Piezoelectric resonator and electronic components using the same
View Patent ↗A piezoelectric resonator is provided which is capable of acquiring an excellent Q characteristic while letting a film thickness of an upper electrode be larger. The piezoelectric resonator has a lower electrode and an upper electrode with a piezoelectric film being sandwiched between them. By applying a voltage between the lower and upper electrodes to let a bulk acoustic wave propagate through inner portions of the piezoelectric layer, a signal having a specified resonant frequency is obtained. The standing wave has a first wave loop at an interface on a side opposite to the piezoelectric film of the upper electrode and a wave node and a second wave loop in inner portions of the upper electrode directing from the interface toward the piezoelectric film. The film thickness of the upper electrode obtained when a wavelength of a standing wave is defined as “λ” is 0.4λ to 0.7λ.
1. A piezoelectric resonator comprising:
a substrate;
a lower electrode formed on said substrate;
an upper electrode formed on said substrate; and
a piezoelectric film being sandwiched between said lower electrode and said upper electrode on said substrate,
wherein a signal having a specified resonant frequency is obtained by applying a voltage between said lower electrode and said upper electrode to let a bulk acoustic wave propagate through an inner portion of said piezoelectric film, and
wherein a standing wave occurring in a vicinity of a resonant frequency in a frequency band being used has a first wave loop at an interface positioned on a side opposite to said piezoelectric film in said upper electrode and both a wave node and a second wave loop in an inner portion of said upper electrode in a direction from said interface toward a side of said piezoelectric film.
2. The piezoelectric resonator as claimed in claim 1 , wherein a film thickness of said upper electrode obtained when a wavelength of said standing wave occurring in said upper electrode is defined as “λ” is 0.4λ to 0.7λ.
3. The piezoelectric resonator as claimed in claim 1 , wherein said upper electrode comprises one of Al (aluminum), Au (gold), and Mo (molybdenum).
4. The piezoelectric resonator as claimed in claim 1 , wherein said upper electrode comprises a stack of layers, said stack comprising a conductive layer, an insulating layer, and another conductive layer.
5. The piezoelectric resonator as claimed in claim 4 , wherein said upper electrode comprises a stack of films, said stack comprising an Al film an SiO 2 (silicon oxide) film, and another Al film and a sum of coefficients of film thicknesses normalized by a wavelength of said standing wave occurring in each of said films is 0.4 to 0.7.
6. The piezoelectric resonator as claimed in claim 1 , further comprising:
an acoustic multi-layer film constructed by stacking films each having a different acoustic impedance and formed between said substrate and said lower electrode; and
an interlayer film having a specified acoustic impedance and having a film thickness obtained when a wavelength of said standing wave is defined as “λ” being 0.01λ to 0.1λ. which is formed between said acoustic multi-layer film and said lower electrode.
7. The piezoelectric resonator as claimed in claim 6 , wherein said interlayer film comprises an AlN (Aluminum Nitride) film.
8. The piezoelectric resonator as claimed in claim 1 , further comprising:
a dielectric film formed between said upper electrode and said piezoelectric film.
9. The piezoelectric resonator as claimed in claim 8 , wherein said dielectric film comprises an SiO 2 film.
10. The piezoelectric resonator as claimed in claim 1 , wherein said piezoelectric resonator comprises one of an SMR (Solidity Mounted Resonator)—type piezoelectric resonator and a diaphragm-type piezoelectric resonator.
11. An electronic component using the piezoelectric resonator stated in claim 1 .
12. The piezoelectric resonator as claimed in claim 1 , wherein a thickness of said upper electrode is based on a wavelength of said standing wave occurring in said upper electrode.
13. The piezoelectric resonator as claimed in claim 1 , wherein a thickness of said upper electrode is sufficient to form said standing wave.
14. The piezoelectric resonator as claimed in claim 1 , wherein a thickness of said upper electrode is at least 0.4λ, where “λ” comprises a wavelength of said standing wave occurring in said upper electrode.
15. The piezoelectric resonator as claimed in claim 1 , wherein said upper electrode comprises a thickness which is greater than 65% of a thickness of said piezoelectric film.
16. A piezoelectric resonator comprising:
a lower electrode formed on a substrate;
a piezoelectric film formed on said lower electrode; and
an upper electrode formed on said piezoelectric film and comprising a thickness such that a standing wave occurring in a vicinity of a resonant frequency in a frequency band being used by said resonator comprises a first wave, a wave node and a second wave loop in said upper electrode.
17. The piezoelectric resonator as claimed in claim 16 , wherein said first wave loop is formed at an interface positioned on a side opposite to said piezoelectric film in said upper electrode, and said wave node and said second wave loop are formed in an inner portion of said upper electrode in a direction from said interface toward a side of said piezoelectric film.
18. A method of forming a piezoelectric resonator, said method comprising:
forming a lower electrode on a substrate;
forming a piezoelectric film on said lower electrode; and
forming an upper electrode on said piezoelectric film, said upper electrode comprising a thickness such that a standing wave occurring in a vicinity of a resonant frequency in a frequency band being used by said resonator comprises a first wave, a wave node and a second wave loop in said upper electrode.