• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.352.1-352.1
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• 2014

Indium Tin Oxide (ITO) films are the most extensively studied and commonly used as ones of TCO films. The ITO films having a high electric conductivity and high transparency are easily fabricated on glass substrate at a substrate temperature over $250^{\circ}C$. However, glass substrates are somewhat heavy and brittle, whereas plastic substrates are lightweight, unbreakable, and so on. For these reasons, it has been recently suggested to use plastic substrates for flexible display application instead of glass. Many reaearchers have tried to produce high quality thin films at rood temperatures by using several methods. Therefore, amorphous ITO films excluding thermal process exhibit a decrease in electrical conductivity and optical transparency with time and a very poor chemical stability. However the amorphous Indium Gallium Zinc Oxide (IGZO) offers several advantages. For typical instance, unlike either crystalline or amorphous ITO, same and higher than a-IGZO resistivity is found when no reactive oxygen is added to the sputter chamber, this greatly simplifies the deposition. We reported on the characteristics of a-IGZO thin films were fabricated by RF-magnetron sputtering method on the PEN substrate at room temperature using 3inch sputtering targets different rate of Zn. The homogeneous and stable targets were prepared by calcine and sintering process. Furthermore, two types of IGZO TFT design, a- IGZO source/drain material in TFT and the other a- ITO source/drain material, have been fabricated for comparison with each other. The experimental results reveal that the a- IGZO source/drain electrode in IGZO TFT is shown to be superior TFT performances, compared with a- ITO source/drain electrode in IGZO TFT.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.289.2-289.2
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• 2016

In-Ga-Zn-O(IGZO) receive great attention as a channel material for thin film transistors(TFTs) as next-generation display panel backplanes due to its superior electrical and physical properties such as a high mobility, low off-current, high sub-threshold slope, flexibility, and optical transparency. For the purpose of fabricating high performance IGZO TFTs, a thermal recovery process above a temperature of $300^{\circ}C$ is required for recovery or rearrangement of the ionic bonding structure. However diffused metal atoms from source/drain(S/D) electrodes increase the channel conductivity through the oxidation of diffused atoms and reduction of $In_2O_3$ during the thermal recovery process. Threshold voltage ($V_{TH}$) shift, one of the electrical instability, restricts actual applications of IGZO TFTs. Therefore, additional investigation of the electrical stability of IGZO TFTs is required. In this paper, we demonstrate the effect of Ti diffusion and modulation of interface traps by carrying out an annealing process on IGZO. In order to investigate the effect of diffused Ti atoms from the S/D electrode, we use secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy, HSC chemistry simulation, and electrical measurements. By thermal annealing process, we demonstrate VTH shift as a function of the channel length and the gate stress. Furthermore, we enhance the electrical stability of the IGZO TFTs through a second thermal annealing process performed at temperature $50^{\circ}C$ lower than the first annealing step to diffuse Ti atoms in the lateral direction with minimal effects on the channel conductivity.

• Journal of the Korean Society of Radiology
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• v.17 no.4
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• pp.625-631
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• 2023

The important requirement of industrial dynamic X-ray detector operating under high tube voltage up to 450 kVp for 24 hours and 7 days is to obtain significantly high radiation resistance. This study presents the radiation resistance characteristics of various thin film transistors (TFTs) with a-Si, poly-Si and IGZO semiconducting layers. IGZO TFT offering dozens of times higher field effect mobility than a-Si TFT was processed with highly hydrogenated plasma in between IGZO semiconducting layer and inter-layered dielectric. The hydrogenated IGZO TFT showed most sustainable radiation resistance up to 10,000Gy accumulated, thus, concluded that it is a sole switching device in X-ray imaging sensor offering dynamic X-ray imaging at high frame rate under extremely severe radiation environment such as automated X-ray inspection.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.5
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• pp.1592-1596
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• 2010

According to the increase of the channel length with fixed width/length, characteristic curves of drain current as a function of gate bias voltage of indium gallium zinc oxide (IGZO) thin-film transistors moved to a positive direction of gate voltage, and field-effect mobility decreased. In case of fixed length and width of channel, field-effect mobility was lower and subthreshold slope was larger when drain bias voltage was higher. Due to large work function of IGZO, band bending at the junction region between IGZO channel and source/drain electrodes was expected to be in opposite direction to that between silicon and metal electrodes; this could explain the above results.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.92-93
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• 2015

빠른 응답속도를 요구하는 고품질 대면적 디스플레이의 박막형 트랜지스터 적용에 있어서 비정질 IGZO 박막에 대한 많은 연구가 진행되어왔으나, 불순물 도입에 의한 5성분계 IGZO 박막의 전기적 특성 향상에 대한 연구는 거의 보고 되지 않고 있다. 따라서 이번 연구에서는 magnetron co-sputtering 법으로 50 nm 두께를 가지는 yttrium이 도핑된 5성분계 Y-IGZO박막과 Y-IGZO/IGZO 하이브리드막을 제조하여 그 전기적, 광학적 특성 및 표면 조도를 관찰 하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.1
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• pp.56-63
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• 2013

IGZO thin films have been prepared by RF magnetron sputtering. The structural, electrical and optical properties of the IGZO thin films have been investigated as a function of deposition condition. XRD analysis of IGZO thin films showed a typical crystallographic orientation with c-axis perpendicular regardless of deposition conditions. The carrier mobility, carrier concentration and resistivity of the IGZO films sputtered at 200 W, 1mTorr and $300^{\circ}C$ were $28.5cm^2/V{\cdot}sec$, $2.6{\times}10^{20}cm^3$, $8.8{\times}10^{-4}{\Omega}{\cdot}cm$ respectively. The optical transmittance were higher than 80% at visible region regardless of the deposition conditions under the experiments above, and specifically higher than 90% at wave length over 500 nm. The absorption edge was shifted to shorter wavelength with increase of carrier concentration.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.2
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• pp.163-168
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• 2014

Bottom gate thin-film transistors were fabricated using solution processed IGZO channel layers with various gallium composition ratios that were annealed on a hot plate. Increasing the gallium ratio from 0.1 to 0.6 induced a threshold voltage shift in the electrical characteristics, whereas the molar ratio of In:Zn was fixed to 1:1. Among the devices, the IGZO-TFTs with gallium ratios of 0.4 and 0.5 exhibited suitable switching characteristics with low off-current and low SS values. The IGZO-TFTs prepared from IGZO films with a gallium ratio of 0.4 showed a mobility, on/off current ratio, threshold voltage, and subthreshold swing value of $0.1135cm^2/V{\cdot}s$, ${\sim}10^6$, 0.8 V, and 0.69 V/dec, respectively. IGZO-TFTs annealed at $300^{\circ}C$, $350^{\circ}C$, and $400^{\circ}C$ were also fabricated. Annealing at lower temperatures induced a positive shift in the threshold voltage and produced inferior electrical properties.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.23.1-23.1
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• 2009

Transparent thin film transistor(TTFT)는 기존의 디스플레이가 가지고 있는 공간적, 시각적 제약을 해소하는 것이 가능하며, 이는 디스플레이 산업 및 기술이 지향하는 대면적, 저가격, 공정의 단순함을 해결해 줄 수 있기 때문에 최근 TTFT에 관한 연구가 급증하고 있다. 산화물 기반의 TFT는 유리, 금속, 플라스틱 등등 그 기판 종류에 상관없이 균일한 제작이 가능하며, 상온 및 저온에서 대면적으로 제작 가능하고, 저렴한 비용으로 제작 가능하다는 장점 때문에 최근 산화물을 기반으로 하는 TFT 연구가 많이 이루어지고 있다. 현재 TTFT 물질로 많이 연구되고 있는 산화물은 ZnO(3.4 eV)나 $InO_x$(3.6 eV), $GaO_x$(4.9 eV), $SnO_x$(3.7 eV)등의 물질과 각각의 조합으로 구성된 재료들이 주로 사용되고 있다. 가장 많은 연구가 이루어진 ZnO 기반의 TFT는 mobility와 switching 속도에서 우수한 특성을 보이나, amorphous ZnO 기반의 TFT의 경우 소자의 안정성이 떨어지는 것으로 보고되고 있다. 따라서 본 연구에서는 ZnO 보다 넓은 bandgap energy를 가질 수 있으며, n-type 특성을 보이고, amorphous 구조로 제작 가능한 IGZO 물질을 사용하여 RF magnetron sputtering 방법으로 박막 증착 온도의 변화를 주어 증착하였고, 증착된 IGZO 박막의 열처리를 통해 이에 따른 특성 변화를 분석하였다. Field emission scanning electron microscope(FESEM)와 surface profiler를 이용하여 IGZO 박막의 표면의 형상과 두께를 확인하였으며, x-ray diffraction(XRD) 분석을 통해 박막의 결정학적 특성을 관찰하였다. TTFT 물질로서 IGZO 박막의 적합성 여부를 확인하기 위하여 TFT를 만든 후 I-V를 측정하였으며, UV-vis를 이용하여 IGZO 박막의 투과율을 분석하여 TTFT로의 응용 가능성을 확인하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.3-3
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• 2010

We investigated the influence of the indium content on the threshold voltage ($V_{th}$) shift of sol-gel-derived indium-gallium-zinc oxide (IGZO) thin film transistors (TFTs). Surplus indium composition ratio into IGZO decreases the value of $V_{th}$ of IGZO TFTs showed huge $V_{th}$ shift in the negative direction. $V_{th}$ shift decreases from 10 to -28.2V as Indium composition ratio is increased. Because the free electron density is increased according to variation of the Indium composition ratio.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.145-148
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• 2007

The authors report on the fabrication of thin film transistors (TFTs) that use amorphous indium-gallium-zinc oxide (a-IGZO) channel and have the channel length (L) and width (W) patterned by dry etching. To prevent the plasma damage of active channel, a 100-nm-thckness $SiO_{x}$ by PECVD was adopted as an etch-stopper structure. IGZO TFT (W/L=10/50${\mu}m$) fabricated on glass exhibited the high performance mobility of $35.8\;cm^2/Vs$, a subthreshold gate voltage swing of $0.59V/dec$, and $I_{on/off}$ of $4.9{\times}10^6$. In addition, 4.1” transparent QCIF active-matrix organic light-emitting diode display were successfully fabricated, which was driven by a-IGZO TFTs.