JP5394948B2 - Elastic wave device - Google Patents

Description

  The present invention relates to an acoustic wave device, and more particularly to an acoustic wave device in which an IDT is sealed.

  Conventionally, acoustic wave devices have been widely used as filters and duplexers used in mobile communication devices and the like. In recent years, in response to the demand for miniaturization, WLP (Wafer Level Package) type acoustic wave devices have been developed in which the package of an acoustic wave device is reduced to the size of an acoustic wave element.

  For example, Patent Document 1 discloses an acoustic wave device in which an electrode pad is formed of Al / Ti / Au / Ti in order from the side closer to the piezoelectric substrate, and the adhesion between the resin part for sealing the IDT and the electrode pad is improved. Has been.

JP 2009-159124 A

  However, in the conventional acoustic wave device, for example, when a crack or the like is generated in the upper layer of the metal layer forming the wiring and the electrode pad, the wiring and the electrode pad may be corroded due to the penetration of moisture.

  In view of the above problems, an object of the present invention is to provide a highly reliable acoustic wave device capable of suppressing corrosion of wiring and electrode pads.

The present invention includes a piezoelectric substrate, an IDT formed on the piezoelectric substrate, a wiring formed on the piezoelectric substrate and electrically connected to the IDT, formed on the piezoelectric substrate, and the wiring An electrode pad electrically connected to the acoustic wave element via an insulating layer formed on the piezoelectric substrate so as to cover the acoustic wave element and the wiring. The wiring in the region in contact with the insulating layer and the electrode pad are composed of a plurality of metal layers, and each of the plurality of metal layers has a higher resistance to corrosion than the metal forming the electrode of the acoustic wave element. An elastic wave device comprising: According to the present invention, corrosion of wiring and electrode pads can be suppressed. Therefore, the reliability of the acoustic wave device can be increased.

  The said structure WHEREIN: The wiring of the area | region which is in contact with the said insulating layer among the said wiring can be set as the structure which does not contain the metal which forms the said IDT. According to this configuration, the corrosion resistance of the wiring and the electrode pad can be increased and corrosion can be effectively suppressed in a region where stress is likely to occur. Therefore, the reliability of the acoustic wave device can be increased.

  In the above structure, the IDT may be made of Al or an alloy containing Al. According to this configuration, good device characteristics can be obtained, and corrosion of the wiring and the electrode pad can be suppressed, thereby improving the reliability of the acoustic wave device.

  In the above configuration, the wiring and the electrode pad may be configured by at least one of Ti, Ta, Au, and Pt. According to this configuration, since the wiring and the electrode pad are formed of a metal having high corrosion resistance, corrosion can be suppressed and the reliability of the acoustic wave device can be improved.

  In the above configuration, the wiring and the electrode pad may be composed of a plurality of metal layers, and each of the plurality of metal layers may be composed of a metal having higher corrosion resistance to moisture than the metal forming the IDT. According to this configuration, even if the wiring and the electrode pad have a multilayer structure, the plurality of metal layers have high corrosion resistance, so that corrosion can be suppressed and the reliability of the acoustic wave device can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, the highly reliable elastic wave device which can suppress corrosion of wiring and an electrode pad can be provided.

FIG. 1A is a plan view illustrating an acoustic wave device according to a comparative example, and FIG. 1B is a cross-sectional view illustrating an acoustic wave device according to a comparative example. FIG. 2A is a plan view illustrating an acoustic wave device according to the first embodiment, and FIG. 2B is a cross-sectional view illustrating the acoustic wave device according to the first embodiment. FIG. 3A to FIG. 3D are cross-sectional views illustrating the method for manufacturing the acoustic wave device according to the first embodiment. FIG. 4A to FIG. 4C are cross-sectional views illustrating the method for manufacturing the acoustic wave device according to the first embodiment.

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

  First, comparative examples will be described in order to clarify the effects of the examples. FIG. 1A is a plan view illustrating an acoustic wave device according to a comparative example, and FIG. 1B is a cross-sectional view illustrating an acoustic wave device according to a comparative example. In FIG. 1A, an insulating layer 12 to be described later is shown through. FIG.1 (b) has illustrated the AB cross section of Fig.1 (a).

  As shown in FIG. 1A and FIG. 1B, an acoustic wave device includes an acoustic wave element 1 including a piezoelectric substrate 2, an IDT (Inter Digital Transducer) 4, a reflector 5, and the like, a protective film 6, and a wiring 3 , Electrode pad 10, insulating layer 12, electrode post 14, and terminal 16. As shown in FIG. 1A, a plurality of IDTs 4 and terminals 16 are electrically connected by wiring 3. The wiring 3 includes an inter-pad wiring 8 that connects between electrode pads 10 to be described later, and a lead-out wiring 7 that connects the IDT 4 and the inter-pad wiring 8. That is, the horizontal wiring in FIG. 1A is the inter-pad wiring 8 and the vertical wiring is the lead wiring 7.

As shown in FIG. 1B, the IDT 4, the reflector 5 and the lead wiring 7 are made of a metal such as Al, for example, and are formed on the piezoelectric substrate 2 made of a piezoelectric material such as LiTaO ₃ or LiNbO ₃ . . The protective film 6 is made of, for example, a silicon compound such as SiO ₂ (silicon dioxide) or SiN (silicon nitride). The protective film 6 covers the Al layer 18 (described later) of the IDT 4, the lead-out wiring 7, and the inter-pad wiring 8. The inter-pad wiring 8 is electrically connected to the IDT 4 through the lead wiring 7. The inter-pad wiring 8 is formed by laminating metal layers such as an Al layer 18, a Ti layer 20, an Au layer 22, and a Ti layer 24 in order from the side closer to the piezoelectric substrate 2.

  The electrode pad 10 is electrically connected to the IDT 4 via the inter-pad wiring 8. The electrode pad 10 is formed by laminating metal layers such as an Al layer 18, a Ti layer 20, and an Au layer 22 in order from the side closer to the piezoelectric substrate 2. The Al layer 18 located in the lowermost layer of the inter-pad wiring 8 and the electrode pad 10 is formed in the process of forming the IDT 4 and is exposed to the outside of the acoustic wave device.

  For example, the insulating layer 12 made of an insulator such as an epoxy resin covers the IDT 4, a part of the lead wiring 7, and the inter-pad wiring 8. As shown in a region surrounded by a dotted line in FIG. 1A, a hollow portion 13 is formed on the upper side of the IDT 4. That is, the insulating layer 12 seals the IDT 4 so that the hollow portion 13 is formed above the IDT 4. Since the hollow portion 13 is formed on the IDT 4, the excitation of the IDT 4 is not hindered. The insulating layer 12 is in contact with a part of the lead wiring 7 and the inter-pad wiring 8.

  An opening is formed in the insulating layer 12, and an electrode post 14 made of a metal such as Cu is formed in the opening. On the electrode post 14, a terminal 16 made of solder such as Sn-Ag is formed. The electrode post 14 is in contact with the Au layer 22 of the electrode pad 10. That is, the IDT 4 is electrically connected to the terminal 16 via the lead wiring 7, the inter-pad wiring 8, the electrode pad 10, and the electrode post 14.

  For example, when the acoustic wave device is heated as in the reflow in the process of mounting the acoustic wave device, the inter-pad wiring 8 is contracted by the contraction of the insulating layer 12 in the region where the inter-pad wiring 8 and the insulating layer 12 are in contact with each other. In some cases, stress was generated. When stress is applied to the inter-pad wiring 8, damage such as cracks may occur in the Au layer 22 and the Ti layers 20 and 24 in the upper layer of the inter-pad wiring 8. When the inter-pad wiring 8 whose upper layer is damaged is placed in a high-temperature and high-humidity environment, moisture may infiltrate from the damaged portion, and the Al layer 18 at the lowest layer of the inter-pad wiring 8 may be corroded by moisture.

  In addition, a stress applied between the electrode pad 10 and the electrode post 14 due to a load or temperature change applied to the acoustic wave device may damage the Ti layer 20 and the Au layer 22 on the electrode pad 10. Also in this case, the Al layer 18 under the electrode pad 10 may be corroded by moisture that has entered from the damaged portion. Furthermore, the Al layer 18 exposed at the end of the acoustic wave device may corrode. The corrosion of the Al layer 18 forming the inter-pad wiring 8 and the electrode pad 10 as described above may reduce the reliability of the acoustic wave device.

  Next, Example 1 will be described. FIG. 2A is a plan view illustrating an acoustic wave device according to the first embodiment, and FIG. 2B is a cross-sectional view illustrating the acoustic wave device according to the first embodiment. The description of the same configuration as that described above is omitted.

  As shown in FIG. 2A, a region of the IDT 4, the reflector 5, and the lead-out wiring 7 that does not contact the insulating layer 12 (this is referred to as a first lead-out wiring 9) is made of Al. On the other hand, the region of the lead-out wiring 7 that contacts the insulating layer 12 (referred to as the second lead-out wiring 11), the inter-pad wiring 8, and the electrode pad 10 do not contain Al. That is, the metal that forms the second lead-out wiring 11, the inter-pad wiring 8, and the electrode pad 10 does not include the metal that forms the IDT 4. In FIG. 2A, among the extraction wiring 7, the black area is illustrated as the first extraction wiring 9 and the white area is illustrated as the second extraction wiring 11.

  As shown in FIG. 2B, more specifically, the inter-pad wiring 8 and the second lead-out wiring 11 are formed by laminating a Ti layer 20, an Au layer 22, and a Ti layer 24 in order from the side closer to the piezoelectric substrate 2. It becomes. The electrode pad 10 is formed by laminating a Ti layer 20 and an Au layer 22 in order from the side closer to the piezoelectric substrate 2. In other words, the electrode pad 10 is obtained by removing the uppermost Ti layer 24 from the inter-pad wiring 8. In other words, each of the metal forming the second lead wiring 11, the metal forming the inter-pad wiring 8, and the plurality of metals forming the electrode pad 10 has higher corrosion resistance to moisture than the metal forming the IDT 4. .

  The height from the upper surface of the piezoelectric substrate 2 to the upper surface of the insulating layer 12 is, for example, 90 μm, and the thickness of the insulating layer 12 on the hollow portion 13 is, for example, 60 μm. The thickness of the Al layer 18 is, for example, 350 nm, the thickness of the Ti layer 20 is, for example, 200 nm, the thickness of the Au layer 22 is, for example, 150 nm, and the thickness of the Ti layer 24 is, for example, 200 nm.

  Next, a method for manufacturing the acoustic wave device according to the first embodiment will be described. FIG. 3A to FIG. 4C are cross-sectional views illustrating the method for manufacturing the acoustic wave device according to the first embodiment.

  As shown in FIG. 3A, an ID layer 4 made of, for example, Al and an Al layer 18 to be the first lead wiring 9 are formed on the piezoelectric substrate 2 by, for example, a vapor deposition method and a lift-off method. At this time, the reflector 5 is also formed. Further, the Al layer 18 is not formed in the region where the second lead-out wiring 11, the inter-pad wiring 8, and the electrode pad 10 are formed.

  As shown in FIG. 3B, the protective film 6 covering the IDT 4 and the Al layer 18 is formed by, for example, sputtering.

  As shown in FIG. 3C, a Ti layer 20, an Au layer 22, and a Ti layer 24 are formed on the piezoelectric substrate 2 in this order from the bottom, for example, by a vapor deposition method and a lift-off method. As a result, the second lead-out wiring 11 and the inter-pad wiring 8 composed of the Ti layer 20, the Au layer 22, and the Ti layer 24 are formed. Further, the electrode pad 10 is formed by removing a part of the Ti layer 24 by etching or the like to expose the Au layer 22.

  As shown in FIG. 3D, for example, an epoxy resin is formed on the IDT 4, the lead-out wiring 7, the inter-pad wiring 8, and the electrode pad 10 by, for example, a tenting method. Thereafter, the epoxy resin is exposed and developed to form an insulating layer 12 having a hollow portion on the IDT 4 and an opening on the electrode pad 10 and covering the IDT 4, the lead-out wiring 7 and the inter-pad wiring 8. .

  As shown in FIG. 4A, an electrode post 14 made of, eg, Cu is formed on the electrode pad 10 by, eg, plating.

  As shown in FIG. 4B, a terminal 16 made of solder such as Sn—Ag is formed on the electrode post 14 by, for example, a printing method.

  As shown in FIG. 4C, the insulating layer 12 and the piezoelectric substrate 2 are cut by a dicing method. Through the above steps, the acoustic wave device according to Example 1 is completed.

  According to the first embodiment, the second lead-out wiring 11, the pad-to-pad wiring 8, and the electrode pad 10 are formed of Ti, Au, or the like, which is more resistant to moisture than Al that forms the IDT 4. For this reason, the corrosion resistance of the 2nd lead-out wiring 11, the pad wiring 8, and the electrode pad 10 increases. Even when the second lead-out wiring 11, the pad-to-pad wiring 8, and the electrode pad 10 are damaged, the corrosion of the second lead-out wiring 11, the inter-pad wiring 8, and the electrode pad 10 can be suppressed. Further, since the inter-pad wiring 8 does not include an Al layer, the Al layer is not exposed to the outside of the acoustic wave device. That is, damage to the inter-pad wiring 8 exposed outside the acoustic wave device can be suppressed. Therefore, the reliability of the acoustic wave device can be increased.

  In the first embodiment, the second lead wiring 11 among the inter-pad wiring 8 and the lead wiring 7 is made of a metal having high corrosion resistance. However, for example, the inter-pad wiring 8 and the lead-out wiring 7 may be made of a metal having high corrosion resistance. In other words, the wiring in at least a part of the wiring 3 and the electrode pad 10 are formed of a metal having higher corrosion resistance to moisture than the metal forming the IDT 4.

  In the first embodiment, the inter-pad wiring 8 that is in contact with the insulating layer 12 and the second extraction wiring 11 that is a region in contact with the insulating layer 12 among the extraction wiring 7 include the metal (Al) that forms the IDT 4. Absent. For this reason, the corrosion resistance of the inter-pad wiring 8 and the lead-out wiring 7 can be enhanced in a region where stress is likely to occur. Therefore, corrosion can be effectively suppressed.

  As shown in FIG. 2A and FIG. 2B, the wiring in the region of the inter-pad wiring 8 and the lead-out wiring 7 in contact with the insulating layer 12, in other words, the wiring in the region not exposed to the hollow portion 13, It does not contain the metal that forms IDT4. On the other hand, the wiring in the region that does not contact the insulating layer 12 among the inter-pad wiring 8 and the lead-out wiring 7, in other words, the wiring in the region exposed to the hollow portion 13 may include a metal that forms the IDT 4. Further, the entire inter-pad wiring 8 and the entire extraction wiring 7 may not include the metal forming the IDT 4. In this case, the lead wire 7 made of, for example, Ti / Au / Ti and not containing Al is connected to the IDT 4 bus bar made of, for example, Al. Since stress is likely to be generated in the region where the insulating layer 12 and the wiring 3 are in contact with each other, the wiring in the region in contact with the insulating layer 12 among the inter-pad wiring 8 and the lead-out wiring 7 does not contain the metal that forms the IDT 4. It is preferable.

  In addition to Au and Ti, for example, Ta and Pt are examples of highly corrosion-resistant metals that form the second lead-out wiring 11, the inter-pad wiring 8, and the electrode pad 10. However, the metal forming the second lead-out wiring 11, the inter-pad wiring 8 and the electrode pad 10 is not limited to these, and it is sufficient that the corrosion resistance against moisture is higher than the metal forming the IDT 4.

  The IDT 4 may be formed using a metal other than Al. However, when Al or an alloy containing Al is used for IDT 4, good device characteristics can be obtained. Accordingly, the IDT 4 is preferably formed using Al or an alloy containing Al. On the other hand, the second lead-out wiring 11, the inter-pad wiring 8, and the electrode pad 10 can be formed of a metal having high corrosion resistance. Thereby, favorable device characteristics can be obtained, and corrosion of the electrode pad and wiring can be suppressed, and the reliability of the acoustic wave device can be improved.

  In the first embodiment, the second lead-out wiring 11, the inter-pad wiring 8 and the electrode pad 10 have a multilayer structure in which a plurality of metal layers are stacked. However, the second lead-out wiring 11, the inter-pad wiring 8 and the electrode pad 10 have a multi-layer structure. It is not limited to. That is, the second lead wiring 11, the inter-pad wiring 8, and the electrode pad 10 may have a single-layer structure made of a metal having higher corrosion resistance than the metal forming the IDT 4. In addition, when using a multilayer structure, corrosion can be suppressed because each of a some metal layer is comprised with the metal whose corrosion resistance is higher than the metal which forms IDT4.

  Although the surface acoustic wave device has been described in the first embodiment, the present invention is applicable to other acoustic wave devices such as a boundary acoustic wave device and an FBAR (Film Bulk Acoustic Resonator). When FBAR is used, the metal forming the upper electrode and the lower electrode sandwiching the piezoelectric film corresponds to the metal forming the IDT in the first embodiment.

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

Elastic wave element 1
Piezoelectric substrate 2
Wiring 3
IDT 4
Lead-out wiring 7
Inter-pad wiring 8
First lead wiring 9
Electrode pad 10
Second lead wiring 11
Insulating layer 12
Hollow part 13
Electrode post 14
Terminal 16
Al layer 18
Ti layer 20, 24
Au layer 22

Claims (5)

A piezoelectric substrate;
An acoustic wave element formed on the piezoelectric substrate;
Wiring formed on the piezoelectric substrate and electrically connected to the acoustic wave element;
An electrode pad formed on the piezoelectric substrate and electrically connected to the acoustic wave element via the wiring;
An insulating layer formed on the piezoelectric substrate so as to cover the acoustic wave element and the wiring, and
Of the wiring, the wiring in the region in contact with the insulating layer and the electrode pad are composed of a plurality of metal layers, and each of the plurality of metal layers is more resistant to moisture than the metal forming the electrode of the acoustic wave element. An elastic wave device comprising a metal having high properties .   2. The acoustic wave device according to claim 1, wherein a wiring in a region in contact with the insulating layer of the wiring does not include a metal that forms an electrode of the acoustic wave element.   The elastic wave device according to claim 1, wherein the elastic wave element is made of Al or an alloy containing Al.   4. The acoustic wave device according to claim 1, wherein the wiring and the electrode pad are made of at least one of Ti, Ta, Au, and Pt. 5.   The wiring and the electrode pad are made of a plurality of metal layers, and each of the plurality of metal layers is made of a metal having higher corrosion resistance to moisture than the metal forming the electrode of the acoustic wave element. The elastic wave device according to any one of 1 to 4.

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