Titanium-Alloyed SAW Device Surface for Low Insertion Loss
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Solution Overview
Problem
The formation of an insulating aluminum oxide layer between the interdigital transducer (IDT) metal layer and the under bump metallurgy (UBM) layer in acoustic wave devices leads to increased insertion loss, reduced adhesion, and difficulties in process control monitoring due to its insulating nature and re-oxidation during processing.
Innovation Solution
A patterned aluminum-based material layer with a titanium-alloyed surface is used, where a titanium-based material layer is selectively etched to expose portions, allowing direct contact with an under bump metallurgy layer, resulting in low contact resistivity and improved adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If aluminum-based material layer is used for IDT metal layer, then conductivity-to-mass ratio is improved, but aluminum oxide layer formation increases insertion loss and reduces adhesion
Solution Approach 1:
A titanium-based material layer is introduced as an intermediary between the aluminum-based IDT metal layer and the UBM layer. This titanium layer prevents direct oxidation of aluminum while enabling reliable metal-to-metal contact with the UBM layer, thereby maintaining both high conductivity-to-mass ratio and good adhesion properties
Solution Approach 2:
The IDT metal layer structure is designed as a composite system combining aluminum-based material (for high conductivity-to-mass ratio) with a titanium-based material layer (for oxidation protection and adhesion enhancement), creating a multi-layer composite structure that leverages the advantages of both materials
2Reliability
If aluminum oxide layer is formed on IDT layer, then aluminum oxidation is self-limiting, but the insulating AIO layer prevents effective etching and increases insertion loss
Solution Approach 1:
The titanium-based material layer serves as an intermediary that replaces the problematic aluminum oxide layer. It provides oxidation protection while maintaining etchability and electrical conductivity, enabling effective via etching and consistent DC contact resistance
Solution Approach 2:
The invention changes the material parameter at the IDT surface from aluminum oxide (insulating, hard to etch) to titanium-based material (conductive, easily etched), thereby improving both manufacturability and electrical performance while maintaining oxidation protection
3Reliability
If AIO layer is present between UBM and IDT metal layer, then aluminum is protected from oxidation, but adhesion and shear strength are reduced
Solution Approach 1:
The titanium-based material layer acts as a mediator that provides both oxidation protection and mechanical adhesion. It forms a strong bond with both the aluminum-based IDT layer and the UBM layer, enabling metal-to-metal contact that withstands mechanical stresses during assembly
Solution Approach 2:
The multi-layer composite structure combines aluminum-based material (for conductivity-to-mass ratio), titanium-based material (for adhesion and oxidation protection), and UBM layer (for electrical connection), creating a system that simultaneously achieves high strength, good adhesion, and oxidation resistance
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 reduces insertion loss, enhances mechanical robustness, and facilitates consistent DC contact resistance, improving the assembly and electrical characteristics of acoustic wave devices.
Implementation Method 1
a titanium-based material layer is disposed over the patterned aluminum-based material layer. Yet another process step includes selectively etching away portions of the titanium based material layer to leave an exposed titanium-alloyed surface
Implementation Method 2
The insulating nature of the AIO layer prevents consistent, low direct current (DC) contact resistance between UBM and the IDT metal layer. This AIO insulating layer also increases insertion loss by limiting conductivity between UBM and IDT layers
Data Source
AI summary
Disclosed is a device that includes a crystalline substrate and a patterned aluminum-based material layer disposed onto the crystalline substrate. The patterned aluminum-based material layer has a titanium-alloyed surface. A titanium-based material layer is disposed over select portions of the titanium-alloyed surface. In an exemplary embodiment, the patterned aluminum-based material layer forms a pair of interdigitated transducers to provide a surface wave acoustic (SAW) device. The SAW device of the present disclosure is usable to realize SAW-based filters for wireless communication equipment.