Effects of defect creation on bidirectional behavior with hump characteristics of InGaZnO TFTs under bias and thermal stress

We investigated the hump characteristics of amorphous indium-gallium -zinc oxide thin-film transistors. The device showed a field effect mobility of 24.3cm2V-1 s-1, a threshold voltage (Vth) of 4.8V, and a subthreshold swing of 120mV/dec. Under positive gate bias stress, Vth showed bidirectional shift with a hump. Vth was positively and negatively shifted in the above-threshold and subthreshold regions, respectively. At high temperatures, Vth was more positively shifted without bidirectional shift. Under simultaneous drain bias stress (VDS,stress), the hump was maintained. However, the bidirectional shift was not observed with an increasing VDS,stress. The hump and positive shift are related to the defect creation of the shallow donor-like and deep-level acceptor-like states, respectively. We performed a two-dimensional device simulation to further investigate this phenomenon. By varying the peak values of the Gaussian shallow donor-like and deep acceptor-like states, we qualitatively confirmed the relationship between the two states and transfer curve changes. © 2015 The Japan Society of Applied Physics.1

Effect of Back-Channel Surface on Reliability of Solution-Processed In_0.51Ga_0.15Zn_0.34O Thin-Film Transistors with Thin Active Layer

We have investigated the degradation mechanism of solution-processed indium–gallium–zinc-oxide (IGZO) thin-film transistors. The threshold voltage shift (ΔVth) followed a linear function under negative gate bias stress (NBS), while it showed a stretched-exponential behavior under positive gate bias stress. The slope of ΔVth for stress time was rarely changed with variations below 0.3 mV/s. The thickness of the fabricated IGZO layer (In0.51Ga0.15Zn0.34O) was approximately 10 nm. The Debye length (LD) was larger than IGZO thickness (tIGZO) due to the fully depleted active layer under NBS. Therefore, the degradation phenomenon under NBS was related to the adsorption at back-channel surface. The back-channel surface could be affected by the gate bias under NBS, and the molecules adsorbed at the IGZO layer were positively charged and induced extra electrons by NBS. We verified that the number of positively charged adsorbates had a proportional relationship with the ΔVth based on the two-dimensional technology computer-aided design (TCAD) simulation. Furthermore, we investigated the degradation phenomenon with the ΔVth equation regarding the adsorbates, and the result confirmed that the adsorption process could cause the linear ΔVth. We experimentally confirmed the effect of back-channel surface by comparing the ΔVth between different atmospheric conditions and LD. Consequently, the reaction at the back-channel surface should be considered to develop the metal-oxide semiconductor devices

Accurate Defect Density-of-State Extraction Based on Back-Channel Surface Potential Measurement for Solution-Processed Metal-Oxide Thin-Film Transistors

We report more accurate extraction method of the defect density of states for solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs). Since the solution-processed IGZO TFTs have a very thin (similar to 8 nm) active semiconductor layer, their back-channel surface potential should be considered in the field-effect method. If the back-channel surface potential is ignored, deviation between theoretically derived and experimentally measured activation energy data becomes more significant as the thickness of the semiconductor layer decreases in comparison with its Debye length. Dependence of the back-channel surface potential on the applied gate voltages was verified by scanning Kelvin probe microscopy and found to be proportional to the gate voltages. The modified field-effect method provided a more accurate model of the activation energy over the subthreshold region and correspondingly more accurate defect density of states of the IGZO TFTs.OAIID:RECH_ACHV_DSTSH_NO:T201718184RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A077977CITE_RATE:2.62FILENAME:발표논문_Accurate Defect Density-of-State Extraction Based on Back-Channel Surface Potential Measurement for Solution-Processed Metal-Oxide Thin-Film Transistors.pdfDEPT_NM:전기·정보공학부EMAIL:[email protected]_YN:YFILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/426941c1-132e-4948-9604-72afdf8900ea/linkN