High-Performance Integrated ZnO Nanowire UV Sensors on Rigid and Flexible Substrates

Due to the large surface area-to-volume ratio and high quality crystal structure, single nanowire (NW)-based UV sensors exhibit very high on/off ratios between photoresponse current and dark current. Practical applications require a large-scale and low-cost integration, compatibility to flexible electronics, as well as reasonably high photoresponse current that can be detected without high-precision measurement systems. In this paper, NW-based UV sensors were fabricated in large-scale by integrating multiple NWs connected in parallel via the contact printing method. Linear scaling of the photoresponse current with the number of NWs is demonstrated. Integrated ZnO NW UV sensors were fabricated on rigid glass and flexible polyester (PET) substrates at the macroscopic scale. The flexible and rigid sensors performed comparably, exhibiting on/off current ratios approximately three orders of magnitude higher than sensors made from polycrystalline ZnO thin films. Under UV irradiance of 4.5 mW cm-2 and 3 V bias, photoresponse currents and on/off current ratios for the rigid and flexible UV sensors reached 12.22 mA and 82 000, and 14.1 mA and 120 000, respectively. This result suggests that lateral integration of semiconductor NWs is an effective approach to large-scale fabrication of flexible NW sensors that inherit the merits of single-NW-based systems with unaffected performance compared to using rigid substrate.