Surface acoustic wave resonator
By using a high-velocity support substrate, acoustic impedance matching layer, and interdigitated electrodes in the surface acoustic wave resonator, the problems of insufficient bandwidth and frequency band in the existing technology are solved, and stable operation of high-frequency broadband is achieved, which is suitable for 5G communication.
Patent Information
- Application Number
- CN202422972054.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-03
- Publication Date
- 2025-11-21
- Estimated Expiration
- 2034-12-03
AI Technical Summary
Existing surface acoustic wave resonators cannot meet the performance requirements of 5G mid-to-high frequency broadband, especially the N79 band, which has insufficient operating frequency and bandwidth.
The structure employs a combination of a supporting substrate, an acoustic impedance matching layer, a bonding layer, and a piezoelectric layer. The crystal sound velocity of the supporting substrate is greater than that of the piezoelectric layer. The acoustic impedance matching layer acts as a transmission springboard. The bonding layer provides a stable connection. Interdigitated electrodes are used to excite and receive sound waves. The electrode materials are appropriately selected to avoid contamination and improve stability.
The operating frequency band and bandwidth of the surface acoustic wave resonator have been expanded, the gain has been improved, and the stability and resistance to environmental interference have been enhanced, ensuring reliable operation under different conditions.
Smart Images
Figure CN223584154U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of radio frequency device technology, and in particular to a surface acoustic wave resonator. Background Technology
[0002] Surface acoustic wave (SAW) resonators are a type of passive bandpass filter that utilizes the piezoelectric effect and the physical characteristics of surface acoustic wave propagation. Due to their small size, strong radiation resistance, high speed, low power consumption, and high reliability, SAW resonators are gaining increasing importance in communication circuit design.
[0003] Currently used surface acoustic wave (SAW) filters employ piezoelectric materials that are mostly single-element materials with high inherent electromechanical coupling coefficients, such as lithium niobate crystals or lithium carbonate crystals. Lithium niobate or lithium carbonate crystals have low sound velocity, making them suitable only for low-frequency, narrow-band applications in SAW resonators. They cannot meet the performance requirements of 5G mid-to-high frequency broadband, especially the N79 band (4.4GHz-5GHz). Utility Model Content
[0004] The purpose of this invention is to provide a surface acoustic wave resonator to solve the problem that existing surface acoustic wave resonators are only applicable to low-frequency narrowband applications.
[0005] To achieve the above objectives, this invention provides a surface acoustic wave (SAW) resonator. The SAW resonator has an operating bandwidth greater than or equal to 600 MHz; and / or, its operating frequency band includes the N79 band. The SAW resonator comprises: a supporting substrate, an acoustic impedance matching layer, a bonding layer, a piezoelectric layer, and electrodes. The supporting substrate, acoustic impedance matching layer, bonding layer, and piezoelectric layer are stacked sequentially. The acoustic impedance matching layer is bonded to the piezoelectric layer via the bonding layer. The crystal velocity corresponding to the supporting substrate is greater than the crystal velocity corresponding to the piezoelectric layer. The electrodes are disposed on the side of the piezoelectric layer facing away from the bonding layer.
[0006] When the above scheme is adopted, the surface acoustic wave resonator provided by this utility model applies an electric field to the piezoelectric layer from the electrical signal input from the electrode when it is in working state. The electric field is converted into an acoustic signal through the inverse piezoelectric effect. The acoustic signal is transmitted to the piezoelectric layer under the electrode through the piezoelectric layer and the supporting substrate. The acoustic signal is converted into an electrical signal output through the direct piezoelectric effect, thereby realizing the filtering function.
[0007] For surface acoustic wave (SAW) resonators, their operating frequency band and bandwidth are directly proportional to the sound velocity of the SAW material. However, the lower sound velocity of piezoelectric materials limits the increase in the operating frequency band and bandwidth of the SAW resonator. Nevertheless, since the sound velocity of the crystal corresponding to the supporting substrate is greater than that of the crystal corresponding to the piezoelectric layer, the bandwidth of the SAW resonator of this invention can be expanded and its operating frequency band increased.
[0008] Meanwhile, the acoustic impedance matching layer, acting as a matching layer for sound wave propagation between films with different crystal sound velocities, serves as a transmission stepping stone. Furthermore, because the supporting substrate and the piezoelectric layer are made of materials with different sound velocities, an interface with a significant difference in sound wave propagation speed is formed. When the sound wave propagates from the piezoelectric layer to the supporting substrate, reflection occurs at the interface, suppressing clutter and increasing the performance of the surface acoustic wave resonator. This reflection increases transmission loss, but the acoustic impedance matching layer at least reduces this reflection, enabling the piezoelectric-converted sound wave to be transmitted to the supporting substrate with low loss, thus improving the gain of the surface acoustic wave resonator provided by this invention. Additionally, bonding the acoustic impedance matching layer and the piezoelectric layer together with a bonding layer makes the connection between them more stable, reducing reflections and clutter caused by an unstable connection interface.
[0009] As one possible implementation, the acoustic impedance matching layer includes at least one of the following: silicon dioxide layer, silicon oxyfluoride layer, silicon oxycarbide layer, silicon oxynitride layer, lithium oxide layer, tantalum pentoxide layer, and silicon nitride layer. In this case, there are many options for the acoustic impedance matching layer, allowing it to be matched with a support substrate and piezoelectric layer made of various materials. When the acoustic impedance matching layer is a silicon dioxide layer, in addition to serving as a transmission buffer between the piezoelectric layer and the support substrate, it can also act as a temperature compensation layer, preventing deformation of the piezoelectric layer due to temperature changes from affecting its operation.
[0010] As one possible implementation, the supporting substrate includes at least one of a diamond substrate, a single-crystal silicon substrate, a sapphire substrate, a silicon carbide substrate, and a quartz crystal substrate. In this case, the sound velocity of the aforementioned substrates is much higher than that of the piezoelectric layer, which is beneficial for expanding the bandwidth and increasing the operating frequency band of the surface acoustic wave resonator provided by this invention.
[0011] As one possible implementation, the piezoelectric layer includes at least one of lithium niobate, lithium tantalate, aluminum nitride, zinc oxide, and quartz. In this case, the aforementioned piezoelectric materials have good piezoelectric properties, high electromechanical coupling coefficients, and low propagation losses. They also have good chemical stability and mechanical hardness, and are not easily affected by various external factors, thus giving the surface acoustic wave resonator provided by this invention good performance and operational stability.
[0012] As one possible implementation, when the acoustic impedance matching layer is a silicon dioxide layer, the thickness of the acoustic impedance matching layer is 0.1 μm to 0.6 μm. In this case, when the silicon dioxide layer is within the aforementioned thickness range, it can prevent the silicon dioxide layer from being too thin, causing the sound wave to directly cross the silicon dioxide layer due to diffraction when it passes through the piezoelectric layer to reach the supporting substrate or, in the opposite direction, through the acoustic impedance matching layer, thus preventing the silicon dioxide layer from failing to act as a transmission springboard; it can also prevent the sound wave from having an excessively thick silicon dioxide layer, resulting in an excessively long transmission path and a longer time required for the sound wave to complete one cycle of oscillation, thereby affecting the bandwidth of the surface acoustic wave resonator provided by this invention.
[0013] As one possible implementation, when the piezoelectric layer is a lithium niobate layer, the tangential direction of the piezoelectric layer is X-tangent and Y-rotation, and the Euler angle is greater than or equal to 30° and less than or equal to 80°.
[0014] As one possible implementation, the electrodes include interdigitated electrodes. In this case, the interdigitated electrodes can effectively excite and receive surface acoustic waves (SAWs). Their unique interdigitated structure can generate a specific electric field distribution on the piezoelectric layer, thereby efficiently converting electrical signals and sound waves. When an electrical signal is applied to the interdigitated electrodes, SAWs are excited in the piezoelectric material through the electric field interaction between the electrodes. Simultaneously, when the SAWs propagate to the interdigitated electrode region, they can be efficiently converted back into electrical signals, greatly improving the excitation and reception efficiency of sound waves. Furthermore, the bond between the interdigitated electrodes and the piezoelectric layer is relatively strong, maintaining stable performance under various environmental conditions. The SAW resonator provided by this invention needs to withstand the influence of various factors such as temperature changes and mechanical vibrations during operation. The stability of the interdigitated electrodes ensures that the SAW device can operate reliably in different environments, improving the reliability and stability of electronic systems using the SAW resonator provided by this invention.
[0015] As one possible implementation, the electrode includes a first metal adhesion layer and a metal electrode layer sequentially stacked along the thickness direction of the supporting substrate. In this case, when manufacturing the surface acoustic wave resonator provided by this invention, depositing the first metal adhesion layer and then the metal electrode layer on the piezoelectric layer first can prevent metal atoms in the metal electrode layer from penetrating into the piezoelectric layer, thereby contaminating the crystal structure of the piezoelectric layer and affecting its piezoelectric performance; furthermore, it can also prevent the electrical signal transmitted from the electrode from being directly transmitted back into the electrode through the metal atoms that have penetrated into the piezoelectric layer, thus failing to pass through the filter of the piezoelectric material and affecting the filtering performance of the surface acoustic wave resonator.
[0016] As one possible implementation, the first metal adhesion layer is a chromium electrode layer, and the metal electrode layer is an aluminum electrode layer. In this case, the adhesion between the chromium electrode layer and the aforementioned piezoelectric material is good, which can improve structural stability. Furthermore, the chromium electrode layer is stable and does not easily diffuse into the piezoelectric layer, thus affecting its crystal structure, making it suitable as the first metal adhesion layer. The aluminum electrode layer is easy to photolithographically etch, making it easier to form interdigitated electrode patterns when manufacturing the surface acoustic wave resonator provided by this invention. Simultaneously, aluminum has appropriate hardness and flexibility, resisting external impacts and deforming along with the piezoelectric layer when it deforms due to temperature changes, preventing stress from the electrodes on the piezoelectric layer and thus avoiding damage.
[0017] As one possible implementation, the thickness of the first metal adhesion layer is 8 nm to 30 nm, and the thickness of the metal electrode layer is 0.04 μm to 0.15 μm.
[0018] With the above technical solution, the thickness of the first metal adhesion layer, within the aforementioned range, can prevent the electric field generated by the metal electrode layer from weakening at the piezoelectric layer due to an excessively thick first metal adhesion layer increasing the distance between the metal electrode layer and the piezoelectric layer. This ensures that the metal electrode layer has strong electric field control over the piezoelectric layer, and the electric field generated by the piezoelectric layer has strong control over the metal electrode layer, thus improving the performance of the surface acoustic wave resonator. Secondly, it also prevents the first metal adhesion layer from being too thin, which would fail to isolate the metal electrode layer and the piezoelectric layer, allowing metal atoms in the metal electrode layer to diffuse into the piezoelectric layer, thereby affecting the crystal structure and piezoelectric properties of the piezoelectric layer. Therefore, when the thickness of the first metal adhesion layer is between 8 nm and 30 nm, the surface acoustic wave resonator provided by this invention exhibits better performance.
[0019] With the above-described technical solution, the thickness of the metal electrode layer, within the aforementioned range, can prevent the surface acoustic wave (SAW) resonator from suffering performance degradation or even damage due to thermal deformation or external force during manufacturing and application. Furthermore, it prevents the need for excessive metal deposition and higher etching power to form the electrode pattern during manufacturing, thus reducing manufacturing costs. Therefore, when the metal electrode layer thickness is between 0.04 μm and 0.15 μm, the SAW resonator provided by this invention exhibits superior performance.
[0020] As one possible implementation, the bonding layer includes a metal bonding layer. In this case, the piezoelectric layer and the supporting substrate are connected together by metal bonding, and the rough surfaces of the piezoelectric layer and the supporting substrate can be smoothed by filling them with the metal bonding layer; the metal bonding strength is also high, which can improve the vibration resistance of the surface acoustic wave resonator provided by this invention; and the metal sound velocity is also high, which will not affect the performance of the surface acoustic wave resonator provided by this invention.
[0021] As one possible implementation, the metal bonding layer includes a low-temperature bonding layer and second metal adhesion layers disposed on both sides of the low-temperature bonding layer along the thickness direction of the supporting substrate. In this case, when processing the surface acoustic wave resonator provided by this invention, in the bonding step, the second metal adhesion layer is first formed on the acoustic impedance matching layer and the piezoelectric layer, then the low-temperature bonding layer is formed on the second metal adhesion layer respectively, and finally the low-temperature bonding layers are bonded together. The second metal adhesion layer has good adhesion to the acoustic impedance matching layer and the piezoelectric layer, which is beneficial for subsequent bonding. The process temperature for bonding the low-temperature bonding layers together is relatively low, which can reduce the thermal budget; it can also avoid the high temperature generated during bonding followed by cooling, which would anneal the piezoelectric layer and change its crystal structure, ensuring that the performance of the piezoelectric layer remains unchanged during processing.
[0022] As one possible implementation, the low-temperature bonding layer includes a copper layer, and the second metal adhesion layer includes a titanium layer. In this case, the low bonding temperature of copper achieves the aforementioned process effect of the low-temperature bonding layer. Furthermore, titanium is stable in the bonding process and does not easily diffuse into the acoustic impedance matching layer and piezoelectric layer during processing. This avoids contamination of the acoustic impedance matching layer and piezoelectric layer by the low-temperature bonding layer, especially contamination of the crystal structure of the piezoelectric layer. This ensures that the piezoelectric properties of the piezoelectric layer remain unchanged after the bonding process, ultimately ensuring that the surface acoustic wave resonator provided by this invention has high operating performance. Attached Figure Description
[0023] The accompanying drawings, which are included to provide a further understanding of the present invention and constitute a part of this invention, illustrate exemplary embodiments of the present invention and, together with the description thereof, serve to explain the present invention and do not constitute an undue limitation thereof. In the drawings:
[0024] Figure 1 Schematic diagram of the longitudinal structure of the surface acoustic wave resonator provided in the embodiment of this utility model Figure 1 ;
[0025] Figure 2 Schematic diagram of the longitudinal structure of the surface acoustic wave resonator provided in the embodiment of this utility model Figure 2 ;
[0026] Figure 3 Schematic diagram of the longitudinal structure of the surface acoustic wave resonator provided in the embodiment of this utility model Figure 3 ;
[0027] Figure 4 Admittance curves comparing the presence and absence of an acoustic impedance matching layer in the surface acoustic wave resonator provided in this embodiment of the utility model.
[0028] Figure label:
[0029] 10 - Supporting substrate, 20 - Acoustic impedance matching layer,
[0030] 30-bonding layer, 40-piezoelectric layer
[0031] 50 - Electrode, 51 - First metal adhesion layer,
[0032] 52 - Metal electrode layer, 31 - First metal adhesive layer,
[0033] 32-Low-temperature bonding layer, 33-Second metal adhesive layer. Detailed Implementation
[0034] To make the technical problems, technical solutions, and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.
[0035] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.
[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.
[0037] In the description of this utility model, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.
[0038] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.
[0039] Please refer to Figure 1 This invention provides a surface acoustic wave (SAW) resonator. The SAW resonator has an operating bandwidth greater than or equal to 600 MHz, and / or, its operating frequency band includes the N79 band. The SAW resonator includes: a supporting substrate 10, an acoustic impedance matching layer 20, a bonding layer 30, a piezoelectric layer 40, and an electrode 50. The supporting substrate 10, acoustic impedance matching layer 20, bonding layer 30, and piezoelectric layer 40 are sequentially stacked; the acoustic impedance matching layer 20 is bonded to the piezoelectric layer 40 via the bonding layer 30. The crystal velocity corresponding to the supporting substrate 10 is greater than the crystal velocity corresponding to the piezoelectric layer 40. The electrode 50 is disposed on the side of the piezoelectric layer 40 opposite to the bonding layer 30.
[0040] The surface acoustic wave resonator provided by this invention operates as follows: an electrical signal input from the electrodes applies an electric field to the piezoelectric layer, which is converted into an acoustic signal through the inverse piezoelectric effect. The acoustic signal is transmitted through the piezoelectric layer and the supporting substrate to the piezoelectric layer under the electrodes, where it is converted back into an electrical signal for output through the direct piezoelectric effect. During this process, filtering is achieved based on the aforementioned principle.
[0041] For surface acoustic wave (SAW) resonators, their operating frequency band and bandwidth are directly proportional to the sound velocity of the SAW material. However, the relatively low sound velocity of piezoelectric materials limits the improvement of the SAW resonator's operating frequency band and bandwidth. But since the sound velocity of the crystal corresponding to the supporting substrate is greater than that of the crystal corresponding to the piezoelectric layer, the bandwidth of the SAW resonator of this invention can be expanded and the operating frequency band increased. Furthermore, the supporting substrate and the piezoelectric layer are made of materials with different sound velocities, forming an interface with a significant difference in sound wave propagation speed, thereby increasing reflection to suppress clutter and improving the performance of the SAW resonator.
[0042] Meanwhile, the acoustic impedance matching layer, acting as a matching layer for sound wave transmission between films with different crystal sound velocities, serves as a transmission stepping stone. Since the sound velocity in the acoustic impedance matching layer is lower than that of the supporting substrate but higher than that of the piezoelectric layer, it can suppress clutter by utilizing the sound velocity difference while reducing the aforementioned reflections between the supporting substrate and the piezoelectric layer. This allows the sound waves converted by the piezoelectric layer to be transmitted to the supporting substrate with low loss, improving the gain of the surface acoustic wave resonator provided by this invention. Furthermore, bonding the acoustic impedance matching layer and the piezoelectric layer together with a bonding layer makes the connection between them more stable, resulting in less reflection and clutter caused by an unstable connection interface.
[0043] In practical applications, this utility model does not impose specific requirements on the operating bandwidth and operating frequency band of the surface acoustic wave resonator. As long as the operating bandwidth of the surface acoustic wave resonator is greater than or equal to 600MHz, and / or the operating frequency band of the surface acoustic wave resonator provided by this utility model includes the N79 frequency band.
[0044] In practical applications, this embodiment of the invention does not specifically limit the material and thickness of the supporting substrate. According to the aforementioned theory, any substrate whose crystal sound velocity is greater than that of the piezoelectric layer is acceptable. For example, at least one of diamond substrate, single-crystal silicon substrate, sapphire substrate, silicon carbide substrate, and quartz crystal substrate can be used. The aforementioned substrates have high sound velocities, which, based on the above principle, can increase the bandwidth and operating frequency of the surface acoustic wave resonator provided by this invention. When at least two substrates are used to form the supporting substrate, the distribution of the at least two substrates can be alternating in a strip, comb, lattice, or concentric circle pattern, or a suitable distribution pattern can be selected according to design requirements.
[0045] Optionally, a diamond substrate can be used as the support substrate because diamond has a high sound velocity, which greatly helps to widen the bandwidth and increase the operating frequency. Furthermore, when the surface acoustic wave (SAW) resonator is used in a transmitter filter, which filters high-power signals, the resistance is high when the electrode width is small, resulting in significant heat dissipation. Combined with the low thermal conductivity of conventional SAW materials, the heat dissipation pressure on the SAW resonator is substantial. Diamond, however, also has high thermal conductivity, which helps improve the heat dissipation of the SAW resonator and avoids changes in the lattice structure of the piezoelectric layer due to high temperatures, thus maintaining the stability of the performance of the SAW resonator provided by this invention.
[0046] As for the thickness of the diamond substrate, it ranges from 5 μm to 25 μm. Specifically, the thickness of the diamond substrate can be 5 μm, 10 μm, 15 μm, 20 μm, or 25 μm.
[0047] With the above-described solution, the thickness of the diamond substrate is within the aforementioned range. This prevents the acoustic signal generated by the piezoelectric layer from leaking from the diamond due to an excessively thin diamond substrate, thus avoiding additional losses and ensuring that the gain of the surface acoustic wave resonator provided by this invention remains unchanged. Furthermore, it also prevents a significant increase in manufacturing costs due to an excessively thick diamond substrate.
[0048] Regarding the aforementioned acoustic impedance matching layer, this embodiment of the invention does not specifically limit the material and thickness of the acoustic impedance matching layer, as long as it satisfies the condition that the crystal sound velocity of the acoustic impedance matching layer is greater than that of the piezoelectric layer and less than that of the supporting substrate, and can function as a stepping stone between the piezoelectric layer and the supporting substrate. For example, the acoustic impedance matching layer can be selected from at least one of silicon dioxide, silicon oxyfluoride, silicon oxycarbide, silicon oxynitride, lithium oxide, tantalum pentoxide, and silicon nitride layers. In this case, there are many choices for the acoustic impedance matching layer, which can be matched with supporting substrates and piezoelectric layers made of various materials.
[0049] Optionally, the acoustic impedance matching layer may be a silicon dioxide layer, because silicon dioxide has low raw material and manufacturing costs, good compatibility with existing semiconductor technologies, and the process of forming silicon dioxide is mature and reliable.
[0050] Regarding the thickness of the acoustic impedance matching layer, it can be understood that the acoustic impedance matching layer acts as a transmission stepping stone for sound waves to travel from the piezoelectric layer to the supporting substrate. If the acoustic impedance matching layer is too thick, the sound wave transmission path will be too long, and the time required for the sound wave to complete one cycle of oscillation will be longer, thus affecting the bandwidth of the surface acoustic wave resonator provided by this invention. Conversely, if the acoustic impedance matching layer is too thin, when the sound wave passes through the acoustic impedance matching layer from the piezoelectric layer to the supporting substrate, or passes through the acoustic impedance matching layer in the opposite direction, it will directly cross the acoustic impedance matching layer due to the diffraction of the sound wave, thus preventing the acoustic impedance matching layer from functioning as a transmission stepping stone. Furthermore, when the acoustic impedance matching layer is made of different materials, its acoustic wave matching effect may differ due to the different sound velocities of the materials and their electromechanical coupling coefficients with the piezoelectric layer and the supporting substrate. Moreover, to effectively couple with sound waves of different frequencies and to achieve the same purpose, the thickness of the acoustic impedance matching layer may also differ for different materials. Therefore, the thickness of the acoustic impedance matching layer can be determined based on the bandwidth and frequency range of the surface acoustic wave resonator in the actual application scenario, as well as the material of the acoustic impedance matching layer; no specific limitations are made here.
[0051] For example, when the acoustic impedance matching layer is a silicon dioxide layer, its thickness can be from 0.1 μm to 0.6 μm. For instance, the thickness of the silicon dioxide layer can be 0 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or 0.6 μm. In this case, according to the aforementioned principle, the silicon dioxide layer will not affect performance due to being too thick, nor will it fail to function as an acoustic impedance matching layer due to being too thin. Furthermore, the thickness of the silicon dioxide layer has a significant impact on the electromechanical coupling coefficient. In this case, since the acoustic waves in the surface acoustic wave resonator are mainly horizontal shear waves (SH waves), the horizontal shear waves have a high propagation speed of 12820 m / s in the diamond substrate material, while the propagation speed in the low-velocity silicon dioxide material is 3750 m / s. Because the acoustic waves are reflected back to the low-velocity layer when propagating from the low-velocity layer to the high-velocity layer, the propagation of acoustic waves into the resonator body and substrate can be suppressed, confining the energy to the piezoelectric layer and electrode region, thereby improving the performance of the surface acoustic wave resonator. Furthermore, since silicon dioxide is a material with a positive temperature coefficient, the temperature coefficient of the resonator can be improved by utilizing the silicon dioxide layer for temperature absorption, thereby obtaining a larger electromechanical coupling coefficient. When the silicon dioxide layer is within the aforementioned thickness range, the surface acoustic wave resonator provided by this invention has a larger bandwidth.
[0052] Regarding the piezoelectric layer included in the surface acoustic wave resonator provided by this invention, this invention does not impose specific limitations on its material and thickness, as long as it possesses good piezoelectric characteristics, electromechanical coupling coefficient, chemical stability, mechanical hardness, and low transmission loss, and meets the performance requirements for specific applications of the surface acoustic wave resonator provided by this invention. For example, the piezoelectric layer can be selected from at least one of lithium niobate, lithium tantalate, aluminum nitride, zinc oxide, and quartz layers. The aforementioned piezoelectric materials have good piezoelectric characteristics, high electromechanical coupling coefficients, and low propagation losses, as well as good chemical stability and mechanical hardness, making them less susceptible to interference from various external factors. Therefore, the surface acoustic wave resonator provided by this invention has good performance and operational stability.
[0053] Optionally, a lithium niobate layer is selected as the piezoelectric layer. In this case, the tangential orientation of the selected lithium niobate layer is X-tangent to Y-rotation, and the Euler angle is greater than or equal to 30° and less than or equal to 80°. For example, the Euler angles of the lithium niobate layer are 30°, 40°, 50°, 60°, 70°, and 80°. Optionally, the tangential orientation of the lithium niobate layer is X-tangent to Y-rotation, and the Euler angle is 60°. In this case, lithium niobate and lithium tantalate are both common piezoelectric materials in surface acoustic wave (SAW) resonators. Since SAW resonators mainly use horizontal shear waves (SH waves), the piezoelectric constant e can be used. 16 The magnitude of the piezoelectric constant e of lithium niobate can be used to roughly determine the electromechanical coupling coefficient of the resonator. 16 -2.53C / m 2 The piezoelectric constant of lithium tantalate e 16-1.59C / m 2 A resonator with a larger electromechanical coupling coefficient has a higher electromechanical transduction efficiency, resulting in a larger bandwidth for the final filter. Therefore, lithium niobate, with its relatively high piezoelectric constant, is used as the piezoelectric material. Furthermore, the chamfer angle of the piezoelectric material affects its piezoelectric constant, which in turn affects the electromechanical coupling coefficient of the resonator. Therefore, the chamfer angle of the piezoelectric material must be carefully selected to obtain better resonator performance. An X-shaped chamfer on lithium niobate results in a larger electromechanical coupling coefficient, while a smaller chamfer angle allows for better excitation of horizontal shear waves. Experiments conducted by the inventors showed that an Euler angle of 60° resulted in the highest electromechanical coupling coefficient.
[0054] Furthermore, the thickness of the lithium niobate layer is 200nm-500nm. For example, the thickness of the lithium niobate layer is 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, or 500nm. Optionally, the thickness of the lithium niobate layer is 300nm.
[0055] With the above technical solution, the thickness of the lithium niobate layer is within the aforementioned range. This prevents the operating frequency band and bandwidth of the surface acoustic wave resonator provided by this invention from decreasing due to an excessively thick lithium niobate layer, thus ensuring that the surface acoustic wave resonator provided by this invention has a high operating frequency band and a wide bandwidth. Secondly, it also prevents the lithium niobate layer from becoming too thin, which would increase the difficulty of its formation process, thereby reducing the cost of manufacturing the surface acoustic wave resonator provided by this invention.
[0056] Regarding the electrodes included in the surface acoustic wave resonator provided by this utility model, the embodiments of this utility model do not impose specific limitations on their shape and pattern, as long as they can meet the performance requirements of the surface acoustic wave resonator provided by this utility model. For example, the shape of the electrodes can be interdigitated, circular, rectangular, or annular. Optionally, the shape of the electrodes is interdigitated, which has the advantage of flexible design, allowing the frequency and bandwidth characteristics of the surface acoustic wave resonator provided by this utility model to be controlled by adjusting parameters such as finger width, finger spacing, and number of finger pairs.
[0057] In practical applications, electrodes can be single-layer structures. For example, an electrode can be a single layer of aluminum, copper, or titanium. Alternatively, it can be a stacked structure composed of multiple conductive layers. The specific structure of the electrode can be set according to actual needs.
[0058] For example, please refer to Figure 2The electrode comprises a first metal adhesion layer 51 and a metal electrode layer 52 sequentially stacked along the thickness direction of the supporting substrate. In this case, when manufacturing the surface acoustic wave resonator provided by the present invention, depositing the first metal adhesion layer 51 and then the metal electrode layer 52 on the piezoelectric layer 40 first can prevent metal atoms in the metal electrode layer 52 from penetrating into the piezoelectric layer 40, thereby keeping the crystal structure of the piezoelectric layer 40 unchanged and ensuring the stability of the piezoelectric performance of the piezoelectric layer 40; furthermore, it can also prevent the electrical signal transmitted from the electrode from being directly transmitted back to the electrode through the piezoelectric layer via the metal atoms that have penetrated into the piezoelectric layer 40, that is, without the inverse piezoelectric effect and without being filtered, thereby ensuring that the filtering performance of the surface acoustic wave resonator provided by the present invention remains stable.
[0059] It should be noted that this invention does not impose specific limitations on the materials and thicknesses of the first metal adhesion layer and the metal electrode layer, as long as they can each perform their respective functions. Optionally, the first metal adhesion layer is a chromium electrode layer, and the metal electrode layer is an aluminum electrode layer. In this case, the adhesion between the chromium electrode layer and the aforementioned piezoelectric material is better, which can improve structural stability. Furthermore, the chromium electrode layer is stable and does not easily diffuse into the piezoelectric layer, thus affecting the crystal structure of the piezoelectric layer, making it suitable as the first metal adhesion layer. The aluminum electrode layer is easy to photolithographically etch, making it easier to form interdigitated electrode patterns when manufacturing the surface acoustic wave resonator provided by this invention. At the same time, aluminum has appropriate hardness and flexibility, which can resist external impacts and deform along with the piezoelectric layer when it deforms due to temperature, avoiding stress on the piezoelectric layer caused by the electrodes, thus preventing damage to the piezoelectric layer and making the structure of the surface acoustic wave resonator provided by this invention more stable.
[0060] Furthermore, the thickness of the aluminum electrode layer is from 0.04 μm to 0.15 μm. Specifically, the thickness of the aluminum electrode layer is 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, 0.11 μm, 0.12 μm, 0.13 μm, 0.14 μm, or 0.15 μm. Optionally, the thickness of the aluminum electrode layer is 0.06 μm.
[0061] With the above-described technical solution, the thickness of the metal electrode layer is within the aforementioned range. This prevents the metal electrode layer from being damaged due to thermal deformation or external force during the manufacturing process and application of the surface acoustic wave (SAW) resonator provided by this invention, thus avoiding performance degradation or even damage to the SAW resonator. Secondly, it also prevents the need for excessive metal deposition and higher etching power to form the electrode pattern during manufacturing, which would increase manufacturing costs. Therefore, the SAW resonator provided by this invention exhibits the best performance when the thickness of the metal electrode layer is between 0.04 μm and 0.15 μm.
[0062] Furthermore, the thickness of the chromium electrode layer ranges from 8 nm to 30 nm. Specifically, the thickness of the chromium electrode layer is 8 nm, 12 nm, 16 nm, 20 nm, 24 nm, 28 nm, or 30 nm. Optionally, the thickness of the chromium electrode layer is 10 nm.
[0063] With the above technical solution, the thickness of the first metal adhesion layer, within the aforementioned range, can prevent the electric field generated by the metal electrode layer from weakening at the piezoelectric layer due to an excessively thick first metal adhesion layer increasing the distance between the metal electrode layer and the piezoelectric layer. This ensures that the metal electrode layer has strong electric field control over the piezoelectric layer, and the electric field generated by the piezoelectric layer has strong control over the metal electrode layer, thus improving the performance of the surface acoustic wave resonator. Secondly, it also prevents the first metal adhesion layer from being too thin, which would fail to isolate the metal electrode layer and the piezoelectric layer, allowing metal atoms in the metal electrode layer to diffuse into the piezoelectric layer, affecting the crystal structure and piezoelectric properties of the piezoelectric layer. Therefore, the surface acoustic wave resonator provided by this invention exhibits the best performance when the thickness of the first metal adhesion layer is between 8 nm and 30 nm.
[0064] If the first metal adhesion layer, i.e., the chromium electrode layer, is too thick, it increases the distance between the aluminum electrode layer and the piezoelectric layer. This weakens the electric field generated by the aluminum electrode layer at the piezoelectric layer, affecting the electric field modulation of the piezoelectric layer by the aluminum electrode layer, and also affecting the modulation of the aluminum electrode layer by the electric field generated by the piezoelectric layer, ultimately impacting the performance of the surface acoustic wave resonator. If the chromium electrode layer is too thin, it cannot effectively isolate the aluminum electrode layer and the piezoelectric layer. Metal atoms in the aluminum electrode layer can still diffuse into the piezoelectric layer, affecting the crystal structure of the piezoelectric layer and its piezoelectric properties.
[0065] Regarding the bonding layer included in the surface acoustic wave resonator of this invention, this invention does not impose specific limitations on its type and thickness, as long as it meets the bonding performance requirements. For example, it can be a combination of one or more of titanium, tungsten, molybdenum, platinum, gold, copper, and aluminum layers.
[0066] In practical applications, the metal bonding layer can be a single-layer structure. For example, the metal electrode layer can be a single layer of titanium, tungsten, molybdenum, platinum, gold, copper, or aluminum. Alternatively, it can be a multilayer structure composed of multiple bonding layers. The specific structure of the metal bonding layer can be set according to actual needs.
[0067] For example, please refer to Figure 3 The metal bonding layer includes a low-temperature bonding layer 32 and a second metal adhesion layer disposed on both sides of the low-temperature bonding layer along the thickness direction of the supporting substrate. The second metal adhesion layer is divided into a first metal adhesion sublayer 31 and a second metal adhesion sublayer 33. In the fabrication of the surface acoustic wave resonator provided by this invention, during the bonding step, the first metal adhesion sublayer 31 is first formed on the acoustic impedance matching layer 20, and the second metal adhesion sublayer 33 is formed on the piezoelectric layer 40. Then, low-temperature bonding layers 32 are formed on the first metal adhesion sublayer 31 and the second metal adhesion sublayer 33 respectively, and finally, the low-temperature bonding layers 32 are bonded together. The second metal adhesion layer has good adhesion to the acoustic impedance matching layer 20 and the piezoelectric layer 40, which is beneficial for subsequent bonding. The low-temperature bonding layers are bonded to each other at a lower process temperature, ranging from 70°C to 150°C, which can reduce the thermal budget. It can also avoid the annealing of the piezoelectric layer 40 caused by the high temperature generated during bonding followed by cooling, which changes the crystal structure of the piezoelectric layer 40 and ensures that the performance of the piezoelectric layer 40 remains unchanged during the processing.
[0068] This embodiment of the invention does not impose specific limitations on the materials and thicknesses of the low-temperature bonding layer and the second metal adhesion layer, as long as the performance requirements described above are met. Optionally, the low-temperature bonding layer is a copper layer with a thickness of 70 nm; the first metal adhesion sublayer and the second metal adhesion sublayer are both titanium layers with a thickness of 10 nm. Copper has a low bonding temperature, which can achieve the aforementioned process effect of the low-temperature bonding layer. Furthermore, titanium is stable in the bonding process and does not easily diffuse into the acoustic impedance matching layer and the piezoelectric layer during processing. This avoids contamination of the acoustic impedance matching layer and the piezoelectric layer by the low-temperature bonding layer, especially contamination of the crystal structure of the piezoelectric layer, thereby ensuring that the piezoelectric performance of the piezoelectric layer remains unchanged after the bonding process, and ultimately ensuring that the surface acoustic wave resonator provided by this invention has high operating performance.
[0069] In practical applications, a support substrate can be directly set, and then other structures included in the surface acoustic wave resonator provided by this utility model can be formed on the support substrate; alternatively, other substrates can be provided first, and then a support substrate can be set on the provided other substrates, and then other structures included in the surface acoustic wave resonator provided by this utility model can be formed on the support substrate.
[0070] As one possible implementation, please refer to Figure 4When the thickness of the silicon dioxide layer is 0.2 μm and the thickness of the aluminum electrode layer is 0.06 μm, the surface acoustic wave resonator provided by this invention has a bandwidth of 628 MHz, a resonant point of 4804 MHz, and an anti-resonant point of 5432 MHz. Compared with the bandwidth of 288 MHz, the resonant point of 4880 MHz, and the anti-resonant point of 5168 MHz when no silicon dioxide layer is used, the bandwidth is widened and it can be applied to the N79 frequency band.
[0071] It should be noted that Figure 4 Only the frequency characteristics with and without a silicon dioxide layer were compared. Figure 4 The two embodiments are in Figure 3 Tested based on the example implementation.
[0072] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.
[0073] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the protection scope of the claims.
Claims
1. A surface acoustic wave resonator, characterized in that, The operating bandwidth of the surface acoustic wave resonator is greater than or equal to 600MHz; And / or, the operating frequency band of the surface acoustic wave resonator includes the N79 band; The surface acoustic wave resonator includes: A supporting substrate, an acoustic impedance matching layer, a bonding layer, and a piezoelectric layer are sequentially stacked; the acoustic impedance matching layer is bonded to the piezoelectric layer through the bonding layer; the crystal sound velocity corresponding to the supporting substrate is greater than the crystal sound velocity corresponding to the piezoelectric layer. And electrodes, disposed on the side of the piezoelectric layer away from the bonding layer.
2. The surface acoustic wave resonator according to claim 1, characterized in that, The acoustic impedance matching layer includes at least one of the following: silicon dioxide layer, silicon fluoride layer, silicon carbon oxide layer, silicon oxynitride layer, lithium oxide layer, tantalum pentoxide layer, and silicon nitride layer; And / or, the supporting substrate includes at least one of diamond substrate, single crystal silicon substrate, sapphire substrate, silicon carbide substrate and quartz crystal substrate; And / or, the piezoelectric layer includes at least one of a lithium niobate layer, a lithium tantalate layer, an aluminum nitride layer, a zinc oxide layer, and a quartz layer.
3. The surface acoustic wave resonator according to claim 1, characterized in that, When the acoustic impedance matching layer is a silicon dioxide layer, the thickness of the acoustic impedance matching layer is 0.1 μm to 0.6 μm.
4. The surface acoustic wave resonator according to claim 1, characterized in that, When the piezoelectric layer is a lithium niobate layer, the tangential direction of the piezoelectric layer is X-tangent and Y-rotation; the Euler angle is greater than or equal to 30° and less than or equal to 80°.
5. The surface acoustic wave resonator according to claim 1, characterized in that, The electrodes include interdigitated electrodes.
6. The surface acoustic wave resonator according to claim 1, characterized in that, The electrode includes a first metal adhesion layer and a metal electrode layer that are sequentially stacked along the thickness direction of the supporting substrate.
7. The surface acoustic wave resonator according to claim 6, characterized in that, The first metal adhesion layer is a chromium electrode layer, and the metal electrode layer is an aluminum electrode layer; And / or, the thickness of the first metal adhesion layer is 8 nm to 30 nm, and the thickness of the metal electrode layer is 0.04 μm to 0.15 μm.
8. The surface acoustic wave resonator according to claim 1, characterized in that, The bonding layer includes a metal bonding layer.
9. The surface acoustic wave resonator according to claim 8, characterized in that, The metal bonding layer includes a low-temperature bonding layer and a second metal adhesion layer disposed on both sides of the low-temperature bonding layer along the thickness direction of the supporting substrate.
10. The surface acoustic wave resonator according to claim 9, characterized in that, The low-temperature bonding layer includes a copper layer, and the second metal adhesion layer includes a titanium layer.