Analog Switching and Artificial Synaptic Behavior of Ag/SiO_x:Ag/TiO_x/p⁺⁺-Si Memristor Device

In this study, by inserting a buffer layer of TiO_x between the SiO_x:Ag layer and the bottom electrode, we have developed a memristor device with a simple structure of Ag/SiO_x:Ag/TiO_x/p⁺⁺-Si by a physical vapor deposition process, in which the filament growth and rupture can be efficiently controlled during analog switching. The synaptic characteristics of the memristor device with a wide range of resistance change for weight modulation by implementing positive or negative pulse trains have been investigated extensively. Several learning and memory functions have been achieved simultaneously, including potentiation/depression, paired-pulse-facilitation (PPF), short-term plasticity (STP), and STP-to-LTP (long-term plasticity) transition controlled by repeating pulses more than a rehearsal operation, and spike-time-dependent-plasticity (STDP) as well. Based on the analysis of logarithmic I-V characteristics, it has been found that the controlled evolution/dissolution of conductive Ag-filaments across the dielectric layers can improve the performance of the testing memristor device.