Development of thermoelectric materials and micro-devices for cooling and power generation
| dc.availability.bitstream | embargoed | |
| dc.check.date | 2024-06-08 | |
| dc.contributor.advisor | Mahmood Razeeb, Kafil | en |
| dc.contributor.author | Lal, Swatchith | |
| dc.contributor.funder | Horizon 2020 | en |
| dc.date.accessioned | 2021-06-08T11:35:49Z | |
| dc.date.available | 2021-06-08T11:35:49Z | |
| dc.date.issued | 2020-12 | |
| dc.date.submitted | 2020-12 | |
| dc.description.abstract | Thermoelectric materials have been widely used for solid-state cooling (as thermoelectric cooler) and power generation (as thermoelectric generator) applications. Integration of thermoelectric thin-film materials into micro-device fabrication offers various advantages compared to bulk thermoelectric devices such as miniaturized size, high-density integration and substantial reduction of the material usage that helps in reducing the weight of the system. Thermoelectric coolers play a vital role in optoelectronic devices. Active photonic device (e.g. lasers) generate incredibly high heat flux levels (~10 kW/cm2) that must be efficiently removed to maintain their performance and reliability; furthermore, active photonic devices must be controlled with a precision of ±0.1 °C. Today’s photonic integrated circuits (PICs) employ macro thermoelectric coolers (TECs) that are inefficient in the thermal management of the device and cannot scale with the growing trends of miniaturisation and high-density integration. On the other hand, micro-thermoelectric coolers (µ-TECs) integrated directly on the laser or other photonic component can more efficiently perform the thermal management of the device. Similarly, these micro-thermoelectric devices can be applied to convert heat into usable electricity as a thermoelectric generator, which has a wide range of applications including wearable electronics and biomedical devices. These micro-thermoelectric generators (µ-TEGs) can convert the body heat to usable electrical energy which can, in turn, be used for powering various wearable vital health monitoring systems, particularly using the low-temperature gradients. This thesis deals with the development of high-performance room temperature thermoelectric materials using electrodeposition technique that offers cost-effectiveness, ease of process control and industrial batch production compatibility. Further, this work aims to integrate the developed materials in the micro-thermoelectric devices, both for cooling and power generation, particularly using available low-temperature gradients near room temperature regimes. As part of this work, p-type BiSbTe material has been developed using a pulse amperometry technique employing a suitable nitric acid bath, and the thermoelectric properties of the developed material are enhanced using additives, particularly sodium do-decyl sulfate surfactant. From the following investigations, it was observed that the overall power factor of the developed materials with the surfactant was 149% higher than the material with no surfactant added into the system due to the densification of the films. Later, this material is optimised using an annealing time-temperature profile to achieve better thermoelectric properties. The inclusion of the Te material layer in between the BiSbTe layers prevented the loss of Te during annealing and helped in maintaining the proper stoichiometry of the material. Using this annealing study, the charge carrier concentration and mobility of the materials are optimised for the higher performance, which led to an increase in the power factor of the material from 11 µW/mK2 to 225 µW/mK2, when annealed for the duration of 1 hr at 350 °C in the N2 atmosphere. As a part of the n-type material development, Cu doped BiTe and Cu doped Te have been developed, both exhibiting significantly improved thermoelectric properties for the electrodeposited materials. Both the materials showcased a crystal symmetry breakdown beyond a certain percentage of copper inclusion in the system, which has led to a significant enhancement of the thermoelectric properties of the material. Cu doped BiTe and Cu doped Te showed a power factor of 3.02 mW/mK2 and 5.60 mW/mK2 respectively, which are one of the best values reported so far. The developed p- and n-type materials are integrated in a silicon-based micro- thermoelectric device for both cooling and power generation applications. Two different approaches to device fabrication have been used. The first approach deals with the reduction of overall cost of the device fabrication, for which flip-chip bonding approach has been undertaken where p- and n-type materials are fabricated on different wafers, which reduced the overall lithographic processing. In the second approach, both p- and n-type materials are fabricated on a single wafer using multiple lithographic steps. This single wafer approach has various advantages such as minimized electrical contact resistances and improved thermal contact over the first method. The micro-devices developed using this method has been employed for both cooling and power generation applications and has been thoroughly investigated. The devices fabricated using flip-chip bonding generated an output voltage of 90 mV for a 10 K temperature gradient with an average electrical resistance of 0.87 Ω for individual thermoelectric leg pair. The average electrical resistance was dropped to 0.28 Ω for a device fabricated using a single wafer approach. An average cooling of 2 K was observed for the devices in cooling mode. The improved thermoelectric materials and optimized fabrication of micro-thermoelectric devices makes them a promising system for both cooling and power generation applications. | en |
| dc.description.status | Not peer reviewed | en |
| dc.description.version | Accepted Version | en |
| dc.format.mimetype | application/pdf | en |
| dc.identifier.citation | Lal, S. 2020. Development of thermoelectric materials and micro-devices for cooling and power generation. PhD Thesis, University College Cork. | en |
| dc.identifier.endpage | 184 | en |
| dc.identifier.uri | https://hdl.handle.net/10468/11453 | |
| dc.language.iso | en | en |
| dc.publisher | University College Cork | en |
| dc.relation.project | info:eu-repo/grantAgreement/EC/H2020::RIA/644453/EU/Thermally Integrated Smart Photonics Systems/TIPS | en |
| dc.relation.project | info:eu-repo/grantAgreement/EC/H2020::RIA/825114/EU/Smart Autonomous Multi Modal Sensors for Vital Signs Monitoring/SmartVista | en |
| dc.rights | © 2020, Swatchith Lal. | en |
| dc.rights.uri | https://creativecommons.org/licenses/by-nc-nd/4.0/ | en |
| dc.subject | Thermoelectric | en |
| dc.subject | Electrodeposition | en |
| dc.subject | Energy harvesting | en |
| dc.subject | Photonic cooling | en |
| dc.subject | Micro thermoelectric device | en |
| dc.title | Development of thermoelectric materials and micro-devices for cooling and power generation | en |
| dc.type | Doctoral thesis | en |
| dc.type.qualificationlevel | Doctoral | en |
| dc.type.qualificationname | PhD - Doctor of Philosophy | en |
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