Ho Doping Of Ba (zr <sub> 0.2 </ Sub> Of Ti <sub> 0.8 </ Sub>) The O <sub> 3 </ Sub> Dielectric Films Growth And Performance Research

As a sort of valuable ferroelectric materials, barium titanate BaTiO₃ (BTO) thin films have recently been of immense scientific and technological interests in the world. BaTiO₃(BTO) exhibit different characteristics related to the type of ionic substitutes and to substitution rate in A site or B site. Barium zirconium titanate (BaZr_xTi_1-xO₃, BZT in brief) is obtained by substituting the ion of B site of the BaTiO₃ with Zr. This is possible because Zr⁴⁺ is chemically more stable than the Ti⁴⁺ that the substitution of Ti⁴⁺ with Zr⁴⁺ would depress the conduction caused by electronic hoping between Ti⁴⁺ and Ti³⁺. Therefore, BZT could exhibit high dielectric tunability with low dielectric loss, so BZT thin films are being developed for tunable microwave device applications.In BZT system and a 0.2/0.8 mole fraction is known to show very good bulk properties, the effects of Ho-doping concentration on microstructure and dielectric properties of BZT films were studied.Firstly, Ho-doped BaZr_0.2Ti_0.8O₃ (BZT-xHo) thin films were prepared by pulse laser deposition (PLD) on Pt/Ti/SiO₂/Si substrates. The effects of Ho-doping concentration on microstructure and dielectric properties of BZT films were studied. Only out-of-plane BZT(111) peaks were observed in all the as-deposited BZT films with different Ho content. With the increasing of Ho content, BZT(111) peaks position shifted to high diffraction angle firstly, then to low, the dielectric constant and dielectric tunability first increased and then decreased, and the dielectric loss first decreased and then increased, which can be interpreted by the different Ho content can substitute different sites in BZT structure. Among the BZT-xHo thin films, BZT-3Ho had the best dielectric properties, whose dielectric constant and tunability were 473 and 66.9%, respectively, the dielectric loss was 1.6%.Secondly, BZT-xHo thin films were deposited on LaNiO₃(LNO) coated LaAlO₃(001) and SrRuO₃(SRO) coated MgO(001) single crystal oxide substrate. It had been found that BZT-xHo thin films could be with a cube-on-cube arrangement on single crystal oxide substrate. The dielectric properties of BZT-xHo thin films had the same tendency with the films deposited on Pt/Ti/SiO₂/Si substrates. BZT-3Ho thin films deposited on LNO/LAO substrates, whose dielectric constant and tunability were 457and 63.3%, respectively. The dielectric loss was 1.9%, and the FOM was 33.3. BZT-3Ho thin films deposited on SRO/MgO substrates, whose dielectric constant and tunability were 404 and 55%, respectively, the dielectric loss was 1.8%, and the FOM was 27.5. The results indicated that as the lattice parameter discrepany between LNO and SRO, the compressive stress of BZT-xHo on LNO is larger than that of BZT-xHo on SRO. The experimental results are benefit for the optimization of the non-linear dielectric properties of BZT thin films.Finally, A comparative study of heterolayered ferroelectric thin films (BZT-xHo/BST)with different film thickness of BZT-xHo and BST was carried out. It had been found that BZT-xHo thin films could be with a cube-on-cube arrangement on single crystal oxide substrate. Compared with homospheric BZT-3Ho thin films, BZT-xHo/BST possess the higher dielectric constant, with the increase of BST film thickness, the dielectric constant and tunability and dielectric loss increased. In this paper, we discussed the enlarge dielectric constant with Maxwell-Magner pattern. Our results indicated that the bilayer structure was beneficial to enhancing the figure of merit (37).