The effect of atomic layer deposition temperature on switching properties of HfOx resistive RAM devices

TiN/HfOx/TiN resistive RAM (RRAM) devices have been fabricated where the hafnium oxide layer has been deposited at three different temperatures via atomic layer deposition (ALD). Material characterization shows the structure of the hafnium oxide is converted from cubic to monoclinic for 400 degrees C. Elemental analysis shows that the temperature affects the stoichiometric behavior of hafnium oxide, with a higher oxygen concentration at 350 degrees C and above. The switching behavior differs significantly for each device whereby the 400 degrees C device shows no successful switching, due to the change in structure to monoclinic. The two lower temperatures both show successful bipolar switching which set at negative voltages. The 300 degrees C device has a higher Roff/Ron of 13.9, with superior endurance. The 350 degrees C device has a lower Roff/Ron of 5.5 and shows deterioration in switching properties as the number of cycles are increased. At 300 degrees C, the oxygen hafnium ratio is at a minimum; hence the greatest amount of oxygen vacancies are present, which results in improved switching characteristics. This supports the theory that oxygen vacancies play a key role in the switching mechanism for metal oxide RRAM devices.