Effect of adsorbate- surface interactions on the electrical properties of bst capacitors for voltage tunable device applications

In recent years, wireless-communications demands of mobile applications have been increasing and a shortage of frequency resources is predicted in near future. Microwave tunable devices are potentially important components of reconfigurable communication systems which are needed to more effectively use frequency resources. Perovskite structure metal titanate (ATiO3) thin films are a leading candidate for microwave voltage tunable dielectric materials due to their high tunability and relatively low loss. Previous studies have indicated that common atmospheric or vacuum system contaminates, such as CO2 and H2O, can have a marked deleterious effect on ATiO3-based capacitor properties. However, the basic mechanisms of the degradation and how these molecules interact and bond to ATiO3 surfaces remains not well understood. In the talk, we will first present the results of studies of the interaction of CO2 and H2O with pristine vacuum fractured surfaces of bulk SrTiO3(001) investigated using x-ray and ultra violet photoemission spectroscopies and density functional theory which helps clarify how these molecules bond and interact with the perovskite structure surface. Secondly, we will present the results of studies with controlled CO2 and H2O exposure to BST thin film surfaces and show how these adsorbates influence the voltage induced tunability and dielectric loss and reliability properties of BST-based thin film capacitors. Based on the results, strategies for minimizing degradation of perovskite structure metal titanate -based thin film capacitors will be discussed. This work was supported in part by the Ministry of Internal Affairs and Communications (MIC) of Japan.