Elastic Wave Filter and Multiplexer

Abstract

The present application relates to an elastic wave filter and multiplexer, and relates to the field of radio frequency. In the present application, there are m electrode fingers among the n electrode fingers of the IDT electrode of the capacitive resonator, and at least one of the ratio of the electrode finger width of any one of the m electrode fingers to the arithmetic average electrode finger width, the ratio of the electrode finger gap to the arithmetic average electrode finger gap, and the ratio of the electrode finger period to the arithmetic average electrode finger period falls within the following range: 0.8 to 0.99 or 1.01 to 1.2; there are p electrode fingers among the n electrode fingers, and the ratio of the electrode width of any one of the p electrode fingers to the arithmetic average electrode finger width, the ratio of the electrode finger gap to the arithmetic average electrode finger gap, and the ratio of the electrode finger period to the arithmetic average electrode finger period are not equal to those of the other p-1 electrode fingers. In this case, the elastic wave filter and multiplexer provided by the present application have a good out-of-band suppression level.

Description

Technical Field

[0001] The present application relates to the field of radio frequency technology, and in particular to an elastic wave filter and a multiplexer capable of improving the out-of-band suppression level. Background Art

[0002] Elastic wave devices, with their low cost, small size, and multifunctionality, have found widespread application in radar, communications, navigation, and other fields. The most commonly used elastic wave devices in mobile phone and base station communications are elastic wave filters, as well as elastic wave duplexers and multiplexers composed of multiple elastic wave filters. In any type of elastic wave filter, interdigital transducer electrodes (IDT electrodes) are placed on a piezoelectric functional material to define multiple series-arm resonators, parallel-arm resonators, and reflectors, as well as multiple series-arm and parallel-arm segments for electrical connection between the IDT electrodes. The bandpass characteristics are achieved by utilizing the frequency characteristics of the IDT electrode's conversion function, which converts electrical signals into elastic waves.

[0003] In the prior art, elastic wave filters based on piezoelectric substrates have received widespread attention due to their high Q-value performance. As is common knowledge, we often improve the rectangularity of elastic wave filters by adding capacitive resonators.

[0004] However, the capacitive resonator added to the common elastic wave filter will reduce the out-of-band suppression of the filter due to its own resonance effect, deteriorate the performance of the filter, and is not conducive to its application in 5G communications. Summary of the Invention

[0005] The purpose of this application is to provide an elastic wave filter and a multiplexer to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above objectives, the technical solutions adopted in this application are:

[0007] In a first aspect, the present application provides an elastic wave filter, comprising:

[0008] a piezoelectric substrate; and

[0009] a conductive material thin film pattern disposed on the piezoelectric substrate, comprising an input terminal, an output terminal, at least one ground terminal, a series arm, a parallel arm, and a series arm resonator, a parallel arm resonator, and a capacitive resonator formed by an IDT electrode and a reflector electrode;

[0010] The IDT electrode of the capacitive resonator includes n electrode fingers spaced apart along the propagation direction of the elastic wave, wherein n is a positive integer, each electrode finger has its own electrode finger width, electrode finger gap, and electrode finger period, the n electrode fingers have an arithmetic average electrode finger width, an arithmetic average electrode finger gap, and an arithmetic average electrode finger period, there are m electrode fingers among the n electrode fingers, and at least one of the ratio of the electrode finger width of any one of the m electrode fingers to the arithmetic average electrode finger width, the ratio of the electrode finger gap to the arithmetic average electrode finger gap, and the ratio of the electrode finger period to the arithmetic average electrode finger period falls within the following range:

[0011] 0.8 to 0.99 or 1.01 to 1.2;

[0012] m is any positive integer less than or equal to n, and m / n≥0.5;

[0013] There are p electrode fingers among the n electrode fingers, and the ratio of the electrode width of any one of the p electrode fingers to the arithmetic average electrode finger width, the ratio of the electrode finger gap to the arithmetic average electrode finger gap, and the ratio of the electrode finger period to the arithmetic average electrode finger period are not equal to those of the other p-1 electrode fingers, and p is any positive integer less than or equal to n, and p / n≥0.3.

[0014] In a possible implementation, the IDT electrode includes a plurality of first electrode fingers and a plurality of second electrode fingers that are interlaced with each other, and a first bus bar and a second bus bar that are opposite to each other in the extending direction of the first electrode fingers and the second electrode fingers;

[0015] Among them, multiple first electrode fingers and multiple second electrode fingers each have their own first end and second end; the first ends of multiple first electrode fingers are directly connected to the first bus bar, and the second ends of multiple first electrode fingers are spaced apart from the second bus bar; the first ends of multiple second electrode fingers are directly connected to the second bus bar, and the second ends of multiple second electrode fingers are spaced apart from the first bus bar.

[0016] In a possible implementation, a ratio of the electrode finger width of any electrode finger among the n electrode fingers to the electrode finger period is β, and 0.4≤β≤0.6.

[0017] In a possible implementation, the capacitive resonator only functions as a capacitor and does not have a resonance function within a specific frequency range, and the capacitive resonator has a reflector or does not have a reflector.

[0018] In a possible implementation, the piezoelectric substrate is a bulk material having piezoelectricity.

[0019] In one possible implementation, the piezoelectric substrate includes:

[0020] a piezoelectric layer, and a support substrate disposed directly beneath the piezoelectric layer; or

[0021] a piezoelectric layer, a low acoustic velocity layer disposed directly below the piezoelectric layer, and a supporting substrate disposed directly below the low acoustic velocity layer; or

[0022] A piezoelectric layer, a low acoustic velocity layer disposed directly below the piezoelectric layer, a trapping material layer disposed directly below the low acoustic velocity layer, and a support substrate disposed directly below the trapping material layer.

[0023] In one possible implementation, the sound velocity of the body wave propagating in the low sound velocity layer is lower than the sound velocity of the body wave propagating in the piezoelectric layer; the sound velocity of the body wave propagating in the supporting substrate is higher than the sound velocity of the body wave propagating in the piezoelectric layer.

[0024] In a possible implementation, the capture material layer is formed of one or more combinations of amorphous silicon, polycrystalline silicon, amorphous germanium, and polycrystalline germanium.

[0025] In a possible implementation, the IDT electrode is formed by stacking one or more metal material films.

[0026] In a second aspect, the present application provides a multiplexer, comprising:

[0027] an antenna terminal connected to the antenna; and

[0028] A plurality of filter devices are commonly connected to the antenna terminal, and at least one of the filter devices is any one of the elastic wave filters described above.

[0029] The beneficial effects of the technical solution provided by this application include at least:

[0030] In the present application, there are m electrode fingers among the n electrode fingers of the IDT electrode of the capacitive resonator, and at least one of the ratio of the electrode finger width of any one of the m electrode fingers to the arithmetic average electrode finger width, the ratio of the electrode finger gap to the arithmetic average electrode finger gap, and the ratio of the electrode finger period to the arithmetic average electrode finger period falls within the following ranges: 0.8 to 0.99 or 1.01 to 1.2; m is any positive integer less than or equal to n, and m / n ≥ 0.5; there are p electrode fingers among the n electrode fingers, and the ratio of the electrode width of any one of the p electrode fingers to the arithmetic average electrode finger width, the ratio of the electrode finger gap to the arithmetic average electrode finger gap, and the ratio of the electrode finger period to the arithmetic average electrode finger period are not equal to those of the other p-1 electrode fingers, p is any positive integer less than or equal to n, and p / n ≥ 0.3. In this case, the elastic wave filter and multiplexer provided by the present application have a good out-of-band suppression level. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings:

[0032] Figure 1 1 shows a top view of the elastic wave filter 100 provided in Comparative Example 1 of the present application;

[0033] Figure 2 It shows that when the piezoelectric substrate is a piezoelectric bulk material Figure 1 A-A' cross-sectional view;

[0034] Figure 3 It shows that when the piezoelectric substrate is a piezoelectric multilayer material Figure 1 A-A' cross-sectional view;

[0035] Figure 4 1 shows a schematic diagram of the topological structure of the elastic wave filter 100 provided in Comparative Example 1 of the present application;

[0036] Figure 5 1 shows a partial top view of the elastic wave filter 100 provided in Comparative Example 1 of the present application;

[0037] Figure 6 shows an insertion loss-frequency curve of the elastic wave filter 100 provided in Comparative Example 1 of the present application;

[0038] Figure 7 A partial structural diagram of the capacitive resonator C1 of the elastic wave filter provided in the first embodiment of the present application is shown;

[0039] Figure 8shows a curve diagram of changes in w and p of the capacitive resonator C1 of the elastic wave filter provided in the first embodiment of the present application before and after weighting;

[0040] Figure 9 The insertion loss-frequency curve of the elastic wave filter provided in the first embodiment of the present application is shown. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0042] Among them, the same parts are represented by the same figure marks. It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to the directions in the drawings of the present application specification, and the words "bottom" and "top", "inside" and "outside" refer to directions toward or away from specific parts, respectively. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present application specification, the meaning of "multiple" is two or more.

[0043] First, the prior art involved in the embodiments of the present application is introduced through comparative example 1.

[0044] Comparative Example 1:

[0045] Figure 1 FIG2 shows a top view of the elastic wave filter 100 provided in Comparative Example 1 of the present application. Figure 1 The direction parallel to the x-axis in the coordinate system is the direction of elastic wave propagation, and the definition is Figure 1 The direction parallel to the y-axis in the coordinate system is the extending direction of the electrode fingers, and the height direction of the elastic wave filter 100 is not shown.

[0046] Specifically, the elastic wave filter 100 includes a piezoelectric substrate 4 and a conductive thin film pattern disposed on the piezoelectric substrate 4. The conductive thin film pattern includes an input terminal 1, an output terminal 2, a first ground terminal 3a, a second ground terminal 3b, series-arm resonators (S1, S2, S3, S4) S1-S4, parallel-arm resonators (P1, P2, P3, P4) P1-P4, a capacitive resonator C1, a series arm 5a, and a parallel arm 5b. The capacitive resonator is not a series-arm resonator or a parallel-arm resonator; it serves solely as a capacitor in the elastic wave filter 100.

[0047] Figure 2 and Figure 3 Shown Figure 1 A-A' cross-sectional view of FIG. Figure 2 The piezoelectric substrate 4 is a piezoelectric bulk material (i.e., it only includes the piezoelectric layer 41). Figure 3 The piezoelectric substrate 4 is a piezoelectric multilayer material. Specifically, the piezoelectric multilayer material is composed of a piezoelectric layer 41 and a non-piezoelectric substrate 20. The non-piezoelectric substrate 20 is arranged below the piezoelectric layer 41, and includes: a low acoustic velocity layer 7, a capture material layer 8 and a supporting substrate 9 from top to bottom; or a low acoustic velocity layer 7 and a supporting substrate 9 from top to bottom; or a supporting substrate 9. The sound velocity of the body wave propagating in the low acoustic velocity layer 7 is lower than the sound velocity of the body wave propagating in the piezoelectric layer 41, and the sound velocity of the body wave propagating in the supporting substrate 9 is higher than the sound velocity of the body wave propagating in the piezoelectric layer 41. In the first comparative example of the present application, the piezoelectric layer 41 is implemented as a 170° YX-lithium niobate film.

[0048] In addition, the conductive material film pattern is arranged on the piezoelectric substrate 4, specifically Figure 1 All the patterns within the rectangular frame of the piezoelectric substrate 4 in FIG. The conductive thin film pattern includes multiple resonators (S1, S2, S3, S4, P1, P2, P3, P4, C1), input terminal 1, output terminal 2, first ground terminal 3a, second ground terminal 3b, series arm 5a, and parallel arm 5b.

[0049] Further, if Figure 1As shown, each resonator (S1, S2, S3, S4, P1, P2, P3, P4, C1) has a plurality of first electrode fingers and a plurality of second electrode fingers interlaced with each other, as well as a first bus bar and a second bus bar opposing each other in the direction in which the first and second electrode fingers extend. The plurality of first electrode fingers have two sets of ends, one of which is electrically connected to the first bus bar and the other is opposed to the second bus bar across a gap. The plurality of second electrode fingers have two sets of ends, one of which is electrically connected to the second bus bar and the other is opposed to the first bus bar across a gap. Simultaneously, a reflector is provided on each side of the series-arm resonator and the parallel-arm resonator along the direction of elastic wave propagation. Each reflector electrode includes a plurality of reflector electrode fingers and a third bus bar and a fourth bus bar opposing each other in the direction in which the plurality of reflector electrode fingers extend. One set of ends of the plurality of reflector electrode fingers is directly connected to the third bus bar, and the other set of ends is directly connected to the fourth bus bar. The plurality of first electrode fingers and the plurality of second electrode fingers include two sublayers formed by stacking a titanium thin film and an aluminum thin film, respectively. The titanium thin film sublayer is directly located on the piezoelectric substrate 4 and has a thickness of 5 nm. The aluminum thin film sublayer is directly located on the titanium thin film sublayer and has a thickness of 220 nm.

[0050] Figure 4 A schematic diagram of the topological structure of the elastic wave filter 100 provided in comparative example 1 of the present application is shown. The topological structure includes an input terminal 1, an output terminal 2, a first ground terminal 3a, a second ground terminal 3b, a series arm resonator (S1, S2, S3, S4), a parallel arm resonator (P1, P2, P3, P4), a capacitive resonator C1, a series arm 5a, and a parallel arm 5b. Series arm resonator, the resonator is connected in series between the input end and the output end. Parallel arm resonator, the resonator is connected to the ground by the node between the series resonators. Capacitive resonator, the resonator is connected in parallel to any series arm resonator or parallel arm resonator. It should be noted that the filter is bidirectional, and either the input end or the output end can be used as the input or output of the filter.

[0051] In order to show the local structure of the capacitor resonator C1 in more detail, Figure 5 A partial top view of the elastic wave filter 100 provided in the first comparative example of the present application is shown. Figure 2The portion of the dotted rectangular frame 6. The capacitive resonator C1 has a plurality of first electrode fingers and a plurality of second electrode fingers that are interlaced with each other, and a first bus bar and a second bus bar that are opposite to each other in the extension direction of the first electrode fingers and the second electrode fingers; the plurality of first electrode fingers have two groups of ends, one group of ends is electrically connected to the first bus bar, and the other group of ends is opposite to the second bus bar across a gap; the plurality of second electrode fingers have two groups of ends, one group of ends is electrically connected to the second bus bar, and the other group of ends is opposite to the first bus bar across a gap. The distance p between adjacent electrode fingers (first and second electrode fingers) is usually referred to as the "period" of the IDT. The width w of the first and second electrode fingers along the direction of elastic wave propagation is usually referred to as the "finger width" of the IDT. Optionally, a reflector is provided on each side of the capacitive resonator C1 along the direction of elastic wave propagation. The capacitive resonator C1 is placed on the piezoelectric substrate 4, and the line width of the electrode finger of the capacitive resonator C1 can be larger than or smaller than the line width of the electrode finger of the series arm resonator S3, depending on the required capacitance value.

[0052] It should be noted that the capacitive resonator in the filter only acts as a capacitor and does not resonate, and its resonant frequency is higher or lower than the operating frequency of the filter. Although it does not resonate, its resonant response still exists.

[0053] Figure 6 The insertion loss-frequency curve of elastic wave filter 100 provided in Comparative Example 1 of the present application is shown. As can be seen from the figure, the resonant response of capacitive resonator C1 in elastic wave filter 100 results in a large spurious mode on the right side of the passband, which degrades the filter's out-of-band suppression.

[0054] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0055] Example 1:

[0056] Based on the elastic wave filter 100 provided in the first comparative example, in order to suppress spurious signals on the right side of the passband, weighting processing of the IDT electrode is performed on the capacitive resonator C1. Figure 7 The figure shows a partial structural diagram of the capacitor resonator C1 of the elastic wave filter provided in the first embodiment of the present application, which is also the distinguishing feature between the first embodiment and the first comparative example. The dotted line portion is the position of the electrode finger after weighting. Based on the electrode fingers of the embodiment, a plurality of electrode fingers undergo a "random" small position and width transformation, so that the w and p of the capacitor resonator C1 of the embodiment are not constant. The benefit obtained by using this weighted processing is that the resonant response of the capacitor resonator C1 is greatly weakened.

[0057] In order to more intuitively display the changing trends of w and p, Figure 8 The following graph shows the variation of w and p in the capacitor resonator C1 of the elastic wave filter provided in Example 1 of the present application before and after weighting. The duty ratio of the IDT's w and p is commonly referred to as the IDT's "duty cycle." As can be seen from the graph, unlike the constant w and p of the IDT before weighting (Comparative Example 1), the w and p of the IDT after weighting (Example 1) undergo "random" small variations, but the IDT's "duty" remains constant before and after weighting.

[0058] In addition, this "random" weighting also has certain requirements for the amount of changes in the electrode fingers w and p. Preferably, more than 30% of the electrode fingers have "random" small changes in w and p.

[0059] Figure 9 The insertion loss-frequency curve of the elastic wave filter provided in Example 1 of the present application is shown. The dotted line is the insertion loss-frequency curve of the elastic wave filter in Comparative Example 1 for comparison. As can be seen from the figure, due to the weakened resonant response of the capacitive resonator C1, the elastic wave filter in Example 1 improves the out-of-band suppression on the right side of the passband by approximately 10dB compared to the elastic wave filter in Comparative Example 1, while ensuring that other frequency characteristics remain constant. This performance improvement is more conducive to the application of elastic wave filters in RF front-end structures.

[0060] In the embodiments disclosed herein, terms such as "installed," "connected," "connected," and "fixed" should be interpreted broadly. For example, "connected" may refer to a fixed connection, a detachable connection, or an integral connection; and "connected" may refer to a direct connection or an indirect connection via an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the embodiments disclosed herein based on specific circumstances.

[0061] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. An elastic wave filter, characterized in that: include: Piezoelectric substrate; as well as a conductive material thin film pattern disposed on the piezoelectric substrate, comprising an input terminal, an output terminal, at least one ground terminal, a series arm, a parallel arm, and a series arm resonator, a parallel arm resonator, and a capacitive resonator formed by an IDT electrode and a reflector electrode; The IDT electrode of the capacitive resonator includes n electrode fingers spaced apart along the propagation direction of the elastic wave, wherein n is a positive integer, each electrode finger has its own electrode finger width, electrode finger gap, and electrode finger period, the n electrode fingers have an arithmetic average electrode finger width, an arithmetic average electrode finger gap, and an arithmetic average electrode finger period, there are m electrode fingers among the n electrode fingers, and at least one of the ratio of the electrode finger width of any one of the m electrode fingers to the arithmetic average electrode finger width, the ratio of the electrode finger gap to the arithmetic average electrode finger gap, and the ratio of the electrode finger period to the arithmetic average electrode finger period falls within the following range: 0.8 to 0.99 or 1.01 to 1.2; m is any positive integer less than or equal to n, and m / n≥0.5; There are p electrode fingers among the n electrode fingers, and the ratio of the electrode width of any one of the p electrode fingers to the arithmetic average electrode finger width, the ratio of the electrode finger gap to the arithmetic average electrode finger gap, and the ratio of the electrode finger period to the arithmetic average electrode finger period are not equal to those of the other p-1 electrode fingers, and p is any positive integer less than or equal to n, and p / n≥0.

3.

2. The elastic wave filter according to claim 1, wherein The IDT electrode includes a plurality of first electrode fingers and a plurality of second electrode fingers interlaced with each other, and a first bus bar and a second bus bar facing each other in the extending direction of the first electrode fingers and the second electrode fingers; Among them, multiple first electrode fingers and multiple second electrode fingers each have their own first end and second end; the first ends of multiple first electrode fingers are directly connected to the first bus bar, and the second ends of multiple first electrode fingers are spaced apart from the second bus bar; the first ends of multiple second electrode fingers are directly connected to the second bus bar, and the second ends of multiple second electrode fingers are spaced apart from the first bus bar.

3. The elastic wave filter according to claim 1, wherein The ratio of the electrode finger width of any one of the n electrode fingers to the electrode finger period is β , and 0.4≤ β ≤0.

6.

4. The elastic wave filter according to claim 1, wherein The capacitive resonator only functions as a capacitor without a resonance function within a specific frequency range, and the capacitive resonator has a reflector.

5. The elastic wave filter according to claim 1, wherein The piezoelectric substrate is a bulk material having piezoelectricity.

6. The elastic wave filter according to claim 1, wherein The piezoelectric substrate comprises: a piezoelectric layer, and a support substrate disposed directly beneath the piezoelectric layer; or a piezoelectric layer, a low acoustic velocity layer disposed directly below the piezoelectric layer, and a supporting substrate disposed directly below the low acoustic velocity layer; or A piezoelectric layer, a low acoustic velocity layer disposed directly below the piezoelectric layer, a trapping material layer disposed directly below the low acoustic velocity layer, and a support substrate disposed directly below the trapping material layer.

7. The elastic wave filter according to claim 6, wherein: The acoustic velocity of the body wave propagating in the low acoustic velocity layer is lower than the acoustic velocity of the body wave propagating in the piezoelectric layer; The acoustic velocity of the bulk wave propagating in the supporting substrate is higher than the acoustic velocity of the bulk wave propagating in the piezoelectric layer.

8. The elastic wave filter according to claim 6, wherein The capture material layer is formed of one or more combinations of amorphous silicon, polycrystalline silicon, amorphous germanium, and polycrystalline germanium.

9. The elastic wave filter according to claim 1, wherein The IDT electrode is formed by stacking one or more metal material films.

10. A multiplexer comprising: an antenna terminal connected to the antenna; as well as A plurality of filter devices are commonly connected to the antenna terminal, and at least one of the filter devices is the elastic wave filter according to any one of claims 1 to 9.

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