JP7351604B2 - Acoustic wave resonators, filters and multiplexers - Google Patents

Description

The present invention relates to an elastic wave resonator, a filter, and a multiplexer, and, for example, to an elastic wave resonator, filter, and multiplexer having a pair of comb-shaped electrodes and a reflector.

An acoustic wave resonator such as a surface acoustic wave resonator includes a pair of comb-shaped electrodes having a plurality of electrode fingers, and reflectors provided on both sides of the comb-shaped electrode. The reflector reflects the elastic waves excited by the pair of comb-shaped electrodes. This causes the elastic waves to be confined within the pair of comb-shaped electrodes.

It is known to make the reflector thicker than the IDT and to make the density of the reflector greater than the density of the IDT (for example, Patent Document 1). It is known that the film thickness within the reflector increases as the distance from the IDT increases (for example, Patent Document 2).

Japanese Patent Application Publication No. 10-209804 Japanese Patent Application Publication No. 2002-290194

However, if the reflector is made thicker than the IDT, or if the density of the reflector is made greater than the density of the IDT, the difference between the frequency of the elastic wave excited by the IDT and the stop band of the reflector may become large. Therefore, the loss of the elastic wave resonator increases.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the characteristics of an elastic wave resonator.

The present invention includes: a piezoelectric substrate; a pair of comb-shaped electrodes provided on the piezoelectric substrate and including a plurality of electrode fingers; a reflector comprising a plurality of grating electrodes having a large film thickness and an average pitch smaller than an average pitch of the plurality of electrode fingers, one comb-shaped electrode of the pair of comb-shaped electrodes; In at least a part of the intersection region where the other comb-shaped electrode of the type electrode overlaps when viewed from the arrangement direction of the plurality of electrode fingers, the electrode fingers of the one comb-shaped electrode and the electrode fingers of the other comb-shaped electrode are provided alternately for each one, and the film thickness of the plurality of grating electrodes is 1.1 times or more and 3.0 times or less the film thickness of the plurality of electrode fingers, and An elastic wave resonator in which the average pitch is 0.95 times or less and 0.8 times or more the average pitch of the plurality of electrode fingers, and the density of the plurality of grating electrodes is greater than or equal to the density of the plurality of electrode fingers. be.

The present invention provides a piezoelectric substrate, a pair of comb-shaped electrodes provided on the piezoelectric substrate and including a plurality of electrode fingers, and a density and a film of the plurality of electrode fingers provided on the outside of the pair of comb-shaped electrodes. a reflector comprising a plurality of grating electrodes having a product of density and film thickness greater than the product of density and film thickness and an average pitch smaller than the average pitch of the plurality of electrode fingers, one of the pair of comb-shaped electrodes. In at least a part of the intersection area where the comb-shaped electrode and the other comb-shaped electrode of the pair of comb-shaped electrodes overlap when viewed from the arrangement direction of the plurality of electrode fingers, the electrode fingers of the one comb-shaped electrode The electrode fingers of the other comb -shaped electrode are provided alternately, and the product of the density and film thickness of the plurality of grating electrodes is equal to the product of the density and film thickness of the plurality of electrode fingers. 1.1 times or more and 3.0 times or less, and the average pitch of the plurality of grating electrodes is 0.95 times or less and 0.8 times or more the average pitch of the plurality of electrode fingers. be.

In the above configuration, an adhesion film that is a titanium film or a chromium film may be provided between the plurality of electrode fingers and the plurality of grating electrodes and the piezoelectric substrate.

In the above structure, the piezoelectric substrate may be a lithium tantalate substrate or a lithium niobate substrate.

The present invention is a filter including the above elastic wave resonator.

The present invention is a multiplexer including the above filter.

According to the present invention, the characteristics of an elastic wave resonator can be improved.

FIG. 1(a) is a plan view of the elastic wave resonator in Example 1, and FIG. 1(b) is a sectional view taken along line AA in FIG. 1(a). FIG. 2 is a diagram showing simulation conditions. FIG. 3 is a diagram showing the IDT transmission characteristics in samples A to E. FIG. 4(a) is a diagram showing the amount of reflection of the reflectors of samples A and D, and FIG. 4(b) is an enlarged view of FIG. 4(a). FIG. 5(a) is a diagram showing the amount of reflection of the reflectors of samples B and E, and FIG. 5(b) is an enlarged view of FIG. 5(a). FIG. 6(a) is a diagram showing the amount of reflection of the reflectors of samples C and D, and FIG. 6(b) is an enlarged view of FIG. 6(a). FIG. 7(a) is a diagram showing the amount of reflection of the reflectors of samples C and E, and FIG. 7(b) is an enlarged view of FIG. 7(a). FIGS. 8A to 8C are cross-sectional views of elastic wave resonators according to Example 1 and Modifications 1 and 2 thereof, respectively. 9A is a circuit diagram of a filter according to a second embodiment, and FIG. 9B is a circuit diagram of a duplexer according to a first modification of the second embodiment.

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

An elastic wave resonator will be explained as an elastic wave device. FIG. 1(a) is a plan view of the elastic wave resonator in Example 1, and FIG. 1(b) is a sectional view taken along line AA in FIG. 1(a). The direction in which the electrode fingers 14 are arranged is the X direction, and the direction in which the electrode fingers 14 extend is the Y direction. The X direction and the Y direction do not necessarily correspond to the X-axis direction and the Y-axis direction of the crystal orientation of the piezoelectric substrate 10.

As shown in FIGS. 1(a) and 1(b), an IDT 22 and a reflector 20 are formed on a piezoelectric substrate 10. The IDT 22 is formed of a metal film 12a with a thickness T1 provided on the piezoelectric substrate 10. The reflector 20 is formed of a metal film 12b formed on the piezoelectric substrate 10 and having a thickness T2. The reflector 20 is placed outside the IDT 22 in the X direction.

The IDT 22 includes a pair of comb-shaped electrodes 16 facing each other. The comb-shaped electrode 16 includes a plurality of electrode fingers 14 and a bus bar 15 to which the plurality of electrode fingers 14 are connected. The area where the electrode fingers 14 of the pair of comb-shaped electrodes 16 intersect is the intersection area 24 . The length of the crossing region 24 is the opening length. The pair of comb-shaped electrodes 16 are provided facing each other so that the electrode fingers 14 are substantially alternated in at least a portion of the crossing region 24 . The elastic waves excited by the plurality of electrode fingers 14 in the intersection region 24 mainly propagate in the X-column direction. The pitch L1 of the electrode fingers 14 of the same comb-shaped electrode 16 is approximately the wavelength λ of the elastic wave. The pitch L1 is the pitch of two electrode fingers 14.

The reflector 20 includes a plurality of grating electrodes 18 and a bus bar 19 to which the plurality of grating electrodes 18 are connected. Grating electrodes 18 are arranged in the X direction and extend in the Y direction. The pitch between two grating electrodes 18 is L2. The reflector 20 reflects the elastic waves (surface acoustic waves) excited by the electrode fingers 14 of the IDT 22 . As a result, the elastic waves are confined within the intersection region 24 of the IDT 22.

The piezoelectric substrate 10 is, for example, a lithium tantalate substrate or a lithium niobate substrate, such as a rotating Y-cut X-propagating lithium tantalate substrate or a rotating Y-cut X-propagating lithium tantalate niobate substrate. The piezoelectric substrate 10 may be bonded to the support substrate directly or via an intermediate layer. The supporting substrate is, for example, a sapphire substrate, a spinel substrate, an alumina substrate, a quartz substrate, or a silicon substrate. The metal films 12a and 12b are films whose main component is, for example, Al (aluminum) or Cu (copper), and are, for example, an Al film or a Cu film. An adhesive film such as a Ti (titanium) film or a Cr (chromium) film may be provided between the electrode fingers 14 and grating electrodes 18 and the piezoelectric substrate 10. The adhesive film is thinner than the electrode fingers 14 and grating electrodes 18 . An insulating film may be provided to cover the electrode fingers 14 and grating electrodes 18. The insulating film functions as a protective film or a temperature compensation film.

The film thicknesses T1 and T2 are, for example, from 50 nm to 500 nm. The width of the electrode fingers 14 and the grating electrode 18 in the X direction is, for example, from 200 nm to 1500 nm. The pitch L1 of the electrode fingers 14 is, for example, from 500 nm to 2500 nm. The capacitance value of the IDT 22 is, for example, 0.1 pF to 10 pF.

[simulation]
Simulations were performed for five samples A to E. Samples A to C correspond to comparative examples, and samples D and E correspond to example 1. FIG. 2 is a diagram showing simulation conditions. In both samples A to E, a 42° rotated Y cut X propagation lithium tantalate substrate was used as the piezoelectric substrate 10, and an aluminum film was used as the metal films 12a and 12b. The opening length was set to 15λ. In the IDT 22, the logarithm was 100, the pitch L1 was 2 μm, the duty ratio was 80%, and the thickness T1 of the metal film 12a was 200 nm. In the reflector 20, the logarithm was set to 15 and the duty ratio was set to 80%.

In samples A and B, the film thickness T2 was 200 nm, which is the same as the film thickness T1, and the pitch L2 was 2.04 μm and 1.97 μm, respectively. In sample C, the pitch L2 was 2 μm, the same as L1, and the film thickness T2 was 350 nm. In samples D and E, the film thickness T2 was 350 nm, and the pitch L2 was 1.90 μm and 1.82 μm, respectively. The pitch ratios of IDT 22 to reflector 20 for samples A to E are 1.02, 0.985, 1.00, 0.95, and 0.91, respectively.

FIG. 3 is a diagram showing the IDT transmission characteristics in samples A to E. As shown in FIG. 3, the resonant frequency fr and the anti-resonant frequency fa are approximately 1923.5 MHz and approximately 1987 MHz, respectively. The anti-resonant frequency fa is located on the higher frequency side than the resonant frequency fr. For filters and the like, a frequency near the resonant frequency fr and the anti-resonant frequency fa is used.

FIG. 4(a) is a diagram showing the amount of reflection of the reflectors of samples A and D, and FIG. 4(b) is an enlarged view of FIG. 4(a). As shown in FIGS. 4(a) and 4(b), in sample A, the frequency at which the amount of reflection is the largest almost coincides with the resonant frequency fr.

FIG. 5(a) is a diagram showing the amount of reflection of the reflectors of samples B and E, and FIG. 5(b) is an enlarged view of FIG. 5(a). As shown in FIGS. 5(a) and 5(b), in sample B, the frequency with the largest amount of reflection almost matches the antiresonance frequency fa.

The frequency band in which the reflection of the reflector 20 is large is called a stop band. Preferably, the frequency of the stop band is near the resonant frequency fr and anti-resonant frequency fa of the IDT 22. Thereby, the reflector 20 efficiently reflects elastic waves near frequencies used in filters and the like. Therefore, elastic waves can be confined by the IDT 22. Thereby, the Q value near the resonance frequency fr and anti-resonance frequency fa of the elastic wave resonator can be improved.

In samples A and B, by adjusting the pitch L2 of the grating electrodes 18 of the reflector 20, the center frequency of the stop band of the reflector 20 can be set to be around the resonant frequency fr and the anti-resonant frequency fa. However, the reflectance of the reflector 20 is low, and the amount of reflection is small. In order to improve the reflectance of the reflector 20, it is conceivable to increase the film thickness T2 of the metal film 12b. However, the film thickness T1 of the metal film 12a of the IDT 22 is set so that characteristics such as loss in the IDT 22 are optimized. Therefore, it is difficult to increase the film thickness T1 together with the film thickness T2. Therefore, in sample C, the film thickness T2 is made larger than the film thickness T1.

FIG. 6(a) is a diagram showing the amount of reflection of the reflectors of samples C and D, and FIG. 6(b) is an enlarged view of FIG. 6(a). FIG. 7(a) is a diagram showing the amount of reflection of the reflectors of samples C and E, and FIG. 7(b) is an enlarged view of FIG. 7(a). As shown in FIGS. 6(a) to 7(b), in sample C, by increasing the film thickness T2, the amount of reflection from the reflector 20 becomes larger than in samples A and B. However, the center frequency of the stop band shifts to a lower frequency than the resonant frequency fr and the anti-resonant frequency fa. For this reason, the reflector 20 cannot efficiently reflect elastic waves near the resonant frequency fr and the anti-resonant frequency fa.

In samples D and E, the film thickness T2 is made larger than the film thickness T1, and the pitch L2 is made smaller than the pitch L1. Thereby, as shown in FIGS. 4(a) to 5(b), in samples D and E, the amount of reflection from the reflector 20 can be made larger than in samples A and B. As shown in FIGS. 6(a) to 7(b), in samples D and E, compared to sample C, the stop band of the reflector 20 can be set near the resonant frequency fr and the anti-resonant frequency fa. Therefore, elastic waves near the resonant frequency fr and the anti-resonant frequency fa excited by the IDT 22 can be efficiently confined within the IDT 22. Thereby, the characteristics of the elastic wave resonator, such as the Q value, can be improved.

The center frequency of the stop band of the reflector 20 is approximately inversely proportional to the average pitch L2 of the grating electrodes 18 of the reflector 20. Therefore, in this simulation example, when the pitch ratio is between 0.95 and 0.91, the center frequency of the stop band is located between the resonant frequency fr and the anti-resonant frequency fa.

[Example 1 and its modifications]
FIGS. 8A to 8C are cross-sectional views of elastic wave resonators according to Example 1 and Modifications 1 and 2 thereof, respectively. As shown in FIG. 8A, in the first embodiment, the thickness T2 of the plurality of grating electrodes 18 of the reflector 20 is larger than the thickness T1 of the plurality of electrode fingers 14 of the IDT 22 (a pair of comb-shaped electrodes 16). , the average pitch L2/2 of the grating electrodes 18 is smaller than the average pitch L1/2 of the electrode fingers 14. Thereby, as in samples D and E, the characteristics of the elastic wave resonator can be improved.

It is preferable that the density of the plurality of grating electrodes 18 is greater than or equal to the density of the plurality of electrode fingers 14. Thereby, the reflectance of the reflector 20 can be increased. It is preferable that the material of the grating electrode 18 and the material of the electrode fingers 14 are approximately the same within the manufacturing error, and the density of the grating electrode 18 and the density of the electrode fingers 14 are approximately the same within the manufacturing error. This allows the number of materials used for the elastic wave resonator to be reduced.

As shown in FIG. 8(b), in the first modification of the first embodiment, the density of the plurality of grating electrodes 18 is greater than the density of the plurality of electrode fingers 14, and the average pitch L2/2 of the grating electrodes 18 is It is smaller than the average pitch L1/2 of 14. As in the first modification of the first embodiment, the amount of reflection of the reflector 20 may be increased by making the density of the metal film 12b of the grating electrode 18 greater than that of the metal film 12a of the electrode finger 14. In this case as well, by making the average pitch L2/2 of the grating electrodes 18 smaller than the average pitch L1/2 of the electrode fingers 14, the center of the stop band can be set near the resonant frequency fr and the anti-resonant frequency fa. It is preferable that the film thickness T2 of the grating electrode 18 and the film thickness T1 of the electrode finger 14 be approximately the same to the extent of manufacturing error. In this way, by increasing the density of the grating electrode 18, the amount of reflection of the reflector 20 can be increased even if the reflector 20 is thin. Therefore, processing of the reflector 20 in the manufacturing process becomes easy.

For example, a film containing Al as a main component is used as the metal film 12a. The metal film 12b is made of, for example, Cu, W (tung gluten), Ru (ruthenium), Mo (molybdenum), Ta (tantalum), Pt (platinum), Pd (palladium), Ir (iridium), Rh (rhodium), Re. The main component is at least one of (rhenium) and Te (tellurium).

As shown in FIG. 8(c), in the second modification of the first embodiment, the density of the plurality of grating electrodes 18 is greater than the density of the plurality of electrode fingers 14, and the film thickness T2 of the plurality of grating electrodes 18 is greater than the density of the plurality of electrode fingers 14. The film thickness is equal to or greater than the film thickness T1 of the electrode finger 14. Thereby, the reflectance of the reflector 20 can be further increased.

In order to increase the amount of reflection of the reflector 20 as in the first embodiment and its modifications, the product of the density and film thickness of the grating electrode 18 may be made larger than the product of the density and film thickness of the electrode fingers 14. .

The relationship between the film thickness T2 of the grating electrode 18 and the film thickness T1 of the electrode fingers 14, and the relationship between the density of the grating electrode 18 and the density of the electrode fingers 14 are determined by considering the loss etc. in the IDT 22 and the reflectance of the reflector 20. It can be decided. For example, the thickness T2 of the grating electrode 18 is preferably 1.1 times or more, more preferably 1.2 times or more, and even more preferably 1.5 times or more the thickness T1 of the electrode fingers 14. The film thickness T2 is preferably three times or less than T1, more preferably two times or less. Further, for example, the density of the grating electrode 18 is preferably 1.1 times or more the density of the electrode fingers 14, more preferably 1.2 times or more, still more preferably 1.5 times or more, preferably 3 times or less, and preferably 2 times or less. More preferred. Furthermore, for example, the product of the film thickness T2 of the grating electrode 18 and the density is preferably 1.1 times or more, more preferably 1.2 times or more, and 1.5 times the product of the film thickness T1 of the electrode fingers 14 and the density. It is more preferably 3 times or less, and more preferably 2 times or less.

In order to match the stop band of the reflector 20 to the resonant frequency fr and the anti-resonant frequency fa, the average pitch L2 of the plurality of grating electrodes 18 is preferably 0.98 times or less than the average pitch L1 of the plurality of electrode fingers 14, and is 0.95. It is more preferably 0.92 times or less, and even more preferably 0.92 times or less. L1 is preferably 0.8 times or more than L2, more preferably 0.85 times or more, and even more preferably 0.91 times or more.

The average pitch of the electrode fingers 14 can be determined by dividing the length of the plurality of electrode fingers 14 in the X direction by the number of electrode fingers 14 (for example, logarithm). The average pitch of the grating electrodes 18 can be determined by dividing the length of the plurality of grating electrodes 18 in the X direction by the number of grating electrodes 18 (for example, by dividing by 1/2 of the number).

When the metal film 12a and/or 12b is a laminated film of a plurality of metal films, the thickness and density of the electrode finger 14 and/or grating electrode 18 are determined by the thickness of the thickest metal film among the plurality of laminated metal films. and density may be compared.

FIG. 9(a) is a circuit diagram of a filter according to the second embodiment. As shown in FIG. 9(a), one or more series resonators S1 to S3 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. The piezoelectric thin film resonator of Example 1 and its modifications can be used for at least one of the one or more series resonators S1 to S3 and the one or more parallel resonators P1 and P2. The number of resonators of the ladder filter can be set as appropriate.

[Modification 1 of Example 2]
FIG. 9(b) is a circuit diagram of a duplexer according to a first modification of the second embodiment. As shown in FIG. 9(b), a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes a signal in the transmission band among the high frequency signals inputted from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 passes a signal in the reception band among the high-frequency signals inputted from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals at other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second embodiment.

Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

Although the 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 variations can be made within the scope of the gist of the present invention as described in the claims. Changes are possible.

10 piezoelectric substrate 12a, 12b metal film 14 electrode finger 16 comb-shaped electrode 18 grating electrode 20 reflector 22 IDT
40 Transmission filter 42 Reception filter

Claims (6)

a piezoelectric substrate;
a pair of comb-shaped electrodes provided on the piezoelectric substrate and including a plurality of electrode fingers;
a reflector provided on the outside of the pair of comb-shaped electrodes and including a plurality of grating electrodes having a thickness greater than the thickness of the plurality of electrode fingers and an average pitch smaller than the average pitch of the plurality of electrode fingers;
Equipped with
In at least a portion of an intersecting region where one comb-shaped electrode of the pair of comb-shaped electrodes and the other comb-shaped electrode of the pair of comb-shaped electrodes overlap when viewed from the arrangement direction of the plurality of electrode fingers, one of the comb-shaped electrodes The electrode fingers of the comb-shaped electrode and the electrode fingers of the other comb-shaped electrode are provided alternately,
The film thickness of the plurality of grating electrodes is 1.1 times or more and 3.0 times or less the film thickness of the plurality of electrode fingers, and the average pitch of the plurality of grating electrodes is the average pitch of the plurality of electrode fingers. 0.95 times or less and 0.8 times or more,
The density of the plurality of grating electrodes is greater than or equal to the density of the plurality of electrode fingers. a piezoelectric substrate;
a pair of comb-shaped electrodes provided on the piezoelectric substrate and including a plurality of electrode fingers;
Provided on the outside of the pair of comb-shaped electrodes, having a product of density and film thickness that is greater than the product of density and film thickness of the plurality of electrode fingers, and an average pitch that is smaller than the average pitch of the plurality of electrode fingers. a reflector including a plurality of grating electrodes;
Equipped with
In at least a portion of an intersecting region where one comb-shaped electrode of the pair of comb-shaped electrodes and the other comb-shaped electrode of the pair of comb-shaped electrodes overlap when viewed from the arrangement direction of the plurality of electrode fingers, one of the comb-shaped electrodes The electrode fingers of the comb-shaped electrode and the electrode fingers of the other comb-shaped electrode are provided alternately,
The product of the density and film thickness of the plurality of grating electrodes is 1.1 times or more and 3.0 times or less the product of the density and film thickness of the plurality of electrode fingers, and the average pitch of the plurality of grating electrodes is is an elastic wave resonator in which the average pitch of the plurality of electrode fingers is 0.95 times or less and 0.8 times or more. 3. The acoustic wave resonator according to claim 1 , further comprising an adhesion film that is a titanium film or a chromium film and is provided between the plurality of electrode fingers and the plurality of grating electrodes and the piezoelectric substrate. The acoustic wave resonator according to any one of claims 1 to 3 , wherein the piezoelectric substrate is a lithium tantalate substrate or a lithium niobate substrate. A filter comprising the elastic wave resonator according to any one of claims 1 to 4 . A multiplexer comprising a filter according to claim 5 .

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