MOCVD of Alkaline Earth Titanates for Integrated RF Capacitors

ABSTRACTThe high permittivity of BaSrTiO3 (BST) gives it the potential to replace discrete “passive” capacitors used in portable and wireless applications with integrated capacitors. Bringing thin film devices directly onto Si and GaAs chips shortens lead length and improves overall circuit Q values by reducing inductance, important at RF frequencies. A metalorganic chemical vapor deposition (MOCVD) process has been developed for this purpose. By modifying the basic BST stoichiometry, we have demonstrated charge storage densities up to 3,000 nF/cm2 with leakages below 10−8 A/cm2 at 3 V, and second order dielectric nonlinearities below 100 ppm/V2. For stoichiometric BST, Q factors are as high as 500 at kHz frequencies, and evidence suggests that low losses can be retained up through the L and S microwave bands (1 -4 GHz) in the modified titanates. These properties make alkaline earth titanate films suitable for use in decoupling and bypass capacitors, as well as switched capacitor filters.