Peter Michael Baumgart

Will the numbers add up for sub-7-nm magnetic spacings? Future metrology issues for disk drive lubricants, overcoats, and topographies

To achieve disk drive recording densities greater than one terabit per square inch, future head-media spacings (HMSs) will need to be less than 7 nm. This will place severe demands on the metrology tools used to measure the thickness and topographies of the contributors to the head-media spacing. Here, we first review some of the metrologies used for characterizing overcoats, lubricants, and topographies and discuss some of the limits that will make it difficult to achieve a sub-7-nm HMS. We next show new results for measuring lubricant redistribution on disk surfaces after contact with a small pad on the slider and present a new method for determining wear rates of these slider contact pads.

Numerical and Experimental Analyses of Nanometer-Scale Flying Height Control of Magnetic Head With Heating Element

Hard drives featuring sliders with active flying-height (FH) control using thermal expansion of a heating element have been recently introduced in products. This approach allows to actively compensate for static FH variations and achieves sub-3-nm clearance during read/write operation. This paper describes a nonlinear numerical model of a perpendicular magnetic recording head for accurate simulation of pole-tip protrusions and their effect on FH change under various conditions, such as at an elevated drive temperature, with the heater activated or during write operation. The model integrates an electrical-thermomechanical finite-element model of slider and a full air-bearing solver, and includes lapped pole-tip recession and slider/disk deformation due to air-bearing pressure. We are able to predict key parameters that are not easily measurable (e.g., minimum/reader/writer FH, different protrusion profiles for ambient temperature, heater actuation, and during writing). We also present novel experimental methods for measuring protrusion and clearance delta profiles with angstrom-level resolution. The modeling results are compared to experimental data under various test conditions showing excellent agreement. From this method, we are able to quickly evaluate and optimize different heater, head, and ABS designs.

Dynamics of contacting head-disk interfaces

We have successfully designed, fabricated, and tested contact recording sliders where most of the suspension load is supported by an air-bearing surface with only a small contact force (<5 mN) acting on the rear contact pad. To understand the contact dynamics, we have developed an integrated approach where experimental results from friction and laser doppler vibrometry are modeled using an air-bearing code modified to include contact forces. A low bounce (<1 nm mean-to-peak) is achieved in our designs by reducing the real area of contact to minimize friction, by increasing disk roughness, and/or by reducing the width of the slider contact pad. Due to the reduced magnetic spacing, these contact recording heads have bit-error rates several orders lower than conventional flying heads.

Influence of contact potential on slider-disk spacing: simulation and experiment

As slider-to-disk spacing becomes smaller than 10 nm, electrostatic and intermolecular forces become increasingly important. Even if the slider and disk are both grounded, a potential difference can exist between them due to the contact potential, which, as we show here, can generate an electrostatic force greater than the van der Waals force. We have developed a method for measuring the contact potential between the slider and disk by monitoring the induced slider motion with a Laser-Doppler-Vibrometer (LDV) and lock-in amplifier while applying ac and dc bias voltages. We find that the first harmonic of the ac driving frequency is minimized when the dc bias voltage cancels the contact potential. We have preformed air bearing modeling of the slider-disk interfaces that also incorporates electrostatic forces. From simulation, we find that the flying height is reduced and the pitch angle increased as the potential difference between the slider and disk is increased.

A novel wear-in-pad approach to minimizing spacing at the head/disk interface

Here we demonstrate a new approach to bring the disk drive recording head close to the disk media, while achieving tight control of the final head-media separation. The slider in this approach has a miniature Wear-In-Pad (WIP) at its trailing edge, encapsulating the read/write elements. As the slider flies over the disk, the slider overcoat and head recession are quickly worn off, resulting in the bottom of read and write elements clearing the disk roughness by only a few nanometers. We show that the Wear-In-Pad is a viable way to achieve the sub 7 nm head-media separations believed to be necessary for Tb/in/sup 2/ recording.

Tribology Of Laser-Textured and Mechanically Textured Media

The tribological properties of mechanically-textured and laser-textured magnetic rigid disks are investigated using typical sub-ambient pressure sliders. The effect of slider design and carbon overcoat properties on stiction and friction is studied using start/stop and drag testing. Stiction, wear, and acoustic emission for several slider-disk combinations are evaluated.

Tribological properties and environmental effects of nano and pico sliders on laser textured media

The tribological performance of nano and pico sliders on commercially available laser textured media is investigated using contact start/stop testing. The acoustic emission signal and the stiction force are determined for a number of typical slider/disk combinations, and the effect of high humidity and elevated temperatures are studied.

WRITE PROTRUSION MODULATION FOR SUB-NANOMETER CONTACT INTERFERENCE

With the continual reduction in slider to disk clearance in hard disk drives, new methods to measure this clearance with high accuracy are needed. Understanding the contact dynamics when touching the disk at sub-nanometer interference levels is an important aspect of the problem. We have developed a new methodology to gradually bring the slider into contact with the disk, based on controlled and localized thermal expansion of the slider as it occurs during the regular write process (write induced protrusion). By applying short pulses to produce time controlled thermal protrusion, the duration of contact can be limited to a few milliseconds, by which short contacts and their contact hysteresis can be investigated.Copyright

Minimum Stable Flying Height with Thermal Protrusion Actuation

With ever increasing areal densities in magnetic recording, novel methods to accurately control the clearance between slider and disk are needed. One recently introduced method is thermal protrusion of a heater element located close the read/write element at the trailing end of a slider. By applying an electric current to the heater coil, the sliders trailing end protrudes towards the disk and can be driven into contact with sufficiently high heating power. Understanding the contact dynamics and the touch-down/take-off hysteresis is an important aspect of controlling the minimum stable distance between the slider and disk. In this paper, a novel method to measure touchdown and take-off hysteresis with a single pulse applied to the heater is introduced. Furthermore, the effect of air bearing compliance as a function of thermal protrusion is investigated. By modifying the pressure profile of the air bearing surface, improved actuation efficiency can be achieved

MENISCUS ADHESION AT ULTRA-LOW FLYING SLIDER-DISK INTERFACES

As head-disk spacings in disk drives approach a few nanometers, adhesive forces between the slider and disk can drastically alter the slider flying dynamics. At these small separations, it is still unclear, however, what type of adhesive force dominates. Most previous studies have concentrated on van der Waals and electrostatic attractive forces [1], which are readily incorporated into air bearing simulations. In this talk, we provide experimental evidence that the dominant adhesive force originates from menisci forming around the low flying portions of the slider air-bearing-surface as the spacing transitions from near-contact to contact.Copyright