Three-Dimensionally Printed Interconnects for Smart Contact Lenses

Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Three-Dimensionally Printed Interconnects for Smart Contact Lenses Hyungjoo Kim,†,‡ Jinseok Kim,§ Jaheon Kang,‡,∥ and Yong-Won Song*,†,‡,⊥ Center for Opto-electronic Materials and Devices and §Center for Bionics, Biomedical Research Institute, Korea Institute of Science and Technology, Seoul 02792, South Korea ‡ KHU-KIST Department of Converging Science and Technology and ∥Department of Ophthalmology, Kyung Hee University Hospital at Gangdong, College of Medicine, Kyung Hee University, Seoul 02447, South Korea ⊥ Division of Nano & Information Technology, KIST School, Korea University of Science and Technology, Seoul 02792, South Korea ACS Appl. Mater. Interfaces Downloaded from pubs.acs.org by DURHAM UNIV on 08/08/18. For personal use only.

†

S Supporting Information *

ABSTRACT: One of the ultimate wearable heath-monitoring gears, smart contact lens, requires miniaturized devices compounded and interconnected with each other on the lens for a successful system functioning. Because of the different device thickness, the interconnect patterns need to be three-dimensional (3D) conforming the steps given by the diversified on-lens devices. Also, the patterns should be lowtemperature processed and flexible considering the mechanical and thermal property of the lens material. We demonstrate the 3D interconnects electrosprayed on a contact lens platform with Ag−Ag nanowire (NWs) composite ink conforming the steps. Quantitative and informative analysis on the interconnects is presented. Thick polyimide film (12.5 μm) in C-shape is employed as a primary substrate to form the 3D patterns that is to be transferred onto the contact lens. The AgNWs act as frames to support the Ag ion inks printed across the steps. The resultant interconnects realized with the Ag/AgNW composite ink with 0.3 wt % AgNW have the sheet resistance (Rs) of 0.396 Ω/□ spanning the height difference of 300 μm. AgNWs also provide durability to the patterns against crack formation and propagation under significant device deformation. Unlike pure Ag pattern which shows the Rs changes of 86.1% in the bending condition, the optimally formulated composite pattern shows the suppressed Rs change of only 15.2% with a bending radius of 3 mm. KEYWORDS: smart contact lens, interconnect, three-dimensional pattern, spray printing, Ag/AgNW composite ink

1. INTRODUCTION

would be required, thereby reducing the process efficiency. Moreover, on the flexible substrate, the mechanical stress concentration factors created during the device-attaching process decrease the performance reliability of the interconnects.13,14 The other scheme involves directly forming the three-dimensional (3D) patterns (i.e., 2D patterns on the height-modulated surface of a substrate with the devices) via a printing process with a conductive ink.15 In this second scheme, the patterns need to cover both of the substrate surface and device electrodes formed on the top surface of the devices. The mechanical and electrical continuity of the patterns need to be guaranteed across the height ranges defined by the devices. Moreover, the patterns should have omnidirectional flexibility on the contact lens. Conventional processes for the conductive film preparation, such as metal

Demand for noninvasive medical devices that allow highly efficient and painless diagnoses for the patients of diabetes has dramatically increased.1 In particular, quite recently, diversified health monitoring tools based on contact lenses, which do not require blood for analysis, have been actively developed.2−7 In order for the smart contact lenses to be functional, several key independent devices, including a biosensor, thin-film battery, and sensor managing chip, need to be organized and assembled onto the lens, which features high flexibility as a substrate.8−12 Here, interconnects that electrically bridge the devices located on the lens are one of the critical factors to realize a functional smart contact lens system. A couple of schemes to form the interconnects can be considered. One of them is patterning the two-dimensional (2D) interconnects right onto the lens substrate, and then positioning the component devices that have the electrodes on the bottom face of the devices and fixing them onto the interconnect layer with a reliable and conductive adhesive. In this case, multiple manufacturing steps © XXXX American Chemical Society

Received: May 25, 2018 Accepted: July 25, 2018 Published: July 25, 2018 A

DOI: 10.1021/acsami.8b08675 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

Korea). The Rs was calculated by multiplying the measured resistance by the corrector factor of 0.9988 corresponding to the geometry of the patterns (see eqs 1−3). After the Rs of the patterns was analyzed, a bending test was performed with an x-axis actuator (NAMIL OPTICAL INSTRUMENTS Co., Korea). To get the change of Rs with respect to the radius of curvature, the radius (ranging from 15 to 3 mm) was precisely controlled with a homemade semicylindrical “guide.” The shapes of patterns were imaged using field-emission scanning electron microscopy (FE-SEM) (Inspect F, Japan). 2.5. Fabrication of Interconnection on Contact Lens. Ctyped PI film (thickness of film: 12.5 μm, PI chip: 60 μm) was prepared as the substrate. Thickness-defined PI flakes were added onto the substrate to emulate actual electronic chips that have the same device thickness. After the metal shadow mask (CS Tech, Korea) was put on the PI substrate, the electrospray process was performed. The patterned C-typed PI film was carefully transferred onto the contact lens, followed by covering with an additional lens for protection.

evaporation and lithography-based vacuum processes at elevated temperatures higher than 300 °C have suffered from critical problems in forming successful 3D patterns on the flexible substrates that tend to degrade at high temperatures.16,17 On the other hand, the printing process ensures very high-efficiency, dramatically simplified processing at room temperature and under ambient pressure.18−21 Unfortunately, recent studies with conductive inks have been limited to 2D patterns, including radio frequency identification devices, electronic tags, and integrated circuit, on flexible substrates.22,23 In this work, we demonstrated the interconnects electrosprayed on a contact lens platform with Ag−Ag nanowire (NW) composite ink conforming the steps successfully. This printing method was able to form the 3D patterns in a single fabrication process at very low temperatures. We employed a 12.5 μm thick polyimide (PI) film, which has physical stability, thermoelectric insulation, and chemical resistance, as a primary substrate to realize the 3D patterns.24 The PI substrate was designed with a C-shape that can be transferred with the preformed 3D patterns onto commercially available contact lenses. Ag-ion ink (InkTec Co., Ltd., Korea) containing AgNWs was adopted as the conductive ink for the spray considering the excellent ink uniformity. The AgNWs acted as frames to support the Ag ion inks being printed across the steps created by the devices. The maximum step height in this work was 300 μm. AgNWs also provided durability to the films against crack formation and propagation under significant device deformation.25,26 The resulting 3D conductive patterns realized by electrospraying of the Ag/AgNW composite ink with 0.3 wt % AgNW had a sheet resistance (Rs) of 0.396 Ω/□ spanning the height difference of 300 μm. Unlike pure Ag and Ag/AgNW composite with 0.1 wt % AgNW, which showed Rs changes of 86.1 and 70.2%, respectively, in the bending test, the optimally formulated composite pattern showed excellent mechanical properties as demonstrated by the Rs increase of only 15.2% with a bending radius of 3 mm.

3. RESULTS AND DISCUSSION Figure 1 illustrates the motivation for this work. Conventional vacuum-based processes suffer from substrate damage and

Figure 1. Operation principle of our printing process for an interconnect designed onto an omnidirectionally flexible substrate. Unlike the conventional vacuum process, the printing process guarantees the patterning onto the side surface of devices at low temperatures.

poor coverage of the conductive coating across the steps (lateral faces of the devices), whereas the low-temperature printing process guarantees no thermal damage on the substrate as well as good coating coverage of the steps that have high surface-to-volume ratios in concave shapes. Figure 2a shows the conceptual design of 3D patterning for connection between components with different heights on a contact lens. Electrospray was employed to ensure a fine and homogeneous printing. Ag/AgNW composite ink is patterned on the flat PI substrate with embedded devices, and then the patterned PI film is transferred onto the lens while adapting to the omnidirectional bending stress given by the lens. Prior to the transfer of the patterns onto the contact lens, a quantitative analysis was performed to determine if the pattern formed by the spray could accommodate the chip thickness of 300 μm. To simplify the experiment, thickness-defined PI flakes were used to replace actual devices (see Figure S1a, Supporting Information). The Rs was measured by a four-point probe method and can be calculated as follows.27,28 ÄÅ ÉÑÄÅ ÉÑ ÅÅÅ π ÑÑÑÅÅÅ V ÑÑÑ R S = FF 1 2Å ÅÅÇ ln 2 ÑÑÑÖÅÅÅÇ I ÑÑÑÖ (1)

2. EXPERIMENTAL SECTION 2.1. Materials. Ag-ion ink in isopropanol (IPA) (10 wt %, InkTec, Korea) and AgNW ink with the NWs (length: 10−20 μm) dispersed in IPA (1 wt %, Ditto Technology, Korea) were mixed to produce Ag/AgNW composite according to the desired AgNW concentrations of 0.1 and 0.3 wt %. PI film was supplied by SKC Kolon PI Inc., and PI tapes were purchased from Finetec. Contact lenses were produced from the optically clear silicone elastomer MED-6015 (NuSil, USA). 2.2. Sample Preparation. PI film (3 cm × 2 cm × 75 μm) was prepared as a substrate. To make a 3D structure with the steps on the substrate, the virtual chips were fabricated with a thickness-defined PI tape instead of the actual chips. Poly(dimethylsiloxane) (PDMS) was used as a mask for the electrospray. 2.3. Patterning of Ag/AgNW Composite. Electrospray printing was selected for overcoming the height difference between the chip and the substrate. Ag/AgNW composite ink in the syringe was sprayed onto the samples covered with the PDMS mask through the metal nozzle. For the electrospray, 9 kV was applied across the droplets of the composite inks. During the spray, the samples placed on the hot plate were heated up to 120 °C with 30 min duration after the spray. Because the concentrations of the Ag/AgNW composite inks were all different, the spray volumes of each ink required to make a pattern of 2 μm thickness were different. The relationship between the pattern thickness and ink dose is shown in the Supporting Information. 2.4. Pattern Characterization. Rs of samples was measured by the four-point probe method using a probe station (MSTECH,

iwy F1jjj zzz = ks{ ln

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ÄÅ ÅÅsinh ÅÅ ÅÇ

{

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ln 2 ÉÑ ÄÅ ÑÑ/ÅÅsinh ÑÑ ÅÅ ÑÖ ÅÇ

()

ÉÑ

( 2ws )ÑÑÑÑÑÖ}

(2)


Research Article


Figure 2. (a) Conceptual illustration for the printing process to form the interconnects on a contact lens with 3D structure. After forming the printed device on a flexible PI substrate, the process is finalized with transferring the printed device onto a contact lens. The inset photo shows the experimental setup of the electrospray. (b) Rs of the pure Ag pattern with 2 μm thickness with respect to different step heights on the different polymer substrates. (c) Rs of the pure Ag patterns as a function of the step height. Multiple curves with different pattern thickness are presented. (d) SEM image of the pure Ag pattern with 2 μm thickness. Because of the repeated spray process, the layered structure was formed. (e) Rs of 2 μm thick patterns prepared with different material compositions was plotted with respect to the step height.

ÅÄÅ π ÑÉÑ ÑÑ = C ijj a , d yzz F2ÅÅÅÅ Ñ j z ÅÇ ln 2 ÑÑÖ kd s {

insulation than both PDMS and Parylene. Optical images of Ag patterns deposited on three different polymer substrates are shown in Figure S1b−d. Note that because of the difference in the thermal expansion coefficient between the PDMS substrate and the Ag pattern, cracks were formed in the Ag pattern during the cooling process immediately after spraying.29,30 On the other hand, PI and Parylene substrates allowed reliable pattern formation.31,32 Figure 2c presents the measured values of Rs corresponding to the thicknesses of the pure Ag pattern formed on the PI substrate, where Rs was found to be inversely proportional to the pattern thickness. Also, thicker patterns can have a higher chance to conform to the steps presented by the devices on the contact lens. On the contrary, if the thickness of the pattern decreases, the strain of the pattern caused by the

(3)

where, F1 and F2 are correction factors for the thickness and size of the fabricated sample, respectively. V, I, w, a, d, and s are voltage, current, pattern thickness, pattern length, pattern width, and spacing between probes, respectively. A correction ÅÄÅ π ÑÉÑ Å ÑÑ was applied to factor of 0.9988 calculated by FF 1 2Å ÅÇ ln 2 ÑÖ measurements on our fabricated samples with w, s, d, and a of 2 μm, 5, 5, and 15 mm, respectively. Figure 2b shows the Rs values when a Ag pattern with 1 μm thickness is formed on three different flexible polymer substrates. PI was selected as the substrate because it showed better Rs characteristics than PDMS and had better dimensional stability and thermoelectric C


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Figure 3. SEM images of (a−c) Ag/AgNW composite patterns with different AgNW concentrations and (d−f) steps covered by the composite inks for different step heights and ink compositions. The insets of (d,e) show the enlarged views of the steps.

% MWCNT ink across the steps with heights of 240 and 300 μm. By observing the optical images shown in Figure S3b−d, we found that the concentration limit of MWCNT is 1 wt % because the composite pattern started to have aggregated MWCNT clusters reducing the conductivity of the patterns.32,35 However, in the case of AgNW, it could be found that the maximum step height remained proportional to the concentration of AgNW without the clustering problem. Moreover, Rs was inversely proportional to the concentration. Finally, the Ag/AgNW composite pattern printed with 0.3 wt % AgNW ink was successfully formed across the step with a height of 300 μm, and it had an Rs of 0.396 Ω/□. We analyzed the SEM images to determine how the patterns could conform to the step height and what the role of the AgNWs as the second phase is (see Figure 3). First, Figure 3a−c shows the microscopic structures of the patterns with different AgNW content. We found that the conductivity of the formed patterns relies on the concentration of AgNW. The resistance of the pure Ag pattern has a relatively high value because of electron scattering at the many contact points of the Ag granules, whereas AgNW, which is an anisotropic material with low defect density that can act as an electron highway, ensures the relatively high conductivity of the Ag/AgNW composite pattern.34,36 Moreover, AgNWs can provide the mechanical properties to the Ag/AgNW composite pattern necessary to conform to the steps. Figure 3d−f shows the SEM images which illustrate the role of the AgNWs at the steps. Figure 3d shows that the step was overcome by multiple Ag rings with diameters of several tens of micrometers formed by the “coffeering effect” of the ink. The inset of Figure 3d presents the magnified image of the patterns formed on a step. On the other hand, Figure 3e shows that the pure Ag pattern across the 240 μm step was not successfully formed. Normally, Ag ions, which are stable in solution with an organic solvent, are heated up during the spraying process for their reduction to the Ag atoms required for the continuous Ag patterns. In the final stage, sintering is performed to prepare the densified atomic structures from the stacked Ag atoms.37 Because of the low viscosity of the pure Ag ink, the originally printed pattern was not maintained during the reduction and the sintering processes. The inset of Figure 3e shows the magnified image of the unsuccessful connection point. Figure 3f shows the shapes of the patterns formed with 0.3 wt % Ag/AgNW

curvature of the lens gets smaller. This result can be confirmed by the following, eq 4:33 id ε (strain) = jjjj P k ij jjY > Y , τ = s jj P k

+ ds yz 1 + 2τ + ρτ 2 zz 2 z{ (1 + τ )(1 + ρτ ) dP Y yz , ρ = P zzz ds Ys z{

(4)

where dP and dS are the thickness of the pattern and the substrate, respectively, and YP and YS are the corresponding Young’s moduli. Therefore, it was necessary to determine the optimal thickness of the pattern that can conform to the target height difference while minimizing the bending stress. Mainly considering the lower saturation of Rs with respect to the thickness, we found that a thickness of 2 μm is very reasonable. Figure 2d shows the SEM image of the cross section of a pure Ag pattern with the designated thickness of 2 μm fabricated under the optimized spray conditions. Note that the spray volume of diversified inks with all different concentrations of the Ag/AgNW was controlled to achieve the 2 μm thickness (see Figure S2 in the Supporting Information). The layered structure indicates that the pattern was formed from the reciprocating motion of the spray tray during the printing process. Unfortunately, the 2 μm thick pure Ag pattern was not able to conform to a total step higher than 180 μm, therefore requiring that a second phase be present that can provide the Ag ink the mechanical strength and durability. Note that the target step height given by the devices is 300 μm. Multiwalled carbon nanotubes (MWCNTs) and AgNWs that ensure a significant conductivity along with material affinity with Ag ink were selected as the second phase for the composite pattern. In Figure 2e, we examined the trend of the Rs of the patterns with respect to step height formed by the PI flakes, so as to ensure the validity of the optimized thickness of the composite patterns. It has been proven in other reports that both MWCNTs and AgNWs work as bridges to link the defects or cracks in the Ag patterns on the polymer substrate.30,32,34 First, the formulated Ag/MWCNT composite ink with 0.15 wt % MWCNT had only a small effect toward overcoming the steps, as can be seen in the figure. Figure S3a in the Supporting Information compares the number of samples that overcame the steps to the total number of fabricated samples, when the Ag/MWCNT composite patterns were made with the 0.15 wt D


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Figure 4. Dynamic characteristics of the patterns: (a) Rs change ratio as a function of bending radius with various Ag/AgNW concentrations. (b) Comparison of Rs change ratio with different AgNW concentrations under bending with the 3 mm bending radius. The inset images in (a,b) show the homemade bending testers. SEM images of (c) pure Ag and (d,e) Ag/AgNW composite patterns formed with 0.1 wt % AgNW ink and 0.3 wt % AgNW ink, respectively, after the repeated bending test (3 mm bending radius, 1000 cycles).

Figure 5. (a) Schematics of the fabrication process for Ag/AgNW composite interconnects on C-shaped PI film (substrate) using the electrospray process. (b) Patterns on the PI film transferred onto a contact lens. (c) Contact lens with the patterns under a tough bending condition. (d) Comparison of resistance change ratio of the interconnects before the transfer, after the transfer without bending, and after the transfer with bending of the transferred patterns on the lens.

composite ink overcoming the target step height of 300 μm. The inset of Figure 3f reveals that the AgNWs mechanically supported the Ag ink to conform to the high step. Importantly, AgNWs increased the overall viscosity of the sprayed composite ink providing a sufficient temporal duration for the reduction and the sintering of the composite ink on the step immediately after spraying.38 As the next step, we checked the dynamic properties on flexing of the Ag and Ag/AgNW patterns, as shown in Figure 4. Figure 4a shows the change of normalized Rs with respect to the bending radius for different AgNW concentrations. The setup for measurement is shown in the inset of Figure 4a, and a detailed photo of the setup is also shown in Figure S4. The printed pattern has a tensile stress in the x-axis direction as the bending proceeds. The change ratio of Rs is defined to be (Rs − Rso)/Rso, where Rso is the initial sheet resistance before deformation and Rs is the sheet resistance with substrate

bending. When the bending radius was varied from 14 to 3 mm, Rs was inversely proportional to the radius in all samples. It was found that Rs increased sharply from a bending radius of 3 mm, whereas Rs was a bit stable before reaching the critical bending radius of 3 mm. The only composite pattern printed with 0.3 wt % Ag/AgNW ink showed a relatively tolerable change of a 15.2%. On the other hand, the composite pattern formed from 0.1 wt % Ag/AgNW ink displayed 70.2% of the initial Rs at 3 mm. Figure 4b shows the Rs change ratio with respect to the bending cycle up to 1000 cycles at a radius of 3 mm. The resistance of each point was measured in the bent position, and a PDMS stopper was used for the effective measurement, as shown in the inset. All of the samples showed almost no change in Rs during 100 cycles, but it was commonly observed that Rs increased significantly after 100 cycles. As a result, the pattern with 0.3 wt % Ag/AgNW composite ink showed the lowest value, and the stability of the mechanical E


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ACS Applied Materials & Interfaces Notes

properties of the patterns under bending got better as the AgNWs were added. The microstructures of the patterns were observed by the SEM immediately after 1000 bending cycles to confirm the role of AgNW under repetitive bending conditions (see Figure 4c−e). As shown in Figure 4c, cracks formed in the pure Ag pattern by bending led to increased resistance. However, even with crack formation, AgNWs made bridges over the cracks as if they were paved electron highways maintaining the conductivity of the pattern (see Figure 4d,e).34 Figure 5a schematically shows the fabrication process of the interconnects realized on a contact lens. The interconnects were fabricated by electrospray through a metal mask in which the shapes of the sensor electrodes and the microchip electrodes were etched onto a C-shaped PI substrate with embedded height-defined PI flakes that substituted for chips. Finally, the C-shaped film with the formed interconnect patterns was carefully transferred onto the contact lens with omnidirectional flexibility (see Figure 5b). We compared the resistance change ratio of the multiple patterns on the contact lens with bending, as shown in Figure 5c. As a result, considering that the radius of curvature of the lens is 7−8 mm, it was confirmed that the resistance change was larger than the result of the bending test. Considering the additional defects in the patterns on a substrate with omnidirectional flexibility that has steps and the additional strain, the patterns on the lens may present a higher resistance than shown in Figure 4 with a bare flat PI substrate.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the Bio & Medical Technology Development Program (grant no. NRF-2015M3A9E2030105) of the National Research Foundation (NRF) funded by the Ministry of Science and ICT, South Korea.

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4. CONCLUSIONS In conclusion, we developed and quantitatively analyzed the interconnects which guarantee omnidirectional flexibility on the contact lens while overcoming the step height defined by devices on the lens based on the electrospray printing. As a result, the patterns displayed 3D shapes printed along the 3D contour of the device-embedded contact lens. It was proved that the incorporation of the AgNWs into the pure Ag ion ink as second phases increased the threshold step height that could be conformed to and improved the mechanical resilience against repetitive bending. Finally, when the Ag/AgNW composite ink with 0.3 wt % AgNW content was sprayed, the conductive patterns overcoming the target step height of 300 μm were formed and transferred onto the contact lens. We expect that such a printing process, along with the customized ink formulation, will contribute to the development of future printed functional electronics, especially on substrates with omnidirectional flexibility. It will also fuel the development of biomedical devices and smart wearable gear with very highprocess efficiencies.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b08675.

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REFERENCES

(1) Lipani, L.; Dupont, B. G. R.; Doungmene, F.; Marken, F.; Tyrrell, R. M.; Guy, R. H.; Ilie, A. Non-invasive, Transdermal, Pathselective and Specific Glucose Monitoring via a Graphene-based Platform. Nat. Nanotechnol. 2018, 13, 504−511. (2) Badugu, R.; Lakowicz, J. R.; Geddes, C. D. A Glucose Sensing Contact Lens: A Non-invasive Technique for Continuous Physiological Glucose Monitoring. J. Fluoresc. 2013, 13, 371−374. (3) Leonardi, M.; Leuenberger, P.; Bertrand, D.; Bertsch, A.; Renaud, P. A Soft Contact Lens with a MEMS Strain Gage Embedded for Intraocular Pressure Monitoring. 12th International Conference on Solid-State Sensors, Actuators and Microsystems, 2003; p 3B2.5. (4) Chu, M. X.; Shirai, T.; Takahashi, D.; Arakawa, T.; Kudo, H.; Sano, K.; Sawada, S.-I.; Yano, K.; Iwasaki, Y.; Akiyoshi, K.; Mochizuki, M.; Mitsubayashi, K. Biomedical Soft Contact-lens Sensor for In Situ Ocular Biomonitoring of Tear Contents. Biomed. Microdevices 2011, 13, 603−611. (5) Badugu, R.; Lakowicz, J. R.; Geddes, C. D. Noninvasive Continuous Monitoring of Physiological Glucose Using a Monosaccharide-sensing Contact Lens. Anal. Chem. 2004, 76, 610−618. (6) Choi, K.; Park, H. G. Smart Reinvention of the Contact Lens with Graphene. ACS Nano 2017, 11, 5223−5226. (7) Chu, M. X.; Miyajima, K.; Takahashi, D.; Arakawa, T.; Sano, K.; Sawada, S.-I.; Kudo, H.; Iwasaki, Y.; Akiyoshi, K.; Mochizuki, M.; Mitsubayashi, K. Soft Contact Lens Biosensor for In Situ Monitoring of Tear Glucose as Non-invasive Blood Sugar Assessment. Talanta 2011, 83, 960−965. (8) Tao, H.; Shum, A. J.; Cowan, M.; Lähdesmäki, I.; Parviz, B. A. A Contact Lens with Embedded Sensor for Monitoring Tear Glucose Level. Biosens. Bioelectron. 2011, 26, 3290−3296. (9) Liao, Y.-T.; Yao, H.; Lingley, A.; Parviz, B.; Otis, B. P. A 3-μW CMOS Glucose Sensor for Wireless Contact-Lens Tear Glucose Monitoring. IEEE J. Solid-State Circuits 2012, 47, 335−344. (10) Chen, G.-Z.; Chan, I.-S.; Leung, L. K. K.; Lam, D. C. C. Soft Wearable Contact Lens Sensor for Continuous Intraocular Pressure Monitoring. Med. Eng. Phys. 2014, 36, 1134−1139. (11) Lee, S.-W.; Lee, K.-Y.; Song, Y.-W.; Choi, W. K.; Chang, J.; Yi, H. Direct Electron Transfer of Enzymes in a Biologically Assembled Conductive Nanomesh Enzyme Platform. Adv. Mater. 2016, 28, 1577−1584. (12) Rim, Y. S.; Bae, S.-H.; Chen, H.; Yang, J. L.; Kim, J.; Andrews, A. M.; Weiss, P. S.; Yang, Y.; Tseng, H.-R. Printable Ultrathin Metal Oxide Semiconductor-based Conformal Biosensors. ACS Nano 2015, 9, 12174−12181. (13) Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Kim, K. S.; Ahn, J.-H.; Kim, P.; Choi, J.-Y.; Hong, B. H. Large-scale Pattern Growth of Graphene Films for Stretchable Transparent Electrodes. Nature 2009, 457, 706−710. (14) Heremans, P.; Tripathi, A. K.; de Jamblinne de Meux, A.; Smits, E. C. P.; Hou, B.; Pourtois, G.; Gelinck, G. H. Mechanical and Electronic Properties of Thin-Film Transistors on Plastic, and Their Integration in Flexible Electronic Applications. Adv. Mater. 2016, 28, 4266−4282. (15) Frandos, N. M.; Yetisen, A. K.; Monteiro, M. J.; Lowe, C. R.; Yun, S. H. Contact Lens Sensors in Ocular Diagnostics. Adv. Healthcare Mater. 2015, 4, 792−810. (16) Kim, J. G.; Takama, N.; Kim, B. J.; Fujita, H. Opticalsoftlithographic Technology for Patterning on Curved Surfaces. J. Micromech. Microeng. 2009, 19, 055017.

Fabrication process and pattern analysis in both static and dynamic conditions (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +82-2-958-5373. ORCID

Yong-Won Song: 0000-0003-2263-1578 F


Research Article

ACS Applied Materials & Interfaces (17) Hsu, P. I.; Bhattacharya, R.; Gleskova, H.; Huang, M.; Xi, Z.; Suo, Z.; Wagner, S.; Sturm, J. C. Thin-film Transistor Circuits on Large-area Spherical Surfaces. Appl. Phys. Lett. 2002, 81, 1723−1725. (18) Merliampi, S.; Laine-Ma, T.; Ruuskanen, P. The Characterization of Electrically Silver Ink Patterns on Flexible Substrates. Microelectron. Reliab. 2009, 49, 782−790. (19) Wu, C.-J.; Sheng, Y.-J.; Tsao, H.-K. Copper Conductive Lines on Flexible Substrates Fabricated at Room Temperature. J. Mater. Chem. C 2016, 4, 3274−3280. (20) Secor, E. B.; Prabhumirashi, P. L.; Puntambekar, K.; Geier, M. L.; Hersam, M. C. Inkjet Printing of High Conductivity, Flexible Graphene Patterns. J. Phys. Chem. Lett. 2013, 4, 1347−1351. (21) Han, J.; Choi, S.; Lim, J.; Lee, B. S.; Kang, S. Fabrication of Transparent Conductive Tracks and Patterns on Flexible Substrate Using a Continuous UV Roll Imprint Lithography. J. Phys. D: Appl. Phys. 2009, 42, 115503. (22) Chen, J.-J.; Zhang, J.; Wang, Y.; Guo, Y.-I.; Feng, Z.-S. A Particle-free Silver Precursor Ink Useful for Inkjet Printing to Fabricate Highly Conductive Patterns. J. Mater. Chem. C 2016, 4, 10494−10499. (23) Khan, S.; Lorenzelli, L.; Dahiya, R. S. Technologies for Printing Sensors and Electronics over Large Flexible Substrates: a review. IEEE Sens. J. 2015, 15, 3164−3185. (24) Han, J.-S.; Tan, Z.-Y.; Sato, K.; Shikida, M. Three-dimensional Interconnect Technology on a Flexible Polyimide Film. J. Micromech. Microeng. 2004, 14, 38−48. (25) Langley, D.; Giusti, G.; Mayousse, C.; Celle, C.; Bellet, D.; Simonato, J.-P. Flexible Transparent Conductive Materials Based on Silver Nanowire Networks: a Review. Nanotechnology 2013, 24, 452001. (26) Ajmal, C. M.; Menamparambath, M. M.; Choi, H. R.; Baik, S. Extraordinarily high conductivity of flexible adhesive films by hybrids of silver nanoparticle-nanowires. Nanotechnology 2016, 27, 225603. (27) Miccoli, I.; Edler, F.; Pfnür, H.; Tegenkamp, C. The 100th anniversary of the four-point probe technique: the role of probe geometries in isotropic and anisotropic systems. J. Phys.: Condens. Matter 2015, 27, 223201. (28) Smits, F. M. Measurement of Sheet Resistivities with the Fourpoint probe. Bell Syst. Tech. J. 1958, 37, 711−718. (29) Meng, Y.; Li, Z. B.; Chen, X.; Chen, J. P. Reducing Wrinkles and Cracks of Metal Films on PDMS Substrate by Hexane Extraction and Oxygen Plasma Etching. Microelectron. Eng. 2014, 130, 8−12. (30) Hoang, P. T.; Salazar, N.; Porkka, T. N.; Joshi, K.; Liu, T.; Dickens, T. J.; Yu, Z. Engineering Crack Formation in Carbon Nanotube-silver Nanoparticle Composite Films for Sensitive and Durable Piezoresistive Sensors. Nanoscale Res. Lett. 2016, 11, 422. (31) Layani, M.; Gruchko, M.; Milo, O.; Balberg, I.; Azulay, D.; Magdassi, S. Transparent Conductive Coatings by Printing Coffee Ring Arrays Obtained at Room Temperature. ACS Nano 2009, 3, 3537−3542. (32) Zhao, D.; Liu, T.; Park, J. G.; Zhang, M.; Chen, J.-M.; Wang, B. Conductivity Enhancement of Aerosol-jet Printed Electronics by Using Silver Nanoparticles Ink with Carbon Nanotubes. Microelectron. Eng. 2012, 96, 71−75. (33) Suo, Z.; Ma, E. Y.; Gleskova, H.; Wagner, S. Mechanics of Rollable and Foldable Film-on-foil Electronics. Appl. Phys. Lett. 1999, 74, 1177−1179. (34) Izumi, K.; Yoshida, Y.; Tokito, S. Soft blanket gravure printing technology for finely patterned conductive layers on three-dimensional or curved surfaces. Jpn. J. Appl. Phys. 2017, 56, 05EA03. (35) Dooher, T.; Dixon, D.; McIlhagger, A. Multiwalled Carbon Nanotube/Polysulfone Composites. J. Thermoplast. Compos. Mater. 2011, 24, 499−515. (36) Ok, K.-H.; Lee, C.-J.; Kwak, M.-G.; Choi, D.-K.; Kim, K.-S.; Jung, S.-B.; Kim, J.-W. Effect of Ag Nanowire Addition into Nanoparticle Paste on the Conductivity of Ag Patterns Printed by Gravure Offset Method. J. Nanosci. Nanotechnol. 2014, 14, 8808− 8812.

(37) Triambulo, R. E.; Cheong, H.-G.; Park, J.-W. All-solutionprocessed Foldable Transparent Electrodes of Ag Nanowire Mesh and Metal Matrix Films for Flexible Electronics. Org. Electron. 2014, 15, 2685−2695. (38) Wu, J.-T.; Lien-Chung Hsu, S.; Tsai, M.-H.; Liu, Y.-F.; Hwang, W.-S. Direct Ink-jet Printing of Silver Nitrate-Silver Nanowire Hybrid Inks to Fabricate Silver Conductive Lines. J. Mater. Chem. 2012, 22, 15599−15605.

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