High-k BaTiO3 nanoparticle films as gate dielectrics for flexible field effect transistors

Abstract

We demonstrate in this work that surface-passivated, monodisperse ferroelectric 15 nm BaTiO₃ nanocubes which exhibit solution processability are viable candidates for the design of insulating layers in flexible capacitors and gate dielectrics in “all inorganic” flexible field effect transistors. The BaTiO₃ nanocubes were characterized by various experimental techniques, including microscopy (electron and scanning probe) and vibrational spectroscopy. The nanocubes present intrinsic switchable dielectric polarization at room temperature, as revealed by piezoelectric force microscopy. By drop casting solutions containing BaTiO₃ colloidal nanocrystals, uniform, crack-free dielectric/ferroelectric films with controllable thicknesses can be fabricated at room temperature. These films were incorporated into flexible capacitors and field effect transistors whose performance was assessed. The BTO capacitor exhibited a low leakage current density (∼8 × 10⁻⁵ A cm⁻²) upon applying a bias voltage of 4 V, whereas the value of the static dielectric constant of the 500 nm-thick films was ε_r = 220 as revealed by dielectric spectroscopy measurements. The BaTiO₃ nanocrystals were incorporated into transparent and flexible field effect transistors (FETs) whereby the semiconducting channel was fabricated from a 10 nm In₂O₃ nanoparticle-based film. FETs exhibited high performance n-type characteristics with a small hysteresis (0.1 ± 0.04 V) and a subthreshold swing SS = 808 mV decade⁻¹ at an operating voltage of 10 V. This study provides a simple, yet highly versatile low-cost alternative for the fabrication of flexible electronic devices such as capacitors and FETs with superior performance characteristics by using colloidal inks containing both high capacitance gate dielectric and semiconducting colloidal nanocrystals.