Al2O3-TiC Sliders Research Articles

Simple Method of Determining the Temperature of Laser Diode Integrated into Heat-Assisted Magnetic Recording Head

We propose a new experimental method of determining the temperature of a laser diode (LD) integrated into a heat-assisted magnetic recording head that utilizes the temperature dependence of the peak wavelength on the LD. Furthermore, we experimentally show the temperature rise of the LD mounted on the trailing side of an Al2O3–TiC slider. On our sample head assembly, the temperature rise is about 4 °C when the optical output power and duty ratio of the LD are 15 mW and 50%, respectively.

Fabrication and experimental study of Al2O3-TiC sliders with piezoelectric nanoactuators for flying height control

A gap flying height (FH) of less than 5 nm between the read/write element and the surface of the disk is required for ultrahigh density recording. A stable and constant FH must also be sustained in the presence of altitude and temperature changes and manufacturing tolerance. A FH adjustment or controlled slider that is capable of adjusting its gap FH has been proposed previously. In this paper we demonstrate an inexpensive and low-temperature approach for integrating piezoelectric materials in the fabrication of current small form-factor Al2O3-TiC sliders. A bulk PZT sheet is bonded onto the back of row-bars and the sliders are separated by a standard dicing process. It requires no deep reactive-ion etching (DRIE) or high temperature processes and is suitable for mass production. A conventional design and a new special air bearing surface (ABS) design have been fabricated and tested by an optical profiler and a FH tester. A nonflying actuation stroke of 0.6–0.8 nm/V has been observed. The FH measurements showed that the ABS plays a key role in increasing the actuation efficiency, which also agrees well with the numerical analysis.

Near Field Heat Assisted Magnetic Recording with a Planar Solid Immersion Lens

In this paper we present experimental heat assisted magnetic recording results using a planar solid immersion mirror (PSIM) fabricated on an Al2O3–TiC slider. The heads were flown at a velocity of 14 m/s, 20–25 nm above a Co/Pt multilayer medium which was deposited on a 60 mm glass disk. It was found that the track width and carrier-to-noise-ratio (CNR) increased with the applied magnetic field. Recording experiments were also performed with PSIMs terminated with 125 µm apertures. This led to narrower tracks and smaller CNR values for the same applied fields compared to recording with a PSIM only.

Experimental Identification of Elastic, Damping and Adhesion Forces in Collision of Spherical Sliders With Stationary Magnetic Disks

This paper deals with the experimental identification of elastic, damping and adhesion forces in the dynamic collision of a spherical slider with a stationary magnetic disk. We used rough Al2O3TiC and smooth glass spherical sliders with a radius of 1 mm, and magnetic disks with four different lubricant film thicknesses of 0, 1, 2, and 3 nm. We found that the Al2O3TiC slider shows ordinary approach and rebound processes, whereas the glass slider showed a velocity drop at the end of the rebound process when the lubricant thickness was 1, 2, and 3 nm. We identified the elastic force factors in the approach and rebound processes, based on Herztian contact theory, and the damping force factors based on a damping force model that is proportional to slider velocity and penetration depth (contact area). From the drop in velocity when the slider and disk separated, we found that the dynamic adhesion force is almost equal to the static pull-off force except for with a 3 nm lubricant thickness. The dynamic adhesion force with a 3 nm lubricant thickness is significantly higher, probably because of squeeze damping effect.

Effect of lubricant bonding fraction at the head–disk interface

Tribochemical studies of the effect of lubricant bonding on the tribology of the head–disk interface (HDI) were conducted using hydrogenated (CHx) carbon disk samples coated with perfluoropolyether ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3–TiC sliders and also thermal desorption experiments in an ultrahigh vacuum (UHV) tribochamber. The friction and catalytic decomposition mechanisms as well as the thermal behavior of ZDOL are described. We observed that a larger mobile lubricant portion significantly enhances the wear durability of the HDI by providing a reservoir to constantly replenish the lubricant displaced in the wear track during drag tests. In the thermal desorption tests we observed two distinct temperatures of desorption. The mobile ZDOL layer is desorbed at the lower thermal desorption temperature and the residual bonded ZDOL layer is desorbed at the higher thermal desorption temperature.

Tribochemistry of monodispersed ZDOL with hydrogenated carbon overcoats

Tribochemical studies of the lubricant molecular weight effect on the tribology of the head/disk interface were conducted using hydrogenated (CHx) carbon disks coated with ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3–TiC sliders and thermal desorption experiments in an ultrahigh vacuum tribochamber. The studies showed that the lubricant interaction with the carbon overcoat varies as a function of lubricant molecular weight. The friction coefficient increases as the molecular weight increases. The higher friction is due to the higher viscosity. The friction and catalytic decomposition mechanisms of ZDOL are described. In general, the perfluoropolyethers polymers are decomposed by chain scission involving the breakage of the backbone bonds to yield free-radical segments. Chain scission can occur by three mechanisms: (1) random degradation, (2) depolymerization, and (3) weak-link degradation. Our studies further support previous observations that catalytic reactions occurred at the endgroups. The lower number of endgroups for ZDOL with higher molecular weight reduces the possibility of the occurrence of catalytic reactions. Moreover, the ZDOL desorbed peak temperatures shifted to higher temperatures with increasing molecular weight in thermal desorption tests. The spreading diffusion coefficient of ZDOL decreases with increasing molecular weight. As the mobility of the lubricant chain decreases, the desorption energy needed to break the lubricants increases, resulting in higher desorption peak temperatures.

Effects of Backbone and Endgroup on the Decomposition Mechanisms of PFPE Lubricants and Their Tribological Performance at the Head-Disk Interface

Tribo-chemical studies of the lubricant endgroup effect on the tribology of the head-disk interface were conducted using carbon disks coated with PFPE lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3-TiC sliders in an ultrahigh-vacuum (UHV) tribochamber. The UHV drag tests show that a good lubricant should have one active OH endgroup and one nonactive endgroup. The active one insures the lubricant is adsorbed very well onto the disk carbon surface, resulting in a lower removal rate of the lubricants during the contact sliding. The nonactive one prevents the catalytic decomposition of the lubricant in the presence of the Al2O3 surface of the uncoated slider. The studies also demonstrate that the catalytic degradation process of ZDOL in the presence of Lewis acid occurs most readily at the acetal units -O-CF2-O within the internal backbones (CF2O and CF2CF2O) instead of the endgroup functionals. Therefore, demnum, without any acetal units, experiences less catalytic degradation with the uncoated Al2O3/TiC sliders as compared to ZDOL.

Tribo-Chemical Wear of Amorphous Carbon Overcoats and TiC in Al2O3-TiC Sliders

Ambient drag experiments were carried out using Al2O3-TiC sliders and carbon-coated aluminum/magnesium substrate disks. Worn carbon of disks resulted in sub-micron particles that transferred to smears under frictional heating and mechanical shear force. Raman analysis found graphitization for carbon debris and smears but not for carbon within wear tracks. The carbon of wear tracks was also considered graphitized but was very superficial. Decomposition of TiC in DLC-coated and uncoated sliders was also observed and caused by carbon diffusion and titanium oxidation. Diffused carbon could be poly-crystalline graphite and amorphous depending on the reactive environment of the interface. Discussions were made on tribo-chemical wear of the interface materials.

Forced Response of PZT Glide Heads1

This paper studies forced response of PZT glide heads through calibrated experiments and finite element analyses. The PZT glide heads consist of an Al2O3TiC slider and a PZT transducer. In the first part of the research, the PZT transducer serves as an actuator exciting the glide heads from 100 kHz to 1.3 MHz. A laser Doppler vibrometer (LDV) and an impedance analyzer are used to measure frequency response functions (FRF) and PZT impedance. In addition, the response of the PZT glide heads is simulated through finite element analyses (FEA). The FEA predict the resonance frequencies with less than 5 percent difference. For the first two slider modes, the FEA also predict resonance amplitudes with good accuracy. In the second part of the research, the PZT transducer serves as a sensor, and the glide head is subjected to an impact force. To produce short impacts experimentally, miniature balls are dropped to the glide heads. The impact force is estimated through the impact duration and the momentum change before and after the impact. Then the impact force and the PZT output voltage are processed to produce FRF. Since the PZT sensor and its circuit form a high-pass filter, the FEA need to consider the slider, the PZT transducer, and the electric circuits simultaneously to produce meaningful results. The FEA predictions agree with the experimental measurements for the first two slider modes as well. [S0742-4787(00)01004-3]

Initiation of lubricant catalytic decomposition by hydrogen evolution from contact sliding on CHx and CNx overcoats

Tribochemical studies of the head/disk interface (HDI) were conducted using hydrogenated (CHx) and nitrogenated (CNx) carbon disk samples coated with perfluoropolyether ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3–TiC sliders and thermal desorption experiments in an ultrahigh vacuum (UHV) tribochamber. We observed that the hydrogen evolution from CHx overcoats initiates lubricant catalytic decomposition with uncoated Al2O3/TiC sliders, forming CF3 (69) and C2F5 (119). The generation of hydrofluoric acid (HF) during thermal desorption experiments provides the formation mechanism of Lewis acid, which is the necessary component for catalytic reaction causing Z-DOL lube degradation. On the other hand, for CNx films, lubricant catalytic decomposition was prevented due to less hydrogen evolution from the CNx overcoat.

The Decomposition Mechanisms and Thermal Stability of ZDOL Lubricant on Hydrogenated Carbon Overcoats

Tribo-chemical studies of the head/disk interface (HDI) were conducted using hydrogenated CHx carbon disk samples coated with perfluoropolyether ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3-TiC sliders and thermal desorption experiments in an ultra-high vacuum (UHV) tribochamber. The friction and catalytic decomposition mechanisms as well as the thermal behavior of ZDOL are described, and data demonstrating the chemical reactions of the lubricant and carbon overcoat are also presented. During the sliding at the carbon-coated slider/ZDOL lubricated CHx disk interface, frictional heating is the primary decomposition mechanism of ZDOL. [S0742-4787(00)01902-0]

Low Wear of Magnetic Disk Slid with Diamond Slider.

Tribological properties of magnetic disk with diamond and Al2O3 TiC sliders were studied by disk contact sliding tester and reciprocating tribo tester, and then the contact principal and shearing stress were analyzed by the boundary element method. The following results were obtained. (1) Friction coefficient of magnetic disk with diamond tip lubricanted with PFPE is low asμ=0.1-0.8 evaluated with magnetic disk contact sliding tester. In contrast, the friction coefficient of magnetic disk slid with Al2O3 TiC slider is as high asμ=0.5-1.4. This result is mainly deduced to the low shear strength of PFPE lubricant between diamond slider and magnetic disk surfaces. (2) Wear rate of magnetic disk slid with Al2O3 TiC slider is larger than that with diamond slider. Plastic deformation damage were formed on the magnetic disk surface with PFPE boundary-lubrication. When a diamond is used as opposite sliders, wear on the magnetic disk surface can be reduced. (3) To clarify the reason why less wear of magnetic disk with diamond slider, stress analysis was carried out by the boundary element method about each sliding combination. The maximum shear stress of magnetic disk surface slid with diamond slider is less than that of the magnetic disk Al2O3 TiC combination. The wear rate of the magnetic disk slid with diamond tip is very little due to the low shearing stress of surface because of the damage seems to be originated from sliding surface. (4) Wear rate of magnetic disk corresponds to the maximum shearing stress on surface. To realize accerarated wear test of magnetic disk contact sliding test with the analysis of maximum shearing stress of surface, the running in effect must be evaluated.

Tribological performance of PFPE and X-1P lubricants at head–disk interface. Part I. Experimental results

X-1P, a cyclic phosphazene lubricant, is studied and compared with polar perfluoropolyether (PFPE) lubricant Z-Dol. Contact angles of lubricants are measured on different solid surfaces. Contact start-stop (CSS), drag, and ball-on-flat tests are performed and the results are discussed. Drag tests under high vacuum are also performed and discussed. Experimental results show that lubricant X-1P exhibits lower static friction and higher durability than lubricant Z-Dol, especially at high humidity. Higher durability is also observed for X-1P under the high vacuum condition compared with lubricant Z-Dol. Diamond-like carbon (DLC) overcoat on the Al2O3–TiC slider surface lowers friction and prolongs durability, especially for lubricant Z-Dol at high humidity, whereas for X-1P, there is no benefit of DLC. X-1P as an additive shows some improvement in durability at high humidity as compared to lubricant Z-Dol.

Lubricant thickness effect on tribological performance of ZDOL lubricated disks with hydrogenated overcoats

Tribo-chemical studies of the lubricant thickness effect on the tribology of the head/disk interface (HDI) were conducted using hydrogenated (CHx) carbon disk samples coated with perfluoropolyether ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3–TiC sliders and thermal desorption experiments in an ultra-high vacuum (UHV) tribochamber. The studies showed that the lubricant interaction with the carbon overcoat varies as a function of lubricant thickness. Wear durability improves considerably for thicknesses more than a monolayer. However, in the sub-monolayer thickness regime, the adhesion of the lubricant to the carbon overcoat is much stronger, as indicated by the fact that a much higher temperature is required to desorb the lubricant. When the lubricant thickness is around or above a monolayer, cohesion among the lubricant molecules plays a greater role and a much lower temperature is needed for lubricant desorption.

Tribochemistry of ZDOL Decomposition on Carbon Overcoats in Ultra-High Vacuum (UHV)

AbstractTribochemical studies of the effect of lubricant bonding on the tribology of the head/disk interface (HDI) were conducted using hydrogenated (CHx) carbon disk samples coated with perfluoropolyether ZDOL lubricant. The studies involved drag tests with uncoated and carboncoated Al2O3-TiC sliders and also thermal desorption experiments in an ultra-high vacuum (UHV) tribochamber. We observed that a larger mobile lubricant portion significantly enhances the wear durability of the (head/disk interface) HDI by providing a reservoir to constantly replenish the lubricant displaced in the wear track during drag tests. In the thermal desorption tests we observed two distinct temperatures of desorption. The mobile ZDOL layer is desorbed at the lower thermal desorption temperature and the residual bonded ZDOL layer is desorbed at the higher thermal desorption temperature. We also observed that the hydrogen evolution from CHx overcoats initiates lubricant catalytic decomposition with uncoated Al2O3/TiC sliders, forming CF3 (69) and C2F5 (119). The generation of Hydroflouric acid (HF) during thermal desorption experiments provides the formation mechanism of Lewis acid, which is the necessary component for catalytic reaction causing Z-DOL lube degradation.

Silicon carbide—;a potential material for magnetic recording sliders

The feasibility of using silicon carbide as a magnetic recording slider material is investigated using stiction tests with different dwell times, contact start-stop (CSS) tests and drag tests at different temperatures and humidities. The stiction and frictional properties of silicon carbide sliders are compared with standard Al2O3-TiC sliders and it is concluded that their tribological behaviour is superior to that of conventional Al2O3-TiC sliders. The results of this study show that silicon carbide is a promising material for magnetic recording sliders.

Degradation of perfluoropolyether lubricants on magnetic recording disks during sliding

Degradation of perfluoropolyether lubricants (Fomblin Z-Dol and Fomblin AM 2001) on the magnetic recording thin-films disks are studied during sliding with an Al2O3-TiC slider under high vacuum. Gaseous products generated from the head/disk interfaces are detected and monitored as a function of sliding distance using a quadrupole mass spectrometer. Effects of overcoats and surface roughnesses of disks on degradation of lubricants and coefficient of friction were also studied. Experimental results show that the gaseous products generated from Z-Dol and AM 2001 lubricants during sliding are quite similar. Degradation of both lubricants is found to take place from the beginning of sliding, and the evolution rate of decomposition fragments decreases with the sliding distance. Removal of the lubricants is accompanied by a rapid rise in the coefficient of friction of the interfaces, followed by gaseous products from the tribochemical reaction of the overcoat material. Surface roughness of the disk has an effect on the sliding distance to failure, but little effect on the decomposition of lubricant.

Friction and durability of ceramic slider materials in contact with lubricated thin-film rigid disks

Slider materials with improved static and kinetic friction and durability of the head-disk interface are required for minimum separation between the head slider and magnetic medium and miniaturization of sliders. Mn-Zn ferrite, calcium titanate, Al2O3-TiC and SiC sliders were used in drag tests, stiction tests and contact start-stop (CSS) tests. The SiC slider exhibits the best tribological performance at all humidities as compared to other sliders. Relevant mechanisms are revealed with measurement of the contact angle of perfluoropolyether (PFPE) lubricants on slider materials, lubricant transfer tests, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red (FTIR) analyses on the slider surfaces before and after tests. Best friction and wear performance of SiC is attributed to lubricant transfer from the lubricated disk to the slider surface and formation of tribochemical films. A lubricant layer on the slider surface protects the slider from wear and also increases the contact angle with the water film, resulting in a low meniscus contribution leading to low stiction. The tribochemical reaction forms a gel-like hydroxide layer on the SiC slider surface which performs as a boundary lubricant, leading to a low coefficient of friction and low wear.

Tribological performance of thin film amorphous carbon overcoats for magnetic recording rigid disks in various environments

An ultrahigh vacuum tribotester equipped with Auger electron analyzer and mass spectrometer is used to study the friction and wear behavior of amorphous carbon coated magnetic thin film rigid disks. The tests include continuous sliding of Al 2O 3-TiC sliders against lubricated and unlubricated polished and textured disks. Operating environment is found to play an important role in the tribological performance of the carbon overcoat. Wear lives were longest in dry nitrogen and argon environments as compared with ambient environment (with oxygen and water vapor), in agreement with some of the previously reported results. The wear lives of the carbon coatings in vacuum were inferior to those in other environments. In comparison, surface roughness and lubrication play a less significant role in friction and wear for the disks tested. Based on this study, we conclude that poor wear life in vacuum results from intimate slider-to-disk contact. The long life in dry Ar and nitrogen as compared with Ar+O 2 and ambient environment, results from the absence of tribochemical oxidation prevalent in the oxidizing environment.

Structure and friction of amorphous carbon films of nanometer thickness

Amorphous carbon films were deposited onto thin film disks by the r.f. sputtering method to a thickness between 0.2 and 3 nm. The film growth behavior was investigated by X-ray photoelectron spectroscopy. The growth mode of the sputtered carbon films was layer by layer (also called Frank der Merwe model). The coefficient of friction between CoCrTa surface and an Al 2O 3-TiC slider is higher than 0.4. The deposition of a carbon film 0.2 nm thick decreases the coefficient of friction to 0.2. This result suggests that the presence of a monolayer-level carbon film helps eliminate sticking or adhesion between the surface and the slider, and allows one to slide smoothly over the other with a well-defined coefficient of friction.