Integration of ink jet and transfer printing for device fabrication using nanostructured materials B. Kumar a,1 , H.S. Tan a , N. Ramalingam b , S.G. Mhaisalkar a, * a School of Materials Science and Engineering, Nanyang Technology University, Nanyang Avenue, Singapore 639798, Singapore b School of Mechanical Engineering and Aerospace Engineering, Nanyang Technology University, Singapore 639798, Singapore ARTICLE INFO Article history: Received 18 August 2008 Accepted 20 October 2008 Available online 26 October 2008 ABSTRACT Low viscosity, dilute inks of carbonaceous materials that tend to run, spread, and dry unevenly pose a major challenge towards ink jet printing approaches. A porous, planar stamp based methodology outlined here combines the advantages of ink jet and transfer printing while enabling printing of dilute inks comprising nanowires, nanotubes, nanopar- ticles, and biological molecules. Integration of ink jet and transfer printing is reported with agarose gel planar stamp, for carbon nanotube inks, enabling the formation of gate modu- lated channels between source and drain electrodes without necessitating any lithography steps. Ó 2008 Elsevier Ltd. All rights reserved. Printed electronics with applications ranging from large- area organic light emitting diode (OLED) based displays to low-cost ubiquitous radio frequency identification (RFID) tags and point-of-care disposable biosensors represent the new wave of electronics that will have a wide ranging im- pact on our lifestyles as well as our health and well-being. Ink jet printing and transfer printing hold the promise to be key enablers of the printed electronics revolution and have found wide ranging applicability in electronic device fabri- cation to microarray based bioassay applications. Ink jet printing has been successfully employed for solution based polymer electronic materials, display devices, printing of biological molecules and tissue engineering [1,2]. Transfer printing is another versatile technique that has been em- ployed to fabricate electronic circuits to micro-arrays for bioassay applications on various substrates [3–6]. The ‘mas- ter mold’ for all the transfer printing applications is typically produced using standard lithography procedures [3–6]. Along with organic and inorganic materials used in printed electronics, carbonaceous materials including graphene sheets, carbon black, and carbon nanotubes (CNTs) represent an exciting class of materials. In particu- lar, solution processed random networks of single walled CNTs (SWCNTs) are widely being explored as active materi- als for field effect transistors (FETs) [7,8] and also as passive components such as transparent electrodes for OLEDs and solar cells [9]. Transfer printing needs lithography processed master mold, whereas ink jet printed low viscosity and con- centration CNT inks have a tendency to run, spread, and dry unevenly on most substrates. Furthermore, multiple prints are needed to create dense CNT networks that yield adequate conductivity or functionality. Thus, although ink jet and transfer printing offer promise for device fabrica- tion, a suitable method that can accommodate low viscosity CNT inks and doesn’t rely on any lithography steps, has proven to be elusive. In this report, a method is proposed to fabricate CNT mi- cro-arrays, patterned films, electrodes and network channel layers for thin film transistors without any lithography pro- cess steps. Water dispersed carboxyl group modified SWCNT ink was first ink jet printed on planar porous agarose stamps to fabricate well defined patterns (please refer to supplemen- tary data for experimental details). These patterns were sub- sequently transferred to silicon oxide, polyethylene terephthalate (PET), PET/Al/sol–gel substrates with procedure outlined in Fig. 1. Use of porous agarose substrate serves two purposes: first it acts as a filter to get a uniform thin or thick film depending on the number of repetitive ink jet prints and second, it acts as a planar stamp to facilitate transfer printing. Agarose is highly hyrdrophilic in nature with a near zero con- tact angle with CNT ink (images not shown here). It is how- ever noted that some form of surface treatments may be effectively used if the stamp used is other than agarose and if the material of the stamp is hydrophobic in nature. The ink jet printing step eliminates the need for lithography pro- cesses and also precisely controls the carbon nanotube 0008-6223/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2008.10.029 * Corresponding author: Fax: +65 6790 9081. E-mail address: subodh@ntu.edu.sg (S.G. Mhaisalkar). 1 Author currently at Material Science and Engineering Program at UC San Diego, USA. CARBON 47 (2008) 313 – 347 321