The failure mechanisms arising from the instability in operation of indium gallium zinc oxide based thin film transistors (TFTs) upon prolonged real application stresses (bias and illumination) have been extensively studied and reported. Positive and negative gate bias conditions, along with high photonic energy wavelengths within visible light spectrum are used as stress conditions. The increased carrier concentration due to photonic excitation of defects within bandgap and ionization of deep level vacancies is compensated by the reduction in off currents under illumination due to the trapping of carriers in the intermetal dielectric. Band lowering at the source-channel junction due to accumulation of negative carriers repelled due to negative gate bias stress further causes high carrier flow into the channel and drives the devices into failure. The defect identification during failure and degradation assisted in proposing suitable low temperature post processing in specific ambients. Reliability tests after specific anneals in oxygen, vacuum, and forming gas ambients confirm the correlation of the defect type with anneal ambient. Annealed TFTs demonstrate high stabilities under illumination stresses and do not fail when subjected to combined stresses that cause failure in as-fabricated TFTs. Oxygen and forming gas anneals are impactful on the reliability and opens an area of study on donor and vacancy behavior in amorphous mixed oxide based TFTs. The subthreshold swing, field-effect mobilities, and off currents provide knowledge on best anneal practices by understanding role of hydrogen and oxygen in vacancy annihilation and transistor switching properties.
|Original language||English (US)|
|Journal||Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films|
|State||Published - Mar 1 2014|
ASJC Scopus subject areas
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films