Jonghak Choi

Thermal Deformation of Thermally Assisted Magnetic Recording Head in Binary Gas Mixture at Various Temperatures

Helium-filled drives and thermally assisted magnetic recording (TAMR) systems are the most promising next-generation magnetic recording technologies. Currently, a fused TAMR system under helium- or air-helium-filled conditions is expected. In the fused system, it is important to accurately predict thermal deformation for a full TAMR head model and change of flying height (FH) at near filed transducer (NFT). In this paper, we first constructed an iterative coupled-field analysis process and a more realistic TAMR head model, including the NFT and even the epoxy components. The heat transfer coefficient was calculated using derived gas mixture properties. And the thermal deformation and protrusion of TAMR head was investigated for various temperature and helium fraction ratios. From the simulation results, the maximum temperature at the laser diode (LD decreased up to 20% due to changes in the heat transfer coefficient and environmental temperature. The epoxy effect induced by the LD heating was around 40%, which is in no way negligible. A thermal protrusion of 1.0–1.5 nm occurred at the NFT at various conditions. After considering the thermal deformation of the epoxy and the protrusion at the NFT, we found that the total FH was reduced with increasing helium fraction ratio and temperature.

Study of Flying Stability of a Thermally Assisted Magnetic Recording System with Laser Diode Mount Light Delivery

The laser diode (LD) is a key component in thermally assisted magnetic recording (TAMR) systems. However, heating from the LD can induce thermal deformation of the slider assembly, and change the gap separation between the slider and disk medium. In this paper, we analyzed the relationship between the slider–medium gap and the optical efficiency of the TAMR head, by considering the thermal effects of epoxy, the adhesive layer, and the near-field transducer (NFT) on the TAMR slider. The epoxy effect was modeled by using finite element (FE) analysis. Five different epoxy models were simulated, and the optimal epoxy model was selected, on the basis of its thermal performance. FE analysis was also carried out to simulate the TAMR slider assembly, which consisted of the LD, NFT, adhesive layer, epoxy, and TAMR head. On the basis of iterative analysis, an FE model was constructed with optimized representation of the epoxy, TAMR head component, and NFT. Thermal analysis of the simulation representation indicated that the epoxy, adhesive layer, and NFT played a significant role in the performance of the TAMR system.

Analysis of slider dynamics induced by various ramp-disk contact situation in hard disk drive

This research investigates to analyze the effect of ramp-disk gap to slider dynamics in operational shock situation. To investigate the effect, simulations is conducted with verified finite element model include various ramp-disk gap. The slider dynamics is more unstable in bigger difference of ramp-disk gap model.

Analysis of Thermal Flying-Height Control System About Humid Air Condition in Hard Disk Drive

This research investigates to analyze the effect of humid air on TFC system. Required parameters of humid air and flying attitude of slider are calculated. Condensation of air bearing at over the saturation vapor pressure is considered. Heat transfer coefficient for humid air condition is calculated. TFC simulation about humid air is conducted.Copyright

Investigation of Slider Dynamics Considering Bias Voltage and Lubricant Charge in the Unsteady Proximity Condition

Abstract The relationship between slider and lubricant becomes increasingly important as the mechanical spacing between slider and disk is reduced to satisfy the demand for higher areal density. At a reduced flying height, the slider easily contacts the lubricant, which can cause slider instability. This study analyzed slider dynamics to improve the head–disk reliability in the unsteady proximity condition, considering bias voltages between the slider, disk, and lubricant. Force–distance curves were measured using atomic force microscopy to investigate changes in lubricant performance induced by an applied voltage. Additionally, the touch-down power and take-off power were measured under various applied voltage conditions. Experiments were carried out to estimate slider instability as a function of charged disk and slider conditions, to improve the slider dynamics in the unsteady proximity condition. The effect of the bias voltage induced by a voltage applied to the lubricant was carefully examined to accurately understand slider dynamics. The relationship between the lubricant behavior and the applied voltage was investigated; the voltage applied to the disk was more influential in improving slider dynamics. Consequently, the effects of bias voltage and lubricant, as induced by a charged disk, should be considered when analyzing slider dynamics to improve head–disk interface reliability in an unsteady proximity condition.

Operational Shock Analysis for 2.5-in Multi-Disk HDD Considering Ramp–Disk Gap Irregularity

With an increased mobility, hard disk drives (HDDs) now use ramp load/unload technology, and multiple disks are used to increase the data capacity. This can result in contact between the ramp and the disks, which negatively affects the slider dynamics under operational shock conditions. There are several types of ramp–disk contact, such as simultaneous, successive, and single contact, and these depend on the distance between the ramp and each disk in a multi-disk HDD. This paper examines the effect of ramp–disk contact on the slider dynamics using a transient shock analysis. The ramp–disk contact affects the head stack assembly bending mode and slider dynamics. The effect of irregular gaps between the disks and adjacent ramp on the slider dynamics is analyzed with the ramp–disk contact force. The simulation shows that the gap irregularity between the ramp and each disk should be as small as possible to improve the stability of the slider dynamics.

Analysis of Slider Dynamics Considering the Mechanical Spacing in the Slider-Lubricant Contact Regime

This paper analyzed the effect of lubricant contact on slider dynamics under the unsteady proximity condition, which is related to the intermolecular forces between the slider and disk. To investigate the slider dynamics, an experiment was conducted with a commercial drive, and the slider dynamics were analyzed during touch-down and takeoff (TO) considering the approach and withdrawal speeds of the slider. The instability of the slider dynamics increased under the rapid withdrawal condition during TO.

Analysis of slider dynamics induced by reduction of heat power in slider-lubricant contact regime

This research investigates to analyze the effect of slider dynamics on lubricant contact situation. To investigate the slider dynamics, experiment with commercial drive is conducted, and slider dynamics with various heat power reduction ratios is verified with experiments. The slider dynamics is unstable in rapidly reduced heat power.

Friction Heating Effect Considering Contact Area in TFC slider

In HDD industry, many technologies have been developed and investigated as means to increase the areal density of drives. Thermal flying-height control has been considered and widely applied in current HDD. When contact occur between TFC slider and disk, the slider has a friction heating induced by highly rotated disk. Moreover, because of the friction heating, additional protrusion of slider can occur. The additional protrusion in contact situation can be a severe effect on head part of slider and disk. Therefore, in this paper, we analyze the friction heating and additional protrusion in contact situation.

A Flying Stability of the Slider With Damaged DLC Layer by Confined Optical Energy in TAMR System

This research investigates to analyze the effect of laser of thermally assisted magnetic recording system on diamond like carbon (DLC) layer of slider. We investigated a damaged DLC layer of slider with laser spot-induced damage and analyze the effect of the damaged DLC layer in slider dynamics. The damaged DLC layer resulted in change of flying height and air bearing stiffness pressure.Copyright