High Voltage Amorphous InGaZnO TFT With F Doped Drain Offset Structure

We report high voltage amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) using a drain offset structure. The a-IGZO TFT with drain offset length (Loff) = 2.5 μm exhibits a maximum operating voltage (VDS, Max) over 90 V, which increases with Loff. The drastic current drop from output characteristics appears for VDS>VDS, Max with a positive threshold voltage shift and increased subthreshold swing from transfer characteristics. We obtain maximum lattice temperatures of ~130 °C for both the conventional and drain offset TFTs due to Joule heating (JH) within the a-IGZO layer by TCAD simulation. It indicates that the rise in temperature by JH is almost independent of Loff. The JH is uniformly distributed over the entire Loff in drain offset TFT compared with a drastic increase near the drain side in conventional TFT. NF3 plasma treatment enhances conductivity at offset region, resulting in large VDS, Max.