Side-by-Side Comparison of Single- and Dual-Active Layer Oxide TFTs: Experiment and TCAD Simulation

Single-active layer (SAL) and dual-active layer (DAL) oxide thin-film transistors (TFTs) are fabricated using the same process conditions and compared side by side. The SAL channel consists of amorphous In-Ga-Zn-O (a-IGZO), and the DAL of ultrathin In-Sn-O and a-IGZO. The DAL TFT exhibits strongly improved performance compared to the SAL TFT such as higher mobility of 31 cm(2).V-1.s(-1), smaller subthreshold swing of 175 mV/dec, and better positive bias temperature stress stability. Technology computer aided design simulation is used to investigate the SAL and DAL device performance. A mapping technique is used to directly correlate the transfer characteristics to the subbandgap density of states. The simulation suggests that the improved performance of the DAL TFT is due to an improved gate insulator/channel interface with an approximately one order of magnitude lower interface trap density.