Flexible and high-performance piezoelectric energy harvesters for flexible self-powered electronic system

Abstract

Chapter 1. Recent years, the research for energy harvesting has significantly increased because we have been facing a problem with environmental pollution (ex. carbon dioxide emission and global warming) and depletion of fossil fuels. Energy harvesting technologies can convert ambient energies such as sunlight, wave, wind, thermal, and mechanical vibrating energies into useful electric energy. Particularly, piezoelectric material based harvesting technologies have great attention due to which can convert very tiny mechanical movements into electric energy. Furthermore, flexible piezoelectric energy harvester (called nanogenerators) with various flexible piezoelectric materials have been widely studied by many research teams. These flexible piezoelectric nanogenerators have used to turn on light emitting diodes (LEDs) / liquid crystal displays (LCDs), stimulate living muscles, and charge batteries/capacitors. Many piezoelectric materials such as ZnO, $BaTiO_3$, $Pb(Zr,Ti)O_3$, $Pb(Mg_{1/3}Nb_{2/3})O_3$ - $PbTiO_3$ have been utilized for these flexible energy harvesting demonstrations. Among these piezoelectric materials, perovskite structured piezoelectric materials have been considered due to their inherently high piezoelectric properties. In this thesis, the flexible energy harvesters enabling by perovskite piezoelectric thin films are introduced.

Chapter 2. An artificial cardiac pacemaker is widely used to normalize function of human heart. However, the repetitive surgeries highly demand for timely replacement of the pacemakers due to their limited lifespan of batteries. The critical infection and bleeding caused by battery related surgery for aged and infirm people of weak immune system, can be resolved by directly recharging battery inside human body or adopting self-powered heart stimulation. In this work, it is experimentally described how flexible single crystal PMN-PT thin film on a thin plastic substrate can be utilized as a high-performance self-powered energy harvester by slight bending motions for artificial cardiac pacemaker. The energy harvesting device generated one of the highest short-circuit current of 0.223 mA and open-circuit voltage of 8.2 V, which was enough to meet the high standard for cardiac nerve stimulation. This flexible PMN-PT thin film nanogenerator applied not only to charge batteries, but also to render artificial pacemaking without external power sources. Chapter 3. A high-performance flexible piezoelectric energy harvester was demonstrated by using a highly piezoelectric single crystalline PMN-PZT thin film grown by a solid-state single crystal growth (SSCG) method. A $Ba(Zr_{0.1},Ti_{0.9})O_3$ single crystal seed was utilized to crystallize a large-area polycrystalline PMN-PZT ceramic into a piezoelectric single crystal film through the SSCG process. The flexible PMN-PZT harvesting device successfully converted bio-mechanical energy into electric output of up to 100 V and 20 μA. We also developed a reconfigurable rectifying circuit for a flexible piezoelectric power management system. Our advanced power conditioning circuit extracted Joule heating energy of 6.25 μJ from the harvesting device by minimizing energy loss, which was 4 times higher energy compared to the conventional bridge rectifying circuit (Joule heating energy of 1.54 $\mu$J). Lastly, a self-powered military boot was fabricated by integration of the flexible PMN-PZT energy device on the heel of a combat boot. By slight motion of human ankle, the self-powered military boot generated electric energy which was large enough to directly turn on a light emitting diode (LED) and a liquid crystal display (LCD).

Chapter 4. A deep brain stimulation (DBS) is widely used to remedy movement and affective disorders by sending electric impulses to specific parts of the brain. Whereas, the repetitive medical operations have to be highly required for timely replacement of the depleted batteries. The periodic medical surgeries could cause medical accidents like critical infection and bleeding. To solve this problem, we have reported flexible single crystalline PIMNT thin film energy harvester for demonstration of self-powered DBS applications. The flexible energy harvester generated open-circuit voltage of 11 V and very high short-circuit current of 0.57 mA, which were enough to directly turn on 120 green light emitting diodes (LEDs) as well as be utilized real-time electrical brain stimulation with out external power source.

Chapter 5. A high-performance flexible piezoelectric energy harvester on a plastic substrate was demonstrated by using a highly piezoelectric PZT film fabricated by an aerosol deposition (AD) method. A high temperature (900 °C) annealing process for AD PZT film was conducted to enhance the intrinsic piezoelectric properties of PZT with effective grain growth. The flexible AD PZT harvesting device can generated an open-circuit voltage of 200 V and a short-circuit current of 35 $\mu$A via instantaneous bending and unbending motion. The output performance of our flexible piezoelectric harvester was comparable with previously reported high output flexible piezoelectric energy harvester utilizing a single crystal piezoelectric material with exceptionally high piezoelectric coefficients. Lastly, a self-powered wireless sensor node system was demonstrated by integration of flexible AD PZT harvesters, rectifying/storage circuit, and RF temperature sensor node. We charged a capacitor up to 4.3 V using the piezoelectric harvesting devices and operate the wireless temperature sensor node for 18 times. The measured temperature data was successfully transmitted into a computer monitoring system in semi-real time.