Summer 2011 Intern Project- Eugene Fang

SILICON NANOWIRE THERMOELECTRIC DEVICES


Eugene Fang

Electrical Engineering and Computer Science
UC Berkeley

Mentor: Ben Curtin
Faculty Advisor: John Bowers
Department: Electrical and Computer Engineering

Silicon has great potential as a thermoelectric material because of its ease of processing and low impact on the environment when compared to traditional thermoelectric materials. Despite the excellent electrical properties of silicon, it is not a good thermoelectric material because of its high thermal conductivity. Silicon nanowires (SiNW) aims to drastically decrease silicon’s thermal conductivity while keeping electrical properties relatively constant. However, thermoelectric characterization of SiNW arrays and other thin-films is largely unexplored. While the immediate objective of this research is to characterize SiNWs as a thermoelectric material, it can also be used for cross-plane characterization of other thin-films. We developed a method of measuring the cross-plane thermal conductivity and Seebeck coefficient (Scp), defined by a voltage (ΔV) induced by a temperature difference (ΔT). To do this, we measure the ΔT across the device, heater power, and the voltage generated for both a silicon reference and a SiNW device. Preliminary results show a thermal conductivity drop by a factor of 16 and a Scp of ~250 μV/K for the SiNW array. Further investigation of device structure and electrical properties are necessary to understand why this is lower than the bulk value of ~350 μV/K. The first generation of these SiNW thermoelectric devices can be further optimized as we learn more, but the developed method for thin-film cross-plane Seebeck characterization is repeatable and will be useful for further measurements of SiNWs and other thermoelectric materials.

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