Piezoelectric-Nanowire-Enabled Power Source for Driving Wireless Microelectronics
Total Page:16
File Type:pdf, Size:1020Kb
ARTICLE Received 4 Jun 2010 | Accepted 23 Sep 2010 | Published 19 Oct 2010 DOI: 10.1038/ncomms1098 Piezoelectric-nanowire-enabled power source for driving wireless microelectronics Sheng Xu1, Benjamin J. Hansen1 & Zhong Lin Wang1 Harvesting energy from irregular/random mechanical actions in variable and uncontrollable environments is an effective approach for powering wireless mobile electronics to meet a wide range of applications in our daily life. Piezoelectric nanowires are robust and can be stimulated by tiny physical motions/disturbances over a range of frequencies. Here, we demonstrate the first chemical epitaxial growth of PbZrxTi1 − xO3 (PZT) nanowire arrays at 230 °C and their application as high-output energy converters. The nanogenerators fabricated using a single array of PZT nanowires produce a peak output voltage of ~0.7 V, current density of 4 µA cm − 2 and an average power density of 2.8 mW cm − 3. The alternating current output of the nanogenerator is rectified, and the harvested energy is stored and later used to light up a commercial laser diode. This work demonstrates the feasibility of using nanogenerators for powering mobile and even personal microelectronics. 1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, USA. Correspondence and requests for materials should be addressed to Z.L.W. (email: [email protected]). NATURE COMMUNICATIONS | 1:93 | DOI: 10.1038/ncomms1098 | www.nature.com/naturecommunications © 2010 Macmillan Publishers Limited. All rights reserved. ARTICLE NatUre cOMMUNicatiONS | DOI: 10.1038/ncomms1098 he search for sustainable micro/nano-powering sources for driving wireless and mobile electronics is an emerging field in today’s energy research, which could offer a fundamental solu- T 1–3 001 tion to the energy needed for driving nanodevices/nanosystems . 100 The piezoelectric nanogenerator that converts mechanical energy into electricity was first demonstrated using ZnO nanowire arrays4. Following this initial discovery, both direct current5,6 and alternat- ing current7 ZnO nanogenerators have been developed. In addition, nanogenerators based on GaN nanowires8 and poly(vinylidene fluo- 9 1,400 F ride) nanofibres have shown promising potential for enhancing the 0 1,200 V (V) F (T) (200) nanogenerator performance. Consequently, a worldwide effort has 1,000 –0.2 800 been launched in this regard, forming a new research field in nanote- (001) –0.4 10 T 600 ) PZ chnology and energy science . The advantage of using nanowires for ) –0.6 (002 400 ) energy harvesting is their high mechanical robustness and respon- (300 –0.8 (003 200 STO (100) siveness to tiny random mechanical disturbances/stimulation. SQRT intensity (counts) 0 Although the output voltage of nanogenerators has been raised to 20 30 40 50 60 70 80 1.2 V using an integration of millions of ZnO nanowires for driv- 2θ (°) 11 ing a single nanowire-based UV/pH sensor , the output power of Figure 1 | PZT nanowire characterization and nanogenerator simulation. the nanogenerators was still too small to power any conventional (a) Scanning electron microscopy image of the epitaxially grown PZT electronic components, such as laser diodes (LDs). nanowire arrays on an Nb-doped STO substrate by hydrothermal Lead zirconate titanate, PbZrxTi1 − xO3 (PZT), is probably the most decomposition. Scale bar, 5 µm. (b) High-resolution TEM image and important piezoelectric material for sensors and actuators, owing to 12,13 electron diffraction pattern (inset) acquired from an as-grown PZT its remarkable piezoelectric performance . However, the fabrica- nanowire, indicating a well-crystallized tetragonal phase with a lattice tion of PZT thin films14 and microfibres15 usually requires high tem- 16 constant of a = 3.93 Å and c = 4.16 Å. Scale bar, 5 nm. (c) Conventional θ − 2θ peratures (~650 °C) to increase the crystallinity , which leads not scan X-ray diffraction spectrum from the as-grown nanowire arrays. (d) only to high cost and incompatibility with general fabrication proc- Finite element calculation (left) of the piezoelectric potential distribution esses but also makes it difficult to integrate with soft materials, even − 10 17 (~1 V) in a PZT nanowire (d33 = 1.52×10 C/N) of 500 nm in width and though a transfer technique has been demonstrated recently . Here, 5 µm in length, under a uniaxial compression of 2.5 µN. The right-hand we report the first chemical epitaxial growth of vertically aligned side schematic diagram is the structure of a multilayered nanogenerator single-crystal PbZr0.52Ti0.48O3 nanowire arrays on a variety of con- fabricated using the nanowire arrays. SQRT indicates square root. ductive and non-conductive substrates by hydrothermal decom- position at 230 °C. Alternating current nanogenerators fabricated using the PZT nanowire arrays showed outstanding output. Using a Fabrication and characterization of the nanogenerator. Finite rectifying circuit, the output electrical energy of the nanogenerator element calculations are used based on a cantilever model that has one was stored with capacitors and later used to light up a commercial end fixed and the other end free. We have three main assumptions. LD. This is a key step in developing sustainable energy technology First, the elastic modulus of the nanowire is isotropic and the piezo- for micro/nanosystems. electric efficient is anisotropic; second, the nanowire is under pure axial compression and free of shear strain; and third, the piezoelectric Results domains are all perfectly aligned. The calculation result shows that, Synthesis and characterization of the PZT nanowire arrays. PZT for a tetragonal PZT nanowire growing along [001] direction with nanowire arrays were grown by a hydrothermal process (Fig. 1a). The a 500 nm diameter and 5 µm length, a uniaxial force of 2.5 µN can reaction equations are given below. During the nucleation and growth create a piezoelectric potential (piezopotential) of ~1 V (Fig. 1d). To of PZT nanowires, the poly(vinyl alcohol) and poly(acrylic acid) use this high piezopotential, nanogenerators were fabricated using perform as capping agents that chemisorb at the side surfaces of the the PZT nanowire arrays grown on conductive Nb-doped SrTiO3 nanowires and thus inhibit their radial growth. Transmission electron (STO) substrates19, following the schematic shown in Figure 1d. microscopy analysis of a single nanowire (Fig. 1b and Supplementary Electrical polarization was required to align the piezoelectric Fig. S1) and X-ray diffraction of nanowire arrays Fig.( 1c) show that the domains in the same direction and in all the nanowires. In the as- as-synthesized nanowires have a tetragonal phase of single crystalline grown nanowires, the dipole moments resulting from the position PZT (space group P4mm) and a [001] growth direction18. The vertical shift of the Ti4 + /Zr4 + ions could take six possible orientations along growth and alignment were enforced by the epitaxial growth on the 〈001〉. An electric poling of the nanowires was made by applying inorganic substrate, which have a better alignment than the nanofibres an external electric field of 100 KV cm − 1 in a dielectric fluid of high fabricated by electrospinning15. A piezoelectric domain boundary was dielectric strength, and with the top electrode being negative and found in the axial direction of the nanowire, but the entire nanowire bottom electrode positive. As a result, a macroscopic piezoelectric preserves a single crystal structure (Supplementary Fig. S1c). polarization was forced to align upwards, normal to the substrate (Supplementary Fig. S2)20. When the PZT nanowires are subject to + − NH3·H2O↔NH4 + OH a uniaxial compressive force, a piezoelectric field is created inside the nanowires, which produces a transient flow of free electrons in − − ZrOCl2·8H2O + 2 OH ↔ZrO(OH)2 + 2 Cl + 8 H2O the external load to screen the piezopotential. When the force is lifted, the piezopotential diminishes and the accumulated electrons Ti(C4H9O)4 + 4 H2O↔Ti(OH)4 + 4 C4H9OH are released. A dynamically applied stress drives the electrons in the external circuit to flow back and forth, resulting in an alternat- 13 ZrO(OH)2 + 12 Ti(OH)4→25 Zr0.52Ti0.48O(OH)2 ↓ + 12 H2O ing output. Shown in Figure 2a is the output voltage profile from a seven-layer integrated nanogenerator under a periodic mechani- − − Pb(NO3)2 + 2 OH ↔Pb(OH)2 + 2 NO3 cal pressing and releasing. The output voltage is reduced compared with the calculated result owing to the following reasons. First, the Pb(OH)2 + Zr0.52Ti0.48O(OH)2→PbZr0.52Ti0.48O3 ↓ + 2 H2O height of the nanowires is non-uniform, and only a few percent NatUre cOMMUNicatiONS | 1:93 | DOI: 10.1038/ncomms1098 | www.nature.com/naturecommunications © 2010 Macmillan Publishers Limited. All rights reserved. NatUre cOMMUNicatiONS | DOI: 10.1038/ncomms1098 ARTICLE 1 1 0.5 a 0.42 V b 3.0E–04 0.8 0.4 0.8 2.5E–04 0.6 0.3 2.0E–04 (V) 0.4 0.6 0.2 p 1.5E–04 R ca 0.1 V 1.0E–04 (V) 0.2 (V) 0.4 5.0E–05 rec NG 0 0.0 V V 0.0E+00 –0.2 0.2 0 2×104 4×104 6×104 8×104 1×105 0 2 4 6 8 10 P Cycles Cycles –0.4 0 c 0.44 1.00 d –0.6 1 0.42 2 0.80 –0.8 –0.2 Power (mW) 0.40 0.60 0 5 10 15 0 5 10 15 ) 0.38 (V 0.40 Time (s) Time (s) 3 4 cap 0.36 V 0.20 0.34 300 LD 0.32 0.00 250 3 2 0.30 –0.20 Laser diode 1 4.10 4.12 4.14 200 1 Time (s) 2 2 150 Figure 3 | Storage of electrical pulses into capacitors to light up a laser (nA) 1 Vcap diode (LD).