Piezoelectric Substrate Bonding with Intermediate Silicon Layer
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Solution Overview
Problem
The bonding of piezoelectric material substrates and silicon substrates through a silicon oxide layer often results in fractures or cracks due to thermal expansion coefficient differences and residual stress, which deteriorates the frequency characteristics and effective resistivity of the bonded body.
Innovation Solution
A method involving physical vapor deposition to form a silicon film on a silicon substrate, followed by heat treatment between 400°C and 600°C to create an intermediate layer, which is then bonded with a piezoelectric material substrate using a silicon oxide bonding layer, reducing residual stress and improving effective resistivity across a wide frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon film is formed by CVD method at high temperature (400-1000°C), then the film can be successfully formed, but large residual stress remains in the film causing fracture of the bonded body
Solution Approach 1:
The patent changes the deposition temperature parameter from conventional high temperature (400-1000°C) to low temperature (room temperature or slightly elevated), which fundamentally alters the film formation mechanism and reduces residual stress while maintaining film quality
Solution Approach 2:
The patent replaces the thermal field (CVD heating) with a chemical field (plasma or vapor phase reaction), allowing film formation without high temperature thermal stress, thus substituting a mechanical/thermal process with a chemical process
2Reliability
If an amorphous Si film or polycrystalline Si film is formed to suppress fixed charges, then effective resistivity improves, but thermal expansion coefficient differences cause fracture during heating
Solution Approach 1:
The patent changes the material structure parameter from amorphous/polycrystalline to single crystal silicon, which has superior mechanical strength and thermal stability, eliminating fracture issues while maintaining electrical performance
Solution Approach 2:
The patent creates a composite structure with single crystal silicon film on silicon substrate, combining the electrical benefits of silicon-based materials with the mechanical strength of single crystal structure to resist thermal stress
3Ease of manufacture
If CVD method is used to form silicon film, then film formation is achieved, but the process is time-consuming and produces large stress
Solution Approach 1:
The patent replaces the thermal field (CVD heating) with a chemical field (plasma or vapor phase reaction), allowing film formation without high temperature thermal stress, thus substituting a mechanical/thermal process with a chemical process
Solution Approach 2:
The patent skips the lengthy high-temperature annealing and stress-relief steps required by CVD by using low-temperature plasma or vapor deposition that forms low-stress films directly, reducing total process time
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 approach effectively suppresses fractures and maintains high effective resistivity over a wide temperature range, enhancing the frequency characteristics of the bonded body while minimizing residual stress.
Implementation Method 1
a silicon film-forming step of forming a silicon film on a supporting substrate comprising silicon by physical vapor deposition method
Implementation Method 2
a heat treatment step of subjecting the silicon film to heat treatment at a temperature of 400° C. or higher and 600° C. or lower to generate an intermediate layer
Data Source
AI summary
A silicon film is provided on a supporting substrate composed of silicon by physical vapor deposition. The silicon film is subjected to heat treatment at a temperature of 400° C. or higher and 600° C. or lower to generate an intermediate layer. The piezoelectric material substrate is bonded to the supporting substrate through a bonding layer of silicon oxide and the intermediate layer. A method of providing an acoustic wave element with a bonded body is also provided.