George Gruner

Scalable Carbon Nanotube Thin Films: Fabrication, Properties and Device Applications

Carbon nanotubes (CNT) have been under investigation for many years as a material suitable for applications in electronic devices. This paper will focus on the development and production of high quality, high performance, and scalable transparent and conductive CNT thin films using solution based roll to roll coating methods. We demonstrate both additive and subtractive methods for patterning conductive nanotube films. Various types of devices incorporating CNT thin films are demonstrated, including EPD e-paper, touch screen, OLED, flexible OPV, and TFT-LCD. Issues involving the integration of CNT electrodes into various devices are discussed, in particular conformal step coverage. Optical and mechanical properties, environmental stability and large scale uniformity together make Unidym’s CNT thin films a viable alternative to transparent conductive oxides in applications requiring transparent, conductive electrodes. INTRODUCTION Thin films of carbon nanotubes (CNT) are a promising candidate in the development of alternatives to indium-tin-oxide thin films in applications requiring transparent, conductive films, and have been investigated by a number of groups. Films with high conductivities up to 6000 S/cm have been reported, and CNT integration into various devices such as organic solar cells, OLEDs, and LCD prototypes have been demonstrated. 1-6 However, most of these systems have suffered from one or more limitations. These limitations have included the high cost of CNT materials, film fabrication processes that are not scalable to large volumes, inferior conductivity, and poor lifetimes. Here we report the fabrication of high performance, scalable CNT films useful in applications for transparent conductors, and describe some applications of these materials demonstrating their usefulness in devices. RESULTS CNT material is synthesized by Unidym by thermal CVD using a proprietary catalyst and reactor system, and formulated into an aqueous ink with the proper rheology for slot-die roll-toroll coating. The concentration of the CNT inks range from 0.2 mg/ml to 1.5 mg/ml, depending on the formulation (Figure 1(a)). CNT thin films were coated by using a conventional roll-to-roll slot-die coater with a custom die head. As show in Figure 1(b), the speed of coating can go up to 150 feet per minute. The ink formulation, ink-substrate interaction, drying and encapsulation are critical to obtain uniform and stable CNT thin films. Unidym has demonstrated 2000 ft long CNT coating which meets the specifications of most resistive and capacitive touch panel applications. Figure 1 (c) shows a 30 inch wide and 2000 ft long roll of CNT coating on PET substrate.

Millimeter Wave Surface Impedance Measurements Of Highly Oriented YBa 2 Cu 3 O 7-8 Thin Films

We have measured the surface impedance of two different orientations of thin films of YBa2Cu307-8 (YBCO) at 100 and 150 GHz. The surface resistance drops rapidly below the transition temperature, but the loss at low temperatures is in disagreement with the convential BCS theory. The measured temperature, frequency, and orientation dependence are presented and discussed.