Correlation of Disk Topography Waves With Nanometer Scale Lubricant Moguls

2017 ◽  
Author(s):  
Andrey Ovcharenko ◽  
Tom Karis ◽  
Jih-Ping Peng
Keyword(s):  
Shear Stress ◽  
Surface Topography ◽  
Areal Density ◽  
Disk Surface ◽  
Peak Height ◽  
Lubricant Thickness ◽  
Height Control ◽  
Magnetic Performance ◽  
Carbon Overcoats ◽  
Fly Height

Magnetic recording disk carbon overcoats are lubricated with nanometer thick films of perfluoropolyether lubricant. It is well-known that lubricant thickness redistribution takes place due to air shear stress oscillation at air bearing resonant frequencies and also due to shear stress oscillation induced by disk topography waves on test tracks. We extended this work to demonstrate correlation between surface topography and lubricant redistribution on whole disk surfaces. Lubricant moguls are shown to form over regions of the disk surface which have topography waves that are half the slider length, and the lubricant thickness peak is out of phase down track from the topography peak height. There is a critical relative humidity above 20% beyond which moguls are readily formed by the slider flying at 10 nm without thermal fly height control. The significance of the lubricant redistribution for drive magnetic performance has long been the subject of debate. These results demonstrate that lubricant thickness redistribution on the order of atomic diameters can degrade magnetic performance, and that the surface topography waves alone can degrade areal density by as much as 2%.

Experimental and Numerical Investigation of Dynamic Instability in the Head Disk Interface at Proximity

2005 ◽  
Vol 127 (3) ◽  
pp. 530-536 ◽  
Author(s):  
Rohit Ambekar ◽  
Vineet Gupta ◽  
David B. Bogy
Keyword(s):  
Dynamic Instability ◽  
Hard Disk Drives ◽  
Areal Density ◽  
Simulation Software ◽  
Flying Height ◽  
Stable Fly ◽  
Lubricant Thickness ◽  
Disk Interface ◽  
The Difference ◽  
Fly Height

As the flying height decreases to achieve greater areal density in hard disk drives, different proximity forces act on the air bearing slider, which results in fly height modulation and instability. Identifying and characterizing these forces has become important for achieving a stable fly height at proximity. One way to study these forces is by examining the fly height hysteresis, which is a result of many constituent phenomena. The difference in the touchdown and takeoff rpm (hysteresis) was monitored for different slider designs, varying the humidity and lubricant thickness of the disks, and the sliders were monitored for lubricant pickup while the disks were examined for lubricant depletion and modulation. Correlation was established between the observed hysteresis and different possible constituent phenomena. One such phenomenon was identified as the Intermolecular Force from the correlation between the lubricant thickness and the touchdown velocity. Simulations using 3D dynamic simulation software explain the experimental trends.

A Method for Characterizing the Head-Disk Interface Dynamics Near the Touchdown Conditions Using the Magnetic Fly-Height

2020 ◽  
Author(s):  
Rahul Rai ◽  
Abhishek Srivastava ◽  
Bernhard Knigge ◽  
Aravind N. Murthy
Keyword(s):  
Hard Disk Drives ◽  
Areal Density ◽  
Disk Surface ◽  
Disk Drives ◽  
Head Disk Interface ◽  
Soft Contact ◽  
Disk Interface ◽  
Magnetic Spacing ◽  
Bearing Stiffness ◽  
Fly Height

Abstract Recent growth in the cloud storage industry has created a massive demand for higher capacity hard disk drives (HDD). A sub-nanometer head media spacing (HMS) remains the most critical pre-requisite to achieve the areal density needed to deliver the next generation of HDD products. Designing a robust head-disk interface (HDI) with small physical clearance requires the understanding of slider dynamics, especially when the head flies in proximity to the disk surface. In this paper, we describe a method using the magnetic read-back signal to characterize the head fly-height modulations as it undergoes a transition from a free-flying state to soft contact with the disk surface. A technique based on the magnetic fly-height sensitivity is introduced for the identification of the transition plane that corresponds to the onset of the touchdown process. Additionally, the proposed magnetic spacing based meteorology is used to study the effect of the air bearing stiffness on the magnitude of the slider vibrations induced by intermittent head-disk interactions. The information about the minimum spacing while maintaining the stable flying conditions can help in reducing the head-disk interaction risk that can enable a low clearance interface.

A Method to Measure the Media Lubricant Loss After HAMR Recording

2016 ◽  
Author(s):  
Dongbo Li ◽  
Shaomin Xiong ◽  
David Braunstein ◽  
Xingcai Guo ◽  
Sripathi Canchi ◽  
...  
Keyword(s):  
Hard Disk Drives ◽  
Areal Density ◽  
Disk Surface ◽  
Thickness Variation ◽  
Laser Exposure ◽  
Lubricant Thickness ◽  
Thickness Change ◽  
Force Microscopy ◽  
Magnetic Switching ◽  
The Media

Heat assisted magnetic recording (HAMR) is anticipated to increase the areal density in hard disk drives to multiple Tb/in2. During HAMR recording, as a near filed laser light heats the media to the temperature above Curie point to assist magnetic switching, the lubricant that is typically applied to the disk surface will be under an intensive thermal stress, which will lead to the lubricant desorption and/or decomposition, and frequently accompanied with the underneath carbon overcoat (COC) graphitization and oxidation. Due to the optical properties change of the COC at such a high temperature, the traditional optical techniques are not appropriate to measure the lubricant thickness post HAMR recording. In this paper, we introduce a new method based on atomic force microscopy (AFM) in different imaging modes to detect the lubricant and also COC thickness change as a result of laser heating with a vertical resolution at the angstrom scale. Using AFM in a soft tapping mode, we can also characterize the lubricant thickness variation with time after laser exposure, which enables the measurement of the lubricant reflow kinetics on HAMR media.

Experimental and Numerical Investigation of Dynamic Instability in the Head Disk Interface at Proximity

2004 ◽  
Author(s):  
Rohit Ambekar ◽  
Vineet Gupta ◽  
David B. Bogy
Keyword(s):  
Dynamic Instability ◽  
Hard Disk Drives ◽  
Areal Density ◽  
Simulation Software ◽  
Flying Height ◽  
Stable Fly ◽  
Lubricant Thickness ◽  
Disk Interface ◽  
The Difference ◽  
Fly Height

As the flying height decreases to achieve greater areal density in hard disk drives, different proximity forces act on the air bearing slider, which results in fly height modulation and instability. Identifying and characterizing these forces has become important for achieving a stable fly height at proximity. One way to study these forces is by examining the fly height hysteresis, which is a result of many constituent phenomena. The difference in the touchdown and takeoff rpm (hysteresis) was monitored for different slider designs, varying the humidity and lubricant thickness of the disks, and the sliders were monitored for lubricant pickup while the disks were examined for lubricant depletion and modulation. Correlation was established between the observed hysteresis and different possible constituent phenomena. One such phenomenon was identified as the Intermolecular Force from the correlation between the lubricant thickness and the touchdown velocity. Simulations using 3D dynamic simulation software explain the experimental trends.

Understanding Instabilities of TFC Femto-Slider and Pico-Slider via Surface Force Theory

2018 ◽  
Author(s):  
Kyosuke Ono
Keyword(s):  
Dynamic Instability ◽  
Surface Force ◽  
Disk Surface ◽  
Adhesive Contact ◽  
Contact Theory ◽  
Height Control ◽  
Meniscus Force ◽  
Static Instability ◽  
Vdw Force ◽  
Fly Height

We formulated the surface pressure of a disk surface that consists of three layers of diamond-like-carbon (DLC) as well as bonded and mobile lubricants based on the asperity adhesive contact theory. We demonstrated that this surface force could well evaluate the touchdown behaviors of a thermal fly-height control (TFC) slider. This theory shows that the touchdown behaviors of a current TFC femto-slider are mainly governed by the asperity meniscus force rather than the van der Waals force (vdW). However, it is shown that the static instability of a pico-slider was generated from the vdW force. Moreover, it is estimated that the dynamic instability of the pico-slider was mainly caused by the meniscus force rather than the vdW force. This surface force theory can allow us to understand consistently various phenomena of slider dynamics.

An Insight Into the Nonlinear Touchdown Dynamics of TFC Active Slider

2013 ◽  
Author(s):  
Gang (Sheng) Chen ◽  
Jianfeng Xu ◽  
J.-Y. Chang
Keyword(s):  
Nonlinear Dynamics ◽  
Hard Disk Drives ◽  
Disk Surface ◽  
Flying Height ◽  
Disk Drives ◽  
Height Control ◽  
Intermittent Contact ◽  
Fly Height ◽  
Insight Into ◽  
Small Spacing

Storage of 10 Tb/in 2 in hard disk drives within the next decade requires a significant change to reduce the physical spacing as little as 0.25 nm at the read-write transducer location. A lot of tribology issues exist to such a low flying height, the touch down and take off instability and hysteresis, the flying height avalanche, the influences of surface topography and morphology, the lubricant modulation and pick-up, robust air bearing surface and suspension design, just to name a few. Understandings of the complex tribo-dynamics issues in the near contact and contact states are very important to further reduce the flying height. At such a small spacing intermittent contact between the slider and disk surface becomes inevitable and the current MEMS-based thermal fly-height control (TFC) technology needs further improvement to satisfy the future needs. How to control the slider to reduce touchdown instability and eventually eliminate bouncing has been a pressing and challenging research topic. Most of existing work on touchdown dynamics applied conventional nonlinear dynamics theory and spectrum as well as harmonics analysis, which could suffer from the assumptions of small nonlinearity and stationary. This study presents a concurrence plot and Lyapunov exponent analysis which could offer an insight to the problem in the context of contemporary nonlinear dynamics theory.

Characterization of TMR Head Durability against Lapping Based on Magnetic Performance

2012 ◽  
Vol 523-524 ◽  
pp. 961-966
Author(s):  
Hideaki Tanaka ◽  
Yukio Maeda
Keyword(s):  
Ion Beam ◽  
Hysteresis Loops ◽  
Areal Density ◽  
Noise Spectrum ◽  
Crystallographic Analysis ◽  
Magnetic Characteristics ◽  
Ion Beam Etching ◽  
Verification Method ◽  
Magnetic Performance

Magnetic recording technologies are continuing to advance toward higher areal densities, driven by the availability of tunneling magnetoresistive (TMR) heads. However, high areal density heads require smaller physical dimensions, and this can render TMR heads more vulnerable to mechanical stresses generated during the lapping process. Although is important to verify the durability of TMR heads against lapping, it is very difficult to perform a crystallographic analysis of the affected layer because of the small dimensions involved. In this study, we attempted to establish an advanced TMR head verification method based on a magnetic performance analysis involving micro-Kerr hysteresis loops and the magnetic noise spectrum. We found that the magnetic performance changed when nanoscale scratches were removed from the lapped surface using ion beam etching. This indicates that the lapping process produces an affected layer which deteriorates the magnetic characteristics of the TMR head. A correlation was also found between the change in magnetic performance and the morphology of lapped surface.

Time-Frequency Analysis of Slider Dynamics and the Effect of Lubricant

2002 ◽  
Author(s):  
Saurabh K. Deoras ◽  
Frank E. Talke
Keyword(s):  
Frequency Analysis ◽  
Disk Surface ◽  
Air Bearing ◽  
Lubricant Film Thickness ◽  
Lubricant Thickness ◽  
Laser Doppler Vibrometry ◽  
Time Frequency Analysis ◽  
Time Frequency ◽  
Pitch Frequency ◽  
Transient Events

The dynamics of pico sliders is investigated during scratch impact using laser Doppler vibrometry. Airbearing frequencies and damping of the pitch frequency are studied as a function of disk velocity for lubricant thickness values of 1.6nm, 1.0nm and 2.0nm. In addition, time-frequency analysis is used to study transient events during slider-scratch impact. The results indicate that the slider dynamics is not only a function of the design of the air-bearing, but also of the velocity and the characteristics of the lubricant film thickness on the disk surface.

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

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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