Hard Disk Drive Head Research Articles

A Study of the Nanoscale Heat Transfer in the HDD Head–Disk Interface Based on a Static Touchdown Experiment

Understanding the heat transfer behavior at the nanoscale head-disk interface (HDI) in hard disk drives is crucial for head design, media design, and failure analysis of the current hard disk drive (HDD) industry, especially for the emerging technologies including heat-assisted magnetic recording (HAMR), microwave-assisted magnetic recording (MAMR), and 2-D magnetic recording (TDMR). Previous experimental studies of both static touchdown technique and theoretical developments of the wave-based phonon conduction have shown enhanced heat transfer at the HDI. To better understand the heat transfer behavior across the HDI, a series of the simulation is necessary to connect the theory and the detailed geometric model of the HDI. In this article, we developed a finite-element model to explain the temperature change of the head during a static touchdown experiment. The wave-based phonon conduction theory is integrated into the simulation through iteration. The simulation results trend in agreement with the theoretical development and the experimental results. This simulation strategy can also be implemented for flying heads to predict the heat transfer behavior under HAMR conditions.

Etching behaviors of tunneling magnetoresistive (TMR) materials by ion beam etching system

In data storage manufacturing, ion etching process is commonly chosen for the preparation of surface patterns, for example, under the read-write head of the hard disk drive (HDD) to form an air bearing surface (ABS). This read-write head consists of a multilayer thin film of different materials to form a tunneling magnetoresistive (TMR) device. In this work, we applied the Monte Carlo-based simulation package to calculate the etching yield of major materials in the HDD head’s structure. The plasma characteristic in the industrial-size ion beam etching (IBE) system has been studied by the special plasma diagnostic probes. Effects of input parameters in IBE system such as incident beam angle, ion beam current and gas flow in the system were considered. Plasma characteristic can be obtained from plasma I-V curve characterization. The sputtering yields of materials were found maximum when an incident angle is about 70° to the normal surface. The floating potential of plasma in the system with the ion/electron compensation from PBN is calculated.

Where Tape and Hard-Disk Technology Meet: The HDD Head–Tape Interface

In this paper, we study the mechanical interface between a hard-disk drive (HDD) head and magnetic recording tape to enable the use of HDD heads to investigate future tape operating points. Tape surface height measurements were obtained using an interferometer microscope for varying wrap angle configurations, tape velocities, and tape tensions. Simultaneously, the readback signal from the read element of the HDD head was captured to study the quality of the contact between the tape and the head. The signal-to-noise ratio (SNR) and bit-error rate (BER) performance of pseudorandom bit sequence (PRBS) data readback experiments are presented. An analytical model is described for estimating the magnetic spacing from the PRBS readback spectrum. In contrast to current commercial tape heads, the HDD head surface has a pronounced topography containing cavities. When tape passes in close proximity, subambient pressures are formed inside these cavities and the resulting pressure differences force the tape toward the head and deform the tape into remarkable shapes. For the topography of the HDD head used, the shape of tape is predominantly determined by the leading and trailing wrap angles. Readback was obtained only in the backward direction (i.e., opposite to the direction of operation in an HDD), with positive leading but negative trailing wrap angles. Better readback is obtained for shallow wrap angles, lower tape velocity, and higher tape tension. Good readback is obtained for leading and trailing wrap angles ~0.3° and -0.2°, respectively. Fits of the analytical model to the spectrum of the readback signal of PRBS data lead to a magnetic spacing estimate of ~30 nm. At 600 kb/in linear density, we measured 11 dB SNR and 7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> BER for PRBS data on perpendicularly oriented particulate barium-ferrite tape.

Improvement in Intersample Response of HDD Head

AbstractThis paper proposes a new design method for controlling a head in a hard disk drive (HDD) system. In the HDD control system, the sampling interval of the head position is restricted, but the hold interval of the control input can be arbitrarily set. Hence, this study discusses a design method for a multi-rate control system, where the sampling and the hold intervxc als are not equal. In this study, a pole-assignment multi-rate control law 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 because those 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 a HDD system, and its effectiveness is demonstrated.

Dynamic Response Measurement of 1-Inch HDD Head Arm Assembly

In this paper, dynamic response of 1-inch hard disk drive (HDD) head arm assembly (HAA) against an impact load is obtained by means of a 3D non-linear finite element model in ANSYS/LS-DYNA and experiments using Optical method. A mass is modeled as a rigid body and is made to collide with the arm. The velocity, displacement, acceleration and the inertial force of the mass are obtained from the time- history of finite element analysis (FEA). In the experiment, a mass that is levitated with an aerostatic linear bearing, and hence encounters negligible friction, is made to collide with the HAA and the dynamic bending test for the arm is realized. During the collision the Doppler frequency shift of the laser beam reflecting from the mass is accurately measured using an optical interferometer. The velocity, the position, the acceleration and the inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. A good correlation between the experimental data and FEA results is observed.

Fast response thermal linear motor with reduced power consumption

This paper presents the principle, fabrication and characterization of a fast response Thermal Linear Motor (TLM) havingreduced heat loss (and thus power consumption) without reduction in mechanical output power. Our double wedge shaped, aluminum TLM is 12 μm and 6 μm wide at the edges respectively center and 400 μm long. Theory and measurements show that this TLM has up to 20% more mechanical output power for the same electrical input power compared to a simple rectangular beam TLM. The TLM is the crucial driving element for our Hard Disk Drive (HDD) thermal micro actuator. The actuator uses two of the here presented TLMs to accurately move the HDD head up to several micrometers.

Dual-stage HDD head positioning using an H∞ almost disturbance decoupling controller and a tracking differentiator

We adopt in this paper a novel control scheme to achieve fast and accurate head positioning for dual-stage actuated hard disk drive (HDD) servo system with actuator saturation and disturbances. This control scheme consists of a tracking differentiator (TD) to avoid actuator saturation as large as possible and an H ∞ almost disturbance decoupling controller to deal with disturbances and improve the tracking performance. More specifically, the TD aims to provide a smooth reference signal in a feedforward way so as to reduce the system error, and further decrease the control inputs to both the VCM actuator and the micro-actuator such that the saturation problem can be effectively avoided. The H ∞ almost disturbance decoupling controller, when it is applied to control the micro-actuator, is able to almost decouple the disturbance and the controlled output such that satisfactory tracking performance can be achieved. Furthermore, the VCM actuator is controlled by a notch filter in series with a lead compensator so as to stabilize the servo loop. Finally, simulation results in time domain and frequency domain verify the effectiveness of the proposed control scheme.

Strain imaging of a ferrite core head

This paper describes magnetic domain observation of a ferrite core head of a hard-disk drive (HDD) using a new method. The principle of the method, strain imaging, is detection and imaging of the strains generated in a magnetic material subjected to an external magnetic field, using a scanning probe microscope (SPM). Because the magnetic-field induced strains involve the factors depending on the magnetization of each domain, we can image domain structures by detecting the surface displacements induced by the strains, using the SPMs. The atomic resolution of the SPMs results in strain imaging with high resolution. We observed that domains aligned to the magnetic field increased with the coil current of the ferrite core head. Nothing, except for magnetic fields provided by the head coil itself, has any magnetic influence on the domain structures of the ferrite core. Thus, this method is suitable for domain observation of HDD heads made of soft materials.

Application of adhesive bonding techniques in hard disk drive head assembly

Current market conditions demand that hard disk drive (HDD) manufacturers adopt advanced technology in every area of drive design to improve drive capacity and performance and simultaneously reduce unit cost. Head stack suppliers in HDD industry are constantly working on high density interconnect technologies to provide faster and higher capacity and cheaper head stack components for disk drives. A low cost method to manufacture HDD head using anisotropic conductive film (ACF) bonding for flex-to-flex interconnection has been developed. This paper describes the process selection work among the current and the newly developed ACF bonding technologies. Bond pad design for ACF process using the finite element analysis method is introduced. Critical process bonding parameters are identified and characterized to give the optimal bonding conditions. Reliability evaluations on the final assemblies indicated that ACF bonding could give a very reliable electrical and mechanical interconnection.

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Multilayer GMR films have a larger MR ratio than spin-valve films and, therefore, have great potential for use as read sensors in HDD (hard disk drive) heads for ultra-high-density recording. Moreover, the MR ratio of multilayer GMR films is twice as large when the sense current flows perpendicular to the plane (CPP) than when it flows in the plane (CIP). We investigated the GMR properties of CPP elements of a Co0.9Fe0.1/Cu multilayer in a structure where the GMR film is under the top terminal layer and connected to the bottom terminal layer through a micron-sized contact hole. An MR ratio of 13.1% and saturation field (Hs) of 150 Oe were obtained. The field sensitivity of 0.1 %/Oe was much larger than that of CIP elements. The value of Hs of the CPP elements was almost constant as a function of the element dimension, because the demagnetization field was insensitive of the sensor size in our CPP element structure and small enough even for submicron elements.