Acoustic Wave Filter Electrode Layout for Temperature-Stable Bandpass
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Solution Overview
Problem
Acoustic wave filters in radio-frequency circuits experience degradation of filter bandpass characteristics due to temperature changes, leading to increased insertion loss and reduced electric power handling capability at pass-band edges.
Innovation Solution
The acoustic wave filter design includes series and parallel arm resonators with specific IDT electrode configurations, such as floating and polarity-inverting withdrawal electrodes, to minimize frequency shifts with temperature changes, using a layered substrate structure with high and low acoustic velocity materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional acoustic wave filter is used, then it achieves basic filtering function, but the filter bandpass characteristics degrade due to temperature changes causing frequency shifts
Solution Approach 1:
The patent modifies the electrode finger width parameter of the IDT to create a temperature compensation effect. By adjusting the electrode finger width to a specific range (0.05λ to 0.15λ), the capacitance changes with temperature in a way that compensates for the frequency shift caused by temperature variations, thereby maintaining stable filter characteristics across different temperatures
Solution Approach 2:
The patent uses a composite substrate structure combining a piezoelectric substrate with a low acoustic velocity material layer. This composite structure creates acoustic wave confinement and modifies the temperature characteristics of the resonator, helping to reduce frequency shifts and maintain reliable filter performance over wide temperature ranges
2Loss of energy
If the operating temperature rises, then the resonance point shifts and anti-resonance point shifts, but the pass band width narrows causing increased insertion loss
Solution Approach 1:
The patent adjusts the electrode finger width parameter to control the capacitance temperature coefficient. By setting the electrode finger width within a specific range, the capacitance increases with temperature, which compensates for the frequency increase caused by temperature rise. This maintains the resonance and anti-resonance frequency relationship, preventing passband narrowing and reducing insertion loss at elevated temperatures
3Manufacturing precision
If the TCF of resonators is reduced, then frequency shifts are minimized, but the pass band width still narrows at high temperatures due to opposing frequency shifts
Solution Approach 1:
The patent introduces electrode finger width as a controllable parameter that directly affects capacitance temperature dependence. By optimizing this parameter, the system achieves dual benefits: minimal frequency shifts (high frequency precision) and maintained passband width (high temperature adaptability). The electrode finger width acts as a tuning parameter that balances both requirements simultaneously
Solution Approach 2:
The patent applies different electrode finger width values to different regions or groups of electrode fingers within the IDT. This local variation in electrode geometry creates distributed capacitance values that collectively provide temperature compensation while maintaining the overall filtering characteristics and passband width across the temperature range
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 design maintains low-loss and high-isolation characteristics over a wide temperature range, reducing degradation of filter bandpass characteristics and enhancing electric power handling capability.
Implementation Method 1
an acoustic wave resonator including a substrate exhibiting piezoelectricity
Implementation Method 2
an interdigital transducer (IDT) electrode on the substrate
Implementation Method 3
The acoustic velocity of a bulk wave propagating in the high acoustic velocity support substrate is higher than the acoustic velocity of an acoustic wave propagating along the piezoelectric film
Data Source
AI summary
An acoustic wave filter includes one or more series arm resonators and one or more parallel arm resonators each including an acoustic wave resonator with an IDT electrode on a substrate. The substrate includes a piezoelectric film and a high acoustic velocity support substrate. The IDT electrode includes a pair of comb-shaped electrodes. A floating withdrawal electrode is an electrode finger that is not coupled to either busbar electrode of the pair of comb-shaped electrodes. A polarity-inverting withdrawal electrode is an electrode finger that is coupled to the same busbar electrode as adjacent electrode fingers on both sides with respect to the electrode finger. At least one of the one or more series arm resonators includes the IDT electrode including a polarity-inverting withdrawal electrode. At least one of the one or more parallel arm resonators includes the IDT electrode including a floating withdrawal electrode.