| 1. |
- Li, Qi, 1990, et al.
(författare)
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Finger Number and Device Performance: A Case Study of Reduced Graphene Oxide Microsupercapacitors
- 2021
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Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2
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Tidskriftsartikel (refereegranskat)abstract
- Microsupercapacitors (MSCs) are recognized as suitable energy storage devices for the internet of things (IoTs) applications. Herein is described the work conducted to assess the areal energy and power densities of MSCs with 2, 10, 20, and 40 interdigital finger electrodes on a fixed device footprint area (the finger interspacing is fixed at 40 μm, and the finger width and length are allowed to vary to fit the footprint area). The MSCs are based on reduced graphene oxide (rGO) materials and fabricated with a spin-coating and etch method. The performance evaluation indicates a strong dependency of areal capacitance and energy density on the number of fingers, and the maximum (impedance match) power density is also influenced to a relatively large extent, whereas the average power density is not sensitive to the configuration parameters in the present evaluation settings (scan rate 20–200 mV s−1 and current density of 100 μA cm−2). For the rGO-based devices, the equivalent distributed resistance may play an important role in determining the device resistance and power-related performance.
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| 2. |
- Li, Qi, 1990, et al.
(författare)
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Graphite paper / carbon nanotube composite: A potential supercapacitor electrode for powering microsystem technology
- 2017
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 922:1
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Konferensbidrag (refereegranskat)abstract
- This work describes fabrication of a flexible supercapacitor electrode. The fabrication starts with graphite paper (GP). Carbon nanotubes (CNTs) are then grown directly to the carbon surface by chemical vapor deposition (CVD), forming a heterogeneous structure of GP/CNT. The integration of CNT enhances capacitive performance while maintaining the flexibility of GP, thus making GP/CNT a promising supercapacitor electrode material for potentially powering microsystem technology.
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| 3. |
- Pamfil, Bogdan, et al.
(författare)
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Multi-Objective Design Optimization of Fractal-based Piezoelectric Energy Harvester
- 2021
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Ingår i: 2021 IEEE 20th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications, PowerMEMS 2021. - 9781665422185 ; , s. 6-9
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Konferensbidrag (refereegranskat)abstract
- This paper studies optimization solutions for a proof-of-concept design methodology for a fractal-based tree energy harvester with a stress distribution optimized structure. The focus is on obtaining a sufficiently high-power output and a high enough stress in the longitudinal branch direction by using Frequency Response Functions. The design methodology shows that using the MATLAB code with Sensitivity Analysis and Multi-objective Optimization in combination with elitist genetic algorithm enables an optimal design.
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| 4. |
- Rajendra Babu Kalai Arasi, Azega, 1995, et al.
(författare)
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Durable Activated Carbon Electrodes with a Green Binder
- 2022
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Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 259:2
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Tidskriftsartikel (refereegranskat)abstract
- Herein, the fabrication and electrochemical performance of thick (180−280 μm) activated carbon (AC) electrodes with carbonized lignin-derived carbon fiber (LCF) inclusions are reported. Efforts are taken in fabricating robust free-standing electrodes from an environmentally friendly binder, microfibrillated cellulose (MFC), considering the biologically hazardous nature of other commonly used binders like polytetrafluoroethylene (PTFE), n-methyl-2-pyrrolidone (NMP), and polyvinylidene fluoride (PVDF). Generally, electrodes composed of MFC binder are prone to cracking upon drying, especially with higher mass loadings, which leads to nonflexibility and poor device stability. The LCF inclusions into the AC electrode with MFC binders not only increase flexibility but also contribute to better conductivity in the electrodes. The LCFs act as an intermediate layer among AC particles and serve as conductive pathways, facilitating exposure of more active surfaces to the electrolyte. A thick electrode with high mass loading of 10 mg cm−2 is achieved. The results show that by incorporating 2 wt% LCF to the AC material, the best device with 5 mg cm−2 delivers a specific capacitance of 97 F g−1, while the specific capacitance of the reference AC device without LCF is 85 F g−1.
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| 5. |
- Smith, Anderson David, 1985, et al.
(författare)
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Carbon-Based Electrode Materials for Microsupercapacitors in Self-Powering Sensor Networks : Present and Future Development
- 2019
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 19:19
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Tidskriftsartikel (refereegranskat)abstract
- There is an urgent need to fulfill future energy demands for micro and nanoelectronics. This work outlines a number of important design features for carbon-based microsupercapacitors, which enhance both their performance and integration potential and are critical for complimentary metal oxide semiconductor (CMOS) compatibility. Based on these design features, we present CMOS-compatible, graphene-based microsupercapacitors that can be integrated at the back end of the line of the integrated circuit fabrication. Electrode materials and their interfaces play a crucial role for the device characteristics. As such, different carbon-based materials are discussed and the importance of careful design of current collector/electrode interfaces is emphasized. Electrode adhesion is an important factor to improve device performance and uniformity. Additionally, doping of the electrodes can greatly improve the energy density of the devices. As microsupercapacitors are engineered for targeted applications, device scaling is critically important, and we present the first steps toward general scaling trends. Last, we outline a potential future integration scheme for a complete microsystem on a chip, containing sensors, logic, power generation, power management, and power storage. Such a system would be self-powering.
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| 6. |
- Smith, Anderson David, 1985, et al.
(författare)
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Toward CMOS compatible wafer-scale fabrication of carbon-based microsupercapacitors for IoT
- 2018
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1052:1
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Konferensbidrag (refereegranskat)abstract
- This work presents a wafer-scale method of microsupercapacitor (MSC) fabrication. Deposition of the electrode precursor, i.e. graphene oxide, is accomplished through spin-coating which allows for potential application in CMOS compatible processes for future integrated on-chip energy storage systems. Our MSCs have an areal capacitance of 0.4 mF/cm2at 10 μA, which is a very promising result. Further, the MSC has good rate capability as its capacitance decreases by only 0.03 mF/cm2when the current increases to 50 μA. The MSCs have a maximum energy density of 0.04 μWh/cm2and a maximum power density as high as 96 μW/cm2. Additionally, the wafer-scale process demonstrates industrial viability.
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| 7. |
- Velasco, Andres, et al.
(författare)
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Investigation of vertical carbon nanosheet growth and its potential for microsupercapacitors
- 2021
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1837:1
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Konferensbidrag (refereegranskat)abstract
- One of the biggest applications that are coming with the Internet of Things (IoT) are miniaturized sensor networks that connect wirelessly to each other and the internet. Microsupercapacitors (MSCs) are ideal to power these devices, with large cyclability and lifetime. Porous carbons are the material of choice for these devices, but their morphology and manufacturing are far from optimized. Vertically oriented graphene MSCs have shown great promise due to their high specific surface areas and conductivity. In this work, the growth of vertically aligned carbon nanosheets (CNS) on 2-inch wafers has been studied, and it has been used as active material to manufacture MSC and transmission line model (TLM) wafers. The fabricated CNS MSC devices show a capacitance of 7.4 ?F (50.7 ?F/cm2, normalized to the area of the electrodes), a five-times increase from previous results obtained by the group.
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| 8. |
- Vyas, Agin, 1992, et al.
(författare)
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A micromachined coupled-cantilever for piezoelectric energy harvesters
- 2018
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Ingår i: Micromachines. - : MDPI AG. - 2072-666X. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a demonstration of the feasibility of fabricating micro-cantilever harvesters with extended stress distribution and enhanced bandwidth by exploiting an M-shaped two-degrees-of-freedom design. The measured mechanical response of the fabricated device displays the predicted dual resonance peak behavior with the fundamental peak at the intended frequency. This design has the features of high energy conversion efficiency in a miniaturized environment where the available vibrational energy varies in frequency. It makes such a design suitable for future large volume production of integrated self powered sensors nodes for the Internet-of-Things
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| 9. |
- Vyas, Agin, 1992, et al.
(författare)
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Alkyl-Amino Functionalized Reduced-Graphene-Oxide–heptadecan-9-amine-Based Spin-Coated Microsupercapacitors for On-Chip Low Power Electronics
- 2022
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Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 259:2
-
Tidskriftsartikel (refereegranskat)abstract
- With the miniaturization of microelectronics, integrated circuits can benefit from an on-chip solid-state power supply. Microsupercapacitors (MSCs), owing to their long lifetimes and complementary metal-oxide-semiconductor (CMOS) compatible fabrication, can be a potential on-chip energy storage unit. MSCs fabricated through spin coating graphene-oxide (GrO) often suffer from insufficient electrode thicknesses that lead to low energy densities. It, therefore, requires functionalizations for GrO that can improve the MSC electrode thickness and, thereby, the performance of the MSC. Thus, herein, the MSCs fabricated of alkyl-amino functionalized reduced-graphene-oxide–heptadecan-9-amine (rGO) are reported for enhanced electrode thickness, high capacitance, and lower series resistance compared with functionalized GrO-based MSCs (GO-MSCs). The functionalized rGO solves a significant issue of inadequate electrode thickness in wafer-scale MSC fabrication while achieving higher energy densities in fewer spin coatings. The rGO-MSC displays an areal capacitance of 108 μF cm−2 compared with 24 μF cm−2 for the GO-MSC while also demonstrating more than twice its power density in an integration compatible ionic liquid electrolyte 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI).
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| 10. |
- Vyas, Agin, 1992, et al.
(författare)
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Comparison of Thermally Grown Carbon Nanofiber-Based and Reduced Graphene Oxide-Based CMOS-Compatible Microsupercapacitors
- 2021
-
Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2
-
Tidskriftsartikel (refereegranskat)abstract
- Microsupercapacitors as miniature energy storage devices require complementary metal-oxide-semiconductor (CMOS) compatible techniques for electrode deposition to be integrated in wireless sensor network sensor systems. Among several processing techniques, chemical vapor deposition (CVD) and spin coating, present in CMOS manufacturing facilities, are the two most viable processes for electrode growth and deposition, respectively. To make an argument for choosing either of these techniques to fabricate MSCs utilizable for an on-chip power supply, we need a comparative assessment of their electrochemical performance. Herein, the evaluation of MSCs with CVD-grown carbon nanofiber (CNF)-based and spin-coated reduced graphene oxide (rGO)-based electrodes is reported. The devices are compared for their capacitance, energy and power density, charge retention, characteristic frequencies, and ease of fabrication over a large sweep of scan rates, current densities, and frequencies. The rGO-based MSCs demonstrate 112 mu F cm(-2) at 100 mV s(-1) and a power density of 12.8 mW cm(-2). The CNF-based MSCs show 269.7 mu F cm(-2) and 30.8 mW cm(-2). CVD-grown CNF outperforms spin-coated rGO in capacitive storage at low frequencies, whereas the latter is better in terms of charge retention and high-frequency capacitance response.
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| 11. |
- Vyas, Agin, 1992, et al.
(författare)
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Enhanced Electrode Deposition for On-Chip Integrated Micro-Supercapacitors by Controlled Surface Roughening
- 2020
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:10, s. 5219-5228
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Tidskriftsartikel (refereegranskat)abstract
- On-chip micro-supercapacitors (MSCs), integrated with energy harvesters, hold substantial promise for developing self-powered wireless sensor systems. However, MSCs have conventionally been manufactured through techniques incompatible with semiconductor fabrication technology, the most significant bottleneck being the electrode deposition technique. Utilization of spin-coating for electrode deposition has shown potential to deliver several complementary metal-oxide-semiconductor (CMOS)-compatible MSCs on a silicon substrate. Yet, their limited electrochemical performance and yield over the substrate have remained challenges obstructing their subsequent integration. We report a facile surface roughening technique for improving the wafer yield and the electrochemical performance of CMOS-compatible MSCs, specifically for reduced graphene oxide as an electrode material. A 4 nm iron layer is deposited and annealed on the wafer substrate to increase the roughness of the surface. In comparison to standard nonroughened MSCs, the increase in surface roughness leads to a 78% increased electrode thickness, 21% improvement in mass retention, 57% improvement in the uniformity of the spin-coated electrodes, and a high yield of 87% working devices on a 2″ silicon substrate. Furthermore, these improvements directly translate to higher capacitive performance with enhanced rate capability, energy, and power density. This technique brings us one step closer to fully integrable CMOS-compatible MSCs in self-powered systems for on-chip wireless sensor electronics. ©
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| 12. |
- Vyas, Agin, 1992, et al.
(författare)
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Impact of electrode geometry and thickness on planar on-chip microsupercapacitors
- 2020
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 10:52, s. 31435-31441
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Tidskriftsartikel (refereegranskat)abstract
- We report an assessment of the influence of both finger geometry and vertically-oriented carbon nanofiber lengths in planar micro-supercapacitors. Increasing the finger number leads to an up-scaling in areal power densities, which increases with scan rate. Growing the nanofibers longer, however, does not lead to a proportional growth in capacitance, proposedly related to limited ion penetration of the electrode.
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| 13. |
- Vyas, Agin, 1992, et al.
(författare)
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Investigation of palladium current collectors for vertical graphene-based microsupercapacitors
- 2019
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1319:1
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Konferensbidrag (refereegranskat)abstract
- As microsystems are reduced in size and become integrated in the Internet of Things (IoT), they require an adequate power supply which can be integrated at the same size scale. Microsupercapacitors (MSCs), if coupled with on-chip harvesters, can offer solutions for a self-sustaining, on-chip power supply. However, the implementation of reliable MSC wafer-scale production compatible with CMOS technology remains a challenge. Palladium (Pd) is known as a CMOS compatible metal and, in this paper, we investigate the use of Pd as a contact material for vertical graphene (VG) electrodes in wafer-scale MSC fabrication. We show that a Ti diffusion barrier is required to prevent short-circuiting for the successful employment of Pd contacts. The fabricated MSCs demonstrate a capacitance of 1.3 μF/cm2 with an energy density of 0.42 μJ/cm2. Thus, utilization of a Ti diffusion barrier with a CMOS compatible Pd metal electrode is a step towards integrating MSCs in semiconductor microsystems.
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| 14. |
- Vyas, Agin, 1992
(författare)
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On-chip electrochemical capacitors and piezoelectric energy harvesters for self-powering sensor nodes
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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 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.
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| 15. |
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| 16. |
- Vyas, Agin, 1992, et al.
(författare)
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Spin-Coated Heterogenous Stacked Electrodes for Performance Enhancement in CMOS-Compatible On-Chip Microsupercapacitors
- 2022
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:4, s. 4221-4231
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Tidskriftsartikel (refereegranskat)abstract
- Integration of microsupercapacitors (MSCs) with on-chip sensors and actuators with nanoenergy harvesters can improve the lifetime of wireless sensor nodes in an Internet-of-Things (IoT) architecture. However, to be easy to integrate with such harvester technology, MSCs should be fabricated through a complementary-metal-oxide-semiconductor (CMOS) compatible technology, ubiquitous in electrode choice with the capability of heterogeneous stacking of electrodes for modulation in properties driven by application requirements. In this article, we address both these issues through fabrication of multielectrode modular, high energy density microsupercapacitors (MSC) containing reduced graphene oxide (GO), GO-heptadecane-9-amine (GO-HD9A), rGO-octadecylamine (rGO-ODA), and rGO-heptadecane-9-amine (rGO-HD9A) that stack through a scalable, CMOS compatible, high-wafer-yield spin-coating process. Furthermore, we compare the performance of the stack with individual electrode MSCs fabricated through the same process. The individual electrodes, in the presence of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI), demonstrate a capacitance of 38, 30, 36, and 105 μF/cm^2 at 20 mV/s^1 whereas the fabricated stack of electrodes demonstrates a high capacitance of 280 μF/cm^2 at 20 mV/s^1 while retaining and enhancing the material-dependent capacitance, charge retention, and power density.
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| 17. |
- Vyas, Agin, 1992, et al.
(författare)
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Surface Roughening with Iron Nanoparticles for Promoted Adhesion of Spin Coated Microsupercapacitor Electrodes
- 2019
-
Ingår i: MRS Advances. - : Springer Science and Business Media LLC. - 2059-8521. ; 4:23, s. 1335-1340
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Konferensbidrag (refereegranskat)abstract
- Microsupercapacitors (MSCs) are miniaturized energy storage devices that can be integrated in an on-chip platform as a component of a power supply for Internet of things' sensors. Integration of these on-chip MSCs require them to be fabricated through CMOS compatible fabrication techniques such as spin coating. One of the biggest challenges in spin coated MSCs is the poor surface adhesion. In this work, we present a CMOS compatible electrode deposition process with enhanced adhesion and retention for reduced graphene oxide (rGO) using spin coating. In order to improve the adhesion and surface uniformity of the deposited electrode material, the surface of Si/SiO 2 wafers was subjected to roughening through Fe nanoparticle formation. A 4 nm thick Fe layer deposition substantially magnified the average mean surface roughness of the substrates. In comparison with substrates without the Fe deposition, the treated ones have more than 300% improvement in surface coverage and rGO mass retention after sonication testing. These results suggest that the surface roughening has a positive influence on electrode deposition via a spin-coating method.
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| 18. |
- Vyas, Agin, 1992
(författare)
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Towards an on-chip power supply: Integration of micro energy harvesting and storage techniques for wireless sensor networks
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The lifetime of a power supply in a sensor node of a wireless sensor network is the decisive factor in the longevity of the system. Traditional Li-ion batteries cannot fulfill the demands of sensor networks that require a long operational duration. Thus, we require a solution that produces its own electricity from its surrounding and stores it for future utility. Moreover, as the sensor node architecture is developed on complimentary metal-oxide-semiconductor technology (CMOS), the manufacture of the power supply must be compatible with it. In this thesis, we shall describe the components of an on-chip lifetime power supply that can harvest the vibrational mechanical energy through piezoelectric microcantilevers and store it in a reduced graphene oxide (rGO) based microsupercapacitor, and that is fabricated through CMOS compatible techniques. Our piezoelectric microcantilevers confirm the feasibility of fabricating micro electro- mechanical-systems (MEMS) size two-degree-of-freedom systems which can solve the major issue of small bandwidth of piezoelectric micro-energy harvesters. These devices use a cut-out trapezoidal cantilever beam to enhance the stress on the cantilever’s free end while reducing the gap remarkably between its first two eigenfrequencies in 400 - 500 Hz and 1 - 2 kHz range. The energy from the M-shaped harvesters will be stored in rGO based microsupercapacitors. These microsupercapacitors are manufactured through a fully CMOS compatible, reproducible, and reliable micromachining processes. Furthermore, we have also demonstrated an improvement in their electrochemical performance and yield of fabrication through surface roughening from iron nanoparticles. We have also examined the possibility of integrating these devices into a power management unit to fully realize a lifetime power supply for wireless sensor networks.
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| 19. |
- Vyas, Agin, 1992, et al.
(författare)
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Towards Integrated Flexible Energy Harvester and Supercapacitor for Self-powered Wearable Sensors
- 2020
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Ingår i: 2019 19TH INTERNATIONAL CONFERENCE ON MICRO AND NANOTECHNOLOGY FOR POWER GENERATION AND ENERGY CONVERSION APPLICATIONS (POWERMEMS).
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Konferensbidrag (refereegranskat)abstract
- We present the first results of a flexible energy harvester and a foldable supercapacitor to power wearable and flexible sensors. The flexible energy harvester is fabricated by using 38 mu m piezoelectric polyvinylidene difluoride (PVDF) sandwiched between carbon electrodes. Both the design and process excel in simplicity and cost-effectiveness. The flexible harvester demonstrates a power output of 2.6 mu W cm(-3) at a resonant frequency of 50 Hz with a 3dB bandwidth of about 11 Hz, which is higher than devices previously reported and similar to a commercial PZT harvester film of same size. A flexible energy storage supercapacitor (GP-SC) was fabricated using a graphite/VACNTs (vertically aligned carbon nanotubes) material as electrodes. A prototype GP-SCs has an areal capacitance of about 1.2 mF cm(-2). Finally, an integrated scheme is proposed for future work.
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