Room-Temperature Conformally Coated Cotton Fabrics for Integrated Textile Sensors

In this work, cotton fabrics were conformally coated with ZnO layers via self-limiting atomic layer deposition (ALD) at substrate temperatures ranging from room temperature up to 120 °C. Structural analysis of coated samples revealed a dominant wurtzite h-ZnO (002) orientation, with grain size increasing from 8.1 to 11.3 nm, and dislocation density decreasing accordingly, as a function of deposition temperature from room temperature to 120 °C. SEM and EDX analyses confirmed that ZnO formed a uniform coating on the cotton fibers and that Zn was homogeneously distributed throughout the textile surface. Direct SEM thickness measurements indicate that the conformal ZnO coating on individual cotton fibers has an average thickness of approximately ∼55 nm. Furthermore, X-ray photoelectron spectroscopy confirmed the surface chemical composition and oxidation states of the films. The measured optical band gaps ranged from 3.18 to 3.28 eV, while Urbach energies decreased with increasing deposition temperature, indicating reduced defect density. Photodetector devices fabricated on ZnO-coated cotton exhibited strong UV photoresponse, with ON/OFF ratios increasing from 1.4 to 161 at 10 V bias, depending on deposition conditions. The highest ON/OFF ratio was observed for the device with thermally deposited ZnO at RT. Time-dependent I-V and I-t measurements confirmed repeatable photoresponse and stable operation under continuous illumination for extended durations. Furthermore, the textile-integrated photodetectors have demonstrated their suitability for flexible and wearable optoelectronic sensing applications by maintaining measurable photoresponse under cyclic bending, uniaxial tensile strain of up to 6%, and severe manual compression. These findings demonstrate the potential of low-temperature ALD-grown ZnO films for inherently integrated textile sensors.