@thesis{vyas_-chip_2022,
	location = {Department of Microtechnology and Nanoscience, Göteborg, Sweden},
	title = {On-chip electrochemical capacitors and piezoelectric energy harvesters for self-powering sensor nodes},
	abstract = {On-chip sensing and communications in the Internet of things platform have benefited from the miniaturization of faster and low power complementary-metal-oxide semi- conductor ({CMOS}) microelectronics. Micro-electromechanical systems technology ({MEMS}) and development of novel nanomaterials have further improved the perfor- mance 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 bat- teries cannot fully fulfill the demands of sensor nodes that require long operational duration. Thus, we require solutions that produce their own electricity from the sur- roundings 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 can- tilever beam, limited by its footprint area i.e. a 1 cm2 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, repro- ducible, 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 electro- chemical 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 capaci- tors. 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.},
	institution = {Chalmers University of Technology},
	type = {phdthesis},
	author = {Vyas, Agin},
	date = {2022-04-29},
	langid = {english},
}