Abstract
The class of transparent conductive oxides includes the material indium tin oxide (ITO) and has become a widely used material of modern every-day life such as in touch screens of smart phones and watches, but also used as an optically transparent low electrically-resistive contract in the photovoltaics industry. More recently ITO has shown epsilon-near-zero (ENZ) behavior in the telecommunication frequency band enabling both strong index modulation and other optically-exotic applications such as metatronics. However, the ability to precisely obtain targeted electrical and optical material properties in ITO is still challenging due to complex intrinsic effects in ITO and as such no integrated metatronic platform has been demonstrated to-date. Here we deliver an extensive and accurate description process parameter of RF-sputtering, showing a holistic control of the quality of ITO thin films in the visible and particularly near-infrared spectral region. We are able to custom-engineer the ENZ point across the telecommunication band by explicitly controlling the sputtering process conditions. Exploiting this control, we design a functional sub-wavelength-scale filter based on lumped circuit-elements, towards the realization of integrated metatronic devices and circuits.
Highlights
Indium Tin Oxide films have been extensively employed for diverse applications in the fields of optics and electronics in both research and industry[1]
We show the holistic control of the quality of indium tin oxide (ITO) thin films in the visible and near-infrared spectral region
We thence develop an interdependently-complete set of metrology processes for determining the conductivity, carrier density, and mobility of these ITO films and bring them in congruence with values obtained from spectroscopic ellipsometry
Summary
Indium Tin Oxide films have been extensively employed for diverse applications in the fields of optics and electronics in both research and industry[1]. The ultimate aim in our work is not characterizing the film optical and electrical properties, which to a certain extent has been reported in[36,37,38,39] for RF-sputtered films, and to provide specific guidelines to other research groups and engineers in the selection of process parameters required to fabricate optimized optical modules based on ITO for integrated photonics and plasmonics It is essential when fabricating ITO-based active optical component to hand-pick the process parameters, which provides favorable initial material conditions (without applying any bias), such as proximity to ENZ or damping, to optimize the device figure of merits, such as insertion losses (IL), extinction ratio (ER), device length (L) and bias required for modulation (e.g. Vπ). The step height of ITO films is measured in multiple areas for estimating the uniformity of the deposition and determining the initial fitting parameters in our spectroscopic ellipsometry
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