Solution-Processed High-k BaTiO3 Nanocrystal Ultrathin Films as Insulators for Thin Film Transistors

Abstract

The development of high-k and ultrathin gate insulators is critically important for advancing the miniaturization of field-effect transistors and realizing the “More than Moore” concept proposed by the IRDS. However, existing high-k gate insulators have yet to achieve an optimal balance among the thickness, band gap, breakdown strength, dielectric constant, and leakage current. In this study, oleic acid-capped BaTiO₃ (BTO) nanocrystals with an average size of 3.85 nm, which can be uniformly dispersed in toluene to form a highly transparent solution, are synthesized by a two-phase method. These nanocrystals form stable dispersion in toluene and enable spin-coating of uniform ultrathin (∼12 nm) films on silicon substrates. The resulting films exhibit a high dielectric constant (∼31), ultralow leakage current density (∼8.3 × 10^–8 A/cm² at 1 MV/cm), a capacitance equivalent thickness (CET) of 1.5 nm, and a breakdown field of 5 MV/cm. When used as the gate dielectric in fully inorganic thin-film transistors (TFTs) with CdS as the channel material, the BTO film yields n-channel device with a subthreshold swing (SS) as low as 70 mV/dec, a threshold voltage of 1.1 V, and an on/off ratio >10⁶. Integration with a monolayer MoS₂ channel produces TFT with an SS of 130 mV/dec and an on/off ratio >10⁵. These results underscore the potential of solution-processed BTO nanocrystalline films as high-performance gate dielectrics for next-generation nanoelectronics.