Multilayer Passivation for Acoustic Wave Filter Electrodes
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Solution Overview
Problem
Acoustic wave filters, particularly those using surface acoustic wave (SAW) devices, face challenges in achieving high effective electromechanical coupling coefficients (k2) and sufficient protection for interdigital transducer electrodes while maintaining low-loss filtering and thermal dissipation, as single-layer passivation materials like silicon nitride degrade k2 and silicon dioxide lacks sufficient protection.
Innovation Solution
A multilayer passivation structure comprising a first silicon-based material, such as silicon oxide, and a second material, such as silicon nitride, with different thicknesses and hardnesses, is used over the interdigital transducer electrode, providing enhanced protection and maintaining a large effective electromechanical coupling coefficient (k2), with the second layer's thickness being thinner than the electrode, and the structure being selectively disposed to avoid bus bars.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer silicon nitride passivation layer is used, then sufficient protection for the interdigital transducer electrode is achieved, but the effective electromechanical coupling coefficient (k2) is degraded
Solution Approach 1:
The single-layer passivation structure is segmented into multiple layers: a first passivation layer (silicon oxide) directly over the interdigital transducer electrode, and a second passivation layer (silicon nitride) over the first passivation layer. This segmentation allows each layer to perform its optimal function - the first layer protects the electrode while the second layer provides additional protection without degrading k2
Solution Approach 2:
The patent uses a composite passivation structure combining silicon oxide and silicon nitride materials. The silicon oxide layer provides protection with minimal k2 degradation, while the silicon nitride layer adds protective functionality. This composite approach achieves sufficient electrode protection while maintaining high effective electromechanical coupling coefficient
2Loss of energy
If a single-layer silicon dioxide passivation layer is used, then the effective electromechanical coupling coefficient (k2) is maintained, but sufficient protection for the interdigital transducer electrode is not achieved
Solution Approach 1:
The passivation function is segmented between two materials: silicon oxide for maintaining k2 and providing partial protection, and silicon nitride for providing sufficient protective coverage. This segmentation resolves the contradiction by distributing protective and electrical functions across different layers
Solution Approach 2:
The composite structure of silicon oxide and silicon nitride layers provides both the electrical performance (maintained k2) and protective functionality (sufficient electrode protection) that neither material can achieve alone
3Reliability
If a thick passivation layer is used, then sufficient protection is achieved, but thermal dissipation is reduced
Solution Approach 1:
The patent optimizes the thickness parameters of the passivation layers to achieve a balance between protection and thermal dissipation. The first passivation layer has a thickness of 5-20 nm and the second passivation layer has a thickness of 20-50 nm, providing sufficient protection while maintaining thermal pathways for heat dissipation
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 multilayer passivation structure effectively protects the interdigital transducer electrode, maintains a high effective electromechanical coupling coefficient (k2), and allows for improved frequency trimming and thermal dissipation, enhancing the performance of acoustic wave devices.
Implementation Method 1
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.
Data Source
AI summary
An acoustic wave device is disclosed, the acoustic wave device can include a piezoelectric layer, an interdigital transducer electrode over the piezoelectric layer, and a multilayer passivation structure over the interdigital transducer electrode. The multilayer passivation structure has a thickness thinner than a thickness of the interdigital transducer electrode.