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Sub 100 nanosecond operation of thermoelectric microcoolers
Keywords: thermoelectrics, high-speed, thermoreflectance imaging
Thermoelectrics have received considerable interest over the past decade for their promising capabilities in power generation, energy conversion and on-demand cooling technologies. For the latter, miniaturised and integrable thin-film coolers are of particular interest as a potential means to address on-chip hot spots in microprocessors and other electronic ICs. Given the highly dynamic workload in these devices, the need arises for a thorough assessment of the transient response and performance of thermoelectric microcoolers. A limited amount of prior work is available on Peltier cooling in pulsed operation. However, the majority of these studies mainly focus on theoretical modeling or numerical simulation, and typically deal with modules having response times in the millisecond range or beyond. /// In this paper, we will present experimental characterisations of custom designed high-speed SiGe superlattice microcoolers with active areas ranging from 10x10 to 50x50 um^2. We investigate both turn-on and turn-off responses to 300ns wide current pulses with ~300kHz repetition rate by means of CCD-based thermoreflectance imaging. This technique provides highly detailed 2-D maps of the transient surface temperature with submicron spatial and 50ns temporal resolutions. Net cooling of 1-1.5 degrees is achieved within 100-300ns. This is over one order of magnitude faster compared to our earlier reports on high-speed operation of thermoelectrics. We also observe excessive heating of the electrode neck, likely induced by insufficient metallisation of the superlattice side contact at the device edge. These results thereby clearly illustrate how parasitics can degrade the device performance, even at such short time scales. Overall, our measurements provide valuable insight into the high-speed thermal dynamics and underlying Peltier and Joule mechanisms in thermoelectric microcoolers.
Bjorn Vermeersch, Postdoctoral Research Associate
Purdue University
West Lafayette, IN

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