Showing papers by "Junsin Yi published in 2010"

ZnO nanowire-embedded Schottky diode for effective UV detection by the barrier reduction effect

Abstract: A zinc oxide nanowire (ZnO NW)-embedded Schottky diode was fabricated for UV detection. Two types of devices were prepared. The ZnO NW was positioned onto asymmetric metal electrodes (Al and Pt) for a Schottky device or symmetric metal electrodes (Al and Al) for an ohmic device, respectively. The Schottky device provided a rectifying current flow and was more sensitive to UV illumination than the ohmic device. The Schottky barrier plays an important role for UV detection by a UV-induced barrier reduction effect. The fabrication of the ZnO NW-embedded Schottky diode and the UV reaction mechanism are discussed in light of the UV light-induced Schottky barrier reduction effect.

High performance nonvolatile memory using SiO2/SiOx/SiOxNy stack on excimer laser-annealed polysilicon and the effect of blocking thickness on operation voltage

Abstract: Silicon-rich SiOx material is a good charge storage candidate for memory applications that promise a large memory window and low operation voltage. Nonvolatile memory (NVM) devices fabricated on excimer laser-annealed polysilicon using SiO2/SiOx/SiOxNy (OOxOn) structure are investigated with SiO2 blocking thicknesses changing from 15 to 20 to 30 nm. The Si-rich SiOx material exposed numerous non-bridging oxygen hole-centre defect sources and a rich silicon phase in the base material. These defects, as well as amorphous silicon clusters existing in the SiOx layer, enhance the charge storage capacity of the device. Retention properties were ensured by 3.2 nm SiOxNy tunnelling layer growth via N2O plasma-assisted oxynitridation. NVM characteristics showed a retention exceeding 85% of the threshold voltage shift after 104 s and greater than 70% after 10 years. Depending on the blocking thickness of 15, 20 or 30 nm, operating voltages varied from ±9 to ±13 V at a programming/erasing duration of only 1 ms. These excellent operating properties of the OOxOn structure make it a potential competitor among the new generation of memory structures on glass.

The investigation of an amorphous SiOx system for charge storage applications in nonvolatile memory at low temperature process

Abstract: Beside silicon nitride, silicon rich SiO x is a good charge storage material for the charge trap type of nonvolatile memory due to the high density of the charge traps. In this study, the charge storage ability of various amorphous SiO x materials has been investigated. By controlling the ratio of N 2 O/SiH 4 gases from a 1:6 to a 2:1 input gas flow rate, the deposited SiO x bandgap changed from 2.3 to 3.9 eV. The charge storage properties of the SiO x system were studied on metal–insulator–semiconductor structures with an insulator stack of SiO 2 /SiO x /SiO x N y on an n-type silicon wafer. In this structure, the SiO 2 was used for the blocking layer and the SiO x N y was used for the tunneling layer. By analyzing the FTIR and the photoluminescence spectra, it is shown that the richest silicon material incorporates numerous non-bridging oxygen hole-center (NBOHC) defect sources and a rich silicon phase in the base material. These defects, as well as the amorphous silicon clusters that exist in the SiO x layer, enhanced the charge storage capacity of the device compared to the oxygen rich SiO x cases. The retention property was optimized by surveying the tunneling thickness of the 2.3, 2.6, 2.9, and 3.2 nm SiO x N y layers.

SiO2 Films Deposited by APCVD with a TEOS/Ozone Mixture and Its Application to the Gate Dielectric of TFTs

Abstract: Silicon dioxide (SiO 2 ) films were deposited using atmospheric pressure chemical vapor deposition (APCVD) with tetraethyl orthosilicate (TEOS) and ozone (O 3 ) as reactant gases These films were used as the gate dielectric of low temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) 0 3 gas was chosen instead of oxygen (0 2 ) gas because the latter is not compatible with the low temperature processing of LTPS TFTs SiO 2 films deposited at low temperatures (<450°C) have low Si-OH contents and electrical properties desirable for gate insulator materials Although the LTPS TFTs were fabricated using low cost SiO 2 films deposited by APCVD as the gate dielectric, the fabricated devices exhibited a field-effect mobility of 49 cm 2 /V s and a subthreshold swing of 490 mV/dec The results demonstrate that SiO 2 deposited by APCVD with TEOS and 0 3 is a promising material for low cost and high quality gate insulators for LTPS TFTs

Investigation of lauric acid dopant as a novel carbon source in MgB2 wire

Abstract: We fabricated lauric acid (LA) doped MgB 2 wires and investigated the effects of the LA doping. For the fabrication of the LA-doped MgB 2 wires, B powder was mixed with LA at 0–5 wt.% of the total amount of MgB 2 using an organic solvent, dried, and then the LA-treated B and Mg powders were mixed stoichiometrically. The powder mixture was loaded into an Fe tube and the assemblage was drawn and sintered at 900 °C for 3 h under an argon atmosphere. We observed that the LA doping induced the substitution of C for the B sites in MgB 2 and that the actual content of C increased monotonically with increasing LA doping level. The LA-doped MgB 2 wires exhibited a lower critical temperature ( T c ), but better critical current density ( J c ) behavior in a high magnetic field: the 5 wt.% LA-doped sample had a J c value of 5.32 × 10 3 A/cm 2 , which was 2.17 times higher than that of the pristine sample (2.45 × 10 3 A/cm 2 ) at 5 K and 6 T, suggesting that LA is an effective C dopant in MgB 2 for enhancing the high-field J c performance.

Optimized surface passivation of n and p type silicon wafers using hydrogenated SiNx layers

Abstract: We have investigated surface passivation of n and p type silicon wafers, obtained by controlling silicon–hydrogen bonding and fixed charge densities with the use of hydrogenated SiNx films. The hydrogenated SiNx films were deposited by single PECVD at 13.56 MHz with SiH4/NH3 gas mixture. The hydrogenated SiNx films of refractive indices 2.55–1.92 and high optical band-gap (> 3.1 eV) were obtained by varying the hydrogenated SiNx film composition. The fixed charge densities, hydrogen-bonding and carrier lifetime performance in n and p type silicon wafer were analyzed. The highest fixed positive charge of 2.66 × 1012 (cm− 2) was for the hydrogenated SiNx film composition of 1.21. Fourier transform infrared spectroscopy measurement was carried out to evaluate the bonding concentration of Si–H and N–H. The minority carrier lifetimes of the hydrogenated SiNx passivated silicon wafers were up to 153 μs and 84 μs for p and n type, respectively. Mechanism of surface passivation depends on the type of silicon wafer. The higher Si–H bond density is the key point of n type passivation quality. The large fixed positive charge is used to measure p type passivation quality.

Memory characteristics of poly-Si using MIC as an active layer on glass substrates

Abstract: In this paper the electrical properties of nonvolatile memory (NVM) using multi-stack gate insulators of oxide–nitride–oxynitride (ONOn) and an active layer of low temperature polycrystalline silicon (LTPS) were investigated. From hydrogenated amorphous silicon (a-Si : H), the LTPS thin film with a high crystalline fraction of 96% and a low surface roughness of 1.28 nm was fabricated by metal induced crystallization (MIC) with annealing conditions of 650 °C for 5 h on glass substrates. The LTPS thin film transistor or the NVM had a field effect mobility of (μFE) 10 cm2 V−1 s−1 and a threshold voltage (VTH) of −3.5 V. The results demonstrated that the NVM had a memory window of 1.6 V with a programming and erasing (P/E) voltage of −14 V and 14 V in 1 ms. Moreover, retention properties of the memory were shown to exceed 80% after 10 years. Therefore, the LTPS fabricated by MIC has become a potential material for NVM application which is employed for the system integration of panel displays.

High charge storage of poly-Si thin film nonvolatile memory devices with oxide–silicon–oxynitride stack structures

Abstract: Polycrystalline silicon (poly-Si) thin film nonvolatile memory (NVM) devices with an oxide–silicon–oxynitride (OSOn) stack structure using an amorphous silicon (a-Si) as a storage layer on a glass panel were fabricated and investigated for high charge storage of memory applications in systems-on-panels (SOPs). Because the band gap of a-Si is lower than that of silicon nitride (SiNx) and a larger band gap offset provides more room for charge storage, a-Si thin layer with high charge injection can be applied to the fabrication of poly-Si NVM devices. The trap densities of a-Si thin films deposited by different flow ratios of H2 and silane (SiH4) were calculated to determine the optimal conditions for the charge storage layer. Poly-Si thin film transistor (TFT) technology, plasma-assisted oxynitridation to deposit an ultra-thin tunneling layer, and an optimal a-Si thin film charge storage layer were used to fabricate poly-Si NVM devices on glass substrate. A large memory window of +3.02 V to −1.68 V was obtained at a low operating voltage with an erasing voltage of +10 V and a programming voltage of −10 V due to high charge storage sites in the a-Si thin film. Our results demonstrate that poly-Si NVM devices with a-Si thin film as a charge storage layer on a glass panel can be applied to system applications of flat panel displays (FPDs) due to their large memory windows at low operating voltage.

Embedded nonvolatile memory devices with various silicon nitride energy band gaps on glass used for flat panel display applications

Abstract: Nonvolatile memory (NVM) devices with a nitride–nitride–oxynitride stack structure on a rough poly-silicon (poly-Si) surface were fabricated using a low-temperature poly-Si (LTPS) thin film transistor technology on glass substrates for application of flat panel display (FPD). The plasma-assisted oxidation/nitridation method is used to form a uniform oxynitride with an ultrathin tunneling layer on a rough LTPS surface. The NVMs, using a Si-rich silicon nitride film as a charge-trapping layer, were proposed as one of the solutions for the improvement of device performance such as the program/erase speed, the memory window and the charge retention characteristics. To further improve the vertical scaling and charge retention characteristics of NVM devices, the high-κ high-density N-rich SiNx films are used as a blocking layer. The fabricated NVM devices have outstanding electrical properties, such as a low threshold voltage, a high ON/OFF current ratio, a low subthreshold swing, a low operating voltage of less than ±9 V and a large memory window of 3.7 V, which remained about 1.9 V over a period of 10 years. These characteristics are suitable for electrical switching and data storage with in FPD application.

Effects of the pyromellitic dianhydride cathode interfacial layer on characteristics of organic solar cells based on poly(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl C 61 butyric acid methyl ester

Abstract: This study examined the performance of poly(3-hexylthiophene-2,5-diyl)(P3HT)- and [6,6]-phenyl C61 butyric acid methyl ester (PCBM)-based organic solar cells (OSCs) with a pyromellitic dianhydride (PMDA) cathode interfacial layer between the active layer and cathode. The effect of inserting the cathode interfacial layer with different thicknesses was investigated. For the OSC samples with a 0.5 nm thick PMDA layer, the power conversion efficiency (PCE) was approximately 2.77% under 100 mW/cm2 (AM1.5) simulated illumination. It was suggested that the PMDA cathode interfacial layer acts as an exciton blocking layer, leading to an enhancement of the OSC performance.

Parameterised structured light imaging for depth edge detection

Abstract: This reported research features parameterised structured light imaging that is practically useful for detecting depth edges. Given input parameters such as the range of distances of an object from the camera/projector and minimum detectable depth difference, the presented method is capable of computing an optimal pattern width and the number of structured light images that are needed to detect all depth edges in the specified range of distances that have at least the given detectable depth difference. Application of this parameter control to the detection of silhouette edges for visual hull reconstruction shows the effectiveness of the method.

Nanocrystalline-Silicon Thin-Film Nonvolatile Memory Devices for Display Applications

Abstract: Nanocrystalline-silicon (nc-Si) nonvolatile memory (NVM) devices with oxynitride-nitride-oxide stack structures were fabricated with directly deposited nanocrystalline-silicon thin films using a low-temperature process. The fabricated bottom-gate nc-Si NVM devices have a wide memory window with a low operating voltage during programming and erasing due to an effective control of the gate dielectrics. In addition, after ten years, the memory device retains a memory window of over 67% between the programming and erasing states. These results demonstrate that these low-priced nc-Si NVM devices have a suitable programming and erasing efficiency for data storage under low-voltage conditions, in combination with excellent charge retention characteristics.

Investigation of Aluminum Metallized Source/Drain Thin Film Transistors Using a Self-Aligned Fabrication Process

Abstract: For a better thin film transistor performance, metal silicide has been studied in order to enhance the conductivity of the source and drain electrodes Although aluminum does not form a metal silicide with silicon, the two materials interpenetrate in an induced crystallization process In such a structure, aluminum can act as a p-type dopant in the silicon lattice In this work, aluminum metallized source/drain thin film transistors with excimer laser-annealed polycrystalline silicon were fabricated using a simple self-aligned process The source/drain regions were patterned with a lift-off process The n-channel characteristics of the as-deposited aluminum source/drain were explored and an improvement in the performance was observed after a heat treatment at 250 °C for 1 h The devices treated at 350 °C for 10 h exhibited p-channel characteristics The device characteristics were compared with another fabricated p-type doped source/drain structure A remarkable enhancement in the performance of the aluminum metallized source/drain devices was observed These structures yielded a peak field effect mobility of about 105 cm2V-1s-1 The simple fabrication process and resulting enhancement in device performance makes this type of structure ideal for use in thin film transistors on glass

Performance Improvement of the Organic Light-Emitting Diodes by Using a LiF/Pyromellitic Dianhydride Stacked Cathode Interfacial Layer

Abstract: A bilayered cathode interfacial structure consisting of lithium fluoride (LiF) and pyromellitic dianhydride (PMDA) was used between Al and tris-(8-hydroxyquinoline) aluminum (Alq 3 ) in the organic light-emitting diode (OLED), and a better performance enhancement compared to the OLED with a single LiF interfacial layer was achieved by using an optimal thickness combination of the bilayered interfacial structure (0.3 nm LiF/0.7 nm PMDA). The bilayered interfacial stucture with an optimum thickness combination decreased the parallel bulk resistance and lowered the electron injection barrier height between Al and Alq 3 according to the impedance and in situ ultraviolet photoelectron spectroscopy measurements, respectively.

Comparative study of CdTe thin film solar cells with wet and dry CdCl 2 treatment process

Abstract: In this work, CdTe films were prepared by r.f. magnetron sputtering. Influence of conventional wet and dry CdCl 2 treatments on the structural and optical properties of CdTe films were investigated by field emission scanning electron microscope (FE-SEM), x-ray diffraction (XRD), and UV-Visible spectrophotometer. Also, CdS/CdTe thin film solar cells were fabricated by all sputtering process and the cell characteristics were studied. The as-deposited CdTe thin films had a zincblende structure highly oriented with the (111) direction parallel to the substrate surface. The CdTe films lose their preferred orientation and become polycrystalline by heat treatment with dry CdCl 2 treatment. The wet CdCl 2 treatment exhibited a similar trend, but is less effective for grain growth than dry CdCl 2 treatment. The photovoltaic properties of the CdS/CdTe solar cell were considerably improved with the increase in the annealing temperature, which was caused by the increase of grain size in CdTe films. However, the wet CdCl 2 process was not suitable for reproducible fabrication.

Self textured transparent conductive oxide film for efficiency improvement in solar cell

Abstract: Transparent conductive oxides have an important role of thin-film solar cell to the side of cost and performance. Especially, an Al doped ZnO film is a very promising material for thin-film solar cell fabrication because of the easy synthesis method as well as the cheap cost induced on the wide availability of its constituent raw materials. The Al-doped ZnO films were prepared by metal organic chemical vapor deposition using a diethylzinc, water vapor and trimethylaluminum (TMA). The introduction of TMA doping source has a great influence on the electrical resistivity and diffused light to wide wavelength range. The haze factor of Al doped ZnO achieved 43 % at 600 nm without additional surface texturing process by simple TMA doping. In this study, the choice of AZO TCO allows the achievement of energy conversion efficiencies to 7.7 %.