WO2016072270A1 - Piezoelectric device - Google Patents

Abstract

A piezoelectric resonator (10) provided with a piezoelectric film (20). Function conductors (211, 212) are formed on the surface of the piezoelectric film (20). The piezoelectric resonator (10) is provided with a support substrate (40) and a fixing layer (30). The fixing layer (30) fixes the piezoelectric film (20) to the support substrate (40). The amount of warp is not uniform in a plurality of directions within a plane parallel to the surface of the piezoelectric film (20). In the above state, the piezoelectric film (20) is supported by the support substrate (40) with the fixing layer (30) interposed therebetween.

Description

Piezoelectric device

The present invention relates to a piezoelectric device in which a conductor is formed on a piezoelectric film.

Patent Document 1 describes a piezoelectric resonator having a membrane structure. In a piezoelectric resonator having a membrane structure, a piezoelectric film on which a resonator conductor pattern such as IDT is formed is supported on a support substrate by a fixed layer. At this time, the region where the resonator conductor pattern is formed in the piezoelectric film is not in contact with the fixed layer. That is, the resonator conductor pattern forming region in the piezoelectric film is supported by the fixed layer so that the cavity is formed.

Patent Document 2 describes a piezoelectric resonator including an acoustic multilayer film. The acoustic multilayer film is disposed between the piezoelectric film and the support substrate.

International Publication No. 2011/052551 Pamphlet International Publication No. 2012/086441 Pamphlet

However, in the piezoelectric resonator in which the piezoelectric film is arranged so as not to be warped as in the above-described structure, the characteristics of the resonator are deteriorated due to spurious effects such as higher order modes, and the characteristics of the piezoelectric device are reduced. It may deteriorate.

Therefore, an object of the present invention is to provide a piezoelectric device capable of reducing the influence of spurious.

The piezoelectric resonator of the present invention includes a piezoelectric film, a resonator conductor pattern formed on the surface of the piezoelectric film, a support substrate, and a fixed layer that fixes the piezoelectric film to the support substrate. The amount of warpage along a plurality of directions in a plane parallel to the surface of the piezoelectric film is not uniform.

In this configuration, the resonance frequency corresponding to the higher harmonics changes without changing the fundamental resonance frequency as compared with the piezoelectric resonator in which the piezoelectric film is arranged so as not to warp. As a result, spurious can be improved.

In the piezoelectric resonator of the present invention, the amount of warp is preferably ± 500 μm or less per 100 mm scanning distance in the direction parallel to the surface. Furthermore, the amount of warpage is preferably ± 300 μm or less.

In this configuration, spurious can be improved and the occurrence of defects in the manufacturing process can be suppressed.

Further, in the piezoelectric resonator according to the present invention, it is preferable that the fixed layer is not in contact with a portion where the resonator conductor pattern is formed in the piezoelectric film in a plan view.

In this configuration, a so-called membrane-structure piezoelectric resonator is formed. This further improves the resonator characteristics.

In the piezoelectric resonator of the present invention, the fixed layer may be an acoustic multilayer film in which high impedance layers and low impedance layers are alternately arranged.

Even with this configuration, the resonator characteristics are further improved.

In the piezoelectric resonator of the present invention, the piezoelectric film is preferably a LiTaO ₃ substrate or a LiNbO ₃ substrate.

In this configuration, a piezoelectric resonator having the above-described effects can be easily formed.

Further, in the piezoelectric resonator of the present invention, the resonator conductor pattern has a structure in which a plurality of comb-like conductors are combined, and it is preferable that the propagating high frequency is a plate wave. Thus, by applying the above-described configuration to the plate-wave piezoelectric resonator, the spurious characteristics of the plate-wave resonator can be improved.

According to the present invention, the influence of spurious can be reduced and the characteristics of the device can be improved.

1 is a plan view of a piezoelectric resonator according to a first embodiment of the present invention. It is side surface sectional drawing of the piezoelectric resonator which concerns on the 1st Embodiment of this invention. It is an enlarged view which shows the curvature of the piezoelectric film in the piezoelectric resonator which concerns on the 1st Embodiment of this invention. It is an impedance characteristic view of the piezoelectric resonator and the comparative example according to the first embodiment of the present invention. It is side surface sectional drawing which shows the shape in each process in the manufacturing method of the piezoelectric resonator which concerns on the 1st Embodiment of this invention. It is side surface sectional drawing of the piezoelectric resonator which concerns on the 2nd Embodiment of this invention.

The piezoelectric resonator according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a piezoelectric resonator according to a first embodiment of the present invention. FIG. 2 is a side cross-sectional view (corresponding to the AA cross-sectional view in FIG. 1) of the piezoelectric resonator according to the first embodiment of the present invention.

The piezoelectric resonator 10 includes a piezoelectric film 20, a fixed layer 30, and a support substrate 40. The fixed layer 30 is bonded to the back surface of the piezoelectric film 20, and the support substrate 40 is bonded to the back surface of the fixed layer 30 (the surface opposite to the surface on which the piezoelectric film 20 abuts). With this configuration, the piezoelectric film 20 is supported on the support substrate 40 by the fixed layer 30.

The piezoelectric film 20 is a piezoelectric body such as LN (LiNbO ₃ ) or LT (LiTaO ₃ ). The fixed layer 30 is an insulator such as SiO ₂ . The support substrate 40 is made of Si, sapphire, glass or the like.

Functional conductors 211 and 212 are formed on the surface of the piezoelectric film 20 (the surface opposite to the surface on the fixed layer 30 side). The functional conductors 211 and 212 have a comb-teeth shape in plan view. The functional conductors 211 and 212 are arranged so as to form a so-called IDT (Interdigital Transducer). With this configuration, a piezoelectric resonator is configured.

The void 300 is formed in the fixed layer 30. The gap 300 is surrounded by the piezoelectric film 20, the fixed layer 30, and the support substrate 40. However, the gap 300 is inserted through the through hole 200 provided in the piezoelectric film 20. The through-hole 200 is used when the gap 300 is formed.

The air gap 300 is provided so as to overlap a portion of the piezoelectric film 20 where the functional conductors 211 and 212 are formed when the piezoelectric resonator 10 is viewed in plan. In other words, the back surface of the portion where the functional conductors 211 and 212 are formed in the piezoelectric film 20 is not in contact with (separated from) the fixed layer 30 and the support substrate 40.

In such a structure, the piezoelectric film 20 has a warp in the region where the functional conductors 211 and 212 are formed. This warp has anisotropy in a plane parallel to the surface of the piezoelectric film 20. Specifically, as indicated by the dotted arrows in FIG. 1, the amount of warpage differs in a plurality of directions in the plane.

For example, the warp amount along the direction parallel to the longitudinal direction of each finger conductor of each functional conductor 211, 212 is Wp1, the warp amount along the direction parallel to the finger conductor arrangement direction is Wp2, and these two directions In contrast, a warp amount along a direction intersecting at a predetermined angle (for example, 45 °) is defined as Wp3. The piezoelectric film 20 is warped so that Wp1 ≠ Wp2 and Wp1 ≠ Wp3.

As described above, since the warp of the piezoelectric film 20 has anisotropy, the following effects can be obtained. FIG. 3 is an enlarged view showing warpage of the piezoelectric film in the piezoelectric resonator according to the first embodiment of the present invention. Note that FIG. 3 exaggerates the warpage.

As shown in the upper diagram of FIG. 3, when a warp Wp1 occurs in the arrangement direction of the finger conductors, the interval between adjacent finger conductors (functional conductors 211 and 212) is different from a state without warp. The amount of change in the interval is determined by the amount of warpage.

As shown in the lower diagram of FIG. 3, when the warp Wp2 is generated in the longitudinal direction of the finger conductor, the finger conductor is extended by the amount of the warp Wp2.

The ratio between the amount of change in the distance between the finger conductors due to warpage in the arrangement direction and the distance between the finger conductors without warping is the amount by which the length of the finger conductors changes due to the warp in the longitudinal direction of the finger conductors. And the ratio with the length of the finger conductor in a state without warping is large.

When such a shape change occurs, the impedance characteristics of the piezoelectric resonator change as shown in FIG. FIG. 4 is an impedance characteristic diagram of the piezoelectric resonator and the comparative example according to the first embodiment of the present invention.

As shown in FIG. 4, the piezoelectric resonator 10 having the warp in the piezoelectric film 20 (characteristic of the thick solid line in FIG. 4) is compared with the piezoelectric resonator having no warp of the piezoelectric film (characteristic of the broken line in FIG. 4). The resonance frequency of the fundamental wave hardly changes. However, the resonance frequency of the higher harmonics changes. In the example of FIG. 4, the resonance frequency of the high-order harmonic shifts to the high frequency side.

Note that, as shown in FIG. 4, even if the arrangement pitch of the functional conductors 211 and 212 is changed, the resonance frequency of the higher-order harmonic can be shifted without substantially changing the resonance frequency of the fundamental wave.

Thus, since the resonance frequency of the higher harmonic can be changed without changing the resonance frequency of the fundamental wave, the spurious characteristics of the piezoelectric resonator 10 can be improved. In particular, as shown in FIG. 4, the spurious characteristics can be improved by keeping the resonance frequency of the higher harmonics away from the resonance frequency of the fundamental wave.

By using the configuration of the present embodiment, the piezoelectric resonator 10 with improved spurious characteristics can be realized. Further, by using the configuration of the present embodiment, spurious characteristics can be improved without changing the arrangement pitch of the functional conductors 211 and 212, that is, without changing the shape of the functional conductors 211 and 212.

The piezoelectric resonator 10 having such a configuration is formed by the following process. FIG. 5 is a side cross-sectional view showing the shape at each step in the method for manufacturing a piezoelectric resonator according to the first embodiment of the present invention.

As shown in FIG. 5A, a sacrificial layer 31 is formed on the back surface of the piezoelectric substrate 20P having a predetermined thickness. The sacrificial layer 31 is formed so as to overlap with and include a portion where the functional conductors 211 and 212 are formed in a process described later. The sacrificial layer 31 is, for example, ZnO. Next, the fixed layer 30 is formed on the back surface of the piezoelectric substrate 20P so as to cover the sacrificial layer 31 and the back surface of the piezoelectric substrate 20P.

Next, as shown in FIG. 5B, the fixed layer 30 is polished and planarized from the surface of the fixed layer 30 opposite to the surface in contact with the piezoelectric substrate 20P and the sacrificial layer 31. Here, the planarization refers to a process of removing a portion protruding by the sacrificial layer 31 and keeping the surface roughness within a predetermined range.

Next, as shown in FIG. 5C, the support substrate 40 is bonded to the flattened surface of the fixed layer 30. For bonding, for example, a resin adhesive is used.

Next, as shown in FIG. 5D, the piezoelectric substrate 20P is polished to form the piezoelectric film 20. Here, the planarization refers to a process of uniformly reducing the thickness of the piezoelectric film 20 and keeping the surface roughness within a predetermined range.

The fixed layer 30 is made of a material that applies a compressive stress to the piezoelectric substrate 20P. For example, the fixed layer 30 is the above-described SiO ₂ . The fixed layer 30 is formed on the back surface of the sacrificial layer 31 and the piezoelectric substrate 20P in an environment where the temperature is increased to a predetermined temperature (for example, 80 °). As a result, the fixed layer 30 is cooled, and compressive stress is applied to the piezoelectric substrate 20P, whereby an anisotropic warp can be generated in the piezoelectric substrate 20P. At this time, the warp is preferably less than 500 μm at a scanning distance of 100 mm in each direction in the plane. Furthermore, the warp is more preferably less than 300 μm at a scanning distance of 100 mm in each direction within the plane. By setting the warpage within this range, the flow of an automatic apparatus (for example, a photolithography apparatus) during the manufacturing process can be surely and easily performed. Moreover, the fall of the adhesion strength to the support substrate 40 mentioned later can also be suppressed. Thereby, generation | occurrence | production of the defect in a manufacturing process can be suppressed.

Next, as shown in FIG. 5E, functional conductors 211 and 212 are formed on the piezoelectric film 20.

Next, as shown in FIG. 5F, a through hole 200 is formed in the piezoelectric film 20.

Then, the sacrificial layer 31 is removed through the through hole 200. For example, the sacrificial layer 31 is removed by wet etching. By this treatment, as shown in FIG. 2, voids 300 are formed in the fixed layer 30.

The piezoelectric resonator 10 is formed by using the above manufacturing method.

Next, a piezoelectric resonator according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 6 is a side sectional view of the piezoelectric resonator according to the second embodiment of the present invention.

The piezoelectric resonator 10A according to the present embodiment is different from the piezoelectric resonator 10 according to the first embodiment in the configuration of the fixed layer 30.

In the piezoelectric resonator 10 </ b> A, the fixed layer 30 is configured by the acoustic multilayer film 60. The acoustic multilayer film 60 has a structure in which layers having high acoustic impedance and layers having low acoustic impedance are alternately stacked. Specifically, it has a structure in which SiO ₂ layers and AlN layers are alternately laminated.

Further, at least one layer constituting the acoustic multilayer film 60 is formed to have anisotropy in warping.

Even with such a configuration, the piezoelectric resonator 10A capable of improving the spurious characteristics can be realized as in the first embodiment.

Note that the piezoelectric resonators 10 and 10A described above are illustrated as examples of a plate-wave piezoelectric resonator, but may be a bulk-wave piezoelectric resonator. However, in a plate-wave piezoelectric resonator, the effect of wave confinement by a membrane structure or an acoustic multilayer film has a great influence on the characteristics of the resonator. For this reason, it is easy to receive the influence of the above-mentioned spurious. However, by using the structure of the above-described embodiment, the influence of spurious can be suppressed. Therefore, a piezoelectric resonator for plate wave with higher performance can be realized.

In addition, although the piezoelectric resonator is shown in the present embodiment, it can be applied to a filter using the piezoelectric resonator and various piezoelectric devices.

10, 10A: Piezoelectric resonator 20: Piezoelectric film 20P: Piezoelectric substrate 30: Fixed layer 31: Sacrificial layer 40: Support substrate 60: Acoustic multilayer film 91: Sacrificial layer 200: Through hole 211, 212: Functional conductor 300: Air gap

Claims (7)

A piezoelectric film;
A functional conductor pattern formed on the surface of the piezoelectric film;
A support substrate;
A fixing layer for fixing the piezoelectric film to the support substrate,
In the region where the functional conductor pattern is formed, the surface of the piezoelectric film is warped, and the amount of warping along a plurality of directions in a plane parallel to the surface of the piezoelectric film is uneven.
Piezoelectric device. The amount of warpage is ± 500 μm or less per 100 mm scanning distance in a direction parallel to the surface.
The piezoelectric device according to claim 1. The warpage amount is ± 300 μm or less.
The piezoelectric device according to claim 2. The fixed layer is not in contact with a portion where the functional conductor pattern is formed in the piezoelectric film in a plan view of the piezoelectric film,
The piezoelectric device according to any one of claims 1 to 3. The fixed layer is an acoustic multilayer film in which high impedance layers and low impedance layers are alternately arranged.
The piezoelectric device according to any one of claims 1 to 3. The piezoelectric film is a LiTaO ₃ substrate or a LiNbO ₃ substrate.
The piezoelectric device according to any one of claims 1 to 5. The functional conductor pattern is a structure in which a plurality of comb-like conductors are combined,
The high frequency that propagates is a plate wave.
The piezoelectric device according to any one of claims 1 to 6.

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