Low Power, Integrated, Thermoelectric Micro-coolers for Microsystems Applications.

Abstract

Advancements in micro-cooling are driven by applications across a number of industries, including biomedical, defense, communications, digital and analog electronics, and MEMS sensors. Thermoelectric coolers are attractive because they offer compact solid-state operation, and can be designed for low-power dissipation, which is a key consideration when targeting mobile applications. . This thesis presents the design, modeling, and measured performance of a new class of integrated thermoelectric microcoolers optimized for low-power operation. Two processes for fabricating microscale thermoelectric coolers using bismuth telluride and antimony telluride are presented. The first process is based on a 3-wafer stack silicon-glass-silicon process that provides excellent thermal isolation, good mechanical support, and full integration capability. Four different cooler designs based on this process were developed. The highest performing 6-stage design achieved cooling of 22.3 K with a power input of only 24.7 mW, and represents the highest reported performance for a multistage, in-plane, thermoelectric microcooler to date. The second process is based on a single wafer with a XeF2 release. Four different cooler variations have been fabricated based on this process, including a 4-stage design with a novel scheme for distributing current to the thermocouples that has achieved more the 17 K of cooling. Although this cooler has not yet produced cooling as high as the best from the silicon-glass-silicon process, the process addresses a number of shortcomings of the silicon-glass-silicon process, including reducing parasitic thermal resistance, and increasing fabrication reliability. Simulations show that coolers produced with this process hold the potential to achieve temperature differences greater than 40 K when paired with the appropriate thermoelectric materials In addition to the achievements stated above, the development of these thermoelectric coolers has produced several contributions. The first is an analysis of the requirements for low-power thermoelectric cooling and application of those requirements to multiple processes and cooler designs. Second, the first planar multistage thermoelectric cooler has been demonstrated. Third, is the integration of thin-film thermoelectric materials with a planar micro-fabrication process, and fourth is the development of a low-power microcooler device that can be integrated with arbitrary MEMS and electronic devices.