Tailoring CuOx Films via Open-Air Spatial Atomic Layer Deposition and Their Application in Room-Temperature Humidity Sensing

Abstract

This study demonstrates the tunability of copper oxide (CuOx) thin films synthesized using open-air atmospheric-pressure spatial atomic layer deposition (AP-SALD). By systematically varying the deposition temperature and copper precursor flow rate, as well as introducing nitrogen doping through in situ oxidant switching (from H2O to ammonium hydroxide (NH4OH)), the crystallinity, oxidation state, chemical composition, carrier concentration, and resistivity of CuOx films are modulated. Under optimized conditions, CuOx films achieve a very low resistivity of 0.178 Ω·cm and a high carrier concentration of 1019 cm−3—among the best reported for AP-SALD-deposited CuOx. As proof of properties tailoring, these films are integrated into interdigitated-electrode devices and evaluated as chemiresistive humidity sensors at room temperature. While CuOx films cannot typically sense humidity at room temperature, a film deposited at 225 °C and 350 sccm Cu flow exhibits a limit of detection of 99 ppm and a sensitivity of 0.244 Ω ppm−1. This work establishes AP-SALD as a powerful tool for tuning CuOx film properties via controlled deposition conditions and in situ doping—enabling application-specific optimization for future optoelectronic or sensing platforms.