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 beam epitaxy grown HfO2 thin films fabricated on highly doped p-type Si substrate at substrate temperatures of 300 and 500 degrees C. Both films correspond to the monoclinic phase (P2(1)/c) of HfO2 and exhibit single crystalline structure with a preferred orientation along ((1) over bar11). The density of the HfO2 layer is found to be 9.1 and 9.2 g/cm(3), whereas the root mean square roughness is 1.3 and 2.4 nm in the films grown at 300 and 500 degrees C, respectively. Both films have an average grain size of similar to 140 nm. These HfO2 films demonstrate forming free volatile resistive switching behavior with SET voltage of -3.1 and -3.6 V, along with the ON/OFF ratio of similar to 2 and similar to 4 for the films deposited at substrate temperatures of 300 and 500 degrees C, respectively. For the films grown at 300 degrees C and 500 degrees C, the retention time is found to be 20 and 30 s, respectively. Memory device based on HfO2 film with higher substrate temperature exhibits a better ON/OFF ratio due to higher crystallinity and the availability of more 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.