Reliable ferroelectricity in sol-gel-derived BiFeO₃ thin films below 200 nm

To evaluate optimizing processing conditions for bismuth ferrite BiFeO3 (BFO) thin films with thicknesses below 200 nm on Pt(111)/Ti/SiO2/Si substrates. The impact of the amorphous components, as well as defects and elemental composition changes and microstructure evolution (i.e., grain size) as regulated by the treatment temperatures (475-600degree celsius) on the ferroelectric and dielectric properties are investigated. The current work shows that with the smallest grain size and the least defects amount achieved in the film annealed at 550degree celsius, the conductivity is compressed greatly. Such a temperature will also allow adequate ferroelectric switching by reducing the amorphous components, which remain the majority below 500degree celsius and thus reinforce the polarization switching. The leakage path is deduced via crystallized grains in BFO thin films instead of the remaining including grain boundaries and amorphous components. The best remanent polarization of similar to 60.4 mu C center dot cm(-2) from PUND measurements excluding the leakage contribution at 500 kV center dot cm(-1) and an excellent fatigue property of 10(6) cycles are achieved. In addition, broadened fabrication temperatures for amorphous-protected polycrystalline BFO thin films from 525 to 575degree celsius, exhibiting superior ferroelectricity than most previously reported BFO thin films below 200 nm, either derived by chemical or physical methods. Ultimately, it is suggested that for leaky ferroelectrics such as BFO, optimal annealing temperature should balance the amorphous components by reducing the annealing temperature while maintaining adequate crystallization for ferroelectric switching.