Interface and Morphology Engineering for Polymer and ZnO Thin-Film Transistors: toward High Mobility and Stability
Date Issued
2011
Date
2011
Author(s)
Fu, Yu
Abstract
In this study, we have demonstrated methods for fabricating air-stable flexible thin film transistor (TFT) that are suitable for large-area production, with two main focuses: (1) solution-processed poly (3-hexylthiophene) (P3HT) TFTs, and (2) atomic-layer-deposited (ALD) zinc oxide (ZnO) TFTs. With P3HT TFTs, we developed a low-temperature and solution-based fabrication process that yields high device performance. Additionally, we developed solution-processed thin-film encapsulation methods to obtain air-stability from the P3HT TFTs. With ZnO TFTs, we developed ALD processes for the ZnO film, the dielectric layer, and the passivation layer, achieving high field-effect mobility, low operation voltage, mechanical flexibility, and stability under a bias stress. The accomplishments of this study include: (1) we systematically determined the causes and characteristics of the air- and encapsulation-induced degradations of P3HT OTFTs, and based on the obtained knowledge, we developed a solution-based encapsulation process that yielded air-stable P3HT OTFTs (nearly free of degradation for > 5500 h in air) without encapsulation- induced degradation; (2) we demonstrated a solvent-vapor-annealing technique which induces reflow of the P3HT film, resulting in drastically improved field-effect mobility (by a factor of 84, to 0.11 cm2/V s); (3) we systematically studied the ZnO/dielectric interface to determine the factors governing the device performance, obtaining exceptionally high field-effect mobility from ALD ZnO TFTs on polyethylene terephthalate (PET) substrate, 16.9 cm2/V s, which was unprecedented for ALD ZnO-based TFTs; moreover, the TFTs exhibited excellent flexibility: nearly free of degradation upon repeated bending (1000 times) to 0.83 cm of radius; (4) we demonstrated ALD passivation of the ZnO TFTs, improving the bias-stress stability of the devices. The results from my research will provide practical information to the development of large-area-processible flexible TFTs.
Subjects
thin film transistor
TFT
poly(3-hexylthiophene)
ZnO
atomic layer deposition
encapsulation
Type
thesis
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