COMMUNICATION © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (1 of 9) 1600237 wileyonlinelibrary.com Self-Powered Wireless Sensor Node Enabled by an Aerosol-Deposited PZT Flexible Energy Harvester Geon-Tae Hwang, Venkateswarlu Annapureddy, Jae Hyun Han, Daniel J. Joe, Changyeon Baek, Dae Yong Park, Dong Hyun Kim, Jung Hwan Park, Chang Kyu Jeong, Kwi-Il Park, Jong-Jin Choi, Do Kyung Kim, Jungho Ryu,* and Keon Jae Lee* Dr. G.-T. Hwang, J. H. Han, Dr. D. J. Joe, C. Baek, D. Y. Park, D. H. Kim, J. H. Park, Dr. C. K. Jeong, Prof. D. K. Kim, Prof. K. J. Lee Department of Materials Science and Engineering Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu Daejeon 34141, Republic of Korea E-mail: keonlee@kaist.ac.kr Dr. V. Annapureddy, Dr. J.-J. Choi, Dr. J. Ryu Functional Ceramics Group Korea Institute of Materials Science (KIMS) 797 Changwondaero Seongsan-gu, Changwon, Gyeongnam 51508, Republic of Korea E-mail: jhryu@kims.re.kr Prof. K.-I. Park Department of Energy Engineering Gyeongnam National University of Science and Technology (GNTech) 33, Dongjin-ro, Jinju, Gyeongsangnam-do 52725, Republic of Korea DOI: 10.1002/aenm.201600237 practical WSN applications. To address this issue, our group recently developed high-performance flexible energy harvesters by using single-crystalline piezoelectric materials with a high piezoelectric d 33 constant of above 2000 pC N –1 . [19–21] Although these energy harvesters provided instantaneous milli-Watt- level peak power to operate various electronic and biomed- ical devices, the high production cost of single crystals could impede the commercialization of flexible piezoelectric energy harvesters. [22,23] The conventional sol-gel coating technique for dense piezoelectric films with a thickness of a few microme- ters is also not favorable for industrial application due to the multiple tedious repetitions of both spin coating and heat treat- ment of each 100-nm layer to minimize film cracking caused by excessive tensile stress during the annealing process. [24] Aerosol deposition (AD), proposed by Akedo and Lebedev, can provide fast, thick, and cost-effective deposition of high- quality piezoelectric films: [25] This unique AD process can instantaneously produce nanograined polycrystalline ceramic thick films that are up to several hundred micrometers in thick- ness, and which have similar piezoelectric properties to those of bulk ceramics on various substrates (e.g., silicon, sapphire, quartz, and metals) without cracking. [26,27] To facilitate high- kinetic-energy bombardment of ceramic particles, micrometer- sized piezoelectric granules are accelerated to a nearly sonic speed (up to 300 m s –1 ) to collide with the target substrates at room temperature, followed by subsequent high-temperature grain growth to improve the piezoelectric properties of the AD films. [28] While application of AD ceramic films in piezoelectric fields such as microelectromechanical systems (MEMS) gen- erators, actuators, and ultrasonic transducers was studied, AD films were not widely exploited for flexible applications due to their intrinsic brittleness and rigidity. [26] Here, we demonstrate a high-performance flexible piezo- electric energy harvester enabled by an AD-based PZT thick film on a plastic substrate to develop a self-powered wireless sensor-node system. A high-temperature (900 °C) annealed crystalline AD PZT film with a thickness of 7 μm on a rigid sapphire substrate was successfully transferred onto a flexible substrate by an inorganic-based laser lift-off (ILLO) without any structural damage or degradation of its properties. [29] Our flex- ible PZT harvesting device can generate an open-circuit voltage of 200 V and a short-circuit current of 35 μA by biomechanical bending/unbending motions. The high-output performance of the AD PZT harvester is comparable with the performance of a previous flexible single-crystal piezoelectric harvester, which is attributed to the high-temperature grain growth of AD films. [20] The harvested electricity was used to directly light up 208 blue In the coming era of internet of things (IoT), the wireless sensor network (WSN) is a key technology to analyze and con- trol all information related to public safety, human healthcare, industrial automation, and environmental monitoring. [1] To operate a WSN, bulky batteries are widely used as the power source, and inevitably these batteries should be periodically replaced due to their limited capacity. [2] However, the battery maintenance of a million sensor nodes would be practically impossible from the perspective of human effort and expenses, which is the biggest obstacle to the wide commercialization of the IoT. [3] In this regard, self-powered energy-harvesting sys- tems for the individual sensor nodes should be developed for maintenance-free, sustainable, and independent operation of extensive WSN applications. [4] Flexible piezoelectric energy harvesters, called nanogenera- tors (NGs), have been studied by many research groups as they can harvest electrical power from ambient mechanical and vibrational energy such as structure/motor vibration, gentle airflow, and even tiny biomechanical movements of mus- cles/organs. [5–10] Many piezoelectric materials, such as ZnO, BaTiO 3 , and Pb(Zr x ,Ti 1–x )O 3 (PZT), were utilized to realize flexible piezoelectric-harvesting devices for self-powered elec- tronics. [11–17] For example, a self-powered wireless sensor node was constructed using a ZnO NG as a power source for a photodetecting sensor. [18] Nevertheless, the relatively low output performance (generated voltage and current of 10 V and 1.4 μA, respectively) of the ZnO device should be improved to realize Adv. Energy Mater. 2016, 6, 1600237 www.MaterialsViews.com www.advenergymat.de