Yuki Shimizu

Dynamically Controlled Thermal Flying-Height Control Slider

To achieve ultra-low flying height, magnetic spacing variations due to manufacturing tolerances and temperature-induced thermal protrusion need to be reduced. We have developed a thermal flying-height control (TFC) slider that carries a micro-thermal actuator. Previous TFC sliders were mainly statically controlled by a constant power supply. Our purpose is to demonstrate dynamic control of a TFC slider to compensate for high-speed magnetic signal modulation using feed-forward control methods. In this report, to dynamically compensate for magnetic signal modulation using TFC, two methods were examined. In method 1, TFC power was adjusted by using only time domain information. In Method 2, TFC power was adjusted by using frequency domain information in addition to time domain information. Method 2 showed better compensation for magnetic signal modulation due to better compensation at higher frequencies. These results showed that a dynamically controlled TFC slider is feasible in compensating for kilohertz order modulation.

Micromagnetic study of the transition parameter and position jitter in perpendicular recording

We examined the transition parameter and position jitter in perpendicular media by micromagnetic simulations that included thermal fluctuations. We observed the effects of grain size, intergranular exchange, anisotropy distributions, and orientation distributions. All these parameters affected both the transition parameter and the M-H loop coercivity squareness (S/sup */). The net effect was a universal dependence of transition parameter on S/sup */. The position jitter normalized by the grain diameter decreased with increasing S/sup */, but a universal curve was not found. In general, a small grain diameter, moderate exchange and low anisotropy distribution increase the high-density signal-to-noise ratio.

Nano-Scale Defect Mapping on a Magnetic Disk Surface Using a Contact Sensor

Targeting both higher touchdown sensitivity and highly accurate nanometer-scale defect detection on a disk surface, a thermal-contact sensor, integrated into a magnetic-head slider, was developed. It was experimentally shown that the contact sensor has sensitivity for detecting head-disk contact at each radial position on a disk surface equivalent to that of a conventional acoustic-emission (AE) sensor. It was also shown that a defect-detection method using the thermal-contact sensor is feasible. Defect mapping, in which a slider inspecting the disk at a certain clearance detects small defects on the disk surface, done with this method was better sensitive with measurements with an optical surface analyzer (OSA). Defect mapping on a proto-type glide tester, based on a conventional glide tester, using the thermal-contact sensor was also demonstrated.

Scratch-Induced Demagnetization of Perpendicular Magnetic Disk

The mechanism of scratch-induced demagnetization was studied in perpendicular magnetic recording (PMR) disks. These scratches, which may occur on the disks surface during head/disk contact, cause demagnetization that results in read/write errors. The scratch-induced demagnetization is thus investigated by the scratch test, observation of atomic force microscopy and magnetic force microscopy, and analysis of transmission electronic microscopy. It was found that the angle of the grain in the recording layer, which is vertically orientated on a PMR disk, was tilted under the scratch. These analyses revealed that scratch-induced demagnetization is caused mainly by plastic deformation which results in grain tilt in the recording layer, rather than by stress. Therefore, a dense and not-easily titled grain structure in the recording layer is needed to produce a reliable hard disk drive (HDD).

Two-Dimensional Flying-Height Modulation Mapping at HDD Drive Level

A measurement system for flying-height modulation of magnetic heads is proposed, and two-dimensional (2-D) flying-height modulation mapping is demonstrated at the drive level. The measurement system is based on the triple harmonic method, which uses a readback signal from the read element of the magnetic head. This technique, which maintains a constant wavelength of the pattern for fly-height modulation measurement, was proposed to achieve 2-D flying-height modulation mapping. Moreover, the frequency response of the measurement system was calibrated, and measurement accuracy was improved

Technique for checking design rules for three-dimensional CAD data

A technique was developed for checking whether three-dimensional CAD shape satisfies design rules. Many design rules related to reliability and manufacturability should be considered in the design stage. Our technique automatically recognizes feature shapes such as a rib and boss from a CAD model shape, and it checks the shape and arrangement. The effectiveness of the technique was demonstrated in a test of the injection-molded part.

Effect of slider surface energy on head disk interface performance

Study of lubricant-coated sliders showed that low slider surface energy increases in stable slider flying and reduces lubricant droplet formation on the disk surface at ultra-narrow clearance. Both component- and drive-level evaluation showed the lubricant pick-up and the flying height it causes were reduced significantly. Furthermore, there was no magnetic spacing increase at the drive-level for the lubricant-coated slider when using contact detection to set the clearance methods.

Development of support system for providing knowledge from displayed documents

Because knowledge and experience, which are derived from design and analysis in product design, are not always reflected in the design process, product flaws that have previously occurred would reappear. It is necessary to develop a system that provides designers with the knowledge and design rules of a design process. We developed a useful design-information delivery system using running software/documents displayed on the PC monitor. This system extracts search keywords from a design-information database. In a validation test, a designer was warned of vibration and sliding when evaluating the strength of a product.

Design of Damped Air Bearings at Head Disk Interface

Small perturbation and modal-analysis methods were employed to systematically study a damped slider’s dynamic characteristics. We found that a design with grooves distributed on a trailing pad effectively improved the slider’s damping at higher frequencies, and the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider with distributed damping grooves on a trailing pad had a higher damping ratio in the third mode, and hence, its responses to disk parallel and wavy motion were greatly reduced. This new design for the damped slider was an effective solution reducing the slider’s modulation.Copyright

Numerical Simulation of Touchdown/Takeoff Hysterisis of Spherical Pad Slider by Considering the Liquid Bridge Between the Slider and Lubricant-Disk

This work carries on a numerical simulation of the touchdown/takeoff (TD/TO) hysterisis of the spherical pad slider. It numerically studies the meniscus bridge’s formation and meniscus force interaction between the spherical pad and lubricant over the disk surface. It proposes a geometry model for the lubricant bridge, and correspondingly, a force model for the meniscus force acting on the spherical pad slider due to the lubricant bridge. By solving the liquid balance state at the meniscus boundary, it obtains the geometry of the liquid bridge. A parametric study is done to study the effects of the geometry of spherical pad, Hamaker constant of lubricant-disk, and surface energy of lubricant on the formation of the liquid bridge. The overflow phenomenon is analyzed to find out the acceptable dimension of the spherical pad design. Moreover, a three-dimensional (3D) model of spherical pad slider/disk interface is built to study the steady-state flying of the spherical pad slider. The different parameters are analyzed to study their effects on the TD/TO hysteresis.Copyright