• 한국정보디스플레이학회:학술대회논문집
• /
• 2007.08a
• /
• pp.904-907
• /
• 2007

We reported a simplified circuit model to investigate the interface states and the quality of a-Si film based on a MIS structure using admittance spectroscopy. The model can be employed easily to monitor the fabrication process of thin-film transistor and to obtain the important parameters.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.04a
• /
• pp.70-71
• /
• 2009

Photoelectric characteristics of a hydrogenated amorphous silicon thin film transistor(a-Si:H TFT) were obtained for the illumination from various backlight sources and the results were compared and analyzed in terms of the photon energy spectral characteristics of the backlights obtained from the integration of the multiplication of the photon energy and the spectral intensity at etch wavelength. It was possible to conclude that the absorption of illuminated backlight to a-Si:H layer and the generation of electrons and holes are mainly carried out at the wavelength less than 500nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.04a
• /
• pp.55-56
• /
• 2008

The photo leakage currents of a conventional hydrogenated amorphous silicon(a-Si:H) thin film transistor(TFT) were investigated and analyzed in the case of illumination from various lightsources such as halogen lamp, cold cathode fluorescent lamp(CCFL) backlight, and white light emitting diode(LED) backlight The photo leakage characteristics showed the apparent differences in the leakage level and in the $I_{on}/I_{off}$ ratio in spite of the similar luminances of light sources. This leakage level is expected to be related to the wavelength of the lowest intensity peak from spectral analysis of light sources.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.21 no.9
• /
• pp.844-847
• /
• 2008

The photo leakage currents of a conventional hydrogenated amorphous silicon(a-Si:H) thin film transistor(TFT) were investigated and analyzed in case of illumination from various light sources such as halogen lamp, cold cathode fluorescent lamp(CCFL) backlight, and white light emitting diode(LED) backlight. The photo leakage characteristics showed the apparent differences in the leakage level and in the $I_{on}/I_{off}$ ratio in spite of the similar luminances of light sources. This leakage level is expected to be related to the wavelength of the lowest intensity peak from the spectral characteristics of light sources.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2004.08a
• /
• pp.305-308
• /
• 2004

We present a novel process for the ultra low temperature (<150$^{\circ}C$) polycrystalline silicon (ULTPS) TFT for the flexible display applications on the plastic substrate. The sequential lateral solidification (SLS) was used for the crystallization of the amorphous silicon film deposited by rf magnetron sputtering, resulting in high mobility polycrystalline silicon (poly-Si) film. The gate dielectric was composed of thin $SiO_2$ formed by plasma oxidation and $Al_2O_3$ deposited by plasma enhanced atomic layer deposition. The breakdown field of gate dielectric on poly-Si film showed above 6.3 MV/cm. Laser activation reduced the source/drain resistance below 200 ${\Omega}$/ㅁ for n layer and 400 ${\Omega}$/ㅁ for p layer. The fabricated ULTPS TFT shows excellent performance with mobilities of 114 $cm^2$/Vs (nMOS) and 42 $cm^2$/Vs (pMOS), on/off current ratios of 4.20${\times}10^6$ (nMOS) and 5.7${\times}10^5$ (PMOS).

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.50 no.4
• /
• pp.161-168
• /
• 2001

Organic thin film transitors(TFTs) are of interest for use in broad area electronic applications. For example, in active matrix liquid crystal displays(AMLCDs), organic TFTs would allow the use of inexpensive, light-weight, flexible, and mechanically rugged plastic substrates as an alternative to the glass substrates needed for commonly used hydrogenated amorphous silicon(a-Si:H). Recently pentacene TFTs with carrier field effect, mobility as large as 2 $cm^2V^{-1}s^{-1}$ have been reported for TFTs fabricated on silicon substrates, and it is higher than that of a-Si:H. But these TFTs are fabricated on silicon wafer and $SiO_2$ was used as a gate insulator. $SiO_2$ deposition process requires a high insulator which is polyimide and photo acryl. We investigated trasfer and output characteristics of the thin film transistors having active layer of pentacene. We calculated field effect mobility and on/off ratio from transfer characteristics of pentacene thin film transistor, and measured IR absorption spectrum of polymide used as the gate dielectric layer. It was found that using the photo acryl as a gate insulator, threshold voltage decreased from -12.5 V to -7 V, field effect mobility increased from 0.012 $cm^2V^{-1}s^{-1}$ to 0.039 $cm^2V^{-1}s^{-1}$ , and on/off current ratio increased from $10^5\;to\;10^6$. It seems that TFTs using photo acryl gate insulator is apt to form channel than TFTs using polyimide gate insulator.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.53 no.5
• /
• pp.237-241
• /
• 2004

Amorphous silicon (a-Si) films are used in a broad range of solar cell, flat panel display, and sensor. Because of the greater ease of deposition and lower processing temperature, thin films are widely used for thin film transistors (TFTs). However, they have lower stability under the exposure of visible light and because of their low field effect mobility ($\mu$$_{FE}$ ) , less than 1 c $m^2$/Vs, they require a driving IC in the external circuits. On the other hand, polycrystalline silicon (poly-Si) thin films have superiority in $\mu$$_{FE}$ and optical stability in comparison to a-Si film. Many researches have been done to obtain high performance poly-Si because conventional methods such as excimer laser annealing, solid phase crystallization and metal induced crystallization have several difficulties to crystallize. In this paper, a new crystallization process using a molybdenum substrate has been proposed. As we use a flexible substrate, high temperature treatment and roll-to-roll process are possible. We have used a high temperature process above 75$0^{\circ}C$ to obtain poly-Si films on molybdenum substrates by a rapid thermal annealing (RTA) of the amorphous silicon (a-Si) layers. The properties of high temperature crystallized poly-Si studied, and poly-Si has been used for the fabrication of TFT. By this method, we are able to achieve high crystal volume fraction as well as high field effect mobility.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.26 no.5
• /
• pp.38-45
• /
• 1989

We have studied the electrical characteristics of the hydrogenated amorphous silicon (a-Si:H) ambiploar thin film transistors (TET'S)using 100ppm boron-doped a-Si:H as an active layer. The enhancement of drain current due to the double injection behavior has been observed in the p-channel operation of the TFT. The drain current decreases with time in streched exponential form when the gate voltage is positive. The result indicates that the dangling bonds created by electron accumulation show identical time dependence as the diffusion of hydrogen in the film. We observed the experimental evidence that the doping efficiency changes either when the gate bias is applied or when the light is illuminated on boron-doped a-Si:H.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.207.2-207.2
• /
• 2013

Oxide-based thin film transistors have been attempted as powerful candidates for driving circuits for active-matrix organic light-emitting diodes and transparent electronics. The oxide TFTs are based on the amorphous multi-component oxides involving zinc, indium, and/or tin elements as main cation sources. The current work employed RF sputtering in order to deposit zinc-tin oxide thin films applicable to transparent oxide thin film transistors. The deposited thin film was characterized and probed in terms of materials and devices. The physical/chemical characterizations were performed using X-ray diffraction, Atomic Force Microscopy, Spectroscopic Ellipsometry, and X-ray Photoelectron Spectroscopy. The thin film transistors were fabricated using a bottom-gated structure where thermally-grown silicon oxide layers were applied as gate-dielectric materials. The inherent properties of oxide thin films are combined with the corresponding device performances with the aim to fabricating the multi-component oxide thin films being optimized towards transparent electronics.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2006.08a
• /
• pp.529-529
• /
• 2006

Several laboratories worldwide have demonstrated the feasibility of producing amorphous silicon thin film transistor (TFT) arrays at temperatures that are sufficiently low to be compatible with flexible foils such as stainless steel or high temperature polyester. These arrays can be used to fabricate flexible high information content display prototypes using a variety of different display technologies. However, several questions must be addressed before this technology can be used for the economic commercial production of displays. These include process optimization and scale-up to address intrinsic electrical instabilities exhibited by these kinds of transistor device, and the development of appropriate techniques for the handling of flexible substrate materials with large coefficients of thermal expansion. The Flexible Display Center at Arizona State University was established in 2004 as a collaboration among industry, a number of Universities, and US Government research laboratories to focus on these issues. The goal of the FDC is to investigate the manufacturing of flexible TFT technology in order to accelerate the commercialization of flexible displays. This presentation will give a brief outline of the FDC's organization and capabilities, and review the status of efforts to fabricate amorphous silicon TFT arrays on flexible foils using a low temperature process. Together with industrial partners, these arrays are being integrated with cholesteric liquid crystal panels, electrophoretic inks, or organic electroluminescent devices to make flexible display prototypes. In addition to an overview of device stability issues, the presentation will include a discussion of challenges peculiar to the use of flexible substrates. A technique has been developed for temporarily bonding flexible substrates to rigid carrier plates so that they may be processed using conventional flat panel display manufacturing equipment. In addition, custom photolithographic equipment has been developed which permits the dynamic compensation of substrate distortions which accumulate at various process steps.