elastic wave device

Abstract

An elastic wave device includes a substrate, an elastic wave component formed on the substrate, a first wiring formed on the substrate and connected to the elastic wave component, a first insulator formed on the first wiring, a second wiring formed on the first insulator, a second insulator covering the first wiring, the first insulator, and at least a portion of the second wiring, and a third insulator covering at least a portion of the second insulator, wherein the second wiring includes a three-dimensional wiring portion that three-dimensionally intersects the first wiring via the first insulator, wherein the compressive stress of the second insulator is greater than the compressive stress of the first insulator and less than the compressive stress of the third insulator. This provides a highly reliable elastic wave device.

Description

Technical Field

[0001] The present invention relates to an elastic wave device such as a surface acoustic wave (SAW) device or a piezoelectric film bulk acoustic resonator (FBAR). Background Art

[0002] Filters using surface acoustic waves (or acoustic wave devices) are currently widely used in the receiver circuits of mobile phones and other devices. As described in most specifications, their structure consists of a resonator (or acoustic wave element) formed by applying comb-shaped electrodes to a piezoelectric substrate such as lithium tantalate or lithium niobate.

[0003] Furthermore, as described in Patent Document 1 (International Publication No. 2011 / 087018), wiring is formed on the piezoelectric substrate to connect external connection terminals such as input and output terminals to the elastic wave device. To accommodate miniaturization of the elastic wave device, these wiring can be formed in a three-dimensional intersecting pattern with an insulating layer interposed therebetween. Summary of the Invention

[0004] The main problems to be solved by the present invention are described as follows. In order to improve the reliability and propagation characteristics of the elastic wave device, improve the temperature coefficient of frequency (TCF) used to measure the change in frequency response due to temperature changes, and improve moisture resistance, an insulator such as silicon nitride is formed on a substrate provided with an elastic wave component. The compressive stress of the insulator such as silicon nitride is large, and a large compressive stress will be generated during the heating process of the process. In the three-dimensional wiring portion formed on the substrate, the insulator used to isolate the wiring that crosses each other will peel off due to the compressive stress. In view of the above problems, the purpose of the present invention is to provide an elastic wave device that can improve the propagation characteristics of the elastic wave device, improve TCF and moisture resistance, and has high reliability.

[0005] The elastic wave device of the present invention includes a substrate, an elastic wave component formed on the substrate, a first wiring formed on the substrate and connected to the elastic wave component, a first insulator formed on the first wiring, a second wiring formed on the first insulator, a second insulator covering the first wiring, the first insulator and at least a portion of the second wiring, and a third insulator covering at least a portion of the second insulator, wherein the second wiring includes a three-dimensional wiring portion that three-dimensionally intersects with the first wiring via the first insulator, wherein the compressive stress of the second insulator is greater than the compressive stress of the first insulator and less than the compressive stress of the third insulator.

[0006] In one aspect of the present invention, the second insulator is formed directly on the second wiring and the first insulator.

[0007] In one aspect of the present invention, the third insulator is made of silicon nitride.

[0008] In one aspect of the present invention, the second insulator is made of silicon dioxide.

[0009] In one aspect of the present invention, the first insulator is made of polyimide.

[0010] In one aspect of the present invention, a cross section of the first insulator perpendicular to its longitudinal direction is trapezoidal.

[0011] In one aspect of the present invention, a surface of the substrate opposite to the principal surface on which the elastic wave component is provided is bonded to a supporting substrate, and the supporting substrate is made of sapphire, alumina, spinel, or silicon.

[0012] In one form of the present invention, the elastic wave component includes a forked electrode and a reflector formed on the substrate, the forked electrode includes a pair of comb-shaped electrodes arranged opposite to each other, each of the comb-shaped electrodes has a plurality of electrode fingers and a bus bar connected to the electrode fingers, and the reflector is arranged on both sides of the forked electrode.

[0013] In one embodiment of the present invention, the elastic wave component is a piezoelectric thin film resonator and includes a lower electrode, an upper electrode, and a piezoelectric film sandwiched between the lower electrode and the upper electrode formed on the substrate, wherein a gap is formed between the lower electrode and the substrate.

[0014] In one form of the present invention, the elastic wave device also includes: a side wall portion surrounding the elastic wave component; and a shell portion that cooperates with the side wall portion to form and seal the elastic wave component in a manner that does not hinder the vibration of the elastic wave component, and the first wiring includes external connection portions electrically connected to each other, wiring directly formed on the substrate relative to the external connection portions, and metal filled in the through holes of the side wall portion and the shell portion.

[0015] Through the present invention, the propagation characteristics of the elastic wave device can be improved. Even if an insulator such as silicon nitride with a large compressive stress is formed on the substrate in order to improve TCF and moisture resistance, the peeling of the insulator used to isolate the intersecting wiring in the three-dimensional wiring part formed on the substrate can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Other features and effects of the present invention will be clearly presented in the embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1FIG. 1 is a cross-sectional view of a first embodiment of the elastic wave device according to the present invention.

[0018] Figure 2 FIG1 is a plan view of an example in which the elastic wave component according to the first embodiment is a surface acoustic wave resonator.

[0019] Figure 3 FIG. 1 is a schematic plan view of a substrate of the elastic wave device according to the first embodiment.

[0020] Figure 4 It is along Figure 3 Section view along section line AA.

[0021] Figure 5 is a cross-sectional view of an elastic wave device according to a comparative example of the first embodiment.

[0022] Figure 6 These are photographs showing whether the first embodiment and the comparative example are peeled off.

[0023] Figure 7 FIG. 1 is a cross-sectional view of an example in which the elastic wave module according to the second embodiment is a piezoelectric thin-film resonator. DETAILED DESCRIPTION

[0024] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0025] (First embodiment)

[0026] Figure 1 FIG is a cross-sectional view of the elastic wave device of the first embodiment. Figure 1 As shown, the elastic wave device 1 of the first embodiment includes a substrate 3 , an elastic wave component 5 , a sidewall 7 , a housing 9 , and an external connection portion 11 .

[0027] In the first embodiment, the substrate 3 is a piezoelectric substrate 3a, for example, made of a piezoelectric single crystal such as lithium tantalate, lithium niobate, or quartz, or a piezoelectric ceramic. Furthermore, the substrate 3 may be bonded to a supporting substrate 13. The supporting substrate 13 may be made of, for example, a sapphire substrate, an alumina substrate, a spinel substrate, or a silicon substrate. In a specific embodiment, the substrate 3 includes a primary surface on which the elastic wave assembly 5 is provided and an opposite surface opposite to the primary surface, the opposite surface being bonded to the supporting substrate 13.

[0028] In the first embodiment, the acoustic wave component 5 is an interdigital transducer (IDT) for exciting surface acoustic waves. Figure 2 FIG. 1 is a top view of an example of the elastic wave component 5 being an elastic surface wave resonator in the first embodiment. Figure 2As shown, an IDT 5a and a reflector 5b are formed on the piezoelectric substrate 3a. The IDT 5a includes a pair of comb-shaped electrodes 5c disposed opposite each other. Each comb-shaped electrode 5c has a plurality of electrode fingers 5d and bus bars 5e connected to the electrode fingers 5d. The reflectors 5b are provided on both sides of the IDT 5a.

[0029] The elastic wave component 5 and the first wiring 15 are made of a suitable metal or alloy such as silver, aluminum, copper, titanium, palladium, etc. In addition, the metal pattern may also be a multi-layer metal structure formed by stacking multiple metal layers.

[0030] In the first embodiment, the side wall 7 surrounds the elastic wave module 5. The housing 9 cooperates with the side wall 7 to form and seal the elastic wave module 5 in a manner that does not hinder the vibration of the elastic wave module 5.

[0031] The sidewall 7 is made of a synthetic resin. Preferably, the sidewall 7 is made of a photosensitive resin. Such a photosensitive resin is easily patterned using photolithography. This allows for easy creation of openings that do not obstruct the vibration of the elastic wave module 5 or through-holes for wiring the external connector 11.

[0032] The photosensitive resin may be photosensitive polyimide, photosensitive epoxy resin, photosensitive silicone, etc. Preferably, in order to achieve precise patterning, photosensitive polyimide may be used, but it is not limited thereto.

[0033] The housing 9 is made of a synthetic resin. The synthetic resin constituting the housing 9 may be, for example, epoxy resin or polyimide, but is not limited thereto. Preferably, epoxy resin may be used and the housing 9 may be formed by a low-temperature curing process.

[0034] The external connection portion 11 includes a first wiring 15 formed on the substrate 3, electrically connecting the elastic wave device 1 to the wiring constituting the input terminal In, the output terminal Out, and the ground terminal GND. In this embodiment, the first wiring 15 includes the external connection portion 11, a wiring directly formed on the substrate relative to the external connection portion 11, and metal 11a, which serves as a lower bump metal filling in the through-holes of the sidewall portion 7 and the housing portion 9. The external connection portion 11, the wiring, and the metal 11a are electrically connected to each other.

[0035] Figure 3 FIG. 1 is a schematic plan view of substrate 3 of elastic wave device 1 according to the first embodiment. Figure 3 The side wall portion 7 , the housing portion 9 , and the external connection portion 11 are omitted.

[0036] like Figure 3As shown, the elastic wave component 5 and the first wiring 15 are formed on the substrate 3 (i.e., the piezoelectric substrate 3a). In order to obtain the desired bandpass filter characteristics, the elastic wave component 5 can appropriately adopt a defective microstrip structure (DMS) design and a ladder design. The first wiring 15 includes wiring constituting an input terminal In, an output terminal Out, and a ground terminal GND. In addition, the first wiring 15 is electrically connected to the elastic wave component 5. In addition, a first insulator 19 is formed on the first wiring 15. The first insulator 19 can be made of, for example, polyimide (manufactured by Toray Industries, Ltd., LT-8151C, compressive stress of 28 to 31 MPa). The film thickness of the first insulator 19 is, for example, 1000 nm.

[0037] Second wiring 17 is formed on first insulator 19. Second wiring 17 includes a three-dimensional wiring portion 17a that intersects first wiring 15 across first insulator 19. Like first wiring 15, second wiring 17 is made of a suitable metal or alloy, such as silver, aluminum, copper, titanium, or palladium. Furthermore, second wiring 17 may have a multilayer metal structure composed of multiple stacked metal layers.

[0038] Figure 4 It is along Figure 3 Cross-sectional view along section line AA. The second insulator 21 covers the first wiring 15, the second wiring 17, and the first insulator 19 provided on the substrate 3. Furthermore, the third insulator 23 covers the second insulator 21. Here, the third insulator 23 is made of a suitable material for the purpose of serving as a protective film for improving reliability, improving TCF, improving moisture resistance, and improving propagation characteristics. The third insulator 23 is made of, for example, silicon nitride (compressive stress 1200-1400 MPa). The film thickness of the third insulator 23 is, for example, 10-30 nm, and preferably, the film thickness is 20 nm. In a specific implementation, the second insulator 21 may cover at least a portion of the first wiring 15, the second wiring 17 and the first insulator 19 provided on the substrate 3, and the third insulator 23 covers at least a portion of the second insulator 21.

[0039] The second insulator 21 can be made of a material having a compressive stress greater than that of the first insulator 19 and less than that of the third insulator 23. The second insulator 21 can be, for example, silicon dioxide (compressive stress 200-400 MPa). The film thickness of the second insulator 21 can be, for example, 5 nm to 30 nm, preferably 10 nm. In practice, the inventors used silicon nitride with a film thickness of 20 nm as the third insulator 23 and produced five prototypes in which the second insulator 21 was formed of silicon dioxide and had film thicknesses of 5 nm, 10 nm, 20 nm, and 30 nm. At this time, in the prototypes of the second insulator formed with film thicknesses of 5 nm, 20 nm, and 30 nm, although the peeling of the first insulator 19 was well suppressed, slight peeling was still observed. In the prototype of the second insulator 21 formed with a film thickness of 10 nm, no peeling of the first insulator 19 was observed.

[0040] like Figure 4 As shown, the cross-section of the first insulator 19 perpendicular to its longitudinal direction is preferably trapezoidal. This allows the second insulator 21 and the third insulator 23 to be stably formed on the first insulator 19. In particular, in the corner region between the top and side surfaces of the first insulator 19, damage or localized thinning of the second insulator 21 and the third insulator 23 must be avoided to stably improve moisture resistance.

[0041] Figure 5 This is a cross-sectional view of an elastic wave device as a comparative example to the first embodiment. In this comparative example, the third insulator 23 covers the first wiring 15, the second wiring 17, and the first insulator 19 provided on the substrate 3. In this comparative example, the second insulator 21 is not formed.

[0042] Figure 6 The following are photos showing the peeling of the first embodiment and the comparative example. In the comparative example elastic wave device, a portion of the first insulator 19 (polyimide) peeled off. On the other hand, in the elastic wave device of the first embodiment, the first insulator 19 (polyimide) did not peel off.

[0043] (Second embodiment)

[0044] Figure 7 FIG2 is a cross-sectional view of an example in which the elastic wave component 5 is a piezoelectric thin film resonator in the second embodiment. Figure 7As shown, a piezoelectric film 25, a lower electrode 27 and an upper electrode 29 are formed on a substrate 3b. The piezoelectric film 25 is sandwiched between the lower electrode 27 and the upper electrode 29. A gap 31 is formed between the lower electrode 27 and the substrate 3b. The lower electrode 27 and the upper electrode 29 excite elastic waves in the piezoelectric film 25 in a thickness longitudinal vibration mode. The substrate 3b can be, for example, a semiconductor substrate such as silicon, or an insulating substrate such as sapphire, alumina, spinel or glass. The piezoelectric film 25 can be, for example, aluminum nitride. The lower electrode 27 and the upper electrode 29 can be, for example, a metal such as ruthenium.

[0045] The other configurations of the second embodiment are the same as those of the first embodiment, and therefore description thereof will be omitted.

[0046] According to the structure of the present invention described above, the propagation characteristics of the elastic wave device can be improved, and even if an insulator such as silicon nitride with a large compressive stress is formed on the substrate in order to improve TCF and moisture resistance, the peeling of the insulator used to isolate the interconnected wiring in the three-dimensional wiring portion formed on the substrate can be suppressed.

[0047] The above description is only a preferred embodiment of the present invention and should not be used to limit the scope of the present invention. That is, any simple equivalent changes and modifications made according to the claims and description of the present invention still fall within the scope of the present invention.

Claims

1. An elastic wave device, characterized in that: The elastic wave device includes a substrate, an elastic wave component formed on the substrate, a first wiring formed on the substrate and connecting the elastic wave component, a first insulator formed on the first wiring, a second wiring formed on the first insulator, a second insulator covering the first wiring, the first insulator and at least a portion of the second wiring, and a third insulator covering at least a portion of the second insulator, wherein the second wiring includes a three-dimensional wiring portion that three-dimensionally intersects with the first wiring via the first insulator, wherein the compressive stress of the second insulator is greater than the compressive stress of the first insulator and less than the compressive stress of the third insulator, the thickness of the second insulator is in the range of 5-10nm, and the thickness of the third insulator is in the range of 10-20nm.

2. The elastic wave device according to claim 1, wherein: The second insulator is directly formed on the second wiring and the first insulator.

3. The elastic wave device according to claim 1, wherein: The third insulator is made of silicon nitride.

4. The elastic wave device according to claim 1, wherein: The second insulator is made of silicon dioxide.

5. The elastic wave device according to claim 1, wherein: The first insulator is made of polyimide.

6. The elastic wave device according to claim 1, wherein: The cross section of the first insulator perpendicular to its longitudinal direction is trapezoidal.

7. The elastic wave device according to claim 1, wherein: The substrate includes a main surface on which the elastic wave component is provided and an opposite surface opposite to the main surface. The opposite surface is bonded to a supporting substrate made of sapphire, alumina, spinel, or silicon.

8. The elastic wave device according to claim 1, wherein: The elastic wave component includes a forked electrode and a reflector formed on the substrate, the forked electrode includes a pair of comb-shaped electrodes arranged opposite to each other, each of the comb-shaped electrodes has a plurality of electrode fingers and a bus bar connected to the electrode fingers, and the reflector is arranged on both sides of the forked electrode.

9. The elastic wave device according to claim 1, wherein: The elastic wave component is a piezoelectric thin film resonator and includes a lower electrode, an upper electrode, and a piezoelectric film sandwiched between the lower electrode and the upper electrode formed on the substrate, with a gap formed between the lower electrode and the substrate.

10. The elastic wave device according to claim 1, wherein: The elastic wave device also includes: a side wall portion surrounding the elastic wave component; and a shell portion that cooperates with the side wall portion to form and seal the elastic wave component in a manner that does not hinder the vibration of the elastic wave component. The first wiring includes external connection portions that are electrically connected to each other, wiring directly formed on the substrate relative to the external connection portions, and metal filled in the through holes of the side wall portion and the shell portion.

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