Abstract
SiO2 is the most significantly used insulator layer in semiconductor devices. Its functionality was recently extended to resistance switching random access memory, where the defective SiO2 played an active role as the resistance switching (RS) layer. In this report, the bias-polarity-dependent RS behaviours in the top electrode W-sputtered SiO2-bottom electrode Pt (W/SiO2/Pt) structure were examined based on the current-voltage (I-V) sweep. When the memory cell was electroformed with a negative bias applied to the W electrode, the memory cell showed a typical electronic switching mechanism with a resistance ratio of ~100 and high reliability. For electroforming with opposite bias polarity, typical ionic-defect-mediated (conducting filament) RS was observed with lower reliability. Such distinctive RS mechanisms depending on the electroforming-bias polarity could be further confirmed using the light illumination study. Devices with similar electrode structures with a thin intervening Si layer between the SiO2 and Pt electrode, to improve the RS film morphology (root-mean-squared roughness of ~1.7 nm), were also fabricated. Their RS performances were almost identical to that of the single-layer SiO2 sample with very high roughness (root-mean-squared roughness of ~10 nm), suggesting that the reported RS behaviours were inherent to the material property.
Highlights
SiO2 is the most significantly used insulator layer in semiconductor devices
Several transition metal oxides (TMOs), such as TiO2, NiO, Ta2O5, and HfO2, have been tested as RS layers because the multi-valence nature of the transition metals would render the RS in these materials achieved[1,2,3,4]
The characteristic feature of the non-polar switching of the SiO2-based RS material, where the voltage for the reset [the switching from a low-resistance state (LRS) to a high-resistance state (HRS), or Vreset] is higher than the voltage for the set may be ascribed to such phase-transition-related switching mechanism, whereas Vset is higher than Vreset in usual TMO-based RS systems[11]
Summary
The positively electroformed cell showed no more switching after ~5,000 and 3,500 cycles for the W/SiO2/Pt and W/SiO2/Si/Pt structures, respectively, as shown in Fig. 8c,d, which suggests the much lower reliability of the CF-mediated iBRS mechanism. While the positively electroformed cell showed stable retention of both states, as expected (see the insets in Fig. 8c,d), the negatively electroformed cell showed certain limitations, especially for the LRS (see the insets in Fig. 8a,b), which can be understood from the carrier trapping-mediated mechanism[39,40] In this case, circuit level supplementation, i.e., reading of the data after a certain period of time and its rewriting, would be necessary. The reactively sputtered SiO2 film showed great potential as an RS material for RRAM, especially when it was negatively electroformed
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