Elastic wave devices, filters, multiplexers, and methods for manufacturing elastic wave devices

Abstract

To provide an elastic wave device capable of suppressing an increase in elastic loss.SOLUTION: An elastic wave device 100 comprises: a silicon substrate 10; a piezoelectric film 14 which is provided on the silicon substrate 10; an upper electrode 16 which is provided on the piezoelectric film 14; a lower electrode 12 which is provided between the silicon substrate 10 and the piezoelectric film 14, which has a cavity 40 between itself and the silicon substrate 10, which is brought into contact with the cavity 40 in a resonance region 50 overlapping the upper electrode 16 with the piezoelectric film 14 in between, and which is made of ruthenium; and a barrier layer 18 which has a ring shape surrounding at least the cavity 40, which has an inner periphery of the ring shape positioned within the cavity 40, the outer periphery of which is positioned on the silicon substrate 10, and the outer periphery of which has a recess 24 connected to the cavity 40 in a plan view.SELECTED DRAWING: Figure 2

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 Art]

[0002] Acoustic wave devices using piezoelectric thin-film resonators are used, for example, as filters and multiplexers in radio devices such as mobile phones. A piezoelectric thin-film resonator has a structure in which a lower electrode and an upper electrode face each other with a piezoelectric film interposed therebetween. A region where the lower electrode and the upper electrode face each other with the piezoelectric film interposed therebetween is a resonance region. A configuration is known in which an air gap is provided below the resonance region so as not to restrict vibration (see, for example, Patent Documents 1 and 2). It is also known to use a laminated film of a chromium film and a ruthenium film for the lower electrode (see, for example, Patent Document 2). [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2005-45694 [Patent Document 2] Japanese Unexamined Patent Publication No. 2014-161001 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] Although a ruthenium film is a preferable material in terms of resonance characteristics, when a ruthenium film is used for a lower electrode, an adhesion layer such as a chromium film needs to be provided because the adhesion between the ruthenium film and a silicon substrate is poor. When the structure is such that an adhesion layer made of a chromium film or the like and a lower electrode made of a ruthenium film are laminated in the resonance region, elastic loss increases if the adhesion layer is a film having a lower acoustic impedance than the lower electrode.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to suppress an increase in elastic loss. [Means for solving the problem]

[0006] The present invention comprises a silicon substrate, a piezoelectric film provided on the silicon substrate, an upper electrode provided on the piezoelectric film, a lower electrode made of ruthenium provided between the silicon substrate and the piezoelectric film, having a gap between itself and the silicon substrate, and contacting the gap in a resonant region that overlaps with the upper electrode across the piezoelectric film, and a barrier layer having at least a ring shape surrounding the gap, with the inner circumference of the ring shape located within the gap and the outer circumference located on the silicon substrate, and having a recess on the outer circumference in a plan view that connects to the gap, or having a hole that penetrates from the top surface to the bottom surface and connects to the gap. The void includes a depression formed on the surface of the silicon substrate and an air layer between the depression and the lower electrode. It is an elastic wave device.

[0008] The present invention relates to a silicon substrate, a piezoelectric film provided on the silicon substrate, an upper electrode provided on the piezoelectric film, a lower electrode made of ruthenium provided between the silicon substrate and the piezoelectric film, having a gap between itself and the silicon substrate, and contacting the gap in a resonant region that overlaps with the upper electrode across the piezoelectric film, and a barrier layer having at least a ring shape surrounding the gap, with the inner circumference of the ring shape located within the gap and the outer circumference located on the silicon substrate, having a recess on the outer circumference in a plan view that connects to the gap, or having a hole that penetrates from the top surface to the bottom surface and connects to the gap, and including a titanium nitride layer, a tantalum nitride layer, a tungsten nitride layer, or a diamond-like carbon layer. An adhesion layer sandwiched between the barrier layer and the lower electrode, having a ring shape and provided along the barrier layer in contact with at least the void, and containing an aluminum layer, cobalt layer, chromium layer, molybdenum layer, nickel layer, tantalum layer, titanium layer, or tungsten layer. and, Equipped with It is an elastic wave device. .

[0010] The present invention is a filter that includes the elastic wave device described above.

[0011] The present invention is a multiplexer comprising the filter described above.

[0012] The present invention is a method for manufacturing an elastic wave device, comprising the steps of: forming a barrier layer on a silicon substrate that has at least a ring shape in plan view and has a recess on the outer circumference of the ring shape, or a hole that penetrates from the top surface to the bottom surface; forming an adhesion layer that covers the surface of the silicon substrate inside the inner circumference of the ring shape of the barrier layer; forming a lower electrode made of ruthenium on the adhesion layer; forming a piezoelectric film on the lower electrode; forming an upper electrode on the piezoelectric film; reacting the adhesion layer with the silicon substrate to form a silicide layer; and introducing an etching medium through the recess or the hole to etch and remove the silicide layer in the resonance region where the lower electrode and the upper electrode overlap with the piezoelectric film in between, thereby forming a gap in contact with the lower electrode.

[0013] In the above configuration, the step of forming the silicide layer can be configured to form the silicide layer by heating the silicon substrate to react the adhesion layer with the silicon substrate.

[0014] In the above configuration, the barrier layer may include a titanium nitride layer, a tantalum nitride layer, a tungsten nitride layer, or a diamond-like carbon layer.

[0015] In the above configuration, the adhesion layer may include an aluminum layer, a cobalt layer, a chromium layer, a molybdenum layer, a nickel layer, a tantalum layer, a titanium layer, or a tungsten layer. [Effects of the Invention]

[0016] According to the present invention, the increase in elastic loss can be suppressed. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a plan view of the elastic wave device according to Example 1. [Figure 2] Figure 2(a) is a cross-sectional view of section AA in Figure 1, and Figure 2(b) is a cross-sectional view of section BB in Figure 1. [Figure 3] Fig. 3(a) is a plan view showing the piezoelectric film, the lower electrode, and the barrier layer in Example 1; Fig. 3(b) is a plan view showing the adhesion layer and the barrier layer; Fig. 3(c) is a plan view showing the barrier layer. [Figure 4] Figs. 4(a) to 4(d) are cross-sectional views (Part 1) illustrating the method for manufacturing the acoustic wave device according to Example 1. [Figure 5] Figs. 5(a) to 5(d) are cross-sectional views (Part 2) illustrating the method for manufacturing the acoustic wave device according to Example 1. [Figure 6] Fig. 6 is a plan view of an acoustic wave device according to a comparative example. [Figure 7] Fig. 7(a) is a cross-sectional view taken along line A-A in Fig. 6, and Fig. 7(b) is a cross-sectional view taken along line B-B in Fig. 6. [Figure 8] Figs. 8(a) to 8(d) are cross-sectional views illustrating the method for manufacturing the acoustic wave device according to a comparative example. [Figure 9] Figs. 9(a) and 9(b) are cross-sectional views showing a case where the adhesion layer under the lower electrode is removed in a comparative example. [Figure 10] Fig. 10(a) is a plan view of an acoustic wave device according to a modification of Example 1, and Fig. 10(b) is a cross-sectional view taken along line A-A in Fig. 10(a). [Figure 11] Fig. 11 is a circuit diagram of a filter according to Example 2. [Figure 12] Fig. 12 is a circuit diagram of a duplexer according to Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, examples of the present invention will be described with reference to the drawings. EXAMPLES

[0019] Figure 1 is a plan view of the elastic wave device 100 according to Example 1. Figure 2(a) is a cross-sectional view AA of Figure 1, and Figure 2(b) is a cross-sectional view BB of Figure 1. Figure 3(a) is a plan view showing the piezoelectric film 14, lower electrode 12, and barrier layer 18 in Example 1, Figure 3(b) is a plan view showing the adhesion layer 26 and barrier layer 18 in Example 1, and Figure 3(c) is a plan view showing the barrier layer 18 in Example 1.

[0020] As shown in Figures 1, 2(a), 2(b), and 3(a) to 3(c), the elastic wave device 100 according to Example 1 has a lower electrode 12 made of a single layer film of ruthenium on a silicon (Si) substrate 10. A gap 40 is formed between the silicon substrate 10 and the lower electrode 12. The gap 40 is formed by a depression 41 provided on the upper surface of the silicon substrate 10 and an air layer 42 between the depression 41 and the lower electrode 12.

[0021] A barrier layer 18 is provided on the silicon substrate 10, having a ring-shaped region 20 in plan view that surrounds the void 40, and a region 22 that extends from region 20. A recess 24 connecting to the void 40 is provided in a part of the outer circumference 19 of the ring-shaped region 20 of the barrier layer 18. The inner circumference 17 of region 20 of the barrier layer 18 is located within the void 40 and is in contact with the void 40, while the outer circumference 19 is located on the silicon substrate 10 except for the recess 24. The recess 24 may be an arc shape in plan view, or it may be an elliptical arc shape or a rectangular shape or other shape. The barrier layer 18 is made of a material that does not form silicides. For example, the barrier layer 18 is a single layer of titanium nitride (TiN) film, tantalum nitride (TaN) film, tungsten nitride (WN) film, or diamond-like carbon (DLC) film, or a laminate of these.

[0022] An adhesion layer 26 is provided sandwiched between the barrier layer 18 and the lower electrode 12. The adhesion layer 26 has a ring-shaped region 28 provided along the region 20 of the barrier layer 18 in contact with the void 40, and a region 30 drawn out from region 28. Region 30 of the adhesion layer 26 is located on the region 22 of the barrier layer 18. The adhesion layer 26 is formed of a material that forms a silicide. For example, the adhesion layer 26 is a single layer or a laminate of an aluminum (Al) film, cobalt (Co) film, chromium (Cr) film, molybdenum (Mo) film, nickel (Ni) film, tantalum (Ta) film, titanium (Ti) film, or tungsten (W) film.

[0023] A piezoelectric film 14 is provided on the lower electrode 12. The piezoelectric film 14 is, for example, a film mainly composed of aluminum nitride (AlN) with the (002) direction as its principal axis. The piezoelectric film 14 may also be a zinc oxide (ZnO) film, a lead zirconate titanate (PZT) film, a lead titanate (PbTiO3) film, a lithium tantalate film, or a lithium niobate film. Furthermore, the piezoelectric film 14 may mainly consist of aluminum nitride and may contain other elements to improve resonance characteristics or piezoelectricity. For example, the piezoelectricity of the piezoelectric film 14 can be improved by using scandium (Sc), two elements from group 2 and group 4, or two elements from group 2 and group 5 as additive elements. Examples of group 2 elements are calcium (Ca), magnesium (Mg), strontium (Sr), or zinc (Zn). Examples of group 4 elements are titanium (Ti), zirconium (Zr), or hafnium (Hf). Group 5 elements include, for example, tantalum (Ta), niobium (Nb), or vanadium (V). Furthermore, the piezoelectric film 14 may mainly consist of aluminum nitride and may also contain boron (B).

[0024] An upper electrode 16 is provided on the piezoelectric film 14 such that a resonance region 50 is formed, which is the region facing the lower electrode 12 with the piezoelectric film 14 in between. The resonance region 50 is located on the air gap 40 and is the region where elastic waves of thickness longitudinal vibration mode or thickness shear vibration mode resonate. The lower electrode 12 has a portion that is in contact with the air gap 40 in the resonance region 50. The portion of the lower electrode 12 that extends out from the resonance region 50 is provided on the region 30 of the adhesion layer 26. The planar shape of the resonance region 50 is, for example, approximately elliptical. In plan view, the size of the air gap 40 is larger than the resonance region 50. Note that the planar shape of the resonance region 50 may be a polygon such as a square or pentagon, or other shapes.

[0025] The upper electrode 16 can be a single layer or a multilayer of ruthenium (Ru), aluminum (Al), chromium (Cr), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), or iridium (Ir). As an example, the upper electrode 16 is a single layer of ruthenium, just like the lower electrode 12. A protective film or the like may be provided on the upper electrode 16.

[0026] [Manufacturing method] Figures 4(a) to 5(d) are cross-sectional views showing the manufacturing method of the elastic wave device 100 according to Example 1. Figures 4(a), 4(b), 5(a), and 5(b) are cross-sections of the area corresponding to the section A and A in Figure 1, and Figures 4(c), 4(d), 5(c), and 5(d) are cross-sections of the area corresponding to the section B and C in Figure 1.

[0027] As shown in Figures 4(a) and 4(c), a barrier layer 18 is deposited on the flat main surface of the silicon substrate 10 using, for example, sputtering, vacuum deposition, or CVD (Chemical Vapor Deposition). Subsequently, the barrier layer 18 is patterned into a desired shape using, for example, photolithography and etching. This forms a barrier layer 18 having a ring-shaped region 20 with a recess 24 in part of the outer circumference 19 in a plan view, and a region 22 extended from region 20 (see also Figure 3(c)). The barrier layer 18 is, for example, a titanium nitride film.

[0028] As shown in Figures 4(b) and 4(d), an adhesion layer 26 and a lower electrode 12 are deposited on the silicon substrate 10 in this order, covering the barrier layer 18, using, for example, sputtering, vacuum deposition, or CVD. Then, the adhesion layer 26 and the lower electrode 12 are patterned into a desired shape using, for example, photolithography and etching. This forms an adhesion layer 26 having a region 29 that covers the upper surface of the silicon substrate 10 inside the region 20 of the barrier layer 18, and a region 31 that is drawn out from region 29 and located on the barrier layer 18. A lower electrode 12 is formed on the adhesion layer 26, having the same shape as the adhesion layer 26 in a plan view. The adhesion layer 26 is, for example, a chromium film, and the lower electrode 12 is a ruthenium film. Because the adhesion layer 26 is provided between the lower electrode 12 and the silicon substrate 10, delamination of the lower electrode 12 from the silicon substrate 10 is suppressed.

[0029] As shown in Figures 5(a) and 5(c), a piezoelectric film 14 is formed on a silicon substrate 10, covering the barrier layer 18, the adhesion layer 26, and the lower electrode 12, for example, using sputtering, vacuum deposition, or CVD. An upper electrode 16 is then formed on the piezoelectric film 14, for example, using sputtering, vacuum deposition, or CVD. Subsequently, the upper electrode 16 and the piezoelectric film 14 are patterned into a desired shape, for example, using photolithography and etching. This creates a piezoelectric film 14 and an upper electrode 16 with the same shape in plan view, and a resonance region 50 is formed where the lower electrode 12 and the upper electrode 16 face each other with the piezoelectric film 14 in between. The piezoelectric film 14 is, for example, an aluminum nitride film, and the upper electrode 16 is, for example, a ruthenium film.

[0030] As shown in Figures 5(b) and 5(d), the region 29 of the adhesion layer 26 is reacted with the silicon substrate 10 to form a silicide layer 32 in the adhesion layer 26 below the resonance region 50. For example, the silicide layer 32 is formed by heating the silicon substrate 10 to react the adhesion layer 26 with the silicon substrate 10. As an example, if the adhesion layer 26 is a chromium film, a silicide layer 32 made of chromium silicide is formed by heating the silicon substrate 10 to 300°C to 500°C. The silicidding reaction proceeds from the interface between the adhesion layer 26 and the silicon substrate 10, spreading according to the heating temperature and heating time. Therefore, the silicide layer 32 is formed not only in the region 29 of the adhesion layer 26 but also in the silicon substrate 10. When forming the silicide layer 32, the heating temperature and heating time are controlled so that the silicide layer 32 is exposed from the recess 24 formed in the barrier layer 18. Furthermore, since the barrier layer 18 is made of a material that does not form silicides, the silicide reaction does not occur in the barrier layer 18 and therefore no silicide layer is formed.

[0031] An etching medium (e.g., an etching solution) is introduced into the silicide layer 32 beneath the lower electrode 12 through a recess 24 formed in the barrier layer 18. As a result, as shown in Figures 2(a) and 2(b), the silicide layer 32 is removed, and a gap 40 is formed between the lower electrode 12 and the silicon substrate 10 below the resonance region 50. The gap 40 is formed by a recess 41 on the upper surface of the silicon substrate 10 and an air layer 42 between the recess 41 and the lower electrode 12. In the resonance region 50, the lower electrode 12 comes into contact with the gap 40. The inner circumference 17 of region 20 of the barrier layer 18 is located within the gap 40 and in contact with the gap 40, while the outer circumference 19 is located on the silicon substrate 10 except for the recess 24. The etching medium is preferably one that does not etch areas other than the silicide layer 32. As an example, if the barrier layer 18 is a titanium nitride film and the silicide layer 32 is a chromium silicide layer, nitric acid is used as the etching medium. As a result, only the silicide layer 32 can be etched without etching the barrier layer 18, the lower electrode 12, or the silicon substrate 10. Thus, the elastic wave device 100 according to Example 1 is formed.

[0032] [Comparative Example] Figure 6 is a plan view of the elastic wave device 500 according to the comparative example. Figure 7(a) is a cross-sectional view of AA in Figure 6, and Figure 7(b) is a cross-sectional view of BB in Figure 6. As shown in Figures 6, 7(a), and 7(b), in the elastic wave device 500 according to the comparative example, a resonance region 150 is formed with the lower electrode 112 and the upper electrode 116 facing each other with a piezoelectric film 114 in between. A gap 140 is formed between the lower electrode 112 and the flat main surface of the silicon substrate 110. The resonance region 150 is located on the gap 140. An adhesion layer 126 is provided between the lower electrode 112 and the gap 140 throughout the resonance region 150. The adhesion layer 126 is provided for adhesion between the lower electrode 112, which is made of a single layer of ruthenium, and the silicon substrate 110. The adhesion layer 126 is, for example, a chromium film. The piezoelectric film 114 is, for example, a film mainly composed of aluminum nitride. The upper electrode 16 is, for example, a single layer of ruthenium film. The lower electrode 112 and the adhesion layer 126 are provided with introduction channels 134 for introducing an etching solution to etch the sacrificial layer. The sacrificial layer is a layer for forming a void 140.

[0033] Figures 8(a) to 8(d) are cross-sectional views showing a method for manufacturing an elastic wave device 500 according to a comparative example. Figures 8(a) and 8(b) are cross-sectional views of the area corresponding to the space between A and A in Figure 6, and Figures 8(c) and 8(d) are cross-sectional views of the area corresponding to the space between B and B in Figure 6. As shown in Figures 8(a) and 8(c), a sacrificial layer 136 is formed on the flat main surface of the silicon substrate 110 to form a void. The sacrificial layer 136 is, for example, a magnesium oxide (MgO) film. Subsequently, the sacrificial layer 136 is covered on the silicon substrate 110 to form an adhesion layer 126 and a lower electrode 112. An introduction path 134 is formed in the lower electrode 112 and the adhesion layer 126.

[0034] As shown in Figures 8(b) and 8(d), a piezoelectric film 114 is formed on the silicon substrate 110 and on the lower electrode 112. An upper electrode 116 is formed on the piezoelectric film 114. A resonance region 150 is formed where the lower electrode 112 and the upper electrode 116 face each other with the piezoelectric film 114 in between. Then, an etching solution (e.g., nitric acid) for etching the sacrificial layer 136 is introduced into the sacrificial layer 136 below the adhesion layer 126 via the introduction path 134. As a result, as shown in Figures 7(a) and 7(b), the sacrificial layer 136 is removed and a void 140 is formed.

[0035] In the comparative example elastic wave device 500, a chromium film adhesion layer 126 is provided on the underside of the ruthenium film lower electrode 112 throughout the entire resonance region 150. While using a ruthenium film for the lower electrode 112 improves resonance characteristics, the presence of a chromium film adhesion layer 126 on the lower electrode 112 results in increased elastic loss because the chromium film has a lower acoustic impedance than the ruthenium film.

[0036] On the other hand, according to Example 1, as shown in Figures 2(a) and 2(b), a barrier layer 18 is provided which has a ring shape that surrounds at least the void 40, with the inner circumference 17 of the ring shape located within the void 40 and the outer circumference 19 located on the silicon substrate 10. The barrier layer 18 is provided with a recess 24 on the outer circumference 19 that connects to the void 40. The lower electrode 12 made of ruthenium is in contact with the void 40 in the resonance region 50. This makes it possible to suppress the increase in elastic loss.

[0037] Furthermore, in Example 1, the barrier layer 18 is made of a material that does not form silicides. This makes it possible to obtain a structure in which a gap 40 is provided between the lower electrode 12 and the silicon substrate 10, in which the lower electrode 12 is in contact, as shown in Figures 4(a) to 5(d). The barrier layer 18 can include a titanium nitride (TiN) layer, a tantalum nitride (TaN) layer, a tungsten nitride (WN) layer, or a diamond-like carbon (DLC) layer as a layer that does not form silicides.

[0038] Furthermore, in Example 1, as shown in Figures 2(a) and 2(b), an adhesion layer 26 is provided, which has a ring shape sandwiched between the barrier layer 18 and the lower electrode 12, and is provided along the barrier layer 18, at least in contact with the void 40, and is made of a material that forms a silicide. This makes it possible to obtain a structure in which a void 40 is provided between the lower electrode 12 and the silicon substrate 10, as shown in Figures 4(a) to 5(d), in which the lower electrode 12 is in contact. In addition, the adhesion between the barrier layer 18 and the lower electrode 12 can be improved. The adhesion layer 26 can include an aluminum (Al) layer, a cobalt (Co) layer, a chromium (Cr) layer, a molybdenum (Mo) layer, a nickel (Ni) layer, a tantalum (Ta) layer, a titanium (Ti) layer, or a tungsten (W) layer as the layer that forms the silicide.

[0039] In Example 1, if the adhesion between the barrier layer 18 and the lower electrode 12 is good, the adhesion layer 26 may not be provided between the barrier layer 18 and the lower electrode 12, and the barrier layer 18 and the lower electrode 12 may be in direct contact.

[0040] In Example 1, as shown in Figures 2(a) and 2(b), the void 40 includes a depression 41 formed on the surface of the silicon substrate 10 and an air layer 42 between the depression 41 and the lower electrode 12. As shown in Figures 4(a) to 5(d), by forming the void 40 using the silicide layer 32, the void 40 is formed to include the depression 41 and the air layer 42.

[0041] In the comparative example, to prevent the adhesion layer 126 from being formed on the underside of the lower electrode 112 in the resonance region 150, it is conceivable to remove the adhesion layer 126 by introducing an etching solution into the void 140 from the introduction passage 134. Figures 9(a) and 9(b) are cross-sectional views showing the case in the comparative example where the adhesion layer 126 on the underside of the lower electrode 112 is removed. As shown in Figures 9(a) and 9(b), by introducing an etching solution into the void 140 from the introduction passage 134 and etching away the adhesion layer 126, a structure can be achieved in which the adhesion layer 126 is not formed on the underside of the lower electrode 112 in the resonance region 150. However, in this case, it is necessary to leave the adhesion layer 126 in regions A and B so that the lower electrode 112 does not peel off from the silicon substrate 110. Because the height of the void 140 is small, capillary action and other factors make it difficult to control the etching solution, making it difficult to control the adhesion layer 126 to remain in regions A and B.

[0042] According to Example 1, as shown in Figures 3(c), 4(a), and 4(c), a barrier layer 18 is formed on the silicon substrate 10, having at least a ring-shaped region 20 in plan view, with a recess 24 on the outer circumference 19 of the ring-shaped region 20. As shown in Figures 4(b) and 4(d), an adhesion layer 26 is formed to cover the surface of the silicon substrate 10 inside the inner circumference 17 of the ring-shaped region 20 of the barrier layer 18. A lower electrode 12 made of ruthenium is formed on the adhesion layer 26. As shown in Figures 5(a) and 5(c), a piezoelectric film 14 is formed on the lower electrode 12. An upper electrode 16 is formed on the piezoelectric film 14. As shown in Figures 5(b) and 5(d), the adhesion layer 26 is reacted with the silicon substrate 10 to form a silicide layer 32. As shown in Figures 2(a) and 2(b), an etching medium is introduced through the recess 24 of the barrier layer 18, and the silicide layer 32 below the resonance region 50 where the lower electrode 12 and the upper electrode 16 overlap with the piezoelectric film 14 in between is etched away to form a gap 40 in contact with the lower electrode 12. The silicide layer 32 formed by the reaction between the adhesion layer 26 and the silicon substrate 10 is easy to control in terms of the formation region of the silicide layer 32. Therefore, it is possible to form a gap 40 in contact with the lower electrode 12 below the resonance region 50 while suppressing the delamination of each component constituting the elastic wave device 100 from the silicon substrate 10. Thus, an elastic wave device 100 that can suppress the increase in elastic loss can be easily manufactured.

[0043] In Example 1, the silicon substrate 10 is heated to react the adhesion layer 26 with the silicon substrate 10, thereby forming the silicide layer 32. Since the silicide reaction proceeds by spreading from the interface between the adhesion layer 26 and the silicon substrate 10 according to the heating temperature and heating time, the formation region of the silicide layer 32 can be easily controlled.

[0044] [Differentiation] Figure 10(a) is a plan view of the elastic wave device 200 according to a modified example of Example 1, and Figure 10(b) is a cross-sectional view AA of Figure 10(a). As shown in Figures 10(a) and 10(b), in the elastic wave device 200 according to a modified example of Example 1, the ring-shaped region 20 of the barrier layer 18 does not have a recess 24. Instead, a hole 25 is provided that penetrates the region 20 from the top surface to the bottom surface and connects to the void 40. The other configurations are the same as in Example 1, so their description is omitted.

[0045] The modified elastic wave device 200 of Example 1 is formed by the same method as in Example 1, except that a barrier layer 18 with holes 25 is formed in a ring-shaped region 20, and an etching medium is introduced into the silicide layer 32 through the holes 25 to etch the silicide layer 32. In the modified example of Example 1, the effect of suppressing the increase in elastic loss is obtained, just as in Example 1. [Examples]

[0046] Figure 11 is a circuit diagram of the filter 300 according to Embodiment 2. As shown in Figure 11, the filter 300 has one or more series resonators S1 to S4 connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. The parallel resonators P1 to P3 are connected between the path between the input terminal Tin and the output terminal Tout and the ground terminal. The elastic wave device of Embodiment 1 can be used for at least one of the series resonators S1 to S4 and the parallel resonators P1 to P3. The number of resonators in the ladder-type filter can be set as appropriate. [Examples]

[0047] Figure 12 is a circuit diagram of the duplexer 400 according to Embodiment 3. As shown in Figure 12, the duplexer 400 has a transmit filter 60 connected between the common terminal Ant and the transmit terminal Tx. A receive filter 62 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 60 allows the transmit band signal from the high-frequency signal input from the transmit terminal Tx to pass to the common terminal Ant as the transmit signal, and suppresses signals of other frequencies. The receive filter 62 allows the receive band signal from the high-frequency signal input from the common terminal Ant to pass to the receive terminal Rx as the received signal, and suppresses signals of other frequencies. At least one of the transmit filter 60 and the receive filter 62 can be the filter of Embodiment 2. Although a duplexer has been described as an example of a multiplexer, a triplexer or quadplexer may also be used.

[0048] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0049] 10...Silicon substrate, 12...Lower electrode, 14...Piezoelectric film, 16...Upper electrode, 17...Inner circumference, 18...Barrier layer, 19...Outer circumference, 20, 22...Region, 24...Recess, 25...Pore, 28, 29, 30...Region, 32...Silicide layer, 40...Void, 41...Depression, 42...Air layer, 50...Resonance region, 60...Transmitting filter, 62...Receiving filter, 100, 200...Elastic wave device, 300...Filter, 400...Duplexer

Claims

1. A silicon substrate and A piezoelectric film provided on the silicon substrate, An upper electrode provided on the piezoelectric film, A lower electrode made of ruthenium is provided between the silicon substrate and the piezoelectric film, having a gap between it and the silicon substrate, and in contact with the gap in a resonant region that overlaps with the upper electrode across the piezoelectric film, A barrier layer comprising at least a ring shape surrounding the void, the inner circumference of the ring shape being located within the void, the outer circumference being located on the silicon substrate, and having a recess on the outer circumference in a plan view that connects to the void, or having a hole that penetrates from the top surface to the bottom surface and connects to the void, The elastic wave device comprises a cavity formed on the surface of the silicon substrate and an air layer between the cavity and the lower electrode.

2. A silicon substrate and A piezoelectric film provided on the silicon substrate, An upper electrode provided on the piezoelectric film, A lower electrode made of ruthenium is provided between the silicon substrate and the piezoelectric film, having a gap between it and the silicon substrate, and in contact with the gap in a resonant region that overlaps with the upper electrode across the piezoelectric film, A barrier layer having at least a ring shape surrounding the void, the inner circumference of the ring shape being located within the void, the outer circumference being located on the silicon substrate, and having a recess on the outer circumference in a plan view that connects to the void, or having a hole that penetrates from the top surface to the bottom surface and connects to the void, and comprising a titanium nitride layer, a tantalum nitride layer, a tungsten nitride layer, or a diamond-like carbon layer, An elastic wave device comprising an adhesion layer sandwiched between the barrier layer and the lower electrode, having a ring shape provided along the barrier layer and in contact with at least the void, and containing an aluminum layer, a cobalt layer, a chromium layer, a molybdenum layer, a nickel layer, a tantalum layer, a titanium layer, or a tungsten layer.

3. A filter comprising the elastic wave device according to claim 1 or 2.

4. A multiplexer comprising the filter described in claim 3.

5. A step of forming a barrier layer on a silicon substrate that has at least a ring shape in plan view, with a recess on the outer circumference of the ring shape, or a hole that penetrates from the top surface to the bottom surface, A step of forming an adhesion layer that covers the surface of the silicon substrate inside the inner circumference of the ring shape of the barrier layer, The steps include forming a lower electrode made of ruthenium on the aforementioned adhesion layer, The steps include forming a piezoelectric film on the lower electrode, The steps include forming an upper electrode on the piezoelectric film, The process involves reacting the adhesion layer with the silicon substrate to form a silicide layer, A method for manufacturing an elastic wave device, comprising the steps of introducing an etching medium through the recess or hole, etching and removing the silicide layer in the resonance region where the lower electrode and the upper electrode overlap with the piezoelectric film in between, thereby forming a gap in contact with the lower electrode.

6. The method for manufacturing an elastic wave device according to claim 5, wherein the step of forming the silicide layer is to heat the silicon substrate to react the adhesion layer with the silicon substrate and form the silicide layer.

7. The method for manufacturing an elastic wave device according to claim 5 or 6, wherein the barrier layer includes a titanium nitride layer, a tantalum nitride layer, a tungsten nitride layer, or a diamond-like carbon layer.

8. The method for manufacturing an elastic wave device according to claim 7, wherein the adhesion layer includes an aluminum layer, a cobalt layer, a chromium layer, a molybdenum layer, a nickel layer, a tantalum layer, a titanium layer, or a tungsten layer.

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