Effect of Gate-Electrode/Gate-Dielectric Interlayer on Gate Screening of Remote Phonon Scattering in InGaZnO Thin-Film Transistor with High-k Gate Dielectric

InGaZnO thin-film transistors with various SiO2 thicknesses (0, 3.5, 8.5, 18.8 nm) in double-layered gate dielectric (NdHfO/SiO2) and different gate doping concentrations (2.4×1015, 1.5×1018, 2.1×1019 /cm3) are fabricated to systematically study the influence of the SiO2 low-k interlayer on the remote phonon scattering (RPS) in the conduction channel originated from the NdHfO high-k layer. The performances of the TFTs show critical dependence on the SiO2 thickness and the gate doping concentration. On the one hand, the channel-carrier mobility increases with the rise of gate doping concentration because more plasmons formed by more gate-electrode holes produce a stronger gate screening effect to suppress the RPS on the channel carriers. On the other hand, the SiO2 interlayer between the gate electrode and the NdHfO layer separates the gate-electrode plasmons and the gate-dielectric phonons, thus weakening the gate screening effect, which is supported by decreasing carrier mobility with increasing SiO2 thickness. Furthermore, through comparison with counterparts without the SiO2 interlayer, the carrier-mobility increment with increasing gate doping concentration is found to decrease from 9.67 cm2V-1s-1/decade to 6.33 cm2V-1s-1/decade due to weakened gate screening effect caused by the insertion of a 19-nm SiO2 interlayer. In summary, the gate screening effect and the RPS-limited channel-carrier mobility can be enhanced by higher gate doping concentration, but reduced by thicker gate-electrode/gate-dielectric interlayer.