Acoustic Wave Multiplexer Duty Ratio Layout for Near-Zero TCF
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Solution Overview
Problem
Existing acoustic wave filters with dielectric films having a temperature coefficient of elastic modulus opposite to that of the piezoelectric substrate do not sufficiently reduce the temperature coefficient of frequency (TCF) of the resonant frequency, leading to instability in communication systems.
Innovation Solution
The acoustic wave filter design includes series and parallel resonators with specific duty ratios and dielectric films of varying thicknesses on a piezoelectric substrate, where the dielectric film thickness is greater than the electrode fingers and the duty ratio of parallel resonators is less than that of series resonators, to achieve a balanced TCF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric film with opposite temperature coefficient of elastic modulus is provided on the electrode fingers, then the temperature coefficient of frequency (TCF) is reduced, but the TCF does not reach near zero and filter stability is insufficient
Solution Approach 1:
The patent applies different dielectric film thicknesses to different resonator types within the same filter. Specifically, the dielectric film thickness on series resonators is set to be different from that on parallel resonators, allowing local optimization of TCF compensation for each resonator type to achieve near-zero overall TCF
Solution Approach 2:
The patent changes the physical parameter of dielectric film thickness to control and compensate TCF. By adjusting the thickness parameter of the dielectric film on different resonators, the elastic modulus temperature coefficient is modified to counterbalance the piezoelectric substrate's TCF, achieving near-zero overall TCF
2Reliability
If different dielectric film thicknesses are used for series and parallel resonators, then TCF is better controlled, but the fabrication process becomes more complex
Solution Approach 1:
The patent segments the dielectric film structure by creating different thickness regions corresponding to series resonators and parallel resonators. This segmentation allows independent optimization of TCF for each resonator type while maintaining a unified filter structure
Solution Approach 2:
The patent implements local quality by providing different dielectric film thicknesses specifically on series resonators versus parallel resonators. This local differentiation enables precise TCF control for each resonator type without requiring complete redesign of the entire filter structure
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 reduces the TCF to near zero, stabilizing the filter's performance across temperature variations and simplifying the fabrication process by using the same dielectric film for both series and parallel resonators.
Implementation Method 1
a surface acoustic wave (SAW) resonator having an interdigital transducer (IDT), which has electrode fingers, formed on a piezoelectric substrate
Implementation Method 2
a dielectric film having a temperature coefficient of elastic modulus that is opposite in sign to that of the piezoelectric substrate
Data Source
AI summary
An acoustic wave filter includes: a piezoelectric substrate; series resonators connected in series and located on the piezoelectric substrate, each of the series resonators including first electrode fingers that are arranged with a first duty ratio and excite an acoustic wave; parallel resonators connected in parallel and located on the piezoelectric substrate, each of the parallel resonators including second electrode fingers that are arranged with a second duty ratio and excite an acoustic wave, the second duty ratio in at least one parallel resonator being less than the first duty ratio in at least one series resonator; and a dielectric film that has a temperature coefficient of elastic modulus that is opposite in sign to that of the piezoelectric substrate, is located on the piezoelectric substrate so as to cover the first and second electrode fingers, has a film thickness greater than those of the first and second electrode fingers.