On-chip electrochemical capacitors and piezoelectric energy harvesters for self-powering sensor nodes
Doktorsavhandling, 2022

On-chip sensing and communications in the Internet of things platform have benefited from the miniaturization of faster and low power complementary-metal-oxide semiconductor (CMOS) microelectronics. Micro-electromechanical systems technology (MEMS) and development of novel nanomaterials have further improved the performance of sensors and transducers while also demonstrating reduction in size and power consumption. Integration of such technologies can enable miniaturized nodes to be deployed to construct wireless sensor networks for autonomous data acquisition. Their longevity, however, is determined by the lifetime of the power supply. Traditional batteries cannot fully fulfill the demands of sensor nodes that require long operational duration. Thus, we require solutions that produce their own electricity from the surroundings and store them for future utility. Furthermore, manufacturing of such a power supply must be compatible with CMOS and MEMS technology. In this thesis, we will describe on-chip electrochemical capacitors and piezoelectric energy harvesters as components of such a self-powered sensor node. Our piezoelectric microcantilevers confirm the feasibility of fabricating micro electro-mechanical-systems (MEMS) size two-degree-of-freedom systems which can address the major issue of small bandwidth of piezoelectric micro-energy harvesters. These devices use a cut-out trapezoidal cantilever beam, limited by its footprint area i.e. a 1 cm$^2$ silicon die, to enhance the stress on the cantilever's free end while reducing the gap remarkably between its first two eigenfrequencies in the 400 - 500 Hz and in the 1 - 2 kHz range. The energy from the M-shaped harvesters could be stored in rGO based on-chip electrochemical capacitors. The electrochemical capacitors are manufactured through CMOS compatible, reproducible, and reliable micromachining processes such as chemical vapor deposition of carbon nanofibers (CNF) and spin coating of graphene oxide based (GO) solutions. The impact of electrode geometry and electrode thickness is studied for CNF based electrodes. Furthermore, we have also demonstrated an improvement in their electrochemical performance and yield of spin coated electrochemical capacitors through surface roughening from iron and chromium nanoparticles. The CVD grown CNF and spin coated rGO based devices are evaluated for their respective trade-offs. Finally, to improve the energy density and demonstrate the versatility of the spin coating process, we manufactured electrochemical capacitors from various GO based composites with functional groups heptadecan-9-amine and octadecanamine. The materials were used as a stack to demonstrate high energy density for spin coated electrochemical capacitors. We have also examined the possibility of integrating these devices into a power management unit to fully realize a self-powering on-chip power supply through survey of package fabrication, choice of electrolyte, and device assembly.

piezoelectric energy harvesters

Energy storage




sensor node

Energy harvesting

spin coating

graphene oxide

Kollectorn, MC2, Kemivagen 9, 41258, Gothenburg, Sweden; Zoom password: 865254
Opponent: Dr. Xiaohong Wang, Tsinghua University, Beijing, 100084, China


Agin Vyas

Chalmers, Mikroteknologi och nanovetenskap, Elektronikmaterial

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Impact of electrode geometry and thickness on planar on-chip microsupercapacitors

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A Micromachined Coupled-Cantilever for Piezoelectric Energy Harvesters

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The usefulness of interconnected devices in the future Internet of things (IoT) depends on their power supplies. Therefore, there is an increasing interest in self-powered sensors and communication devices with an operational lifetime that is not limited by a battery that needs to be replaced.

The two main components of a self-powering solution are energy harvesting and energy storage devices. Energy harvesters derive their energy from the ambient eg in the form of solar, wind, and kinetic energy. Energy storage devices store the energy derived from the energy harvester. Energy harvesters integrated with an energy storage system can potentially replace batteries, creating a self-sustaining IoT platform. Furthermore, if the manufacturing of such devices is compatible with electronics manufacturing processes, then we can significantly reduce the cost of manufacturing. In this thesis, we describe carbon-based electrochemical capacitors and silicon-based piezoelectric energy harvesters as components of such a self-powered sensor node intended for on-chip integration with microelectronics while envisioning a better and greener future.











Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5112



Kollectorn, MC2, Kemivagen 9, 41258, Gothenburg, Sweden; Zoom password: 865254


Opponent: Dr. Xiaohong Wang, Tsinghua University, Beijing, 100084, China

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