Publication: Design and fabrication of all-solution-processed low-voltage organic thin film transistors using direct-write printing technique towards flexible electronics applications
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Date
2024-12-01
Authors
Nur Syahadah, Yusof
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Abstract
Amidst the rising global demand for printed electronics and wearable devices, researchers have investigated various manufacturing techniques to fabricate organic devices, including Organic Thin Film Transistors (OTFTs). As a pivotal deposition method in printed electronics, inkjet printing enables the deposition of solution processable materials onto various substrates via simpler fabrication steps at lower processing temperatures, which is suitable for flexible electronic applications. Although the inkjet printer has been the predominant option in manufacturing organic devices, nonetheless, the persistent clogging issue encountered at the printer’s nozzles has emerged as a major drawback of this technique. Furthermore, the stringent requirements of the conductive inks and substrate states have limited the material selection and hampered the efforts to commercialize OTFT fully in the market. Besides, oxide-based dielectric materials such as Silicon Dioxide (SiO2) have been exploited thanks to their remarkable electrical characteristics in OTFTs. However, the practical implementation of OTFTs is significantly impeded by the high operating voltage resulting from a low gate capacitance density of conventional SiO2 dielectric.
Thus, this study presents a simple and direct solution-based fabrication approach to develop a low-voltage OTFT. A novel direct-write printing technique was employed to deposit the electrodes, i.e., source/drain and gate terminals of OTFTs at low temperatures of less than 150 ℃ and in ambient conditions. At the same time, a spin coating deposition method was utilized to deposit both a small molecule 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) organic semiconducting layer and a high-k dielectric layer. The proposed OTFT devices demonstrated high electrical performances and good morphological characteristics. Remarkably, the fabricated OTFT using a high-k Polyvinylpyrrolidone (PVP) dielectric on a Polyethylene Terephthalate (PET) substrate achieved a channel length of 120 µm with saturation mobility of 6.86 × 10-1 cm2/Vs, a threshold voltage of –3.5 V, an On/Off current ratio of 106, and a subthreshold swing of 105.9 mV/decade. On top of that, this work also successfully developed the OTFT working at low operating voltage, below –5 V. Moreover, the proposed method was also utilized to establish OTFT-based temperature sensors demonstrating sensitivity up to 0.17 µA/℃. The integration of direct-write printing technology into the high-k dielectric layer offers a novel bottom up approach to fabricating organic-related devices, mainly the OTFTs, at lower processing temperatures suitable for flexible and wearable electronic applications.