Surface acoustic wave filter having mass-added film formed on electrode

Abstract

Provided is a surface acoustic wave filter having a mass-added film formed on a plurality of electrodes. The surface acoustic wave filter includes: a substrate on which a support substrate, an energy limiting layer, and a piezoelectric layer are stacked in this order; a first bus bar and a second bus bar extending in a first direction on the substrate and spaced apart from each other in a second direction perpendicular to the first direction; a plurality of IDT electrodes alternately extending in the second direction from the first bus bar and the second bus bar and spaced apart from each other in the first direction; and a mass additional film extending in the first direction to cover top surfaces of the plurality of IDT electrodes and a top surface of the substrate exposed between the plurality of IDT electrodes. The thickness of the mass addition film on the top surface of the substrate and the thickness of the mass addition film on the top surfaces of the plurality of IDT electrodes are different from each other.

Description

Technical Field

[0001] The present invention relates to a surface acoustic wave filter having a mass-added film formed on a plurality of electrodes, and more particularly to a surface acoustic wave filter capable of suppressing unnecessary lateral modes and spurious and improving insertion loss by forming a mass-added film in a form covering a plurality of alternately arranged interdigital transducer (IDT) electrodes. Background Art

[0002] Surface acoustic wave (SAW) refers to a wave that propagates along the surface of an elastic solid. The energy of the surface acoustic wave is concentrated near the surface and propagates, which is equivalent to a mechanical wave. A surface acoustic wave device is an electromechanical device that uses the interaction between surface acoustic waves and conduction electrons and uses surface acoustic waves transmitted to the surface of a piezoelectric crystal. Surface acoustic wave devices can be used in a very wide range of industrial applications including sensors, oscillators, filters, etc., and can be miniaturized and lightweight, with many advantages such as robustness, stability, sensitivity, low cost, and real-time performance.

[0003] Spurious may be generated due to the unwanted transverse modes of the SAW filter, and the performance may be adversely affected due to the increase in insertion loss. In order to reduce the transverse modes, a method of reducing the propagation speed of the surface acoustic wave by forming a piston at the end of each IDT electrode has been proposed.

[0004] Reference Figure 1A and 1B , showing a structure formed by overlapping pistons and alternatingly arranged IDT electrodes. Figure 1A The SAW filter shown is configured such that a mass addition film 40 is formed under each IDT electrode 30, and Figure 1B The SAW filter shown in the figure is configured to form a mass addition film 40 below the IDT electrode 30. Figure 1A Each mass additional film 40 shown in FIG. 1 is integrated together so that it is not separated. In this way, in the SAW filter according to the prior art, the piston structure can be implemented in various forms. Summary of the invention

[0005] Therefore, the present invention is proposed in view of the above problems, and its purpose is to provide a method for improving the Q factor and K by adding a mass additional film. 2 A SAW filter with excellent characteristics in reducing both transverse modes and spurious.

[0006] The technical problems of the present invention are not limited to the above-mentioned technical problems, and those skilled in the art will clearly understand other unmentioned technical problems from the following description.

[0007] To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a surface acoustic wave (SAW) filter having a mass addition film formed on a plurality of electrodes, the SAW filter comprising: a substrate on which a supporting substrate, an energy confinement layer and a piezoelectric layer are sequentially stacked; a first busbar and a second busbar extending along a first direction on the substrate and spaced apart from each other in a second direction perpendicular to the first direction; a plurality of IDT electrodes extending alternately from the first busbar and the second busbar along a second direction and spaced apart from each other in the first direction; a gap formed in a space between an end of an IDT electrode extending from the first busbar and the second busbar, or a space between an end of an IDT electrode extending from the second busbar and the first busbar; and a mass addition film extending along the first direction to cover top surfaces of the plurality of IDT electrodes, wherein when a width of the gap is G, a width in the first direction of an end portion of the IDT electrode formed in the gap due to an alignment error is a, and a thickness of the mass addition film on the IDT electrode is t, (a / G) / t is satisfied. 1 / 2 ≤0.08.

[0008] In some embodiments of the present invention, the density of the mass-added film may be 5 g / cm3 or less.

[0009] In some embodiments of the present invention, the SAW filter may further include: a first dummy electrode extending from the second busbar to face the end of the IDT electrode extending from the first busbar; a second dummy electrode extending from the first busbar to face the end of the IDT electrode extending from the second busbar, wherein the gap may be formed in the space between one end of the IDT electrode extending from the first busbar and the first dummy electrode and in the space between one end of the IDT electrode extending from the second busbar and the second dummy electrode.

[0010] In some embodiments of the present invention, the mass-added film may extend along the first direction to cover one end of the plurality of IDT electrodes.

[0011] In some embodiments of the present invention, the plurality of IDT electrodes may include: a plurality of first IDT electrodes, which extend from the first bus bar along the second direction and are separated from each other in the first direction; and a plurality of second IDT electrodes, which extend from the second bus bar along the second direction, are separated from each other in the first direction, and are arranged alternately with the plurality of first IDT electrodes, wherein the mass addition film may include: a first mass addition film, which covers one end of the plurality of first IDTs; and a second mass addition film, which covers one end of the plurality of second IDTs.

[0012] In some embodiments of the present invention, the mass-adding film may include at least one of SiO2, Ta2O5, and Al2O3.

[0013] In some embodiments of the present invention, the thickness of the mass-adding film on the top surface of the plurality of IDT electrodes may be greater than the thickness of the mass-adding film on the top surface of the substrate.

[0014] In some embodiments of the present invention, the thickness of the mass-adding film on the top surface of the substrate may be 95% or less of the thickness of the mass-adding film on the top surfaces of the plurality of IDT electrodes.

[0015] In some embodiments of the present invention, the mass-added film may extend in an integral form across the plurality of IDT electrodes so as to completely fill the region between the plurality of IDT electrodes.

[0016] In order to achieve the above-mentioned purpose, according to another aspect of the present invention, a surface acoustic wave filter having a mass addition film formed on a plurality of electrodes is provided, the SAW filter comprising: a substrate; a plurality of IDT electrodes formed on the substrate and extending alternately from a first busbar and a second busbar facing each other; at least one reflector formed on the substrate and adjacent to the plurality of IDT electrodes; and a mass addition film extending to cover the top surfaces of the plurality of IDT electrodes, the top surface of the substrate exposed between the plurality of IDT electrodes, and at least a portion of the reflector, wherein the thickness of the mass addition film on the top surface of the substrate and the thickness of the mass addition film on the top surfaces of the plurality of IDT electrodes are different from each other.

[0017] In some embodiments of the present invention, the mass-added film may cover at least a portion of an outermost electrode of at least one reflector and may be formed to have a top surface having a square or elliptical shape.

[0018] In some embodiments of the present invention, a portion of the mass-added film on the plurality of IDT electrodes and a portion of the mass-added film on the reflector may be spaced apart from each other.

[0019] Details of other specific embodiments are included in the detailed description and accompanying drawings.

[0020] According to a surface acoustic wave filter having a mass added film formed on a plurality of IDT electrodes according to an embodiment of the present invention, since the mass added film is formed to cover one end of the plurality of IDT electrodes, unnecessary lateral modes and spurious signals can be suppressed and insertion loss can be reduced.

[0021] In addition, since the surface acoustic wave filter of the present invention forms the mass-added film on the top of the electrode instead of the bottom, it is possible to prevent the Q value and K 2 The value is reduced, and since the mass additional film is formed as a linear pattern formed integrally, rather than a dot pattern arranged only on the top of each electrode, the increase in alignment difficulty and manufacturing cost can also be suppressed.

[0022] The effects of the present invention are not limited to the above-mentioned effects, and those skilled in the art will clearly understand other unmentioned effects from the description of the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figures 1A to 1B is a diagram illustrating a surface acoustic wave (SAW) filter including a piston structure according to the prior art.

[0024] Figure 2 is a top view showing a surface acoustic wave filter having mass added films formed on a plurality of electrodes according to one embodiment of the present invention.

[0025] Figure 3 is along Figure 2 Cross-sectional view along line A-A'.

[0026] Figure 4 and 5 Along Figure 2 Cross-sectional views along lines BB' and CC'.

[0027] Figure 6 and 7 FIG. 1 is a diagram for explaining the effect of a surface acoustic wave filter having a mass added film formed on a plurality of electrodes according to an embodiment of the present invention.

[0028] Figure 8 FIG. 1 is a diagram for explaining the effect of the thickness ratio of the mass-added film in the surface acoustic wave filter according to one embodiment of the present invention.

[0029] Figures 9 to 12 are diagrams illustrating surface acoustic wave filters according to various embodiments of the present invention.

[0030] Fig.13A and 13B The diagram is a diagram for explaining the effect of the misaligned formation of the mass adding film when the mass adding film is formed on the top of the IDT electrode and the top of the piezoelectric body in the SAW filter according to one embodiment of the present invention.

[0031] Fig.14 is a graph showing the tolerance range of the alignment error of the mass added film density where the stray amplitude is less than 10 dB.

[0032] Fig.15 is a graph showing the misalignment width value (horizontal axis) of the mass addition film normalized by λ determined by the interval between the first IDT electrode and the second IDT electrode, and the measured amplitude of a spurious mode that can be formed in the surface acoustic wave filter when the thickness of the mass addition film is changed.

[0033] Fig.16A table showing a correlation derived using the misalignment width value of the mass-addition film normalized by λ determined by the interval between the first IDT electrode and the second IDT electrode and the thickness value of the mass-addition film is shown.

[0034] Description of symbols

[0035] 100, 1000, 1500, 1600: SAW filter

[0036] 110: Base plate 120, 125: Busbar

[0037] 130, 135: IDT electrode 140, 145: quality additional film

[0038] 150, 155: dummy electrodes 1200, 1300: reflectors DETAILED DESCRIPTION

[0039] The advantages and features of the present invention and the methods for achieving these advantages and features will become clear through the embodiments described in detail below and the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and will be implemented in various different forms. These embodiments are only used to make the disclosure of the present invention complete and fully inform those skilled in the art of the scope of the present invention, which is defined by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

[0040] When a component is said to be "connected" or "coupled" to another component, it includes both the case where it is directly connected or coupled to the other component and the case where other components are interposed therebetween. On the contrary, when a component is said to be "directly connected to" or "directly coupled to" another component, it indicates that no other components intervene. "And / or" includes each of the items mentioned and all combinations of one or more of the items.

[0041] The terms used in this specification are intended to describe embodiments rather than to limit the present invention. In this specification, singular forms also include plural forms unless otherwise specified in the article. The terms "include" and / or "comprising..." used in this specification mean that the components, steps, operations and / or elements mentioned do not exclude the existence or addition of one or more other components, steps, operations and / or elements.

[0042] Although the words "first", "second", etc. are used to describe different components, these components are certainly not limited by these terms. These terms are only used to distinguish one component from other components. Therefore, it goes without saying that the first component mentioned below can also be the second component within the technical spirit of the present invention.

[0043] Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used as the meanings generally understood by those skilled in the art. In addition, unless clearly and specifically defined, terms defined in commonly used dictionaries will not be idealized or over-interpreted.

[0044] Figure 2 1 is a diagram of a surface acoustic wave (SAW) filter 100 having a mass added film formed on a plurality of electrodes according to an embodiment of the present invention, Figures 3 to 5 Along Figure 2 Cross-sectional views along lines A-A', B-B' and CC'.

[0045] Reference Figures 2 to 5 According to an embodiment of the present invention, a surface acoustic wave (SAW) filter 100 having a mass addition film formed on a plurality of electrodes may include a substrate 110, a first bus bar 120, a second bus bar 125, a plurality of first IDT electrodes 130, a plurality of second IDT electrodes 135, a first mass addition film 140, and a second mass addition film 145.

[0046] The substrate 110 may be a multi-layer substrate including a plurality of layers. Although these layers may include, for example, a support substrate including silicon, a high acoustic velocity film including amorphous silicon a-Si or polycrystalline silicon, a low acoustic velocity film including silicon dioxide SiO2, and a piezoelectric film including a material such as LiTaO3 (LT) or LiNbO3 (LN) located on the top of the low acoustic velocity film, i.e., the uppermost layer, the present invention is not limited thereto, and a plurality of layers are omitted in the figure and shown as the substrate 110.

[0047] The first bus bar 120 and the second bus bar 125 extend in the first direction D1 and are spaced apart from each other in the second direction D2 , and may be disposed on the substrate 110 .

[0048] The first busbar 120 can be configured to include, for example, at least one or more materials selected from metals such as aluminum (Al) or an alloy film containing aluminum, copper (Cu), tungsten (W), molybdenum (Mo), gold (Au), silver (Ag), palladium (Pd), nickel (Ni), and metal materials such as titanium (Ti), magnesium (Mg), zinc (Zn), cadmium (Cd), scandium (Sc) and ruthenium (Ru).

[0049] The second busbar 125 may also include a similar conductive material as the first busbar 120 , and when the first busbar 120 and the second busbar 125 are formed by the same deposition process or other similar processes, the first busbar 120 and the second busbar 125 may be configured to include the same material.

[0050] The plurality of first IDT electrodes 130 may be configured to extend from the first bus bar 120 in the second direction D2. In addition, the plurality of second IDT electrodes 135 may be configured to extend from the second bus bar 125 in the second direction D2.

[0051] A plurality of first IDT electrodes 130 and second IDT electrodes 135 may be spaced apart from each other in the first direction D1 , and one first IDT electrode 130 and another IDT electrode 135 may be alternately arranged adjacent to each other.

[0052] The plurality of first IDT electrodes 130 and the second IDT electrodes 135 may include a conductive material. The plurality of first IDT electrodes 130 may be formed as one body with the first bus bar 120, and the plurality of second IDT electrodes 135 may be formed as one body with the second bus bar 125. That is, each of the IDT electrodes 130 and 135 may be formed simultaneously by the same process as the bus bars 120 and 125, such as a deposition process, and one end of the IDT electrode is connected to the bus bars 120 and 125.

[0053] The first mass additional film 140 may extend in the first direction D1 to pass through the plurality of first and second IDT electrodes 130 and 135. The first mass additional film 140 may be formed to cover the top surfaces of the plurality of first and second IDT electrodes 130 and 135, and the top surface of the substrate 110 exposed between the plurality of first and second IDT electrodes 130 and 135. In addition, the first mass additional film 140 is formed to cover the top surface of one end 131 of the plurality of first IDT electrodes 130, where the one end 131 refers to the other end of one end of the first IDT electrode 130 connected to the first bus bar 120 shown in the figure.

[0054] The first mass additional film 140 may be integrally formed to extend across the plurality of first and second IDT electrodes 130 and 135. That is, the first mass additional film 140 passes through the plurality of first and second IDT electrodes 130 and 135 and completely fills the region between the plurality of electrodes to form a linear pattern shape.

[0055] The first mass additional film 140 may include an insulator. As the density increases, in order to effectively suppress spurious emission, the thickness of the first mass additional film 140 needs to be reduced.

[0056] In some embodiments of the present invention, the first mass additional film 140 is formed such that the deposition thickness on the substrate 110 is different from the deposition thickness on the first IDT electrode 130. In more detail, referring to Figure 3, the second thickness t2 of the first mass additional film 141 covering the top surface of the first IDT electrode 130 or the second IDT electrode 135 is greater than the first thickness t1 of the first mass additional film 142 covering the top surface of the substrate 110. That is, in the deposition process of forming the first mass additional film 140 when the substrate 110 and the first IDT electrode 130 have been formed, the deposition rate is adjusted by controlling the gas amount (e.g., flow rate), input power, deposition atmosphere, etc., whereby the first mass additional films 141 and 142 with different thicknesses can be formed according to the deposition position.

[0057] Figure 6 is a top view showing a SAW filter according to another embodiment of the present invention, Figure 7 is shown along Figure 6 Cross-sectional view of the SAW filter along line AA'.

[0058] Reference Figure 6 In the SAW filter 200 according to another embodiment of the present invention, the first mass additional film 240 may be formed to cover the first IDT electrodes 230 and the second IDT electrodes 235 without covering the top surface of the substrate 210 exposed between the plurality of first IDT electrodes 230 and the second IDT electrodes 235. That is, the first mass additional film 240 may be formed in a dot shape on the first IDT electrodes 230 and the second IDT electrodes 235 and aligned in the first direction D1 and spaced apart from each other.

[0059] The second mass additional film 245 may also be formed to cover the first IDT electrode 230 and the second IDT electrode 235 without covering the top surface of the substrate 210 exposed between the plurality of first IDT electrodes 230 and the second IDT electrodes 235. At this time, the first mass additional film 240 and the second mass additional film 245 may be formed to be spaced apart from each other in the second direction D2, and the first mass additional film 240 and the second mass additional film 245 may be formed on one first IDT electrode 230 and spaced apart from each other in the second direction D2. At this time, the second mass additional film 245 may be formed at one end, i.e., the edge portion, of the first IDT electrode 230, and the first mass additional film 240 may be formed at the edge portion of the second IDT electrode 235. Since the configurations of the first mass additional film 240 and the second mass additional film 245 are the same as those described above with reference to Figures 2 to 6 The mass adding films 140 and 145 included in the SAW filter 100 described in hereinafter are the same except that the first mass adding film 240 and the second mass adding film 245 do not cover the top surface of the substrate 210, and other detailed descriptions will be omitted.

[0060] like Figure 7As shown, the first mass additional film 240 may be formed only on the first IDT electrode 230 or the second IDT electrode 235. At this time, although the side profile of the first mass additional film 240 may match the side profile of the first IDT electrode 230 or the second IDT electrode 235, the present invention is not limited thereto.

[0061] More specifically, refer to Figure 8 , the first IDT electrode 230 and the first mass additional film 240 may have a tapered side surface through an etching process when they are formed. That is, the cross-sectional shape of the first IDT electrode 230 and the first mass additional film 240 is close to a trapezoid whose width narrows toward the top surface. At this time, the first IDT electrode 230 and the first mass additional film 240 may be formed so that the bottom width of the first mass additional film 240 matches the top width of the first IDT electrode 230. At the same time, as Figure 8 As shown, although they may be formed such that a top surface end of the first IDT electrode 230 matches a bottom surface end of the first mass addition film 240 , a side profile of the first IDT electrode 230 and a side profile of the first mass addition film 240 may not match each other.

[0062] For example, Figure 8 As shown, the angle formed between the side wall 231 of the first IDT electrode and the bottom surface (the top surface of the substrate 210) and the angle formed between the side wall 241 of the first mass additional film and the bottom surface (the top surface of the first IDT electrode 230) can be different from each other. However, the present invention is not limited to this, and it is entirely possible that the side walls of the first IDT electrode 230 and the first mass additional film 240 can be aligned on a straight line like one structure, because the side wall profiles of the first IDT electrode 230 and the first mass additional film 240 can match each other according to the process conditions for forming the first IDT electrode 230 and the first mass additional film 240. In addition, referring to Figures 1A to 1B as well as Figures 9 to 10 , the effects that can be obtained by setting the thickness condition of the first mass additional film 140 as described above in the SAW filters 100 and 200 according to the embodiments of the present invention are described in more detail.

[0063] Fig. 9 and 10 1 and 10 are diagrams for explaining the effect of the position and shape of the mass addition film on the SAW filter according to the embodiment of the present invention.

[0064] Reference Fig. 9 and 10 , the graph shows the Q factor measured in the SAW filter with piston structure for four cases ( Fig. 9 ) and K 2 ( Fig.10The red curve shows the Q factor and K measured in the structure of forming a mass addition film covering multiple IDT electrodes and the top surface of the substrate as described in the embodiment of the present invention. 2 The green curve shows the structure in which a mass additional film is formed only under each of the multiple IDT electrodes ( Figure 1A ) measured in Q factor and K 2 The yellow curve shows the structure with a mass-added film formed integrally under multiple IDT electrodes ( Figure 1B ) measured in Q factor and K 2 The blue curve shows the structure in which the mass additional film is formed only on the multiple IDT electrodes without forming the mass additional film on the top surface of the substrate ( Figure 7 ) measured in Q factor and K 2 value.

[0065] First, if Figure 1A and 1B As shown, in the structure in which a mass additional film is formed under each of the plurality of IDT electrodes, it can be determined that due to the Q value and K 2 The decrease in value leads to a decrease in filter performance. Since the mass addition film is formed of an insulator such as SiO2, SiN, Ta2O5 or Al2O3 and is used for insulation of multiple IDT electrodes, Q and K are reduced compared to the case where the IDT electrodes are directly connected to the piezoelectric substrate. 2 In particular, the decrease in Q value is in the yellow curve, i.e., in Figure 1B This is more obvious in the structure shown in which the mass addition film 40 is integrally formed under the plurality of IDT electrodes 30 .

[0066] Therefore, it can be considered Figure 7 In the structure shown, a mass addition film is formed on the IDT electrode without covering the substrate to prevent Q and K 2 However, when the pattern of the mass additional film 240 is as Figure 7 As shown, when formed in a dot pattern, the difficulty of pattern alignment may increase.

[0067] Fig.11A It is displayed in Figure 7 Figure 2 shows a diagram of pattern alignment errors that may occur in a SAW filter. Fig. 11B It is displayed due to Fig.11A A plot of the variation in spurious amplitude due to misalignment is shown.

[0068] Reference Fig.11A , showing the case where the quality-added film pattern is aligned to be formed on the IDT electrode ( Fig.11A (b) in the figure, the case where the mass addition film pattern is misaligned in the first direction X (a) and the case where the mass addition film pattern is misaligned in the second direction Y (c). Fig. 11B The change in spurious amplitude due to alignment is shown, where a curve (black) and spurious S1 due to an error in the first direction X, a curve (brown) and spurious S2 due to an error in the second direction Y, and a curve (blue) in which the mass-added film pattern is aligned without error are shown together.

[0069] As shown in the figure, the amplitude of the spurious signal is affected by the alignment error in the first direction X or the second direction Y. In particular, from the amplitude of the spurious signal S1 generated by the alignment error in the first direction X, it can be known that the spurious signal is more sensitive to the alignment error in the first direction X.

[0070] Therefore, when it is desired to prevent the mass-added film 240 from generating an error in the first direction X on the IDT electrode 230, the mass-added film 240 should be formed to have a width smaller than the width of the IDT electrode 230, and in some cases, the pattern of the mass-added film 240 may be formed to be smaller than 80% of the width of the IDT electrode 230. For example, in a 2 GHz SAW filter, when the width of the IDT electrode is about 400 nm, the width of the mass-added film 240 may be only 320 nm at most. In addition, considering factors such as the alignment tolerance of the photolithography process, the width of the mass-added film is further reduced, and in order to obtain the same effect, the thickness of the required mass-added film is further increased, and therefore, the process cost may be further increased.

[0071] Although it is possible to increase Fig.11A The mass-added film is formed in the form of the width in the second direction Y, that is, the longitudinal direction of the IDT electrode, but this is also limited because the mass-added film should be formed within a range that does not interfere with the central resonance area of ​​the IDT electrode. Therefore, a method is required that can most simply prevent an increase in process cost and suppress spurious by setting a range that allows alignment tolerance.

[0072] Therefore, it is preferred to form the SAW filter 100 according to an embodiment of the present invention so that the first mass added film 140 covers the top surface of the substrate 110 exposed between the adjacent IDT electrodes 130 and 135 connected to each other in a linear pattern rather than a dot pattern, while covering the top surfaces of the plurality of first IDT electrodes 130 .

[0073] At this time, by forming the SAW filter 100 so that the second thickness t2 of the first mass adding film 141 covering the top surface of the first IDT electrode 130 is greater than the first thickness t1 of the first mass adding film 142 covering the top surface of the substrate 110, Q and K are minimized. 2 The value decreases.

[0074] The thickness of the mass-added film is determined by its density. As the density of the mass-added film increases, the required thickness decreases. However, the higher the density of the material, the thinner the required thickness is, but the more sensitive it is to changes in the stray amplitude per 1 nm thickness change, which will be referred to in Fig.12 Give a description.

[0075] Fig.12 The experimental results comparing the lengths when Ta2O5 having a density of 8.2 g / cm3 and SiO2 having a density of 2.65 g / cm3 are selected in the mass added film of the SAW filter 100 according to one embodiment of the present invention are shown.

[0076] Reference Fig.12 Although the tolerance range of the thickness of the mass-added film for reducing the spurious amplitude to 10 dB or less when using low-density SiO2 is 25 nanometers or more, the tolerance range of the thickness of the mass-added film for reducing the spurious amplitude to 10 dB or less when using high-density Ta2O5 is limited to 5 nanometers. Since high-density materials are more sensitive to spurs, it can be seen that using low-density materials as mass-added films is more advantageous in terms of process control.

[0077] In mass-added films, the degree of suppression of stray amplitudes is almost determined by the total mass. In the case of high-density materials, the permissible thickness range is smaller and the tolerance range for misalignment is also smaller. This will be referred to in Fig.13A and 13B Give a description.

[0078] Fig.13A and 13B FIG. 1 is a diagram for explaining the effect of the misaligned formation of the mass adding film when the mass adding film is formed on the top of the IDT electrode and the top of the piezoelectric body in the SAW filter according to one embodiment of the present invention.

[0079] Reference Fig.13A , when the alignment error of the second mass adding film 145 is a, the second mass adding film 145 may be formed in a form of invading the gap 160, that is, the space between the one end 131 of the first IDT electrode 130 and the first dummy electrode 150 to a degree a. Although not shown, the first mass adding film 140 may also be formed in the gap between the second IDT electrode 135 and the second dummy electrode 155 due to the alignment error. In addition, Fig. 13B In another embodiment shown, when the first dummy electrode 150 or the second dummy electrode 155 is not formed, the gap 160 may include a space between the end 131 of the first IDT electrode 130 and the second bus bar 125 .

[0080] When the first mass adding film 140 or the second mass adding film 145 is formed in the gap 160 due to misalignment, the acoustic velocity in the gap 160 is reduced, so the spurious suppression function is inevitably reduced. Therefore, it may be considered to tilt the first mass adding film 140 or the second mass adding film 145 in a direction away from the gap so as not to form the first mass adding film 140 or the second mass adding film 145 in the gap.

[0081] For example, a surface acoustic wave device formed using KrF laser lithography generally shows an alignment error of about 150 nanometers. Considering this point in the process, one end of the first mass addition film 140 or the second mass addition film 145 is as far away from the gap 160 as possible by about 150 nanometers so that the first mass addition film 140 or the second mass addition film 145 is not formed in the gap 160. However, when the alignment error occurs in the inner direction of the first IDT electrode 130 or the second IDT electrode 135 instead of the gap 160, as the portion not covered by the mass addition film including the end 131 or 136 of the first or second IDT electrode increases, there is a problem in that the effect of suppressing spurious is reduced.

[0082] Since the surface acoustic wave filter according to the embodiment of the present invention can maintain the spurious amplitude less than 10 dB even if the first mass additional film 140 or the second mass additional film 145 is formed in the form of intruding the gap 160, it is not necessary to form the first mass additional film 140 or the second mass additional film 145 to be spaced apart from the gap 160 by more than a predetermined distance in consideration of the alignment tolerance level of the facility. Therefore, the spurious suppression function can be further improved.

[0083] Fig.14 is a graph showing the alignment error tolerance range for mass added film density where the stray amplitude is less than 10 dB.

[0084] Reference Fig.14 , the horizontal axis represents the alignment error of the mass-added film, and the vertical axis represents the amplitude (dB) of the stray mode. At this time, the alignment error represents a number normalized by the wavelength λ determined by the spacing of the IDT electrodes. A positive number means that the alignment error is in the direction away from the gap (toward the center of the IDT electrode), and a negative number means that the alignment error is in the direction close to the gap. Fig.14 As shown, it can be observed that as the density of mass-added film material increases, the sensitivity due to alignment errors also increases.

[0085] In addition, the alignment error of the mass-added film (a), the thickness of the mass-added film, and the width of the gap will be Fig.15 and 16 Described in.

[0086] Reference Fig.15, which is a graph showing the alignment error width (a) value (horizontal axis) of the mass addition films 140 and 145 normalized by λ determined by the interval between the first IDT electrode 130 and the second IDT electrode 135, and the measured amplitude of the spurious mode that can be formed in the surface acoustic wave filter when the thickness (t) of the mass addition films 140 and 145 is changed. As described above, as the thickness (t) of the mass addition films 140 and 145 increases, the normalized alignment error width for controlling the amplitude of the spurious mode within 10 dB increases.

[0087] Fig.16 A table showing the correlation derived using the misalignment width (a) value of the mass-added films 140 and 145 normalized by λ determined by the interval between the first IDT electrode 130 and the second IDT electrode 135 and the thickness (t) value of the mass-added films 140 and 145, including the calculated value (a / G) / t 1 / 2 The range in which the spurious mode is maintained within 10 dB is highlighted. In summary, the amplitude of the spurious mode that can be formed in the surface acoustic wave filter can be suppressed below 10 dB within the range that satisfies the correlation equation representing the thickness of the mass-added film and the degree of alignment error, the thickness of the mass-added film being defined by the correlation equation shown below.

[0088] (a / G) / t 1 / 2 ≤0.08

[0089] In some embodiments of the present invention, a plurality of first dummy electrodes 150 and second dummy electrodes 155 may be formed extending from the first bus bar 120 or the second bus bar 125. The first dummy electrode 150 may extend from the second bus bar 125 along the second direction D2 to face one end 131 of the first IDT electrode 130, and the second dummy electrode 155 may extend from the first bus bar 120 along the second direction D2 to face one end 136 of the second IDT electrode 135.

[0090] The first dummy electrode 150 can fill the gap between the end 131 of the first IDT electrode 130 and the second bus bar 125 to suppress the generation of unnecessary transverse modes. Similarly, the second dummy electrode 155 can also be located between the end 136 of the second IDT electrode 135 and the first bus bar 120 to suppress the generation of unnecessary transverse modes and reduce insertion loss.

[0091] Although the embodiments of the present invention are described above with reference to the accompanying drawings, it will be appreciated by those skilled in the art that the present invention can be implemented in other specific forms without changing the technical spirit or basic features. Therefore, the embodiments described above should be understood to be illustrative in all aspects and not restrictive.

Claims

1. A surface acoustic wave filter having a mass-added film formed on a plurality of electrodes, characterized in that: include: a substrate on which a supporting substrate, an energy confinement layer and a piezoelectric layer are sequentially stacked; a first bus bar and a second bus bar extending along a first direction on the substrate and spaced apart from each other in a second direction perpendicular to the first direction; a plurality of IDT electrodes extending alternately from the first bus bar and the second bus bar along the second direction and spaced apart from each other in the first direction; a gap formed in a space between a tip of an IDT electrode extending from the first bus bar and the second bus bar, or a space between a tip of an IDT electrode extending from the second bus bar and the first bus bar; as well as a mass additional film extending in a first direction to cover top surfaces of the plurality of IDT electrodes, Wherein, when the width of the gap is G, the width in the first direction of the end portion of the IDT electrode formed in the gap due to the alignment error is a, and the thickness of the mass-added film on the IDT electrode is t, (a / G) / t is satisfied. 1 / 2 ≤0.

08.

2. The surface acoustic wave filter according to claim 1, characterized in that The density of the mass-added film is 5g / cm 3 or smaller.

3. The surface acoustic wave filter according to claim 1, characterized in that Further including: a first dummy electrode extending from the second bus bar to face a distal end of the IDT electrode extending from the first bus bar; a second dummy electrode extending from the first bus bar to face a distal end of the IDT electrode extending from the second bus bar, The gap is formed in a space between one end of the IDT electrode extending from the first bus bar and the first dummy electrode and in a space between one end of the IDT electrode extending from the second bus bar and the second dummy electrode.

4. The surface acoustic wave filter according to claim 1, characterized in that The quality-added film includes at least one of SiO2, Ta2O5 and Al2O3.

5. The surface acoustic wave filter according to claim 1, characterized in that The mass addition film extends in an integral form across the plurality of IDT electrodes so as to completely fill the region between the plurality of IDT electrodes.

6. The surface acoustic wave filter according to claim 1, characterized in that The mass additional film passes through the plurality of IDT electrodes and does not cover the top surface of the substrate exposed between the plurality of IDT electrodes.

7. The surface acoustic wave filter according to claim 6, characterized in that The bottom surface width of the mass addition film matches the top surface width of the IDT electrode covered by the mass addition film.

8. A surface acoustic wave filter having a mass-added film formed on a plurality of electrodes, characterized in that: The surface acoustic wave filter comprises: a substrate on which a supporting substrate, an energy confinement layer and a piezoelectric layer are sequentially stacked; a first bus bar and a second bus bar extending along a first direction on the substrate and spaced apart from each other in a second direction perpendicular to the first direction; a plurality of IDT electrodes extending alternately from the first bus bar and the second bus bar in the second direction and spaced apart from each other in the first direction; and a mass addition film extending in a first direction to cover top surfaces of the plurality of IDT electrodes and a top surface of the substrate exposed between the plurality of IDT electrodes, wherein The thickness of the mass adding film on the top surface of the substrate and the thickness of the mass adding film on the top surfaces of the plurality of IDT electrodes are different from each other.

9. The surface acoustic wave filter according to claim 8, characterized in that The mass addition film extends along the first direction to cover one ends of the plurality of IDT electrodes.

10. The surface acoustic wave filter according to claim 9, characterized in that Multiple IDT electrodes include: a plurality of first IDT electrodes extending from the first bus bar in the second direction and spaced apart from each other in the first direction; and A plurality of second IDT electrodes extend from the second busbar along the second direction, are spaced apart from each other in the first direction, and are alternately arranged with the plurality of first IDT electrodes, wherein: Quality additional films include: A first mass additional film covering one end of the plurality of first IDTs; and A second mass additional film covers one ends of the plurality of second IDTs.

11. The surface acoustic wave filter according to claim 8, characterized in that The quality-added film includes at least one of SiO2, Ta2O5 and Al2O3.

12. The surface acoustic wave filter according to claim 8, characterized in that The thickness of the mass-adding film on the top surfaces of the plurality of IDT electrodes is greater than the thickness of the mass-adding film on the top surface of the substrate.

13. The surface acoustic wave filter according to claim 8, characterized in that The mass addition film extends in an integral form across the plurality of IDT electrodes so as to completely fill the region between the plurality of IDT electrodes.

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