Towards integrated metatronics: a holistic approach on precise optical and electrical properties of Indium Tin Oxide

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.

Broadband frequency translation through time refraction in an epsilon-near-zero material

“…The magnitude of the frequency translation is primarily limited by the linear loss, higherorder nonlinear optical effects, dispersion, and the interplay between the pulse width and the interaction time. We note that the ENZ spectral region of ITO and other conducting oxides can be tuned at any wavelength between 1 µm and 3 µm by choosing the appropriate doping level 49,50 . Furthermore, because the effect is present in a bulk, homogeneous and isotropic material, one can engineer nanostructures incorporating ENZ media such as plasmonic waveguides, photonic crystal waveguides, and dynamic metasurfaces to arbitrarily control the sign and the magnitude of the frequency shift in order to build efficient octave-spanning frequency tuners while simultaneously lowering the required pump power by a few orders of magnitude 9 .…”

Coupling-enhanced dual ITO layer electro-absorption modulator in silicon photonics

“…1). Without bias, the dual ITO layers are in flat band condition (assuming same doping levels verified in ref 31 , thus the ITO layers are in a low-loss state (ITO is dielectric with low carrier concentration). Here, the DC's beating length is much longer than the island length resulting in high transmission at the bus waveguide ( Fig.…”

“…For instance, we measure an initial carrier concentration (without electrical bias) of 1.2 × 10 BC cm FG for our as-deposited ITO from Hall-bar measurement, which is rather low due to the absence of a post-deposition thermal treatment. Then broadband (193-1690 nm) ellipsometric spectroscopy is performed and fitted with the Lorentz oscillator, Cauchy model and Drude models in order to extract the ITOs film parameters at zero bias giving a damping rate of 9.5 × 10 BG rad/s, at the lowest mean square error (MSE) 31 . Fabricated devices, (with the 10 nm Al2O3 gate oxide) show an ITO carrier concentration in the accumulation layer of 5.1 × 10 HR cm FG for 4 V electrical bias, while the optical property of ITO with carrier concentration is plotted in Fig.…”

Integrated photonic FFT for photonic tensor operations towards efficient and high-speed neural networks

“…We selected a minimum waveguide bending radius of 50 μm to keep the radiative bending losses low, resulting in a delay-line spiral area of 3.9 × 10 −3 mm 2 for T. Sampling is required to obtain the frequency components of the transfer function of the FFT, realized with back-end electrooptic modulators in silicon photonics e.g. Ref [16] or alternatively with emerging modulator-concepts featuring heterogeneous integration of strong-index changes materials such as transparent conductive oxides featuring strong light matter interaction near epsilon near zero (ENZ) operating points [54,55], and micrometer compact MZI ITObased modulators [21][22][23], see also work from the Wong and Brongersma groups (see Figure 4 for nanophotonics- Figure 2: Two options of implementing an optical temporal FFT. Photonic CNN paradigm utilizing Fourier-optics based on integrated photonics.…”