Interpreting anomalies observed in oxide semiconductor TFTs under negative and positive bias stress

TitleInterpreting anomalies observed in oxide semiconductor TFTs under negative and positive bias stress
Publication TypeJournal Article
Year of Publication2016
AuthorsJin JW a, Nathan A b, Barquinha P c, Pereira L c, Fortunato E c, Martins R c, Cobb B d
JournalAIP Advances
KeywordsAnomalous behavior, Charge migration, Charge trapping/detrapping, Dielectric materials, Electron-donating, Gate dielectrics, Instantaneous polarization, Oxide semiconductor thin film transistors, Oxide semiconductors, Positive gate bias, Reconfigurable hardware, Thin film transistors, Threshold voltage, Trapping/detrapping

Oxide semiconductor thin-film transistors can show anomalous behavior under bias stress. Two types of anomalies are discussed in this paper. The first is the shift in threshold voltage (VTH) in a direction opposite to the applied bias stress, and highly dependent on gate dielectric material. We attribute this to charge trapping/detrapping and charge migration within the gate dielectric. We emphasize the fundamental difference between trapping/detrapping events occurring at the semiconductor/dielectric interface and those occurring at gate/dielectric interface, and show that charge migration is essential to explain the first anomaly. We model charge migration in terms of the non-instantaneous polarization density. The second type of anomaly is negative VTH shift under high positive bias stress, with logarithmic evolution in time. This can be argued as electron-donating reactions involving H2O molecules or derived species, with a reaction rate exponentially accelerated by positive gate bias and exponentially decreased by the number of reactions already occurred. © 2016 Author(s).