Improved ferroelectric characteristics of ALD lanthanum-doped hafnium oxide thin film by controlling post-cooling time

• ALD lanthanum-doped HfO 2 thin film shows the ferroelectric characteristics. • As the post cooling time is shorter, the higher tensile stress is obtained, leading to the higher remanent polarization. • Stable orthorhombic crystal structure can be achieved by stronger tensile stress. A study was conducted on how the subsequent cooling time affects the ferroelectric (FE) characteristics of atomic layer deposited (ALD) lanthanum (La) doped HfO 2 thin films after the crystallization heat treatment in the form of TiN/La-doped HfO 2 /TiN metal-ferroelectric-metal (MFM) device structure. The ALD La-doped HfO 2 thin film was cooled to room temperature in a chamber (“chamber cooling” - slower cooling) or in an air atmosphere (“air cooling” - faster cooling). Based on the polarization vs electric field (P-E) hysteresis curve, the double remanent polarization (2P r ) values of the chamber cooling and air-cooling are 9.5 μC/cm 2 and 40 μC/cm 2 , respectively. This drastic improvement stems from more orthorhombic phase formation within La-doped HfO 2 thin film, which is confirmed by smaller grain size, higher amount of oxygen vacancies, and more tensile stress within HfO 2 thin film. Our results suggest that FE properties of La-doped HfO 2 -based thin film can be significantly modulated by post cooling processes.