Epitaxial growth of bazn_1/3ta_2/3o₃ thin-films for microwave applications

BaZn_1/3Ta_2/3O₃ (BZT) ceramics are widely used in current microwave communication applications due to the material's large-dielectric constant (ε_r > 25), ultra-low loss tangent (tan δ < 2×10^-5 at 2 GHz) and a near-zero temperature-coefficient of resonant frequency (τ_f∼O). In this paper, we report the first growth of epitaxial BZT thin films. The films are grown on MgO substrates using pulsed laser deposition. X-ray diffraction data indicate the films have a disordered pseudocubic perovskite structure with a small tetragonal distortion (i.e. a = b = 4.100 A; c = 4.088 A). An optimized substrate temperature of 575°C results in films which are over 98% oriented in the (001) direction and are relatively smooth (rms roughness of 5.2 A). X-ray diffraction φ scans of off-axis (202) reflection show four-fold symmetry, indicating a high degree of in-plane epitaxy, albeit with small angle grain boundaries. The refractive index of epitaxial BZT films is inferred to be 5 from Fabry-Perot fringes in optical transmission spectra. Substrate temperatures during growth are limited to ∼600°C as a result of Zn loss.