Piezoelectric Substrate Bonding via Ceramic Interlayer
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Solution Overview
Problem
Direct bonding of piezoelectric single crystal substrates to ceramic supporting bodies using existing methods often results in low bonding strength and cracking due to thermal expansion differences, leading to separation during processing steps.
Innovation Solution
A method involving the formation of a bonding layer with materials like mullite, alumina, tantalum pentoxide, titanium oxide, or niobium pentoxide on the ceramic substrate, followed by surface activation with a neutralized beam for direct bonding at ambient temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If plasma activation method is used for direct bonding of piezoelectric single crystal substrate to ceramic supporting body, then bonding can be achieved at ambient temperature, but cracks are generated due to thermal expansion difference during heating after bonding
Solution Approach 1:
A bonding layer made of ceramic material is introduced as an intermediary between the piezoelectric single crystal substrate and the ceramic supporting body. This bonding layer has a thermal expansion coefficient that is lower than that of the piezoelectric substrate, serving as a buffer to reduce thermal stress during heating after bonding, thereby preventing cracks while maintaining bonding strength
Solution Approach 2:
The thermal expansion coefficient parameter is carefully selected for the bonding layer material to be lower than that of the piezoelectric substrate. This parameter change creates a gradient structure that gradually accommodates thermal expansion differences, reducing stress concentration and preventing crack formation during temperature changes
2Strength
If no heating is performed after bonding, then thermal expansion cracks are prevented, but bonding strength becomes low causing separation during processing steps
Solution Approach 1:
The bonding layer acts as a stress-buffering intermediary that allows the system to withstand heating without generating cracks. Its lower thermal expansion coefficient creates a protective gradient that reduces thermal stress, enabling reliable bonding even after heating during processing steps
Solution Approach 2:
The bonding layer is prepared in advance with specific material properties (lower thermal expansion coefficient) to cushion against future thermal stress. This pre-configured protective layer prevents cracks before they can occur during subsequent heating processes
3Ease of manufacture
If intermediate layer made of silicon, silicon oxide, silicon nitride or aluminum nitride is used, then bonding can be achieved, but bonding strength is still insufficient causing separation in subsequent processing steps
Solution Approach 1:
The thermal expansion coefficient parameter of the bonding layer is specifically optimized to be lower than that of the piezoelectric substrate, creating a protective gradient that reduces thermal stress. This parameter optimization ensures both manufacturability and high bonding strength that prevents separation during processing
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 enhances bonding strength and prevents separation during processing, allowing for robust and reliable bonding of piezoelectric single crystal substrates to ceramic supporting bodies.
Implementation Method 1
irradiating neutralized beam onto a surface of the bonding layer to active the surface of the bonding layer
Data Source
AI summary
It is formed, over a supporting body made of a ceramic, a bonding layer composed of one or more material selected from the group consisting of mullite, alumina, tantalum pentoxide, titanium oxide and niobium pentoxide. Neutralized beam is irradiated onto a surface of the bonding layer to activate the surface of the bonding layer. The surface of the bonding layer and the piezoelectric single crystal substrate are bonded by direct bonding.