Jih-Ping Peng

Numerical and Experimental Evaluation of Discrete Track Recording Technology

Feasibility of discrete track recording (DTR) was evaluated in this paper. Flying height loss due to DTR structure was predicted by an averaged flow model, and it was verified by the touchdown pressure measurement. Based on the spacing analysis, it was concluded that dynamic flying control would be necessary for DTR. The magnetic model showed that the DTRs main advantage is in off-track performance while maintaining similar on-track SNR. Magnetic performance of DTR samples was also measured on the spin-stand, and the results were compared to the model

Thermal Protrusion-Induced Air Bearing Slider Instability at Disk Proximity and Light Contact

As the head-disk spacing is locally reduced to a few nanometers by the introduction of thermal fly-height control sliders, the instability of the flying slider at disk proximity and the detection of slider-disk contacts are of fundamental importance. Slider-disk contacts have been reported in several component-level experimental studies by observing an increase in averaged acoustic emission or laser Doppler vibrometry signals. In this paper, we investigate the transient slider dynamics at multiple locations on a slider body to study the instability from the conditions of disk proximity to light contacts. We define the onset of contact using the pattern transitions of acoustic emission signals, and we study separately the instabilities at the sliders trailing edge center (TEC), leading edge center (LEC), and down-track direction (DTD). The results show there is an evolution of slider instability that occurs during the transition from flying to contacts. Slider dynamics modulation in the DTD are more sensitive to the onset of contacts than at the LEC, whereas the dynamics at the TEC show the least instability. The results suggest that the down-track modulation, which happens prior to a severe TEC modulation, provides a preferred early contact detection criterion that can be used to prevent a more engaged slider-disk contact and mechanical wear.

Experimental and Simulation Study of Thermal Protrusion-Induced Head-Disk Contact Instabilities in Hard Disk Drives

Stability of the thermal fly height control slider has profound effects on the read-write performance and reliability of the head-disk interface. As magnetic storage technologies evolve aggressively toward higher areal density in hard disk drives, the fly height around the transducer area on the slider has achieved a read-write physical spacing of \({\sim }2\) nm, and is expected to be even lower to meet the magnetic storage road map in the near future. At such a low spacing, instabilities can occur in terms of slider vibration and prominent lubricant transfer from the disk to the slider, resulting in significant interface change that raises reliability concerns. In this paper, we experimentally investigate the thermal protrusion induced slider instability at contact proximities, and perform numerical simulations to explain the measured dynamics at head-disk contacts. The results suggest that as the sliders thermal protrusion area approaches the disk surface, instabilities mainly come from down-track force excitations. These excitations lead to more significant vibrations in the down-track direction and on the sliders leading edge rather than its trailing edge. The behavior of slider vibration at disk proximity is also dependent on the head-gimbal-assembly design.

Surface evolution of perfluoropolyether film at high speed quasi-contact conditions

Nanoscale analysis characterized by microscopy with atomic resolution demand that the targeted surface remains nearly static. Therefore, the interaction between two fast moving surfaces requires a unique methodology to capture its dynamics when contacts are of nominal area on the order of 100 μm2 but only a few angstroms in depth. We present a contact study of the head-disk interface in hard disk drives, which consists of a disk surface coated with a molecularly thin perfluoropolyether lubricant and a slider surface moving slightly separated from it with a relative velocity of 20 m/s and with 10 nm spacing. By investigating the slider dynamics and lubricant topography in-situ, we disclose that high-speed contact initiates when the slider shears the top surface of the lubricant. Such contact can pile up molecules a few angstroms high as “moguls” or annihilate existing ones through a 5–10 A interference. The transitional spacing regime of mogul evolution is defined as “quasi-contact,” and it is the initial ...

Effect of Lubricant Fragments on Lubricant Transfer: A Molecular Dynamics Simulation

A modified coarse-grained, bead-spring model was used to investigate the effect of lubricant fragments (LF) on lubricant transfer from a rotating disk to a slider in this paper. The simulation results indicate that full lubricant molecules cannot transfer to the slider surface for large enough slider to disk spacing. However, degraded lubricant molecules, namely LF, are able to transfer from the disk to the slider. LF with lower molecular weight is easier to transfer to the slider. The amount of the transferred LF decreases with increased spacing between the slider and the disk. The amount of the transferred lubricant also depends on the lubricant decomposed position, i.e., LF without end groups are more readily transferred to the slider.

Study of Head-Disk Interface Characterization Using Touchdown Sensor and Electromagnetic Signal in Hard Disk Drives

With the introduction of thermal fly-height control sliders, the local head-disk clearance can be reduced to a range from ~10 nm to contact. This actively controlled touchdown (TD) has been used as a way to study the head-disk interface (HDI), the characteristics of which greatly affect the areal density and reliability of drives. In this paper, a high spatial resolution TD study is performed at the drive level using TD sensor signals and head-media spacing signals. Different flying stages, including passive flying, TD transition, and over push modulation, are identified from the experimental results. A correlation between the aforementioned signals at the passive flying stage is found to represent the disk surface property. The passive flying stage and over push modulation stage of TD are further analyzed in both the time and frequency domains. By establishing a correlation between the fly height and the temperature response, we can provide insight into the heat transfer model for the HDI.

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 Wallaces spacing equation. It was demonstrated that the pressure sensor is effective in maintaining constant spacing at wide range of altitudes.

Wear Between Lift Tab and Load/Unload Ramp in Hard Disk Drives

A method was developed to characterize wear between the suspension lift tab and the load/unload ramp during load/unload testing in hard disk drives. The change of the friction force between the lift tab and the load/unload ramp was obtained by measuring the change of the voice coil motor (VCM) current. Scanning electron microscopy was used to evaluate the amount of wear debris deposited on the lift tab. The change of the VCM current was correlated with the area of adhering wear debris on the lift tab surface as a function of load/unload cycles and temperature. Energy-dispersive X-ray analysis was performed to identify the chemical composition of the wear debris and determine the wear mechanism.

Study of the head disk interface using touchdown sensors and electro-magnetic signals in hard disk drives

A correlation between touchdown sensor and head-media spacing signals is established and discussed in this paper. Experiments are performed on commercially available air bearing drives operating at 7200 rpm. The correlation between fly height and the temperature response provides insights on the heat transfer model in head disk interface.

Effect of Flying Pitch and Roll Angles on Lubricant Transfer Between Disk and Slider

In this paper, the effect of flying pitch angle and flying roll angle on lubricant transfer from the disk to the slider was experimentally studied. A flying height tester, which can measure flying pitch angle and flying roll angle of a slider, was used to study lubricant transfer from the disk to the slider without head/disk contacts. Transparent glass disks with a thin layer of lubricant were used. A charge-couple device camera was used to observe in situ, the lubricant transfer and lubricant flow on the slider surface, while time-of-flight secondary ion mass spectrometry was used to identify lubricant distribution on the slider surface after the test. The experimental results showed that lubricant flow follows the slider skew direction, i.e., lubricant flow goes toward the outer trailing edge (TE) of the slider when it flies at the inner diameter, and toward the inner TE of the slider when it flies at the outer diameter. In addition, flying roll angle plays a more dominant role than flying pitch angle on lubricant transfer from the disk to the slider.