Influence of Polymer Coating on Device Properties of Carbon Nanotube Field-Effect Transistors

1. Introduction Flexible and transparent field-effect transistors (FETs) based on organic or inorganic materials are now one of the most attractive research objects because they have potential to bring innovation in conventional electronic device systems. Recently, high-performance flexible integrated circuits using carbon nanotube thin-film transistors (CNT-TFT) have been developed [1-3]. These devices have shown excellent device properties, however, both optical transparency and mechanical flexibility are limited due to the use of opaque metal electrodes and brittle oxide dielec-trics. To realize extremely flexible and highly transparent devices, we suggest that robust and pliable materials such as carbon electrodes (carbon nanotube networks or graphene), polymer dielectrics and thin plastic substrates should be used for device components. In our previous work, we used as-grown single-walled carbon nanotubes (SWNTs) as both electrode and channel material, and poly(vinyl alcohol) (PVA) employed as die-lectric layer and substrate, thus realizing extremely flexible (radius of curvature, R = 1.0 mm) and transparent (more than 80% transmittance in the visible range) CNT-FETs [4]. On the other hand, the conduction type of the CNT-FETs changed from p-type to ambipolar behavior by poly(vinyl alcohol) (PVA) coating. Singh et al. also reported such ambipolar conversion using PVA as dielectric layer in organic FETs [5]. However, the conversion mechanism has not yet been clarified. Here, we try to understand why carrier transport behavior of CNT-FET can be changed by polymer coating and also to control the device properties (e.g. p/n type, threshold voltage, etc.). To control the polarity of FETs, as well as to realize high-performance flexible electronic devices, it is very important to clarify interfacial interaction between CNTs and polymers.