• Transactions on Electrical and Electronic Materials
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• v.17 no.1
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• pp.18-20
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• 2016

Transparent and conducting IGZO thin films were deposited by RF magnetron sputtering on thin Cu coated glass substrates to investigate the effect of a Cu buffer layer on the structural, optical, and electrical film properties. Although X-ray diffraction (XRD) analysis revealed that both the IGZO single layer and IGZO/Cu bi-layered films were in the amorphous phase, the IGZO/Cu films showed a lower resistivity of 5.7×10⁻⁴ Ωcm due to the increased mobility and high carrier concentration. The decreased optical transmittance of the IGZO/Cu films was also attributed to a one order of magnitude higher carrier concentration than the IGZO films. From the observed results, the thin Cu layer is postulated to be an effective buffer film that can enhance the opto-electrical performance of the IGZO films in transparent thin film transistors.

• Journal of Sensor Science and Technology
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• v.28 no.5
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• pp.329-333
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• 2019

Solution-processed oxide thin-film transistors (TFTs) have garnered great attention, owing to their many advantages, such as low-cost, large area available for fabrication, mechanical flexibility, and optical transparency. Negative bias stress (NBS)-induced instability of sol-gel IGZO TFTs is one of the biggest concerns arising in practical applications. Thus, understanding the bias stress effect on the electrical properties of sol-gel IGZO TFTs and proposing an effective recovery method for negative bias stressed TFTs is required. In this study, we investigated the variation of transfer characteristics and the corresponding electrical parameters of sol-gel IGZO TFTs caused by NBS and positive bias recovery (PBR). Furthermore, we proposed an effective PBR method for the recovery of negative bias stressed sol-gel IGZO TFTs. The threshold voltage and field-effect mobility were affected by NBS and PBR, while current on/off ratio and sub-threshold swing were not significantly affected. The transfer characteristic of negative bias stressed IGZO TFTs increased in the positive direction after applying PBR with a negative drain voltage, compared to PBR with a positive drain voltage or a drain voltage of 0 V. These results are expected to contribute to the reduction of recovery time of negative bias stressed sol-gel IGZO TFTs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.6
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• pp.473-479
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• 2011

In this paper, we have compared amorphous InGaZnO (a-IGZO) thin-film transistor (TFT) with the nano-crystalline embedded-IGZO ($N_c$-embedded-IGZO) TFT fabricated by solid-phase crystallization (SPC) technique. The field effect mobility (${\mu}_{FE}$) of $N_c$-embedded-IGZO TFT was 2.37 $cm^2/Vs$ and the subthreshold slope (S-factor) was 0.83 V/decade, which showed lower performance than those of a-IGZO TFT (${\mu}_{FE}$ of a-IGZO was 9.67 $cm^2/Vs$ and S-factor was 0.19 V/decade). This results originated from generation of oxygen vacancies in oxide semiconductor and interface between gate insulator and semiconductor due to high temperature annealing process. However, the threshold voltage shift (${\Delta}V_{TH}$) of $N_c$-embedded-IGZO TFT was 0.5 V, which showed 1 V less shift than that of a-IGZO TFT under constant current stress during $10^5$ s. This was because there were additionally less increase of interface trap charges in Nc-embedded-IGZO TFT than a-IGZO TFT.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.178.1-178.1
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• 2015

In and Ga doped ZnO (IGZO) thin films were prepared by radio frequency magnetron sputtering without intentional substrate heating on glass substrate and TiO2-deposited glass substrates to consider the effect of a thin TiO2 buffer layer on the optical and electrical properties of the films. The thicknesses of the TiO2 buffer layer and IGZO films were kept constant at 5 and 100 nm, respectively. Since the IGZO/TiO2 bi-layered films show the higher FOM value than that of the IGZO single layer films, it is supposed that the IGZO/TiO2 bi-layered films will likely perform better in TCO applications than IGZO single layer films.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.112.1-112.1
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• 2012

산화물 기반의 TFT (Thin Film Transistor) 는 유리, 금속, 플라스틱 등 기판 종류에 상관없이 균일한 제작이 가능하며, 상온 및 저온에서 대면적으로 제작이 가능하고, 저렴한 비용으로 제작 가능하다는 장점 때문에 최근 많은 연구가 이루어지고 있다. 현재 TFT 물질로 많이 연구되고 있는 산화물 중 가장 많은 연구가 이루어진 ZnO 기반의 TFT는mobility와 switching 속도에서 우수한 특성을 보이나, 트렌지스터의 안정성이 떨어지는 것으로 보고되고 있다. 그러나 a-IGZO의 경우 결정학적으로 비정질이며, 상온 및 저온에서 대면적으로 제작이 가능하고, 높은 전자 이동도의 특성을 가지고 있는 장점 때문에 최근 차세대 산화물 트렌지스터로 각광받고 있다. IGZO 물질의 경우 s 오비탈의 중첩으로 인해 높은 전자 이동도의 특성을 가지며, IGZO 물질 내 전자의 이동은 IGZO의 조성과 구조적 특성에 영향을 받는다. IGZO 물질의 구성 성분은 $In_2O_3$, $Ga_2O_3$, ZnO 성분으로 이루어져 있으며, $In_2O_3$의 경우 주로 carrier 를 생성하고 IGZO TFT의 mobility를 향상시키는 물질로 알려져 있다. 본 연구에서는 $In_2O_3$ nanoparticle의 density를 조절하여 첨가함으로써 IGZO TFT 소자 특성에 미치는 평가를 진행하였다. $In_2O_3$ nanoparticle의 density변화에 따른 interparticle spacing과 IGZO계면 사이의 미세구조와 전기적인 특성간의 상관관계를 연구하기 위하여 IGZO TFT 특성은 HP 4145B 측정을 통하여 확인하였고, $In_2O_3$ nanoparticle의 분포와 결정성은 AFM과 XRD, TEM을 통해 분석하고 In2O3 nanoparticle의 유무에 따른 IGZO channel 층의 조성 변화를 STEM과 AES를 통해 비교 및 분석하였다.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.71-77
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• 2014

In this paper, we investigated the effects of high-energy electron beam irradiation (HEEBI) on the optical transmittance of InGaZnO (IGZO) films grown on transparent Corning glass substrates, with a radio frequency magnetron sputtering technique. The IGZO thin films deposited at low temperature were treated with HEEBI in air at room temperature (RT) with an electron beam energy of 0.8 MeV and doses of $1{\times}10^{14}-1{\times}10^{16}electrons/cm^2$. The optical transmittance of the IGZO films was measured using an ultraviolet visible near-infrared spectrophotometer (UVVIS). The detailed estimation process for separating the transmittance of HEEBI-treated IGZO films from the total transmittance of IGZO films on transparent substrates treated with HEEBI is given in this paper. Based on the experimental results, we concluded that HEEBI with an appropriate dose of $10^{14}electrons/cm^2$ causes a maximum increase in the transparency of IGZO thin films. We also concluded that HEEBI treatment with an appropriate dose shifted the optical band gap ($E_g$) toward the lower energy region from 3.38 to 3.31 eV. This $E_g$ shift suggested that HEEBI in air at RT with an appropriate dose acts like a thermal annealing treatment in vacuum at high temperature.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.42.2-42.2
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• 2011

산화물 기반의 TFT (Thin Film Transistor) 는 유리, 금속, 플라스틱 등 기판 종류에 상관없이 균일한 제작이 가능하며, 상온 및 저온에서 대면적으로 제작이 가능하고, 저렴한 비용으로 제작 가능하다는 장점 때문에 최근 많은 연구가 이루어지고 있다. 현재 TFT 물질로 많이 연구되고 있는 산화물 중 가장 많은 연구가 이루어진 ZnO 기반의 TFT는 mobility와 switching 속도에서 우수한 특성을 보이나, 트렌지스터의 안정성이 떨어지는 것으로 보고 되고 있다. 그러나 IGZO 물질의 경우 결정학적으로 비정질이며, 상온 및 저온에서 대면적으로 제작이 가능하고, 높은 전자 이동도의 특성을 가지고 있는 장점 때문에 최근 차세대 산화물 트렌지스터로 각광받고 있다. IGZO 물질의 경우 s 오비탈의 중첩으로 인해 높은 전자 이동도의 특성을 가지며, IGZO 물질 내 전자의 이동은 IGZO의 조성과 구조적 특성에 영향을 받는다. IGZO 물질의 구성 성분은 $In_2O_3$, $Ga_2O_3$, ZnO 성분으로 이루어져 있으며, $In_2O_3$의 경우 주로 carrier를 생성하고 IGZO TFT의 mobility를 향상시키는 물질로 알려져 있다. 본 연구에서 $In_2O_3$ nanoparticle을 density를 변화시켜 첨가하여 IGZO TFT 소자 제작 및 특성에 대한 평가를 진행하였다. $In_2O_3$ nanoparticle의 density에 따른 interparticle spacing과 IGZO계면 사이의 미세구조와 전기적인 특성간의 상관관계를 연구하기 위하여 IGZO TFT 특성은 HP 4145B 측정을 통하여 확인하였고, $In_2O_3$ nanoparticle의 분포와 결정성은 XRD와 AFM을 통해 분석하고, $In_2O_3$ nanoparticle의 첨가가 IGZO 소자에 미치는 가능성을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.99-99
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• 2010

Recently, amorphous transparent oxide semiconductors (TOS) have been widely studied for many optoelectronic devices such as AM-OLED (active-matrix organic light emitting diodes). The TOS TFTs using a-IGZO channel layers exhibit a high electron mobility, a smooth surface, a uniform deposition at a large area, a high optical transparency, a low-temperature fabrication. In spite of many advantages of the sputtering process such as better step coverage, good uniformity over large area, small shadow effect and good adhesion, there are not enough researches about characteristics of a-IGZO thin films. In this study, therefore, we focused on the electrical properties of a-IGZO thin films as a channel layer of TFTs. TFTs with the a-IGZO channel layers and Y2O3 gate insulators were fabricated. Source and drain layers were deposited using ITO target. TFTs were deposited on unheated non-alkali glass substrates ($5cm{\times}5cm$) with a sintered ceramic IGZO disc (3 inch $\varnothing$, 5mm t), Y2O3 disc (3 inch $\varnothing$, 5mm t) and ITO disc (3 inch $\varnothing$, 5mm t) as a target by magnetron sputtering method. The O2 gas was used as the reactive gas. Deposition was carried out under various sputtering conditions to investigate the effect of sputtering process on the characteristics of a-IGZO thin films. Correlation between sputtering factors and electronic properties of the film will be discussed in detail.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.43.1-43.1
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• 2011

Hydrogenated amorphous Si (a-Si:H), low temperature poly Si (LTPS) 등 기존 thin film transistors (TFTs)에 사용되던 채널 물질을 대체할 재료로써 다양한 연구가 진행되고 있는 amorphous indium-gallium-zinc-oxide (a-IGZO)는 TFT에 적용하였을 때 뛰어난 전기적 특성과 재연성을 나타낼 뿐만 아니라 넓은 밴드갭을 가져 투명소자로도 응용이 가능하다. 본 연구에서는 a-IGZO의 열처리에 따른 소자의 전기적 특성과 조성 분포의 관계를 확인하기 위해 다음과 같이 실험을 진행하였다. Si/SiO2 기판 위에 DC sputter를 이용하여 IGZO를 증착하고 $350^{\circ}C$에서 열처리를 한 후 evaporator로 Al 전극을 형성시켰다. 이 때 전기적 특성의 변화를 비교하기 위해 열처리 한 샘플과 열처리 하지 않은 샘플에 대해 I-V 특성을 측정하였고, 채널 내부의 조성 분포 변화를 transmission electron microscopy (TEM)의 energy dispersive spectrometer (EDS)를 이용하여 관찰하였다. 그 결과 열처리 된 a-IGZO 채널 층의 산소 비율이 감소하였으며 전체적인 조성이 고르게 분포 되었고 전기적 특성은 향상되었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.217-217
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• 2016

The amorphous InGaZnO (a-IGZO) is widely accepted as a promising channel material for thin-film transistor (TFT) applications owing to their outstanding electrical properties [1, 2]. However, a-IGZO TFTs have still suffered from their bias instability with illumination [1-4]. Up to now, many researchers have studied the sub-gap density of states (DOS) as the root cause of instability. It is well known that defect states can influence on the performances and stabilities of a-IGZO TFTs. The defects states should be closely related with the deposition condition, including sputtering power, and pressure. Nevertheless, it has not been reported how these defects are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOIs) can be generated by electron attachment in oxygen atom near target surface and then accelerated up to few hundreds eV by a self-bias; at this time, the high energy bombardment of NOIs induce defects in oxide thin films. Recently, we have reported that the properties of IGZO thin films are strongly related with effects of NOIs which are generated during the sputtering process [5]. From our previous results, the electrical characteristics and the chemical bonding states of a-IGZO thin films were depended with the bombardment energy of NOIs. And also, we suggest that the deep sub-gap states in a-IGZO as well as thin film properties would be influenced by the bombardment of high energetic NOIs during the sputtering process.In this study, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process to prevent the NOIs bombardment effects and present how much to be improved the properties of a-IGZO thin film by this new deposition method. We deposited a-IGZO thin films by MFSS on SiO2/p-Si and glass substrate at various process conditions, after which we investigated the morphology, optical and electrical properties of the a-IGZO thin films.