A structure for suppressing transverse modes of a surface acoustic wave device

Abstract

The present invention discloses a structure for suppressing the transverse mode of a surface acoustic wave device, which includes a piezoelectric layer and an electrode layer located on the piezoelectric layer. The electrode layer includes bus bars, interdigital electrodes, and dummy fingers; the bus bars include two parallel bus bars, and the dummy fingers and the interdigital electrodes are arranged between the two bus bars to form an IDT pattern. The dummy fingers and the interdigital electrodes on the same bus bar are arranged crosswise in sequence, and all the dummy fingers on each bus bar are arranged opposite to the interdigital electrodes on the other bus bar one by one and there is a gap between the two. Bus bar thickening layers are respectively provided on the two bus bars to increase the mass loading in the bus bar area, thereby reducing the acoustic wave propagation speed in the bus bar area, so that the acoustic velocity in the bus bar area is between the main mode velocity and the first transverse mode velocity. While suppressing the transverse clutter mode, the present invention solves the problems of the reduction of the device Q value, the increase in size, and the complexity of the processing technology brought about by the prior art.

Description

Technical Field

[0001] The present invention relates to surface acoustic wave devices, and particularly to a structure for suppressing transverse modes of surface acoustic wave devices, belonging to the technical field of surface acoustic wave devices. Background Art

[0002] Surface Acoustic Wave (SAW) filters are widely used in the fields of national defense and mobile communication due to their advantages such as low loss, small size, low cost, and high reliability. With the increasing performance requirements for SAW devices in various application fields, the third-generation SAW devices (Film Bulk Acoustic Resonator, FSAW for short) have emerged. Compared with ordinary SAW and TCSAW devices, FSAW has advantages such as lower insertion loss, higher temperature stability, larger bandwidth, and higher power tolerance. However, transverse clutter modes are likely to occur within the passband of FSAW filters. The existence of transverse modes will increase the insertion loss of the device, reduce the rectangularity of the device, etc., easily leading to a decrease in the signal-to-noise ratio of the application system and causing signal distortion. Therefore, it is necessary to suppress this.

[0003] Currently, there are mainly three commonly used suppression methods: the cosine weighting method, the Piston method, and the finger tilt method. Among them, both the cosine weighting method and the finger tilt method will increase the device size and at the same time reduce the Q value of the device; while the Piston method will greatly increase the process implementation difficulty when applied to high frequencies.

[0004] From the above analysis, it can be seen that the existing transverse mode suppression methods still face problems such as a decrease in the Q value of the device, an increase in size, and a complex processing technology. Summary of the Invention

[0005] Aiming at the above deficiencies existing in the prior art, the purpose of the present invention is to provide a structure for suppressing transverse modes of surface acoustic wave devices. While suppressing transverse clutter modes, the present invention solves the problems such as a decrease in the Q value of the device, an increase in size, and a complex processing technology brought about by the prior art.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A structure for suppressing transverse modes of a surface acoustic wave device, comprising a piezoelectric layer and an electrode layer located on the piezoelectric layer. The electrode layer includes bus bars, interdigital electrodes, and dummy fingers. The bus bars include a first bus bar and a second bus bar arranged in parallel. The dummy fingers and the interdigital electrodes are multiple in the same number and are arranged between the first bus bar and the second bus bar to form an IDT pattern. The dummy fingers and the interdigital electrodes on the same bus bar are sequentially arranged in equal intervals and cross each other. All the dummy fingers on each bus bar are arranged opposite to the interdigital electrodes on the other bus bar one by one and there is a gap between them. It is characterized in that: bus bar thickening layers are respectively provided on the two bus bars to increase the mass load in the bus bar area, thereby reducing the acoustic wave propagation speed in the bus bar area. The increased mass load of the bus bar thickening layer makes the acoustic velocity in the bus bar area between the main mode velocity and the first transverse mode velocity.

[0008] Preferably, the thickness of the bus bar thickening layer is 0.01 - 3 times the thickness of the bus bar.

[0009] Preferably, the length of the bus bar thickening layer is the same as the length of the bus bar and is aligned with both ends of the bus bar. The width of the bus bar thickening layer is less than or equal to the width of the bus bar. The inner sides of the two bus bar thickening layers facing each other are aligned with the inner sides of the corresponding bus bars.

[0010] In the present invention, the material of the bus bar thickening layer is aluminum, copper, gold, platinum, silicon dioxide or silicon nitride.

[0011] Further, the bus bar thickening layer is a single-layer or multi-layer structure.

[0012] Further, the width of the dummy finger is the same as that of the interdigital electrode, and the length of the dummy finger is 0.1 - 7 times the interdigital period p.

[0013] The length of the gap is 0.1 μm - 2 μm.

[0014] The material of the electrode layer is aluminum, copper, gold or platinum, and the electrode layer is a single layer or multiple layers; the electrode layer is fabricated by an electron beam coating process.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] In the present invention, by increasing the bus bar thickening layer to increase the mass load in the bus bar area, thereby reducing the acoustic wave propagation speed in the bus bar area, so that the acoustic velocity in the bus bar area is between the main mode and the velocity of the first transverse mode (adjacent to the main mode). In this way, in addition to the energy of the main mode being confined between the two bus bars, the energy of other higher-order transverse modes is leaked to the bus bar area and beyond, thereby achieving the purpose of suppressing transverse clutter modes, reducing the passband ripple of the device, reducing the passband insertion loss, and improving the anti-interference ability of the system.

[0017] While suppressing the transverse clutter mode, the present invention solves the problems of reduced device Q value, increased size, and complex processing technology caused by the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic structural diagram of the surface acoustic wave device of the present invention for suppressing the transverse mode;

[0019] Figure 2 is Figure 1 top view of;

[0020] Figure 3 It is a simulated admittance curve diagram of the structure of a conventional surface acoustic wave device;

[0021] Figure 4 It is a simulated admittance curve diagram of the structure of the surface acoustic wave device for suppressing the transverse mode provided by the embodiment of the present invention.

[0022] Among them, 1 - piezoelectric layer; 2 - bus bar; 3 - bus bar thickening layer; 4 - interdigital electrode; 5 - gap; 6 - dummy finger. DETAILED DESCRIPTION OF THE INVENTION

[0023] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Referring to Figure 1 and Figure 2 , a structure of a surface acoustic wave device for suppressing the transverse mode of the present invention includes a piezoelectric layer 1 and an electrode layer located on the piezoelectric layer. The electrode layer includes a bus bar 2, an interdigital electrode 4, and a dummy finger 6; the bus bar 2 includes a first bus bar and a second bus bar arranged in parallel. The dummy finger 6 and the interdigital electrode 4 are multiple with the same number and are arranged between the first bus bar and the second bus bar to form an IDT pattern. The dummy fingers and the interdigital electrodes on the same bus bar are alternately arranged at equal intervals in sequence. All the dummy fingers on each bus bar are arranged opposite to the interdigital electrodes on the other bus bar one by one and there is a gap 5 between them. Bus bar thickening layers 3 are respectively provided on the two bus bars 2 to increase the mass load in the bus bar area, thereby reducing the acoustic wave propagation speed in the bus bar area. The increased mass load of the bus bar thickening layer 3 makes the acoustic velocity in the bus bar 2 area between the main mode velocity and the first transverse mode velocity.

[0025] Preferably, the IDT pattern is arranged by crossing positive and negative electrodes, and the positive and negative electrodes are arranged periodically with a period of p.

[0026] The thickness of the bus bar thickening layer 3 is 0.01 - 3 times the thickness of the bus bar 2.

[0027] The length of the bus bar thickening layer 3 is the same as that of the bus bar 2 and is aligned with both ends of the bus bar 2. The width of the bus bar thickening layer 3 is less than or equal to the width of the bus bar 2. The inner sides of the two bus bar thickening layers facing each other are aligned with the inner sides of the corresponding bus bars, so that the influence of the speed change caused by the bus bar thickening layer is exactly adjacent to the speed in the IDT region, so as to cause an appropriate speed difference.

[0028] Preferably, the material of the bus bar thickening layer 3 is a common material for surface acoustic wave devices including aluminum, copper, gold, platinum, silicon dioxide, and silicon nitride, and is a single-layer or multi-layer structure.

[0029] The width of the dummy finger 6 is the same as that of the interdigital electrode 4, and the length of the dummy finger is 0.1-7 times the interdigital period p.

[0030] The length of the gap 5 is 0.1 μm - 2 μm.

[0031] Preferably, the material of the electrode layer is a common electrode material for surface acoustic wave devices including aluminum, copper, gold, and platinum. The electrode layer is a single layer or multiple layers; the electrode layer is fabricated by an electron beam coating process.

[0032] As Figure 3 、 Figure 4 shown, the simulated admittance curves of the conventional structure and the structure for suppressing the transverse mode of a surface acoustic wave device provided by an embodiment of the present invention are respectively given. The gap 5 of both structures is 0.2 μm, the length of the dummy finger 6 is 2.356 times the interdigital period, the interdigital period is 2.39 μm, the widths of the interdigital electrode and the dummy finger are both 0.56 μm, the electrodes are all aluminum electrodes, the piezoelectric layer is 42°YX-LiTaO3(600nm) / SiO2(500nm) / Si(1μm), and the electrode thickness of the conventional structure is 180 nm. The thicknesses of the bus bar 2, the interdigital electrode 4, the gap 5, and the dummy finger 6 of the structure of the embodiment of the present invention are 180 nm, and the thickness of the bus bar thickening layer 3 is 170 nm (0.944 times the electrode thickness); comparison Figure 3 and Figure 4 It can be clearly seen that after adopting the structure of the present invention, the transverse mode clutter of the device is well suppressed.

[0033] The present invention reduces the acoustic wave propagation speed in the bus bar area by increasing the mass load in the bus bar area, so that the acoustic speed in the bus bar area is between the speeds of the main mode and the first transverse mode (adjacent to the main mode). In this way, in addition to the energy of the main mode being confined between the two bus bars, the energy of other higher-order transverse modes is leaked to the bus bar area and beyond, thereby suppressing the transverse clutter mode.

[0034] The above embodiments of the present invention are merely examples for illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes and modifications can be made based on the above description. It is impossible to enumerate all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A structure for suppressing the transverse mode of a thin-film surface acoustic wave device, comprising a piezoelectric layer and an electrode layer located on the piezoelectric layer. The electrode layer includes bus bars, interdigital electrodes, and dummy fingers. The bus bars include a first bus bar and a second bus bar arranged in parallel. The dummy fingers and the interdigital electrodes are multiple and have the same number, and are arranged between the first bus bar and the second bus bar to form an IDT pattern. The dummy fingers and the interdigital electrodes on the same bus bar are sequentially arranged at equal intervals and cross each other. All the dummy fingers on each bus bar are arranged opposite to the interdigital electrodes on the other bus bar one by one and there is a gap between them. It is characterized in that: Bus bar thickening layers are respectively provided on the two bus bars to increase the mass loading in the bus bar area, thereby reducing the sound wave propagation speed in the bus bar area. The increased mass loading of the bus bar thickening layer makes the sound speed in the bus bar area between the main mode speed and the first transverse mode speed, so that in addition to the energy of the main mode being confined between the two bus bars, the energy of other higher-order transverse modes is leaked to the bus bar area and beyond. The length of the bus bar thickening layer is the same as that of the bus bar and is aligned with both ends of the bus bar. The width of the bus bar thickening layer is less than or equal to the width of the bus bar. The opposite inner sides of the two bus bar thickening layers are aligned with the inner sides of the corresponding bus bars and are in a vertical state.

2. The structure for suppressing the transverse mode of a thin-film surface acoustic wave device according to claim 1, characterized in that: The thickness of the bus bar thickening layer is 0.01 - 3 times the thickness of the bus bar.

3. The structure for suppressing transverse modes of a thin-film surface acoustic wave device according to claim 1, wherein: The material of the bus bar thickening layer is aluminum, copper, gold, platinum, silicon dioxide or silicon nitride.

4. The structure for suppressing the lateral mode of a thin-film surface acoustic wave device according to claim 1, wherein: The bus bar thickening layer is of a single-layer or multi-layer structure.

5. The structure for suppressing the lateral mode of a thin-film surface acoustic wave device according to claim 1, characterized in that: The width of the dummy finger is the same as that of the interdigital electrode, and the length of the dummy finger is 0.1 - 7 times the interdigital period p.

6. The structure for suppressing the lateral mode of a thin-film surface acoustic wave device according to claim 1, characterized in that: The length of the gap is 0.1 μm - 2 μm.

7. The structure for suppressing transverse modes of a thin-film surface acoustic wave device according to claim 1, wherein: The material of the electrode layer is aluminum, copper, gold or platinum, and the electrode layer is of a single layer or multiple layers; the electrode layer is fabricated by an electron beam coating process.

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