Ceramic Substrate Surface Control for Strong SAW Wafer Bonding
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Solution Overview
Problem
The production cost of SAW devices is high due to the use of single-crystalline sapphire substrates, and existing ceramic substrates with decreased surface roughness via Van der Waals bonding do not achieve sufficient bonding strength between the piezoelectric and ceramic substrates.
Innovation Solution
A ceramic substrate with a polycrystalline structure and a surface roughness of 0.01 nm to 3.0 nm in terms of Sa, and fewer than 5 projections/depressions of 1 nm or more and fewer than 1 of 2 nm or more in a 50 μm square region, bonded to a piezoelectric substrate through Van der Waals force, enhancing bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a ceramic substrate with decreased surface roughness is used to reduce production cost, then the bonding strength between piezoelectric and ceramic substrates becomes insufficient
Solution Approach 1:
The invention changes the surface roughness parameters of the ceramic substrate to an optimal range (Sa: 0.03-3.0 nm, Sz: 0.1-20 nm) that simultaneously achieves cost-effectiveness and sufficient bonding strength (0.5 J/m² or more). This parameter optimization resolves the contradiction by finding the sweet spot where the substrate is affordable yet maintains reliable bonding.
Solution Approach 2:
The invention applies different surface quality requirements to different aspects: the overall surface roughness is controlled within specific ranges to enable Van der Waals bonding, while locally minimizing projections and depressions to prevent bonding defects. This localized quality control ensures both cost-effectiveness and bonding reliability.
2Ease of manufacture
If the surface roughness is decreased to enable Van der Waals bonding, then production cost is reduced, but bonding strength remains insufficient
Solution Approach 1:
The invention establishes specific parameter ranges for surface roughness (Sa: 0.03-3.0 nm, Sz: 0.1-20 nm) that enable reliable Van der Waals bonding. By controlling these parameters, the invention achieves both cost reduction through ceramic substrate usage and bonding reliability of 0.5 J/m² or more, preventing separation during subsequent processing.
Solution Approach 2:
The invention adopts the bonding approach from high-performance applications (using Van der Waals force like in single-crystal substrates) but adapts it to ceramic materials, copying the bonding mechanism while using more cost-effective substrate material.
3Ease of manufacture
If projections and depressions on the ceramic substrate surface are not controlled, then manufacturing is simpler, but bonding strength and reliability decrease
Solution Approach 1:
The invention sets quantitative limits on the number of projections and depressions (less than 5 per 50μm square region for 1nm+ height, less than 1 for 2nm+ height) that maintain manufacturing feasibility while ensuring bonding strength. These parameter controls prevent bonding defects without requiring excessive manufacturing complexity.
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 configuration ensures a bonding strength of 0.5 J/m2 or more, reducing production costs while maintaining reliable bonding between the ceramic and piezoelectric substrates, preventing separation and chipping during electrode and chip formation.
Implementation Method 1
a piezoelectric substrate and a ceramic substrate whose surface roughness Ra (arithmetic mean roughness) is decreased are bonded to each other through Van der Waals force
Data Source
AI summary
A ceramic substrate is formed of a polycrystalline ceramic and has a supporting main surface. The supporting main surface has a roughness of 0.01 nm or more and 3.0 nm or less in terms of Sa. The number of projections and depressions with a height of 1 nm or more in a square region with 50 μm sides on the supporting main surface is less than 5 on average, and the number of projections and depressions with a height of 2 nm or more in the square region is less than 1 on average.