Hong-Seok Choi

A New Poly-Si TFT Current-Mirror Pixel for Active Matrix Organic Light Emitting Diode

A new poly-Si thin-film-transistor (TFT) current-mirror-active-matrix-organic-light-emitting-diode (AMOLED) pixel, which successfully compensates for the variation of the threshold voltage as well as mobility in the excimer laser annealed poly-Si TFT pixel, is designed and fabricated. The OLED current (IOLED) of the proposed pixel does not depend on the operating temperature. When the temperature of pixel is increased from 27 degC to 60 degC, the I OLED of the new pixel circuit composed of four TFTs and one capacitor increases only about 1.5%, while that of a conventional pixel composed of two TFTs and one capacitor increases about 37%. At room temperature, nonuniformity of the IOLED in the proposed circuit was also considerably suppressed at around 9%. We have successfully fabricated a 1.2-in AMOLED panel (96times96timesred green blue) to evaluate the performance of the proposed pixel. A troublesome residual image caused by the hysteresis phenomenon of the poly-Si TFT was almost eliminated in the proposed AMOLED panel as a result of current programming

Excimer Laser Induced Crystallization of Polycrystalline Silicon Films by Adding Oxygen

We have investigated the behaviors of the grain-growth and the electrical properties in excimer laser-induced polycrystalline silicon films by adding oxygen (poly-SiO x ). The melting and solidification times in laser-induced crystallization were increased by adding oxygen into amorphous silicon films which promoted the grain-growth. The dark conductivity of poly-SiO x films was decreased with the increase of oxygen concentration up to 6.32 x 10 20 cm -3 . However, the degradation of dark conductivity by light stress was improved in poly-SiO x films probably due to the stable silicon networking. We have also observed that the electrical stability was enhanced in the poly-SiO x films with oxygen concentration of 9.1 x 10 19 cm -3 without much decrease of dark conductivity.

Combining histogram-wise and pixel-wise matchings for kernel tracking through constrained optimization

In this paper, we propose a constrained optimization approach to improving both the robustness and accuracy of kernel tracking which is appropriate for real-time video surveillance due to its low computational load. Typical tracking with histogram-wise matching provides robustness but has insufficient accuracy, because it does not involve spatial information. On the other hand, tracking with pixel-wise matching achieves accurate performance but is not robust against deformation of a target object. To find the best compromise between robustness and accuracy, in our paper, we combine histogram-wise matching and pixel-wise template matching via constrained optimization problem. Firstly, we propose a novel weight image representing both the probability of foreground and the degree of similarity between the template and a candidate target image. The weight image is used to formulate an objective function for the histogram-wise weight matching. Then the pixel-wise matching is formulated as a constrained optimization problem using the result of the histogram-wise weight matching. In consequence, the proposed approach optimizes pixel-wise template similarity (for accuracy) under the constraints of histogram-wise feature similarity (for robustness). Experimental results show the combined effects, and demonstrate that our method outperforms recent tracking algorithms in terms of robustness, accuracy, and computational cost.

Highly efficient current scaling AMOLED panel employing a new current mirror pixel circuit fabricated by excimer laser annealed poly-Si TFTs

We propose and fabricate highly efficient current scaling AMOLED panel employing excimer laser annealed poly-Si TFTs, which successfully compensate the non-uniformity of IOLED due to the grain boundaries and residual image caused by a hysteresis phenomenon in poly-Si TFT. The proposed 2.4 inch panel employing a new current mirror pixel circuit successfully reduces a nonuniformity of the luminance from 41% to 9.1%, and eliminates residual image, compared with conventional 2-TFT pixel array. The proposed pixel circuit can also increase the data current by 57% and decrease the pixel charging time by 21%, compared with a traditional current mirror pixel

A novel method for a smooth interface at poly-SiO x /SiO 2 by employing selective etching

We have investigated the excimer laser recrystallization of slightly oxygen-added amorphous silicon (a-SiO/sub x/) films for the application to the active layer of thin film transistors. We also propose a new method to reduce the surface roughness of poly-SiO/sub x/ films by etching the grain boundaries selectively. SEM images show that the Si-O bonds are well segregated into the poly-Si grain boundaries after laser crystallization and the surface morphology is remarkably improved after the selective buffered oxide etchant (BOE) etching of the grain boundaries. The electrical conductivity measurement shows that the activation energies of poly-SiO/sub x/ and poly-Si films have an identical value of 0.52 eV. This may confirm that oxygen-induced defects do not cause any difference in the electrical performance even at the oxygen concentration of 0.18 at.%. Moreover, the electrical mobility and subthreshold slope of poly-SiO/sub x/ TFTs are considerably improved by employing the proposed method, which smooths the poly-SiO/sub x//SiO/sub 2/ interface.We have investigated the excimer laser recrystallization of slightly oxygen-added amorphous silicon (a-SiO/sub x/) films for the application to the active layer of thin film transistors. We also propose a new method to reduce the surface roughness of poly-SiO/sub x/ films by etching the grain boundaries selectively. SEM images show that the Si-O bonds are well segregated into the poly-Si grain boundaries after laser crystallization and the surface morphology is remarkably improved after the selective buffered oxide etchant (BOE) etching of the grain boundaries. The electrical conductivity measurement shows that the activation energies of poly-SiO/sub x/ and poly-Si films have an identical value of 0.52 eV. This may confirm that oxygen-induced defects do not cause any difference in the electrical performance even at the oxygen concentration of 0.18 at.%. Moreover, the electrical mobility and subthreshold slope of poly-SiO/sub x/ TFTs are considerably improved by employing the proposed method, which smooths the poly-SiO/sub x//SiO/sub 2/ interface.

A Novel LDD-Structured Poly-Si Thin Film Transistors with High ON/OFF Ratio

We have fabricated a new polycrystalline silicon thin film transistor (poly-Si TFT), entitled a gate-overlapped lightly doped drain (GO-LDD) TFT, which may reduce the leakage current without sacrificing the ON current. Both the source/drain and LDD region of GO-LDD TFT are formed simultaneously by employing the buffer oxide without any additional LDD doping. Experimental results show that the leakage current of the proposed TFTs is decreased by the magnitude of two orders without sacrificing the ON current. The low-temperature ion shower doping is also employed to fabricate both the source/drain and LDD in the GO-LDD TFTs without a troublesome ion implantation.

Properties of Iron Oxide Films Grown by Pulsed Laser Deposition

Epitaxial magnetite (Fe 3 O 4 ) thin films have been grown on MgO(001) substrates by pulsed laser deposition. The films have characteristics of the “Verwey transition”: the electric conductivity decreases by about one order of magnitude and the magnetization curve shows anomaly at the transition temperature, i.e. about 125 K. Effects of annealing the Fe 3 O 4 thin films at various oxygen partial pressures have also been investigated. Phase identification was made using XRD techniques and infrared reflectivity measurements. The surface morphologies were studied by SEM and AFM. Under an oxidizing atmosphere, the Fe 3 O 4 phase is transformed mainly into α-Fe 2 O 3 , and this transformation is accompanied by development of needle-like structures along directions of MgO substrate. It is also found that electrical and magnetic properties of the iron oxide films are changed significantly by the annealing process.

4-Channel Push-Pull VCSEL Drivers for HDMI Active Optical Cable in 0.18-μm CMOS

The price and power consumption of standard HDMI cables exponentially rise when the data rate increases or cable runs longer. HDMI active optical cable (AOC) can potentially solve price and power issues since fibers are tolerant to loss. However, additional optical components such as vertical-cavity surface-emitting laser (VCSEL) and photodiode (PD) are required. Therefore, drivers and transimpedance amplifiers should be designed carefully for normal operations. In this paper, two types of 4-channel VCSEL drivers for HDMI AOC are presented. The first type of the driver passes data and bias separately. It uses off-chip capacitors for AC coupling. On the other hand, the second type of the driver passes data including DC value without using off-chip capacitors. Structures of the both drivers are based on push-pull current-mode logic (CML) to achieve better power efficiency. Drivers fabricated in 0.18-μm CMOS process consume 36.5 mW/channel at 6 Gb/s and 24.7 mW/channel at 12 Gb/s, respectively.

In-Situ Fabrication of Gate Oxide and Poly-Si Film by XeCl Excimer Laser Annealing

We have proposed a new method to form the gate oxide and recrystallize the polycrystalline silicon (poly-Si) active layer simultaneously. During the irradiation of excimer laser, the poly-Si film is recrystallized while the oxygen ion impurities, which are injected into the amorphous silicon (a-Si) film, are activated by laser energy and react with silicon atoms to form SiO2. Our experimental results show that a high quality oxide, a poly-Si film with fine grain, and a smooth and clean interface between oxide and poly-Si film have been successfully obtained by the proposed fabrication method. The maximum oxide breakdown electric field which exceeds 7 MV/cm is obtained.

Laser induced implanted oxide (Ll2Ox) and polycrystalline silicon film simultaneously fabricated by excimer laser irradiation

A method to form the gate oxide and recrystallize the polycrystalline silicon (poly-Si) active layer simultaneously is proposed. During the irradiation of excimer laser, the poly-Si film is recrystallized while the oxygen ion impurities injected into the amorphous silicon (a-Si) film are activated by laser energy and react with silicon atoms to form SiO2. Our experimental results show that a high quality oxide and a poly-Si film with fine grain have been fabricated successfully by the proposed method. High quality interface between oxide and poly-Si films has also been obtained.