Choice of Metal as Gate Electrode of Thin-Film Transistor With High-k Gate Dielectric

Abstract

Pentacene organic thin-film transistors (OTFTs) with HfLaON high-k gate dielectric have been fabricated using various gate-electrode materials, including different metals (Al, Au, Cu, Cr, Ti and Pt), as well as n-type highly-doped Si (n+-Si) and lowly-doped Si (n-Si). The OTFTs with metal gates exhibit significantly higher channel-carrier mobility (4.65 cm2V-1s-1 to 9.21 cm2V-1s-1) than their counterparts with n+-Si gate (1.52 cm2V-1s-1) and n-Si gate (0.12 cm2V-1s-1). Furthermore, among the metal-gate samples, despite having similar pentacene grain size and gate-dielectric surface roughness, the Ti-gate sample obtains the highest channel-carrier mobility of 9.21 cm2V-1s-1. This should be attributed to its highest gate plasmon energy resulting from both high electron concentration and low effective electron mass in its gate electrode, thus producing the strongest gate screening effect on the remote phonon scattering (RPS) arising from the thermal vibration of the high-k gate dielectric. In summary, metals with high plasmon energy (e.g. Ti, Al) should be chosen as the gate electrode material to achieve high channel-carrier mobility in TFT.