Anti-Screening Effect of Gate-Electrode Holes on Remote Phonon Scattering in InGaZnO Thin-Film Transistors

InGaZnO thin-film transistors (IGZO TFTs) adopting p-type Si with different doping concentrations as the gate electrodes are fabricated to study the effects of the electrical coupling between the gate electrode and the gate dielectric on the carrier mobility in the IGZO channel. In general, the carrier mobility is found to increase with increasing gate doping concentration because more holes in the gate electrode can screen/suppress the remote phonon scattering of the gate dielectric on the channel electrons (the screening effect). However, for certain gate doping concentrations, the carrier mobility surprisingly shows a decrease instead (the anti-screening effect). This has three implications: 1) like the free electrons in the n-Si gate electrode of OTFT, the holes in the p-Si gate electrode can oscillate about the dopant ions; 2) when the oscillation frequency is close/equal to the atomic vibration frequency of the high-
${k}$
gate dielectric, the resulting resonance between the gate electrode and the gate dielectric can enhance the atomic vibration of the latter to increase the remote phonon scattering on the channel carriers of the IGZO TFTs; and 3) the anti-screening effect could occur in any MOS-based devices.