Run-Han Wang

The interaction of perfluoro-polyether lubricant with hydrogenated carbon

The incorporation of a limited amount of hydrogen in the amorphous carbon (a-C:H) overcoat improves the CSS durability of thin film media lubricated with perfluoropolyether (PFPE). A mechanism is proposed to explain this phenomenon. With increasing H content in C, the likely bonding sites for the lubricant such as the carboxyl end groups and dangling bonds decrease in the carbon films. Mobility of the lubricant measured by two different techniques was found to increase with increasing H. The improved interface durability is attributed to the enhanced lubricant mobility on hydrogenated carbon.

Head protrusion and its implications on head-disk interface reliability

As magnetic recording areal density increases the mechanical spacing between the head and the disk continues to shrink. Head protrusion, induced by write current heating of the coil and yoke during recording at operating temperature, may interfere with the disk. In this work, we have measured the head temperatures as a function of write current, frequency and flying conditions. The rise in coil temperature for a flying head was found to be much less than a head on the load/unload ramp. The measured temperature coefficient was consistent with the simulation. The amount of head protrusion was measured as a function of the write current. The head-disk interaction of the interface after 100000 write current bursts resulted in alumina wear. Some of the effects of head protrusion on the interface reliability are discussed.

12 Gb/in/sup 2/ recording demonstration with SV read heads and conventional narrow pole-tip write heads

We have successfully demonstrated magnetic recording at areal densities as high as 12 Gb/in/sup 2/ at a data rate of 14/spl sim/15 MB/s using separate spin-valve read heads and narrow pole-tip inductive write heads on low noise Co alloy thin film disks. In this work, the nominal target densities were 350 Kbpi/spl times/34 Ktpi. To make these densities possible, large signal-to-noise gains were attained with the use of high performance spin-valve read heads and low noise thin film media. At the same time, very narrow track write heads were designed and fabricated by extending conventional photolithographic techniques. Finally, small magnetic spacings between the head and the disk were attained with low flying ABS designs and improved head and disk surfaces. Recording tests showed satisfactory writability and large readback signal of around 2 mV//spl mu/m. The 50% rolloff densities were as high as 10 Kfc/mm, while the write and read trackwidths were as narrow as 0.7 and 0.5 /spl mu/m respectively. An overall assessment of the parametric recording results indicated an areal density capability of at least 10 Gb/in/sup 2/. This projection was confirmed by error rate testing with an EPR-4 channel, where very low ontrack errors of 10/sup -10//spl sim/10/sup -9/ were achieved at 315/spl sim/380 Kbpi. Furthermore, squeeze measurements revealed well-defined 747 behavior with offtrack maxima at 0.7/spl sim/0.8 /spl mu/m trackpitch. The product of linear and track densities for the write and read head combinations tested indeed showed that an areal density of 11/spl sim/12 Gb/in/sup 2/ has been achieved.

Head-Disk Dynamics in the Flying, Near Contact, and Contact Regimes

To achieve an areal density approaching 50 Gb/in. 2 for the magnetic storage of data in hard disk drives requires reduced mechanical and magnetic spacing. Off-track jitter caused by airflow or contact can cause track misregistration on the order of 20-70 nm which may be excessive for adequate servo performance. The magnetic signal can be used to identify both the vertical spacing modulation due to the air bearing modes and off-track jitter due to suspension modes with nanometer resolution. We find that the off-track jitter in the flying regime is driven by airflow and is a strong function of the disk velocity and the suspension type. In the contact regime, the vertical spacing modulation and off-track jitter increase due to contact. Using a laser Doppler vibrometer we identified the leading contribution to the off-track jitter to be primarily the first torsional mode (T1) and to a lesser extent the first bending mode (B1) of the suspension.

The effect of hydrogen in carbon overcoats on the tribology of the head-disk interface

The effect of hydrogen in the carbon overcoat on the CSS durability of thin film media lubricated with perfluoropolyether (PFPE) is reported. A strain-gauge force transducer and optical surface analyzer (OSA) were employed to investigate the failure mechanism. The OSA provided in-situ monitoring of lubricant migration and modification as well as carbon wear. Durability improved with increasing hydrogen content over the range from 12 to 36 at% of H. The improvement is attributed to changes in lubricant bonding and mobility as a function of hydrogen content.

Tribology Of Laser Textured Disks With Thin Overcoat

The adoption of dual zone texturing on magnetic disks allows the flying height of the head to be reduced over the data zone compared to a fully textured disk. Laser texture offers a technique far precise topography control and the placement of the landing zone. In this study the effects of the clearance between the head and the disk, and the presence or absence of overcoat on the air bearing surface on contact start-stop performance are evaluated. The wear mechanism of the laser bump by the head was investigated with in situ monitors and followed by surface analysis. Acceptable durability and stiction performance for contact start-stop operation is feasible with a few nm of clearance.

Nanoindentation and the tribology of head-disk interface components

Nanoindentation data are presented for three different but interrelated components of the thin film disk magnetic recording system-the air bearing slider/recording head, the disk substrate, and the sputter deposited thin film disk recording medium. Hardness traces across the slider trailing edge demonstrate the hardness of the NiFe, sputtered Al/sub 2/O/sub 3/, and the ceramic Al/sub 2/O/sub 3//TiC are 8, 10 and 24-40 GPa, respectively. Lapping under non-optimum, aggressive conditions can lead to significant recession in these components which is directly related to their hardness. The hardness and modulus have been measured for a number of alternate substrate materials ranging from AlMg/NiP to glass and glass ceramic. The ability of these substrates to resist damage from slider shock forces is presented and generally increases with substrate hardness, although other criteria (fracture toughness and plasticity initiation) rue required to rationalize all the data. Finally, hardness and modulus of carbon overcoat films are presented which have been sputtered under various conditions. The process variations lead to variations in hardness, the hardness/modulus (H/E) parameter, and tribological performance in slider/disk testing. The applicability of these mechanical property parameters to the wear degradation is discussed.

Challenges of the head-disk interface for near contact and contact recording

As the magnetic recording areal density approaches 10 Gb/in/sup 2/, the mechanical spacing between the head and the disk is expected to reduce rapidly below 20 nm. This lends to an increase of head-disk interaction which may induce an unacceptable level of interfacial wear. In this study experimental air bearing sliders were designed and fabricated to fly in close proximity or substantial contact with the disk. The durability of the interface decreased with decreasing mechanical clearance. The amount of head and disk wear was determined. The metrology and some of the challenges in maintaining a functional interface are presented.

Head-disk interface considerations at 10-nm flying height

As magnetic recording density increases toward hundreds of Gb/in/sup 2/, both the magnetic spacing and head-disk clearance decrease to <10 nm. By one estimate, the magnetic spacing for 1 Tb/in/sup 2/ is about 6 nm and the read width is /spl sim/30 nm. There are at least two different approaches to achieving this. The first is an extension of the traditional flying interface and the second is contact recording. In the former case, one needs to be concerned about maintaining adequate clearance both at sea level and at higher elevation, whereas in the latter case wear and corrosion of the heads and disks may pose major challenges. An example of how head-disk interference takes place in a disk drive is given for an experimental 10-nm flying slider. The effects of radial flying height profile, takeoff height of the disk, and disk curvature on mechanical spacing are presented. The results of changes occurring on the air bearing surface and the disks after long-term flyability tests are discussed.

The challenges beyond proximity head-disk interface

lntsoduction As the areal density for magnetic recording increases towards I O Gb/in’, the mechanical spacing between the head and the disk is expected to reduce rapidly below 20 nm. This leads to an increase of head-disk interaction which may induce unacceptable level of magnetic jitter and wear of the interface. In this study experimental air bearing sliders were designed and fabricated to fly near and below the take-off-hei&t of the disks. The durability of the interface was tested and the challenges in maintaining a functional interface will be discussed.