Volatile resistive switching characteristics of molecular beam epitaxy grown HfO2 thin films

In this work, we have explored the structure, morphology and resistive switching aspects of molecular beamepitaxy grown HfO2 thin films fabricated on highly doped p-type Si substrate at substrate temperatures of 300and 500 ◦C. Both films correspond to the monoclinic phase (P21/c) of HfO2 and exhibit single crystallinestructure with a preferred orientation along (111). The density of the HfO2 layer is found to be 9.1 and 9.2 g/cm3,whereas the root mean square roughness is 1.3 and 2.4 nm in the films grown at 300 and 500 ◦C, respectively.Both films have an average grain size of ~ 140 nm. These HfO2 films demonstrate forming free volatile resistiveswitching behavior with SET voltage of − 3.1 and − 3.6 V, along with the ON/OFF ratio of ~ 2 and ~ 4 for thefilms deposited at substrate temperatures of 300 and 500 ◦C, respectively. For the films grown at 300 ◦C and500 ◦C, the retention time is found to be 20 and 30 s, respectively. Memory device based on HfO2 film withhigher substrate temperature exhibits a better ON/OFF ratio due to higher crystallinity and the availability ofmore oxygen vacancies. A comprehensive mechanism of resistive switching is also discussed in this article,considering the transport of oxygen vacancies and the electromigration of Ag ions.