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

Advances in the microelectronics industry have made it possible to fabricate a multitude of microdevices, such as microprocessors, microsensors, microcontrollers, and microinstruments. These electronic microdevices have significantly reduced power requirements but at the same time require more attention in terms of integrated thermal management and power management and distribution. Micro thermoelectric converters are considered a promising technology approach for meeting some of these new requirements. Thermoelectric microdevices can convert rejected or waste heat into usable electric power, at moderate (200-500K) temperatures and often with small temperature differentials. They can also be easily integrated and provide effective cooling for devices specific in optoelectronics, such as mid-lR lasers, densc-wavclength-di vision-multiplexing (DWDM) components and charge-coupled-device (CCD) detectors. 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 (Bi2Te3/Bi2.xSbxTe3). 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 μm 1700 μm In cooling mode, we evaluated device performance using an IR camera and differential thermal imaging software. We were able to detect a maximum cooling effect of about 2K. In power generation mode, a 75 watt light source was illuminated directly above the device while the current generated was measured. A detailed step-by-step overview of the fabrication process will be given, as well as specifics in testing setups, results and future directions.