Acoustic Wave Filter Layout With Low-Permittivity Dielectric Isolation
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Solution Overview
Problem
Acoustic wave filter devices face a decrease in filter characteristics due to parasitic capacitance caused by impedance mismatching and electromagnetic interference, resulting from a close distance between functional elements and electrodes with high permittivity substrates.
Innovation Solution
Incorporating a dielectric portion with lower permittivity than the piezoelectric substrate between the functional elements and electrodes to reduce parasitic capacitance, thereby maintaining or improving filter characteristics by minimizing impedance mismatching and electromagnetic coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the distance between the functional element and the electrode is reduced to improve coupling efficiency, then the device size is minimized, but parasitic capacitance increases causing impedance mismatching and filter characteristic degradation
Solution Approach 1:
A dielectric portion with lower permittivity than the piezoelectric substrate is introduced as an intermediary between the functional element and the electrode. This intermediate layer reduces the parasitic capacitance formed between the electrode and functional element while allowing the electrode to remain close to the functional element for efficient coupling, thus resolving the contradiction between miniaturization and filter characteristic maintenance
Solution Approach 2:
The dielectric portion is selectively positioned only in the region between the electrode and functional element where parasitic capacitance occurs, rather than uniformly across the entire device. This localized application of different dielectric properties reduces parasitic capacitance precisely where needed without compromising overall device performance or size
2Reliability
If a substrate with high permittivity is used to improve acoustic wave confinement, then the acoustic wave filter performance is enhanced, but parasitic capacitance between the electrode and functional element increases
Solution Approach 1:
The patent maintains the high permittivity piezoelectric substrate for acoustic wave confinement while introducing a localized low permittivity dielectric portion only in the region between the electrode and functional element. This spatial differentiation of dielectric properties allows the substrate to provide acoustic wave confinement benefits while the localized dielectric portion reduces parasitic capacitance in the critical coupling region
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 dielectric portion effectively reduces parasitic capacitance, preventing a decrease in filter characteristics and maintaining isolation and return loss, thus enhancing the performance of acoustic wave filter devices.
Implementation Method 1
a distance between the second functional element and an electrode for the first functional element provided to the substrate at which the second functional element is disposed is reduced, such that an unnecessary parasitic capacitance may be generated therebetween
Implementation Method 2
The dielectric portion is located between the first functional element and the first electrode and has a permittivity lower than a permittivity of the first piezoelectric substrate
Implementation Method 3
a first piezoelectric substrate including a first principal surface and a second principal surface, a first functional element on the first principal surface
Data Source
AI summary
A duplexer includes a piezoelectric substrate including an upper surface and a lower surface, a functional element on the lower surface, a flat plate electrode on a side of the upper surface of the piezoelectric substrate, and a dielectric portion that is located between the functional element and the flat plate electrode and has a permittivity lower than a permittivity of the piezoelectric substrate.