JP6981772B2 - Elastic wave device - Google Patents

Description

The present invention relates to an elastic wave device, for example, an elastic wave device having a comb-shaped electrode.

In recent years, wireless devices such as mobile phones have been rapidly reduced in size, enhanced in functionality, and improved in quality, and filters using surface acoustic wave resonators have been used in their high-frequency circuits. The surface acoustic wave resonator has an IDT (Interdigital Transducer) on which the electrode fingers face each other on the piezoelectric substrate.

It is known to provide a discharge induction pattern having a plurality of gaps narrower than the electrode pattern between at least one of the input terminal and the output terminal and the ground so that the IDT is not destroyed by static electricity applied to the input terminal or the output terminal. (For example, Patent Document 1). It is known to provide a thin film having varistor characteristics in order to suppress destruction due to static electricity (for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2005-191744 Japanese Unexamined Patent Publication No. 2006-20285

In Patent Document 1, the gap of the discharge induction pattern is made narrower than the gap between the electrode fingers of the IDT. It is difficult to form such a narrowly spaced pattern. Further, providing a special thin film having varistor characteristics as in Patent Document 2 is a burden on manufacturing.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an elastic wave device having a discharge element that can be easily formed.

The present invention has a piezoelectric substrate and a pair of comb-shaped electrodes provided on the piezoelectric substrate, each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected, and the plurality of electrode fingers facing each other. Between the input pad provided on the piezoelectric substrate, the output pad provided on the piezoelectric substrate, and the ground pad provided on the piezoelectric substrate, respectively, between the input pad and the output pad. A filter comprising a plurality of resonators connected to and comprising the pair of comb-shaped electrodes, and a first electrically connected to any one of the input pad and the output pad without the plurality of resonators. electrode and a second electrode overlapping the first electrode in plan view in electrically connected to at least a portion without passing through the plurality of resonators to the ground pad, the first electrode and the second electrode and the plane The distance of the minimum gap between the first electrode and the second electrode in the visually overlapping region, which is smaller than the thickness of each of the first electrode and the second electrode and the pair of comb-shaped electrodes face each other. a discharge element having an insulating film having a thickness not more small,
It is an elastic wave device provided with.

In the above configuration, the width of the first electrode becomes narrower toward the second electrode, the width of the second electrode becomes narrower toward the first electrode, and the tip of the first electrode on the second electrode side. overlap in a plan view in a portion other than an edge of the second electrode, the tip of the first electrode side of the second electrode may be configured to overlap in a plan view in a portion other than an edge of the first electrode ..

In the above configuration, the capacitance between the first electrode and the second electrode can be 0.1 pF or less.

In the above structure, one and the ground pad is connected to the first electrode of the input pad and the output pad is provided with a metal film formed on the piezoelectric substrate to the metal film, the metal film The first electrode is formed of either the metal film or the metal layer and does not include the metal film and the other of the metal layer, and the second electrode is formed of a metal layer made of a different material from the above. , The structure may be formed from the other of the metal film and the metal layer and may not include one of the metal film and the metal layer.

In the above configuration, the pair of comb-shaped electrodes may be formed from the metal film.

According to the above configuration, the insulating film may be a silicon oxide film or a silicon nitride film.

According to the present invention, it is possible to provide an elastic wave device having a discharge element that can be easily formed.

FIG. 1 is a plan view of the elastic wave filter according to the first embodiment. 2 (a) is a plan view of the surface acoustic wave resonator in the first embodiment, and FIG. 2 (b) is a sectional view taken along the line AA of FIG. 2 (a). FIG. 3 is a plan view showing another example of the surface acoustic wave resonator in the first embodiment. 4 (a) is a plan view of the periphery of the discharge element in the first embodiment, and FIG. 4 (b) is a sectional view taken along the line AA of FIG. 4 (a). 5 (a) to 5 (d) are cross-sectional views showing a method of manufacturing the discharge element and the surface acoustic wave resonator according to the first embodiment.

Hereinafter, examples will be described with reference to the drawings.

FIG. 1 is a plan view of the elastic wave filter according to the first embodiment. As shown in FIG. 1, an elastic surface wave resonator 25, a wiring 32, a pad 34, and a discharge element 30 are provided on the piezoelectric substrate 10. The surface acoustic wave resonator 25 has a reflector 24 provided on both sides of the IDT 20 and the IDT 20. As the surface acoustic wave resonator 25, series resonators S1 to S3 and parallel resonators P1 to P4 are provided. A bump 36 is provided on the pad 34. The bump 36 corresponds to the input terminal In, the output terminal Out, and the ground terminal Gnd.

The series resonators S1 to S3 are connected in series between the input terminal In and the output terminal Out. The parallel resonators P1 to P4 are connected in parallel between the input terminal In and the output terminal Out. The series resonators S1 to S3 are each divided into three in series. The parallel resonators P1 and P4 are each divided into two in series. The parallel resonators P2 and P3 are each divided into two in parallel.

The discharge element 30 includes facing regions 28, electrodes 26 and 27. The facing region 28 is electrically connected to the input terminal In and the output terminal Out, respectively, via the electrodes 26 and 27. The piezoelectric substrate 10 is, for example, a lithium tantalate substrate or a lithium niobate substrate. The wiring 32 and the pad 34 are metal films such as gold, copper, and aluminum. The bump 36 is a metal bump such as a gold bump or a solder bump.

2 (a) is a plan view of the surface acoustic wave resonator in the first embodiment, and FIG. 2 (b) is a sectional view taken along the line AA of FIG. 2 (a). As shown in FIGS. 2A and 2B, the IDT 20 and the reflector 24 are provided on the piezoelectric substrate 10. The IDT 20 and the reflector 24 are formed by a metal film 12 formed on the piezoelectric substrate 10. An insulating film 14 is provided on the piezoelectric substrate 10 so as to cover the IDT 20 and the reflector 24.

The IDT 20 has a pair of comb-shaped electrodes 22. Each of the comb-shaped electrodes 22 has a plurality of electrode fingers 21 and a bus bar 23 to which the plurality of electrode fingers 21 are connected. Of the comb-shaped electrodes 22, one electrode finger 21 and the other electrode finger 21 are provided substantially alternately. One electrode finger 21 of the comb-shaped electrode 22 and the other electrode finger 21 face each other. When an AC signal is applied to the IDT 20, elastic waves propagating in the direction in which the electrode fingers 21 are arranged are excited. The pitch of the electrode fingers 21 of the same comb-shaped electrode 22 substantially corresponds to the wavelength λ of the elastic wave. Let G1 be the distance of the electrode fingers 21 in the gap between the electrode fingers 21 and the bus bar 23, and G3 be the distance of the gap between the adjacent electrode fingers 21. The distances G1 and G3 are, for example, 350 nm.

The metal film 12 is, for example, an aluminum film or a copper film. The insulating film 14 is, for example, a silicon oxide film or a silicon nitride film.

FIG. 3 is a plan view showing another example of the surface acoustic wave resonator in the first embodiment. As shown in FIG. 3, the comb-shaped electrode 22 has a plurality of dummy electrode fingers 21a facing each of the plurality of electrode fingers 21 of the other comb-shaped electrode 22 in the extending direction of the electrode finger 21. The distance of the gap between the electrode finger 21 and the dummy electrode finger 21a is G2. The distances G2 and G3 are, for example, 350 nm. Other configurations are the same as those in FIG. 2A, and the description thereof will be omitted.

4 (a) is a plan view of the periphery of the discharge element in the first embodiment, and FIG. 4 (b) is a sectional view taken along the line AA of FIG. 4 (a). As shown in FIG. 4 (a), the discharge element 30 has electrodes 26 and 27 and a facing region 28. Electrodes 26 and 27 are connected to pads 34a and 34b, respectively. The pads 34a and 34b are pads corresponding to, for example, the output terminal Out and the ground terminal Gnd in FIG. 1. As shown in FIG. 4B, the metal film 12 is provided on the piezoelectric substrate 10. An insulating film 14 is provided so as to cover the metal film 12. The insulating film 14 on the metal film 12 is provided with an opening 38. A metal layer 16 is provided on the metal film 12. The metal layer 16 is provided with a barrier layer 15 and a low resistance layer 17 provided on the barrier layer 15. The metal layer 16 is electrically connected to the metal film 12 via the opening 38.

The pads 34a and 34b are formed by laminating a metal film 12 and a metal layer 16. The electrode 26 is provided on the insulating film 14 and is provided integrally with the metal layer 16 of the pad 34a. The electrode 27 is provided between the piezoelectric substrate 10 and the insulating film 14, and is provided integrally with the metal film 12 of the pad 34b. In the facing region 28, the electrodes 26 and 27 face each other with the insulating film 14 interposed therebetween. The facing region 28 is, for example, a square.

The metal film 12 is, for example, a metal film 12 forming the IDT 20 and the reflector 24, and the film thickness is, for example, 100 nm. The insulating film 14 is, for example, a silicon oxide film, a silicon nitride film, or an aluminum oxide film, and has a film thickness of, for example, 15 nm. The barrier layer 15 functions as a barrier that suppresses mutual diffusion between the metal film 12 and the low resistance layer 17. Alternatively, the adhesion between the metal film 12 and the low resistance layer 17 and the adhesion between the insulating film 14 and the low resistance layer 17 are strengthened. The barrier layer 15 is a metal having a higher melting point than the low resistance layer 17, and is, for example, titanium, tungsten, tantalum, molybdenum, niobium, or ruthenium. The film thickness of the barrier layer 15 is, for example, 200 nm. The low resistivity layer 17 is a material having a resistivity lower than that of the barrier layer 15, and is, for example, a gold layer, a copper layer, or an aluminum layer. The film thickness of the low resistance layer 17 is, for example, 1 μm.

5 (a) to 5 (d) are cross-sectional views showing a method of manufacturing the discharge element and the surface acoustic wave resonator according to the first embodiment. As shown in FIG. 5A, the metal film 12 is formed on the piezoelectric substrate 10. The metal film 12 is formed by a vapor deposition method and a lift-off method, or a sputtering method and an etching method. The metal film 12 forms the surface acoustic wave resonator 25, the electrode 27, and the lower part of the pad.

As shown in FIG. 5B, the insulating film 14 is formed so as to cover the metal film 12. The insulating film 14 is formed by using a CVD (Chemical Vapor Deposition) method or the like. As shown in FIG. 5 (c), the opening 38 is formed in the pad region of the insulating film 14. The opening 38 is formed, for example, by using an etching method.

As shown in FIG. 5D, the metal layer 16 is formed on the insulating film 14 so as to be in electrical contact with the metal film 12 through the opening 38. The metal layer 16 is formed, for example, by using an electrolytic plating method. The pads 34a and 34b are formed of the metal film 12 and the metal layer 16, and the discharge element 30 is formed of the electrodes 26 and 27 and the insulating film 14 sandwiched between the electrodes 26 and 27. As the insulating film 14 of the discharge element 30, the same film as the protective film of the surface acoustic wave resonator 25 is used.

When static electricity is applied to the output terminal Out in FIG. 1, the electric charge destroys the insulating film 14 in the facing region 28 of the discharge element 30 and flows from the electrodes 26 to 27. As a result, it is possible to suppress the application to the surface acoustic wave resonator 25 in the surface acoustic wave filter. Therefore, it is possible to suppress the destruction of the surface acoustic wave resonator 25 due to static electricity.

Example 1 was used as a transmission filter for band 7, and it was simulated whether the capacitance of the discharge element 30 affects the filter characteristics. As a result, it was found that when the capacitance of the discharge element 30 is 0.1 pF or less, the filter characteristics hardly change, but when the capacitance exceeds 0.1 pF, the filter characteristics deteriorate.

For example, when the insulating film 14 is a silicon oxide film or a silicon nitride film, the area of the facing region 28 is calculated. The film thickness of the insulating film 14 is 15 nm. The relative permittivity of silicon oxide and silicon nitride is 3.9 and 7.5, respectively. The area of the opposite region 28 of the electrostatic capacitance of the facing region 28 is 0.1pF is, 43 .mu.m ² when the silicon oxide film, a 23 .mu.m ² when the silicon nitride film. Assuming that the facing region 28 is square, the length of one side of the facing region 28 is 6.5 μm for the silicon oxide film and 4.5 μm for the silicon nitride film. If the area of the facing region 28 and the length of one side of the facing region 28 are made smaller than these, the capacitance of the discharge element 30 becomes smaller than 0.1 pF. As a result, deterioration of the filter characteristics can be suppressed. The electrodes 26 and 27 may face each other with the insulating film 14 interposed therebetween, but the length of one side of the facing region 28 is preferably 500 nm or more in consideration of the alignment accuracy between the electrodes 26 and 27.

The discharge in the facing region 28 is likely to occur mainly at the tip 40 of the electrode 26 and / or 27. In order to improve the reproducibility of discharge failure, it is preferable to sharpen the tips of the electrodes 26 and 27. As a result, the shape of the tip 40 does not change even if the electrodes 26 and 27 are misaligned. Therefore, the discharge can be performed with good reproducibility. In order to make the facing region 28 square, the angle of the tips of the electrodes 26 and 27 is 90 °. The planar shape of the facing region 28 may be a rectangle, a rhombus, a parallelogram, or the like, in addition to the square.

According to the first embodiment, as shown in FIGS. 1 to 3, the electrode 26 (first electrode) is electrically connected to at least one of a pair of comb-shaped electrodes of the series resonator S3 and the parallel resonator P4. There is. The electrode 27 (second electrode) is electrically connected to a pad 34 (ground pad) corresponding to the ground terminal Gnd. As shown in FIGS. 4A and 4B, the electrode 27 overlaps the electrode 26 at least in part. The insulating film 14 is provided between the electrodes 26 and 27 in the facing region 28 where the electrodes 26 and 27 overlap. As a result, when static electricity is applied to at least one of the comb-shaped electrodes, the electric charge flows to the ground terminal Gnd via the discharge element 30. The insulating film 14 has a film thickness smaller than the film thickness of each of the electrodes 26 and 27. As a result, when static electricity is applied to the insulating film 14, electric charges flow through the insulating film 14. Therefore, the destruction of the comb-shaped electrode can be suppressed.

It is difficult to control the gap of the discharge induction pattern as in Patent Document 1. In the first embodiment, the discharge characteristics can be controlled by the film thickness of the insulating film 14. The control of the insulating film 14 is easier than the control of the gap of the pattern. Therefore, the discharge element 30 can be formed accurately and easily. Further, by reducing the film thickness of the insulating film 14, it is not necessary to provide a special thin film having varistor characteristics as in Patent Document 2. Therefore, the discharge element 30 can be easily formed.

The insulating film 14 is a silicon oxide film or a silicon nitride film. As a result, it is not necessary to provide a special thin film as in Patent Document 2. Therefore, the discharge element 30 can be easily formed. Another element such as IDT may be interposed between the pair of comb-shaped electrodes and the discharge element 30. The film thickness of the insulating film 14 is preferably 1/2 or less, more preferably 1/5 or less of the film thickness of each of the electrodes 26 and 27.

The comb-shaped electrode is connected between the input pad corresponding to the input terminal In and the output pad corresponding to the output terminal Out, and the electrode 26 is connected to either the input pad or the output pad without the comb-shaped electrode. To. As a result, when static electricity is applied to at least one of the input terminal In and the output terminal Out, the electric charge flows to the ground terminal Gnd via the discharge element 30. Therefore, the destruction of the comb-shaped electrode can be suppressed.

The film thickness of the insulating film 14 is smaller than the distance of the minimum gap in which the pair of comb-shaped electrodes 20 face each other. As a result, the insulating film 14 of the discharge element 30 is destroyed before the space between the pair of comb-shaped electrodes 20 is destroyed, and the destruction of the comb-shaped electrodes 20 can be suppressed. The distance of the minimum gap in which the pair of comb-shaped electrodes 20 face each other is at least one of the distances G1 to G3 in FIGS. 2 (a) and 3. The film thickness of the insulating film 14 is preferably 2/3 or less of the distance G1 to G3, and more preferably 1/2 or less.

As shown in FIG. 4A, the width of the electrode 26 becomes narrower toward the electrode 27, and the width of the electrode 27 becomes narrower toward the electrode 26. As a result, the insulating film 14 is destroyed at the tips of the electrodes 26 and / or 27. Therefore, the reproducibility of discharge failure can be improved.

In order not to deteriorate the filter characteristics, the capacitance between the electrodes 26 and 27 is preferably 0.1 pF or less, more preferably 0.05 pF or less, still more preferably 0.03 pF or less.

The pads 34a and 34b are formed of the metal film 12 and the metal layer 16. The electrode 26 is formed of the metal layer 16 and does not include the metal film 12, and the electrode 27 is formed of the metal film 12 and does not include the metal layer 16. As a result, as shown in FIGS. 5 (a) to 5 (d), an increase in the manufacturing process can be suppressed. The electrode 26 is formed of the metal film 12 and does not include the metal layer 16, and the electrode 27 may be formed of the metal layer 16 and does not include the metal film 12.

The pair of comb-shaped electrodes 20 are formed of the metal film 12. This makes it possible to suppress an increase in the manufacturing process.

The barrier layer 15 preferably contains a metal layer having a higher dielectric weight than the low resistance layer 17 in order to suppress melting when the discharge element 30 is broken.

The number of series resonators and parallel resonators of the ladder type filter shown in FIG. 1 can be arbitrarily set. Although the ladder type filter has been described as an example of the elastic wave device, the elastic wave device may include a multiple mode filter. The elastic wave device may include a multiplexer such as a duplexer.

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

10 Piezoelectric substrate 12 Metal film 14 Insulation film 15 Barrier layer 16 Metal layer 17 Low resistance layer 20 IDT
21 Electrode Finger 22 Comb Electrode 23 Bus Bar 24 Reflector 25 Surface Acoustic Wave Resonator 26, 27 Electrode 28 Opposite Area 30 Discharge Element 32 Wiring 34 Pad 36 Bump

Claims (7)

Piezoelectric board and
A pair of comb-shaped electrodes provided on the piezoelectric substrate, each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected, and the plurality of electrode fingers facing each other.
An input pad provided on the piezoelectric substrate, an output pad provided on the piezoelectric substrate, and a ground pad provided on the piezoelectric substrate are connected between the input pad and the output pad, respectively. A filter comprising a plurality of resonators comprising the pair of comb-shaped electrodes.
A first electrode electrically connected to either one of the input pad and the output pad without the plurality of resonators, and at least one electrode electrically connected to the ground pad without the plurality of resonators. A second electrode that overlaps with the first electrode in plan view, and a second electrode provided between the first electrode and the second electrode in a region where the first electrode and the second electrode overlap in plan view are provided in the section. A discharge element having an insulating film having a film thickness smaller than the film thickness of each of the one electrode and the second electrode and smaller than the distance of the minimum gap facing the pair of comb-shaped electrodes.
An elastic wave device equipped with. The width of the first electrode becomes narrower toward the second electrode, the width of the second electrode becomes narrower toward the first electrode, and the tip of the first electrode on the second electrode side is the second electrode. The elastic wave device according to claim 1, wherein the tip of the second electrode on the first electrode side overlaps a portion other than the edge of the electrode in a plan view, and the tip of the second electrode overlaps a portion other than the edge of the first electrode in a plan view. The elastic wave device according to claim 1 or 2, wherein the capacitance between the first electrode and the second electrode is 0.1 pF or less. One of the input pad and the output pad connected to the first electrode and the ground pad are made of a metal film provided on the piezoelectric substrate and a material different from the metal film provided on the metal film. Formed from a metal layer
The first electrode is formed from either one of the metal film and the metal layer and does not include the other of the metal film and the metal layer, and the second electrode is formed from the other of the metal film and the metal layer. The elastic wave device according to any one of claims 1 to 3, wherein the metal film and one of the metal layers are not included. The elastic wave device according to claim 4, wherein the pair of comb-shaped electrodes is formed of the metal film. The elastic wave device according to any one of claims 1 to 5, wherein the insulating film is a silicon oxide film or a silicon nitride film. The elastic wave device according to any one of claims 1 to 6, wherein a part of the insulating film covers the pair of comb-shaped electrodes.

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