Scandium-Aluminum BAW Resonator Electrodes for 5 GHz Loss Control
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Solution Overview
Problem
Film bulk acoustic resonators operating at 5 GHz frequencies face manufacturing difficulties and performance deterioration due to the need for ultra-thin electrodes and piezoelectric layers, with high acoustic impedance materials like molybdenum increasing electrical loss and low impedance materials like aluminum causing mechanical dynamic loss and crystal orientation issues.
Innovation Solution
A bulk acoustic wave resonator design incorporating a substrate with a lower electrode and a piezoelectric layer, where either or both electrodes are made of an aluminum alloy including scandium, which improves mechanical strength and chemical resistance, and the piezoelectric layer is formed using aluminum nitride or doped aluminum nitride with rare earth metals to enhance crystal orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an electrode material having a high degree of high acoustic impedance such as molybdenum (Mo) is used, then the operating frequency of 5 GHz may be implemented with a thickness of 1000 Å, but electrical loss increases as the thickness of the electrode decreases
Solution Approach 1:
The patent uses a composite electrode structure consisting of multiple layers with different materials (Mo/Ru/W/Ir/Pt/Cu/Ti/Ta/Ni/Cr or their alloys) instead of a single material. This composite structure allows optimization of both acoustic impedance for high-frequency operation and electrical conductivity to minimize electrical loss, resolving the contradiction between achieving 5 GHz operation and reducing electrical loss.
2Quantity of substance
If an electrode material having low acoustic impedance such as aluminum (Al) is used, then the thickness of each electrode can be increased to 2000 Å, but mechanical property is poor and mechanical dynamic loss is large
Solution Approach 1:
The patent employs composite electrode materials combining Al with other metals (Mo/Ru/W/Ir/Pt/Cu/Ti/Ta/Ni/Cr or their alloys) to create a structure that maintains the low acoustic impedance and higher thickness capability of aluminum while incorporating the superior mechanical strength of the other materials, thereby reducing mechanical dynamic loss.
3Quantity of substance
If pure aluminum (Al) is used for electrodes, then the thickness can be increased, but crystal orientation of the piezoelectric layer is deteriorated due to hillock formation by electromigration or mechanical deformation
Solution Approach 1:
The composite electrode structure prevents hillock formation and electromigration issues by distributing stress and current density across multiple material layers with different properties, thereby maintaining flat surfaces that ensure proper crystal orientation of the piezoelectric layer during deposition.
4Speed
If the thickness of the piezoelectric layer is reduced to 3000 Å for 5 GHz operation, then high frequency is achieved, but manufacturing precision and performance deteriorate
Solution Approach 1:
The patent optimizes the thickness parameters of both the electrode (1000-2000 Å) and piezoelectric layer (3000-4000 Å) to achieve the desired 5 GHz operating frequency while maintaining manufacturing precision and performance through the synergistic effect of the composite electrode structure.
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 design reduces electrical loss and improves crystal orientation of the piezoelectric layer, facilitating stable deposition and manufacturing, while maintaining mechanical strength and chemical resistance, thus addressing the challenges of high-frequency operation.
Implementation Method 1
a piezoelectric layer disposed on the lower electrode
Data Source
AI summary
A bulk acoustic wave resonator includes: a substrate; a lower electrode disposed on the substrate; a piezoelectric layer at least partially disposed on the lower electrode; and an upper electrode disposed on the piezoelectric layer, wherein either one or both of the lower electrode and the upper electrode includes a layer of aluminum alloy including scandium (Sc).