Glass Substrate Surface Roughness Gradient for Fly Stiction Prevention
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Solution Overview
Problem
Conventional glass substrates for magnetic disks fail to adequately prevent fly stiction phenomenon at nanosized fly heights, leading to unstable magnetic head operation and potential head crashes, especially in smaller HDDs where increased surface roughness and waviness control are insufficient.
Innovation Solution
A glass substrate with specific surface roughness and waviness characteristics, where Ra1≦0.8 nanometer, 0 nanometer<Ra1−Ra2≦0.2 nanometer, Wa1≦0.6 nanometer, and 0 nanometer<Wa2−Wa1≦0.2 nanometer, is employed to control air molecule interactions and substrate shape characteristics over wider ranges, preventing fly stiction by optimizing the surface and waviness in annular areas of the glass substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the fly height is reduced to increase information recording density, then the S/N ratio improves and recording density increases, but fly stiction phenomenon occurs frequently causing unstable operation and potential head crashes
Solution Approach 1:
The patent applies local quality by creating different surface roughness characteristics at different radial positions of the glass substrate. Specifically, the inner circumferential surface is made smoother (Ra1) than the outer circumferential surface (Ra2), with Ra1-Ra2 being controlled within 0.05-0.2 nm. This localized variation in surface quality optimizes the balance between fly height control and prevention of fly stiction at different locations on the disk surface.
Solution Approach 2:
The patent changes the surface roughness parameter across the substrate by controlling the difference in average surface roughness between inner and outer circumferential surfaces. By precisely controlling Ra1-Ra2 within 0.05-0.2 nm and ensuring both values are below 0.5 nm, the invention modifies the physical parameters of the substrate surface to prevent fly stiction while maintaining nanosized fly height stability.
2Volume of moving object
If the magnetic disk size is reduced for portable devices, then device size decreases and portability improves, but relative linear velocity between magnetic head and disk decreases causing fly stiction
Solution Approach 1:
For downsized magnetic disks, the patent applies local quality by implementing non-uniform surface roughness distribution across the reduced disk area. The inner circumferential surface is made smoother than the outer surface, creating localized optimization that compensates for the reduced overall disk size and lower rotational velocities, thereby preventing fly stiction in compact HDD designs.
Solution Approach 2:
The patent changes the surface roughness parameters specifically for downsized disks by controlling Ra1 and Ra2 to be below 0.5 nm with a difference of 0.05-0.2 nm. This parameter optimization is tailored to the reduced dimensions of portable HDDs, enabling stable nanosized fly height operation even at lower relative linear velocities.
3Ease of manufacture
If conventional surface roughness control is applied, then manufacturing is simpler, but fly stiction cannot be sufficiently prevented at nanosized fly heights
Solution Approach 1:
The patent applies local quality by implementing differentiated surface roughness control at inner and outer circumferential regions. This allows standard polishing processes to naturally create the desired roughness gradient, maintaining ease of manufacture while achieving superior fly stiction prevention through the inherent variations in surface quality across the disk surface.
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
The controlled surface roughness and waviness effectively reduce the adhesion of the magnetic head, preventing fly stiction and ensuring stable operation even in downsized HDDs, enhancing the reliability of magnetic recording and reproduction.
Implementation Method 1
The controlled surface roughness and waviness effectively reduce the adhesion of the magnetic head, preventing fly stiction
Data Source
AI summary
A glass substrate for a magnetic disk satisfies Ra1≦0.8 [nm], 0 [nm]≦Ra1−Ra2≦0.2 [nm], Wa1≦0.6 [nm], and 0 [nm]≦Wa2−Wa1≦0.2 [nm]. Ra1 is an average surface roughness of a first annular area between 1 mm and 3 mm outward from an inner periphery of a main surface of the glass substrate, Ra2 is an average surface roughness of a second annular area between 1 mm and 3 mm inward from an outer periphery of the main surface, Wa1 is an average waviness of the first area in a circumferential direction of the glass substrate having a cycle of 300 μm to 5 mm, and Wa2 is an average waviness of the second area in the circumferential direction having a cycle of 300 μm to 5 mm.