The effect of aluminum doping on crystallinity, non-lattice oxygen, and resistance switching of Al-doped HfO₂ films deposited by reactive sputtering

In this work, the resistance switching characteristics of Al-doped HfO₂ thin films were investigated with by systematically varying the Al concentration and analyzing of the microstructure and the chemical bonding states. TiN/Al-doped HfO₂/Pt metal-insulator-metal stacks were fabricated with various Al concentrations of up to 16.8% by using reactive DC magnetron co-sputtering. X-ray diffraction and transmission electron microscopy measurement showed that HfO₂ doped with more than 10.4% Al had an amorphous structure, while HfO₂ doped with Al of less than 5.6% had a crystalline structure. X-ray photoelectron spectroscopy (XPS) showed that the concentration of non-lattice oxygen in Aldoped HfO₂ films increased with increasing Al up to 5.6% and was saturated for Al concentrations above 5.6%. TiN/Al-doped HfO₂/Pt stacks showed typical bipolar resistance switching characteristics. HfO₂ doped with Al = 5.6% showed the smallest grains and the smallest uniformity in the forming electric field and the SET/RESET resistance distribution. We conclude that the grain boundaries play a more important role than point defects such as non-lattice oxygen in the resistance switching.