Fabrication and characterization of ferro- and piezoelectric multilayer devices for high frequency applications: Dissertation

By means of thin film technology a reduction of size, cost, and power consumption of electronic circuits can be achieved. The required specifications are attained by proper design and combina-tions of innovative materials and manufacturing technologies. This thesis focuses on the develop-ment and fabrication of low-loss ceramic thin film devices for radio and microwave frequency applications. The materials, growth conditions, and physical properties of the films and device structures are discussed in detail. Moreover, special emphasis is placed on the integration of highly conductive low-loss electrode materials into parallel-plate structures. The thin films were prepared by sequential magnetron sputtering from metallic and ceramic depo-sition targets. The devices under study include tunable ferro-electric barium strontium titanate and lead strontium titanate parallel-plate capacitors, and piezoelectric aluminum nitride thin film bulk acoustic wave resonators. Furthermore, tantalum pentoxide and tantalum nitride thin films were in-vestigated for capacitor and resistor applications. As electrode material we used Au, Cu, Mo, and Pt. The use of highly conductive low-loss Cu electrodes was only possible after the development of a new layer transfer fabrication method for parallel-plate ceramic devices. This method, which was successfully used to fabricate tunable ferroelectric capacitors and AlN bulk acoustic wave resonators, allows for high-quality ceramic film growth on suitable substrate and seed layers and, most importantly, deposition of the bottom and top electrodes after high-temperature reactive sput-tering of the ceramic material. Optimization of the ceramic growth conditions and the integration of these func-tional materials into low-loss parallel-plate structures resulted in state-of-the-art device performance. Key achievements include, device quality factors of more than 100 up to GHz frequency in ferroelectric parallel-plate capacitors, the tai-loring of ferroelectric film properties using substrate bias during magnetron sputtering, and very efficient electro-acoustic coupling in Mo/AlN/Mo bulk acoustic wave resonators.