Metal oxide resistive memory switching mechanism based on conductive filament properties

Abstract

By combining electrical, physical, and transport/atomistic modeling results, this study identifies critical conductive filament (CF) features controlling TiN/HfO2/TiN resistive memory (RRAM) operations. The leakage current through the dielectric is found to be supported by the oxygen vacancies, which tend to segregate at hafnia grain boundaries. We simulate the evolution of a current path during the forming operation employing the multiphonon trap-assisted tunneling (TAT) electron transport model. The forming process is analyzed within the concept of dielectric breakdown, which exhibits much shorter characteristic times than the electroforming process conventionally employed to describe the formation of the conductive filament. The resulting conductive filament is calculated to produce a non-uniform temperature profile along its length during the reset operation, promoting preferential oxidation of the filament tip. A thin dielectric barrier resulting from the CF tip oxidation is found to control filament resistance in the high resistive state. Field-driven dielectric breakdown of this barrier during the set operation restores the filament to its initial low resistive state. These findings point to the critical importance of controlling the filament cross section during forming to achieve low power RRAM cell switching.

Optimal stoichiometry for nucleation and growth of conductive filaments in HfOx

“…For HfO 2 , and similar oxides like NiO, TaO and CoO, there is increasing evidence that resistive switching can be understood in terms of the so-called filament model [2,8,[11][12][13][14][15][16][17]. Briefly, the idea is that application of a forming voltage across a thin insulating metal oxide film leads to the growth of a conducting filament between the electrodes which lowers the resistance of the junction.…”

“…Resistive switching memories based upon hafnium dioxide (HfO 2 ) are receiving increasing interest due to their compatibility with current transistor technology and their demonstrated exceptional performance [1][2][3][4][5][6][7][8][9][10][11][12]. For HfO 2 , and similar oxides like NiO, TaO and CoO, there is increasing evidence that resistive switching can be understood in terms of the so-called filament model [2,8,[11][12][13][14][15][16][17].…”

Electrical characterization and modeling of pulse-based forming techniques in RRAM arrays

“…8. The differences in the HRS current values can be ascribed to the differences in the filament size [4]. The black dashed line shows the limit I = G 0 V with G 0 = 2e 2 /h the quantum conductance unit corresponding to the creation of a single mode nanowire, where e is the electron charge and h the Planck's constant.…”

“…However, an intensive research activity is still to be performed on this innovative technology in order to increase RRAM reliability and performance. After the concept validation on single cells [2,3,4], the characterization of array structures is mandatory to bring such technology to a maturity level [5]. RRAM behavior is based on the possibility of electrically modifying the conductance of a Metal-Insulator-Metal (MIM) stack: the Set operation moves the cell in a low resistive state (LRS), whereas Reset brings the cell back to a high resistive state (HRS).…”

Kinetic Monte Carlo of transport processes in Al/AlOx/Au-layers: Impact of defects

“…In resistive switches they are supposed to form conductive filaments. 9,13 The charge states of defects is a critical issue in this context. Hence, density functional theory (DFT) studies, see Section III A, provide significant information on defects in AlO x .…”