multiplexer

Abstract

The present application provides a multiplexer capable of simultaneously communicating signals of a plurality of frequency bands separated in frequency with low loss. The multiplexer is provided with an elastic wave filter having a first passband and a filter having a second passband, the center frequency of the second passband being 1.35 times or more the center frequency of the first passband, and the first elastic wave resonator connected closest to a common terminal in the elastic wave filter is provided with a piezoelectric substrate, an IDT electrode having a plurality of electrode fingers, and an insulating layer arranged to be embedded in the IDT electrode, in a case where the wavelength of the IDT electrode is λ and the film thickness of the insulating layer is t, the following relationship is satisfied: (t / λ)×100≤20.124×(fc2 / fc1) 2 -92.823×(fc2 / fc1)+119.41.

Description

Technical Field

[0001] This invention relates to multiplexers. Background Technology

[0002] Patent Document 1 discloses a demultiplexer (multiplexer) comprising: a first filter connected to a common junction and having a surface acoustic wave (SAW) filter and an SAW resonator; and a second filter connected to the common junction. By making the thickness of the dielectric film covering the SAW filter greater than the thickness of the dielectric film covering the SAW resonator, spurious emissions generated in the passband of the second filter can be reduced.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-220929

[0006] With the development of high-capacity and multi-band mobile communications, there is a demand for multiplexers that can communicate simultaneously with signals from multiple frequency bands that are more separated by frequency with low loss. Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Therefore, the present invention was made to solve the above-mentioned problems, and its object is to provide a multiplexer capable of simultaneously communicating signals of multiple frequency bands separated by frequency with low loss.

[0009] Technical solutions for solving the problem

[0010] One aspect of the present invention relates to a multiplexer comprising: a common terminal; an elastic wave filter connected to the common terminal, having a first passband including at least a portion of a first frequency band; and a first filter connected to the common terminal, having a second passband including at least a portion of a second frequency band, the center frequency of the second passband being at least 1.35 times the center frequency of the first passband. The elastic wave filter includes a plurality of elastic wave resonators, wherein the first elastic wave resonator connected closest to the common terminal among the plurality of elastic wave resonators comprises: a piezoelectric substrate having a first main surface containing lithium niobate; and an IDT (Interdigital Transducer) electrode disposed on the first main surface, having a plurality of first electrode fingers. A plurality of second electrode fingers, a first busbar electrode connecting one end of the plurality of first electrode fingers to each other, and a second busbar electrode connecting one end of the plurality of second electrode fingers to each other; and an insulating layer disposed on a first main surface and configured to embed IDT electrodes, in a first elastic wave resonator, when the wavelength of the IDT electrodes defined by the plurality of first electrode fingers or the plurality of second electrode fingers is set as λ, the film thickness of the insulating layer in the region between adjacent electrode fingers of the plurality of first electrode fingers and the plurality of second electrode fingers is set as t, the center frequency of the first passband is set as fc1, and the center frequency of the second passband is set as fc2, the following relationship is satisfied: (t / λ)×100≤20.124×(fc2 / fc1) 2 -92.823×(fc2 / fc1)+119.41.

[0011] Invention Effects

[0012] According to the present invention, a multiplexer is provided that can simultaneously communicate signals of multiple frequency bands separated by frequency with low loss. Attached Figure Description

[0013] Figure 1 This is a circuit diagram of the multiplexer involved in the implementation method.

[0014] Figure 2 This is a diagram showing the frequency relationships of the filters that constitute the multiplexer involved in the implementation.

[0015] Figure 3 These are top and cross-sectional views of the first elastic wave resonator according to the implementation method.

[0016] Figure 4 This is a cross-sectional view of the first elastic wave resonator involved in a variation of the implementation.

[0017] Figure 5 This is a graph showing the reflection characteristics of the elastic wave filter according to the embodiment.

[0018] Figure 6It is a graph showing the relationship between the center frequency ratio of the multiplexer involved in the embodiment and the film thickness-to-wavelength ratio of the first elastic wave resonator.

[0019] Explanation of reference numerals in the attached figures

[0020] 10: IDT electrode;

[0021] 11a, 11b: Electrode fingers;

[0022] 12a, 12b: Busbar electrodes;

[0023] 20A, 20B: Reflective electrodes;

[0024] 50: Piezoelectric substrate;

[0025] 50a, 51a, 51b: Main face;

[0026] 50A: Piezoelectric substrate;

[0027] 51: Piezoelectric layer;

[0028] 52: Low-sound-velocity layer;

[0029] 53: Hypersonic layer;

[0030] 54: Support base plate;

[0031] 60: Insulation layer;

[0032] 70: Dielectric layer;

[0033] 100: Multiplexer;

[0034] 101: Common terminal;

[0035] 102, 103, 104, 105, 201, 202: Input / output terminals;

[0036] 200: Elastic wave filter;

[0037] 210, 220, 230: Filters;

[0038] 211, 212, 213, 214: Series arm resonators;

[0039] 221, 222, 223: Parallel arm resonators. Detailed Implementation

[0040] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, the embodiments described below are either general or specific examples. The numerical values, shapes, materials, constituent elements, arrangements of constituent elements, and connection methods shown in the following embodiments are examples and are not intended to limit the scope of the invention.

[0041] Furthermore, the figures are schematic diagrams that have been appropriately emphasized, omitted, or proportionally adjusted for the purpose of illustrating the invention, and are not necessarily rigorous illustrations. Sometimes they differ from the actual shapes, positional relationships, and proportions. In the figures, substantially identical structures are labeled with the same reference numerals, and sometimes repeated descriptions are omitted or simplified.

[0042] In addition, terms such as "parallel" and "perpendicular" that indicate the relationship between elements, terms such as "rectangle" that indicate the shape of elements, and numerical ranges that do not only indicate strictness but also imply substantially equivalent ranges, such as including a few percent degree of error.

[0043] Furthermore, in this disclosure, the passband of the elastic wave device or elastic wave filter is defined as the frequency band between two frequencies that are 3 dB greater than the minimum insertion loss within that passband.

[0044] Furthermore, in the resonant characteristics of the elastic wave device disclosed herein, the resonant frequency and anti-resonant frequency are derived, for example, by contacting the two input and output terminals of the elastic wave device with an RF probe when the elastic wave device is not connected to other circuit elements, and measuring the reflection characteristics (impedance characteristics) using a network analyzer or the like.

[0045] Furthermore, in this disclosure, the term "main component of the material" refers to a component that accounts for more than 50% by weight in the material. The aforementioned main component may exist in any of the following states: single crystal, polycrystalline, and amorphous, or a mixture thereof.

[0046] Furthermore, in this disclosure, the term "frequency band" means at least one of an uplink operating frequency band and a downlink operating frequency band within a frequency band predefined by standardization organizations such as 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers), etc., for communication systems built using Radio Access Technology (RAT). In this embodiment, the communication system can be, for example, an LTE (Long Term Evolution) system, a 5G (5th Generation)-NR (New Radio) system, and a WLAN (Wireless Local Area Network) system, but is not limited to these. Additionally, the term "uplink operating frequency band" within a frequency band means the frequency range within that frequency band designated for uplink use. Furthermore, the term "downlink operating frequency band" within a frequency band means the frequency range within that frequency band designated for downlink use.

[0047] (Implementation Method)

[0048] [1 Circuit structure of multiplexer 100]

[0049] An example of the circuit structure of the multiplexer 100 involved in the implementation method will be described. Figure 1 This is a circuit diagram of the multiplexer 100 according to the embodiment. As shown in the figure, the multiplexer 100 includes an elastic wave filter 200, filters 210, 220 and 230, a common terminal 101, and input / output terminals 102, 103, 104 and 105. The common terminal 101 is connected to an antenna, for example.

[0050] The elastic wave filter 200 is connected between the common terminal 101 and the input / output terminal 102, and has a first passband that includes at least a portion of frequency band A (first frequency band). The first passband, for example, includes the receiving frequency band (A-Rx) of frequency band A. The elastic wave filter 200 is a trapezoidal bandpass filter comprising series arm resonators 211, 212, 213, and 214, parallel arm resonators 221, 222, and 223, and input / output terminals 201 and 202. Each of the series arm resonators 211-214 and the parallel arm resonators 221-223 is an elastic wave resonator. Detailed construction of the series arm resonators 211-214 and the parallel arm resonators 221-223 will be described later. Alternatively, the elastic wave filter 200 may not be a trapezoidal bandpass filter; for example, it may be an elastic wave filter with longitudinally coupled resonators.

[0051] Series arm resonators 211 to 214 are connected in series from input / output terminal 201 toward input / output terminal 202 in the series arm path connecting input / output terminals 201 and 202, in the order of series arm resonators 211, 212, 213, and 214. Series arm resonator 211 is an example of the first elastic wave resonator, and is connected closest to the common terminal 101 among the multiple elastic wave resonators constituting elastic wave filter 200. Parallel arm resonator 221 is connected between the connection node of series arm resonators 211 and 212 and ground. Parallel arm resonator 222 is connected between the connection node of series arm resonators 212 and 213 and ground. Parallel arm resonator 223 is connected between the connection node of series arm resonators 213 and 214 and ground.

[0052] Furthermore, the elastic wave filter 200 is not limited to a trapezoidal filter having four series arm resonators and three parallel arm resonators. The elastic wave filter 200 can also be a trapezoidal filter containing one or more series arm resonators and one or more parallel arm resonators. In addition, the first elastic wave resonator among the plurality of elastic wave resonators constituting the elastic wave filter 200 that is closest to the common terminal 101 can also be a parallel arm resonator.

[0053] Filter 210 is connected between common terminal 101 and input / output terminal 103, and has a third passband that includes at least a portion of frequency band B. The third passband, for example, includes the receive band (B-Rx) of frequency band B. Filter 210 can be an elastic wave filter, or it can be an LC filter, dielectric filter, etc., and the filter construction is arbitrary.

[0054] Filter 220 is connected between common terminal 101 and input / output terminal 104, and has a fourth passband that includes at least a portion of frequency band C. The fourth passband, for example, includes the receive band (C-Rx) of frequency band C. Filter 220 can be an elastic wave filter, or it can be an LC filter, dielectric filter, etc., and the filter construction is arbitrary.

[0055] Filter 230 is an example of a first filter, connected between common terminal 101 and input / output terminal 105, and for example has a second passband that includes at least a portion of frequency band D (the second frequency band). The second passband, for example, includes the receive band (D-Rx) of frequency band D. Filter 230 can be an elastic wave filter, or it can be an LC filter, dielectric filter, etc., and the filter construction is arbitrary.

[0056] Alternatively, filters 210 and 220 may not be included in multiplexer 100. Regarding the number of filters constituting multiplexer 100, as long as there are two or more, including elastic wave filter 200 and filter 230, it is acceptable.

[0057] Furthermore, at least one of the elastic wave filter 200 and filters 210 to 230 may also be a transmission filter having a passband that includes the transmission frequency band.

[0058] Figure 2 This is a diagram illustrating the frequency relationships of the filters constituting the multiplexer 100 according to the embodiment. The center frequency fc220 of the fourth passband of filter 220 and the center frequency fc230 of the second passband of filter 230 are each in a frequency range that is at least 1.35 times and less than 2 times the center frequency fc200 of the first passband of elastic wave filter 200. Furthermore, it is preferable that the center frequency fc220 of the fourth passband and the center frequency fc230 of the second passband are each in a frequency range that is greater than 1.4 times the center frequency fc200 of the first passband. Alternatively, the center frequency fc220 may not be in a frequency range that is at least 1.35 times and less than 2 times the center frequency fc200.

[0059] In this embodiment, frequency band A (first frequency band) is, for example, a composite frequency band including frequency bands n75 and n76 used for 5G-NR. Furthermore, frequency band B (second frequency band) is, for example, frequency band B3 used for LTE or frequency band n3 used for 5G-NR. Furthermore, frequency band C is, for example, frequency band B1 used for LTE or frequency band n1 used for 5G-NR. Furthermore, frequency band D is, for example, frequency band B7 used for LTE or frequency band n7 used for 5G-NR.

[0060] [2 Construction of elastic wave filter 200]

[0061] The construction of the series arm resonators 211 to 214 and the parallel arm resonators 221 to 223 constituting the elastic wave filter 200 will be described.

[0062] Figure 3 These are top and cross-sectional views of the series arm resonator 211 according to the embodiment. Figure 3 (a) is a view of the main surface 50a of the piezoelectric substrate 50 from the z-axis positive side (showing the insulating layer 60). Figure 3 (b) is Figure 3 A cross-sectional view at line III-III in (a). Figure 3 As shown, the series arm resonator 211 includes an IDT electrode 10, reflective electrodes 20A and 20B, a piezoelectric substrate 50, an insulating layer 60, and a dielectric layer 70.

[0063] IDT electrode 10 is disposed on the main surface 50a of piezoelectric substrate 50. For example... Figure 3 As shown in (a), the IDT electrode 10 has a plurality of electrode fingers 11a and a plurality of electrode fingers 11b and busbar electrodes 12a and 12b.

[0064] Multiple electrode fingers 11a are an example of multiple first electrode fingers, arranged parallel to each other. Multiple electrode fingers 11b are an example of multiple second electrode fingers, arranged parallel to each other. Multiple electrode fingers 11a and multiple electrode fingers 11b are arranged in parallel and interleaved with each other. Busbar electrode 12a is an example of a first busbar electrode, configured to connect one end of multiple electrode fingers 11a to each other. Busbar electrode 12a extends in a direction (x-axis direction) intersecting the extension direction (y-axis direction) of multiple electrode fingers 11a. Busbar electrode 12b is an example of a second busbar electrode, configured to connect one end of multiple electrode fingers 11b to each other. Busbar electrode 12b extends in a direction (x-axis direction) intersecting the extension direction (y-axis direction) of multiple electrode fingers 11b. Busbar electrodes 12a and 12b are arranged opposite each other, sandwiching multiple electrode fingers 11a and multiple electrode fingers 11b. The other end of the multiple electrode fingers 11a is opposite to the bus bar electrode 12b, and the other end of the multiple electrode fingers 11b is opposite to the bus bar electrode 12a.

[0065] Reflective electrodes 20A and 20B are disposed on both sides of IDT electrode 10 in a direction perpendicular to the extending direction of electrode fingers 11a and 11b (x-axis direction), such that they are adjacent to IDT electrode 10. Alternatively, at least one of the reflective electrodes 20A and 20B may not be disposed on both sides of IDT electrode 10.

[0066] The IDT electrode 10, the reflective electrode 20A, and the reflective electrode 20B can each be made of metals or alloys such as Ti, Al, Cu, Pt, Au, Ag, and Pd. Alternatively, they can be made of multiple layers of the aforementioned metals or alloys.

[0067] Here, the wavelength λ of the IDT electrode 10 is explained. The wavelength λ of the IDT electrode 10 is a unit of length defined by the repetition period of the electrode fingers 11a or 11b. The electrode finger spacing p of the IDT electrode 10 is half the wavelength λ. Furthermore, in the IDT electrode 10, when the spacing between adjacent electrode fingers is not fixed, the wavelength λ of the IDT electrode 10 is expressed as the average wavelength λ of the IDT electrode 10. AVE To define. Regarding the average wavelength λ of IDT electrode 10. AVE If the total number of electrode fingers 11a and 11b included in the IDT electrode 10 is set as Ni, and the distance between the center of the electrode finger at one end of the IDT electrode 10 located in the direction of elastic wave propagation and the electrode finger at the other end is set as Di, then it is defined as 2×Di / (Ni-1).

[0068] Furthermore, in the case where the IDT electrode 10 includes a so-called spaced-out electrode, the average wavelength λ is calculated... AVEWhen the total number of electrode fingers Ni is used, excluding the number of interval rejection electrodes, and the center-to-center distance Di is used, excluding the linewidth L of the interval rejection electrode and one of the two gaps (gap width S) adjacent to the interval rejection electrode. Furthermore, the interval rejection electrode includes a floating interval rejection electrode, a polarity reversal electrode, and a fill electrode. A floating interval rejection electrode is an electrode finger that is not connected to either of the two opposing busbar electrodes and is arranged parallel to the electrode finger connected to either of the two busbar electrodes. A polarity reversal electrode is an electrode finger that is connected to the same busbar electrode as the electrode fingers connected to its two sides and is arranged parallel to the electrode fingers on both sides. A fill electrode is an electrode finger that has a width at least twice the average electrode finger width of the electrode fingers other than the fill electrode and is arranged parallel to the electrode fingers other than the fill electrode.

[0069] The wavelength λ of the IDT electrode 10 can be measured by taking a top view of the main surface 50a of the piezoelectric substrate 50 on which the IDT electrode 10 is formed, and / or by taking a cross-section of the cross-section perpendicular to the extension direction of the electrode fingers 11a and 11b, using a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), or a transmission electron microscope (TEM), thereby measuring the line width and the gap width.

[0070] The piezoelectric substrate 50 is an example of a piezoelectric substrate, having a main surface 50a (first main surface) containing a piezoelectric single crystal. The piezoelectric substrate 50 is, for example, a single-crystal piezoelectric substrate containing lithium niobate. Alternatively, the piezoelectric substrate 50 may also be a single-crystal piezoelectric substrate containing lithium tantalate, quartz, or potassium nitride.

[0071] An insulating layer 60 is disposed on the main surface 50a and configured to embed the IDT electrode 10. More specifically, the insulating layer 60 is configured on the main surface 50a to cover the upper surfaces of the electrode fingers 11a and 11b of the IDT electrode 10, and the film thickness t60 of the insulating layer 60 in the region between the electrode fingers 11a and 11b is more than 90% of the film thickness t11 of the electrode fingers 11a and 11b. The insulating layer 60 is, for example, a layer with silicon dioxide (SiO2) as the main component. By adjusting the film thickness t60 of the insulating layer 60, spurious emissions generated on both the low-frequency and high-frequency sides of the resonant band of the series arm resonator 211 can be reduced.

[0072] In addition, preferably, the insulating layer 60 is configured on the main surface 50a such that the film thickness t60 is greater than or equal to the film thickness t11 of the electrode fingers 11a and 11b in the region between the electrode fingers 11a and 11b.

[0073] The dielectric layer 70 is configured to cover the insulating layer 60. The dielectric layer 70 is preferably a layer in which the velocity of the propagating bulk wave is higher than that of the bulk wave propagating on the piezoelectric substrate 50. For example, silicon nitride (SiN) or a material with silicon nitride as the main component can be used.

[0074] Alternatively, the series arm resonators 212-214 and the parallel arm resonators 221-223 may each have the same structure as the series arm resonator 211 described above, except for the electrode parameters of the IDT electrode 10 (wavelength λ, number of electrode finger pairs, electrode finger duty cycle, cross width, etc.) and the film thickness t60 of the insulating layer 60. In this case, the series arm resonators 211-214 and the parallel arm resonators 221-223 may also be formed on a common piezoelectric substrate 50.

[0075] In addition, in the series arm resonators 211-214 and the parallel arm resonators 221-223, the piezoelectric substrate 50 may also have a stacked structure including a piezoelectric layer, an intermediate layer and a support substrate. Figure 4 This is a cross-sectional view of a series arm resonator 211 according to a modified embodiment. The series arm resonator 211 according to this modified embodiment includes an IDT electrode 10 (in... Figure 4 The diagram shows electrodes 11a and 11b, and reflective electrodes 20A and 20B (in...). Figure 4 (Not shown in the figure), piezoelectric substrate 50A, insulating layer 60, and dielectric layer 70. Compared with the series arm resonator 211 of the embodiment, the only difference in the structure of the piezoelectric substrate 50A is that the series arm resonator 211 of this modification is that the structure is the same as that of the series arm resonator 211 of the embodiment. Hereinafter, the description of the series arm resonator 211 of this modification will be omitted for the sake of the same structure as that of the series arm resonator 211 of the embodiment, and the description will focus on the piezoelectric substrate 50A, which has a different structure.

[0076] like Figure 4 As shown, the piezoelectric substrate 50A is piezoelectric and includes a piezoelectric body layer 51, a low-velocity layer 52, a high-velocity layer 53, and a support substrate 54.

[0077] The piezoelectric layer 51 has a main surface 51a (first main surface) and a main surface 51b facing each other. The IDT electrode 10, the reflective electrodes 20A and 20B are disposed on the main surface 51a. The piezoelectric layer 51 can be made of, for example, lithium niobate or a material with the above materials as the main component. Alternatively, the piezoelectric layer 51 can also be made of lithium tantalate, quartz or potassium nitride as the main component.

[0078] The support substrate 54 is disposed on the main surface 51b side of the piezoelectric layer 51, and is a substrate that supports the piezoelectric layer 51, the IDT electrode 10, and the reflective electrodes 20A and 20B. The support substrate 54 may contain, for example, a non-oxide material, such as silicon (Si), silicon carbide (SiC), or materials with these materials as the main components. Since silicon and silicon carbide have high thermal conductivity, using these materials as the support substrate 54 can improve the heat dissipation of the series arm resonator 211.

[0079] A low-velocity sound layer 52 is disposed between the piezoelectric layer 51 and the support substrate 54, and is a layer in which the sound velocity of the propagating bulk wave is lower than that of the bulk wave propagating in the piezoelectric layer 51. The low-velocity sound layer 52 can be, for example, made of silicon oxide (e.g., silicon dioxide) or a material with silicon oxide as the main component.

[0080] Furthermore, as a material for the low-velocity layer 52, for example, dielectrics such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or silicon oxide with added fluorine, carbon, or boron, or materials with the above materials as the main component, can also be used.

[0081] The high-velocity acoustic layer 53 is disposed between the low-velocity acoustic layer 52 and the support substrate 54, and is a layer in which the velocity of the propagating bulk wave is higher than that of the bulk wave propagating in the piezoelectric layer 51. The high-velocity acoustic layer 53 can be, for example, made of silicon nitride (SiN) or a material in which silicon nitride is the main component.

[0082] Furthermore, materials used as the hypersonic layer 53 can include, for example, aluminum nitride (AlN), silicon nitride (SiN), zirconium oxide, cordierite, mullite, block talc, forsterite, spinel, celene, and other ceramics, alumina, silicon oxynitride, DLC (diamond-like carbon), diamond, and other dielectrics, or materials using the above materials as the main component. Additionally, the spinel contains an aluminum compound containing one or more elements selected from Mg, Fe, Zn, Mn, etc., and oxygen. Examples of the spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0083] According to the series arm resonator 211 of the modified example, compared with the elastic wave resonator using a single-layer piezoelectric substrate, the resonant frequency and the Q value at the anti-resonant frequency can be improved. That is, an elastic wave resonator with a high Q value can be constructed, and therefore, this elastic wave resonator can be used to construct a filter with low insertion loss.

[0084] Furthermore, the series arm resonators 212-214 and the parallel arm resonators 221-223 may each have the same structure as the series arm resonator 211 in the modified example, except for the electrode parameters of the IDT electrode 10 (wavelength λ, number of electrode finger pairs, electrode finger duty cycle, cross width, etc.) and the film thickness of the insulating layer 60. In this case, the series arm resonators 211-214 and the parallel arm resonators 221-223 may also be formed on a common piezoelectric substrate 50A.

[0085] [3 Thickness range of insulating layer 60 to reduce reflection loss]

[0086] Next, the thickness range of the insulating layer 60 in the elastic wave filter 200 for reducing reflection loss in the second and fourth passbands will be explained.

[0087] Figure 5 This is a graph showing the reflection characteristics of the elastic wave filter 200 according to the embodiment. The vertical axis of the same graph shows the reflection loss at the input and output terminals 201 of the elastic wave filter 200 unit. In addition, the film thickness-to-wavelength ratio (%) shown in the same graph is the ratio of the film thickness t60 of the insulating layer 60 to the wavelength λ of the series arm resonator 211 ((t60 / λ)×100).

[0088] like Figure 5 As shown, in the frequency band higher than the center frequency fc200 of the elastic wave filter 200, the reflection loss increases. With a film thickness-to-wavelength ratio of 28.3%, the frequency ratio (relative to the frequency of fc200) for the point M1 where the reflection loss reaches 1.5 dB is 1.42; with a film thickness-to-wavelength ratio of 24.0%, the frequency ratio for the point M2 where the reflection loss reaches 1.5 dB is 1.53; with a film thickness-to-wavelength ratio of 19.7%, the frequency ratio for the point M3 where the reflection loss reaches 1.5 dB is 1.71; and with a film thickness-to-wavelength ratio of 15.4%, the frequency ratio for the point M4 where the reflection loss reaches 1.5 dB is 1.92. In other words, the smaller the film thickness-to-wavelength ratio, the higher the frequency band where the reflection loss is below 1.5 dB expands.

[0089] In filters 220 and 230, which have a center frequency of 1.35 to 2 times relative to fc200, approximately one-third of the reflection loss (dB) of the elastic wave filter 200 at fc220 and fc230 is added to the insertion loss of the passband of filters 220 and 230. From this perspective, when receiving signals from at least one of the elastic wave filter 200 and filters 220 and 230 simultaneously, compared to receiving signals from a single filter, the insertion loss degradation of the passband of that filter should be less than 0.5 dB. In other words, the maximum reflection loss of the elastic wave filter 200 at fc220 and fc230 should be less than 1.5 dB.

[0090] according to Figure 5 For a filter that receives signals simultaneously with the elastic wave filter 200, it is preferable that its center frequency is further away from the higher frequency side relative to fc200, and the film thickness-to-wavelength ratio of the elastic wave filter 200 is smaller.

[0091] Figure 6 This is a graph showing the relationship between the center frequency ratio x of the multiplexer 100 according to the embodiment and the film thickness wavelength ratio y (%) of the series arm resonator 211. More specifically, the horizontal axis shows the center frequency ratio x (1.35 to 2.0) of the filters that receive signals simultaneously with the elastic wave filter 200, for example, including the center frequency ratio of filter 220 and elastic wave filter 200 (fc220 / fc200 = 1.45), and the center frequency ratio of filter 230 and elastic wave filter 200 (fc230 / fc200 = 1.80). Furthermore, the vertical axis shows the film thickness wavelength ratio y (%) where the reflection loss of the elastic wave filter 200 is 1.5 dB. Figure 6 In the middle, draw (black dots) according to Figure 5 The relationship between the center frequency ratio x and the film thickness wavelength ratio y (%) is obtained from the reflection characteristics of the series arm resonator 211 shown. Approximate formulas for these plotted points can be shown by Equation 1.

[0092] y = 20.124 × x 2 -92.823×x+119.41 (1.35≤x≤2.0) (Equation 1)

[0093] Equation 1 shows the film thickness-to-wavelength ratio y (%) where the reflection loss of the elastic wave filter 200 is 1.5 dB when the center frequency ratio x is between 1.35 and 2.0. Therefore, when the center frequency of the elastic wave filter 200 is set to fc1 and the center frequency of the filter simultaneously receiving the elastic wave filter 200 is set to fc2, the film thickness-to-wavelength ratio y (%) (= (t60 / λ) × 100) where the reflection loss of the elastic wave filter 200 is 1.5 dB or less can be shown by the following Equation 2.

[0094] (t60 / λ)×100≤20.124×(fc2 / fc1) 2 -92.823×(fc2 / fc1)+119.41 (Equation 2)

[0095] Therefore, by specifying the film thickness t60 of the insulating layer 60 of the first elastic wave resonator closest to the common terminal 101 in accordance with Equation 2 above, it is possible to provide a multiplexer 100 that can simultaneously communicate with at least one of the elastic wave filter 200 and filters 220 and 230, which are separated from the elastic wave filter 200 at a higher frequency side.

[0096] Among the multiple elastic wave resonators in the elastic wave filter 200, the reflection characteristics of the first elastic wave resonator, which is closest to the common terminal 101, have the greatest impact on the transmission characteristics of filters 210, 220, and 230. Therefore, by specifying the film thickness t60 of the insulating layer 60 of the first elastic wave resonator according to Equation 2 above, the degradation of the insertion loss of at least one of filters 220 and 230 can be more effectively suppressed.

[0097] Furthermore, in the series arm resonator 211, the film thickness t60 of the insulating layer 60 is preferably larger than the film thickness t11 of the electrode fingers 11a and 11b. This allows for the widespread suppression of spurious emissions from both the low-frequency and high-frequency sides of the first passband of the elastic wave filter 200.

[0098] Furthermore, not only the series arm resonator 211, but also all the elastic wave resonators (series arm resonators 211 to 214 and parallel arm resonators 221 to 223) in the elastic wave filter 200 can satisfy the relation of Equation 2.

[0099] This allows for a further reduction in reflection loss in the frequency band where the center frequency ratio of the elastic wave filter 200 is 1.35 to 2.0.

[0100] Furthermore, in this case, it is preferable that in each of the elastic wave resonators (series arm resonators 211-214 and parallel arm resonators 221-223) of the elastic wave filter 200, the film thickness t60 of the insulating layer 60 is greater than the film thickness t11 of the electrode fingers 11a and 11b. This allows for more extensive suppression of spurious signals on both the low-frequency and high-frequency sides of the first passband of the elastic wave filter 200.

[0101] [4. Effects, etc.]

[0102] As described above, the multiplexer 100 according to the embodiment includes: a common terminal 101; an elastic wave filter 200 connected to the common terminal 101, having a first passband including at least a portion of a first frequency band; and a filter 230 connected to the common terminal 101, having a second passband including at least a portion of a second frequency band, the center frequency fc2 of the second passband being at least 1.35 times the center frequency fc1 of the first passband. The elastic wave filter 200 includes a plurality of elastic wave resonators, and the first elastic wave resonator connected closest to the common terminal 101 among the plurality of elastic wave resonators includes: a piezoelectric substrate 50 having a main surface 50a, comprising lithium niobate; and an IDT electrode. An electrode 10, disposed on the main surface 50a, has a plurality of electrode fingers 11a, a plurality of electrode fingers 11b, a busbar electrode 12a connecting one end of the plurality of electrode fingers 11a to each other, and a busbar electrode 12b connecting one end of the plurality of electrode fingers 11b to each other; and an insulating layer 60, disposed on the main surface 50a and configured to embed the IDT electrode 10. In the first elastic wave resonator, when the wavelength of the IDT electrode 10 defined by the plurality of electrode fingers 11a or the plurality of electrode fingers 11b is set to λ, and the film thickness of the insulating layer 60 in the region between adjacent electrode fingers of the plurality of electrode fingers 11a and the plurality of electrode fingers 11b is set to t, the following relationship is satisfied:

[0103] (t / λ)×100≤20.124×(fc2 / fc1) 2 -92.823×(fc2 / fc1)+119.41 (Equation 3).

[0104] Therefore, by specifying the film thickness t of the insulating layer 60 according to Equation 3 above, it is possible to provide a multiplexer 100 that can simultaneously communicate with the elastic wave filter 200 and the filter 230, which is separated to the high-frequency side at a frequency ratio of more than 1.35 times that of the elastic wave filter 200, with low loss.

[0105] For example, in the multiplexer 100, in the first elastic wave resonator, the film thickness t of the insulating layer 60 in the region between adjacent electrode fingers of the plurality of electrode fingers 11a and the plurality of electrode fingers 11b is greater than the film thickness t11 of the plurality of electrode fingers 11a and the plurality of electrode fingers 11b.

[0106] Therefore, it can suppress spurious signals on both the low-frequency and high-frequency sides of the first passband of the elastic wave filter 200.

[0107] For example, in the multiplexer 100, the elastic wave filter 200 has multiple elastic wave resonators, each of which includes: a piezoelectric substrate 50 having a main surface 50a containing lithium niobate; an IDT electrode 10 disposed on the main surface 50a, having multiple electrode fingers 11a, multiple electrode fingers 11b, a busbar electrode 12a connecting one end of the multiple electrode fingers 11a to each other, and a busbar electrode 12b connecting one end of the multiple electrode fingers 11b to each other; and an insulating layer 60 disposed on the main surface 50a and configured to embed the IDT electrode 10. In each of the multiple elastic wave resonators, when the wavelength of the IDT electrode 10 defined by the multiple electrode fingers 11a or multiple electrode fingers 11b is set to λ, and the film thickness of the insulating layer 60 in the region between adjacent electrode fingers of the multiple electrode fingers 11a and multiple electrode fingers 11b is set to t, the relationship of Equation 3 is satisfied.

[0108] This allows for a further reduction in reflection loss in the frequency band where the center frequency ratio of the elastic wave filter 200 is above 1.35.

[0109] For example, in the multiplexer 100, in each of the plurality of elastic wave resonators, the film thickness t of the insulating layer 60 in the region between adjacent electrode fingers of the plurality of electrode fingers 11a and the plurality of electrode fingers 11b is greater than the film thickness t11 of the plurality of electrode fingers 11a and the plurality of electrode fingers 11b.

[0110] Therefore, it is possible to suppress spurious signals more broadly than the first passband of the elastic wave filter 200, both at lower and higher frequencies.

[0111] For example, in the multiplexer 100, the center frequency fc2 of the second passband is less than twice the center frequency fc1 of the first passband.

[0112] Therefore, by specifying the film thickness t of the insulating layer 60 according to Equation 3, it is possible to reduce the reflection loss in the frequency band with a center frequency ratio of 1.35 or higher and 2 or lower.

[0113] For example, in the multiplexer 100, the piezoelectric substrate 50 is a single-crystal piezoelectric substrate containing lithium niobate.

[0114] Therefore, by adjusting the film thickness t of the insulating layer 60, it is possible to reduce spurious emissions on both the low-frequency and high-frequency sides of the resonant band of the first elastic wave resonator, and further improve the frequency-temperature characteristics of the first elastic wave resonator.

[0115] For example, in the multiplexer involved in the modified example, the piezoelectric substrate 50A includes: a piezoelectric layer 51 having opposing main surfaces 51a and 51b; a support substrate 54 disposed on the main surface 51b side of the piezoelectric layer 51; a low-velocity layer 52 disposed between the piezoelectric layer 51 and the support substrate 54, having a volume wave velocity lower than that of the piezoelectric layer 51 and the support substrate 54; and a high-velocity layer 53 disposed between the low-velocity layer 52 and the support substrate 54, having a volume wave velocity higher than that of the low-velocity layer 52.

[0116] Therefore, compared with elastic wave resonators using a single-layer piezoelectric substrate, the resonant frequency and the Q value at the anti-resonant frequency can be improved. That is, a first elastic wave resonator with a high Q value can be constructed, and thus a filter with low insertion loss can be constructed using the first elastic wave resonator.

[0117] For example, in the multiplexer 100, the first frequency band includes at least one of the frequency band n75 and the frequency band n76 used for 5G-NR.

[0118] For example, in the multiplexer 100, the second frequency band is frequency band B1, frequency band B3 or frequency band B7 used for LTE, or frequency band n1, n3 or n7 used for 5G-NR.

[0119] (Other implementation methods)

[0120] The present invention has been described above with examples of embodiments and modifications, but the present invention is not limited to the above embodiments and modifications. Other embodiments implemented by combining any of the constituent elements in the above embodiments and modifications, as well as modifications that can be conceived by those skilled in the art by implementing the above embodiments and modifications without departing from the spirit of the present invention, are also included in the present invention.

[0121] Industrial availability

[0122] As a multiplexer configured at the front end, this invention can be widely used in communication devices such as portable telephones.

Claims

1. A multiplexer, comprising: Common terminal; An elastic wave filter, connected to the common terminal, has a first passband that includes at least a portion of a first frequency band; and The first filter, connected to the common terminal, has a second passband that includes at least a portion of the second frequency band. The center frequency of the second passband is more than 1.35 times the center frequency of the first passband. The elastic wave filter includes multiple elastic wave resonators. The first elastic wave resonator among the plurality of elastic wave resonators, which is closest to the common terminal, has the following features: A piezoelectric substrate having a first main surface containing lithium niobate; An interdigitated transducer (IDT) electrode is disposed on the first main surface and has a plurality of first electrode fingers, a plurality of second electrode fingers, a first busbar electrode connecting one end of the plurality of first electrode fingers to each other, and a second busbar electrode connecting one end of the plurality of second electrode fingers to each other; and An insulating layer is disposed on the first main surface and configured to embed the IDT electrode. In the first elastic wave resonator, when the wavelength of the IDT electrode defined by the plurality of first electrode fingers or the plurality of second electrode fingers is set to λ, the film thickness of the insulating layer in the region between adjacent electrode fingers of the plurality of first electrode fingers and the plurality of second electrode fingers is set to t, the center frequency of the first passband is set to fc1, and the center frequency of the second passband is set to fc2, the following relationship is satisfied: (t / λ)×100≤20.124×(fc2 / fc1) 2 -92.823×(fc2 / fc1)+119.41。 2. The multiplexer according to claim 1, wherein, In the first elastic wave resonator, the thickness of the insulating layer in the region between adjacent first electrode fingers and among the plurality of second electrode fingers is greater than the thickness of the plurality of first electrode fingers and among the plurality of second electrode fingers.

3. The multiplexer according to claim 1, wherein, Each of the plurality of elastic wave resonators has: A piezoelectric substrate having a first main surface containing lithium niobate; An IDT electrode is disposed on the first main surface and has a plurality of first electrode fingers, a plurality of second electrode fingers, a first busbar electrode connecting one end of the plurality of first electrode fingers to each other, and a second busbar electrode connecting one end of the plurality of second electrode fingers to each other. as well as An insulating layer is disposed on the first main surface and configured to embed the IDT electrode. In each of the plurality of elastic wave resonators, when the wavelength of the IDT electrode defined by the plurality of first electrode fingers or the plurality of second electrode fingers is set to λ, and the film thickness of the insulating layer in the region between adjacent electrode fingers of the plurality of first electrode fingers and the plurality of second electrode fingers is set to t, the following relationship is satisfied: (t / λ)×100≤20.124×(fc2 / fc1) 2 -92.823×(fc2 / fc1)+119.41。 4. The multiplexer according to claim 3, wherein, In each of the plurality of elastic wave resonators, the thickness of the insulating layer in the region between adjacent electrode fingers of the plurality of first electrode fingers and the plurality of second electrode fingers is greater than the thickness of the plurality of first electrode fingers and the plurality of second electrode fingers.

5. The multiplexer according to any one of claims 1 to 4, wherein, The center frequency of the second passband is less than twice the center frequency of the first passband.

6. The multiplexer according to any one of claims 1 to 5, wherein, The piezoelectric substrate is a single-crystal piezoelectric substrate containing lithium niobate.

7. The multiplexer according to any one of claims 1 to 5, wherein, The piezoelectric substrate comprises: A piezoelectric layer having a first main surface and a second main surface that are opposite to each other; A support substrate is disposed on the second main surface side of the piezoelectric layer; A low-velocity sound layer is disposed between the piezoelectric layer and the support substrate, and has a volume wave velocity lower than that of the piezoelectric layer and the support substrate. as well as A high-velocity layer is disposed between the low-velocity layer and the support substrate, and has a volume wave velocity higher than that of the low-velocity layer.

8. The multiplexer according to any one of claims 1 to 7, wherein, The first frequency band includes at least one of the frequency band n75 and the frequency band n76 used for 5G-NR.

9. The multiplexer according to any one of claims 1 to 8, wherein, The second frequency band is frequency band B1, frequency band B3 or frequency band B7 used for LTE, or frequency band n1, n3 or n7 used for 5G-NR.

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