Remote Phonon Scattering in InGaZnO Thin-Film Transistor with Double-Layered High-κ Gate Dielectric

Double-layered high-κ gate dielectric (high-κ NdHfO on low-κ SiO₂) and p-Si gate electrodes with different doping concentrations are employed in the fabrication of InGaZnO thin-film transistors (IGZO TFTs) to investigate the effects of the low-κ SiO₂ interlayer on the remote phonon scattering (RPS) of the high-κ gate dielectric and thus the carrier mobility in the IGZO channel. Compared with previous research on IGZO TFTs with single-layered NdHfO gate dielectric, the experimental results show that with the insertion of a SiO₂ film between the NdHfO layer and the p-Si gate electrode, the carrier mobility performance presents obvious differences: (1) the mobility increment with increasing gate doping concentration falls around 56% due to the reduced gate screening effect on the RPS caused by the increased separation and thus weakened electrical coupling between the gate electrode and the high-κ NdHfO layer; (2) the disappearance of the large mobility reduction for the sample with gate doping concentration of 1.0 × 10¹⁸–1.9 × 10¹⁸/cm³ produced by the resonance between the gate electrode and the high-κ NdHfO layer (thus enhanced RPS) due to their weakened electrical coupling; and surprisingly, (3) the emergence of large mobility reductions for the two samples with gate doping concentrations of 2.8 × 10¹⁸–3.1 × 10¹⁸/cm³ and 2.7 × 10¹⁸–7.9 × 10¹⁸/cm³ caused by the resonance between the relatively rigid low-κ SiO₂ interlayer and the adjacent gate electrode (thus enhanced RPS). In summary, this work demonstrates that the low-κ layer in a double-layered high-κ gate dielectric can also have significant effects on the RPS and thus carrier mobility in metal-oxide-semiconductor (MOS) devices.