Fabrication and characterization of sol-gel-derived zinc oxide thin-film transistor (original) (raw)
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Int. J. Electrochem …, 2012
A low-cost, ultra-thin, transparency and high-quality zinc oxide (ZnO) film was successfully demonstrated as the carrier transporting and semiconducting layer for thin-film transistor (TFT) devices. The ZnO ultra-thin film with 3.7 nm in thickness was spin-coated from zinc acetate sol-gel solution under electroless condition. The film structure was characterized by atomic force microscopy and x-ray diffraction spectroscopy, respectively. Among various processing temperatures, the electrical property of the fabricated TFT verified the devices could be successfully achieved from suitable annealing temperature of 300 to 700 °C. However, the higher treatment temperature of 800 to 900 °C deteriorated the transistor property due to the loss of oxygen vacancy. The electrical properties of these ZnO-based n-type TFTs were obtained as follows: the mobility (μ sat ) ranged from 0.47 to 1.78 cm 2 V −1 s −1 , the on/off current ratio ranged from 5.7 × 10 5 to 1.6 × 10 6 , and the threshold voltage ranged from 9.7 to 17.3 V. The long-term (100 days) characterization for the evaluation of the ultra-thin ZnO TFT reliability on the mobility and on/off current ratio strongly suggested the effectiveness of solutionprocessed ultra-thin film transistors. This proposed efficient sol-gel solution method to fabricate transparent ZnO ultra-thin film was relatively simple and cost-effective technique, and could be used as a new candidate of material for next-generation electronic devices to meet the growing demand of small feature bioelectronic sensor, light emitting diode and flexible panel.
Surface and Coatings Technology, 2007
ZnO thin-film transistors (TFTs) have attracted considerable R&D interest due to their high transparency and low photosensitivity compared with typical a-Si:H TFTs. The electrical characteristics of ZnO thin films may be controlled by doping with ternary element, for instance Al, Ga, In, Mg, Zr, etc. In this study, Zn 1 − x Mg x O (x = 0 to 0.36) thin films were deposited on glass substrates by spin coating. The as-deposited films were baked at 300°C for 10 min and then annealed at 500°C for 1 h in air. The results show that, addition of Mg-species in ZnO films markedly enhanced the uniformity of film thickness and improved optical properties. The Zn 0.8 Mg 0.2 O film exhibited the best transparency of 92%, an increase of ∼ 15% over a pure ZnO film, and the rms roughness value decreased to 1.63. The Zn 1 − x Mg x O TFTs were demonstrated to have n-type enhancement behavior. The optimum device with Zn 0.8 Mg 0.2 O channel layer had a field-effect mobility of 0.1 cm 2 /V s, a threshold voltage of 6.0 V, and an on/off ratio more than 10 7 .
2018
This dissertation aims to explore film and device characteristics of zinc oxide (ZnO) based channel layers fabricated via the sol-gel spin-coating growth technique. ZnO is wide band gap semiconductor with a wide range of industrial applications and numerous electronic applications such as optoelectronics, flexible transparent electronics and sensors. ZnO films were synthesized with different number of layers by repeating the spin-coating process and then annealed at different temperatures. Micro-Raman, Photoluminescence (PL), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were used for film characterization and to investigate crystal quality of the films. The results indicated an increase in the magnitude of E2 High Raman shift as well as the near-band-edge PL peak as the annealing temperature increased. This intensification was related to the enlargement of grain size as a result of higher annealing temperature. The area under the curve ratio for UV PL over visible PL, in addition to the intensification of E2 High Raman peak, suggested higher film quality as the annealing temperature increases. However, SEM images revealed that annealing temperatures higher than 800 result in the formation of gaps between grains, causing non-continuity in the film. Bottom gate thin film transistors (TFTs) were fabricated and Current-Voltage (I-V) and Capacitance-Voltage (C-V) measurements were implemented to investigate a possible "kink-effect" (also known as the "hump-effect") in the multilayer-channel samples, due to the renowned surface oxygen chemisorption in oxide semiconductors. The measurements hint to the possibility of depletion layer formation at the ZnO-ZnO interlayerinterfaces. The kink effect disappeared after high doses of radiation, suggesting the likelihood of iv the distortion of the depletion layers due to the displacement damage. After 18 months, the kink effect in unirradiated samples remained existent and in the irradiated samples, it remained absent. Multilayer ZnO TFTs were exposed to a 60 Co radiation source and the robustness of ZnO TFTs against gamma irradiation was verified by comparing the transfer and output characteristics of TFTs and the PL of the channel layers before and after irradiation. By applying High Resolution Digital Optical Microscopy and Atomic Force Microscopy (AFM), it was found that the thickness of the ZnO was drastically influenced by the irradiation. A model was provided to explain the possible etching mechanism. Three effective medium approximations were applied to theoretically investigate the modification of the refractive index of the flexible conductive polymer matrix Poly(3,4-ethylenedioxythiophene) and Poly(styrene sulfonic acid) (PEDOT:PSS) by gallium doped ZnO nanoparticle inclusions, as a function of volume fraction of nanoparticle inclusions. Calculations determined the desired volume fraction of the gallium doped nanoparticles to be between 45% and 71% when gallium dopant concentration varies between 0 and 4 percent. v Acknowledgments My endless appreciations go to my advisor, Prof. Minseo Park, for believing in me, for his precious instructions, his inspirations and invaluable support in every way possible. This work would not have been possible without his patronage, endless encouragement and compassion. I would like to thank Prof. Hamilton for his valuable advices and directions during our project. My deep appreciations go to Prof. Ayayi Claude Ahyi for his patience, valuable counsels and teachings. In addition to training me on fabrication processes and device measurements, Mrs. Tami Isaac-Smith was always sympathetic and kind. Thank you, Tami. I also want to thank Mr. Max Cichon for all his help, including gamma irradiation of the samples. My great appreciations go to Prof. Sarit Dhar for giving me insightful instructions, as well as giving me the opportunity to use the atomic force microscope. My deep gratitude goes to Prof. Michael Bozack for his support and for accepting to kindly serve as my committee member in such a short notice. My appreciations also go to Prof. Majid Beidaghi for his encouragement, collaboration, for kindly accepting to serve as my external committee member and for his inspection of my dissertation. In addition, I would like to thank Dr. Burcu Ozden for her companionship, benevolence, loyalty and integrity; Dr. Mobassar Hasssan Sk for his friendship and our invaluable conversations; Dr. Shiqiang Wang for selflessly helping me when needed; and Mr. Muhammed Shezad Sultan for his grace and brotherly love, as well as his kind help on data analysis. I want to deeply thank Mr. Kosala Yapabandara, Mr. Min Khanal and Mr. Sunil Uprety for our precious discussions and for all the help they provided me with. My thanks vi go to Mr. Chungman Yang for his friendship and for training me on fabrication processes; Mr. Benjamin Schoenek and Mr. Suman Das for helping me with AFM images; and Mr. Asanka Jayawardena for our fruitful discussions over four-probe measurement and DLTS. My deep gratitude goes to Dr. Jie Jiang for his advices on ZnO sample preparations and characterization instructions. My thanks and commendations go to Mr. Uisub Shin, Mr. Sangjong Ko and Ms. Suhyeon Youn for their friendship and providing me with a considerable amount of assistance with Raman and PL measurements and data analysis. I would also like to thank Dr. Fei Tong for training me on Raman Spectroscopy and Dr. Yoonsung Chung for assisting us in our sample preparation. Finally, I wish to express my deepest love to my treasured parents Mr. and Mrs. Davoud Mirkhani Rashti and Azam Heydarian, and my beloved sisters Poopak, Mahak and Mehrak. My innermost gratitude goes my cherished wife, future Dr. Nasrin Mohabbati Kalejahi, for her passionate support, immeasurable love, and her boundless dedication and selflessness.
Post-Heat Treatment on the Properties of Sol-Gel Derived ZnO Thin Films for Transparent Electronics
2017
Highly transparent and conducting sol-gel derived ZnO thin lms were deposited using spin coating method onto a glass substrate. The deposited lms were post-heated at di erent temperatures between 250◦C and 550◦C. The in uence of post-heating temperatures on the optoelectronic properties were investigated. Experimental results showed the polycrystalline nature of the lms with a hexagonal wurtzite structure, preferably oriented along c-axis. The crystallinity of the ZnO thin lms improved after post-heat treatment. The average optical transmittance of the lms increases from 67% to 89% as the post-heating temperature is increased from 250◦C to 450◦C. The Photoluminescence (PL) spectra shows a dominant UV emission peak around 378 nm due to free exciton emission and a broad peak at ∼ 522 nm is due to non-stoichiometric intrinsic defects. The electrical resistivity decreased after post-heat treatment. A minimum resistivity of 4.92 ×10−2 Ω cm was obtained after the lm was heated at a temper...
Journal of Materials Science: Materials in Electronics, 2013
The aim of this work is the production of tin oxide thin films with a suitable optoelectronic properties required for application as transparent electrodes. Using a simple and inexpensive homemade spray pyrolysis system of tin chloride (SnCl 2) onto glass substrates. The motivation for the use of this technique is its simplicity and effectiveness of preparation. The effect of the molarity (0.05-0.25 mol/l) on structural, optical and electrical film properties was investigated. Q3 The results obtained with several characterization techniques such as DRX, AFM, UV-visible transmission and four probe points measurements are well consistent and suggest that the prepared films were uniform and well adherent to the substrates. All the films are polycrystalline in nature with a tetragonal structure having a preferential orientation along the (1 1 0) plane. The obtained SnO 2 films, not only have an average transmittance greater than 80% in the visible region, but also have an optical band gap between 3.84 and 4.14 eV depending on the spraying solution concentration. Moreover, the measured electrical conductivity at room temperature was found in the order of 10 2 (cm) −1 .
Electronic Materials Letters, 2019
Solution processing of metal oxide-based semiconductors is an attractive route for low-cost fabrication of thin films devices. ZnO thin films were synthesized from one-step spin coating-pyrolysis technique using zinc neodecanoate precursor. X-ray diffraction (XRD), UV-visible optical transmission spectrometry and photoluminescence spectroscopy suggested conversion to polycrystalline ZnO phase for decomposition temperatures higher than 400 °C. A 15 % precursor concentration was found to produce optimal TFT performance on annealing at 500 °C, due to generation of sufficient charge percolation pathways. The device performance was found to improve upon increasing the annealing temperature and the optimal saturation mobility of 0.1 cm 2 V −1 s −1 with I ON /I OFF ratio ~ 10 7 was achieved at 700 °C annealing temperature. The analysis of experimental results based on theoretical models to understand charge transport envisaged that the grain boundary depletion region is major source of deep level traps and their effective removal at increased annealing temperature leads to evolution of transistor performance. Graphic Abstract Single-step spin coating-pyrolysis synthesis of ZnO thin films from non-aqueous precursor zinc neodecanoate has been investigated for transistor applications.
The effects of post-annealing on the performance of ZnO thin film transistors
Thin Solid Films, 2011
In this study, we investigated the effects of a post-annealing process on the performance and stability of zinc oxide thin film transistors fabricated by atomic layer deposition. After the post-annealing process in ambient air at 250°C for 2 h, the value of the saturation mobility increased from 1.2 to 1.8 cm/Vs, the subthreshold swing decreased from 0.53 to 0.34 V/decade, and the I on /I off ratio increased from 3.1 × 10 6 to 1.7 × 10 7. The positive bias stability was also enhanced after post-annealing. These results are related to the formation of another phase in which the difference of enthalpy between the semiconductor material and contact metal electrode causes the carrier concentration at the metal/semiconductor interface to increase, leading to decreased contact resistivity. Additionally, internal modification of the semiconductor/dielectric interface and/or improving the semiconductor structure, which is related to a change in the oxidation state of Zn through the incorporation of oxygen and/or hydroxide, can result in improved device performance.
Journal of the American Ceramic Society, 2008
Zinc oxide (ZnO) thin films were prepared under different conditions on glass substrates using a sol-gel process. The microstructure of ZnO films was investigated by means of diffraction analysis, and plan-view and cross-sectional scanning electron microscopy. It was found that the preparation conditions strongly affected the structure and the optoelectronic properties of the films. A structural evolution in morphology from spherical to columnar growth was observed. The crystallinity of the films was improved and columnar film growth became more dominant as the zinc concentration and the substrate withdrawal speed decreased. The individual layer thickness for layerby-layer homoepitaxy growth that resulted in columnar grains was o20 nm. The grain columns are grown through the entire film with a nearly unchanged lateral dimension through the full film thickness. The columnar ZnO grains are c-axis oriented perpendicular to the interface and possess a polycrystalline structure. Optical transmittance up to 90% in the visible range and electrical resistivity as low as 6.8 Â 10 À3 . X . cm were obtained under optimal deposition conditions.
Synthesis Sol-Gel Derived Highly Transparent ZnO Thin Films for Optoelectronic Applications
Advances in Materials Physics and Chemistry, 2012
In this work, ZnO thin films were derived by sol-gel using two different techniques; dip coating and spin coating technique. The films were deposited onto glass substrate at room temperature using sol-gel composed from zinc acetate dehydrate, monoethanolamine, isopropanole, and de-ionized water, the films were preheated at 225˚C for 15 min. The crystallographic structures of ZnO films were investigated using X-ray diffraction (XRD); the result shows that the good film was prepared at dip coating technique, it was polycrystalline and highly c-orientation along (002) plane, the lattice constant ratio (c/a) was calculated at (002), it was about 1.56. The structure of thin films, prepared by spin coating technique, was amorphous with low intensity and wide peaks. The optical properties of the prepared film were studied using UV-VIS spectrophotometer with the range 190-850 nm, and by using the fluorescence spectrometer. The optical characterization of ZnO thin films that were prepared by the dip coating method have good transmittance of about 92% in the visible region, it can be noted from the fluorescence spectrometer two broad visible emission bands centered at 380 nm and 430 nm. The optical energy gaps for the direct and indirect allowed transitions were calculated, the values were equal 3.2 eV and 3.1 eV respectively. Dip coating technique create ZnO films with potential for application as transparent electrodes in optoelectronic devices such as solar cell.