Chen-Kuo Huang

Thermoelectric microdevice fabrication process and evaluation at the Jet Propulsion Laboratory (JPL)

In the Materials and Device Technology Group at JPL, we have developed a unique fabrication method for a thermoelectric microdevice that utilizes standard integrated circuit techniques in combination with electrochemical deposition of compound semiconductors (Bi/sub 2/Te/sub 3//Bi/sub 2-x/Sb/sub x/Te/sub 3/). Our fabrication process is innovative in the sense that we are able to electrochemically micro mold different thermoelectric elements, with the flexibility of adjusting geometry, materials composition or batch scalability. Successive layers of photoresist were patterned and electrochemically filled with compound semiconductor materials or metal interconnects (Au or Ni). A thermoelectric microdevice was built on either glass or an oxidized silicon substrate containing 63 couples (63 n-legs/63 p-legs) at approximately 20 microns in structure height and with a device area close to 1700 /spl mu/m x 1700 /spl mu/m. In cooling mode, we evaluated device performance using an IR camera and differential thermal imaging software.

Development of advanced lithium-ion rechargeable cells with improved low temperature performance

Due to future plans to explore Mars and the outer planets, NASA has interest in developing lithium-ion rechargeable batteries that are capable of operating at low temperatures. To address these problems, we have initiated research focused upon the development of advanced electrolyte systems for lithium-ion cells with improved low temperature performance. Promising electrolyte solutions were selected based on conductivity and stability considerations and incorporated into C/LiCoO/sub 2/ cells for evaluation. The discharge capacity and rate capability as a function of temperature were evaluated in two types of lithium-ion cells, consisting of graphite-based systems with EC-based electrolytes and coke-based systems with PC-based electrolytes. Some of the experimental lithium-ion cells fabricated with these electrolytes were found to be capable of operating at temperatures as low as -30/spl deg/C (both charging and discharging at -30/spl deg/C) and provide more than 55% of the room temperature capacity. Cycle life testing of the these cells at -20/spl deg/C and at room temperature is in progress. Some of the cells have completed more than 500 cycles to date (100% DOD).

Electronic and thermoelectric properties of Ce3Te4 and La3Te4 computed with density functional theory with on-site Coulomb interaction correction

The electronic properties and Seebeck coefficients of Ce3Te4 and La3Te4 are computed using Density Functional Theory with on-site Coulomb interaction correction. We found that the Seebeck coefficients of Ce3Te4 and La3Te4 are almost equal at temperatures larger than the Curie temperature of Ce3Te4, and in good agreement with the measurements reported by May et al. [Phys. Rev. B 86, 035135 (2012)]. At temperatures below the Curie temperature, the Seebeck coefficient of Ce3Te4 increases due to the ferromagnetic ordering, which leads the f-electron of Ce to contribute to the Seebeck coefficient in the relevant range of electron concentration.

Development of New High Temperature Power Generating Couples for the Advanced Thermoelectric Converter (ATEC)

Radioisotope Thermoelectric Generators (RTGs) have served as a reliable source of space power for decades, enabling robotic spacecraft to explore regions of the Solar System where photovoltaic systems are impractical. The increased power requirements for future missions, combined with the reduced availability of radioisotope fuel, has prompted the development of a higher specific power, higher efficiency converter system employing thermocouples with advanced thermoelectric materials. The challenges in incorporating these advanced materials into power generating thermocouples suitable for operation in a space-rated RTG are discussed herein.

Electrochemical Deposition of (Bi,Sb) 2 Te 3 for Thermoelectric Microdevices

The experimental techniques developed, as well as the transport properties of some of the films and filled templates, will be presented.

Comparison of Carbon and Metal Oxide Anode Materials for Rechargeable Li-Ion Cells

The state of the art (SOA) Li-ion cells utilize carbon anodes. However, to improve specific energy, energy density, and safety of cells using carbon anodes, alternative anodes must be developed. Recently, Fuji Film Inc. has suggested the use of tin oxide based anodes in Li-ion cells. It is believed mat cells containing tin oxide based anodes have the potential to meet the need for NASAs future missions. As a result, we conducted an analysis to compare the performance of cells containing carbon anodes and cells containing tin oxide anodes. The comparison between these cells involved the following: 1) reaction mechanisms between Li and carbon and reaction mechanisms between Li and tin oxide, 2) half-cell and full-cell performance characteristics, 3) interactions between the anode materials and electrolyte types and compositions, and 4) the optimization of binder composition.