Effects of gate-electrode plasmons on remote phonon scattering in thin-film transistor with perovskite barium titanate as high-k gate dielectric

Pentacene thin-film transistors (TFTs) with perovskite barium titanate (BTO) as a high-k gate dielectric have been fabricated on n-type silicon substrates (as gate electrode) at four different carrier concentrations of about 1015, 1017, 1019, and 1020 cm−3. The channel-carrier mobility of the TFT increases with increasing gate carrier concentration at both room temperature and a high temperature of 80 °C. With the help of a theoretical mobility model, this work shows that (i) the optical phonons in the high-k perovskite BTO can scatter holes in the neighboring pentacene channel (namely remote phonon scattering) to reduce their mobility; (ii) like the optical phonons in conventional high-k hafnium-based oxides, those in the high-k perovskite BTO can also be electrically coupled with plasmons (generated by carrier oscillation about dopant ions) in the gate electrode to suppress gate-dielectric vibration and thus remote phonon scattering, resulting in a carrier-mobility increase in the TFT channel, known as the gate screening effect. Higher gate-electrode carrier concentration produces higher-energy plasmons, while higher gate-electrode carrier mobility leads to weaker plasmon damping, both contributing to stronger plasmon coupling with the gate-dielectric phonons to enhance the gate screening effect in TFTs.