Thermoelectric Cooling

In this chapter, design and analysis study of thermoelectric cooling systems are described. Thermoelectric (TE) cooling technology has many advantages over the conventional vapor-compression cooling systems. These include: they are more compacted devices with less maintenance necessities, have lower levels of vibration and noise, and have a more precise control over the temperature. These advantages have encouraged the development of new applications in the market. It is likely to use TE modules for cooling the indoor air and hence compete with conventional air-conditioning systems. These systems can include both cooling and heating of the conditioned space. In order to improve the performance of the TE cooling systems, the hot side of the TE should be directly connected to efficient heat exchangers for dissipation of the excessive heat. Finally, TE cooling systems can be supplied directly by photovoltaic to produce the required power to run these cooling systems

Computational Thermoelectricity Applied to Cooling Devices

This chapter presents a numerical formulation within the finite element method in order to computationally simulate thermoelectric devices. For this purpose, a theoretical formulation based on nonequilibrium thermodynamics with historical notes is previously outlined. Then, a brief description of the finite element is reported to express the thermodynamics governing equations in an amenable form to be numerically discretized. Finally, several applications of cooling thermoelectrics are performed to highlight the benefits of the finite element method. In particular, a commercial thermoelectric device is simulated and several variables such as extracted heat, voltage drop, and temperature distributions inside the thermoelements are represented for different operating conditions. In conclusion, the present numerical tool could be used as a virtual laboratory for the design and optimization of Peltier cells

Design of a thermoelectric generator with fast transient respose

Thermoelectric modules are currently used both in Peltier cooling and in Seebeck mode for electricity generation. The developments experienced in both cases depend essentially on two factors: the thermoelectric properties of the materials that form these elements (mainly semiconductors), and the external structure of the semiconductors. Figure of Merit Z is currently the best way of measuring the efficiency of semiconductors, as it relates to the intrinsic parameters of the semiconductor: Seebeck coefficient, thermal resistance, and thermal conductivity. When it comes to evaluating the complete structure, the Coefficient of Performance (COP) is used, relating the electrical power to the thermal power of the module. This paper develops a Thermoelectric Generator (TEG) structure which allows minimising the response time of the thermoelectric device, obtaining short working cycles and, therefore, a higher working frequency.Preprin

HOTSPOT REMEDIATION USING GERMANIUM SELF COOLING TECHNOLOGY

Localized thermoelectric "self cooling" in semiconductor materials is among the most promising approaches for the remediation of on-chip hot spots resulting from the shrinking feature sizes and faster switching speeds of nanoelectronic components. Self cooling in a germanium chip is investigated, using 3-dimensional, thermal-electric, coupled numerical simulations, for a range of systems and geometric parameters. The results suggest that localized cooling, associated with the introduction of an electric current on the back surface of a germanium chip, can effectively reduce the hot spot temperature rise on the active side of the chip. It was found that self cooling in a 100µm thick chip could provide between 3.9ºC and 4.5ºC hotspot temperature reduction. When using a germanium layer above an electrically insulated silicon layer, self-cooling was found to yield an additional 1ºC to 2º C temperature reduction. A streamlined computational tool is developed to facilitate the identification of optimal cooling parameters

On-Chip Thermoelectric Cooling of Semiconductor Hot Spot

The Moore's Law progression in semiconductor technology, including shrinking feature size, increasing transistor density, and faster circuit speeds, is leading to increasing total power dissipations and heat fluxes on silicon chip. Moreover, in recent years, increasing performance has resulted in greater non-uniformity of on-chip power dissipation, creating microscale hot spots that can significantly degrade the processor performance and reliability. Application of conventional thermal packaging technology, developed to provide uniform chip cooling, to such chip designs results in lower allowable chip power dissipation or overcooling of large areas of the chip. Consequently, novel thermoelectric cooler (TEC) has been proposed recently for on-chip hot spot cooling because of its unique ability to selectively cool down the localized microscale hot spot. In this dissertation the potential application of thermoelectric coolers to suppress on-chip hotspots is explored using analytical modeling, numerical simulation, and experimental techniques. Single-crystal silicon is proposed as a potential thermoelectric material due to its high Seebeck coefficient and its thermoelectric cooling performance is investigated using device-level analytical modeling. Integrated on silicon chip as an integral, on-chip thermoelectric cooler, silicon microcooler can effectively reduce the hotspot temperature and its effectiveness is investigated using analytical modeling and numerical simulation, and found to be dependent of doping concentration in silicon, electric contact resistance, hotspot size, hotspot heat flux, die thickness and microcooler size. The other novel on-chip hotspot cooling solution developed in this dissertation is to use a mini-contact enhanced TEC, where the mini-contact pad connects the silicon chip and the TEC to concentrate the thermoelectric cooling power onto a spot of top surface of the silicon chip and therefore significantly improve the hotspot cooling performance. Numerical simulation shows hotspot cooling is determined by thermal contact resistance, thermoelectric element thickness, chip thickness, etc. Package-level experiment demonstrates that spot cooling performance of such mini-contact enhanced TEC can be improved by about 100%

DESIGN OF A NOVEL THERMO-ELECTRIC COOLING DEVICE CAPABLE OF ACHIEVING CRYOGENIC TEMPERATURES FOR DENTAL PULP TESTING

Dental pulp testing is a diagnostic test in endodontics to test whether the dental pulp is dead or alive. Thermal tests (cold and hot) and electrical pulp testing techniques are two of the most common pulp sensibility tests currently being used. Although cold tests have shown more promising results in comparison to other techniques, the current methods used for cold testing have safety concerns as they involve direct application of the cold agent to the tooth. This study proposed a thermoelectric cooling based dental pulp testing device capable of achieving cryogenic temperatures and varying this temperature below 0℃ up to -60℃. This device is safe in operation and provides availability for on-site application due to its portability and stand-alone features. Thermoelectric cooling is based on the Peltier effect, which allows a temperature difference across a thermoelectric module and results in one side of the module becoming cold while the other side becomes hot. The challenge for such devices based on the Peltier effect is that the heat on the hot side of the module needs to be dissipated so that it is not too hot to burn the patient’s skin. This study explored the application of the phase change cooling technique in the form of heat pipes and vapor chambers to address this challenge. Finally, a thermoelectric cooling system capable of achieving -60℃ at the probe for pulp sensibility testing was proposed through modeling and simulation in Comsol Multiphysics software and experimentally validated using off-the-shelf hardware

Miniature Thermoelectric Coolers for On-Chip Hot Spots

Following Moore's Law, semiconductor transistor density has doubled roughly every 18 months to alleviate increasing IC performance demands. Growing microprocessor complexity and performance, coupled with the functional integration of logic and memory components in chip architecture, have led to highly non-uniform on-chip power distribution. The resulting localized high heat flux "hot spots" are becoming a major difficulty due to their propensity for degrading microprocessor performance and for significantly reducing chip reliability. Most conventional cooling techniques provide uniform cooling to the device and do not focus much attention on the hot spots themselves. Therefore, other innovative and novel thermal management techniques must be explored to aggressively and selectively combat the deleterious effects of on-chip hot spots. This thesis explores two previously proposed thermal management techniques utilizing thermoelectrics to cool on-chip hot spots: the silicon microcooler with an integrated SiGe superlattice layer and the mini-contact enhanced conventional thermoelectric cooler (TEC)

The Space Technology 8 Mission

The Space Technology 8 (ST8) mission is the latest in NASA’s New Millennium Program technology demonstration missions. ST8 includes a spacecraft bus built by industry, flying four new technology payloads in low- Earth orbit. This paper will describe each payload, along with a brief description of the mission and spacecraft. The payloads include a miniature loop heat pipe intended to save mass and power on future small satellites, designed and built by NASA’s Goddard Space Flight Center; a lightweight, 35g/m linear mass, 40-m deployable boom intended as a future solar sail mast built by ATK Space Systems; a deployable, lightweight Ultraflex solar array producing 175W/kg, also built by ATK Space Systems; and a high-speed, parallel-processing computer system built of state-of-the-art COTS processors, demonstrating SEU tolerance without the need for radiation-hardened electronics, and 100M operations per second per Watt processing throughput density

On-Chip Thermoelectric Hotspot Cooling

Increased power density and non-uniform heat dissipation present a thermal management challenge in modern electronic devices. The non-homogeneous heating in chips results in areas of elevated temperature, which even if small and localized, limit overall device performance and reliability. In power electronics, hotspot heat fluxes can be in excess of 1kW/cm2. Although novel package-level and chip-level cooling systems capable of removing the large amounts of dissipated heat are under development, such “global” cooling systems typically reduce the chip temperature uniformly, leaving the temperature non-uniformity unaddressed. Thus, advanced hotspot cooling techniques, which provide localized cooling to areas of elevated heat flux, are required to supplement the new “global” cooling systems and unlock the full potential of cutting-edge power devices. Thermoelectric coolers have previously been demonstrated as an effective method of producing on-demand, localized cooling for semiconductor photonic and logic devices. The growing need for the removal of localized hotspots has turned renewed attention to on-chip thermoelectric cooling, seeking to raise the maximum allowable heat flux of thermoelectrically-cooled semiconductor device hotspots. This dissertation focused on the numerical and empirical determination of the operational characteristics and performance limits of two specific thermoelectric methods for high heat flux hotspot cooling: monolithic thermoelectric hotspot cooling and micro-contact enhanced thermoelectric hotspot cooling. The monolithic cooling configuration uses the underlying electronic substrate as the thermoelectric material, eliminating the need for a discrete cooler and its associated thermal interface resistance. Micro-contact enhanced cooling uses a contact structure to concentrate the cooling produced by the thermoelectric module, enabling the direct removal of kW/cm2 level heat fluxes from on-chip hotspots. To facilitate empirical validation of on-chip thermoelectric coolers and characterization of advanced thin film thermoelectric coolers, it was found necessary to develop a novel laser heating system, using a high power laser and short-focal length optics. The design and use of this illumination system, capable of creating kW/cm2-level, mm-sized hotspots, will also be described