Oxide-based two-terminal resistive random access memory (RRAM) is considered one of the most promising candidates for next-generation nonvolatile memory. Rice university introduce here a new RRAM memory structure employing a nanoporous (NP) silicon oxide (SiOx) material which enables unipolar switching through its internal vertical nanogap. Through the control of the stochastic filament formation at low voltage, the NP SiOx memory exhibited an extremely low electroforming voltage (1.6 V) and outstanding performance metrics. These include multibit storage ability (up to 9-bits), a high ON–OFF ratio (up to 107 A), a long high-temperature lifetime (≥104 s at 100 °C), excellent cycling endurance (≥105), sub-50 ns switching speeds, and low power consumption (6 × 10–5 W/bit). Also provided is the room temperature processability for versatile fabrication without any compliance current being needed during electroforming or switching operations. Taken together, these metrics in NP SiOx RRAM provide a route toward easily accessed nonvolatile memory applications.
“This memory is superior to all
other two-terminal unipolar resistive memories by almost every metric,” Tour
said. “And because our devices use silicon oxide — the most studied material
on Earth — the underlying physics are both well-understood and easy to
implement in existing fabrication facilities.” Tour is Rice’s T.T. and W.F.
Chao Chair in Chemistry and professor of mechanical engineering and
nanoengineering and of computer science.
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Tour and colleagues began work on
their breakthrough RRAM technology more than five years ago. The basic
concept behind resistive memory devices is the insertion of a dielectric
material — one that won’t normally conduct electricity — between two wires.
When a sufficiently high voltage is applied across the wires, a narrow
conduction path can be formed through the dielectric material.
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The presence or absence of these
conduction pathways can be used to represent the binary 1s and 0s of digital
data. Research with a number of dielectric materials over the past decade has
shown that such conduction pathways can be formed, broken and reformed
thousands of times, which means RRAM can be used as the basis of rewritable
random-access memory.
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RRAM is under development
worldwide and expected to supplant flash memory technology in the marketplace
within a few years because it is faster than flash and can pack far more
information into less space. For example, manufacturers have announced plans
for RRAM prototype chips that will be capable of storing about one terabyte
of data on a device the size of a postage stamp — more than 50 times the data
density of current flash memory technology.
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The key ingredient of Rice’s RRAM
is its dielectric component, silicon oxide. Silicon is the most abundant
element on Earth and the basic ingredient in conventional microchips.
Microelectronics fabrication technologies based on silicon are widespread and
easily understood, but until the 2010 discovery of conductive filament
pathways in silicon oxide in Tour’s lab, the material wasn’t considered an
option for RRAM.
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Since then, Tour’s team has raced
to further develop its RRAM and even used it for exotic new devices like
transparent flexible memory chips. At the same time, the researchers also
conducted countless tests to compare the performance of silicon oxide
memories with competing dielectric RRAM technologies.
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