A resonator and a method of manufacturing the same

Abstract

The application discloses a resonator and a preparation method thereof. The resonator comprises a piezoelectric layer and an interdigital transducer which are sequentially arranged along a sound wave propagation direction, an aperture direction and a thickness direction. The resonator has a sound wave guiding area and bus areas on both sides in the aperture direction. In the bus areas, a medium layer is arranged between the piezoelectric layer and the interdigital transducer, which is used for adjusting the transverse propagation characteristics of the bus areas, so that the bus areas do not support effective transverse transmission of sound waves in the working frequency band. A frame layer is arranged between the sound wave guiding area and each adjacent bus area, and the frame layer is located on the side of the interdigital transducer away from the piezoelectric layer, which is used for providing transverse reflection or band gap constraint for the sound wave in the aperture direction. The projections of the medium layer and the frame layer on the device plane do not overlap each other, and the medium layer can form an inclined side wall or be partially embedded in the piezoelectric layer. The scheme can effectively suppress transverse leakage and spurious modes, reduce insertion loss, and improve the quality factor and out-of-band suppression degree of the device.

Description

Technical Field

[0001] This invention relates to the field of resonator technology, and in particular to a resonator and its fabrication method. Background Technology

[0002] Thin-film piezoelectric acoustic devices include surface acoustic wave (SAW) devices, bulk acoustic wave (BAW) devices, and guided acoustic wave devices. These devices typically involve forming a buried oxide (BOX) layer on a silicon substrate, growing a piezoelectric layer on top, and depositing an interdigital transducer (IDT) electrode on the surface of the piezoelectric layer. Through coupling between electrodes and the piezoelectric layer, the input electrical signal is converted into an acoustic wave propagating along the surface or bulk of the piezoelectric layer. To enable electrode leads and electrical interconnections between electrodes, a bus line is usually formed on the device surface. Thin-film piezoelectric acoustic devices are widely used in applications such as radio frequency filtering, resonance, and transduction. Their performance indicators include low insertion loss, quality factor (Q), spurious mode suppression, and good process consistency.

[0003] In traditional structures, the interdigital transducer (IDT) region in the center of the device constitutes the main acoustic waveguide region, used for exciting and receiving acoustic waves; on both sides of it in the aperture direction are bus regions, which are usually only bounded by simple metal extensions or sound-absorbing layers. However, due to insufficient differences in the stacked structure and boundary conditions between the central waveguide region and the bus regions, the transverse dispersion curve often falls within the operating frequency band, causing acoustic waves to diffuse in the aperture direction and enter the bus regions, resulting in transverse energy leakage and stray modes. These transverse stray energies interfere with the propagation of the dominant mode, manifesting as increased insertion loss, decreased out-of-band rejection, and reduced quality factor. Summary of the Invention

[0004] This application provides a resonator designed to address the technical problem that, when existing acoustic devices are used, transverse sound waves tend to diffuse into the bus region in the aperture direction, leading to transverse energy leakage, stray mode interference, and increased insertion loss.

[0005] To achieve the above objectives, embodiments of this application provide a resonator having a sound wave propagation direction, an aperture direction perpendicular to the sound wave propagation direction, and a thickness direction perpendicular to both the sound wave propagation direction and the aperture direction.

[0006] In the aperture direction, the resonator includes a sound wave guiding region and bus regions located on opposite sides of the sound wave guiding region;

[0007] In the thickness direction, the resonator includes a stacked piezoelectric layer and an interdigital transducer; wherein,

[0008] A dielectric layer is provided between the piezoelectric layer of each bus region and the interdigital transducer. The dielectric layer is used to adjust the lateral propagation characteristics of the corresponding bus region in order to suppress the lateral acoustic wave propagation of the corresponding bus region in the operating frequency band.

[0009] A frame layer is provided between the acoustic wave guiding region and each adjacent bus region. The frame layer is located on the side of the interdigital transducer facing away from the piezoelectric layer. The frame layer is used to provide lateral reflection or bandgap constraint for the acoustic wave in the aperture direction.

[0010] The orthographic projections of the dielectric layer and the frame layer on the device plane do not overlap, and the device plane is perpendicular to the thickness direction.

[0011] To achieve the above objectives, this application also proposes a method for fabricating a resonator, comprising:

[0012] S1. A silicon wafer substrate containing a buried oxide layer is provided, wherein the buried oxide layer is formed on the upper surface of the silicon wafer substrate;

[0013] S2. A piezoelectric layer is formed on the side of the buried oxide layer that is away from the silicon wafer substrate;

[0014] S3. Form a dielectric layer on the piezoelectric layer of the bus region using one of the following two methods:

[0015] S3.1. Deposit a dielectric material on the surface of the piezoelectric layer, perform patterned etching on the dielectric material to the upper surface of the piezoelectric layer, and form inclined sidewalls in the direction of the dielectric material near the acoustic wave guiding region; or,

[0016] S3.2. Trenches are etched in the piezoelectric layer, and a dielectric material is deposited in the trenches. The thickness of the deposited dielectric material is greater than the depth of the trenches. Excess dielectric material is removed and polished so that the top surface of the dielectric layer and the top surface of the piezoelectric layer are on the same plane.

[0017] S4. An interdigital transducer is formed on the side of the piezoelectric layer and dielectric layer facing away from the silicon wafer substrate;

[0018] S5. A frame layer is formed between the acoustic wave guiding area and each adjacent bus area.

[0019] The technical solution provided in this application embodiment includes a central acoustic wave guiding region and bus regions on both sides in the aperture direction of the device; in the thickness direction, interdigital transducers are formed on the piezoelectric layer to define the acoustic wave guiding region; in each bus region, a dielectric layer is disposed between the piezoelectric layer and the interdigital transducer; a frame layer is disposed between the acoustic wave guiding region and the adjacent bus region on the side of the interdigital transducer facing away from the piezoelectric layer; and it is specified that the orthographic projections of the dielectric layer and the frame layer on the device plane do not overlap.

[0020] The dielectric layer, located between the piezoelectric layer and the electrodes in the bus region, alters the local stacking of the bus region, thereby increasing the equivalent transverse phase velocity in this area or pushing the transverse dispersion curve away from the operating band. Within the operating band, the bus region no longer supports an effective transverse propagation path, and acoustic energy tends to remain in the central guide region. The frame layer, located between the guide region and the bus region, forms a transversely high-impedance boundary or bandgap boundary through its material and geometry, reflecting the transverse waves leaking from the guide region back to the guide region, achieving secondary confinement of energy. The non-overlapping planar structure of the dielectric layer and the frame layer avoids disturbance of the frame boundary conditions by the dielectric layer, ensuring consistent reflection characteristics in the aperture direction and reducing the risk of opening transverse transmission channels caused by layout offset. As a result, a stable acoustic waveguide cavity is formed in the central region, lateral leakage is significantly reduced, transverse stray modes are suppressed, and the insertion loss, quality factor, and out-of-band rejection of the resonator are improved accordingly. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of an embodiment of the resonator of the present invention;

[0023] Figure 2 for Figure 1 A schematic diagram of the cross-section after sectioning along line AB;

[0024] Figure 3 This is a cross-sectional schematic diagram of another embodiment of the resonator;

[0025] Figure 4 A schematic diagram of a portion of the process of an embodiment of the present invention (in this embodiment, the dielectric layer is disposed on the surface of the piezoelectric layer).

[0026] Figure 5 This is a schematic diagram of another part of a process according to an embodiment of the present invention (in this embodiment, the dielectric layer is disposed on the surface of the piezoelectric layer).

[0027] Figure 6 This is a schematic diagram of a process in another embodiment of the present invention (in which the dielectric layer is embedded in the piezoelectric layer);

[0028] Figure 7 This is a schematic diagram of another part of a process according to another embodiment of the present invention (in this embodiment, the dielectric layer is embedded in the piezoelectric layer);

[0029] Figure 8 This is a diagram of the lateral diaphragm dispersion curve of the resonator.

[0030] Explanation of icon numbers:

[0031] 1a. Acoustic wave guiding region; 1b. Bus region; 1c. Gap region; 1. Silicon wafer substrate; 2. Buried oxide layer; 3. Piezoelectric layer; 4. Dielectric layer; 41. Inclined surface; 5. Interdigital transducer; 6. Frame layer; 7. Bus electrode.

[0032] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0035] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the term "and / or" throughout the text includes three solutions; taking A and / or B as an example, it includes technical solution A, technical solution B, and a technical solution that simultaneously satisfies A and B. Furthermore, the technical solutions of various embodiments can be combined with each other, provided that they are feasible for those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0036] One embodiment of this application provides a resonator.

[0037] Please see Figures 1 to 3 The resonator has a sound wave propagation direction, an aperture direction perpendicular to the sound wave propagation direction, and a thickness direction perpendicular to the sound wave propagation direction and the aperture direction.

[0038] In the aperture direction, the resonator includes a sound wave guiding region 1a and bus regions 1b located on opposite sides of the sound wave guiding region 1a;

[0039] In the thickness direction, the resonator includes a stacked piezoelectric layer 3 and an interdigital transducer 5; wherein,

[0040] A dielectric layer 4 is provided between the piezoelectric layer 3 and the interdigital transducer 5 of each bus region 1b. The dielectric layer 4 is used to adjust the lateral propagation characteristics of the corresponding bus region 1b to suppress the lateral acoustic wave propagation of the corresponding bus region 1b in the working frequency band.

[0041] A frame layer 6 is provided between the acoustic wave guiding region 1a and each adjacent bus region 1b. The frame layer 6 is located on the side of the interdigital transducer 5 facing away from the piezoelectric layer 3. The frame layer 6 is used to provide lateral reflection or bandgap constraint for acoustic waves in the aperture direction.

[0042] The orthographic projections of the dielectric layer 4 and the frame layer 6 on the device plane do not overlap, and the device plane is perpendicular to the thickness direction.

[0043] Specifically, in the structure of this embodiment, please refer to Figure 1 , Figure 2 and Figure 3The resonator is defined in three mutually orthogonal directions: the direction of sound wave propagation, the aperture direction perpendicular to it, and the thickness direction. For ease of understanding, a Cartesian coordinate system can be established, defining the direction of sound wave propagation as the x-axis, the aperture direction as the y-axis, and the thickness direction as the z-axis. Thus, the device plane is the plane formed by the x-axis and y-axis, while the z-axis corresponds to the stacking direction of the device.

[0044] In the aperture direction, the resonator structure includes a central acoustic wave guiding region 1a and bus regions 1b located on both sides of it. The acoustic wave guiding region 1a mainly includes interdigital transducers 5 disposed on the surface of the piezoelectric layer 3. The interdigital transducers 5 are composed of several staggered metal electrode strips, with adjacent electrode strips connected to different electrode ports. When a radio frequency signal is applied to the electrode port, the piezoelectric layer 3 undergoes strain in the electrode region and excites acoustic waves; when the acoustic waves propagate in the piezoelectric layer 3 and return to the region, they cause a potential difference between the electrodes, realizing the mutual conversion of electrical energy and acoustic energy. This mechanism is a common application of the piezoelectric effect and is widely used in surface acoustic wave devices and bulk acoustic wave devices, so it will not be elaborated further in this specification.

[0045] Bus region 1b serves as the electrode lead-out and interconnection area. Bus electrodes 7 are typically positioned on both sides of the acoustic wave guiding region 1a to electrically connect the electrode ports of the interdigital transducer 5 to external circuitry. The bus electrodes 7 are usually formed of conductive metallic materials, such as aluminum, copper, molybdenum, or their alloys, and their thickness can be adjusted from tens to hundreds of nanometers depending on process requirements. Because bus region 1b and acoustic wave guiding region 1a transition continuously on the piezoelectric layer 3 and lack significant structural differences or acoustic boundaries, acoustic waves easily diffuse from acoustic wave guiding region 1a to bus region 1b and propagate along it, causing lateral energy leakage and stray modes.

[0046] In the thickness direction, the core stacked structure of the resonator includes a piezoelectric layer 3 and interdigital transducers 5 on its surface. The piezoelectric layer 3 can be formed of piezoelectric thin film materials such as aluminum nitride, zinc oxide, or lithium niobate, and its thickness can be designed in the range of hundreds of nanometers to several micrometers depending on the target operating frequency. A dielectric layer 4 is placed between the piezoelectric layer 3 and the interdigital transducers 5 in the bus region 1b. Common materials include silicon dioxide, silicon nitride, and aluminum oxide, and the thickness is typically 10–100 nm. The dielectric layer 4 can reduce the possibility of sound waves entering the bus region 1b by changing the local acoustic impedance and propagation velocity, so that the bus region 1b does not support effective transverse sound wave propagation within the operating frequency band.

[0047] A frame layer 6 is disposed between the acoustic wave guiding region 1a and the adjacent bus region 1b. The frame layer 6 is located on the side of the interdigital transducer 5 facing away from the piezoelectric layer 3 and can be formed of a high acoustic impedance metal (such as tungsten, tantalum, molybdenum, etc.) or a high acoustic impedance dielectric. The frame layer 6 provides a reflection boundary in the aperture direction or forms a bandgap constraint within a specific frequency band, thereby effectively preventing acoustic waves from diffusing into the bus region 1b. It should be noted that the orthographic projections of the dielectric layer 4 and the frame layer 6 on the device plane do not overlap, that is, they do not overlap in the top view direction, in order to avoid mutual interference between the two constraint structures and ensure the stability of the lateral acoustic wave constraint.

[0048] By introducing a dielectric layer 4 in the bus region 1b to weaken its lateral propagation capability, and introducing a frame layer 6 between the acoustic wave guiding region 1a and the bus region 1b to provide reflection or bandgap limitation, the resonator forms a double constraint in the aperture direction, significantly reducing lateral energy leakage and stray modes, thereby improving the quality factor and operational stability of the resonator.

[0049] Please see Figure 8 The attached figure shows the transverse dispersion curves (real part) of the resonator in different regions. The horizontal axis in the figure represents the wavenumber (denoted as k). t The ordinate is radix (rad / μm), and the ordinate is frequency (f, GHz). The distribution of the curve is used to characterize the propagation modes that may exist within the device under different transverse wavenumber conditions.

[0050] The legend in the lower right corner of the figure identifies the regions and structural conditions represented by the different curves. Specifically, "Stack=BL,θ" tilt "=0°, cov =50%" indicates a baseline stack (BL), under which the tilt angle θ of the electrode pattern is determined. tilt The blue curve represents the reference level, with a coverage cov of 50% and a 0° angle. The orange curve corresponds to "BusRegion, Stack: BL," indicating the use of the reference stack-up structure in bus region 1b. The green curve corresponds to "BusRegion, Stack: 20 nm Si3N4, 140 nm AlCu," indicating the introduction of 20 nm silicon nitride and 140 nm aluminum-copper layers in bus region 1b. The red curve corresponds to "Gap Region, Stack: BL," indicating the use of the reference stack-up structure in gap region 1c. The light brown background area represents the stopband, the frequency range where lateral modes are not permitted.

[0051] As shown in the figure, under the same wavenumber conditions, the green curve (i.e., the structure with dielectric layer 4 and metal layer introduced in bus region 1b) shows a significant upward shift in frequency compared to the orange curve (conventional bus region 1b structure). This change indicates that the introduction of dielectric layer 4 and metal layer alters the lateral propagation characteristics of bus region 1b, raising the lateral modal frequencies and causing some modes to enter the bandgap region, thus achieving a stronger confinement effect on lateral energy. In other words, the acoustic energy is effectively confined within the acoustic wave guiding region 1a, reducing leakage to bus region 1b. This experimental result is consistent with the theoretical design, providing a direct verification of the effectiveness of the structure of this invention in suppressing lateral energy diffusion and enhancing energy confinement capability.

[0052] Optionally, the material of the dielectric layer 4 is one or more of silicon dioxide, silicon nitride, aluminum nitride, hafnium oxide, silicon carbide, tungsten dioxide, aluminum oxide, titanium dioxide, and tantalum pentoxide.

[0053] The phrase "one or more" implies that dielectric layer 4 can be composed of a single material or a composite of two or more materials. For example, dielectric layer 4 can be made solely of silicon dioxide to achieve good dielectric properties and process compatibility; it can also employ a stacked structure of silicon nitride and aluminum oxide to enhance mechanical strength while maintaining insulation properties; or it can be a combination of aluminum nitride and tantalum pentoxide to simultaneously obtain high acoustic impedance and stable chemical properties. By using materials individually or in combination, the dielectric constant, acoustic impedance, and process compatibility of dielectric layer 4 can be flexibly adjusted, thereby meeting the needs of different device designs for lateral propagation suppression and overall performance optimization.

[0054] Optionally, the thickness of the dielectric layer 4 is greater than or equal to 10 nm and less than or equal to 100 nm. The lower limit of the thickness is set because when the thickness of the dielectric layer 4 is close to 10 nm, its effect on regulating the lateral propagation characteristics of the bus region 1b just becomes apparent. For example, at 10 nm or 11 nm, although a certain degree of upward shift of the dispersion curve can be achieved, the suppression effect is relatively limited. When the thickness increases to 20 nm or 30 nm, the constraint capability of the lateral mode is significantly enhanced, and the diffusion of acoustic waves to the bus region 1b can be more effectively suppressed. At 50 nm or 60 nm, the dielectric layer 4 can provide a stable acoustic impedance difference while taking into account process repeatability. At close to 100 nm, such as 90 nm or 95 nm, although the constraint capability is still good, an excessively thick dielectric layer 4 may introduce large residual stress, thereby affecting the bonding stability between the piezoelectric layer 3 and the electrode layer. If the dielectric layer 4 is less than 10 nm, such as 5 nm or 8 nm, its adjustment of acoustic characteristics is insufficient and it is difficult to achieve the expected effect. If the thickness exceeds 100 nm, such as 120 nm or 150 nm, it is easy to cause frequency shift or process stress problems. Therefore, controlling the thickness within the range of 10 nm to 100 nm can not only ensure effective suppression of transverse acoustic wave propagation, but also take into account both process feasibility and device stability.

[0055] In one embodiment, the frame layer 6 is made of one or more of the following materials: titanium, chromium, silver, copper, aluminum-copper alloy, molybdenum, tantalum, platinum, tungsten, and tantalum nitride.

[0056] Specifically, these materials are all metals or metal compounds, possessing good electrical conductivity and high acoustic impedance, enabling them to reflect or confine sound waves in the aperture direction. For example, frame layer 6 can be made of tungsten alone, whose high density enhances transverse sound wave reflection; copper or aluminum-copper alloys can also be used, balancing conductivity and process compatibility; platinum or tantalum can also be selected to improve structural stability and corrosion resistance. Furthermore, frame layer 6 can also be composed of two or more composite materials, such as a layer of titanium or chromium superimposed on a copper layer to form a composite frame, thereby simultaneously meeting multiple requirements for adhesion, process reliability, and acoustic performance.

[0057] In another embodiment, the frame layer 6 is made of one or more of silicon dioxide, silicon nitride, aluminum nitride, hafnium dioxide, silicon carbide, tungsten dioxide, aluminum oxide, titanium dioxide, and tantalum pentoxide.

[0058] Specifically, these materials are all dielectric materials, typically possessing high dielectric constants, good insulation, and high hardness and stability. When the frame layer 6 uses a dielectric material, it can provide acoustic impedance differences without introducing additional conductive channels, thereby forming transverse acoustic wave reflection or bandgap confinement. For example, the frame layer 6 can be made of silicon dioxide, which has mature processing technology and stable dielectric properties; it can also be made of aluminum nitride or aluminum oxide to enhance mechanical strength and thermal stability; or it can be made of high dielectric constant materials such as tungsten dioxide or tantalum pentoxide to achieve stronger acoustic wave confinement with a smaller thickness. In addition, the frame layer 6 can also be composed of multiple dielectric composites, such as a stacked structure of silicon dioxide and silicon nitride, to simultaneously consider stress regulation and acoustic properties.

[0059] Optionally, the thickness of the frame layer 6 is greater than or equal to 15 nm and less than or equal to 300 nm.

[0060] When the thickness of frame layer 6 is close to the lower limit, such as 15nm or 20nm, although frame layer 6 can create a certain acoustic impedance difference in the aperture direction, its reflection capability is limited, and it can only constrain some transverse acoustic waves. When the thickness increases to 50nm or 80nm, the acoustic reflection effect is significantly enhanced, and acoustic waves are more difficult to penetrate the frame layer 6 region into bus region 1b. When the thickness is further increased to 150nm or 200nm, frame layer 6 can form a stable transverse acoustic wave barrier, and the constraint effect is more obvious, which is suitable for the design requirements of high-performance resonators. When the thickness is close to the upper limit, such as 280nm or 300nm, although the acoustic constraint capability is still good, the excessively thick frame layer 6 may introduce large residual stress, resulting in uneven stress in the overall film layer of the device, and even affecting the process stability of the device during large-size fabrication. If the thickness of frame layer 6 is less than 15nm, such as 10nm or 12nm, its acoustic wave reflection capability is insufficient and it is difficult to play its design role; if the thickness exceeds 300nm, such as 350nm or 400nm, it may lead to a decrease in process compatibility and cause the device frequency characteristics to shift. Therefore, controlling the thickness of frame layer 6 within the range of 15nm to 300nm can ensure effective reflection of transverse acoustic waves while taking into account both process feasibility and device reliability.

[0061] Optionally, a plurality of spaced gap regions 1c are provided between the frame layer 6 and the dielectric layer 4 along the direction of sound wave propagation, and the gap regions 1c are the exposed areas of the piezoelectric layer 3.

[0062] The so-called gap region 1c refers to the area that does not cover the frame layer 6 and the dielectric layer 4, leaving the piezoelectric layer 3 exposed in this region. By introducing the gap region 1c between the frame layer 6 and the dielectric layer 4, spatial isolation between the two can be achieved on the device plane, preventing the frame layer 6 and the dielectric layer 4 from overlapping in the same location. In this way, the dielectric layer 4 can focus on adjusting the lateral dispersion characteristics of the bus region 1b, while the frame layer 6 undertakes the lateral reflection or bandgap constraint of the acoustic waves, and their functions do not interfere with each other. At the same time, the existence of the gap region 1c provides a transition band for different functional regions, which helps to reduce the complexity of the local stacked structure, alleviate stress concentration problems, and improve the stability and consistency of the device in the actual process fabrication. Thus, although the gap region 1c does not directly participate in the reflection or constraint of acoustic waves, it indirectly ensures the effective confinement of acoustic waves in the aperture direction through spatial isolation and structural optimization.

[0063] In this application, the dielectric layer 4 has at least two implementations. In one implementation, please refer to [link to relevant documentation]. Figure 2 , Figure 4 and Figure 5 The dielectric layer 4 is disposed on the surface of the piezoelectric layer 3. An inclined surface is formed on the side wall of the dielectric layer 4 near the frame layer 6. The inclined surface is inclined from the top surface of the dielectric layer 4 toward the top surface of the piezoelectric layer 3 and extends toward the frame layer 6.

[0064] This structural design creates a transition between the dielectric layer 4 and the frame layer 6 at their proximity, avoiding stress concentration issues that might arise from right-angled sidewalls. The tilted surface not only improves the geometric fit between the dielectric layer 4 and the frame layer 6 but also allows for a gradual transition when sound waves propagate laterally into this region, further reducing scattering effects and ensuring the constrained stability of sound waves in the aperture direction. Simultaneously, this tilted structure facilitates process implementation, enabling stable pattern boundaries to be formed during photolithography and etching processes, thus improving the manufacturability and consistency of the device.

[0065] Optionally, the angle between the inclined surface and the top surface of the piezoelectric layer 3 is greater than or equal to 15° and less than or equal to 90°.

[0066] When the angle is less than 15°, the tilted surface is too gentle, making it difficult to form an effective geometric transition structure. This weakens the constraint on transverse acoustic waves and easily leads to uneven morphology during etching. When the angle exceeds 90°, the tilted surface transforms into a concave or reverse structure, losing its tilt transition characteristics and instead causing stress concentration and enhanced acoustic wave scattering. By controlling the angle between 15° and 90°, a reasonable geometric matching relationship can be formed between the device structure and acoustic wave propagation. This allows the acoustic waves to transition gradually as they propagate into this region, reducing energy scattering and facilitating the implementation of stable sidewall structures using conventional photolithography and etching processes. Therefore, this angle range satisfies both acoustic performance requirements and process feasibility.

[0067] In practice, the included angle can be 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85° or 89°, etc., which will not be listed here.

[0068] In another implementation, please refer to Figure 3 , Figure 6 and Figure 7 At least a portion of the dielectric layer 4 is embedded within the piezoelectric layer 3. This structure can be achieved by pre-forming trenches in the piezoelectric layer 3 and filling and depositing dielectric material within the trenches. Compared to completely distributing the dielectric layer 4 on the surface of the piezoelectric layer 3, the embedded structure enhances the bonding strength between the dielectric layer 4 and the piezoelectric layer 3, reducing the risk of delamination at the interface. Simultaneously, the embedded portion allows the dielectric layer 4 and the piezoelectric layer 3 to form a more compact whole, which helps suppress scattering effects caused by interlayer interface discontinuities, thereby ensuring the stability of sound wave propagation in the aperture direction. Furthermore, the embedded design can avoid excessive stacking of the device surface while maintaining the required thickness of the dielectric layer 4, helping to maintain overall flatness and improving the fabrication accuracy of the subsequent interdigital transducer 5 and bus electrode 7.

[0069] Optionally, the top surface of the dielectric layer 4 is located on the same plane as the top surface of the piezoelectric layer 3. This design is typically achieved by forming trenches in the piezoelectric layer 3, filling them with dielectric material, and then removing excess dielectric material via chemical mechanical polishing (CMP) or an equivalent planarization process. The advantage of this structure is that the device surface remains generally flat, allowing for continuous and uniform electrode morphology during subsequent deposition of the interdigital transducer 5 and the bus electrode 7, avoiding breakage, open circuits, or uneven thickness caused by surface variations. Simultaneously, the flush alignment of the dielectric layer 4 and the piezoelectric layer 3 reduces the scattering effect of sound waves during propagation, ensuring a stable propagation path for sound waves in the aperture direction. Furthermore, the planarized structure helps improve lithography accuracy and process consistency, thereby enhancing the manufacturability and repeatability of the device.

[0070] Another embodiment of this application provides a method for fabricating a resonator, the method comprising the following steps:

[0071] S1. A silicon wafer substrate 1 containing a buried oxide layer 2 is provided, wherein the buried oxide layer 2 is formed on the upper surface of the silicon wafer substrate 1;

[0072] S2. A piezoelectric layer 3 is formed on the side of the buried oxide layer 2 that is away from the silicon wafer substrate 1;

[0073] S3. A dielectric layer 4 is formed on the piezoelectric layer 3 of the bus region 1b using one of the following two methods:

[0074] S3.1. Deposit a dielectric material on the surface of the piezoelectric layer 3, perform patterned etching on the dielectric material, etching to the upper surface of the piezoelectric layer 3, and form inclined sidewalls in the direction of the dielectric material near the acoustic wave guiding region 1a; or,

[0075] S3.2. Trenches are etched in the piezoelectric layer 3, and a dielectric material is deposited in the trenches. The thickness of the deposited dielectric material is greater than the depth of the trenches. Excess dielectric material is removed and polished so that the top surface of the dielectric layer 4 and the top surface of the piezoelectric layer 3 are on the same plane.

[0076] S4. An interdigital transducer 5 is formed on the side of the piezoelectric layer 3 and the dielectric layer 4 facing away from the silicon wafer substrate 1.

[0077] S5. A frame layer 6 is formed between the acoustic wave guiding area 1a and each adjacent bus area 1b.

[0078] In this application, there are two preparation processes corresponding to the two structures of the dielectric layer 4. Please refer to [link / reference]. Figures 4 to 5 For the surface-type dielectric layer 4, the preparation process is as follows:

[0079] A dielectric material is deposited on the surface of the piezoelectric layer 3. The dielectric layer 4 can be a single layer or a multilayer stack; the material can be one or more of silicon dioxide, silicon nitride, aluminum nitride, hafnium oxide, silicon carbide, tungsten dioxide, aluminum oxide, titanium dioxide, and tantalum pentoxide, with a thickness preferably of 10–100 nm. The deposition method can be sputtering or evaporation, and the layout position corresponds to the bus region 1b, so that the dielectric layer 4 is located between the piezoelectric layer 3 and the subsequent interdigital transducer 5. By introducing this thin dielectric layer 4 into the bus region 1b, the local stacking and equivalent acoustic impedance are changed, which can raise the lateral dispersion curve of the bus region 1b in the frequency direction, making it less likely to support lateral propagation within the operating band, thereby weakening the channel for acoustic energy diffusion to the bus region 1b.

[0080] The dielectric layer 4 is subjected to photolithography and etching, with the etching terminating at the upper surface of the piezoelectric layer 3, and an inclined sidewall is formed at the edge near the frame layer 6. The angle between the sidewall and the upper surface of the piezoelectric layer 3 is preferably 15° to 90°. This inclined geometry reduces stress concentration and morphological defects caused by right-angled edges, and provides a geometric transition for sound waves, reducing lateral scattering, which is beneficial for maintaining energy confinement and process consistency in the aperture direction.

[0081] Interdigital transducers 5 are formed on the patterned dielectric layer 4. They are achieved using metal deposition combined with patterning or stripping processes. The electrodes (interdigital transducers 5) can be multilayer metal stacks, and the materials can be selected from one or a combination of titanium, chromium, silver, copper, aluminum-copper alloy, molybdenum, tantalum, platinum, tungsten, and tantalum nitride. The total electrode thickness is preferably 50–600 nm. The interdigital transducers 5 are disposed in the acoustic wave guiding region 1a and coupled with the piezoelectric layer 3 to achieve electro-acoustic energy conversion. Below the bus region 1b is the aforementioned dielectric layer 4 stack structure, creating a discernible acoustic partition between the guiding region and the bus region 1b, thereby achieving suppression of transverse modes.

[0082] A frame layer 6 is formed between the acoustic wave guiding region 1a and the adjacent bus region 1b. The process can be patterning after metal (or dielectric) deposition, or it can be achieved through stripping. The frame layer 6 can be a metal system (such as titanium, chromium, silver, copper, aluminum-copper alloy, molybdenum, tantalum, platinum, tungsten, tantalum nitride) or a dielectric system (such as silicon dioxide, silicon nitride, aluminum nitride, hafnium oxide, silicon carbide, tungsten dioxide, aluminum oxide, titanium dioxide, tantalum pentoxide), with a preferred thickness of 15–300 nm. The frame layer 6 is located on the side of the interdigital transducer 5 facing away from the piezoelectric layer 3, providing high acoustic impedance reflection or bandgap confinement in the aperture direction. Simultaneously, following the arrangement rule that the frame layer 6 and the dielectric layer 4 do not overlap in the orthographic projection of the device plane, several exposed piezoelectric layer 3 gap regions 1c can be left between them along the acoustic wave propagation direction, thereby achieving spatial isolation of the functional areas and avoiding mutual disturbance of boundary conditions. By combining the reduction of the lateral propagation capability of the bus region 1b by the dielectric layer 4 with the reflection / bandgap constraint of the lateral wave by the frame layer 6, this embodiment can significantly reduce lateral energy leakage and stray modes, improve insertion loss and quality factor, while maintaining good compatibility and manufacturability with conventional thin-film device processes.

[0083] For embedded media layer 4, please refer to Figure 6 and Figure 7 The preparation process is as follows:

[0084] At the selected bus region 1b on the surface of the piezoelectric layer 3, a recessed region (i.e., the trench in step S3.2) is formed by photolithography and etching, with a preferred recess depth of 10–200 nm. The establishment of this recessed region is to provide space for subsequent filling of the dielectric layer 4, allowing the dielectric layer 4 to be partially embedded in the piezoelectric layer 3, thereby creating a significant difference in geometry and material stacking from the acoustic wave guiding region 1a, laying the foundation for the modulation of lateral acoustic modes.

[0085] While maintaining the protection of the photoresist, a dielectric material is deposited in the recessed area. The deposition thickness must be greater than the recess depth to ensure that the dielectric material can fill the trench and cover the upper surface of the photoresist. The material of the dielectric layer 4 can be one or more of silicon dioxide, silicon nitride, aluminum nitride, hafnium oxide, silicon carbide, tungsten dioxide, aluminum oxide, titanium dioxide, and tantalum pentoxide. The deposition structure can be a single layer or a stacked combination. Since the dielectric layer 4 is partially embedded with the piezoelectric layer 3, the equivalent acoustic thickness after stacking is reduced compared to conventional surface deposition schemes, which can generate a stronger wave impedance difference between the bus region 1b and the acoustic wave guiding region 1a, which is beneficial for enhancing lateral energy isolation.

[0086] While removing the photoresist, the residual dielectric material above the photoresist is also removed, leaving the dielectric layer 4 filling the recessed area. As a result, the top surface of the dielectric layer 4 is higher than the original surface of the piezoelectric layer 3 recessed area, forming a flush structure integrated with the piezoelectric layer 3.

[0087] Excess protrusions are removed from the surfaces of piezoelectric layer 3 and dielectric layer 4 using a chemical mechanical polishing (CMP) process, bringing their top surfaces to the same plane. The polishing thickness can be 10–150 nm. After this step, the surface of dielectric layer 4 is completely flush with the surface of piezoelectric layer 3, avoiding local stress concentration and acoustic wave scattering caused by the step structure, and further improving device consistency and manufacturability.

[0088] Interdigitated transducers 5 are deposited and patterned on the planarized surface of the structure. The electrode layer can be a multilayer metal stack, and the materials can be titanium, chromium, silver, copper, aluminum-copper alloy, molybdenum, tantalum, platinum, tungsten, or tantalum nitride, with a preferred thickness of 50–600 nm. This electrode is disposed in the acoustic wave guiding region 1a and coupled with the piezoelectric layer 3 to achieve electro-acoustic conversion; while in the bus region 1b, it is stacked on the aforementioned embedded dielectric layer 4, forming a region with significantly different acoustic properties from the guiding region.

[0089] A frame layer 6 is formed between the acoustic wave guiding region 1a and the bus region 1b. The process involves deposition followed by etching or stripping. The material can be a metallic system (titanium, chromium, silver, copper, aluminum-copper alloy, molybdenum, tantalum, platinum, tungsten, tantalum nitride) or a dielectric system (silicon dioxide, silicon nitride, aluminum nitride, hafnium oxide, silicon carbide, tungsten dioxide, aluminum oxide, titanium dioxide, tantalum pentoxide), with a preferred thickness of 15–300 nm. The frame layer 6 is located on the side of the interdigital transducer 5 facing away from the piezoelectric layer 3, forming lateral reflection or bandgap confinement, and synergistically suppressing lateral energy diffusion with the embedded dielectric layer 4.

[0090] In summary, this embodiment achieves a partially embedded dielectric layer 4 structure by pre-forming trenches in the piezoelectric layer 3 and filling them with dielectric material. This flush arrangement not only improves the lateral propagation characteristics of the bus region 1b but also avoids the scattering effect caused by surface protrusions. Compared with conventional surface deposition schemes, it offers further improvements in process consistency, lateral energy isolation, and device frequency stability.

[0091] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A resonator, characterized by, The resonator has a sound wave propagation direction, a diameter direction perpendicular to the sound wave propagation direction, and a thickness direction perpendicular to the sound wave propagation direction and the diameter direction; In the diameter direction, the resonator comprises a sound wave guiding area (1a) and bus areas (1b) located on opposite sides of the sound wave guiding area (1a); In the thickness direction, the resonator comprises a stacked piezoelectric layer (3) and an interdigital transducer (5); wherein, A dielectric layer (4) is arranged between the piezoelectric layer (3) and the interdigital transducer (5) of each bus area (1b), and the dielectric layer (4) is used to adjust the transverse propagation characteristics of the corresponding bus area (1b) to suppress the transverse sound wave propagation of the corresponding bus area (1b) within the working frequency band; A frame layer (6) is arranged between the sound wave guiding area (1a) and each adjacent bus area (1b), and the frame layer (6) is located on the side of the interdigital transducer (5) away from the piezoelectric layer (3), and the frame layer (6) is used to provide transverse reflection or bandgap constraint for sound waves in the diameter direction; The dielectric layer (4) and the frame layer (6) do not overlap in the normal projection on the device plane, and the device plane is perpendicular to the thickness direction.

2. The resonator of claim 1, wherein The material of the dielectric layer (4) is one or more of silicon dioxide, silicon nitride, aluminum nitride, hafnium oxide, silicon carbide, tungsten dioxide, aluminum oxide, titanium dioxide, and tantalum pentoxide.

3. The resonator of claim 1, wherein The material of the frame layer (6) is one or more of titanium, chromium, silver, copper, aluminum-copper alloy, molybdenum, tantalum, platinum, tungsten, and tantalum nitride; or, The material of the frame layer (6) is one or more of silicon dioxide, silicon nitride, aluminum nitride, hafnium dioxide, silicon carbide, tungsten dioxide, aluminum oxide, titanium dioxide, and tantalum pentoxide.

4. The resonator of claim 1, wherein The thickness of the dielectric layer (4) is greater than or equal to 10 nm and less than or equal to 100 nm; and / or, The thickness of the frame layer (6) is greater than or equal to 15 nm and less than or equal to 300 nm.

5. The resonator of claim 1, wherein A plurality of gap areas (1c) are arranged between the frame layer (6) and the dielectric layer (4) in the sound wave propagation direction, and the gap areas (1c) are exposed areas of the piezoelectric layer (3).

6. The resonator of claim 1, wherein The dielectric layer (4) is arranged on the surface of the piezoelectric layer (3), and an inclined surface is formed on the side wall of the dielectric layer (4) close to the frame layer (6), the inclined surface is arranged inclined from the top surface of the dielectric layer (4) to the top surface of the piezoelectric layer (3), and extends towards the side of the frame layer (6).

7. The resonator of claim 6, wherein The angle between the inclined surface and the top surface of the piezoelectric layer (3) is greater than or equal to 15° and less than or equal to 90°.

8. The resonator of claim 1, wherein At least a part of the structure of the dielectric layer (4) is embedded in the piezoelectric layer (3).

9. The resonator of claim 8, wherein, The top surface of the dielectric layer (4) and the top surface of the piezoelectric layer (3) are in the same plane.

10. A method of manufacturing a resonator, characterized by, The method is used for preparing the resonator as claimed in any one of claims 1 to 9, and the method comprises the following steps: S1, providing a silicon wafer substrate (1) containing a buried oxygen layer (2), and the buried oxygen layer (2) is formed on the upper surface of the silicon wafer substrate (1); S2, forming a piezoelectric layer (3) on the side of the buried oxide layer (2) away from the silicon wafer substrate (1); S3, forming a dielectric layer (4) on the piezoelectric layer (3) of the bus region (1b) by one of the following two ways: S3.1, depositing a dielectric material on the surface of the piezoelectric layer (3), performing patterned etching on the dielectric material, etching to the upper surface of the piezoelectric layer (3), and forming an inclined sidewall in the direction of the dielectric material close to the acoustic wave guiding region (1a); or, S3.2, etching a groove in the piezoelectric layer (3), depositing a dielectric material in the groove, the thickness of the deposited dielectric material being greater than the depth of the groove, removing the excess dielectric material and polishing, so that the top surface of the dielectric layer (4) and the top surface of the piezoelectric layer (3) are located in the same plane; S4, forming an interdigital transducer (5) on the side of the piezoelectric layer (3) and the dielectric layer (4) away from the silicon wafer substrate (1); S5, forming a frame layer (6) between the acoustic wave guiding region (1a) and each adjacent bus region (1b), respectively.

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