Solution-Processed Carbon Nanotube Field-Effect Transistors Treated by Material Post-Treatment Approaches

Abstract

The preparation of semiconducting carbon nanotube (s-CNT) thin films by solution processing has become the mainstream approach nowadays. However, residual polymers are always inevitable during the sorting of s-CNTs in solution. These residual polymers will degrade the electrical properties of the CNTs. Although several post-treatment approaches have been reported to be effective in improving the performance of the device, there is no deep analysis and comprehensive comparison of these approaches, so there is no overall guidance on the optimum treatment of CNTs for performance improvement. In this work, we characterize CNT thin film with three post-treatment methods, including annealing (A), yttrium oxide coating and decoating (Y), and annealing combined with YOCD (A + Y), and evaluate and compare the performance of Field Effect Transistors (FETs) based on the above mentioned CNT thin film. The result shows that the CNT thin film treated by the A + Y method is the clearest and flattest; the average roughness determined from the overall AFM image is reduced by 28% (from 1.15–1.42 nm (O) to 0.826–1.03 nm (A + Y)), which is beneficial in improving the device contact quality, uniformity, and stability. The on-state current (Ion) of the FETs with CNTs treated by A, Y, and A + Y is improved by 1.2 times, 1.5 times, and 1.75 times, respectively, compared with that of FETs fabricated by untreated CNTs (O for original CNTs), indicating that the A + Y is the optimum post-treatment method for the A + Y and combines the effect of the other two methods. Accordingly, the contact and channel resistance (2Rc and Rch) of the CNT FETs treated by different post-treatment methods including A, Y, and A + Y is reduced by 0.18/0.24 times, 0.37/0.32 times, and 0.48/0.41 times, respectively. The ratio of improvement in device performance is about 1:2 for the contact and channel sections for a transistor with a 500 nm channel length, and this ratio will go up further with the channel length scaling; together with the decay in the channel resistance optimization effect in the scaling device, it is necessary to adopt more methods to effectively reduce the contact resistance further.