Acoustic Wave Resonator Film Stack for Stable Temperature Response
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Acoustic wave devices with multiple IDT electrodes of different wavelengths exhibit varying temperature characteristics due to differences in normalized film thicknesses of piezoelectric and dielectric films, leading to inconsistent frequency performance across resonators.
Innovation Solution
The acoustic wave device incorporates a high acoustic velocity member, a piezoelectric thin film, and a silicon oxide film, with IDT electrodes of varying wavelengths, where the wavelength normalized film thicknesses of the silicon oxide and piezoelectric films are carefully controlled to ensure y ≤ 350% and y < 1.6x(-0.01) + 0.05x(-0.6) - 1, and the silicon oxide film thickness is maintained between 0% and 8%, to minimize temperature coefficient variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a piezoelectric thin film with thickness about equal to or smaller than 3.5λ is used, then higher frequency and increased Q value are achieved, but differences in temperature characteristics are increased among multiple acoustic wave resonators
Solution Approach 1:
The patent changes the physical parameters of the dielectric film (thickness and material composition) to adjust the temperature coefficient of frequency. By setting the dielectric film thickness to 0.05λ to 0.2λ and using specific materials with appropriate dielectric constants, the patent compensates for temperature variations in the piezoelectric thin film, thereby maintaining consistent temperature characteristics across multiple resonators with different wavelengths.
Solution Approach 2:
The patent employs a composite structure combining piezoelectric thin film with dielectric film layers. This composite configuration allows the dielectric film to counterbalance the temperature coefficient of frequency of the piezoelectric material, achieving improved temperature stability while maintaining the high-frequency performance enabled by the thin piezoelectric layer.
2Reliability
If a dielectric film is laminated between the piezoelectric substrate and IDT electrode, then the absolute value of temperature coefficient of frequency TCF is reduced, but bandwidth ratio is adjusted to be a smaller value
Solution Approach 1:
The patent optimizes the dielectric film thickness parameter within the range of 0.05λ to 0.2λ to achieve a balance between temperature coefficient reduction and bandwidth maintenance. This parameter optimization allows the dielectric film to provide temperature compensation while minimizing its negative impact on the bandwidth ratio of the acoustic wave resonators.
3Device complexity
If multiple acoustic wave resonators with different wavelengths are formed within one chip, then device integration is achieved, but differences in normalized film thicknesses cause variations in temperature characteristics
Solution Approach 1:
The patent implements a universal dielectric film configuration that serves multiple functions across resonators with different wavelengths. By applying the same dielectric film thickness ratio (0.05λ to 0.2λ) and material composition to all resonators on the chip, the patent achieves temperature compensation for each individual resonator while maintaining consistent temperature characteristics across the entire integrated device.
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 temperature characteristic differences between IDT electrodes, maintaining excellent frequency temperature characteristics without significantly narrowing the bandwidth ratio, and improves frequency stability in high-frequency front-end circuits and communication devices.
Implementation Method 1
a piezoelectric thin film, capable of coping with a higher frequency
Implementation Method 2
an acoustic velocity of a bulk wave propagating through the high acoustic velocity member is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric thin film
Data Source
AI summary
An acoustic wave device includes IDT electrodes with different wavelengths determined by electrode finger pitches. A piezoelectric thin film is laminated directly on or indirectly above a high acoustic velocity member. A silicon oxide film is laminated on the piezoelectric thin film, IDT electrodes are laminated on the silicon oxide film. When λ represents a wavelength of one of the IDT electrodes having the shortest wavelength, y represents a wavelength normalized film thickness (%) that is a percentage of a film thickness of the piezoelectric thin film with respect to the wavelength λ, and x represents a wavelength normalized film thickness (%) that is a percentage of a film thickness of the silicon oxide film with respect to the wavelength λ, y is equal to or smaller than about 350% and y<1.6x(−0.01)+0.05x(−0.6)−1 is satisfied.