Acoustic wave device, filter, multiplexer and method of manufacturing acoustic wave device

Abstract

To provide an acoustic wave device capable of suppressing occurrence of cracks in a wiring layer.SOLUTION: An acoustic wave device includes: a piezoelectric substrate 14; a series resonator S4 provided on the piezoelectric substrate 14 and having a plurality of electrode fingers 18a; a parallel resonator P4 provided on the piezoelectric substrate 14 and having a plurality of electrode fingers 18b which each include a material different from that of each of the electrode fingers 18a; a first base conductive layer 36 provided on the piezoelectric substrate 14, connected to the series resonator S4, and having the same layer structure as each of the electrode fingers 18a; a second base conductive layer 38 provided on the piezoelectric substrate 14, connected to the parallel resonator P4, having the same layer structure as each of the electrode fingers 18b, and facing the first base conductive layer 36 with a gap 50 interposed therebetween; and a wiring layer 34 provided from the upper side of the first base conductive layer 36 to the upper side of the second base conductive layer 38 and connecting the series resonator S4 with the parallel resonator P4.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave device, a filter, a multiplexer, and a method for manufacturing an acoustic wave device. [Background technology]

[0002] Surface acoustic wave (SAW) resonators are known as acoustic wave devices used in communication devices such as smartphones. A surface acoustic wave resonator has an IDT (Interdigital Transducer) with multiple electrode fingers on a piezoelectric substrate. Surface acoustic wave resonators are known to be used in high-frequency filters for removing unwanted signals outside the frequency band used for communication (e.g., Patent Documents 1-3). It is also known that two surface acoustic wave resonators have different numbers of stacked electrode fingers (e.g., Patent Documents 4 and 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-89069 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-244523 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-28980 [Patent Document 4] International Publication No. 2003 / 005577 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-333296 Summary of the Invention [Problem to be solved by the invention]

[0004] The electrode fingers of the first acoustic wave resonator and the second acoustic wave resonator may be made of different materials. In this case, the first electrode fingers of the first acoustic wave resonator and the second electrode fingers of the second acoustic wave resonator are formed in separate processes. The wiring layers connecting the first acoustic wave resonator and the second acoustic wave resonator are formed on the underlying conductive layers connected to the respective resonators. To simplify the manufacturing process, the first underlying conductive layer connected to the first acoustic wave resonator is formed simultaneously with the first electrode fingers, and the second underlying conductive layer connected to the second acoustic wave resonator is formed simultaneously with the second electrode fingers. In such cases, cracks may occur in the wiring layers formed from the first underlying conductive layer to the second underlying conductive layer, resulting in increased electrical resistance or disconnection.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to suppress the occurrence of cracks in wiring layers. [Means for solving the problem]

[0006] The present invention provides an acoustic wave device comprising: a piezoelectric substrate; a first acoustic wave resonator provided on the piezoelectric substrate and having a plurality of first electrode fingers; a second acoustic wave resonator provided on the piezoelectric substrate and having a plurality of second electrode fingers including a material different from that of the plurality of first electrode fingers; a first underlying conductive layer provided on the piezoelectric substrate, connected to the first acoustic wave resonator, and having the same layer structure as the plurality of first electrode fingers; a second underlying conductive layer provided on the piezoelectric substrate, connected to the second acoustic wave resonator, having the same layer structure as the plurality of second electrode fingers, and facing the first underlying conductive layer across a gap; and a wiring layer provided from above the first underlying conductive layer to above the second underlying conductive layer, connecting the first acoustic wave resonator and the second acoustic wave resonator.

[0007] In the above configuration, the thickness of the first conductive underlayer may be constant throughout the first conductive underlayer, and the thickness of the second conductive underlayer may be constant throughout the second conductive underlayer.

[0008] In the above configuration, the thickness of the wiring layer may be at least twice the thickness of the larger of the first underlying conductive layer and the second underlying conductive layer.

[0009] In the above configuration, the distance between the first underlying conductive layer and the second underlying conductive layer facing each other through the gap can be at least one time the thickness of the larger of the first underlying conductive layer and the second underlying conductive layer.

[0010] In the above configuration, the plurality of first electrode fingers and the plurality of second electrode fingers may be arranged in the same direction, and the gap may be provided between the first acoustic wave resonator and the second acoustic wave resonator in the arrangement direction.

[0011] The present invention is a filter including the above-described acoustic wave device.

[0012] In the above configuration, the first acoustic wave resonator may be a series resonator connected in series between an input terminal and an output terminal, the second acoustic wave resonator may be a parallel resonator connected in parallel between the input terminal and the output terminal, the plurality of first electrode fingers may include a first conductive layer which is a titanium nitride layer and a second conductive layer provided on the first conductive layer, and the plurality of second electrode fingers may include a third conductive layer which is a titanium layer and a fourth conductive layer provided on the third conductive layer and made of the same material as the second conductive layer.

[0013] The present invention is a multiplexer including the filter described above.

[0014] The present invention provides a method for fabricating a piezoelectric substrate including forming a first acoustic wave resonator having a plurality of first electrode fingers and a first underlying conductive layer connected to the first acoustic wave resonator and having the same layer structure as the plurality of first electrode fingers; forming a first mask layer on the piezoelectric substrate to cover the first acoustic wave resonator and the first underlying conductive layer; depositing a conductive film on the piezoelectric substrate using the first mask layer as a mask; and removing the first mask layer and then forming a second mask layer on the piezoelectric substrate having openings at least at ends of the conductive film. a step of etching the conductive film using the second mask layer as a mask to form a second acoustic wave resonator having a plurality of second electrode fingers, and a second underlying conductive layer connected to the second acoustic wave resonator, having the same layer structure as the plurality of second electrode fingers, and facing the first underlying conductive layer across a gap; and a step of removing the second mask layer and then forming a wiring layer connecting the first acoustic wave resonator and the second acoustic wave resonator from on the first underlying conductive layer to on the second underlying conductive layer.

[0015] In the above configuration, the step of forming the second mask layer may be configured to form the second mask layer so that the opening is positioned at a protrusion formed at the end of the conductive film.

[0016] In the above configuration, the step of forming the first mask layer can be configured to form the first mask layer so as to completely cover the first acoustic wave resonator and the first underlying conductive layer in an area larger than the area in which the first acoustic wave resonator and the first underlying conductive layer are formed. [Effects of the Invention]

[0017] According to the present invention, it is possible to suppress the occurrence of cracks in the wiring layer. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a plan view of a filter according to a first embodiment. [Figure 2]FIG. 2(a) is a plan view of a surface acoustic wave resonator, FIG. 2(b) is a cross-sectional view of electrode fingers of a series resonator in Example 1, and FIG. 2(c) is a cross-sectional view of electrode fingers of a parallel resonator. [Figure 3] 3(a) and 3(b) are cross-sectional views of Structure A and Structure B of the acoustic wave resonator used in the experiment. [Figure 4] 4(a) is a diagram showing the pass characteristics of ladder-type filter A, and FIG. 4(b) is a diagram showing the pass characteristics of ladder-type filter B. As shown in FIG. [Figure 5] 5(a) is a plan view of the vicinity of the series resonator and parallel resonator in FIG. 1, FIG. 5(b) is a cross-sectional view taken along line AA in FIG. 5(a), and FIG. 5(c) is a cross-sectional view of the vicinity of the wiring layer in FIG. 5(b). [Figure 6] 6(a) to 6(c) are cross-sectional views (part 1) illustrating a method for manufacturing the series resonator, the parallel resonator, and the wiring layer in the first embodiment. [Figure 7] 7(a) to 7(c) are cross-sectional views (part 2) illustrating a method for manufacturing the series resonator, the parallel resonator, and the wiring layer in the first embodiment. [Figure 8] 8(a) to 8(c) are cross-sectional views (part 3) illustrating a method for manufacturing the series resonator, the parallel resonator, and the wiring layer according to the first embodiment. [Figure 9] 9(a) to 9(c) are cross-sectional views (part 1) showing a method for manufacturing a series resonator, a parallel resonator, and a wiring layer in a comparative example. [Figure 10] 10(a) to 10(c) are cross-sectional views (part 2) showing a method for manufacturing a series resonator, a parallel resonator, and a wiring layer in a comparative example. [Figure 11] FIG. 11 is a circuit diagram of a duplexer according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0020] In the first embodiment, an example of a filter will be described. Fig. 1 is a plan view of a filter 100 according to the first embodiment. The arrangement direction of the electrode fingers 18 is defined as the X direction, the extension direction of the electrode fingers 18 as the Y direction, and the thickness direction of the piezoelectric substrate 14 as the Z direction. The X direction and the Y direction do not necessarily correspond to the X axis direction and the Y axis direction of the crystal orientation of the piezoelectric substrate 14. When the piezoelectric substrate 14 is a rotated Y-cut X-propagation substrate, the X direction corresponds to the X axis direction of the crystal orientation.

[0021] As shown in FIG. 1, a piezoelectric substrate 14 is provided on a support substrate 10. One or more series resonators S1 to S6 and one or more parallel resonators P1 to P5 are provided on the piezoelectric substrate 14. A plurality of terminals 30 are provided on the lower surface of the support substrate 10. The plurality of terminals 30 include an input terminal Tin, an output terminal Tout, and a ground terminal Tg. The series resonators S1 to S6 are connected in series between the input terminal Tin and the output terminal Tout through via wiring 32 and a wiring layer 34 that penetrate the support substrate 10. One end of each of the parallel resonators P1 to P5 is connected between the series resonators S1 to S6 through the wiring layer 34, and the other end is connected to the ground terminal Tg through the wiring layer 34 and the via wiring 32.

[0022] The support substrate 10 is, for example, a sapphire substrate, alumina substrate, spinel substrate, quartz substrate, quartz substrate, silicon carbide substrate, or silicon substrate. The piezoelectric substrate 14 is, for example, a single-crystal lithium tantalate substrate, a single-crystal lithium niobate substrate, or a quartz substrate. The piezoelectric substrate 14 may be, for example, a rotated Y-cut X-propagation lithium tantalate substrate or a rotated Y-cut X-propagation lithium niobate substrate, or may be, for example, a 30° to 50° rotated Y-cut X-propagation lithium tantalate substrate. An insulating film such as silicon oxide and / or aluminum oxide may be provided between the support substrate 10 and the piezoelectric substrate 14.

[0023] The series resonators S1 to S6 and the parallel resonators P1 to P5 are surface acoustic wave resonators. FIG. 2(a) is a plan view of a surface acoustic wave resonator 40. As shown in FIG. 2(a), the surface acoustic wave resonator 40 has an IDT 22 and a reflector 24. The reflectors 24 are provided on both sides of the IDT 22 in the X direction. The IDT 22 has a pair of opposing comb electrodes 20. The comb electrode 20 has a plurality of electrode fingers 18 and a bus bar 19 to which the plurality of electrode fingers 18 are connected. A region where the electrode fingers 18 of the pair of comb electrodes 20 intersect is an intersection region 25. The pair of comb electrodes 20 have the electrode fingers 18 alternately arranged in at least a part of the intersection region 25. An acoustic wave excited mainly by the plurality of electrode fingers 18 in the intersection region 25 propagates mainly in the X direction. The pitch of the electrode fingers 18 of one of the pair of interdigital transducers 20 (the pitch between the centers of the electrode fingers 18) is approximately equal to the wavelength λ of the acoustic wave. If the pitch of the electrode fingers 18 is D, then the pitch of the electrode fingers 18 of one interdigital transducer 20 is D, which is the pitch of two electrode fingers 18. The reflector 24 reflects the acoustic waves (surface acoustic waves) excited by the electrode fingers 18. This confines the acoustic waves within the intersecting region 25 of the IDT 22. An insulating film may be provided to cover the electrode fingers 18. The insulating film functions as a protective film or a temperature compensation film.

[0024] FIG. 2(b) is a cross-sectional view of the electrode fingers 18a of the series resonators S1 to S6 in the first embodiment, and FIG. 2(c) is a cross-sectional view of the electrode fingers 18b of the parallel resonators P1 to P5. As shown in FIG. 2(b), in the series resonators S1 to S6, the IDTs 22, such as the electrode fingers 18a, and the reflectors 24 are formed by a conductive film 42a provided on the piezoelectric substrate 14. The conductive film 42a includes a first conductive layer 43 provided on the piezoelectric substrate 14 and a second conductive layer 44 provided on the first conductive layer 43. The first conductive layer 43 is, for example, a polycrystalline or amorphous titanium nitride (TiN) layer. The first conductive layer 43 may contain intentional or unintentional impurities other than titanium (Ti) and nitrogen (N). The sum of the titanium content and nitrogen content in the first conductive layer 43 is, for example, 80 atomic % or more, or 90 atomic % or more. The ratio of the nitrogen content (atomic %) to the sum of the titanium content (atomic %) and the nitrogen content (atomic %) is, for example, 0.01 or more and 0.99 or less, and typically 0.3 or more and 0.6 or less. The second conductive layer 44 is, for example, a polycrystalline or amorphous aluminum (Al) layer or an aluminum alloy layer.

[0025] As shown in FIG. 2(c), in the parallel resonators P1 to P5, the IDTs 22, such as the electrode fingers 18b, and the reflectors 24 are formed by a conductive film 42b provided on the piezoelectric substrate 14. The conductive film 42b includes a layer of a different material than the conductive film 42a. The conductive film 42b includes a third conductive layer 45 provided on the piezoelectric substrate 14 and a fourth conductive layer 46 provided on the third conductive layer 45. The third conductive layer 45 is, for example, a polycrystalline or amorphous titanium (Ti) layer. The third conductive layer 45 may contain intentional or unintentional impurities other than titanium. The fourth conductive layer 46 is formed of the same material as the second conductive layer 44 of the series resonators S1 to S6, for example, a polycrystalline or amorphous aluminum layer or aluminum alloy layer.

[0026] When the second conductive layer 44 and the fourth conductive layer 46 are aluminum layers, they may contain intentional or unintentional impurities other than aluminum. When the second conductive layer 44 and the fourth conductive layer 46 are aluminum alloy layers, they may contain at least one element of copper (Cu), magnesium (Mg), scandium (Sc), zirconium (Zr), titanium (Ti), neodymium (Nd), and silicon (Si) other than aluminum. When the second conductive layer 44 and the fourth conductive layer 46 are aluminum alloy layers, they may contain intentional or unintentional impurities other than aluminum and the metal elements constituting the aluminum alloy. The aluminum content in the second conductive layer 44 and the fourth conductive layer 46 is, for example, 80 atomic % or more, or 90 atomic % or more. The second conductive layer 44 and the fourth conductive layer 46 may be metal layers such as copper layers, copper alloy layers, molybdenum layers, or molybdenum alloy layers.

[0027] As shown in Fig. 1, the piezoelectric substrate 14 is not provided in the peripheral region of the support substrate 10. In a plan view seen from the +Z direction, a frame 15 is provided on the support substrate 10 so as to surround the piezoelectric substrate 14 and the series resonators S1 to S6 and parallel resonators P1 to P5 provided on the piezoelectric substrate 14. A lid is provided on the frame 15 so as to form a gap between the frame 15 and the piezoelectric substrate 14, and Fig. 1 shows the lid in a see-through manner. The series resonators S1 to S6 and the parallel resonators P1 to P5 are sealed in the gap formed on the piezoelectric substrate 14 by the frame 15 and the lid.

[0028] [experiment] Elastic wave resonators with Structures A and B were fabricated. Figures 3(a) and 3(b) are cross-sectional views of Structures A and B of the elastic wave resonators used in the experiments. As shown in Figure 3(a), in Structure A, insulating layers 11, 12, and 13 are provided in this order on a support substrate 10. A piezoelectric substrate 14 is provided on insulating layer 13. Insulating layer 12 is a temperature compensation film. The provision of insulating layer 12 reduces the frequency temperature coefficient. Insulating layer 11 is a boundary layer. The provision of insulating layer 11 confines the main mode surface acoustic wave within the piezoelectric substrate 14 and insulating layer 12 and suppresses spurious responses caused by unwanted waves. Insulating layer 13 is a bonding layer. The provision of insulating layer 13 strengthens the bond between insulating layer 12 and piezoelectric substrate 14. The interface between the support substrate 10 and insulating layer 11 is rough. This scatters unwanted waves at the interface, suppressing spurious responses. The other interfaces are mirror-finished. The electrode fingers 18 provided on the piezoelectric substrate 14 are a laminated film of a titanium (Ti) layer 60 and an aluminum copper alloy (AlCu) layer 62.

[0029] 3(b), in Structure B, the electrode fingers 18 provided on the piezoelectric substrate 14 are a laminated film of a titanium nitride (TiN) layer 64 and an aluminum copper alloy (AlCu) layer 62. The other configurations are the same as those of Structure A, so a description thereof will be omitted.

[0030] The conditions for producing structures A and B are as follows. Common conditions for structures A and B Support substrate 10: sapphire substrate with a thickness of 150 μm and a rough upper surface Insulating layer 11: Aluminum oxide layer with a thickness T1 of 2.8 μm Insulating layer 12: silicon oxide layer with a thickness T2 of 0.45 μm Insulating layer 13: Aluminum oxide layer with a thickness T3 of 0.01 μm Piezoelectric substrate 14: 42° rotated Y-cut X-propagation lithium tantalate substrate with a thickness T4 of 0.7 μm Conditions for Structure A Ti layer 60 of electrode finger 18: thickness 0.07 μm The AlCu alloy layer 62 of the electrode finger 18: thickness is 0.12 μm Conditions for Structure B TiN layer 64 of electrode finger 18: thickness 0.07 μm The AlCu alloy layer 62 of the electrode finger 18: thickness is 0.12 μm

[0031] We fabricated ladder-type filter A, which uses elastic wave resonators of structure A as the series and parallel resonators, and ladder-type filter B, which uses elastic wave resonators of structure B as the series and parallel resonators, and measured the temperature characteristics of their passband characteristics. Figure 4(a) shows the passband characteristics of ladder-type filter A, and Figure 4(b) shows the passband characteristics of ladder-type filter B. The passband characteristics are shown at ambient temperatures of 25°C, 50°C, and 85°C.

[0032] As shown in Figures 4(a) and 4(b), for both ladder filters A and B, the frequency increases as the temperature increases on the low-frequency side of the pass band. On the other hand, the frequency decreases as the temperature increases on the high-frequency side of the pass band. This is thought to be because, in acoustic wave resonators, the temperature characteristics at the resonant frequency and the anti-resonant frequency are different. The frequency change with temperature on the low-frequency side is smaller for ladder filter A than for ladder filter B. For example, at an attenuation of -20 dB, the temperature coefficient of frequency (TCF) on the low-frequency side of ladder filter A is approximately 0 ppm / K, while the TCF on the low-frequency side of ladder filter B is approximately +10 ppm / K. The frequency change with temperature on the high-frequency side is larger for ladder filter A than for ladder filter B. For example, at an attenuation of −20 dB, the TCF on the high-frequency side of ladder filter A is approximately −25 ppm / K, while the TCF on the high-frequency side of ladder filter B is approximately −15 ppm / K. This is thought to be because the elastic wave resonator with structure A used in ladder filter A uses a Ti layer 60 as the underlying layer for electrode fingers 18, while the elastic wave resonator with structure B used in ladder filter B uses a TiN layer 64 as the underlying layer for electrode fingers 18. That is, the Young's modulus of titanium (or titanium nitride) and aluminum constituting electrode fingers 18 changes with temperature, and the temperature change is greater than that of the piezoelectric substrate 14. On the other hand, the Young's modulus of titanium nitride is greater than that of titanium. Therefore, even if the Young's modulus of the TiN layer 64 and the AlCu alloy layer 62 changes with temperature, the TiN layer 64 is less likely to deform. This is thought to be because the TCF shifts in the positive direction when the TiN layer 64 is used compared to when the Ti layer 60 is used.

[0033] The low-frequency shoulder of a ladder filter is formed by the parallel resonators, and the high-frequency shoulder is formed by the series resonators. Therefore, in order to reduce the temperature change of both the low-frequency and high-frequency sides of the frequency, it is preferable to use a TiN underlayer for the electrode fingers of the series resonators of the ladder filter and a Ti underlayer for the electrode fingers of the parallel resonators.

[0034] In this way, for example, from the viewpoint of reducing the frequency temperature change on both the low-frequency side and the high-frequency side, the electrode fingers of the series resonator and the electrode fingers of the parallel resonator may be formed using different materials.

[0035] Fig. 5(a) is a plan view of the vicinity of the series resonator S4 and the parallel resonator P4 in Fig. 1, Fig. 5(b) is a cross-sectional view taken along line AA in Fig. 5(a), and Fig. 5(c) is a cross-sectional view of the vicinity of the wiring layer 34 in Fig. 5(b). In Fig. 5(a), the wiring layer 34 connecting the series resonator S4 and the parallel resonator P4 is hatched. As shown in Figs. 5(a) to 5(c), a first underlying conductive layer 36 connected to the series resonator S4 and a second underlying conductive layer 38 connected to the parallel resonator P4 are provided on the piezoelectric substrate 14.

[0036] The first underlying conductive layer 36 connected to the series resonator S4 has the same layer structure as the electrode fingers 18a of the series resonator S4. That is, the first underlying conductive layer 36 includes a first conductive layer 43, which is a titanium nitride layer provided on the piezoelectric substrate 14, and a second conductive layer 44, which is an aluminum layer or an aluminum alloy layer provided on the first conductive layer 43. In the first underlying conductive layer 36 and the electrode fingers 18a, the first conductive layers 43 have the same thickness, and the second conductive layers 44 have the same thickness. "Having the same thickness" allows for differences of the order of manufacturing error.

[0037] The second underlying conductive layer 38 connected to the parallel resonator P4 has the same layer structure as the electrode fingers 18b of the parallel resonator P4. That is, the second underlying conductive layer 38 includes a third conductive layer 45 that is a titanium layer provided on the piezoelectric substrate 14, and a fourth conductive layer 46 that is an aluminum layer or an aluminum alloy layer provided on the third conductive layer 45. In the second underlying conductive layer 38 and the electrode fingers 18b, the third conductive layers 45 have the same thickness, and the fourth conductive layers 46 have the same thickness.

[0038] The first conductive underlayer 36 and the second conductive underlayer 38 face each other with a gap 50 therebetween. The distance L between the first conductive underlayer 36 and the second conductive underlayer 38 across the gap 50 is, for example, 1 to 10 times the larger of the thickness T11 of the first conductive underlayer 36 and the thickness T12 of the second conductive underlayer 38. For example, the thickness T11 of the first conductive underlayer 36 and the thickness T12 of the second conductive underlayer 38 are 400 nm to 500 nm, and the distance L of the gap 50 is 500 nm to 5 μm.

[0039] The wiring layer 34 is provided from on the first underlying conductive layer 36 to on the second underlying conductive layer 38. The wiring layer 34 is provided to fill a gap 50 between the first underlying conductive layer 36 and the second underlying conductive layer 38. The series resonator S4 and the parallel resonator P4 are electrically connected by the wiring layer 34. The wiring layer 34 includes a first layer 35 and a second layer 37 provided on the first layer 35. The first layer 35 is, for example, an adhesion layer, and is a titanium (Ti) layer. The second layer 37 is, for example, a gold (Au) layer. The thickness T13 of the wiring layer 34 is at least twice the larger of the thickness T11 of the first underlying conductive layer 36 and the thickness T12 of the second underlying conductive layer 38. For example, the thickness T13 of the wiring layer 34 is 1 μm to 2 μm. Furthermore, for example, the distance L of the gap 50 is at least 0.5 times but not more than 3 times the thickness T13 of the wiring layer 34. The wiring layer 34 may completely fill the gap 50, or may have a cavity in part of the gap 50. The reason why the wiring layer 34 is provided on the first underlying conductive layer 36 and the second underlying conductive layer 38 is to reduce the resistance due to the electrical connection between the series resonator S4 and the parallel resonator P4, stabilize the characteristics, and increase reliability.

[0040] Although FIGS. 5(a) to 5(c) illustrate the connection point between the series resonator S4 and the parallel resonator P4, the other connection points between the series resonators and the parallel resonators also have the same structure.

[0041] [Manufacturing method] 6(a) to 8(c) are cross-sectional views illustrating a manufacturing method for the series resonator S4, the parallel resonator P4, and the wiring layer 34 in the first embodiment. FIGS. 6(a) to 8(c) show cross sections corresponding to FIG. 5(b). As shown in FIG. 6(a), the piezoelectric substrate 14 is bonded to the support substrate 10 at room temperature using, for example, a surface activation method, and then the piezoelectric substrate 14 is polished using, for example, a chemical mechanical polishing (CMP) method. This results in the piezoelectric substrate 14 being bonded directly or indirectly to the upper surface of the support substrate 10. Then, a first conductive film 43a and a second conductive film 44a are formed in this order on the piezoelectric substrate 14 using, for example, a sputtering method or a vacuum deposition method.

[0042] 6(b), a mask layer 80 is formed on the second conductive film 44a to cover the region where the series resonator S4 and the first underlying conductive layer 36 are to be formed. The mask layer 80 is formed of, for example, a resist.

[0043] 6(c), the second conductive film 44a and the first conductive film 43a are removed by, for example, etching using the mask layer 80 as a mask. Then, the mask layer 80 is removed. This results in the formation of a series resonator S4 having electrode fingers 18a including the first conductive layer 43 and the second conductive layer 44, and a first underlying conductive layer 36 connected to the series resonator S4 and having the same layer structure as the electrode fingers 18a.

[0044] 7(a), a mask layer 82 is formed on the piezoelectric substrate 14 to cover the series resonator S4 and the first conductive underlayer 36. The mask layer 82 is formed of, for example, a resist. The mask layer 82 is formed so as to completely cover the series resonator S4 and the first conductive underlayer 36 over an area larger than the area in which the series resonator S4 and the first conductive underlayer 36 are formed.

[0045] 7(b), using the mask layer 82 as a mask, a third conductive film 45a and a fourth conductive film 46a are formed in this order on the piezoelectric substrate 14 by, for example, sputtering or vacuum deposition. At this time, protrusions 66 that rise along the side surfaces of the mask layer 82 are formed on the third conductive film 45a and the fourth conductive film 46a.

[0046] 7(c), the mask layer 82 is removed by, for example, a lift-off method. Even after the mask layer 82 is removed, the protrusions 66 formed on the third conductive film 45a and the fourth conductive film 46a remain. The protrusions 66 are also called burrs. The height of the protrusions 66 from the upper surface of the fourth conductive film 46a is, for example, 300 nm to 800 nm, depending on the thickness of the third conductive film 45a and the fourth conductive film 46a.

[0047] 8(a), a mask layer 84 is formed to cover the series resonator S4 and the first underlying conductive layer 36, and to cover the region where the parallel resonator P4 and the second underlying conductive layer 38 are to be formed, and to have openings at the ends of the third conductive film 45a and the fourth conductive film 46a where the protrusions 66 are formed. The mask layer 84 is formed of, for example, a resist.

[0048] As shown in FIG. 8( b), the fourth conductive film 46 a and the third conductive film 45 a are removed by, for example, etching using the mask layer 84 as a mask. Then, the mask layer 84 is removed. This results in the formation of a parallel resonator P4 having electrode fingers 18 b including the third conductive layer 45 and the fourth conductive layer 46, and a second underlying conductive layer 38 connected to the parallel resonator P4 and having the same layer structure as the electrode fingers 18 b. The second underlying conductive layer 38 is formed opposite the first underlying conductive layer 36 across a gap 50. The protrusions 66 formed on the third conductive film 45 a and the fourth conductive film 46 a are removed by etching. Therefore, the thickness of the second underlying conductive layer 38 is uniform throughout the second underlying conductive layer 38.

[0049] 8(c), for example, a first layer 35 and a second layer 37 are formed using a vacuum deposition method and a lift-off method, thereby forming a wiring layer 34 from on the first underlying conductive layer 36 to on the second underlying conductive layer 38. The wiring layer 34 is formed to fill the gap 50. The series resonator S4 and the parallel resonator P4 are electrically connected by the wiring layer 34.

[0050] In this way, the electrode fingers 18a of the series resonator S4 and the electrode fingers 18b of the parallel resonator P4 contain different materials, so the series resonator S4 and the parallel resonator P4 are formed in separate processes. Therefore, the first underlying conductive layer 36 connected to the series resonator S4 and the second underlying conductive layer 38 connected to the parallel resonator P4 are also formed in separate processes.

[0051] [Comparative Example] 9(a) to 10(c) are cross-sectional views showing a method for manufacturing the series resonator S4, the parallel resonator P4, and the wiring layer 34 in the comparative example. First, the same steps as those shown in FIGS. 6(a) to 6(c) are performed. Next, as shown in FIG. 9(a), a mask layer 82 is formed on the piezoelectric substrate 14 to cover the series resonator S4 and the first conductive underlayer 36. At this time, the mask layer 82 is not allowed to cover the end of the first conductive underlayer 36 so that the first conductive underlayer 36 and the second conductive underlayer 38 are connected.

[0052] 9(b), for example, sputtering or vacuum deposition is used to deposit a third conductive film 45a and a fourth conductive film 46a in this order on the piezoelectric substrate 14. Because the ends of the first conductive underlayer 36 are not covered with the mask layer 82, the third conductive film 45a and the fourth conductive film 46a are also formed on the ends of the first conductive underlayer 36. In the third conductive film 45a and the fourth conductive film 46a, protruding portions 66 are formed on the first conductive underlayer 36 along the side surfaces of the mask layer 82.

[0053] 9(c), the mask layer 82 is removed by, for example, a lift-off method. Even after the mask layer 82 is removed, the protrusions 66 formed on the third conductive film 45a and the fourth conductive film 46a remain.

[0054] 10(a), a mask layer 84 is formed to cover the series resonator S4 and the first underlying conductive layer 36, and also to cover the region where the parallel resonator P4 and the second underlying conductive layer 38 are to be formed. The protrusions 66 formed on the third conductive film 45a and the fourth conductive film 46a are also covered by the mask layer 84.

[0055] 10(b), the fourth conductive film 46a and the third conductive film 45a are removed by, for example, etching using the mask layer 84 as a mask. Then, the mask layer 84 is removed. This results in the formation of a parallel resonator P4 having electrode fingers 18b including the third conductive layer 45 and the fourth conductive layer 46, and a second underlying conductive layer 38 connected to the parallel resonator P4 and having the same layer structure as the electrode fingers 18b. The protrusions 66 remain because they were covered with the mask layer 84.

[0056] As shown in FIG. 10( c), the wiring layer 34 is formed from the first conductive underlayer 36 to the second conductive underlayer 38 by forming the first layer 35 and the second layer 37 using, for example, vacuum deposition and lift-off. Because the end of the second conductive underlayer 38 is located on the first conductive underlayer 36, the wiring layer 34 has a thin portion at the end of the second conductive underlayer 38. Furthermore, because a protrusion 66 is formed at the end of the second conductive underlayer 38, the wiring layer 34 is likely to become even thinner. For this reason, cracks 67 may occur in the thin portions of the wiring layer 34. The occurrence of the cracks 67 increases the electrical resistance of the wiring layer 34, and if the cracks 67 are large, the wiring layer 34 may be broken.

[0057] 5(a) and 5(b), the first underlying conductive layer 36 and the second underlying conductive layer 38 are provided opposite each other with a gap 50 therebetween. This makes it difficult for the wiring layer 34, which is provided from the first underlying conductive layer 36 to the second underlying conductive layer 38, to have a thin portion. This makes it possible to prevent cracks from occurring in the wiring layer 34, and to prevent an increase in electrical resistance and disconnection of the wiring layer 34.

[0058] 5(b) and 5(c), in Example 1, the thickness T11 of the first underlying conductive layer 36 is constant throughout the first underlying conductive layer 36. The thickness T12 of the second underlying conductive layer 38 is constant throughout the second underlying conductive layer 38. That is, the first underlying conductive layer 36 and the second underlying conductive layer 38 do not have protrusions 66 formed thereon, unlike the second underlying conductive layer 38 in the comparative example. This prevents the wiring layer 34 from having thin portions, thereby preventing cracks from occurring in the wiring layer 34. Note that a constant thickness allows for differences within the order of manufacturing error, and allows for a difference of 5% or less between the maximum thickness and the minimum thickness relative to the average thickness.

[0059] According to the manufacturing method of Example 1, as shown in FIG. 6(c), a series resonator S4 (first acoustic wave resonator) having electrode fingers 18a and a first underlying conductive layer 36 connected to the series resonator S4 and having the same layer structure as the electrode fingers 18a are formed on a piezoelectric substrate 14. As shown in FIG. 7(a), a mask layer 82 (first mask layer) covering the series resonator S4 and the first underlying conductive layer 36 is formed on the piezoelectric substrate 14. As shown in FIG. 7(b), a third conductive film 45a and a fourth conductive film 46a (conductive films) are formed on the piezoelectric substrate 14 using the mask layer 82 as a mask. As shown in FIG. 8(a), after removing the mask layer 82, a mask layer 84 (second mask layer) having openings at least at the ends of the third conductive film 45a and the fourth conductive film 46a is formed on the piezoelectric substrate 14. 8(b), the third conductive film 45a and the fourth conductive film 46a are etched using the mask layer 84 as a mask to form a parallel resonator P4 (second acoustic wave resonator) including electrode fingers 18b, and a second underlying conductive layer 38 connected to the parallel resonator P4, having the same layer structure as the electrode fingers 18b, and facing the first underlying conductive layer 36 across a gap 50. After removing the mask layer 84 as shown in FIG. 8(c), the wiring layer 34 connecting the series resonator S4 and the parallel resonator P4 is formed from on the first underlying conductive layer 36 to on the second underlying conductive layer 38. This makes it possible to prevent the wiring layer 34 from becoming thin in places, and to prevent cracks from occurring in the wiring layer 34.

[0060] 8(a), the mask layer 84 (second mask layer) is formed so that openings are positioned at the protrusions 66 formed at the ends of the third conductive film 45a and the fourth conductive film 46a. As a result, as shown in FIG. 8(b), the protrusions 66 are removed by etching the third conductive film 45a and the fourth conductive film 46a using the mask layer 84 as a mask, which can prevent the wiring layer 34 from having thin portions. Therefore, the wiring layer 34 can be prevented from having cracks.

[0061] 7(a), in the manufacturing method of Example 1, the mask layer 82 (first mask layer) is formed in an area larger than the area where the series resonator S4 and the first conductive underlying layer 36 are formed, so as to completely cover the series resonator S4 and the first conductive underlying layer 36. This reduces the difference in the amount of etching in the area where the parallel resonator P4 is formed and the amount of etching in the area where the protrusion 66 is formed, as shown in FIG.

[0062] Furthermore, in Example 1, the thickness T13 of the wiring layer 34 is at least twice the larger of the thickness T11 of the first underlying conductive layer 36 and the thickness T12 of the second underlying conductive layer 38. This ensures that the wiring layer 34 has a considerable thickness even in thin locations, making it possible to prevent cracks from occurring in the wiring layer 34.

[0063] In Example 1, the distance L of the gap 50 between the first underlying conductive layer 36 and the second underlying conductive layer 38 is 1 to 10 times the larger of the thickness T11 of the first underlying conductive layer 36 and the thickness T12 of the second underlying conductive layer 38. When the distance L is 1 or more times the larger of the thicknesses T11 and T12, the wiring layer 34 is easily formed in the gap 50, thereby improving the reliability of the electrical connection between the series resonator S4 and the parallel resonator P4 by the wiring layer 34. From the viewpoint of improving the reliability of the electrical connection, the distance L is preferably 1.5 or more times the larger of the thicknesses T11 and T12, more preferably 2 or more times, and even more preferably 2.5 or more times. When the distance L is 10 or less times the larger of the thicknesses T11 and T12, the gap 50 can be formed in a narrow space between the series resonator S4 and the parallel resonator P4. The distance in the X direction between the series resonator S4 and the parallel resonator P4 is, for example, ¼ or less of the length of the electrode fingers 18 of the resonator having the shorter length in the Y direction of the electrode fingers 18 of the series resonator S4 or the parallel resonator P4. From the viewpoint of miniaturizing the device by narrowing the width between the resonators, the distance L is preferably 8 times or less, more preferably 6 times or less, and even more preferably 4 times or less, of the larger of the thicknesses T11 and T12.

[0064] In addition, in the first embodiment, the gap 50 between the first and second underlying conductive layers 36 and 38 is provided between the series resonator S4 and the parallel resonator P4 in the X direction. Although the acoustic waves excited by the series resonator S4 and the parallel resonator P4 mainly propagate in the X direction, the gap 50 can reduce interference caused by the propagation of acoustic waves between the series resonator S4 and the parallel resonator P4.

[0065] In the first embodiment, the electrode fingers 18a of the series resonator S4 include a first conductive layer 43 that is a TiN layer and a second conductive layer 44 provided on the first conductive layer 43. The electrode fingers 18b of the parallel resonator P4 include a third conductive layer 45 that is a Ti layer and a fourth conductive layer 46 that is provided on the third conductive layer 45 and is made of the same material as the second conductive layer 44. This makes it possible to reduce the frequency temperature variation on both the low-frequency side and the high-frequency side of the passband, as described with reference to FIGS. 4(a) and 4(b).

[0066] In Example 1, as in structures A and B in FIGS. 3(a) and 3(b), insulating layer 11, insulating layer 12, and insulating layer 13 may be provided between support substrate 10 and piezoelectric substrate 14. Only insulating layer 13 may be provided, or only insulating layers 12 and 13 may be provided. Furthermore, the interface between support substrate 10 and insulating layer 11 is not limited to a rough surface and may be a mirror surface, or the interface between support substrate 10 and insulating layer 11 may be a rough surface and the interface between insulating layer 11 and insulating layer 12 may also be a rough surface. If insulating layer 11 is not provided, the interface between support substrate 10 and insulating layer 12 may be a rough surface. Furthermore, piezoelectric substrate 14 may not be provided on support substrate 10.

[0067] Although the first embodiment exemplifies a case in which two acoustic wave resonators connected by providing a wiring layer on two underlying conductive layers disposed with a gap therebetween are used in a filter, the present invention is not limited to this case and may also be used in other cases, such as a sensor including these two acoustic wave resonators. [Example]

[0068] FIG. 11 is a circuit diagram of a duplexer 200 according to a second embodiment. As shown in FIG. 11, in the duplexer 200, a transmit filter 70 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 72 is connected between the common terminal Ant and a receive terminal Rx. The transmit filter 70 passes, to the common terminal Ant, signals in the transmit band among the high-frequency signals input from the transmit terminal Tx as transmit signals, and suppresses signals of other frequencies. The receive filter 72 passes, to the receive terminal Rx, signals in the receive band among the high-frequency signals input from the common terminal Ant as receive signals, and suppresses signals of other frequencies. At least one of the transmit filter 70 and the receive filter 72 can be the filter of the first embodiment. Note that, although a duplexer has been shown as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0069] 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 variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0070] 10...support substrate, 11...insulating layer, 12...insulating layer, 13...insulating layer, 14...piezoelectric substrate, 15...frame body, 18, 18a, 18b...electrode fingers, 19...bus bar, 20...comb-shaped electrode, 22...IDT, 24...reflector, 25...intersection area, 30...terminal, 32...via wiring, 34...wiring layer, 35...first layer, 36...first underlying conductive layer, 37...second layer, 38...second underlying conductive layer, 40...surface acoustic wave resonator, 42a, 42b...conductive film, 43... First conductive layer, 43a...first conductive film, 44...second conductive layer, 44a...second conductive film, 45...third conductive layer, 45a...third conductive film, 46...fourth conductive layer, 46a...fourth conductive film, 50...gap, 60...Ti layer, 62...AlCu alloy layer, 64...TiN layer, 66...protrusion, 67...crack, 70...transmitting filter, 72...receiving filter, 80...mask layer, 82...mask layer, 84...mask layer, 100...filter, 200...duplexer

Claims

1. a piezoelectric substrate; a first acoustic wave resonator provided on the piezoelectric substrate and having a plurality of first electrode fingers; a second acoustic wave resonator provided on the piezoelectric substrate and having a plurality of second electrode fingers including a material different from that of the plurality of first electrode fingers; a first underlying conductive layer provided on the piezoelectric substrate, connected to the first acoustic wave resonator, and having the same layer structure as the plurality of first electrode fingers; a second underlying conductive layer provided on the piezoelectric substrate, connected to the second acoustic wave resonator, having the same layer structure as the plurality of second electrode fingers, and facing the first underlying conductive layer with a gap therebetween; an interconnection layer provided on the first underlying conductive layer and extending over the second underlying conductive layer, the interconnection layer connecting the first acoustic wave resonator and the second acoustic wave resonator;

2. the thickness of the first conductive underlayer is constant throughout the first conductive underlayer; The acoustic wave device according to claim 1 , wherein the second underlying conductive layer has a constant thickness throughout the second underlying conductive layer.

3. 3. The acoustic wave device according to claim 1, wherein the thickness of the wiring layer is at least twice the thickness of the larger of the first underlying conductive layer and the second underlying conductive layer.

4. 3. The acoustic wave device according to claim 1, wherein the distance between the first underlying conductive layer and the second underlying conductive layer facing each other through the gap is at least one time the thickness of the larger of the first underlying conductive layer and the second underlying conductive layer.

5. the plurality of first electrode fingers and the plurality of second electrode fingers are arranged in the same direction, The acoustic wave device according to claim 1 , wherein the gap is provided between the first acoustic wave resonator and the second acoustic wave resonator in the arrangement direction.

6. A filter comprising the acoustic wave device according to claim 1 or 2.

7. the first acoustic wave resonator is a series resonator connected in series between an input terminal and an output terminal, the second acoustic wave resonator is a parallel resonator connected in parallel between the input terminal and the output terminal, the plurality of first electrode fingers include a first conductive layer that is a titanium nitride layer and a second conductive layer provided on the first conductive layer; 7. The filter according to claim 6, wherein the plurality of second electrode fingers include a third conductive layer that is a titanium layer, and a fourth conductive layer that is provided on the third conductive layer and is made of the same material as the second conductive layer.

8. A multiplexer including the filter of claim 6.

9. forming, on a piezoelectric substrate, a first acoustic wave resonator having a plurality of first electrode fingers, and a first underlying conductive layer connected to the first acoustic wave resonator and having the same layer structure as the plurality of first electrode fingers; forming a first mask layer on the piezoelectric substrate to cover the first acoustic wave resonator and the first underlying conductive layer; forming a conductive film on the piezoelectric substrate using the first mask layer as a mask; After removing the first mask layer, forming a second mask layer on the piezoelectric substrate, the second mask layer having an opening at least at an end of the conductive film; etching the conductive film using the second mask layer as a mask to form a second acoustic wave resonator having a plurality of second electrode fingers; and a second underlying conductive layer connected to the second acoustic wave resonator, having the same layer structure as the plurality of second electrode fingers, and facing the first underlying conductive layer with a gap therebetween; and after removing the second mask layer, forming a wiring layer that connects the first acoustic wave resonator and the second acoustic wave resonator from on the first underlying conductive layer to on the second underlying conductive layer.

10. The method for manufacturing an acoustic wave device according to claim 9 , wherein the step of forming the second mask layer includes forming the second mask layer so that the opening is positioned at a protrusion formed at the end of the conductive film.

11. 11. The method for manufacturing an acoustic wave device according to claim 9, wherein the step of forming the first mask layer includes forming the first mask layer so as to completely cover the first acoustic wave resonator and the first underlying conductive layer in an area larger than an area in which the first acoustic wave resonator and the first underlying conductive layer are formed.

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