SAW Filter Grounded Side Wall Parasitic Capacitance

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Solution Overview

Problem

Conventional electronic elements with surface acoustic wave (SAW) resonators suffer from parasitic capacitance and inadequate separation characteristics due to electrical isolation of the side wall from the filter circuit, leading to deteriorated propagation characteristics.

Innovation Solution

An electronic filter is designed with a piezoelectric substrate, a sealing substrate, and an electrically conductive side wall connected to ground potential, which encloses the filter circuit and includes protrusions or separation walls to suppress electromagnetic coupling and enhance separation characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the side wall is electrically isolated from the filter circuit, then the filter circuit is protected from electromagnetic interference, but parasitic capacitance is generated between signal pads via the side wall causing deteriorated propagation characteristics

Engineering Contradiction:

Improveelectromagnetic interference protectionVSAvoidpropagation characteristics

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent introduces an electrically conductive side wall that serves as a ground reference intermediary between the filter circuit and the external environment. By connecting the side wall to ground potential, it provides a controlled reference that prevents unwanted capacitive coupling between signal pads while maintaining electromagnetic interference protection.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the electrical parameter of the side wall from isolated (high impedance) to grounded (zero potential). This parameter change transforms the side wall from a source of parasitic capacitance into a stable ground reference, eliminating the harmful capacitive coupling effect while preserving shielding functionality.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If conventional sealing structure is used with electrically isolated side wall, then manufacturing is simplified, but separation characteristics are insufficient

Engineering Contradiction:

Improvesealing structure fabricationVSAvoidseparation characteristics

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent makes the side wall multi-functional by simultaneously providing mechanical support for the sealing substrate, electromagnetic shielding, and ground reference functionality. This universal approach maintains the simplicity of the sealing structure while adding separation characteristics through the grounded configuration.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent applies equipotentiality by connecting the side wall to ground potential, creating a zero-voltage reference surface. This equipotential configuration prevents potential differences between different parts of the side wall, eliminating parasitic capacitance effects while maintaining the simple sealing structure.

Inventive Principle:

Principle #12Equipotentiality

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 effectively suppresses parasitic capacitance and improves propagation characteristics by ensuring stable SAW propagation and enhanced separation performance in the filter device.

Implementation Method 1

surface acoustic wave (SAW) resonators

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Implementation Method 2

element substrate made of piezoelectric body

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 3

parasitic capacitance 111 as shown in FIG. 2 such that the propagation characteristics of the filter circuit may be deteriorated

Methodology Applied

Scientific EffectParasitic capacitance: Parasitic Capacitance

Data Source

PatentUS10778183B2Saw-based electronic elements and filter devices

Publication Date: 2020.09.15 SKYWORKS PANASONIC FILTER SOLUTIONS JAPAN

AI summary

Aspects and examples provide electronic elements and filter devices configured to prevent deterioration of the propagation characteristics caused by input and output signals being electromagnetically coupled to an electric conductor side wall. In one example an electronic filter includes an element substrate having a top surface, a bottom surface, a side surface, and piezoelectric body. A circuit including a plurality of SAW resonators is formed on the top surface of the element substrate. The electronic filter further includes a sealing substrate having a top surface and a bottom surface, and a side wall including an electric conductor and formed to define a cavity between the top surface of the element substrate and the bottom surface of the sealing substrate, the side wall enclosing a periphery of the circuit and being connected to a ground potential of the circuit.