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Vanadium dioxide (VO2) is a promising candidate for electronic and optical switching applications in the terahertz frequency range due to the metal to insulator transition (MIT). In this study, the use of VO2 patterned as a metamaterial surface or coupled as a homogeneous layer with a metallic metamaterial surface on top is investigated in terms of performance. High-quality VO2 thin films were deposited on c-cut sapphire substrates by using the dc magnetron sputtering technique. A change in resistivity by a factor of 104 MIT in VO2 was observed allowing to investigate its use as a controllable metamaterial. The layer was patterned using a unique geometry (four-cross shaped) that operates in the THz frequency range. To understand its performance as a tunable THz filter, the four-cross structure fabricated from VO2 is compared to one fabricated from Au on VO2 bare film using UV lithography and ion beam etching techniques. The spectral performances of metamaterials were assessed using THz-Time Domain Spectroscopy (THz-TDS) and results were compared with simulations based on CST Microwave Studio. Absence of the resonant effects in the purely developed VO2 device, while clear observation of the MIT behavior shows the strong dependency of the inductive and/or capacitive effects of the four-cross structure on conductivity of the surface metamaterial, which is clearly observable for the Au-based device. In the latter case, the resonant transmittance of the filter can be effectively modulated by change in temperature. [ABSTRACT FROM AUTHOR]

We have investigated the reduction of unwanted interfacial SiO2 layer at HfO2/Si interface brought about by the deposition of thin Hf metal buffer layer on Si substrate prior to the deposition of HfO2 thin films for possible direct contact between HfO2 thin film and Si substrate, necessary for the future generation devices based on high-κ HfO2 gate dielectrics. Reactive rf magnetron sputtering system along with the attached in-situ spectroscopic ellipsometry (SE) was used to predeposit Hf metal buffer layer as well as to grow HfO2 thin films and also to undertake the in-situ characterization of the high-κ HfO2 thin films deposited on n-type (100) crystalline silicon substrate. The formation of the unwanted interfacial SiO2 layer and its reduction due to the predeposited Hf metal buffer layer as well as the depth profiling and also structure of HfO2 thin films were investigated by in-situ SE, Fourier Transform Infrared spectroscopy, and Grazing Incidence X-ray Diffraction. The study demonstrates that the predeposited Hf metal buffer layer has played a crucial role in eliminating the formation of unwanted interfacial layer and that the deposited high-κ HfO2 thin films are crystalline although they were deposited at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: HfO2 thin films were prepared by reactive DC magnetron sputtering technique on (100) p-Si substrate. The effects of O2/Ar ratio, substrate temperature, sputtering power on the structural properties of HfO2 grown films were studied by Spectroscopic Ellipsometer (SE), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and X-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiOx suboxide layer at the HfO2/Si interface is unavoidable. The HfO2 thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O2/Ar gas ratio during sputtering, and substrate temperature. XRD spectra show that the deposited films have (111) monoclinic phase of HfO2, which is also supported by FTIR spectra. XPS depth profiling spectra shows that highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO2 to form HfO2, leaving Si–Si bonds behind. [Copyright &y& Elsevier]