Energy science is becoming an increasingly important multi-disciplinary area, for not only addressing the worldwide energy crisis, but also realizing desired power sources with advanced features for portable electronic devices and sensor networks. Very recently, based on triboelectric effect and electrostatic induction, a fundamentally new technology, triboelectric nanogenerator, has been demonstrated which shows unique merits. But so far, the main limitation for continuing optimizing their output performance is a lack of fundamental understanding of their core working mechanism. In this thesis research, we first unveil the fundamental theory and output characteristics of triboelectric nanogenerators. Then, we apply the developed theory to the TENG-based self-powered system design. We have developed the first genuine self-powered system to meet mW requirement of personal electronics. The system includes a multilayered TENG, a power management circuit with 60% total efficiency, and a low leakage energy storage device. Our power management circuit provides the total efficiency that is about two magnitudes higher than the traditional direct charging. And the total system performance is 330 times higher than the state-of-art designs. Driven by palm tapping, this power unit can provide a continuous DC electricity of 1.044 mW on average power in a regulated and managed manner that can be universally applied as a standard power source for continuously driving numerous conventional electronics, such as a thermometer, a heart rate monitor (electrocardiograph/ECG system), a pedometer, a wearable electronic watch, a scientific calculator, and a wireless radio-frequency communication system. Our study demonstrates the first power unit that utilizes widely accessible biomechanical energy source to sustainably drive a broad range of commercial mobile and wearable electronic devices. This self-charging unit is a paradigm shift towards infinite-lifetime energy sources that can never be achieved solely by batteries.

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Novel technology which can provide new solutions and enable augmented capabilities to CMOS based technology is highly desired. Piezotronic nanodevices and integrated systems exhibit potential in achieving these application goals. By combining laser interference lithography and low temperature hydrothermal method, an effective approach for ordered growth of vertically aligned ZnO NWs array with high-throughput and low-cost at wafer-scale has been developed, without using catalyst and with a superior control over orientation, location/density and morphology of as-synthesized ZnO NWs. Beyond the materials synthesis, by utilizing the gating effect produced by the piezopotential in a ZnO NW under externally applied deformation, strain-gated transistors (SGTs) and universal logic operations such as NAND, NOR, XOR gates have been demonstrated for performing piezotronic logic operations for the first time. In addition, the first piezoelectrically-modulated resistive switching device based on piezotronic ZnO NWs has also been presented, through which the write/read access of the memory cell is programmed via electromechanical modulation and the logic levels of the strain applied on the memory cell can be recorded and read out for the first time. Furthermore, the first and by far the largest 3D array integration of vertical NW piezotronic transistors circuitry as active pixel-addressable pressure-sensor matrix for tactile imaging has been demonstrated, paving innovative routes towards industrial-scale integration of NW piezotronic devices for sensing, micro/nano-systems and human-electronics interfacing. The presented concepts and results in this thesis exhibit the potential for implementing novel nanoelectromechanical devices and integrating with MEMS/NEMS technology to achieve augmented functionalities to state-of-the-art CMOS technology such as active interfacing between machines and human/ambient as well as micro/nano-systems capable of intelligent and self-sufficient multi-dimensional operations.

With the threatening of global warming and energy crises, searching for renewable and green energy resources with reduced carbon emissions is one of the most urgent challenges to the sustainable development of human civilization. In the past decades, increasing research efforts have been committed to seek for clean and renewable energy sources as well as to develop renewable energy technologies. Mechanical motion ubiquitously exists in ambient environment and people’s daily life. In recent years, it becomes an attractive target for energy harvesting as a promising supplement to traditional fuel sources and a potentially alternative power source to battery-operated electronics. Until recently, the mechanisms of mechanical energy harvesting are limited to transductions based on piezoelectric effect, electromagnetic effect, electrostatic effect and magnetostrictive effect. Widespread usage of these techniques is likely to be shadowed by possible limitations, such as structure complexity, low power output, fabrication of high-quality materials, reliance on external power sources and little adaptability on structural design for different applications. In 2012, triboelectric nanogenerator (TENG), a creative invention for harvesting ambient mechanical energy based on the coupling between triboelectric effect and electrostatic effect has been launched as a new and renewable energy technology. The concept and design presented in this thesis research can greatly promote the development of TENG as both sustainable power sources and self-powered active sensors. And it will greatly help to define the TENG as a fundamentally new green energy technology, featured as being simple, reliable, cost-effective as well as high efficiency.

In a wide range of industries, machine condition monitoring is one of the most cost effective ways to minimise maintenance efforts and machine downtime. To implement such a system, wireless solutions have increasingly become an attractive proposition due to the ease of installation and minimal infrastructure alternation. However, currently most wireless sensors in the world are powered by a finite battery source. The dependence of batteries not only requires frequent maintenance, but also has adverse environmental consequences associated with battery disposal. These reasons render massive deployment of wireless sensors in the industry problematic. With the advances in semiconductors, power consumption of wireless sensors has been continuously decreasing. It is an inevitable trend for self-powered wireless sensors to emerge and become the norm for machine and environmental monitoring. In this research, vibration is chosen to be the energy source to enable self-powered wireless sensors due to its ubiquitousness in machinery and industrial environments. As a result of relying on resonance, the biggest challenge for vibration-based energy harvesters is their narrow bandwidth. Even a small deviation of the vibration frequency can dramatically reduce the power output. The primary goal of this research is to address this problem. In particular, Piezoelectric generators are identified to be the most suitable technology. In this work, extensive theoretical and experimental studies are conducted in single mass and multi-modal harvesters, and in resonance tuning harvesters by modulus and impedance matching as well as by mechanical actuation. Mathematical modelling plays a significant role in energy harvester designs. A dynamic model that generalises the single degree of freedom models and the continuum models is derived and validated by experiments. The model serves as the building block for the whole research, and it is further refined for the investigation of modulus and impedance matching. In the study of multi-modal harvesters, a continuum model for double-mass piezoelectric cantilever beams is derived and experimentally validated. To study the feasibility of resonance tuning by mechanical means, prototypes were built and performance evaluated. This document details the theoretical basis, concepts and experimental results that extend the current knowledge in the field of energy harvesting. This research work, being highly industrially focused, is believed to be a very significant step forward to a commercial energy harvester that works for a wide range of vibration frequencies.

Today’s information-centered world leads the ever-increasing consumer demand for more powerful, multifunctional portable devices. Additionally, recent developments on long-lasting energy sources and compliant, flexible systems, have introduced new required features to the portable devices industry. For example, wireless sensor networks are in urgent need of self-sustainable, easy-to-deploy, mobile platforms, wirelessly interconnected and accessible through a cloud computing system. The objective of my doctoral work is to develop integration strategies to effectively fabricate mechanically flexible, energy-independent systems, which could empower sensor networks for a great variety of new exciting applications. The first module, flexible electronics, can be achieved through several techniques and materials. Our main focus is to bring mechanical flexibility to the state-of-the-art high performing silicon-based electronics, with billions of ultra-low power, nano-sized transistors. Therefore, we have developed a low-cost batch fabrication process to transform standard, rigid, mono-crystalline silicon (100) wafer with devices, into a thin (5-20 m), mechanically flexible, optically semi-transparent silicon fabric. Recycling of the remaining wafer is possible, enabling generation of multiple fabrics to ensure lowcost and optimal utilization of the whole substrate. We have shown mono, amorphous and poly-crystalline silicon and silicon dioxide fabrics, featuring industry’s most advanced high-/metal-gate based capacitors and transistors. The second module consists on the development of efficient energy scavenging systems. First, we have identified an innovative and relatively young technology, which can address at the same time two of the main concerns of human kind: water and energy. Microbial fuel cells (MFC) are capable of producing energy out the metabolism of bacteria while treating wastewater. We have developed two micro-liter MFC designs, one with carbon nanotubes (CNT)-based anode and the second with a more sustainable design and easy to implement. Power production ranges from 392 to 100 mW/m3 depending on design. Additionally we have explored a flexible thermoelectric generator (0.139 μW/cm2) and a lithium-ion battery (~800 μAh/m2) for back-up energy generation and storage. Future work includes the implementation of a self-powered System-on-Package which gathers together energy generation, storage and consumption. Additionally we are working to demonstrate Complementary Metal-Oxide-Semiconductor (CMOS) circuitry on our flexible platform, as well as memory systems.

Modern electronics continues to push past boundaries of integration and functional density toward elusive, completely autonomous, self-powered microsystems. As systems continue to shrink, however, less energy is available on board, leading to short device lifetimes (run-time or battery life). Extended battery life is particularly advantageous in the systems with limited accessibility, such as biomedical implants and structure-embedded micro-sensors. The power management process usually requires compact and efficient power converters to be embedded in these microsystems. This dissertation introduces switched-capacitor (SC) power converter designs that make all these techniques realizable on silicon.Four different integrated SC power converters with multiple control schemes are designed here to provide low-power high-efficient power sources. First, a monolithic step-down power converter with subthreshold z-domain digital pulse-width modulation (DPWM) controller is proposed for ultra-low power microsystems. The subthreshold design significantly reduces the power dissipation in the controller. Second, an efficient monolithic master-slave complementary power converter with a feedback controller that purely operates in subthreshold operation region is discussed to tailor for the aforementioned ultra-low power applications. Third, we introduce an efficient monolithic step-down SC power stage with multiple-gain control and on-chip capacitor sizing for self-powered microsystems. The multiple-gain control helps the converter to constantly maintain high efficiency over a large input/output range. The size-adjustable pumping capacitors allow the output voltage to be regulated at different desired levels, with a constant 50% duty ratio. The monolithic implementations in these three integrated CMOS power converters effectively suppress noise and glitches caused by parasitic components due to bonding, packaging and PCB wiring. Fourth, an efficient step-up and step-down SC power converter with multiple-gain closed-loop controller is presented. The measurements and simulation results in these four power converters demonstrate the techniques proposed in this research. The approaches presented in this dissertation are evidently viable for realizing compact and high efficient SC power converters, contributing to next generation power-efficient microsystems designs.