Glass Substrate Roll-off Control for Magnetic Head Stability
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Solution Overview
Problem
The magnetic head experiences unstable floating due to air flow disturbances from the shape of the outer peripheral end surface of the information recording medium, leading to reduced recording density and increased risk of head crashes.
Innovation Solution
The information recording medium glass substrate is designed with specific roll-off values and variations at different radial positions, and an inclined surface near the outer peripheral end surface, optimizing the shape to minimize air flow disturbances and ensure stable magnetic head floating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the floating height is reduced to increase recording density, then the S/N ratio of received signal is improved and recording density increases, but the magnetic head becomes more susceptible to air flow disturbances and head crashes
Solution Approach 1:
The invention applies local quality by creating a specific inclined surface structure only at the outer peripheral end surface region of the glass substrate, while maintaining different flatness specifications at different radial positions. The inclined surface is formed within a specific radial distance range (0.3mm to 1.5mm from the outer peripheral end surface), making the air flow control function localized to where it is most needed during head transition, without affecting the overall substrate properties
Solution Approach 2:
The invention uses curvature by forming an inclined surface with a specific gradient (0.02 to 0.2 mm/mm) at the outer peripheral end surface. This curved/angled transition surface modifies the air flow pattern during head entry, preventing sudden air flow disturbances that would occur with a sharp edge, thereby reducing glide avalanche while maintaining stable floating at low heights
2Measurement precision
If the floating height is reduced to improve S/N ratio, then signal quality increases, but the risk of head crash increases due to surface irregularities
Solution Approach 1:
The invention implements local quality control by specifying different flatness tolerances at different radial positions on the glass substrate. The region within 1.5mm from the outer peripheral end surface is controlled to have flatness of 0.3µm or less, while other regions have looser flatness requirements of 1.0µm or less. This localized precision control ensures smooth head entry without unnecessary manufacturing complexity across the entire substrate
Solution Approach 2:
The inclined surface is formed in advance during glass substrate manufacturing, creating a pre-conditioned entry path for the magnetic head. This preliminary structural modification ensures that when the head transitions from retracted to recording position, it encounters a gradual air flow transition rather than sudden disturbances, preventing glide avalanche before it can occur
3Reliability
If the outer peripheral end surface shape is optimized to reduce air flow disturbance, then magnetic head floating stability improves, but manufacturing complexity increases
Solution Approach 1:
The invention controls specific geometric parameters of the outer peripheral end surface: the inclined surface gradient is maintained between 0.02 to 0.2 mm/mm, and the radial width of the inclined surface region is controlled to be 0.3mm to 1.5mm from the outer peripheral end surface. These quantified parameter ranges provide clear manufacturing targets that balance performance improvement with manufacturing feasibility
Solution Approach 2:
The inclined surface creates a controlled curvature/gradient at the outer peripheral end, transitioning from the flat recording surface to the edge. This curved transition with specific gradient parameters (0.02 to 0.2 mm/mm) modifies air flow patterns to prevent glide avalanche, while the gradual nature of the curvature makes it compatible with standard glass polishing and finishing processes
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 design prevents air flow disturbances, allowing for stable magnetic head floating and high-density data recording with a recording density of 500 Gbit/inch² or more, reducing the risk of head crashes and improving data storage efficiency.
Implementation Method 1
A DFH (Dynamic Flying Height) mechanism is employed in information recording devices in order to increase the recording density. The distance (hereinafter referred to as 'floating height') between the magnetic head and the outermost surface
Implementation Method 2
When entering the recording surface of the information recording medium from the retracted position, the magnetic head is likely to be affected by air flow disturbance resulting from the shape of the outer peripheral end surface
Data Source
AI summary
An information recording medium glass substrate and an information recording medium are provided in which a first roll-off variation and a second roll-off variation fall within the following ranges: 180 Å≦first roll-off variation≦990 Å (condition 1) and 650 Å≦second roll-off variation≦3700 Å (condition 2).