Slider–bump contact and flying height calibration

It is a big challenge to determine ultra-low slider flying height accurately. The standard bump disk method is probably the most reliable and acceptable method so far. One of the key issues to determine slider-flying height with the bump disk method is the complicated slider–bump interaction process and the possible disturbance of the bumps on the slider flying performance. Our knowledge about the slider–bump interaction process is still very limited due to the lack of an effective and powerful experimental technique to study it. In this work, the slider–bump interaction process was studied with a dynamic flying height-attitude (3D) system. The interaction process was also simulated to compare with the experimental observations and to help determine the slider–bump contact points in the experimental observations. The accuracy of flying height (FH) calibration with the bump disk method and the minimum slider–bump interference height required for the testing system used in this study to detect the onset of slider–bump contact were analyzed and discussed. It is proved that the 3D system is a very useful and powerful tool for the application. Many details of the slider–bump interaction process can be revealed with the 3D system. It is found that the calibrated FH is much more accurate than that predicated by the simulations.     

An Air Bearing Slider for Small Diameter Disk Storage Devices

The authors propose a novel slider design. The tri-pad slider has three separate air bearing surfaces, one in the front of the slider and the other two in the back of the slider. This design permits the optimization of the air bearing stiffness and flying attitude without changing the minimum flying height. It can minimize the effect of skew angle on the flying height, and offers ample room for a larger size thin film head element. Samples were fabricated and flying characteristics at several velocities, as well as the dynamic flying stability, were investigated.     

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.     

Flying Height Drop Due to Air Entrapment in Lubricant

Recently, it is found experimentally that the flying height of an air bearing slider is influenced by the lubricant on the disk. It is explained as the air molecules are entrapped in the lubricant under the slider due to the high air bearing pressure, causing the reduction in air bearing force, and hence, the flying height decreases accordingly. This paper employs both experiment and simulation to study such a phenomenon. First, the flying height vibration signals of a slider are detected by a laser Doppler vibrometer, on both lubed and delubed disks. It is observed that the heater touchdown power of the slider is approximately 3.4 mW more for delubed disk than the lubed disk. It suggests that the lubricant may cause the flying height lower. Second, a new model is developed to describe the pressure drop due to the air entrapment. Next, simulations are conducted on three different slider designs based on the new model. Flying height drops are investigated due to the air entrapment. The simulation results are compared with published experimental results, and good correlations are observed for the values of the parameters alpha and beta selected. Finally, the effects of solubility on the flying height are discussed, and the flying height drops are evaluated. It is suggested that the slider design must consider the phenomenon to get more accurate simulation results on flying height.     

Effect of environment humidity and temperature on stationary and transient flying responses of air bearing slider

It is well known that the environment humidity and temperature have a significant influence on the flying height of an air bearing slider. However, not many research papers address this topic, especially when the transient flying response is considered. This paper studies the influences of the environment humidity and temperature on both the stationary and transient flying responses of slider by simulation. A slider design for the thermal protrusion application is addressed. The reason for causing the drop of the air bearing pressure is discussed, and the methods for decreasing the drop are proposed. It is observed that the environment humidity and temperature may determine whether the slider is in full flying state or in partial flying/partial dragging state, when the slider is released from a certain height. The reason may be due to the high humidity and temperature which weakens the air bearing. As a result, the air bearing becomes not strong enough to support well the full flying of slider when the influence of the intermolecular force is significant. Slider vibrations for the full flying case and the partial flying/partial dragging case are analyzed in frequency domain, and the slider vibration frequencies are discussed. It shows that the environment temperature and humidity have significant effects on both the stationary and transient flying responses of the slider.     

安装误差对纳米间隙磁头飞行姿态的影响研究

考虑安装误差引起的磁头俯仰角误差和侧翻角误差,建立了磁头飞行数学模型,通过数值方法分析了安装误差对纳米间隙磁头飞行姿态主要参数的影响,并与试验结果进行了对比分析。结果表明,俯仰角误差对飞行高度和俯仰角有明显影响,随着俯仰角安装误差的增加,磁头飞高和俯仰角偏差增加,对侧翻角的影响可以忽略。侧翻角误差只对侧翻角有明显影响,随着侧翻角安装误差的增加,磁头飞行侧翻角偏差增加,对磁头飞行高度和俯仰角的影响可以忽略,理论分析和实验结果吻合较好。磁头设计和装配时,应控制磁头的俯仰角安装误差。     

LOW FLYING HEIGHT MEASUREMENT WITH MULTI-WAVELENGTH INTERFEROMETRY

A method for measurement of ultra-low flying height in head-disk spacing is described. Three different wavelengths are selected out from white light by filters to measure the spacing simultaneously. Besides solving the ambiguity problem, a more reliable result is achieved by using weighted average of measurement results from three different wavelengths, where the weight is dependent upon spacing. Fringe-bunching correction algorithm （FBC） and spot-tilling technique are adopted to suppress calibration and random errors. Moreover, incident bandwidth correction （IBC） method is introduced to compensate the error caused by low monochromaticity of incident light. Based on dynamic flying height tester （DFHT Ⅱ）, with the redesigned of photo-electric conversion and signal acquirement module, an instrument has been developed. And comparing the experimental data from the instrument with those from a KLA-FHT D6, the discrepancy is less than 5%. It indicates that the instrument is suitable to perform ultra-low flying height measurement and satisfies the reauirement of magnetic heads manufacturing.     

Study of a Spherical-Pad Head Slider for Stable Low-Clearance Recording in Near-Contact Regime

A slider with an air-bearing surface that has a small spherical pad around the read/write elements on the trailing center pad was developed to reduce the meniscus and friction forces and slider clearance loss. While the slider which has a spherical pad of a radius less than 10 mm, the meniscus force is reduced to less than 10% of the air-bearing lift force, thus, flying height modulation is decreased and instability are suppressed. Evaluation using an air-bearing surface model with a spherical pad showed that slider clearance was increased by 1 nm at a 5-nm nominal flying height. Evaluation using touchdown-takeoff testing of a spherical pad slider fabricated by depositing carbon on the center pad air-bearing surface by means of the lift-off resist technique showed that the spherical pad slider had a very small friction force and acoustic emission output up to a 5-nm interference height. It thus provides instability-free sliding in the near-contact regime.     

Analysis of Surface Textured Air Bearing Sliders with Rarefaction Effects

A numerical model is developed to study the effect of texture on air bearing sliders for large Knudsen numbers. The effect of texture location, texture size, and density on the pressure generation is studied. First, a textured plane slider parallel to the disk surface is investigated, and the texture parameters are determined that result in optimum pressure generation. Then, a plane inclined slider is studied using optimum texture parameters found in the parallel slider case. Thereafter, the effect of texture on the steady state flying characteristics of an actual magnetic recording slider is investigated. Finally, the flying height modulation, pitch, and roll motion of a textured slider (pico and femto form factors) are determined numerically by exciting the slider using a step on the disk. Comparison of the results for textured and untextured sliders is made. It is found that textured sliders show better dynamic performance compared to the untextured sliders in terms of stiffness and damping.     

Numerical Simulation of the Head/Disk Interface for Patterned Media

The use of patterned media is a new approach proposed to extend the recording densities of hard disk drives beyond 1 Tb/in.². Bit-patterned media (BPM) overcome the thermal stability problems of conventional media by using single-domain islands for each bit of recorded information, thereby eliminating the magnetic transition noise (Albrecht et al., Magnetic Recording on Patterned Media, 2003). Considering steady state conditions, we have transferred the pattern from the disk surface onto the slider surface and have investigated the pressure generation due to the bit pattern. To reduce the numerical complexity, we have generated the bit pattern only in the areas of the slider near the trailing edge, where the spacing is small. Cylindrical protrusions were modeled using very small mesh size on the order of nanometers to obtain the flying characteristics for the entire slider air bearing surface (ABS) using the “CMRR” finite element Reynolds equation simulator (Duwensee et al., Microsyst Technol, 2006; Wahl et al., STLE Tribol Trans, 39(1), 1996). The effect of pattern height, pattern diameter, slider skew angle, and slider pitch angle on flying height of a typical slider is investigated. Numerical results show that the flying height decreases for a patterned slider and the change in flying height is a function of the pattern height and ratio of the pattern diameter to the pattern pitch. In comparison to discrete track media, the flying height loss is larger for a patterned slider disk interface for the same recessed area of pattern.     

Development of flying type head/slider for optical recording technology

Flying-type sliders with the integration of optical components were developed for Near-Field Recording (NFR) and Far-Field Recording (FFR) technologies. The key design issue was the integration of the optical components with the slider. Due to the size of the lenses mounted on it, the slider had to be relatively large, corresponding to the size of a micro-slider. Also, the non-uniform distribution of the slider body density was incorporated in the design. As for the optical disk substrate, a plastic material such as polycarbonate was investigated because of its manufacturing convenience and cost effectiveness. The flying and tribological performance of the prototype optical sliders on various media were assessed. The results showed that the tribological characteristics of the slider/disk interface were sensitive to several factors including the properties of the disk. Adequate flying characteristics of the optical sliders on glass (NFR) and plastic (FFR) disks could be attained by optimizing these parameters.     

Drive level measurement of flying height modulation and control of slider disk contact

A drive level measurement of flying height modulation and a demonstration of slider-disk contact control was conducted. The results of the flying height modulation strongly agree with those obtained from a Laser Doppler Vibrometer (LDV) measurement. The modulation was mainly caused by curvature caused by disk clamping. Furthermore, feedback control of a slider-disk contact was successfully demonstrated. Friction force was controlled at a small value to maintain the slider so that it flew over the disk in the light contact regime.     

Investigation of Head/Disk Contacts in Helium–Air Gas Mixtures

The shock response of a pico-type magnetic recording slider in different helium–air gas mixtures is investigated numerically. A finite element-based air bearing simulator and a slider/disk contact model including van der Waals and friction forces are coupled to determine the contact characteristics between slider and disk. The minimum flying height and the maximum contact force are studied as a function of helium percentage and disk velocity. The results show that the dynamic performance of the slider is not affected substantially as long as the helium percentage is <50 % but is increasingly more affected if the helium percentage becomes larger than 50 %.     

Frequency Analyses of Air Bearing Slider in Near Contact and Contact States

Determining the air bearing frequencies is important and essential to understand the complex flying performances of slider. However, in typical flying height test, it is usually difficult to distinguish the air bearing frequencies in the experimental data, especially when the slider is in full flying state. In such a case, it is optional to employ simulation to help determine the air bearing frequencies and their harmonic components. This paper performs both time and frequency domain simulations to analyze air bearing frequencies of a pemto slider and compare the results with experimental data obtained using laser Doppler vibrometer. It is found that the simulation results are well correlated with the experimental results. Time domain simulation provides not only the air bearing frequencies, but also the harmonic frequencies. Frequency domain simulation, on the other hand, provides clear identification of the three dominant air bearing frequencies, with additional information such as air bearing stiffness and damping obtainable. It is suggested that simulations in both time and frequency domains should be conducted to assist in determining the air bearing frequencies and their harmonic components.     

Thermal sensor for in situ flying height measurements of optical flying heads

The application of flying head technology in optical recording promises a considerable increase in recording density. It may be used for both far field and near field recording. For dynamic in situ flying height and flight attitude measurements, a prototype of a thermal test head has been developed. It takes advantage of the heat transfer in sub-micrometer air bearings as well as its dependence from the air gap width. Such a test head has a slider with a similar air bearing surface as the recording head, but with thermo-resistive sensors that are energized by Joule's heat and embedded at each of the four corners. The paper describes the head design and the fabrication technology and provides first experimental test results as well.     

Static and Dynamic Slider Air-Bearing Behavior in Heat-Assisted Magnetic Recording Under Thermal Flying Height Control and Laser System-Induced Protrusion

The air bearing’s response to regions of elevated temperature on its bounding surfaces (the slider and disk) may be an important consideration in the head–disk interface design of heat-assisted magnetic recording (HAMR) systems. We implement the general non-isothermal molecular gas lubrication equation into an iterative static solver and dynamic air-bearing solver to evaluate the effect of localized heating of the air-bearing surface (ABS) due to the near-field transducer (NFT). The heat-dissipating components in our simplified HAMR design are the NFT, laser diode, and thermal flying height control (TFC) heater. We investigate the effect of each HAMR slider component on ABS temperature and thermal deformation and the slider’s flying height. The NFT induces a localized thermal spot and protrusion on the larger TFC bulge, and it is the location of maximum temperature. This ABS temperature profile alters the air-bearing pressure distribution, increasing the pressure at the hot NFT location compared with predictions of an isothermal air-bearing solver, so that the center of the pressure acting on the ABS is slightly closer to the trailing edge, thereby decreasing the pitch angle and increasing the minimum flying height. Other researchers have shown that the NFT’s thermal response time may be much faster than its protrusion response time (Xu et al. in IEEE Trans Magn 48:3280–3283, 2012). The slider’s dynamic response to a time-varying NFT thermal spot on the ABS while the combined TFC and NFT induced thermal protrusion remains constant is investigated with our dynamic air-bearing solver. We simulate the slider’s step response to a suddenly applied ABS temperature profile and a pulsed temperature profile that represents laser-on over data zones and laser-off over servo zones. The sudden (step) or rapid (pulse) increase in ABS temperature induces a sudden or rapid increase in pressure at the NFT location, thereby exciting the air bearing’s first pitch mode. For the slider design and simulation conditions used here, the result of the pitch mode excitation is to alter the position of the center of pressure in the slider’s length direction, thereby changing the pitch moment. In response, the pitch angle and minimum flying height change. The step response decays after approximately 0.15 ms. Because the laser duty cycle is much shorter than this response time, a periodic disturbance is predicted for the center of pressure coordinate, pitch angle, and minimum flying height. The peak-to-peak minimum flying height modulations are relatively small (only up to 0.126 nm); more significantly, the time-averaged minimum flying height increases 0.5 nm for the NFT that reached 208 °C compared to simulations of the isothermal ABS at ambient temperature.     

磁记录悬浮滑块灵敏度分析

在借鉴硬盘浮动技术研究工作的基础上，对有关浮动技术问题进行了系统深入的研究，研究了滑块几何参数对浮动性能的影响，确定了滑块的几何参数(尺寸)对应于滑块最小飞高容差的各参数的容差。     

Simulation of Static Flying Attitudes with Different Heat Transfer Models for a Flying-Height Control Slider with Thermal Protrusion

The thermal flying height control (TFC), aka dynamic fly height (DFH), technique has been recently used in the head disk interface of hard disk drives to obtain a lower head-media spacing. The air bearing cooling effect, i.e., the heat conduction between the slider and the air film, has been incorporated in the numerical thermal–mechanical simulation of the slider’s static performance. However, the heating effect of the viscous dissipation of the air flow has not been considered yet. In this article, both effects are included in the simulation of a flying slider with its flying height controlled by thermal protrusion, and different models for the air bearing cooling are used to obtain the slider’s static flying attitudes. The simulation results directly show that the air bearing cooling is dominant compared with the viscous heating. All of the air bearing cooling models, including a recent one that considers the dependence of the air molecular mean free path on the air temperature, have simulation results close to each other. The largest relative difference in the simulated flying height is less than 9% even when the transducer flying height is lowered to below 2 nm.     

表面结构对纳米级气膜稀薄流域分布的影响

磁头与磁盘的特征高度目前已经下降到纳米量级,在此微小间隙下,气体表现出明显的稀薄效应特征。建立适用于纳米间隙下的控制方程,并根据方程特点采用特殊处理方法成功对控制方程进行数值求解,采用数值分析和实验方法分析表面结构变化对稀薄流域和磁头飞行姿态的影响。研究结果表明：在纳米级气膜润滑间隙下,采用逆 Knud-sen 数来划分稀薄流域比仅从特征膜厚高度方面考虑更合理;负压型磁头的主要工作区间在滑流区和过渡区,且过渡流域所占比例要明显高于滑流区域。稀薄效应最大的区域不是在气膜厚度最薄的磁头尾部,而是在压力突然下降且气膜较薄的阶梯过渡区域;磁头 U 型气垫、尾端两侧浅台阶和中间台阶结构变化会影响气流流向,从而影响压力分布,使得稀薄流域也跟随发生变化。     

Sensitivity analysis of pico and femto sliders

The flying height sensitivity of pico and femto sliders on air bearing contour design, operating conditions and manufacturing tolerances was studied numerically. A Monte Carlo analysis was performed to evaluate the distribution of flying height, pitch angle and roll angle, assuming the selected independent variables have normal distributions. Two types of pico sliders and one type of femto sliders were modeled and simulated. The results show that flying height is strongly influenced by the contour design of the air bearing slider. The resulting distributions of flying height, pitch angle and roll angle are near Gaussian.