Abstract
Columnar microstructures are critical for obtaining good resistance switching properties in SiOx resistive random access memory (ReRAM) devices. In this work, the formation and structure of columnar boundaries are studied in sputtered SiOx layers. Using TEM measurements, we analyze SiOx layers in Me–SiOx–Mo heterostructures, where Me = Ti or Au/Ti. We show that the SiOx layers are templated by the Mo surface roughness, leading to the formation of columnar boundaries protruding from troughs at the SiOx/Mo interface. Electron energy-loss spectroscopy measurements show that these boundaries are best characterized as voids, which in turn facilitate Ti, Mo, and Au incorporation from the electrodes into SiOx. Density functional theory calculations of a simple model of the SiO2 grain boundary and column boundary show that O interstitials preferentially reside at the boundaries rather than in the SiO2 bulk. The results elucidate the nature of the SiOx microstructure and the complex interactions between the metal electrodes and the switching oxide, each of which is critically important for further materials engineering and the optimization of ReRAM devices.
Highlights
Over the last 20 years, various resistive random access memory (ReRAM) devices have been studied to produce the generation of nonvolatile memory technology, currently dominated by flash memory
The SiOx layer is found to have a uniform thickness, which results in the roughness of the SiOx/Mo interface being conformal to the Me/SiOx interface
In the five coordinated Si configuration, the incorporated O bonds to a surface Si atom, resulting in a dangling O that traps Mulliken charge between 0.5 and 0.7∣e∣. These results demonstrate that both neutral and charged oxygen atoms prefer to move to grain boundaries (GBs) and column boundaries (CBs) and reside there, forming peroxy species and water molecules
Summary
Over the last 20 years, various resistive random access memory (ReRAM) devices have been studied to produce the generation of nonvolatile memory technology, currently dominated by flash memory. ReRAM offers a range of advantages over the incumbent memory technologies in terms of programming speed, higher endurance, and potentially better energy efficiency.. Regardless of the choice of dielectric, ReRAM devices operate by the field-induced switching between a high resistance state (HRS) and at least one low resistance state (LRS). Filamentary ReRAM devices are driven by the formation and modulation of conductive filaments (CFs) by appropriate external electric fields.. The most critical measures of device performance include the forming and switching voltages, programming speed, high endurance, good retention, and low variability of both resistance states and switching voltages Filamentary ReRAM devices are driven by the formation and modulation of conductive filaments (CFs) by appropriate external electric fields. The most critical measures of device performance include the forming and switching voltages, programming speed, high endurance, good retention, and low variability of both resistance states and switching voltages
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