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Water-Related Instabilities in Pentacene Thin-Film Transistors
L. Mariucci,S. Cipolloni,D. Simeone,M. Cuscuna,L. Maiolo,A. Minotti,A. Pecora,A. Valletta,G. Fortunato 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1
We have analyzed the hysteresis of the transfer characteristics of pentacene thin-film transistors (TFTs) measured under different environmental conditions (vacuum, oxygen, dry nitrogen, air and nitrogen with different relative humidities). The results showed that, whereas the characteristics in dry atmospheres are quite stable, the hysteresis increases with the percentage of moisture, indicating that adsorbed water is the main cause of the environmental instability in pentacene TFTs. In addition, transient current experiments have been carried out in air. Through these measurements, we have been able to evaluate a characteristic time of drain current reduction of several seconds. These results indicate that the environmental instability is not simply related to charge trapping in localized gap states and slower phenomena should also be considered.
Self-Heating Effects in p-Channel Polysilicon TFTs Fabricated on Different Substrates
G. Fortunato,M. Cuscuna,P. Gaucci,L. Maiolo,L. Mariucci,A. Pecora,A. Valletta,F. Templier 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1
The self-heating-related instability was studied in p-channel polysilicon TFTs fabricated on glass, stainless steel (SS) and polyimide (PI) substrates. We found that while the devices fabricated on glass and PI presented substantial device degradation when operated in the self-heating region, the devices fabricated on SS were very stable when bias stressed under similar conditions. From extensive analysis of the phenomenon through numerical simulations, we found that the device degradation could be reproduced perfectly by interface state generation and uniform positive charge injection into the gate oxide along the channel. Additional defects, located in narrow (100 nm) regions at the gate edges, were also introduced to fully reproduce the apparent field effect mobility enhancement. In order to explain the role of the substrate on the stability, we analyzed three different structures by using 3-dimensional numerical simulations, coupling the thermodynamic and the transport models. The results from the simulations clearly demonstrate that devices fabricated on SS operate at much lower temperatures, thus explaining the observed better stability.