Design, Fabrication and Material Properties of Temperature Stable Performance Consistent Tunable Devices

摘要

The premier candidate active material for tunable microwave phase shifter devices is single composition, paraelectric BaSrTiO_3 (BST). However, there is concern that in practical applications the device performance will be compromised due to the temperature dependence of the BST based device capacitance. We report a device design which controls the magnitude and the sign of the temperature coefficient of capacitance (TCC) via a multilayer paraelectric BST/buffer layer/ferroelectric BST coplanar device structure. To realize this multilayer device structure we have designed, fabricated, and optimized a 10 mol% Al doped Ta_2O_5 barrier layer with low loss (tan ? = 0.004), moderate permittivity (epsilon_r = 42.8), low TCC (-20 ppm/°C), and a low bias stability of capacitance (0.4%). The thin film integration of the barrier layer with the BST layers was optimized for structure, microstructure, interfacial/surface morphology, and dielectric properties as a function of Al doping concentration, annealing temperature, material growth and integration process parameters.