Grounded Conductive Layer in Multi-Layer SAW Substrates

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Solution Overview

Problem

Surface acoustic wave (SAW) filters face challenges in meeting stringent filter specifications due to high frequency drift over temperature, while Bulk Acoustic Wave (BAW) filters are more expensive and larger in size, making them less suitable for certain applications.

Innovation Solution

A surface acoustic wave device with a multi-layer piezoelectric substrate that includes a lithium-based piezoelectric layer and a conductive layer between the piezoelectric layer and the substrate, electrically connected to a grounding structure, which improves receive and transmit isolation by attenuating parasitic capacitance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional SAW filter structure is used, then the device size and manufacturing cost are kept low, but the frequency drift over temperature is high and isolation performance is poor

Engineering Contradiction:

Improveisolation performanceVSAvoidfrequency drift over temperature

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The piezoelectric substrate is segmented into multiple layers (first piezoelectric layer, second piezoelectric layer) with a conductive layer inserted between them. This segmentation allows the conductive layer to serve as an independent grounding structure that shields parasitic capacitance, thereby improving isolation performance without affecting the overall SAW filter functionality

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A conductive layer is introduced as an intermediary element between the first and second piezoelectric layers. This conductive layer is electrically connected to a grounding structure and acts as a shield to reduce parasitic capacitance between signal ports, thereby improving transmit and receive isolation

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If BAW filters are used instead of SAW filters, then isolation performance and frequency stability are improved, but the device size and manufacturing cost increase

Engineering Contradiction:

Improveisolation performanceVSAvoiddevice size

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

Instead of changing the entire SAW filter structure to a BAW filter, the invention applies a localized modification by inserting a conductive layer with grounding structure at a specific location within the SAW filter. This local quality enhancement provides BAW-like isolation performance while maintaining the compact SAW filter form factor

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention creates a composite structure by combining the SAW filter base structure with an additional conductive layer and grounding structure. This composite design integrates the advantages of both SAW (compact size) and BAW (good isolation) structures into a single hybrid configuration

Inventive Principle:

Principle #40Composite materials

3Reliability

If a conductive layer with grounding structure is added to the SAW filter, then transmit and receive isolation is improved by attenuating parasitic capacitance, but the device complexity and manufacturing steps increase

Engineering Contradiction:

Improvetransmit and receive isolationVSAvoidmulti-layer structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The conductive layer is merged with the existing piezoelectric substrate structure during the manufacturing process. The grounding structure is integrated with the interdigital transducer electrode patterns, combining multiple functions (shielding, grounding, and electrical connection) into a unified structure that reduces overall device complexity despite the added functionality

Inventive Principle:

Principle #5Merging (Combining)

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 enhances isolation performance and reduces temperature drift, making it suitable for demanding RF filter applications with improved size and cost efficiency compared to traditional SAW and BAW filters.

Implementation Method 1

Methodology Applied

Scientific EffectParasitic capacitance: Capacitance

Implementation Method 2

A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer on which the interdigital transductor electrode is disposed

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11671072B2Multi-layer piezoelectric substrate with conductive layer

Publication Date: 2023.06.06 SKYWORKS SOLUTIONS INC

AI summary

An acoustic wave device is disclosed. The acoustic wave device can include a piezoelectric layer positioned over a substrate. The acoustic wave device can also include an interdigital transducer electrode positioned over the piezoelectric layer. The acoustic wave device can also include a grounding structure positioned over the piezoelectric layer. The acoustic wave device can also include a conductive layer positioned under the substrate such that the substrate is positioned between the conductive layer and the grounding structure. The acoustic wave device can further include an electrical pathway that electrically connects the conductive layer to the grounding structure.