Development of Improved Microwave Dielectric Materials and Devices using Advanced Experimental and Theoretical Methods

Our work has made important progress towards developing a fundamental understanding of the microscopic mechanism that causes loss in high performance microwave dielectrics, and can explain why some dielectric materials exhibit markedly better performance than others. Ab-initio electronic structure calculations elucidated the physical reason for this desirable microwave properties in BaCd13Ta23O3 BCT and BaZn13Ta23O3 BZT. The presence of significant charge transfer between cation d-orbitals provides a degree of covalent directional bonding between atoms that resist angular distortions, a property absent in conventional ionic compounds. We have also been able to show a direct correlation between the number of point defects present and enhanced microwave loss. High quality single-crystalline BZT films were also produced, for the first time. The availability of single crystal materials is essential to the fundamental studies. Zn-enriched targets and high oxygen pressures are used to compensate for Zn loss during film growth. The BaZn13Ta23O3 films have an indirect band gap of 3.0 eV and a refractive index of 1.91 in the visible. Development of high dielectric-constant material with diminished microwave loss and a near-zero temperature coefficient of resonant frequency, will enable the production of smaller and higher performance microwave devices.