Microelectromechanical Systems Energy Harvester Research Articles

MEMS post-processed self-assembled electret for vibratory energy harvesters

Electret-based microelectromechanical system (MEMS) vibratory energy harvesting is a key technology for converting the mechanical energy of environmental vibrations into electricity. Unfortunately, conventional electret charging methods generally rely on high-voltage and high-temperature processes that present limitations to MEMS design and production. Here, we show a MEMS post-processed self-assembled electret (SAE) that enables the integration of electrets with MEMS vibratory devices via evaporation as a post-MEMS process. Owing to the spontaneous orientation of polar molecules, the surface potential of the SAE can build up at room temperature in a microscopic region without charging processes, which enhances the design and fabrication flexibility of electret-based MEMS energy harvesters. We develop a MEMS vibratory device followed by post-processing the SAE and confirm induced electrical currents caused by the electrical field of the SAE at the vibrational input. This SAE-based MEMS technology is a promising design guideline for highly integrated single-chip MEMS vibratory energy harvesters.

Piezoelectric MEMS—evolution from sensing technology to diversified applications in the 5G/Internet of Things (IoT) era

The rapid development of the fifth-generation mobile networks (5G) and Internet of Things (IoT) is inseparable from a large number of miniature, low-cost, and low-power sensors and actuators. Piezoelectric microelectromechanical system (MEMS) devices, fabricated by micromachining technologies, provide a versatile platform for various high-performance sensors, actuators, energy harvesters, filters and oscillators (main building blocks in radio frequency front-ends for wireless communication). In this paper, we provide a comprehensive review of the working mechanism, structural design, and diversified applications of piezoelectric MEMS devices. Firstly, various piezoelectric MEMS sensors are introduced, including contact and non-contact types, aiming for the applications in physical, chemical and biological sensing. This is followed by a presentation of the advances in piezoelectric MEMS actuators for different application scenarios. Meanwhile, piezoelectric MEMS energy harvesters, with the ability to power other MEMS devices, are orderly enumerated. Furthermore, as a representative of piezoelectric resonators, Lamb wave resonators are exhibited with manifold performance improvements. Finally, the development trends of wearable and implantable piezoelectric MEMS devices are discussed.

Design and simulation of the compact MEMS energy harvester based on aluminium nitride

A device for converting the energy of mechanical vibrations to electricity by the piezoelectric effect is presented. A main part of the transducer is a multilayer cantilever with the inertial mass at the tip. A piezoelectric layer is made of 0.5 μm thick aluminum nitride. A feature of the device is the compact lateral size of about 1 mm, which is 10 times smaller in comparison with conventional harvesters. The device is fully compatible with microelectromechanical systems (MEMS) technology. The cantilever has a natural frequency of 45-160 Hz, depending on the size and inertial mass. The transducer generates the output voltage of 0.35 V, which is high enough for rectifying by the diode bridge. The output power of 2.7 nW is relatively low due to the small size. Nevertheless, the figure of merit is higher than that for conventional AlN-based energy harvesters.

Spray-coated electret materials with enhanced stability in a harsh environment for an MEMS energy harvesting device

The charge stability of electret materials can directly affect the performance of electret-based devices such as electrostatic energy harvesters. In this paper, a spray-coating method is developed to deposit an electret layer with enhanced charge stability. The long-term stability of a spray-coated electret is investigated for 500 days and shows more stable performance than a spin-coated layer. A second-order linear model that includes both the surface charge and space charge is proposed to analyze the charge decay process of electrets in harsh environments at a high temperature (120 °C) and high humidity (99% RH); this model provides better accuracy than the traditional deep-trap model. To further verify the stability of the spray-coated electret, an electrostatic energy harvester is designed and fabricated with MEMS (micro-electromechanical systems) technology. The electret material can work as both the bonding interface and electret layer during fabrication. A maximum output power of 11.72 μW is harvested from a vibrating source at an acceleration of 28.5 m/s2. When the energy harvester with the spray-coated electret is exposed to a harsh environment (100 °C and 98% RH), an adequate amount of power can still be harvested even after 34 h and 48 h, respectively.

Fully Integrated Microsolenoid With Closed Magnetic Circuit for High Power Density MEMS Electromagnetic Vibration Energy Harvesters

This letter presents a highly efficient microsolenoid integrated with a closed magnetic circuit to enhance the power density of microelectromechanical systems (MEMS) electromagnetic energy harvesters. Compared with most MEMS electromagnetic energy harvesters adopting an air-cored planar coil, a high permeability closed magnetic circuit is specifically designed and integrated inside the microsolenoid with multiple wire turns for higher electromechanical coupling, which contributes to the effective increased power density of the MEMS energy harvester. Moreover, the wafer-level microsolenoid is compatible with nonlinear springs, which bring higher power output over a wideband frequency range. At an acceleration of 1 g , the prototype shows a load power of 265.2 µW and normalized power density of 5.9 mW·cm-3·g-2 with a load resistance of 40.1 Ω, accompanied with a half-power bandwidth of 30 Hz. The fully integrated solenoid is compatible with other soft magnetic-material and frequency-broadening mechanisms, providing adequate potential for comprehensive performance enhancement of MEMS electromagnetic energy harvesters.

Modeling and Piezoelectric Analysis of Nano Energy Harvesters.

The expedient way for the development of microelectromechanical systems (MEMS) based devices are based on two key steps. First, perform the simulation for the optimization of various parameters by using different simulation tools that lead to cost reduction. Second, develop the devices with accurate fabrication steps using optimized parameters. Here, authors have performed a piezoelectric analysis of an array of zinc oxide (ZnO) nanostructures that have been created on both sides of aluminum sheets. Various quantities like swerve, stress, strain, electric flux, energy distribution, and electric potential have been studied during the piezo analysis. Then actual controlled growth of ZnO nanorods (NRs) arrays was done on both sides of the etched aluminum rod at low-temperature using the chemical bath deposition (CBD) method for the development of a MEMS energy harvester. Micro creaks on the substrate acted as an alternative to the seed layer. The testing was performed by applying ambient range force on the nanostructure. It was found that the voltage range on topside was 0.59 to 0.62 mV, and the bottom side was 0.52 to 0.55 mV. These kinds of devices are useful in low power micro-devices, nanoelectromechanical systems, and smart wearable systems.

Development Trends and Perspectives of Future Sensors and MEMS/NEMS.

With the fast development of the fifth-generation cellular network technology (5G), the future sensors and microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS) are presenting a more and more critical role to provide information in our daily life. This review paper introduces the development trends and perspectives of the future sensors and MEMS/NEMS. Starting from the issues of the MEMS fabrication, we introduced typical MEMS sensors for their applications in the Internet of Things (IoTs), such as MEMS physical sensor, MEMS acoustic sensor, and MEMS gas sensor. Toward the trends in intelligence and less power consumption, MEMS components including MEMS/NEMS switch, piezoelectric micromachined ultrasonic transducer (PMUT), and MEMS energy harvesting were investigated to assist the future sensors, such as event-based or almost zero-power. Furthermore, MEMS rigid substrate toward NEMS flexible-based for flexibility and interface was discussed as another important development trend for next-generation wearable or multi-functional sensors. Around the issues about the big data and human-machine realization for human beings’ manipulation, artificial intelligence (AI) and virtual reality (VR) technologies were finally realized using sensor nodes and its wave identification as future trends for various scenarios.

Optimization of a Piezoelectric Energy Harvester and Design of a Charge Pump Converter for CMOS-MEMS Monolithic Integration.

The increasing interest in the Internet of Things (IoT) has led to the rapid development of low-power sensors and wireless networks. However, there are still several barriers that make a global deployment of the IoT difficult. One of these issues is the energy dependence, normally limited by the capacitance of the batteries. A promising solution to provide energy autonomy to the IoT nodes is to harvest residual energy from ambient sources, such as motion, vibrations, light, or heat. Mechanical energy can be converted into electrical energy by using piezoelectric transducers. The piezoelectric generators provide an alternating electrical signal that must be rectified and, therefore, needs a power management circuit to adapt the output to the operating voltage of the IoT devices. The bonding and packaging of the different components constitute a large part of the cost of the manufacturing process of microelectromechanical systems (MEMS) and integrated circuits. This could be reduced by using a monolithic integration of the generator together with the circuitry in a single chip. In this work, we report the optimization, fabrication, and characterization of a vibration-driven piezoelectric MEMS energy harvester, and the design and simulation of a charge-pump converter based on a standard complementary metal–oxide–semiconductor (CMOS) technology. Finally, we propose combining MEMS and CMOS technologies to obtain a fully integrated system that includes the piezoelectric generator device and the charge-pump converter circuit without the need of external components. This solution opens new doors to the development of low-cost autonomous smart dust devices.

A sub-cc nonlinear piezoelectric energy harvester for powering leadless pacemakers.

A miniature nonlinear piezoelectric energy harvester is developed to power state of the art leadless cardiac pacemakers from cardiac motions. The energy harvester is integrated in the leadless pacemaker and is connected to the myocardium. The energy harvester converts myocardial motions to electricity to power leadless pacemakers. The energy is stored in a battery or supercapacitor and is used for pacing. The device is composed of a bimorph piezoelectric beam confined in a gray iron frame. The system is assembled at high temperature and operated at the body temperature. The mismatch in the coefficients of thermal expansion of the beam and the frame causes the beam to buckle in body temperature. This intentional buckling makes the beam unstable and improves the power production and robustness of the device. Having high natural frequency is a major problem in microelectromechanical systems energy harvesters. Considering the small size of the energy harvester, 0.5 cm3, the natural frequency is expected to be high. In our design, the natural frequency is lowered significantly using a buckled beam and a proof mass. Since the beam is buckled, the design is bistable and nonlinear, which could increase the output power. In this article, the device is analytically modeled, and the natural frequencies and mode shapes of the energy harvester are analytically derived. The terms corresponding to geometric nonlinearities are included in the electromechanical coupled governing equations. The simulations show that the device generates sufficient electricity to power leadless pacemakers.

High Figure of Merit Nonlinear Microelectromagnetic Energy Harvesters for Wideband Applications

We report a new approach for designing high-performance microelectromechanical system (MEMS) electromagnetic energy harvesting devices, which can operate at low frequency (<;1 kHz) over the ultrawide bandwidth of 60-80 Hz. The output from the devices is increased significantly at a low optimized load and this overall enhancement in performances is benchmarked using a power integral (Pf) figure-of-merit. The experimental results show that the efficient nonlinear designs produce large Pf values, giving rise to one of the highest normalized Pf densities among the reported MEMS scale nonlinear energy harvesting devices. This improvement is achieved by suitably designing the nonlinear spring architectures, where the nonlinearity arises from the stretching strain of the specifically designed fixed-fixed configured spring arms under large deflections and gives rise to wideband output response. Different fundamental modes of the mechanical structures are brought relatively close, which further widens the power-frequency response by topologically varying the spring architectures and by realizing the same using the thin silicon-on-insulator substrate using MEMS processing technology. In addition, we have used the magnet as proof mass to increase the output in contrary to conventional approach of using the coil as the proof mass in micro-electromagnetic energy harvesters. The high performance obtained from the MEMS energy harvesters with integrated double layer micro-coil is compared with the same using wire wound copper coil. The experimentally obtained results are qualitatively explained by using a finite-element analysis of the designed structures.

A 4-DOF MEMS Energy Harvester Using Ultrasonic Excitation

This paper presents a microelectromechanical systems (MEMS)-based energy harvester that is designed to harvest electrical energy from an external source of ultrasonic waves. The harvester features a novel 4-degree-of-freedom (DOF) mechanical design that uses three translational resonance modes and one rotational mode, with electrostatic transducers being implemented to perform the conversion of mechanical to electrical energy. The 4-DOF design of the system allows energy to be harvested regardless of the device’s orientation, which holds particular benefits for potential applications that include the powering of implanted biomedical devices. Full characterization of the fabricated MEMS harvester is performed, which shows that the device is able to generate electrical power outputs of 180, 189, and 49.1 nW due to ultrasonic excitation from the $x$ -, $y$ -, and $z$ -directions, respectively.

Optimization method for designing multimodal piezoelectric MEMS energy harvesters

Energy harvesters (EH) are devices that convert environmental energy (i.e. thermal, vibrational or electromagnetic) into electrical energy. One of the most promising solutions consists in transforming energy from vibrations using a piezoelectric material placed onto a mechanical resonator. The intrinsic drawback of this solution is the typically high quality factor of the device which works effectively only within a narrow bandwidth. To overcome this limitation it is possible to tune the mechanical resonance of the device, to introduce non-linear elements (e.g. magnets) or to design the mechanical resonator with a multimodal behaviour. In ultra low power applications the aspect of integration is of utmost importance and so micro electro-mechanical systems (MEMS)-based EHs are preferable. Within this scenario the multimodal solution is the more suitable considering the technological constraints imposed by the micromachining manufacturing process. In this paper, we describe the optimization of a given multimodal mechanical geometry in order to maximize the number of resonances within a certain frequency band. The proposed optimization is finite element method (FEM)-based and it uses modal and harmonic simulations for both selecting the useful modes and then designing the device in a way that presents those modes within a predefined frequency range. This mechanical optimization is the first step for maximizing the output power of a multimodal piezoelectric energy harvester. The second step focuses on the optimization of the piezoelectric transducer geometry targeting the resonant modes defined in the first step. The optimization procedure is applied to an array of cantilever used as a case study.

An Electromagnetic MEMS Energy Harvester Array with Multiple Vibration Modes

This paper reports the design, micromachining and characterization of an array of electromagnetic energy harvesters (EHs) with multiple frequency peaks. The authors present the combination of three multi-modal spring-mass structures so as to realize at least nine resonant peaks within a single microelectromechanical systems (MEMS) chip. It is assembled with permanent magnet to show an electromagnetic-based energy harvesting capability. This is the first demonstration of multi-frequency MEMS EH existing with more than three resonant peaks within a limited frequency range of 189 to 662 Hz. It provides a more effective approach to harvest energy from the vibration sources of multiple frequency peaks.

Micro-Electro-Mechanical System (MEMS)-Based Piezoelectric Energy Harvester for Ambient Vibrations

The ambient vibration-based micro electromechanical systems (MEMS) piezoelectric harvester has become an important subject in most research publications. Providing a green and virtually infinite alternative power source to traditional energy sources, this harvester will significantly expand the applications of wireless sensor networks and other technologies. Using piezoelectric materials to harvest the ambient vibrations that surround a system is one method that has seen a dramatic rise in the power-harvesting applications. The simplicity associated with piezoelectric micro-generators makes them very attractive for MEMS applications in which ambient vibrations are harvested and converted into electric energy. These micro generators can become an alternative to the battery-based solutions in the future, especially for remote systems. In this paper, we proposed a model and presented the simulation of a MEMS-based arrayed energy harvester under ambient vibration excitation using the Coventorware approach. This arrayed cantilever-based MEMS energy harvester that operates under ambient excitation of frequency band of 67 to 70Hz, within a base acceleration of 0.2 to 1.3g produces an output power of 6.8μw and 0.4 volts at 20.1 k-ohms load.

Wide Bandwidth Piezoelectric MEMS Energy Harvesting

ABSTRACTPiezoelectric Microelectromechanical Systems (MEMS) has been proven to be an attractive technology for harvesting small energy from the ambient vibration. Recent advancements in piezoelectric materials and harvester structural design, individually or in combination, have improved MEMS energy harvesters to achieve high enough power density, compactness and ultra wide bandwidth, bringing us closer towards battery-less autonomous sensors systems and networks in near future. Among the breakthroughs, non-linear resonating beam for wide bandwidth resonance is the key development to enable robust operation of MEMS energy harvesters over the unpredictable and uncontrollable frequency spectra of ambient vibration. We expect that a coin size harvester will be able to harvest about 100μW continuous power at below 100 Hz and less than 0.5 g input vibration and at reasonable cost.

Fabrication of aluminium doped zinc oxide piezoelectric thin film on a silicon substrate for piezoelectric MEMS energy harvesters

Thin film piezoelectric materials play an essential role in micro electro mechanical system (MEMS) energy harvesting due to its low power requirement and high available energy densities. Non-ferroelectric piezoelectric materials such as ZnO and AlN are highly silicon compatible making it suitable for MEMS energy harvesters in self-powered microsystems. This work primarily describe the design, simulation and fabrication of aluminium doped zinc oxide (AZO) cantilever beam deposited on silicon substrate. AZO was chosen due its high piezoelectric coupling coefficient, ease of deposition and excellent bonding with silicon substrate. Doping of ZnO with Al has improved the electrical properties, conductivity and thermal stability. The proposed design operates in transversal mode (d31 mode) which was structured as a parallel plated capacitor using Si/Al/AZO/Al layers. The highlight of this work is the successful design and fabrication of Al/AZO/Al on silicon as the substrate to make the device CMOS compatible for electronic functionality integration. Design and finite element modeling was conducted using COMSOL™ software to estimate the resonance frequency. RF Magnetron sputtering was chosen as the deposition method for aluminium and AZO. Material characterization was performed using X-ray diffraction and field emission scanning electron microscopy to evaluate the piezoelectric qualities, surface morphology and the cross section. The fabricated energy harvester generated 1.61 V open circuit output voltage at 7.77 MHz resonance frequency. The experimental results agreed with the simulation results. The measured output voltage is sufficient for low power wireless sensor nodes as an alternative power sources to traditional chemical batteries.

Parametric Study of Zigzag Microstructure for Vibrational Energy Harvesting

A comprehensive parametric study is presented on the vibration and the energy harvesting performance of a low-frequency zigzag energy harvester. The zigzag microelectromechanical systems (MEMS) vibrational energy harvesters have low natural frequencies which match the low-frequency range of ambient vibrations. The harvesters can, therefore, be designed to resonate with ambient excitation. The power produced by energy harvesters at resonance is orders of magnitude larger than off resonance power. The paper aims at providing an easy-to-use, comprehensive tool for designing the harvesters for different applications. The two key characteristics of the vibrational energy harvesters are their resonance frequency and their power transfer function. We formulate both vibrations and power production of the zigzag MEMS harvesters in nondimensional equations. The paper advances the state of the art in MEMS energy harvesting research area by identifying the dimensionless parameters governing mechanical vibrations and energy generation. We also investigate how the resonant frequency and the maximum power vary with each of the corresponding dimensionless parameters. The graphs summarize the parametric studies and provide sufficient tools for design of zigzag harvesters. The natural frequencies are related to six dimensionless variables, and the power transfer functions depend on 12 dimensionless parameters. <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $\hfill$</tex></formula> [2010-0298]

A MEMS Self-Powered Sensor and RF Transmission Platform for WSN Nodes

We report a new microelectromechanical systems (MEMS) self-powered sensor and RF transmission platform for wireless sensor network (WSN) nodes which can operate at energy levels orders of magnitude lower than current equivalent systems. Using the microgenerator as a power amplifier to drive a passive kick-and-resonate transmitter architecture as an alternative to a standard power hungry transmitter, this platform eliminates the need for both secondary energy storage and power conditioning circuits. This enables a significant reduction in the size, weight, complexity and cost, and allows operation at much lower excitation frequencies. The prototype platform consists of a MEMS rolling-rod microgenerator, the output voltage of which is used to kick a resonant loop antenna. The generator can be directly primed by a suitable voltage-output sensor. This is the first platform to achieve wireless sensor transmission powered only by a MEMS energy harvester.

Back Cover: Piezoelectric MEMS generator based on the bulk PZT/silicon wafer bonding technique (Phys. Status Solidi A 12/2011)

As shown by Tang et al. (pp. 2913-2919), a Pb(Zr,Ti)O3 (PZT) thick film with excellent properties can be fabricated by lapping bulk PZT after bonding it to a silicon wafer at 105 °C by employing epoxy resin with preferable thermostability as the intermediate adhesive layer. Based on this technique, a piezoelectric generator for micro-electro-mechanical systems (MEMS) technology was fabricated and its performance was tested. The results show that the new thick-film preparation method is compatible with MEMS technology and the PZT thick film retains the excellent performance of bulk PZT. This method provides a new way for the preparation of high performance piezoelectric MEMS energy harvesting elements.

Efficient Physical Modeling of MEMS Energy Harvesting Devices With VHDL-AMS

In this paper, we propose a VHDL-AMS implementation of a physical model of a microelectromechanical systems (MEMS) piezoelectric microgenerator. Such an executable model acts as a bridge between specifications and fabricated devices. Usually, physical and geometrical parameters of electromechanical parts of a system are only considered in lower levels of the design flow, typically using finite-element tools, which, despite their accuracy, do not allow efficient optimization of the structure properties and dimensions. Thus, it would be very interesting to have a model of the entire harvesting system (the MEMS piezoelectric microgenerator cascaded with the electronic circuit) to perform efficient optimization. Some features like damping effects and process fluctuations have considerable impact on the performance of MEMS, especially the resonant structures. We propose a method of integrating such features early in the design flow, while keeping the simulation time reasonable. The resulting model is reusable, predictive (comparable to experimental results) and respects Kirchhoff laws. Consequently, it can be integrated in global simulation of multidomain and mixed signal systems like wireless sensor nodes.