Piezoelectric Substrate Bonding with Nitrogen-Plasma Interface Control
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Solution Overview
Problem
The characteristics of piezoelectric devices, particularly acoustic wave devices, are deteriorated when lithium niobate or lithium tantalate substrates are thinned, leading to reduced admittance ratios at resonance and anti-resonance frequencies due to crystallinity damage and insufficient bonding strength.
Innovation Solution
A bonded body is created with a piezoelectric material substrate, such as lithium niobate or lithium tantalate, on a silicon oxide layer, where a higher nitrogen concentration is introduced at the interface between the piezoelectric material and the silicon oxide layer, achieved by irradiating nitrogen plasma at 150° C. or lower, to enhance bonding strength and prevent crystallinity deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the piezoelectric material substrate is thinned to reduce device size, then the device dimensions are improved, but the crystallinity is deteriorated and bonding strength is reduced
Solution Approach 1:
The patent applies preliminary action by performing plasma activation treatment on the bonding surfaces before bonding. This pre-treatment creates reactive groups and improves surface energy, ensuring strong bonding even when the substrate is thinned to extremely thin layers (1-10 μm). The activation is done in advance to prevent crystallinity deterioration during subsequent processing.
Solution Approach 2:
The patent changes physical and chemical parameters of the bonding interface by controlling plasma treatment conditions (power, gas flow rate, treatment time) and bonding temperature. These parameter adjustments optimize the bonding strength while maintaining substrate integrity at reduced thickness, resolving the contradiction between thinning and bonding strength.
2Device complexity
If the piezoelectric material substrate is thinned to improve device integration, then the device complexity is reduced, but the manufacturing precision is deteriorated due to crystallinity damage
Solution Approach 1:
The patent replaces mechanical thinning methods (which cause mechanical stress and crystallinity damage) with plasma activation and chemical mechanical polishing (CMP). This substitution of processing methods enables precise thickness control down to extremely thin layers while preserving crystallinity, thus improving manufacturing precision despite reduced substrate thickness.
Solution Approach 2:
The patent uses plasma activation in a controlled atmosphere to prevent oxidation and contamination of the bonding surfaces. This inert environment protection maintains surface quality and crystallinity during the thinning process, ensuring high manufacturing precision even when substrates are thinned for simpler device structures.
3Strength
If plasma activation is used to bond lithium tantalate to silicon oxide, then the bonding strength is improved, but the temperature control becomes critical to prevent crystallinity damage
Solution Approach 1:
The patent introduces plasma activation as an intermediary process between the bonding surfaces. This plasma treatment creates reactive intermediates on the surface that enable strong bonding at lower temperatures, mediating the interaction between lithium tantalate and silicon oxide without requiring high temperatures that would damage crystallinity.
Solution Approach 2:
The patent optimizes bonding temperature parameters by combining plasma activation with controlled heating. The plasma treatment allows bonding to proceed at lower temperatures (reducing thermal stress), while subsequent mild heating enhances the bonding strength. This parameter optimization resolves the contradiction between achieving strong bonding and maintaining temperature control to protect crystallinity.
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 maintains the performance of the bonded body even at thinner piezoelectric material substrate thicknesses, preventing the deterioration of acoustic wave device characteristics and ensuring stable admittance ratios.
Implementation Method 1
a processing face 1d of the piezoelectric material substrate 1A is activated by irradiating nitrogen plasma
Implementation Method 2
the bonding face of the piezoelectric material substrate and the bonding face of the silicon oxide layer on the supporting substrate are bonded to each other
Data Source
AI summary
A bonded body includes a supporting substrate, silicon oxide layer provided on the supporting substrate, and a piezoelectric material substrate provided on the silicon oxide layer and composed of a material selected from the group consisting of lithium niobate, lithium tantalate and lithium niobate-lithium tantalite. A nitrogen concentration at an interface between the piezoelectric material substrate and silicon oxide layer is higher than a nitrogen concentration at an interface between the silicon oxide layer and the supporting substrate.