Solid State Phenomena Vols. 124-126

Abstract: Co thin films were deposited by remote plasma atomic layer deposition (ALD) method using dicobalt hexacarbonyl t-butylacetylene (C12H10O6(Co)2) or cyclopentadienyl cobalt dicarbonyl (CpCo(CO)2) as the Co precursor. The impurity contents were minimized when the Co films deposited by remote plasma ALD with H2 plasma within the process pressure range of 0.1~2 Torr at plasma power of 300W. Co-Cp bond in CpCo(CO)2 precursor was easily broken under H2 remote plasma atmosphere. The carbon content of Co films were examined with Auger electron spectroscopy (AES) and Rutherford backscattering spectroscopy (RBS) to be ~21 at.% with C12H10O6(Co)2, and ~7 at.% with CpCo(CO)2. The surface morphologies of Co films were measured with atomic force microscope (AFM) and root mean square (RMS) values of Co films using C12H10O6(Co)2 and CpCo(CO)2 were 1.73
and 1.51
, respectively.

Abstract: Vanadium pentoxide xerogel films intercalated by poly (ethylene oxide), PEO, were prepared using direct intercalation method via a sol-gel route. The electrical and electrochromic characterization of the films were conducted. The electrical properties along and across V-O layers have been evaluated. The results indicate that the proper amount of PEO can increase the electrical conductivity and charge density of the films. The electrochromism of the films upon lithium intercalation was investigated by ex-situ transmittance measurement. The films display a reversible multichromism (orange
green
blue) upon Li+ ion insertion/extraction.

Abstract: Tin doped indium oxide (ITO) films were deposited on plastic films by RF superimposed DC magnetron sputtering method using an In2O3 – 10 wt.% SnO2 target without intentionally heating substrates. We have investigated the effects of an RF superimposed DC power system on the electrical, optical, and mechanical properties of the ITO films by using Four-Point Probe, Hall Effect Measurement, UV-Vis-NIR Spectrophotometer, XRD, and Residual Stress Measurement. With increasing the amount of RF power superimposed on DC power, the sputtering discharge voltages of DC power supply were decreased from –290 V to –100 V, i.e., plasma impedance decreased with an increase of the amount of RF power. The resistivity of the samples drastically decreases with increasing RF power, and shows the lowest value of 3.8×10-4 8·cm. Hall effect measurements explain that the increase of carrier mobility is strongly related with the enhancement of the resistivity of ITO films even though there is no difference on its concentration. The RF power superimposed on DC power also reduces the residual stress of the samples up to the stress level of ~ 200 MPa at optimum values of RF power.

Abstract: Low temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) are demanded to fabricate high performance liquid crystal displays (LCD) and organic light-emitting diode displays (OLED). The mobility of poly-Si TFT can be two orders of magnitude higher than that of amorphous Si (a-Si) TFT. Excimer laser annealing has been studied to be the most promising technology to meet the stringent requirement in high speed operation. The process parameters were identified as a-Si thickness, laser energy density, overlap ratio, annealing atmosphere and pre-clean condition. The a-Si layer of 40-50 nm was deposited by plasma enhanced chemical vapor deposition (PECVD). The XeCl excimer laser was irradiated on the a-Si film at room temperature under N2 or N2/O2 environment. The energy density ranged 250-400 mJ/cm2, and the overlap ratio was 95-99%. The highly aligned poly-Si array thin film could be obtained. The grain size has been about 0.31x0.33 μm2, and the regular arrangement in poly-Si grains was discussed. In addition, the PMOS TFT has been fabricated from the aligned poly-Si array. The mobility was as high as 100 cm2/Vs and the sub-threshold swing was around 0.24 V/dec. The threshold voltage was -1.25 V and the on/off current ratio was about 106.

Abstract: An investigation is reported by coating BaMgAl10O17:Eu2+ phosphor by silicon oxide using catalyzed atomic layer deposition. Nanoscaled SiO2 films were prepared at room temperature using tetraethoxysilane (TEOS), H2O and NH3 as precursors, reactant gas and catalyst, respectively. AES analysis showed the surface composition of coated phosphor was silicon oxide. In TEM and FE-SEM analysis, the growth rate was about 0.7 Å/cycle and the surface morphology became smoother and clearer than that of uncoated phosphor. The photoluminescence intensity (PL) increased up to 11.04% as ALD cycle increased up to 200 ALD cycle. This means that the reactive surface of uncoated phosphors is uniformly grown with stable silicon oxide to reduce the dead surface layer without change of bulk properties. Moreover, it is found that nanoscaled SiO2 films are quite effective for the improvement of the aging characteristics of photoluminescence.

Abstract: Bi and Eu co-doped Y2O3 was used as a red phosphor with a very high efficiency synthesized by the solid state reaction and co-precipitation The emission spectrum consisted of a weak band at 581, 587, 593 and 599 nm corresponding to the 5D0 → 7F1 transition, with sharp peaks of maximum intensity occurring at about 611 nm due to the 5D0 → 7F2 transition of Eu3+. In addition, the excitation spectrum exhibited a broad band between 250 and 550 nm with peaks occurring at about 310 – 400 nm and a sharp peak at 465.5 nm. The relative emission intensity was improved by co-precipitation synthesis as compared to solid state reaction synthesis. This implies that an appropriate co-precipitation synthesis could improve the luminescent efficiency, particularly for the samples prepared with the optimized firing temperature of 1100 °C.

Abstract: We report on the fabrication of dual-gate pentacene organic thin-film transistors (OTFTs) using a plasma-enhanced atomic layer deposited (PEALD) 150 nm thick Al2O3 as a bottom gate dielectric and a 300 nm thick parylene or a PEALD 200 nm thick Al2O3 as both a top gate dielectric and a passivation layer. The threshold voltage (Vth) of OTFT with a 300 nm thick parylene as a top gate dielectric is changed from 4.7 V to 1.3 V and that with a PEALD 200 nm thick Al2O3 as a top gate dielectric is changed from 1.95 V to -9.8 V when the voltage bias of top gate electrode is changed from -10 V to 10 V. The change of Vth of OTFT with the dual-gate structure has been successfully understood by an analysis of electrostatic potential.

Abstract: Amorphous silicon thin films were deposited below 160oC on PES plastic films using PECVD. After thin film deposition using PECVD, thin film failures such as film delamination and cracking often occurred. For successful growth of thin films (about 2000 Å) without their failures, it is necessary to solve the critical problem related to the internal compressive stress (some GPa) leading to delamination at a threshold thickness value of the films. The Griffith’s theory explains the failure process by looking at the excess of elastic energy inside the film, which overcomes the cohesive energy between film and substrate. In this work, reducing a-Si layer film thickness and optimizing a barrier SiNx layer have produced stable a-Si films at 150oC, over PES substrates.

Abstract: To improve luminescent properties of the phosphor, spherical BaMgAl10O17:Eu2+ particles have been synthesized using a liquid phase reaction composed of two-stage precipitations. This phosphor particles exhibited uniform size (0.4 ㎛) with narrow distribution and were well-dispersed without agglomeration. The single phase of phosphor was formed by firing at the temperature of about 1350°C. The preparation conditions in this synthetic process for spherical BaMgAl10O17:Eu2+ particles were optimized on the basis of emission intensity by the excitation at 147 nm. The emission spectra showed the typical broad band due to the transition of Eu2+ activator from 4f65d1 to 4f7 in BaMgAl10O17:Eu2+. The maximum emission intensity for this spherical blue phosphor was obtained by reduction treatment at 1450°C.