Piezoelectric Notch Filter Layout for Stopband and Ripple Suppression
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Solution Overview
Problem
Existing notch filters using piezoelectric substrates face challenges in minimizing stopband response and ripples within the passband, particularly when using multilayer structures with high and low-acoustic-velocity members, which often result in increased spurious emissions and device characteristics degradation.
Innovation Solution
A notch filter design incorporating a substrate with a high-acoustic-velocity member, a low-acoustic-velocity film, and a piezoelectric thin film, featuring an interdigital transducer electrode and reflectors with a specifically optimized IR gap and electrode finger configuration to reduce stopband response and ripples, including IR gap ranges of 0.1λ to 0.9λ and 21 or fewer electrode fingers in the reflector, and wavelength ratios of 0.91λ to 5λ.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multilayer structure with high-acoustic-velocity member, low-acoustic-velocity film, and piezoelectric thin film is used, then Q-value is high and device characteristics are excellent, but stopband response increases and ripples in passband increase
Solution Approach 1:
The patent optimizes the IR gap parameter within specific ranges (0.05λ ≤ GIR ≤ 0.95λ, preferably 0.1λ ≤ GIR ≤ 0.9λ) to control the interaction between reflector and interdigital transducer electrode. This parameter adjustment reduces stopband response while preserving the high Q-value benefits of the multilayer structure.
Solution Approach 2:
The patent applies different acoustic velocity characteristics to different layers: high-acoustic-velocity member at the bottom, low-acoustic-velocity film in the middle, and piezoelectric thin film at the top. This localized differentiation of acoustic properties enables the structure to achieve high Q-value while controlling stopband response through the optimized IR gap.
2Productivity
If the number of electrode fingers in reflector is reduced to 21 or less, then productivity increases and device characteristics improve, but reflector effectiveness may be compromised
Solution Approach 1:
The patent sets the number of electrode fingers in the reflector to 21 or less, optimizing this discrete parameter to balance manufacturing simplicity with device performance. This reduction in electrode finger count simplifies fabrication while the optimized IR gap ensures adequate reflector effectiveness is maintained.
3Object-generated harmful factors
If IR gap is optimized within 0.1λ to 0.9λ, then stopband response and ripples are significantly reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent defines a specific range for the IR gap (0.1λ ≤ GIR ≤ 0.9λ) that balances ripple reduction with manufacturing feasibility. This optimized range provides sufficient tolerance for fabrication variations while achieving significant ripple suppression in the passband.
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
The design significantly reduces or prevents stopband response and ripples in the passband, enhancing the notch filter's performance by minimizing spurious emissions and improving productivity through optimized electrode configurations.
Implementation Method 1
a piezoelectric thin film provided on the low-acoustic-velocity film; an interdigital transducer electrode provided on the piezoelectric thin film
Implementation Method 2
an acoustic velocity of a bulk wave propagating in the low-acoustic-velocity film is lower than an acoustic velocity of an acoustic wave propagating in the piezoelectric thin film, an acoustic velocity of a bulk wave propagating in the high-acoustic-velocity member is higher than the acoustic velocity of an acoustic wave propagating in the piezoelectric thin film
Data Source
AI summary
A notch filter includes a substrate having piezoelectricity, the substrate including a high-acoustic-velocity member, a low-acoustic-velocity film provided on the high-acoustic-velocity member, and a piezoelectric thin film provided on the low-acoustic-velocity film; an interdigital transducer electrode provided on the piezoelectric thin film; and reflectors provided on both sides of the interdigital transducer electrode in an acoustic wave propagation direction. An IR gap is within one of two ranges: 0.1λ≤GIR<0.5λ or 0.5λ<GIR≤0.9λ, where λ is a wavelength determined by an electrode finger pitch of the interdigital transducer electrode, and the IR gap is a distance between electrode finger centers of an electrode finger of the interdigital transducer electrode closest to the reflector out of the electrode fingers of the interdigital transducer electrode, and an electrode finger of the reflector closest to the interdigital transducer electrode, out of the electrode fingers of the reflector.