Shinji Koganezawa

Shear mode piezoelectric microactuator for magnetic disk drives

We developed a new piezoelectric microactuator for dual-stage actuator systems in magnetic disk drives. This actuator exploits the shear mode of piezoelectric elements and drives the head suspension assembly. This paper describes the structure of our piezoelectric actuator, its mechanical characteristics, and the experimental results of a life test after driving the piezoelectric elements in an atmosphere of high temperature and humidity.

High-speed orthogonal power effect actuator for recording at over 10000 TPI

A new type of rotary actuator for HDDs is presented. To suppress the resonance gain in the quasi-rigid body mode caused by the stiffness of support bearings, we propose orthogonal driving. The designed actuator for a 3.5-inch drive shows a quasi-rigid body mode gain of less than 5 dB, and a fundamental resonance frequency of approximately 10 kHz. The results agree with those from finite element analysis.

Effect of dual-stage actuator on positioning accuracy in 10 k rpm magnetic disk drives

We have developed a piezoelectric micro-actuator for dual-stage actuator systems in magnetic disk drives. This microactuator, which drives the head suspension assembly, is based on the shear deformation of piezoelectric elements. We installed the microactuator in one of Fujitsus 3.5-inch commercial drives for evaluation of the servo system of dual-stage actuator. This paper describes the effect of the dual-stage servo system on positioning accuracy compared with the single actuator.

A high-performance and low-profile moving-magnet actuator for disk drives

We have developed a high-performance moving-magnet rotary actuator for very low-profile magnetic disk drives. A small moving magnet and efficient low-profile magnetic circuit construction give high acceleration and reduce power consumption to 50% that of moving coil actuators. The arrangement of the coils and yokes increases the design flexibility. The actuator does, however, suffer from a magnetic bias force and large inductance. >

Slider Wear on Disks Lubricated by Ultra-Thin Perfluoropolyether Lubricants with Different Molecular Weights

In this study, the wear properties of a magnetic head slider on disks lubricated by ultra-thin perfluoropolyether (PFPE) lubricants with different molecular weights were evaluated by the continuous sliding of magnetic head sliders using the slider contact by the dynamic flying height control. Two types of PFPE lubricants (Z-tetraol and D-4OH) with different molecular weights were evaluated. Results show that the slider wear depended on the coverage of the lubricant film; i.e., the lubricant film with sufficient coverage reduced slider wear. The lubricant film with a low molecular weight (low-Mw), including a lubricant material with a Fomblin and Demnum main chain, exhibited better coverage on a diamond-like carbon surface. Sliders with a low-Mw lubricant film showed less wear than those of a high molecular weight (high-Mw), and the depletion of the low-Mw lubricant film was less than that of the high-Mw lubricant film.

Rotating Symmetrical Piezoelectric Microactuators for Magnetic Head Drives

A unique piezoelectric microactuator for the head-slider drive dual-stage actuator systems in magnetic disk drives has been developed. This microactuator is based on a rotating symmetrical structure and a symmetrical operation. The piezoelectric actuator elements used in the system have a simple rectangular multilayered structure. A prototype model with pico slider and head suspension has been tested to demonstrate 0.86 µm displacement at a dc applied voltage of 30 V and observed main resonant frequency of over 20 kHz. No fluctuation in flying height was observed.

Ultrathin PFPE/DLC hybrid overcoat for magnetic disks by photoelectron-assisted chemical vapor deposition

We developed a new method for using photoelectron-assisted chemical vapor deposition to deposit perfluoropolyether (PFPE) lubricant on a diamond-like carbon (DLC) overcoat. PFPE lubricant in the vapor phase was deposited on the DLC surface of a magnetic disk with a bias voltage between the disk surface and a counter electrode above the disk surface during ultraviolet irradiation. The bias voltage accelerated photoelectron emission from the DLC surface, and the photoelectrons partially dissociated the PFPE molecules in the vapor phase. The dissociated molecules then chemically bonded to the DLC surface. According to the experimental results, the bonded ratio of PFPE molecules to the DLC surface was approximately 100%. An ultrathin PFPE/DLC hybrid overcoat was produced as a monolithic film. This hybrid film exhibited a much lower surface energy than the reference Z-tetraol lubricant film and a high water contact angle of over 100°. This hybrid film can increase the head–media clearance and improve some read/write characteristics by using the actual heads.

External Electric Field Assisted Ultraviolet Irradiation for Bonding of Lubricant Film on Magnetic Disks

In this paper, we sought to determine if, during ultraviolet (UV) exposure, the external electric field could control the bonded lubricant thickness. During UV irradiation, the effect of the external electric field on both the bonded lubricant thickness and surface free energy was studied. The lubricant films after UV irradiation were analyzed using time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Because of the negative electric field, the polar component of the surface free energy was reduced, while the bonded lubricant thickness increased. Based on the results of the TOF-SIMS analysis, we concluded that these findings resulted from the negative electric field accelerating the photoelectron emission, and because of these photoelectrons, the bonding between the end groups and diamond-like carbon surface increased.

Degradation of Carbon Overcoat Subjected to Laser Heating in an Inert Gas Environment in Thermally Assisted Magnetic Recording

Because the diamond-like carbon (DLC) thin film overcoat on a hard disk surface plays an important role in maintaining the reliability and durability of the head-disk interface, DLC degradation is a critical issue in thermally assisted magnetic recording (TAMR). The use of helium in hard disk drives (HDDs) is being developed to decrease air-induced structural vibrations, windage loss, and temperature rise. TAMR technology is suggested to be put to practical use in a helium environment in HDDs. In this paper, fundamental experiments have been conducted to understand the structural stability or degradation of an ultrathin DLC overcoat subjected to laser heating in an inert gas environment. An inert gas environment was simulated using nitrogen gas. The degradation of DLC thin films fabricated through chemical vapor deposition was investigated by varying the laser irradiation duration and controlling the intensity of the laser, and it was evaluated through Raman spectroscopy. The differences in the damage mechanisms between an inert gas and air environments were elucidated. We found that the degradation of DLC thin films by oxidation would be significantly less in an inert gas environment than in an air environment.

Adsorption Properties of an Ultrathin PFPE Lubricant With Ionic End-Groups for DLC Surfaces

This paper examines the adsorption properties of the perfluoropolyether (PFPE) lubricant SNH2 with an ionic end-group (i.e., amine salt with a diphenylether moiety) for magnetic disk surfaces in heat-assisted magnetic recording (HAMR) drives. For comparison, the well-known lubricant Z-tetraol was used as a reference material. Initially, strong interactions between the ionic end-groups of SNH2 and an applied electric field in the lubricant solution were established. The surface free energy and bonding ratio were also compared before and after ultraviolet (UV) light exposure to diamond-like carbon (DLC) disk surfaces onto, which the lubricants were coated, with their photoelectron currents measured during UV exposure. In addition, the structural characteristics of the SNH2 lubricant on the DLC surface were analyzed using a time-of-flight secondary mass spectroscopy. Furthermore, the thermal stabilities of the lubricant films were compared following laser heating. Overall, SNH2 showed higher adsorption to the DLC surface than Z-tetraol and interacted more strongly with the electric field in the lubricant solution. Furthermore, although SNH2 without UV exposure showed a large polar surface energy, this energy decreased considerably after UV exposure. This decrease is attributed to interactions between photoelectrons emitted from the DLC surface and the ionic bonds of the SNH2 molecules; the cationic segments of the SNH2 ionic bonds dissociate, whereas the anionic main-chains chemisorb on the DLC surface at the electron holes generated from the ejected photoelectrons. SNH2 after the UV exposure showed high thermal stability because of its strong bonding to the DLC surface. Overall, these results demonstrate that a PFPE lubricant with ionic end-groups may be an effective lubricant for HAMR applications.