Microstructure/dielectric property relationship of low temperature synthesised (Na,K)NbO_x thin films

摘要

Thin films of (Na,K)NbO_x (NKN) were grown by reactive RF magnetron sputtering on polycrystalline Pt_(80)Ir_(20) substrates, at relatively low growth temperatures between 300℃ and 450℃. The results show that the electrical performance and the microstructure of the films are a strong function of the substrate temperature. X-ray diffraction of films grown up to 400℃ revealed the formation of only one crystalline NKN-phase with a preferred (002)-orientation, However, a mixed orientation together with a secondary, paraelectric potassium niobate phase, were observed for NKN films deposited at 450℃. The differences in the microstructure explains the variations in the dielectric constants and losses: The single phase NKN films displayed a dielectric constant and a dielectric loss of 506 and 0.011, respectively, while the films with mixed phases exhibited values of 475 and 0.022, respectively. The possibility of fabricating NKN films with relatively high dielectric properties at low growth temperatures, as demonstrated here, is of high technological importance.