Nano-contact, contact detection and prevention in high density hard disk drives
Date of Issue2012
School of Mechanical and Aerospace Engineering
Centre for Mechanics of Micro-Systems
This thesis presented theoretical and experimental studies of the characteristics of the head/disk interface at very low flying height for the next generation high density hard disk drives. The study started with a discussion of the tribological background of the head/disk interface and presented a review of the literature related to studies of the head/disk interface. Then the thermal protrusion of a thermal flying height control (TFC) slider and the patterned media were chosen to perform a contact analysis at the head-disk interface (HDI). Results obtained from finite element analysis for the contact pressure at elastic-plastic asperity micro contacts and subsurface stress distribution were presented. Subsequently, an active slider based on piezoelectric shear-mode actuation was proposed and investigated for flying height control. A finite element model of a PZT slider using shear-mode deformation was developed. The electromechanical simulation and air-bearing simulation were performed to investigate the shear-mode deformation and the static flying attitude of the PZT slider. The effects of location of the PZT sheet and the dimension of air bearing surface on the static flying attitude of the PZT slider were studied. This was followed by a novel structure design of an active- slider with a piezoelectric actuator at the top of the slider body and a soft layer between the substrate and head elements. A parametric simulation was performed to obtain an optimized dimension of the PZT actuator and the most effective soft material. Then a slider structure with large actuation efficiency was achieved. Thereafter, a ZnO piezoelectric contact sensor integrated with thermal flying height control (TFC) slider for contact detection was proposed and investigated. The effects of the contact force and thermal-stress on voltage output of the integrated contact sensor in TFC slider were investigated using finite element method. The simulation results showed that the shear-mode ZnO sensor is more sensitive to contact force than the transverse-mode ZnO sensor. Parametric optimization was performed to achieve high sensitivity for the contact sensor. Finally, piezoelectric micro cantilever with high quality ZnO films were fabricated and characterized to demonstrate the feasibility of an integrated piezoelectric contact sensor and possible active slider. The dynamic performance of the piezoelectric cantilever was characterized by impedance analyzer and LDV. A silicon cantilever with a small ZnO sensor was fabricated. The dynamic performance of this cantilever excited by a mechanical impact was investigated. The experimental results showed that the response from the sensor and the LDV measurements are very similar to each other, which indicated that the thin film ZnO sensor is of good sensitivity.