High Track Density Research Articles

Individual Neutron Monitoring with CR-39 Detectors at an Accelerator Centre

A new personal neutron dosimetry system at the Paul Scherrer Institute (PSI) is based on chemically etched CR-39 detectors (PN3) with different radiators, and an automatic readout system, the Autoscan 60. The most relevant neutron fields at the PSI accelerator have an energy range up to 600 MeV with peak energies around 1-5 and 50-100 MeV due to evaporation and cascade processes in the concrete shieldings, and partly thermalised spectra that occur at the entrance to the labyrinths. The main radiators used for PN3 are polyethylene (PE) for fast neutrons and PE with lithium for thermal and fast neutrons. For extremely high track densities (corresponding to a dose up to 5 Sv) a transmission spectrometer is used for evaluation, since automatic counting by Autoscan 60 saturates at doses above 100 mSv. The system has been tested for linearity, energy dependence up to 300 MeV neutron energy, angular dependence, and radon background response. It was then calibrated for realistic neutron fields at PSI. The detection limit for these high energy fields is about 0.3 mSv. In addition, calculations have been performed to determine the response of the dosemeter to typical spectra in nuclear power plants.

RICH pattern recognition for LHCb

An algorithm for performing pattern recognition in RICH detectors is described. It uses a maximum-likelihood technique, comparing the predicted and observed distributions of detected photoelectrons. The algorithm is able to handle regions of high track density, for which LHCb provides a good example.

The NA49 large acceptance hadron detector

The NA49 detector is a wide acceptance spectrometer for the study of hadron production in p+p, p+A, and A+A collisions at the CERN SPS. The main components are 4 large-volume TPCs for tracking and particle identification via d E/d x. TOF scintillator arrays complement particle identification. Calorimeters for transverse energy determination and triggering, a detector for centrality selection in p+A collisions, and beam definition detectors complete the set-up. A description of all detector components is given with emphasis on new technical realizations. Performance and operational experience are discussed in particular with respect to the high track density environment of central Pb+Pb collisions.

Electrostatic microactuator and design considerations for HDD applications

A flexure-based rotary electrostatic microactuator is described. This microactuator is for application in a high track-density hard disk drive (HDD). It is fabricated using a high aspect-ratio stencil electroplating process. This paper emphasizes the practical system-level issues that affect the device design. The micro-actuator is demonstrated in a 3.5 form-factor HDD. With a servo bandwidth of 5 kHz, a one-track seek can be completed in under 0.2 ms. This batch-fabricated electro-static microactuator provides a low-cost, high-performance solution for achieving very high track-densities.

A microactuator for head positioning system of hard disk drives

We proposed a new microactuator to realize high track density of Hard Disk Drives (HDDs). The proposed actuator is an electrostatic actuator with multiple parallel plate electrodes and it drives only a Read/Write (R/W) head element. The actuator is fabricated by micromachining technologies. We show the desired design parameters of actuators which will achieve 40 kilo track per inch (TPI). The required driving gap aspect ratio for a silicon actuator and a nickel actuator are 20 and 50 respectively. The aspect ratio of 20 for silicon will be realized by an Inductively Coupled Plasma (ICP) etching process and the aspect ratio of 50 for nickel will be fabricated by a novel electroforming process with vertical sacrificial layer.

Modeling and TMR (track misregistration) budget design for head-positioning of high track-density disk drives

A design tool for track misregistration (TMR) budget of disk drives have been developed. This tool includes R/W head, disk, channel and head-positioning model. An appropriate parameter set which satisfies a given soft error rate (SER) and off-track capability (OTC), is derived using this tool. It is shown that results of simulations using this tool match experimental ones. A TMR budget design for 10 Gbit/in/sup 2/ is calculated. In this design, positioning accuracy of NRRO and RRO should be 0.096 /spl mu/m (/spl plusmn/3/spl sigma/) and 0.084 pm (/spl plusmn/3/spl sigma/) respectively to achieve 31.4 ktpi.

A gas microstrip detector with low noise preamplifier/shaper integrated onto a common silicon substrate

Gas microstrip detectors have been integrated with low noise preamplifier and shaper electronics on a common silicon substrate. These devices were fabricated at the Hewlett-Packard company using a standard 0.8 μm process. This unique approach offers advantages over conventional microstrip design: ease of fabrication, lower noise, and higher channel density. The detector/electronics assembly was tested in a small drift chamber. An energy resolution of 18% FWHM and a noise level of 80 e − r.m.s per channel were obtained with a gas gain of about 200. These integrated microstrip detectors are being developed as the readout devices for a small, high-resolution Time Projection Chamber (MicroTPC). Low mass and high resolution make the MicroTPC well suited for use as a vertex detector, especially in high track-density environments such as RHIC and the LHC.

スピンバルブヘッドのオフトラック特性に対する交換結合バイアス磁場の影響

The off-track performance of magnetic recording heads is a key issue in achieving high track density. In this study, the position error signal (PES) and off-track capability (OTC) were calculated for spin-valve heads. The position error became large when the direction of the exchange bias field deviated and was disordered in the pinned layer. The OTC also as increased the deviation angle of the disordered direction of the exchange bias field decreased. Therefore, an angular deviation of less than 10 degree is necessary to obtain reliable tracking.

Dual-stage servo controller for HDD using MEMS microactuator

A MEMS microactuator provides a low-cost and high-performance solution to realize high track densities of HDD, because of the batch fabrication process and its clean mechanical characteristics. However, the servo system to control such a dual-stage system tends to be more complicated than a conventional HDD system. In this paper, a simple and efficient design method of a dual-stage servo controller for HDD applications is described. The experimental results of the track following control with the dual-stage actuator using a conventional VCM and a MEMS microactuator showed that the fourth-order servo controller can achieve a high bandwidth of more than 2 kHz.

Interaction between track and linear densities

In this work, we report a micromagnetic simulation study on narrow track recording characteristics in thin film media. It is found that, arising from interaction between track density and linear density, a sub-micron trackwidth imposes a limitation on linear density. In order to achieve a high track density greater than 75,000 tpi while keeping the required high linear density, eliminating the interaction between track and linear densities is needed, by either optimized medium design or head design.

An electrostatic microactuator using LIGA process for a magnetic head tracking system of hard disk drives

We demonstrate an electrostatic micro actuator which is fabricated by LIGA process. The actuator is designed for a magnetic head tracking system of hard disk drives (HDDs). The actuator is essential to achieve very high track density of HDDs. We realize the aspect ratio of 125 by the LIGA process using a Si-Au mask. We propose to use PMMA molds both as the mechanical structure and as the insulator between electrodes. We believe there are great opportunity for the LIGA process in making micro actuators of HDDs.

Key issues in the design of magnetic tapes for linear systems of high track density

Areal densities for data tape systems have been increasing exponentially ever since the first product introduction in the early 1950's. Increases in linear density have provided the major part of the increases in recording density. Now, however, the time has come to push harder on track densities. The signal-to-noise issues for higher track densities are relatively well understood. However, the use of full-time track following, with multi-channel heads, adds additional issues to the list of tape design objectives for future systems of very high track density. The ultimate drive error performance will now be impacted by lateral tape motion, relative azimuth angle between tape and head, and track spacing variation due to dimensional changes in the tape. Controlling lateral tape motion and relative azimuth angle requires improvements in tape edge quality, the overall tape-path design, and the writing of the original servo signals on the tape. Controlling the track spacing problem will require better understanding of tape dimensional stability and how it is influenced by environmental changes, by pack stresses, and by tape design and processing. We conclude with suggestions of how to achieve the improvements necessary to stay on the required areal density trend line.

A high bandwidth piezoelectric suspension for high track density magnetic data storage devices

Maintaining the trend towards higher track densities and data rates in magnetic recording devices requires track following servo systems of increasing bandwidth for reliable storage and retrieval of data. The increase in bandwidth is limited by the presence of mechanical resonance modes and other nonlinearities in the voice coil motor (VCM) actuators. One approach to overcoming the problem is by using a dual-stage servo mechanism. In such a mechanism, a VCM is used as a primary stage while a microactuator is used as a secondary stage. The paper proposes a planar piezoelectric actuator design and a piezoelectric suspension made of the planar piezoelectric actuator. The design has a high bandwidth, simple structure and low cost. A prototype of the piezoelectric suspension is designed, fabricated and tested. The experimental results demonstrate that the piezoelectric suspension can satisfy the requirements for the dual-stage servo system.

Off-track performance of thin film single pole head for perpendicular double-layered media

Side-fringing is an important factor for high track density recording. Track width written with a flying single pole flying head was measured through off-track profiles. The results show almost no side-fringing. The erase band width was around 25 nm for the off-track overwrite profile.

Dual stage actuators for high density rotating memory devices

Maintaining the trend towards higher track densities and data rates in rotating memory devices require track following servo systems of increasing bandwidth for reliable storage and retrieval (R/W) of data. The bandwidth requirements are even more severe in the emerging portable computing applications. Increase in bandwidth under strict constraints on over-sampling is limited by the presence of mechanical resonance modes and other nonlinearities in the voice coil motor (VCM) actuators. One approach to overcoming the problem is by using a dual or a compound actuator. In such a mechanism, a VCM is used as a primary stage while the recording head is mounted on the secondary stage which in turn is mounted on the VCM. The secondary stage provides rapid small-motion and position correction to the recording head. Several dual-stage configurations have been proposed using electrostatic, piezoelectric and electromagnetic secondary actuators. The paper proposes a piezoelectric stack micro-actuator design for a disk drive. It preserves the present suspension and head assembly. A prototype of the actuator is designed, fabricated, and tested. The test results are presented. A dual actuator tracking servo system is proposed. The scheme is a promising alternative for providing high bandwidth actuation for future high performance drives.

映像情報ストレージ技術 光ヘッド用Ｓｉ偏向ミラーの設計

A new electrostatic torsion mirror with a silicon/silicon structure has been developed for optical heads. It positions the beam spot accurately on an optical disk having a high track density. This torsion mirror is composed of a hexagonal mirror plate, twin supporting beams, and a pair of driving electrodes. The natural frequency of mirror rotation is defined by the moment of inertia of the mirror plate and the stiffness of the beams. The squeeze effect between the mirror plate and the electrodes generates the damping force. These mechanical parameters are designed to satisfy the specifications for a high-frequency positioning of the beam spot. Experimental frequency responses showed that a test model had a second modal mechanical frequency of over 50 kHz, and the characteristics were in good agreement with the designed values. This torsion mirror will make possible more accurate spot positioning than can be achieved using conventional electromagnetic actuators.

Effectiveness of 0.28 keV carbon K ultrasoft X-rays at producing simple and complex chromosome exchanges in human fibroblasts in vitro detected using FISH

Purpose: To study the effects of carbon K ultrasoft X-rays, which produce a single photoelectron with a track length of 7 nm, on the production of structural chromosome-type changes. Materials and methods: Untransformed human fibroblasts (HF12) were irradiated in G1 phase. Aberrations were analysed using fluorescence in situ hybridization using multi-coloured chromosome specific DNA probes for chromosomes 1 and 2 and an alpha satellite pan-centromeric probe. Results: C K X-rays have a high efficiency per unit absorbed dose for producing simple and complex exchanges. Mean absorbed doses of 0.33-1.31 Gy produce simple exchanges with a predominantly linear dose dependency, and visibly complex exchanges increased by more than the power 2 of the dose, with no evidence of a linear component. The proportion of exchanges that are visibly complex ranged from 9% to 46%. Conclusions: The linear response for simple exchanges provides further support to the hypothesis that damaged DNA may be able to interact with undamaged DNA. The high proportion of complex exchanges may be due to the increased efficiency of double-strand break induction and to the high density of tracks per unit absorbed dose targeting pre-existing sites, some of which may be close to the incident nuclear membrane.

DEFLECTION CHARACTERISTICS OF SPLIT ELECTRODE INPLANE BENDING PIEZOELECTRIC ACTUATORS WITH VARYING WIDTH

The cantilever split-morph, a new type of piezoelectric actuator, have been designed for dual-stage head positioning servo system of high density hard disk drives. In this actuator configuration, a PZT ceramic plate, with one end mechanically clamped and the other free, was poled along its thickness and divided into two symmetric parts along length by splitting electrodes. Driving voltages are preferably so arranged that they make one of the two parts expand by the “31”action while the other part, i.e., the symmetric part, contracts. This will result in a bending motion of the actuator along the direction of its width. The driving voltage-tip displacement characteristics of the actuator have been investigated by theoretical analysis, finite element modeling and experiment. Theoretical analysis indicated that the electric field induced stress is much smaller than stretch strength of piezoelectric ceramic. Tip displacement measured by Michelson interferometer is a little larger than the calculated result. This is mainly due to the increase of piezoelectric coefficient d31 at high driving field. Tip displacement of 1 to 2μm can be achieved at 20 to 50V driving voltage for the split-morph whose size is similar to that of the existing suspension. As to 25 kTPI (track per inch) high track density hard disk drives, this actuating stroke can cover at least one track width and meet the primary requirements of dual-stage head positioning servo system for displacement of the secondary actuator.

Inter-track interference free coding and equalization

A new coding technique using improved inter-track orthogonal coding (ITOC) was proposed for high track density and/or multi-track recording. The coding has, in principle, the ability to eliminate cross talk from adjacent tracks. The new coding was compared with direct NRZI by a computer simulation. The coding showed superior characteristics to the NRZI in terms of signal-to-noise ratio (S/N) and bit error rate (BER) for additive and jitter noise. These simulation results were confirmed by experiments. Furthermore, to improve the performance of ITOC, PR4 and integral equalization for wave form equalization were also studied. It was shown that the new coding technique has a high ability to establish high track density recording with neither guard bands nor azimuth, and to realize a collective reading system of multi-track channel signals by a single head or simultaneous reading by array heads.

A Personal Neutron Dosimetry System Based on Etched Track and Automatic Readout by Autoscan 60

An instrument for reading chemically etched CR-39 elements, the Autoscan 60, has become commercially available. Based on this readout system a new personal neutron dosemeter badge has been developed. PN3 detectors (NE Technology) are used with a two step etching process. The radiators are polyethylene (PE), polyethylene with 6 Li and aluminium. In a nuclear reaction of 6 Li with thermal neutrons alpha particles and tritons ( 3 H) are produced. While the range of alpha particles (9 μm) is too short to be detected with a two step etching procedure, tritons (range = 52 μm in CR-39) easily reach the sensitive layer of the detector and increase the response for thermal neutrons to a value determined by the 6 Li concentration in the PE radiator. Aluminium inhibits the production of recoil protons and hence, causes a lower response to fast neutrons as compared to PE. From the ratio of the readings behind PE and Al, spectral information can be derived, especially in accident situations when the track density is high and a radiation field analysis is required. For extremely high track densities a microscope is used for evaluation, since automatic counting by Autoscan 60 saturates at doses above 50 mSv. The system has been tested for reproducibility, linearity, energy dependence up to 66 MeV neutron energy, angular dependence, radon background response and multiple use of CR-39 detectors.