Gap medium filled surface acoustic wave resonator

Abstract

The utility model provides a kind of gap dielectric filling surface acoustic wave resonator, including piezoelectric substrate and IDT electrode being arranged on the piezoelectric substrate, the IDT electrode includes two oppositely arranged electrode strips, multiple electrode finger strips and false finger respectively with two electrode strips electrically connected and cross arrangement.The utility model fills insulating medium layer in the gap between false finger and electrode finger strip, so that the sound speed in the area where insulating medium layer is located is close to even consistent with the sound speed in the area of finger strip, effectively reduces the energy loss in the original gap area, and improves the Q value of resonator.

Description

Technical Field

[0001] This invention relates to the field of surface acoustic wave resonator technology, wherein dielectric filling is performed on the gap region between the interdigital electrode strip and the dummy finger to improve the performance of the surface acoustic wave resonator. Background Technology

[0002] With the rapid development of mobile communication technology, surface acoustic wave (SAW) filters are playing an increasingly important role in radio frequency front-ends due to their small size and excellent performance. The SAW resonator is the basic building block of the SAW filter, and its performance directly affects the filter's performance.

[0003] In surface acoustic wave (SAW) resonators, a suitable metal film thickness is typically designed tangentially based on the selected piezoelectric material to achieve optimal electromechanical coupling coefficient and quality factor (Q value). However, due to structural limitations of SAW filters, gaps inevitably exist laterally in the interdigitated electrodes of the filter's resonator to achieve electrical isolation. Acoustic waves leak into the substrate as they propagate in these regions, reducing the Q value. While reducing the gap width or adding appropriately long interdigitated electrodes can mitigate this energy leakage or adjust its frequency band to some extent, some acoustic wave leakage into the substrate remains and is difficult to eliminate completely. Utility Model Content

[0004] In view of the shortcomings of the prior art, the purpose of this utility model is to provide a surface acoustic wave resonator structure that reduces or even eliminates energy leakage in the gap region, so as to solve the problem that the Q value of surface acoustic wave resonators decreases due to energy leakage in the prior art.

[0005] The objective of this utility model can be achieved through the following technical solutions: A gap-filled surface acoustic wave resonator, characterized in that the resonator includes a piezoelectric substrate, interdigital transducer electrodes on one side surface of the piezoelectric substrate, each interdigital transducer electrode including a first electrode and a second electrode opposite to the first electrode, the first electrode having one or more first fingers and first dummy fingers spaced perpendicularly at intervals, the second electrode having one or more second fingers and second dummy fingers spaced perpendicularly at intervals, the first and second fingers being spaced apart, and gap regions being left between the tips of the first and second dummy fingers and between the tips of the second and first dummy fingers; an insulating dielectric filling layer is disposed in the gap region; after the addition of the insulating dielectric filling layer, the relationship between the sound velocity v1 in the arrangement direction of the first and second fingers and the sound velocity v2 in the finger region in the finger arrangement direction is 0.8×v2<v1<1.2×v2; the length L of the insulating dielectric filling layer is greater than 0.2λ and less than 0.5λ; the width W of the insulating dielectric filling layer is greater than 0.2λ and less than 0.8λ; the thickness of the insulating dielectric filling layer is greater than 0.5λ. The thickness of the metal film of the first or second finger strip is equal to or less than twice the thickness of the metal film of the first or second finger strip.

[0006] Furthermore, in the aforementioned gap dielectric-filled surface acoustic wave resonator, the insulating dielectric filling layer is made of polycrystalline silicon, silicon dioxide, aluminum oxide, silicon nitride, or silicon oxynitride.

[0007] The beneficial effects of this invention are that, due to the filling of the insulating dielectric layer, the sound velocity in the original gap region decreases and becomes close to or even the same as the sound velocity in the finger strip region, which reduces the transverse energy loss in the gap region caused by the mode conversion of sound waves. At the same time, the added insulating dielectric layer weakens the energy leakage of sound waves to the substrate, further reducing the bulk wave leakage energy loss in the gap region. Therefore, the Q value of the resonator can be significantly improved. Attached Figure Description

[0008] Figure 1 is a top view of the structure of a prior art SAW resonator; Figure 2 is a top view schematic diagram of the resonator structure of this utility model; Figure 3 is a schematic cross-sectional view of the resonator of this utility model; Figure 4 is a comparison diagram of the deformation distribution of the existing technology and the structure of the present invention in the simulation; Figure 5 is a comparison of the admittance and conductance curves of the prior art and the present invention in the simulation. Figure 6 is a comparison of the quality factor curves of the existing technology and the present invention in the simulation.

[0009] Wherein, 100 - piezoelectric substrate, 200 - interdigital transducer, 201 - first electrode, 202 - second electrode, 203 - first finger strip, 204 - second finger strip, 205 - first pseudo-finger, 206 - second pseudo-finger, 207 - gap region, 208 - insulating dielectric filling layer. Detailed Implementation

[0010] Figure 1 shows a top view of a prior art SAW resonator, which includes: The piezoelectric substrate 100, wherein the material of the piezoelectric film includes lithium tantalate (LiTaO3) or lithium niobate (LiNbO3). Interdigital transducer 200 is disposed on one side surface of piezoelectric substrate 100, and the material can be one, multiple layers or alloy of metals such as aluminum, copper, titanium, gold, and platinum.

[0011] The interdigital transducer 200 includes: A first electrode 201 and a second electrode 202, wherein the first electrode 201 and the second electrode 202 are arranged parallel to each other along the x-direction and along the y-direction.

[0012] A first finger strip 203 and a second finger strip 204, wherein one end of the first finger strip 203 along its length in the y-direction is connected to a first electrode 201. One end of the second finger strip 204 along its length in the y-direction is connected to a second electrode 202. The first finger strip 203 and the second finger strip 204 extend along the x-direction as follows: Figure 1 As shown, they are arranged in parallel, intersecting intervals.

[0013] The first prosthetic finger 205 and the first finger strip 203 are perpendicularly disposed on one side of the first electrode 201 and are electrically connected to each other. The second prosthetic finger 206 and the second finger strip 204 are perpendicularly disposed on one side of the second electrode 2021 and are electrically connected to each other. The first electrode 201 and the second electrode 202 are inserted into each other at an interval, and a gap area 207 is left between the tip of the first prosthetic finger 205 and the tip of the second finger strip 204, and between the tip of the second prosthetic finger 206 and the tip of the first finger strip 203.

[0014] The implementation of this utility model is as follows: Figure 2 and Figure 3 As shown, the gap region 207 is filled with an insulating medium of a certain thickness to form an insulating medium filling layer 208. The insulating medium material can be polycrystalline silicon, silicon dioxide, aluminum oxide, silicon nitride, or silicon oxynitride.

[0015] Specifically, the distance can be greater than 0.2λ and less than 0.5λ, and should be determined based on the edge distance between the dummy finger and the finger strip, where λ is the distance between the first finger strip 203 and the second finger strip 204 along the x-direction. Preferably, the length L of the insulating dielectric filling layer 208 used in this embodiment is equal to the length of the gap region 207 described in the prior art, minimizing the energy leakage from the resonator into the piezoelectric substrate 100. It is worth noting that in order to increase the Q value, the prior art requires minimizing the length of the gap region 207, for example, to less than 0.2λ, which undoubtedly places high demands on the process conditions and reduces the yield of large-scale production. After adding the insulating dielectric filling layer 280, the edge distance between the dummy finger and the finger strip can be increased to more than 0.5λ while still maintaining a high Q value, reducing the requirements on the process.

[0016] However, it should not overlap with adjacent finger strip areas. Preferably, in this embodiment of the invention, the width of the insulating dielectric filling layer 208 is equal to the width of the finger strip.

[0017] Specifically, as a preferred embodiment, the insulating dielectric filling layer 208 material used in this utility model embodiment is silicon dioxide, and its thickness is 1.4 times the metal film thickness of the first finger strip 203 / the second finger strip 204.

[0018] Figure 4 shows, from top to bottom, the three-dimensional deformation distribution diagrams of the prior art and the embodiment of the present invention, respectively, based on finite element simulation. As an example, the piezoelectric substrate 100 is made of 42°YX tangential lithium tantalate, the interdigitated electrodes 200 are made of aluminum, and the insulating dielectric filling region is made of silicon dioxide. As shown in the three-dimensional deformation distribution diagram of the prior art, acoustic waves leak energy into the piezoelectric substrate 100 near the gap region 207. However, the three-dimensional deformation distribution diagram of the embodiment of the present invention shows that the deformation is almost entirely concentrated on the surface of the piezoelectric substrate 100, with no energy leakage occurring near the insulating dielectric filling region 208.

[0019] like Figure 5 The diagram illustrates the frequency variations of the admittance and conductance of the present invention embodiment and the prior art reference example. The admittance and conductance of the present invention embodiment are represented by solid lines, while those of the prior art reference example are represented by dashed lines. A comparison of the two shows that the surface acoustic wave resonator at the resonant frequency (… Figure 5 The conductivity and admittance characteristics in the frequency region between the resonant frequency (f1 in Figure 5) and the anti-resonant frequency (f2 in Figure 5) are improved. The improvement in conductivity near the resonant frequency is particularly significant. At the same frequency, the conductivity of the resonator in this embodiment is lower than that of the reference model, and the conductivity is reduced by 2dB to 5dB in some frequency ranges. Currently, with the continuous optimization of the resonator structure, a difference of 1dB can bring a significant competitive advantage.

[0020] Figure 6 shows a comparison of the quality factor of the present invention and a prior art reference example as a function of frequency. Clearly, the prior art reference example has a smaller Q value near the resonant frequency, which is due to... Figure 4 The sound wave energy leaks into the piezoelectric substrate 100 as shown. However, after adding a dielectric filling layer, this energy loss is reduced or even eliminated, and the Q value increases by 100-270 in certain frequency ranges, corresponding to the frequency range of decreased conductivity shown in Figure 5.

[0021] It is worth noting that the piezoelectric substrate 100 used in this embodiment is made of 42° YX tangential lithium tantalate and operates in a leaky surface wave mode. It is foreseeable that the dielectric filling structure proposed in this invention can improve the performance of any resonator made of a piezoelectric substrate with other suitable tangential or material operating in a leaky surface wave mode, and should be within the protection scope of this patent.

[0022] In summary, this invention improves the structure of the surface acoustic wave resonator by filling the gap between the dummy finger and the finger strip with an insulating dielectric layer, effectively reducing acoustic energy leakage and increasing the Q value of the resonator. Therefore, this invention effectively overcomes the shortcomings of the prior art and has high industrial application value.

Claims

1. A surface acoustic wave resonator with a gap medium filled, characterized in that, The resonator includes a piezoelectric substrate (100), and interdigital transducer electrodes (200) on one side surface of the piezoelectric substrate (100). The interdigital transducer electrodes (200) include a first electrode (201) and a second electrode (202) opposite to the first electrode (201). The first electrode (201) is provided with one or more first fingers (203) and first dummy fingers (205) spaced perpendicularly at intervals. The second electrode (202) is provided with one or more second fingers (204) and second dummy fingers (206) spaced perpendicularly at intervals. 3) The first and second finger strips (204) are spaced apart from each other, and gap areas (207) are left between the tip of the first dummy finger (205) and the tip of the second finger strip (204) and between the tip of the second dummy finger (206) and the tip of the first finger strip (203); an insulating medium filling layer (208) is provided in the gap area (207); after the insulating medium filling layer (208) is added, the relationship between the sound velocity v1 in this area in the arrangement direction of the first finger strip (203) and the second finger strip (204) and the sound velocity v2 in the finger strip area in the finger strip arrangement direction is 0.8 × v2. < v1 < 1.2×v2; the length L of the insulating dielectric filling layer (208) is greater than 0.2λ and less than 0.5λ; the width W of the insulating dielectric filling layer (208) is greater than 0.2λ and less than 0.8λ; the thickness of the insulating dielectric filling layer (208) is greater than 0.5 times the metal film thickness of the first finger strip (203) or the second finger strip (204) and less than 2 times the metal film thickness of the first finger strip (203) or the second finger strip (204).

2. The gap-filled surface acoustic wave resonator according to claim 1, characterized in that, The insulating dielectric filling layer (208) is made of polycrystalline silicon, silicon dioxide, aluminum oxide, silicon nitride, or silicon oxynitride.

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