• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.389-392
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• 2009

Metal oxides have been proposed as an alternative channel material to hydrogenated amorphous silicon in thin film transistors (TFTs) because their higher mobility and stability make them suitable for transistor active layers. Thin films of indium zinc oxide (IZO) were deposited using a High Target Utilization Sputtering (HiTUS) system on various dielectrics, some of which were also deposited with the HiTUS. Investigations into bottom-gated IZO TFTs have found mobilities of 8 $cm^2V\;^1s^{-1}$ and switching ratios of $10^6$. There is a variation in the threshold voltage dependent on both oxygen concentration, and dielectric choice. Silica, alumina and silicon nitride produced stable TFTs, whilst hafnia was found to break down as a result of the IZO.

• Journal of Information Display
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• v.13 no.3
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• pp.113-118
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• 2012

Metal oxide semiconductors were considered promising materials as backplanes of future displays. Moreover, the adoption of carrier-suppressing metal into indium-zinc oxide (IZO) has become one of the most important themes in the metal oxide research field. In this paper, efforts to realize and optimize IZO with diverse types of carrier suppressors are summarized. Properties such as the band gap of metal in the oxidized form and its electronegativity were examined to confirm their relationship with the metal's carrier-suppressing ability. It was concluded that those two properties could be used as indicators of the carrier-suppressing ability of a material. As predicted by the properties, the alkali earth metals and early transition metals used in the research effectively suppressed the carrier and optimized the electrical properties of the metal oxide semiconductors. With the carrier-suppressing metals, IZO-based thin-film transistors with high (above $1cm^2/V{\cdot}s$) mobility, a lower than 0.6V/dec sub-threshold gate swing, and an over $3{\times}10^6$ on-to-off current ratio could be achieved.

• Korean Journal of Materials Research
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• v.28 no.12
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• pp.758-762
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• 2018

The transfer characteristics of zinc tin oxide(ZTO) on silicon dioxide($SiO_2$) thin film transistor generally depend on the electrical properties of gate insulators. $SiO_2$ thin films are prepared with argon gas flow rates of 25 sccm and 30 sccm. The rate of ionization of $SiO_2$(25 sccm) decreases more than that of $SiO_2$(30 sccm), and then the generation of electrons decreases and the conductivity of $SiO_2$(25 sccm) is low. Relatively, the conductivity of $SiO_2$(30 sccm) increases because of the high rate of ionization of argon gases. Therefore, the insulating performance of $SiO_2$(25 sccm) is superior to that of $SiO_2$(30 sccm) because of the high potential barrier of $SiO_2$(25 sccm). The $ZTO/SiO_2$ transistors are prepared to research the $CO_2$ gas sensitivity. The stability of the transistor of $ZTO/SiO_2$(25 sccm) as a high insulator is superior owing to the high potential barrier. It is confirmed that the electrical properties of the insulator in transistor devices is an important factor to detect gases.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.11
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• pp.15-19
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• 2007

This paper reports the effects of Ar ion beam surface treatment on a $SiO_2$ dielectric layer in organic thin film transistors. We compared the electrical properties of pentacene-based OTFTs, treated by $O_2$ plasma or Ar ion beam treatments and characterized the states of the surface of the dielectric by using atomic force microscopy and X-ray photoelectron spectroscopy. For the sample which received $O_2$ plasma treatment, the mobility increased significantly but the on/off current ratio was found very low. The Ar ion beam-treated sample showed a very high on/off current ratio as well as a moderately improved mobility. XPS data taken from the dielectric surfaces after each of treatments exhibit that the ratio of between Si-O bonds and O-Si-O bonds was much higher in the $O_2$ plasma treated surface than in the Ar ion beam treated surface. We believe that our surface treatment using an inert gas, Ar, carried out an effective surface cleaning while keeping surface damage very low, and also the improved device performances was achieved as a consequence of improved surface condition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.11-11
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• 2010

Thin-film-transistors (TFTs) that can be deposited at low temperature have recently attracted lots of applications such as sensors, solar cell and displays, because of the great flexible electronics and transparent. Transparent and flexible transistors are being required that high mobility and large-area uniformity at low temperature [1]. But, unfortunately most of TFT structures are used to be $SiO_2$ as gate dielectric layer. The $SiO_2$ has disadvantaged that it is required to high driving voltage to achieve the same operating efficiency compared with other high-k materials and its thickness is thicker than high-k materials [2]. To solve this problem, we find lots of high-k materials as $HfO_2$, $ZrO_2$, $SiN_x$, $TiO_2$, $Al_2O_3$. Among the High-k materials, $Al_2O_3$ is one of the outstanding materials due to its properties are high dielectric constant ( ~9 ), relatively low leakage current, wide bandgap ( 8.7 eV ) and good device stability. For the realization of flexible displays, all processes should be performed at very low temperatures, but low temperature $Al_2O_3$ grown by sputtering showed deteriorated electrical performance. Further decrease in growth temperature induces a high density of charge traps in the gate oxide/channel. This study investigated the effect of growth temperatures of ALD grown $Al_2O_3$ layers on the TFT device performance. The ALD deposition showed high conformal and defect-free dielectric layers at low temperature compared with other deposition equipments [2]. After ITO was wet-chemically etched with HCl : $HNO_3$ = 3:1, $Al_2O_3$ layer was deposited by ALD at various growth temperatures or lift-off process. Amorphous InGaZnO channel layers were deposited by rf magnetron sputtering at a working pressure of 3 mTorr and $O_2$/Ar (1/29 sccm). The electrodes were formed with electron-beam evaporated Ti (30 nm) and Au (70 nm) bilayer. The TFT devices were heat-treated in a furnace at $300^{\circ}C$ and nitrogen atmosphere for 1 hour by rapid thermal treatment. The electrical properties of the oxide TFTs were measured using semiconductor parameter analyzer (4145B), and LCR meter.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.1
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• pp.17-22
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• 2011

ZnO-based thin-film transistors (TFTs) have been fabricated and the mechanical characteristics of electric circuits, such as stress, strain, and deformation are analyzed by the finite element method (FEM). In this study, a mechanical-stability design guide for such systems is proposed; this design takes into account the stress and deformation of the bridge to estimate the stress distribution in an $SiO_2$ film with 0 to 5% stretched on 0.5-${\mu}m$-thick. The predicted buckle amplitude of $SiO_2$ bridges agrees well with experimental results within 0.5% error. The stress and strain at the contact point between bridges and a pad were measured in a previous structural analysis. These structural analysis suggest that the numerical measurement of deformation, SU-8 coating thickness for Neutral Mechanical Plane (NMP) and ITO electrode size on a dielectric layer was useful in enhancing the structural and electrical stabilities.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.1
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• pp.1-7
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• 2012

We have developed a new gate driver circuit for liquid crystal displays using oxide thin-film transistors (TFTs). In the new gate driver, negative gate bias is applied to turn off the oxide TFTs because the oxide TFT occasionally has negative threshold voltage (VT). In addition, we employed three parallel pull-down TFTs that are turned on in turns to enhance the stability. SPICE simulation showed that the proposed circuit worked successfully covering the VT range of -3 V ~ +6 V And fabrication results confirmed stable operation of the new circuit using oxide TFTs.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.594-600
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• 2014

A threshold voltage compensation pixel circuit was developed for active-matrix organic light emitting diodes (AMOLEDs) using amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO-TFTs). Oxide TFTs are n-channel TFTs; therefore, we developed a circuit for the n-channel TFT characteristics. The proposed pixel circuit was verified and proved by circuit analysis and circuit simulations. The proposed circuit was able to compensate for the threshold voltage variations of the drive TFT in AMOLEDs. The error rate of the OLED current for a threshold voltage change of 3 V was as low as 1.5%.

• 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.

• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.539-542
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• 2011

Thin-film transistors (TFTs) are fabricated using an amorphous indium gallium zinc oxide (a-IGZO) channel layer by rf-magnetron sputtering. Oxygen partial pressure significantly changed the transfer characteristics of a-IGZO TFTs. Measurements performed on a-IGZO TFT show the change of threshold voltage in the transistor channel layer and electrical properties with varying $O_2$ ratios. The device performance is significantly affected by adjusting the $O_2$ ratio. This ratio is closely related with the modulation generation by reducing the localized trapping carriers and defect centers at the interface or in the channel layer.