Filter and duplexer

Abstract

A filter and a duplexer, which relate to the technical field of filtering devices. The filter comprises a plurality of resonators, which comprise a plurality of first resonators and a plurality of second resonators, wherein the plurality of first resonators are sequentially connected in series to form a series loop, and the plurality of second resonators are connected to the series loop in parallel to form a plurality of parallel loops. The resonators each comprise: a substrate; an acoustic reflection structure, which is located on the substrate; a seed layer, which is located on the substrate and covers the acoustic reflection structure; a bottom electrode, which is located on the seed layer; a piezoelectric layer, which is located on the bottom electrode; a top electrode, which is located on the piezoelectric layer; and a boundary ring, which is located on the top electrode, wherein an air gap located between the top electrode and the piezoelectric layer is formed at an edge of a resonance area of the resonator, the boundary ring is located in the resonance area, and the width of the boundary ring of at least one first resonator is greater than the width of the boundary ring of each of the other first resonators. The duplexer comprises the filter described above. The filter can significantly mitigate the near-passband suppression on the right side of the filter.

Description

Filter and duplexer

[0001] Cross-reference to related applications

[0002] The present application claims priority from the Chinese patent application No. 202410461548.X filed on April 16, 2024, and entitled "Filter and duplexer", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of filter devices, in particular to a filter and a duplexer. BACKGROUND

[0004] Radio frequency front-end filters, duplexers and multiplexers based on thin film bulk acoustic wave devices are widely used in smart phones, communication terminals and communication base stations due to their small size, low insertion loss, fast roll-off and low power consumption. Among them, a typical thin film bulk acoustic wave filter is composed of thin film bulk acoustic wave resonators in series and parallel forms. In the passband, the series thin film bulk acoustic wave resonators exhibit low resistance characteristics, and the parallel thin film bulk acoustic wave resonators exhibit high resistance characteristics, so the passband loss is small. Out of the passband, the series thin film bulk acoustic wave resonators exhibit high resistance characteristics, and the parallel thin film bulk acoustic wave resonators exhibit low resistance characteristics, so that the out-of-band suppression can be achieved.

[0005] With the continuous development of wireless technology, the communication frequency bands are increasing, the signals are becoming more and more crowded, and the protection bandwidth is becoming narrower, so higher requirements are put forward for the out-of-band suppression of the filter. At present, the methods for increasing the out-of-band suppression of the filter mainly include two kinds, which are increasing the thin layer mass load and increasing the inductance. However, the thin layer mass load is difficult to accurately control due to the short deposition time, which makes it difficult to mass produce; and although increasing the inductance can improve the out-of-band suppression at a specific frequency of the filter, the Q value of the inductance is generally not high, which is easy to worsen the near-band roll-off of the filter, so that the near-band suppression performance of the filter is limited. Therefore, how to provide a new solution to improve the near-band suppression problem of the filter is a difficult problem to be solved at present.

[0006] SUMMARY

[0007] The purpose of the present application is to provide a filter and a duplexer, which can significantly improve the right side near-band suppression of the filter.

[0008] Embodiments of the present application are implemented as follows:

[0009] In one aspect of the present application, a filter is provided, which includes a plurality of resonators, the plurality of resonators including a plurality of first resonators and a plurality of second resonators, the plurality of first resonators being connected in series to form a series loop, and the plurality of second resonators being connected in parallel to the series loop to form a plurality of parallel loops; a resonator includes a substrate, an acoustic reflecting structure on the substrate, a seed layer on the substrate and covering the acoustic reflecting structure, a bottom electrode on the seed layer, a piezoelectric layer on the bottom electrode, a top electrode on the piezoelectric layer, and a boundary ring on the top electrode; an air gap is formed between the top electrode and the piezoelectric layer at an edge of a resonance region of the resonator, the boundary ring is located within the resonance region, and a width of the boundary ring of at least one first resonator is greater than a width of the boundary ring of the rest of the first resonators. The filter can significantly improve the right side near-band rejection of the filter.

[0010] Optionally, an acute angle is provided between an outer peripheral wall of the bottom electrode and a bottom surface of the bottom electrode within the resonance region.

[0011] Optionally, the acute angle is between 15° and 60°.

[0012] Optionally, a right angle is provided between an outer peripheral wall of the top electrode and a bottom surface of the top electrode within the resonance region.

[0013] Optionally, an outer contour of a normal projection of the boundary ring on the top electrode coincides with an edge of the top electrode.

[0014] Optionally, the filter further includes an input matching inductor and an output matching inductor connected to opposite ends of the plurality of first resonators, and a ground inductor connected to a ground end of the second resonators.

[0015] Optionally, the acoustic reflecting structure is a first cavity formed in the substrate.

[0016] Alternatively, the substrate includes a first substrate, a second substrate, and an insulating layer between the first substrate and the second substrate; the second substrate is provided with a second cavity and a protection wall surrounding the second cavity, and the acoustic reflecting structure is the second cavity defined by the protection wall.

[0017] Alternatively, the acoustic reflecting structure is a Bragg reflecting layer formed on the substrate, the Bragg reflecting layer including low acoustic impedance layers and high acoustic impedance layers alternately and stacked.

[0018] Optionally, a width of the air gap of at least one first resonator is greater than a width of the air gap of the rest of the first resonators.

[0019] Optionally, the substrate is a silicon substrate, an SOI substrate, or a sapphire substrate.

[0020] In another aspect of the present application, a duplexer is provided, which includes the filter described above. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor based on these drawings.

[0022] Fig. 1 is a structural schematic diagram of a filter provided by some embodiments of the present application;

[0023] Fig. 2 is a structural schematic diagram of a resonator provided by some embodiments of the present application;

[0024] Fig. 3 is one of the top views of Fig. 2;

[0025] Fig. 4 is a structural schematic diagram of a resonator provided by some embodiments of the present application;

[0026] Fig. 5 is a top view of Fig. 4;

[0027] Fig. 6 is a structural schematic diagram of a resonator provided by some embodiments of the present application;

[0028] Fig. 7 is a diagram showing the relationship between the series resonant frequency of a resonator and the width of a boundary ring according to some embodiments of the present application;

[0029] Fig. 8 is a diagram showing the relationship between the parallel resonant frequency of a resonator and the width of a boundary ring according to some embodiments of the present application;

[0030] Fig. 9 is a simulation result diagram of a filter according to some embodiments of the present application;

[0031] Fig. 10 is a partial enlarged view of the simulation result in Fig. 9;

[0032] Fig. 11 is another top view of Fig. 2.

[0033] Fig. 11 is another top view of Fig. 2. DETAILED DESCRIPTION

[0034] The implementations set forth below represent the necessary information for enabling those skilled in the art to practice the implementations and illustrate best modes of practicing them. Upon reading the following description, one skilled in the art will understand how to implement the concepts in practice without undue experimentation. One skilled in the art will realize that the concepts can be practiced with embodiments other than those explicitly described.

[0035] It will be understood that, although the terms first, second, etc. can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0036] It will be understood that when an element such as a layer, region, or substrate is referred to as being "on" or extending "onto" another element, it can be directly on or extend directly onto the other element or intervening elements can also be present. In contrast, when an element such as a layer, region, or substrate is referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. It will be understood that elements shown in the figures are for illustration only and that, in reality, positions and other configurations of the elements can differ depending on the implementation.

[0037] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" can be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as shown in the figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0039] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0040] Please refer to FIG. 1 to FIG. 3, the embodiment provides a filter, the filter includes a plurality of resonators, the plurality of resonators includes a plurality of first resonators and a plurality of second resonators, the plurality of first resonators are sequentially connected in series to form a series loop, and the plurality of second resonators are connected in parallel on the series loop to form a plurality of parallel loops; the resonator includes a substrate 10, an acoustic reflection structure on the substrate 10, a seed layer 20 on the substrate 10 and covering the acoustic reflection structure, a bottom electrode 30 on the seed layer 20, a piezoelectric layer 40 on the bottom electrode 30, a top electrode 50 on the piezoelectric layer 40, and a boundary ring 60 on the top electrode 50; an air gap 70 between the top electrode 50 and the piezoelectric layer 40 is formed at the edge of the resonant region of the resonator, the boundary ring 60 is located in the resonant region, and the width d1 of the boundary ring of at least one first resonator is greater than the width d1 of the boundary ring of the remaining first resonators. The filter can significantly improve the right side near-band suppression of the filter.

[0041] The present application includes a plurality of resonators, wherein the plurality of resonators are a plurality of first resonators and a plurality of second resonators, please refer to FIG. 1, the plurality of first resonators are first resonator S1, first resonator S2, first resonator S3 and first resonator S4, and the plurality of first resonators are sequentially connected in series to form a series loop. It should be noted that the above-mentioned first resonators include four, which are only examples and not a limitation on the specific number of first resonators. In other embodiments, those skilled in the art can select other numbers of first resonators as needed.

[0042] The second resonators are respectively a second resonator P1, a second resonator P2, a second resonator P3 and a second resonator P4 in FIG. 1. The second resonators are connected in parallel to the above-mentioned series resonant circuit to form a plurality of parallel resonant circuits. The number of the second resonators is not limited in the present application, and the above-mentioned four second resonators are only examples.

[0043] The substrate 10 of the resonator can be a silicon substrate 10, an SOI substrate 10 or a sapphire substrate 10. Any one of the above-mentioned substrates 10 can be selected according to actual needs.

[0044] The acoustic reflection structure is located on the substrate 10, which can be located inside the substrate 10 or on the surface of the substrate 10, and the present application does not make specific limitations. For example, the acoustic reflection structure can be realized in the following three ways:

[0045] In the first possible implementation, the acoustic reflection structure can be a first cavity 11 formed in the substrate 10, as shown in FIGS. 2 and 3. The size of the first cavity 11 can be determined according to the resonant area of the resonator and other actual needs, and the present application does not make limitations.

[0046] In the second possible implementation, please refer to FIGS. 4 and 5, the substrate 10 includes a first substrate 12, a second substrate 13 and an insulating layer 14 located between the first substrate 12 and the second substrate 13; the second substrate 13 is provided with a second cavity 131 and a protection wall 15 surrounding the second cavity 131, and the acoustic reflection structure is the second cavity 131 defined by the protection wall 15.

[0047] That is, in this implementation, the acoustic reflection structure is located in the second substrate 13 and is defined by the protection wall 15 surrounding the second substrate 13. That is, the acoustic reflection structure is located in the protection wall 15.

[0048] In the third possible implementation, please refer to FIG. 6, the acoustic reflection structure is a Bragg reflection layer 16 formed on the substrate 10, and the Bragg reflection layer 16 includes low acoustic impedance layers 162 and high acoustic impedance layers 161 which are alternately and stacked.

[0049] The number of the high acoustic impedance layers and the low acoustic impedance layers 162 is not limited in the present application and can be determined according to actual needs. The acoustic reflection structure provided by the present application can be realized in any one of the above-mentioned structural forms, and the skilled in the art can determine according to actual needs.

[0050] The seed layer 20 is formed on the substrate 10 and covers the acoustic reflecting structure. When the acoustic reflecting structure is the first cavity 11, the seed layer 20 is formed on the exposed substrate 10 and covers the first cavity 11 as shown in Fig. 2; when the acoustic reflecting structure is the second cavity 131, the seed layer 20 is formed on the exposed second substrate 13 and covers the second cavity 131 as shown in Fig. 4; when the acoustic reflecting structure is the Bragg reflecting layer 16, the seed layer 20 is formed on the Bragg reflecting layer 16 as shown in Fig. 6.

[0051] The bottom electrode 30, the piezoelectric layer 40 and the top electrode 50 are formed on the seed layer 20 in sequence. It is to be noted that the areas where the acoustic reflecting structure, the bottom electrode 30, the piezoelectric layer 40 and the top electrode 50 overlap each other form the resonance areas of the resonators.

[0052] Further, the air gap 70 is formed between the top electrode 50 and the piezoelectric layer 40, and the air gap 70 is formed at the edge of the resonance area. As shown in Figs. 2, 4 and 6, the air gap 70 can be formed by arching the edge of the top electrode 50 upward so that the edge of the top electrode 50 does not contact the piezoelectric layer 40. The air gap 70 can be configured to reflect the lateral acoustic wave, thereby improving the Q value of the device.

[0053] The boundary ring 60 is formed in the resonance area as shown in Figs. 3, 5 and 11. In the embodiment, the width dl of the boundary ring of at least one of the first resonators is greater than the width dl of the boundary ring of the rest of the first resonators, that is, the width dl of the boundary ring of at least one of the first resonators in the series circuit is greater than the width dl of the boundary ring of the rest of the first resonators.

[0054] The boundary ring 60 can be configured to reflect the lateral acoustic wave, and in combination with the air gap 70, the reflection of the lateral acoustic wave can be further improved, thereby improving the Q value.

[0055] In addition, as shown in Fig. 7, the test results of the relationship between the series resonance frequency of the resonator and the width dl of the boundary ring show that the series resonance frequency of the resonator does not change substantially with the change of the width dl of the boundary ring.

[0056] As shown in Fig. 8, the test results of the relationship between the parallel resonance frequency of the resonator and the width dl of the boundary ring show that the parallel resonance frequency of the resonator decreases with the increase of the width of the boundary ring 60.

[0057] Therefore, as shown in Figs. 7 and 8, if a certain series resonator in the circuit of the filter has a greater width of the boundary ring 60 than the other series resonators, a lower parallel resonance frequency can be achieved, thereby forming a new inflection point or zero point at the proximity band of the filter, and further increasing the proximity band rejection of the filter.

[0058] Please refer to FIG. 9 and FIG. 10, by setting the boundary ring 60 and setting the width d1 of the boundary ring of at least one first resonator to be greater than the width d1 of the boundary ring of other first resonators, a turning point (the turning point is circled in FIG. 10) can be formed at the position of the right side passband of the filter, so that the right side passband suppression of the filter is obviously improved, for example, the suppression of the filter at 5.945GHz is improved from 56.995dB of the traditional scheme to 70.788dB. It can be seen that after using the filter provided by the present application, the right side passband suppression of the filter can be obviously improved.

[0059] In summary, the filter provided by the present application comprises a plurality of resonators, the plurality of resonators comprises a plurality of first resonators and a plurality of second resonators, the plurality of first resonators are sequentially connected in series to form a series loop, and the plurality of second resonators are connected in parallel to the series loop to form a plurality of parallel loops; the resonator comprises a substrate 10, an acoustic reflection structure located on the substrate 10, a seed layer 20 located on the substrate 10 and covering the acoustic reflection structure, a bottom electrode 30 located on the seed layer 20, a piezoelectric layer 40 located on the bottom electrode 30, a top electrode 50 located on the piezoelectric layer 40, and a boundary ring 60 located on the top electrode 50; an air gap 70 between the top electrode 50 and the piezoelectric layer 40 is formed at the edge of the resonant region of the resonator, the boundary ring 60 is located in the resonant region, and the width d1 of the boundary ring of at least one first resonator is greater than the width d1 of the boundary ring of the remaining first resonators. By setting the boundary ring 60 and the air gap 70, the present application can reflect transverse acoustic waves, thereby improving the device quality factor; by setting the boundary ring 60 and setting the width d1 of the boundary ring of at least one first resonator to be greater than the width d1 of the boundary ring 60 of other first resonators, a clear turning point can be formed at the position of the right side passband of the filter, so that the right side passband suppression of the filter is obviously improved.

[0060] Optionally, an acute angle is formed between the outer peripheral wall of the bottom electrode 30 and the bottom surface of the bottom electrode 30 in the resonant region. Please refer to FIG. 2, an included angle α is formed between the outer peripheral wall of the bottom electrode 30 and the bottom surface of the bottom electrode 30, and the included angle α is an acute angle.

[0061] Optionally, the acute angle is between 15° and 60°. For example, the acute angle can be 15°, 20°, 30°, 50° or 60°.

[0062] In order to make the performance of the filter better, optionally, a right angle is formed between the outer peripheral wall of the top electrode 50 and the bottom surface of the top electrode 50 in the resonant region, please refer to FIG. 2.

[0063] In addition, in the embodiment, the outer contour of the orthographic projection of the boundary ring 60 on the top electrode 50 coincides with the edge of the top electrode 50. That is, the outer edge of the boundary ring 60 is aligned with the edge of the top electrode 50, as shown in FIG. 2.

[0064] Referring back to FIG. 1, the filter further includes an input matching inductor L1 and an output matching inductor L2 connected to opposite ends of the plurality of first resonators, and a ground inductor connected to the ground end of the second resonator. The number of the ground inductors is the same as the number of the second resonators, and each ground end of the second resonators is grounded through a ground inductor. In the embodiment, the second resonator includes four resonators, and correspondingly, the ground inductors also include four ground inductors, namely, a ground inductor L3, a ground inductor L4, a ground inductor L5 and a ground inductor L6.

[0065] Of course, the filter further includes an input port and an output port, wherein the input port is located at the input end of the input matching inductor L1, and the output port is located at the output end of the output matching inductor L2. In the embodiment, the input matching inductor L1, the output matching inductor L2 and the plurality of ground inductors are configured to adjust the filter characteristics.

[0066] Referring to FIG. 11, the width d2 of the air gap of at least one first resonator is greater than the width d2 of the air gap of the remaining first resonators. The width d2 of the air gap of the first resonator can be referred to FIG. 11.

[0067] In another aspect of the present application, a duplexer is provided, which includes the filter described above. The specific structure of the filter and its technical effects have been described and explained in detail in the foregoing, and will not be repeated here. By using the filter designed as described above, the duplexer can form a clear inflection point at the position of the right side near band of the filter, so that the right side near band suppression of the filter can be significantly improved.

[0068] The above only describes optional embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

[0069] In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, various possible combinations will not be described again in the present application. Industrial applicability

[0070] The filter of the present application can reflect transverse acoustic waves, thereby improving the device quality factor; and can form a clear inflection point at the position of the right side near band of the filter, thereby improving the right side near band suppression of the filter.

Claims

1. A filter, characterized by, The filter comprises a plurality of resonators, the plurality of resonators comprising a plurality of first resonators and a plurality of second resonators, the plurality of first resonators being connected in series to form a series loop, and the plurality of second resonators being connected in parallel to the series loop to form a plurality of parallel loops; the resonator comprises a substrate, an acoustic reflecting structure on the substrate, a seed layer on the substrate and covering the acoustic reflecting structure, a bottom electrode on the seed layer, a piezoelectric layer on the bottom electrode, a top electrode on the piezoelectric layer, and a boundary ring on the top electrode; An air gap between the top electrode and the piezoelectric layer is formed at an edge of a resonance region of the resonator, the boundary ring is located in the resonance region, and the width of the boundary ring of at least one of the first resonators is greater than the width of the boundary ring of the remaining first resonators.

2. The filter of claim 1, wherein, An acute angle is formed between an outer peripheral wall of the bottom electrode and a bottom surface of the bottom electrode in the resonance region.

3. The filter of claim 2, wherein, The acute angle is between 15° and 60°.

4. The filter of claim 1, wherein, A right angle is formed between an outer peripheral wall of the top electrode and a bottom surface of the top electrode in the resonance region.

5. The filter of claim 1, wherein, The outer contour of the orthographic projection of the boundary ring on the top electrode coincides with the edge of the top electrode.

6. The filter of claim 1, wherein, The filter further comprises an input matching inductor and an output matching inductor connected to opposite ends of the plurality of first resonators, and a ground inductor connected to a ground end of the second resonator.

7. The filter according to any one of claims 1 to 6, characterized in that, The acoustic reflecting structure is a first cavity formed in the substrate; Alternatively, the substrate comprises a first substrate, a second substrate, and an insulating layer between the first substrate and the second substrate; the second substrate is provided with a second cavity and a protection wall surrounding the second cavity; and the acoustic reflecting structure is the second cavity defined by the protection wall. Alternatively, the acoustic reflecting structure is a Bragg reflecting layer formed on the substrate, the Bragg reflecting layer comprising low acoustic impedance layers and high acoustic impedance layers arranged alternately and in layers.

8. The filter of claim 1, wherein, The width of the air gap of at least one of the first resonators is greater than the width of the air gap of the remaining first resonators.

9. The filter of claim 1, wherein, The substrate is a silicon substrate, an SOI substrate, or a sapphire substrate.

10. A diplexer, characterized by The filter comprises the filter according to any one of claims 1 to 9. The filter comprises the filter according to any one of claims 1 to 9.

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