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Kim Y.,Hongik University | Park S.,Hongik University | Kim S.,Urbana University | Kim B.-K.,Viatron Technologies | And 3 more authors.
Thin Solid Films | Year: 2017

Xe-arc flashings of 0.4–1.0 ms in pulse duration annealed indium tin oxide (ITO) thin-films deposited on flexible polymeric substrates at room temperature. As flexible substrates, highly transparent polyimide (PI) thin-films of 16 μm in thickness were prepared on a carrier glass. Measuring optical characteristics of the ITO and the PI thin-films and using the Maxwell equations, we estimated complex refractive indices of ITO and PI materials. With the use of these optical properties, one-dimensional conduction/radiation heat transfer simulation was carried out to predict the temperature variations in the specimens, assuring that the temperature in the ITO thin-film during the flash lamp annealing (FLA) process exceeded its crystallization point. Experimental FLA process resulted in a significant enhancement of the electrical conductivities as well as in a slight increase of optical transmittances of the specimen and was compared with the conventional furnace annealing (CFA) process of 1 h. Microscopic changes in the specimen during the annealing processes were compared using the X-ray diffraction pattern, atomic force microscope, and scanning electron microscope (SEM) measurements. Especially SEM images confirmed that sudden degradations in the electrical conductivities of ITO thin-films observed under higher power FLA or higher temperature CFA conditions were strongly related to the physical damages in the thin-films, which were incurred due to the thermal expansion mismatch between the ITO thin-film and the PI substrate at high temperatures. © 2017 Elsevier B.V.


Jin W.-B.,Hongik University | Park Y.,University of Illinois at Urbana - Champaign | Kim B.-K.,Viatron Technologies | Kim H.J.,Viatron Technologies | And 6 more authors.
International Journal of Thermal Sciences | Year: 2014

Thermal warpage of a glass substrate after a flash lamp annealing process for crystallization of amorphous silicon thin-film is critical to subsequent fabrication processes for manufacturing large-scale displays. This phenomenon is understood through the structural mismatching of hypothetical two-layers in a homogeneous glass structure: thermally softened and uninfluenced, and is mechanistically different from that induced by the mismatch in coefficients of thermal expansions among heterogeneous thin-film structures. Thin subsurface region experiencing the intensified heating is softened, the stress in the region is relaxed, and finally the softened region is shrunk laterally, while uninfluenced part of the substrate remains as it is. The model assumes that the shrunk subsurface layer, of which the thickness is proportional to the thermal penetration, is bonded to the uninfluenced part completely. Due to structural mismatching the substrate is deformed considerably and warped towards the light source (the flash lamp) according to the curvature-flash duration relationship, γ = C2η(1 - C1η1/2). This relationship is confirmed by numerical simulation results based on a viscoelastic model and by experimental observations. © 2014 Elsevier Masson SAS. All rights reserved.


Kim D.-H.,Hongik University | Kim B.-K.,Viatron Technologies | Kim H.J.,Viatron Technologies | Suh Y.K.,Dong - A University | Park S.,Hongik University
International Journal of Thermal Sciences | Year: 2013

In current display manufacturing processes, thermal treatment of glass backplanes is widely applied for hydrogen degassing, crystallization of thin-films, tempering, forming, and precompaction processes and so on. Since thermal uniformity during those processes is critical to homogeneity of mechanical and electronic characteristics of nano/micro structures of end products, it is important to estimate the duration of transient heating stages and thermal non-uniformities on a single glass substrate or in a stack of glasses. An electric muffle furnace for glass backplanes of 1.5 × 1.85 m in size and 0.5 mm in thickness was manufactured and temperature fields of the muffle and glass backplanes were measured to estimate the effective emissivity of the furnace. Using the simplified heat transfer model based on thermal radiation and natural convection, thermal fields for a glass stack of the number of sheets from 1 to 12 and for glasses of size, 2.2 × 2.5 m were calculated for practical design and manufacturing of the muffle furnace for large-scale displays, e.g. up to 8th generation. © 2013 Elsevier Masson SAS. All rights reserved.


Park J.-W.,Hongik University | Kim B.-K.,Viatron Technologies | Kim H.J.,Hongik University | Park S.,Hongik University
Thin Solid Films | Year: 2014

Tin oxide thin films were deposited on glass substrates in an in-line atmospheric pressure chemical vapor deposition reactor under various conditions, which were numerically simulated using a commercial package. A soda-lime glass sheet was used as a deposition substrate, and SnCl4 and H 2O in gas phase were separately supplied as the precursor and the oxidizer, respectively. By assuming that the main chemical reactions followed the Rideal-Eley mechanism, the experimentally determined deposition rates were fitted to obtain the reaction factors needed to describe the deposition process. The role of barrier gas injection for minimizing unwanted surface reaction or particle generation inside of the reactor, and not on the target (glass backplane itself) has been elucidated. Furthermore, the optimal operating conditions for the deposition on glass with the additives such as CH 3OH and HF have been investigated. © 2013 Elsevier B.V.


Do W.,Hongik University | Jin W.-B.,Hongik University | Choi J.,Hongik University | Bae S.-M.,Hongik University | And 4 more authors.
Materials Research Bulletin | Year: 2014

Boron-implanted polycrystalline Si thin films on glass substrates were subjected to a short duration (1 ms) of intense visible light irradiation generated via a high-powered Xe arc lamp. The disordered Si atomic structure absorbs the intense visible light resulting from flash lamp annealing. The subsequent rapid heating results in the electrical activation of boron-implanted Si thin films, which is empirically observed using Hall measurements. The electrical activation is verified by the observed increase in the crystalline component of the Si structures resulting in higher transmittance. The feasibility of flash lamp annealing has also been demonstrated via a theoretical thermal prediction, indicating that the flash lamp annealing is applicable to low-temperature polycrystalline Si thin films. © 2014 Elsevier Ltd.


Hwang J.-H.,Hongik University | Kim H.J.,Hongik University | Kim B.-K.,Viatron Technologies | Jin W.-B.,Hongik University | And 3 more authors.
International Journal of Thermal Sciences | Year: 2015

Applying an in-line Xe-arc flash lamp annealing (FLA) process for the fabrication of low-temperature polycrystalline silicon (LTPS) on a large-scale glass substrate, this study investigates the effects of scanning multishot irradiations on the thermo-mechanical deformation of the substrate and the microscopic phase-change of the amorphous silicon (a-Si) thin-film. A glass substrate with thin-film structures was preheated at 650 °C, exposed to sequential multiple flashes, and thus heated rapidly far beyond the glass softening temperature to achieve crystallization of a-Si. Temperature variations in the substrate were predicted by one-dimensional heat conduction model with radiation absorption, and the structural deformations were simulated through a FEM code and compared to the experimental observations. The maximum temperatures arisen in the substrate during the second or subsequent flash irradiations were substantially lower than that during the first irradiation owing to reduced absorptions of flash energies. These absorption reductions were resulted from phase-changes of silicon from amorphous to polycrystalline. Those temperatures, however, were still sufficiently high to cause a significant thermal warpage, resulting in the bathtub shape of the substrate. The critical mechanisms for the warpage were the structural shrinkage and the gravitational sagging. In addition, the microscopic structural characteristics of the LTPS fabricated by the scanning multishot FLA process were explored through optical and Raman spectroscopies, and transmission electron microscopy. © 2015 Elsevier Masson SAS.


Kim D.-H.,Hongik University | Kim B.-K.,Viatron Technologies | Kim H.J.,Hongik University | Park S.,Hongik University
Thin Solid Films | Year: 2012

Experimental and theoretical investigations on flash lamp annealing (FLA) of amorphous silicon (a-Si) film on glass were carried out with a view to practical applications in large-window display industries. A Xe arc flash lamp of 950 mm in length and 22 mm in bore diameter was applied with nominal input voltage of 7 kV and flash duration of 400 μs. Prior to the annealing process, the specimen for FLA was preheated at 650°C, which was very close to the service temperature of the glass specimen used in this study. By employing a focusing elliptic reflector, maximum light energy density of up to 8.4 J/cm 2 could be attained with an active exposure width of 2 cm. Crystallization of a-Si could be achieved in solid-phase by applying a flash beam with light density of at least 5 J/cm 2, and its phase-transition characteristics that varied with energy densities could be explained by theoretically estimated temperature fields. Electron microscopy observations confirmed that solid-phase crystallization preceded melting of a-Si due to relatively long flashing (heating) duration of 400 μs, which was comparable to solid-phase crystal-growth times at elevated temperatures. © 2012 Elsevier B.V. All rights reserved.


Kim Y.,Hongik University | Park S.,Hongik University | Kim B.-K.,Viatron Technologies | Kim H.J.,Hongik University | Hwang J.-H.,Hongik University
International Journal of Heat and Mass Transfer | Year: 2015

Abstract Using a Xe-arc flashing of 0.4 ms, indium tin oxide (ITO) thin-films widely applied to fabricate transparent conducting electrodes for solar cells and displays are annealed at room temperature in order to improve their electric conductance and optical transmittances. ITO thin-films of 100 nm in thickness are deposited on a glass substrate of 500 μm in thickness by the magnetron sputtering method. Ray-tracing calculation estimates that heat absorbed in the thin-film during flash lamp annealing (FLA) process with using an additional back-reflector increases by about 2.8 times greater than that without using the back-reflector. Simulation based on one-dimensional conduction/radiation heat transfer model shows that the film temperatures during the FLA process exceed the crystallization point of the ITO material, indicating that its physical properties have been varied accordingly. Undergoing the short experimental FLA process, resistivity of the specimen has been decreased by about 30%, which is comparable to the ones obtained from conventional furnace annealing at temperatures ranging 200-300 °C for an hour, while the transmittances in the visible light range have been slightly increased. Morphological features of the films are investigated using XRD, XPS, AFM, and SEM, indicating that the specimens treated by the FLA or in furnace have crystallites larger than that of the as-received. © 2015 Elsevier Ltd


Kim D.H.,Hongik University | Kim D.H.,Viatron Technologies | Kim B.-K.,Hongik University | Kim H.J.,Hongik University
Transactions of the Korean Society of Mechanical Engineers, B | Year: 2012

The flash lamp annealing (FLA) process has been considered highly promising for manufacturing lowtemperature polysilicon on large-scale backplanes. Based on a theoretical estimation, this study clarifies the critical mechanisms of glass backplane deformation during the FLA process. A simulation using a commercial FEM code with viscoelastic models shows that the local region, whose temperature is larger than the glass softening point, undergoes permanent structural shrinkage owing to stress relaxation. For larger backplanes (4th Gen), structural shrinkages and gravitational deflection are critical to deformation in the FLA process, resulting in an "M" shape; in smaller backplanes (0th Gen), the latter is negligible, resulting in a "U" shape. © 2011 The Korean Society of Mechanical Engineers.


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