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Author: Amber Nicole Reed Publisher: ISBN: Category : Sputtering (Physics) Languages : en Pages : 158
Book Description
Zinc oxide (ZnO) is an emerging thin film transistor (TFT) material for transparent flexible displays and sensor technologies, where low temperature synthesis of highly crystallographically ordered films over large areas is critically needed. This study maps plasma assisted synthesis characteristics, establishes polycrystalline ZnO growth mechanisms and demonstrates for the first time low-temperature and scalable deposition of semiconducting grade ZnO channels for TFT applications using reactive high power impulse magnetron sputtering (HiPIMS). Plasma parameters, including target currents, ion species and their energies were measured at the substrate surface location with mass spectroscopy as a function of pressure and applied voltage during HiPIMS of Zn and ZnO targets in O2/Ar. The results were correlated to film microstructure development investigated with x-ray diffraction, atomic force microscopy, scanning electron microscopy and transmission electron microscopy which helped establish film nucleation and growth mechanisms. Competition for nucleation by (100), (101) and (002) oriented crystallites was identified at the early stages of film growth, which can result in a layer of mixed crystal orientation at the substrate interface, a microstructural feature that is detrimental to TFT performance due to increased charge carrier scattering in back-gated TFT devices. The study revealed that nucleation of both (100) and (101) orientations can be suppressed by increasing the plasma density while decreasing ion energy. After the initial nucleation layer, the microstructure evolves to strongly textured with the (002) crystal plane oriented parallel to the substrate surface. The degree of (002) alignment was pressure-dependent with lower deposition pressures resulting in films with (002) alignment less than 3.3°, a trend attributed to less energy attenuation of the low energy (2- 6 eV) Ar+, O+, and O2+ ions observed with mass spectrometry measurements. At pressures of 7 mTorr and lower, a second population of ionized gas (Ar+, O+, and O2+) species with energies up to 50 eV appeared. The presence of higher energy ions corresponded with a bimodal distribution of ZnO grain sizes, confirming that high energy bombardment has significant implications on microstructural uniformity during large area growth. Based on the established correlations between process parameters, plasma characteristics, film structure and growth mechanisms, optimum deposition conditions for (002) oriented nanocrystalline ZnO synthesis at 150 °C were identified and demonstrated for both silicon oxide wafers of up to 4 inch diameter and on flexible polymer (Kapton) substrates. The feasibility of the low temperature processing of ZnO films for TFT applications was verified by preliminary tests with back-gated device prototypes. Directions of future research are outlined to further develop this low temperature growth method and apply results of this study for ZnO applications in semiconductor devices.
Author: Amber Nicole Reed Publisher: ISBN: Category : Sputtering (Physics) Languages : en Pages : 158
Book Description
Zinc oxide (ZnO) is an emerging thin film transistor (TFT) material for transparent flexible displays and sensor technologies, where low temperature synthesis of highly crystallographically ordered films over large areas is critically needed. This study maps plasma assisted synthesis characteristics, establishes polycrystalline ZnO growth mechanisms and demonstrates for the first time low-temperature and scalable deposition of semiconducting grade ZnO channels for TFT applications using reactive high power impulse magnetron sputtering (HiPIMS). Plasma parameters, including target currents, ion species and their energies were measured at the substrate surface location with mass spectroscopy as a function of pressure and applied voltage during HiPIMS of Zn and ZnO targets in O2/Ar. The results were correlated to film microstructure development investigated with x-ray diffraction, atomic force microscopy, scanning electron microscopy and transmission electron microscopy which helped establish film nucleation and growth mechanisms. Competition for nucleation by (100), (101) and (002) oriented crystallites was identified at the early stages of film growth, which can result in a layer of mixed crystal orientation at the substrate interface, a microstructural feature that is detrimental to TFT performance due to increased charge carrier scattering in back-gated TFT devices. The study revealed that nucleation of both (100) and (101) orientations can be suppressed by increasing the plasma density while decreasing ion energy. After the initial nucleation layer, the microstructure evolves to strongly textured with the (002) crystal plane oriented parallel to the substrate surface. The degree of (002) alignment was pressure-dependent with lower deposition pressures resulting in films with (002) alignment less than 3.3°, a trend attributed to less energy attenuation of the low energy (2- 6 eV) Ar+, O+, and O2+ ions observed with mass spectrometry measurements. At pressures of 7 mTorr and lower, a second population of ionized gas (Ar+, O+, and O2+) species with energies up to 50 eV appeared. The presence of higher energy ions corresponded with a bimodal distribution of ZnO grain sizes, confirming that high energy bombardment has significant implications on microstructural uniformity during large area growth. Based on the established correlations between process parameters, plasma characteristics, film structure and growth mechanisms, optimum deposition conditions for (002) oriented nanocrystalline ZnO synthesis at 150 °C were identified and demonstrated for both silicon oxide wafers of up to 4 inch diameter and on flexible polymer (Kapton) substrates. The feasibility of the low temperature processing of ZnO films for TFT applications was verified by preliminary tests with back-gated device prototypes. Directions of future research are outlined to further develop this low temperature growth method and apply results of this study for ZnO applications in semiconductor devices.
Author: Felipe de Campos Carreri Publisher: Fraunhofer Verlag ISBN: 9783839612873 Category : Technology & Engineering Languages : en Pages : 0
Book Description
The scope of this work is to investigate and to develop advanced HIPIMS processes for deposition of oxides, utilizing industrial-scale equipment and technology. Two classes of oxide materials were studied: insulating (aluminum oxide) and conducting oxides (indium-tin oxide and aluminum-doped zinc oxide). The electrical properties of the oxides have a significant influence on the process design, as the issues and approaches for deposition of insulating materials are fairly different from conducting materials. Different types of reactive process control were also investigated, utilizing optical emission spectroscopy to control the oxygen flow and lambda probes to control the discharge power. A non-reactive process was also studied for indium-tin oxide.
Author: Martin Mickan Publisher: ISBN: Category : Languages : en Pages :
Book Description
Transparent conducting oxides (TCOs) are an important class of materials with many applications such as low emissivity coatings, or transparent electrodes for photovoltaics and flat panel displays. Among the possible TCO materials, Al-doped ZnO (AZO) is studied due to its relatively low cost and abundance of the raw materials. Thin films of AZO are commonly produced using physical vapour deposition techniques such as magnetron sputtering. However, there is a problem with the homogeneity of the films using reactive direct current magnetron sputtering (DCMS). This homogeneity problem can be related to the bombardment of the growing film with negative oxygen ions, that can cause additional acceptor defects and the formation of insulating secondary phases. In this work AZO films are deposited by high power impulse magnetron sputtering (HiPIMS), a technique in which high instantaneous current densities are achieved by short pulses of low duty cycle. In the first part of this thesis, the possibility to improve the homogeneity of the deposited AZO films by using HiPIMS is demonstrated. This improvement can be related to the high instantaneous sputtering rate during the HiPIMS pulses, so the process can take place in the metal mode. This allows for a lower oxygen ion bombardment of the growing film, which can help to avoid the formation of secondary phases. Another problem of AZO is the stability of the properties in humid environments. To assess this problem, the degradation of the electrical properties after an aging procedure was investigated for films deposited by both DCMS and by HiPIMS. A method was proposed, to restore the properties of the films, using a low temperature annealing under N2 atmosphere. The improvement of the electrical properties of the films could be related to a diffusion process, where water is diffusing out of the films. Then, the influence of the substrate temperature on the properties of AZO films deposited by HiPIMS was studied. The electrical, optical and structural properties were found to improve with increasing substrate temperature up to 600° C. This improvement can be mostly explained by the increase in crystalline quality and the annealing of defects. Finally, the deposition of AZO films on flexible PET substrates was investigated. The films are growing as a thick porous layer of preferentially c-axis oriented columns on top of a thin dense seed layer. The evolution of the sheet resistance of the films after bending the films with different radii was studied. There is an increase in the sheet resistance of the films with decreasing bending radius, that is less pronounced for thicker films.
Author: Mary E. Kinsella Publisher: Springer Nature ISBN: 3030407799 Category : Technology & Engineering Languages : en Pages : 182
Book Description
This book provides insight into research and development of key aerospace materials that have enabled some of the most exciting air and space technologies in recent years. The stories are shared with you by the women who experienced them, those engineers and scientists in the labs, on the shop floors, or on the design teams contributing to the realization of these technologies. Their work contributes to the world in the challenging and vital field of aerospace materials, and their stories seethe with a pride and a passion for the opportunity to make these important contributions. As an important part of the Women in Science and Engineering book series, the work highlights the contribution of women leaders in Aerospace Materials, inspiring women and men, girls and boys to enter and apply themselves to secure our future in an increasingly connected world.
Author: Norbert H. Nickel Publisher: Springer Science & Business Media ISBN: 140203475X Category : Science Languages : en Pages : 245
Book Description
Recently, a significant effort has been devoted to the investigation of ZnO as a suitable semiconductor for UV light-emitting diodes, lasers, and detectors and hetero-substrates for GaN. Research is driven not only by the technological requirements of state-of-the-art applications but also by the lack of a fundamental understanding of growth processes, the role of intrinsic defects and dopants, and the properties of hydrogen. The NATO Advanced Research Workshop on “Zinc oxide as a material for micro- and optoelectronic applications”, held from June 23 to June 25 2004 in St. Petersburg, Russia, was organized accordingly and started with the growth of ZnO. A variety of growth methods for bulk and layer growth were discussed. These techniques comprised growth methods such as closed space vapor transport (CSVT), metal-organic chemical vapor deposition, reactive ion sputtering, and pulsed laser deposition. From a structural point of view using these growth techniques ZnO can be fabricated ranging from single crystalline bulk material to polycrystalline ZnO and nanowhiskers. A major aspect of the ZnO growth is doping. n-type doping is relatively easy to accomplish with elements such al Al or Ga. At room temperature single crystal ZnO exhibits a resistivity of about 0. 3 -cm, an electron mobility of 2 17 -3 225 cm /Vs, and a carrier concentration of 10 cm . In n-type ZnO two shallow donors are observable with activation energies of 30 – 40 meV and 60 – 70 meV.
Author: Chennupati Jagadish Publisher: Elsevier ISBN: 0080464033 Category : Science Languages : en Pages : 600
Book Description
With an in-depth exploration of the following topics, this book covers the broad uses of zinc oxide within the fields of materials science and engineering:- Recent advances in bulk , thin film and nanowire growth of ZnO (including MBE, MOCVD and PLD), - The characterization of the resulting material (including the related ternary systems ZgMgO and ZnCdO), - Improvements in device processing modules (including ion implantation for doping and isolation ,Ohmic and Schottky contacts , wet and dry etching), - The role of impurities and defects on materials properties - Applications of ZnO in UV light emitters/detectors, gas, biological and chemical-sensing, transparent electronics, spintronics and thin film
Author: Amber Nicole Reed
Author: Amber Nicole Reed
Author: Felipe de Campos Carreri
Author: Martin Mickan
Author: Mary E. Kinsella
Author: Jiaye Huang
Author: Norbert H. Nickel
Author: Chennupati Jagadish
Author: 
Author: Asim Aijaz
Author: Khairul Nadzrin Rosli