Composite Substrate Structure for Thin Crack-Resistant Piezoelectric Layers
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Solution Overview
Problem
Existing piezoelectric element thinning technologies, such as SAW devices, face challenges in maintaining mechanical strength while achieving thinness, as they often rely on substrates with lower mechanical strength, leading to potential cracking issues.
Innovation Solution
A composite substrate configuration where a high-mechanical-strength substrate overlaps with a piezoelectric substrate, featuring a hole with a covering layer composed of the stronger substrate material, preventing crack generation and enhancing adhesion and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the piezoelectric substrate is thinned to reduce device thickness, then the overall device size is reduced, but the mechanical strength decreases and cracking occurs
Solution Approach 1:
The patent uses a composite structure where a thin piezoelectric substrate (first substrate) is bonded to a thicker supporting substrate (second substrate) with higher mechanical strength. This composite configuration allows the piezoelectric layer to be thin for device miniaturization while the supporting substrate provides the necessary mechanical strength to prevent cracking and maintain structural integrity.
2Length of moving object
If the piezoelectric substrate is thinned to achieve reduced device thickness, then device miniaturization is achieved, but reliability decreases due to increased cracking risk
Solution Approach 1:
The composite substrate structure provides mechanical reinforcement through the supporting substrate, significantly reducing the risk of cracking in the thin piezoelectric layer during device operation and handling, thereby improving reliability while maintaining thinness.
Solution Approach 2:
The patent applies a covering layer containing components of the second substrate at the interface region between the two substrates, particularly at the hole portion. This localized reinforcement provides additional mechanical strength and crack prevention at the critical interface area where stress concentration occurs, enhancing reliability without increasing overall device thickness.
3Strength
If a covering layer is added at the interface to prevent cracking, then mechanical strength and reliability are improved, but device complexity increases
Solution Approach 1:
The covering layer is applied selectively at the interface region and hole portion rather than uniformly across the entire substrate, providing targeted reinforcement only where needed. This localized approach improves interface strength and crack resistance while minimizing the increase in device complexity and material usage.
Data Source
AI summary
A composite substrate is a plate-shaped body where a first substrate and a second substrate overlap. The composite substrate includes a hole in the first substrate and the second substrate in a thickness direction of the plate-shaped body. A ratio A/B of an average thickness A of the first substrate to an average thickness B of the second substrate is ⅕ or less. An interface between the first substrate and the second substrate on an inner wall of the plate-shaped body that is positioned at the hole includes a part that is covered by a covering layer that contains a component that composes the second substrate.