Surface acoustic wave resonator, preparation method thereof and surface acoustic wave filter
By applying radio frequency power during the fabrication process of the surface acoustic wave filter to form a planarized and densified temperature compensation layer, the frequency drift problem caused by temperature changes is solved, and the temperature stability and performance of the filter are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-14
AI Technical Summary
Surface acoustic wave (SAW) filters are sensitive to temperature changes during operation, resulting in significant frequency drift. Existing technologies struggle to effectively suppress performance degradation caused by defects in the temperature compensation layer.
By applying radio frequency power during the fabrication process, a temperature compensation layer is formed using a deposition process. The temperature compensation layer is planarized and densified to improve its coverage and avoid the formation of defects such as protrusions and holes.
It effectively suppresses frequency drift caused by temperature changes, improves the temperature stability and performance of the filter, reduces passband collapse, bandwidth narrowing and passband clutter, and improves the quality factor and passband bandwidth of the filter.
Smart Images
Figure CN121864050A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor technology, and more specifically, to a surface acoustic wave resonator and its fabrication method, and a surface acoustic wave filter. Background Technology
[0002] Radio frequency (RF) front-end chips in wireless communication devices include RF power amplifiers, RF switches, RF filters, RF multiplexers (e.g., duplexers, quadplexers, etc.), and low-noise amplifiers. Among these, RF filters include surface acoustic wave (SAW) filters, bulk acoustic wave (BAW) filters, micro-electro-mechanical system (MEMS) filters, and integrated passive device (IPD) filters.
[0003] A surface acoustic wave (SAW) filter is a filter that uses interdigitated transducers fabricated on the surface of a piezoelectric material or thin film to convert electrical signals into surface acoustic waves, which then convert them back into electrical signals. The center frequency of the filter can be controlled by adjusting the spacing between the interdigitated transducers. The SAW resonator, as the core component of the SAW filter, directly affects its performance.
[0004] Surface acoustic wave (SAW) filters offer advantages such as high design flexibility, wide frequency selectivity, and low transmission loss. However, they also suffer from frequency sensitivity to temperature changes and significant frequency drift. With the advent of 5G mobile communication technology, the increasingly congested spectrum and the substantial increase in the number of filters have placed new demands on their overall performance. In particular, efforts are being made to improve the temperature stability of SAW filters to reduce the impact of temperature on operating frequency, and to develop SAW filters with smaller frequency temperature coefficients to meet the requirements of these new technologies. Summary of the Invention
[0005] This application provides a surface acoustic wave (SAW) resonator and its fabrication method, as well as a SAW filter. By optimizing the fabrication process, the formation of defects in the temperature compensation layer is effectively suppressed, thereby avoiding negative impacts on the performance of the SAW filter (e.g., insertion loss and passband bandwidth).
[0006] One aspect of this application provides a method for fabricating a surface acoustic wave resonator, including forming a substrate, including forming a piezoelectric layer; forming interdigitated electrodes on the piezoelectric layer; and forming a temperature compensation layer on the piezoelectric layer, covering the interdigitated electrodes, wherein the temperature compensation layer is formed using a deposition process; wherein forming the temperature compensation layer includes applying radio frequency power for planarizing and densifying the temperature compensation layer.
[0007] Optionally, the interdigital electrode has an interdigital depth-to-width ratio greater than or equal to 0.7.
[0008] Optionally, the piezoelectric layer may be made of lithium tantalate or lithium niobate, and the temperature compensation layer may be made of silicon dioxide.
[0009] Optionally, the deposition process includes one of the following: physical vapor deposition, chemical vapor deposition, or atomic layer deposition.
[0010] Optionally, forming the temperature compensation layer includes: forming the temperature compensation layer using a physical vapor deposition process, with an applied radio frequency power greater than 260W.
[0011] Optionally, forming the temperature compensation layer includes: forming the temperature compensation layer using a chemical vapor deposition process, with an applied radio frequency power greater than 50W.
[0012] Optionally, forming the temperature compensation layer includes: forming the temperature compensation layer using an atomic layer deposition process, with the applied radio frequency power being less than or equal to 20W.
[0013] Optionally, forming the substrate further includes: providing a substrate; forming an intermediate layer on the substrate, the intermediate layer being located between the substrate and the piezoelectric layer.
[0014] In another aspect of the embodiments of this application, a surface acoustic wave resonator is provided, which is prepared by the surface acoustic wave resonator preparation method of any one of the foregoing claims.
[0015] In another aspect of the embodiments of this application, a surface acoustic wave filter is provided, including the aforementioned surface acoustic wave resonator.
[0016] This application provides a method for fabricating a surface acoustic wave (SAW) resonator, including forming a substrate, including forming a piezoelectric layer; forming interdigitated electrodes on the piezoelectric layer; and forming a temperature compensation layer on the piezoelectric layer, covering the interdigitated electrodes. The temperature compensation layer is formed using a deposition process. Forming the temperature compensation layer includes applying radio frequency (RF) power to planarize and densify the temperature compensation layer. In this method, during the deposition of the temperature compensation layer, RF power is applied to the target material on the instrument. The bias voltage generated by the RF power not only suppresses protrusions on the temperature compensation layer but also effectively solves the problem of poor coverage of the interdigitated electrodes by the temperature compensation layer during deposition, resulting in defects such as cracks and holes between the interdigitated electrodes. This achieves a planarized and densified temperature compensation layer, thereby avoiding problems such as filter passband collapse, bandwidth narrowing, and passband clutter caused by defects in the temperature compensation layer. Attached Figure Description
[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 A schematic diagram of a surface acoustic wave resonator; Figure 2 A comparative diagram showing the effect of structural defects in the temperature compensation layer of a surface acoustic wave resonator on the resonant frequency curve. Figure 3 A schematic diagram of structural defects in the temperature compensation layer of a surface acoustic wave resonator; Figure 4 A comparative diagram showing the effect of structural defects in the temperature compensation layer of a surface acoustic wave resonator on the resonant frequency curve. Figure 5 A schematic flowchart illustrating a method for fabricating a surface acoustic wave resonator according to an embodiment of this application; Figure 6 A schematic diagram of the structure of a surface acoustic wave resonator provided in an embodiment of this application; Figure 7 A schematic flowchart illustrating a method for fabricating a surface acoustic wave resonator according to an embodiment of this application; Figure 8 This is a schematic diagram of the structure of a surface acoustic wave resonator fabricated using a fabrication method for a surface acoustic wave resonator provided in an embodiment of this application. Figure 9This is a schematic diagram of the structure of a surface acoustic wave resonator fabricated using a fabrication method for a surface acoustic wave resonator provided in an embodiment of this application. Figure 10 This is a schematic diagram of the structure of a surface acoustic wave resonator fabricated using a fabrication method for a surface acoustic wave resonator provided in an embodiment of this application. Figure 11 A schematic flowchart illustrating a method for fabricating a surface acoustic wave resonator according to another embodiment of this application; Figure 12 A schematic flowchart illustrating a method for fabricating a surface acoustic wave resonator according to another embodiment of this application; Figure 13 A schematic flowchart illustrating a method for fabricating a surface acoustic wave resonator according to another embodiment of this application; Figure 14 This is a schematic diagram of the structure of a surface acoustic wave resonator provided in another embodiment of this application.
[0019] Icons: 10-Substrate; 11-Base; 12-Intermediate layer; 13-Piezoelectric layer; 20-Interdigital electrode; 30-Temperature compensation layer. Detailed Implementation
[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. It should be noted that, in the absence of conflict, the various features in the embodiments of this application can be combined with each other, and the combined embodiments are still within the protection scope of this application.
[0021] In the description of this application, it should be noted that the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and therefore should not be construed as limiting this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0022] Surface acoustic wave (SAW) filters are filters made by utilizing the property that sound waves propagate along the surface of piezoelectric materials or piezoelectric films. They have the advantages of high design flexibility, wide frequency selectivity and low transmission loss. However, the operating frequency of SAW filters is quite sensitive to temperature changes, resulting in a large frequency drift when the temperature changes.
[0023] like Figure 1As shown, the surface acoustic wave resonator includes a substrate 10, which includes a piezoelectric layer 13; interdigitated electrodes 20 located on the piezoelectric layer 13; and a temperature compensation layer 30 located on the piezoelectric layer 13, covering the interdigitated electrodes 20.
[0024] Frequency drift caused by temperature changes is suppressed by selecting the material of the temperature compensation layer 30 and matching the materials of the temperature compensation layer 30 and the piezoelectric layer 13.
[0025] However, the temperature compensation layer 30 is fabricated on the piezoelectric layer 13 after the interdigitated electrodes 20 are formed. Since the thickness of the interdigitated electrodes 20 is greater than the upper surface of the piezoelectric layer 13, the formed temperature compensation layer 30 usually protrudes from the top of the interdigitated electrodes 20, resulting in an uneven surface of the temperature compensation layer 30. Figure 1 As shown. Figure 1 The protrusions in the temperature compensation layer 30 shown cause the frequency temperature coefficient and electromechanical coupling coefficient of the surface acoustic wave resonator to deviate from their ideal values, thereby introducing clutter into the passband region of the surface acoustic wave filter. Figure 2 The comparison images show that the left image shows a protrusion on the temperature compensation layer 30 corresponding to the interdigitated electrode 20, while the right image shows no protrusion on the temperature compensation layer corresponding to the interdigitated electrode 20. According to... Figure 2 The comparison shows that when the temperature compensation layer 30 has a protrusion, there is obvious in-band clutter in the area highlighted in red in the left figure, which increases the filter insertion loss.
[0026] Moreover, such as Figure 1 As shown, during the formation of the temperature compensation layer 30, due to the small aspect ratio of the interdigitated fingers of the interdigitated electrodes 20 and the small spacing between adjacent interdigitated fingers, holes or gaps appear in the temperature compensation layer 30 at the positions corresponding to the interdigitated fingers of the interdigitated electrodes 20. For this, refer to... Figure 3 Microscopic images from the fabrication process show that holes or gaps between the interdigitated fingers can cause passband collapse in the filter, increasing passband insertion loss, resulting in narrower bandwidth and the formation of in-band clutter anomalies. For example... Figure 4 The comparison images show the passband waveforms under ideal conditions, where there are no holes or gap defects at the positions between the interdigital electrodes 20 corresponding to the temperature compensation layer 30. There is no waveform collapse, representing a normal waveform under ideal conditions. The three superimposed passband waveforms in the right image correspond to different degrees of holes or gap defects at the positions between the interdigital electrodes 20 corresponding to the temperature compensation layer 30. It can be seen that all three waveforms in the right image exhibit varying degrees of waveform collapse, and their bandwidth is relatively smaller than that of the left image. Figure 1 It narrows to some extent.
[0027] Based on this, embodiments of this application provide a method for fabricating a surface acoustic wave resonator, such as... Figure 5As shown, the fabrication method of a surface acoustic wave resonator includes the following steps: S101, Forming a substrate, including forming a piezoelectric layer.
[0028] S102, forming interdigitated electrodes located on the piezoelectric layer.
[0029] S103. Forming a temperature compensation layer on the piezoelectric layer, covering the interdigitated electrodes; wherein, forming the temperature compensation layer adopts a deposition process; wherein, forming the temperature compensation layer includes: applying radio frequency power for planarization and densification of the temperature compensation layer.
[0030] like Figure 6 As shown, firstly, step S101 involves forming a substrate, including forming a piezoelectric layer 13.
[0031] In this embodiment, the piezoelectric layer 13 is made of lithium tantalate (LiTaO3, LT). In another embodiment, the piezoelectric layer is made of lithium niobate (LiNbO3, LN).
[0032] In this embodiment, the substrate is a single-layer substrate, that is, the piezoelectric layer 13 is the substrate. In another embodiment, the substrate is a multi-layer composite substrate, including a base and an intermediate layer and a piezoelectric layer sequentially disposed on the base.
[0033] Next, in step S102, interdigitated electrodes 20 are formed on the piezoelectric layer 13.
[0034] It should be noted that the surface of the piezoelectric layer 13 needs to have a good surface condition. Therefore, those skilled in the art should understand that, between steps S101 and S102, a pretreatment of the surface of the piezoelectric layer 13 may be added according to the needs of device fabrication. The pretreatment may include surface cleaning, surface polishing, defect correction, etc.
[0035] After meeting the surface conditions required for the fabrication of the interdigitated electrode 20, the interdigitated electrode 20 is fabricated on the substrate, and the interdigitated electrode 20 is located on the piezoelectric layer 13.
[0036] The interdigitated electrode 20 includes multiple interdigitated electrode strips, which are arranged at intervals. The interdigitated electrode strips in the interdigitated electrode 20 are patterned on the substrate according to a preset size and thickness, and the distance between adjacent electrode strips is also formed according to preset parameters.
[0037] In this embodiment, the aspect ratio of the interdigital electrode strip of the interdigital electrode 20 is greater than or equal to 0.7.
[0038] It should be noted that the interdigitated electrode 20 is a structure formed on the substrate before the temperature compensation layer 30, and the aspect ratio of the interdigitated electrode strips affects the deposition coverage of the temperature compensation layer 30. If the aspect ratio of the interdigitated electrode strips is large, the coverage of the temperature compensation layer 30 formed on the interdigitated electrode 20 will be poor, which can easily lead to unevenness of the temperature compensation layer 30 and the appearance of holes or gaps between the interdigitated electrode strips.
[0039] like Figure 6 As shown, in step S103, a temperature compensation layer 30 is formed. The temperature compensation layer 30 is located on the piezoelectric layer 13 and covers the interdigitated electrode 20. The temperature compensation layer 30 is formed by a deposition process.
[0040] During the deposition process to form the temperature compensation layer 30, radio frequency power is applied to the target material of the machine to improve the directionality of charged particles (e.g., ions) through the bias voltage generated by the radio frequency power, thereby adjusting the internal stress and deposition density of the temperature compensation layer 30, thereby reducing or even eliminating the protrusion of the temperature compensation layer 30 at the position corresponding to the top of the interdigitated electrode 20. In particular, it can eliminate the holes or gaps that may be generated between adjacent interdigitated electrode strips when depositing the temperature compensation layer 30, thereby achieving a planarized and denser temperature compensation layer 30.
[0041] In this embodiment, the temperature compensation layer 30 is made of silicon dioxide.
[0042] The fabrication method of the surface acoustic wave resonator in this application embodiment applies radio frequency power to the target material of the machine during the deposition of the temperature compensation layer 30. The bias voltage generated by the radio frequency power not only suppresses the protrusions on the temperature compensation layer 30, but also effectively solves the problem of poor coverage of the temperature compensation layer 30 on the interdigital electrodes 20 during the deposition process, resulting in defects such as cracks and holes between the interdigital electrode strips of the interdigital electrodes 20. This achieves a flattened and denser temperature compensation layer 30, thereby avoiding problems such as filter passband collapse, bandwidth narrowing, and passband clutter caused by defects in the temperature compensation layer 30.
[0043] In some feasible implementations, the deposition process for forming the temperature compensation layer 30 can be any one of physical vapor deposition, chemical vapor deposition, and atomic layer deposition.
[0044] It should be noted that when different specific deposition processes are used to form the temperature compensation layer 30, the applied radio frequency power also needs to be adjusted accordingly based on the characteristics and variations of the different deposition processes. The following sections will provide specific explanations for different deposition processes.
[0045] In this embodiment, as Figure 7As shown, step S103 includes: S1031, forming a temperature compensation layer using a physical vapor deposition process, with an applied radio frequency power greater than 260W.
[0046] During the physical vapor deposition process, radio frequency (RF) power is provided. The RF power source can be set on the target side of the machine. The RF power provided is greater than 260W to enhance the directionality of ions bombarding the target. This can improve the density and adhesion of the formed temperature compensation layer 30 film, improve step coverage and deep hole filling ability, reduce or even eliminate the protrusion of the temperature compensation layer 30 at the position corresponding to the top of the interdigitated electrode 20, and in particular, eliminate the holes or gaps that may be generated between adjacent interdigitated electrode strips when depositing the temperature compensation layer 30.
[0047] like Figure 8 As shown, when providing 180W-210W of RF power during the physical vapor deposition process, the temperature compensation layer 30 has a protrusion at the top of the interdigitated electrode 20. Figure 8 The medium temperature compensation layer 30 covers the structure between adjacent interdigitated electrode strips, reducing the width and depth of pores and cracks.
[0048] like Figure 9 As shown, when 220W-260W of RF power is provided during the physical vapor deposition process, the morphology of the temperature compensation layer 30 on the interdigitated electrode 20 is further improved, and the surface protrusion of the temperature compensation layer 30 is reduced, compared to... Figure 8 It can be seen that the temperature compensation layer 30 enhances the ion directional bombardment, improves the step coverage, and further reduces the width and depth of pores and cracks in the structure covering the adjacent interdigitated electrode strips.
[0049] like Figure 10 As shown, when the RF power is further increased during the physical vapor deposition process to provide 270W-300W RF power, the morphology of the temperature compensation layer 30 on the interdigitated electrode 20 is further improved. Figure 10 As can be seen, the temperature compensation layer 30 is smooth, dense and uniform in density. Due to the precise directionality of ion bombardment under the assistance of the bias voltage generated by the radio frequency power, the step coverage is good, especially the structure covering the adjacent interdigital electrode strips. There are no defects such as holes and cracks, and the surface is flat.
[0050] Combination Figures 8-10As the radio frequency (RF) power is gradually increased during the physical vapor deposition (PVD) process of the temperature compensation layer 30, and with the continuous enhancement of ion directional bombardment, the step coverage and deep hole filling capabilities are improved. The structural smoothness and density of the temperature compensation layer 30 are enhanced, and the size of defects such as pores and cracks in the temperature compensation layer 30 covering adjacent interdigitated electrode strips gradually decreases until they disappear. However, it is also known that the RF power cannot be increased indefinitely, otherwise it may cause thin film damage, excessive stress, and interface deterioration on the formed temperature compensation layer 30, and may also lead to problems such as a decrease in step coverage and deep hole filling capabilities.
[0051] In another embodiment, such as Figure 11 As shown, step S103 includes: S1032, forming a temperature compensation layer using a chemical vapor deposition process, with an applied radio frequency power greater than 50W.
[0052] Chemical vapor deposition processes include one of the following: plasma-enhanced chemical vapor deposition (PECVD), low-pressure chemical vapor deposition (LPCVD), high-density plasma chemical vapor deposition (HDPCVD), and inductively coupled plasma chemical vapor deposition (ICPCVD).
[0053] Providing more than 50W of radio frequency power during the chemical vapor deposition process improves the thin film step coverage and deep hole filling ability, promotes thin film densification and improves thin film uniformity during the formation of temperature compensation layer 30, reduces or even eliminates the protrusion of temperature compensation layer 30 at the position corresponding to the top of interdigital electrode 20, and in particular can eliminate the holes or gaps that may be generated between adjacent interdigital electrode strips when depositing temperature compensation layer 30.
[0054] In another embodiment, such as Figure 12 As shown, step S103 includes: S1033, forming a temperature compensation layer using an atomic layer deposition process, with the applied radio frequency power being less than or equal to 20W.
[0055] Providing RF power of less than or equal to 20W in atomic layer deposition process improves thin film step coverage and deep hole filling capability, enhances thin film density and quality, and improves film uniformity and consistency.
[0056] In another embodiment, such as Figure 13 As shown, step S101 further includes: S1011, Provides a substrate.
[0057] S1012, Form an intermediate layer, located on the substrate, between the substrate and the piezoelectric layer.
[0058] In this embodiment, a bonding process is used to join the intermediate layer and the piezoelectric layer. In another embodiment, an adhesive method can be used to join the substrate and the piezoelectric layer.
[0059] like Figure 14 As shown, this application provides a surface acoustic wave resonator, including: a substrate 10, including a base 11 and an intermediate layer 12 and a piezoelectric layer 13 sequentially disposed on the base 11; interdigitated electrodes 20 located on the piezoelectric layer 13; and a temperature compensation layer 30 located on the piezoelectric layer 13, covering the interdigitated electrodes 20.
[0060] In another aspect of the embodiments of this application, a surface acoustic wave resonator is provided, which is prepared by the surface acoustic wave resonator preparation method of any one of the foregoing claims.
[0061] The surface acoustic wave resonator prepared by the method of this application embodiment, by applying radio frequency power to the target material of the machine during the deposition of the temperature compensation layer 30, not only suppresses the protrusions on the temperature compensation layer 30, but also effectively solves the problem of defects such as cracks and holes between the interdigital electrode strips of the interdigital electrode 20 caused by the poor coverage of the temperature compensation layer 30 on the interdigital electrode 20 prepared on the piezoelectric layer 13 during the deposition process of the temperature compensation layer 30. This achieves a flattened and denser temperature compensation layer 30, thereby avoiding problems such as filter passband collapse, bandwidth narrowing, and passband clutter caused by defects in the temperature compensation layer 30, improving the quality factor of the surface acoustic wave resonator prepared by the method of this application embodiment, increasing the passband bandwidth of the surface acoustic wave filter prepared by the method of this application embodiment, and reducing insertion loss and clutter generation.
[0062] In another aspect of the embodiments of this application, a surface acoustic wave filter is provided, including the aforementioned surface acoustic wave resonator.
[0063] Surface acoustic wave (SAW) filters, as frequency selective devices, play a significant role in suppressing high-order harmonics, image information, transmitted leakage signals, and various parasitic clutter interference in electronic information equipment. They can achieve filtering of amplitude-frequency and phase-frequency characteristics with varying degrees of precision. Therefore, the SAW filter of this application embodiment can be widely used in radar, mobile communications, and other fields.
[0064] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A method for fabricating a surface acoustic wave resonator, characterized in that, include: Forming a substrate, including forming a piezoelectric layer; Interdigitated electrodes are formed on the piezoelectric layer; A temperature compensation layer is formed on the piezoelectric layer and covers the interdigitated electrodes; wherein the temperature compensation layer is formed by a deposition process. The formation of the temperature compensation layer includes applying radio frequency power to planarize and densify the temperature compensation layer.
2. The method according to claim 1, characterized in that, The interdigital electrode has an interdigital depth-to-width ratio greater than or equal to 0.
7.
3. The method according to claim 1, characterized in that, The piezoelectric layer is made of lithium tantalate or lithium niobate, and the temperature compensation layer is made of silicon dioxide.
4. The method according to any one of claims 1 to 3, characterized in that, The deposition process includes one of the following: physical vapor deposition, chemical vapor deposition, and atomic layer deposition.
5. The method according to claim 4, characterized in that, The formation of the temperature compensation layer includes: forming the temperature compensation layer using a physical vapor deposition process, and applying a radio frequency power greater than 260W.
6. The method according to claim 4, characterized in that, The formation of the temperature compensation layer includes: forming the temperature compensation layer using a chemical vapor deposition process, and applying a radio frequency power greater than 50W.
7. The method according to claim 4, characterized in that, The formation of the temperature compensation layer includes: forming the temperature compensation layer using an atomic layer deposition process, wherein the applied radio frequency power is less than or equal to 20W.
8. The method according to claim 1, characterized in that, The substrate formation further includes: providing a substrate; forming an intermediate layer on the substrate, the intermediate layer being located between the substrate and the piezoelectric layer.
9. A surface acoustic wave resonator, characterized in that, It is prepared using the fabrication method of surface acoustic wave resonator as described in any one of claims 1-8.
10. A surface acoustic wave filter, characterized in that, Includes the surface acoustic wave resonator as described in claim 9.