Ferroelectric ZrO2 ultrathin films on silicon for metal-ferroelectric-semiconductor capacitors and transistors

Enhanced ferroelectric properties of nanoscale ZrO2 thin films by an HfO2 seed layer are demonstrated in metal-ferroelectric-semiconductor (Si) capacitors and transistors prepared with a low thermal budget of 400 °C. The seeding effect of the HfO2 layer leads to the enhancement of crystallization into the orthorhombic phase and the increase of remnant polarization of the sub-10 nm ZrO2/HfO2 bilayer structure. The ferroelectric field-effect transistor with the ZrO2/HfO2 bilayer gate stack reveals a large memory window of ~1.2 V and a steep subthreshold swing below 60 mV/decade. As compared with the Hf0.5Zr0.5O2 thin film, superior ferroelectric properties of the ZrO2/HfO2 bilayer structure show great potential for ferroelectric memory devices fabricated on Si substrates.