Li2CO3 Layer on LiNbO3 Substrate for Acoustic Wave Devices

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Solution Overview

Problem

The existing manufacturing processes for acoustic wave devices using piezoelectric substrates like LiNbO3 and LiTaO3 face productivity issues and risk of substrate cracking due to charging and heating during vacuum batch processing, leading to transportation failures during wafer handling.

Innovation Solution

Incorporating a Li2CO3 layer on the second main surface of the piezoelectric substrate, which is formed using laser irradiation, providing a low-resistance surface that prevents charging and allows smooth transportation, thus enhancing productivity by avoiding sticking issues and reducing the risk of substrate damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a film made of resistive material is formed by sputtering on the piezoelectric substrate, then charging of the substrate is suppressed, but vacuum batch processing is necessary and productivity is poor

Engineering Contradiction:

Improvecharging suppressionVSAvoidproductivity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent replaces the sputtering process (vacuum-based physical deposition) with a chemical solution process. The resistive film is formed by applying a slurry containing resistive material particles and suspending it in liquid, then drying it. This substitution eliminates the need for vacuum equipment and batch processing, enabling continuous manufacturing and significantly improving productivity while maintaining the charging suppression function.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If a film made of resistive material is formed by sputtering on the piezoelectric substrate, then charging of the substrate is suppressed, but heating of the substrate during sputtering causes cracks

Engineering Contradiction:

Improvecharging suppressionVSAvoidsubstrate integrity

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent replaces the sputtering process with a chemical solution process that does not require high-power ion bombardment or significant heating. The resistive film is deposited by drying a slurry at low temperatures, eliminating the thermal stress that causes substrate cracking while preserving the charging suppression functionality through the resistive material layer.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If Al film is formed by vapor deposition or plating on the piezoelectric substrate, then charging is suppressed, but vacuum batch processing is necessary and productivity is poor

Engineering Contradiction:

Improvecharging suppressionVSAvoidproductivity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent replaces vapor deposition or plating processes with a chemical solution process. Instead of using vacuum-based physical vapor deposition or electrochemical plating, the resistive film is formed by applying a slurry and drying it at low temperature. This eliminates vacuum equipment requirements and enables continuous processing, dramatically improving productivity while achieving the same charging suppression effect.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If Al film or the like is formed by plating on the piezoelectric substrate, then charging is suppressed, but a large amount of time is necessary and productivity is poor

Engineering Contradiction:

Improvecharging suppressionVSAvoidprocessing time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces the time-consuming plating process with a rapid chemical solution process. The resistive film is formed by simply applying a slurry and drying it, which takes minimal time compared to the electrochemical reactions and multiple steps required for plating. This dramatically reduces processing time and improves productivity while maintaining charging suppression functionality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 Li2CO3 layer effectively prevents charging of the piezoelectric substrate, significantly reducing transportation failures and maintaining high productivity by allowing easy handling and processing without substrate cracking, as demonstrated in examples using both LiNbO3 and LiTaO3 substrates.

Implementation Method 1

a Li2CO3 layer that is provided on the second main surface of the piezoelectric substrate

Methodology Applied

Scientific EffectElectrical conductivity: Conduction (electrical)

Implementation Method 2

which is formed using laser irradiation

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Data Source

PatentUS11637232B2Acoustic wave device including Li2CO3 layer on piezoelectric substrate made of LiNbO3 or LiTaO3

Publication Date: 2023.04.25 MURATA MFG CO LTD

AI summary

An acoustic wave device includes a piezoelectric substrate made of LiNbO3 or LiTaO3 and including first and second main surfaces that face each other, a functional electrode provided on the first main surface of the piezoelectric substrate to excite acoustic waves, and a Li2CO3 layer provided on the second main surface of the piezoelectric substrate.