Piezoelectric composite thin film resonator
First Claim
1. A piezoelectric thin film resonator comprising a first thin film formed of a semiconductor or an insulator material, a lower electrode formed on said first thin film, a piezoelectric thin film formed on said lower electrode, a second thin film formed of a material having an opposite resonant frequency temperature coefficient as compared to the corresponding coefficients of said piezoelectric thin film and positioned on said piezoelectric thin film, another piezoelectric thin film formed on said second thin film, and an upper electrode formed on said other piezoelectric thin film, the total thickness of the two piezoelectric thin films and said second thin film being within the range of 50 μ
- m to 3 μ
m and the ratio of the thickness of said second thin film to the thickness of said two piezoelectric thin films being in the range of 0.085 to 0.093.
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Abstract
A piezoelectric composite thin-film resonator has good temperature stability and resonance response, in a fundamental thickness-extensional vibration mode. Spurious vibrations caused by even-number order harmonic overtones are suppressed. The resonator has a thin film of SiO2 or other materials having a resonant frequency temperature coefficient which is opposite to that of the piezoelectric material. The SiO2 layer is inserted between two thin films of ZnO, CdS, AlN, or other piezoelectric materials. This sandwiched structure is positioned between a pair of electrode films and is supported by an insulative or a semiconductive film which is in turn fixed to a substrate. The thicknesses of the thin films have values such that an overall temperature coefficient of the resonant frequency may be at or near substantially zero. In order to better remove the even-number order harmonics, it is preferable to cover the upper electrode film with a thin film of semiconductor or insulator material.
247 Citations
20 Claims
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1. A piezoelectric thin film resonator comprising a first thin film formed of a semiconductor or an insulator material, a lower electrode formed on said first thin film, a piezoelectric thin film formed on said lower electrode, a second thin film formed of a material having an opposite resonant frequency temperature coefficient as compared to the corresponding coefficients of said piezoelectric thin film and positioned on said piezoelectric thin film, another piezoelectric thin film formed on said second thin film, and an upper electrode formed on said other piezoelectric thin film, the total thickness of the two piezoelectric thin films and said second thin film being within the range of 50 μ
- m to 3 μ
m and the ratio of the thickness of said second thin film to the thickness of said two piezoelectric thin films being in the range of 0.085 to 0.093. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- m to 3 μ
- 10. A piezoelectric thin film resonator in a fundamental thickness-extensional-vibration mode comprising a first thin film as a substrate, a lower electrode partially formed on said first thin film, a piezoelectric thin film continuously formed on said first thin film and said lower electrode, a second thin film formed of a material having a temperature coefficient of a resonant frequency of the fundamental thickness-extensional-vibration mode which is opposite to the corresponding coefficient of said piezoelectric thin film and covering said piezoelectric thin film, another piezoelectric thin film covering said second thin film, and an upper electrode partially formed on said other piezoelectric thin film, said second thin film being free from any mechanical contact other than with the two piezoelectric thin films, the relative thickness of said second thin film to said two piezoelectric thin films being selected so that spurious vibrations caused by even-number order harmonic overtones may be substantially suppressed with a reduced temperature coefficient at the resonant frequency of the fundamental thickness-extensional-vibration mode of said resonator.
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