• Journal of Sensor Science and Technology
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• v.23 no.3
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• pp.207-210
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• 2014

$TiO_2$ oxide semiconductor is being widely studied in various applications such as photocatalyst and photosensor. Pd/$TiO_2$ gas sensor is mainly used to detect $H_2$, CO and ethanol. This study focus on increasing hydrogen detection ability of Pd/$TiO_2$ in room temperature through Al-doping. Pd/$TiO_2$ was fabricated by the hydrothermal method. Contacting to Aluminum (Al) foil led to Al doping effect in Pd/$TiO_2$ by thermal diffusion and enhanced hydrogen sensing response. $TiO_2$ nanoparticles were sized at ~30 nm of diameter from scanning electron microscope (SEM) and maintained anatase crystal structure after Al doping from X-ray diffraction analysis. Presence of Al in $TiO_2$ was confirmed by X-ray photoelectron spectroscopy at 73 eV. SEM-energy dispersive spectroscopy measurement also confirmed 2 wt% Al in Pd/$TiO_2$ bulk. The gas sensing test was performed with $O_2$, $N_2$ and $H_2$ gas ambient. Pd/Al-doped $TiO_2$ did not response $O_2$ and $N_2$ gas in vacuum except $H_2$. Finally, the normalized resistance ratio ($R_{H2on}/R_{H2off}$) of Pd/Al-doped $TiO_2$ increases about 80% compared to Pd/$TiO_2$.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.207-207
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• 2011

Amorphous transparent oxide semiconductors (a-TOS) have been widely studied for many optoelectronic devices such as AM-OLED (active-matrix organic light emitting diodes). Recently, Nomura et al. demonstrated high performance amorphous IGZO (In-Ga-Zn-O) TFTs.1 Despite the amorphous structure, due to the conduction band minimum (CBM) that made of spherically extended s-orbitals of the constituent metals, an a-IGZO TFT shows high mobility.2,3 But IGZO films contain high cost rare metals. Therefore, we need to investigate the alternatives. Because Aluminum has a high bond enthalpy with oxygen atom and Alumina has a high lattice energy, we try to replace Gallium with Aluminum that is high reserve low cost material. In this study, we focused on the electrical properties of IZO:Al thin films as a channel layer of TFTs. IZO:Al were deposited on unheated non-alkali glass substrates (5 cm ${\times}$ 5 cm) by magnetron co-sputtering system with two cathodes equipped with IZO target and Al target, respectively. The sintered ceramic IZO disc (3 inch ${\phi}$, 5 mm t) and metal Al target (3 inch ${\phi}$, 5 mm t) are used for deposition. The O2 gas was used as the reactive gas to control carrier concentration and mobility. Deposition was carried out under various sputtering conditions to investigate the effect of sputtering process on the characteristics of IZO:Al thin films. Correlation between sputtering factors and electronic properties of the film will be discussed in detail.

• Journal of Sensor Science and Technology
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• v.24 no.6
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• pp.364-367
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• 2015

Tin oxide thin films were fabricated on glass substrates by the successive ionic layer adsorption and reaction (SILAR) method at room temperature and ambient pressure. Before measuring their properties, all samples were annealed at $500^{\circ}C$ for 2 h in air. Film thickness increased with the number of cycles; X-ray diffraction patterns for the annealed $SnO_2$ thin films indicated a $SnO_2$ single phase. Thickness of the $SnO_2$ films increased from 12 to 50 nm as the number of cycles increased from 20 to 60. Although the optical transmittance decreased with thickness, 50 nm $SnO_2$ thin films exhibited a high value of more than 85%. Regarding electronic properties, sheet resistance of the films decreased as thickness increased; however, the measured resistivity of the thin film was nearly constant with thickness ($3{\times}10^{-4}ohm/cm$). From Hall measurements, the 50 nm thickness $SnO_2$ thin film had the highest mobility of the samples ($8.6cm^2/(V{\cdot}s)$). In conclusion, optical and electronic properties of $SnO_2$ thin films could be controlled by adjusting the number of SILAR cycles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.533-533
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• 2007

The stress effect of SiGe p-type metal oxide semiconductors field effect transistors(MOSFETs) has been investigated to compare device properties using Si bulk and partially depleted silicon on insulator(PD SOI). The electrical properties in SiGe PD SOI presented enhancements in subthreshold slope and drain induced barrier lowering in comparison to SiGe bulk. The reliability of gate oxides on bulk Si and PD SOI has been evaluated using constant voltage stressing to investigate their breakdown (~ 8.5 V) characteristics. Gate leakage was monitored as a function of voltage stressing time to understand the breakdown phenomena for both structures. Stress induced leakage currents are obtained from I-V measurements at specified stress intervals. The 1/f noise was observed to follow the typical $1/f^{\gamma}$ (${\gamma}\;=\;1$) in SiGe bulk devices, but the abnormal behavior ${\gamma}\;=\;2$ in SiGe PD SOI. The difference of noise frequency exponent is mainly attributed to traps at silicon oxide interfaces. We will discuss stress induced instability in conjunction with the 1/f noise characteristics in detail.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.59-62
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• 2019

In this study, we have developed solution-processed, F-doped In-Ga-Zn-O semiconductors and investigated their applications to thin-film transistors. In order for forming the appropriate channel layer, precursor solutions were formulated by dissolving the metal salts in the designated solvent and an additive, ammonium fluoride, was incorporated additionally as a chemical modifier. We have studied thermal and chemical contributions by a thermal annealing and an incorporation of chemical modifier, from which it was revealed that electrical performances of the thin-film transistors comprising the channel layer annealed at a low temperature can be improved significantly along with an addition of ammonium fluoride. As a result, when the 20 mol% fluorine was incorporated into the semiconductor layer, electrical characteristics were accomplished with a field-effect mobility of $1.2cm^2/V{\cdot}sec$ and an $I_{on}/_{off}$ of $7{\times}10^6$.

• Journal of Sensor Science and Technology
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• v.30 no.3
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• pp.175-180
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• 2021

In this paper, methods for improving the sensitivity of gas sensors to NO₂ gas are presented. A gas sensor was fabricated based on an SnO₂ nanowire network using the vapor-phase-growth method. In the gas sensor, the Au electrode was replaced with a fluorinedoped tin oxide (FTO) electrode, to achieve high sensitivity at low temperatures and concentrations. The gas sensor with the FTO electrode was more sensitive to NO₂ gas than the sensor with the Au electrode: notably, both sensors were based on typical SnO₂ nanowire network. When the Au electrode was replaced by the FTO electrode, the sensitivity improved, as the contact resistance decreased and the surface-to-volume ratio increased. The morphological features of the fabricated gas sensor were characterized in detail via field-emission scanning electron microscopy and X-ray diffraction analysis.

• Journal of Sensor Science and Technology
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• v.31 no.6
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• pp.455-460
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• 2022

Brush-like ZnO hierarchical nanostructures decorated with MgxZn1-xO (x = 0.1, 0.2, 0.3, 0.4, and 0.5) were fabricated and examined for application to a gas sensor. They were synthesized using vapor phase growth (VPG) on indium tin oxide (ITO) substrates. To generate electronic accumulation at ZnO surface, MgZnO nanoparticles were prepared by sol-gel method, and the ratio of Mg and Zn was adjusted to optimize the device for NO₂ gas detection. As the electrons in the accumulation layer generated by the heterojunction reacted faster and more frequently with the gas, the sensitivity and speed improved. When tested as sensing materials for gas sensors at 100 ppm NO₂ at 300℃, these MgZnO decorated ZnO nanostructures exhibited an improvement from 165 to 514 times compared to pristine ZnO. The response and recovery time of the MgZnO decorated ZnO samples were shorter than those of the pristine ZnO. Various analyzing techniques, including field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD) were employed to confirm the growth morphology, atomic composition, and crystalline information of the samples, respectively.

• Journal of Sensor Science and Technology
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• v.23 no.5
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• pp.314-319
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• 2014

Here, we review the various methods for the preparation of vanadium dioxide ($VO_2$) films and nanowires, and their potential applications to the sensors such as gas sensor, strain sensor, and temperature sensor. $VO_2$ is an interesting material on account of its easily accessible and sharp Mott metal-insulator transition (MIT) at ${\sim}68^{\circ}C$ in the bulk. The MIT is also triggered by the electric field, stress, magnetic field etc. This paper involves exceptionally sensitive hydrogen sensors based on the catalytic process between hydrogen molecules and Pd nanoparticles on the $VO_2$ surface, and fast responsive sensors based on the self-heating effects which leads to the phase changes of the $VO_2$. These features will be seen in this paper and can enable strategies for the integration of a $VO_2$ material in advanced and complex functional units such as logic gates, memory, FETs for micro/nano-systems as well as the sensors.

• Journal of Sensor Science and Technology
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• v.23 no.5
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• pp.305-309
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• 2014

Well-ordered $TiO_2$ nanotubes with Au nanoparticles are a desirable configuration to enhance the gas sensing properties such as response and selectivity due to their high surface area to volume ratio and catalytic effect of Au nanoparticles. We have synthesized the well-ordered $TiO_2$ nanotubes directly on a Pt IDEs patterned $SiO_2/Si$ substrate and then decorated Au nanoparticles on inner and outer surface of $TiO_2$ nanotubes using electrodeposition method. The Au-decorated $TiO_2$ nanotubes shows ultrahigh response to $C2_H_5OH$ and the highest increasing ratio to $H_2$ compared with other gases.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1619-1626
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• 2017

Electronic components that are used in high-level radiation environment require a semiconductor device having a radiation-hardened characteristic. In this paper, we proposed a radiation-hardened I-gate n-MOSFET (n-type Metal Oxide Semiconductors Field Effect Transistors) using a layout modification technique only. The proposed I-gate n-MOSFET structure is modified as an I-shaped gate poly in order to mitigate a radiation-induced leakage current in the standard n-MOSFET structure. For verification of its radiation-hardened characteristic, the M&S (Modeling and Simulation) of the 3D (3-Dimension) structure is performed by TCAD (Technology Computer Aided Design) tool. In addition, we carried out an evaluation test using a $Co^{60}$ gamma-ray source of 10kGy(Si)/h. As a result, we have confirmed the radiation-hardened level up to a total ionizing dose of 20kGy(Si).