Elastic Wave Device Bonding Layer Stress Distribution
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Solution Overview
Problem
Elastic wave devices with stacked structures experience warpage and fractures due to stress from bonding methods, leading to degraded electrical characteristics and increased risk of fractures during handling and conveyance.
Innovation Solution
Incorporating a bonding layer made of metal oxide or nitride, such as a Ti layer, within the low-acoustic-velocity film or at specific interfaces between films, to reduce warpage and enhance bonding strength without applying excessive stress to the piezoelectric film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If multiple layers are formed on the piezoelectric film side by conventional bonding methods, then bonding strength is improved, but warpage occurs and electrical characteristics are degraded
Solution Approach 1:
A bonding layer comprising a metal oxide layer and a metal nitride layer is introduced as an intermediary between the piezoelectric film and other layers. This bonding layer distributes stress more evenly, prevents warpage, maintains electrical characteristics, and provides strong bonding strength through its composite structure of oxide and nitride layers.
2Ease of manufacture
If conventional bonding methods are used to bond the supporting substrate, then bonding is achieved, but fractures occur during conveyance due to warpage
Solution Approach 1:
The bonding layer acts as a stress-distributing intermediary that prevents warpage during bonding, thereby eliminating the cause of fractures during conveyance while maintaining ease of manufacture through conventional bonding processes.
Solution Approach 2:
The bonding layer uses a composite structure of metal oxide and metal nitride layers, combining the advantages of both materials to provide both bonding strength and warpage prevention, ensuring fracture resistance during conveyance.
3Strength
If stress is concentrated in the piezoelectric film during bonding, then bonding strength is improved, but warpage and fractures increase
Solution Approach 1:
The bonding layer serves as a stress-distributing intermediary that spreads the bonding stress across a larger area and more evenly, preventing concentration of stress in the piezoelectric film while maintaining strong bonding strength and preventing warpage.
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 solution effectively prevents warpage and fractures, maintaining the electrical characteristics and ensuring stable operation of the elastic wave devices during production and handling by distributing stress more evenly and providing strong electrical insulation.
Implementation Method 1
This bonding can be performed by a method such as bonding by hydrophilization, activation bonding, atomic diffusion bonding, or metal diffusion bonding.
Implementation Method 2
the bonding layer is disposed at any position from an inside of the high-acoustic-velocity film to an interface between the low-acoustic-velocity film and the piezoelectric film
Implementation Method 3
an acoustic velocity of a bulk wave that propagates through the low-acoustic-velocity film is lower than an acoustic velocity of a bulk wave that propagates through the piezoelectric film; a high-acoustic-velocity film which is stacked on a surface of the low-acoustic-velocity film on a side opposite to the piezoelectric film and in which an acoustic velocity of a bulk wave that propagates through the high-acoustic-velocity film is higher than an acoustic velocity of an elastic wave that propagates through the piezoelectric film
Implementation Method 4
a piezoelectric film
Data Source
AI summary
An elastic wave device includes a high-acoustic-velocity film, a low-acoustic-velocity film, and a piezoelectric film stacked on a substrate in this order, and a bonding layer is disposed at any position from inside of the high-acoustic-velocity film to an interface between the low-acoustic-velocity film and the piezoelectric film. Alternatively, an elastic wave device includes a low-acoustic-velocity film and a piezoelectric film stacked on a high-acoustic-velocity substrate, and a bonding layer is located in the low-acoustic-velocity film or at an interface between the piezoelectric film and the low-acoustic-velocity film.