JP2008211385A - Manufacturing method of piezoelectric thin film, resonator, and filter for uwb using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a piezoelectric thin film improving crystallinity in the piezoelectric thin film, to provide a resonator improving crystallinity in the piezoelectric film, and to provide a filter for UWB using the resonator. <P>SOLUTION: In the manufacturing method of the piezoelectric thin film includes, a buffer layer formation process, a piezoelectric thin film formation process, and a stress application layer formation process. In the buffer layer formation process, a buffer layer 2, which is made of a material having a thermal coefficient of expansion intermediate between a piezoelectric material and a substrate material, is formed by a sputtering method, or the like on one surface side of a support substrate 1 made of the material (substrate material) whose thermal coefficient of expansion is smaller than that of the material (piezoelectric material) of the piezoelectric thin film 3. In the piezoelectric thin film formation process, the piezoelectric thin film 3 is formed on the buffer layer 2 by the sputtering method, or the like. In the stress application layer formation process, a stress application layer 4, which is made of a material whose thermal coefficient of expansion is smaller than that of the piezoelectric material and applies stress to the piezoelectric thin film 3, is formed on the piezoelectric thin film 3 by the sputtering method, or the like. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a piezoelectric thin film, a resonance device, and a UWB filter using the same.

  Conventionally, as a resonance device applicable to a high frequency filter used in a high frequency band of 3 GHz or more in the field of mobile communication equipment such as a mobile phone, a lower electrode and a piezoelectric thin film on one surface side of a support substrate made of a silicon substrate There has been proposed a BAW resonator that includes a resonator composed of an upper electrode and an AlN as a material for a piezoelectric thin film (see, for example, Patent Document 1). In Patent Document 1, FBAR (Film Bulk Acoustic Resonator) is described as a BAW resonator, but recently, SMR (Solidly Mounted Resonator) has attracted attention as a BAW resonator in addition to FBAR. . In the BAW resonator, the resonance frequency is inversely proportional to the film thickness of the piezoelectric thin film, and the resonance frequency can be increased as the film thickness of the piezoelectric thin film is reduced.

  By the way, when the above-described resonance device is applied to a filter for UWB (Ultra Wide Band), as a material of the piezoelectric thin film, the center frequency is higher than that of AlN whose bandwidth is only 4 to 5% of the center frequency. On the other hand, it is conceivable to employ PZT (lead zirconate titanate) capable of obtaining a bandwidth of about 10%.

  Here, as a resonance device employing PZT as a piezoelectric material, for example, as shown in FIG. 5, an insulating layer 7 ′ made of a silicon oxide film is formed on one surface of a support substrate 1 ′ made of a silicon substrate, A resonance device in which a lower electrode 5 'is formed on an insulating layer 7', a piezoelectric thin film 3 'made of PZT is formed on the lower electrode 5', and an upper electrode 6 'is formed on the piezoelectric thin film 3'. Has been proposed (see, for example, Patent Document 2). Here, in the resonance device of FIG. 5, the lower electrode 5 ', the piezoelectric thin film 3', and the upper electrode 6 'constitute a resonator 10'.

As a method for manufacturing a piezoelectric thin film for manufacturing a piezoelectric thin film made of a piezoelectric material on one surface side of a support substrate, for example, a sputtering method, a CVD method, a sol-gel method, an aerosol deposition method, and the like are known ( For example, see Patent Documents 1 to 3).
JP 2002-140075 A JP-A-10-126204 JP 2006-165102 A

  In the method for manufacturing a piezoelectric thin film described in Patent Documents 1 to 3, since the piezoelectric thin film and the base of the piezoelectric thin film use different materials, even if both are materials having good lattice matching, When the film is formed at high temperature, a thermal stress corresponding to the difference in thermal expansion coefficient between the two is generated in the piezoelectric thin film, the crystallinity of the piezoelectric thin film is lowered due to the thermal stress, and the electromechanical coupling coefficient is reduced. End up.

  The present invention has been made in view of the above-mentioned reasons, and its object is to provide a method for manufacturing a piezoelectric thin film capable of improving the crystallinity of the piezoelectric thin film, a resonance device capable of improving the crystallinity of the piezoelectric thin film, and the same It is to provide a filter for UWB using the above.

  The invention according to claim 1 is a method for manufacturing a piezoelectric thin film, which is formed on a surface of a support substrate and made of a material having a coefficient of thermal expansion different from that of the support substrate. A buffer layer forming step of forming a buffer layer made of a material having a thermal expansion coefficient intermediate between the material of the support substrate and the piezoelectric thin film; and a piezoelectric thin film forming step of forming a piezoelectric thin film on the buffer layer; A stress applying layer forming step of forming a stress applying layer made of a material having a smaller thermal expansion coefficient than the material of the piezoelectric thin film on the piezoelectric thin film and applying a stress to the piezoelectric thin film.

  According to the present invention, the buffer layer forming step of forming a buffer layer made of a material having a thermal expansion coefficient intermediate between the material of the support substrate and the material of the piezoelectric thin film on one surface side of the support substrate, and on the buffer layer Piezoelectric thin film forming step for forming a piezoelectric thin film, and a stress applying layer for forming a stress applying layer on the piezoelectric thin film made of a material having a smaller thermal expansion coefficient than that of the piezoelectric thin film, and applying stress to the piezoelectric thin film By continuously performing the forming process, the residual stress in the piezoelectric thin film can be reduced, and the crystallinity of the piezoelectric thin film can be improved.

  According to a second aspect of the present invention, there is provided a piezoelectric thin film manufacturing method for manufacturing a piezoelectric thin film on one surface side of a support substrate, wherein the one of the support substrates made of a material having a smaller thermal expansion coefficient than the material of the piezoelectric thin film. A piezoelectric thin film forming step for forming a piezoelectric thin film on the surface, and a stress applying layer for applying stress to the piezoelectric thin film made of a material having a smaller thermal expansion coefficient than the piezoelectric thin film material is formed on the piezoelectric thin film. A stress application layer forming step.

  According to the present invention, the piezoelectric thin film forming step of forming the piezoelectric thin film on one surface of the support substrate made of a material having a smaller thermal expansion coefficient than the material of the piezoelectric thin film, and the piezoelectric thin film on the piezoelectric thin film Residual stress in the piezoelectric thin film can be reduced by continuously performing a stress applying layer forming step of forming a stress applying layer that is made of a material having a smaller thermal expansion coefficient than the material and applies stress to the piezoelectric thin film, The crystallinity of the piezoelectric thin film can be improved.

  According to a third aspect of the present invention, there is provided a support substrate, a lower electrode formed on one surface side of the support substrate, a piezoelectric thin film formed on the opposite side of the lower electrode to the support substrate side, and a lower electrode in the piezoelectric thin film The piezoelectric thin film is manufactured by the method for manufacturing a piezoelectric thin film according to claim 1, wherein the piezoelectric thin film is provided with an upper electrode formed on the side opposite to the upper electrode.

  According to this invention, since the piezoelectric thin film is manufactured by the method for manufacturing a piezoelectric thin film according to the first aspect, the crystallinity of the piezoelectric thin film in the resonance device can be improved.

  According to a fourth aspect of the invention, the resonance device according to the third aspect is used.

  According to the present invention, it is possible to provide a UWB filter using a resonance device that improves the crystallinity of a piezoelectric thin film.

  According to the first and second aspects of the invention, there is an effect that the crystallinity of the piezoelectric thin film can be improved.

  In the invention of claim 3, there is an effect that the crystallinity of the piezoelectric thin film in the resonance device can be improved.

  According to the invention of claim 4, there is an effect that it is possible to provide a UWB filter using a resonance device in which the crystallinity of the piezoelectric thin film is improved.

(Embodiment 1)
In the present embodiment, as shown in FIG. 1, a method for manufacturing a piezoelectric thin film 3 for manufacturing a piezoelectric thin film 3 on one surface side of a support substrate 1 will be described.

  In the method for manufacturing the piezoelectric thin film 3 of the present embodiment, the piezoelectric material and the piezoelectric material are formed on the one surface side of the support substrate 1 made of a material (substrate material) having a smaller coefficient of thermal expansion than the material of the piezoelectric thin film 3 (piezoelectric material). A buffer layer forming step of forming the buffer layer 2 made of a material having a thermal expansion coefficient intermediate to that of the substrate material by a sputtering method or the like is performed, and then the piezoelectric thin film 3 is formed on the buffer layer 2 by a sol-gel method or the like. A piezoelectric thin film forming step is performed, and subsequently, a stress applying layer 4 made of a material having a smaller thermal expansion coefficient than the piezoelectric material is applied on the piezoelectric thin film 3 by a sputtering method or the like. A stress application layer forming step is performed.

Here, when the material of the piezoelectric thin film 3 is, for example, PZT, the material of the support substrate 1 is, for example, Si or SiO _2, and the material of the buffer layer 2 is, for example, PT (PbTiO ₃ ), PLT ((Pb, La For example, SiO ₂ may be used as the material of the stress applying layer 4 such as TiO ₃ ). The material of the piezoelectric thin film 3 is not limited to PZT, and for example, AlN, Bi—Ti—O based materials such as Bi ₃ Ti ₄ O ₁₂ , BaBi—Ti—O based materials, ZnO, LiNbO _3, etc. The material of the support substrate 1, the material of the buffer layer 2, and the material of the stress application layer 4 may be appropriately selected according to the coefficient of thermal expansion of the material of the piezoelectric thin film 3.

  By the way, in the manufacturing method of the piezoelectric thin film 3 of this embodiment, the buffer layer 2, the piezoelectric thin film 3, and the stress application layer 4 are continuously formed on the one surface side of the support substrate 1 by the sol-gel method or the sputtering method. I am doing so. The method of continuously forming the buffer layer 2, the piezoelectric thin film 3, and the stress applying layer 4 is not limited to the sputtering method or the sol-gel method, and may be a CVD method, for example.

  According to the method of manufacturing the piezoelectric thin film 3 of the present embodiment described above, the piezoelectric thin film is obtained by continuously performing the above-described buffer layer forming step, the piezoelectric thin film forming step, and the stress applying layer forming step. 3 can be reduced, the crystallinity of the piezoelectric thin film 3 can be improved, and the piezoelectric thin film 3 having a large electromechanical coupling coefficient can be obtained.

  In the method for manufacturing the piezoelectric thin film 3 described above, the piezoelectric thin film 3 is formed on the buffer layer 2 on the one surface of the support substrate 1, but the coefficient of thermal expansion is smaller than that of the piezoelectric material of the piezoelectric thin film 3. A piezoelectric thin film forming step for forming the piezoelectric thin film 3 on one surface of the support substrate 1 made of a material, and a stress on the piezoelectric thin film 3 made of a material having a smaller thermal expansion coefficient than the piezoelectric material on the piezoelectric thin film 3. A manufacturing method may be adopted so that the stress applying layer forming step for forming the stress applying layer 4 for applying the stress is continuously performed. Also in this manufacturing method, the residual stress in the piezoelectric thin film 3 can be reduced, and the piezoelectric body. The crystallinity of the thin film 3 can be improved, and the piezoelectric thin film 3 having a large electromechanical coupling coefficient can be obtained. Here, by adopting a material having substantially the same coefficient of thermal expansion as the material of the support substrate 1 as the material of the stress application layer 4, the residual stress in the piezoelectric thin film 3 can be further reduced. The electromechanical coupling coefficient can be improved by improving the crystallinity.

(Embodiment 2)
In this embodiment, as shown in FIG. 2 (e), the support substrate 1 and the resonator 10 formed on one surface side of the support substrate 1 are provided, and the resonator 10 is the one surface of the support substrate 1. The lower electrode 5 formed on the side, the piezoelectric thin film 3 formed on the opposite side of the lower electrode 5 from the support substrate 1 side, and the upper part formed on the opposite side of the piezoelectric thin film 3 from the lower electrode 5 side A resonance device composed of a BAW resonator composed of the electrode 6 will be described.

  In the resonance device of this embodiment, an opening 1 a is formed in the support substrate 1 to expose the surface of the lower electrode 5 opposite to the piezoelectric thin film 3 side. In short, the resonance apparatus of the present embodiment has an FBAR that suppresses propagation of elastic wave energy to the support substrate 1 side by increasing the acoustic impedance ratio between the lower electrode 5 and the medium immediately below the lower electrode 5. It is composed.

  In the resonance device of the present embodiment, the resonance frequency of the resonator 10 is set to 4 GHz, and the thickness of the piezoelectric thin film 3 is set to 300 nm. However, these numerical values are only examples and are particularly limited. It is not a thing. For example, when designing the resonance frequency in the range of 3 GHz to 5 GHz, the thickness of the piezoelectric thin film 32 may be appropriately set in the range of 200 nm to 600 nm.

  The above-described resonator 10 employs PZT as the material of the piezoelectric thin film 3, and employs Pt as the material of the lower electrode 5 and Pt as the material of the upper electrode 6, but the material of the lower electrode 5 is Pt. For example, Ir may be used, and the material of the upper electrode 6 is not limited to Pt. For example, Mo, Ir, Ru, or the like may be employed.

  By the way, the resonator 10 in this embodiment is a material having a thermal expansion coefficient between the material of the support substrate 1 and the material of the piezoelectric thin film 3 (piezoelectric material) between the lower electrode 5 and the piezoelectric thin film 3. The buffer layer 2 is formed, and a stress is applied between the piezoelectric thin film 3 and the upper electrode 6, which is made of a material having a smaller thermal expansion coefficient than the piezoelectric material of the piezoelectric thin film 3 and applies stress to the piezoelectric thin film 3. Layer 4 is formed.

In the resonance device of this embodiment, the insulating layer 8 made of a SiO ₂ film or a Si ₃ N ₄ film is laminated on the opposite side of the stress applying layer 4 from the piezoelectric thin film 3 side, and is formed on the insulating layer 8. The upper electrode 6 is in contact with the stress applying layer 4 through the opened hole 9. Here, the opening 9 of the insulating layer 8 has a tapered shape in which the opening area gradually increases as the distance from the stress applying layer 4 increases, and the upper electrode 6 has the insulating layer 8 on the one surface side of the base substrate 1. And the inner surface of the opening 9 in the insulating layer 8 and the surface of the stress applying layer 4.

In this embodiment, PZT is adopted as the material of the piezoelectric thin film 3, the material of the stress applying layer 4 such as Si and SiO ₂ as the material of the support substrate 1, and the material of the buffer layer 2 such as PT and PLT as the material of the buffer layer 2. For example, SiO ₂ may be used. The material of the piezoelectric thin film 3 is not limited to PZT, and for example, AlN, Bi—Ti—O based materials such as Bi ₃ Ti ₄ O ₁₂ , BaBi—Ti—O based materials, ZnO, LiNbO _3, etc. The material of the support substrate 1, the material of the buffer layer 2, and the material of the stress application layer 4 may be appropriately selected according to the coefficient of thermal expansion of the material of the piezoelectric thin film 3.

  Hereinafter, a method for manufacturing the resonance device of the present embodiment will be described with reference to FIGS.

  First, the lower electrode 5 is formed on the entire surface of one surface side of the support substrate 1 (the upper surface side in FIG. 2A) by forming a lower electrode 5 by, for example, sputtering or vapor deposition. ) Is obtained.

  Next, a buffer layer forming step is performed in which the buffer layer 2 is formed by sputtering on the one surface side of the support substrate 1 (here, on the lower electrode 5), and then the piezoelectric thin film 3 is formed on the buffer layer 2. 2 (b) by performing a piezoelectric thin film forming step for forming the above-mentioned stress applying layer 4 on the piezoelectric thin film 3 by a sputtering method. The structure shown in is obtained. In short, in this embodiment, the manufacturing method of the piezoelectric thin film 3 described in Embodiment 1 is used as a manufacturing method of the piezoelectric thin film 3, and the buffer layer 2, The piezoelectric thin film 3 and the stress applying layer 4 are continuously formed by sputtering. The method of continuously forming the buffer layer 2, the piezoelectric thin film 3, and the stress applying layer 4 is not limited to the sputtering method or the sol-gel method, and may be a CVD method, for example.

  After the above-described stress applying layer 4 is formed, piezoelectric conversion is performed by patterning the piezoelectric conversion portion including the buffer layer 2, the piezoelectric thin film 3, and the stress applying layer 4 into a desired planar shape by using a photolithography technique and an etching technique. A partial patterning process is performed, and subsequently, a lower electrode patterning process is performed in which the lower electrode 31 is patterned into a desired planar shape using a photolithography technique and an etching technique, thereby obtaining the structure shown in FIG.

  Thereafter, for example, after a photoresist is spin-coated on the entire surface of the support substrate 1 on the one surface side, the photoresist is patterned to form a resist layer in a portion corresponding to a region where the opening 9 of the insulating layer 8 is to be formed. Next, the insulating layer 8 is formed on the entire surface of the one surface side of the support substrate 1 by the CVD method or the like, and then the resist layer is removed by the lift-off method to thereby form the opening 9 in the insulating layer 8. After forming, an upper electrode forming step of forming the upper electrode 6 on the stress applying layer 4 is performed to obtain the structure shown in FIG. In the upper electrode forming step, for example, the upper electrode 6 is formed on the entire surface of the one surface side of the support substrate 1 by a sputtering method, a vapor deposition method, or the like, and then the planar shape is formed using a photolithography technique and an etching technique. Patterning may be performed.

  After performing the above-mentioned upper electrode formation process, after performing the mask layer formation process which forms the mask layer patterned for the above-mentioned opening part 1a formation on the other surface side of support substrate 1, using the said mask layer as a mask, 2 (e) by performing an opening portion forming step for forming the opening portion 1a by dry etching or wet etching of the support substrate 1, and subsequently performing a mask layer removing step for removing the mask layer. A resonance device having the structure shown in FIG.

  In manufacturing the above-described resonance device, a plurality of resonance devices may be formed at the wafer level using a wafer as the above-described support substrate 1 and then divided into individual resonance devices in a dicing process.

  In the resonance device of the present embodiment described above, the piezoelectric thin film 3 is formed by continuously performing the above-described buffer layer forming step, the piezoelectric thin film forming step, and the stress applying layer forming step. The residual stress in the piezoelectric thin film 3 can be reduced, and the crystallinity of the piezoelectric thin film 3 can be improved.

  By the way, when the above-described resonance device is applied as a high frequency 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. Are formed on the one surface side of the same support substrate 1 (only two are shown in FIG. 3 but, for example, eight are formed), and these resonators 10 are not shown. If the ladder-type filter as shown in FIG. 4 is connected by wiring, the cost and size of the UWB filter can be reduced.

Further, in the above-described resonance device, the opening portion 1 a is provided on the support substrate 1, but instead of providing the opening portion 1 a on the support substrate 1, the piezoelectric thin film 3 is formed on the one surface of the support substrate 1. It is also possible to form an acoustic mirror (acoustic multilayer film) that reflects the bulk acoustic wave generated in step 1, and form the resonator 10 on the acoustic mirror. In short, the above-described resonance device may constitute an SMR, whereas it constitutes an FBAR. The acoustic mirror includes a low acoustic impedance layer made of a material having a relatively low acoustic impedance (for example, SiO ₂ ) and a high acoustic impedance layer made of a material having a relatively high acoustic impedance (for example, W). The film thickness of the low acoustic impedance layer and the high acoustic impedance layer may be formed alternately. The film thickness of the resonance frequency of the piezoelectric thin film 3 is set to a value that is a quarter of the wavelength of the elastic wave (bulk elastic wave). do it.

By the way, when manufacturing a resonance device including such an acoustic mirror, a low acoustic impedance layer composed of a SiO ₂ layer and a high acoustic impedance layer composed of a W layer are alternately laminated on the one surface of the support substrate 1. After forming the acoustic mirror, when the piezoelectric thin film 3 made of the PZT thin film is formed by the sol-gel method without providing the buffer layer on the one surface side of the support substrate 1, the precursor of the PZT thin film is formed. In order to prevent the W layer of the high acoustic impedance layer from being oxidized and expanding the volume of the high acoustic impedance layer or changing the acoustic impedance during annealing in which the film is sintered in a high concentration O ₂ gas atmosphere. The sintering temperature conditions are limited, and it is difficult to optimize the sintering conditions.

On the other hand, after the buffer layer 2 made of PT or PLT is formed on the acoustic mirror by a sputtering method or the like that can be formed in an atmosphere having a lower O ₂ concentration than the sol-gel method, the piezoelectric thin film is formed. If 3 is formed by the sol-gel method, a laminated film of the lower electrode 5 and the buffer layer 2 is formed on the surface side of the acoustic mirror before the piezoelectric thin film 3 is formed by the sol-gel method. Therefore, it becomes easy to optimize the sintering conditions when the piezoelectric thin film 3 made of the PZT thin film is formed using the sol-gel method, and the crystallinity of the piezoelectric thin film 3 formed using the sol-gel method is improved. Improvements can be made.

6 is an explanatory diagram of a method for manufacturing a piezoelectric thin film in Embodiment 1. FIG. FIG. 10 is a main process sectional view for illustrating the method for manufacturing the resonance device in the second embodiment. It is a schematic sectional drawing of the filter for UWB which applied the resonance apparatus same as the above. It is a circuit diagram of the filter for UWB which applied the resonance apparatus same as the above. It is a schematic sectional drawing of the resonance apparatus which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support substrate 2 Buffer layer 3 Piezoelectric thin film 4 Stress application layer 5 Lower electrode 6 Upper electrode

Claims (4)

  A piezoelectric thin film manufacturing method for manufacturing a piezoelectric thin film made of a material having a coefficient of thermal expansion different from that of a support substrate on one surface side of the support substrate, wherein the material of the support substrate and the piezoelectric body are formed on the one surface side of the support substrate. A buffer layer forming step for forming a buffer layer made of a material having a thermal expansion coefficient intermediate to that of the thin film material, a piezoelectric thin film forming step for forming a piezoelectric thin film on the buffer layer, and a piezoelectric body on the piezoelectric thin film A method of manufacturing a piezoelectric thin film, comprising: a stress applying layer forming step of forming a stress applying layer made of a material having a smaller thermal expansion coefficient than that of the thin film material and applying stress to the piezoelectric thin film.   A piezoelectric thin film manufacturing method for manufacturing a piezoelectric thin film on one surface side of a support substrate, wherein the piezoelectric thin film is formed on the surface of the support substrate made of a material having a smaller thermal expansion coefficient than the material of the piezoelectric thin film. A piezoelectric thin film forming step to be formed; and a stress applying layer forming step of forming a stress applying layer made of a material having a smaller thermal expansion coefficient than that of the piezoelectric thin film on the piezoelectric thin film and applying a stress to the piezoelectric thin film. A method of manufacturing a piezoelectric thin film, comprising:   A support substrate, a lower electrode formed on one surface side of the support substrate, a piezoelectric thin film formed on the opposite side of the lower electrode to the support substrate side, and a piezoelectric thin film formed on the opposite side of the lower electrode side A resonance apparatus comprising: the upper electrode, wherein the piezoelectric thin film is manufactured by the method for manufacturing a piezoelectric thin film according to claim 1.   A UWB filter using the resonance device according to claim 3.

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