3 research outputs found

    Probing the Structure and Chemistry of Perylenetetracarboxylic Dianhydride on Graphene Before and After Atomic Layer Deposition of Alumina

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    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

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    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

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    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 π-electron layers of 4-[[4-[bis­(2-hydroxyethyl)­amino]­phenyl]­diazenyl]-1-[4-(diethoxyphosphoryl) benzyl]­pyridinium 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
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