Thermal Fly-Height Control Write Pole Positioning in TAR Drives
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Solution Overview
Problem
In thermally-assisted recording (TAR) disk drives with thermal fly-height control (TFC), maintaining optimal write pole fly-height during writing operations is challenging due to heat-induced protrusion and retraction of the write pole, leading to potential data errors if the fly-height is not correctly managed.
Innovation Solution
The write current is turned on prior to heating the recording layer, and the thermal fly-height control power is adjusted to ensure the write pole reaches its optimal position before heat is applied, combining write current and heat to maintain the optimal fly-height for writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the write current is turned on during heating of the recording layer, then writing can be performed, but the write pole fly-height becomes unstable due to thermal expansion and contraction
Solution Approach 1:
The write current is turned on before the heating cycle begins, allowing the write pole to expand to its optimal position in advance. This preliminary action ensures that when heating starts and causes thermal expansion, the write pole is already at the correct fly-height, preventing instability during the critical writing phase.
Solution Approach 2:
The system anticipates the thermal expansion that will occur during heating by pre-positioning the write pole through premature application of write current. This cushioning effect compensates for the upcoming thermal changes, ensuring stable fly-height throughout the heating and writing process.
2Reliability
If thermal fly-height control power is reduced to compensate for write pole protrusion, then fly-height can be maintained, but the optimal fly-height is achieved too late for reliable writing
Solution Approach 1:
Instead of waiting for thermal expansion to occur and then reducing TFC power to compensate, the system applies write current before heating starts. This preliminary action causes the write pole to expand to its optimal position in advance, eliminating the time delay associated with post-heating fly-height adjustment.
Solution Approach 2:
The conventional approach is to reduce TFC power after heating to compensate for protrusion. The invention inverts this sequence by applying write current before heating, using the write current itself to establish the optimal fly-height rather than relying on subsequent TFC power reduction.
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 method ensures accurate and reliable writing by maintaining the optimal write pole fly-height, reducing the likelihood of data errors and improving writing performance in TAR disk drives with TFC.
Implementation Method 1
a magnetic field from the write head to lower the coercivity enough for writing to occur
Implementation Method 2
a laser source and an optical waveguide coupled to a near-field transducer (NFT) for heating the recording material on the disk
Implementation Method 3
The NFT is typically located at the air-bearing surface (ABS) of the air-bearing slider that also supports the read/write head and rides or 'files' above the disk surface
Implementation Method 4
When current is applied to the heater the heater expands and causes the head to expand and thus move closer to the disk surface
Implementation Method 5
the coercivity of the magnetic material of the recording layer on the disk is temperature dependent
Implementation Method 6
The slider has a disk-facing air-bearing surface (ABS) that causes the slider to ride on a cushion or bearing of air generated by rotation of the disk
Data Source
AI summary
A thermally-assisted recording (TAR) disk drive operates by turning on write current prior to the application of heat to the recording layer by the near-field transducer (NFT). In a TAR disk drive that uses thermal fly-height control (TFC), TFC power is at a first power level that keeps the write pole at a predetermined fly-height. The write current is then turned on, either simultaneously with or after a reduction in TFC power. The write pole then reaches its optimal fly-height as a result of the combination of write pole protrusion caused by the write current and retraction of the write pole caused by the reduction in TFC power. After the write pole has reached its optimal fly-height, heat is applied to the recording layer by the NFT. The combination of write current and heat causes writing to occur at the optimal write pole fly-height.