Future High-density Memory Applications Research Articles

Bilayer Metal-Oxide Conductive Bridge Memory Technology for Improved Window Margin and Reliability

In this paper, a detailed reliability analysis of metal-oxide conductive bridge memories (CBRAM) is presented. This paper mostly focuses on electrical characterization of metal-oxide CBRAM devices endurance, using optimized program/erase conditions, and data retention at high temperature. The addition of a thin metal-oxide layer (0.5 nm-thick Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) in the bottom of the GdO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> memory stack significantly increases the R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> and the memory window (more than one decade), with improved endurance performance (up to 105 cycles) with respect to the monolayer CBRAM device. Meanwhile, high thermal stability was also achieved (two decades of window margin are constantly maintained beyond 24 h at 250 °C). The bilayer oxide GdOX/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> CBRAM is a promising technology for potential future high density memory applications.

A Fully Transparent Resistive Memory for Harsh Environments.

A fully transparent resistive memory (TRRAM) based on Hafnium oxide (HfO2) with excellent transparency, resistive switching capability, and environmental stability is demonstrated. The retention time measured at 85 °C is over 3 × 104 sec, and no significant degradation is observed in 130 cycling test. Compared with ZnO TRRAM, HfO2 TRRAM shows reliable performance under harsh conditions, such as high oxygen partial pressure, high moisture (relative humidity = 90% at 85 °C), corrosive agent exposure, and proton irradiation. Moreover, HfO2 TRRAM fabricated in cross-bar array structures manifests the feasibility of future high density memory applications. These findings not only pave the way for future TRRAM design, but also demonstrate the promising applicability of HfO2 TRRAM for harsh environments.

Bipolar Resistive Switching Memory Characteristics Using Al/Cu/GeOx/W Memristor

Low power operations of resistive switching memory using Al/Cu/GeOx/W memristor have been reported for the first time. Under the SET process the copper ions migrate through defects into the GeOx solid-electrolyte and there is the formation of a copper filament by reduction process. However, the RESET process or dissolution of this filament occurs by an oxidation process. Excellent uniformity with narrow distributions of SET/RESET voltages and low resistance states (LRS) are obtained. Furthermore, high resistance ratio of >104 with multi-level (MLC) operation and low SET and RESET powers (~19 and ~ 8.36 µW) are advantages for future high density memory applications.

Bipolar resistance switching in high-performance Cu/ZnO:Mn/Pt nonvolatile memories: active region and influence of Joule heating

Manganese-doped ZnO dielectric films sandwiched between Cu and Pt electrodes were prepared and investigated for nonvolatile resistive memory applications. These structures exhibit promising bipolar resistive switching (RS) behavior with a large ON/OFF ratio (∼103), suitable threshold voltages (1.4 and −0.7 V for SET and RESET, respectively), long retention (>104 s at 85 °C) and low write current (10 μA). A study on the ZnO:Mn thickness dependence of threshold voltages reveals that RS should be an interfacial effect rather than bulk behavior. By elevating current compliance during the SET process, an anomalous transition from bistable memory switching to monostable threshold switching was observed, which is attributed to the instability of conductive filaments induced by Joule heating effects. Apart from this, fast voltage sweep cycles without efficient heat dissipation were also found to accelerate the hard dielectric breakdown of the device, reflecting the impact of accumulative Joule heating. These results reveal the possible influences of Joule heating effects on bipolar resistance switching and thus the necessity of avoiding them in future high-density memory applications. Conceivable solutions are considered to be reducing the operating currents and improving the heat dissipation of memory devices based on our experiments.

Electric-field penetration into metals: consequences for high-dielectric-constant capacitors

A consequence of the finite electronic screening length in metals is that electric fields penetrate short distances into the metal surface. Using a simple, semiclassical model of an idealized capacitor, we estimate the capacitance correction due to the distribution of displacement charge in the metal electrodes. We compare our result with experimental data from thin-film high-dielectric-constant capacitors, which are currently leading contenders for use in future high-density memory applications. This intrinsic mechanism contributes to the universally-seen decrease in measured dielectric constant with capacitor film thickness.