Closed-loop control of a laser assisted carbon nanotube growth process for interconnects in flexible electronics
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Closed-loop control of a laser assisted carbon nanotube growth process for interconnects in flexible electronics Yoeri van de Burgt1,2, Yves Bellouard1, Rajesh Mandamparambil2 and Andreas Dietzel1,2 1 Department of Mechanical Engineering, Eindhoven University Technology, Den Dolech 2, Eindhoven, The Netherlands. Tel: +31402472186. E-mail: [email protected] 2 Holst Centre/TNO – Netherlands Organization for Applied Scientific Research, HTC31, Eindhoven, The Netherlands. ABSTRACT A feedback control mechanism based on infrared radiation monitoring coupled with reflectivity information was developed to control the temperature of a laser assisted chemical vapor deposition process for the growth of carbon nanotube forests. An infrared laser operating at 808 nm is focused on a silicon substrate containing a 20 nm-aluminum-oxide layer and a 1.5 nm-iron catalyst layer. The growth takes place in an argon/ hydrogen/ ethylene gaseous environment. SEM and Raman spectroscopy analysis show that good controllability and reproducibility is achieved over multiple experiments. INTRODUCTION In recent years, flexible electronics have gained significant importance in the development of flexible displays, wearable devices, intelligent clothes and ambient intelligence [1][2][3]. To mass produce these flexible devices, roll-to-roll manufacturing process involving lamination of various functional multilayer device stacks is used. These functional layers need eventually to be electrically interconnected. Conventional interconnects are made out of metals, pastes or inks filled with metal particles which poses mechanical as well as process related performance issues. We propose to use carbon nanotubes (CNTs) embedded in a polymer matrix as interconnects for flexible electronics. This is motivated by the excellent electrical properties of CNTs (~10.1010 A cm-2) [4] . In this research, a laser assisted chemical vapor deposition method (LACVD) [5] is used to locally grow CNT forests on a silicon substrate in a carbonaceous environment. Laser assisted CVD opens up a range of possibilities for different materials and geometries that are sensitive to heat. CNT length, diameter and density are interesting parameters to tailor for controlling the electrical, mechanical and conformability performances of the interconnects. For example, an obvious requirement is that the CNTs need to be as long as the thickness of the interconnecting layer between the functional layers. The structure, geometry and characteristics of CNTs forests are known to be strongly dependent from the heating profile applied during the growth process [6]. A current limitation of LACVD set-ups [7] [8] is the lack of an accurate temperature control at the laser spot. Here we present a feedback control mechanism based on infrared radiation monitoring from the CNT growth region triggered by information collected from dynamic reflectivity measurements. The origin of the measured infrared radiation (from 700 to 1700 nm) is essentially of thermal origin and therefore provides indirect inf
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