Two-dimensional thermoelectric transport for electronics cooling
Nimmagadda, Lakshmi Amulya
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https://hdl.handle.net/2142/127338
Description
Title
Two-dimensional thermoelectric transport for electronics cooling
Author(s)
Nimmagadda, Lakshmi Amulya
Issue Date
2024-11-07
Director of Research (if dissertation) or Advisor (if thesis)
Sinha, Sanjv
Doctoral Committee Chair(s)
Sinha, Sanjv
Committee Member(s)
Eckstein, James
Smith, Kyle
Ertekin, Elif
Department of Study
Mechanical Sci & Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Thermoelectric transport
electronics cooling
two-dimensional materials
Abstract
Thermoelectric materials are significant due to their widespread applications in power generation and refrigeration across various industries such as consumer electronics, communications, medical experiments, automobiles, and aerospace. Despite the advantages of compactness, absence of moving parts and fast response times, thermoelectric devices are limited in their performance due to their material properties. This dissertation investigates thermoelectric materials both from an applied and a fundamental perspective. First, in the context of emerging thermal management in heterogeneous packaging, we explore on-chip Peltier cooling over short durations. Using a thermoelectric transport model of a unipolar device, we identify the requirements in terms of thermoelectric properties to achieve net cooling under a heat load when the Peltier heat flows parallel to the Fourier heat. The main requirement is a high thermoelectric power factor (S2σ), which is the combination of the Seebeck coefficient (S) and electrical conductivity (σ). Such high power factors are not realizable in bulk materials but may exist in more exotic materials, specifically two-dimensional materials and/or topological insulators. We report measurements of power factor on two such materials, single-layer MoS2, a two-dimensional material and few quint-layer Bi2Se3, a three-dimensional topological insulator. The presence of localized or trap states in single layer MoS2 affects thermoelectric transport. With the help of theory, we explain the influence of localized states on the thermoelectric power factor of single-layer MoS2. The experimental results show that an improvement in S2σ of single-layer MoS2 is possible by enabling transport through extended states counteracting the effect of trap states. This is achieved by having using hBN/MoS2 on Si/SiO2 to prevent charge trapping. The charge transport in Bi2Se3 is understood using the results from the measurement of S and σ. We confirm the presence of a two-dimensional electron gas (2DEG) in addition to topological surface states (TSSs) as observed in other experimental studies on thin film Bi2Se3. Analyzing the data, we model the transport to enable a relative quantification of the Seebeck coefficient associated with each transport channel. We observe that highly conducting surface states improve S2σ of 10nm thick Bi2Se3 when compared to its bulk value at room temperature.
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