HfO2 and ITO Resistive Random-Access Memory

Abstract: The purpose of this work is of evaluating the choice of HfO2 and ITO as the dielectric and the top electrode in high performance resistive random-access memory (RRAM), respectively. The study is twofold, as it quantifies performance according to standard figures of merit for this technology, as well as provides insight into the physics of current conduction for this material choice. Results are achieved thanks to the probing of structures processed by the Nano Electronics group in Lund, followed by direct observations on the produced I−V characteristics and more involved data analysis. Specifically, different models according to different mechanisms of current conduction in a dielectric are fitted to the measured data, and physical parameter extraction is used as a mean to evaluate goodness of fit. It is discovered that several modes that were thought to potentially describe conduction in RRAM can instead not be the case, for confusing (if not impossible) parameters are extrapolated for them. An important result is thus that no matter how great a fit may be numerically, one cannot simply claim that a given mechanism of conduction is a good physical interpretation of a studied system without corroborating its fit with relevant parameter extraction. It is concluded that the only reasonable and available interpretation of measured devices is that of Ohmic type conduction, followed by space-charge (at higher voltages) in the high resistance state of RRAM, and solely Ohmic type in the low resistance state. The latter relates to not observing conduction through a barrier, which was expected as HfO2 and ITO RRAM has previously been found to be modulated by a self-compliance effect. Based on this interpretation, a computer model is developed in Python, and its output is put to the test by comparison with data from a different sample (i.e. not related to the observations that lead to the creation of the model itself). The universality of the model is found to be satisfying, hinting at the achieved interpretation being adequate. Concerning raw performance of the studied devices, resistive switching at low and steady voltages is observed, which relates to envisioning low power operation for HfO2 and ITO structures.