Filter With Insulating Film Reducing Capacitive Coupling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing filters with additional circuits for canceling unnecessary waves outside the pass band face signal leakage issues due to wiring interactions, leading to inadequate attenuation outside the designated frequency band.
Innovation Solution
A filter design incorporating a substrate with a piezoelectric layer, a filter circuit, and an additional circuit with an acoustically coupled resonator, where an insulating film with a lower dielectric constant than the piezoelectric layer is used between the substrate and the sub-wiring line to reduce capacitive coupling and prevent signal leakage, ensuring effective attenuation outside the pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an additional circuit is connected in parallel with the filter circuit to cancel unnecessary waves outside the pass band, then the attenuation outside the pass band is improved, but signal leakage occurs between the wiring of the additional circuit and the wiring of the filter circuit
Solution Approach 1:
An insulating film is introduced as an intermediary layer between the sub-wiring line of the additional circuit and the piezoelectric layer of the substrate. This insulating film acts as a mediator that prevents direct capacitive coupling between the additional circuit wiring and the filter circuit, thereby eliminating signal leakage while preserving the attenuation function of the additional circuit.
Solution Approach 2:
The harmful capacitive coupling effect is extracted and eliminated by removing the direct contact between the sub-wiring line and the piezoelectric layer. The insulating film isolates the additional circuit wiring from the substrate, separating the signal paths and preventing unwanted interactions while maintaining the functional integrity of both circuits.
2Device complexity
If the sub-wiring line is directly connected to the substrate without an insulating film, then the device complexity is reduced, but signal leakage occurs between the additional circuit and filter circuit wiring
Solution Approach 1:
The insulating film serves as a minimal yet effective intermediary that prevents signal leakage without significantly complicating the device structure. By placing this thin film only where needed (between the sub-wiring line and substrate), the design achieves electrical isolation with minimal additional complexity.
Solution Approach 2:
The insulating film is applied locally only in the region where the sub-wiring line contacts the substrate, rather than covering the entire substrate. This localized approach provides the necessary electrical isolation to prevent signal leakage while minimizing the overall device complexity and maintaining manufacturing simplicity.
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 solution ensures robust attenuation outside the pass band by minimizing signal leakage between the filter and additional circuit wiring, enhancing the filter's frequency selectivity and power handling capabilities.
Implementation Method 1
an insulating film with a lower dielectric constant than the piezoelectric layer is used between the substrate and the sub-wiring line to reduce capacitive coupling and prevent signal leakage
Implementation Method 2
a substrate with a piezoelectric layer, a filter circuit, and an additional circuit with an acoustically coupled resonator
Implementation Method 3
an additional circuit with an acoustically coupled resonator, where an insulating film with a lower dielectric constant than the piezoelectric layer is used between the substrate and the sub-wiring line
Data Source
AI summary
A filter includes a substrate including a piezoelectric layer, and first and second signal electrodes, a filter circuit on a first path connecting the first signal electrode and the second signal electrode, and an additional circuit on a second path connected in parallel with at least a portion of the first path. The filter circuit includes one or more resonators and a main wiring line on the substrate, and the additional circuit includes a sub-wiring line and an acoustically coupled resonator on the substrate, the acoustically coupled resonator including acoustic wave resonators adjacent to each other. An insulating film is between the substrate and the sub-wiring line. A dielectric constant of the insulating film is smaller than a dielectric constant of the piezoelectric layer.