Electrical surface modification and characterization of metallic thin films using scanning probe microscope (SPM) nanolithography method

Thesis (Master)--Izmir Institute of Technology, Physics, Izmir, 2009Includes bibliographical references (leaves: 89-96)Text in English; Abstract: Turkish and Englishxiii, 96 leavesThis thesis focuses on local oxidation of metallic thin films using atomic force microscopy (AFM). The primary aim of this thesis is to investigate the growth kinetics of oxide forms of these metallic materials and characterize the resulted oxide structures. In this study, tantalum, hafnium and zirconium thin films were used to be oxidized via AFM. During this work, metallic thin films were grown on Si and SiOx substrates with DC magnetron sputtering method. Thin films were characterized via x-ray diffraction, scanning electron microscopy and atomic force microscopy. Oxidation experiments were performed under different environmental conditions to explore the effect of influential parameters; such as bias voltage, oxidation time and relative humidity, and line shape oxide structures were created on metallic films. Dimensional analysis of created oxide structures was carried out measuring height and line-width of oxide lines as a function of applied voltage, oxidation time and relative humidity. In addition to the dimensional analysis, electrical characterization of metal-oxides was performed via AFM electrical characterization methods which are two terminal I-V measurements, electric force microscopy and spreading resistance measurements. At the end of the thesis, the capability of this method to create lateral metal-oxide-metal junction was shown oxidizing a tantalum stripe and performing in-situ resistance measurement. Patterning of tantalum stripes was accomplished by standard photolithography process and lift-off technique

Electrical surface modification and characterization of metallic thin films using scanning probe microscope (SPM) nanolithography method

Thesis (Master)--Izmir Institute of Technology, Physics, Izmir, 2009Includes bibliographical references (leaves: 89-96)Text in English; Abstract: Turkish and Englishxiii, 96 leavesThis thesis focuses on local oxidation of metallic thin films using atomic force microscopy (AFM). The primary aim of this thesis is to investigate the growth kinetics of oxide forms of these metallic materials and characterize the resulted oxide structures. In this study, tantalum, hafnium and zirconium thin films were used to be oxidized via AFM. During this work, metallic thin films were grown on Si and SiOx substrates with DC magnetron sputtering method. Thin films were characterized via x-ray diffraction, scanning electron microscopy and atomic force microscopy. Oxidation experiments were performed under different environmental conditions to explore the effect of influential parameters; such as bias voltage, oxidation time and relative humidity, and line shape oxide structures were created on metallic films. Dimensional analysis of created oxide structures was carried out measuring height and line-width of oxide lines as a function of applied voltage, oxidation time and relative humidity. In addition to the dimensional analysis, electrical characterization of metal-oxides was performed via AFM electrical characterization methods which are two terminal I-V measurements, electric force microscopy and spreading resistance measurements. At the end of the thesis, the capability of this method to create lateral metal-oxide-metal junction was shown oxidizing a tantalum stripe and performing in-situ resistance measurement. Patterning of tantalum stripes was accomplished by standard photolithography process and lift-off technique

Nanoimprinted high-frequency surface acoustic wave devices: generation, characterization and acousto-electric transport

This thesis deals with both the excitation and characterization of high-frequency SAWs, as well as with SAW-induced charge transport by using an electrical excitation method. SAWs are widely used and very important in both research and industry. In piezoelectric materials, they can be excited through the inverse piezoelectric effect by using interdigital transducers (IDTs). Because of the piezoelectricity of the material, a piezoelectric potential wave accompanies the mechanical wave. The unique SAW properties make them suitable not only for signal processing, but also for sensing applications, photonics, and charge transport. The SAW frequency is determined by the periodicity of the IDT electrodes and the acoustic velocity of the material. Almost for all applications, there is a strong demand for higher frequencies, for example to\ud enhance the processing speed or to reach the single-charge manipulation regime

Scanning probe oxidation lithography on Ta thin films

A Semi-Contact Scanning Probe Lithography Technique (SC-SPL) has been applied to create nano-oxide patterns on Ta thin films grown by DC magnetron sputtering method on SiO 2/Si substrates. The height and linewidth profiles of nano-oxide lines created by a conductive AFM tip on Ta film surfaces were measured as a function of applied voltage, oxidation time, humidity, and tip apex curvature. The AFM surface measurements show that the height of the oxides increases linearly with increasing voltage; but there was no oxide growth, when less than 4 V was applied even at 85% relative humidity. Electrical measurements were performed and the resistivities of the TaO x layer and Ta film were obtained as 5.76 × 10 8 and 1.4 × 10 5 Ohm-cm, respectively.DPT (State Planning Organization of Turkey) DPT2003KI20390; IYTE 20041YTE22 and 2006IYTE2

Local oxidation nanolithography on Hf thin films using atomic force microscopy (AFM)

Well controlled Hf oxide patterns have been grown on a flat Hf thin film surface produced by the dc magnetron sputtering method on Si and SiOx substrates. These patterns have been created by using the technique of semi-contact scanning probe lithography (SC-SPL). The thickness and width of the oxide patterns have been measured as a function of applied voltage, duration and relative humidity. There is a threshold voltage even at 87% humidity, due to insufficient energy required to start the oxide growth process for a measurable oxide protrusion. Electrical characterization was also performed via the I-V curves of Hf and HfOx structures, and the resistivity of HfO x was found to be 4.284 × 109 Ω cm. In addition to the I-V curves, electric force microscopy and spreading surface resistance images of Hf and HfOx were obtained.TÜBİTAK project number 107T117; DPT2003K120390 and Izmir Institute of Technology project number of 2004IYTE22 and 2006IYTE2

High-quality global hydrogen silsequioxane contact planarization for nanoimprint lithography

The authors present a novel global contact planarization technique based on the spin-on-glass material hydrogen silsequioxane (HSQ) and demonstrate its excellent performance on patterns of 70 nm up to several microns generated by UV-based nanoimprint lithography. The HSQ layer (∼165 nm) is spin coated on the imprinted organic layer and planarized by pressing it with a flat wafer at room temperature. Before retracting the planarization wafer, the HSQ is hardened by baking at 120 or 70 °C, depending on the underlying material. Fluorine-based reactive ion etching (RIE) is used to etch the HSQ (etch-back) down to the top of the features in the organic imprint layer. Subsequently, oxygen-based RIE is used to etch the organic imprint layer in the exposed regions, thereby transferring the imprinted pattern down to the substrate. The etch selectivity between the HSQ and the underlying layers is found to be more than 1:100, enabling very accurate pattern transfer with excellent critical dimension control and well-defined undercut profile suitable for further metal liftoff processes. The dependence of the contact planarization quality on the HSQ spinning speed and pressure is investigated, achieving a global planarization degree as good as 93%, an improvement of 45% compared to standard spin-coating planarization

Gas Sensing Properties of p-Co3O4/n-TiO2 Nanotube Heterostructures

In this paper, we fabricated p-Co3O4/n-TiO2 heterostructures and investigated their gas sensing properties. The structural and morphological characterization were performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy analysis (XPS). The electrical properties of the heterostructure were studied within the temperature range from 293 K to 423 K. Changes in electrical properties and sensing behavior against reducing and oxidizing gases were attributed to the formation of p–n heterojunctions at the Co3O4 and TiO2 interface. In comparison with sensing performed with pristine TiO2 nanotubes (NTs), a significant improvement in H2 sensing at 200 °C was observed, while the sensing response against NO2 decreased for the heterostructures. Additionally, a response against toluene gas, in contrast to pristine TiO2 NTs, appeared in the Co3O4/TiO2 heterostructure samples

WS2 thin film based quartz crystal microbalance gas sensor for dimethyl methylphosphonate detection at room temperature

WS2 thin films were deposited on quartz crystal microbalance (QCM) oscillators via radio frequency magnetron sputtering to detect hazardous gases at room temperature (RT). WS2 coated QCM sensors were tested against various hazardous gases including acetone, toluene, xylene, isopropyl-alcohol, hydrogen cyanide, hydrogen sulfide, ammonia, dimethyl methylphosphonate (DMMP, nerve agent simulant) and 2-Chloroethyl ethyl sulfide (mustard simulant). It was observed that fabricated sensors exhibit superior sensor performance to DMMP gas at RT. Additionally, one of the sensors showed reliable stability, high sensitivity, and a low theoretical limit of detection of 5 ppb. As a result, WS2 coated QCM sensor has a great potential for the monitoring of nerve agent