Self‐Powered Wireless Sensor Node Enabled by an Aerosol‐Deposited PZT Flexible Energy Harvester

Abstract

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][20][21] Although these energy harvesters provided instantaneous milli-Wattlevel peak power to operate various electronic and biomedical 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 micrometers is also not favorable for industrial application due to the multiple tedious repetitions of both spin coating and heat treatment 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 highquality piezoelectric films: [25] This unique AD process can instantaneously produce nanograined polycrystalline ceramic thick films that are up to several hundred micrometers in thickness, 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 highkinetic-energy bombardment of ceramic particles, micrometersized 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) generators, 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 piezoelectric 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 flexible 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]

Comprehensive biocompatibility of nontoxic and high-output flexible energy harvester using lead-free piezoceramic thin film

“…52 On the contrary, our AD-formed KNN f-PEH device is strikingly superior to these representative previous reports of flexible lead-free generators. The high performance in this work is even comparable to that of prior high-performance lead-based f-PEHs made by sol-gel PZT films, 11,65 AD-formed PZT thick film, 55 and solid-grown Pb(Mg 1/3 Nb 2/3 )O 3 -PZT (PMN-PZT) thick film 66 with IDEs under similar deformations. This remarkable output performance of our lead-free f-PEH stems from the high-quality and dense AD-formed L-KNN piezoceramic thin film.…”

“…More detailed conditions of the ADM and LLO processes are delineated in our previous reports. 11,[54][55][56] Both Raman spectra before and after the LLO clearly manifest the tetragonal/orthorhombic symmetries of L-KNN maintained during the LLO process, 58 and high crystallinity was confirmed by X-ray diffraction (XRD) patterns (Figs. S2(a) and S2(b)).…”

“…S4(a)), comparable to that of a previously reported AD-formed PZT film, considering different thickness factors. 55 As displayed in the second downward peak of Fig. 3(b), the KNN-based f-PEH generated maximum signals up to 140 V and 1.8 µA during reciprocating bending/unbending with a strain of ∼0.25%.…”

“…53,54 Recently, our group developed a new deposition method, aerosol deposition method (ADM), which is a gas-deposition process that uses as-synthesized particles directly with an accelerated gas to build colloidal aerosol flows. [54][55][56] Herein, we demonstrate a high-performance KNN-based flexible piezoelectric energy harvester (f-PEH) using the ADM with the laser lift-off (LLO) process and investigate overall biocompatibility features ( Fig. 1).…”

Modulation of surface physics and chemistry in triboelectric energy harvesting technologies

“…With the advent of the Fourth Industrial Revolution and the Internet of Things (IoTs), the demand of diverse sensors that can interactively communicate with users has increased dramatically [1][2][3][4]. Unlike typical ones, these devices should be comfortable to carry or wear or even attach to curved surfaces.…”