Control and elimination of biaxial strain in laser-ablated epitaxial BaxSr1-xTiO3 films

We report the in-plane (a) and out-of-plane (c) lattice parameters of epita xial laser-ablated Ba0.4Sr0.6TiO3 films on MgO for a range of O-2 depositio n pressures (40-250 mTorr) near the observed transition from a <c to a >c. From these lattice parameters, we calculate the residual strain and stress in terms of hydrostatic and biaxial components. Both components increase sh arply with O-2 pressure between 85 and 100 mTorr, consistent with ion peeni ng effects. Postdeposition annealing decreases the hydrostatic strain, but increases the biaxial tension. For both as-deposited and annealed films, we obtain samples with no biaxial strain (i.e., a=c), within experimental unc ertainty. Overall, the strain is a combination of hydrostatic and biaxial c omponents, both of which affect the dielectric response. Therefore, conside ration and control of both types of strain is important for the optimum per formance of devices such as tunable microwave devices and high-density memo ries. (C) 2000 American Institute of Physics. [S0003-6951(00)01533-3].