Grain boundaries as preferential sites for resistive switching in the HfO2 resistive random access memory structures

Abstract

Resistive switching (RS) phenomenon in the HfO2 dielectric has been indirectly observed at device level in previous studies using metal-insulator-metal structures, but its origin remains unclear. In this work, using the enhanced conductive atomic force microscope (ECAFM), we have been able to obtain in situ direct observation of RS with nanometric resolution. The ECAFM measurements reveal that the conductive filaments exhibiting the RS are primarily formed at the grain boundaries, which were shown exhibiting especially low breakdown voltage due to their intrinsic high density of the oxygen vacancies.

Optimal stoichiometry for nucleation and growth of conductive filaments in HfOx

“…This can be achieved either by deliberately growing a substoichiometric oxide film or by inserting an oxygen scavenging metal layer such as Ti or Hf [9]. There is evidence that in polycrystalline HfO x films oxygen deficiency is enhanced near extended defects, such as grain boundaries, which subsequently serve as precursors for filament growth [11,12,19,20]. This observation is also supported by theoretical predictions which show that oxygen vacancies can be up to 0.8 eV more stable at m-HfO 2 grain boundaries relative to the bulk crystal [21].…”

“…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].…”

Repeatable unipolar/bipolar resistive memory characteristics and switching mechanism using a Cu nanofilament in a GeOx film

“…Cu þ ions can migrate through the Ge-rich GeO x nanograin boundary because the boundary site has more defects. 22 The filament is thought to be a chain type. The corresponding dissolution of the Cu nanofilament under a negative polarity of <V RESET on the TE is shown in Figure 1(d).…”

Dielectric properties of amorphous Zr–Al–O and Zr-Si-O thin films

“…Polycrystalline dielectrics are expected to exhibit a lower breakdown field than that of amorphous dielectrics due to the presence of grain boundaries. 10 We are using these two systems to determine the effect of the presence or absence of crystallinity on the dielectric constant and the breakdown field, and to determine the systematic effect of the Zr/Si or Zr/ Al ratio on these properties. This information provides insight regarding the mechanism for the observed enhancement of the dielectric response.…”