Yansheng Ma

Air-Bearing Design Towards Highly Stable Head–Disk Interface at Ultralow Flying Height

Pushing recording density towards tera-bit per square inch and beyond requires reducing flying height to 2.5-3 nm or below. One critical challenge at such ultralow flying height is the possible head-disk crash or unstable head-disk spacing due to short-range interaction forces, such as electrostatic force, intermolecular forces, lubricant interaction force, and so on. Slider design and design strategy are investigated in this work aiming at significantly increased stability of the head-disk spacing at ultralow flying height. Nonzero surface roughness leads to a roughness-limited possible minimum flying height. A stable head-disk interface requires a full air-bearing domination even at a roughness-imposed minimum flying height. Here, the air-bearing domination means that both air-bearing force and air-bearing stiffness are larger than the combination of various short-range forces and the corresponding stiffness. Investigations presented in this paper indicate that high pressure and high-pressure concentration technology are effective approaches to extending the domination of air-bearing force towards such a roughness-limited possible minimum flying height. Slider designs, proposed by authors, exhibit satisfying flying height stability even at the roughness-limited minimum flying height

Effects of intermolecular forces on deep sub-10 nm spaced sliders

Summary form only given. The deduction of slider/disk spacing into sub-10nm range reveals some physical phenomena and interactions that are trivial and rare to be noticed for a slider flying far above 10nm spacing. The intermolecular forces, such as van der Waals and Casimir forces, become so important in the range that any negligence is expected to be impractical. The effects of intermolecular forces on the ABS design have been reported, and it is also found that the Casimir effect is serious in the head disk interface. It is an obvious challenge to introduce the intermolecular forces to the current HDI modeling so as to simulate a femto slider with a nanometer spaced flying height.

Lubricant transfer from disk to slider in hard disk drives

The physics behind lubricant transfer from disk to slider and lubricant accumulation on the slider in hard disk drives is explained. The effect of slider air bearing pressure on the lubricant transfer is discussed. It is found that the lubricant transfer is not affected by slider air bearing pressure. Lubricant molecular weight plays a dominant role in the lubricant transfer and lubricant accumulation. The amount of lubricant transfer and accumulation decreases dramatically with the increase in lubricant molecular weight. A thinner lubricant and higher bonding ratio of lubricant on disk surface reduce the lubricant transfer and accumulation obviously.

Effect of Laser Heating Duration on Lubricant Depletion in Heat Assisted Magnetic Recording

Heat assisted magnetic recording (HAMR) is a promising choice to overcome the superparamagnetic limit in magnetic recording to further increase the areal recording density of hard disk drive media. However, HAMR brings about serious problems to slider-disk interface, such as lubricant depletion on disk surface at the high temperature in HAMR. Experimental studies of lubricant depletion under laser irradiation are still very limited so far. It is essential to do experimental studies under real HAMR conditions or under equivalent conditions when a standalone laser is used to emulate HAMR system. Laser heating duration in one heating and cooling process in HAMR is as short as 1 ns. It is believed that lubricant depletion under such short heating duration should be different from that under long time continuous heating. In this work, the effect of laser heating duration in one heating and cooling process on lubricant depletion is studied experimentally on a self-developed HAMR tester. Laser power, laser heating rate and laser heating duration of the tester are tunable and comparable with that of a HAMR head laser. The tester also supports macroscopic study. A method to control laser focus point on disk surface is also developed, which is the prerequisite to control laser heating temperature. From the experimental studies, it is found that longer laser heating duration results in more severe lubricant depletion. It is also found that lubricant depletion under laser heating is caused by both lubricant flow on disk surface and lubricant loss via evaporation/decomposition.

Experimental Study of Lubricant Depletion in Heat Assisted Magnetic Recording over the Lifetime of the Drive

Heat assisted magnetic recording (HAMR) is a promising choice to overcome the superparamagnetic limit in magnetic recording and further increase the areal recoding density of hard disk drive. However, it is expected that HAMR causes lubricant depletion problem on disk surface under the high temperature in the heating assisted writing process. Experimental studies of the lubricant depletion under HAMR conditions are still very limited so far. Lubricant depletion over the lifetime of the drive still remains unaddressed. In this study, a self-developed HAMR tester is introduced. The methods to control the repeatability of laser heating temperature, to determine laser heating temperature, and to adjust laser heating temperature are explained. Laser heating time in the test is correlated with that in the drive. Lubricant depletion is determined quantitatively and the relationship between lubricant depletion depth and laser heating time is established. Then, lubricant depletion depth over the lifetime of the drive is predicated. It is found that almost all lubricant on the disk surface will be depleted over the lifetime of the drive.

Experimental Study of Lubricant Depletion in Heat Assisted Magnetic Recording

Heat assisted magnetic recording (HAMR) is a promising choice to overcome the superparamagnetic limit in magnetic recording and further increase the areal recoding density of a hard disk drive. However, HAMR brings about serious lubricant depletion problems on the disk surface due to the high temperature in the heat assisted writing process. Experimental studies of the lubricant depletion under HAMR conditions are still very limited so far. It is essential to do experimental studies under real HAMR conditions or under equivalent conditions if a stand-alone laser is used to emulate the HAMR system. In this work, a self-developed HAMR tester is introduced. A method to control the repeatability of laser heating temperature is explained. Lubricant depletion, accumulation, loss, the percentage of accumulation to depletion, and the depth of depletion are determined quantitatively. The effects of laser power, total laser-on-time and laser-off-time in one laser heating and cooling cycle on lubricant depletion are studied experimentally with the HAMR tester. From the experimental studies, it is found that lubricant accumulation at the edge of the lubricant depletion track takes a considerable percentage of the lubricant depletion and the lower the laser heating temperature, the higher the percentage is. Furthermore, media cooling time plays a significant role in lubricant depletion for the media without a heat sink layer and on glass substrate.

Lube Depletion Caused by Thermal-Desorption in Heat Assisted Magnetic Recording

Heat assisted magnetic recording is a promising technique to overcome the superparamagnetic limit. However, it brings about serious problems to the slider-disk interface. One of the problems is lube depletion on disk surface caused by laser heating. In this work, the process of lube depletion caused by lube desorption during laser heating is explained. The effects of lube molecular weight, laser heating temperature, slider air-bearing pressure, etc. on the lube depletion are studied. It is found that lube thinning rate at disk surface decreases dramatically with the increase in lube molecular weight. It is a possible solution to overcome the lube depletion problem by using high molecular weight lube. Lube thinning rate can also be decreased significantly by lowering laser heating temperature, lowering slider air-bearing pressure over the laser heating area, and lowering lube vapor pressure.

Visualization and characterization of slider-disk interactions in dynamic load/unload processes

A novel visualization technique proposed by the authors was used to study slider-disk interactions during loading and unloading operations. The outcomes of the study prove that the visualization technique is a convenient, effective, and promising method for the investigation of slider-disk interactions. The performance of designed loading/unloading system can be evaluated effectively in a very short period of time. Many details, such as contact mode, type of contact, and so on, which have been invisible before, are now observable and have been revealed in this study.

Flying height-attitude observation and investigation of sliders in load/unload process

A novel flying height-attitude testing system was developed based on white-light interferometry. Flying heights at three desired locations on the slider surface can be determined simultaneously with this system and, thus, slider attitude can be fully determined from the measurement results. Load and unload processes were systematically studied with this system and some details were revealed.

Effect of Electrostatic Force on Slider-Lubricant Interaction

The intensity of slider-lubricant interaction is characterized by the amount of lubricant transferred from free lubricant region to bonded lubricant region in this study. The effect of electrostatic force on the slider-lube interaction is investigated by comparing the intensity of lubricant transferring under the same flying height but different electrostatic force conditions. Bump disks are used to calibrate slider and ensure the consistency of flying height under different experimental conditions. Results indicate that the slider-lubricant interaction can be increased significantly when sufficient interface voltage is present at the head-disk interface. The amount of lubricant transferred across the head-disk interface is found to increase with the increase in the applied interface voltage