In this work, we report on the critical role of the substrate selection to determine the amount of the metastable orthorhombic ferroelectric phase in La doped HfO2 films. Films grown on LSMO with smaller cLSMO (larger in-plane lattice parameter ultimately determined by the substrate selection) show larger amount of orthorhombic phase. While comparing La doped films with films doped with Zr grown in the same conditions, it is observed that La doping results in larger remanent polarization.
Films on scandate substrates (GdScO3 and TbScO3) have high values of Pr = 25 - 29 mC/cm2. The large effect of both doping and stress indicates that both impact on the functional properties of HfO2 without competing, instead these cooperate and large remanent polarization can be obtained. Remarkably important for the integration of ferroelectric hafnium oxide with other functional materials, the number of substrates where the ferroelectric phase grows is larger for La: HfO2 than for Hf0.5Zr0.5O2 films.
Oxides for new-generation electronics
Synergetic contributions of chemical doping and epitaxial stress to polarization in ferroelectric HfO2 films