An accurate locally active memristor model for S-type negative differential resistance in NbOx

Abstract

A number of important commercial applications would benefit from the introduction of easily manufactured devices that exhibit current-controlled, or “S-type,” negative differential resistance (NDR). A leading example is emerging non-volatile memory based on crossbar array architectures. Due to the inherently linear current vs. voltage characteristics of candidate non-volatile memristor memory elements, individual memory cells in these crossbar arrays can be addressed only if a highly non-linear circuit element, termed a “selector,” is incorporated in the cell. Selectors based on a layer of niobium oxide sandwiched between two electrodes have been investigated by a number of groups because the NDR they exhibit provides a promisingly large non-linearity. We have developed a highly accurate compact dynamical model for their electrical conduction that shows that the NDR in these devices results from a thermal feedback mechanism. A series of electrothermal measurements and numerical simulations corroborate this model. These results reveal that the leakage currents can be minimized by thermally isolating the selector or by incorporating materials with larger activation energies for electron motion.

Multidimensional Simulation of Threshold Switching in NbO2 Based on an Electric Field Triggered Thermal Runaway Model

“…The model parameters for the CC-NDR simulation are chosen as: serial resistor R s = 3.3 kΩ, memory LRS R M,LRS = 4 kΩ, length of the threshold regime l Th = 5 nm, and T amb = 293.15 K. The simulated I-V D , I-V app , and I-V Th curves are shown in Figure 8 a. In addition to the results of previous studies, [ 10,11 ] we simulate a full S-type NDR curve for the case of the I-V D characteristic including the negative slope after the turn-on point, which gradually changes into a positive slope at higher currents. [ 7,11,32 ] The origin of the continuous NDR behavior is the transition to a continuous temperature increase in the NbO 2 regime with increasing applied voltage as shown in the T Th versus V app plot in Figure 8 b.…”

“…It might even be increased by stacking multiple layers of passive matrices to a 3D structure. [7][8][9][10][11][12][13][14][15][16][17][18] Threshold devices show an abrupt resistance change at a certain voltage stress V Th,ON . [ 1,4 ] This serious issue is alleviated by either complementary resistive switching devices or by the integration of a selector device in addition to the passive ReRAM, so called "1S1R" structures.…”

“…[7][8][9][10][11][12][13][14][15][16][17][18] Threshold devices show an abrupt resistance change at a certain voltage stress V Th,ON . In the recent works of Slesazeck et al [ 11 ] and Gibson et al [ 10 ] it is shown that the negative slope of the NDR current-voltage characteristics can be reproduced quite nicely by the Poole-Frenkel (PF) conduction mechanism in combination with a moderate Joule heating and an external serial resistance. In contrast to the memristive operation threshold switching is volatile: The resistance state switches to OFF Th as soon as the voltage is reduced below the turn-off voltage V Th,OFF .…”

The future of electronics based on memristive systems

“…For some material systems, such as VO 2 or NbO 2 , this process leads to an observed negative differential resistance (NDR), generating a strong but volatile change in the conductance. In fact, many forms of NDR can be ultimately described as a positive feedback-driven effect based on internal temperature coupled to the electronic transport 73,74 . Consequently, owing to the inherent positive feedback, only a small amount of input signal is needed to generate a large effect, thus supplying the needed neuronal amplification alluded to earlier.…”

Anatomy of Ag/Hafnia‐Based Selectors with 1010 Nonlinearity

“…Examples of conventional two-terminal thin-film based selectors include Schottky diodes [17] , tunneling junctions [18,19] , ovonic threshold switches (OTS) [20][21][22][23] and metal-insulator transitions (MIT) [24][25][26][27][28] . Kim et al has demonstrated 32×32 crossbar array composed of a stacked Schottky diode and a unipolar memristor.…”