Mingsheng Zhang

Air-Bearing Design Towards Highly Stable Head–Disk Interface at Ultralow Flying Height

Pushing recording density towards tera-bit per square inch and beyond requires reducing flying height to 2.5-3 nm or below. One critical challenge at such ultralow flying height is the possible head-disk crash or unstable head-disk spacing due to short-range interaction forces, such as electrostatic force, intermolecular forces, lubricant interaction force, and so on. Slider design and design strategy are investigated in this work aiming at significantly increased stability of the head-disk spacing at ultralow flying height. Nonzero surface roughness leads to a roughness-limited possible minimum flying height. A stable head-disk interface requires a full air-bearing domination even at a roughness-imposed minimum flying height. Here, the air-bearing domination means that both air-bearing force and air-bearing stiffness are larger than the combination of various short-range forces and the corresponding stiffness. Investigations presented in this paper indicate that high pressure and high-pressure concentration technology are effective approaches to extending the domination of air-bearing force towards such a roughness-limited possible minimum flying height. Slider designs, proposed by authors, exhibit satisfying flying height stability even at the roughness-limited minimum flying height

Preparation and characterization of ZnO microcantilever for nanoactuation

Zinc oxide [ZnO] thin films are deposited using a radiofrequency magnetron sputtering method under room temperature. Its crystalline quality, surface morphology, and composition purity are characterized by X-ray diffraction [XRD], atomic force microscopy [AFM], field-emission scanning electron microscopy [FE-SEM], and energy-dispersive X-ray spectroscopy [EDS]. XRD pattern of the ZnO thin film shows that it has a high c-axis-preferring orientation, which is confirmed by a FE-SEM cross-sectional image of the film. The EDS analysis indicates that only Zn and O elements are contained in the ZnO film. The AFM image shows that the films surface is very smooth and dense, and the surface roughness is 5.899 nm. The microcantilever (Au/Ti/ZnO/Au/Ti/SiO2/Si) based on the ZnO thin film is fabricated by micromachining techniques. The dynamic characterizations of the cantilever using a laser Doppler vibrometer show that the amplitude of the cantilever tip is linear with the driving voltage, and the amplitude of this microcantilevers tip increased from 2.1 to 13.6 nm when the driving voltage increased from 0.05 to 0.3 Vrms. The calculated transverse piezoelectric constant d31 of the ZnO thin film is -3.27 pC/N. This d31 is high compared with other published results. This ZnO thin film will be used in smart slider in hard disk drives to do nanoactuation in the future.

Light Delivery System for Heat-Assisted Magnetic Recording

Heat-assisted magnetic recording (HAMR) technology needs a light delivery system with an incorporated near-field transducer (NFT) as a minute heat generator. A novel system for light delivery with a triangular spot size converter (SSC) and an optical fiber is proposed. The advantages of using a triangular SSC are optical efficiency and integration tolerance between the optical fiber and the NFT. It also has good affinity to conventional head fabrication process. The optical fiber enables flexible laser location. It was confirmed that fabricated triangular SSC can propagate light and reduce beam spot. Computer simulations and experiments demonstrated possibility of integration of light delivery system between NFT, SSC, and optical fiber. Flyability of a pico slider with an optical fiber was also demonstrated. It shows that the optical fiber does not have a big impact on flyability below 10 nm flying height and off-track vibration.

Effect of Electrostatic Force on Slider-Lubricant Interaction

The intensity of slider-lubricant interaction is characterized by the amount of lubricant transferred from free lubricant region to bonded lubricant region in this study. The effect of electrostatic force on the slider-lube interaction is investigated by comparing the intensity of lubricant transferring under the same flying height but different electrostatic force conditions. Bump disks are used to calibrate slider and ensure the consistency of flying height under different experimental conditions. Results indicate that the slider-lubricant interaction can be increased significantly when sufficient interface voltage is present at the head-disk interface. The amount of lubricant transferred across the head-disk interface is found to increase with the increase in the applied interface voltage

Flying height adjustment by slider's air bearing surface profile control

A new active slider structure is proposed for the flying height adjustment. A bulk PZT ceramic is bonded onto the backside of slider directly. The PZT actuator adjusts the flying height by control of air bearing surface profile. The total thickness of the active slider is same as a standard pico slider. This structure is easy to fabricate and compatible with standard product, it also keeps the air bearing surface intact. The thicknesses of the PZT and the glue are optimized with numerical simulations. This active slider has been demonstrated and the observed flying height adjustment is 2.3nm.

Development of Spin-Torque Oscillators and High CoPt Media With Small Grain Size for Microwave-Assisted Magnetic Recording

We report the selection of materials and design of spin-torque oscillators (STOs) which are able to operate in an alternative magnetic field (variable frequency) of magnitude ~8000 Oe, generate large enough in-plane ac magnetic field in the recording media, and have tunable high frequency at low driving current for microwave-assisted magnetic recording (MAMR) based on micromagnetic simulations. The mechanism and integration approaches of STOs with the current recording system to have the least driving current are also presented. This paper also covers the material choice, layer-stack optimization, and process development on Cox Pt1-x alloy films with extremely high coercivity of more than 1.5 T (Ku of about 1.5 × 107 erg/cc), well-isolated small grains of size 6-7 nm, for the extension of perpendicular magnetic recording and MAMR.

Writer Footprint Measurement on Spinstand and Media Transition Curvature Characteristics

The head media integration played a very important role to push up the areal density of perpendicular recording successfully. Besides the success of good sensitivity and high resolution reader at desired feature size of recording bit, the advanced writing process is the key enabler to sustain the areal density growth continuously. The sharper field gradient of writer and the narrower switching field distribution of recording media improve the transition jitter and promote the SNR of recording media. Without reducing grain size, the areal density of perpendicular recording has been increased by a few times. In this work, we investigate the performance of writing process via the measurement of head field footprint in recording media on the Spinstand. The feature size variations of head footprint at different writing current and different flying height (FH) illustrate the effective writing process visually. The transition curvature with transition width value at the trailing edge of writer pole is the key indicator to show the linear density capability related to writing process.

A ZnO thin-film driven microcantilever for nanoscale actuation and sensing

Zinc oxide (ZnO) thin film as a piezoelectric material for microelectromechanical system (MEMS) actuators and sensors was evaluated. ZnO thin films were deposited using radio frequency (RF) magnetron sputtering. Process parameters such as gas ratio, working pressure, and RF power were optimized for crystalline structure. The ZnO thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Good quality of ZnO thin films was further confirmed by a high transverse piezoelectric coefficient d 31. A microcantilever was then designed, fabricated, and characterized. Design formulas of resonant frequency, actuation, and sensing sensitivities were derived. The resonant frequency was determined by an impedance analyzer. Tip deflection on nanometer level was demonstrated with the cantilever used as an actuator. The actuation sensitivity was found to be 12.2 nm/V. As a sensor, the cantilever was calibrated against a reference accelerometer. The sensing sensitivity was characterized to be 46 mV/g. The characterization results were compared with design specifications. The differences were caused mainly by thickness control in etching. This study showed that ZnO is a promising piezoelectric material for MEMS actuators and sensors in terms of excellent process compatibility and good piezoelectric performance.

Study of Piezoelectric ZnO Thin Films for Contact Sensing and Head Actuation

To realize higher areal densities towards 10 Tb/in2 in hard disk drives, the flying height between slider and disk needs to decrease to the near-contact region. It is essential to monitor head-disk interactions to prevent instability and damage from occuring on the head-disk interface. This paper presents deposition and characterization of zinc oxide (ZnO) thin films for smart sliders. ZnO thin films with different c-axis orientations and sputtering durations were prepared using RF magnetron sputtering and their physical properties were measured by scanning electron microscopy. A piezoelectric ZnO sensor array was fabricated using fabrication techniques compatible with standard slider micromachining process. The simulation results indicated the sensor array was capable of detecting different contact locations.

Design and Analysis of a Slider-Level Piezoelectric Sensor Array for Head-Disk Contact Detection

To realize higher areal densities towards 10 Tbit/in2, the ever decreasing flying height of the slider approaches the near-contact regime. It is essential to monitor head-disk interactions to prevent instability and damage to the head-disk interface. In this study, a piezoelectric sensor array embedded on the slider was proposed for head-disk contact detection. Integrability of the sensor array with standard slider fabrication process was considered in the design. Dynamic response of the sensor array to typical contact scenarios was obtained by finite element analysis. Simulation results suggest that the sensor array is adequately sensitive and capable of identifying contact location under intermittent head-disk contact.