Role of oxygen vacancies in ferroelectric or resistive switching hafnium oxide.

HfO 2 shows promise for emerging ferroelectric and resistive switching (RS) memory devices owing to its excellent electrical properties and compatibility with complementary metal oxide semiconductor technology based on mature fabrication processes such as atomic layer deposition. Oxygen vacancy (V o ), which is the most frequently observed intrinsic defect in HfO 2 -based films, determines the physical/electrical properties and device performance. V o influences the polymorphism and the resulting ferroelectric properties of HfO 2 . Moreover, the switching speed and endurance of ferroelectric memories are strongly correlated to the V o concentration and redistribution. They also strongly influence the device-to-device and cycle-to-cycle variability of integrated circuits based on ferroelectric memories. The concentration, migration, and agglomeration of V o form the main mechanism behind the RS behavior observed in HfO 2 , suggesting that the device performance and reliability in terms of the operating voltage, switching speed, on/off ratio, analog conductance modulation, endurance, and retention are sensitive to V o . Therefore, the mechanism of V o formation and its effects on the chemical, physical, and electrical properties in ferroelectric and RS HfO 2 should be understood. This study comprehensively reviews the literature on V o in HfO 2 from the formation and influencing mechanism to material properties and device performance. This review contributes to the synergetic advances of current knowledge and technology in emerging HfO 2 -based semiconductor devices.