Scalable Single-Step Open-Air Combinatorial Growth of Multifunctional Metal Oxide Thin Films by Spatial Atomic Layer Deposition.

Compositionally graded metal oxide thin films enable rapid exploration of structure-property relationships, yet their fabrication typically relies on vacuum-based, multistep processes. Here, we present an atmospheric-pressure spatial atomic layer approach that enables the single-step, open-air synthesis of zinc-tin-oxide (ZTO) thin films with lateral compositional gradients over 3-in. wafer-scale substrates. A custom reactor head with spatially tailored precursor delivery generates continuous and reproducible composition gradients in under 1 h without vacuum processing or sequential depositions. Comprehensive structural, morphological, optical, and compositional characterization confirms smooth lateral variations in ZTO film composition and crystallinity, with Sn/Zn atomic ratios spanning approximately 0.4-0.8 across one of the films, forming unique material libraries in a single open-air deposition step. As a proof of concept, the graded ZTO films are integrated into chemiresistive sensor arrays comprising 20 compositionally distinct sensing columns on a single wafer, exhibiting composition- and temperature-dependent (at 200 °C) responses to volatile organic compounds within a single device platform. Additionally, electrical measurements performed across the gradient show unique current-voltage properties at each composition, alluding to multi-usage in electronic applications within the same chip. This work establishes a scalable and cost-effective strategy for rapid fabrication of oxide material libraries and wafer-scale collective device assemblies under ambient conditions.