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 π-electron layers of 4-[[4-[bis(2-hydroxyethyl)amino]phenyl]diazenyl]-1-[4- (diethoxyphosphoryl) benzyl]pyridinium bromide) (PAE) and HfO₂ 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/cm²) 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^-7 A/cm² at ±2 MV/cm using photolithographically patterned contacts (0.04 mm ²). The sizable Hf-SAND capacitances are attributed to relatively large PAE coverages on the HfO₂ 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_ON:I_OFF) of ∼10⁵ with steep 150 mV/dec subthreshold swings and intrinsic field-effect mobilities up to 137 cm²/(V s). Large-area devices (>0.2 mm²) 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^-6 A/cm ² at ±2 V) and enhances Hf-SAND multilayer capacitance densities to nearly 1 μF/cm², 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.