Impact of Bottom Electrode Crystallinity on Ferroelectricity of La-Doped HfO2

This study investigated the effect of the bottom electrodes on the ferroelectricity of La-doped HfO2 (HLO) capacitors. The remanent polarization (2Pr) of HLO capacitors with different bottom electrodes, including heavily doped p-type single crystal Ge and Si substrates, TiN, and polycrystalline Ge (poly-Ge), varies significantly. The TiN/HLO/Ge capacitors demonstrate superior ferroelectric performance owing to the absence of a dielectric interfacial layer and the single crystallinity of Ge substrates. Furthermore, improving the crystallinity of bottom electrodes can result in a considerable enhancement in remanent polarization. The pre-annealing process carried out on poly-Ge electrode is found to be effective in stabilizing the orthorhombic phase and enhancing the ferroelectricity of HLO capacitors, with 2Pr values increasing from $14.8 ~\mu \text{C}$ /cm2 to $27.5 ~\mu \text{C}$ /cm2. Similar results are observed in capacitors with annealed TiN as bottom electrodes. It is irrefutable that the ferroelectricity of HLO capacitors strongly depends on the crystallinity of the bottom electrode. This discovery offers a solid explanation and experimental evidence for the effect of the bottom electrodes on ferroelectric devices and provides novel insights for optimizing ferroelectric properties.