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Dongsik Kong,Hyun Kwang Jung,Yongsik Kim,Minkyung Bae,Jaeman Jang,Jaehyeong Kim,Woojoon Kim,Inseok Hur,김동명,김대환 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.21
The effect of the active layer thickness (T_(IGZO) ) on the negative bias illumanation stress (NBIS)-induced threshold voltage shift (VT ) in amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) is investigated and explained by using a subgap density-of-states model. The NBIS-induced VT in a-IGZO TFT with a thinner T_(IGZO) is negatively larger than that in a-IGZO TFTs with a thicker T_(IGZO) . The T_(IGZO) -dependent VT is found to be caused by either hole trapping into the gate insulator near the interface or oxygen vacancy (Vo) ionization, which is activated more by a larger surface electric field EIGZO as T_(IGZO) becomes thinner.
Dongsik Kong,Hyun-Kwang Jung,Yongsik Kim,Minkyung Bae,Yong Woo Jeon,Sungchul Kim,Dong Myong Kim,Dae Hwan Kim IEEE 2011 IEEE electron device letters Vol.32 No.10
<P>The effect of the active layer thickness (<I>T</I><SUB>IGZO</SUB>) on the negative bias stress (NBS)-induced threshold voltage shift (Δ<I>VT</I>) in amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) is investigated and explained by using a subgap density-of-states (DOS) model. The NBS-induced negative Δ<I>VT</I> in a-IGZO TFT with a thinner <I>T</I><SUB>IGZO</SUB> is larger than that with a thicker <I>T</I><SUB>IGZO</SUB>. Based on the simulation result with the subgap DOS model, it is concluded that the <I>T</I><SUB>IGZO</SUB>-dependent Δ<I>VT</I> is originated from the accelerated creation of shallow donor states due to a higher surface electric field in a-IGZO TFTs with a thinner <I>T</I><SUB>IGZO</SUB>.</P>
김용식,Minkyung Bae,Dongsik Kong,Hyun Kwang Jung,Jaehyeong Kim,Woojoon Kim,Inseok Hur,김동명,김대환 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.21
The physical origins of the negative bias illumination stress (NBIS)-induced threshold voltage shift (VT ) in amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) under ambient light from a backlight unit are quantitatively and systematically investigated. Furthermore, a methodology for extracting the instability parameters is proposed and demonstrated. For the quantitative analysis, the subgap density-of-states (DOS)-based DC I-V model is intensively used. The NBIS time-evolution of the measured IDS-VGS characteristics is reproduced very well via the proposed methodology and instability parameters. Consequently, photo-excited electron detrapping, followed by ionization of oxygen vacancies (VO^(+2)) and field-enhanced VO^(+2) diffusion, followed by hole trapping into the gate insulator, are found to be the dominant mechanisms in NBIS-induced instability of a-IGZO TFTs.
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>
Jaeman Jang,Jae Chul Park,Dongsik Kong,Kim, D. M.,Jang-Sik Lee,Byeong-Hyeok Sohn,Il Hwan Cho,Dae Hwan Kim IEEE 2011 IEEE transactions on electron devices Vol.58 No.11
<P>The amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT)-based nonvolatile transparent Flash memory devices were fabricated with gold (Au) nanocrystal storage layer. The performance and the reliability of transparent memory devices have been characterized by experiment and technology computer-aided design simulation. This memory device shows a large-enough memory window ΔV = 4.7 V at the program/erase (P/E) voltage <I>V</I><SUB>PGM</SUB>/<I>V</I><SUB>ERS</SUB> = 35/-35 V for the P/E time <I>T</I><SUB>PGM</SUB>/ <I>T</I><SUB>ERS</SUB> = 3/25 s. The memory window was kept almost the same after 1050 P/E cycles; however, the center voltage of the memory window (<I>VC</I>) was shifted in a negative direction. The cycling effect was explained by the change in the density of states (DOS) and the acceptor-like interface-trap density <I>D</I><SUB>itA</SUB>(<I>E</I>) in the a-IGZO channel layer with increasing P/E cycles. The main mechanism for the change in <I>VC</I> was found to be the accelerated injection of holes into the gate insulator due to the energy band bending during the erase operation.</P>
Extraction of the Channel Mobility in InGaZnO TFTs Using Multifrequency Capacitance–Voltage Method
In-Tak Cho,Ick-Joon Park,Dongsik Kong,Dae Hwan Kim,Jong-Ho Lee,Sang-Hun Song,Hyuck-In Kwon IEEE 2012 IEEE electron device letters Vol.33 No.6
<P>In this letter, we propose a mobility-extraction method using the frequency-independent capacitances extracted from the multifrequency capacitance-voltage method in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs). This method does not use the long-channel metal-oxide-semiconductor field-effect transistor (MOSFET) current-voltage ( I-V) model and can include the effect of subgap states on the calculation of the mobility. Considering that the I-V characteristics of the disordered semiconductor transistor do not exactly follow those of the long-channel MOSFET model and the subgap states significantly affect the electrical behavior of the disordered semiconductor transistors, the proposed method is expected to be useful in the extraction of the exact values of the mobilities in disordered semiconductor transistors including a-IGZO TFTs.</P>
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>