Decreasing the Vth shift of InGaZnO thin-film transistors under positive and negative bias stress using SU-8 as etch-stop and passivation layer

In order to expand the InGaZnO (IGZO) technology to several applications other than displays, including integrated circuits with certain complexity, it is necessary to mitigate the Vth shift under bias stress. For this purpose, the use of a passivated semiconductor channel has demonstrated its effectiveness in improving the Vth reliability. In this work, staggered bottom gate IGZO thin-film transistors were fabricated using a 450 nm SU-8 2000.5 film as a passivation and etch-stop layer. The thin-film transistors (TFTs) were fabricated by a full lithography process and the SU-8 film determined the maximum processing temperature of 200 °C. Positive and negative bias stress were performed during 1200 s on 150 μm/40 μm (W/L) TFTs stressed at low field (2 MV cm−1) and high field (4 MV cm−1) leading to a maximum Vth shift of 0.12 V and −0.38 V, respectively. The negative Vth shift was associated to an undesired mechanism dominated by hydrogen migration. The spin coated SU-8 passivation layer demonstrated higher device stability and it can be also used for future interconnection between transistors.