Thermal Fly-height Control Technology Research Articles

Investigations of Adhesion under Different Slider-Lube/Disk Contact States at the Head–Disk Interface

Adhesion is the key factor influencing the failure of the hard disk drive operating under ultra-low flying height. In order to mitigate the negative effects of adhesion at the head–disk interface (HDI) and promote further development of the thermal flying height control (TFC) technology, an adhesive contact model based on the Lifshitz theory accounting for the thermal protrusion (TP) geometry of TFC slider, the layered structures of the head and disk, and the operation states of the slider was proposed to investigate the static contact characteristics at the HDI. The simulation results demonstrated the undesirable unstable regions during the transitions between different operation states and the necessity of applying TFC technology. The reduction in the head–media spacing (HMS) was found to be achieved by properly increasing the TP height, decreasing the thickness of the lubricant layer or the thickness of the diamond–like carbon (DLC) layer during the flying state or the TP–lube contact state. At the TP–DLC contact regime, the attractive interaction was stronger than other states, and the strong repulsive interaction made the HMS difficult to be further reduced through the increase in the TP height or the decrease in the lubricant thickness.

気体軸受圧力による磁気ディスク媒体及びスライダの表面変形

The slider/disk spacing of magnetic disk drives has been reduced in order to increase the recording density. Especially, the thermal flying-height control technology, where the electromagnetic transducer is protruded into the slider/disk spacing by heating the slider partially, contributes to make the flying height less than 2nm. Because of the narrower gas bearing clearance, the bearing pressure rises up to several tens times of atmospheric pressure. This pressure rise causes the deformation of slider and disk surface. The slider and disk surface deformation causes the change of gas bearing clearance and consequently the change of air bearing pressure. The pressure change causes the flying attitude. The flying characteristics also may be different from that of expected at the design, where the effect of deformation is not included. It is important to estimate correct flying characteristics affected by the deformation to realize stable flying and accurate recording. We introduced iterative method for searching the flying attitude affected by the slider/disk deformation. We obtained the air bearing pressure by solving the molecular gas lubrication equation numerically. And the simple numerical method, which utilizes the elastic half-space assumption, was employed for calculating the deformation of pressurized disk surface. The finite element method was applied to analyze the slider deformation. And the effect of deformation on the slider attitude is evaluated.

Thermal fly-height controlled glide for disk defect detection and defect size estimation for hard disk drives

Current hard disk drives use thermal fly-height control (TFC) during read/write operations. In this study, we use TFC technology during the disk glide process to determine sub-5 nm height defects. We also utilize TFC to measure the height of the defect during glide operation. Additionally, we magnetically mark the disk locations where defects are detected for further post-processing of the defects using optical surface analysis, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The defect height estimation during the glide was confirmed to be accurate by AFM and SEM analysis. Finally, we will present the TFC glide sensitivity showing capability of detecting smaller defects than conventional non-TFC glide technologies.

Dynamic Thermal Responses of Heat-Assisted Magnetic Recording Head in Data Writing Process

In the data writing process of heat-assisted magnetic recording (HAMR), due to the existence of servo sectors in the magnetic recording media, the laser power has to be “off” when the near field optical transducer passes over the servo sectors so as to protect the servo sector from being erased. In this paper, HAMR head dynamic thermal responses to the laser source heating and transducer absorption in the data writing process are studied. The results show that the dynamic temperature response times of the laser source and air-bearing surface are around 1 s. The transducer temperature can almost follow the transducer heating change (caused by absorption) because of its very fast temperature response which is around 2 μs. However, the transducer protrusion response time to the transducer absorption is 2 ~ 3 ms. Owing to the long response times of the slider temperature to the laser source heating and the transducer protrusion to its laser absorption, the fly height changes caused by the slider temperature increase and the transducer protrusion may be compensated with the thermal fly height control technology.

Optimization of thermal fly-height control slider geometry for Tbit/in2 recording

Magnetic storage advances including thermal fly-height control (TFC) technology were able to reduce the clearance between the read/write elements of the slider and the disk surface to increase the recording density of hard disk drives without compromising the stability of the head–disk interface (HDI). Sliders employing TFC technology are designed for flying recording and can yield clearances of few nanometers. However, it is estimated that TFC technology alone cannot provide the even smaller clearances necessary to achieve Tbit/in2 recording densities primarily due to the presence of instability-inducing vibrations at the HDI. In this work we perform optimization of the geometry of TFC technology sliders to achieve extremely high-density recording. We propose a flyability parameter coupled with a dynamic, contact mechanics-based friction model of the HDI that accounts for TFC geometry and its influence on the HDI dynamics. Optimization results are analyzed and an operating actuation range is identified that can yield Tbit/in2 recording densities with Angstrom-level clearance and minimized vibrations while also accounting for manufacturing and operational tolerances. This allows for light (lubricant) contact or ‘surfing’ recording. The proposed methodology can be used to reduce wear at the interface and investigate the feasibility of contact recoding.

Pressure Sensor Implementation for Head Media Spacing Reduction

Altitude performance is one of the key considerations in the head media interface design for hard disk drives (HDD). With conventional head media interface without thermal fly-height control (TFC), it is necessary to budget in the air bearing fly-height loss due to altitude effect. In order to reduce the sensitivity to altitude, some other performance need to be sacrificed. With TFC technology, there is an alternative approach to achieve superior altitude performance without trading off other performance. A pressure sensor is installed to the HDD to monitor the ambient pressure. When the pressure changes, the pressure sensor reports the pressure to the channel, and the TFC heater power is adjusted accordingly to maintain a constant fly-height at all altitudes. The pressure sensor has been implemented in the HDD successfully. The objective of this paper is to characterize the pressure sensor performance in the HDD application. The head-media spacing (HMS) was monitored with pressure sensor compensation turned off and on when exposed to different pressure to simulate altitude effects. The HMS was measured with harmonic sensor based on Wallace's spacing equation. It was demonstrated that the pressure sensor is effective in maintaining constant spacing at wide range of altitudes.

A-3 ヘッドディスククリアランスに与える湿度の影響(口頭発表:ヘッド・ディスク・インターフェイス)

To increase the areal recording density of hard disk drives, the magnetic spacing between the head and magnetic disk must be reduced. Therefore, the head-disk clearance also has to be reduced. Thermal flying height control technology has been applied to move the head element close to the disk in recent hard disk drives. However, it is necessary to control flying height properly to keep the same clearance because it changes in various environmental conditions. We have focused on studying the effect of environmental conditions on the clearance. In a humid environment, it is generally observed that a slider loses its flying height possibly due to the pressure drops caused by water vapor condensation in the air bearing. In our experiment, the effect of humidity on clearance was investigated quantitatively with an environmentally controlled component tester. Our finding was that the clearance variation due to humidity is because of not only flying height decrease but also disk touch-down height increase.

1110 熱式浮上量調整スライダにおける浮上変化効率の考察(要旨講演,一般セッション:情報機器コンピュータメカニクス)

To decrease magnetic spacing on head/disk interface of hard disk drive (HDD), magnetic spacing variations due to manufacturing tolerances and environmental variations should be reduced. To solve this problem, thermal flying height control (TFC) technology, which carries micro actuator near magnetic element, is applied. TFC technology can control the magnetic spacing during HDD operation by applying power. It is known that reduction of flying height is compensated by increasing in air bearing force due to TFC protrusion. This effect obstructs efficient flying height control. Larger TFC power is required to decrease magnetic spacing further. To ensure the reliability of magnetic element and reduce consumption power of HDD, TFC efficiency should be improved. In this report, we have investigated theoretically and experimentally how to improve the TFC efficiency for air bearing surface (ABS) design. We developed prototype slider of improved TFC efficiency design and investigated TFC related characteristics. As a result, the new design shows higher TFC efficiency than that of conventional design.