• International Journal of Control, Automation, and Systems
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• v.3 no.2
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• pp.252-257
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• 2005

In this work, we propose a simple but efficient method to design a target temperature trajectory for pulling speed tracking control of the crystal grower in the Czochralski crystallization process. In the suggested method, the model predictive control strategy is used to incorporate the complex dynamic effect of the heater temperature on the pulling speed into the temperature trajectory design quantitatively. The feedforward trajectories designed by the proposed method were implemented on 200 mm and 300 mm silicon crystal growers in the commercial Czochralski process. The application results have demonstrated its excellent and consistent tracking performance of pulling speed along whole bulk crystal growth.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.3
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• pp.199-205
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• 2010

The crystallization speed (v) of amorphous (InTe)$_x$(GeTe) (x = 0.1, 0.3 and 0.5) films and their thermal, optical and electrical behaviors have been investigated using nano-pulse scanner (wavelength = 658 nm, laser beam diameter < 2 ${\mu}m$), X-ray diffraction (XRD), 4-point probe and UV-vis-IR spectrophotometer. These results were compared with those of $Ge_2Sb_2Te_5$ (GST) film, comprehensively utilized for phase-change random access memory (PRAM). Both v-value and thermal stability of (InTe)$_{0.1}$(GeTe) and (InTe)$_{0.3}$(GeTe) films could be enhanced in comparison with those of the GST. Contrarily, the v-value in the (InTe)$_{0.5}$(GeTe) film was so drastically deteriorated that we could not quantitatively evaluate it. This deterioration is thought because amorphous (InTe)$_{0.5}$(GeTe) film has relatively high reflectance, resulting in too low absorption to cause the crystallization. Conclusively, it could be thought that a proper compositional (InTe)$_x$(GeTe) films (e.g., x < 0.3) may be good candidates with both high crystallization speed and thermal stability for PRAM application.

• Journal of Magnetics
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• v.9 no.4
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• pp.101-104
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• 2004

The crystallization behaviours of nanocomposite made by a function of quenching rate (roller speed) were studied. The results showed that there was one step c$\mathbb{r}$ystallization process for the alloy quenched at roller speed of 32 m/s, which could be shown as, Am (amorphouse) + ${\alpha}-Fe/Nd_2Fe_{14}B$ ${\rightarrow}$ ${\alpha}-Fe/Nd_2Fe_{14}B$ . For the alloy quenched at roller speed of 40 m/s, there was steps crystallization process taking place at different temperatures, which could be shown as, Am ${\rightarrow}$ ${\alpha}-Fe/Nd_2Fe_{23}B_3+Nd_2Fe_{14}B+Am`$ ${\rightarrow}$ ${\alpha}-Fe/Nd_2Fe_{14}B$. The presence of transition phase ($Nd_2Fe_{23}B_3$) was harmful to get fine and uniform grain size during crystallization process. Uniform microstructures and high magnetic properties could be attained for the as-quenched alloy containing less amorphous phase and no presence of transition phase during annealing treatment. For the alloy prepared at roller speed of 32 m/s, the following properties were obtained, $B_r= 0.904 T,_iH_c = 801 kA/m, (BH)_{max} = 122 kJ/m^3 and M_r/M_s = 0.6$.

• Fibers and Polymers
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• v.6 no.1
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• pp.19-27
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• 2005

High-speed melt spinning of syndiotactic polystyrene was carried out using high and low molecular weight poly­mers, HM s-PS and LM s-PS, at the throughput rates of 3 and 6 g/min. The effect of take-up velocity on the structure and properties of as-spun fibers was investigated. Wide angle X-ray diffraction (WAXD) patterns of the as-spun fibers revealed that the orientation-induced crystallization started to occur at the take-up velocities of 2-3 km/min. The crystal modification was a-form. Birefringence of as-spun fibers showed negative value, and the absolute value of birefringence increased with an increase in the take-up velocity. The cold crystallization temperature analyzed through the differential scanning calorimetry (OSC) decreased with an increase in the take-up velocity in the low speed region, whereas as the melting temperature increased after the on-set of orientation-induced crystallization. It was found that the fiber structure development proceeded from lower take-up velocities when the spinning conditions of higher molecular weight and lower throughput rate were adopted. The highest tensile modulus of 6.5 GPa was obtained for the fibers prepared at the spinning conditions of LM s-PS, 6 g/min and 5 km/min, whereas the highest tensile strength of 160 MPa was obtained for the HM s-PS fibers at the take-up velocity of 2 km/min. Elongation at break of as-spun fibers showed an abrupt increase, which was regarded as the brittle-duc­tile transition, in the low speed region, and subsequently decreased with an increase in the take-up velocity. There was a uni­versal relation between the thermal and mechanical properties of as-spun fibers and the birefringence of as-spun fibers when the fibers were still amorphous. The orientation-induced crystallization was found to start when the birefringence reached -0.02. After the starting of the orientation-induced crystallization, thermal and mechanical properties of as-spun fibers with similar level of birefringence varied significantly depending on the processing conditions.

• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.34-41
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• 2005

We report some recent results in the rewritable Blu-ray Disc with enhanced overwrite cyclability by using the growth dominant eutectic based Ge(Sb70Te30)+Sb recording layer, GeN interface layer and write strategy optimization. We have developed phase-change optical media with appropriate write strategy for 36(i.e., 1X)-72Mbps(i.e., 2X) dual speed Blu-ray Disc system and fur the future high speed optical data storage. For recording layer, eutectic-based Ge(Sb70Te30)+Sb material was used and Sb/Te ratio and Ge content were optimized to obtain proper erasability and archival stability of recorded amorphous marks. The recording layer is wrapped up in GeN interface layers to obtain overwrite cyclability and higher crystallization speed. In addition, we designed appropriate write strategy so called Time-Shifted Multipulse (TSMP) write strategy where starting position of multipulse parts are shined from reference clock. With this write strategy, the jitter characteristics of the disc was improved and we found that leading edge jitter was improved much more than trailing edge jitter in 1X-2X speed recording. Finally, we investigated the higher speed feasibility of 144Mbps(i.e., 4X) by adopting some elemental doping to the eutectic based Ag-In-Sb-Te recording layer and structural optimization of constitution layers in Blu-ray Disc. In the paper, we report the effect of Sn addition for the feasibility of higher speed recording. The addition of Sn shows increases of the crystallization speed of phase change recording layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.226-226
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• 2010

Boron Nitride (BN) doped GeSbTe films were grown by the ion beam sputtering deposition (IBSD). The in-situ sheet resistance data and the x-ray diffraction patterns showed the crystallization is suppressed due to the BN incorporation. The phase change speed in BN doped GeSbTe films were investigated using the static tester equipped with nanosecond pulsed laser. The phase change speed for BN doped GST films become faster than the corresponding values for an undoped GST film. The Johnson-Mehl-Avrami(JMA) plot and Avrami coefficient for laser crystallization showed that the change in growth mode during the laser crystallization is a most important factor for the phase change speed in the BN doped GST films. The JMA results and the atomic force microscopy (AFM) images indicate that the origin of the change in the crystalline growth mode is due to an increase in the number of initial nucleation sites which is produced by the incorporated BN. In addition, the retension properties for the laser writing/erasing are remarkably improved in BN doped GeSbTe films owing to the stability of the incorporated BN.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.3
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• pp.449-462
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• 1996

On the reaction crystallization of lanthanum oxalate effects of operation conditions of impeller speed, concentration and feed rate of reactant, and reaction temperature on the nucleation and growth of crystals were investigated experimentally. In general, at low supersation the analysis of crystallization processes is relatively clear. However, at high wupersaturation, which is usually applied in industrial crystallization, the processes are exhibited in much complication. In this study the lanthanum oxalate was crystallized by the reaction crystallization of high concentration of lanthanum chloride and oxalic acid in single-jet semi batch reactor. Agitation of solution and suspension in the reactor influenced to enhance the reaction process and crystal growth process which gave opposite effect on the crystallization of lanthanum oxalate. In our experiment since increase of impeller speed gave more influence on the reaction process rather than on the crystal growth process, the supersaturation concentration increased with increase of impeller speed, then resulted in decrease of mean crystal size. By the same effect of reactant concentration and feed rate, the decrease of mean crystall size of lanthanum oxalate was observed with increasing the reactant concentration and feed rate. In case of increasing reaction temperature, the mean crystal size increased. The morphology of lanthanum oxalate crystal was not changed within the variation ranges of the operation conditions which were applied in our experiment.

• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.93-98
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• 2005

Rewritable optical disk is one of the essential data storage media in these days, which takes advantage of the different optical properties in the amorphous and crystalline states of phase change materials. As well known, data transfer rate is one of the most important parameter of the phase change optical disks, which is mostly limited by the crystallization speed of recording media. Therefore, we doped Sn/Bi to $Ge_2Sb_2Te_5$ alloy in order to improve the crystallization speed and investigated the dependence of phase change characteristics on Sn/Bi doping concentration. The Sn/Bi doped $Ge_2Sb_2Te_5$ thin film was deposited by RF magnetron co-sputtering system and phase change characteristics were investigated by X-ray diffraction (XRD), static tester, UV-visible spectrophotometer, electron probe microanalysis (EPMA), inductively coupled plasma mass spectrometer (ICP-MS) and atomic force microscopy (AFM). Optimum doping concentration of Bi and Sn were 5${\~}$6 at.$\%$ and the minimum time for crystallization was below than 20 ns. This improvement is correlated with the simple crystalline structure of Sn/Bi doped $Ge_2Sb_2Te_5$ and the reduced activation barrier arising from Sn/Bi doping. The results indicate that Sn/Bi might play an important role in the transformation kinetics of phase change materials..

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.655-659
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• 1998

The effect of quenching speed of melt-spinning on intrinsic coercivity ($_iH_c$$) of annealed ribbons and the crystallization behavior from amorphous $Nd_{14.73}Fe_{78.67}B_{6.60}$ alloy have been studied. We have found that the intrinsic coecivity for annealed melt-spun ribbon is reduced with increasing of quenching rate. $\alpha$-Fe and $Fe_3B$ were formed as intermediate phases prior to the formation of $Nd_2Fe_{14}B$ phase during crystallization. The $Fe_3B$ is disappeared with crystallization of $Nd_2Fe_{14}B$ phase. But the $\alpha$-Fe phase is retained in fully crystallized ribbon by annealing. The intrinsic coercivity loss of annealed ribbon with increasing of quenching speed is believed to be due to existence of soft magnetic phase $\alpha$-Fe in annealed ribbons.

• Korean Chemical Engineering Research
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• v.47 no.6
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• pp.740-746
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• 2009

In the present study, the drowning-out crystallization of L(+)-calcium lactate was investigated in order to develop the crystallization separation process. The crystallization of the calcium lactate was induced by injecting the alcoholic anti-solvent into the aqueous solution of calcium lactate and the control of the calcium lactate crystal size during the crystallization was primarily investigated under the consideration of the anti-solvent species, anti-solvent composition and agitation speed as the key operating factors. Alcohols of methanol, ethanol, n-propanol and i-propanol were used as the anti-solvent for the drowning-out crystallization. Prior to the crystallization experiment, the solubility of calcium lactate in the water-alcohol mixture was measured along with the variation of the alcohol species and composition, which was necessary to estimate the supersaturation level of the crystallization. By the drowning-out crystallization, the calcium lactate crystals of the fabric shape were obtained. Using the ethanol as the antisolvent, the fabric crystals close to the needle shape were produced. However, the hairy crystals were obtained by using the propanol as the anti-solvent. Due to such morphological features, the crystals was highly apt to form the aggregates. The aggregation of the crystals was intensified as increasing the alcohol fraction in the water-alcohol mixture. Meanwhile, the agitation caused the breakage of crystals, resulting in the decrease of the crystal size. Therefore, the crystal size in the crystallization was predominantly determined by the competition between the crystal aggregation and breakage.