Browsing by Author "Barquinha, Pedro"
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- Improving positive and negative bias illumination stress stability in parylene passivated IGZO transistorsPublication . Kiazadeh, Asal; Gomes, Henrique L.; Barquinha, Pedro; Martins, Jorge; Rovisco, Ana; Pinto, Joana V.; Martins, Rodrigo; Fortunato, ElviraThe 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. Published by AIP Publishing.
- Operational stability of solution based zinc tin oxide/SiO2 thin film transistors under gate bias stressPublication . Kiazadeh, Asal; Salgueiro, Daniela; Branquinho, Rita; Pinto, Joana; Gomes, Henrique L.; Barquinha, Pedro; Martins, Rodrigo; Fortunato, ElviraIn this study, we report solution-processed amorphous zinc tin oxide transistors exhibiting high operational stability under positive gate bias stress, translated by a recoverable threshold voltage shift of about 20% of total applied stress voltage. Under vacuum condition, the threshold voltage shift saturates showing that the gate-bias stress is limited by trap exhaustion or balance between trap filling and emptying mechanism. In ambient atmosphere, the threshold voltage shift no longer saturates, stability is degraded and the recovering process is impeded. We suggest that the trapping time during the stress and detrapping time in recovering are affected by oxygen adsorption/desorption processes. The time constants extracted from stretched exponential fitting curves are approximate to 10(6) s and 10(5) s in vacuum and air, respectively. (C) 2015 Author(s).