Characterization of thin-film decoupling and high-frequency (Ba,Sr)TiO3 capacitors on Al2O3 ceramic substrates

In this paper we present the results of the characterization of parallel-plate thin-film (Ba1-xSrx)TiO3 (BST) capacitors, to demonstrate their suitability for use as decoupling capacitors (a capacitance as high as 0.34muF and a capacitance density of up to 70 fF/mum(2)) and as tunable RF components (a small capacitance from 0.5 pF to 16pF, a high tunability of 4.22:1 at 10 V and a capacitance density of up to 34fF/mum(2)). BST films of different compositions, (Ba0.7Sr0.3)TiO3 and (Ba0.5Sr0.5)TiO3, were grown by metal-organic decomposition (MOD) and RF magnetron reactive sputtering on Pt/TiOx/SiO2/Al2O3 ceramic substrates. For large capacitors (2.25 mm(2)), capacitance and tan E were measured at low frequencies (1 kHz) using an LCR meter. Smaller capacitors (16mum(2) to 961 mum(2)) were characterized in the frequency range of 0.01-20 GHz. Capacitance, tan delta and equivalent series resistance (ESR) were extracted from two port scattering parameters obtained using a vector network analyzer (VNA). The relationships between dielectric loss, tunability and commutation quality factor (CQF) vs BST composition and deposition conditions were outlined.