Slider-disk Interaction Research Articles

Experimental study of slider–disk interaction process with thermal-flying-height controlled slider

Thermal flying height (TFC) controlled slider has been introduced in hard disk drive recently. Flying height at the read/write elements of the slider is controlled by thermal pole tip protrusion. Interactions between the TFC slider and disk can be very gentle because the low flying height thermal protrusion area is usually very small. It is still a big challenge to detect very gentle interactions. In this work, a very sensitive method to study very gentle slider–disk interaction in frequency domain has been developed and details of the TFC slider–disk interactions from gentle to strong have been revealed. It is proved that higher heating power is required to initiate the vibration in which higher stiffness part of the slider air-bearing is involved.

Slider–Lubricant Interaction and Corresponding Tribocurrent

The tribo-current phenomenon is one of the important effects associated with intermittent slider-disk interaction. By the experiment to simulate interaction with a conductive probe and measure the induced current simultaneously using a conductive atomic force microscopy, some critical points, which divide the probe-sample interaction into probe-disk, probe-lubricant, and noncontact, can be observed. Similar phenomena were also observed when flying a thermal flying-height control slider over a specially prepared disk. This proposed technique might be applied to ascertain the dynamic interaction exactly between the slider and the lubricant, which would be the critical issue for accurate studying of ldquofly- and lubricant-contact recordingrdquo approaches in which the slider will be in continuous contact with the lubricant.

TOF-SIMS analysis for thermal effect study of hard disk lubricant

Temperature is an important factor that affects the performance of hard disk drive. Through Time-Of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) analysis, the thermal effects on hard disk Z-DOL lubricant is studied, the related thermal evaporation and decomposition mechanism is proposed, and the lubricant composition change on the wear track of the hard disk surface after slider–disk interaction is reported in this paper.

Effect of relative humidity and disk acceleration on tribocharge build-up at a slider–disk interface

High performance disk drives require high spindle speed. The spindle speed of typical hard disk drives has increased in recent years from 5400 to 15000 rpm and even higher speeds are anticipated in the near future. The increasing disk velocity leads to increasing disk acceleration and slider–disk interaction. As the head-to-disk spacing continues to decrease to facilitate increasing recording densities in disk drives, the slider–disk interaction has become much more severe due to the direct contact of head and disk surfaces in both start/stop and flying cases. The slider–disk interaction in contact-start-stop (CSS) mode is an important source of particle generation and tribocharge. Charge build-up in the slider–disk interface can cause electrostatic discharge (ESD) damage and lubricant decomposition. In turn, ESD can cause severe melting damage to MR or GMR heads. We measured the tribocurrent/voltage build-up generated at increasing disk acceleration. In addition, we examined the effects of relative humidity on the tribocharge build-up. We found that the tribocurrent/voltage was generated during pico-slider/disk interaction and that its level was below 250 pA and 0.5 V, respectively. Tribocurrent/voltage build-up was reduced with increasing disk acceleration. Higher humidity conditions (75–80%) yielded lower levels of tribovoltage/current. Therefore, a higher tribocharge is expected at a lower disk acceleration and lower relative humidity condition.

Engineering issue study of triple harmonic method for in situ flying height analysis

In situ flying height testing technology is becoming more and more important in slider–disk interaction analysis and manufacturing quality control of disk drives and head-related components. Triple harmonic method is a quite promising choice for in situ flying height analysis, compared with other in situ methods reported up to now. This paper reports results of investigations on engineering issues of applying triple harmonic method for in situ flying height analysis. The paper reports results of analysis on the effects of various testing conditions on flying height testing repeatability and accuracy. Results suggest that working at reasonable high channel density and working on the ratio between third and first harmonics will be an advantage in terms of both flying height testing sensitivity and testing repeatability. Comparing with media thickness effect, the gap-length variation among different heads will be important if it is to study flying height difference among different heads and the testing is at high channel density. Also, it is suggested to work at AC erased track, in order to reduce the non-linearity caused by hard transition.

Observation of Slider Landing Process in Hard Disk Drive

With the decrease in slider flying height, slider flying instability caused by slider–disk interactions is becoming a big concern. Novel technology has to be employed to further improve our understandings about slider–disk interaction. In this work, a slider flying height-attitude testing (3D) system was employed to study slider–disk interaction during a slider landing process to demonstrate its capability for the application. It is shown that great details of slider–disk interactions and subtle variations of the slider flying attitude during the landing process can be revealed with the 3D system. Slider dynamic flying height and attitude (pitch and roll angles) during the landing process can be determined from the data recorded in one test. Furthermore, analysis in frequency domain can be done not only on flying height, but also on pitch and roll angles directly. It is found that the slider landing process can have different stages during which slider performance and characteristics of slider–disk interaction are different.

하드 디스크 드라이브 회전수 변화가 드라이브 내 나노 오염 입자 발생에 미치는 영향

In high-density hard disk doves, the slider should be made to fly close to the magnetic recording disk to generate better signal resolution and at an increasingly high velocity to achieve better data rate. The slider disk interaction in CSS (contact-start-stop) mode is an Important source of particle generation. Contamination particles In the hard disk drive can cause serious problems including slider crash and thermal asperities We Investigated the number and the Sizes of particles generated in the hard disk drive, operating at increasing disk rotational speeds, in the CSS mode CNC (condensation nucleus counter) and PSS (particle Size selector) were used for this investigation In addition, we examined the particle components by using SEM (scanning electron microscopes), AES (auger electron spectroscopy), and TOF-SIMS (time of flight-secondary Ions mass spectrometry) The increasing disk rotational speed difectly affected the particle generation by slider disk interaction The number of particles that were generated increased With the disk rotational speed. The particle generation rate Increased rapidly at motor speeds above 8000 rpm Tins Increase may be due to the Increased slider disk Interaction. Particle Sizes ranged from 14 to 200 nm. The particles generated by slider disk Interaction came from the lubricant on the disk, coating layer of the disk, and also slider surface.<br/>

Effect of disk rotational speed on contamination particles generated in a hard disk drive

In high-density hard disk drives, the slider should be made to fly close to the magnetic recording disk to generate better signal resolution and at an increasingly high velocity to achieve better data rate. The slider disk interaction in CSS (contact-start-stop) mode is an important source of particle generation. Contamination particles in the hard disk drive can cause serious problems including slider crash and thermal asperities. We investigated the number and the sizes of particles generated in the hard disk drive, operating at increasing disk rotational speeds, in the CSS mode. Condensation nucleus counter (CNC) and PSS (particle size selector) were used for this investigation. In addition, we examined the particle components by using SEM (scanning electron microscopes), AES (auger electron spectroscopy) and TOF-SIMS (time of flight-secondary ions mass spectrometry). The increasing disk rotational speed directly affected the particle generation by slider disk interaction. The number of particles that were generated increased with the disk rotational speed. The particle generation rate increased rapidly at motor speeds above 8000 rpm. This increase may be due to the increased slider disk interaction. Particle sizes ranged from 14 to 200 nm. The particles generated by slider disk interaction came from the lubricant on the disk, coating layer of the disk, and also slider surface.

Tribocharge build-up and decay at a slider-disk interface

As the gap between the head and disk decreases and the sensitivity of recording transducers increases, the head and disk are more likely to come in contact, which may damage the recording transducer during start/stop and flying cases. One important effect associated with the intermittent head-disk contacts is the tribocharge/tribocurrent phenomenon. In this study, tribocharge and tribocurrent generation during a pico-slider/disk interaction were measured by using an electrometer. These triboelectrical properties were compared with friction force and acoustic emission signals. The electrical potential difference between the slider and the disk was caused by mechanical interactions between them. The tribocharge was generated during the slider-disk interaction and its saturation charge level was about 1 V. The tribocharge build-up level was independent of the slider-disk interaction time. However, the tribocharge decayed when there was no interaction between the slider and the disk. The decay of tribocharge was inversely proportional to the square root of time. Tribocurrent generation coincided with tribocharge generation. The tribocurrent was also independent of the slider-disk interaction time. The current level measured in this study may not reach the electrostatic discharge (ESD) damage level, but it can induce the dissociation of lubricant.

A study of the lubricant displacement under a flying head slider caused by slider-disk interaction

Even if no contact occurs between the disk and slider, lubricant flow is affected by several factors correlated with head-disk interaction. In particular, air-bearing pressure and disk surface topography have significant effects on thin lubricant films, and they may possibly cause uneven lubricant distribution. In this paper, we study the lube displacement under a flying head slider caused by slider-disk interaction, especially the effects of air bearing pressure and disk surface topography, which we detected by executing flyability tests using an optical surface analyzer.

Sliding contact energy measurement using a calibrated acoustic emission transducer

Acoustic emission (AE) transducers are commonly used to monitor the intensity of mechanical contacts in various sliding applications including magnetic head-disk interfaces (HDI). The authors introduce a method to obtain the electrical energy of the AE transducer from the output signal voltage. Calibration experiments were run to determine the calibration factor for converting the AE electrical energy to mechanical energy that is released during mechanical contacts at the HDI. Analytical models to calculate the energy released as a result of mechanical contacts arising from slider-disk interaction, from the presence of particulate contamination at the HDI, and those from head-disk interactions during dynamic load/unload (L/UL) in L/UL drives are presented. Experimental results for some of the cases described by the models are presented.

Mapping of slider-disk interaction

A novel methodology has been introduced to map slider-disk interactions and, thus, study the potential of magnetic decay caused by such interactions. Investigations are focused on the visualization of such interactions. The methodology is based on a specially prepared disk which is of the same structure as a conventional magnetic disk except a magnetooptical (MO) layer is used, which is of low Curie temperature, to replace the magnetic layer of the magnetic disk media. Interactions that generate a temperature above the Curie temperature of the MO material are recorded, visualized and analyzed by optical and magnetic tools. It is noticed that the signatures of the interactions recorded are mainly line-like. Results also indicate that slider-disk contact during the interaction process is also a contact vibration process and the vibration frequency is not a constant. Results presented in this work also show the unique advantage of the proposed method in visualizing severe slider-disk interaction which cannot be revealed by either atomic force microscopy (AFM) or high-resolution observation of carbon wear or lubricant degradation with optical surface analyzers.

A novel method for the study of slider-disk interaction in high performance disk drives

This work reports a novel method for the visualization of slider-disk or slider-particle-disk interactions. The method is based on a special testing disk which is same as the conventional magnetic disk media except using a layer of magneto-optical (MO) material to replace the magnetic layer of the magnetic disk media. The magnetization in the MO layer will be switched by a small external field applied if the temperature generated by the interactions is higher than the Curie temperature of the MO material. The proposed method and corresponding setup were used successfully in the experimental study of slider-disk and slider-particle-disk interactions.

Tribological performance of nano-thin fluoropolymer coated sliders

With the increase in recording density, any accumulation on slider surface can cause serious problems, such as high fly–stiction and extensive slider–disk interaction. Therefore, how to mitigate the accumulation on slider surface and thus, improve the stability and reliability of head–disk interface is becoming an important issue. In this work, a nanothin fluoropolymer overcoat with very good oleophobic and hydrophobic properties was applied on slider surface with a dipping process. Tribological performance, such as fly–stiction, normal stiction, and takeoff and landing processes, of the coated sliders was studied. Test results show that although normal stiction is not lowered, normal stiction modulation is reduced obviously by the overcoat. Fly–stiction and its modulation of coated sliders are much smaller than those of uncoated sliders. Coated sliders show much better takeoff and landing performance during contact start stop tests. After tests, the surfaces of tested sliders and disks were examined with an optical microscope, surface reflectance analyzer, and TOF–SIMS to interpret the tribological performance of the coated sliders. It can be concluded that the fluoropolymer overcoat reduces the amount of accumulation on slider surface and thus, improves the tribological performance of the coated sliders.

Slider-disk interaction and tribologically induced signal decay

The thermal energy generated during slider-disk interaction is another factor which leads to the decay of recorded magnetic signal on disk media. As technology moves to sub-10 nm spaced head-disk systems, high spindle speed, ramp load/unload mechanism, and high seeking speed, the likelihood of such thermal energy generation increases and so is the intensity of such interaction. Experimental results presented in this work indicate that signal can be decayed by slider disk contact in load/unload operation, even when the contact cannot be detected easily by AE sensor attached at the end of the suspension arm. A special disk is proposed and used for the visualization of potential tribological decay. The disk uses a layer of magneto-optical material with low Curie temperature to replace the magnetic layer used in magnetic media and record the traces left by potential sources of tribologically induced decay. The method and corresponding setup were used successfully in the study of the effectiveness of anti-particulate designs and the identification of the worst case among loading and unloading operations at high longitudinal load/unload speed.

Flying height measurement considering the effects of the slider-disk interaction

As technology moves to a mechanical head-disk spacing of 4-8 nm for the recording density beyond 100 Gb/in/sup 2/, new testing methodology becomes necessary to achieve both high sensitivity in flying height measurement and accurate characterization of slider-lube-disk interaction. This paper reports a polarization intensity interferometer which retains high sensitivity in fly-height measurement even when the slider-disk spacing is down to nanometer level. The setup can also study the effect of slider-lube-disk interaction on the flying performance of the slider. This is achieved by covering the commercial glass disk substrate with a layer of carbon overcoat and a layer of lubricant which are same as those used in the actual disk media. Both simulation and experimental investigations were conducted and the results agree well with each other. Results also indicate that it is important to take the slider-disk interaction into account in the flying height measurement of the nanometer spaced head-disk interface.

Slider-disk interaction and its effect on the flying performance of slider

This paper reports a novel optical head-disk interaction tester setup and experimental investigations into the effects of slider-disk interaction in nanometer spaced head-disk interface. The setup revealed quantitatively the lubricant induced change of slider-disk spacing before the slider enters its fully flying status. The setup was also applied to investigate the slider sinking process which is caused by the meniscus force when the slider starts to rest on disk surface. Results shows that such a setup has the advantage of quantitative characterization of slider-disk interface compared with acoustic emission method. Furthermore, the results also demonstrate its advantages in reflecting the actual interaction between slider, lube, and disk surface, compared with the current optical flying height testers.

An experimental study of slider vibration in nanometer spaced head-disk interface

This paper reports results of experimental investigations into slider-disk interaction and slider vibration in nanometer spaced head-disk interface. The investigations were based on an slider-disk interface (HDI) configuration which retains the tribological features of the interface formed by the functional head slider and disk media but make the optical monitoring and quantitative measuring of the slider disk spacing possible. The effects of the lubricant and its thickness on the HDI dynamics were also studied. The results indicate that the slider vibration is dependent not only on slider air-bearing surface design but also strongly on lubricant and other interface conditions.

A theoretical model of slider–disk interaction and AE sensing process for studying interface phenomena and estimating unknown parameters

Theoretical models were developed for comprehensively accounting for the AE sensing process in the measurement of interfaces between different sliders and magnetic rigid disks. The models include tribological factors and system dynamics factors such as contact force, sliding velocity, lubricant thickness, topographic parameters, mechanical parameters, system transfer functions and filter design parameters. The theoretical models agree well with the experimental results conducted for different slider–disk interfaces. The models are also well correlated with extensively published experimental results.

Landing zone skew angle, long term stiction, and contamination build up on slider surfaces of disk drives

This work presents results of experimental investigation on the relationship between landing zone skew angle, long term stiction, and contamination build up on slider surface caused by slider-disk interaction in the landing zone. Results indicate that larger skew angle in the landing zone will lead to higher long-term stiction force and increases the likelihood of linelike contamination build up on slider surface.