Magnetic-Disk Glass Substrate Wavelength-Specific Roughness Control

The patent applies different surface roughness requirements to different wavelength components. Specifically, it controls the arithmetic mean roughness Ra for wavelength components of 10 to 50 nm to be 0.15 nm or less, while allowing other wavelength ranges to have different roughness characteristics. This localized control of surface quality at specific wavelength ranges resolves the contradiction by preventing magnetic head collision (requiring smooth surface) while maintaining crystalline orientation dispersion control (requiring specific roughness characteristics for magnetic particle alignment).

The patent changes the parameter specification from general surface roughness to wavelength-component-specific roughness. By introducing the wavelength range (10 to 50 nm) as a controlling parameter and setting Ra ≤ 0.15 nm for this specific range, the patent achieves both substrate reliability and controlled crystalline orientation dispersion. This parameter differentiation allows independent optimization of surface smoothness for collision prevention while maintaining magnetic particle orientation quality.

The patent focuses surface roughness control on the specific wavelength range of 10 to 50 nm, which is critical for magnetic particle orientation at high recording densities. By applying localized quality control to this wavelength range rather than uniformly across all wavelengths, the patent enables higher storage capacity while maintaining manufacturability and SNR performance.

The patent introduces wavelength-range-specific parameter control (Ra ≤ 0.15 nm for 10-50 nm wavelengths) to address the difficulties in surface roughness control at high recording densities. This parameter specification enables precise control of magnetic particle orientation even as recording density increases, thereby maintaining SNR while achieving higher storage capacity.

The patent applies local quality control by specifying surface roughness requirements only for the wavelength range of 10 to 50 nm, which is sufficient to prevent magnetic head collision while allowing other surface characteristics to remain within acceptable ranges. This localized approach enables safer operation with projected magnetic head elements.

The patent changes the surface roughness parameter specification to target the critical wavelength range (10-50 nm) that affects collision risk. By setting Ra ≤ 0.15 nm for this specific wavelength range, the patent reduces collision probability while maintaining the accuracy benefits of reduced flying height through other means.