Permittivity increase of yttrium-doped Hf O2 through structural phase transformation

An approach to control the dielectric properties of hafnium-based oxide films with an intentional structural phase transformation was proposed and demonstrated. Yttrium serves effectively as a dopant to induce a phase transformation from the monoclinic to the cubic phase even at 600 °C. The yttrium-doped Hf O2 films show higher permittivity than undoped Hf O2, and the permittivity as high as 27 is obtained by 4 at. % yttrium doping. The permittivity enhancement by yttrium doping can be explained by the shrinkage of molar volume due to the structural phase transformation. The advantage of yttrium doping is more pronounced at higher temperatures, since the permittivity of undoped Hf O2 is reduced significantly, whereas that of 17 at. % yttrium-doped film shows no change even at 1000 °C.