3 research outputs found
Probing the Structure and Chemistry of Perylenetetracarboxylic Dianhydride on Graphene Before and After Atomic Layer Deposition of Alumina
The superlative electronic properties of graphene suggest
its use
as the foundation of next-generation integrated circuits. However,
this application requires precise control of the interface between
graphene and other materials, especially the metal oxides that are
commonly used as gate dielectrics. Toward that end, organic seeding
layers have been empirically shown to seed ultrathin dielectric growth
on graphene via atomic layer deposition (ALD), although the underlying
chemical mechanisms and structural details of the molecule/dielectric
interface remain unknown. Here, confocal resonance Raman spectroscopy
is employed to quantify the structure and chemistry of monolayers
of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on graphene
before and after deposition of alumina with the ALD precursors trimethyl
aluminum (TMA) and water. Photoluminescence measurements provide further
insight into the details of the growth mechanism, including the transition
between layer-by-layer growth and island formation. Overall, these
results reveal that PTCDA is not consumed during ALD, thereby preserving
a well-defined and passivating organic interface between graphene
and deposited dielectric thin films
Quantitatively Enhanced Reliability and Uniformity of High‑κ Dielectrics on Graphene Enabled by Self-Assembled Seeding Layers
The full potential of graphene in integrated circuits
can only
be realized with a reliable ultrathin high-κ top-gate dielectric.
Here, we report the first statistical analysis of the breakdown characteristics
of dielectrics on graphene, which allows the simultaneous optimization
of gate capacitance and the key parameters that describe large-area
uniformity and dielectric strength. In particular, vertically heterogeneous
and laterally homogeneous Al<sub>2</sub>O<sub>3</sub> and HfO<sub>2</sub> stacks grown via atomic-layer deposition and seeded by a
molecularly thin perylene-3,4,9,10-tetracarboxylic dianhydride organic
monolayer exhibit high uniformities (Weibull shape parameter β
> 25) and large breakdown strengths (Weibull scale parameter, <i>E</i><sub>BD</sub> > 7 MV/cm) that are comparable to control
dielectrics grown on Si substrates
Ambient-Processable High Capacitance Hafnia-Organic Self-Assembled Nanodielectrics
Ambient and solution-processable,
low-leakage, high capacitance
gate dielectrics are of great interest for advances in low-cost, flexible,
thin-film transistor circuitry. Here we report a new hafnium oxide-organic
self-assembled nanodielectric (Hf-SAND) material consisting of regular,
alternating Ï€-electron layers of 4-[[4-[bisÂ(2-hydroxyethyl)Âamino]Âphenyl]Âdiazenyl]-1-[4-(diethoxyphosphoryl)
benzyl]Âpyridinium bromide) (PAE) and HfO<sub>2</sub> nanolayers. These
Hf-SAND multilayers are grown from solution in ambient with processing
temperatures ≤150 °C and are characterized by AFM, XPS,
X-ray reflectivity (2.3 nm repeat spacing), X-ray fluorescence, cross-sectional
TEM, and capacitance measurements. The latter yield the largest capacitance
to date (1.1 μF/cm<sup>2</sup>) for a solid-state solution-processed
hybrid inorganic–organic gate dielectric, with effective oxide
thickness values as low as 3.1 nm and have gate leakage <10<sup>–7</sup> A/cm<sup>2</sup> at ±2 MV/cm using photolithographically
patterned contacts (0.04 mm<sup>2</sup>). The sizable Hf-SAND capacitances
are attributed to relatively large PAE coverages on the HfO<sub>2</sub> layers, confirmed by X-ray reflectivity and X-ray fluorescence.
Random network semiconductor-enriched single-walled carbon nanotube
transistors were used to test Hf-SAND utility in electronics and afforded
record on-state transconductances (5.5 mS) at large on:off current
ratios (<i>I</i><sub>ON</sub>:<i>I</i><sub>OFF</sub>) of ∼10<sup>5</sup> with steep 150 mV/dec subthreshold swings
and intrinsic field-effect mobilities up to 137 cm<sup>2</sup>/(V
s). Large-area devices (>0.2 mm<sup>2</sup>) on Hf-SAND (6.5 nm
thick)
achieve mA on currents at ultralow gate voltages (<1 V) with low
gate leakage (<2 nA), highlighting the defect-free and conformal
nature of this nanodielectric. High-temperature annealing in ambient
(400 °C) has limited impact on Hf-SAND leakage densities (<10<sup>–6</sup> A/cm<sup>2</sup> at ±2 V) and enhances Hf-SAND
multilayer capacitance densities to nearly 1 μF/cm<sup>2</sup>, demonstrating excellent compatibility with device postprocessing
methodologies. These results represent a significant advance in hybrid
organic–inorganic dielectric materials and suggest synthetic
routes to even higher capacitance materials useful for unconventional
electronics