Multi-Layer IDT Electrodes for Corrosion-Stable Acoustic Wave Devices
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Solution Overview
Problem
Conventional acoustic wave devices face issues with electrode finger corrosion and frequency variation due to the use of silicon oxide dielectric films, which affect the performance and reliability of the devices.
Innovation Solution
The acoustic wave device incorporates a piezoelectric substrate with interdigital transducer (IDT) electrodes and employs a dual dielectric film structure, where a silicon dioxide film contacts the substrate between electrode fingers and a non-oxide film, such as silicon nitride, is placed on the electrode fingers to prevent corrosion and minimize frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon oxide dielectric film is used to cover the IDT electrode, then the TCF (temperature coefficient of frequency) is improved, but the electrode fingers suffer from corrosion
Solution Approach 1:
A non-oxide dielectric film (such as silicon nitride or silicon oxynitride) is introduced as an intermediary layer between the IDT electrode and the silicon oxide dielectric film. This intermediate layer acts as a protective barrier that prevents corrosion of the electrode fingers by the silicon oxide film, while allowing the silicon oxide film to maintain its TCF improvement function. The mediator layer thus resolves the contradiction by enabling the harmful effects of silicon oxide to be eliminated while preserving its beneficial TCF characteristics.
Solution Approach 2:
The dielectric structure is designed as a composite of multiple materials: a non-oxide dielectric film (silicon nitride or silicon oxynitride) combined with a silicon oxide dielectric film. This composite structure combines the corrosion-resistant properties of non-oxide materials with the TCF-stabilizing properties of silicon oxide, thereby simultaneously achieving both improved reliability and protection against electrode finger corrosion.
2Object-affected harmful factors
If the dielectric film is formed to cover the IDT electrode completely, then corrosion protection is improved, but frequency variation increases
Solution Approach 1:
The dielectric film structure is designed with local quality variations: the non-oxide dielectric film is selectively positioned to provide corrosion protection where needed (at the electrode-dielectric interface), while the silicon oxide dielectric film is positioned to provide TCF stabilization in regions where it benefits frequency stability. This spatial differentiation of material properties allows simultaneous achievement of corrosion protection and frequency stability.
Solution Approach 2:
The invention changes the material parameters of the dielectric film from a uniform silicon oxide structure to a multi-layer structure with different material compositions (non-oxide and oxide layers). By adjusting the thickness and composition parameters of each layer, the system achieves optimal balance between corrosion protection and frequency stability, resolving the contradiction through parameter optimization.
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
This configuration effectively prevents electrode finger corrosion and reduces frequency variations, enhancing the stability and performance of the acoustic wave device by using dielectric films with opposite temperature coefficients and different propagation speeds.
Implementation Method 1
piezoelectric substrate, IDT electrode including plural electrode fingers disposed above an upper surface of the piezoelectric substrate
Implementation Method 2
The temperature coefficient of frequency (TCF) of silicon oxide has a sign opposite to that of piezoelectric substrate 102, so that dielectric film 104 made of silicon oxide may improve the TCF of acoustic wave device 101
Data Source
AI summary
A surface acoustic wave device comprises a substrate and an interdigital transducer (IDT) electrode disposed on the substrate. The IDT electrode includes a lower electrode layer having a lower surface in contact with an upper surface of the substrate and an upper electrode layer having a lower surface defining a base in contact with an upper surface of the lower electrode layer. Side surfaces of the lower electrode layer are substantially perpendicular to the upper surface of the substrate. Side surfaces of the upper electrode layer are disposed at an acute angle relative to the upper surface of the substrate.