Eunkyu Jang

Write-to-read coupling study of various interconnect types

The use of suspension interconnects has brought about a great concern for the coupling of the write signal into read lines during write operations. The cross-talk coupling can result in amplitude degradation of giant magnetoresistive (GMR) element at high data rates. In this study, write-to-read couplings of GMR heads during writing operations are studied as a function of write frequency for various interconnects. The coupling current of interconnects with a ground plane is 2–3 times smaller than interconnect without the ground plane. It was found that the ground plane is more important in write-to-read coupling than separation between write and read traces.

Three-dimensional electromagnetic analysis of hard disk drive suspension interconnects with periodic apertures in reference plane

S parameters were obtained using the 3D finite element HFSS code in order to characterize suspension interconnects. An idealized suspension interconnect with periodic rectangular apertures in the stainless steel reference plane is studied to investigate the effect of aperture geometry on characteristic impedance and insertion loss of a differential line. We compared the result of 3D analysis with that of 2D analysis in characteristic impedance. The impedance from the 3D simulation is lower than the predicted value from the 2D simulation by 5 Ω for 50% windowed structure. It was shown that there are attenuation poles at certain frequency ranges as in band-stop filters when the window pitch or window length is large.

Heating and cooling effect of giant magnetoresistive heads during writing operations

The temperature change of giant magnetoresistive (GMR) heads is studied at various write frequencies and write currents by measuring the dc resistance of GMR heads during writing operations. To investigate the effect of a disk on the temperature rise, the test was performed at two different conditions: first, head loaded on a disk, and second, head unloaded. There are five kinds of heating sources of spin valve (SV) heads during writings; (1) dc interconnect heating, (2) dc write coil heating, (3) ac interconnect heating, (4) write-to-read cross-talk of interconnect, and (5) ac write coil heating. The primary cause for the temperature rise of the SV head during writing is write-to-read cross-talk of interconnect, when the head is loaded on a disk. When the head is unloaded, dc or ac heating of the write coil is the main cause of temperature rise of the SV head. It was found that a disk plays an important role in the temperature change of GMR heads during writing as a cooling source. The disk hardly reduce...

HDD-level electrostatic discharge (ESD) failure voltage of tunneling magnetoresisive (TMR) heads

HDD-level electrostatic discharge (ESD) failure voltage of drives equipped with TMR heads and flying height control heaters is measured. An ESD gun is used up to 30 kV to simulate ESD events on the base plate of HDD. In this study, ESD sensitivity of two different types of HDD (Type A and Type B) was studied. The test results showed that the average failure voltage of Type A drive (12 kV) is lower than Type B (21 kV) even though HSA-level ESD failure voltages are similar. Disk, disk damper, write-to-read crosstalk, and location of ground via in suspension interconnect play important roles in ESD sensitivity of the TMR head.

Magnetic and thermal effects of flying height control heater voltage on tunneling magnetoresistive heads

The resistance and signal amplitude of tunneling magnetoresistive (TMR) heads were investigated as a function of flying height control (FHC) heater voltage under nonflying condition. The resistance and signal amplitude measured with a quasistatic tester (QST) both during and after FHC heater voltage application are substantially different from the initial values. The change of resistance or amplitude is reversible up to 3.2V (∼204°C). However, there are permanent changes in TMR signal amplitude after voltage applications of 3.4V (∼225°C) and above. An additional test, where QST performances of heads were measured only after FHC voltage applications, was carried out to distinguish between magnetic fields from the FHC heater and from the QST. Still, there are significant changes in resistance and amplitude. Pin layer reversals by the FHC heater current were also observed.

Effects of the suspension interconnect on ESD failures of the head stack assemblies

With increasing recording density and shrinking size of giant magnetoresistive (GMR) read/write heads, the GMR sensor is getting more sensitive to electrostatic discharge (ESD) events. In this study, two different types of head stack assembly (Type A and Type B) were studied in terms of ESD sensitivity. Both head stack assemblies (HSA) consist of head gimbal assemblies (HGA), preamplifier, E-block, flexible printed cable (FPC), voice coil motor (VCM) coil, and 20-pin connector for 3.5-in drive. Type A is a conventional HSA consisting of two or four HGAs with long tail suspensions whereas Type B is a head stack consisting of one HGA with FPC interconnect instead of a long tail. ESD events were simulated by zapping 20-pin connector with an ESD gun. A quasi-static tester (QST) was used for amplitude and resistance measurement of GMR heads after each ESD event. The test results showed that the failure voltage of Type B (1.0-1.2 kV) is much lower than Type A (4.0-5.0 kV). Furthermore, failed HSAs showed different failure modes: preamplifier damage for Type A and read sensor damage for Type B. To understand the main reason for low failure voltage for Type B, we investigated ESD sensitivity by modifying Type B with different interconnects, bonding methods, and arm actuator structures. These results indicate that the write-to-read crosstalk of interconnect (from preamplifier to head slider) during ESD events caused low failure voltage for Type B. It was found that the metallic structure surrounding the VCM coil is another cause for the low failure voltage of Type B.

Write induced magnetic field in spin-valve heads

The magnetic field at a spin valve (SV) element is measured by exciting the inductive write head with a pulse current. The measured write-induced magnetic field can be used as an indicator of write-induced stability. A piggyback type SV head and a merged type SV head are compared in terms of the magnetic field at the SV. While the write-induced magnetic field of the merged head saturates at 40 mA as current increases, that of piggyback head does not saturate even at 120 mA. The method reported here can be used to evaluate the SV magnetic performance and to obtain the yoke saturation curve of the inductive write head in a merged SV head.

Overwrite Performance Change due to Air-Flow Induced Vibration of Head Stack Assembly

Overwrite (OW) performances of two different types of head stack assemblies (HSA) were compared as a function of slider location on disks. Both HSAs have the same types of head slider, suspension interconnect, and preamplifier but have different mechanical platform and different arm structure. OW performance in the outer diameter (OD) zone is worse than the inner diameter (ID) zone by more than 2 dB for Type B HSA but not for Type A. This paper investigates the mechanism of OW degradation of Type B HSA at the OD. It was found that the mechanical vibrations owing to disk flutter and arm structure are key factors to the OW degradation.

Effect of slider conductive adhesive on EMI radiation of hard disk drives

EMI radiations from hard disk drives are measured outside a computer in a 3 m anechoic chamber. Hard disk drives with two different adhesive materials between the suspension and head slider are compared in EMI radiation level. The average EMI radiation of one type is 52.87 dBmuV/m while that of the other is 46.34 dBmuV/m. The main causes for EMI radiation difference of the two types of drives are investigated in this study. They have different DC resistance, breakdown voltage, and capacitance between the suspension and head slider when used in head gimbal assembly. It was found that the capacitance between slider and suspension is a critical factor for EMI radiation of hard disk drives.

Write frequency dependence of power loss in inductive heads

In this paper, the AC power loss due to joule heating from the write coil is calculated using Fourier series approach. This calculation is to predict TPTP as functions of write current, write frequency (up to 1 GHz), current rise time, and overshoot. After deriving the Fourier series for a periodic current waveform at harmonic frequencies (I/sub n/), we compute the power loss (I/sub n//sup 2/ Rac) at each harmonic. Sum of power loss of each harmonic will give the total AC power loss of inductive head. A GMR head for 60 Gb/in/sup 2/ areal density is used for this study.