• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.3
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• pp.153-161
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• 2011

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 (a-IGZO) 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 $V_{DD}$=20 V.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.276-276
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• 2014

High-performance, fully-transparent, and top-gated oxide thin-film transistor (TFT) was successfully fabricated with Ta2O5 high-k gate dielectric on a glass substrate. Through a self-passivation with the gate dielectric and top electrode, the top-gated oxide TFT was not affected from H2O and O2 causing the electrical instability. Heat-treated InSnO (ITO) was used as the top and source/drain electrode with a low resistance and a transparent property in visible region. A InGaZnO (IGZO) thin-film was used as a active channel with a broad optical bandgap of 3.72 eV and transparent property. In addition, using a X-ray diffraction, amorphous phase of IGZO thin-film was observed until it was heat-treated at 500 oC. The fabricated device was demonstrated that an applied electric field efficiently controlled electron transfer in the IGZO active channel using the Ta2O5 gate dielectric. With the transparent ITO electrodes and IGZO active channel, the fabricated oxide TFT on a glass substrate showed optical transparency and high carrier mobility. These results expected that the top-gated oxide TFT with the high-k gate dielectric accelerates the realization of presence of fully-transparent electronics.

• Journal of the Semiconductor & Display Technology
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• v.18 no.4
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• pp.6-11
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• 2019

For a wider application of laser direct patterning, selective laser ablation of indium tin oxide (ITO) film on transparent oxide semiconductor (TOS) thin film was carried out using a diode-pumped Q-switched Nd:YVO₄ laser at a wavelength of 1064 nm. In case of the laser ablation of ITO on indium gallium zinc oxide (IGZO) film, both of ITO and IGZO films were fully etched for all the conditions of the laser beams even though IGZO monolayer was not ablated at the same laser beam condition. On the contrary, in case of the laser ablation of ITO on zinc oxide (ZnO) film, it was possible to etch ITO selectively with a slight damage on ZnO layer. The selective laser ablation is expected to be due to the different coefficient of thermal expansion (CTE) between ITO and ZnO.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.301-301
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• 2012

Amorphous In-Ga-Zn-O (a-IGZO)는 광학적으로 투명하고 높은 전자이동도를 가지고 있어서 차세대 thin-film-transistor의 channel layer 물질로 각광받고 있다. 이러한 a-IGZO를 TFT channel layer로 사용하기 위해서는 소스 드레인 전극물질과 IGZO박막의 계면에서 ohmic contact을 만드는 것도 중요하다. 하지만 산화물 반도체의 특성상 금속물질을 증착시킬 때 산화금속계면을 형성하기 때문에 ohmic contact이 형성되기 어려운 것으로 알려져 있다. Au는 보통 전극물질로 많이 사용되는데, 이는 전기전도도가 매우 높고, 독특한 산화환원반응 특성을 보이지만, 화학반응을 잘 일으키지 않는 안정성을 가지는 성질에 기인한다. 본 연구진은 Au가 a-IGZO에 증착 시에 일어나는 표면의 화학적 상태변화를 이해하기 위해 방사광을 이용한 고분해능 광전자 분광법을 이용하여 표면변화를 분석하였다. Au는 (Au 4f) 증착 초기엔 약간의 gold oxide가 함께 형성되지만, 주로 metal gold의 형태로 존재하였다. In 3d, Ga 3d, O 1s, Zn 3d 각각의 스펙트럼에서는 Au 증착으로 인해 낮은 결합에너지에 새로운 state가 나타났다. 한편, In은 상대적으로 다른 원소들에 비해 Au와 좀 더 결합을 잘 하는 것으로 나타났는데 이는, In 5s 전자궤도가 전도메커니즘에서 중요한 역할을 하기 때문에, In-Au의 상대적인 강한 결합은 a-IGZO의 전기적 특성 변화에 기여할 수 있음을 의미한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.293.2-293.2
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• 2016

The In this paper, we have fabricated the solution processed In-Ga-ZnO thin film transistors (IGZO TFTs) by varying indium and gallium ratio. The indium ratio of IGZO TFTs was changed from 1 to 5 at fixed gallium and zinc oxide atomic percent of 1:1 and gallium ratio was varied from 1 to 5 at fixed indium and zinc oxide atomic percent of 1:1. When the indium ratio was increased at fixed gallium and zinc oxide ratio of 1:1, threshold voltage was negatively shifted from 1.03 to -6.18 V and also mobility was increased from 0.018 to $0.076cm2/V{\cdot}sec$. It means that the number of carriers in IGZO TFTs were increased due to great formation of the oxygen vacancies which generate electrons. In contrast, when the gallium ratio was increased in IGZO TFTs with indium and zinc oxide ration of 1:1, the on/off current ratio was increased from $1.88{\times}104$ to $2.22{\times}105$. It is because gallium have stronger chemical bonds with oxygen than that with the zinc and indium ions that lead to the decreased in electron concentration.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.211.2-211.2
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• 2015

In order to investigate the effect of front channel in DAL (dual active layer) TFT (thin film transistor), we successfully fabricated DAL TFT composed of ITZO and IGZO as active layer using the solution process. In this structure, ITZO and IGZO active layer were used as front and back channel, respectively. The front channel was changed from 0.05 to 0.2 M at fixed 0.3 M IGZO of back channel. When the mol concentration of front channel was increased, the threshold voltage (VTH) was increased from 2.0 to -11.9 V and off current also was increased from 10-12 to 10-11. This phenomenon is due to increasing the carrier concentration by increasing the volume of the front channel. The saturation mobility of DAL TFT with 0.05, 0.1, and 0.2 M ITZO were 0.45, 4.3, and $0.65cm2/V{\cdot}s$. Even though 0.2 M ITZO has higher carrier concentration than 0.05 and 0.1 M ITZO, the 0.1 M ITZO/0.3 M IGZO DAL TFT has the highest saturation mobility. This is due to channel defect such as pores and pin-holes. These defect sites were created during deposition process by solvent evaporation. Due to these defect sites, the 0.1 M ITZO/0.3 M IGZO DAL TFT shows the higher saturation mobility than that of DAL TFT with front channel of 0.2 M ITZO.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1097-1100
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• 2008

We demonstrate that the performance of amorphous indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFT) can be optimized by controlling the interfaces between IGZO and sandwiching insulators and by proper deposition of IGZO layer. Specifically, contact and channel resistances are decreased by reducing IGZO bulk resistance and optimizing dry-etch process, respectively. Field-effect mobility ($\mu_{FE}$) and subthreshold gate swing (S) are further enhanced by fine-tuning IGZO deposition condition.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.160-160
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• 2015

InGaZnO (IGZO) thin-film transistors (TFTs) are very promising due to their potential use in high performance display backplane [1]. However, the stability of IGZO TFTs under the various stresses has been issued for the practical IGZO applications [2]. Up to now, many researchers have studied to understand the sub-gap density of states (DOS) as the root cause of instability [3]. Nomura et al. reported that these deep defects are located in the surface layer of the IGZO channel [4]. Also, Kim et al. reported that the interfacial traps can be affected by different RF-power during RF magnetron sputtering process [5]. It is well known that these trap states can influence on the performances and stabilities of IGZO TFTs. Nevertheless, it has not been reported how these defect states are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOI) can be generated by electron attachment in oxygen atom near target surface and accelerated up to few hundreds eV by self-bias of RF magnetron sputter; the high energy bombardment of NOIs generates bulk defects in oxide thin films [6-10] and can change the defect states of IGZO thin film. In this study, we have confirmed that the NOIs accelerated by the self-bias were one of the dominant causes of instability in IGZO TFTs when the channel layer was deposited by conventional RF magnetron sputtering system. Finally, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process [9-10] to eliminate the NOI bombardment effects and present how much to be improved the instability of IGZO TFTs by this new deposition method.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.340.2-340.2
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• 2014

최근 비정질 산화물 반도체는 가시광 영역에서의 투명도와 낮은 공정 온도, 그리고 높은 Field-effect mobility로 인해 Thin film transistors의 Active channel layer의 재료로 각광 받고 있다. ZnO, IZO, IGO, ITGO등의 많은 산화물 반도체들이 TFT의 채널층으로의 적용을 위해 활발히 연구되고 있으며, 특히 비정질 IGZO는 비정질임에도 불구하고 Mobility가 $10cm^2/Vs$ 정도로 기존의 a-Si:H 보다 높은 Mobility 특성을 나타내고 있어 대화면 디스플레이와 고속 구동을 위한 LCD에 적용 할 수 있으며 또한 낮은 공정 온도로 인해 플렉서블 디스플레이에 응용될 수 있다는 장점이 있다. 우리는 RF magnetron sputtering법으로 증착한 비정질 IGZO TFT(Thin Film Transistors)의 전기적 특성과 IGZO 박막의 특성에 미치는 RF power의 영향을 연구하였다. 제작한 TFTs의 Active channel layer는 산소분압 1%, Room temperature에서 RF power별(50~150 W)로 Si wafer 기판 위에 30nm로 증착 하였고 100 nm의 $SiO_2$가 절연체로 사용되었다. 또한 박막 특성을 분석하기 위해 같은 Chamber 분위기에서 100 nm로 IGZO 박막을 증착하였다. 비정질 IGZO 박막의 X-ray reflectivity(XRR)을 분석한 결과 RF Power가 50 W에서 150 W로 증가 할수록 박막의 Roughness는 22.7 (${\AA}$)에서 6.5 (${\AA}$)로 감소하고 Density는 5.9 ($g/cm^3$)에서 6.1 ($g/cm^3$)까지 증가하는 경향을 보였다. 또한 제작한 IGZO TFTs는 증착 RF Power가 증가함에 따라 Threshold voltage (VTH)가 0.3~4(V)로 증가하는 경향을 나타내고 Filed-effect mobility도 6.2~19 ($cm^2/Vs$)까지 증가하는 경향을 보인다. 또한 on/off ratio는 모두 > $10^6$의 값을 나타내며 subthreshold slope (SS)는 0.3~0.8 (V/decade)의 값을 나타낸다.

• 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.