Surface acoustic wave device having different acoustic impedances, electronic device

Abstract

The present application relates to the technical fields of surface acoustic wave device, and particularly relates to a surface acoustic wave device with different acoustic impedance, electronic equipment, comprising a piezoelectric substrate, an IDT electrode and a reflection grating arranged on the piezoelectric substrate, the reflection grating is arranged on both sides of the IDT electrode along a first direction, and the reflection grating comprises a plurality of reflection electrodes arranged at intervals along the first direction; the acoustic impedance of the plurality of reflection electrodes varies along the first direction, and the reflection electrodes with different acoustic impedance adopt different manufacturing materials or a single manufacturing material with different material properties. The present application provides a surface acoustic wave device with different acoustic impedance, electronic equipment, which is miniaturized, the unwanted oscillation in the passband frequency response is significantly weakened, the quality factor is significantly improved, and the transverse parasitic mode is effectively suppressed.

Description

Technical Field

[0001] This invention relates to the field of surface acoustic wave (SAW) device technology, and particularly to a SAW device and electronic device with different acoustic impedances. Background Technology

[0002] Surface acoustic wave (SAW) devices mainly consist of a piezoelectric substrate, an inductively coupled plasma (IDT) electrode, and a reflective grating. Both the IDT electrode and the reflective grating are mounted on the piezoelectric substrate, converting electrical signals into surface acoustic waves. These devices are widely used in mobile communication devices such as smartphones and tablets. With the rapid development of mobile communication technology, higher demands are being placed on the performance and size of SAW devices (such as resonators and filters). For example, while ensuring miniaturization, there are requirements to significantly reduce unwanted oscillations in the frequency response, achieve a higher quality factor (Q), and more effective suppression of transverse parasitic modes.

[0003] Therefore, it is essential to develop a miniaturized surface acoustic wave device that significantly reduces unwanted oscillations in its frequency response, significantly improves its quality factor, and effectively suppresses transverse parasitic modes. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a surface acoustic wave device or electronic device with different acoustic impedances that is miniaturized, has significantly reduced unwanted oscillations in frequency response, has a significantly improved quality factor, and effectively suppresses transverse parasitic modes, in order to solve the problems existing in the prior art mentioned above.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a surface acoustic wave device with different acoustic impedance, including a piezoelectric substrate and an IDT electrode and a reflective grating disposed on the piezoelectric substrate. The reflective grating is disposed on both sides of the IDT electrode along a first direction. The reflective grating includes a plurality of reflective electrodes spaced apart along the first direction. The acoustic impedance of the plurality of reflective electrodes varies along the first direction, and the reflective electrodes with different acoustic impedances are made of different materials or a single material with different material properties.

[0006] Furthermore, the acoustic impedance of the reflective electrode in the reflective grating increases in the direction away from the IDT electrode.

[0007] Furthermore, the acoustic impedance of the reflective electrode in the reflective grating decreases in the direction away from the IDT electrode.

[0008] Furthermore, the acoustic impedance of the reflective electrode in the reflective grating gradually changes in the direction away from the IDT electrode.

[0009] Furthermore, the acoustic impedance of the reflective electrode in the reflective grating changes in a stepwise manner away from the IDT electrode.

[0010] Furthermore, the acoustic impedance of at least one reflective electrode in the reflective grating is gradually varied or / and the acoustic impedance of at least one reflective electrode in the reflective grating is stepped.

[0011] Furthermore, at least one of the reflective electrodes in the reflective grating exhibits a gradual and stepwise change in acoustic impedance.

[0012] Furthermore, the acoustic impedance of each reflective electrode in the reflective grating is not the same.

[0013] Furthermore, the reflective grating contains reflective electrodes with the same acoustic impedance.

[0014] An electronic device includes a communication circuit and the aforementioned surface acoustic wave device with different acoustic impedance connected to the communication circuit.

[0015] The beneficial effects of this invention are:

[0016] (1) In this invention, multiple reflective electrodes are made of different materials or a single material with different material properties, and have different acoustic impedances. This makes the acoustic impedance of multiple reflective electrodes change along the first direction, forming an acoustic impedance step, which can "weight" the reflection and control the reflection coefficient (κ). Furthermore, the electrode fingers of the IDT electrode and the reflective electrode of the reflective grating can form a "soft" boundary, thereby reducing Fresnel ripples, significantly reducing unwanted oscillations in the frequency response, and providing a smoother passband.

[0017] (2) In this invention, the different acoustic impedances of the reflective grating determine the change in the sound velocity below the reflective grating, creating a deeper “potential well” for the surface wave, forcing the energy to remain below the IDT electrode, and significantly improving the quality factor (Q).

[0018] (3) In this invention, the reflective grating is modulated with different acoustic impedances, which increases the acoustic impedance at the end of the electrode, making the transverse velocity distribution tend to be flat, and thus the wave propagation mode is similar to a flat "piston" rather than a curved piston, thereby eliminating the parasitic transverse mode spikes that destroy the passband of the device and suppressing the transverse parasitic mode more effectively.

[0019] (4) The present invention utilizes different manufacturing materials or a single manufacturing material with different material properties to create acoustic impedance steps, providing high impedance contrast. Since the stopband width is proportional to the acoustic impedance mismatch, a higher impedance contrast will result in a wider stopband, thereby allowing the use of fewer reflective electrodes without energy loss, and adapting to miniaturized designs. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Figure 1This is a top view of the first type of surface acoustic wave device shown in an embodiment of the present invention.

[0022] Figure 2 This is a cross-sectional view along the AA direction of the first type of surface acoustic wave device shown in the embodiment of the present invention.

[0023] Figure 3 This is a top view of the second type of surface acoustic wave device shown in an embodiment of the present invention.

[0024] Figure 4 This is a BB-direction cross-sectional view of the second type of surface acoustic wave device shown in an embodiment of the present invention.

[0025] Figure 5 This is a schematic diagram of the acoustic impedance change of the first type of reflective electrode in this invention.

[0026] Figure 6 This is a schematic diagram of the acoustic impedance change of the second type of reflective electrode in this invention.

[0027] Figure 7 This is a schematic diagram of the acoustic impedance change of the third type of reflective electrode in this invention.

[0028] Figure 8 This is a schematic diagram of the acoustic impedance change of the fourth type of reflective electrode in this invention.

[0029] Figure 9 This is a schematic diagram of the acoustic impedance change of the fifth type of reflective electrode in this invention.

[0030] Figure 10 This is a schematic diagram of the acoustic impedance change of the sixth type of reflective electrode in this invention.

[0031] Figure 11 This is a schematic diagram of the acoustic impedance change of the seventh type of reflective electrode in this invention.

[0032] Figure 12 This is a passband performance diagram of a surface acoustic wave device shown in an embodiment of the present invention.

[0033] Figure 13 The comparative example in this invention shows the passband performance of the surface acoustic wave device.

[0034] In the figure: 100, piezoelectric substrate; 110, substrate; 120, piezoelectric layer; 130, functional layer; 200, IDT electrode; 210, first busbar; 220, electrode finger; 300, reflective grating; 310, second busbar; 320, reflective electrode. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0036] In this application, the first direction is the direction of acoustic propagation of surface acoustic waves, i.e., the X direction shown in the figure; the second direction is the extension direction of the electrode finger 220 in the IDT electrode 200, i.e., the Y direction shown in the figure; and the third direction is the stack thickness direction of the device structure, i.e., the Z direction shown in the figure.

[0037] Example 1

[0038] like Figure 1 As shown, a surface acoustic wave device with different acoustic impedances includes a piezoelectric substrate 100 and an IDT electrode 200 and a reflective grating 300 disposed on the piezoelectric substrate 100. The reflective grating 300 is disposed on both sides of the IDT electrode 200 along a first direction. The reflective grating 300 includes a plurality of reflective electrodes 320 spaced apart along the first direction. The acoustic impedance of the plurality of reflective electrodes 320 varies along the first direction, and the reflective electrodes 320 with different acoustic impedances are made of different materials or a single material with different material properties.

[0039] Multiple reflective electrodes 320 are made of different materials or a single material with different material properties (density, sound velocity, or doping), resulting in different acoustic impedances. This causes the acoustic impedance of the multiple reflective electrodes 320 to vary along the first direction, forming an acoustic impedance step. This allows for "weighting" of reflections, controlling the reflection coefficient (κ), and the electrode fingers 220 of the IDT electrode 200 and the reflective electrodes 320 of the reflective grating 300 can form a "soft" boundary, thereby reducing Fresnel ripple, significantly reducing unwanted oscillations in the frequency response, and providing a smoother passband. Using different materials or a single material with different material properties to create an acoustic impedance step provides high impedance contrast. Since stopband width is proportional to acoustic impedance mismatch, higher impedance contrast leads to a wider stopband, allowing for the use of fewer reflective electrodes 320 without energy loss, thus facilitating miniaturization designs.

[0040] In surface acoustic wave (SAW) devices, the stopband width is the energy band gap formed by Bragg reflection caused by acoustic impedance mismatch, which prevents sound waves from propagating within that frequency range.

[0041] Specifically, the IDT electrode 200 includes a pair of first busbars 210 and a plurality of electrode fingers 220. The pair of first busbars 210 are spaced apart along a second direction, and the plurality of electrode fingers 220 are disposed between the pair of first busbars 210 and spaced apart along a first direction. This is prior art and will not be described in detail here. The layer thickness of the IDT electrode 200 is preferably 80 nm, the electrode fingers 220 are preferably 299, the period λ is 1.15 μm, and the metallization eta is 0.45. The reflective gate 300 also includes a pair of second busbars 310, which are spaced apart along a second direction, and a plurality of reflective electrodes 320 are disposed between the pair of second busbars 310. The layer thickness of the reflective gate 300 is preferably 80 nm, the period λ is 1.15 μm, and the metallization eta is 0.45.

[0042] like Figure 2 As shown, the piezoelectric substrate 100 includes a substrate 110 and a piezoelectric layer 120 disposed on the substrate 110, and an IDT electrode 200 and a reflective gate 300 are disposed on the piezoelectric layer 120.

[0043] Specifically, the substrate 110 preferably adopts a 4H-SiC structure, that is, a 4H type silicon carbide crystal structure; the piezoelectric layer 120 is preferably X-cut -47°YLiNbO3 (lithium niobate), and the layer thickness is preferably 200nm.

[0044] In some embodiments, the piezoelectric substrate 100 further includes a functional layer 130 disposed between the substrate 110 and the piezoelectric layer 120, such as Figure 3 and Figure 4 As shown.

[0045] Specifically, the material for the functional layer 130 is preferably silicon dioxide (SiO2), and the layer thickness is preferably 50 nm.

[0046] like Figure 5 and Figure 6 As shown, the acoustic impedance of the reflective electrode 320 in the reflective grating 300 decreases in the direction away from the IDT electrode 200, that is, the acoustic impedance ref1>ref2>ref3>ref4>ref5>ref6.

[0047] Specifically, the acoustic impedance of the reflective electrode 320 in the reflective grating 300 preferably changes gradually or in a stepwise manner in the direction away from the IDT electrode 200.

[0048] like Figure 5 As shown, the acoustic impedance of the reflective electrodes 320 in the reflective grating 300 changes in a stepwise manner away from the IDT electrode 200, that is, the acoustic impedance of the multiple reflective electrodes 320 in the reflective grating 300 changes in a jump manner away from the IDT electrode 200. Figure 5In this process, the acoustic impedance of multiple reflective electrodes 320 varies in a stepwise manner away from the IDT electrode 200. The acoustic impedance of each reflective electrode 320 is constant, but not limited to this, the acoustic impedance of each reflective electrode 320 can also be gradually varied.

[0049] like Figure 6 As shown, the acoustic impedance of the reflective electrodes 320 in the reflective grating 300 gradually changes in the direction away from the IDT electrode 200, that is, the acoustic impedance of the multiple reflective electrodes 320 in the reflective grating 300 changes continuously in the direction away from the IDT electrode 200. Figure 6 In this context, the continuous change in acoustic impedance is a linear change with inconsistent slopes, but it is not limited to this; it can also be a linear change with consistent slopes or a nonlinear change. From Figure 6 As can be seen, the acoustic impedances at the opposite ends of adjacent line segments are the same, thus ensuring the continuous change of acoustic impedance.

[0050] In some embodiments, the acoustic impedance of the reflective electrode 320 in the reflective grating 300 increases in the direction away from the IDT electrode 200, that is, the change in acoustic impedance is related to... Figure 5 and Figure 6 The opposite of that in the diagram is not shown here.

[0051] The different acoustic impedances of the reflector 300 determine the change in sound velocity below the reflector 300, creating a deeper "potential well" for surface waves, forcing the energy to remain below the IDT electrode 200, and significantly improving the quality factor (Q).

[0052] In this embodiment, the acoustic impedance of each reflective electrode 320 in the reflective grating 300 is not the same, such as Figure 5 and Figure 6 As shown.

[0053] In some embodiments, the reflective grating 300 contains reflective electrodes 320 with the same acoustic impedance, such as... Figure 7 As shown.

[0054] like Figure 7 As shown, the acoustic impedance ref1 has one reflective electrode 320, the acoustic impedance ref2 has two reflective electrodes 320, and the acoustic impedance ref3 has three reflective electrodes 320. However, it is not limited to this. It is also possible that the acoustic impedance ref1, ref2, and ref3 each have two reflective electrodes 320, or the acoustic impedance ref1 has four reflective electrodes 320, the acoustic impedance ref2 has one reflective electrode 320, and the acoustic impedance ref3 has one reflective electrode 320. The specific number can be determined according to the actual situation to achieve acoustic impedance modulation.

[0055] The reflector grating 300 uses different acoustic impedance modulations to increase the acoustic impedance at the electrode end, making the transverse velocity distribution tend to be flat. This makes the wave propagation mode similar to a flat "piston" rather than a curved piston, thereby eliminating the parasitic transverse mode spikes that disrupt the device passband and more effectively suppressing transverse parasitic modes.

[0056] In some embodiments, the acoustic impedance of at least one reflective electrode 320 in the reflective grating 300 is gradually varied or / and the acoustic impedance of at least one reflective electrode 320 in the reflective grating 300 is stepped, such as... Figures 8-10 As shown.

[0057] like Figure 8 As shown, the acoustic impedance of the first reflective electrode 320 in the reflective grating 300 gradually changes, while the acoustic impedance of the remaining reflective electrodes 320 remains constant. Figure 9 As shown, the acoustic impedance of the second reflective electrode 320 in the reflective grating 300 changes in a stepwise manner, while the acoustic impedance of the remaining reflective electrodes 320 remains constant. Figure 10 As shown, the acoustic impedance of the first reflective electrode 320 in the reflective grating 300 changes gradually, the acoustic impedance of the second reflective electrode 320 changes in a stepwise manner, and the acoustic impedance of the remaining reflective electrodes 320 remains constant.

[0058] In some embodiments, at least one reflective electrode 320 in the reflective grating 300 exhibits a gradual and stepped change in acoustic impedance, such as... Figure 11 As shown.

[0059] like Figure 11 As shown, the acoustic impedance of the first reflective electrode 320 in the reflective grating 300 changes gradually and then in a stepwise manner, while the acoustic impedance of the remaining reflective electrodes 320 remains constant. Of course, the acoustic impedance of the first reflective electrode 320 can also change gradually, then in a stepwise manner, and finally change gradually again.

[0060] from Figure 12 and Figure 13 It can be seen that by modulating the acoustic impedance of the reflective electrodes 320 in the reflective grating 300, the transverse parasitic mode can be effectively suppressed and the quality factor (Q) can be significantly improved. In the implementation case, there are eight pairs of reflective electrodes 320 with acoustic impedance ref1, made of copper (Cu); six pairs of reflective electrodes 320 with acoustic impedance ref2, made of titanium (Ti); and six pairs of reflective electrodes 320 with acoustic impedance ref3, made of aluminum (Al). In the comparative case, there are twenty pairs of reflective electrodes 320, all with an acoustic impedance of ref.

[0061] It is important to emphasize that the acoustic impedance difference in this application is formed using different fabrication materials or a single fabrication material with different material properties, and is not achieved by changing the width (duty cycle), thickness, or position of the reflective electrode 320. Existing technologies achieve acoustic impedance differences by changing the width, sacrificing linewidth accuracy and losing the optimal linewidth process window; while changing the thickness leads to poor surface flatness. This application uses different fabrication materials or a single fabrication material with different material properties to create acoustic impedance differences without changing the width, thickness, or position of the reflective electrode 320. It controls the phase shift of the wave and its reflection intensity and energy limitations, avoids the precision limitations of geometric etching, retains the optimal linewidth process window, and achieves a planar design, which is beneficial for back-end packaging processes such as flip-chip bonding.

[0062] This application applies to all surface acoustic wave devices, including surface acoustic wave devices on piezoelectric insulators (POI-SAW), temperature compensated surface acoustic wave devices (TC-SAW), transverse exciter acoustic wave devices (XBAR), and conventional surface acoustic wave devices.

[0063] Example 2

[0064] An electronic device includes a communication circuit and a surface acoustic wave device with different acoustic impedances as described in Embodiment 1, which is connected to the communication circuit.

[0065] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A surface acoustic wave device with different acoustic impedances, comprising a piezoelectric substrate (100) and an IDT electrode (200) and a reflective grating (300) disposed on the piezoelectric substrate (100), wherein the reflective grating (300) is disposed on both sides of the IDT electrode (200) along a first direction, and the reflective grating (300) includes a plurality of reflective electrodes (320) spaced apart along the first direction; characterized in that: The acoustic impedance of the plurality of reflective electrodes (320) varies along the first direction, and the reflective electrodes (320) with different acoustic impedances are made of different materials or a single material with different material properties.

2. The surface acoustic wave device with different acoustic impedances according to claim 1, characterized in that: The acoustic impedance of the reflective electrode (320) in the reflective grating (300) increases in the direction away from the IDT electrode (200).

3. The surface acoustic wave device with different acoustic impedances according to claim 1, characterized in that: The acoustic impedance of the reflective electrode (320) in the reflective grating (300) decreases in the direction away from the IDT electrode (200).

4. The surface acoustic wave device with different acoustic impedances according to claim 2 or 3, characterized in that: The acoustic impedance of the reflective electrode (320) in the reflective grating (300) gradually changes in the direction away from the IDT electrode (200).

5. The surface acoustic wave device with different acoustic impedances according to claim 2 or 3, characterized in that: The acoustic impedance of the reflective electrode (320) in the reflective grating (300) changes in a stepwise manner away from the IDT electrode (200).

6. The surface acoustic wave device with different acoustic impedances according to claim 2 or 3, characterized in that: The acoustic impedance of at least one reflective electrode (320) in the reflective grating (300) is gradually varied or / and the acoustic impedance of at least one reflective electrode (320) in the reflective grating (300) is stepped.

7. The surface acoustic wave device with different acoustic impedances according to claim 2 or 3, characterized in that: The acoustic impedance of at least one reflective electrode (320) in the reflective grating (300) varies gradually and in a stepwise manner.

8. The surface acoustic wave device with different acoustic impedances according to claim 2 or 3, characterized in that: The acoustic impedance of each reflective electrode (320) in the reflective grating (300) is different.

9. The surface acoustic wave device with different acoustic impedances according to claim 2 or 3, characterized in that: The reflective grating (300) contains reflective electrodes (320) with the same acoustic impedance.

10. An electronic device, characterized in that: It includes a communication circuit and a surface acoustic wave device with different acoustic impedances as described in any one of claims 1-9, which is connected to the communication circuit.

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