T.S. Low

Laser removal of particles from magnetic head sliders

A quantitative investigation of laser‐induced removal of particles from magnetic head slider surfaces has been carried out. The damage thresholds of magnetic head sliders for laser fluence and pulse number were found to be about 150 mJ/cm2 and 5000 pulses at 100 mJ/cm2, respectively. For laser fluence or pulse number above the damage threshold, laser irradiation onto magnetic head slider surfaces can cause microcracks around the pole tips. It is found that laser cleaning efficiency increases with increasing laser fluence and pulse number, but does not depend on repetition rate up to 30 Hz. Laser cleaning efficiency of removing particles from magnetic head slider surfaces can reach about 90% for Al particles and 100% for Sn particles, respectively, under appropriate conditions without causing damage. The mechanisms of laser cleaning of particles from magnetic head slider are laser‐induced surface vibration, particle vibration, particle thermal expansion, and ablation with high laser fluence, which produce forces strong enough to detach particles from slider surfaces. Based on the above cleaning mechanisms, the dependence of laser cleaning efficiency on laser parameters can be explained.

Robust design for torque optimization using response surface methodology

This paper discusses response surface methodology (RSM) as an efficient approach to parametric model building and design optimization. Application of RSM is presented for torque optimization in spindle motor design. A window-zoom-in method is studied to improve the optimization procedure. Finite-element analysis and RSM using mixed resolution central composite design are utilized to determine the optimum torque performance. Analysis of variance summaries and response surface plots help to locate the parameter settings to produce parts with the desired quality.

Dual stage actuators for high density rotating memory devices

Maintaining the trend towards higher track densities and data rates in rotating memory devices require track following servo systems of increasing bandwidth for reliable storage and retrieval (R/W) of data. The bandwidth requirements are even more severe in the emerging portable computing applications. Increase in bandwidth under strict constraints on over-sampling is limited by the presence of mechanical resonance modes and other nonlinearities in the voice coil motor (VCM) actuators. One approach to overcoming the problem is by using a dual or a compound actuator. In such a mechanism, a VCM is used as a primary stage while the recording head is mounted on the secondary stage which in turn is mounted on the VCM. The secondary stage provides rapid small-motion and position correction to the recording head. Several dual-stage configurations have been proposed using electrostatic, piezoelectric and electromagnetic secondary actuators. The paper proposes a piezoelectric stack micro-actuator design for a disk drive. It preserves the present suspension and head assembly. A prototype of the actuator is designed, fabricated, and tested. The test results are presented. A dual actuator tracking servo system is proposed. The scheme is a promising alternative for providing high bandwidth actuation for future high performance drives.

Studies of carbon nitride thin films synthesized by KrF excimer laser ablation of graphite in a nitrogen atmosphere

Carbon nitride thin films were deposited on silicon wafers by pulsed KrF excimer laser (wavelength 248 nm, duration 23 ns) ablation of graphite in a nitrogen atmosphere. Different excimer laser fluences and pressures of the nitrogen atmosphere were used in order to achieve a nitrogen content as high as possible in the deposited thin films. Fourier transform infrared and x-ray photoelectron spectroscopies were used to identify the binding structure and the content of the nitrogen species in the deposited thin films. The N/C ratio 0.42 was obtained at an excimer laser fluence of 0.8u2009Ju2009cm−2 at a repetition rate of 10 Hz under a nitrogen pressure of PN=100u2009mTorr. A high content of C=N double bond instead of C≡N triple band was indicated in the deposited thin films. Ellipsometry was used to analyze the optical properties of the deposited thin films. The carbon nitride thin films have amorphous-semiconductorlike characteristics with an optical band gap Eopt of 0.42 eV.

Investigation on magnetic saturation in switched reluctance motor using 2D hybrid finite element method

This paper investigates the magnetic saturation in switched reluctance motor. A two-dimensional hybrid finite element method is used to describe magnetic behaviors, energy conversion loops and electromagnetic torque generated for non-saturated and saturated motors, respectively. The analysis shows that magnetic saturation in motor benefits the output capability just under certain constraints. In some cases, the non-saturated motor can produce more torque than that of the saturated motor. In whatever the nonsaturated or saturated motor, high maximum nonsaturated inductance L/sub au/ is recommended, which is beneficial to output torque produced.

Analysis of Unbalanced-Magnetic-Pulls in hard disk drive spindle motors using a hybrid method

In spindle motor design and analysis, calculation of the torque and force is an essential step for the performance prediction. A method for the calculation of the Unbalanced-Magnetic-Pull (UMP) is proposed in this paper. As the method is based on the combination of the strength of analytical and numerical methods, it can yield more accurate results than traditional methods, and can be conveniently implemented in the computer aided design/analysis softwares for spindle motors.

Audible acoustic wave emission in excimer laser interaction with materials

Audible acoustic wave generation during excimer laser interaction with materials has been investigated. It is found that the amplitudes of acoustic waves depend on laser fluence, pulse number, and substrate material characteristics and can be used to determine the nature of laser–material interactions. When laser fluence is below the ablation threshold of the materials, the amplitudes are reduced to zero at large pulse number due to the cleaning of contaminants on the substrate surface. As laser fluence becomes higher than the ablation threshold, the amplitudes of acoustic waves also reduce with increasing pulse number but to a constant level instead of zero due to laser ablation of substrate materials. Since the surface contamination can be completely removed by a few pulses at high laser fluence, the constant level is attributed to the material ablation. It is also found that the constant level increases with laser fluence. By establishing a relationship between the amplitudes and laser parameters, real...

Micro electrostatic actuators in dual-stage disk drives with high track density

This paper presents a dual-stage actuator for high-density disk drive, using a voice coil motor (VCM) rotary actuator as a coarse actuator and a linear micro electrostatic actuator as a fine actuator. The micro electrostatic actuator proposed has trapezoidal static comb fingers and straight movable comb fingers. It has a linear static displacement voltage characteristic in a working range of 4 /spl mu/m, sufficient for fine positioning of a read/write head. The actuator has a fast and stable dynamic response with a related setting of parameters. By adjusting micro leaf-spring constant and the mass of a micro HGA subsystem, the micro actuator system can achieve a 10 kHz bandwidth.

Electromagnetic design for hard disk drive spindle motors with fluid film lubricated bearings

This paper discusses the problems associated with the electromagnetic design of hard disk drive (HDD) spindle motor having fluid film bearings. It will highlight the effect of the unbalanced electromagnetic pull in the radial direction of FFB spindle which uses permanent magnet brushless DC motors with slotted stator core. An analytical approach is employed for predicting the magnetic field and motor performance. Results obtained from this approach are compared with finite element analysis.

Design trends of spindle motors for high performance hard disk drives

Reducing the unbalanced radial force and reduction of cogging torque are important for the future high performance spindle motors. In this paper, the effects of the pole and slot number combinations on the cogging torque and unbalanced radial force are discussed and a detail investigation on the unbalanced radial force is made using FEM. It is shown that the unbalanced radial force is substantial in the starting condition and in the delta connection winding. The unbalanced radial force can be largely reduced by optimization of the pole arc to pitch ratio.