Harnessing inherent charge retention characteristics of ZnO thin films for capacitive ultraviolet dosimeters

Over the years, ZnO, a well-known transparent semiconducting oxide (TSO) has been continuously investigated due to its inherent electronic and optoelectronic properties. Despite its remarkable visible blind optoelectronic properties, its application as a UV-specific detector remains a challenge due to its slow recovery. Although this charge retention characteristic is beneficial for synaptic applications, it becomes disadvantageous for UV detection and monitoring purposes. Thus, a gap remains in utilising this well-established TSO's charge retention characteristics as a UV detector and cumulative dosage calculator in the visible-blind region. Hence, an alternate instrumentation strategy is needed to exploit the UV-only absorption properties of ZnO to demonstrate a reliable UV-based dosimeter. In this work, we exploit the structural design of interdigitated electrodes (IDE) to utilise the capacitive properties of RF-sputtered ZnO thin films. Significantly large capacitance changes in the range of 10 ⁻¹¹ – 10 ⁻⁹ F are observed in the device upon UV illumination. The ZnO-based device demonstrates an increasing trend in capacitive changes upon cumulative UV exposure, even at low intensities of 50 μW/cm² which, remains unobserved in its resistive changes. The performance of the devices is evaluated under the influence of humidity and temperature and its feasibility as a dosimeter is demonstrated. Such a demonstration on a flexible platform provides a pathway for integrating ZnO thin films as a wearable UV dosimeter monitoring device in the future.