Piezoelectric Thin Film Structure with Aluminum Oxide Barrier
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Solution Overview
Problem
Conventional angular velocity detection apparatuses using piezoelectric thin films face issues with lead (Pb) diffusion during film formation, leading to deteriorated piezoelectric performance and reduced sensor sensitivity due to the three-layer structure of SiO2, Pt, and PZT layers.
Innovation Solution
A four-layer piezoelectric thin film structure is introduced, comprising a substrate, silicon oxide film, first and second aluminum oxide films, a lower electrode layer, a piezoelectric film layer, and an upper electrode layer, which suppresses Pb diffusion by incorporating additional aluminum oxide films to stabilize piezoelectric properties and improve signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a three-layer structure (SiO2, Pt, PZT) is used to form the piezoelectric thin film, then the film formation process is simplified, but Pb diffusion occurs during firing leading to deteriorated piezoelectric performance
Solution Approach 1:
An aluminum oxide barrier layer is introduced between the PZT layer and the SiO2 substrate to prevent Pb diffusion. This intermediary layer acts as a diffusion barrier, blocking the harmful interaction between PZT and SiO2 during the firing process while allowing the overall structure to be formed in a single process sequence.
Solution Approach 2:
The patent uses a composite multilayer structure combining SiO2, aluminum oxide, Pt, and PZT layers. Each material is selected for its specific properties: SiO2 for substrate and insulation, aluminum oxide for Pb diffusion barrier, Pt for electrode functionality, and PZT for piezoelectric performance. The composite structure achieves both ease of manufacture and high reliability.
2Object-affected harmful factors
If the SiO2 layer is used to prevent Pb diffusion, then diffusion protection is provided, but Pb still diffuses into the substrate during firing process
Solution Approach 1:
The aluminum oxide layer serves as a more effective intermediary barrier between PZT and SiO2 substrate. It has lower Pb solubility and acts as a diffusion barrier, preventing Pb from reaching the SiO2 substrate while maintaining the protective function against Pb diffusion.
Solution Approach 2:
The patent modifies the barrier layer material from SiO2 to aluminum oxide, changing the chemical and physical parameters of the barrier. Aluminum oxide has different diffusion characteristics with lower Pb solubility, thereby improving the precision of Pb diffusion control during firing.
3Device complexity
If a conventional three-layer structure is used, then device complexity is reduced, but oscillation noise increases and S/N ratio deteriorates
Solution Approach 1:
The patent employs a composite five-layer structure (SiO2, aluminum oxide, Pt, PZT, and upper electrode) that provides both mechanical stability for low oscillation noise and optimized piezoelectric properties for high S/N ratio. The combination of materials with complementary properties achieves both low complexity and high measurement precision.
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 stabilized piezoelectric thin film structure enhances the sensitivity and reduces oscillation noise in angular velocity detection, maintaining high sensitivity and improving the signal-to-noise ratio by preventing Pb diffusion and decoupling oscillation and detection modes.
Implementation Method 1
a piezoelectric film layer (302) disposed on the lower electrode layer (301)
Implementation Method 2
a first aluminum oxide film (48) disposed on the silicon oxide film (41)... suppressing the diffusion of Pb from the PZT film
Implementation Method 3
when an angular velocity is applied to the arm while the arm oscillates in the horizontal direction, the arm also oscillates in the vertical direction by Coriolis force
Data Source
AI summary
A piezoelectric thin film structure includes a substrate, a silicon oxide film disposed on the substrate, a first aluminum oxide film disposed on the silicon oxide film, a lower electrode layer disposed on the first aluminum oxide film, a piezoelectric film layer disposed on the lower electrode layer, and an upper electrode layer disposed on the piezoelectric film layer.