JP2015231147A - Elastic wave device - Google Patents

Abstract

An elastic wave device capable of suppressing collapse of a three-dimensional intersection while suppressing parasitic capacitance is provided. The present invention relates to a piezoelectric substrate, an IDT provided on the piezoelectric substrate for exciting an elastic wave, a signal wiring provided on the piezoelectric substrate connected to the IDT, and the piezoelectric substrate. The ground wiring 24 is connected to the IDT 14 and crosses over the signal wiring 22, and the signal wiring 22 and the ground wiring 24 are three-dimensionally crossed. And an insulator 36 provided in a part in a direction parallel to the upper surface of the piezoelectric substrate 10 below the ground wiring 24 at the three-dimensional intersection 34 so that the space 40 is formed. . [Selection] Figure 1

Description

  The present invention relates to an acoustic wave device, for example, an acoustic wave device including wirings that are three-dimensionally crossed.

  As an acoustic wave device using an acoustic wave, an acoustic wave device including an electrode for exciting an acoustic wave on a substrate and wiring connected to the electrode is known. In such an acoustic wave device, there is a case where wirings are three-dimensionally crossed on a substrate. For example, a structure is known in which an insulating film is provided over the entire three-dimensional intersection of a lower wiring and an upper wiring so that the upper wiring straddles over the lower wiring (for example, see Patent Document 1). . For example, a structure in which the entire three-dimensional intersection of the lower wiring and the upper wiring is hollow and the upper wiring straddles over the lower wiring is also known (see, for example, Patent Documents 2 and 3).

JP-A-5-167387 Japanese Patent Laid-Open No. 10-65006 Japanese Unexamined Patent Publication No. 2012-9899

  In the structure in which the insulating film is provided in the entire three-dimensional intersection of the lower wiring and the upper wiring, a large parasitic capacitance is generated between the upper and lower wirings due to the dielectric constant of the insulating film. On the other hand, when the entire solid intersection of the lower wiring and the upper wiring has a hollow structure, the solid intersection is crushed by an external force.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an elastic wave device that can suppress collapse of a three-dimensional intersection while suppressing parasitic capacitance.

  The present invention includes a substrate, an electrode for exciting an elastic wave provided on the substrate, a first wiring provided on the substrate connected to the electrode, and connected to the electrode on the substrate. A hollow space is formed under the second wiring provided at the three-dimensional intersection where the first wiring and the second wiring cross three-dimensionally crossing over the first wiring and the first wiring and the second wiring. As described above, an acoustic wave device comprising: an insulator provided in a part in a direction parallel to the upper surface of the substrate under the second wiring at the three-dimensional intersection. ADVANTAGE OF THE INVENTION According to this invention, it can suppress that a three-dimensional intersection part is crushed, suppressing parasitic capacitance.

  The said structure WHEREIN: The said insulator is provided in the center part of the said solid intersection in the extension direction of the said 2nd wiring in the said solid intersection, and the both ends of the said 2nd wiring in the said solid and the solid intersection The hollow space can be formed between the two.

  The said structure WHEREIN: The said insulator is provided on the said 1st wiring in the said three-dimensional intersection, The said hollow space is formed on the said board | substrate of the part in which the said first wiring in the said three-dimensional intersection is not provided. It can be set as the structure which has.

  The said structure WHEREIN: The said insulator is provided apart from the said 1st wiring in the side of the said 1st wiring in the said solid intersection, and the said hollow space forms on the said 1st wiring in the said solid intersection It can be set as the structure currently made.

  In the above configuration, a third wiring is provided between the substrate and the second wiring and does not straddle the first wiring, and the insulator includes the first wiring and the third wiring. A configuration may be employed in which the first wiring and the third wiring are provided apart from each other on the substrate.

  In the above configuration, a third wiring is provided between the substrate and the second wiring and does not straddle the first wiring, and the third wiring extends from the second wiring at the three-dimensional intersection. The protrusion may have a protruding portion whose upper surface is exposed, and the insulator may be provided apart from the first wiring on the protruding portion of the third wiring.

  In the above configuration, the second wiring may be thicker than the first wiring.

  In the above configuration, the first wiring may be a signal wiring and the second wiring may be a ground wiring.

  The said structure WHEREIN: The said insulator can be set as the structure which is insulating resin.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that a three-dimensional intersection part is crushed, suppressing parasitic capacitance.

FIG. 1A is a top view illustrating the acoustic wave device according to the first embodiment, and FIG. 1B is a cross-sectional view taken along a line AA in FIG. FIG. 2A to FIG. 2D are diagrams (part 1) illustrating the method for manufacturing the acoustic wave device according to the first embodiment. FIG. 3A to FIG. 3D are diagrams (part 2) illustrating the method for manufacturing the acoustic wave device according to the first embodiment. FIGS. 4A to 4D are views (No. 3) illustrating the method for manufacturing the acoustic wave device according to the first embodiment. FIG. 5A and FIG. 5B are diagrams (part 4) illustrating the method for manufacturing the acoustic wave device according to the first embodiment. 6A is a cross-sectional view showing an acoustic wave device according to Comparative Example 1, and FIG. 6B is a cross-sectional view showing an acoustic wave device according to Comparative Example 2. FIG. 7A is a cross-sectional view illustrating an elastic wave device according to Modification 1 of Embodiment 1, and FIG. 7B is a cross-sectional view illustrating an acoustic wave device according to Modification 2 of Embodiment 1.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1A is a top view illustrating the acoustic wave device according to the first embodiment, and FIG. 1B is a cross-sectional view taken along a line AA in FIG. As shown in FIGS. 1A and 1B, the acoustic wave device 100 according to the first embodiment includes two surface acoustic wave (SAW) elements 12 provided on a piezoelectric substrate 10. . The SAW element 12 includes an IDT (Interdigital Transducer) 14 and a reflector 16. The IDT 14 is an electrode that excites a surface acoustic wave. The reflectors 16 are provided on both sides of the IDT 14 in the direction in which the surface acoustic wave propagates. The IDT 14 includes a pair of comb electrodes. For the piezoelectric substrate 10, for example, a piezoelectric body such as lithium tantalate (LiTaO ₃ ) or lithium niobate (LiNbO ₃ ) can be used. The IDT 14 and the reflector 16 are made of a metal such as aluminum (Al), for example. The thickness of the IDT 14 and the reflector 16 is, for example, about 350 nm.

  One unbalanced terminal 18 is connected to one of the two SAW elements 12 via the signal wiring 23 to the IDT 14 located in the center. To the other of the two SAW elements 12, two balanced terminals 20 are connected to an IDT 14 located in the center via a signal wiring 23. One of the unbalanced terminal 18 and the balanced terminal 20 is an input terminal, and the other is an output terminal.

  The two SAW elements 12 are connected in series by the IDTs 14 located outside each other being connected by the signal wiring 22. A ground wiring 24 is connected to the comb electrode to which the reflector 16 and the signal wiring of the IDT 14 are not connected. The ground wiring 24 surrounds the reflector 16 and the outer IDT 14 and extends between the two SAW elements 12. Since the signal wiring 22 and the ground wiring 24 are provided on the piezoelectric substrate 10, the ground wiring 24 extending between the two SAW elements 12 crosses the signal wiring 22 three-dimensionally.

  The ground wiring 24 is a laminated metal film in which a first metal layer 26, a second metal layer 28, and a third metal layer 30 are laminated in order from the piezoelectric substrate 10 side. A wiring 32 is provided between the ground wiring 24 and the piezoelectric substrate 10. The wiring 32 does not straddle over the signal wiring 22 but has a protruding portion 38 that protrudes from the ground wiring 24 and is exposed at the three-dimensional intersection 34 where the signal wiring 22 and the ground wiring 24 intersect three-dimensionally.

  The signal wirings 22 and 23 and the wiring 32 are made of a metal such as aluminum (Al), for example, and are made of the same metal as the IDT 14 and the reflector 16, for example. The thicknesses of the signal wirings 22 and 23 and the wiring 32 are, for example, about 350 nm. The first metal layer 26 of the ground wiring 24 serves as a seed layer in an electroplating method to be described later. For example, the first metal layer 26 is a laminated metal film in which a titanium (Ti) layer and a copper (Cu) layer are laminated from the piezoelectric substrate 10 side. is there. The second metal layer 28 is made of a low resistivity metal to reduce the resistance of the ground wiring 24, and is, for example, a copper (Cu) layer. The third metal layer 30 is formed for bumps and is, for example, a gold (Au) layer. The thickness of the ground wiring 24 is, for example, about 4 μm to 5 μm, and is thicker than the signal wiring 22.

  An insulator 36 is provided in a part in the direction parallel to the upper surface of the piezoelectric substrate 10 below the ground wiring 24 at the three-dimensional intersection 34. In other words, a hollow space 40 is formed in a part under the ground wiring 24 at the three-dimensional intersection 34. The insulator 36 is provided on the signal wiring 22 at the center of the three-dimensional intersection 34 in the extending direction of the ground wiring 24 at the three-dimensional intersection 34. A hollow space 40 is formed between the insulator 36 and both end portions of the ground wiring 24 at the three-dimensional intersection 34. For the insulator 36, for example, an insulating resin such as polyimide can be used.

  The height H of the three-dimensional intersection 34 is, for example, about 1 μm. The upper surface of the insulator 36 may or may not be in contact with the ground wiring 24. From the viewpoint of suppressing the collapse of the three-dimensional intersection 34, the upper surface of the insulator 36 is preferably in contact with the ground wiring 24. From the viewpoint of suppressing the parasitic capacitance between the signal wiring 22 and the ground wiring 24, it is preferable that the upper surface of the insulator 36 is not in contact with the ground wiring 24. When the upper surface of the insulator 36 is not in contact with the ground wiring 24, the upper surface of the insulator 36 may be higher than the upper surface of the signal wiring 22, but from the point of suppressing the collapse of the three-dimensional intersection 34, The height of the insulator 36 from the piezoelectric substrate 10 is preferably 1/2 or more of the height H of the three-dimensional intersection 34, more preferably 2/3 or more, and even more preferably 3/4 or more. .

  An interval L between both end portions of the ground wiring 24 in the three-dimensional intersection 34 is, for example, about 20 μm to 30 μm. The width W1 of the insulator 36 may be wider, the same, or narrower than the width of the signal wiring 22. 1A and 1B illustrate a case where the width W1 of the insulator 36 is wider than the width of the signal wiring 22. In view of suppressing parasitic capacitance, the width W1 of the insulator 36 is preferably 1/2 or less of the distance L between the three-dimensional intersections 34, more preferably 1/3 or less, and further preferably 1/4 or less. preferable. In addition, as shown in FIG. 1A, the length of the insulator 36 may be the same as the width W2 of the ground wiring 24 at the three-dimensional intersection 34 or shorter than the width W2, but may be longer than the width W2. preferable. The width W2 of the ground wiring 24 is, for example, 30 μm, and the length of the insulator 36 is, for example, 40 μm.

  Next, a method for manufacturing the acoustic wave device of Example 1 will be described. FIG. 2A to FIG. 5B are diagrams illustrating a method for manufacturing the acoustic wave device according to the first embodiment. 2 (a), FIG. 2 (c), FIG. 3 (a), FIG. 3 (c), FIG. 4 (a), FIG. 4 (c), and FIG. It is a top view which shows the manufacturing method of a device. 2 (b), FIG. 2 (d), FIG. 3 (b), FIG. 3 (d), FIG. 4 (b), FIG. 4 (d), and FIG. It is sectional drawing which shows the manufacturing method of a device, and is sectional drawing of the location corresponded between AA of Fig.1 (a).

  As shown in FIGS. 2A and 2B, the SAW element 12, the signal wirings 22 and 23, and the wiring 32 are formed on the piezoelectric substrate 10. In forming these, a manufacturing method generally used for forming the SAW element 12 and the like can be used. The SAW element 12, the signal wirings 22, 23, and the wiring 32 are formed with the same material and the same film thickness. The Thereafter, a photosensitive insulating resin (for example, polyimide) is applied on the piezoelectric substrate 10 and then exposed and developed to form the insulator 36 on the signal wiring 22.

  As shown in FIGS. 2C and 2D, a first resist film 42 having an opening in the region where the wiring 32 is formed and covering the other region is formed. The first resist film 42 is preferably formed so as to cover a part of the end of the wiring 32 positioned on the side of the signal wiring 22 in the portion where the three-dimensional intersection is formed.

  As shown in FIGS. 3A and 3B, the first metal layer 26 is formed on the entire surface of the piezoelectric substrate 10 by using, for example, a sputtering method. As described above, the first metal layer 26 functions as a seed layer in the electrolytic plating method described later. As shown in FIGS. 3C and 3D, a second resist film 44 having an opening in a region where the ground wiring, the unbalanced terminal, and the balanced terminal are formed and covering the other region is formed.

  As shown in FIGS. 4A and 4B, the second metal layer 28 and the third metal layer 30 are sequentially formed in the opening region of the second resist film 44 using, for example, electrolytic plating. Thereafter, as shown in FIGS. 4C and 4D, the second resist film 44 is peeled off.

  As shown in FIGS. 5A and 5B, the first resist film 42 and the first metal layer 26 formed thereon are removed by lift-off. The first resist film 42 can be removed by lift-off because the stripping solution enters from the corners of the first resist film 42 where the first metal layer 26 is difficult to be formed. As a result, the ground wiring 24 including the laminated metal film in which the first metal layer 26 to the third metal layer 30 are laminated, the unbalanced terminal 18, and the balanced terminal 20 are formed. At the three-dimensional intersection 34 between the signal wiring 22 and the ground wiring 24, the first resist film 42 is removed by lift-off, so that a hollow space 40 is formed on the side of the insulator 36.

  Here, in describing the effect of the elastic wave device of Example 1, the elastic wave device of the comparative example will be described. 6A is a cross-sectional view showing an acoustic wave device according to Comparative Example 1, and FIG. 6B is a cross-sectional view showing an acoustic wave device according to Comparative Example 2. When the insulator 46 is provided on the entire solid intersection 34 between the signal wiring 22 and the ground wiring 24 as in Comparative Example 1 in FIG. 6A, the gap between the signal wiring 22 and the ground wiring 24 is provided. A large parasitic capacitance is generated, resulting in deterioration of out-of-band attenuation characteristics and the like. As in Comparative Example 2 in FIG. 6B, the insulator is not provided at the three-dimensional intersection 34 between the signal wiring 22 and the ground wiring 24, and the entire three-dimensional intersection 34 is a hollow space 40. The three-dimensional intersection 34 will be crushed by external force. For example, when the wafer is separated into pieces by the dicing method, the three-dimensional intersection 34 is crushed by an external force. When the three-dimensional intersection 34 is crushed, the ground wiring 24 may be disconnected or the ground wiring 24 may contact the signal wiring 22.

  On the other hand, in the first embodiment, as shown in FIG. 1B, the hollow space 40 is formed below the ground wiring 24 at the three-dimensional intersection 34. An insulator 36 is provided in a part in a direction parallel to the upper surface of the piezoelectric substrate 10. As a result, a part of the three-dimensional intersection 34 is hollowed out, so that the parasitic capacitance between the signal wiring 22 and the ground wiring 24 can be suppressed. Moreover, since the insulator 36 functions as a reinforcing column, the three-dimensional intersection 34 can be prevented from being crushed.

  As shown in FIG. 1B, the insulator 36 may be provided at the center of the three-dimensional intersection 34 in the direction in which the ground wiring 24 extends in the three-dimensional intersection 34. The hollow space 40 may be formed between the insulator 36 and both end portions of the ground wiring 24 at the three-dimensional intersection 34. By providing the insulator 36 at the central portion of the three-dimensional intersection 34, the three-dimensional intersection 34 can be effectively prevented from being crushed.

  As shown in FIG. 1B, the insulator 36 may be provided on the signal wiring 22 at the three-dimensional intersection 34. The hollow space 40 may be formed on a portion of the piezoelectric substrate 10 where the signal wiring 22 in the three-dimensional intersection 34 is not provided. By providing the insulator 36 on the signal wiring 22, it is possible to prevent the ground wiring 24 from contacting the signal wiring 22 even if the three-dimensional intersection 34 is crushed. Further, from the viewpoint of suppressing the ground wiring 24 from coming into contact with the signal wiring 22, the insulator 36 is preferably provided so as to cover the signal wiring 22 with a width wider than that of the signal wiring 22.

  When the ground wiring 24 that is the upper wiring is thicker than the signal wiring 22 that is the lower wiring, the three-dimensional intersection 34 is easily crushed. Therefore, it is preferable to apply the present invention in such a case. In the first embodiment, the ground wiring 24 straddles the signal wiring 22. Although the signal wiring 22 may straddle the ground wiring 24, the ground wiring 24 is made thicker than the signal wiring 22 in order to reduce the resistance. When straddling, the three-dimensional intersection 34 tends to be crushed. Therefore, it is preferable to apply the present invention when the ground wiring 24 crosses over the signal wiring 22 three-dimensionally.

  The insulator 36 is not limited to being made of an insulating resin, and may be made of another insulator. For example, the insulator 36 may be a SOG (Spin on Glass) film. However, when an insulating resin is used for the insulator 36, there is an advantage that a thick film of, for example, 1 μm or more can be easily obtained. When an SOG film is used as the insulator 36, the insulator 36 is formed by coating the entire surface of the SOG film in FIG. 2A and FIG. 2B and then removing unnecessary portions by etching. can do.

  FIG. 7A is a cross-sectional view illustrating an elastic wave device according to Modification 1 of Embodiment 1, and FIG. 7B is a cross-sectional view illustrating an acoustic wave device according to Modification 2 of Embodiment 1. FIG. 7A and FIG. 7B illustrate a cross section of a portion corresponding to AA in FIG. As shown in FIG. 7A, in the first modification of the first embodiment, the insulator 36a is provided on the piezoelectric substrate 10 between the signal wiring 22 and the wiring 32 so as to be separated from the signal wiring 22 and the wiring 32. It has been. The hollow space 40 is at least formed on the signal wiring 22 at the three-dimensional intersection 34. Other configurations are the same as those in FIG. 1B of the first embodiment, and thus the description thereof is omitted.

  As shown in FIG. 7B, in the second modification of the first embodiment, the insulator 36 b is provided on the protruding portion 38 of the wiring 32 so as to be separated from the signal wiring 22. The hollow space 40 is at least formed on the signal wiring 22 at the three-dimensional intersection 34. Other configurations are the same as those in FIG. 1B of the first embodiment, and thus the description thereof is omitted.

  As in the first modification and the second modification of the first embodiment, the insulators 36 a and 36 b may be provided on the side of the signal wiring 22 at the three-dimensional intersection 34 and away from the signal wiring 22. The hollow space 40 may be formed on the signal wiring 22 at the three-dimensional intersection 34. In this case, the parasitic capacitance between the signal wiring 22 and the ground wiring 24 can be effectively suppressed.

  In the first modification of the first embodiment, the insulator 36 a is provided on the piezoelectric substrate 10 between the signal wiring 22 and the wiring 32 so as to be separated from the signal wiring 22 and the wiring 32. In this case, the insulator 36a can be provided closer to the central portion of the three-dimensional intersection 34 than the insulator 36b of the second modification of the first embodiment. For this reason, compared with the modification 2 of Example 1, it can suppress that the solid intersection part 34 is crushed.

  In the second modification of the first embodiment, the insulator 36 b is provided on the protruding portion 38 of the wiring 32 so as to be separated from the signal wiring 22. In this case, the insulator 36b can be provided away from the signal wiring 22 as compared with the insulator 36a of the first modification of the first embodiment. For this reason, compared with the modification 1 of Example 1, parasitic capacitance can be made small.

  In the modification 2 of the first embodiment to the first embodiment, the ground wiring 24 is shown as an example in which the ground wiring 24 crosses over one signal wiring 22 as an example, but the ground wiring 24 includes two or more signal wirings 22. It may be a case where a three-dimensional intersection is made across the top. From the viewpoint of suppressing the collapse of the three-dimensional intersection 34, it is preferable that a plurality of insulators are provided. The plurality of insulators are preferably provided symmetrically with respect to the central portion of the three-dimensional intersection 34 as shown in FIGS. 7 (a) and 7 (b). When a plurality of insulators are provided, the sum of the widths W1 (see FIG. 1B) of each of the plurality of insulators is 1 / of the interval L (see FIG. 1B) of the three-dimensional intersection 34. The case of 2 or less is preferable, the case of 1/3 or less is more preferable, and the case of 1/4 or less is more preferable.

  In the first embodiment, the case of an unbalanced-balanced multimode elastic wave filter has been described as an example, but a balanced-balanced or unbalanced-unbalanced multimode elastic wave filter may be used. Another elastic wave device such as a ladder filter may be used. Furthermore, the present invention is not limited to a surface acoustic wave device, and may be a love wave device, a boundary acoustic wave device, or a piezoelectric thin film resonator (FBAR) device. In the case of an FBAR device, a lower electrode and an upper electrode provided on a substrate such as a silicon substrate with a piezoelectric film interposed therebetween are electrodes that excite elastic waves.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

10 Piezoelectric substrate 12 SAW element 14 IDT
16 reflector 22 signal wiring 24 ground wiring 26 first metal layer 28 second metal layer 30 third metal layer 32 wiring 34 three-dimensional intersection 36-36b insulator 40 hollow space 36-36b insulator 38 protrusion

Claims (9)

A substrate,
An electrode for exciting an elastic wave provided on the substrate;
A first wiring connected to the electrode on the substrate;
A second wiring that is connected to the electrode on the substrate and crosses the first wiring in a three-dimensional manner;
The substrate under the second wiring at the three-dimensional intersection so that a hollow space is formed under the second wiring at the three-dimensional intersection where the first wiring and the second wiring intersect three-dimensionally And an insulator provided in a part in a direction parallel to the upper surface of the elastic wave device. The insulator is provided at a central portion of the three-dimensional intersection in the extending direction of the second wiring at the three-dimensional intersection,
The acoustic wave device according to claim 1, wherein the hollow space is formed between the insulator and both end portions of the second wiring at the three-dimensional intersection. The insulator is provided on the first wiring at the three-dimensional intersection,
3. The acoustic wave device according to claim 1, wherein the hollow space is formed on the substrate where the first wiring is not provided in the three-dimensional intersection. The insulator is provided on the side of the first wiring at the three-dimensional intersection and away from the first wiring,
3. The acoustic wave device according to claim 1, wherein the hollow space is formed on the first wiring at the three-dimensional intersection. A third wiring provided between the substrate and the second wiring and not straddling the first wiring;
The elastic material according to claim 4, wherein the insulator is provided on the substrate between the first wiring and the third wiring so as to be separated from the first wiring and the third wiring. Wave device. A third wiring provided between the substrate and the second wiring and not straddling the first wiring;
The third wiring has a protruding portion that protrudes from the second wiring at the three-dimensional intersection and has an upper surface exposed.
5. The acoustic wave device according to claim 4, wherein the insulator is provided apart from the first wiring on the projecting portion of the third wiring. 6.   The acoustic wave device according to claim 1, wherein the second wiring is thicker than the first wiring.   8. The acoustic wave device according to claim 1, wherein the first wiring is a signal wiring, and the second wiring is a ground wiring. 9. The acoustic wave device according to claim 1, wherein the insulator is an insulating resin.

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