Glass Substrate for Magnetic Disk with Ultra-Low Roughness
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Solution Overview
Problem
The challenge is to create a glass substrate for magnetic disks with extremely low surface roughness and few defects, as conventional methods often result in a trade-off between surface roughness and defect reduction, particularly for multi-component glasses like aluminosilicate, which are necessary for high recording densities like 160 GB or more per disk.
Innovation Solution
A magnetic disk glass substrate with an arithmetic mean roughness (Ra) of 0.12 nm or less and fewer than 1 defect per 24 cm², achieved through a polishing and cleaning process using additives like carboxylic acids and polyvalent amines in the polishing liquid, which are also present in the cleaning liquid to maintain surface quality and remove adhering matter effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the surface roughness is reduced to a very low level (Ra ≈ 0.1 nm), then the surface flatness is improved, but the number of defects on the surface increases
Solution Approach 1:
The patent changes the chemical composition parameters of the glass substrate by specifying precise ranges of SiO2 (67-75 wt%), B2O3 (3-10 wt%), Al2O3 (0.5-5 wt%), and other components. This compositional optimization enables achieving both ultra-low surface roughness (Ra ≤ 0.1 nm) and reduced defect density simultaneously, resolving the trade-off between surface flatness and defect reduction
Solution Approach 2:
The patent employs a multi-component glass composite material system combining SiO2, B2O3, Al2O3, and various metal oxides in specific proportions. This composite glass composition provides both the surface flatness required for low Ra values and the structural integrity to minimize defects, overcoming the limitations of single-component or simpler glass formulations
2Reliability
If conventional cleaning methods are used to remove adhering matter, then the cleaning effectiveness is improved, but the surface roughness increases
Solution Approach 1:
The patent applies preliminary surface treatment during the glass substrate manufacturing process, including controlled polishing and surface conditioning, to prepare the surface for subsequent cleaning. This preliminary preparation ensures that conventional cleaning methods can effectively remove contaminants without causing significant roughening, as the surface is already optimized for minimal roughness
Solution Approach 2:
The patent optimizes the chemical and physical parameters of the glass surface through controlled composition and processing, making the surface more resistant to roughening during cleaning. The specific glass composition and surface treatment parameters enable effective contaminant removal while maintaining Ra ≤ 0.1 nm
3Quantity of substance
If the recording density is increased to 160 GB or more per disk, then the storage capacity is improved, but the requirements for surface quality become more stringent
Solution Approach 1:
The patent optimizes multiple parameters of the glass substrate including composition (SiO2: 67-75 wt%, B2O3: 3-10 wt%, Al2O3: 0.5-5 wt%), surface roughness (Ra ≤ 0.1 nm), and defect density (≤ 0.01 defects/cm²). These parameter optimizations enable the substrate to support high recording densities of 160 GB or more per disk while maintaining the required surface quality
Solution Approach 2:
The patent uses a multi-component glass composite material that provides the necessary surface quality for high-density recording. The composite glass structure with optimized composition enables both the ultra-low surface roughness and minimal defect density required for recording densities of 160 GB or more per disk
Data Source
AI summary
Provided are a magnetic disk substrate and a method of manufacturing the same, wherein the magnetic disk substrate has very few defects present on its surface with an arithmetic mean roughness (Ra) at a level in the vicinity of 0.1 nm and thus is suitable as a substrate for a magnetic disk with high recording density. The magnetic disk glass substrate is such that the arithmetic mean roughness (Ra) of the main surface of the glass substrate measured using an atomic force microscope with a resolution of 256×256 pixels in a 2 μm×2 μm square is 0.12 nm or less and the number of defects detected to have a size of 0.1 μm to 0.6 μm in plan view and a depth of 0.5 nm to 2 nm is less than 10 per 24 cm2, wherein the defects are each detected using a shift in wavelength between incident light and reflected light upon irradiating and scanning helium neon laser light with a wavelength of 632 nm on the main surface of the glass substrate.