High-Output Lead-Free Flexible Piezoelectric Generator Using Single

Subscriber access provided by University of Florida | Smathers Libraries

Functional Inorganic Materials and Devices

High-output lead-free flexible piezoelectric generator using single-crystalline GaN thin film Jie Chen, Seung Kyu Oh, Haiyang Zou, Shahab Shervin, Weijie Wang, Sara Pouladi, Yunlong Zi, Zhong Lin Wang, and Jae-Hyun Ryou ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b01281 • Publication Date (Web): 29 Mar 2018 Downloaded from http://pubs.acs.org on March 29, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

High-output lead-free flexible piezoelectric generator using single-crystalline GaN thin film Jie Chen†‡, Seung Kyu Oh†§, Haiyang Zou, Shahab Shervin†, Weijie Wang†, Sara Pouladi†‡, Yunlong Zi⊥, Zhong Lin Wang and Jae-Hyun Ryou*†‡§ †

Department of Mechanical Engineering, University of Houston, Houston, TX 77204-4006, USA.

‡

Materials Science and Engineering Program, University of Houston, Houston, TX 77204, USA. §

Texas Center for Superconductivity at UH (TcSUH) and Advanced Manufacturing Institute (AMI), University of Houston, Houston, TX 77204, USA.

School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30331-0245, USA.

ABSTRACT

Piezoelectric generators (PEGs) are a promising power source for future self-powered electronics by converting ubiquitous ambient mechanical energy into electricity. However, most of the high-output PEGs are made from lead zirconate titanate (PZT), in which the hazardous lead could be a potential risk to both the human and environment, limiting their real applications. IIInitride (III-N) can be a potential candidate to make stable, safe, and efficient PEGs, due to its

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 27

high chemical stability and piezoelectricity. Also, PEGs are preferred to be flexible rather than rigid, in order to better harvest the low-magnitude mechanical energy. Herein, a high-output, lead-free, and flexible PEG (F-PEG) is made from GaN thin film by transferring a singlecrystalline epitaxial layer from silicon substrate to a flexible substrate. The output voltage, current density, and power density can reach 28 V, 1 µA·cm-2, and 6 µW·cm-2, respectively, by bending the F-PEG. The generated electric power by human finger bending is high enough to light commercial visible LEDs and charge commercial capacitors. The output performance is maintained higher than 95% of its original value after 10,000-cycle test. This highly stable, high-output, and lead-free GaN thin-film F-PEG has the great potential for future self-powered electronic devices and systems.

KEYWORDS: flexible, III-nitride, thin film, piezoelectric, generator

INTRODUCTION Increasing popularity of wearable and implantable electronics for health and environment motoring poses great challenges to the power supply, which are required to be flexible, small, and endurable.1-4

Although high-capacity flexible batteries and supercapacitors have been

developed and could be one of the choices,5-6 the trade-off between dimension and capacity does not allow them to meet the requirement of both small size and long run time. As a result, they require frequent replacement or recharging, which are quite inconvenient and costly. Energy harvesters, which convert ambient energy into electricity can be an ideal power supply choice.7-9 Among the energy harvesting devices, piezoelectric generators (PEGs) are preferred in many applications, since the mechanical energy, which is the source of the PEGs, is ubiquitous around


2

Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


us, from daily activities such as walking, to basic biological processes such as breathing.10-14 Other energy harvesters are limited either by service conditions or availability of the energy sources. For instance, solar cells only work when exposed to light and thermoelectric generators may not generate enough power since temperature gradient cannot be very high around the human body.15 Although there are many kinds of piezoelectric materials showing promising properties for making PEGs, the choice is limited when it comes to wearable or implantable applications, since the output performance, flexibility, stability, and biocompatibility should be taken into account simultaneously.

Although polymers such as polyvinylidene difluoride (PVDF) show good

flexibility, complicated electrospinning or mechanical stretching and electric poling are needed. Moreover, their piezoelectric performance is still not comparable to their inorganic competitors.16-17 Lead zirconate titanate (PZT) has high piezoelectric coefficients and can be made high-output flexible PEGs (F-PEGs);18-21 however, its applications are still limited since the material contains lead which causes a potential hazard to both human health and the environment.22 Lead-free F-PEGs using materials such as perovskite zinc stannate (ZnSnO3) and barium titanate (BaTiO3) have been reported; however, their output power still needs to be improved.23-26 Zinc oxide (ZnO)-based PEGs are biocompatible; however, the stability is not satisfied especially when the working environment is rich in water.27 Gallium nitride (GaN), as a material in group III-nitride (III-N) having wurtzite crystal structure is well studied and can be epitaxially grown to a single crystalline material with precise control. Furthermore, epitaxial GaN does not require additional electric poling process that is required for PZT and PVDF. GaN also shows high piezoelectricity, stability, and biocompatibility,28-29 which have been proved by the III-N nanowire-based PEGs.30-32 However, nanowire-based PEGs are very complicated to


3


Page 4 of 27

fabricate and their overall output is still low, since the orientation of nanowires is difficult to control and significant portion of the device is filled with non-piezoelectric materials.33 Recently, a research on GaN thin-film rigid PEGs shows that the output can be improved by replacing nanowires with thin film.34 Unfortunately, the rigid device requires very high pressure, on the scale of mega pascal, to work, which is not suitable for harvesting the biomechanical energy with a small force magnitude. By making thin-film PEGs flexible, sensitivity to small mechanical energy can be significantly improved.35 In the present study, we report an F-PEG fabricated from single-crystalline GaN thin film by a simple thin-film-transfer method, in which large-area GaN is transferred from a brittle silicon (Si) substrate to a foreign flexible substrate. The output voltage, current density, and power density of the GaN F-PEG were studied systematically by buckling the GaN F-PEG periodically. Potential applications of using the GaN F-PEG to charge energy storage devices and power electronics were also demonstrated. EXPERIMENTAL SECTION GaN thin-film growth.

A single-crystalline GaN thin film was grown on a Si (111)

substrate by metalorganic chemical vapor deposition (MOCVD) using precursors of trimethylgallium (Ga(CH3)3), trimethylaluminum (Al(CH3)3), and ammonia (NH3) with hydrogen (H2) carrier gas.36 Native SiO2 on the surface of the Si substrate was removed by wet etching before the epitaxial growth. An AlN buffer layer (100 nm) was first grown without the formation of Al-Si eutectic or Si3N4 at the interface of Si and AlN. Compositionally graded AlxGa1-xN layers (600 nm) were deposited to manage strains in the substrate and layers. An ~1.8-µm-thick GaN layer was grown at 1050 °C. The epitaxial structure was crack-free after the


4

Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cool-down. The thin film was unintentionally doped with suppressed auto doping,37 resulting in a free electron concentration of the layer less than 1×1015 cm-3. GaN thin-film F-PEG fabrication. The fabrication of F-PEG from GaN grown on Si substrate (GaN/Si) is schematically illustrated in Supporting Information Figure S1a. A multilayered device structure with GaN thin film sandwiched between two electrodes was adopted, since the thin film was grown along c-axis of the hexagonal structure, which will be explained in the Results and Discussion section. First, a stack of Ni/Au (5 nm/100 nm) metals, which is to be a part of bottom electrode of F-PEG, was deposited on GaN by electron beam (e-beam) evaporation.

A Cu mechanical supporting layer (~20 µm) was deposited subsequently by

electroplating using CuSO4 electrolyte solution (0.1 M) at a current density of 0.1 A·cm-2 to prevent the GaN thin film from cracking during Si removal process, then covered by a sputtered Au layer (100 nm) to protect the Cu during Si etching. GaN/Si with the bottom electrode was flipped and attached to Kapton tape (50 µm, Uline) or PET (Polyethylene terephthalate) (180 µm, CS Hyde) substrate by UV curable polymer (NOA 73, Norland) with the Si substrate facing up. Next, Si was removed by wet chemical etching using a solution consisting of hydrofluoric acid (HF, 49%), acetic acid (CH3COOH), and nitric acid (HNO3, 70%) with volume fractions of 0.80, 0.15, and 0.05, respectively. After the Si substrate removal, Ni/Au (5 nm/100 nm) top electrode was deposited on N-face of the GaN layer. Wires were connected to top and bottom electrodes by silver paste (Ted Pella). Finally, device was sealed by UV curable polymer (NOA 73, Norland). Material and device characterization. Structure and crystalline quality of III-N layers were characterized by high-resolution x-ray diffraction (HR-XRD) (D8 Discover, Bruker). The morphology of the thin film surface and device cross section was investigated by optical


5


Page 6 of 27

microscope (OM) (Keyence VHX 2000) and scanning electron microscope (SEM) (XL-30FEG, FEI), respectively. Electrical measurements. The F-PEG was buckled by a programmable linear motor (LinMot) to convert mechanical energy into electricity. The voltage pulse during bending up and bending down process was measured by an oscilloscope (TDS3012B, Tektronix) with an internal impedance of 1 MΩ. Output voltages and currents of the F-PEG at different external load resistances were measured by an electrometer (Model 6514, Keithley). Current-voltage (I-V) characteristic curve was measured by a source meter (Model 2602B, Keithley). RESULTS AND DISCUSSION Figure 1 shows the structural quality of III-N thin film used for the fabrication of F-PEG. Two theta-omega (2θ-ω) scan of x-ray diffraction (XRD), shown in Figure 1a, confirms that the epitaxial layers are grown along [0001] c-axis of wurtzite structure in the out-of-plane direction on Si (111) illustrated in Figure 1d, as evidenced by the presence of the only (0002) peak and no other peaks from GaN, AlGaN, and AlN layers. The linewidth of the GaN (0002) peak of rocking curve is also very narrow, about 0.14° (494 arcsec.) in full width at half maximum (FWHM), as shown in Figure 1b, indicating negligible tilt spread in (0001) plane of c-axis textured crystal grains. Rotational phi (φ) scan of the GaN (101 2) planes shows six separate peaks located 60° apart with similar intensities (Figure 1c), indicating the crystal grains are also aligned in-plane along a-axis. The XRD analysis shows that the thin film is single-crystalline. The single-crystalline thin film has several advantages over the polycrystalline materials for piezoelectric applications. First, since the crystal is aligned perfectly in a single direction, high piezoelectric effect can be obtained without further electric poling, which can simplify the fabrication process. In contrast, electric poling at severe conditions is a necessary step for


6

Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


polycrystalline ferroelectric materials to improve their piezoelectric performance. For example, a recently reported F-PEG based on PZT ceramic thin film was electrically poled at 120 °C in a strong electric field of 100 kV·cm-1 for 3 hours.21 Second, piezoelectricity of single crystal is not easily affected by the environment temperature since the crystal alignment does not change with temperature, while the piezoelectricity of electrically poled polycrystalline materials is degraded and lost at high temperatures close to Curie temperatures, 100‒500 °C, depending on the materials.38 Last, less/no grain boundaries reduce the density of free carries in the material, thus free carrier screening effect is subsided and effective output can be improved.39-40 Low leakage currents in the range of -40 V to 40 V of the thin film confirm the good electrical properties for the PEG (Supporting Information Figure S2a). After the transfer of GaN thin film to a flexible substrate, the film maintains its integrity without the formation of crystalline imperfections such as cracks, as shown in the optical microscope image of Figure 2a. The transferred thin film can be bent by human fingers without causing any mechanical damage as shown in Figure 2b. For wurtzite crystal structure, the polarization mainly changes along c-axis which is the direction perpendicular to the thin film surface, when mechanical strain is applied.

The F-PEG device structure is rather simple

consisting of the GaN layer (and AlGaN and AlN layers) sandwiched between top and bottom electrodes, as schematically illustrated in Figure 2c and shown by the cross-sectional scanning electron microscopy (SEM) image of Figure 2d. The top surface of the F-PEG is covered by a soft polymer (NOA 73), as shown in Supporting Information Figure S1b, that can protect the wires from detaching while not affecting the strain in the III-N thin film.41


7


Output characteristics of the GaN thin-film F-PEG were theoretically analyzed.

Page 8 of 27

For the

sandwich-structured F-PEG (Figure 2c), the GaN thin film is under plane-strain condition during bending.42 In this condition, the effective piezoelectric constant, e is: e = e31 −

c13

e c33 33

(1)

where e31 and e33 are piezoelectric constants, c13 and c33 are elastic constants. The effective dielectric constant, is: 2

e k = k33 + 33 c33

(2)

where k33 is the dielectric constant. Theoretical open-circuit voltage can be calculated by: e

Voc = εtT k

(3)

where ε is the uniaxial strain, and tT is the thickness of the thin film. The induced short-circuit current density by change of polarization as a result of strain is given by: d

Jsc = eε = eε dt

(4)

where ε is the strain rate of thin film, a function of time during bending. The ideal open-circuit voltage and short-circuit current density of the F-PEG were analyzed according to Equation 3 and 4, as graphed in Supporting Information Figure S3, using e31 = -0.49 C·m-2, e33 = 0.73 C·m-2, c13 = 106 GPa, c33 = 398 GPa, and k33 = 8.41×10-11 C·V-1m-1.43 Even for relatively thin GaN (2.5 µm), the F-PEG has the potential to generate a voltage of 20 V by applying ~0.1% uniaxial strain. The short-circuit current density increases linearly with the strain rate and can reach 1 µA·cm-2 with a strain rate of 1‒2 %·s-1. The strain, i.e., the output voltage, can be controlled by the degree of bending, and the strain rate, i.e., the current density, can be controlled by the speed of bending.


8

Page 9 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


To verify that the electric signal by bending of the flexible device originates from piezoelectric effect, rather than the environment noise,44 output voltage was compared by bending up and down the F-PEG while connecting Ga-face electrode to the positive input of the electrometer and N-face electrode to the negative input.45 Figure 3 shows the output characteristics depending on the mode of the bending. The neutral plane of the F-PEG is located in the Cu layer of the bottom electrode. Also, the top surface of the thin film is N-faced, since the as-grown thin film is Gafaced and is flipped during the thin-film-transfer process. When the F-PEG is bent up (concave curvature), the GaN thin film is stretched along c-axis by compressive in-plane strain, so the polarization increases (∆P > 0), thus a positive voltage pulse is induced and electrons are collected on the Ga-face electrode (Figure 3a and c). During release from the bending-up state, polarization goes back to original state, and the accumulated electrons on Ga-face electrode generate a negative voltage pulse, and flow back to the N-face electrode. Thus, during the bending up and releasing cycle, positive-negative twin voltage pulses are shown in Figure 3e. When the F-PEG is bent down (convex curvature) as shown in Figure 3b and d, negative-positive twin voltage pulses are shown as in Figure 3f. The opposite voltage generated by different bending modes comes from the opposite change of polarization, confirming that the electric power originates from the piezoelectric effect of the GaN thin film. This comparison experiment can also be used as an effective way to verify the film growth direction and polarity for III-N or similar asymmetric compound materials.46 Figure 4 shows output characteristics of GaN thin-film F-PEG with an effective area of 1×1 cm2. Open-circuit voltage and short-circuit current were measured by periodic buckling of the flexible device (length L = 40 mm) with different compressions, s and various speeds, v. The compression and speed of the buckling process can be controlled by the travel range and


9


Page 10 of 27

acceleration/deceleration with a linear motor, which is described in detail in Supporting Information Figure S4. Since the strain in the film during the buckling is proportional to the square root of the compression, √s,47 the open circuit voltage is also proportional to √s (Equation 3). A relation between the voltage and compression is estimated by fitting the experiment data of change in voltage with s (Figure 4a), as shown in Figure 4b, Voc V) = 5.93 s mm)

(5)

The open-circuit voltage can be simply tuned by changing the compressions to meet a certain voltage requirement. A maximum open-circuit voltage of 28 V is obtained at a compression of 20 mm. Since the strain rate is proportional to the square root of acceleration, √a, the short-circuit current density is also proportional to √a (Equation 4). An estimated relation between the shortcircuit current density and acceleration is shown in Figure 4d by fitting the experiment data of Figure 4c, Jsc µA · cm2 = 0.67 a m · s2 (6) Short-circuit current density can be tuned by the compression speed. Furthermore, the shortcircuit current can also be tuned in a significantly wider range by changing the device area. It can be noticed that the voltage and current responses (Figure 4a and c) on the positive (bending) side are higher than those on the negative (releasing) side. Ideally, the peak voltage on the positive side should be the open-circuit voltage at maximum strain, and the voltage will drop to zero when strain is fully released, i.e., no voltage will appear on the negative side. However, due to non-infinite impedance of the electrometer, a certain amount of free electrons that is less than the piezoelectric charge will be accumulated on the electrodes and generate a smaller negative voltage during the release (Figure 3). The asymmetric output current is a result of


10

Page 11 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


lower leakage current during bending than during releasing, which can be obtained from the Schottky type I-V characteristics in Supporting Information Figure S2a. Also, the larger voltage decay constant during bending than during releasing (Supporting Information Figure S2b) can confirm this explanation.48 In practical applications where the external load is not infinitely high, the induced electric charge cannot be accumulated on the electrode as much as the ideal case. Thus, real output voltage is reduced with decreasing load resistance, as shown in Figure 5a, which is typical for output characteristic of the PEGs. For the GaN F-PEG developed in this study, output voltage is less than 1 V when the load resistance is less than 1 MΩ, and starts to increase rapidly with the external load resistance, and finally reaches a stable value of 17 V when external load exceeds 100 MΩ. While the output voltage increases with external load, the current decreases, because the electron flow is limited by higher resistance. Considering the power is the product of voltage and current, there should be a maximum power at a certain load resistance. Under the bending condition of a compression of 15 mm and an acceleration of 1.5 m·s-2, optimized peak and average power densities of 6 µW·cm-2 and 3.5 µW·cm-2, respectively, are obtained at a load of ~50 MΩ, as shown in Figure 5b. At the maximum power density, the voltage and current density is ~10 V and ~0.6 µA·cm-2, respectively.

An energy conversion efficiency of ~1% was

estimated using a method in reference 35. Besides the output power characteristics, durability of the device during mechanical bending is another important property in the F-PEG, since it is subjected to repeated mechanical bending cycles for the operation. To test the durability, we measured the voltage by buckling the F-PEG with a compression of 5 mm at a frequency of 2.5 Hz. After more than 10,000 cycles, the output


11


Page 12 of 27

voltage was still maintained as high as 95% of its original value, as shown in Figure 5c and d, indicating the good reliability of the GaN thin-film F-PEG. For practical applications, the GaN thin-film F-PEG was used to power visible light-emitting diodes (LEDs) and charge capacitors. By connecting the F-PEG directly with a commercial green LED, as schematically shown in Figure 6a, the LED can be lighted up by buckling of the device repeatedly with a human hand. Figure 6c shows a captured picture when the LED is turned on from the Supporting Information Video S1. For some applications, the external load may not be high enough to achieve enough voltage to power the electronics directly and the electronics may not need to work continuously, the generated electricity from F-PEG can be stored the in the energy storage devices first and used later. As shown schematically in Figure 6b, when the switch is connected to point 1, the F-PEG charges the capacitor, when the switch is connected to point 2, the electricity stored in the capacitor powers the LED. The GaN thin-film F-PEG can charge the 0.1 µF capacitor to a voltage of 7 V within 10 s (25 cycles), as shown in the charging curve in Figure 6e. The electric energy stored in the capacitor can power the commercial green LED to higher brightness, as shown in Figure 6d. The demonstrations confirm that the GaN thin-film F-PEG can generate enough electric energy to power commercial electronics, and has great potential to be a reliable power supply choice for future self-powered electronics. CONCLUSION In summary, a GaN thin-film F-PEG has been developed by transferring a large-area damagefree GaN layer from a Si substrate to a foreign flexible substrate. By buckling the device with different compressions, s and accelerations, a, voltage and currents were generated with relationships of Voc V) = 5.93 s mm) and Jsc µA · cm2 = 0.67 a m · s2 . For example,


12

Page 13 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


when the device was buckled at compressions of higher than 5 mm (i.e., lateral dimension reduction from 40 mm to shorter than 35 mm), voltages higher than 10 V were generated. The optimized power density can reach 6 µW·cm-2. The F-PEG can not only power commercial green LEDs directly, but also charge the commercial capacitor to ~7 V in less than 10 seconds. Most importantly, the GaN F-PEG shows excellent performance reliability with 95% output voltage after 10,000 cycles of severe buckling test. This lead-free, high-output, and durable GaN thin-film F-PEG can be a promising power supply choice for future wearable or implantable electronics.

ASSOCIATED CONTENT Supporting Information The following file is available free of charge. Schematic of F-PEG fabrication process, I-V curve, theoretical analysis of the output, and mechanical buckling process. (PDF) Directly power a commercial LED by bending F-PEG with human hand. (Video)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ORCID

Present Address


13


⊥Department

Page 14 of 27

of Mechanical and Automation Engineering, The Chinese University of Hong

Kong, Shatin, NT, Hong Kong, China Notes The authors declare no competing financial interest. ACKNOWLEDGMENT J.-H. Ryou acknowledges partial financial support from Texas Center for Superconductivity at the University of Houston (TcSUH). REFERENCES (1) Chen, C.; Shang, Z.; Gong, J.; Zhang, F.; Zhou, H.; Tang, B.; Xu, Y.; Zhang, C.; Yang, Y.; Mu, X. Electric Field Stiffening Effect in c-Oriented Aluminum Nitride Piezoelectric Thin Films. ACS Appl. Mater. Interfaces 2018, 10 (2), 1819-1827. (2) Pantelopoulos, A.; Bourbakis, N. G. A Survey on Wearable Sensor-Based Systems for Health Monitoring and Prognosis. IEEE Transactions on Systems, Man, and Cybernetics, Part C (Applications and Reviews) 2010, 40 (1), 1-12. (3) Wang, Z. L.; Wu, W. Nanotechnology‐Enabled Energy Harvesting for Self‐Powered Micro‐/Nanosystems. Angew. Chem. Int. Ed. 2012, 51 (47), 11700-11721. (4) Wang, J.; Li, S.; Yi, F.; Zi, Y.; Lin, J.; Wang, X.; Xu, Y.; Wang, Z. L. Sustainably powering wearable electronics solely by biomechanical energy. Nat. Commun. 2016, 7, 12744. (5) Lee, S.-Y.; Choi, K.-H.; Choi, W.-S.; Kwon, Y. H.; Jung, H.-R.; Shin, H.-C.; Kim, J. Y. Progress in flexible energy storage and conversion systems, with a focus on cable-type lithiumion batteries. Energy Environ. Sci. 2013, 6 (8), 2414-2423.


14

Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Pushparaj, V. L.; Shaijumon, M. M.; Kumar, A.; Murugesan, S.; Ci, L.; Vajtai, R.; Linhardt, R. J.; Nalamasu, O.; Ajayan, P. M. Flexible energy storage devices based on nanocomposite paper. Proc. Natl. Acad. Sci. U.S.A. 2007, 104 (34), 13574-13577. (7) Wang, Z. L. Toward self-powered sensor networks. Nano Today 2010, 5 (6), 512-514. (8) Wang, Z. L.; Zhu, G.; Yang, Y.; Wang, S.; Pan, C. Progress in nanogenerators for portable electronics. Mater. Today 2012, 15 (12), 532-543. (9) Kumar, B.; Kim, S.-W. Recent advances in power generation through piezoelectric nanogenerators. J. Mater. Chem. 2011, 21 (47), 18946-18958. (10) Wang, Z. L. Towards self ‐ powered nanosystems: from nanogenerators to nanopiezotronics. Adv. Funct. Mater. 2008, 18 (22), 3553-3567. (11) Zeng, W.; Shu, L.; Li, Q.; Chen, S.; Wang, F.; Tao, X.-M. Fiber-Based Wearable Electronics: A Review of Materials, Fabrication, Devices, and Applications. Adv. Mater. 2014, 26 (31), 5310-5336. (12) Hu, Y.; Wang, Z. L. Recent progress in piezoelectric nanogenerators as a sustainable power source in self-powered systems and active sensors. Nano Energy 2015, 14, 3-14. (13) Starner, T. Human-powered wearable computing. IBM systems Journal 1996, 35 (3.4), 618629. (14) Invernizzi, F.; Dulio, S.; Patrini, M.; Guizzetti, G.; Mustarelli, P. Energy harvesting from human motion: materials and techniques. Chem. Soc. Rev. 2016, 45 (20), 5455-5473. (15) Kim, S. J.; We, J. H.; Cho, B. J. A wearable thermoelectric generator fabricated on a glass fabric. Energy Environ. Sci. 2014, 7 (6), 1959-1965.


15


Page 16 of 27

(16) Persano, L.; Dagdeviren, C.; Su, Y.; Zhang, Y.; Girardo, S.; Pisignano, D.; Huang, Y.; Rogers, J. A. High performance piezoelectric devices based on aligned arrays of nanofibers of poly (vinylidenefluoride-co-trifluoroethylene). Nat. Commun. 2013, 4, 1633. (17) Siddiqui, S.; Kim, D.-I.; Duy, L. T.; Nguyen, M. T.; Muhammad, S.; Yoon, W.-S.; Lee, N.E. High-performance flexible lead-free nanocomposite piezoelectric nanogenerator for biomechanical energy harvesting and storage. Nano Energy 2015, 15, 177-185. (18) Hwang, G.-T.; Kim, Y.; Lee, J.-H.; Oh, S.; Jeong, C. K.; Park, D. Y.; Ryu, J.; Kwon, H.; Lee, S.-G.; Joung, B. Self-powered deep brain stimulation via a flexible PIMNT energy harvester. Energy Environ. Sci. 2015, 8 (9), 2677-2684. (19) Hwang, G.-T.; Park, H.; Lee, J.-H.; Oh, S.; Park, K.-I.; Byun, M.; Park, H.; Ahn, G.; Jeong, C. K.; No, K.; Kwon, H.; Lee, S.-G.; Joung, B.; Lee, K. J. Self-Powered Cardiac Pacemaker Enabled by Flexible Single Crystalline PMN-PT Piezoelectric Energy Harvester. Adv. Mater. 2014, 26 (28), 4880-4887. (20) Jeong, C. K.; Park, K.-I.; Son, J. H.; Hwang, G.-T.; Lee, S. H.; Park, D. Y.; Lee, H. E.; Lee, H. K.; Byun, M.; Lee, K. J. Self-powered fully-flexible light-emitting system enabled by flexible energy harvester. Energy Environ. Sci. 2014, 7 (12), 4035-4043. (21) Park, K. I.; Son, J. H.; Hwang, G. T.; Jeong, C. K.; Ryu, J.; Koo, M.; Choi, I.; Lee, S. H.; Byun, M.; Wang, Z. L. Highly‐efficient, flexible piezoelectric PZT thin film nanogenerator on plastic substrates. Adv. Mater. 2014, 26 (16), 2514-2520. (22) Ibn-Mohammed, T.; Koh, S. C. L.; Reaney, I. M.; Acquaye, A.; Wang, D.; Taylor, S.; Genovese, A. Integrated hybrid life cycle assessment and supply chain environmental profile evaluations of lead-based (lead zirconate titanate) versus lead-free (potassium sodium niobate) piezoelectric ceramics. Energy Environ. Sci. 2016, 9 (11), 3495-3520.


16

Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Gupta, M. K.; Kim, S.-W.; Kumar, B. Flexible High-Performance Lead-Free Na0.47K0.47Li0.06NbO3 Microcube-Structure-Based Piezoelectric Energy Harvester. ACS Appl. Mater. Interfaces 2016, 8 (3), 1766-1773. (24) Wu, J. M.; Xu, C.; Zhang, Y.; Yang, Y.; Zhou, Y.; Wang, Z. L. Flexible and Transparent Nanogenerators Based on a Composite of Lead‐Free ZnSnO3 Triangular‐Belts. Adv. Mater. 2012, 24 (45), 6094-6099. (25) Park, K.-I.; Xu, S.; Liu, Y.; Hwang, G.-T.; Kang, S.-J. L.; Wang, Z. L.; Lee, K. J. Piezoelectric BaTiO3 thin film nanogenerator on plastic substrates. Nano Lett. 2010, 10 (12), 4939-4943. (26) Yan, J.; Jeong, Y. G. High Performance Flexible Piezoelectric Nanogenerators based on BaTiO3 Nanofibers in Different Alignment Modes. ACS Appl. Mater. Interfaces 2016, 8 (24), 15700-15709. (27) Dagdeviren, C.; Hwang, S. W.; Su, Y.; Kim, S.; Cheng, H.; Gur, O.; Haney, R.; Omenetto, F. G.; Huang, Y.; Rogers, J. A. Transient, biocompatible electronics and energy harvesters based on ZnO. Small 2013, 9 (20), 3398-3404. (28) Ryou, J.-H.; Yoder, P. D.; Liu, J.; Lochner, Z.; Kim, H.; Choi, S.; Kim, H. J.; Dupuis, R. D. Control of quantum-confined stark effect in InGaN-based quantum wells. IEEE J. Sel. Topics Quantum Electron. 2009, 15 (4), 1080-1091. (29) Jewett, S. A.; Makowski, M. S.; Andrews, B.; Manfra, M. J.; Ivanisevic, A. Gallium nitride is biocompatible and non-toxic before and after functionalization with peptides. Acta biomaterialia 2012, 8 (2), 728-733.


17


Page 18 of 27

(30) Huang, C.-T.; Song, J.; Lee, W.-F.; Ding, Y.; Gao, Z.; Hao, Y.; Chen, L.-J.; Wang, Z. L. GaN Nanowire Arrays for High-Output Nanogenerators. J. Am. Chem. Soc. 2010, 132 (13), 4766-4771. (31) Wang, X.; Song, J.; Zhang, F.; He, C.; Hu, Z.; Wang, Z. Electricity Generation based on One‐Dimensional Group‐III Nitride Nanomaterials. Adv. Mater. 2010, 22 (19), 2155-2158. (32) Huang, C.-T.; Song, J.; Tsai, C.-M.; Lee, W.-F.; Lien, D.-H.; Gao, Z.; Hao, Y.; Chen, L.-J.; Wang, Z. L. Single-InN-Nanowire Nanogenerator with Upto 1 V Output Voltage. Adv. Mater. 2010, 22 (36), 4008-4013. (33) Lin, L.; Lai, C.-H.; Hu, Y.; Zhang, Y.; Wang, X.; Xu, C.; Snyder, R. L.; Chen, L.-J.; Wang, Z. L. High output nanogenerator based on assembly of GaN nanowires. Nanotechnology 2011, 22 (47), 475401. (34) Kang, J.-H.; Ebaid, M.; Jeong, D. K.; Lee, J. K.; Ryu, S.-W. Efficient energy harvesting of a GaN p–n junction piezoelectric generator through suppressed internal field screening. J. Mater. Chem. C 2016, 4 (15), 3337-3341. (35) Kang, J.-H.; Jeong, D. K.; Ryu, S.-W. Transparent, Flexible Piezoelectric Nanogenerator Based on GaN Membrane Using Electrochemical Lift-Off. ACS Appl. Mater. Interfaces 2017, 9 (12), 10637-10642. (36) Hiroyasu, I.; Guang-Yuan, Z.; Naoyuki, N.; Takashi, E.; Takashi, J.; Masayoshi, U. GaN on Si Substrate with AlGaN/AlN Intermediate Layer. Jpn. J. Appl. Phys. 1999, 38 (5A), L492L494. (37) Van de Walle, C. G.; Stampfl, C.; Neugebauer, J. Theory of doping and defects in III–V nitrides. J. Cryst. Growth 1998, 189-190, 505-510.


18

Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(38) Wu, J. G.; Shi, H. D.; Zhao, T. L.; Yu, Y.; Dong, S. X. High-Temperature BiScO3-PbTiO3 Piezoelectric Vibration Energy Harvester. Adv. Funct. Mater. 2016, 26 (39), 7186-7194. (39) Wang, C. H.; Liao, W. S.; Lin, Z. H.; Ku, N. J.; Li, Y. C.; Chen, Y. C.; Wang, Z. L.; Liu, C. P. Optimization of the output efficiency of GaN nanowire piezoelectric nanogenerators by tuning the free carrier concentration. Adv. Energy Mater. 2014, 4 (16), 1400392. (40) Sohn, J. I.; Cha, S. N.; Song, B. G.; Lee, S.; Kim, S. M.; Ku, J.; Kim, H. J.; Park, Y. J.; Choi, B. L.; Wang, Z. L. Engineering of efficiency limiting free carriers and an interfacial energy barrier for an enhancing piezoelectric generation. Energy Environ. Sci. 2013, 6 (1), 97-104. (41) Dagdeviren, C.; Yang, B. D.; Su, Y.; Tran, P. L.; Joe, P.; Anderson, E.; Xia, J.; Doraiswamy, V.; Dehdashti, B.; Feng, X.; Lu, B.; Poston, R.; Khalpey, Z.; Ghaffari, R.; Huang, Y.; Slepian, M. J.; Rogers, J. A. Conformal piezoelectric energy harvesting and storage from motions of the heart, lung, and diaphragm. Proc. Natl. Acad. Sci. U.S.A. 2014, 111 (5), 19271932. (42) Dagdeviren, C.; Joe, P.; Tuzman, O. L.; Park, K.-I.; Lee, K. J.; Shi, Y.; Huang, Y.; Rogers, J. A. Recent progress in flexible and stretchable piezoelectric devices for mechanical energy harvesting, sensing and actuation. Extreme Mech. Lett. 2016, 9, 269-281. (43) Hanada, T. Basic properties of ZnO, GaN, and related materials. In Oxide and Nitride Semiconductors; Springer: 2009; pp 1-19. (44) Alexe, M.; Senz, S.; Schubert, M. A.; Hesse, D.; Gosele, U. Energy Harvesting Using Nanowires? Adv. Mater. 2008, 20 (21), 4021-4026. (45) Kang, B.; Wang, H.-T.; Tien, L.-C.; Ren, F.; Gila, B.; Norton, D.; Abernathy, C.; Lin, J.; Pearton, S. Wide Bandgap Semiconductor Nanorod and Thin Film Gas Sensors. Sensors 2006, 6 (6), 643-666.


19


Page 20 of 27

(46) Stacia, K.; Haoran, L.; Matthew, L.; Yanling, H.; Nathan, P.; Jing, L.; David, F. B.; Nicholas, A. F.; James, S. S.; Steven, P. D.; Umesh, K. M. Recent progress in metal-organic chemical vapor deposition of N-polar group-III nitrides. Semicond. Sci. Technol. 2014, 29 (11), 113001. (47) Su, Y. W.; Dagdeviren, C.; Li, R. Measured Output Voltages of Piezoelectric Devices Depend on the Resistance of Voltmeter. Adv. Funct. Mater. 2015, 25 (33), 5320-5325. (48) Johar, M. A.; Kang, J.-H.; Ha, J.-S.; Lee, J. K.; Ryu, S.-W. Controlled conductivity of ptype CuxO/GaN piezoelectric generator to harvest very high piezoelectric potential. J. Alloys Compd. 2017, 726, 765-771.


20

Page 21 of 27

FIGURES AND CAPTIONS (a)

(b) Si (111)

Intensity (a.u.)

Intensity (a.u.)

GaN (0002)

AlGaN (0002)

494 arcsec.

AlN (0002)

28

30 32 34 36 2 Theta (degree)

38

40

(c)

-180 -120

16.8

17.0

17.2 17.4 Omega (degree)

(d)

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


17.6

c

a3 60 °

a1

-60 0 60 Phi (degree)

120

180

a2

GaN/Si

Figure 1. (a)-(c) X-ray diffraction (XRD) analysis of GaN thin film epitaxially grown on Si (111) substrate: (a) 2 theta-omega scan, (b) GaN (0002) plane rocking curve, and (c) GaN (101 2) plane rotational phi scan. (d) Schematic illustration of the crystal orientation of the III-N thin film on Si (111) with c-axis of wurtzite structure perpendicular to the substrate surface.


21


(a)

Page 22 of 27

(b)

500 µm

(c)

(d) Top electrode (Ni/Au) Top electrode GaN thin film Bottom electrode Substrate GaN 11 µm µm

Bottom electrode (Ni/Au/Cu)

Figure 2. (a) Optical microscope image of thin film transferred onto PET substrate. (b) Digital photo of the transferred thin film bending by a human hand. (c) Schematic structure of the GaN thin-film F-PEG. (d) Scanning-electron microscopy (SEM) cross-sectional image of the F-PEG.


22

Page 23 of 27

(a)

(b)

Bend up

Bend down

Release

Release

(c)

e-

e-

N

N

N

∆P

Ga Flat (no e- flow)

Ga Ga Release

Bend up

(d)

Ga

∆P

Flat (no e- flow)

Ga

Bend down

Voltage (V)

2

0 -1

-3

3

Bend up

1

-2

Release

(f)

3 2

N

N

Ga

(e)

e-

eN

Voltage (V)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Release

0.0

0.5

Release

1 0 -1 -2

1.0 1.5 Time (s)

2.0

-3

Bend down

0.0

0.5

1.0 1.5 Time (s)

2.0

Figure 3. Schematic illustration of the F-PEG in (a) bend up-release and (b) bend down-release processes. Polarization induced electricity during (c) bend up-release and (d) bend down-release processes. Corresponding voltage response during repeated (e) bend up-release, and (f) bend down-release processes by human fingers, with positive input (red) of electrometer connected to Ga-face electrode and negative input (black) connected to N-face electrode, with a load resistance of 1 MΩ.


23


(a) 30 25 20 15 10 5 0 -5

30

s = 20

25

s = 15 s = 10

Voltage (V)

Voltage (V)

(b)

s=5

20 15 2

R = 0.988

10

= .

5 0 0 5 10 15 20 25 30 35 40 45 50 Time (s)

0

(d) 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8

a = 1.0

a = 1.5

a = 0.5 a = 0.3 a = 0.1

0

10 20 30 40 50 60 70 Time (s)

Peak current density (µ µAcm-2)

(c) Current density (µ µ Acm-2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 27

5 10 15 Compression (mm)

20

0.8 0.6 0.4

2

R = 0.975

μ · = . ·

0.2 0.0 0.0

0.5 1.0 1.5 Acceleration (ms-2)

2.0

Figure 4. (a) Output open-circuit voltage with compressions of s = 5, 10, 15, and 20 mm, respectively, and (b) relation between open-circuit voltage and compression. (c) Output shortcircuit current at accelerations of a = 0.1, 0.3, 0.5, 1.0, and 1.5 m·s-2, respectively, and (d) relation between peak short-circuit current density and acceleration.


24

1.0 0.8 0.6 0.4 0.2 0.0 1

3

4

5

6

7

8

6

Peak Average

5 4 3 2 1 0

101 102 103 104 105 106 107 108 109 Load (Ω Ω)

10 10 10 10 10 10 10 10 Load (Ω Ω)

(c) 8

(d) 7

0

9 8 7 6 5 4 3 2 1 0

100 80 60 40 20 0

6 5 4 3 2 1 0

Voltage (V)

Voltage (V)

7 6 5 4 3 2 1 0 -1

2

(b)

Power density (µ µWcm-2)

18 16 14 12 10 8 6 4 2 0

1.2

Voltage (V)

1.4

Relative voltage (%)

(a)

Voltage (V)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Current density (µ µ Acm-2)

Page 25 of 27

0 2000 4000 6000 8000 10000 Cycles

2000

4000

6000 Cycles

8000

10000

9120 9121 9122 9123 Cycles

Figure 5. (a) Output current density and voltage with various loads at a compression of 15 mm and an acceleration of 1.5 m·s-2. (b) Peak and average power densities at different load resistances ranging from 5 Ω to 1 GΩ. (c) Amplitude of output voltage during over 10,000 cycles test, with a compression of 5 mm at a frequency of 2.5 Hz. The inset figure shows the corresponding change of peak voltage. (d) A zoomed view of red dotted region of (c).


25


(a)

(c)

(d)

(b)

(e) Voltage (V)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 27

8 7 6 5 4 3 2 1 0

0

5

10

0

2

4

Cycles 15 20 25

6 8 10 Time (s)

30

35

12

14

Figure 6. Schematic circuit of GaN thin-film F-PEG for actual applications: (a) directly power the LED and (b) charge a capacitor when switch connects to point 1, and power the LED when switch connects to point 2. Snapshot of the green LED being instantaneously lighted up (c) by F-PEG directly and (d) by capacitor charged by an F-PEG. (e) Charging curve of the capacitor by the F-PEG.


26

Page 27 of 27

TOC 30 25 20 15 10 5 0 -5

s=20 s=15 s=10 s=5

0 5 10 15 20 25 30 35 40 45 50

Time (s)

Voltage (V)

Voltage (V)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


8 7 6 5 4 3 2 1 0

0

Cycles 5 10 15 20 25 30 35

0

2

4

6 8 10 12 14 Time (s)


27

High-Output Lead-Free Flexible Piezoelectric Generator Using Single

Recommend Documents