• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.8
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• pp.491-495
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• 2017

We investigated solution-processed indium-zinc oxide (IZO) thin-film transistors (TFTs) by inserting a 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) buffer layer. This buffer layer efficiently tuned the energy level between the semiconducting oxide channel and metal electrode by increasing charge extraction, thereby enhancing the overall device performance: the IZO TFT with embedded PBD layer (thickness: 5 nm; width: $2,000{\mu}m$; length: $200{\mu}m$) exhibited a field-effect mobility of $1.31cm^2V^{-1}s^{-1}$, threshold voltage of 0.12 V, subthreshold swing of $0.87V\;decade^{-1}$, and on/off current ratio of $9.28{\times}10^5$.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1351-1355
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• 2018

The photocurrent characteristics of zinc-oxide (ZnO) thin-film transistors (TFTs) prepared using radio-frequency sputtering and spin-coating methods were investigated. Various characterization methods were used to compare the physical and the chemical properties of the sputtered and the spin-coated ZnO films. X-ray photoelectron spectroscopy was used to investigate the chemical composition and state of the ZnO films. The transmittance and the optical band gap were measured by using UV-vis spectrometry. The crystal structures of the prepared ZnO films were examined by using an X-ray diffractometer, and the surfaces of the films were investigated by using scanning electron microscopy. ZnO TFTs were prepared using both sputter and solution processes, both of which showed photocurrent characteristics when illuminated by light. The sputtered ZnO TFTs had a photoresponsivity of 3.08 mA/W under illumination with 405-nm light while the solution-processed ZnO TFTs had a photoresponsivity of 5.56 mA/W. This study provides useful information for the development of optoelectronics based on ZnO.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1002-1004
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• 2009

Solution-processed indium-gallium-zinc-oxide thin-film transistors were fabricated by sol-gel method. By a combinatorial study of InGaZnO multi-component system, optimum molar ratio of In, Ga, and Zn has been selected. By adjusting the In:Ga:Zn molar ratio, TFTs with field-effect mobility of 0.5 ~ 1.5 $cm^2$/V-s, threshold voltage of -5 ~ 5 V, and subthreshold slope of 1.5 ~ 2.5 V/decade were achieved.

• Journal of the Semiconductor & Display Technology
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• v.13 no.3
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• pp.35-38
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• 2014

Flat panel displays fabricated on glass substrate use amorphous Si for data processing circuit. Recent progress in display technology requires a new material to replace the amorphous Si, and ZnO is a good candidate. ZnO is a wide bandgap (3.3 eV) semiconductor with high mobility and good optical transparency. ZnO is usually grown by sputtering using ZnO ceramic target. However, ceramic target is more expensive than metal target, and making large area target is very difficult. In this work we studied characteristics of ZnO thin-film transistor grown by rf sputtering using Zn metal target and $CO_2$. ZnO film was grown at $450^{\circ}C$ substrate temperature, with -70 V substrate bias voltage applied. By using these methods, our ZnO TFT showed $5.2cm^2/Vsec$ mobility, $3{\times}10^6$ on-off ratio, and -7 V threshold voltage.

• Transactions on Electrical and Electronic Materials
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• v.12 no.6
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• pp.271-274
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• 2011

Screen-printed source and drain electrodes were used for a spin-coated and inkjet-processed zinc-tin oxide (ZTO) TFTs for the first time. Source and drain were silver nanoparticles. Channel length was patterned using screen printing technology. Different silver nanoinks and process parameters were tested to find optimal source and drain contacts Relatively good electrical properties of a screen-printed inkjet-processed oxide TFT were obtained as follows; a mobility of 1.20 $cm^2$/Vs, an on-off current ratio of $10^6$, a Vth of 5.4 V and a subthreshold swing of 1.5 V/dec.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1586-1589
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• 2009

We investigated the influence of chemical compositions of gallium and indium cations on the performance of solgel derived amorphous gallium indium zinc oxide (a-GIZO) based thin-film transistors (TFTs). Systematical composition study allows us to understand the solutionprocessed a-GIZO TFTs. Understanding of the compositional influence can be utilized for tailoring the solution processed amorphous oxide TFTs for the specific applications.

• Transactions on Electrical and Electronic Materials
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• v.16 no.2
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• pp.62-64
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• 2015

We have investigated zinc tin oxide (ZTO) thin films under various silicon ratios. ZTO TFTs were fabricated by solution processing with the bottom gate structure. Furthermore, annealing process was performed at different temperatures in various annealing conditions, such as air, vacuum and wet ambient. Completed fabrication of ZTO TFT, and the performance of TFT has been compared depending on the annealing conditions by measuring the transfer curve. In addition, structure in ZTO thin films has been investigated by X-ray diffraction spectroscopy (XRD) and Scanning electron microscope (SEM). It is confirmed that the electrical performance of ZTO TFTs are improved by adopting optimized annealing conditions. Optimized annealing condition has been found for obtaining high mobility.

• Transactions on Electrical and Electronic Materials
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• v.18 no.3
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• pp.141-143
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• 2017

Novel structured thin film transistors (TFTs) of amorphous silicon zinc tin oxide (a-SZTO) were designed and fabricated with a thin metal layer between the source and drain electrodes. A SZTO channel was annealed at $500^{\circ}C$. A Ti/Au electrode was used on the SZTO channel. Metals are deposited between the source and drain in this novel structured TFTs. The mobility of the was improved from $14.77cm^2/Vs$ to $35.59cm^2/Vs$ simply by adopting the novel structure without changing any other processing parameters, such as annealing condition, sputtering power or processing pressure. In addition, stability was improved under the positive bias thermal stress and negative bias thermal stress applied to the novel structured TFTs. Finally, this novel structured TFT was observed to be less affected by back-channel effect.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.257-257
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• 2011

The amorphous indium-gallium-zinc-oxide (a-IGZO) materials for use in high performance display research fields are strongly investigated due to its good performance, such as high mobility and better transparency. However, the stability of a-IGZO materials is increasingly becoming one of critical issues due to the sub-gap electron trap sites induced by rough interfaces during deposition processing. It is well-known that the threshold voltage shift is related to interface roughness and oxygen vacancy formed by breaking weak chemical bonds. Here, we report the better properties of transparent oxide transistors by reducing the threshold voltage shift with an external rf plasma supported magnetron sputtering system. Mainly, our sputtering method causes the surface of sample to be sleek, so that it prevents the formation of various defects, such as shallow electron trap sites in the interface. External rf power was applied from 0 to 50W during RF sputtering process to enhance the stability of our oxide transistor without having a large voltage shift. To observe the effects of external rf-plasma source on the properties of our devices, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) are carried out to observe surface roughness and morphology of sputtered thin film. In addition, typical electrical properties, such as I-V characteristics are analyzed.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.479-479
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• 2011

Flexible inverters based on complementary thin-film transistor (CTFTs) are important because they have low power consumption and other advantages over single type TFT inverters. In addition, integrated CTFTs in flexible electronic circuits on low-cost, large area and mechanically flexible substrates have potentials in various applications such as radio-frequency identification tags (RFIDs), sensors, and backplanes for flexible displays. In this work, we introduce flexible complementary inverters using pentacene and amorphous indium gallium zinc oxide (IGZO) for the p-channel and n-channel, respectively. The CTFTs were fabricated on polyimide (PI) substrate. Firstly, a thin poly-4-vinyl phenol (PVP) layer was spin coated on PI substrate to make a smooth surface with rms surface roughness of 0.3 nm, which was required to grow high quality IGZO layers. Then, Ni gate electrode was deposited on the PVP layer by e-beam evaporator. 400-nm-thick PVP and 20-nm-thick ALD Al2O3 dielectric was deposited in sequence as a double gate dielectric layer for high flexibility and low leakage current. Then, IGZO and pentacene semiconductor layers were deposited by rf sputter and thermal evaporator, respectively, using shadow masks. Finally, Al and Au source/drain electrodes of 70 nm were respectively deposited on each semiconductor layer using shadow masks by thermal evaporator. Basic electrical characteristics of individual transistors and the whole CTFTs were measured by a semiconductor parameter analyzer (HP4145B, Agilent Technologies) at room temperature in the dark. Performance of those devices then was measured under static and dynamic mechanical deformation. Effects of cyclic bending were also examined. The voltage transfer characteristics (Vout- Vin) and voltage gain (-dVout/dVin) of flexible inverter circuit were analyzed and the effects of mechanical bending will be discussed in detail.