The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

Advanced Thermoelectric Design: From Materials and Structures to Devices

The limitation of hot spot cooling in microchips represents an important hurdle for the electronics industry to overcome with coolers yet to exceed the efficiencies required. Nanotechnology-enabled heat sinks that can be magnetophoretically formed onto the hot spots within a microfluidic environment are presented. CrO2 nanoparticles, which are dynamically chained and docked onto the hot spots, establish tuneable high-aspect-ratio nanofins for the heat exchange between these hot spots and the liquid coolant. These nanofins can also be grown and released on demand, absorbing and releasing the heat from the hot spots into the microfluidic system. It is shown that both high aspect ratio and flexibility of the fins have a dramatic effect on increasing the heat sinking efficiency. The system has the potential to offer a practical cooling solution for future electronics.

Dynamic nanofin heat sinks

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Nanostructured thermoelectric materials: current research and future challenge

We study the photoresponse of single-layer MoS(2) field-effect transistors by scanning photocurrent microscopy. We find that, unlike in many other semiconductors, the photocurrent generation in single-layer MoS(2) is dominated by the photothermoelectric effect and not by the separation of photoexcited electron-hole pairs across the Schottky barriers at the MoS(2)/electrode interfaces. We observe a large value for the Seebeck coefficient for single-layer MoS(2) that by an external electric field can be tuned between -4 × 10(2) and -1 × 10(5) μV K(-1). This large and tunable Seebeck coefficient of the single-layer MoS(2) paves the way to new applications of this material such as on-chip thermopower generation and waste thermal energy harvesting.

Large and Tunable Photothermoelectric Effect in Single-Layer MoS2

We study the photoresponse of single-layer MoS2 field- effect transistors by scanning photocurrent microscopy. We find that, unlike in many other semiconductors, the photocurrent generation in single-layer MoS2 is dominated by the photothermoelectric effect and not by the separation of photoexcited electron−hole pairs across the Schottky barriers at the MoS2/electrode interfaces. We observe a large value for the Seebeck coefficient for single-layer MoS2 that by an external electric field can be tuned between −4 × 10 2 and −1 × 10 5 μ VK −1 . This large and tunable Seebeck coefficient of the single-layer MoS2 paves the way to new applications of this material such as on- chip thermopower generation and waste thermal energy harvesting.

Large and Tunable Photothermoelectric Effect in Single-Layer MoS 2

There is a significant need for site-specific and on-demand cooling in electronic, optoelectronic and bioanalytical devices, where cooling is currently achieved by the use of bulky and/or over-designed system-level solutions. Thermoelectric devices can address these limitations while also enabling energy-efficient solutions, and significant progress has been made in the development of nanostructured thermoelectric materials with enhanced figures-of-merit. However, fully functional practical thermoelectric coolers have not been made from these nanomaterials due to the enormous difficulties in integrating nanoscale materials into microscale devices and packaged macroscale systems. Here, we show the integration of thermoelectric coolers fabricated from nanostructured Bi2Te3-based thin-film superlattices into state-of-the-art electronic packages. We report cooling of as much as 15 degrees C at the targeted region on a silicon chip with a high ( approximately 1,300 W cm-2) heat flux. This is the first demonstration of viable chip-scale refrigeration technology and has the potential to enable a wide range of currently thermally limited applications.

On-chip cooling by superlattice-based thin-film thermoelectrics

A method of forming a thermoelectric device may include providing a substrate having a surface, and thermally coupling a thermoelectric p-n couple to a first portion of the surface of a substrate. Moreover, the thermoelectric p-n couple may include a p-type thermoelectric element and an n-type thermoelectric element. In addition, a thermally conductive field layer may be formed on a second portion of the surface of the substrate adjacent the first portion of the surface of the substrate. Related structures are also discussed.

Methods of Forming Embedded Thermoelectric Coolers With Adjacent Thermally Conductive Fields and Related Structures

A method of forming a thermoelectric device may include forming a pattern of conductive traces, and forming an electrically insulating matrix between the conductive traces of the pattern of conductive traces. In addition, a plurality of thermoelectric elements may be electrically and mechanically coupled to the pattern of conductive traces so that each conductive trace of the pattern of conductive traces has one of the plurality of thermoelectric elements thereon. In addition, the plurality of thermoelectric elements may be free of the electrically insulating matrix. Related methods and structures are also discussed.

Methods of forming thermoelectric devices including electrically insulating matrixes between conductive traces and related structures

An electronic assembly may include a packaging substrate, an integrated circuit (IC) semiconductor chip, a plurality of metal interconnection structures, and a thermoelectric heat pump. The integrated circuit (IC) semiconductor chip may have an active side including input/output pads thereon and a back side opposite the active side, and the IC semiconductor chip may be arranged with the active side facing the first surface of the packaging substrate. The plurality of metal interconnection structures may be between the active side of the IC semiconductor chip and the first surface of the packaging substrate, and the plurality of metal interconnection structures may provide mechanical connection between the active side of the IC semiconductor chip and the first surface of the packaging substrate. The thermoelectric heat pump may be coupled to the packaging substrate with the thermoelectric heat pump being configured to actively pump heat between the IC semiconductor chip and the packaging substrate. Related methods and structures are also discussed.

David A. Koester

Papers

On-chip cooling by superlattice-based thin-film thermoelectrics

Methods of Forming Embedded Thermoelectric Coolers With Adjacent Thermally Conductive Fields and Related Structures

Methods of forming thermoelectric devices including electrically insulating matrixes between conductive traces and related structures

Electronic Assemblies Providing Active Side Heat Pumping and Related Methods and Structures

Electronic assemblies providing active side heat pumping