Elsevier

Nano Energy

Volume 35, May 2017, Pages 415-423
Nano Energy

Communication
Performance-enhanced triboelectric nanogenerator enabled by wafer-scale nanogrates of multistep pattern downscaling

https://doi.org/10.1016/j.nanoen.2017.04.012Get rights and content

Highlights

  • Performance-enhanced TENG was demonstrated via 8-in. wafer-scale sub-50 nm grating by the multistep pattern downscaling.

  • Well-aligned and size-tunable nanograting for TENG enhanced power by a factor of 200 compared to the non-patterned.

  • Investigation of output signal according to nanoscale-tuned surface were studied to improve performance and stability.

Abstract

Herein, we report a triboelectric nanogenerator (TENG) with improved performance using extremely-long sub-50 nm grating patterns with high aspect ratio (4,000,000:1) fabricated by the multistep pattern downscaling (MS-PaD) method, which is advantageous in terms of fast throughput, high resolution, cost-effectiveness, industrial compatibility, and large-area scalability in nanofabrication. The intensely-arrayed nanograting pattern is replicated to the flexible substrate on the 8-in. wafer-scale without any defects for the nanograting-assisted TENG (NGTENG). As the well-aligned nanoscale morphology in sub-50 nm grating leads to efficient triboelectric charges, the NGTENG shows an outstanding performance enhancement by a factor of 200 compared to non-patterned surface during repetitive contact electrification. To demonstrate capability of self-powered electronics, the output power from the NGTENG is directly used for charging a commercial capacitor and turning on the LEDs. In addition, theoretical study of triboelectric signals according to nanoscale-tuned metal electrodes were investigated to improve the effective output and robustness of triboelectric device.

Introduction

Energy harvesting technology to generate electricity using waste mechanical energy sources (e.g., the movement of organisms, breezes, fluidic flows) has been recently studied for constant power supplying in electronic devices [1], [2], [3], [4], [5], [6]. Among various approaches to the mechanical energy harvesting, triboelectric nanogenerators (TENGs), based on triboelectrification and electrostatic induction, have received enormous attraction for versatility, cost-effective fabrication and outstanding performance [7], [8], [9], [10]. Substantial researches on triboelectric energy harvesters have concentrated on morphological modifications of the surface into both micro- and nano-scale to achieve increased surface areas for effective charge amount and efficient electric potential [11], [12], [13], [14], [15]. However, microscale surface patterning can induce excessive friction force compared to that on the nanoscale, which results in unintended secondary effects such as heat generation and severe wear [16]. Although there have been numerous reports to form nanostructures for enhanced triboelectrification, e.g. chemical synthesis [17], [18], an ion injection method [19] and block copolymer patterning [16], [20], these bottom-up processes have several drawbacks, such as limited size control, poor scalability and low throughput yields.

Recently, our group developed a well-controlled nanograting pattern via top-down multistep spacer lithography, called multi-spacer pattern downscaling (MS-PaD), which enables repetitive pattern-size reduction up to sub-50 nm resolution with high uniformity in 8-in. wafer-scale [21]. The novel MS-PaD method for the ultra-long nanograting shows superior characteristics such as high throughput, large-area scalability, and excellent compatibility with CMOS processes, compared to other top-down approaches such as e-beam and deep ultraviolet (DUV) lithography. The MS-PaD approach offsets the disadvantages in both bottom-up and top-down nanofabrication, thus resolving the aforementioned problems related to the surface engineering.

Herein, we demonstrated a performance-enhanced TENG enabled by the MS-PaD for defect-free nanograting patterning. The highly-long nanograting pattern in 8-in. wafer-scale integration was flawlessly transferred onto a flexible substrate to fabricate nanograting-assisted TENG (NGTENG). As the low-cost and facile MS-PaD is combined with the TENG device, the productivity could be improved for large-area and reliable energy harvesting devices. Using the sub-50 nm patterns with high aspect ratio (4,000,000:1), the well-aligned and size-adjustable nanopatterns were applied to the TENG, showing the power enhancement by a factor of 200 compared to the non-patterned surface. Charging a capacitor and lighting up 60 green and 60 blue commercialized LEDs were successfully performed by the NGTENG for self-powered energy harvesting. In addition, throughout the uniformity of the nanograting pattern, we conducted systematic analyses in energy harvesting signals and surficial effects associated with triboelectric metal electrodes on the nanopatterns. According to the trade-off between conducting and flattening effects on nanoscale valleys/grooves, the influences of triboelectrification-related nanopatterned electrodes on TENG performance were investigated.

Section snippets

Fabrication of a flexible nanograting replica

Polyurethane acrylate (PUA) resin (HC11M-J5, Minuta technology Co., Ltd.) which is sensitive to ultraviolet (UV) light, was prepared to transfer the nanograting pattern of the Si wafer onto the flexible substrate. The PUA resin was applied to the nanograting mother template in a dropwise manner and coated via spinning at 2000 rpm for 30 s. After covering the flexible polyethylene terephthalate substrate (PET, 125 µm in thickness) followed by weak optical curing to solidify the percolated PUA resin

Result and discussion

Fig. 1a schematically illustrates the representative fabrication process of MS-PaD for the aligned nanograting template and the nanopattern transfer onto the flexible substrate. The initial poly-Si nanograting pattern was formed by conventional optical lithography on an 8-in. Si wafer with alternatively deposited spacers and poly-Si layers, serving as protection layers and pattern receivers, respectively. Stitching error was controlled to less than 30 nm to achieve seamlessness, perfect

Conclusion

In summary, we successfully developed the MS-PaD assisted nanopatterning with the sub-50 nm grating and aspect ratio of 4,000,000:1 using a spacer lithography technology. The sub-50 nm nanopatterns were replicated on the flexible substrate in 8-in. wafer-scale to fabricate the nanograting-based TENG (NGTENG). The flexible nanograting replica enhances the contact electrification as a counterpart triboelectric electrode, together with the fluorinated polymer. The NGTENG exhibited the performance

Acknowledgment

H.S. Wang, and C.K. Jeong contributed equally to this work. This work was supported by Korea-Sweden research cooperation program (No. 2014R1A2A1A12067558) and Global Frontier R&D Program on Center for Integrated Smart Sensors (No. CISS-2016M3A6A6929958) funded by the Ministry of Science, ICT and Future Planning (MSIP) through the National Research Foundation of Korea (NRF).

Hee Seung Wang received his B.S. and M.S. degree in Materials Science and Engineering (MSE) from Korea University in 2015 and from Korea Advanced Institute of Science and Technology (KAIST) in 2017, respectively. He is currently working toward his Ph.D. and his research topic is triboelectric energy harvesting.

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    Hee Seung Wang received his B.S. and M.S. degree in Materials Science and Engineering (MSE) from Korea University in 2015 and from Korea Advanced Institute of Science and Technology (KAIST) in 2017, respectively. He is currently working toward his Ph.D. and his research topic is triboelectric energy harvesting.

    Chang Kyu Jeong received his B.S. degree in Materials Science and Engineering (MSE) from Hanyang University in 2011 and his M.S./Ph.D. degrees from Korea Advanced Institute of Science and Technology (KAIST) in 2013/2016, respectively. After working on a postdoctoral research fellow in KAIST Institute for NanoCentury (KINC), he is currently a postdoctoral senior researcher in MSE at Pennsylvania State University. His research topics are piezoelectric ceramics, ionic polymers, nanocomposites and biomaterials for sensor and energy applications.

    Min-Ho Seo received his B.S. and M.S. degree in Electrical Engineering (EE) from Pusan National University in 2011 and Korea Advanced Institute of Science and Technology (KAIST) in 2013, respectively, where he is currently working toward his Ph.D. degree. His research topics are development of micro/nano-fabrication and its applications.

    Daniel J. Joe received a B.S. degree in Electrical Engineering at the University of Illinois at Urbana-Champaign (UIUC) in 2008 and a Ph.D. degree in Electrical and Computer Engineering at Cornell University in 2014. Currently, he is a BK21 Plus postdoctoral research associate in the Department of Materials Sciences and Engineering at Korea Advanced Institute of Science and Technology (KAIST). His current research interests involve various flexible thin-film materials and devices including energy harvesters, acoustic sensors, pressure sensors, etc.

    Jae Hyun Han received his B.S. degree in Materials Science and Engineering (MSE) from Sungkyunkwan University in 2014 and M.S. degree from KAIST in 2016. He is currently working toward his Ph.D. at KAIST under the supervision of Prof. Keon Jae Lee. His doctoral research interests include piezoelectric and triboelectric energy harvesting, flexible sensors, and laser lift-off (LLO) process.

    Prof. Jun-Bo Yoon received his Ph.D. in Electrical Engineering (EE) at Korea Advanced Institute of Science and Technology (KAIST). During his Ph.D. research, he worked on a high-Q micromachined inductor, which was cited as the best work on planar inductors at that time in the RF MEMS book of Gabriel Rebeiz. After Postdoctoral Research Fellow at University of Michigan, he returned as a Research Assistant Professor to the Department of Electrical Engineering at KAIST in 2000, where he is currently a Professor. His research interests include RF MEMS, display MEMS, and micro/nanoelectromechanical switches for solid-state memory/logic applications.

    Prof. Keon Jae Lee received his Ph.D. in Materials Science and Engineering (MSE) at University of Illinois, Urbana-Champaign (UIUC). During his Ph.D. at UIUC, he involved in the first co-invention of “Flexible Single-crystalline Inorganic Electronics”, using top-down semiconductors and soft lithographic transfer. Since 2009, he has been a professor in MSE at KAIST. His current research topics are self-powered flexible electronic systems including energy harvesting/storage devices, LEDs, large scale integration (LSI), high density memory and laser material interaction for in-vivo biomedical and flexible applications.

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    These authors contributed equally to this work.

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