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Sungwoo Jun,Chunhyung Jo,Hagyoul Bae,Hyunjun Choi,Dae Hwan Kim,Dong Myong Kim IEEE 2013 IEEE electron device letters Vol.34 No.5
<P>We report a unified subthreshold coupling factor technique for a simultaneous extraction of the surface potential (ψ<SUB>S</SUB>) and the subgap density-of-states [DOS: g(E)] over the bandgap in amorphous semiconductor thin film transistors (TFTs). It is fully based on the experimental gate bias-dependent coupling factor [m(V<SUB>GS</SUB>)] under subthreshold bias. Through the proposed technique only with current-voltage data under subthreshold operation, a unified extraction of the DOS with a consistent mapping of the gate bias (V<SUB>GS</SUB>) to the subgap energy is obtained. Applying to amorphous InGaZnO TFTs, g(E) is obtained to be a superposition of two exponential functions with N<SUB>TA</SUB> = 1.62 × 10<SUP>17</SUP> eV<SUP>-1</SUP> cm<SUP>-3</SUP> and kT<SUB>TA</SUB> = 0.026 eV for the tail states while N<SUB>DA</SUB> = 6.5 × 10<SUP>16</SUP> eV<SUP>-1</SUP> cm<SUP>-3</SUP> and kT<SUB>DA</SUB> = 0.22 eV for the deep states.</P>
Sungju Choi,Hyeongjung Kim,Chunhyung Jo,Hyun-Suk Kim,Sung-Jin Choi,Dong Myong Kim,Park, Jozeph,Dae Hwan Kim IEEE 2015 IEEE electron device letters Vol.36 No.7
<P>Thin-film transistors using In-Ga-Zn-O (IGZO) semiconductors were evaluated under current stress by applying positive voltages to the gate and drain electrodes. Initially, the transfer characteristics exhibit identical threshold voltages (V-T) when the source and drain electrodes are interchanged during measurement (forward and reverse V-DS sweep). However, as stress time increases, larger shifts in V-T are observed under forward V-DS sweep than under reverse V-DS sweep conditions. Subgap states analyses based on the photoresponse of capacitance-voltage (C-V) curves suggest that local annihilation of donor-like traps occurs near the drain electrode. Hump-like features are clearly observed in the C-V curves collected between the drain and gate electrodes, while they do not appear in the C-V data obtained between the source and the gate. Based on the above, a local charge trapping model is introduced in order to interpret the device degradation. In this model, the major carrier electrons are trapped more abundantly near the source electrode due to the presence of a Schottky junction between IGZO and the source/drain electrodes.</P>
Sungju Choi,Hyeongjung Kim,Chunhyung Jo,Hyun-Suk Kim,Sung-Jin Choi,Dong Myong Kim,Park, Jozeph,Dae Hwan Kim IEEE 2015 IEEE electron device letters Vol.36 No.12
<P>Thin-film transistors using In-Ga-Zn-O (IGZO) semiconductors were evaluated under positive bias stress with different gate and drain voltages (VGS and VDS, respectively). The transfer characteristics with respect to stress time were examined, focusing on the threshold voltage (V-T) values obtained when the source and drain electrodes are interchanged during readout (forward and reverse VDS sweep). The V-T values shift toward either negative or positive values during stress, while transitions from negative to positive shifts are also observed. The negative V-T shift under positive bias stress is interpreted to occur by the generation of donor-like states related to ionized oxygen vacancies. On the other hand, positive V-T shifts result from the trapping of electrons near the IGZO/gate insulator interface. The transitions from negative to positive V-T shift are believed to result from the local electron trapping mechanism that gradually takes over donor-like state creation. From the experimental results and TCAD device simulation, it is suggested that a competition occurs between donor-like state creation and electron trapping. The relative magnitudes of the VGS and VDS fields determine which mechanism dominates, providing an analytical insight for the design of stable devices for driving transistors in AMOLED backplanes.</P>
Hagyoul Bae,Hyunjun Choi,Sungwoo Jun,Chunhyung Jo,Yun Hyeok Kim,Jun Seok Hwang,Jaeyeop Ahn,Oh, Saeroonter,Jong-Uk Bae,Sung-Jin Choi,Dae Hwan Kim,Dong Myong Kim IEEE 2013 IEEE electron device letters Vol.34 No.12
<P>We report a novel technique for simultaneous extraction of subgap donor- and acceptor-like density of states [g<SUB>D</SUB>(E) and g<SUB>A</SUB>(E)] over the subgap energy range (E<SUB>V</SUB> <;E<;E<SUB>C</SUB>) using a single-scan monochromatic photonic capacitance-voltage technique in n-channel amorphous indium-gallium-zinc-oxide thin-film transistors. In the proposed technique, we applied two different equivalent circuit models for the photoresponsive carriers excited from g<SUB>D</SUB>(E) and g<SUB>A</SUB>(E) under depletion (V<SUB>GS</SUB> <; V<SUB>FB</SUB>) and accumulation (V<SUB>GS</SUB> <; V<SUB>FB</SUB>) bias by employing a sub-bandgap optical source that includes a relation between photon energy (E<SUB>ph</SUB>) and bandgap energy (E<SUB>g</SUB>) as h<SUB>v</SUB> = E<SUB>ph</SUB> <; E<SUB>g</SUB>.</P>
A Study on the Performance Improvement and Analysis Method of the LILW Disposal Container Cover
Hyungoo Kang,Hoseog Dho,Hyeonwoo Oh,Jungwoo Jo,Yeseul Cho,Chunhyung Cho 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1
Radioactive waste disposal facility in Korea, radioactive waste packaged in 200 L drums is placed in a concrete disposal container and disposed of at an underground silo type (cave) disposal facility. At this time, the disposal container cover is seated on the top of the disposal container, and if the disposal container and the cover are not completely combined, the container cover is raised up from the top of the disposal container, so safety problems may occur when stacking the disposal container. Therefore, various methods exist to secure a margin for the pure height inside the disposal container. The disposal container cover only covers the upper surface of the container to shield radiation, and structural performance is not required. Therefore, the method of processing the cover, such as a method of making the cover of the disposal container thin, is the easiest method to apply. In this study, a method to reduce the thickness of the cover of a concrete disposal container was devised, and structural performance under usability conditions such as lifting and seating was analyzed. In addition, the disposal container cover has a reinforced concrete form in which dissimilar materials (concrete and steel) are combined, an integrated analysis was performed to secure the reliability of the analysis results for this, and the analysis results were described. It was found that the proposed disposal container cover structure can improve usability by reducing the stress concentration phenomenon.
Inseok Hur,Hagyoul Bae,Woojoon Kim,Jaehyeong Kim,Hyun Kwang Jeong,Chunhyung Jo,Sungwoo Jun,Jaewook Lee,Yun Hyeok Kim,Dae Hwan Kim,Dong Myong Kim IEEE 2013 IEEE electron device letters Vol.34 No.2
<P>Due to voltage drops across parasitic resistances in semiconductor devices, extracted performance parameters can be strongly dependent on the geometrical structure. In this letter, we report a characterization technique for the intrinsic field-effect mobility μ<SUB>FEo</SUB> in amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) by de-embedding the parasitic source and drain resistances <I>R</I><SUB>S</SUB> and <I>R</I><SUB>D</SUB>, respectively. We obtained the channel-length (<I>L</I>) -independent intrinsic field-effect mobility μ<SUB>FEo</SUB> from TFTs with various channel lengths on the same wafer. We expect that this characterization technique for <I>L</I>-independent intrinsic field-effect mobility is useful for accurate characterization, consistent modeling, and robust simulation of a-IGZO TFT circuits.</P>