Reduced screening of remote phonon scattering in thin-film transistors caused by gate-electrode/gate-dielectric interlayer

Pentacene organic thin-film transistors have been fabricated with their NdTaO gate dielectrics annealed at 200 °C, 400 °C, and 800 °C to study the effects of remote phonon scattering caused by the thermal vibration of the gate dielectric on the carrier transport in the conduction channel. Although the sample annealed at 800 °C can achieve the best dielectric quality (reflected by its lowest oxide-charge density, smallest dielectric surface roughness, and largest pentacene grain size), it shows the lowest carrier mobility of 0.44 cm2/V·s as compared to the highest mobility of 1.69 cm2/V·s for the control sample without dielectric annealing. In addition, this mobility degradation increases with increasing annealing temperature in spite of improving dielectric quality. Transmission electron microscopy shows that higher annealing temperature results in the formation of a thicker Si-gate/gate-dielectric interlayer, which increases the separation between the Si-gate plasmons and the gate-dielectric dipoles to weaken the screening effect of the gate electrode on the remote phonon scattering of the high-k gate dielectric, resulting in a lower carrier mobility. Measurements at high temperatures also support the effects of the interlayer.