Ultraviolet sensing using a TiO2 nanotube integrated high resolution planar microwave resonator device

Abstract

This paper presents a unique integrated UV light sensing concept and introduces a device with a detection limit of 1.96 nW cm⁻². The combination of a high quality factor, a microwave planar resonator (Q ∼ 50 000) with a semiconducting nanomaterial enables a revolutionary potential paradigm for photodetection of low light intensities and small form factors. The presenting device employs a high-resolution microwave microstrip resonator as the signal transducer to convert the variant dielectric properties (permittivity and conductivity) of the nanotube membrane into electrical signals such as the resonant frequency, quality factor and resonant amplitude. The microwave resonator has an active feedback loop to improve the initial quality factor of the resonator from 200 to 50 000 and leads to boosting of the sensing resolution by orders of magnitude. Anatase TiO₂ nanotubes are assembled on the surface of the microwave resonator. Upon exposure to UV light, electron–hole pair generation, trapping and recombination in the nanotubes are exploited as a unique signature to quantify the UV light intensity. The change of dielectric properties of the nanotube membrane is monitored using the underlying active microwave resonator. The proposed concept enables the detection and monitoring of UV light at high resolution, with very small exposure power and integrated form factors.