Step-Bunched Sapphire Composite Substrate for Low-Wave-Loss Bonding
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Solution Overview
Problem
The existing composite substrates for piezoelectric devices face challenges with low bonding strength and significant reflection of bulk waves at the bonding interface between the piezoelectric and support substrates, particularly due to residual stress and crystal defects from mechanical roughening processes, and difficulties in controlling anisotropic etching of sapphire substrates.
Innovation Solution
A composite substrate is created by directly bonding a piezoelectric substrate to a sapphire substrate with a step bunch structure formed through heat-treating the sapphire substrate at a predetermined off-angle to specific crystal planes in an oxidizing atmosphere, enhancing bonding strength and reducing bulk wave reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a mechanical roughening treatment such as lapping process is used to reduce bulk wave reflection, then the reflection of bulk waves is reduced, but a processing altered layer containing residual stress and crystal defects is formed which decreases bonding strength
Solution Approach 1:
The patent replaces the mechanical lapping process with a chemical etching process using phosphoric acid to create the stepped structure. This substitution eliminates the mechanical contact that causes residual stress and crystal defects, while still achieving the goal of reducing bulk wave reflection through the formation of a controlled stepped structure on the sapphire substrate surface
Solution Approach 2:
The patent changes the approach from mechanical parameter control (lapping pressure, speed) to chemical parameter control (etching solution concentration, temperature, time). By controlling the etching parameters, a stepped structure is formed that reduces bulk wave reflection without creating a damaged processing altered layer, thus maintaining bonding strength
2Ease of manufacture
If anisotropic etching of sapphire is used to form concavo-convex structure, then the processing is simplified, but it is difficult to control the shape due to small rate difference between crystal orientations
Solution Approach 1:
The patent applies local quality by creating a stepped structure with specific local geometries on the sapphire substrate surface. By controlling the etching conditions, different regions of the substrate develop specific step heights and widths, creating a localized stepped pattern that provides precise shape control for reducing bulk wave reflection while maintaining manufacturing simplicity
3Loss of time
If anisotropic etching is used to form concavo-convex structure, then the processing time is reduced, but it only makes a concavo-convex of a specific crystal orientation
Solution Approach 1:
The patent achieves universality by making the etching process applicable to various sapphire substrate orientations. The phosphoric acid etching method can create stepped structures on sapphire substrates with different crystal orientations (c-plane, a-plane, m-plane, r-plane), providing a universal solution that works across different material specifications and device requirements without changing the fundamental process
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 results in a composite substrate with high bonding strength and reduced bulk wave reflection, minimizing noise generation and improving device performance by absorbing reflected waves and reducing crystal defects and residual stress.
Implementation Method 1
heat treating the sapphire substrate in an oxidizing atmosphere to form a step bunch on the surface of the sapphire substrate
Data Source
AI summary
A composite substrate of the present disclosure is a composite substrate in which a piezoelectric substrate and a sapphire substrate are directly bonded, and a bonding surface of the sapphire substrate has a step bunch structure. A piezoelectric device of the present disclosure includes the composite substrate. A method for manufacturing a composite substrate includes the steps of: preparing a piezoelectric substrate and a sapphire substrate including a surface having a predetermined off-angle to a specific crystal plane, heat treating the sapphire substrate in an oxidizing atmosphere to form a step bunch on the surface of the sapphire substrate, and bonding the piezoelectric substrate and the surface of the sapphire substrate directly.