Effect of the work function of gate electrode on hysteresis characteristics of organic thin-film transistors with Ta2O5/polymer as gate insulator

Organic thin-film transistors (OTFTs) using high dielectric constant material tantalum pentoxide (Ta2O5) and benzocyclobutenone (BCBO) derivatives as double-layer insulator were fabricated. Three metals with different work function, including Al (4.3 eV), Cr (4.5 eV) and Au (5.1 eV), were employed as gate electrodes to study the correlation between work function of gate metals and hysteresis characteristics of OTFTs. The devices with low work function metal Al or Cr as gate electrode exhibited high hysteresis (about 2.5 V threshold voltage shift). However, low hysteresis (about 0.7 V threshold voltage shift) OTFTs were attained based on high work function metal Au as gate electrode. The hysteresis characteristics were studied by the repetitive gate voltage sweep of OTFTs, and capacitance–voltage (C–V) and trap loss-voltage (Gp/ω−V) measurements of metal–insulator–semiconductor (MIS) devices. It is proved that the hysteresis characteristics of OTFTs are relative to the electron injection from gate metal to Ta2O5 insulator. The electron barrier height between gate metal and Ta2O5 is enhanced by using Au as gate electrode, and then the electron injection from gate metal to Ta2O5 is reduced. Finally, low hysteresis OTFTs were fabricated using Au as gate electrode.