Elastic Wave Device Stress Relief via Support Layer
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Solution Overview
Problem
Elastic wave devices with piezoelectric thin films, such as LiTaO3, are prone to cracking and chipping due to external forces during bonding and dicing, and suffer from interfacial delamination, making it difficult to detect defects using leak detection methods.
Innovation Solution
The design includes a film stack with a piezoelectric thin film, a high-acoustic-velocity film, and a low-acoustic-velocity film, along with a support layer and cover member forming a hollow space, and a first insulating layer extending from the film stack to the support substrate, reducing stress on the piezoelectric film and preventing disconnection, while allowing for effective leak detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If piezoelectric thin films (e.g., LiTaO3) are used in elastic wave devices, then device performance is improved, but the films are easily cracked and chipped due to external force during bonding and dicing
Solution Approach 1:
A support layer is provided beneath the piezoelectric thin film stack in regions where the film stack is absent. This support layer acts as a cushioning structure that absorbs and distributes external forces applied during bonding and dicing processes, preventing stress concentration on the fragile piezoelectric thin film and thereby preventing cracking and chipping before they can occur
Solution Approach 2:
The support layer serves as an intermediary structure between the piezoelectric thin film stack and the external environment. It mediates the transmission of external forces, protecting the piezoelectric thin film from direct exposure to mechanical stress during manufacturing processes such as bonding and dicing
2Reliability
If a hollow structure with sealed condition is used in elastic wave devices, then device protection is improved, but it becomes difficult to detect defects using leak detection methods
Solution Approach 1:
The support layer is configured with a specific pattern that segments the structure, creating regions where the film stack is present and regions where it is absent. This segmentation allows the support layer to provide protection while maintaining areas accessible for leak detection, resolving the contradiction between sealed protection and defect detectability
Solution Approach 2:
The support layer is strategically positioned in specific regions where the film stack is absent, creating local variations in structure. This local quality approach allows the hollow structure to maintain its protective sealed condition in most areas while having specific localized regions that enable leak detection functionality
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 significantly reduces or prevents cracking, chipping, and interfacial delamination, enabling easy screening of defective devices through leak detection.
Implementation Method 1
a piezoelectric thin film stacked on the low-acoustic-velocity film
Implementation Method 2
The low-acoustic-velocity film is a film along which a bulk wave propagates at a lower acoustic velocity than a bulk wave propagates along the piezoelectric thin film. The high-acoustic-velocity film is a film along which a bulk wave propagates at a higher acoustic velocity than an elastic wave propagates along the piezoelectric thin film
Data Source
AI summary
An elastic wave device includes a support substrate, a film stack including a piezoelectric thin film, and an IDT electrode. The film stack is partially absent in a region outside a region where the IDT electrode is located in plan view. The elastic wave device further includes a support layer located on the support substrate in at least a portion of a region where the film stack is partially absent and surrounds a region where the film stack is located in plan view and a cover member located on the support layer. The cover member defines a hollow space facing the IDT electrode together with the piezoelectric thin film and the support layer.