Ferroelectricity in Lu doped HfO₂ layers

Doped HfO₂ has become a promising candidate for non-volatile memory devices since it can be easily integrated into existing CMOS technology. Many dopants like Y, Gd, and Sr have been investigated for the stabilization of ferroelectric HfO₂. Here, we report the fabrication of capacitors comprising ferroelectric HfO₂ metal-insulator-metal structures with TiN bottom and top electrodes using the dopant Lu. Amorphous 5% Lu doped HfO₂ was deposited by pulsed laser deposition and afterwards annealed to achieve the ferroelectric, orthorhombic phase (space group Pbc2₁). The polarization of the layers was confirmed by capacitance-voltage, polarization-voltage, and current-voltage measurements. Depending on the anneal temperature, the remanent polarization changes and the initial state of the oxide varies. The layer exhibits initially a pinched hysteresis up to an annealing temperature of 600 °C and an unpinched hysteresis at 700 °C. The maximum polarization is about 11 μC/cm² which is measured after 10⁴ cycles and stable up to 10⁶ cycles. The influence of the layer thickness on the oxide properties is investigated for 10-40 nm thick HfLuO; however, a thickness dependence of the ferroelectric properties is not observed.