RF Sputtered CeO₂Thin Films-Based Oxygen Sensors

Abstract

In this paper, we report the scalable, high sensitivity, fast response, and low operating temperature Cerium oxide (CeO ₂ ) thin film-based oxygen sensors by optimizing CeO ₂ film thickness. CeO ₂ thin films of thickness ranging from 90 to 340 nm have been deposited at 400°C using radio frequency (RF) magnetron sputtering on Al ₂ O ₃ substrates. Ellipsometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) have been used to characterize the CeO ₂ films for their thickness, structural, compositional/chemical, and surface morphology properties. Gas sensors have been fabricated using CeO ₂ film as a sensing material and tested in an oxygen gas environment. CeO ₂ film with an optimum thickness of 260 nm has shown high sensitivity (12.6) and fast response time (≤10 s) along with fast recovery time (15 s) at a low operating temperature of 400°C. To the best of our knowledge, these are the best values reported till date for undoped CeO ₂ thin film-based oxygen sensors. Furthermore, from the sensor's response, it was observed that there was no drifting from the baseline. This superior performance of CeO ₂ thin film-based oxygen sensor may be attributed to the combination of three factors, i.e., 1) high surface energy and reactivity due to the presence of (200) oriented CeO ₂ plane; 2) low resistance due to better crystallinity; and 3) perfect stoichiometry with required roughness.