Piezoelectric resonator, method of manufacturing piezoelectric resonator, and filter, duplexer, and communication device using piezoelectric resonator
View Patent ↗A piezoeletric resonator includes: a substrate; a lower electrode formed on or above the substrate; a piezoeletric body formed on or above the lower electrode; an upper electrode formed on or above the piezoeletric body; and a cavity under a vibrating portion formed by the lower electrode, the piezoeletric body, and the upper electrode. Where a resonant frequency of vibration with a thickness of the vibrating portion being a half of a wavelength is taken as fr, an average of ultrasonic velocity in a material forming the cavity is taken as Vc, and a value determined based on the resonant frequency fr and the average of ultrasonic velocity Vc is taken as λc (=Vc/fr), a depth of the cavity is set so as to be equal to or larger than n×λc/2−λc/8 and equal to or smaller than n×λc/2+λc/8.
1. A piezoeletric resonator, comprising:
a substrate;
a lower electrode formed on or above the substrate;
a piezoeletric body formed on or above the lower electrode;
an upper electrode formed on or above the piezoeletric body; and
a cavity under a vibrating portion formed by the lower electrode, the piezoeletric body, and the upper electrode, the cavity having a trapezoidal shape in section, wherein
where a resonant frequency of vibration with a thickness of the vibrating portion being a half of a wavelength is taken as fr,
an average of ultrasonic velocity in a material forming the cavity is taken as Vc, and
a value determined based on the resonant frequency fr and the average of ultrasonic velocity Vc is taken as λc (=Vc/fr),
a depth of the cavity is set so as to be equal to or larger than n×λc/2−λc/8 and equal to or smaller than n×λc/2+λc/8, where n is an integer.
2. The piezoeletric resonator according to claim 1 , wherein the depth of the cavity is set as n×λc/2.
3. The piezoeletric resonator according to claim 1 , wherein
when the piezoeletric resonator is used to form a band-pass filter,
the depth of the cavity is determined so that no spurious resonant frequency is present within a frequency range of a half of a desired pass-bandwidth of the band-pass filter.
4. The piezoeletric resonator according to claim 3 , wherein
when the band-pass filter is used for Personal Communications Services (PCS),
the depth of the cavity is set so as to be equal to or larger than n×λc/2−λc/10 and equal to or smaller than n×λc/2+λc/10.
5. A filter including a plurality of piezoeletric resonators, wherein
at least one of the piezoeletric resonators includes:
a substrate;
a lower electrode formed on or above the substrate;
a piezoeletric body formed on or above the lower electrode;
an upper electrode formed on or above the piezoeletric body; and
a cavity under a vibrating portion formed by the lower electrode, the piezoeletric body, and the upper electrode, the cavity having a trapezoidal shape in section and
where a resonant frequency of vibration with a thickness of the vibrating portion being a half of a wavelength is taken as fr,
an average of ultrasonic velocity in a material forming the cavity is taken as Vc, and
a value determined based on the resonant frequency fr and the average of ultrasonic velocity Vc is taken as λc (=Vc/fr),
a depth of the cavity is set so as to be equal to or larger than n×λc/2−λc/8 and equal to or smaller than n×λc/2+λc/8, where n is an integer.
6. A duplexer formed by a filter including a plurality of piezoeletric resonators, wherein
at least one of the piezoeletric resonators includes:
a substrate;
a lower electrode formed on or above the substrate;
a piezoeletric body formed on or above the lower electrode;
an upper electrode formed on or above the piezoeletric body; and
a cavity under a vibrating portion formed by the lower electrode, the piezoeletric body, and the upper electrode, the cavity has a trapezoidal shape in section and
where a resonant frequency of vibration with a thickness of the vibrating portion being a half of a wavelength is taken as fr,
an average of ultrasonic velocity in a material forming the cavity is taken as Vc, and
a value determined based on the resonant frequency fr and the average of ultrasonic velocity Vc is taken as λc (=Vc/fr),
a depth of the cavity is set so as to be equal to or larger than n×λc/2−λc/8 and equal to or smaller than n×λc/2+λc/8, where n is an integer.
7. A communication device including a piezoeletric resonator, wherein
the piezoeletric resonator includes:
a substrate;
a lower electrode formed on or above the substrate;
a piezoeletric body formed on or above the lower electrode;
an upper electrode formed on or above the piezoeletric body; and
a cavity under a vibrating portion formed by the lower electrode, the piezoeletric body, and the upper electrode, the cavity has a trapezoidal shape in section and
where a resonant frequency of vibration with a thickness of the vibrating portion being a half of a wavelength is taken as fr,
an average of ultrasonic velocity in a material forming the cavity is taken as Vc, and
a value determined based on the resonant frequency fr and the average of ultrasonic velocity Vc is taken as λc (=Vc/fr),
a depth of the cavity is set so as to be equal to or larger than n×λc/2−λc/8 and equal to or smaller than n×λc/2+λc/8, where n is an integer.