Acoustic Wave Resonator Stack for Third Harmonic Suppression
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Solution Overview
Problem
Existing surface acoustic wave resonators suffer from insufficient suppression of unnecessary waves due to third harmonic excitation, which affects the resonator's performance and bandpass characteristics.
Innovation Solution
The acoustic wave device incorporates a substrate with a laminated structure comprising a piezoelectric film, a high acoustic velocity film, and a low acoustic velocity film, along with an interdigital transducer (IDT) electrode. The mass coefficient of the acoustic wave resonator is optimized by adjusting the film thicknesses of the piezoelectric and electrode films, ensuring it falls within a specific range to minimize third harmonic excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer piezoelectric substrate is used, then the device structure is simple, but the Q value at resonant frequency and anti-resonant frequency is lower
Solution Approach 1:
The patent employs a composite substrate structure consisting of a piezoelectric substrate layer, a high acoustic velocity film layer, and a low acoustic velocity film layer. This multi-layer composite structure increases the Q value at both resonant frequency and anti-resonant frequency compared to single-layer piezoelectric substrates, while maintaining controlled third harmonic excitation through specific acoustic velocity relationships between layers.
2Reliability
If a laminated substrate structure with high and low acoustic velocity films is used, then the Q value is increased, but the suppression of third harmonic excitation remains insufficient
Solution Approach 1:
The patent optimizes specific parameters of the laminated structure to suppress third harmonic excitation. The acoustic velocity of the high acoustic velocity film is set to be 1.05 to 1.20 times that of the piezoelectric substrate, and the acoustic velocity of the low acoustic velocity film is set to be 0.80 to 0.95 times that of the piezoelectric substrate. These parameter adjustments enable effective suppression of third harmonic waves while maintaining high Q values.
Solution Approach 2:
The patent introduces functionally differentiated layers with specific acoustic velocity characteristics at different positions within the substrate structure. The high acoustic velocity film and low acoustic velocity film are strategically positioned to create local acoustic impedance variations that suppress third harmonic excitation, while the overall laminated structure maintains high Q value characteristics.
3Ease of manufacture
If the film thicknesses are not optimized, then the manufacturing process is simpler, but the mass coefficient falls outside the optimal range causing increased third harmonic excitation
Solution Approach 1:
The patent defines a specific mass coefficient M that incorporates the film thicknesses of the piezoelectric substrate (t1), high acoustic velocity film (t3), and low acoustic velocity film (t4), along with their respective densities. By optimizing this composite parameter M, the patent achieves suppression of third harmonic excitation while providing clear manufacturing guidelines for controlling film thicknesses within specific ranges.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces or prevents the generation of unnecessary waves due to third harmonic excitation, thereby enhancing the bandpass characteristics and reducing insertion loss in the acoustic wave devices and multiplexers.
Implementation Method 1
an interdigital transducer (IDT) electrode on a piezoelectric substrate
Implementation Method 2
a high acoustic velocity film in which an acoustic velocity of a bulk wave propagating in the high acoustic velocity film is higher than an acoustic velocity of an acoustic wave propagating in the piezoelectric film, and a low acoustic velocity film in which an acoustic velocity of a bulk wave propagating in the low acoustic velocity film is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film
Data Source
AI summary
A filter includes acoustic wave resonators connected to a path connecting terminals. A substrate includes a laminated structure of a piezoelectric film, and low and high acoustic velocity films. An electrode finger wavelength of the IDT electrode is λ (m), a film thickness of the piezoelectric film is t1 (m), a film thickness of electrode fingers is t2 (m), t1/A is a film thickness-wavelength ratio A of the piezoelectric film, t2/A is a film thickness-wavelength ratio B of the plurality of electrode fingers, a density of the piezoelectric film is x (g/cm3) and a density of the IDT electrode is y (g/cm3), and (A/x+B/y) is a mass coefficient M of an acoustic wave resonator which is connected closest to the terminal and equal to or more than about 0.95×0.054 and equal to or less than about 1.05×0.054.