JP6428206B2 - Elastic wave resonator, elastic wave filter, and duplexer - Google Patents

Description

  The present invention relates to an elastic wave resonator in which an IDT electrode is provided on a piezoelectric substrate, and an elastic wave filter and duplexer having the elastic wave resonator.

  2. Description of the Related Art Conventionally, an acoustic wave resonator has been widely used as a resonator constituting a bandpass filter used for a mobile phone or the like. For example, Patent Document 1 below discloses an acoustic wave resonator including a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate. Patent Document 1 describes that the IDT electrode is formed of an Al film.

JP-A-2-295212

  However, when the IDT electrode is composed of an Al film like the elastic wave resonator of Patent Document 1, the linearity of the signal may be lowered. For this reason, when the elastic wave resonator disclosed in Patent Document 1 is used for a duplexer transmission filter, the level of a nonlinear signal generated from the transmission filter increases, and reception sensitivity may decrease.

  An object of the present invention is to provide an elastic wave resonator capable of suppressing the generation of a nonlinear signal, and an elastic wave filter and duplexer having the elastic wave resonator.

  An acoustic wave resonator according to the present invention includes a piezoelectric substrate and an IDT electrode formed on the piezoelectric substrate and made of Al or an alloy mainly composed of Al, and mainly composed of the Al or Al. The crystallinity of the alloy is lower than the crystallinity of triaxially oriented Al or an alloy mainly composed of Al.

  In a specific aspect of the acoustic wave resonator according to the present invention, the half width of the peak of the {200} plane of the Al or Al-based alloy obtained by X-ray diffraction measurement is 27 degrees or more. In this case, the crystallinity of Al can be further reduced. Therefore, generation of nonlinear signals can be further suppressed.

  In another specific aspect of the acoustic wave resonator according to the present invention, the alloy mainly composed of Al is an alloy of Al and Cu. In this case, generation of a nonlinear signal can be further effectively suppressed.

  An elastic wave filter according to the present invention is an elastic wave filter having a plurality of elastic wave resonators, and at least one of the plurality of elastic wave resonators is configured according to the present invention. It is an elastic wave resonator.

  The duplexer according to the present invention is a duplexer that includes a plurality of acoustic wave resonators, and includes a bandpass first filter and a second filter having a different passband from the first filter, Of the plurality of elastic wave resonators of the first and second filters, at least one elastic wave resonator is an elastic wave resonator configured according to the present invention.

  In the acoustic wave resonator according to the present invention, the crystallinity of Al or Al-based alloy constituting the IDT electrode is lower than the crystallinity of triaxially-oriented Al or Al-based alloy. ing. Therefore, the elastic wave resonator according to the present invention can suppress the generation of nonlinear signals.

(A) is typical front sectional drawing of the elastic wave resonator which concerns on one Embodiment of this invention, (b) is a typical top view which shows the electrode structure. (A) is a schematic diagram which shows the unit cell of Al crystal, (b)-(d) is a schematic diagram which shows the orientation state of a crystal | crystallization with triaxial orientation, uniaxial orientation, or non-orientation. It is a pole figure of the {200} plane when performing X-ray diffraction measurement using Al used for the IDT electrode constituting the acoustic wave resonator according to the present invention as a sample. FIG. 4 is a diagram showing an X-ray diffraction profile when scanning in the ω direction with φ fixed at a peak near φ = 90 degrees in the pole figure of FIG. 3. It is a figure which shows the relationship between the half value width of the peak in the {200} plane of Al obtained by X-ray diffraction measurement, and the 3rd harmonic level. It is a figure which shows the relationship between a harmonic generation frequency and a 3rd harmonic level. 1 is a schematic circuit diagram of a duplexer according to an embodiment of the present invention.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  It should be pointed out that each embodiment described in this specification is an exemplification, and a partial replacement or combination of configurations is possible between different embodiments.

(Elastic wave resonator)
FIG. 1A is a schematic front sectional view of an acoustic wave resonator according to an embodiment of the present invention, and FIG. 1B is a schematic plan view showing an electrode structure thereof. The acoustic wave resonator 1 has a piezoelectric substrate 2. An IDT electrode 3 is laminated on the main surface of the piezoelectric substrate 2.

The piezoelectric substrate 2 is a substrate made of LiTaO ₃ . However, as the piezoelectric substrate 2, may be used a substrate made of other piezoelectric single crystal such as LiNbO _3, it may be used a substrate made of piezoelectric ceramics.

  Although schematically shown in FIG. 1A, the electrode structure shown in FIG. 1B is formed on the piezoelectric substrate 2. That is, the IDT electrode 3 and the reflectors 4 and 5 disposed on both sides of the IDT electrode 3 in the surface acoustic wave propagation direction are formed. Thus, a 1-port surface acoustic wave resonator is configured.

  As shown in FIG. 1B, the IDT electrode 3 includes first and second bus bars and a plurality of first and second electrode fingers. The plurality of first electrode fingers and the plurality of second electrode fingers are interleaved with each other.

  An elastic wave is generated by applying a voltage to a plurality of first and second electrode fingers and exciting them. A plurality of first and second electrode fingers extend in a direction orthogonal to the direction in which the elastic wave propagates. The plurality of first electrode fingers are connected to the first bus bar. On the other hand, the plurality of second electrode fingers are connected to the second bus bar.

  The IDT electrode 3 is made of Al. The IDT electrode 3 may be made of an alloy mainly composed of Al. The alloy mainly composed of Al means an alloy containing 50% by weight or more of Al, and examples thereof include an alloy of Al and Cu (AlCu alloy).

  The IDT electrode 3 may be composed of a laminated metal film of the above-mentioned Al or Al-based metal and another metal. As another metal constituting the laminated metal film, for example, Ti, Pt, Mo, W, Au, Cu, Ag, Ni, Cr, or an alloy thereof can be used. The number of laminated metal films is not particularly limited.

  In the present embodiment, the crystallinity of Al constituting the IDT electrode 3 is lower than the crystallinity of Al triaxially oriented.

  FIG. 2A is a schematic diagram of a unit cell of an Al crystal. FIGS. 2B to 2D are schematic views showing the orientation state of a triaxially oriented, uniaxially oriented or non-oriented crystal. Triaxial orientation refers to orientation in all three directions of the x-axis, y-axis, and z-axis of the unit cell shown in FIG.

  As shown in FIG. 2C, when uniaxially oriented, it is oriented only in the z-axis direction. A random crystal structure is formed in the x-axis and y-axis directions. However, even if it is not the z axis, it may be oriented in one axis direction among the x axis and the y axis.

  Further, as shown in FIG. 2D, in the case of non-orientation, a random crystal structure is formed in any of the x-axis, y-axis, and z-axis directions.

  In this specification, “lower than the crystallinity of triaxially oriented Al” means that the degree of orientation in at least one of the x-axis, y-axis, and z-axis is lower than in the case of triaxial orientation. Say. In the case of “lower than the crystallinity of triaxially oriented Al”, the case where the Al crystal is in a uniaxially or non-oriented state is also included. The same applies to the case where the IDT electrode 3 is made of Al or an alloy mainly composed of Al.

The method for forming the electrode by breaking the crystallinity from the triaxially oriented Al is not particularly limited. For example, when an electrode is formed by plasma treatment, the crystallinity of Al can be adjusted by changing the power and the treatment time. Note that CF ₄ gas can be used in the plasma treatment.

  In the acoustic wave resonator 1, as described above, the crystallinity of Al is lower than the crystallinity of triaxially oriented Al. When the crystallinity of Al is low, the third-order nonlinear coefficient in the elastic constant of Al becomes small. Therefore, generation of a nonlinear signal is suppressed in the elastic wave resonator 1.

  In the present invention, when the IDT electrode is made of an alloy mainly composed of Al, similarly, the crystallinity of the alloy mainly composed of Al is the same as that of the alloy mainly composed of Al that is triaxially oriented. Lower than crystallinity. Therefore, similarly, when the IDT electrode is made of an alloy mainly composed of Al, generation of a nonlinear signal in the acoustic wave resonator can be suppressed.

  In the present invention, it is more preferable that the half width of the peak of the Al {200} plane obtained by X-ray diffraction measurement is 27 degrees or more.

  As the half width of the peak increases, the crystallinity of Al decreases. That is, the third-order nonlinear coefficient in the elastic constant of Al becomes small. Therefore, in this case, generation of nonlinear signals in the elastic wave resonator can be further suppressed.

  In addition, the upper limit of the half width of the peak is not particularly limited as long as the half width of the peak is obtained. That is, Al may be completely amorphous (amorphous).

  X-ray diffraction measurement is performed by a wide-angle X-ray diffraction method. As X-rays, CuKα rays (wavelength 1.541Å) are used.

  A method for obtaining the half width of the peak by the X-ray diffraction method will be described below with reference to FIGS.

  FIG. 3 is a pole figure of the {200} plane when X-ray diffraction measurement is performed using Al as a sample. The half width of the peak can be obtained using an X-ray diffraction profile scanned in the ω direction with the angle φ fixed at the point where the peak intensity in the pole figure of FIG. 3 is maximum.

  FIG. 4 is a diagram showing an X-ray diffraction profile when scanning in the ω direction with φ fixed in the vicinity of φ = 90 degrees in the pole figure of FIG. Since the half width of the peak is the sum of the Gaussian function f (ω) and the Lorentz function g (ω) as shown in the following formula (1), it can be obtained by peak fitting with the peak shown in FIG.

h (ω) = (1−k) · f (ω) + k · g (ω) (1)
(In Formula (1), k is a constant of 0 ≦ k ≦ 1)

  FIG. 5 is a graph showing the relationship between the half-value width of the peak on the {200} plane of Al obtained by X-ray diffraction measurement and the third-order harmonic level. In FIG. 5, the third harmonic level means that the third harmonic level shown in FIG. 6 is a peak.

  From FIG. 5, it can be seen that the third harmonic level is lowered as the half width of the peak in the {200} plane of Al increases. It can also be seen that the third-order harmonic level is further reduced when the half width of the peak on the {200} plane of Al is 27 degrees or more. That is, it can be seen that generation of nonlinear signals in the acoustic wave resonator can be further suppressed.

  In the present invention, even when an alloy mainly composed of Al is used instead of Al, similarly, it is preferable that the half-value width of the peak of the {200} plane in the X-ray diffraction profile is 27 degrees or more. Thereby, it is possible to further suppress a decrease in linearity of the signal of the acoustic wave resonator.

[Elastic wave filter and duplexer]
FIG. 7 is a schematic circuit diagram of a duplexer according to an embodiment of the present invention. The duplexer according to the present embodiment includes a first filter 7 and a second filter 8 that are commonly connected to the antenna 6.

  The first filter 7 is a band-pass transmission filter. The first filter 7 is a ladder type filter. The first filter 7 has an input terminal 10a that is a transmission terminal and an output terminal 10b. A plurality of series arm resonators S1 to S4 are arranged on a series arm connecting the input terminal 10a and the output terminal 10b.

  A parallel arm resonator P1 is connected between a connection point between the series arm resonator S1 and the series arm resonator S2 and the ground potential. A parallel arm resonator P2 is connected between a connection point between the series arm resonator S3 and the series arm resonator S4 and the ground potential.

  The second filter 8 is a reception filter having a pass band different from that of the first filter 7. The second filter 8 includes a longitudinally coupled resonator type acoustic wave filter 12. The second filter 8 has an input terminal 11a and an output terminal 11b as a receiving terminal. An acoustic wave resonator 9 is connected between the input terminal 11 a and the longitudinally coupled resonator type acoustic wave filter 12. The input terminal 11a is connected to the antenna 6 through a common connection point with the output terminal 10b.

  In the present invention, a longitudinally coupled resonator filter, a lattice filter, or the like may be used as the first filter. Further, a ladder filter, a lattice filter, or the like may be used as the second filter.

  Usually, in the transmission filter in the duplexer, when the level of the generated nonlinear signal increases, the reception sensitivity of the reception filter tends to decrease.

  In contrast, in the present embodiment, the series arm resonator S4 of the first filter 7 is an elastic wave resonator configured according to the present invention. That is, the crystallinity of Al or an alloy mainly composed of Al constituting the IDT electrode of the series arm resonator S4 is lower than the crystallinity of an alloy composed mainly of Al or Al that is triaxially oriented.

  Therefore, the level of the non-linear signal generated in the series arm resonator S4 is suppressed, and therefore the duplexer according to the present embodiment does not easily reduce the reception sensitivity.

  However, in the present invention, at least one of the plurality of elastic wave resonators constituting the elastic wave filter may be an elastic wave resonator configured according to the present invention. That is, the crystallinity of the Al or Al-based alloy constituting the IDT electrode should be lower than the crystallinity of triaxially-oriented Al or Al-based alloy.

  Further, in the duplexer according to the present invention, when the transmission filter and the reception filter having different pass bands are included, at least one elastic wave resonator of the transmission filter may be an elastic wave resonator configured according to the present invention. .

  That is, the crystallinity of the Al or Al-based alloy constituting the IDT electrode should be lower than the crystallinity of triaxially-oriented Al or Al-based alloy. As a result, it is possible to suppress a decrease in reception sensitivity of the reception filter.

DESCRIPTION OF SYMBOLS 1,9 ... Elastic wave resonator 2 ... Piezoelectric substrate 3 ... IDT electrode 4, 5 ... Reflector 6 ... Antenna 7 ... First filter 8 ... Second filter 10a, 11a ... Input terminal 10b, 11b ... Output terminal 12 ... longitudinally coupled resonator type acoustic wave filters S1 to S4 ... series arm resonators P1 and P2 ... parallel arm resonators

Claims (4)

A piezoelectric substrate;
An IDT electrode formed on the piezoelectric substrate and composed of Al or an alloy mainly composed of Al; and
The crystallinity of the alloy mainly composed of Al or Al is rather low than crystallinity of an alloy mainly composed of Al or Al are 3-axis oriented,
An elastic wave resonator in which the half width of the peak of the {200} plane of the Al or Al-based alloy obtained by X-ray diffraction measurement is 27 degrees or more . The acoustic wave resonator according to claim 1, wherein the alloy mainly composed of Al is an alloy of Al and Cu. An acoustic wave filter having a plurality of acoustic wave resonators,
Wherein the plurality of acoustic wave resonators, at least one acoustic wave resonator, an elastic wave resonator according to claim 1 or 2, the elastic wave filter. A duplexer having a plurality of acoustic wave resonators, and comprising a band-pass first filter and a second filter having a different pass band from the first filter;
Wherein one of the first and second at least one of the plurality of elastic wave resonators of the filter, at least one acoustic wave resonator, an elastic wave resonator according to claim 1 or 2, duplexer.