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

Jong Woo Jin, Arokia Nathan, Pedro Barquinha, Luís Pereira, Elvira Fortunato, Rodrigo Martins, Brian Cobb

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


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.

Original languageEnglish
Article number085321
JournalRSC Advances
Issue number8
Publication statusPublished - 1 Aug 2016




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