Author: Michael Allen Motyka
Publisher:
ISBN:
Category :
Languages : en
Pages : 220

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Author: Bryan Douglas Gauntt
Publisher:
ISBN:
Category :
Languages : en
Pages : 170

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Author: Kerry Elizabeth Wells
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Mengyang Zou
Publisher:
ISBN:
Category : Bolometer
Languages : en
Pages : 68

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Book Description
Microbolometer IR imagers consist of an array of thermally sensitive pixels that change resistance as infrared radiation is focused onto the array. Commonly used thermoresisitive materials are amorphous silicon (a-Si) and vanadium oxide (VOx). Despite their use in image sensors, these films are extremely difficult to produce with widely varying process conditions being reported in the literature. Therefore, the goal of this work was to examine the process windows of some of these methods, including novel approaches such as oxygen ion assisted deposition (IAD), aluminum-induced crystallization and glancing angle deposition. Among the thermoresistive materials, vanadium oxide has been widely used in microbolometers due to their excellent thermoresistive properties, relatively fast thermal time constants and high temperature coefficient of resistance (TCR). In our work, we examined different physical vapor deposition methods including: RF reactive sputtering of metallic vanadium to produce vanadium oxide, thermal evaporation of vanadium films and subsequent oxidation, and Oxygen Ion-Assisted Deposition (IAD) of e-beam evaporated vanadium. In addition to VOx, amorphous silicon is also desirable because it can be easily integrated into the CMOS fabrication processes more than VOx. The hydrogenated amorphous silicon produced by PECVD has a high TCR and a relatively high optical absorption coefficient. In addition to PECVD, we used a glancing angle deposition and also examined a novel approach to create polycrystalline silicon from aluminum-induced crystallization.

Author: Yao Jin
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
A vanadium oxide (VO x) thin film is the most common imaging layer used in commercial uncooled focal plane arrays for infrared cameras. These VOx thin films have an x value ranging from 1.3 to 2 and have low resistivity (0.1 to 10 [omega] cm), high temperature coefficient of resistance (TCR) (-2 to -3 %/K), and low 1/f noise. Reactive ion beam sputtering is typically used to deposit these VOx thin films for commercial thermal imaging cameras. However, the reactive ion beam deposition system for the VOx is reported to have less than desirable throughput and a narrow process window. In this work, the potential for reactive pulsed-dc magnetron sputtering of nanocomposite VOx thin films for microbolometer applications was investigated. VOx thin films with resistivity from 10-4 to 105 [omega] cm with a TCR from 0 to -4.3 %/K were deposited by reactive sputtering from a metallic vanadium target in argon/oxygen mixtures with substrate bias. Magnetron sputtered VOx shows bolometric properties comparable to those of commercial-grade IBD prepared VOx. Important limitations for manufacturing implementation of reactive magnetron sputtering such as hysteresis oxidation and non-uniform oxidation of the vanadium target surface were evaluated. The VOx film deposition rate, resistivity, and temperature coefficient of resistance were correlated to oxygen to argon ratio, processing pressure, target-to-substrate distance, and oxygen inlet positions. To deposit VOx in the resistivity range of 0.1--10 [omega] cm with good uniformity and process control, it was found that a lower processing pressure, larger target-to-substrate distance, and an oxygen inlet near the substrate are useful. Other processing methods employing magnetron sputtering were investigated such as co-sputtering of V and V2O5 target, sputtering from a VC target, a V2O5 target, and a V2Ox target but initial investigation of these methods did not yield a superior process to the simple sputtering of a pure metallic vanadium target. Another technique, biased target ion beam deposition (BTIBD), was investigated for deposition VOx thin films with potential alloy additions. In this BTIBD system, ions with energy lower than 25 eV were generated remotely and vanadium targets are negatively biased independently for sputtering. High TCR (

Author: Adem Ozcelik
Publisher:
ISBN:
Category :
Languages : en
Pages : 97

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Author: Hernan M. R.
Publisher:
ISBN:
Category : Science
Languages : en
Pages :

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Book Description
This chapter describes a new deposition method proposed to achieve Vanadium Oxide VOx/V2O5 thin films with high temperature coefficient of resistance (TCR), intended to be used as functional material in IR microsensors (bolometers). The main aim of the work is to attain a deposition method compatible with the lift-off microstructuring technique in order to avoid the use of a reactive-ion etching (RIE) process step to selectively remove the VOx/V2O5 deposited layer in the course of the definition of the bolometer geometry, preventing the harmful effects linked to the spatial variability and the lack of selectivity of the RIE process. The proposed technique makes use of a two-stage process to produce the well-controlled VOx or V2O5 thin films by applying a suitable thermal annealing to a previously deposited layer, which was obtained before at room temperature by RF magnetron sputtering and patterned by lift-off. A set of measurements has been carried out with thin films attained in order to check the quality and properties of the materials achieved with this method. The results reached with V2O5 pure phase films are consistent with a charge transport model based on the small polarons hopping derived from Mott's model under the Schnakenberg form.

Author: Haitian Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
Transition metal oxides have attracted tremendous research interest due to their fertile functional properties, including ferroelectricity, magnetism, high temperature superconductivity and metal to insulator transition (MIT). Over recent decades, one of the research focuses has been utilizing these functional features in device applications, which requires a deeper understanding of the material science and also advances in thin film deposition in order to tailor these properties. The binary vanadium dioxide has drawn much attention due to its orders of magnitude change in resistivity during the MIT near room temperature, opening up the possibilities to use this material as next generation transistors, memory devices and radio frequency switches in communication applications. However, to bridge the gap between the frontier of fundamental research in VO2 films and their realization in commercial products, wafer scale growth of the oxide thin films with electronic grade is necessary. This task requires precise control over the valence state of normally multivalent transition metal cations, while the device performance will be largely derogated if the valence state is not well controlled. To deposit the VO2 with precise valence state control on wafer scale, a combinatorial approach was used to establish a valence state gradient of vanadium cation, from which the optimal condition for stoichiometric VO2 was extracted. Under the optimal growth condition, a high quality 30-nm thick VO2 film was grown on 3 inch sapphire wafer, showing the highest MIT resistivity ratio for ultrathin films on wafer scale, which is relevant for modern device applications.Besides the growth of high quality MIT thin films on wafer scale, a novel strategy to optically write and erase complex circuitry into VO2 thin films was also developed. Weve successfully demonstrated the optically induced MIT in VO2 which is persistent after the light source is turned off. We use this method to optically imprint local conductive areas into an otherwise insulating VO2 film. In contrast to conventional thin film patterning techniques that require chemical etching of patterns defined through lithography steps, the optical imprint is performed by irradiating single crystalline VO2 thin films with focused ultraviolet light in a nitrogen atmosphere. A conductive pattern is sketched into the resistive VO2 matrix, resulting in a close to 4 orders of magnitude increase in electrical conductivity at room temperature. Significantly, the inscribed pattern, which is permanent, can be completely erased by a few minutes thermal annealing process at moderately elevated temperature. This development can potentially find its application in reconfigurable optical elements. It can also be harnessed as rewritable bottom electrode material for back-gating structures by inscribing complex contacting schemes using UV radiation. Beyond the binary vanadium oxides, Mott insulators such as LaVO3 have recently been suggested as promising solar cell materials with suitable band gap, high absorption coefficient, as well as the potential to beat the Shockley-Queisser limit owing to their unique strong electron-electron correlation effect that is not present in conventional semiconductors. However, the quality of strongly correlated oxides has been far inferior compared to conventional semiconductors. The high defect concentration of oxide thin films impedes the realization of Mott solar cells with competitive performance due to the lack of stoichiometry control. By taking advantage of the unique self-regulated growth mechanism available in hybrid molecular beam epitaxy, strongly correlated LaVO3 films were grown which revealed a record-low defect concentration. The optical and electrical properties of these films were studied as a function of stoichiometry and a more than two orders of magnitude improvement in defect-related properties compared to results reported in literature was demonstrated, showing that Mott insulators can indeed be synthesized with high perfection using hybrid molecular beam epitaxy.

Author: Nikolay Nikitenkov
Publisher: BoD – Books on Demand
ISBN: 953513003X
Category : Science
Languages : en
Pages : 446

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Book Description
Development of the thin film and coating technologies (TFCT) made possible the technological revolution in electronics and through it the revolution in IT and communications in the end of the twentieth century. Now, TFCT penetrated in many sectors of human life and industry: biology and medicine; nuclear, fusion, and hydrogen energy; protection against corrosion and hydrogen embrittlement; jet engine; space materials science; and many others. Currently, TFCT along with nanotechnologies is the most promising for the development of almost all industries. The 20 chapters of this book present the achievements of thin-film technology in many areas mentioned above but more than any other in medicine and biology and energy saving and energy efficiency.

Author: Yi Long
Publisher: CRC Press
ISBN: 1000393577
Category : Science
Languages : en
Pages : 416

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Book Description
The usage of building energy accounts for 30–40% of total energy consumption in developed countries, exceeding the amount for industry or transportation. Around 50% energy for building services is contributed by heating, ventilation, and air-conditioning (HVAC) systems. More importantly, both building and HVAC energy consumptions are predicted to increase in the next two decades. Windows are considered as the least energy-efficient components of buildings. Therefore, smart windows are becoming increasingly important as they are capable of reducing HVAC energy usage by tuning the transmitted sunlight in a smart and favoured way: blocking solar irradiation on hot days, while letting it pass through on cold days. Compared with other type of smart windows, thermochromic windows have the unique advantages of cost-effectiveness, rational stimulus, and passive response. This book covers fabrication of vanadium dioxide–based smart windows, discusses various strategies to enhance their performance, and shares perspectives from the top scientists in this particular field.