RRAM Memories with ALD High-K Dielectrics: Electrical Characterization and Analytical Modeling

Abstract

Resistive switching phenomena with adequate repetitiveness on Ta2O5-TiO2-Ta2O5 and TiO2-Ta2O5-TiO2 stacks are reported. In particular, 5–nm-thick TiO2 films embedding a monolayer of Ta2O5 show the best behavior in terms of bipolar cycles loop width, with separate low and high resistive states up to two orders of magnitude. Tantalum oxide layer increases the defect density in titania that becomes less leaky, and thus, resistive switching effects appear. Small signal ac parameters measured at low and medium frequencies, namely capacitance and conductance, also show hysteretic behavior during a whole bipolar switching cycle. This means that the memory state can be read at 0 V, without any power consumption. High-frequency measurements provide information about dipole relaxation frequency values in the dielectric bulk, and this can be connected with resistive switching behavior. Finally, a double tunneling barrier model fits I-V curves at the low-resistance state even at the bias range where reset occurs and a sharp fall takes place.