Low fly-height slider design for load/unload

Intermolecular and surface forces contribute significantly to the total forces acting on air bearing sliders for flying heights below 5 nm. Their contributions to the total force increase sharply with the reduction in flying height, and hence their existence can no longer be ignored in air bearing simulation for hard disk drives. Various experimentally observed dynamic instabilities can be explained by the inclusion of these forces in the model for low flying sliders. In this paper parametric studies are presented using a 3-DOF model to better understand the effect of the Hamaker constants, suspension pre load and pitch angle on the dynamic stability/instability of the sliders. A stiffness matrix is used to characterize the stability in the vertical, pitch, and roll directions. The fly height diagrams are used to examine the multiple equilibriums that exist for low flying heights. It has been found that the system instability increases as the magnitude of the van der Waals force increases. It has also been found that higher suspension pre load and higher pitch angles tend to stabilize the system.

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Analog Frontend for Tribo-Current-Based Fly-Height Sensor for Magnetic Hard Disk Drive

IEEE Transactions on Circuits and Systems I Regular Papers ◽

10.1109/tcsi.2017.2725961 ◽

2018 ◽

Vol 65 (2) ◽

pp. 556-566

Author(s):

Arup Polley ◽

Pankaj Pandey ◽

Bryan E. Bloodworth ◽

Costin Cazana

Keyword(s):

Hard Disk Drive ◽

Hard Disk ◽

Disk Drive ◽

Magnetic Hard Disk ◽

Fly Height

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HDI-32 WEAR MODELING OF THE HEAD/DISK INTERFACE AT LOW FLY HEIGHT

Proceedings of JSME-IIP/ASME-ISPS Joint Conference on Micromechatronics for Information and Precision Equipment IIP/ISPS joint MIPE ◽

10.1299/jsmemipe.2003.253 ◽

2003 ◽

Vol 2003 (0) ◽

pp. 253-254

Author(s):

Peng Wei ◽

Yiao Tee Hsia

Keyword(s):

Head Disk Interface ◽

Disk Interface ◽

Wear Modeling ◽

Fly Height

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Performance Optimization of Thermal Nano-Actuator for Fly Height Control in Disk Drives

ASME/STLE 2009 International Joint Tribology Conference ◽

10.1115/ijtc2009-15137 ◽

2009 ◽

Author(s):

Haisan Tan ◽

Bo Liu ◽

Mingsheng Zhang ◽

Shengkai Yu

Keyword(s):

Performance Optimization ◽

Power Input ◽

Vertical Position ◽

Disk Drives ◽

Height Control ◽

Line Spacing ◽

Simulation Results ◽

Heater Design ◽

Fly Height ◽

Actuator Design

Slider with thermal fly height control (TFC) uses a thermal heater to produce localized thermal protrusion and adjust the vertical position of the read/write head. This paper reports authors’ efforts in exploring large protrusion stroke with minimal heater power input whilst preserving heater robustness in the TFC slider, with an optimized thermal nano-actuator design. Effects of both heater line width and line spacing on TFC slider performances are investigated. A novel ‘Stream-River’ heater design approach is proposed. Simulation results conclude that the “Stream-River” approach is of both high power-protrusion efficiency and high heater robustness.

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Ranking of Thermal Asperity (TA) Interaction During Seeking Under Various Fly-Height Conditions

ASME 2020 29th Conference on Information Storage and Processing Systems ◽

10.1115/isps2020-1962 ◽

2020 ◽

Author(s):

Abhishek Srivastava ◽

Bernd Lamberts ◽

Ning Li ◽

Bernhard Knigge

Keyword(s):

Theoretical Analysis ◽

State Interaction ◽

Idle State ◽

Height Control ◽

Interaction Mechanisms ◽

Industry Standard ◽

Maximum Benefit ◽

Protection Mechanisms ◽

Fly Height ◽

Experimental Corroboration

Abstract HDD heads have various interaction mechanisms with thermal asperities (TAs), and protection mechanisms need to be put in place to ensure the head-disk interaction (HDI) resulting from them is eliminated or minimized to the highest extent possible. It is straightforward to not allow the head sit-on-track on cylinders that have such TAs on them, and the same principle can be extended to so-called high TAs (HTAs), whose height is more than the fly height of the head, so heads do not inadvertently interact with the TA even when motion is triggered on another head, since the entire head stack moves together. Similar TA interactions also occur when the head seeks across the tracks. Typical short seeks have thermal fly-height control (TFC) turned on while it is turned on during long seeks, which is greater than a few hundred tracks. Heads can also interact with TAs during retract and arrival of the head during such long seeks. Finally, background media scan (BGMS), which is an industry standard, when the drive enters an idle state. Interaction with HTAs can also occur when the drive enters such a state. Typical seek avoidance attempts to eliminate TA interaction during seeking, however it is not straightforward to determine which of the seek mechanism: TFC On during short seeks, retract/arrival during long seeks, HTA interaction during long seeks with TFC off, or idle TA interaction causes the greatest HDI. Through theoretical analysis and experimental corroboration, this paper intends to rank the various modes of TA interaction, so by developing features for eliminating or minimizing them in that order could help bring the maximum benefit for achieving minimum lifetime reduction of the head due to such interaction.

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A Method to Reduce Head-Disk Interface (HDI) Degradation Risk During Thermal Asperity (TA) Mapping in a Hard Disk Drive

ASME 2020 29th Conference on Information Storage and Processing Systems ◽

10.1115/isps2020-1960 ◽

2020 ◽

Author(s):

Abhishek Srivastava ◽

Rahul Rai ◽

Karthik Venkatesh ◽

Bernhard Knigge

Keyword(s):

Hard Disk Drive ◽

Bias Voltage ◽

Disk Drive ◽

Test Time ◽

Head Disk Interface ◽

Disk Interface ◽

Height Control ◽

Contact Sensor ◽

Fly Height ◽

Sample Set

Abstract One of the issues in thermal asperity (TA) detection using an embedded contact sensor (ECS) is the degradation caused to the read/write elements of the head while interacting with the TA. We propose a method to reduce such head-disk interaction (HDI) during TA detection and classification by flying higher at low thermal fly-height control (TFC) power, which minimizes the interaction of the TA with the head. The key idea is to scan the head at higher fly height, but with higher ECS bias voltage. Initial experiments have shown that the TA count follows a negative cubic relationship with the backoff at various bias levels, and that it follows a square relationship with bias at various backoff levels. Using a sample set, the calibration curves i.e. the golden relationship between these parameters can be established. Using these, one can start the TA detection at the highest backoff and high ECS bias, and start to estimate the nominal TA count. By mapping out these TAs and ensuring the head does not fly over them again to prevent HDI, the fly height can then be lowered, and the rest of the TA cluster can be scanned. Following this method iteratively, the entire TA cluster can be mapped out with minimal interaction with the head. Although this method entails an increase in the test time to detect and map all TAs, compared to detecting them with TFC being on, this can help improve the reliability of the drive by protecting the sensitive read/write elements especially for energy assisted recording from HDI.

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