• Title/Summary/Keyword: Field Effect Mobility

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The Characteristics of Amorphous-Oxide-Semiconductor Thin-Film-Transistors According to the Active-Layer Structure (능동층 구조에 따른 비정질산화물반도체 박막트랜지스터의 특성)

  • Lee, Ho-Nyeon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.10 no.7
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    • pp.1489-1496
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    • 2009
  • Amorphous indium-gallium-zinc-oxide thin-film-transistors (TFTs) were modeled successfully. Dependence of TFT characteristics on structure, thickness, and equilibrium electron-density of the active layer was studied. For mono-active-layer TFTs, a thinner active layer had higher field-effect mobility. Threshold voltage showed the smallest absolute value for the 20 nm active-layer. Subthreshold swing showed almost no dependence on active-layer thickness. For the double-active-layer case, better switching performances were obtained for TFTs with bottom active layers with higher equilibrium electron density. TFTs with thinner active layers had higher mobility. Threshold voltage shifted in the minus direction as a function of the increase in the thickness of the layer with higher equilibrium electron-density. Subthreshold swing showed almost no dependence on active-layer structure. These data will be useful in optimizing the structure, the thickness, and the doping ratio of the active layers of oxide-semiconductor TFTs.

Study on the Electrical Characteristics of Solution-processed ZrInZnO Thin-film Transistors (액상공정으로 제작된 ZrInZnO 박막 트랜지스터의 전기적 특성에 관한 연구)

  • Jeong, Tae-Hoon;Kim, Si-Joon;Yoon, Doo-Hyun;Jeong, Woong-Hee;Kim, Dong-Lim;Lim, Hyun-Soo;Kim, Hyun-Jae
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.24 no.6
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    • pp.458-462
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    • 2011
  • Soution-processed ZrInZnO (ZIZO) thin-film transistors (TFTs) with varying Zr content were fabricated. The ZIZO TFT (Zr=20 at. %/Zn) has an optimal performance with the saturation field effect mobility of 0.77 $cm^2/Vs$, the threshold voltage (Vth) of 2.1 V, the on/off ratio of $4.95{\times}10^6$, and subthreshold swing (S.S) of 0.73 V/decade. Using this optimized ZIZO TFT, the positive and negative gate bias stress according to annealing temperature was also investigated. While the Vth shifts dramatically after 1,000 s of both gate bias stresses, variations in the S.S are negligible. It suggests that electrons or holes are tem porarily trapped in the gate insulator, the semiconductor, or the interface between both layers.

Improvement in the bias stability of zinc oxide thin-film transistors using an $O_2$ plasma-treated silicon nitride insulator

  • Kim, Ung-Seon;Mun, Yeon-Geon;Gwon, Tae-Seok;Park, Jong-Wan
    • Proceedings of the Korean Vacuum Society Conference
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    • 2010.02a
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    • pp.180-180
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    • 2010
  • Thin film transistors (TFTs) based on oxide semiconductors have emerged as a promising technology, particularly for active-matrix TFT-based backplanes. Currently, an amorphous oxide semiconductor, such as InGaZnO, has been adopted as the channel layer due to its higher electron mobility. However, accurate and repeatable control of this complex material in mass production is not easy. Therefore, simpler polycrystalline materials, such as ZnO and $SnO_2$, remain possible candidates as the channel layer. Inparticular, ZnO-based TFTs have attracted considerable attention, because of their superior properties that include wide bandgap (3.37eV), transparency, and high field effect mobility when compared with conventional amorphous silicon and polycrystalline silicon TFTs. There are some technical challenges to overcome to achieve manufacturability of ZnO-based TFTs. One of the problems, the stability of ZnO-based TFTs, is as yet unsolved since ZnO-based TFTs usually contain defects in the ZnO channel layer and deep level defects in the channel/dielectric interface that cause problems in device operation. The quality of the interface between the channel and dielectric plays a crucial role in transistor performance, and several insulators have been reported that reduce the number of defects in the channel and the interfacial charge trap defects. Additionally, ZnO TFTs using a high quality interface fabricated by a two step atomic layer deposition (ALD) process showed improvement in device performance In this study, we report the fabrication of high performance ZnO TFTs with a $Si_3N_4$ gate insulator treated using plasma. The interface treatment using electron cyclotron resonance (ECR) $O_2$ plasma improves the interface quality by lowering the interface trap density. This process can be easily adapted for industrial applications because the device structure and fabrication process in this paper are compatible with those of a-Si TFTs.

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Solution-processed Dielectric and Quantum Dot Thin Films for Electronic and Photonic Applications

  • Jeong, Hyeon-Dam
    • 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.

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Transparent and Flexible All-Organic Multi-Functional Sensing Devices Based on Field-effect Transistor Structure

  • Trung, Tran Quang;Tien, Nguyen Thanh;Seol, Young-Gug;Lee, Nae-Eung
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.02a
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    • pp.491-491
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    • 2011
  • Transparent and flexible electronic devices that are light-weight, unbreakable, low power consumption, optically transparent, and mechanical flexible possibly have great potential in new applications of digital gadgets. Potential applications include transparent displays, heads-up display, sensor, and artificial skin. Recent reports on transparent and flexible field-effect transistors (tf-FETs) have focused on improving mechanical properties, optical transmittance, and performances. Most of tf-FET devices were fabricated with transparent oxide semiconductors which mechanical flexibility is limited. And, there have been no reports of transparent and flexible all-organic tf-FETs fabricated with organic semiconductor channel, gate dielectric, gate electrode, source/drain electrode, and encapsulation for sensor applications. We present the first demonstration of transparent, flexible all-organic sensor based on multifunctional organic FETs with organic semiconductor channel, gate dielectric, and electrodes having a capability of sensing infrared (IR) radiation and mechanical strain. The key component of our device design is to integrate the poly(vinylidene fluoride-triflouroethylene) (P(VDF-TrFE) co-polymer directly into transparent and flexible OFETs as a multi-functional dielectric layer, which has both piezoelectric and pyroelectric properties. The P(VDF-TrFE) co-polumer gate dielectric has a high sensitivity to the wavelength regime over 800 nm. In particular, wavelength variations of P(VDF-TrFE) molecules coincide with wavelength range of IR radiation from human body (7000 nm ~14000 nm) so that the devices are highly sensitive with IR radiation of human body. Devices were examined by measuring IR light response at different powers. After that, we continued to measure IR response under various bending radius. AC (alternating current) gate biasing method was used to separate the response of direct pyroelectric gate dielectric and other electrical parameters such as mobility, capacitance, and contact resistance. Experiment results demonstrate that the tf-OTFT with high sensitivity to IR radiation can be applied for IR sensors.

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Silicon Oxidation in Inductively-Coupled N2O Plasma and its Effect on Polycrystalline-Silicon Thin Film Transistors (유도결합 N2O 플라즈마를 이용한 실리콘 산화막의 저온성장과 다결정 실리콘 박막 트랜지스터에의 영향)

  • Won, Man-Ho;Kim, Sung-Chul;Ahn, Jin-Hyung;Kim, Bo-Hyun;Ahn, Byung-Tae
    • Korean Journal of Materials Research
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    • v.12 no.9
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    • pp.724-728
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    • 2002
  • Inductively-coupled $N_2$O plasma was utilized to grow silicon dioxide at low temperature and applied to fabricate polycrystalline-silicon thin film transistors. At $400^{\circ}C$, the thickness of oxide was limited to 5nm and the oxide contained Si≡N and ≡Si-N-Si≡ bonds. The nitrogen incorporation improved breakdown field to 10MV/cm and reduced the interface charge density to $1.52$\times$10^{11}$ $cm^2$ with negative charge. The $N_2$O plasma gate oxide enhanced the field effect mobility of polycrystalline thin film transistor, compared to $O_2$ plasma gate oxide, due to the reduced interface charge at the $Si/SiO_2$ interface and also due to the reduced trap density at Si grain boundaries by nitrogen passivation.

Study on Basic Properties of Single Crystalline ZnO Nanowire (단결정 산화아연 나노선의 기초 물성 연구)

  • Ra, H.W.;Khan, R.;Kim, J.T.;Yeo, C.H.;Im, Y.H.
    • Journal of the Korean Vacuum Society
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    • v.18 no.4
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    • pp.259-265
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    • 2009
  • We fabricated the field effect transistor using single crystalline ZnO nanowires synthesized by a conventional thermal evaporation method and investigated their basic properties under the various conditions such as ultraviolet irradiation, reducing gas and electrolyte. The typical carrier concentration and mobility of the single crystalline ZnO nanowire with a diameter of 100 nm and length of 5 um were $1.30{\times}10^{18}cm^{-3}$ and $15.6cm^2V^{-1}s^{-1}$, respectively. The current of ZnO nanowire under ultraviolet irradiation significantly increased about 400 times higher as compared to in the darkness. In addition, the ZnO nanowire showed typical sensing characteristics for $H_2$ and CO due to well-known surface reactions and typical current-voltage characteristics under the 0.1 M NaCl electrolyte.

Crystal field splitting energy for $CdGa_2Se_4$ epilayers obtained by photocurrent measurement (광전류 측정으로부터 얻어진 $CdGa_2Se_4$ 에피레이어의 결정장 갈라짐에 대한 에너지)

  • Hong, Kwang-Joon
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2009.06a
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    • pp.144-145
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    • 2009
  • Single crystal $CdGa_2Se_4$ layers were grown on a thoroughly etched semi-insulating GaAs(100) substrate at $420^{\circ}C$ with the hot wall epitaxy (HWE) system by evaporating the poly crystal source of $CdGa_2Se_4$ at $630\;^{\circ}C$. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of single crystal $CdGa_2Se_4$ thin films measured with Hall effect by van der Pauw method are $8.27\;\times\;10^{17}\;cm^{-3}$, $345\;cm^2/V{\cdot}s$ at 293 K, respectively. The photocurrent and the absorption spectra of $CdGa_2Se_4$/SI(Semi-Insulated) GaAs(100) are measured ranging from 293 K to 10K. The temperature dependence of the energy band gap of the $CdGa_2Se_4$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g$(T) = 2.6400 eV - ($7.721\;{\times}\;10^{-4}\;eV/K)T^2$/(T + 399 K). Using the photocurrent spectra and the Hopfield quasi cubic model, the crystal field energy(${\Delta}cr$) and the spin-orbit splitting energy(${\Delta}so$) for the valence band of the $CdGa_2Se_4$ have been estimated to be 106.5 meV and 418.9 meV at 10 K, respectively. The three photocurrent peaks observed at 10 K are ascribed to the $A_1$-, $B_1$-, and $C_{11}$-exciton peaks.

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A New Approach for Practical Classification of Herbicide and for Effective Use by Two-dimensional Ordination Analysis (Two-Dimensional Ordination 분석법에 의한 제초제살초 Spectrum 분류와 효과적인 사용법)

  • Kim Soon Chul
    • Korean journal of applied entomology
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    • v.22 no.2 s.55
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    • pp.147-159
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    • 1983
  • In general, herbicides have been classified according to selectivity, mobility. time of application, methods of application, mode of action and chemical property and structure. However, there was no generally accepted classification system for practical use in the field. The primary processes affected by the majority of herbicides are the growth process through cell elongation and/or cell division, the photosynthetic process specifically the light reaction, the oxidative phosphorylation and the integrity of the membrane systems. The usual approach in the study of the mechanism by which herbicides kill or inhibit the growth of plants is to initially determine the morphological phototoxicity systems, The mechanism by which a herbicide kills a plant or suppresses its development is actually the resultant effect of primary and secondary(or side) effects. In most instances, the death of the plant is due to the secondary effects. To induce the desired response, a herbicide must be able to gain entry into the plants and once inside, to be transported within the plant to its site(s) of activity in concentrations great enough. Obstacles to the entry and movement of herbicides in plants are generally classified by leaf and soil obstacles, translocation obstacles and biochemical obstacles, and these obstacles are also strongly influenced by plant species and by environmental factors such as light, temperature, rainfall and relative humidity. And hence, in most instances, results obtained from laboratory or greenhous vary from those of field experiment. Author attempted to classify herbicides from the field experiment using the two-dimensional ordination analysis to obtain practical information for selecting effective herbicides or to choose effective herbicide combinations for increasing herbicidal efficacy or reducing the chemical cost. Based on this two-dimensional diagram, desired herbicides or combinations were selected and further investigated for the interaction effects whether these combinations are synergistic, additive or antagonistic. From the results, it was concluded that these new approach could possibly be give more comprehensive informations about effective use of herbicide than any other systems.

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Bacterial Behavior in Soil under Electric Field and its Effect on Electrokientic Bioremediation (전기장하 토양내에서 미생물 이동특성과 동전기 생물학적복원의 효과)

  • Kim, Sang-Joon;Park, Ji-Yeon;Lee, You-Jin;Yang, Ji-Won
    • KSBB Journal
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    • v.21 no.3
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    • pp.175-180
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    • 2006
  • In this study, it could be found that the microbial movement in soil under electric field mainly occurred by electrophoresis and electroosmosis. The contribution of electrophoresis on the microbial mobility and flux was generally higher than that of electroosmosis. In the electrokinetic(EK) bioremediation of a pentadecane-contaminated soil, the microbial population increased simultaneously at anode and cathode regions of the soil specimen because both electrophoresis and electroosmosis affected on the microbial movement. After initial operation, the microbial population was high in order of anode, middle, and cathode regions due to their negatively-charged surface and oxygen generation at anode. However, the uniform contaminant removal was achieved by the microbial movement with two-directionality.