The fabrication and material properties of compositionally multilayered Ba1-xSrxTiO3 thin films for realization of temperature insensitive tunable phase shifter devices

Compositionally layered BaxSr1-xTiO3 (Ba0.60Sr0.40TiO3-Ba0.75Sr0.25TiO3-Ba0.90Sr0.10TiO3) 220 nm thin film heterostructures were fabricated on Pt coated high resistivity Si substrates via the metal organic solution deposition technique (MOSD). Optimization of the material design was achieved by evaluating two integration schemes, namely, the single- and multianneal process protocols. Materials characterization demonstrated that both film process protocols resulted in smooth, dense, crack-free films with a single phase perovskite structure. Rutherford backscattering spectroscopy revealed compositionally distinct layers and severe elemental interdiffusion for the films fabricated via the multianneal and single-anneal process protocols, respectively. The retention of the compositional layering subsequent to film crystallization deemed the multianneal processed BaxSr1-xTiO3 (BST) film suitable for evaluation of dielectric properties. The dielectric properties were compared to both paraelectric uniform composition BST and to the relevant compositionally graded BST films reported in the technical literature. Our results made evident that the multiannealed compositionally layered BST films possessed higher permittivity (epsilon(r)=360) and lower dissipation factor (tan delta=0.012) with respect to both uniform composition paraelectrie Ba0.60Sr0.40TiO3 film fabricated via the same MOSD processing method and the relevant literature values for compositionally graded BST films. The multilayered BST material design exhibited minimal dielectric dispersion in the range of 90 to - 10 degrees C, showing a 6.4% decrease in permittivity (corresponding to a temperature coefficient of capacitance TCC20-90=-0.921) as the temperature was elevated from 20 to 90 degrees C and only a 2.1 increase in permittivity (TCC20-(-10)=-0.716) as the temperature was lowered from 20 to -10 degrees C. Additionally, the dielectric tunability of the multilayered BST structures over the temperature range of -10-90 degrees C was temperature independent. Our results show that the multilayered BST design has excellent dielectric properties and the enhanced tunability and dielectric loss are stable over a relatively broad temperature range of -10-90 degrees C, thereby making them excellent candidates for the next generation of enhanced performance temperature stable tunable devices. (c) 2007 American Institute of Physics.