Metal-tube contact is known to play an important role in carbon nanotube field-effect transistors (CNT-FETs) which are fabricated on individual CNTs. Less attention has been paid to the contact effect in network type carbon nanotube thin film transistors (CNT-TFTs). In this study, we demonstrate that contact plays an even more important role in CNT-TFTs than in CNT-FETs. Although the Schottky barrier height at the metal-tube contact can be tuned by the work function of the metal, similar to the case in CNT-FETs, the contact resistance (Rc) forms a much higher proportion of the total resistance in CNT-TFTs. Interestingly, the contact resistivity was found to increase with channel length, which is a consequence of the percolating nature of the transport in CNT films, and this behavior does not exist in CNT-FETs and normal 2D Ohmic conductors. Electrical transport in CNT-TFTs has been predicted to scale with channel length by stick percolation theory. However, the scaling behavior is also impacted, or even covered up by the effect of Rc. Once the contact effect is excluded, the covered scaling behavior can be revealed correctly. A possible way of reducing Rc in CNT-TFTs was proposed. We believe the findings in this paper will strengthen our understanding of CNT-TFTs, and even accelerate the commercialization of CNT-TFT technology.

Patterning micro-structures on highly hydrophobic surface by photolithography is usually inevitable for fabricating devices based on electrowetting effects. The key challenges for such photolithography processes are how to coat photoresist uniformly and maintain the hydrophobicity of the highly hydrophobic surface, which are usually two contradict aspects. Moreover, the patterned microstructure must adhere to the highly hydrophobic surface excellently, which is critical for device application. However, a simple and robust fabrication process that fulfills all the above requirements was seldom reported. In this paper, we developed a sacrificial layer photolithography strategy on highly hydrophobic surface. Photoresist is easily coated uniformly all over the substrate by introducing a sacrificial layer between the photoresist and the highly hydrophobic surface. The hydrophobicity of the exposed hydrophobic surface was maintained and the adhesion of the microstructures to the substrate is excellent. An electrowetting display sample was demonstrated by this fabrication strategy, which showed dynamic image displaying with response time less than 40 ms. The strategy is applicable to both rigid and flexible substrate and manufacturing compatible. We believe our developed photolithography process is important for research and development of devices based on electrowetting effect.

Carbon nanotube thin film transistors (CNT-TFTs) are promising candidates for future high performance and low cost macro-electronics. However, most of the reported CNT-TFTs are fabricated in small quantities on a relatively small size substrate. The yield of large scale fabrication and the performance uniformity of devices on large size substrates should be improved before the CNT-TFTs reach real products. In this paper, 25 200 devices, with various geometries (channel width and channel length), were fabricated on 4-in. size ridged and flexible substrates. Almost 100% device yield were obtained on a rigid substrate with high out-put current (>8 μA/μm), high on/off current ratio (>105), and high mobility (>30 cm2/V·s). More importantly, uniform performance in 4-in. area was achieved, and the fabrication process can be scaled up. The results give us more confidence for the real application of the CNT-TFT technology in the near future.

The contact resistance effect in the network type carbon nanotube thin film transistors (CNT-TFTs) is studied by using different contact metals. It is shown that palladium (Pd) can form an ohmic type contact with the carbon nanotube thin film, and gold (Au) forms an almost ohmic contact. On-state current and carrier mobility in the devices of these two contacts are high. In contrast, both titanium (Ti) and aluminum (Al) form Schottkytype contacts with the carbon nanotube thin film. The barrier height and the contact resistance of the Al contact are higher than those of the Ti contact. Therefore, the on-state current and carrier mobility are relatively low in the corresponding devices of these two types of contacts. These results indicate that the performance of CNT-TFTs can be tuned by the contact metal, which is important for the commercialization of CNT-TFTs.