NbO2 selector device with Ge2Sb2Te5 thermal barrier for low off current (300 nA) and low power operation

Abstract

This study investigated the impact of a Ge2Sb2Te5 (GST) thermal barrier on the performance of NbO2-based selector devices. Our findings showed that the GST barrier could significantly decrease the off-state leakage current from 3 μA to 300 nA without increasing the threshold switching voltage owing to its insulation properties and high thermal resistance. We also found that the GST barrier can effectively contain the Joule heat within the NbO2 switching region, as confirmed through a cryogenic analysis of the thermal resistance of GST. The results showed that the GST/NbO2 device had a thermal resistance 3.48 times higher than that of a single-layer NbO2 device. Our results provide design guidelines for utilizing a barrier layer to reduce the leakage current in low-power threshold switching devices.

Enhancement of NbO2-based oscillator neuron device performance via cryogenic operation

“…Cryogenic operating conditions can efficiently enhance both the on/off resistance ratio and the oscillation amplitude (V th -V h ) of the NbO 2 -based neuron device [18,19]. seen that the current increases only from 120 to 77 K because the switching power increases, which will be elaborated on later [10]. Additionally, as temperature decreases, both V th and V h rise, but the increase in V th outpaces that of V h , leading to a large oscillation amplitude, as represented in figure 2(d).…”

“…Furthermore, according to earlier studies, the size of the switching filament region remains consistent, irrespective of the size of the bottom electrode [26]. This is evident in figure 3(e), where the resistance at 120 K remains nearly constant regardless of the bottom electrode size, implying that only the switching current persists at 120 K. Furthermore, there is a problem with decreasing the temperature to below 120 K. According to the field triggered thermal runaway (FTTR) model, which explains the NbO 2 switching mechanism, an internal temperature increase is required for NbO 2 threshold switching, as expressed in the following equation [10,20,21,27,28].…”

“…Interestingly, the metallic resistance is higher at 120 K than at 300 K ambient temperature. To analyze these results, we simulated the solid-phase heat transfer using COMSOL Multiphysics [10,28]. The heat transfer equation for the solid phase was employed, as expressed in the following equation.…”

“…In previous studies, various barrier layers were introduced to increase the on/off resistance ratio by blocking the leakage current path [9][10][11][12][13][14]. However, the voltage division between the barrier layer and the on-state NbO 2 can cause an increase in the hold voltage, leading to a decrease in the oscillation amplitude [15].…”

“…In order to investigate the optimal conditions for operating oscillator neurons at cryogenic, we performed an indepth analysis to understand the interplay between the switching current flowing in the switching filament area and the leakage current in the amorphous matrix area as the temperature changes [10,11]. By applying the Poole-Frenkel conduction model, we identified the barrier energy in each region with respect to the temperature [20,21].…”