Acoustic Wave Electrode Dielectric Stack for Corrosion and TCF Stability
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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 top of 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 temperature coefficient of frequency (TCF) is improved, but the electrode fingers suffer from corrosion
Solution Approach 1:
A first dielectric film made of non-oxide material is introduced as an intermediary layer between the IDT electrode and the silicon oxide second dielectric film. This intermediate layer protects the electrode fingers from corrosion by the silicon oxide film while allowing the silicon oxide film to provide its TCF compensation function.
Solution Approach 2:
The patent uses a composite dielectric film structure combining two different materials: a non-oxide dielectric material (such as silicon nitride or silicon carbide) and silicon oxide. This composite structure provides both corrosion protection and TCF stability simultaneously.
2Object-affected harmful factors
If the dielectric film is formed to cover the electrode fingers completely, then corrosion protection is improved, but frequency variation increases due to dielectric loading
Solution Approach 1:
The first dielectric film is selectively positioned only in regions where corrosion protection is needed, such as on the sides and bottom of the electrode fingers, while the second dielectric film (silicon oxide) is positioned in regions where TCF compensation is needed. This local differentiation allows each material to perform its optimal function without unnecessary dielectric loading.
Solution Approach 2:
The dielectric coverage is segmented into two distinct layers with different materials and positions: the first dielectric film provides localized corrosion protection, while the second dielectric film provides TCF compensation. This segmentation prevents excessive dielectric loading on the electrode fingers while maintaining both protection and frequency stability.
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
An acoustic wave device comprises an IDT electrode disposed above an upper surface of a piezoelectric substrate and includes a plurality of electrode fingers configured to excite a main acoustic wave. A first dielectric film made of an oxide is disposed above the upper surface of the piezoelectric substrate and covers the plurality of electrode fingers. A second dielectric film made of non-oxide is disposed between the first dielectric film and each of the plurality of electrode fingers. A third dielectric film is disposed between the piezoelectric substrate and the plurality of electrode fingers. A speed of a transverse wave propagating through the third dielectric film is greater than a speed of the main acoustic wave propagating through the piezoelectric substrate. The third dielectric film contacts the first dielectric film between adjacent electrode fingers of the plurality of electrode fingers.