Development of CeO2-HfO2Mixed Oxide Thin Films for High Performance Oxygen Sensors

Abstract

In this work, the authors report the fabrication and characterization of CeO2 -HfO2 mixed oxide thin film based oxygen gas sensors. The atomic concentrations of the individual elements Ce and Hf in the mixed oxide (CeO2 -HfO2) thin films were controlled and tuned using a novel method in RF sputtering to achieve better oxygen sensing characteristics. The characteristics of the sensing film were evaluated using various characterization techniques such as TEM-EDS, FESEM-EDS, XPS and XRD. The XPS and EDS data revealed that the Hf concentration increases with an increase in size as well as number of the HfO2 pellets that are placed on a 3-inch CeO2 target during sputtering. From the XRD and XPS analysis, it was found that the mixed oxide film with 10-11% Hf atomic concentration has the best sensing characteristics. The superior sensing characteristics of the CeO2 -HfO2 film can be attributed to the existence of a highly reactive plane (200) with the highest surface energy and a strongly reduced surface with oxygen vacancy formation due to the presence of Ce3+ ions and HfOx, x < 2 on the surface of the mixed oxide film. The sensor film detected the presence of oxygen gas even at low temperatures (< 400°C); however, the response time and recovery time were slightly higher. The sensor film of thickness 220 nm with Hf concentration between 10-11% showed excellent sensitivity (15), fast response and recovery times of 8 s and 10 s respectively at an operating temperature of 400°C, which are the best values reported till date for CeO2 based oxygen sensors. © 2001-2012 IEEE.