HAMR Write Head Dual Waveguide Fly-Height Sensing
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Solution Overview
Problem
Current HAMR disk drives lack an accurate method for in-drive fly-height measurement, which is crucial for maintaining recording performance and reliability, especially as fly-heights approach below 10 nm, and existing methods using the read head are not precise due to the distance between the read and write heads.
Innovation Solution
A system with a primary waveguide directing laser light to a near-field transducer and a second waveguide with a sensor portion optically coupled to the primary waveguide for reflecting light from the disk, allowing for precise measurement of the spacing between the air-bearing surface and the disk, using a detector to provide a signal for fly-height adjustment or write inhibition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the read head is used to calculate fly-height from readback signal, then fly-height measurement is possible, but measurement precision deteriorates due to distance between read and write heads
Solution Approach 1:
The write head's near-field transducer and waveguide structure are made to serve dual functions: both writing data to the disk and sensing fly-height through optical reflection measurement, eliminating the need for a separate read head for measurement purposes
Solution Approach 2:
The sensing function is merged with the write head assembly by utilizing the existing near-field transducer and waveguide structure for both data writing and fly-height measurement, placing the sensor at the same location as the write head
2Productivity
If fly-height is reduced to below 10 nm for improved recording performance, then recording density improves, but reliability deteriorates due to lack of accurate fly-height control
Solution Approach 1:
The system continuously measures fly-height using optical reflection at the write head location and provides feedback control to maintain precise spacing, enabling reliable operation at ultra-low fly-heights below 10 nm through active stabilization
Solution Approach 2:
The mechanical fly-height control is supplemented or replaced with optical sensing and control systems that use light reflection measurements to detect and regulate the spacing between the write head and disk surface with nanometer precision
3Measurement precision
If a second waveguide sensor is added to the slider for fly-height measurement, then measurement precision improves, but device complexity increases
Solution Approach 1:
The second waveguide structure serves multiple functions: it acts as both an optical sensor for fly-height measurement and integrates with the existing HAMR write head assembly, reducing the need for completely separate sensing systems
Solution Approach 2:
The second waveguide sensor is integrated within or alongside the primary waveguide structure of the write head, nesting the sensing function within the existing data writing infrastructure to minimize additional complexity
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
Enables accurate fly-height measurement and control, improving recording performance and reliability by ensuring the write head maintains optimal spacing, preventing data loss and enhancing thermal stability of recorded bits.
Implementation Method 1
a second waveguide with a sensor portion optically coupled to the primary waveguide for receiving light reflected from the disk
Implementation Method 2
The second waveguide has an output end for providing the signal to the detector
Data Source
AI summary
A heat-assisted magnetic recording (HAMR) disk drive with a primary waveguide that directs laser light from a laser diode to a near-field transducer includes a second waveguide for sensing the head-disk spacing or fly-height. The second waveguide has a sensor portion that senses the spacing and directs light representative of the spacing to the second waveguide's output end. The second waveguide may include a second or reference portion that is connected to the sensor portion and directs light representative of light input from the laser diode. The combined light from the two portions is directed to the second waveguide's output end. A detector, which may be a photo-diode, is located at the second waveguide's output end and provides a signal that may be coupled to a thermal fly-height controller to increase or decrease the fly-height.