Sung Pyo Park
Yonsei University
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Featured researches published by Sung Pyo Park.
Scientific Reports | 2016
Young Jun Tak; Byung Du Ahn; Sung Pyo Park; Si Joon Kim; Ae Ran Song; Kwun-Bum Chung; Hyun Jae Kim
Indium–gallium–zinc oxide (IGZO) films, deposited by sputtering at room temperature, still require activation to achieve satisfactory semiconductor characteristics. Thermal treatment is typically carried out at temperatures above 300 °C. Here, we propose activating sputter- processed IGZO films using simultaneous ultraviolet and thermal (SUT) treatments to decrease the required temperature and enhance their electrical characteristics and stability. SUT treatment effectively decreased the amount of carbon residues and the number of defect sites related to oxygen vacancies and increased the number of metal oxide (M–O) bonds through the decomposition-rearrangement of M–O bonds and oxygen radicals. Activation of IGZO TFTs using the SUT treatment reduced the processing temperature to 150 °C and improved various electrical performance metrics including mobility, on-off ratio, and threshold voltage shift (positive bias stress for 10,000 s) from 3.23 to 15.81 cm2/Vs, 3.96 × 107 to 1.03 × 108, and 11.2 to 7.2 V, respectively.
Journal of information display | 2016
Young Jun Tak; Sung Pyo Park; Tae Soo Jung; Heesoo Lee; Won Gi Kim; Jeong Woo Park; Hyun Jae Kim
ABSTRACT Activation using the simultaneous UV-thermal (U-T) treatment of sputter-processed InGaZnO (IGZO) thin-film transistors (TFTs) is suggested. This treatment was performed to lower the activation temperature from 300°C (thermal activation alone) to 150°C as well as to improve the electrical characteristics and stability. Despite the low temperature, the U-T-treated devices showed superior electrical characteristics and stability compared to the devices that were only thermally activated (300°C): the mobility improved from 5.19 ± 1.8 to 16.20 ± 1.5 cm2/Vs, the on-off ratio increased from (5.58 ± 3.21) × 108 to (2.50 ± 2.23) × 109, and the threshold voltage shift (under positive bias stress for 1000 s) decreased from 7.1 to 2.2 V. These improvements are attributed to the following two contributions: (1) generation of reactive oxygen radical at a low temperature and (2) decomposition-rearrangement of the metal oxide (MO) bonds in the IGZO active layer. Contributions (1) and (2) effectively increased the MO bonds and decreased the defect-site-related oxygen vacancies.
Journal of Materials Chemistry C | 2014
Doo Hyun Yoon; Young Jun Tak; Sung Pyo Park; Joohye Jung; Heesoo Lee; Hyun Jae Kim
In our previous work, the pristine sol-NiOx/Si based device did not exhibit reproducible resistive switching due to the presence of native interlayer oxide. To solve this problem, we investigated high-pressure hydrogen gas annealing at a stack of Al/sol-NiOx/Si to engineer the interface and bulk layer simultaneously. Different from the pure nitrogen high-pressure gas annealing which only affects the bulk properties of the system, we found that the high-pressure hydrogen gas can alter both the interfaces and bulk layers. As a result, the native interlayer oxide thickness at the NiOx/Si interface was reduced and the overall density of oxygen vacancies was increased due to the reduction of atomic hydrogen. Consequently, a good condition for less randomized generation of conducting pathways was secured which led to improved stability of high- and low-resistance states, as well as a larger ratio of high and low resistances regardless of a high free energy of formation at the bottom electrode (Si).
Scientific Reports | 2017
Seonghwan Hong; Sung Pyo Park; Yeong Gyu Kim; Byung Ha Kang; Jae Won Na; Hyun Jae Kim
We report low-temperature solution processing of hafnium oxide (HfO2) passivation layers for amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs). At 150 °C, the hafnium chloride (HfCl4) precursor readily hydrolyzed in deionized (DI) water and transformed into an HfO2 film. The fabricated HfO2 passivation layer prevented any interaction between the back surface of an a-IGZO TFT and ambient gas. Moreover, diffused Hf4+ in the back-channel layer of the a-IGZO TFT reduced the oxygen vacancy, which is the origin of the electrical instability in a-IGZO TFTs. Consequently, the a-IGZO TFT with the HfO2 passivation layer exhibited improved stability, showing a decrease in the threshold voltage shift from 4.83 to 1.68 V under a positive bias stress test conducted over 10,000 s.
Nanomaterials | 2017
Yeong Gyu Kim; Young Jun Tak; Sung Pyo Park; Hee Jun Kim; Hyun Jae Kim
Flexible and transparent conducting electrodes are essential for future electronic devices. In this study, we successfully fabricated a highly-interconnected metal-mesh structure (MMS) using a self-formable cracked template. The template—fabricated from colloidal silica—can be easily formed and removed, presenting a simple and cost-effective way to construct a randomly and uniformly networked MMS. The structure of the MMS can be controlled by varying the spin-coating speed during the coating of the template solution or by stacking of metal-mesh layers. Through these techniques, the optical transparency and sheet resistance of the MMS can be designed for a specific purpose. A double-layered Al MMS showed high optical transparency (~80%) in the visible region, low sheet resistance (~20 Ω/sq), and good flexibility under bending test compared with a single-layered MMS, because of its highly-interconnected wire structure. Additionally, we identified the applicability of the MMS in the case of practical devices by applying it to electrodes of thin-film transistors (TFTs). The TFTs with MMS electrodes showed comparable electrical characteristics to those with conventional film-type electrodes. The cracked template can be used for the fabrication of a mesh structure consisting of any material, so it can be used for not only transparent electrodes, but also various applications such as solar cells, sensors, etc.
Journal of Physics D | 2016
Jae Won Na; Yeong Gyu Kim; Tae Soo Jung; Young Jun Tak; Sung Pyo Park; Jeong Woo Park; Si Joon Kim; Hyun Jae Kim
The role of an interface as an electron-trapping layer in double-stacked indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) was investigated and interface location-controlled (ILC) IGZO TFTs were introduced. In the ILC TFTs, the thickness of the top and bottom IGZO layers is controlled to change the location of the interface layer. The system exhibited improved electrical characteristics as the location of the interface layer moved further from the gate insulator: field-effect mobility increased from 0.36 to 2.17 cm2 V−1 s−1, and the on-current increased from 2.43 × 10−5 to 1.33 × 10−4 A. The enhanced electrical characteristics are attributed to the absence of an electron-trapping interface layer in the effective channel layer where electrons are accumulated under positive gate bias voltage.
Advanced Materials | 2018
Sung Pyo Park; Young Jun Tak; Hee Jun Kim; Jin Hyeok Lee; Hyukjoon Yoo; Hyun Jae Kim
Resistive random access memory (RRAM) devices are fabricated through a simple solution process using glucose, which is a natural biomaterial for the switching layer of RRAM. The fabricated glucose-based RRAM device shows nonvolatile bipolar resistive switching behavior, with a switching window of 103 . In addition, the endurance and data retention capability of glucose-based RRAM exhibit stable characteristics up to 100 consecutive cycles and 104 s under constant voltage stress at 0.3 V. The interface between the top electrode and the glucose film is carefully investigated to demonstrate the bipolar switching mechanism of the glucose-based RRAM device. The glucose based-RRAM is also evaluated on a polyimide film to verify the possibility of a flexible platform. Additionally, a cross-bar array structure with a magnesium electrode is prepared on various substrates to assess the degradability and biocompatibility for the implantable bioelectronic devices, which are harmless and nontoxic to the human body. It is expected that this research can provide meaningful insights for developing the future bioelectronic devices.
ACS Applied Materials & Interfaces | 2018
Tae Soo Jung; Heesoo Lee; Sung Pyo Park; Hee Jun Kim; Jin Hyeok Lee; Dongwoo Kim; Hyun Jae Kim
We explored the effects of hypochlorous acid (HClO) oxidation on p-type oxide semiconductors. HClO generates oxygen radicals (O·) (strong reactive oxygen species) that affect the chemical state of p-type copper oxide (CuO x) thin films by reacting with CuO x. On robust oxidation by HClO, the numbers of Cu-O bonds increased and the numbers of copper vacancies serving as hole carriers decreased. In the modified CuO x thin-film transistors (TFTs), switching was evident. The subthreshold swing was 0.70 V/dec, the on-/off-current ratio was 4.86 × 104, and the field effect mobility was 2.83 × 10-3 cm2/V·s. Pristine CuO x TFTs did not exhibit switching.
ACS Applied Materials & Interfaces | 2018
Jun Ki Kang; Sung Pyo Park; Jae Won Na; Jin Hyeok Lee; Dongwoo Kim; Hyun Jae Kim
Eco-friendly solution-processed oxide thin-film transistors (TFTs) were fabricated through photocatalytic reaction of titanium dioxide (PRT). The titanium dioxide (TiO2) surface reacts with H2O under ultraviolet (UV) light irradiation and generates hydroxyl radicals (OH•). These hydroxyl radicals accelerate the decomposition of large organic compounds such as 2-methoxyethanol (2ME; one of the representative solvents for solution-processed metal oxides), creating smaller organic molecular structures compared with 2ME. The decomposed small organic materials have low molar masses and low boiling points, which help improving electrical properties via diminishing defect sites in oxide channel layers and fabricating low-temperature solution-processed oxide TFTs. As a result, the field-effect mobility improved from 4.29 to 10.24 cm2/V·s for IGZO TFTs and from 2.78 to 7.82 cm2/V·s for IZO TFTs, and the Vth shift caused by positive bias stress and negative bias illumination stress over 1000 s under 5700 lux decreased from 6.2 to 2.9 V and from 15.3 to 2.8 V, respectively. In theory, TiO2 has a permanent photocatalytic reaction; as such, hydroxyl radicals are generated continuously under UV irradiation, improving the electrical characteristics of solution-processed IZO TFTs even after four iterations of TiO2 recycling in this study. Thus, the PRT method provides an eco-friendly approach for high-performance solution-processed oxide TFTs.
Scientific Reports | 2017
Hong Jae Kim; Young Jun Tak; Sung Pyo Park; Jae Won Na; Yeong-gyu Kim; Seonghwan Hong; Pyeong Hun Kim; Geon Tae Kim; Byeong Koo Kim; Hyun Jae Kim
In this study, we propose a self-activated radical doping (SRD) method on the catalyzed surface of amorphous oxide film that can improve both the electrical characteristics and the stability of amorphous oxide films through oxidizing oxygen vacancy using hydroxyl radical which is a strong oxidizer. This SRD method, which uses UV irradiation and thermal hydrogen peroxide solution treatment, effectively decreased the amount of oxygen vacancies and facilitated self-passivation and doping effect by radical reaction with photo-activated oxygen defects. As a result, the SRD-treated amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) showed superior electrical performances compared with non-treated a-IGZO TFTs. The mobility increased from 9.1 to 17.5 cm2/Vs, on-off ratio increased from 8.9 × 107 to 7.96 × 109, and the threshold voltage shift of negative bias-illumination stress for 3600 secs under 5700 lux of white LED and negative bias-temperature stress at 50 °C decreased from 9.6 V to 4.6 V and from 2.4 V to 0.4 V, respectively.