• Journal of Information Display
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• v.12 no.1
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• pp.47-50
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• 2011

Highly stable amorphous indium.gallium.zinc-oxide (a-IGZO) thin-film transistors (TFTs) were fabricated with an etchstopper and via-hole structure. The TFTs exhibited 40 $cm^2$/V s field-effect mobility and a 0.21 V/dec gate voltage swing. Gate-bias stress induced a negligible threshold voltage shift (${\Delta}V_{th}$) at room temperature. The excellent stability is attribute to the via-hole and etch-stopper structure, in which, the source/drain metal contacts the active a-IGZO layer through two via holes (one on each side), resulting in minimized damage to the a-IGZO layer during the plasma etching of the source/drain metal. The comparison of the effects of the DC and AC stress on the performance of the TFTs at $60^{\circ}C$ showed that there was a smaller ${\Delta}V_{th}$ in the AC stress compared with the DC stress for the same effective stress time, indicating that the trappin of the carriers at the active layer-gate insulator interface was the dominant degradation mechanism.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.693-696
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• 2011

Recently, amorphous oxide semiconductors (AOSs) based thin-film transistors (TFTs) have received considerable attention for application in the next generation displays industry. The research trends of AOSs based TFTs investigation have focused on the high device performance. The electrical properties of the TFTs are influenced by trap density. In particular, the threshold voltage ($V_{th}$) and subthreshold swing (SS) essentially depend on the semiconductor/gate-insulator interface trap. In this article, we investigated the effects of Ar plasma-treated $SiO_2$ insulator on the interfacial property and the device performances of amorphous indium gallium zinc oxide (a-IGZO) TFTs. We report on the improvement in interfacial characteristics between a-IGZO channel layer and gate insulator depending on Ar power in plasma process, since the change of treatment power could result in different plasma damage on the interface.

• Korean Journal of Materials Research
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• v.33 no.12
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• pp.511-516
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• 2023

Amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs) with a coplanar structure were fabricated to investigate the feasibility of their potential application in large size organic light emitting diodes (OLEDs). Drain currents, used as functions of the gate voltages for the TFTs, showed the output currents had slight differences in the saturation region, just as the output currents of the etch stopper TFTs did. The maximum difference in the threshold voltages of the In-Ga-Zn-O (a-IGZO) TFTs was as small as approximately 0.57 V. After the application of a positive bias voltage stress for 50,000 s, the values of the threshold voltage of the coplanar structure TFTs were only slightly shifted, by 0.18 V, indicative of their stability. The coplanar structure TFTs were embedded in OLEDs and exhibited a maximum luminance as large as 500 nits, and their color gamut satisfied 99 % of the digital cinema initiatives, confirming their suitability for large size and high resolution OLEDs. Further, the image density of large-size OLEDs embedded with the coplanar structure TFTs was significantly enhanced compared with OLEDs embedded with conventional TFTs.

• Journal of the Korean Ceramic Society
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• v.47 no.4
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• pp.329-332
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• 2010

In order to investigate the effect of tail state on the electrical and the optical properties in amorphous IGZO(a-IGZO), a-IGZO films were deposited at room temperature on fused silica substrats using pulsed laser deposition method. The laser pulse energy was used as the processing parameter. In-situ post annealing was carried out at $150^{\circ}C$ right after the film deposition. The $O_2$ partial pressure during the deposition and the post annealing was fixed to 10mTorr. The carrier mobility of the a-IGZO films had a range from 2 to $18\;cm^2/Vs$ at carrier concentrations greater than $10^{18}\;cm^{-3}$. As the laser energy density increased, the Hall mobility increased. And post annealing improved the Hall mobility, as well. The optical property was examined using the ultraviolet-visible spectroscopy. The a-IGZO films that have low Hall mobility exhibited stronger and broader absorption tails in >3.0 eV region. Post annealing reduced the intensity of the tail-like absorption. The absorption tail in a-IGZO films is an important factor which affects the electrical and the optical properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.338.2-338.2
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• 2014

투명반도체산화물은 우수한 광학적, 전기적 특성을 가지고 있기 때문에 차세대 박막트랜지스터의 채널층으로 각광을 받고 있다. 특히, 그 중에서도 a-IGZO를 이용한 TFT는 높은 가시광선 투과율(>80%)과 큰 전하이동도(>10 cm2/Vs) 를 갖는 등 좋은 광학적, 전기적 특성을 갖기 때문에 많은 연구가 이루어졌다. 여러 연구들에 의하면, a-IGZO TFT는 소스/드레인의 전극으로 어떤 물질을 사용하는지에 따라서 동작특성에 큰 영향을 미치는 것으로 알려져 있다. 일반적으로, a-IGZO 박막은 n형 반도체로써 일함수가 작은 금속과는 ohmic contact를 형성하고, 일함수가 큰 금속과는 Schottky barrier를 형성한다고 알려져 있다. 이와 관련된 대부분의 이전의 연구들에서는 각각의 전극물질에 따라 전기적인 특성변화에 초점을 맞춰서 연구하였다. 본 연구에서는 일함수가 작은 Ag와 일함수가 큰 Au를 a-IGZO의 박막 위에 얇게 증착하면서 이에 따른 고분해능 광전자분광(high-resolution x-ray photoelectron spectroscopy) 정보의 변화를 분석함으로써, 금속의 증착에 따른 금속층과 a-IGZO 표면 및 계면에서의 화학적 상태의 변화를 연구하였다. Au 4f, Ag 3d는 metallic property를 나타내기 이전까지는 lower binding energy(BE) 쪽으로 shift하였으며, In 3d 또한 lower BE 성분이 크게 증가하였다. O 1s, Ga 3d, Zn 3d들은 상대적으로 적은 변화를 나타내었는데, 이는 Ag, Au가 In과 상대적으로 더 많이 상호작용한다는 것을 의미한다. 본 발표에서는 이들 core level의 정보들과, 가전자대의 분광정보, 그리고 band bending의 정보가 제시될 것이며, 이 정보들은 metal 증착에 따른 contact 특성을 이해하는데 기여할 것으로 기대한다.

• ETRI Journal
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• v.31 no.6
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• pp.660-666
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• 2009

We investigate the effects of interfacial dielectric layers (IDLs) on the electrical properties of top-gate In-Ga-Zn-oxide (IGZO) thin film transistors (TFTs) fabricated at low temperatures below $200^{\circ}C$, using a target composition of In:Ga:Zn = 2:1:2 (atomic ratio). Using four types of TFT structures combined with such dielectric materials as $Si_3N_4$ and $Al_2O_3$, the electrical properties are analyzed. After post-annealing at $200^{\circ}C$ for 1 hour in an $O_2$ ambient, the sub-threshold swing is improved in all TFT types, which indicates a reduction of the interfacial trap sites. During negative-bias stress tests on TFTs with a $Si_3N_4$ IDL, the degradation sources are closely related to unstable bond states, such as Si-based broken bonds and hydrogen-based bonds. From constant-current stress tests of $I_d$ = 3 ${\mu}A$, an IGZO-TFT with heat-treated $Si_3N_4$ IDL shows a good stability performance, which is attributed to the compensation effect of the original charge-injection and electron-trapping behavior.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.166-166
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• 2010

Recently, TFTs based on amorphous oxide semiconductors (AOSs) such as ZnO, InZnO, ZnSnO, GaZnO, TiOx, InGaZnO(IGZO), SnGaZnO, etc. have been attracting a grate deal of attention as potential alternatives to existing TFT technology to meet emerging technological demands where Si-based or organic electronics cannot provide a solution. Since, in 2003, Masuda et al. and Nomura et al. have reported on transparent TFTs using ZnO and IGZO as active layers, respectively, much efforts have been devoted to develop oxide TFTs using aforementioned amorphous oxide semiconductors as their active layers. In this thesis, I report on the performance of thin-film transistors using amorphous indium gallium zinc oxides for an active channel layer at room temperature. $SiO_2$ was employed as the gate dielectric oxide. The amorphous indium gallium zinc oxides were deposited by RF magnetron sputtering. The carrier concentration of amorphous indium gallium zinc oxide was controlled by oxygen pressure in the sputtering ambient. Devices are realized that display a threshold voltage of 1.5V and an on/off ration of > $10^9$ operated as an n-type enhancement mode with saturation mobility with $9.06\;cm^2/V{\cdot}s$. The devices show optical transmittance above 80% in the visible range. In conclusion, the fabrication and characterization of thin-film transistors using amorphous indium gallium zinc oxides for an active channel layer were reported. The operation of the devices was an n-type enhancement mode with good saturation characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.8-8
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• 2009

Thin-film transistors (TFTs) were fabricated using amorphous indium gallium zinc oxide (a-IGZO) channels by rf-magnetron sputtering at room temperature. We have studied the effect of oxygen partial pressure on the threshold voltage($V_{th}$) of a-IGZO TFTs. Interestingly, the $V_{th}$ value of the oxide TFTs are slightly shifted in the positive direction due to increasing $O_2$ ratio from 1.2 to 1.8%. The device performance is significantly affected by varying $O_2$ ratio, which is closely related with oxygen vacancies provide the needed free carriers for electrical conduction.

• Journal of Information Display
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• v.11 no.4
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• pp.160-164
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• 2010

Organic light-emitting devices (OLEDs) have shown superior characteristics and are expected to dominate the nextgeneration flat-panel displays. Active-matrix organic light-emitting diode (AMOLED) displays, however, have stringent demands on the performance of the backplane. In this paper, the development of thin-film transistors (TFTs) based on indium gallium zinc oxide (IGZO) on both Gen 1 and 6 glasses, and their decent characteristics, which meet the AMOLED requirements, are shown. Further, several display prototypes (e.g., 2.4" AMOLED, 2.4" transparent AMOLED, and 32" AMLCD) using IGZO TFTs are demonstrated to confirm that they can indeed be strong candidates for the next-generation TFT technology not only of AMOLED but also of AMLCD (active-matrix liquid crystal display).

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.100-101
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• 2012

The plasma damage free and room temperature processedthin film deposition technology is essential for realization of various next generation organic microelectronic devices such as flexible AMOLED display, flexible OLED lighting, and organic photovoltaic cells because characteristics of fragile organic materials in the plasma process and low glass transition temperatures (Tg) of polymer substrate. In case of directly deposition of metal oxide thin films (including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS)) on the organic layers, plasma damages against to the organic materials is fatal. This damage is believed to be originated mainly from high energy energetic particles during the sputtering process such as negative oxygen ions, reflected neutrals by reflection of plasma background gas at the target surface, sputtered atoms, bulk plasma ions, and secondary electrons. To solve this problem, we developed the NBAS (Neutral Beam Assisted Sputtering) process as a plasma damage free and room temperature processed sputtering technology. As a result, electro-optical properties of NBAS processed ITO thin film showed resistivity of $4.0{\times}10^{-4}{\Omega}{\cdot}m$ and high transmittance (>90% at 550 nm) with nano- crystalline structure at room temperature process. Furthermore, in the experiment result of directly deposition of TCO top anode on the inverted structure OLED cell, it is verified that NBAS TCO deposition process does not damages to the underlying organic layers. In case of deposition of transparent conductive oxide (TCO) thin film on the plastic polymer substrate, the room temperature processed sputtering coating of high quality TCO thin film is required. During the sputtering process with higher density plasma, the energetic particles contribute self supplying of activation & crystallization energy without any additional heating and post-annealing and forminga high quality TCO thin film. However, negative oxygen ions which generated from sputteringtarget surface by electron attachment are accelerated to high energy by induced cathode self-bias. Thus the high energy negative oxygen ions can lead to critical physical bombardment damages to forming oxide thin film and this effect does not recover in room temperature process without post thermal annealing. To salve the inherent limitation of plasma sputtering, we have been developed the Magnetic Field Shielded Sputtering (MFSS) process as the high quality oxide thin film deposition process at room temperature. The MFSS process is effectively eliminate or suppress the negative oxygen ions bombardment damage by the plasma limiter which composed permanent magnet array. As a result, electro-optical properties of MFSS processed ITO thin film (resistivity $3.9{\times}10^{-4}{\Omega}{\cdot}cm$, transmittance 95% at 550 nm) have approachedthose of a high temperature DC magnetron sputtering (DMS) ITO thin film were. Also, AOS (a-IGZO) TFTs fabricated by MFSS process without higher temperature post annealing showed very comparable electrical performance with those by DMS process with $400^{\circ}C$ post annealing. They are important to note that the bombardment of a negative oxygen ion which is accelerated by dc self-bias during rf sputtering could degrade the electrical performance of ITO electrodes and a-IGZO TFTs. Finally, we found that reduction of damage from the high energy negative oxygen ions bombardment drives improvement of crystalline structure in the ITO thin film and suppression of the sub-gab states in a-IGZO semiconductor thin film. For realization of organic flexible electronic devices based on plastic substrates, gas barrier coatings are required to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency flexible AMOLEDs needs an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}gm^{-2}day^{-1}$. The key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (under ${\sim}10^{-6}gm^{-2}day^{-1}$) is the suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. For formation of high quality single inorganic gas barrier layer, we developed high density nano-structured Al2O3 single gas barrier layer usinga NBAS process. The NBAS process can continuously change crystalline structures from an amorphous phase to a nano- crystalline phase with various grain sizes in a single inorganic thin film. As a result, the water vapor transmission rates (WVTR) of the NBAS processed $Al_2O_3$ gas barrier film have improved order of magnitude compared with that of conventional $Al_2O_3$ layers made by the RF magnetron sputteringprocess under the same sputtering conditions; the WVTR of the NBAS processed $Al_2O_3$ gas barrier film was about $5{\times}10^{-6}g/m^2/day$ by just single layer.