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Kihwan Kim,Saeroonter Oh 대한전자공학회 2019 Journal of semiconductor technology and science Vol.19 No.1
We investigate the effect of strain on the device characteristics of gate-all-around (GAA) NMOS with various configurations, including crystal orientation, cross-sectional shape, and strain conditions, via device simulation. After verifying the strain dependence of mobility of various surface orientations with the literature, we apply the strain transport model to GAA MOSFETs which have different sidewall orientations depending on the channel direction. Drive current enhancement is the largest for the (001)/<110> case under large uniaxial tensile strain values exceeding 1%. In addition, we found that cross-sectional width of the nanosheet is a key parameter in maximizing the drive current for a given footprint. Optimization of device and strain configuration of single-stacked GAA devices is necessary to meet device performance specifications for sub-7nm technology.
Effect of mechanical stress on the stability of flexible InGaZnO thin-film transistors
정현준,한기림,옥경철,이현모,Saeroonter Oh,박진성 한국정보디스플레이학회 2017 Journal of information display Vol.18 No.2
Demonstrated herein is the effect of mechanical stress on the device performance and stability of amorphous indium–gallium–zinc oxide thin-film transistors (TFTs) on a flexible polyimide substrate. Flexible TFTs were placed on jigs with various bending radii to apply different degrees of mechanical strain on them. When the tensile strain on the TFTs was increased from 0.19% to 0.93%, the threshold voltage shifted after a 10,000 s increase in bias–temperature–stress (BTS), under vacuum conditions. The BTS instability was further exacerbated when the device was exposed to the air ambient at a 0.93% strain. The device reliability deteriorated due to the increase in the subgap density of states as well as the enhanced ambient effects via the strain-induced gas permeation paths.
Ki-Lim Han,Hyeon-Su Cho,옥경철,Saeroonter Oh,박진성 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.6
Previous studies have reported on the mechanical robustness and chemical stability of fl exible amorphous indium gallium zincoxide (a-IGZO) thin-fi lm transistors (TFTs) on plastic substrates both in fl at and curved states. In this study, we investigatehow the polyimide (PI) substrate aff ects hydrogen concentration in the a-IGZO layer, which subsequently infl uences thedevice performance and stability under bias-temperature-stress. Hydrogen increases the carrier concentration in the activelayer, but it also electrically deactivates intrinsic defects depending on its concentration. The infl uence of hydrogen variesbetween the TFTs fabricated on a glass substrate to those on a PI substrate. Hydrogen concentration is 5% lower in deviceson a PI substrate after annealing, which increases the hysteresis characteristics from 0.22 to 0.55 V and also the thresholdvoltage shift under positive bias temperature stress by 2 × compared to the devices on a glass substrate. Hence, the analysisand control of hydrogen fl ux is crucial to maintaining good device performance and stability of a-IGZO TFTs.
Sheng, Jiazhen,Lee, Hwan-Jae,Oh, Saeroonter,Park, Jin-Seong American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.49
<P>Amorphous indium zinc oxide (IZO) thin films were deposited at different temperatures, by atomic layer deposition (ALD) using [1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]indium (INCA-1) as the indium precursor, diethlzinc (DEZ) as the zinc precursor, and hydrogen peroxide (H2O2) as the reactant. The ALD process of IZO deposition was carried by repeated supercycles, including one cycle of indium oxide (In2O3) and one cycle of zinc oxide (ZnO). The IZO growth rate deviates from the sum of the respective In2O3 and ZnO growth rates at ALD growth temperatures of 150, 175, and 200 degrees C. We propose growth temperature-dependent surface reactions during the In2O3 cycle that correspond with the growth-rate results. Thin-film transistors (TFTs) were fabricated with the ALD-grown IZO thin films as the active layer. The amorphous IZO TFTs exhibited high mobility of 42.1 cm(2) V-1 s(-1) and good positive bias temperature stress stability. Finally, flexible IZO TFT was successfully fabricated on a polyimide substrate without performance degradation, showing the great potential of ALD-grown TFTs for flexible display applications.</P>
Properties of hafnium-aluminum-zinc-oxide thin films for the application of oxide-transistors
Lee, Sang-Hyuk,Jun, Hyun-Sik,Park, Ju-Hee,Kim, Won,Oh, Saeroonter,Park, Jin-Seok Elsevier 2016 THIN SOLID FILMS - Vol.620 No.-
<P><B>Abstract</B></P> <P>Hafnium-aluminum zinc oxide (HAZO) films as an active layer of oxide-transistors with different hafnium (Hf) contents were deposited via co-sputtering of separate targets. The effects of the sputtering power during co-sputtering on the structural, optical, electrical, and chemical properties of the HAZO films were examined. As the sputtering power increased, the structure of the HAZO films changed from polycrystalline to amorphous, and the HfO bonds in the HAZO films increased, but the ZnO bonds decreased. Also, a bottom-gate-type thin-film transistor (TFT) using the HAZO film as its channel layer was fabricated and characterized. The TFTs using HAZO layer at room temperature as channel layer exhibited the device characteristics, such as a field effect mobility of 0.45cm<SUP>2</SUP>/V·s, a threshold voltage of 17.18V, a subthreshold swing of 0.85V/decade, an on/off current ratio of 3.68×10<SUP>7</SUP>, and a visible transmittance of 82.7%. It was discovered that the changes of the electrical characteristics of the HAZO TFTs were closely related to the changes of the ZnO/HfO bonding ratio.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hafnium-aluminum-zinc-oxide (HAZO) films were deposited via co-sputtering. </LI> <LI> Hf content was controlled by varying the sputtering powers of Hf or HfO<SUB>2</SUB> targets. </LI> <LI> Chemical, structural, and optical properties of HAZO films were analyzed. </LI> <LI> The properties of HAZO films strongly depended on the Hf or HfO<SUB>2</SUB> sputtering power. </LI> <LI> Effects of Hf contents on the characteristics of HAZO-TFTs have been analyzed. </LI> </UL> </P>
Jeong, Hyun-Jun,Han, Ki-Lim,Jeong, Kyung-Sub,Oh, Saeroonter,Park, Jin-Seong IEEE 2018 IEEE electron device letters Vol.39 No.7
<P>We investigated the effects of repetitive mechanical bending stress on top-gate amorphous InGaZnO thin-film transistors (TFTs). Electrical parameters were gradually degraded under repetitive tensile bending stress. After 50 000 bending cycles, some TFTs showed gate leakage current increase during positive gate bias thermal stress. After 60 000 bending cycles, conduction path was physically severed to an open state. However, when an additional organic layer was deposited on the TFTs as a stress-reduction layer, device characteristics were unaffected by repetitive mechanical stress up to 100 000 cycles. Finite element structural simulations show the vulnerable stress-concentrated regions that cause leakage current, contact resistance increase, and interface traps. Electrical deterioration under repetitive bending is significantly mitigated by applying a stress-reduction layer.</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>
Hagyoul Bae,Hyojoon Seo,Sungwoo Jun,Hyunjun Choi,Jaeyeop Ahn,Junseok Hwang,Jungmin Lee,Oh, Saeroonter,Jong-Uk Bae,Sung-Jin Choi,Dae Hwan Kim,Dong Myong Kim IEEE 2014 IEEE transactions on electron devices Vol.61 No.10
<P>A sub-bandgap optoelectronic differential ideality factor technique is proposed for extraction of the intrinsic density-of-states (DOS) over the bandgap in amorphous semiconductor thin-film transistors (TFTs). In the proposed technique, the gate bias-dependent differential change in the difference of ideality factors (dAη(V<SUB>GS</SUB>)/dV<SUB>GS</SUB>) between dark and sub-bandgap photonic excitation condition is employed. With the sub-bandgap photons (hν <; E<SUB>g</SUB>), the photonic excitation of electrons is confined only from the localized DOS over the bandgap. We applied the proposed technique to a-InGaZnO TFTs with W/L = 50/25 μm/μm and extracted the energy distribution of the intrinsic DOS for the localized states over the bandgap.</P>
Kim, Dae Hwan,Choi, Sungju,Jang, Juntae,Kang, Hara,Kim, Dong Myong,Choi, Sung-Jin,Kim, Yong-Sung,Oh, Saeroonter,Baeck, Ju Heyuck,Bae, Jong Uk,Park, Kwon-Shik,Yoon, Soo Young,Kang, In Byeong SOCIETY FOR INFORMATION DISPLAY 2017 Journal of the Society for Information Display Vol. No.
<P>Proposed decomposition is validated by reproducing the PBTS time-evolution of I-V characteristics through the technology computer-aided design simulation into which the extracted DOS and charge trapping are incorporated. It is also found that the quantitative decomposition of PBTS-induce Delta V-T accompanied with the multiple stretched-exponential models enables an effective assessment of the complex degradation nature of multiple PBTS physical processes occurring simultaneously. Our results can be easily applied universally to any device with any stress conditions, along with guidelines for process optimization efforts toward ultimate PBTS stability.</P>