JP2021057797A - Bulk acoustic wave resonator and manufacturing method of the same - Google Patents

Abstract

To provide a bulk acoustic wave resonator that can form a piezoelectric film on a surface of a lower layer electrode with a flat surface and improve its characteristics.SOLUTION: The bulk acoustic wave resonator includes a support substrate and a lower layer electrode film 2, a piezoelectric film 3, and an upper layer electrode film 4 stacked on the support substrate. The lower layer electrode film 2 has a flat surface. The piezoelectric film 3 is stacked on the lower electrode film 2. A recess 7 is provided on a surface of the periphery, and a part of the surface is cut out. The upper layer electrode film 4 covers the recess 7 and is stacked on top of the piezoelectric film 3.SELECTED DRAWING: Figure 5

Description

The present invention relates to a bulk elastic wave resonator and a method for manufacturing the same.

In recent years, with the worldwide spread of smartphones and the ever-increasing demand for wireless communication services using microwaves, commonly known as wearables and IoT (Internet of Things), radio waves are a limited resource. In order to make effective use of (microwaves), it is required to selectively extract radio waves of a required frequency from microwaves overflowing in space. For example, at present, the service is expanding to use not only the frequency band of 2.5 GHz or less but also the high frequency band of 3 GHz or more, and a high frequency filter is used to selectively extract radio waves in a predetermined frequency band. .. This type of high-frequency filter is required to have high performance such as no temperature drift and steep skirt characteristics.

Instead of a thin-film bulk elastic wave resonator that is arranged so that the piezoelectric film is sandwiched between the upper and lower electrode films and an air layer (cavity) is provided below the lower electrode film to serve as an acoustic reactor, or instead of the cavity. A mirror-type bulk elastic wave resonator in which reflective layers of different materials are laminated on a support substrate and an acoustic mirror is provided has the possibility of satisfying the above requirements.

By the way, in this type of bulk elastic wave resonator, it is known that laterally propagated waves leak from the edge portion and the characteristics (Q value) deteriorate. Therefore, a method of increasing the mismatch of acoustic impedance and increasing the reflectance at the edge portion by thickening a part of the lower layer electrode of the edge portion is disclosed (Patent Document 1, FIG. 14).

Japanese Unexamined Patent Publication No. 2007-6501

Among the conventionally proposed bulk elastic wave resonators, in the bulk elastic wave resonator having a structure in which a part of the lower layer electrode is thickened, a piezoelectric film is laminated on the uneven lower layer electrode in the manufacturing process. Become. In general, when a piezoelectric film is formed on an uneven surface, the orientation deteriorates and the characteristics deteriorate. Therefore, an object of the present invention is to provide a bulk elastic wave resonator capable of forming a piezoelectric film on the surface of a lower electrode having a flat surface and improving its characteristics, and a method for manufacturing the same.

In order to achieve the above object, the invention according to claim 1 of the present application is a bulk elastic wave resonator provided with a support substrate and a lower layer electrode film, a piezoelectric film and an upper layer electrode film laminated on the support substrate, and the surface thereof is formed. The flat lower electrode film, the piezoelectric film laminated on the lower electrode film, and the surface of the peripheral edge portion provided with a recess formed by cutting out a part of the surface, and the recess are covered with the piezoelectric film. It is characterized by including the upper electrode film laminated on the upper layer.

The invention according to claim 2 of the present application is characterized in that, in the bulk elastic wave resonator according to claim 1, a part of the recess is not covered with the upper electrode film.

The invention according to claim 3 of the present application is a step of preparing a support substrate and a step of preparing the support substrate in a method of manufacturing a bulk elastic wave resonator in which a lower electrode film, a piezoelectric film and an upper electrode film are laminated on the support substrate, and on the support substrate. The step of forming the lower electrode film having a flat surface and the piezoelectric film having a flat surface are laminated on the lower electrode film and patterned into a desired shape, and one of the surfaces is formed on the surface of the peripheral edge portion. It is characterized by including a step of forming a recess formed by cutting out a portion and a step of forming the upper layer electrode film covering a part or all of the recess on the piezoelectric film.

Since the bulk elastic wave resonator of the present invention is configured to include a piezoelectric film laminated on a lower electrode film having a flat surface, the piezoelectric film has uniform orientation and does not cause deterioration of characteristics.

Further, in the bulk elastic wave resonator of the present invention, a portion having a different thickness of the piezoelectric film is arranged on the peripheral edge portion by arranging a recess, and an upper electrode film is formed so as to fill the recess. As a result, a part of the thickness becomes thicker, and impedance mismatch can be easily formed. Further, instead of covering all the recesses arranged on the surface of the outer peripheral portion of the piezoelectric film with the upper layer electrode film, a region not covered with the upper layer electrode film is provided on a part of the outer peripheral side of the recesses, thereby forming the peripheral portion. Impedance mismatch can be further formed, and the reflectance at the peripheral portion can be increased. As a result, elastic waves can be confined in the FBAR (Film Bulk Acoustic Resonator) section, resulting in a bulk elastic wave resonator having a large Q value.

The method for manufacturing a bulk elastic wave resonator of the present invention has a desired impedance by appropriately selecting so as to cover all the recesses arranged on the surface of the outer peripheral portion of the piezoelectric film or to cover a part of the recesses. Inconsistencies can be easily formed.

It is explanatory drawing of the manufacturing process of the bulk elastic wave resonator of 1st Example of this invention. It is explanatory drawing of the manufacturing process of the bulk elastic wave resonator of 1st Example of this invention. It is explanatory drawing of the manufacturing process of the bulk elastic wave resonator of 1st Example of this invention. It is explanatory drawing of the manufacturing process of the bulk elastic wave resonator of 1st Example of this invention. It is explanatory drawing of the manufacturing process of the bulk elastic wave resonator of 1st Example of this invention. It is explanatory drawing of the bulk elastic wave resonator of 1st Example of this invention. It is explanatory drawing of the bulk elastic wave resonator of the 2nd Example of this invention.

The bulk elastic wave resonator according to the present invention has a configuration including a piezoelectric film having uniform orientation laminated on a flat lower layer electrode film, and an impedance interface is further formed on the peripheral edge portion to leak laterally propagated waves. Therefore, it is possible to obtain a bulk elastic wave resonator having excellent characteristics. Hereinafter, examples of the present invention will be described in detail according to the manufacturing process.

The first embodiment of the present invention will be described by taking a thin film bulk elastic wave resonator provided with a cavity as an example. First, a silicon nitride film 5 as a sacrificial layer is deposited in a region where a cavity portion is planned to be formed on a support substrate 1 made of a silicon substrate or the like. The thickness of the silicon nitride film 5 is about 1 micron. After that, an insulating film 6 such as a silicon oxide film is formed on the entire surface and flattened by etching back (FIG. 1). In this step, if the surface becomes flat, a sacrificial layer is formed in the region where the cavity is to be formed, and the cavity can be formed by removing the sacrificial layer in a later step, another material may be selected. , Other methods may be adopted. For example, a method may be used in which the surface of the support substrate 1 in the region where the cavity portion is planned to be formed is removed in a concave shape, and the sacrificial layer is filled in the concave portion.

Next, a multilayer film constituting a bulk elastic wave resonator is formed. This multilayer film covers the silicon nitride film 5 which is the region where the cavity is to be formed, and is formed so as to reach the insulating film 6. For example, the lower electrode film 2 made of molybdenum (Mo) and the piezoelectric film 3 made of aluminum nitride (AlN) are laminated and formed. As shown in FIG. 2, the surface of the lower electrode film 2 is flat, and the piezoelectric film 3 having a flat surface is laminated on the flat lower electrode film 2. The piezoelectric film 3 laminated in this way can be a columnar polycrystal in which the crystal orientation (c-axis) is aligned in the direction perpendicular to the substrate surface, and is a uniform and high-quality film.

After that, the laminated film of the piezoelectric film 3 and the lower electrode film 2 is patterned into a desired shape, and a plurality of recesses 7 are formed on the peripheral edge of the piezoelectric film 3 (FIG. 3). The recess 7 can be formed without deteriorating the characteristics of the piezoelectric film 3 by adopting a normal dry etching method.

Here, the shape of the recess 7 can be appropriately set such as a groove extending along the peripheral edge portion and a shape in which independent holes are aligned along the peripheral edge portion. Further, the opening width and depth of the recess 7 are set so that when the upper electrode film described later is laminated and formed, the upper electrode film is filled in the recess 7 and the thickness of the upper electrode film in the recess 7 becomes thicker. It is preferable to do so.

After that, the upper electrode film 4 made of molybdenum or the like is formed on the entire surface and patterned into a desired shape. In the example shown in FIG. 4, the upper electrode film 4 is filled in the recess 7 and the surface is flat.

Then, by removing the silicon nitride film 5 from an opening (not shown), a bulk elastic wave resonator having a cavity 8 is completed (FIG. 5).

The bulk elastic wave resonator formed in this way is λ / 4 when the length of the frame portion of the upper electrode film 4 covering the peripheral edge portion of the piezoelectric film 3 shown in FIG. 6 is the wavelength λ of the elastic wave (Lamb wave). Impedance increases by setting it to an odd multiple of. As a result, it was confirmed that the elastic wave (Lamb wave) was reflected by the frame portion and could be confined in the FBAR portion, and the Q value became large.

Next, a second embodiment will be described. In the first embodiment, the recess 7 formed on the peripheral edge of the piezoelectric film 3 is completely covered with the upper electrode film 4. However, by making a part of the recess 7 exposed, it is possible to form regions having different impedances.

Specifically, as shown in FIG. 7, the structure is such that a part of the recesses 7 is exposed. In a bulk elastic wave resonator having such a shape, in addition to a region having a different impedance formed by the frame portion, a region having a different impedance including a region where the recess 7 is exposed is formed on the peripheral edge portion thereof. As a result, an impedance interface is formed and characteristics are expected to be improved.

Although the present invention has been described above, it goes without saying that the present invention is not limited thereto. For example, even if the surface of the upper electrode film 4 is not flat over the entire surface depending on the shape of the recess 7 such as a mixture of recesses having different widths, the recess 7 is filled with the upper electrode film 4 and its thickness. Is formed thicker than the thickness of the upper electrode film 4 on the FBAR portion, so that there is no problem as long as the impedance interface is formed.

Further, the piezoelectric film is not limited to aluminum nitride, and scandium aluminum nitride (Al _1-x Sc _x N), zinc oxide (ZnO), and lead zirconate titanate (PZT) can also be used. Further, the upper electrode film or the lower electrode film can be formed of a metal thin film such as platinum (Pt), titanium (Ti), iridium (Ir), and ruthenium (Ru) instead of molybdenum.

Further, it can be applied not only to the cavity type bulk elastic wave resonator but also to the multilayer thin film mirror type bulk elastic wave resonator.

1: Support substrate 2: Lower electrode film 3: Piezoelectric film 4: Upper electrode film 5: Silicon nitride film, 6: Insulation film, 7: Recess, 8: Cavity

Claims (3)

In a bulk elastic wave resonator provided with a support substrate and a lower electrode film, a piezoelectric film, and an upper electrode film laminated on the support substrate.
The lower electrode film having a flat surface and
The piezoelectric film laminated on the lower electrode film and provided with a recess formed by cutting out a part of the surface on the surface of the peripheral portion, and the piezoelectric film.
A bulk elastic wave resonator comprising the upper electrode film which covers the recess and is laminated on the piezoelectric film. In the bulk elastic wave resonator according to claim 1,
A bulk elastic wave resonator characterized in that a part of the recess is not covered with the upper electrode film. In a method for manufacturing a bulk elastic wave resonator in which a lower electrode film, a piezoelectric film, and an upper electrode film are laminated on a support substrate.
The process of preparing the support board and
A step of forming the lower electrode film having a flat surface on the support substrate, and
A step of laminating and forming the piezoelectric film having a flat surface on the lower electrode film, patterning it into a desired shape, and forming a recess formed by cutting out a part of the surface on the surface of the peripheral edge portion.
A method for manufacturing a bulk elastic wave resonator, which comprises a step of forming the upper electrode film that covers a part or all of the recesses on the piezoelectric film.

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