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Yongsik Kim,Minkyung Bae,Woojoon Kim,Dongsik Kong,Hyun Kwang Jung,Hyungtak Kim,Sunwoong Kim,Dong Myong Kim,Dae Hwan Kim IEEE 2012 IEEE transactions on electron devices Vol.59 No.10
<P>A combination of the multifrequency <I>C</I>- <I>V</I> and the generation-recombination current spectroscopy is proposed for a complete extraction of density of states (DOS) in amorphous InGaZnO thin-film transistors (a-IGZO TFTs) over the full subband-gap energy range (<I>EV</I> ≤ <I>E</I> ≤ <I>EC</I>) including the interface trap density between the gate oxide and the a-IGZO active layer. In particular, our result on the separate extraction of acceptor- and donor-like DOS is noticeable for a systematic design of amorphous oxide semiconductor TFTs because the former determines their dc characteristics and the latter does their threshold voltage (<I>VT</I>) instability under practical operation conditions. The proposed approach can be used to optimize the fabrication process of thin-film materials with high mobility and stability for mass-production-level amorphous oxide semiconductor TFTs.</P>
Minkyung Bae,Yongsik Kim,Dongsik Kong,Hyun Kwang Jeong,Woojoon Kim,Jaehyeong Kim,Inseok Hur,Dong Myong Kim,Dae Hwan Kim IEEE 2011 IEEE electron device letters Vol.32 No.11
<P>Analytical drain current and gate capacitance models for amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) over sub- and above-threshold regions are proposed by adopting an effective carrier density for the dominant carrier density. The effective carrier density fully considers the free carriers in the conduction band, the localized subgap deep states, and tail states over the bandgap for analytical <I>I</I>-<I>V</I> and <I>C</I>-<I>V</I> characteristics. The proposed analytical models are verified by comparing the measured <I>I</I>-<I>V</I> and <I>C</I>-<I>V</I> characteristics. The proposed models make a time-efficient simulation of a-IGZO TFT-based circuits possible due to their analytical form.</P>
Dae Hwan Kim,Yong Woo Jeon,Sungchul Kim,Yongsik Kim,Yun Seop Yu,Dong Myong Kim,Hyuck-In Kwon IEEE 2012 IEEE electron device letters Vol.33 No.1
<P>In this letter, we show that the physics-based equation that was derived for amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) in our previous work can be successfully incorporated into the SPICE model via Verilog-A. The proposed model and extracted SPICE parameters successfully reproduce the measured current-voltage characteristics of amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs and the load line diagram of a-IGZO TFT inverters. The main advantage of our model is that each parameter has its physical meaning and most of them can be related with the fabrication conditions of AOS TFTs. To show the advantage of the proposed models and extracted SPICE parameters more clearly, we investigate the effect of ionized donor concentration (<I>N</I><SUB>D</SUB><SUP>+</SUP>) on the inverter circuit operation and determine the optimum value of <I>N</I><SUB>D</SUB><SUP>+</SUP> and device dimensions considering the tradeoff between the power consumption and the output swing in a-IGZO inverters. The proposed physics-based SPICE model via Verilog-A is expected to play a significant role in the process optimization and circuit design with AOS TFTs.</P>
Physics-Based SPICE Model of a-InGaZnO Thin-Film Transistor Using Verilog-A
Yong Woo Jeon,Inseok Hur,Yongsik Kim,Minkyung Bae,Hyun Kwang Jung,Dongsik Kong,Woojoon Kim,Jaehyeong Kim,Jaeman Jang,Dong Myong Kim,Dae Hwan Kim 대한전자공학회 2011 Journal of semiconductor technology and science Vol.11 No.3
In this work, we report the physics-based SPICE model of amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) and demonstrate the SPICE simulation of amorphous InGaZnO (aIGZO) TFT inverter by using Verilog-A. As key physical parameter, subgap density-of-states (DOS) is extracted and used for calculating the electric potential, carrier density, and mobility along the depth direction of active thin-film. It is confirmed that the proposed DOS-based SPICE model can successfully reproduce the voltage transfer characteristic of a-IGZO inverter as well as the measured I-V characteristics of a-IGZO TFTs within the average error of 6% at V/)/)=20 V.
Kang, Donghyun,Shin, Jungkwon,Cho, Yongsik,Kim, Hyeon-Seop,Gu, Young-Ran,Kim, Haedong,You, Kwon Tae,Chang, Moon Jong,Chang, Chong Bum,Kang, Seung-Baik,Kim, Jong-Seo,Kim, V. Narry,Kim, Jin-Hong American Association for the Advancement of Scienc 2019 Science translational medicine Vol.11 No.486
<P>A progressive loss of cartilage matrix leads to the development of osteoarthritis (OA). Matrix homeostasis is disturbed in OA cartilage as the result of reduced production of cartilage-specific matrix and increased secretion of catabolic mediators by chondrocytes. Chondrocyte senescence is a crucial cellular event contributing to such imbalance in matrix metabolism during OA development. Here, we identify miR-204 as a markedly up-regulated microRNA in OA cartilage. miR-204 is induced by transcription factors GATA4 and NF-κB in response to senescence signals. Up-regulated miR-204 simultaneously targets multiple components of the sulfated proteoglycan (PG) biosynthesis pathway, effectively shutting down PG anabolism. Ectopic expression of miR-204 in joints triggers spontaneous cartilage loss and OA development, whereas miR-204 inhibition ameliorates experimental OA, with concomitant recovery of PG synthesis and suppression of inflammatory senescence-associated secretory phenotype (SASP) factors in cartilage. Collectively, we unravel a stress-activated senescence pathway that underlies disrupted matrix homeostasis in OA cartilage.</P>
A FRACTIONAL STEP MESHFREE POINT COLLOCATION METHOD FOR THE INCOMPRESSIBLE NAVIER-STOKES EQUATIONS
Yongsik Kim 한국산업응용수학회 2007 한국산업응용수학회 학술대회 논문집 Vol.2 No.1
A fractional-step point collocation method by meshfree approximation is presented for solving non-stationary incompressible Navier-Stokes equations. A single node set and auxiliary local points to each node point are used in the present study. In the momentum equations, the diffusion terms are discretized by a meshfree approximation FMLSRK(Fast Moving Least Square reproducing Kernel Approximation) on a given node set, while the inertia terms are discretized by using local points. In the pressure correction step, the divergence of intermediate velocity is calculated using local points which results local mass conservation. The Crank-Nicolson method is employed to the viscous and the convective terms for the second order accuracy in time stepping. The present numerical scheme is applied to several numerical experiments to prove its accuracy and efficiency.