IGZO-Based Simple, Scalable, and Linear Response Semitransparent Sensors for Sub-ppm NO₂ Detection

In this work, we present a chemiresistive sensor based on amorphous Indium Gallium Zinc Oxide (IGZO) for efficiently detecting sub ppm NO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>. Two-terminal devices were fabricated with inter-digitated electrodes and sputtered amorphous Indium Gallium Zinc Oxide (IGZO). IGZO films, used as the sensing material, were sputter deposited from an IGZO target having an In:Ga:Zn composition of 1:1:5. NO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors based on sputtered thin films from a target of In:Ga:Zn::1:1:5 composition have not been reported previously. The devices are very simple in terms of design, and the fabrication involves only two major steps of material deposition through hard masks. Elimination of lithographic techniques allows low-cost and scalable production, where many devices can be fabricated on a large area substrate, which can later be easily cut into individual devices. The devices are partially transparent owing to good transparency of IGZO and their responses to sub ppm NO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentrations are linear. The device with lower thickness (~10 nm) of IGZO shows maximum response (R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub>/R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub>) of 2.85. An exceptionally high linearity with a coefficient of determination (R<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) of 0.9912 was achieved for NO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentrations from 1 ppm to 0.05 ppm at a moderate temperature of 250 °C. Fabricating gas sensors based on IGZO-115 can lead to highly transparent gas sensors, which could be useful for applications such as smart sensing windows. Moreover, using IGZO-115 can allow fabrication of gas sensors and their signal conditioning electronic circuits on the same platform, as IGZO-115 has traditionally been used for transistors and integrated circuits.