ACOUSTIC WAVE DEVICE

Abstract

An acoustic wave device includes a piezoelectric substrate made of LiNbO.sub.3 or LiTaO.sub.3 and including first and second main surfaces that face each other, an IDT electrode provided on the first main surface of the piezoelectric substrate, and a Li.sub.2CO.sub.3 layer provided on the second main surface of the piezoelectric substrate.

Claims

1. An acoustic wave device comprising: a piezoelectric substrate made of LiNbO.sub.3 or LiTaO.sub.3 and including first and second main surfaces that face each other; an IDT electrode provided on the first main surface of the piezoelectric substrate; and a Li.sub.2CO.sub.3 layer provided on the second main surface of the piezoelectric substrate.

2. The acoustic wave device according to claim 1, wherein the Li.sub.2CO.sub.3 layer is provided on a portion of the second main surface of the piezoelectric substrate.

3. The acoustic wave device according to claim 1, wherein the piezoelectric substrate is made of LiNbO.sub.3.

4. The acoustic wave device according to claim 1, wherein the Li.sub.2CO.sub.3 layer includes a pattern shape.

5. The acoustic wave device according to claim 1, wherein the IDT electrode is located inside a hollow portion; and the Li.sub.2CO.sub.3 layer overlaps with the hollow portion.

6. The acoustic wave device according to claim 1, wherein the Li.sub.2CO.sub.3 layer overlaps with the IDT electrode.

7. The acoustic wave device according to claim 1, further comprising: a terminal electrode provided on the second main surface of the piezoelectric substrate; wherein the Li.sub.2CO.sub.3 layer overlaps with the terminal electrode.

8. The acoustic wave device according to claim 1, further comprising a wiring electrode located on the first main surface of the piezoelectric substrate.

9. The acoustic wave device according to claim 1, further comprising: a wiring electrode located on the first main surface of the piezoelectric substrate; wherein the Li.sub.2CO.sub.3 layer overlaps with the wiring electrode.

10. An acoustic wave device comprising: a piezoelectric substrate including first and second main surfaces that face each other; a functional electrode provided on the first main surface of the piezoelectric substrate to excite acoustic waves; and a first layer provided on the second main surface of the piezoelectric substrate; wherein a surface resistivity of the first layer is lower than a surface resistivity of the piezoelectric substrate.

11. The acoustic wave device according to claim 10, wherein the surface resistivity of the first layer is about 10.sup.5Ω to 10.sup.7Ω.

12. The acoustic wave device according to claim 10, wherein the surface resistivity of resistivity of the piezoelectric substrate is greater than or equal to about 10.sup.8Ω.

13. The acoustic wave device according to claim 10, wherein the first layer is provided on a portion of the second main surface of the piezoelectric substrate.

14. The acoustic wave device according to claim 10, wherein the piezoelectric substrate is made of LiNbO.sub.3.

15. The acoustic wave device according to claim 10, wherein the functional electrode is located inside a hollow portion; and the first layer overlaps with the hollow portion.

16. The acoustic wave device according to claim 10, wherein functional electrode is an IDT electrode; and the first layer overlaps with the IDT electrode.

17. An acoustic wave device comprising: a piezoelectric substrate made of LiNbO.sub.3 or LiTaO.sub.3 and including first and second main surfaces that face each other; a functional electrode provided on the first main surface of the piezoelectric substrate to excite acoustic waves; and a lasered layer formed by laser irradiation of the piezoelectric substrate provided on the second main surface of the piezoelectric substrate.

18. The acoustic wave device according to claim 17, wherein the lasered layer is provided on a portion of the second main surface of the piezoelectric substrate.

19. The acoustic wave device according to claim 17, wherein the piezoelectric substrate is made of LiNbO.sub.3.

20. The acoustic wave device according to claim 17, wherein functional electrode is an IDT electrode; and the first layer overlaps with the IDT electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a front sectional view of an acoustic wave device according to a first preferred embodiment of the present invention.

[0014] FIG. 2 is a front sectional view of an acoustic wave device according to a second preferred embodiment of the present invention.

[0015] FIG. 3 is a diagram illustrating the relationship between laser output and surface resistivity when a piezoelectric substrate made of LiNbO.sub.3 is irradiated with a laser.

[0016] FIG. 4 is a diagram illustrating the relationship between laser output and surface resistivity when a piezoelectric substrate made of LiTaO.sub.3 is irradiated with a laser.

[0017] FIG. 5 is a diagram illustrating XPS spectra of C1s of LiNbO.sub.3 substrates of acoustic wave devices of an example 1 of a preferred embodiment of the present invention and a comparative example 1.

[0018] FIG. 6 is a diagram illustrating XPS spectra of Li1s of LiNbO.sub.3 substrates of the acoustic wave devices of example 1 and comparative example 1.

[0019] FIG. 7 is a diagram illustrating XPS spectra of C1s of second main surfaces of piezoelectric substrates made of LiTaO.sub.3 in acoustic wave devices of an example 2 of a preferred embodiment of the present invention and a comparative example 2.

[0020] FIG. 8 is a diagram illustrating XPS spectra of Li1s of the second main surfaces of piezoelectric substrates made of LiTaO.sub.3 in the acoustic wave devices of example 2 and comparative example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereafter, the present invention will be clarified by describing preferred embodiments of the present invention with reference to the drawings.

[0022] The preferred embodiments described in the present specification are non-limiting illustrative examples and portions of the configurations illustrated in different preferred embodiments can be substituted for one another or combined with one another.

[0023] FIG. 1 is a front sectional view of an acoustic wave device according to a first preferred embodiment of the present invention.

[0024] An acoustic wave device 1 preferably has a WLP structure. The acoustic wave device 1 includes a piezoelectric substrate 2 preferably made of LiNbO.sub.3, for example. The piezoelectric substrate 2 may instead be made of LiTaO.sub.3, for example. The piezoelectric substrate 2 includes a first main surface 2a and a second main surface 2b that is on the opposite side from the first main surface 2a. An IDT electrode 3 and reflectors 4 and 5 are provided as functional electrodes on the first main surface 2a. The acoustic wave device 1 is preferably configured as a one-port surface acoustic wave resonator, for example. However, the structure of the functional electrodes including the IDT electrode 3 and the reflectors 4 and 5 and so on is not limited to this example. Functional electrodes may be provided so as to define an acoustic wave filter and other acoustic wave elements, for example.

[0025] Wiring line electrodes 6 and 7 are provided on the first main surface 2a. The wiring line electrodes 6 and 7 are electrically connected to the IDT electrode 3 in a portion that is not illustrated.

[0026] A frame-shaped support layer 9 is provided on the first main surface 2a of the piezoelectric substrate 2. The support layer 9 defines a hollow portion X. The support layer 9 surrounds the portion where the IDT electrode 3 is provided. The support layer 9 is made of a suitable insulating material such as, for example, a composite resin.

[0027] A cover 10 is fixed to the support layer 9 so as to close the frame-shaped opening of the support layer 9. The cover 10 is preferably made of, for example, an insulating ceramic such as alumina or a composite resin. The region enclosed by the cover 10, the support layer 9, and the piezoelectric substrate 2 defines the hollow portion X. The IDT electrode 3 is located inside the hollow portion X.

[0028] A plurality of through holes penetrate through the support layer 9 and the cover 10. Under bump metal layers 11 and 12 are respectively provided inside the through holes. One end of the under bump metal layer 11 is bonded to the wiring line electrode 6 and the other end of the under bump metal layer 11 is bonded to a metal bump 13. One end of the under bump metal layer 12 is bonded to the wiring line electrode 7 and the other end of the under bump metal layer 12 is bonded to a metal bump 14. The metal bumps 13 and 14 are located on the outside of the cover 10.

[0029] The acoustic wave device 1 can be mounted on, for example a printed circuit board or the like using the metal bumps 13 and 14. The metal bumps 13 and 14 are made of a metal or an alloy such as solder or Au, for example.

[0030] The IDT electrode 3, the reflectors 4 and 5, the wiring line electrodes 6 and 7, and the under bump metal layers 11 and 12 are made of a suitable metal or alloy. Furthermore, the IDT electrode 3, the reflectors 4 and 5, and so on may be made of multilayer metal films including a plurality of metal films.

[0031] A Li.sub.2CO.sub.3 layer 8 is stacked on the second main surface 2b of the piezoelectric substrate 2. In FIG. 1, the Li.sub.2CO.sub.3 layer 8 covers the entire or substantially the entire second main surface 2b. However, the Li.sub.2CO.sub.3 layer 8 may instead be provided on only a portion of the second main surface 2b. In other words, the Li.sub.2CO.sub.3 layer 8 may be provided in a partial manner on a portion of the second main surface 2b of the piezoelectric substrate 2. In this case, the planar shape and pattern shape of the Li.sub.2CO.sub.3 layer 8 are not particularly limited. In other words, an arbitrary planar shape may be used such as, for example, a plurality of dot-shaped Li.sub.2CO.sub.3 layers 8.

[0032] The electrical resistance, i.e., the surface resistivity of Li.sub.2CO.sub.3 is about 10.sup.5Ω to 10.sup.7Ω, for example. On the other hand, the surface resistivity of LiNbO.sub.3 is greater than or equal to about 10.sup.8Ω, for example. In other words, the electrical resistance of Li.sub.2CO.sub.3 is lower than that of LiNbO.sub.3.

[0033] A transporting arm is used in a process of manufacturing or mounting an acoustic wave device. In this case, at the mother piezoelectric wafer stage prior to the mother piezoelectric wafer being divided into individual chips, the transporting arm is used to support the surface of the piezoelectric wafer on the opposite side from the surface on which the IDT electrode will be formed and transport the piezoelectric wafer. If the piezoelectric wafer is susceptible to becoming charged, there is a risk of the piezoelectric wafer becoming stuck to the transporting arm and not releasing from the transporting arm.

[0034] In contrast, in the acoustic wave device 1, the Li.sub.2CO.sub.3 layer 8 is provided on the second main surface 2b of the piezoelectric substrate 2 and, therefore, the piezoelectric substrate 2 is not susceptible to becoming charged. Therefore, the acoustic wave device 1 whose piezoelectric substrate is at the wafer stage prior to dividing of the wafer can be smoothly transported by the transporting arm. In addition, the Li.sub.2CO.sub.3 layer 8 can be easily formed by irradiating one surface of the piezoelectric substrate at the wafer stage with a laser. Therefore, it is unlikely that a reduction in productivity will occur.

[0035] FIG. 2 is a front sectional view of an acoustic wave device according to a second preferred embodiment of the present invention.

[0036] A piezoelectric substrate 22 of an acoustic wave device 21 is preferably made of LiNbO.sub.3 or LiTaO.sub.3, for example. In the acoustic wave device 21, wiring line electrodes 6 and 7 are connected to terminal electrodes 25 and 26 via connection electrodes 23 and 24. The wiring line electrodes 6 and 7 are provided on a first main surface 22a of the piezoelectric substrate 22. The terminal electrodes 25 and 26 are stacked on a second main surface 22b of the piezoelectric substrate 22 with a Li.sub.2CO.sub.3 layer 8 and insulating layers 27 and 28 interposed therebetween.

[0037] First ends of the connection electrodes 23 and 24 are connected to the wiring line electrodes 6 and 7 and second ends of the connection electrodes 23 and 24 are connected to the terminal electrodes 25 and 26. Therefore, the acoustic wave device 21 can be mounted on a printed circuit board or the like, for example, using the terminal electrodes 25 and 26. The connection electrodes 23 and 24 extend along the side surfaces of the piezoelectric substrate 22, which connect the first main surface 22a and the second main surface 22b to each other.

[0038] The boundaries between the wiring line electrodes 6 and 7 and the connection electrodes 23 and 24 and the boundaries between the connection electrodes 23 and 24 and the terminal electrodes 25 and 26 are not clear in FIG. 2. However, the positions of these boundaries are not particularly restricted since these members are manufactured in an integrated manner using the same metal material. For example, the portions located on the first main surface 22a may be regarded as the wiring electrodes 6 and 7 and the portions located on the insulating layers 27 and 28 may be regarded as the terminal electrodes 25 and 26. Furthermore, the portions that connect the wiring line electrodes 6 and 7 and the terminal electrodes 25 and 26 to each other may be regarded as the connection electrodes 23 and 24.

[0039] The connection electrodes 23 and 24 and the terminal electrodes 25 and 26 can be made using a metal material similarly to the wiring line electrodes 6 and 7.

[0040] The insulating layers 27 and 28 are preferably made of an insulating ceramic or a composite resin such as silicon oxide or silicon oxynitride, for example.

[0041] In the acoustic wave device 21, a cover 10 is provided to close the opening of a support layer 9. Thus, a hollow portion X is provided.

[0042] The rest of the configuration of the acoustic wave device 21 is the same or substantially the same as that of the acoustic wave device 1. Therefore, the same portions are denoted by the same reference symbols and description thereof is omitted.

[0043] In the present preferred embodiment, the Li.sub.2CO.sub.3 layer 8 is provided on the second main surface 22b. Therefore, in the case of the acoustic wave device 21, the piezoelectric substrate 22 is not susceptible to becoming charged when transporting the acoustic wave device 21 or when transporting a piezoelectric substrate at the mother wafer stage using a transporting arm. Therefore, transportation using a transporting arm can be easily performed. As described above, the Li.sub.2CO.sub.3 layer 8 can be easily formed using laser irradiation. Therefore, it is unlikely that a reduction in productivity will occur.

[0044] Next, a specific description will be provided of an example of the process of forming the Li.sub.2CO.sub.3 layer 8 by laser irradiation while referring to FIGS. 3 to 8.

[0045] FIG. 3 is a diagram illustrating the relationship between laser light output and the post-laser-irradiation surface resistivity of the surface of a wafer irradiated with a laser when the surface of a piezoelectric wafer made of LiNbO.sub.3 is irradiated with laser light. A nanosecond pulse laser was used as the laser. The wavelength was about 355 nm, the pulse width was about 10 ns, the frequency was about 250 kHz, the beam diameter was about 25 μm, the scanning speed was about 500 nm/s, and the scanning pitch was about 20 μm. Under these conditions, the laser output was changed to various values and the corresponding values of the surface resistivity of the surface of the piezoelectric substrate were obtained.

[0046] As is clear from FIG. 3, the surface resistivity was high with a value greater than or equal to about 1.0×10.sup.8Ω in a laser output range from 0 W, i.e., prior to the laser irradiation, to about 0.2 W. In contrast, the surface resistivity dropped when the laser output exceeded about 0.3 W, and in particular, the surface resistivity had a value less than or equal to about 1.0×10.sup.7Ω when the laser output exceeded about 0.4 W. This is attributed to the formation of a low-resistance Li.sub.2CO.sub.3 layer on the surface of the piezoelectric substrate due to the laser irradiation.

[0047] FIG. 4 illustrates the relationship between the laser light output and the post-laser-irradiation surface resistivity of the surface of a piezoelectric wafer irradiated with a laser when a laser is irradiated in the same or substantially the same manner as described above using a piezoelectric wafer made of LiTaO.sub.3.

[0048] In this case, the laser irradiation conditions were as follows. A nanosecond pulse laser was used. The wavelength was about 532 nm, the pulse width was about 25 ns, the frequency was about 500 kHz, the beam diameter was about 30 μm, the scanning speed was about 100 nm/s, and the scanning pitch was about 20 μm. Under these conditions, the laser output was changed to various values and the entirety or substantially the entirety of one surface of a piezoelectric wafer was processed.

[0049] As is clear from FIG. 4, the surface resistivity was high with a value greater than or equal to about 1.0×10.sup.10Ω in a laser output range from 0 W, i.e., prior to the laser irradiation, to about 0.3 W. In contrast, it is clear that the surface resistivity rapidly dropped to less than or equal to about 1.0×10.sup.7Ω when the laser output exceeded about 0.4 W. This is attributed to the formation of a low-resistance Li.sub.2CO.sub.3 layer on the surface of the piezoelectric substrate due to the laser irradiation.

[0050] Next, specific examples 1 and 2 of preferred embodiments of the present invention will be described.

Example 1

[0051] A piezoelectric wafer made of LiNbO.sub.3 was prepared in order to manufacture the acoustic wave device 1 according to the first preferred embodiment. The surface of the piezoelectric wafer on the opposite side from the surface where the IDT electrode was to be formed was subjected to laser irradiation. A nanosecond pulse laser was used and the irradiation conditions were as follows.

[0052] The wavelength was about 355 nm, the pulse width was about 10 ns, the frequency was about 250 kHz, the average output was about 0.4 W, the beam diameter was about 25 μm, the scanning speed was about 500 nm/s, and the scanning pitch was about 20 μm. The entirety or substantially the entirety of one surface of the piezoelectric wafer was processed under these conditions. The acoustic wave device 1 was manufactured using the piezoelectric wafer obtained as described above. The incidence of transportation failures in this manufacturing process, i.e., the incidence of failures in which the equipment stopped due to the piezoelectric wafer becoming charged and sticking to the transporting arm, was close to 0%. For comparison, the incidence of such transportation failures in a comparative example 1, in which a piezoelectric wafer that had not been subjected to laser processing was used, was about 3%.

[0053] FIG. 5 is a diagram illustrating the XPS spectra of C1s of the LiNbO.sub.3 substrates of the acoustic wave devices of example 1 and comparative example 1. The solid line represents the results of example 1 and the broken line represents the results of comparative example 1. The results of example 1 are results for a surface that has been subjected to the laser processing described above. It is clear from FIG. 5 that the binding energy intensity is high at about 289.7 eV, which indicates the binding energy of O═C—O, in example 1, whereas the intensity at this binding energy value is low in comparative example 1.

[0054] On the other hand, FIG. 6 is a diagram illustrating the XPS spectra of Li1s of the LiNbO.sub.3 substrates of the acoustic wave devices of example 1 and comparative example 1. In FIG. 6 as well, the solid line represents the results of example 1 and the broken line represents the results of comparative example 1.

[0055] It can be seen that the intensity at about 55.4 eV resulting from Li.sub.2CO.sub.3 is high with a value of about 0.60 a.u. in example 1, whereas the intensity at this binding energy value is low in comparative example 1.

[0056] Therefore, it is clear from FIGS. 5 and 6 that a Li.sub.2CO.sub.3 layer is formed on one surface of the piezoelectric wafer by laser irradiation in example 1.

Example 2

[0057] LiTaO.sub.3 was prepared for the piezoelectric wafer instead of LiNbO.sub.3 and the piezoelectric wafer was irradiated with a laser. The laser irradiation conditions were as follows.

[0058] The wavelength was about 532 nm, the pulse width was about 25 ns, the frequency was about 500 kHz, the average output was about 0.5 W, the beam diameter was about 30 μm, the scanning speed was about 100 nm/s, and the scanning pitch was about 20 μm. The entire or substantially the entire surface of the piezoelectric wafer was irradiated with laser light under these conditions.

[0059] The acoustic wave device 1 of Example 2 was obtained with the WLP structure manufacturing process in the same or substantially the same way as in example 1 using a piezoelectric wafer obtained as described above. Furthermore, an acoustic wave device of a comparative example 2 was prepared in the same or substantially the same way as in example 2 except that a piezoelectric wafer was used that had not been subjected to laser processing.

[0060] In example 2, the incidence of failures in which the equipment stopped due to the piezoelectric wafer becoming charged and sticking to the transporting arm was 0%. In contrast, in comparative example 2, the incidence of transportation failures was about 3%.

[0061] As described above, it was also possible to reliably reduce or prevent transportation failures by providing a Li.sub.2CO.sub.3 layer in the acoustic wave device 1 in which LiTaO.sub.3 is used.

[0062] FIG. 7 is a diagram illustrating XPS spectra of C1s of second main surfaces of the piezoelectric substrates made of LiTaO.sub.3 in the acoustic wave devices of example 2 and comparative example 2. FIG. 8 is a diagram illustrating XPS spectra of Li1s of the second main surfaces of the piezoelectric substrates made of LiTaO.sub.3 in the acoustic wave devices of example 2 and comparative example 2. In FIGS. 7 and 8, the solid line represents the results of example 2 and the broken line represents the results of comparative example 2. The XPS spectra of the laser irradiated surface in example 2 are illustrated.

[0063] It is clear from FIG. 7 that the intensity at about 289.7 eV, which is the value of the binding energy of the O═C—O bond, is much higher in example 2 than in comparative example 2. In addition, it is clear from FIG. 8 that the intensity at a binding energy value of about 55.4 eV, which arises from Li.sub.2CO.sub.3, is also higher in example 2 than in comparative example 2.

[0064] Therefore, it is also clear that a Li.sub.2CO.sub.3 layer is formed by the above-described laser irradiation in example 2.

[0065] In examples 1 and 2 described above, a nanosecond pulse laser was used, but the laser device used to radiate the laser light is not particularly limited. For example, a Kr—F excimer laser or a femtosecond laser may be used. In addition, the irradiation conditions only need to be selected in accordance with the laser device, the area and thickness of the Li.sub.2CO.sub.3 layer to be formed, and so on and are not particularly limited.

[0066] While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.