• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.471-471
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• 2013

Highly stable and high performance amorphous oxide semiconductor thin film transistors (TFTs) were fabricated using 4-mercaptophenol (4MP) doped ZnO by atomic layer deposition (ALD). The 4 MP concentration in ZnO films were varied from 1.7% to 5.6% by controlling Zn: 4MP pulses. The carrier concentrations in ZnO thin films were controlled from $1.017{\times}10^{20}$/$cm^3$ to $2,903{\times}10^{14}$/$cm^3$ with appropriate amount of 4MP doping. The 4.8% 4MP doped ZnO TFT revealed good device mobility performance of $8.4cm^2V-1s-1$ and on/off current ratio of $10^6$. Such 4MP doped ZnO TFTs were stable under ambient conditions for 12 months without any apparent degradation in their electrical properties. Our result suggests that 4 MP doping can be useful technique to produce more reliable oxide semiconductor TFT.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.443-443
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• 2012

We fabricated a-IGZO TFT with AZO/Ag/AZO transparent multilayer source/drain contacts by rf magnetron sputtering. Enhanced electrical device performance of a-IGZO TFT with AZO/Ag/AZO multilayer S/D electrodes (W/L = = 400/50 mm) was achieved with a subs-threshold swing of 3.78 V/dec, a minimum off-current of 10-12 A, a threshold voltage of 1.80 V, a field effect mobility of 10.86 cm2/Vs, and an on/off ration of 9x109. It demonstrated the potential application of the AZO/Ag/AZO film as a promising S/D contact material for the fabrication of the high performance TFTs.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.1
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• pp.26-29
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• 2006

Transparent ZnO thin films were prepared by KrF pulsed laser deposition (PLD) technique and applied to a bottom-gate type thin film transistor device as an active channel layer. A high conductive crystalline Si substrate was used as an metal-like bottom gate and SiN insulating layer was then deposited by LPCVD(low pressure chemical vapour deposition). An aluminum layer was then vacuum evaporated and patterned to form a source/drain metal contact. Oxygen partial pressure and substrate temperature were varied during the ZnO PLD deposition process and their influence on the thin film properties were investigated by X-ray diffraction(XRD) and Hall-van der Pauw method. Optical transparency of the ZnO thin film was analyzed by UV-visible phometer. The resulting ZnO-TFT devices showed an on-off ration of $10^6$ and field effect mobility of 2.4-6.1 $cm^2/V{\cdot}s$.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.12
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• pp.559-561
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• 2003

We report a new excimer laser annealing method which successfully results in a single grain boundary formation in the channel of polycrystalline silicon thin film transistor. The proposed method is based on lateral grain growth and employs aluminum patterns which act as selective beam mask and lateral heat sink. The maximum grain size obtained by the proposed method is about 1.6${\mu}{\textrm}{m}$ in the length. The grainboundaries should be arranged parallel with the direction of current flow for the best device performance, so we propose a new device fabrication method and a new poly-Si TFT structure. Poly-Si TFT fabricated by the proposed method exhibits considerably improved electrical characteristics, such as high field effect mobility exceeding 240 $cm^2$/Vsec.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.209.2-209.2
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• 2013

We proposed and fabricated zinc oxide thin-film transistors (TFTs) employing 4-mercaptophenol (4MP) doped ZnO by atomic layer deposition (ALD) that results in highly stable and high performance. The 4MP concentration in ZnO films were varied from 1.7% to 5.6% by controlling Zn:4MP pulses. The n-type carrier concentrations in ZnO thin films were controlled from $1.017{\times}10^{20}/cm^3$ to $2.903{\times}10^{17}/cm^3$ with appropriate amount of 4MP doping. The 4.8% 4MP doped ZnO TFT revealed good device mobility performance of 8.4 $cm^2/Vs$ and the on/off current ratio of 106. Such 4MP doped ZnO TFTs exhibited relatively good stability (${\Delta}V_{th}$: 2.4 V) under positive bias-temperature stress while the TFTs with only ZnO showed a 4.3 ${\Delta}V_{th}$ shift, respectively.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.149-152
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• 2005

We present the characterization of poly-Si TFT fabricated below on Plastic Substrate below $170^{\circ}C$ on plastic substrate using excimer laser crystallization of Xe sputtered Si films. Gate insulator with a breakdown field exceeding 8 MV/cm was deposited by using inductively coupled plasma CVD. Finally, we successfully fabricate TFT with a electron field-effect mobility value greater than $290\;cm^2/Vsec$.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.37-37
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• 2010

Silicate-silsesquioxane or siloxane-silsesquioxane hybrid thin films are strong candidates as matrix materials for ultra low dielectric constant (low-k) thin films. We synthesized the silicate-silsesquioxane hybrid resins from tetraethoxyorthosilicate (TEOS) and methyltrimethoxysilane (MTMS) through hydrolysis and condensation polymerization by changing their molar ratios ([TEOS]:[MTMS] = 7:3, 5:5, and 3:7), spin-coating on Si(100) wafers. In the case of [TEOS]:[MTMS] 7:3, the dielectric permittivity value of the resultant thin film was measured at 4.30, exceeding that of the thermal oxide (3.9). This high value was thought to be due to Si-OH groups inside the film and more extensive studies were performed in terms of electronic, ionic, and orientational polarizations using Debye equation. The relationship between the mechanical properties and the synthetic conditions of the silicate-silsesquioxane precursors was also investigated. The synthetic conditions of the low-k films have to be chosen to meet both the low orientational polarization and high mechanical properties requirements. In addition, we have investigated a new solution-based approach to the synthesis of semiconducting chalcogenide films for use in thin-film transistor (TFT) devices, in an attempt to develop a simple and robust solution process for the synthesis of inorganic semiconductors. Our material design strategy is to use a sol-gel reaction to carry out the deposition of a spin-coated CdS film, which can then be converted to a xerogel material. These devices were found to exhibit n-channel TFT characteristics with an excellent field-effect mobility (a saturation mobility of ${\sim}\;48\;cm^2V^{-1}s^{-1}$) and low voltage operation (< 5 V). These results show that these semiconducting thin film materials can be used in low-cost and high-performance printable electronics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.467-468
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• 2006

We report on the fabrication of P3HT-based thin-film transistors (TFT) that consist of indium-zinc-oxide (IZO), PVP (poly-vinyl phenol), and Ni for the source-drain (S/D) electrode, gate dielectric, and gate electrode, respectively. The IZO S/D electrodes of which the work function is well matched to that of P3HT were deposited on a P3HT channel by thermal evaporation of IZO and showed a moderately low but still effective transmittance of ~25% in the visible range along with a good sheet resistance of ${\sim}60{\Omega}/{\square}$. The maximum saturation current of our P3HT-based TFT was about $15{\mu}A$ at a gate bias of -40V showing a high field effect mobility of $0.05cm^2/Vs$ in the dark, and the on/off current ratio of our TFT was about $5{\times}10^5$. It is concluded that jointly adopting IZO for the S/D electrode and PVP for gate dielectric realizes a high-quality P3HT-based TFT.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.341-341
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• 2012

Recently, oxide semi-conductor materials have been investigated as promising candidates replacing a-Si:H and poly-Si semiconductor because they have some advantages of a room-temperature process, low-cost, high performance and various applications in flexible and transparent electronics. Particularly, amorphous indium-gallium-zinc-oxide (a-IGZO) is an interesting semiconductor material for use in flexible thin film transistor (TFT) fabrication due to the high carrier mobility and low deposition temperatures. In this work, we demonstrated improvement of flexibility in IGZO TFTs, which were fabricated on polyimide (PI) substrate. At first, a thin poly-4vinyl phenol (PVP) layer was spin coated on PI substrate for making a smooth surface up to 0.3 nm, which was required to form high quality active layer. Then, Ni gate electrode of 100 nm was deposited on the bare PVP layer by e-beam evaporator using a shadow mask. The PVP and $Al_2O_3$ layers with different thicknesses were used for organic/inorganic multi gate dielectric, which were formed by spin coater and atomic layer deposition (ALD), respectively, at $200^{\circ}C$. 70 nm IGZO semiconductor layer and 70 nm Al source/drain electrodes were respectively deposited by RF magnetron sputter and thermal evaporator using shadow masks. Then, IGZO layer was annealed on a hotplate at $200^{\circ}C$ for 1 hour. Standard electrical characteristics of transistors were measured by a semiconductor parameter analyzer at room temperature in the dark and performance of devices then was also evaluated under static and dynamic mechanical deformation. The IGZO TFTs incorporating hybrid gate dielectrics showed a high flexibility compared to the device with single structural gate dielectrics. The effects of mechanical deformation on the TFT characteristics will be discussed in detail.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.151-151
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• 2009

Recently, there has been increasing interest in amorphous oxide semiconductors to find alternative materials for an amorphous silicon or organic semiconductor layer as a channel in thin film transistors(TFTs) for transparent electronic devices owing to their high mobility and low photo-sensitivity. The fabriction of amorphous oxide-based TFTs at room temperature on plastic substrates is a key technology to realize transparent flexible electronics. Amorphous oxides allows for controllable conductivity, which permits it to be used both as a transparent semiconductor or conductor, and so to be used both as active and source/drain layers in TFTs. One of the materials that is being responsible for this revolution in the electronics is indium-zinc-tin oxide(IZTO). Since this is relatively new material, it is important to study the properties of room-temperature deposited IZTO thin films and exploration in a possible integration of the material in flexible TFT devices. In this research, we deposited IZTO thin films on polyethylene naphthalate substrate at room temperature by using magnetron sputtering system and investigated their properties. Furthermore, we revealed the fabrication and characteristics of top-gate-type transparent TFTs with IZTO layers, seen in Fig. 1. The experimental results show that by varying the oxygen flow rate during deposition, it can be prepared the IZTO thin films of two-types; One a conductive film that exhibits a resistivity of $2\times10^{-4}$ ohm${\cdot}$cm; the other, semiconductor film with a resistivity of 9 ohm${\cdot}$cm. The TFT devices with IZTO layers are optically transparent in visible region and operate in enhancement mode. The threshold voltage, field effect mobility, on-off current ratio, and sub-threshold slope of the TFT are -0.5 V, $7.2\;cm^2/Vs$, $\sim10^7$ and 0.2 V/decade, respectively. These results will contribute to applications of select TFT to transparent flexible electronics.