Effects of substrate on the crystalline structure and microwave dielectric properties of Bi1.5Mg1.0Nb1.5O7 sol-gel thin films

Cubic pyrochlore Bi1.5Mg1.0Nb1.5O7 (BMN) thin films were prepared on substrates including amorphous glass, mono-crystal silicon and poly-crystal Ba(Mg1/3Nb2/3)O3 ceramic by sol-gel technique with rapid thermal annealing (RTA). The effects of different substrates on the structures and microwave dielectric properties were investigated. The results showed that the BMN thin film deposited on the Si(1 0 0) exhibited best crystallinity and highest dielectric constant, with strong (2 2 2) orientation. While the glass and ceramic samples presented relative lower crystallinity and dielectric constant, with a slightly (2 2 2) and (4 0 0) orientations, respectively. Dielectric relaxation was observed in the film on ceramic substrate in the microwave frequency region. It was found that the crystalline structures were remarkably influenced by the type of the substrates, which was mainly due to the thermal mismatch between the films and the substrates. The substrate-dependence of the microwave dielectric properties in the BMN thin films was attributed to the combined effects of crystallinity, orientation and thermal strain.