Bias-temperature-stress (BTS) induced electrical instability of the RF sputter amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) was investigated. Both positive and negative BTS were applied and found to primarily cause a positive and negative voltage shift in transfer (<i>I</i><sub>DS</sub> - <i>V</i><sub>GS</sub>) characteristics, respectively. The time evolution of bulk-state density (<i>N</i><sub>BS</sub>) and characteristic temperature of the conduction-band-tail-states (<i>T<sub>G</sub></i> are extracted. Since both values showed only minor changes after BTS, the results imply that observed shift in TFT <i>I</i><sub>DS</sub> - <i>V</i><sub>GS</sub> curves were primarily due to channel charge injection/trapping rather than defect states creation. We also demonstrated the validity of using stretch-exponential equation to model both positive and negative BTS induced threshold voltage shift (Δ<i>V</i><sub>th</sub>) of the a-IGZO TFTs. Stress voltage and temperature dependence of Δ<i>V</i><sub>th</sub> evolution are described.
© 2009 IEEEPDF Article