Low-Voltage Polymer Thin-Film Transistors with High-k HfTiO Gate Dielectric Annealed in NH3 or N2

OTFTs with P3HT as organic semiconductor and HfTiO as gate dielectric have been studied in this work. The HfTiO dielectric film was prepared by RF sputtering of Hf and DC sputtering of Ti at room temperature. Subsequently, the dielectric film was annealed in an NH3 or N-2 ambient at 200 degrees C. Then a layer of OTS was deposited by spin-coating method to improve the surface characteristics of the gate dielectric. Afterwards, P3HT was deposited by spin-coating method. The OTFTs were characterized by I-V measurement and 1/f noise measurement. The OTFT with gate dielectric annealed in NH3 displays higher carrier mobility, smaller threshold voltage, smaller sub-threshold swing, and lower 1/f noise level than the OTFT annealed in N-2. Moreover, the HfTiO dielectric film annealed in NH3 shows higher dielectric constant. In summary, HfTiO film annealed in NH3 at low temperature is a promising candidate to act as the gate dielectric of high-quality low-voltage OTFTs.