David Kuo

Effect of lubricant on flyability and read-write performance in the ultra-low flying regime

The effect of lubricant on flyability and read-write performance in ultra-low flying regime has been studied over the disks with lubricant on one half of disk surface thicker than the other half. The dynamics of a slider was monitored using Acoustic Emission (AE) and Laser Doppler Vibrometer (LDV). An instability characteristic of a slider flying over the thick lubricant region has been observed and this instability intensifies as flying height decreases and the step thickness increases. After the slider flies over the disks, it has been found that lubricant re-distribution occurs as lubricant is carried by the flying slider from the thick lubricant region and deposited onto the thin lubricant region. Possible mechanisms were discussed to explain the observations. Finally, recording tests were performed and the magnetic spacing loss due to the lubricant steps was estimated.

Glide avalanche prediction from surface topography

As the head/disk spacing continues to decrease, the demand for thin film disks with glide capability below 20 nm becomes more pressing. As a consequence, the design of such media requires an ever increasing control of the surface topography to a nanometer level. This paper is an attempt to analytically predict the intrinsic glide capability of a textured disk, given the knowledge of its peak height distribution, as measured by a surface profilometer. This model also takes into account the long wavelength component of the topography, or waviness, by treating it as an independent variable leading to a broadening of the peak height distribution. This analysis also predicts relationships between various roughness parameters. Experimental data obtained on a total of 27 media surfaces of various types compare favorably to the theoretical predictions.

Head-disc dynamics of low resonance laser textures-a spectrogram analysis

Spectrogram analysis provides a systematic way to study the head-disc interface dynamics and demonstrates how the frequency spectrum varies during the head take-off or landing. The regular pattern laser texture has strong input excitations, which includes not only the fundamental frequency of bump pitch density but also the higher order harmonics. When the excitation frequencies intercept the system resonance frequencies, such as the slider/sensor body natural frequencies, the sensor output is amplified, which causes a false reading in the glide testing and glide avalanche measurement. Spiral-line laser texture solves the problem of resonance by completely removing the source of excitation.

Free Vibration Analysis of PZT Glide Heads

This paper studies natural frequencies and mode shapes of a glide head with a piezoelectric transducer (PZT) through calibrated experiments and a finite element analysis. In the experiments, the PZT transducer served as an actuator exciting the glide head from 100 kHz to 1.3 3 MHz, and a laser Doppler vibrometer (LDV) measured displacement of the glide head at the inner or outer rail. The natural frequencies were measured through PZT impedance and frequency response functions from PZT to LDV. In the finite element analysis, the glide head was meshed by brick elements. The finite element results show that there are two types of vibration modes: slider modes and PZT modes. Only the slider modes are important to glide head applications. Moreover, natural frequencies predicted from the finite element analysis agree well with the experimental results within 5% of error. Finally, the finite element analysis identifies four critical slider dimensions whose tolerance will significantly vary the natural frequencies: PZT bonding length, wing thickness, slider thickness, and air bearing recess depth.

Experimental and theoretical studies of PZT glide head vibration

This paper studies the natural frequencies of a PZT glide head through calibrated experiments and a finite element analysis (FEA). In the experimental studies, the PZT served as an actuator exciting the glide head from 100 kHz to 1.3 MHz, and a laser Doppler vibrometer (LDV) measured the displacement of the glide head at the inner or outer rail. The natural frequencies were measured through PZT impedance and frequency response functions of PZT to LDV. In FEA, the slider, PZT, and glue (epoxy) were meshed by brick elements. Natural frequencies predicted from FEA agree well with the experimental results with a 5% difference. Therefore, modeling of the epoxy layer is critical in predicting the natural frequencies of PZT glide heads.