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  Piezoelectric resonator, piezoelectric filter, duplexer, communication apparatus, and method for manufacturing piezoelectric resonatorUSPTO Application #: 20070221494Title: Piezoelectric resonator, piezoelectric filter, duplexer, communication apparatus, and method for manufacturing piezoelectric resonator Abstract: A piezoelectric thin film resonator having a stabilized temperature characteristic of resonant frequency, a method for manufacturing the same, and a communication apparatus using the piezoelectric thin film resonator are provided. The piezoelectric thin film resonator is provided with a substrate having an opening, first and second insulation films which are provided on one surface of the substrate while covering the opening and which primarily include SiO2 and Al2O3, respectively, Al2O3 having oxygen defect and being in an amorphous state, and a piezoelectric thin film which is provided on the second insulation film and is sandwiched between electrodes and which primarily includes ZnO. (end of abstract) Agent: Murata Manufacturing Company, Ltd. C/o Keating & Bennett, LLP - Mclean, VA, US Inventors: Hajime YAMADA, Masaki TAKEUCHI, Hideki KAWAMURA, Hiroyuki FUJINO, Yukio YOSHINO, Ken-ichi UESAKA, Tadashi NOMURA, Daisuke NAKAMURA, Yoshimitsu USHIMI, Takashi HAYASHI USPTO Applicaton #: 20070221494 - Class: 204192220 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Non-distilling Bottoms Treatment, Coating, Forming Or Etching By Sputtering, Glow Discharge Sputter Deposition (e.g., Cathode Sputtering, Etc.), Specified Deposition Material Or Use, Insulator Or Dielectric The Patent Description & Claims data below is from USPTO Patent Application 20070221494. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a Divisional Application of U.S. patent application Ser. No. 11/094,622 filed Mar. 30, 2005, currently pending which is a Divisional Application of U.S. patent application Ser. No. 10/329,602 filed Dec. 27, 2002, now U.S. Pat. No. 6,906,451. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a piezoelectric resonator, a piezoelectric filter including a piezoelectric resonator, a duplexer, a communication apparatus, and a method for manufacturing a piezoelectric resonator. [0004] 2. Description of the Related Art [0005] A piezoelectric resonator provided with a piezoelectric thin film on a substrate has been used as a filter for a communication device. [0006] Some piezoelectric resonators include piezoelectric vibration portions in which a piezoelectric thin film is sandwiched between opposed upper and lower electrodes, and a high-frequency signal is applied to the sandwiched piezoelectric thin film via the electrodes such that the piezoelectric thin film vibrates in a thickness vibration mode. Examples of such piezoelectric resonators include a diaphragm type piezoelectric resonator having an opening in a substrate which is covered with a diaphragm made of laminated thin films, and the piezoelectric vibration portion is supported by this diaphragm. [0007] FIG. 42 is a sectional view showing the structure of a conventional piezoelectric resonator (see, for example, Japanese Unexamined Patent Application Publication No. 2001-279438). [0008] This piezoelectric resonator includes a substrate 201, a plurality of substrate films 202 and 203, a pair of electrodes 204 and 206, and a piezoelectric thin film 205. Since the substrate film is defined by a plurality of layers as described above, each substrate film shares functions, for example, chemical stability and adhesiveness, and as a result, improvement of the performance and reliability of the piezoelectric resonator are achieved. [0009] Furthermore, some piezoelectric resonators include piezoelectric vibration portions in which a piezoelectric thin film is sandwiched between opposed upper and lower electrodes, and a high-frequency signal is applied to the sandwiched piezoelectric thin film via the electrodes and, therefore, the piezoelectric thin film vibrates in a thickness vibration mode. Examples of such piezoelectric resonators include a diaphragm type piezoelectric resonator having a structure in which an opening of a substrate is covered with a diaphragm made of laminated thin films, and the piezoelectric vibration portion is supported by this diaphragm. [0010] In some piezoelectric resonators having a diaphragm structure, the residual stress during diaphragm formation is adjusted to be nearly zero and, thereby, the resonant characteristics are improved, or the diaphragm surface is flattened with high precision and, thereby, the resonant characteristics are improved (see, for example, Japanese Unexamined Patent Application Publication No. 2000-244030). [0011] Japanese Unexamined Patent Application Publication No. 2001-279438 discloses an example of a piezoelectric resonator in which the lower substrate film 202 of a plurality of substrate films is made of SiNx, the upper substrate film is made of Al.sub.2O.sub.3, and the piezoelectric thin film is made of ZnO. [0012] However, regarding the configuration of such a conventional piezoelectric resonator, since each of the temperature coefficient of resonant frequencies (TCF) of SiNx, Al.sub.2O.sub.3, and ZnO has a negative value, when the substrate films 202 and 203 made of SiNx and Al.sub.2O.sub.3 are combined with the piezoelectric thin film 205, the temperature coefficient of resonant frequency in the basic mode is deteriorated. [0013] Furthermore, regarding the piezoelectric resonator in which the residual stress during diaphragm formation is adjusted to be nearly zero, when the diaphragm surface is not flat, the crystallinity and orientation property of the piezoelectric vibration portion are reduced and, therefore, the resonant characteristics cannot be sufficiently improved. Regarding the piezoelectric resonator in which the diaphragm surface is flattened, when the stress remains, the resonant characteristics cannot be sufficiently improved. SUMMARY OF THE INVENTION [0014] In order to overcome the problems described above, preferred embodiments of the present invention provide a piezoelectric resonator having a stabilized temperature characteristic of resonant frequency, a method for manufacturing such a novel piezoelectric resonator, a piezoelectric filter including the novel piezoelectric resonator, a duplexer, and a communication apparatus. [0015] Furthermore, preferred embodiments of the present invention provide a piezoelectric resonator having reduced residual stress in a diaphragm and improved flatness of the diaphragm surface and, therefore, having outstanding resonant characteristics. [0016] A piezoelectric resonator according to a preferred embodiment of the present invention includes a substrate and a vibration portion provided on the substrate, the vibration portion having a structure in which top and bottom surfaces of a thin film portion including at least one layer of piezoelectric thin film are sandwiched between at least a pair of upper and lower electrodes facing each other in the thickness direction, wherein first and second insulation films are arranged between the substrate and the vibration portion, and the temperature coefficient of resonant frequency of one of the first insulation film, the second insulation film, and the piezoelectric thin film and the temperature coefficients of resonant frequencies of the others have opposite signs. [0017] According to preferred embodiments of the present invention, since the first and second insulation films and the piezoelectric thin film are defined by the film having a positive temperature coefficient of resonant frequency and the film having a negative temperature coefficient of resonant frequency, by setting the film thickness ratio thereof at a proper value, the temperature coefficient of resonant frequency is reduced and, therefore, the frequency temperature characteristic of the entire piezoelectric resonator is stabilized. [0018] Preferably, in the piezoelectric resonator according to this preferred embodiment the present invention, one of the first and second insulation films primarily includes Al.sub.2O.sub.3 or SiO.sub.2, or the first insulation film primarily includes Al.sub.2O.sub.3 and the second insulation film primarily includes SiO.sub.2. In this case, since the insulation film primarily including SiO.sub.2 is subject to a compressive stress while the insulation film primarily including Al.sub.2O.sub.3 is subject to a tensile stress, the stress of the entire piezoelectric resonator is controlled, and since Al.sub.2O.sub.3 has a high thermal conductivity and outstanding exoergic compared with those of SiO.sub.2, etc., the temperature increase of an element due to an input electric power can be reduced and, therefore, outstanding electric-power resistance can be achieved. [0019] Preferably, in the piezoelectric resonator according to this preferred embodiment of the present invention, the arithmetic average surface roughness (Ra) of the lower electrode is preferably about 2.5 nm or less. With this arithmetic average the piezoelectric resonator achieves a Q of at least about 200. The arithmetic average surface roughness (Ra) is defined by the stipulation of JIS B0601-2001. [0020] Preferably, in the piezoelectric resonator according to preferred embodiments of the present invention, the upper layer of the first and second insulation films primarily includes Al.sub.2O.sub.3, and the arithmetic average surface roughness (Ra) thereof is about 1.0 nm or less. According to this feature, the arithmetic average surface roughness (Ra) of the lower electrode provided on the upper layer insulation film is preferably about 2.5 nm or less, and the piezoelectric resonator achieves a Q of at least about 200. [0021] Preferably, in the piezoelectric resonator according to preferred embodiments of the present invention, the upper layer of the first and second insulation films primarily includes Al.sub.2O.sub.3, and the stress therein is between about 250 MPa and about 400 MPa on a tensile stress basis. According to this feature, since film formation of the lower electrode provided on the upper layer insulation film is performed with outstanding orientation properties, a piezoelectric resonator having outstanding resonant characteristics is produced. [0022] Preferably, in the piezoelectric resonator according to preferred embodiments of the present invention, the upper layer of the first and second insulation films primarily includes SiO.sub.2, and the arithmetic average surface roughness (Ra) thereof is about 1.0 nm or less. According to this feature, the arithmetic average surface roughness (Ra) of the lower electrode provided on the upper layer insulation film is preferably about 2.5 nm or less, and the piezoelectric resonator achieves a Q of at least about 200. Continue reading... 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