Dielectric ceramics/TiO2/single-crystalline silicon nanomembrane heterostructure for high performance flexible thin-film transistors on plastic substrates

Abstract

A dielectric ceramics/TiO₂/single-crystalline silicon nanomembrane (SiNM) heterostructure is designed and fabricated for high performance flexible thin-film transistors (TFTs). Both the dielectric ceramics (Nb₂O₃–Bi₂O₃–MgO) and TiO₂ are deposited by radio frequency (RF) magnetron sputtering at room temperature, which is compatible with flexible plastic substrates. And the single-crystalline SiNM is transferred and attached to the dielectric ceramics/TiO₂ layers to form the heterostructure. The experimental results demonstrate that the room temperature processed heterostructure has high quality because: (1) the Nb₂O₃–Bi₂O₃–MgO/TiO₂ heterostructure has a high dielectric constant (∼76.6) and low leakage current. (2) The TiO₂/single-crystalline SiNM structure has a relatively low interface trap density. (3) The band gap of the Nb₂O₃–Bi₂O₃–MgO/TiO₂ heterostructure is wider than TiO₂, which increases the conduction band offset between Si and TiO₂, lowering the leakage current. Flexible TFTs have been fabricated with the Nb₂O₃–Bi₂O₃–MgO/TiO₂/SiNM heterostructure on plastic substrates and show a current on/off ratio over 10⁴, threshold voltage of ∼1.2 V, subthreshold swing (SS) as low as ∼0.2 V dec⁻¹, and interface trap density of ∼10¹² eV⁻¹ cm⁻². The results indicate that the dielectric ceramics/TiO₂/SiNM heterostructure has great potential for high performance TFTs.