Ultra-thin a-SiN_x protective overcoats for hard disks and read/write heads

This paper reports that amorphous silicon nitride （a-SiNx） overcoats were deposited at room temperature by microwave ECR plasma enhanced unbalanced magnetron sputtering. The 2 nm a-SiNs overcoat has better anti-corrosion properties than that of reference a-CNx overcoats （2 4.5 nm）. The superior anti-corrosion performance is attributed to its stoichiometric bond structure, where 94.8% Si atoms form Si-N asymmetric stretching vibration bonds. The N/Si ratio is 1.33 as in the stoichiometry of Si3N4 and corresponds to the highest hardness of 25.0 GPa. The surface is atomically smooth with RMS 〈 0.2 nm. The ultra-thin a-SiNx overcoats are promising for hard disks and read/write heads protective coatings.

OPTIMAL TRACK SEEKING CONTROL OF DUAL-STAGE ACTUATOR FOR HIGH DENSITY HARD DISK DRIVES

Based on generalized the variation method, by introducing Hamilton function and Lagrange multiplier, this paper proposed a linear quadratic optimal control strategy for an incomplete controllable system with fixed terminal state and time. Applying the proposed optimal control to the simple two-input dual-stage actuator magnetic head positioning system with three degrees-of-freedom, the simulation results show that the system has no residual vibration at the terminal position and time, which can reduce the total access time during head positioning process. To verify the validation of the optimal control strategy of three degrees-of-freedom spring-mass models in actual magnetic head positioning of hard disk drives, a finite element model of an actual magnetic head positioning system is presented. Substituting the optimal control force from simple three degrees-of-freedom spring-mass models into the finite element model, the simulation results show that the magnetic head also has no residual vibration at the end of track-to-track travel. That is to say, the linear quadratic optimal control technique based on simple two-input dual- stage actuator system with three degrees-of-freedom proposed in this paper is of high reliability for the industrial application of an actual magnetic head positioning system.

Design of Intersample Response in a Hard Disk Control System

The present paper discusses a design method for the head position in a Hard Disk Drive （HDD） control system. In the HDD control system, the sampling interval of the head position is constrained because of the hardware specifications, but the hold interval of the control input is not constrained. In the present study, a multirate control system is designed, in which the sampling and the hold intervals are not equal. A multirate control law, which stabilizes a closed-loop system, is extended using newly introduced parameters such that the sample response of the plant output is maintained. Furthermore, intersample ripples in the steady state are eliminated using the new design parameters, which can be selected independently of the sample response. As a result, the intersample response can be improved independently of the sample response. The proposed method is applied to a benchmark problem of an HDD system, and its effectiveness is demonstrated.

Vibration Response Characteristics against the Radial and Axial Shocks on Small Size Hard Disk Drive Spindle Supported by Oil Film Bearings

This paper describes the experimental study on shock response of FDB （fluid dynamic bearing） spindle for HDDs （hard disk drives）. The FDBs are widely used as rotating shaft support elements for HDD spindle motors. Recently, the opportunity for the HDD spindle motors exposed to external vibration has been increasing because the HDDs are used for various information related equipment such as mobile PCs （personal computers）, video cameras, car navigation systems and so on. Hence, the rotating shaft has a possibility to come in contact with the bearing by external shocks and it causes wear or seizure to the bearing surface. To avoid the problem, it is extremely important to know how the spindle moves against the large shock on HDDs experimentally. However, as far as the authors know, there are few experimental studies treating the shock response of HDD spindles. In this paper, firstly, we propose a new test rig and experimental method for shock response of FDB spindles. Then the shock tests against the radial and axial disturbance on FDB spindle for 2.5＂ HDD are conducted. Finally, the experimental results of shock response waveforms and maximum displacement of disk are shown.

STRUCTURE AND BINDING STATE OF CN_x FILMS SYNTHESIZED BY FACING TARGETS SPUTTERING

CN x films were made by a facing targets sputtering ( FTS) systemon the Si(100) substrate under different N 2 partial pressure. XRD, XPS, FTIR and Raman Spectroscopy( RS) were measured to investigate the structure and the binding state of the film. The films are amorphous and the N/C increases with the N 2 partial pressure increasing and reaches 0 46 when the N 2 pressure is 100%. The N incorporated C forms N sp 2C and N sp 3C mainly and there is a small amount of C≡N.

Identification Method of Dynamic Coefficients of Fluid Film Bearings for HDD Spindle Motors

Fluid film bearings are widely used as support elements of rotating shaft for HDD （hard disk drive） spindle motors. Recently, the opportunity for the HDD spindle motors exposed to external vibration has been increasing because the HDDs are used for various information related equipments such as mobile PCs, car navigation systems. Hence, the rotating shaft has a possibility to come in contact with the bearing and it causes wear or seizure to the bearing surface. In order to avoid the problems, it is extremely important to enhance the dynamic characteristics of the fluid film bearings for spindles. However, verification from both theory and experiment of dynamic characteristics such as spring coefficients and damping coefficients is rare and few. In this paper, the bearing vibration characteristics when the HDD spindle is oscillated are investigated theoretically and experimentally. And then the identification method ofoil film coefficients of fluid film bearing spindles is described.

A hybrid storage technology for low power consumption and high I/O performance in an IPTV set-top box

A new method of prefetching data blocks from the NVCache to the page cache in main memory and cascading prefetching n-blocks from a hard disk to the NVCache together was proposed to reduce the spin-up frequency of a hybrid hard disk drive and thus enhance I/O performance.The proposed method consists of three steps:1) Analyzing the pattern of read requests in block units;2) Determining the number of blocks prefetched to the NVCache;3) Replacing blocks in the NVCache according to the block replacement policy.The proposed method can reduce the latency time of a hybrid hard disk and optimize the power consumption of an IPTV set-top box.Experimental results show that the proposed method provides better average response time compared to an existing adaptive multistream prefetching(AMP) method by 25.17%.It also reduces by 20.83% the average power consumption over that of the existing external caching in energy saving storage system(EXCES) method.

The spreading behaviour of perfluoropolyether droplets on solid surfaces

The spread of perfluoropolyether （PFPE） droplets on solid surfaces has been measured from the top-down view through a microscope system. Effects of substrates, molecular weight and end-group functionality on spreading of the PFPE droplets have been studied experimentally and the results were compared with those by molecular dynamics （MD） simulations. Silicon wafer and diamond-like carbon （DLC） substrates were used to study the effect of substrates on spreading. Two types of PFPE, Z-dol and Z-tetraol, with the same chain structure and various molecular weights （2000 and 4000 g/mol） were employed in experiments. Effect of molecular weight has been investigated through comparing the spreading of Z-dol 2000 and Z-dol 4000, and it is found that the increase of molecular weight will decrease the mobility of PFPE. Comparison between spreading of Z-dol and Z-tetraol of the same molecular weight proved that functional end group plays a significant role on the spreading of PFPE, which confirmed the MD simulation results.

A Brief Discussion of Data Storage Principle and Data Recovery Technology

According to relevant data statistics, each year, nearly 70% of users have disc data loss because of misuse, viral damage, physical damage and hardware failure, bringing irreparable damage to enterprises, institutions and individuals. So data recovery technology has attracted wide attention of users and how to use data recovery technology to help to recover lost data and to minimize the loss has become an urgent need. This paper starts from the software and hardware failure to analyze two aspects of hard disk data loss, data storage structure theory, and combined with practical experience, it elaborates data damage type and related recovery methods.

Abrasive-free polishing of hard disk substrate with H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry

The effect of tert-butyl hydroperoxide-sodium pyrosulfite((CH3)3COOH-Na2S2O5)as an initiator system in H2O2-based slurry was investigated for the abrasive-free polishing(AFP)of a hard disk substrate.The polishing results show that the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry exhibits a material removal rate(MRR)that is nearly 5 times higher than that of the H2O2 slurry in the AFP of the hard disk substrate.In addition,the surface polished by the slurry containing the initiator exhibits a lower surface roughness and has fewer nano-asperity peaks than that of the H2O2 slurry.Further,we investigate the polishing mechanism of H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry.Electron spin-resonance spectroscopy and auger electron spectrometer analyses show that the oxidizing ability of the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry is much greater than that of the H2O2 slurry.The results of potentiodynamic polarization measurements show that the hard disk substrate in the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry can be rapidly etched,and electrochemical impedance spectroscopy analysis indicates that the oxide film of the hard disk substrate formed in the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry may be loose,and can be removed easily during polishing.The better oxidizing and etching ability of H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry leads to a higher MRR in AFP for hard disk substrates.

In situ electron holography of the dynamic magnetic field emanating from a hard-disk drive writer

The proliferation of mobile devices in society accessing data via the ＂cloud＂ is imposing a dramatic increase in the amount of information to be stored on hard disk drives （HDD） used in servers. Forecasts are that areal densities will need to increase by as much as 35% compound per annum and by 2,020 cloud storage capacity will be around 7 zettabytes corresponding to areal densities of 2 Tb/in^2. This requires increased performance from the magnetic pole of the electromag- netic writer in the read/write head in the HDD. Current state-of-art writing is undertaken by morphologically complex magnetic pole of sub 100 nm dimensions, in an environment of engineered magnetic shields and it needs to deliver strong directional magnetic field to areas on the recording media around 50 nm × 13 nm. This points to the need for a method to perform direct quantitative measurements of the magnetic field generated by the write pole at the nanometer scale. Here we report on the complete in situ quantitative mapping of the magnetic field generated by a functioning write pole in operation using electron holography. The results point the way towards a new nanoscale magnetic field source to further develop in situ transmission electron microscopy.

k-Dimensional hashing scheme for hard disk integrity verification in computer forensics

Verifying the integrity of a hard disk is an important concern in computer forensics,as the law enforcement party needs to confirm that the data inside the hard disk have not been modified during the investigation.A typical approach is to compute a single chained hash value of all sectors in a specific order.However,this technique loses the integrity of all other sectors even if only one of the sectors becomes a bad sector occasionally or is modified intentionally.In this paper we propose a k-dimensional hashing scheme,kD for short,to distribute sectors into a kD space,and to calculate multiple hash values for sectors in k dimensions as integrity evidence.Since the integrity of the sectors can be verified depending on any hash value calculated using the sectors,the probability to verify the integrity of unchanged sectors can be high even with bad/modified sectors in the hard disk.We show how to efficiently implement this kD hashing scheme such that the storage of hash values can be reduced while increasing the chance of an unaffected sector to be verified successfully.Experimental results of a 3D scheme show that both the time for computing the hash values and the storage for the hash values are reasonable.

HARD DISK DRIVES CONTROL IN MOBILE APPLICATIONS

In this paper, control design is investigated for hard disk drives in mobile applications with unknown external arbitrarily fast time-varying disturbances. The disturbances can be estimated with exponential accuracy using the proposed disturbance observer based on a series of integral filters. The position error signal will converge to zero with the proposed control technique for systems subjected to the unknown disturbances. The effectiveness of the proposed method is demonstrated by extensive simulation studies.

Differential Evolution Based High-order Peak Filter Design with Application to Compensation of Contact-induced Vibration in HDD Servo Systems

Sensitivity loop shaping using add-on peak filters is a simple and effective method to reject narrow-band disturbances in hard disk drive （HDD） servo systems. The parallel peak filter is introduced to provide high-gain magnitude in the concerned frequency range of open-loop transfer function. Different from almost all the known peak filters that possess second-order structures, we explore in this paper bow high-order peak filters can be designed to improve the loop shaping performance. The main idea is to replace some of the constant coefficients of common second-order peak filter by frequency-related transfer functions, and then differential evolution （DE） algorithm is adopted to perform optimal design. We creatively introduce chromosome coding and fitness function design, which are original and the key steps that lead to the success of DE applications in control system design. In other words, DE is modified to achieve a novel design for hard disk drive control. Owing to the remarkable searching ability of DE, the expected shape of sensitivity function can be achieved by incorporating the resultant high-order peak filter in parallel with baseline feedback controller. As a result, a seventh-order peak filter is designed to compensate for contact-induced vibration in a high-density HDD servo system, where the benefits of high-order filter are clearly demonstrated.

Beam design for voice coil motors used for energy harvesting purpose with low frequency vibrations:A finite element analysis

In this study,a numerical approach is established to design a beam coupled to a Voice Coil Motor(VCM)with the aim to maximize the displacement in the inductive transducer.A finite element model is developed to simulate a VCM with different beams applying a harmonic analysis.The VCM is extracted from a recycled hard disk drive(HDD)and a parametric modal analysis is performed to identify the material parameters of the HDD and the beam.These parameters are obtained comparing the real vibration modes and natural frequencies(VCM-beam)with those determined from the finite element model.A numerical-experimental case study is carried out to demonstrate that if a beam is designed for a specific low frequency vibration between 0 and 10 Hz,the displacements are maximized in the VCM.For this purpose,real acceleration measurements taken from three individuals are used to provide the vibration signals in the numerical model.A beam is designed for one of the individuals using the natural frequency values determined from the measured signals.Results show that the displacements are maximized in the model which coincides with the natural frequency of the chosen individual.The main purpose of this research is to establish a design tool for energy harvesting purposes with VCM based on low frequency vibration sources as for example gait motions.

Investigation of HDD Ramp Unloading Processes with an Efficient Scheme

Ramp load/unload(L/UL)mechanisms are widely used to rest sliders in hard disk drives(HDDs).Loading/unloading a slider swiftly and smoothly is crucial in a HDD design.A novel,efficient simulation scheme is proposed to investigate the behaviors of a head disk interface(HDI)in ramp unloading processes.A dual scale model is enabled by decoupling the nano-meter scale change of an air bearing and the micro-or milli-meter scale deformation of a suspension.A modified Reynolds equation governing the air bearing was solved numerically.The slider design was characterized with performance functions.Three stages in an unloading process were analyzed with a lumped parameter suspension model.Key parameters for the model were estimated with a comprehensive finite element suspension model.Finally,simulation results are presented for a commercial HDI design.

A 3.8 GHz programmable gain amplifier with a 0.1 dB gain step

A broadband programmable gain amplifier（PGA） with a small gain step and low gain error has been designed in 0.13 m CMOS technology. The PGA was implemented with open-loop architecture to provide wide bandwidth. A two-stage gain control method, which consists of a resistor ladder attenuator and an active fine gain control stage, provides the small gain step. A look-up table based gain control method is introduced in the fine gain control stage to lower the gain error.The proposedPGAshows a decibel-linear variable gainfrom4 to20 dB with a gain step of 0.1 dB and a gain error less than˙0.05 dB. The 3-dB bandwidth and maximum IIP3 are 3.8 GHz and 17 dBm, respectively.