H. Li et al., Dependence of dielectric properties on internal stresses in epitaxial barium strontium titanate thin films, APPL PHYS L, 78(16), 2001, pp. 2354-2356
A series of heteroepitaxial BaxSr1-xTiO3 thin films with composition x = 0.
50 were deposited on (001) MgO substrates by pulsed-laser deposition. The t
hickness of the films was varied from 14 to 500 nm to produce a systematica
lly decreasing level of in-plane tensile stresses. The microstructural and
crystallographic features of the films were determined via transmission ele
ctron microscopy and x-ray diffraction. A theoretical treatment of the in-p
lane misfit strain as a function of film thickness is in agreement with the
measured out-of-plane lattice parameters. Electrical measurements indicate
a drop in the dielectric constant from 2350 for highly stressed thin films
to 1700 for relaxed thicker films. The variation in the dielectric constan
t with the misfit strain is in accordance with a thermodynamic model develo
ped. The relationship between the dielectric constant and electric field is
also described by extending the thermodynamic model and taking the effect
of electric field into account. A new definition of tunability is adopted t
o study the effect of strain on tunability. (C) 2001 American Institute of
Physics.