Resonator and narrowband surface acoustic wave filter

Abstract

The invention provides a resonator and a narrow-band surface acoustic wave filter, and relates to the technical field of filters, the resonator provided by the invention comprises a piezoelectric substrate, a transducer and reflecting gratings, the transducer and the reflecting gratings are both arranged on the piezoelectric substrate, the reflecting gratings are located at two sides of the transducer, the transducer is provided with multiple groups of interdigital electrodes, and the interdigital electrodes are arranged on the piezoelectric substrate. Each group of interdigital electrodes comprises a grounding electrode group and a terminal electrode group, the grounding electrode group comprises a plurality of first interdigital electrodes which are sequentially arranged at intervals and are used for grounding, and the terminal electrode group comprises a plurality of second interdigital electrodes which are sequentially arranged at intervals and are used for accessing electric signals. The resonator provided by the invention can effectively reduce the passband width of the filter without sacrificing insertion loss, out-of-band rejection and rectangularity.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a resonator and a narrowband surface acoustic wave filter. Background Art

[0002] With the congestion of communication channels, the mutual interference between channels is extremely serious. It is necessary to filter out interference signals through narrowband filters to improve the signal transmission quality. Traditional crystal filters can achieve narrowband filtering functions, but affected by their processing accuracy, their operating frequencies are very low, and the device volume is large, which cannot meet the application requirements of high frequency and small volume.

[0003] Surface acoustic wave filters have become a widely used filter due to their many advantages such as low loss, small volume, light weight, good temperature stability, high consistency, good reliability, easy integration, and flexible design. They are widely used in military electronic systems such as radio, satellite, radar, communication, and electronic countermeasures, and have also become the preferred device for realizing narrowband filtering functions.

[0004] For narrowband filters, foreign researchers have used zinc oxide / sapphire substrates to study and design 5 types of IDT (Inter-digital Transducer) type longitudinal coupling structure surface acoustic wave filters. Among them, when the device operates at 1.5 GHz, the relative bandwidth is 2.4%; when it operates at 2.4 GHz, the relative bandwidth is only 1.7%. Some researchers have studied the basic characteristics of several layered structure surface acoustic waves. Among some structures including diamond layers, the SiO 2 / ZnO / Diamond structure is one of the most promising structures. In particular, high-frequency and narrowband filters are suitable for many scenarios, such as being applied to optical communication systems and retiming filters of resonators. In these application scenarios, a smaller frequency temperature coefficient (TCF) is required. Through numerical calculations and experiments, it is found that zero TCF and an acoustic wave velocity of about 10000 m / s can be achieved in the first-order Rayleigh wave mode. Using this structure, a narrowband surface acoustic wave filter with an insertion loss of about 10 dB and a center frequency of about 2.5 GHz can be successfully fabricated. The filter with the SiO 2 / IDT / ZnO / Diamond layered structure is greatly affected by factors such as sputtering gas composition, substrate temperature, sputtering pressure, target-substrate distance, and gas flow rate during the growth of zinc oxide thin films. Moreover, the surface acoustic wave phase velocity and electromechanical coupling coefficient of zinc oxide itself are relatively low, which easily leads to an increase in the insertion loss of the filter and a relatively low power tolerance. Therefore, there are still great limitations in the fabrication of high-frequency and low-loss narrowband filters.

[0005] Beyond materials research, achieving narrowband through device structure improvement is also a research direction. Some scholars have proposed a new design technique for ladder-type surface acoustic wave filters. Connecting an additional resonator to the series arm or parallel arm in the ladder filter topology can create two transmission zeros in the response passband of the filter. This technique is applicable to the design of ladder filters with a narrow passband and high rectangularity. However, adding a resonator will increase the loss additionally, and the resonance frequency regulation of the resonator requires more precision.

[0006] Therefore, how to effectively reduce the passband width of the filter without sacrificing insertion loss, out-of-band rejection, and rectangularity is an urgent problem to be solved. Summary of the Invention

[0007] The purpose of the present invention is to provide a resonator and a narrowband surface acoustic wave filter, which can effectively reduce the passband width of the filter without sacrificing insertion loss, out-of-band rejection, and rectangularity.

[0008] To achieve the above purpose, the present invention provides the following technical solutions:

[0009] In the first aspect, the present invention provides a resonator, which includes a piezoelectric substrate, a transducer, and a reflection grating. The transducer and the reflection grating are both arranged on the piezoelectric substrate. The reflection grating is located on both sides of the transducer. The transducer has multiple sets of interdigital electrodes. Each set of interdigital electrodes includes a grounding electrode group and a terminal electrode group. The grounding electrode group includes multiple first interdigital electrodes arranged at intervals in sequence and used for grounding. The terminal electrode group includes multiple second interdigital electrodes arranged at intervals in sequence and used for accessing an electrical signal.

[0010] Further, in the transducer, the grounding electrode group and the terminal electrode group are arranged alternately, and the arrangement direction is parallel to the direction from one side of the reflection grating to the other side of the reflection grating.

[0011] Further, each grounding electrode group includes 2 to 5 first interdigital electrodes, and each terminal electrode group includes 2 to 5 second interdigital electrodes.

[0012] Further, the thickness of the first interdigital electrode and the second interdigital electrode is 5 nm to 5 μm;

[0013] The width of the first interdigital electrode and the second interdigital electrode is 20 nm to 20 μm;

[0014] The length of the first interdigital electrode and the second interdigital electrode is 100 nm to 1000 μm.

[0015] Further, the grounding electrode group includes Na first interdigital electrodes. The width of the first one of the first interdigital electrodes in the arrangement direction of the first interdigital electrodes is a, and the widths of the second to the Na-th first interdigital electrodes are (1 + m)*a, where m ranges from -0.05 to 0.05.

[0016] Further, the terminal electrode group includes Nb second interdigital electrodes. The width of the first one of the second interdigital electrodes in the arrangement direction of the second interdigital electrodes is b, and the widths of the second to the Nb-th second interdigital electrodes are (1 + n)*b, where n ranges from -0.05 to 0.05.

[0017] Further, the widths of the second to the Na-th first interdigital electrodes are the same or different;

[0018] The widths of the second to the Nb-th second interdigital electrodes are the same or different.

[0019] Further, the electric field direction formed by the first interdigital electrode and the second interdigital electrode forms an Euler angle with the +y-axis direction in the global coordinate system of the piezoelectric substrate, and the value of the Euler angle ranges from -90 to +90°.

[0020] Further, the piezoelectric substrate includes a support substrate and a piezoelectric layer, or the piezoelectric substrate includes only a piezoelectric layer;

[0021] Both the transducer and the reflection grating are disposed on the piezoelectric layer.

[0022] In a second aspect, the present invention further provides a narrowband surface acoustic wave filter, including the resonator described in the above solution.

[0023] The resonator and the narrowband surface acoustic wave filter provided by the present invention can produce the following beneficial effects:

[0024] Compared with the prior art, the resonator provided by the present invention changes the single interdigital electrode configured in the conventional grounding electrode group and terminal electrode group into multiple interdigital electrodes, reducing the transduction coefficient and making the electromechanical coupling coefficient of the transducer smaller. The bandwidth that can be achieved by the multi-interdigital transducer is narrower than that of the conventional single-interdigital transducer. It is possible to implement a narrowband surface acoustic wave filter using a piezoelectric material with a relatively large electromechanical coupling coefficient without sacrificing insertion loss, out-of-band rejection, and rectangularity.

[0025] The narrowband surface acoustic wave filter provided in the second aspect of the present invention has the resonator provided in the first aspect of the present invention, and thus has all the beneficial effects of the resonator provided in the first aspect of the present invention. Description of the Drawings

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 The front view of the first resonator provided by the embodiment of the present invention;

[0028] Figure 2 The front view of the partial structure of the first resonator provided by the embodiment of the present invention;

[0029] Figure 3 The top view of the first resonator provided by the embodiment of the present invention;

[0030] Figure 4 The front view of the second resonator provided by the embodiment of the present invention;

[0031] Figure 5 The front view of the partial structure of the second resonator provided by the embodiment of the present invention;

[0032] Figure 6 The simulation admittance diagram of the first resonator provided by the embodiment of the present invention;

[0033] Figure 7 The simulation admittance diagram of the existing resonator;

[0034] Figure 8 The simulation admittance diagram of the second resonator provided by the embodiment of the present invention.

[0035] Icon: 1 - Piezoelectric substrate; 2 - Reflection grating; 3 - Ground electrode group; 31 - First interdigital electrode; 4 - Terminal electrode group; 41 - Second interdigital electrode. Specific embodiments

[0036] The following will clearly and completely describe the technical solutions of the present invention with reference to the drawings. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0037] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0038] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] The following will describe the specific embodiments of the present invention in detail with reference to the drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0040] An embodiment of the first aspect of the present invention is to provide a resonator, as Figures 1 to 3 shown, including a piezoelectric substrate 1, a transducer, and a reflection grating 2. The transducer and the reflection grating 2 are both disposed on the piezoelectric substrate 1. The reflection grating 2 is located on both sides of the transducer. The transducer has multiple sets of interdigital electrodes. Each set of interdigital electrodes includes a ground electrode group 3 and a terminal electrode group 4. The ground electrode group 3 includes multiple first interdigital electrodes 31 arranged at intervals in sequence and used for grounding. The terminal electrode group 4 includes multiple second interdigital electrodes 41 arranged at intervals in sequence and used for accessing electrical signals.

[0041] Compared with the prior art, in the resonator provided in the above embodiment, the ground electrode group 3 of the transducer includes multiple first interdigital electrodes 31, and the terminal electrode group 4 of the transducer includes multiple second interdigital electrodes 41. By changing the single interdigital electrode configured in the conventional ground electrode group 3 and the terminal electrode group 4 into multiple interdigital electrodes, the transduction coefficient is reduced, so that the electromechanical coupling coefficient of the transducer becomes smaller. The bandwidth that the multi-interdigital transducer can achieve is narrower than that of the conventional single-interdigital transducer. It is possible to implement a narrowband surface acoustic wave filter using a piezoelectric material with a relatively large electromechanical coupling coefficient without sacrificing the insertion loss, out-of-band rejection, and rectangularity.

[0042] Specifically, as Figure 1As shown, in the ground electrode group 3, the arrangement direction of the plurality of first interdigital electrodes 31 is parallel to the direction from one side reflection grating 2 to the other side reflection grating 2. In the ground electrode group 3, the arrangement direction of the plurality of first interdigital electrodes 31 is parallel to the direction from one side reflection grating 2 to the other side reflection grating 2

[0043] In addition, as Figure 1 shown, in the transducer, the ground electrode group 3 and the terminal electrode group 4 are alternately arranged, and the arrangement direction is parallel to the direction from one side reflection grating 2 to the other side reflection grating 2.

[0044] Among them, the total number of finger roots of the two side reflection gratings 2 is 1 to 500, and the total number of finger roots of the first interdigital electrode 31 and the second interdigital electrode 41 in the transducer is 10 to 3000.

[0045] In an alternative embodiment, each ground electrode group 3 includes 2 to 5 first interdigital electrodes 31, specifically including 2, 3, 4, or 5. Each terminal electrode group 4 includes 2 to 5 second interdigital electrodes 41, specifically including 2, 3, 4, or 5.

[0046] As Figures 1 to 3 shown, each ground electrode group 3 includes 2 first interdigital electrodes 31, and each terminal electrode group 4 includes 2 second interdigital electrodes 41. As Figures 4 to 5 shown, each ground electrode group 3 includes 3 first interdigital electrodes 31, and each terminal electrode group 4 includes 3 second interdigital electrodes 41

[0047] In an alternative embodiment, as Figure 1 shown, the thickness L 1 of the first interdigital electrode 31 and the second interdigital electrode 41 is 5 nm to 5 μm; as Figure 3 shown, the width L 2 of the first interdigital electrode 31 and the second interdigital electrode 41 is 20 nm to 20 μm; the length L 3 of the first interdigital electrode 31 and the second interdigital electrode 41 is 100 nm to 1000 μm.

[0048] In an alternative embodiment, the ground electrode group 3 includes Na first interdigital electrodes 31. Along the arrangement direction of the first interdigital electrodes 31, the width of the first first interdigital electrode 31 is a, and the width of the second to the Na-th first interdigital electrodes 31 is (1 + m) * a, where the value range of m is -0.05 to 0.05.

[0049] That is to say, among the second to the Na-th first interdigital electrodes 31, the width difference between any first interdigital electrode 31 and the first first interdigital electrode 31 is within ±5%.

[0050] Specifically, the widths of the second to the Na-th first interdigital electrodes 31 may be the same, that is, m of each first interdigital electrode 31 takes the same value, or the widths may be different, that is, m of each first interdigital electrode 31 takes different values.

[0051] Preferably, the widths of the second to the Na-th first interdigital electrodes 31 are the same as the width of the first first interdigital electrode 31.

[0052] In an alternative embodiment, the terminal electrode group 4 includes Nb second interdigital electrodes 41. Along the arrangement direction of the second interdigital electrodes 41, the width of the first second interdigital electrode 41 is b, and the widths of the second to the Nb-th second interdigital electrodes 41 are (1 + n)*b, where the value range of n is -0.05 to 0.05.

[0053] That is to say, among the second to the Nb-th second interdigital electrodes 41, the width difference between any one second interdigital electrode 41 and the first second interdigital electrode 41 is within ±5%.

[0054] Specifically, the widths of the second to the Nb-th second interdigital electrodes 41 may be the same, that is, m of each second interdigital electrode 41 takes the same value, or the widths may be different, that is, m of each second interdigital electrode 41 takes different values.

[0055] Preferably, the widths of the second to the Nb-th second interdigital electrodes 41 are the same as the width of the first second interdigital electrode 41.

[0056] In addition, the selectable electrode materials for the first interdigital electrodes 31 and the second interdigital electrodes 41 include: gold, silver, aluminum, copper, platinum, titanium, chromium, tungsten, and alloys of two or more of the above materials.

[0057] In an alternative embodiment, the electric field direction formed by the first interdigital electrodes 31 and the second interdigital electrodes 41 forms an Euler angle with the +y-axis direction in the global coordinate system of the piezoelectric substrate 1, and the value range of the Euler angle is -90 to +90°.

[0058] In an alternative embodiment, the piezoelectric substrate 1 includes a support substrate and a piezoelectric layer. The support substrate is located on the bottom side of the piezoelectric layer, or the piezoelectric substrate 1 only includes the piezoelectric layer; both the transducer and the reflection grating 2 are disposed on the piezoelectric layer.

[0059] Among them, the material of the support substrate may be lithium tantalate crystal, lithium niobate crystal or quartz, etc., and the piezoelectric layer may include at least one of zinc oxide thin film, aluminum nitride thin film, lithium tantalate thin film, lithium niobate thin film, and quartz thin film.

[0060] Preferably, the piezoelectric substrate 1 is a single crystal lithium tantalate material, and the value range of the Euler angle is 36 to 50°.

[0061] Specifically, the thickness range of the support substrate is 100 um to 1 mm, and the thickness range of the piezoelectric layer is 100 nm to 1 um.

[0062] Taking Figures 1 to 3 as an example, the advantages of the above resonator are specifically described as follows:

[0063] As Figures 1 to 3 shown, each group of ground electrode groups 3 includes 2 first interdigital electrodes 31, and each group of terminal electrode groups 4 includes 2 second interdigital electrodes 41. Figure 6 is the simulated admittance diagram of the above structure, where the abscissa represents the frequency and the ordinate represents the resonator admittance value.

[0064] The calculation formula for the electromechanical coupling coefficient of the resonator is:

[0065]

[0066] From Figure 6 it can be seen that the resonance frequency fr of the resonator is 1006 MHz, and the anti-resonance frequency fa is 1035 MHz. It can be calculated that the electromechanical coupling coefficient K of this structure is 6.72%.

[0067] As a comparison, the conventional structure is simulated and analyzed. When each group of ground electrode groups 3 includes 1 first interdigital electrode 31 and each group of terminal electrode groups 4 includes 1 second interdigital electrode 41, Figure 7 is the simulated admittance diagram of the above structure, where the abscissa represents the frequency and the ordinate represents the resonator admittance value.

[0068] From Figure 7 it can be seen that the resonance frequency fr of the resonator is 985 MHz, and the anti-resonance frequency fa is 1026 MHz. It can be calculated that the electromechanical coupling coefficient K of this structure is 9.48%.

[0069] Comparing the two structures, the electromechanical coupling coefficient of the double interdigital structure is greatly reduced compared to the single interdigital structure, which is beneficial to the design of narrowband filters and can achieve narrowband filtering using conventional materials.

[0070] As Figure 4 and Figure 5 shown, each group of ground electrode groups 3 includes 3 first interdigital electrodes 31, and each group of terminal electrode groups 4 includes 3 second interdigital electrodes 41. Figure 8 is the simulated admittance diagram of the above structure, where the abscissa represents the frequency and the ordinate represents the resonator admittance value.

[0071] From Figure 8 it can be seen that the resonance frequency fr of the resonator is 1003 MHz, and the anti-resonance frequency fa is 1029 MHz. It can be calculated that the electromechanical coupling coefficient K of this structure is 6.1%.

[0072] Comparing the interdigital structure with the conventional single-finger structure, the electromechanical coupling coefficient of the interdigital structure is also greatly reduced compared to the single-finger structure, which is beneficial to the design of narrowband filters and enables narrowband filtering to be achieved using conventional materials.

[0073] In summary, without changing the piezoelectric substrate 1, by adjusting the interdigital electrode structure, a significant reduction in the electromechanical coupling coefficient can be achieved, which can solve the problem of few available materials and structures for existing narrowband filters. At the same time, it is suitable for surface acoustic wave filters made of most piezoelectric materials and has a low cost.

[0074] An embodiment of the second aspect of the present invention provides a narrowband surface acoustic wave filter, and the narrowband surface acoustic wave filter provided by the embodiment of the second aspect of the present invention includes the above resonator.

[0075] The narrowband surface acoustic wave filter provided by the second aspect of the present invention has the resonator provided by the embodiment of the first aspect of the present invention, and thus has all the beneficial effects of the resonator provided by the embodiment of the first aspect of the present invention.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A resonator, characterized in that: The invention comprises a piezoelectric substrate (1), a transducer and a reflection grating (2), wherein the transducer and the reflection grating (2) are both arranged on the piezoelectric substrate (1), the reflection grating (2) is located on both sides of the transducer, and the transducer has a plurality of groups of interdigitated electrodes, each group of the interdigitated electrodes comprises a grounding electrode group (3) and a terminal electrode group (4), the grounding electrode group (3) comprises a plurality of first interdigitated electrodes (31) arranged in sequence and used for grounding, and the terminal electrode group (4) comprises a plurality of second interdigitated electrodes (41) arranged in sequence and used for receiving electrical signals.

2. The resonator according to claim 1, characterized in that In the transducer, the ground electrode group (3) and the terminal electrode group (4) are arranged alternately, and the arrangement direction is parallel to the direction from the reflection grating (2) on one side to the reflection grating (2) on the other side.

3. The resonator according to claim 1, characterized in that Each of the grounding electrode groups (3) comprises 2 to 5 of the first interdigital electrodes (31), and each of the terminal electrode groups (4) comprises 2 to 5 of the second interdigital electrodes (41).

4. The resonator according to claim 1, characterized in that The thickness of the first interdigital electrode (31) and the second interdigital electrode (41) is 5 nm to 5 um; The width of the first interdigital electrode (31) and the second interdigital electrode (41) is 20 nm to 20 um; The length of the first interdigital electrode (31) and the second interdigital electrode (41) is 100 nm to 1000 um.

5. The resonator according to claim 1, characterized in that The grounding electrode group (3) comprises Na first interdigital electrodes (31), the width of the first first interdigital electrode (31) along the arrangement direction of the first interdigital electrodes (31) is a, the width of the second to Nath first interdigital electrodes (31) is (1+m)*a, and the value range of m is -0.05 to 0.

05.

6. The resonator according to claim 5, characterized in that The terminal electrode group (4) comprises Nb second interdigital electrodes (41), the width of the first second interdigital electrode (41) along the arrangement direction of the second interdigital electrodes (41) is b, and the widths of the second to Nb-th second interdigital electrodes (41) are (1+n)*b, and the value range of n is -0.05 to 0.

05.

7. The resonator according to claim 6, characterized in that The widths of the second to Na-th first interdigitated electrodes (31) are the same or different; The widths of the second to Nb-th second interdigital electrodes (41) are the same or different.

8. The resonator according to claim 1, characterized in that The direction of the electric field formed by the first interdigital electrode (31) and the second interdigital electrode (41) forms an Euler angle with the +y-axis direction in the global coordinate system of the piezoelectric substrate (1), and the value of the Euler angle is -90 to +90 degrees.

9. The resonator according to claim 1, characterized in that The piezoelectric substrate (1) comprises a supporting substrate and a piezoelectric layer, or the piezoelectric substrate (1) comprises a piezoelectric layer; The transducer and the reflection grating (2) are both arranged on the piezoelectric layer.

10. A narrow-band surface acoustic wave filter, characterized in that: Comprising a resonator as claimed in any one of claims 1 to 9.

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