Tracking Method for Digital Optical-Disk Systems

Maeda, Takeshi; Uno, Motoo; Takasago, M.

doi:10.1143/jjap.38.101

Cited by 5 publications

(3 citation statements)

References 3 publications

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“…Although GeTe is mainly characterized by octahedral coordination in both crystalline and disordered phases, it is known that some tetrahedral structures form in the amorphous state. [ 42–44 ] These structures are promoted by homopolar Ge‐Ge bonds, which are present in the liquid and partly survive during the very fast quenching required to create a glass. [ 45,46 ] We have monitored the change in the fraction of Ge atoms with tetrahedral coordination as a function of temperature in our models of liquid and supercooled liquid GeTe (Figure S7, Supporting Information).…”

Section: Discussionmentioning

confidence: 99%

Atomistic Study of the Configurational Entropy and the Fragility of Supercooled Liquid GeTe

Chen,

Campi,

Bernasconi

et al. 2024

Adv Funct Materials

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Phase‐change materials (PCMs) are an important family of alloys employed in non‐volatile memories and neuromorphic devices. These devices exploit the ability of PCMs to undergo rapid transitions between amorphous and crystalline phases at moderately high temperature. At ambient conditions, both phases are stable. These properties imply a very strong temperature dependence of the crystallization kinetics, which has been attributed to the high fragility of the supercooled liquid phase. In this work, the fragility index of GeTe, an important PCM, is extracted from a computational exploration of the potential energy landscape of the system by molecular dynamics simulations. For this purpose, a neural‐network potential is used to describe the interatomic interactions, which enables the evaluation of the configurational entropy in the deeply supercooled regime. The viscosity and the relaxation times are also calculated in the same temperature range. Finally, the Adam‐Gibbs relation is used to extrapolate the data to low temperatures and estimate the glass transition temperature and the fragility index. The latter quantity turns out to be of the order of 135–140, which shows that liquid GeTe is a highly fragile system.

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Section: Discussionmentioning

confidence: 99%

Atomistic Study of the Configurational Entropy and the Fragility of Supercooled Liquid GeTe

Chen,

Campi,

Bernasconi

et al. 2024

Adv Funct Materials

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“…Previous studies reveal that there is a systematical deviation between a‐GeTe produced by melt‐quenching and a‐GeTe prepared by magnetron sputter‐ or vapor‐deposition. For the former case [ 21–25,5 ] a rather octahedral coordination is reported, in contrast to the latter case, [ 26–30 ] where a predominantly tetrahedral coordination is found. Thus, the local amorphous structure of GeTe is considered to be strongly dependent on the preparation conditions.…”

Section: Introductionmentioning

confidence: 99%

Evolution of Short‐Range Order of Amorphous GeTe Upon Structural Relaxation Obtained by TEM Diffractometry and RMC Methods

Stenz,

Pries,

Surta

et al. 2023

Advanced Science

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Glasses frequently reveal structural relaxation that leads to changes in their physical properties including enthalpy, specific volume, and resistivity. Analyzing the short‐range order (SRO) obtained from electron diffraction by transmission electron microscopy (TEM) in combination with Reverse‐Monte‐Carlo (RMC) simulations is shown to provide information on the atomic arrangement. The technique elaborated here features several benefits including reliability, accessibility, and allows for obtaining detailed structural data quickly. This is demonstrated with a detailed view of the structural changes in the as‐deposited amorphous phase change material (PCM) GeTe. The data show a significant increase in the average bond angle upon thermal treatment. At the same time the fraction of tetrahedrally coordinated Ge atoms decreases due to an increase in octahedrally distorted and pyramidal motifs. This finding provides further evidence for the atomic processes that govern structural relaxation in amorphous GeTe and other PCMs. A thorough literature review finally unveils possible origins of the large discrepancies reported on the structure of amorphous GeTe.

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“…Tracking control input is commanded periodically and discretely [7]. However, an ODD system has a continuous TES, and an ODD tracking controller can update control input as fast as computation power allows given that sufficiently high performance analog-to-digital and digital-to-analog converters are available [8]. However, HDDS needs a tracking method different from ODD and HDD, because HDDS has different TES characteristics.…”

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confidence: 99%

Design of Tracking Controller for Holographic Digital Data Storage

Lee

Kwak

Chung

et al. 2007

2007 IEEE International Conference on Control Applications

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In this paper we present a new tracking control method for holographic digital data storage systems. Holographic data storage systems that use disk media need a different tracking method from those of optical and hard disk drives. Here we present the design and implementation of the controller. Due to the intermittent characteristics of the tracking error signal (TES), the tracking controller is designed to regulate the tracking error only while valid TES is generated. Since the valid TES appears intermittently, we use a feedforward controller while the TES is not valid. Furthermore, the feedback control and feedforward control are mode switched depending on the Radio Frequency Sum signal level. We also show the stability of the closed loop system employing the mode switching controller. Experimental results show the effectiveness of the proposed tracking control algorithm. For a ±100 µm repeatable runout at 1 Hz, we were able to reduce the TES to 3.13 µm (1σ) with feedforward mode switching control.

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Tracking Method for Digital Optical-Disk Systems

Cited by 5 publications

References 3 publications

Atomistic Study of the Configurational Entropy and the Fragility of Supercooled Liquid GeTe

Atomistic Study of the Configurational Entropy and the Fragility of Supercooled Liquid GeTe

Evolution of Short‐Range Order of Amorphous GeTe Upon Structural Relaxation Obtained by TEM Diffractometry and RMC Methods

Design of Tracking Controller for Holographic Digital Data Storage

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