JP2008211392A - Resonator and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase both a mechanical quality coefficient and an electromechanical coupling coefficient. <P>SOLUTION: In a resonator, a piezoelectric thin-film layer 3 is composed by laminating a piezoelectric thin film 30 that is formed by AlN as a first layer and a piezoelectric thin film 31 that is formed by PZT as a second layer, and is interposed between lower and upper electrodes 20, 40 in a thickness direction, thus composing the piezoelectric thin-film layer 3 by laminating a plurality of piezoelectric thin films 30, 31 formed by a plurality of kinds of piezoelectric materials (AlN, PZT), where the relationship of the polarizability differs from that of the mechanical quality coefficient, and hence increasing both the mechanical quality coefficient and the electromechanical coupling coefficient as compared with when the piezoelectric film is composed of a single piezoelectric material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a resonator using bulk acoustic waves and a manufacturing method thereof.

Conventionally, in the field of mobile communication devices such as mobile phones, BAW (Bulk Acoustic Wave) has adopted AlN (aluminum nitride) as a piezoelectric thin film material as a high-frequency filter used in a high-frequency band of 3 GHz or higher. A resonator has been proposed (see, for example, Patent Document 1). In Patent Document 1, FBAR (Film Bulk Acoustic Resonator)) is described as a BAW resonator. Recently, in addition to FBAR, SMR (Solidly Mounted Resonator) has attracted attention as a BAW resonator. Yes.
Special table 2003-534695 gazette

  By the way, the inventor of the present application considered applying the BAW resonator as a broadband high-frequency filter to, for example, a UWB (Ultra Wide Band) type device. Therefore, as the material of the piezoelectric thin film, the effective electromechanical coupling coefficient (an index representing the efficiency of converting electric energy into mechanical energy) is relatively small, and the bandwidth can be widened only by 4 to 5% with respect to the center frequency. Attention was paid to PZT (lead zirconate titanate), which has a relatively large effective electromechanical coupling coefficient compared to AlN and can obtain a bandwidth of about 10% with respect to the center frequency. However, in a high frequency filter (so-called UWB filter) applied to a UWB device, a mechanical quality factor (a piezoelectric body has a natural vibration) related to the steepness of the filter cutoff characteristic (steepness of rising and falling resonance characteristics). PZT is required to have a characteristic of a constant of about 300 or more and an effective electromechanical coupling coefficient of about 0.35 to 0.39. Although an effective electromechanical coupling coefficient of about 0.35 to 0.5 can be easily manufactured, it is difficult to set the mechanical quality coefficient to 300 or more because of high acoustic loss. On the other hand, AlN having a mechanical quality factor of 1000 or more can be manufactured relatively easily, but the effective electromechanical coupling factor is 0.25 or less.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a resonator capable of increasing both the mechanical quality factor and the electromechanical coupling factor, and a method for manufacturing the resonator.

  In order to achieve the above object, a first aspect of the present invention provides a base substrate, a lower electrode formed on one surface side of the base substrate, and a piezoelectric thin film layer formed on the opposite side of the lower electrode to the base substrate side. And an upper electrode formed on the opposite side to the lower electrode side of the piezoelectric thin film layer, wherein the piezoelectric thin film layer is made of a plurality of types of piezoelectric materials having different polarizabilities and mechanical quality factors. A plurality of formed piezoelectric thin films are laminated, and the plurality of types of piezoelectric materials are characterized in that the mutual relationship between the polarizabilities and the mechanical quality factor are different.

  The invention of claim 2 is characterized in that, in the invention of claim 1, aluminum nitride and lead zirconate titanate are included as the plurality of types of piezoelectric materials.

  The invention of claim 3 is the invention of claim 2, wherein the thickness of the piezoelectric thin film formed of lead zirconate titanate is made thinner than the thickness of the piezoelectric thin film formed of aluminum oxide. And

  In order to achieve the above object, a fourth aspect of the present invention is a method of manufacturing the resonator according to any one of the first to third aspects, wherein a lower electrode is formed on one surface side of a base substrate. A step of forming a piezoelectric thin film made of any one type of piezoelectric material on the side of the lower electrode opposite to the base substrate side, and a type different from the one type of piezoelectric material on the side of the piezoelectric thin film opposite to the base substrate side And a step of forming an upper electrode on the side opposite to the lower electrode side in the piezoelectric thin film layer formed by laminating a plurality of piezoelectric thin films.

  According to the present invention, a piezoelectric thin film layer is formed by laminating a plurality of piezoelectric thin films each formed of a plurality of types of piezoelectric materials having different magnitude relationships between polarizabilities and mechanical quality factors. Therefore, both the mechanical quality factor and the electromechanical coupling factor can be increased as compared with the case where the piezoelectric thin film is formed of a single piezoelectric material.

  Hereinafter, embodiments in which the technical idea of the present invention is applied to a BAW resonator will be described in detail with reference to the drawings.

(Embodiment 1)
In the present embodiment, as shown in FIG. 1H, the base substrate 10, the lower electrode 20 formed on one surface side of the base substrate 10, and the lower electrode 20 formed on the side opposite to the base substrate 10 side. The piezoelectric thin film layer 3 and the upper electrode 40 formed on the opposite side of the piezoelectric thin film layer 3 from the lower electrode 20 side are provided.

  Here, in the present embodiment, the base substrate 10 is divided into a single crystal silicon substrate 11 whose main surface is a (100) plane and bulk acoustic waves generated on the main surface of the silicon substrate 11 and generated in the piezoelectric thin film layer 3. It is comprised with the acoustic multilayer film 12 to reflect. In short, the BAW resonator of this embodiment constitutes an SMR in which the lower electrode 20 is formed on the acoustic multilayer film 12 on the one surface side of the base substrate 10.

  The acoustic multilayer film 12 is formed by alternately laminating a low acoustic impedance layer 12a made of a material having a relatively low acoustic impedance and a high acoustic impedance layer 12b made of a material having a relatively high acoustic impedance. 20 is formed on the uppermost low acoustic impedance layer 12a. The film thicknesses of the low acoustic impedance layer 12a and the high acoustic impedance layer 12b may be set to a value that is a quarter of the wavelength of the elastic wave (bulk elastic wave) at the resonance frequency of the piezoelectric thin film layer 3.

In this embodiment, SiO ₂ is used as the material of the low acoustic impedance layer 12a, W is used as the material of the high acoustic impedance layer 12b, Pt is used as the material of the lower electrode 20, and Al is used as the material of the upper electrode 40. The material is not particularly limited. For example, Ir may be used as the material of the lower electrode 20, and examples of the material of the low acoustic impedance layer 12a include Si, poly-Si, Al, and polymer. As the material of the high acoustic impedance layer 12b, for example, Au, Mo, AlN, ZnO or the like may be adopted, and as the material of the upper electrode 40, for example, Mo or the like may be adopted. Good. Further, instead of the silicon substrate 11 in the base substrate 10, an MgO substrate having a main surface of (100) plane, an STO (SrTiO ₃ ) substrate having a main surface of (100) plane, or the like may be used.

  By the way, the piezoelectric thin film layer 3 in the present embodiment includes a plurality (two layers in the illustrated example) of piezoelectric thin films 30, each formed of a plurality of types of piezoelectric materials (AlN and PZT) having different polarizabilities and mechanical quality factors. 31 is laminated. However, the direction of spontaneous polarization of each piezoelectric thin film 30, 31 is aligned with the thickness direction of the film.

  As described in the prior art, AlN is a piezoelectric material having a relatively large mechanical quality factor but a relatively small electromechanical coupling coefficient, whereas PZT has a relatively small mechanical quality factor. The piezoelectric material has a relatively large electromechanical coupling coefficient, and further has a characteristic that the polarizability of PZT is larger than the polarizability of AlN. That is, when the polarizability of AlN is Pr1, the mechanical quality factor is Q1, the polarizability of PZT is Pr2, and the mechanical quality factor is Q2, the polarities Pr1 and Pr2 of both and the mechanical quality factors Q1 and Q2 are Have a relationship of Pr1 <Pr2, Q1> Q2. That is, the two types of piezoelectric materials (AlN and PZT) used in the present embodiment are different in the magnitude relationship between the polarizabilities Pr1 and Pr2 and the magnitude relationship between the mechanical quality factors Q1 and Q2 (reversed).

  Here, the manufacturing method of this embodiment is demonstrated, referring FIG.

First, a low acoustic impedance layer 12a made of a SiO ₂ film and a high acoustic impedance layer 12b made of a W film are formed on a main surface side of a single crystal silicon substrate 11 which is a base of the base substrate 10, for example, a sputtering method or a CVD method. By forming the acoustic multilayer film 12 by alternately forming the film, the structure shown in FIG. 1A is obtained.

  Thereafter, the entire surface on one surface side (the upper surface side in FIG. 1A) of the base substrate 10 composed of the silicon substrate 11 and the acoustic multilayer film 12 is made of a first conductive material (for example, Pt, Ir, etc.). By forming the first conductive layer 20a serving as the base of the lower electrode 20 by, for example, sputtering or vapor deposition, the structure shown in FIG. 1B is obtained. In the present embodiment, the first conductive layer 20a is composed of a Pt layer. However, the first conductive layer 20a is not limited to a single layer structure, for example, a Ti layer on the acoustic multilayer film 12 And a Pt layer on the Ti layer.

  Next, the structure shown in FIG. 1C is formed by forming the first piezoelectric thin film 30a on the entire surface of the base substrate 10 on the one surface side (here, the surface of the first conductive layer 20a). Get. However, the piezoelectric material forming the first piezoelectric thin film 30a may be either AlN or PZT. Furthermore, the structure shown in FIG. 1D is obtained by forming the second-layer piezoelectric thin film 31a on the surface of the first-layer piezoelectric thin film 30a opposite to the base substrate 10 (the upper surface in FIG. 1). However, the piezoelectric material forming the second piezoelectric thin film 31a is different from the piezoelectric material forming the first piezoelectric thin film 30a. For example, when the first piezoelectric thin film 30a is made of AlN, the second layer is thin. When the piezoelectric thin film 31a is formed of PZT and the first piezoelectric thin film 30a is formed of PZT, the second piezoelectric thin film 31a is formed of AlN.

  After laminating two layers of piezoelectric thin films 30a and 31a made of different piezoelectric materials as described above, the second layer of piezoelectric thin film 31a is patterned into a desired planar shape using a photolithographic technique and an etching technique. By forming the piezoelectric thin film 31 made of a part of the thin film 31a, the structure shown in FIG. Similarly, by using photolithography technology and etching technology, the first piezoelectric thin film 30a is patterned into the same planar shape as the second piezoelectric thin film 31 to form a piezoelectric thin film 30 comprising a part of the piezoelectric thin film 30a. By doing so, the structure shown in FIG.

  Subsequently, by using the photolithography technique and the etching technique, the first conductive layer 20a is patterned into a desired planar shape to form the lower electrode 20 made of a part of the conductive layer 20a, thereby FIG. The structure shown in g) is obtained.

  Thereafter, a second conductive layer made of a second conductive material (for example, Al, Mo, Pt, etc.) and serving as the basis of the upper electrode 40 is formed on the entire surface of the base substrate 10 by sputtering or vapor deposition. Then, the second conductive layer is patterned into a desired planar shape using a photolithography technique and an etching technique to form an upper electrode 40 made of a part of the second conductive layer. By doing so, a BAW resonator having the structure shown in FIG. In the present embodiment, the second conductive layer is composed of an Al layer. However, the second conductive layer is not limited to a single layer structure, and may be a multilayer structure.

  In manufacturing the BAW resonator described above, a large number of BAW resonators may be formed at the wafer level using a wafer as the silicon substrate 11 described above, and then divided into individual BAW resonators in a dicing process.

  In the BAW resonator of the present embodiment described above, for example, the piezoelectric thin film layer 3 is configured by laminating the first piezoelectric thin film 30 formed of AlN and the second piezoelectric thin film 31 formed of PZT. The piezoelectric thin film layer 3 is sandwiched between the lower electrode 20 and the upper electrode 40 in the thickness direction. Accordingly, the piezoelectric thin film layer 3 is formed by laminating a plurality of piezoelectric thin films 30 and 31 each formed of a plurality of types of piezoelectric materials (AlN and PZT) having different magnitude relationships between polarizabilities and mechanical quality factors. Therefore, both the mechanical quality factor and the electromechanical coupling coefficient can be increased as compared with the case where the piezoelectric thin film is formed of a single piezoelectric material. Here, in order to bring the polarizability Pr0 of the entire piezoelectric thin film layer 3 closer to the polarizability Pr2 of the piezoelectric material having the higher polarizability (in this case, PZT), the piezoelectric material (PZT) having the higher polarizability is used. The film thickness of the piezoelectric thin film 31 may be made thinner than the film thickness of the piezoelectric thin film 30 made of the piezoelectric material (AlN) having the lower polarizability, and the piezoelectric film made of AlN with respect to the film thickness of the piezoelectric thin film 31 made of PZT. The film thickness of the thin film 30 is desirably about 30 to 40 times.

By the way, when the above-described BAW resonator is applied as a filter having a sharp cutoff characteristic and a wide bandwidth in a high frequency band of 3 GHz or more, for example, a UWB filter, as shown in FIG. A plurality of resonators 5 composed of the piezoelectric thin film layer 3 and the upper electrode 40 are formed on the same base substrate 10 (only two are shown in FIG. 2, for example, eight are formed) Thus, if these resonators 5 are connected to form a ladder type filter as shown in FIG. 3, the cost and size of the UWB filter can be reduced. In the configuration in which the plurality of resonators 5 are formed on the same base substrate 10, as described above, the low acoustic impedance layer 12a of the acoustic multilayer film 12 is made of an insulating material such as SiO ₂ and the high acoustic impedance layer 12b. In the case where W, which is a metal material, is used as the material, for example, the high acoustic impedance layer 12b is used in order to prevent crosstalk between the adjacent resonators 5 via the high acoustic impedance layer 12b. May be appropriately patterned at the time of manufacture so as to form a pattern separated for each resonator 5.

  In this embodiment, the piezoelectric thin film layer 3 is configured by laminating two layers of piezoelectric thin films 30 and 31. However, the piezoelectric thin film layer 3 may be configured by laminating three or more piezoelectric thin films. However, even when three or more layers are stacked, it is necessary to alternately stack piezoelectric thin films formed of different types of piezoelectric materials. Furthermore, in this embodiment, the piezoelectric thin film layer 3 is configured using two types of piezoelectric materials. For example, the piezoelectric thin film layer 3 is formed by stacking piezoelectric thin films formed of three types of piezoelectric materials of AlN, PZT, and ZnO. The thin film layer 3 may be configured. A seed layer for controlling the crystal orientation of the piezoelectric thin film 31 made of PZT may be formed between the second piezoelectric thin film 31 made of PZT and the first piezoelectric thin film 30 made of AlN. . As a material for the seed layer, for example, PbTiO3, PbLaTiO3, or the like may be employed.

(Embodiment 2)
The basic configuration of the BAW resonator of the present embodiment shown in FIG. 4 (h) is substantially the same as that of the first embodiment, and a single crystal silicon substrate having one (100) surface is adopted as the base substrate 10. The base substrate 10 is different from the first embodiment in that an opening 13 is formed to expose the surface of the lower electrode 20 opposite to the piezoelectric thin film layer 3 side. In short, the BAW resonator of the present embodiment has an FBAR that suppresses the propagation of elastic wave energy to the base substrate 10 side by increasing the acoustic impedance ratio between the lower electrode 20 and the medium immediately below the lower electrode 20. It is composed. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted.

  Hereinafter, the method for manufacturing the BAW resonator according to the present embodiment will be described with reference to FIG. 4, but the same steps as those for the method for manufacturing the BAW resonator described in the first embodiment will be briefly described.

  First, the first conductive layer 20a serving as the basis of the lower electrode 20 is formed on the entire surface of one surface side of the base substrate 10 (upper surface side in FIG. 4A). For example, the structure shown in FIG. 4A is obtained by forming by sputtering or vapor deposition.

  Next, the structure shown in FIG. 4B is formed by forming the first piezoelectric thin film 30a on the entire surface of the base substrate 10 on the one surface side (here, the surface of the first conductive layer 20a). Get. Furthermore, the structure shown in FIG. 4C is obtained by forming the second-layer piezoelectric thin film 31a on the surface of the first-layer piezoelectric thin film 30a opposite to the base substrate 10 (the upper surface in FIG. 4).

  After laminating two layers of piezoelectric thin films 30a and 31a made of different piezoelectric materials as described above, the second layer of piezoelectric thin film 31a is patterned into a desired planar shape using a photolithographic technique and an etching technique. By forming the piezoelectric thin film 31 made of a part of the thin film 31a, the structure shown in FIG. 4D is obtained. Similarly, by using photolithography technology and etching technology, the first piezoelectric thin film 30a is patterned into the same planar shape as the second piezoelectric thin film 31 to form a piezoelectric thin film 30 comprising a part of the piezoelectric thin film 30a. By doing so, the structure shown in FIG.

  Subsequently, by using the photolithography technique and the etching technique, the first conductive layer 20a is patterned into a desired planar shape to form the lower electrode 20 made of a part of the conductive layer 20a, thereby FIG. The structure shown in f) is obtained.

  Thereafter, a second conductive layer serving as a basis for the upper electrode 40 is formed on the entire surface of the one surface side of the base substrate 10 by a sputtering method, a vapor deposition method, or the like, and subsequently, a photolithography technique and an etching technique are used. Then, the second conductive layer is patterned into a desired planar shape to form the upper electrode 40 made of a part of the second conductive layer, thereby obtaining the BAW resonator having the structure shown in FIG. .

Next, a mask layer (for example, resist layer, SiO ₂ film) patterned for forming the opening 13 is formed on the other surface side of the base substrate 10, and an alkaline solution (for example, KOH) is formed using the mask layer as a mask. , An opening portion 13 is formed by performing anisotropic etching using an aqueous solution of TMAH, NaOH, or the like, or dry etching using an inductively coupled plasma type etching apparatus, and then removing the mask layer. Thus, the BAW resonator having the structure shown in FIG. When the opening 13 is formed by anisotropic etching using an alkaline solution, it is not necessary to provide a mask on the one surface side of the base substrate 10 if the material of the upper electrode 40 is Pt. When the material of the electrode 20 is Al, it is necessary to provide a mask for protecting the upper electrode 20 on the one surface side of the base substrate 10.

  In the BAW resonator of the present embodiment described above, similarly to the first embodiment, for example, the first piezoelectric thin film 30 formed of AlN and the second piezoelectric thin film 31 formed of PZT are stacked to form a piezoelectric layer. A thin film layer 3 is formed, and the piezoelectric thin film layer 3 is sandwiched between the lower electrode 20 and the upper electrode 40 in the thickness direction, and a plurality of types of piezoelectric elements having different polarities and mechanical quality factors are different. Since the piezoelectric thin film layer 3 is configured by laminating a plurality of piezoelectric thin films 30 and 31 each formed of materials (AlN and PZT), compared to the case where the piezoelectric thin film is configured by a single piezoelectric material, Both the mechanical quality factor as well as the electromechanical coupling factor can be increased. The BAW resonator of this embodiment can also be applied to a UWB filter as in the first embodiment.

  In this embodiment, the piezoelectric thin film layer 3 is configured by laminating two layers of piezoelectric thin films 30 and 31. However, the piezoelectric thin film layer 3 may be configured by laminating three or more piezoelectric thin films. However, even when three or more layers are stacked, it is necessary to alternately stack piezoelectric thin films formed of different types of piezoelectric materials. Furthermore, in this embodiment, the piezoelectric thin film layer 3 is configured using two types of piezoelectric materials. For example, the piezoelectric thin film layer 3 is formed by stacking piezoelectric thin films formed of three types of piezoelectric materials of AlN, PZT, and ZnO. The thin film layer 3 may be configured. A seed layer for controlling the crystal orientation of the piezoelectric thin film 31 made of PZT may be formed between the second piezoelectric thin film 31 made of PZT and the first piezoelectric thin film 30 made of AlN. .

FIG. 6 is a main process sectional view for illustrating the method for manufacturing the BAW resonator in the first embodiment. It is a schematic sectional drawing of the filter for UWB in the same as the above. It is a circuit diagram of the filter for UWB in the same as the above. FIG. 10 is a main process sectional view for illustrating the method for manufacturing the BAW resonator in the second embodiment.

Explanation of symbols

3 Piezoelectric thin film layer 10 Base substrate 20 Lower electrode 30 Piezoelectric thin film (AlN thin film)
31 Piezoelectric thin film (PZT thin film)
40 Upper electrode

Claims (4)

A base substrate, a lower electrode formed on one surface side of the base substrate, a piezoelectric thin film layer formed on the opposite side of the lower electrode to the base substrate side, and a piezoelectric thin film layer formed on the opposite side of the lower electrode side A resonator comprising an upper electrode formed,
A piezoelectric thin film layer is formed by laminating a plurality of piezoelectric thin films each formed of a plurality of types of piezoelectric materials having different polarizabilities and mechanical quality factors, and the plurality of types of piezoelectric materials have a magnitude relationship between each other. And the mechanical quality factor are different in size.   2. The resonator according to claim 1, wherein the plurality of types of piezoelectric materials include aluminum nitride and lead zirconate titanate.   3. The resonator according to claim 2, wherein the thickness of the piezoelectric thin film formed of lead zirconate titanate is made thinner than the thickness of the piezoelectric thin film formed of aluminum oxide.   A manufacturing method for manufacturing the resonator according to any one of claims 1 to 3, wherein a step of forming a lower electrode on one surface side of the base substrate and a side of the lower electrode opposite to the base substrate side are provided. A step of forming a piezoelectric thin film made of one type of piezoelectric material, a step of forming a piezoelectric thin film made of a piezoelectric material of a different type from the one type of piezoelectric material on the opposite side of the piezoelectric thin film from the base substrate side, And a step of forming an upper electrode on a side opposite to the lower electrode side in the piezoelectric thin film layer formed by laminating the piezoelectric thin films.

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