Lateral variations of the surface electric potential and elastic stiffness of ultrathin Hf0.5Zr0.5O2 films on silicon

Lateral variations of the surface electric potential and the elastic properties of ultrathin HfxZr1−xO2 films have strong impact on the performance of lead-free ferroelectric devices. Here, we compared lateral uniformity of electric and elastic properties of polycrystalline thin Hf0.55Zr0.45O2 films (10 nm–50 nm) prepared by sputtering on Si. Crystallization of 10-nm-thick films at 600° C and 700 °C resulted in predominantly crystal grains with the orthorhombic and tetragonal phases. Scanning probe microscopy methods including the Kelvin potential microscopy and the force modulation microscopy were employed to investigate the material properties at the nanoscale. Lateral variation of the elastic stiffness and the surface electric potential corresponded to the lateral dimension of grains in pristine films. Point sub-100-nm capacitors formed with a Pt-coated cantilever as a moving electrode showed the ferroelectric behavior. The position-dependent polarization switching and a relative stability of the crystal phases at 1 MV/cm–2 MV/cm were observed in the annealed films. The absence of the monoclinic phase, minimal surface roughness, uniformity of the electric potential, and high elastic modulus made 10-nm Hf0.55Zr0.45O2 films annealed at 600 °C–700 °C in nitrogen as the appealing material for applications in scaled ferroelectric devices.