- Email: [email protected]
Development of reel-to-reel process system for roller-imprint on plastic fibers
Microelectronic Engineering 88 (2011) 2059–2062
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Development of reel-to-reel process system for roller-imprint on plastic fibers Harutaka Mekaru a,b,⇑, Akihiro Ohtomo a,c, Hideki Takagi a,b, Mitsunori Kokubo a,c, Hiroshi Goto a,c a
Macro Bio-Electromechanical-Autonomous-Nano-Systems (BEANS) Center, BEANS Project, 1-2-1, Namiki, Tsukuba, Ibaraki 305-8564, Japan Research Center for Ubiquitous MEMS and Micro Engineering, National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1, Namiki, Tsukuba, Ibaraki 305-8564, Japan c Toshiba Machine Co., Ltd., 2063-3, Ooka, Numazu, Shizuoka 410-8510, Japan b
a r t i c l e
i n f o
Article history: Available online 24 December 2010 Keywords: Roller nanoimprint, Reel-to-reel process Plastic optical fiber Electroformed-Ni mold MEMS
a b s t r a c t We are developing a woven fabric of micro-electro-mechanical-systems (MEMS) where smart fibers are woven to make large-size flexible devices. MEMS structures and electric circuits are formed on the surface of individual fibers to serve as smart fibers where they can function as sensors and actuators. Moreover, when smart fibers are inter-woven it becomes necessary to process electric contact and physical positioning guides on the surfaces of warp and woof fibers. To transfer various patterns on the surface of a fiber at high speed, a batch process by thermal nanoimprinting is pursued. We then developed a new-type roller nanoimprint system to precisely transfer fine patterns from a plane mold onto the curved surface of a fibrous substrate. In this system, a fiber is sandwiched by two molds and rolls under the traction force of sliding molds traveling in opposite directions. At the end of their travel the molds are separated. The molds are moved in directions opposite to their previous directions of travel. This brings the molds back to their inital positions. Then, the fiber is moved by a preset distance using a reel-to-reel feeder. A new cycle starts again. With this method, 5-lm-width square and 5-lm-diameter circular dotted patterns with 10 lm pitch were successfully transferred onto a 250-lm-diameter plastic optical fiber (POF) covering its full surface. Moreover, we succeeded in a continuous molding on the entire curved surface of 1.6 m long POF using a reel-to-reel feeder as a batch processing operation with a pitch of 16 mm by a repetition of roller-imprinting for 100 times. No significant difference was observed when the shapes and depths of the imprinted patterns obtained from the first imprinting were compared with those of obtained from the 100th imprinting. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction We are applying semiconductor manufacturing processes on the curved surface of a fibrous substrate like optical fibers instead of using the conventional plane substrate of Si wafers. Here we are developing smart fibers by putting micro-electro-mechanical-systems (MEMS) structures and electronic circuits on the surface of the fibers. With techniques like these, we plan to develop largearea displays and wearable health checkers by the alternate weaving of smart fibers. To produce such woven MEMS devices, a technology that can produce smart fibers in high volume and with high throughput is required. Hence, we are investigating the possibility where a thermal imprint technology can be applied for patterning on the surface of the fibers. Several techniques have been reported for the processing of high precision structures of nano-micro size by hot embossing [1] and thermal nanoimprinting [2] that are ⇑ Corresponding author at: Macro Bio-Electromechanical-Autonomous-NanoSystems (BEANS) Center, BEANS Project, 1-2-1, Namiki, Tsukuba, Ibaraki 3058564, Japan. Tel.: +81 29 861 7020; fax: +81 29 861 7167. E-mail address: [email protected] (H. Mekaru). 0167-9317/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2010.12.043
linked with several kinds of device developments. Hot embossing and thermal nanoimprinting are suitable for mass production because these are low-cost technologies that can transfer patterns by simply pressing a heated mold against a molding product. Therefore, the materials that can be processed by these technologies have to be thermoplastics or glass materials that can respond to glass transition temperature. In one case where hot embossing is employed to make MEMS on fibers, Henzi et al. fabricated microstructures for coupling an optical fiber on polymethyl methacrylate (PMMA) substrates for light guiding devices are made [3], Qi et al. reported success in patterning on PMMA substrates to fabricate microfluidic devices inserted by optical fibers for fluorescence detection [4]. However, in neither case hot embossing was used for processing the fiber. As in a case where fibers arranged on a plastic substrate were thermal transformed by hot-embossing. W. Jordan used carbon fibers arranged in one or two mutually perpendicular orientations sandwiched between two polycarbonate (PC) substrates, and a mold with hexagonal channels was pressed on PC substrates. Then, they succeeded in fabricating high-strength multilayered honeycomb laminate structures [5]. Schift et al. reported their success in transferring a 1-lm pitch grating pattern
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on the surface of a 180-lm-diameter poly ether sulphone (PES) fiber in form of a spiral structure, as was done in a case where the surface of the fiber was processed by hot embossing [6]. They hot-embossed on PES fibers by a loading force of 0.75 N using a nickel shim mounted on a metal cylinder while heating a contact area of 50 lm in width and 800 lm in length at 210 °C. Roller hot embossing and roller nanoimprinting using a cylinder mold are very attractive technologies because of their mass producing capabilities. A roller imprinting is planned to be applied as a technique with which we can process smart fibers at high speed. However, it is very difficult to apply the process on arbitrarily shaped patterns such as MEMS structures and electronic circuits of nano-micro size on the cylindrical surface of roller mold. Hence, we have thermal-imprinted on the surfaces of various fibers using a plane mold as the first step toward achieving reel-to-reel imprinting using a cylinder mold. For instance, in the case where a smart fiber was inter-woven, positioning guide structures with a rectangle [7] and arc [8] cross-sectional shape could be formed on the surface of a 90-lm-diameter nylon fiber. Moreover, this method succeeded in fabricating line/space and dotted microstructures on a quartz fiber with a cross-sectional shape of a 200-lm
Fig. 1. Roller imprint procedure using sliding plane molds.
square [9]. In this case, a glass-like carbon mold produced by MEMS technologies was used and the heating temperature and contact force were 1350 °C and 300 N. In addition, a pseudo MEMS pattern was roller-imprinted on the entire surface of a Teflon-perfluoroalkoxy (PFA) inlet tube with its outside diameter of 1/16 inch and the inside diameter of 0.02 or 0.03 inch [10]. In this exploratory research, we sandwiched a Teflon-PFA inlet tube between a plane mold and a buffer sheet, and were able to transfer mold patterns comprising coils and comb actuators onto the surface of a cylindrical Teflon-PFA inlet tube by thermal roller-imprinting. However, because fibers and tubes were imprinted after they had been cut into small pieces, in some cases a continuous processing could not be carried out. We then, developed a reel-to-reel processing system built into a roller-imprint device, and transferred intermittently a mold pattern onto the cylindrical surface of plastic optical fibers (POF) based on previous results. 2. Reel-to-reel sliding roller imprint system Fig. 1 shows a procedure for roller-imprinting on the surface of a plastic fiber using plane molds. A plastic fiber is placed between two plane molds fixed to upper and lower loading stages. The plastic fiber rolls on the mold pattern of the plane molds under a suitable traction force caused by the sliding of the plane molds in opposite directions. Reel stations in both sides are rotated while synchronized with the movement of the plane molds. After imprinting, the plane molds are separated from the plastic fiber. The molds are moved back to their initial positions. Then, the fiber is moved by a preset distance using a reel-to-reel feeder. A new cycle starts, after separating the molds and moving the fiber to the same preset distance as in the previous case. Fine patterns can continuously be processed on the entire surface of plastic fiber by sequentially repeating these processes and sending the plastic fiber through gaps between the imprinted patterns. A technical challenge faced here is to twist the plastic fiber by the gyration in a series of operations while plane molds move alternately in parallel. We therefore designed a system so that reel feeders could rotate dynamically. An upper illustration in Fig. 2 is a schematic image of the entire system. This system that specializes in thermal imprint on the fibers is primarily composed of a sending reel station,
Fig. 2. Schematic of reel-to-reel processing system and photographs of (a) sending reel station before and during rotation, (b) loading stages before and during rollerimprinting, and (c) winding reel station before and during rotation.
H. Mekaru et al. / Microelectronic Engineering 88 (2011) 2059–2062
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Fig. 3. (a) Photograph of 250-lm-diameter POF after roller-imprinting, (b) Photograph of POF patterned intermittently, (c) Optical micrograph of 5-lm dotted pattern on imprinted POF.
Fig. 4. Cross-sectional schematic image of sliding roller-imprint and optical micrographs of mold patterns and imprinted patterns on the surface of POF after the 1st and 100th shots.
sliding roller-imprint stages, a winding reel station, and a tension controller. The bottom pictures in Fig. 2 show each reel station of both reel-to-reel feeders and a setup of press stages. The maximum diameter of the reel was 300 mm. The reel station was designed to rotate by 180° while synchronized with the moving plane molds (as shown by black arrows in the bottom left and right figures), thus preventing any twist in the plastic fiber during the imprinting. Electroformed-Ni molds with a size of 15 15 2 mm3 were mounted on Aluminum loading stages. A self-assembled monolayer (SAM) of a release agent Optool HD-2101TH [11] (Daikin Industries Ltd.) was formed on the surface of the electroformedNi mold. A plastic fiber was placed on the center of the mold pattern area. The maximum contact force was 300 N, and the maximum heating temperature was 250 °C. The maximum feeding speed of this system was 40 m/min. The tension was controlled between 0 and 100 N using a several weights. The size of this system is 3.6 m in length, 1 m in width, and 1.75 m in height. 3. Imprinting results In this experiment, we selected a POF CK-10 (Mitsubishi Rayon Co., Ltd.) that comprised a 240-lm-diameter polymenthyl methac-
rylate (PMMA) core and 5-lm-thick florine resin clads as molding materials. The glass transition temperatures of the core and clads were approximately 110 °C, and below room temperature, respectively. The contact force, heating temperature, and contact time were set at 12 N, 50 °C, and 0.5 s, respectively. The width of the sliding plane mold was 0.4 mm. Considering the sliding distance of the both upper and lower molds, it became possible to imprint a total width of 0.8 mm. The 250-lm-diameter of the fiber approximately amounted to 785 lm as its circumference. Therefore, a plastic fiber can be imprinted covering its entire circumference. Fig. 3(b) is an expanded photograph of an imprinted plastic fiber. The discolored sections in the figure (white arrows) are the patterned sections. Fig. 3(c) shows an observed optical micrograph of the imprinted patterns using a five line confocal microscope Optelics S130 (Lasertec Corp.). It is thus confirmed that a fine pattern was completely transfered on the surface of POF. Each square dotted pattern of 5 lm in width and pitch of 10 lm, and circle dotted pattern of 5 lm in diameter, and pitch of 10 lm were selected as a pattern of upper and lower plane molds respectively in thermal roller-imprint experiments. Fig. 4 shows an optical micrograph of square and circle mold patterns, and imprinted patterns after the first and 100th shots. Regardless of the kind of pattern or the
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4. Summary
Fig. 5. Relationship between shot number and imprinted depth on the surface of POF.
shot frequency, 5-lm-width square and 5-lm-diameter circular dotted patterns with 10 lm pitch were successfully transferred. Fig. 5 shows measured results of imprinted depths for every ten shots on the POF continuously roller-imprinted from the first through the 100th shots, as obtained by a five line confocal microscope. The upper mold pattern was a 3.22 lm high convex square dotted pattern. On the other hand, the lower mold pattern was a 3.28 lm high convex circle dotted pattern. When the imprinted depths of 11 areas picked from the square dotted patterns on the surface of POF were compared among each other, the minimum value was 2.99 lm (at the 50th shot), and the maximum value was 3.20 lm (at the 10th shot). In the case of the circle dotted patterns, the minimum depth was 2.83 lm (at the 40th shot) and the maximum depth was 3.20 lm (at the 60th shot). Considering the heights of convex mold patterns, the molding rate (imprinted depth/mold height) amounted to approximately 88–99%. The differences between the minimum values and the maximum values of both patterns were found to be 0.21 and 0.37 lm, respectively. Originally, the irregularity on the surface of the plastic fiber that had existed before imprinting was also observed. Therefore, these differences show that a considerably uniform and continuous imprinting could be executed. The processing time for single roller-imprinting was 14.2 s. This reel-to-reel process was repeated 100 times by establishing a pitch of 16 mm. The total processing time was roughly 24 min. No significant differences were seen among a set of 11 imprinted patterns chosen between the first and 100th imprinting operations.
We developed a new-type roller nanoimprinting system to precisely transfer fine patterns from a plane mold onto the curved surface of a fibrous substrate. With this system, 5-lm-width square and 5-lm-diameter circular dotted patterns with 10 lm pitch were successfully imprinted covering the entire surface of a 250-lm-diameter POF. Imprinted conditions such as contact force, heating temperature of plane molds, and contact time were 12 N, 50 °C and 0.5 s, respectively. A POF was moved intermittently with a reel-to-reel feeder under the same condition, and a continuous imprint experiment was executed 100 times over a pitch of 16 mm. As a result, a molding rate of 88% or more was achieved. Excellent imprinted patterns were obtained and compared with the convex mold pattern of approximately 3.2 lm in height. Moreover, the imprinted depth almost corresponded well, regardless of the shape of the mold pattern, square or circle. In this roller imprint process, one single cycle time was 14.2 s and the total processing time was roughly 24 min. We succeeded in intermittent roller-imprinting on a POF of 1.6 m length. From these results, it was confirmed that our system working with a sliding roller-imprint mechanism and a reel-to-reel feeder was effective as a technique for intermittently transferring fine patterns on the cylindrical surface of the fiber. Acknowledgement This work was supported by New Energy and Industrial Technology Development Organization (NEDO). References [1] M. Worgull, Hot Embossing: Theory and Technology of Microreplication (Micro and Nano Technologies Series), William Andrew Pub., Oxford, UK, 2009. [2] C.M. Sotomayor Torres, Alternate Lithography: Unleashing the Potentials of Nanotechnology (Nanostructure Science and Technology), Plenum Pub. Corp., New York, USA, 2003. [3] P. Henzi, D.G. Rabus, K. Bade, U. Wallrabe, J. Mohr, Proc. SPIE 5454 (2004) 64. [4] S. Qi, X. Liu, S. Ford, J. Barrows, G. Thomas, K. Kelly, A. McCandless, K. Lian, J. Goettert, S.A. Soper, Lab Chip 2 (2002) 88. [5] W. Jordan, J. Eng. Mater. Technol. 127 (2005) 257. [6] H. Schift, M. Halbeisen, U. Schütz, B. Delahoche, K. Vogelsang, J. Gobrecht, Microelectron. Eng. 83 (2006) 855. [7] H. Mekaru, O. Koizumi, A. Ueno, M. Takahashi, Microelectron. Eng. 87 (2010) 922. [8] H. Mekaru, M. Takahashi, J. Vac. Sci. Technol. A28 (2010) 706. [9] H. Mekaru, C. Okuyama, A. Ueno, M. Takahashi, J. Vac. Sci. Technol. B27 (2009) 2820. [10] H. Mekaru, E. Fukushima, Y. Hiyama, M. Takahashi, J. Vac. Sci. Technol. B27 (2009) 2814. [11] T. Motoji, Tribology 249 (2008) 54 [in Japanese].
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Development of reel-to-reel process system for roller-imprint on plastic fibers Harutaka Mekaru a,b,⇑, Akihiro Ohtomo a,c, Hideki Takagi a,b, Mitsunori Kokubo a,c, Hiroshi Goto a,c a
Macro Bio-Electromechanical-Autonomous-Nano-Systems (BEANS) Center, BEANS Project, 1-2-1, Namiki, Tsukuba, Ibaraki 305-8564, Japan Research Center for Ubiquitous MEMS and Micro Engineering, National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1, Namiki, Tsukuba, Ibaraki 305-8564, Japan c Toshiba Machine Co., Ltd., 2063-3, Ooka, Numazu, Shizuoka 410-8510, Japan b
a r t i c l e
i n f o
Article history: Available online 24 December 2010 Keywords: Roller nanoimprint, Reel-to-reel process Plastic optical fiber Electroformed-Ni mold MEMS
a b s t r a c t We are developing a woven fabric of micro-electro-mechanical-systems (MEMS) where smart fibers are woven to make large-size flexible devices. MEMS structures and electric circuits are formed on the surface of individual fibers to serve as smart fibers where they can function as sensors and actuators. Moreover, when smart fibers are inter-woven it becomes necessary to process electric contact and physical positioning guides on the surfaces of warp and woof fibers. To transfer various patterns on the surface of a fiber at high speed, a batch process by thermal nanoimprinting is pursued. We then developed a new-type roller nanoimprint system to precisely transfer fine patterns from a plane mold onto the curved surface of a fibrous substrate. In this system, a fiber is sandwiched by two molds and rolls under the traction force of sliding molds traveling in opposite directions. At the end of their travel the molds are separated. The molds are moved in directions opposite to their previous directions of travel. This brings the molds back to their inital positions. Then, the fiber is moved by a preset distance using a reel-to-reel feeder. A new cycle starts again. With this method, 5-lm-width square and 5-lm-diameter circular dotted patterns with 10 lm pitch were successfully transferred onto a 250-lm-diameter plastic optical fiber (POF) covering its full surface. Moreover, we succeeded in a continuous molding on the entire curved surface of 1.6 m long POF using a reel-to-reel feeder as a batch processing operation with a pitch of 16 mm by a repetition of roller-imprinting for 100 times. No significant difference was observed when the shapes and depths of the imprinted patterns obtained from the first imprinting were compared with those of obtained from the 100th imprinting. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction We are applying semiconductor manufacturing processes on the curved surface of a fibrous substrate like optical fibers instead of using the conventional plane substrate of Si wafers. Here we are developing smart fibers by putting micro-electro-mechanical-systems (MEMS) structures and electronic circuits on the surface of the fibers. With techniques like these, we plan to develop largearea displays and wearable health checkers by the alternate weaving of smart fibers. To produce such woven MEMS devices, a technology that can produce smart fibers in high volume and with high throughput is required. Hence, we are investigating the possibility where a thermal imprint technology can be applied for patterning on the surface of the fibers. Several techniques have been reported for the processing of high precision structures of nano-micro size by hot embossing [1] and thermal nanoimprinting [2] that are ⇑ Corresponding author at: Macro Bio-Electromechanical-Autonomous-NanoSystems (BEANS) Center, BEANS Project, 1-2-1, Namiki, Tsukuba, Ibaraki 3058564, Japan. Tel.: +81 29 861 7020; fax: +81 29 861 7167. E-mail address: [email protected] (H. Mekaru). 0167-9317/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2010.12.043
linked with several kinds of device developments. Hot embossing and thermal nanoimprinting are suitable for mass production because these are low-cost technologies that can transfer patterns by simply pressing a heated mold against a molding product. Therefore, the materials that can be processed by these technologies have to be thermoplastics or glass materials that can respond to glass transition temperature. In one case where hot embossing is employed to make MEMS on fibers, Henzi et al. fabricated microstructures for coupling an optical fiber on polymethyl methacrylate (PMMA) substrates for light guiding devices are made [3], Qi et al. reported success in patterning on PMMA substrates to fabricate microfluidic devices inserted by optical fibers for fluorescence detection [4]. However, in neither case hot embossing was used for processing the fiber. As in a case where fibers arranged on a plastic substrate were thermal transformed by hot-embossing. W. Jordan used carbon fibers arranged in one or two mutually perpendicular orientations sandwiched between two polycarbonate (PC) substrates, and a mold with hexagonal channels was pressed on PC substrates. Then, they succeeded in fabricating high-strength multilayered honeycomb laminate structures [5]. Schift et al. reported their success in transferring a 1-lm pitch grating pattern
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H. Mekaru et al. / Microelectronic Engineering 88 (2011) 2059–2062
on the surface of a 180-lm-diameter poly ether sulphone (PES) fiber in form of a spiral structure, as was done in a case where the surface of the fiber was processed by hot embossing [6]. They hot-embossed on PES fibers by a loading force of 0.75 N using a nickel shim mounted on a metal cylinder while heating a contact area of 50 lm in width and 800 lm in length at 210 °C. Roller hot embossing and roller nanoimprinting using a cylinder mold are very attractive technologies because of their mass producing capabilities. A roller imprinting is planned to be applied as a technique with which we can process smart fibers at high speed. However, it is very difficult to apply the process on arbitrarily shaped patterns such as MEMS structures and electronic circuits of nano-micro size on the cylindrical surface of roller mold. Hence, we have thermal-imprinted on the surfaces of various fibers using a plane mold as the first step toward achieving reel-to-reel imprinting using a cylinder mold. For instance, in the case where a smart fiber was inter-woven, positioning guide structures with a rectangle [7] and arc [8] cross-sectional shape could be formed on the surface of a 90-lm-diameter nylon fiber. Moreover, this method succeeded in fabricating line/space and dotted microstructures on a quartz fiber with a cross-sectional shape of a 200-lm
Fig. 1. Roller imprint procedure using sliding plane molds.
square [9]. In this case, a glass-like carbon mold produced by MEMS technologies was used and the heating temperature and contact force were 1350 °C and 300 N. In addition, a pseudo MEMS pattern was roller-imprinted on the entire surface of a Teflon-perfluoroalkoxy (PFA) inlet tube with its outside diameter of 1/16 inch and the inside diameter of 0.02 or 0.03 inch [10]. In this exploratory research, we sandwiched a Teflon-PFA inlet tube between a plane mold and a buffer sheet, and were able to transfer mold patterns comprising coils and comb actuators onto the surface of a cylindrical Teflon-PFA inlet tube by thermal roller-imprinting. However, because fibers and tubes were imprinted after they had been cut into small pieces, in some cases a continuous processing could not be carried out. We then, developed a reel-to-reel processing system built into a roller-imprint device, and transferred intermittently a mold pattern onto the cylindrical surface of plastic optical fibers (POF) based on previous results. 2. Reel-to-reel sliding roller imprint system Fig. 1 shows a procedure for roller-imprinting on the surface of a plastic fiber using plane molds. A plastic fiber is placed between two plane molds fixed to upper and lower loading stages. The plastic fiber rolls on the mold pattern of the plane molds under a suitable traction force caused by the sliding of the plane molds in opposite directions. Reel stations in both sides are rotated while synchronized with the movement of the plane molds. After imprinting, the plane molds are separated from the plastic fiber. The molds are moved back to their initial positions. Then, the fiber is moved by a preset distance using a reel-to-reel feeder. A new cycle starts, after separating the molds and moving the fiber to the same preset distance as in the previous case. Fine patterns can continuously be processed on the entire surface of plastic fiber by sequentially repeating these processes and sending the plastic fiber through gaps between the imprinted patterns. A technical challenge faced here is to twist the plastic fiber by the gyration in a series of operations while plane molds move alternately in parallel. We therefore designed a system so that reel feeders could rotate dynamically. An upper illustration in Fig. 2 is a schematic image of the entire system. This system that specializes in thermal imprint on the fibers is primarily composed of a sending reel station,
Fig. 2. Schematic of reel-to-reel processing system and photographs of (a) sending reel station before and during rotation, (b) loading stages before and during rollerimprinting, and (c) winding reel station before and during rotation.
H. Mekaru et al. / Microelectronic Engineering 88 (2011) 2059–2062
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Fig. 3. (a) Photograph of 250-lm-diameter POF after roller-imprinting, (b) Photograph of POF patterned intermittently, (c) Optical micrograph of 5-lm dotted pattern on imprinted POF.
Fig. 4. Cross-sectional schematic image of sliding roller-imprint and optical micrographs of mold patterns and imprinted patterns on the surface of POF after the 1st and 100th shots.
sliding roller-imprint stages, a winding reel station, and a tension controller. The bottom pictures in Fig. 2 show each reel station of both reel-to-reel feeders and a setup of press stages. The maximum diameter of the reel was 300 mm. The reel station was designed to rotate by 180° while synchronized with the moving plane molds (as shown by black arrows in the bottom left and right figures), thus preventing any twist in the plastic fiber during the imprinting. Electroformed-Ni molds with a size of 15 15 2 mm3 were mounted on Aluminum loading stages. A self-assembled monolayer (SAM) of a release agent Optool HD-2101TH [11] (Daikin Industries Ltd.) was formed on the surface of the electroformedNi mold. A plastic fiber was placed on the center of the mold pattern area. The maximum contact force was 300 N, and the maximum heating temperature was 250 °C. The maximum feeding speed of this system was 40 m/min. The tension was controlled between 0 and 100 N using a several weights. The size of this system is 3.6 m in length, 1 m in width, and 1.75 m in height. 3. Imprinting results In this experiment, we selected a POF CK-10 (Mitsubishi Rayon Co., Ltd.) that comprised a 240-lm-diameter polymenthyl methac-
rylate (PMMA) core and 5-lm-thick florine resin clads as molding materials. The glass transition temperatures of the core and clads were approximately 110 °C, and below room temperature, respectively. The contact force, heating temperature, and contact time were set at 12 N, 50 °C, and 0.5 s, respectively. The width of the sliding plane mold was 0.4 mm. Considering the sliding distance of the both upper and lower molds, it became possible to imprint a total width of 0.8 mm. The 250-lm-diameter of the fiber approximately amounted to 785 lm as its circumference. Therefore, a plastic fiber can be imprinted covering its entire circumference. Fig. 3(b) is an expanded photograph of an imprinted plastic fiber. The discolored sections in the figure (white arrows) are the patterned sections. Fig. 3(c) shows an observed optical micrograph of the imprinted patterns using a five line confocal microscope Optelics S130 (Lasertec Corp.). It is thus confirmed that a fine pattern was completely transfered on the surface of POF. Each square dotted pattern of 5 lm in width and pitch of 10 lm, and circle dotted pattern of 5 lm in diameter, and pitch of 10 lm were selected as a pattern of upper and lower plane molds respectively in thermal roller-imprint experiments. Fig. 4 shows an optical micrograph of square and circle mold patterns, and imprinted patterns after the first and 100th shots. Regardless of the kind of pattern or the
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4. Summary
Fig. 5. Relationship between shot number and imprinted depth on the surface of POF.
shot frequency, 5-lm-width square and 5-lm-diameter circular dotted patterns with 10 lm pitch were successfully transferred. Fig. 5 shows measured results of imprinted depths for every ten shots on the POF continuously roller-imprinted from the first through the 100th shots, as obtained by a five line confocal microscope. The upper mold pattern was a 3.22 lm high convex square dotted pattern. On the other hand, the lower mold pattern was a 3.28 lm high convex circle dotted pattern. When the imprinted depths of 11 areas picked from the square dotted patterns on the surface of POF were compared among each other, the minimum value was 2.99 lm (at the 50th shot), and the maximum value was 3.20 lm (at the 10th shot). In the case of the circle dotted patterns, the minimum depth was 2.83 lm (at the 40th shot) and the maximum depth was 3.20 lm (at the 60th shot). Considering the heights of convex mold patterns, the molding rate (imprinted depth/mold height) amounted to approximately 88–99%. The differences between the minimum values and the maximum values of both patterns were found to be 0.21 and 0.37 lm, respectively. Originally, the irregularity on the surface of the plastic fiber that had existed before imprinting was also observed. Therefore, these differences show that a considerably uniform and continuous imprinting could be executed. The processing time for single roller-imprinting was 14.2 s. This reel-to-reel process was repeated 100 times by establishing a pitch of 16 mm. The total processing time was roughly 24 min. No significant differences were seen among a set of 11 imprinted patterns chosen between the first and 100th imprinting operations.
We developed a new-type roller nanoimprinting system to precisely transfer fine patterns from a plane mold onto the curved surface of a fibrous substrate. With this system, 5-lm-width square and 5-lm-diameter circular dotted patterns with 10 lm pitch were successfully imprinted covering the entire surface of a 250-lm-diameter POF. Imprinted conditions such as contact force, heating temperature of plane molds, and contact time were 12 N, 50 °C and 0.5 s, respectively. A POF was moved intermittently with a reel-to-reel feeder under the same condition, and a continuous imprint experiment was executed 100 times over a pitch of 16 mm. As a result, a molding rate of 88% or more was achieved. Excellent imprinted patterns were obtained and compared with the convex mold pattern of approximately 3.2 lm in height. Moreover, the imprinted depth almost corresponded well, regardless of the shape of the mold pattern, square or circle. In this roller imprint process, one single cycle time was 14.2 s and the total processing time was roughly 24 min. We succeeded in intermittent roller-imprinting on a POF of 1.6 m length. From these results, it was confirmed that our system working with a sliding roller-imprint mechanism and a reel-to-reel feeder was effective as a technique for intermittently transferring fine patterns on the cylindrical surface of the fiber. Acknowledgement This work was supported by New Energy and Industrial Technology Development Organization (NEDO). References [1] M. Worgull, Hot Embossing: Theory and Technology of Microreplication (Micro and Nano Technologies Series), William Andrew Pub., Oxford, UK, 2009. [2] C.M. Sotomayor Torres, Alternate Lithography: Unleashing the Potentials of Nanotechnology (Nanostructure Science and Technology), Plenum Pub. Corp., New York, USA, 2003. [3] P. Henzi, D.G. Rabus, K. Bade, U. Wallrabe, J. Mohr, Proc. SPIE 5454 (2004) 64. [4] S. Qi, X. Liu, S. Ford, J. Barrows, G. Thomas, K. Kelly, A. McCandless, K. Lian, J. Goettert, S.A. Soper, Lab Chip 2 (2002) 88. [5] W. Jordan, J. Eng. Mater. Technol. 127 (2005) 257. [6] H. Schift, M. Halbeisen, U. Schütz, B. Delahoche, K. Vogelsang, J. Gobrecht, Microelectron. Eng. 83 (2006) 855. [7] H. Mekaru, O. Koizumi, A. Ueno, M. Takahashi, Microelectron. Eng. 87 (2010) 922. [8] H. Mekaru, M. Takahashi, J. Vac. Sci. Technol. A28 (2010) 706. [9] H. Mekaru, C. Okuyama, A. Ueno, M. Takahashi, J. Vac. Sci. Technol. B27 (2009) 2820. [10] H. Mekaru, E. Fukushima, Y. Hiyama, M. Takahashi, J. Vac. Sci. Technol. B27 (2009) 2814. [11] T. Motoji, Tribology 249 (2008) 54 [in Japanese].