Impact of oxygen exchange reaction at the ohmic interface in Ta₂O₅-based ReRAM devices

Abstract

Interface reactions constitute essential aspects of the switching mechanism in redox-based resistive random access memory (ReRAM). For example, the modulation of the electronic barrier height at the Schottky interface is considered to be responsible for the toggling of the resistance states. On the other hand, the role of the ohmic interface in the resistive switching behavior is still ambigious. In this paper, the impact of different ohmic metal-electrode (M) materials, namely W, Ta, Ti, and Hf on the characteristics of TaO ReRAM is investigated. These materials are chosen with respect to their free energy for metal oxide formation and, associated, their impact on the formation energy of oxygen vacancy defects at the M/TaO interface. The resistive switching devices with Ti and Hf electrodes that have a negative defect formation energy, show an early RESET failure during the switching cycles. This failure process with Ti and Hf electrode is attributed to the accumulation of oxygen vacancies in the TaO layer, which leads to permanent breakdown of the metal-oxide to a low resistive state. In contrast, the defect formation energy in the TaO with respect to Ta and W electrodes is positive and for those highly stable resistive switching behavior is observed. During the quasi-static and transient-pulse characterization, the ReRAM devices with the W electrode consistently show an increased high resistance state (HRS) than with the Ta electrode for all RESET stop voltages. This effect is attributed to the faster oxygen exchange reaction at the W-electrode interface during the RESET process in accordance to lower stability of WO than TaO. Based on these findings, an advanced resistive switching model, wherein also the oxygen exchange reaction at the ohmic M-electrode interface plays a vital role in determining of the resistance states, is presented.

Field‐ and irradiation‐induced phenomena in memristive nanomaterials

“…Contrary to the active ohmic electrodes of relatively high thickness [26], no scavenging effect is observed for the thin Zr layer inserted between the inert top Au electrode and oxide material. The comparison with the reference Au/oxide/TiN/Ti devices has shown that the presence of a thin adhesive Zr layer results in some changes of differential resistances and dielectric properties (decrease in dielectric losses) of the capacitors in the initial state.…”

Resistive Switching in Stabilized Zirconia Films Studied by Conductive Atomic Force Microscopy

“…In this scope, yttria stabilized zirconia (YSZ) ZrO 2 (Y) is very promising for RRAM applications since the V O concentration in YSZ is equal to 1/2 that of Y, and can be controlled precisely by varying Y molar fraction [4]. Although a lot of work was devoted to studying RS, many details of the RS mechanism in oxides are not clarified completely yet [5], including the processes at the metal-dielectric interfaces, particularly, the electric-field induced transition of O 2− ions from the dielectric into the metal electrode and back [6]. For deeper understanding of the microscopic details of RS mechanism, the appropriate experimental techniques are needed.…”

The influence of non-stoichiometry on the switching kinetics of strontium-titanate ReRAM devices

“…10,[13][14][15][16][17] Current studies are discussing the possibility of oxygen transfer reactions between the oxide and the metal electrodes as additional effects involved in VCM-type resistive switching. [18][19][20] Due to its thoroughly investigated defect chemistry, strontium titanate (STO) is often used as a model system for resistive switching. 21,22 Recently, several studies have dealt with the influence of stoichiometry on resistive switching in STO, revealing differences in forming voltage and statistics, 23 data retention, 24 or even switching/no-switching.…”