made of silicon oxide (SiO2). Acoustic impedance can be defined as the resistance presented by a system to the acoustic flow generated by the acoustic pressure applied to the system, and can be calculated by multiplying the material density by the wave phase velocity of interest. The main function of the TC layer 106 is to provide effective temperature compensation (TC) of the device 100. Changes in ambient temperature and operation of the device 100 at high input power values ​​may affect the temperature of the device 100 itself. The change in frequency stability with temperature is described by the temperature coefficient of frequency (TCF). The temperature drift of the device 100 is related to the change in the stiffness coefficient of the piezoelectric material with temperature, but also to thermal expansion that affects the size of the device 100 and the density of the piezoelectric material. Most materials become "softer" when exposed to increased temperature, resulting in a decrease in the speed of the acoustic wave (corresponding to a negative first-order TCF), while other materials become "harder" and the speed of the acoustic wave increases with increasing temperature (corresponding to a positive first-order TCF). For example, LiNbO3, LiTaO3, and AlN have negative TCF values, while silicon oxide has a positive TCF value. By combining these materials together and carefully selecting their dimensions, a device 100 with a zero or near-zero TCF value can be designed. In addition to its primary TC function, the TC layer 106 is also used to provide a bond or adhesion between the piezoelectric layer 104 and the c-BAs-based substrate 102. Similarly, the TC layer 106 can have a thickness defined based on the wavelength λ of the dominant mode of the acoustic wave. In a preferred embodiment, the thickness of each of the piezoelectric layer 104 and the TC layer 106 is in the range of 0.1λ to 0.5λ.

[0058] Optionally, the device 100 may include an additional trap-rich material layer 114 disposed between the TC layer 106 and the c-BAs-based substrate 102. As used in the exemplary embodiments disclosed herein, a trap-rich layer may refer to a layer having a high density of electrically active carrier traps (e.g., the density of such traps may be selected based on the characteristics of other layers constituting the multilayer structure of the device 100). The trap-rich material may be represented by any polycrystalline material, such as polysilicon and doped versions thereof. In addition, the trap-rich material layer 114 may have a thickness defined based on the wavelength λ of the main mode of the acoustic wave. In a preferred embodiment, the trap-rich material layer 114 has a thickness in the range of 0.1λ to λ.

[0059] although Figure 1Although not shown in the figure, the device 100 may include an optional passivation layer covering the piezoelectric layer 104 and the IDT (ie, the electrodes and inter-electrode spacing of the IDT). The passivation layer may be made of SiO2, silicon nitride (Si3N4), or a combination thereof.

[0060] Figure 2 A schematic cross-sectional view of a device 200 for generating acoustic waves provided by a second exemplary embodiment is shown. The device 200 is intended to be used in RF filters and multiplexers. Similar to the device 100, the device 200 has a multilayer structure including a c-BAs-based substrate 202, a piezoelectric layer 204 disposed on the c-BAs-based substrate 202, a TC layer 206 disposed between the piezoelectric layer 204 and the c-BAs-based substrate 202, and an IDT formed on the surface of the piezoelectric layer 104. For simplicity, Figure 2 Again, only two metal ladder electrodes or finger electrodes 208, 110 of the IDT are shown, which are connected to separate electrical bus bars of the IDT. In general, the piezoelectric layer 204, TC layer 206, and IDT of the device 200 can be configured in the same or similar manner as the piezoelectric layer 104, TC layer 106, and IDT of the device 100, respectively. Therefore, the spacing 212 between the electrodes 208, 210 can be defined in the same or similar manner as the spacing 112.

[0061] Meanwhile, the c-BAs-based substrate 202 is different from the c-BAs-based substrate 102 in that it is also a layered structure including an underlying support layer 214 and a c-BAs layer 216. The underlying support layer 214 may be made of quartz, diamond, fused quartz, sapphire, yttrium aluminum garnet (YAG), silicon (Si), gallium nitride (GaN), gallium arsenide (GaAs), or silicon carbide (SiC). The c-BAs layer 216 may be a polycrystalline layer or may have a crystal orientation <111> , <110> or <100> The c-BAs layer 216 may have a thickness that is also defined based on the wavelength of the dominant mode of acoustic waves in the piezoelectric layer 204. In a preferred embodiment, the thickness of the c-BAs layer 216 is in the range of 0.25λ to 2λ, where λ is the wavelength of the dominant mode of acoustic waves in the piezoelectric layer 204.

[0062] Optionally, the device 200 may include an additional trap rich material layer 218 disposed between the TC layer 206 and the c-BAs base substrate 202 (ie, between the TC layer 206 and the c-BAs layer 216). The trap rich material layer 218 may have the same thickness as the trap rich material layer 114.

[0063] Additionally, an optional passivation layer covering the piezoelectric layer 204 and the IDT (ie, the electrodes and inter-electrode spacing of the IDT) may be added to the multilayer structure of device 200. The optional passivation layer of device 200 may be made in the same or similar manner as the optional passivation layer of device 100.

[0064] Figure 3 A schematic cross-sectional view of a device 300 for generating acoustic waves provided by a third exemplary embodiment is shown. The device 300 is intended to be used for RF filters and multiplexers. Similar to the device 100, the device 300 has a multilayer structure including a c-BAs-based substrate 302, a piezoelectric layer 304 disposed on the c-BAs-based substrate 302, an IDT formed on the surface of the piezoelectric layer 304, and a TC layer 306 covering the piezoelectric layer 304 and the IDT.

[0065] To keep it simple, Figure 3 Again, only two metal ladder electrodes or finger electrodes 308, 310 of the IDT are shown, which are connected to separate electrical bus bars of the IDT. In general, the c-BAs-based substrate 302 and the IDT of the device 300 can be configured in the same or similar manner as the c-BAs-based substrate 102 and the IDT of the device 100, respectively. Therefore, the spacing 312 between the electrodes 308, 310 can be defined in the same or similar manner as the spacing 112. In another embodiment, the c-BAs-based substrate 302 can be implemented in the same or similar manner as the c-BAs-based substrate 202.

[0066] As for the piezoelectric layer 304 and the TC layer 306, they can be made of the same materials as the piezoelectric layer 104 and the TC layer 106, respectively, but their thicknesses are preferably in the following different ranges: 0.15λ to λ for the piezoelectric layer 304, and 0.15λ to 0.5λ for the TC layer 306. In addition, since the TC layer 306 covers the piezoelectric layer 304 and the TC layer 306, the TC layer 306 also serves as a passivation layer in the multilayer structure of the device 300.

[0067] Optionally, the device 300 may include an additional trap rich material layer 314 disposed between the piezoelectric layer 304 and the c-BAs based substrate 302. The trap rich material layer 314 may be made in the same or similar manner as the trap rich material layer 114.

[0068] It should be noted that there may be some other embodiments, in which any other substrate having an acoustic velocity of 4000 m / s to 5500 m / s and / or a shear acoustic impedance of 10 MRayl to 40 MRayl can be used to replace the c-BAs-based substrate 102, 202 or 302. In other words, c-BAs can be replaced by any material having a shear acoustic velocity and / or a shear acoustic impedance within the above range.

[0069] Figure 4A and Figure 4B Shows <100> FSAW devices on Si-based substrates ( Figure 4A ) and device 100( Figure 4B ) is compared with the simulated admittance of the device 100. <111> c-BAs-based substrate 102. The simulated admittance is represented by two curves: "G" is related to the conductance (i.e. the real part of the admittance) and "Y" is related to the absolute admittance. The influence of choosing a suitable crystal orientation can be observed: for <100> Si-based FSAW devices have spurious modes in the range of 2500 to 3000 MHz, while <111> In the case of the device 100 with a c-BAs-based substrate, these spurious modes are effectively suppressed.

[0070] Figure 5 1 shows a schematic block diagram of an acoustic wave resonator 500 provided by an exemplary embodiment. The acoustic wave resonator 500 includes a device 502 for generating an acoustic wave and two (e.g., distributed) reflectors 504 and 506. The device 502 can be implemented as one of the devices 100, 200, 300. The reflectors 504 and 506 can be made of metal grids. The reflectors 502 and 504 are formed so that the IDT of the device 502 is placed between them. More specifically, the reflectors 502 and 504 are arranged along the propagation direction of the acoustic wave excited by the IDT (i.e., in the Figure 5 The left and right sides of the IDT in the device 502 are arranged on the piezoelectric layer of the device 502 (i.e., on the piezoelectric layer 104, 204, or 304). In this configuration, the acoustic wave excited by the IDT is repeatedly reflected toward the IDT by each of the reflectors 502 and 504, thereby generating resonance. It should be noted that the RF filter may include one or more acoustic wave resonators 500, and the one or more acoustic wave resonators 500 may be connected in series and / or in bypass connection.

[0071] Figure 6A schematic block diagram of a multiplexer 600 provided by an exemplary embodiment is shown. The multiplexer 600 includes a circuit card 602 and an array 604 of five RF filters RF F1 to RF F5, each filter having one or more acoustic wave resonators 500. In one embodiment, each RF filter RF F1 to RF F5 can be identical. In other embodiments, the RF filters RF F1 to RF F5 can be implemented in different ways (e.g., using different numbers of acoustic wave resonators). The multiplexer 600 also includes two impedance matching components 606 (e.g., implemented as inductors and / or capacitors), which are arranged on the same surface of the circuit card 602 as the RF filters RF F1 to RF F5. One of the components 606 may be used to provide impedance matching between the RF filters RF F1 to RF F5 and an antenna to which each of the RF filters RF F1 to RF F5 is to be coupled, and another component of the component 606 may be used to provide impedance matching between the RF filters RF F1 to RF F5 and a radio frequency integrated circuit (RFIC) to which each of the RF filters RF F1 to RF F5 is to be coupled. It should be noted that Figure 6 The number of RF filters and impedance matching components shown in FIG. 1 is for illustrative purposes only and should not be construed as any limitation of the present disclosure.

[0072] Although exemplary embodiments of the present disclosure are described herein, it should be noted that any various changes and modifications may be made in the embodiments of the present disclosure without departing from the scope of legal protection defined by the appended claims. In the appended claims, the word "comprising" does not exclude other element 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 device for generating sound waves, characterized in that: include: Cubic boron arsenide (c-BAs) based substrate; A piezoelectric layer is disposed on the c-BAs-based substrate; an interdigital transducer (IDT) disposed on the piezoelectric layer, the IDT being configured to excite the acoustic wave in response to an applied radio frequency (RF) signal; A temperature compensation (TC) layer is disposed between the c-BAs-based substrate and the piezoelectric layer or covers the piezoelectric layer and the IDT.

2. The device according to claim 1, characterized in that The c-BAs-based substrate has a crystal orientation <111> , <110> or <100> .

3. The device according to claim 1, characterized in that The c-BAs-based substrate includes an underlying support layer and a c-BAs layer disposed on the underlying support layer.

4. The device according to claim 3, characterized in that The underlying support layer is made of quartz, diamond, fused silica, sapphire, yttrium aluminum garnet (YAG), silicon (Si), gallium nitride (GaN), gallium arsenide (GaAs) or silicon carbide (SiC).

5. The device according to claim 3 or 4, characterized in that The c-BAs layer is a polycrystalline layer or has a crystal orientation <111> , <110> or <100> .

6. The device according to any one of claims 3 to 5, characterized in that The c-BAs layer has a thickness defined based on a wavelength of a dominant mode of the acoustic wave in the piezoelectric layer.

7. The device according to claim 6, characterized in that The thickness of the c-BAs layer is in the range of 0.25λ to 2λ, wherein λ is the wavelength of the main mode of the acoustic wave in the piezoelectric layer.

8. The device according to any one of claims 1 to 7, characterized in that The shear acoustic impedance of the TC layer is lower than the shear acoustic impedance of the piezoelectric layer or the c-BAs-based substrate.

9. The device according to any one of claims 1 to 8, characterized in that The TC layer is disposed between the c-BAs-based substrate and the piezoelectric layer, and wherein the device further comprises a passivation layer covering the piezoelectric layer and the IDT.

10. The device according to claim 9, characterized in that The passivation layer is made of a dielectric material including at least one of silicon oxide (SiO2) and silicon nitride (Si3N4).

11. The device according to any one of claims 1 to 10, characterized in that The acoustic wave is one of a surface acoustic wave (SAW), a Lamb wave, and a shear horizontal plate wave.

12. The device according to any one of claims 1 to 11, characterized in that The piezoelectric layer is made of: lithium tantalate (LiTaO3), lithium niobate (LiNbO3), aluminum nitride (AlN), scandium (Sc) or yttrium (Y) doped AlN (AlScxN, AlN:Y), lithium iodate (LiIO3), zinc oxide (ZnO), lead zirconate titanate (PZT), potassium niobate (KNbO3), sodium niobate (NaNbO3), gadolinium-doped cerium oxide (Gd:CeO2) or quartz.

13. The device according to claim 12, characterized in that The piezoelectric layer is made of: θY-X LiTaO3, where θ = (20°–65°)∪(115°–135°); or θY-X LiNbO3, where θ = (0°–90°) ∪ (115°–135°).

14. The device according to any one of claims 1 to 13, characterized in that Each of the piezoelectric layer and the TC layer has a thickness defined based on the wavelength of the main mode of the acoustic wave in the piezoelectric layer.

15. The device according to claim 14, characterized in that The TC layer is disposed between the c-BAs-based substrate and the piezoelectric layer, and wherein the thickness of each of the piezoelectric layer and the TC layer is in the range of 0.1λ to 0.5λ, wherein λ is the wavelength of the main mode of the acoustic wave in the piezoelectric layer.

16. The device according to claim 14, characterized in that The TC layer covers the piezoelectric layer and the IDT, and wherein the thickness of the piezoelectric layer is in the range of 0.15λ to λ, and the thickness of the TC layer is in the range of 0.15λ to 0.5λ, wherein λ is the wavelength of the main mode of the acoustic wave in the piezoelectric layer.

17. The device according to any one of claims 1 to 16, characterized in that The TC layer is disposed between the c-BAs-based substrate and the piezoelectric layer, and wherein the device further comprises a trap-rich material layer disposed between the c-BAs-based substrate and the TC layer.

18. The device according to any one of claims 1 to 16, characterized in that The TC layer covers the piezoelectric layer and the IDT, and wherein the device further includes a trap-rich material layer disposed between the c-BAs-based substrate and the piezoelectric layer.

19. The device according to claim 17 or 18, characterized in that The thickness of the trap rich material layer is in the range of 0.1λ to λ, wherein λ is the wavelength of the main mode of the acoustic wave in the piezoelectric layer.

20. A radio frequency (RF) filter, characterized in that: include: at least one acoustic wave resonator, each acoustic wave resonator comprising: At least one device according to any one of claims 1 to 19; Two reflectors are arranged such that the IDT of each device in the at least one device is located between the two reflectors.

21. A multiplexer, characterized in that: include: Circuit cards; The at least two RF filters of claim 20, each of the at least two RF filters being mounted on the circuit card; at least one first impedance matching component disposed on the circuit card for providing impedance matching between the at least two RF filters and an antenna to which each of the at least two RF filters is to be coupled; At least one second impedance matching component is arranged on the circuit card and is used to provide impedance matching between the at least two RF filters and a radio frequency integrated circuit (RFIC) to which each of the at least two RF filters is to be coupled.

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