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Improving positive and negative bias illumination stress stability in parylene passivated IGZO transistors

Gomes, H.L.

Applied Physics Letters Vol. 109, Nº 5, pp. 051606 - 051606, August, 2016.

ISSN (print): 1077-3118
ISSN (online): 0003-6951

Scimago Journal Ranking: 1,67 (in 2016)

Digital Object Identifier: 10.1063/1.4960200

Abstract
The impact of a parylene top-coating layer on the illumination and bias stress instabilities of indium-gallium-zinc oxide thin-film transistors (TFTs) is presented and discussed. The parylene coating substantially reduces the threshold voltage shift caused by continuous application of a gate bias and light exposure. The operational stability improves by 75%, and the light induced instability is reduced by 35%. The operational stability is quantified by fitting the threshold voltage shift with a stretched exponential model. Storage time as long as 7 months does not cause any measurable degradation on the electrical performance. It is proposed that parylene plays not only the role of an encapsulation layer but also of a defect passivation on the top semiconductor surface. It is also reported that depletion-mode TFTs are less sensitive to light induced instabilities. This is attributed to a defect neutralization process in the presence of free electrons.