Chao-Hui Yang

An Experimental and Simulation Study of Touchdown Dynamics

Dynamic flying height technology has been widely employed for reducing the mechanical spacing between the magnetic heads and the disk. As the recording density of hard disk drives approach 1 Tbit/in2, the spacing is decreased to sub 1 nm. At such low spacing, the touchdown (TD) dynamics becomes extremely critical. First, it affects the accuracy of the spacing setting, or TD detection. Second, it affects the hard disk drive reliability, such as writing modulation, wear, instability, etc. It decides how low the slider can fly stably and reliably. In this paper, we tried to have a better understanding of the TD dynamics with several designs of experiments first. We found that there were two stages in the whole TD process. In the first TD stage, a low frequency (30-150 kHz) vibration appeared. It was a suspension mode that was excited by the lubricant on the disk. In the second stage, a high frequency vibration (200-400 kHz) appeared. It was the second pitch mode of the slider air bearing excited by the contact between the slider and the disk. Based on these experimental observations, we propose modeling and simulation procedures with a combination of a full suspension model and a simplified air bearing model. Simulation can predict these two TD frequencies very well. Therefore, it could be applied to design head/disk interface to help achieve preferred TD behaviors.

Slider Pitch Moment Associated With Dimple Friction

In the design of a magnetic recording disk file, pitch moment exerted by the flexure on the slider is usually treated as a product of flexure pitch static attitude and pitch-stiffness (k p ), both measured in the absence of preload (gram-load). However, a slider operates in the presence of preload, which permits a large dimple friction to exist. We shall show by elementary beam theory that the pitch moment due to dimple friction is appreciable. The lever-arm of dimple friction is proportional to the bow height, and is independent of the slope of the flexure. To minimize the pitch moment associated with dimple friction, hence improving fly-height distribution, the flexure must how toward the disk. These results are confirmed by optical fly-height tests.

Tribology of proximity magnetoresistive head–disk interface for 5 Gb/in.2 recording

Low fly-height magnetoresistive (MR) sliders and low glide-height laser-texture thin film disks were introduced to meet the tribological challenges of proximity MR recording, with which an areal density of 5 Gb/in.2 has been achieved when using the sliders with dual-stripe MR heads and the disks with low-noise media. The 30% pico sliders employed two air-bearing designs with a fly height around 12.5 nm. The thin film disks used superfinish substrates with a glide-avalanche-height falling well below 10.0 nm. In the contact start/stop (CSS) zones, small crater-shape laser texture bumps were generated to meet both low stiction and low glide-height requirements. An 80 A thin amorphous nitrogenated carbon was added over the magnetic layers as a protective overcoat. A layer of perfluoropolyether with an additive of phosphazene compounds was applied on the disk surface to improve the reliability of head–disk interfaces. The near contact head–disk interface survived for 20 k-cycle hot/wet and hot/dry CSS tests wi...

Low cross talk interconnect for magnetic recording head

Read sensor in a magnetic recording head is susceptible to EOS from the cross talk induced by the write current transition. A significant component comes from the electrical interconnect between the head and the pre-amplifier. The magnitude increases as the transition time shortens, the line length increases and the read/write line separation decreases. As the read sensor dimension shrinks and becomes more delicate for higher recording density, such as TMR, it is more susceptible to the cross talk. The interconnect typically consists of two pairs of lines; one for write and one for read. For read sensor, it is the differential mode cross talk which is critical. It is well known that wire twisting can significantly reduce cross talk. However, with the planar microstrip line structure of interconnect commonly used today, it is difficult to cross the traces. Recently, progress was made that vias between trace and the stainless ground plane can be created. As a result, trace-pair twisting can be achieved with an innovative structure, where one trace is terminated at a via which connects to a short segment of isolated stainless steel to cross over the other trace then reconnects to the remaining trace segment through a second via. The objective of this study is to verify the concept and demonstrate the significance of this effect. It also provides insight to understand some of the characteristics of cross talk in an interconnect for magnetic recording head.