RF Sputtered CeO2 Thin Films-Based Oxygen Sensors

Abstract

In this paper, we report the scalable, high sensitivity, fast response, and low operating temperature Cerium oxide (CeO<inf>2</inf>) thin film-based oxygen sensors by optimizing CeO<inf>2</inf> film thickness. CeO<inf>2</inf> thin films of thickness ranging from 90 to 340 nm have been deposited at 400°C using radio frequency (RF) magnetron sputtering on Al<inf>2</inf>O<inf>3</inf> substrates. Ellipsometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) have been used to characterize the CeO<inf>2</inf> films for their thickness, structural, compositional/chemical, and surface morphology properties. Gas sensors have been fabricated using CeO<inf>2</inf> film as a sensing material and tested in an oxygen gas environment. CeO<inf>2</inf> 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<inf>2</inf> 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<inf>2</inf> 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<inf>2</inf> plane; 2) low resistance due to better crystallinity; and 3) perfect stoichiometry with required roughness. © 2001-2012 IEEE.