JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 19, NO. 5, OCTOBER 2010 1243 A Novel Method to Guarantee the Speciﬁed Thickness and Surface Roughness of the Roll-to-Roll Printed Patterns Using the Tension of a Moving Substrate Changwoo Lee, Hyunkyoo Kang, Changwan Kim, and Keehyun Shin Abstract—Roll-to-roll (R2R) continuous printing is an attrac- tive technology for mass-producing ﬂexible printed electronics. Many studies have been conducted in this ﬁeld. The application of the R2R printing process, however, requires information per- taining to system parameters such as substrate ﬂexibility, ink formulation, and printing method as well as the curing method for conductive ink. We show that the quality of a printed pattern (thickness and surface roughness) could be affected by tension variation of the ﬂexible bare substrate in spite of the optimal settings of the ink, substrate, and printing method. In addition, an ink-transfer mechanism for the R2R printed electronics is analyzed to reveal the relationships between the dynamic surface roughness and tension of a moving web. Since the dynamics of the physical problem are complex, simple meta models using a design of experiment are developed. The experimental results are found to be in agreement with the meta models. It is found that the two important factors for achieving the desired thickness and surface roughness of the R2R printed patterns are optimal tension and control accuracy of the operating tension. [2009-0196] Index Terms—Ink-transfer mechanism, matching correlation, roll-to-roll (R2R) printed electronics, surface roughness of the R2R printed pattern, tension, thickness of the R2R printed pattern. I. I NTRODUCTION T HE ELECTRONICS industry is growing as an integral part of our society. A ubiquitous society will be realized when people can track all items with low-cost radio frequency identiﬁcation tags instead of the current barcode method. For electronic tags to be applied on all goods, it is important that the cost of each tag be less than a few cents [1]. Reducing costs is one of the key issues in meeting the requirements of the markets. To maintain high productivity while keeping costs down, conventional printing methods such as sheet printing, Manuscript received August 6, 2009; revised July 9, 2010; accepted July 9, 2010. Date of publication September 7, 2010; date of current version October 1, 2010. This work was supported in part by the Seoul R&BD Program (10848), Korea, and in part by the Korea Foundation for International Cooperation of Science and Technology (KICOS) under Grant K20710140597- 07A0404-05110 from the Korean Ministry of Education, Science and Technol- ogy (MEST). Subject Editor C. Liu. C. Lee is with the Flexible Display Roll to Roll Research Center, Konkuk University, Seoul 143-701, Korea (e-mail: changwoo1220@gmail.com). H. Kang, C. Kim, and K. Shin are with the Department of Mechanical Engineering, Konkuk University, Seoul 143-701, Korea (e-mail: hyunkyoo@ konkuk.ac.kr; goodant@konkuk.ac.kr; khshin@konkuk.ac.kr). Color versions of one or more of the ﬁgures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identiﬁer 10.1109/JMEMS.2010.2067194 ink jetting, and spin coating have been applied in fabricating printed electronic devices because they use very small amounts of functional ink, thus allowing for high accessibility and low capital costs [2]–[6]. However, these are serial methods exhibiting very low throughputs. Roll-to-roll (R2R) printed electronics have been proven to be a method that is suitable for mass production, as all the units of electronic devices such as organic thin-ﬁlm transistors (TFTs) and R-L-C resonators can be printed continuously. Of course, this demands a high- quality functional ink and a precise control of the moving substrate. Earlier studies were carried out on the applications of the R2R printing processes, such as gravure, ﬂexography, and offset, to name a few [7]–[9]. In the R2R printing process, the web or printed substrate moves from the unwinder to the winder through a system of rollers and processing sections (e.g., drying, curing, and printing). The settings and properties of each sections are important in ensuring the quality of the text or images printed on the substrate as well as the quality of the web itself (e.g., wrinkling or buckling). The quality and productivity of the printed electronic devices depend on mechanical factors (such as tension, registration, geometric quality of a printed pattern, and nip pressure in a printing section) and on the aspects of the formulation of the ink (e.g., viscosity and ink pigment). In general, the functional quality of a printed electronic device is affected by the chemical characteristics of the materials (viscosity and surface tension of an ink, adhesiveness of a bare substrate, etc.) and mechanical issues (cell stylus, cell depth in a printing cylinder, dot size of a cell, nip force, doctoring, etc.) [10]–[22]. Small changes in the properties of the ink such as viscosity, surface tension, and solid contents can result in major variations in the printing qualities (e.g., the thickness and surface roughness of the R2R printed layer) [10]–[13]. The ink-transfer process, which is responsible for determining the printed thickness and the uniformity be- tween the printing cylinder and the ﬂexible substrate, can be inﬂuenced by the surface of a bare substrate. Consequently, a corona pretreatment process was generally used to increase the surface roughness of a bare substrate before the printing process [14]. The performance of a printed transistor can deteriorate due to the nonuniformity of the printed drain–source regions [15]–[18]. Previous research demonstrates that high-quality electronic applications are dependent on the characteristics of the ink, characteristics of the substrate, and printing methods. In this paper, the ink-transfer mechanism was analyzed based 1057-7157/$26.00 © 2010 IEEE