Journal of Mechanical Science and Technology 29 (4) (2015) 1697~1702 www.springerlink.com/content/1738-494x DOI 10.1007/s12206-015-0342-4 Positional accuracy of micropatterns in the roll-to-roll imprinting process using a wrapped roll mold † Eun Soo Hwang 1 , Sin Kwon 2 , Dongmin Kim 3 , Young Tae Cho 4,* and Yoon Gyo Jung 4 1 Manufacturing Technology Center, Samsung Electronics, Co., Ltd., Suwon, 443-742, Korea 2 Korea Institute of Machinery & Materials, Daejeon, 305-343, Korea 3 Korea Research Institute of Standards and Science, Daejeon, 305-340, Korea 4 School of Mechatronics, Changwon National University, Changwon, 641-773, Korea (Manuscript Received August 18, 2014; Revised November 12, 2014; Accepted December 12, 2014) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract Various micropatterns in flexible devices can be fabricated using the roll-to-roll (R2R) imprinting process, wherein a raw flexible plas- tic film is released from a roller and subjected to several patterning processes such as imprint lithography. In case a thin-film-transistor liquid-crystal display (TFT-LCD) is formed on the flexible film, overlay accuracy becomes the most important factor in the patterning process. To achieve positional accuracy, the process parameters that affect dimensional changes should be analyzed. In our system, the roll mold was fabricated by wrapping a thin film sheet to the roller. During the process, the substrate was deformed by web tension and bent by overall system architecture. Thus, web tension, misalignment angle, mold thickness, and substrate bending effects were regarded as the main parameters, which were analyzed and modeled into mathematical formulas. Positional errors and their tolerances were esti- mated using the formulas, and process parameters were designed to compensate for each error. Finally, the color filters in the flexible TFT-LCD display were manufactured using R2R imprinting and ink-jet printing. Dimensional error can be minimized to approximately ±15 μm for the entire area of 200 mm × 150 mm. Keywords: Roll-to-roll process; Imprint lithography; Flexible display; Positional accuracy of micropattern; Web control; Wrapped roll mold ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction Roll-to-roll (R2R) printing techniques have been considered as viable means to produce flexible electronic devices at low cost and high speed. The R2R process can be used to produce consumer electronics products such as e-papers [1], flexible cholesteric liquid crystal displays (LCDs) [2], flexible solar battery chargers, and flexible organic light emitting diodes. Given that this process shows great potential to reduce the manufacturing costs of flexible LCDs, the R2R printing tech- nique has attracted considerable attention from LCD manufac- turers [3]. For the production of flexible electronics, several other printing methods such as flexography, offset, and gra- vure printing techniques have been reported [4-7]. However, the minimum line width obtained using these methods are typically within the range of tens of microns. In addition, posi- tion accuracy in these printing systems is not as good as that in conventional photolithography [8]. Therefore, improving fea- ture resolution and position accuracy during the patterning process remains as a technical challenge. H. Zhang et al. [1] reported pattern distortions in R2R pho- tolithographic process. Based on their experiments, web stretch attributed to tension in the R2R process is a major cause of overlay errors. Given that the overlay offset induced by tension is a non-symmetric distortion, this offset cannot be compensated for by optical lens magnification in their R2R photolithography system [9, 10]. In this regard, another tech- nique, that is, an R2R self-aligned imprint lithography process, has been developed to achieve accurate overlay alignment [3]. Although exact alignment between layers has been achieved, position errors can still occur because a soft mold wrapped on a quartz cylinder has been used in the process. As an alterna- tive approach, E. Meinder et al. [11] used a carrier wafer for patterning on flexible substrates. However, microdeformations can still occur in the substrate as a result of the lamination process and the mismatch in the coefficient of thermal expan- sion. Another group reported on the R2R nanoimprint lithog- raphy (R2R NIL) process, which enables the fabrication of submicron features [12]. However, they produced a single optical layer pattern. Moreover, the overlay alignment in the R2R process was not considered. A method to realize the pattern roll mold for R2R NIL was reported by the authors, wherein a nickel sheet mold was fab- * Corresponding author. Tel.: +82 1052288912, Fax.: +82 2132750101 E-mail address: ytcho@changwon.ac.kr † Recommended by Editor Haedo Jeong © KSME & Springer 2015