4 research outputs found
Imaging the Three-Dimensional Conductive Channel in Filamentary-Based Oxide Resistive Switching Memory
Filamentary-based oxide resistive
memory is considered as a disruptive technology for nonvolatile data
storage and reconfigurable logic. Currently accepted models explain
the resistive switching in these devices through the presence/absence
of a conductive filament (CF) that is described as a reversible nanosized
valence-change in an oxide material. During device operation, the
CF cycles billion of times at subnanosecond speed, using few tens
of microamperes as operating current and thus determines the whole
device’s performance. Despite its importance, the CF observation
is hampered by the small filament size and its minimal compositional
difference with the surrounding material. Here we show an experimental
solution to this problem and provide the three-dimensional (3D) characterization
of the CF in a scaled device. For this purpose we have recently developed
a tomography technique which combines the high spatial resolution
of scanning probe microscopy with subnanometer precision in material
removal, leading to a true 3D-probing metrology concept. We locate
and characterize in three-dimensions the nanometric volume of the
conductive filament in state-of-the-art bipolar oxide-based devices.
Our measurements demonstrate that the switching occurs through the
formation of a single conductive filament. The filaments exhibit sizes
below 10 nm and present a constriction near the oxygen-inert electrode.
Finally, different atomic-size contacts are observed as a function
of the programming current, providing evidence for the filament’s
nature as a defects modulated quantum contact
Direct Probing of the Dielectric Scavenging-Layer Interface in Oxide Filamentary-Based Valence Change Memory
A great
improvement in valence change memory performance has been
recently achieved by adding another metallic layer to the simple metal–insulator–metal
(MIM) structure. This metal layer is often referred to as oxygen exchange
layer (OEL) and is introduced between one of the electrodes and the
oxide. The OEL is believed to induce a distributed reservoir of defects
at the metal–insulator interface thus providing an unlimited
availability of building blocks for the conductive filament (CF).
However, its role remains elusive and controversial owing to the difficulties
to probe the interface between the OEL and the CF. Here, using Scalpel
SPM we probe multiple functions of the OEL which have not yet been
directly measured, for two popular VCMs material systems: Hf/HfO<sub>2</sub> and Ta/Ta<sub>2</sub>O<sub>5</sub>. We locate and characterize
in three-dimensions the volume containing the oxygen exchange layer
and the CF with nanometer lateral resolution. We demonstrate that
the OEL induces a thermodynamic barrier for the CF and estimate the
minimum thickness of the OEL/oxide interface to guarantee the proper
switching operations is ca. 3 nm. Our experimental observations are
combined to first-principles thermodynamics and defect kinetics to
elucidate the role of the OEL for device optimization
Influence of the Chalcogen Element on the Filament Stability in CuIn(Te,Se,S)<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> Filamentary Switching Devices
In
this paper, we report on the use of CuInX<sub>2</sub> (X = Te, Se,
S) as a cation supply layer in filamentary switching applications.
Being used as absorber layers in solar cells, we take advantage of
the reported Cu ionic conductivity of these materials to investigate
the effect of the chalcogen element on filament stability. In situ
X-ray diffraction showed material stability attractive for back-end-of-line
in semiconductor industry. When integrated in 580 μm diameter
memory cells, more volatile switching was found at low compliance
current using CuInS<sub>2</sub> and CuInSe<sub>2</sub> compared to
CuInTe<sub>2</sub>, which is ascribed to the natural tendency for
Cu to diffuse back from the switching layer to the cation supply layer
because of the larger difference in electrochemical potential using
Se or S. Low-current and scaled behavior was also confirmed using
conductive atomic force microscopy. Hence, by varying the chalcogen
element, a method is presented to modulate the filament stability
Influence of Carbon Alloying on the Thermal Stability and Resistive Switching Behavior of Copper-Telluride Based CBRAM Cells
We report the improved thermal stability
of carbon alloyed Cu<sub>0.6</sub>Te<sub>0.4</sub> for resistive memory
applications. Copper–tellurium-based memory cells show enhanced
switching behavior, but the complex sequence of phase transformations
upon annealing is disadvantageous for integration in a device. We
show that addition of about 40 at % carbon to the Cu-telluride layer
results in an amorphous material up to 360 °C. This material
was then integrated in a TiN/Cu<sub>0.6</sub>Te<sub>0.4</sub>-C/Al<sub>2</sub>O<sub>3</sub>/Si resistive memory cell, and compared to pure
Cu<sub>0.6</sub>Te<sub>0.4</sub>. Very attractive endurance (up to
1 × 10<sup>3</sup> cycles) and retention properties (up to 1
× 10<sup>4</sup> s at 85 °C) are observed. The enhanced
thermal stability and good switching behavior make this material a
promising candidate for integration in memory devices