Edward Siivola

Large external ΔT and cooling power densities in thin-film Bi2Te3-superlattice thermoelectric cooling devices

Experimental I-V-Tc-ΔT data of thin-film superlattice thermoelectric modules is used to determine the internal ΔT, cross-plane Seebeck coefficient, effective thermal interface resistance, device ZT, and Qmax. We demonstrate 55K of external cooling at 300K (Tcmin=244.8K), with an estimated heat pumping capacity of 128W∕cm2. The average ZT300 for the best superlattice devices is 0.75, compared to 0.66 for a bulk BixSb2−xTe3∕Bi2SexTe3−x device. Our model indicates a significantly higher internal ΔT occurs across the active thermoelectric element, which was verified using buried thermocouples.

Portable power sources using combustion of butane and thermoelectrics

RTI is currently developing cascade and segmented thermoelectric (TE) power modules to achieve a thermal-to-electric efficiency target of 20%. In this context, we have achieved significant power levels with advanced bulk SiGe TE modules developed individually. Power levels over 1 W/sub e/ per module - with 11 W/sub e/ demonstrated by using 10 modules - now make a new thermoelectrics-based man-portable power supply potentially very attractive. These new modules are able to operate at high temperatures (>700/spl deg/C) and are thereby able to effectively utilize the temperature from direct combustion of any fuel such as butane, propane, natural gas, diesel or other logistics fuels. Combining: (1) these high-temperature SiGe TE modules with (2) a combustor with (3) a lightweight heat exchanger could enable TE to address man-portable off-grid requirements for fueled power sources.

Measurement and analysis of power conversion efficiency in thin-film and segmented thermoelectric devices

A method for evaluating the power conversion efficiency, and hence ZT/sub M/, of thin-film superlattice, bulk single-stage, and segmented-bulk thermoelectric devices is discussed. The challenge in measuring performance of small-scale devices is the difficulty of explicitly measuring temperatures at TE material junctions. An indirect method, using limited thermocouple measurements and electrical voltage/current measurements, will be detailed in this presentation. A temperature gradient is established across the device, and the resulting open-circuit voltage produced is recorded. In the case of a segmented device, a system of equations and unknowns is formulated and solved numerically, taking into account the variation of bulk material properties with temperature. The results are the temperature gradients across each material leg, allowing for computation of the heat transferred, and thus conversion efficiency. A summary of exceptional results are outlined for a single stage thin-film device and a three-stage cascaded device.

High efficiency segmented bulk devices cascaded with high-performance superlattice cold-stage

Segmented bulk single-couple devices have been fabricated using SiGe, PbTe, and TAGS materials. Initial optimization studies have yielded power generation efficiencies in excess of 12%, with cold-side temperatures of /spl sim/175/spl deg/C and hot-side temperatures of /spl sim/700/spl deg/C. The goal is to cascade these devices with high-performance Bi/sub 2/Te/sub 3/-superlattice cold-stage operating between 25/spl deg/C to 175/spl deg/C. We will be discussing the trade space between segmented and cascaded assemblies as it relates to the thermal and electrical matching between the different layers and device complexity. It will be shown how layer matching affects overall device performance and how this knowledge can be used to determine the optimal design. We will also discuss the methodologies used to meet the various challenges of high temperature materials assembly including ohmic contacts, diffusion barriers, and CTE induced stresses. Measurement results of device performance will be provided to illustrate the consequences of the methodologies used. We will also include results from early integration of these 2-stage segmented devices to thin-film superlattice cold-stage device to yield three stage power devices.

Superlattice Thermoelectrics for Thermal Management of Electronics and Optoelectronics

Solid-state cooling technologies using advanced superlattice thermoelectric materials are likely to provide not only near-term solutions for the hot-spots but also scalable refrigeration solutions for the entire chip. We discuss our development efforts with the superlattice thermoelectric technology for advanced microprocessor thermal management. We also discuss the development of similar technologies for application in the thermal management of optoelectronic components. The performance of small footprint thermoelectric modules fabricated using the thin film superlattice materials are discussed. We have begun early reliability studies on the superlattice materials, devices, and modules and the early results are positive. Advanced reliability studies using full Mil-spec and Telecordia-like power cycling are being undertaken for full commercial implementation of such advanced thermoelectric components.© 2005 ASME

Development of wafer-scale cooling/heating thermoelectric arrays using thin-film superlattice devices

Thin-film superlattice thermoelectric material was used to fabricate 2-inch wafer scale thermoelectric module arrays. These arrays employ a promising thermoelectric device technology that exhibits a significant enhancement in the thermoelectric device figure of merit (ZT) at 300 K, cooling/heating power densities in excess of 100 Watts/cm/sup 2/, and response times significantly faster than bulk devices. To power and characterize these devices, we have developed a high-speed computer controlled multi-channel power supply with integrated real-time infrared imaging. This system allows creation of individual temperature control profiles, and exploits the rapid response time of the thin-film device. Using this system, we demonstrate high-speed operation and compare the response times of bulk and thin-film devices in the same format. Finally, applications of thin-film thermoelectric arrays are considered.