AVS2013 Session TC-TuP: Transparent Conductors and Printable Electronics Poster Session
Time Period TuP Sessions | Topic TC Sessions | Time Periods | Topics | AVS2013 Schedule
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TC-TuP-1 Solution Processed Oxide and TFT Application by UV Treatment
J Park, J.-H. Yang, C.-S. Hwang (ETRI, Republic of Korea) Recently transparent semiconducting oxides are quite interesting due to their novel properties and intensive applications , for example, transparent flexible display and photovoltaics. Among them, zinc tin oxide is a typical amorphous semiconducting film which can be used as an active layer in the thin film transistor without any rare elements like In or Ga. For the practical reason, the solution process can be a promising way to extend these smart oxide materials into the everyday like applications. We applied a precursor-based solution process to make an amorphous semiconducting Zinc Tin Oxide film and combined UV-based post-treatment to enhance their physical and chemical properties at the moderate tempratures. The electrical, optical properties will be presented and explained on the physical and chemical analysis. |
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TC-TuP-2 A Universal Method of Producing Transparent Electrodes Using Wide-Bandgap Materials: Direct Ohmic Contact to p-AlGaN
Hee-Dong Kim, SukWon Kim, KyoungHeon Kim, SuJin Kim (Korea University, Republic of Korea); Moon-Deock Kim (Chungnam National University, Republic of Korea); TaeGeun Kim (Korea University, Republic of Korea) Indium-doped tin oxide (ITO) is the most popular transparent conductive electrodes (TCEs) used in flat screen displays and lighting technologies for decades. However, due to indium's limited supply and increasing cost, there has been a big push for many years to find alternatives or replacements of ITO (i.e., indium-free TCEs); many scientist and engineers have been working with zinc oxide and other metal-oxide materials but this area still remains quite challenging. Here we worked towards something different, developing new ways to give a current path between the TCEs using ordinary wide-bandgap materials and p-(Al)GaN layers via conducting filaments (CFs), which can be formed using electrical breakdown (or forming) processes, for ultraviolet light-emitting diodes (UV LEDs). UV LED is one of the eco-friendly optical sources for different wavelengths in the UV A to C regimes (200–400 nm), useful for various applications including sterilization and high color rendering index lighting. However, currently, the external quantum efficiency of the UV LED, particularly in UV-C bands, is extremely low (3-11%). One of the primary reasons for this low efficiency is a large absorption in narrow-bandgap contact layers for ohmic contact. To fundamentally solve this problem, we should obtain a direct ohmic contact to the p-AlGaN layers using UV-transparent conductive electrodes, as depicted in the right figure below. However, with conventional ohmic methods, it is almost impossible to make such contact and therefore no report has been made so far. In this article, we present a universal method of producing transparent electrodes with high conductivity and high optical transmittance in the UV A to C regimes (as well as visible-to-infrared regimes) using electrical breakdown to form CFs providing a current path between the TCEs and the semiconductor, which leads to a large reduction in their contact resistance. As a result, we found the contact resistance between the TCEs and the p-GaN layers (or p-AlGaN layers) to be on the order of 10-5 Ω·cm2 (or 10-3 Ω·cm2) while optical transmittance was maintained at up to 95% for the AlN-based TCEs at 250 nm. |
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TC-TuP-3 High Frequency Characteristics of Inkjet-Printed Copper Circuits Sintered by Atmospheric-Pressure Plasma
Kwang-Seok Kim, Kwang-Ho Jung, Bum-Geun Park, Seung-Boo Jung (Sungkyunkwan University, Republic of Korea) Inkjet printing has been developed as an innovative alternative to conventional photolithography and etching process for production of conductive circuits, due to its low cost, high resolution, and the ease of mass production. However, there are still impediments for inkjet printing to be utilized to microwave and millimeter-wave applications. Most of recent studies for circuit construction have focused on the conductivity or some mechanical properties of inkjet-printed circuits while their high frequency performance has been rarely investigated. Herein, we evaluated the signal transmission properties of the inkjet-printed circuits at high frequency. Conductive nanoink containing copper nanoparticles was printed onto a polyimide substrate, and it was sintered by atmospheric-pressure plasma (APP). Plasma power, treatment time and gas flows were varied to investigate the influence of APP parameters on the high frequency characteristics of the inkjet-printed circuits. The microstructural evolution and thickness profiles of the inkjet-printed circuits were analyzed by field emission scanning electron spectroscopy and three-dimensional nano-scan view, respectively. A network analyzer and Cascade's probe system in the frequency range of 20 MHz to 20 GHz were employed to measure scattering-parameters of the inkjet-printed circuits. The experimental results showed that the high-frequency signal transmission properties of the inkjet-printed circuits sintered by APP were affected by the microstructural evolution depending on the APP treatment conditions and the edge-shape control of printed structures. |
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TC-TuP-4 Bending Properties of In and Ga Doped Zinc Oxide Films Deposited on Plastic Substrates by Magnetron Sputtering
Koichi Nagamoto, Takeshi Kondo (LINTEC Corporation, Japan); Kiyoshi Ishii (Utsunomiya University, Japan) Transparent conductive oxides (TCO) on polymer substrates are prospected as a key material for next-generation devices such as flexible displays and photovoltaics. The advantages of polymer substrates include light-weight, low cost, a multiplicity of materials with tailored properties, shock absorption and highly flexibility. However, polymer substrates also have disadvantages such as low heat resistance and large thermal expansion coefficient compared with glass substrates. A main challenge for an efficient TCO on polymer substrate is not only to choose conductive oxide materials having capability of growing at low substrate temperature, but also to develop a deposition processes in order to obtain good electrical characteristics. Thus, in this study structural, electrical and optical properties of highly transparent conductive polycrystalline Ga-doped ZnO (GZO) and In, Ga-doped ZnO (IGZO) films deposited on plastic substrates at below 100 °C by magnetron sputtering were investigated. The dependences of crystal structure, electrical and optical properties of the GZO and IGZO films on plastic substrates have been systematically studied. The surfaces of plastic substrates and optically properties were controlled by coating buffer layers (CBLs). The aim of this study is to investigate the effect of surface roughness of plastic substrates on characteristics of GZO and IGZO films of less than 150 nm thickness, such as structural and electrical characteristics. Then optically properties of GZO and IGZO films, for example transmittance, reflectance, yellow index, haze, a* and b* value, were depend on GZO and IGZO films thickness and CBLs. The GZO and IGZO films in the thicknesses range from 20 to 120 nm were prepared by magnetron sputtering. The resistivity and average transmittance in the visible wavelength region of GZO films of 120 nm thickness on plastic substrates were 1.0 x 10-3 ohm·cm and more than 85 %, respectively. |
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TC-TuP-5 Influence of Rapid Thermal Annealing Treatment on Various Properties of Texture-Etched Al- or Ga-Doped ZnO Thin Films Deposited by Magnetron Sputtering
Tadatsugu Minami, Jun-ichi Nomoto, Toshihiro Miyata, Toshinori Yamanaka (Kanazawa Institute of Technology, Japan) This paper describes an investigation of the influence of a rapid thermal annealing (RTA) treatment on various properties of transparent conducting Al- or Ga-doped ZnO (AZO or GZO) thin films that was conducted in an effort to develop thin-film transparent electrodes suitable for thin-film solar cell applications. These doped ZnO thin films were deposited by an r.f. power superimposed d.c. magnetron sputtering deposition using AZO or GZO target : prepared with Al2O3 contents of 0.5-2 wt.% or Ga2O3 contents of 0.5-5.7 wt.%, respectively. The optical and electrical properties and texture-etched surface structures as well as the stability of electrical properties after use for long terms in moist environment in these thin films were found to be considerably influenced after heat treatment with RTA at 500oC for 5 min in air. In particular, the obtained electrical properties in these thin films were considerably dependent on the RTA treatment conditions as well as the kind and content of impurity doped into the films. For example, the heat treatment with RTA always decreased the carrier concentration in both the AZO and GZO films, irrespective of the doped impurity content, whereas the resulting carrier concentration in as-deposited AZO and GZO thin films increased as the impurity content doped into the films was increased. In addition, the Hall mobilities in both the AZO and GZO films doped with impurity contents up to approximately 1.25 at.% always decreased after heat treatment with RTA, which is in contrast to the slight increase of the Hall mobilities exhibited in films doped with an impurity content above approximately 1.5 at.%. The etch pit size developed in AZO and GZO films that were surface textured by wet-chemical etching in 0.2 mol./l HCl at 25oC tended to increase as the content of impurity doped in the films was increased up to approximately 2.5 at.%; however, the etch pit size obtained in GZO films decreased as this content was increased further. It should be noted that the heat treatment with RTA resulted in considerably enhanced etch pit size in these films, irrespective of the kind and content of doped impurity. As a result, in the films that were wet-chemically etched after being heat treated with RTA, the transmittance and the haze value in the near infrared range of 800-1200nm both increased as the size of the etch pits increased. It should be noted that the improvement in the transmittance and the haze value obtained in texture-etched AZO and GZO thin films heat treated with RTA is sufficient to enable the use of the surface textured these films described above for thin-film transparent electrode applications in thin-film solar cells. |