Ferroelectricity in nanocrystalline Hf0.5Zr0.5O2 thin films

Abstract: Hafnium dioxide (HfO_2) based thin films doped with various dopants (Si, Ge, Al, Gd, Sr, Zr) have been found to exhibit ferroelectricity. These dopants were found to stabilize the III orthorhombic phase in the hafnium oxide based thin films. This characteristic enables and allows various applications ranging from Non-volatile memory, Ferroelectric Field-Effect-Transistors, to Negative Capacitance Field-Effect-Transistors. In this master thesis, ZrO_2 were used as a dopant to vary the crystallinity of HfO_2 during rapid thermal annealing at various temperatures in nitrogen ambient. The structure of Hf_0.5Zr_0.5O_2 (HZO) was fabricated using 50% ZrO_2 and 50% HfO_2 with precise control by the Atomic Layer Deposition technique. A planar metal-ferroelectric insulator-metal capacitor (Au/TiN/HZO/TiN/Si) was fabricated and analyzed using a probe station to investigate the electrical properties. Prior to the top metal deposition, the surface and interface properties such as thickness, roughness, and density, were observed using x-ray reflectivity measurement. Polycrystallinity was observed using grazing-incidence x-ray diffraction measurements in only a few samples. The potential issues related to the process steps are discussed. The electrical measurements showed large leakage. A reference capacitor, Au/HfO_2/TiN/Si structured capacitor was fabricated. This pure HfO_2 based capacitor did not show leakage behavior. Further paths to improvement is discussed.