JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 20, NO. 5, OCTOBER 2011 1201 Multistage Planar Thermoelectric Microcoolers Andrew J. Gross, Gi Suk Hwang, Baoling Huang, Hengxi Yang, Niloufar Ghafouri, Student Member, IEEE, Hanseup Kim, Member, IEEE, Rebecca L. Peterson, Member, IEEE, Ctirad Uher, Massoud Kaviany, Fellow, ASME, and Khalil Najafi, Fellow, IEEE Abstract—Many types of microsystems and microelectro- mechanical systems (MEMS) devices exhibit improved perfor- mance characteristics when operated below room temperature. However, designers rarely pair such devices with integrated cool- ing solutions because they add complexity to the system and often have power consumption which far exceeds that of the microsys- tem itself. We report the design, fabrication, and testing of both one- and six-stage thermoelectric (TE) microcoolers that target MEMS applications through optimization for low-power opera- tion. Both coolers use thin-film Bi 2 Te 3 and Sb 2 Te 3 as the n- and p-type TE materials, respectively, and operate in a planar configu- ration. The six-stage cooler has demonstrated a ΔT = 22.3 ◦ C at a power consumption of 24.8 mW, while the one-stage cooler has demonstrated a ΔT = 17.9 ◦ C at a lower power consumption of 12.4 mW. [2011-0087] Index Terms—Microcooler, microelectromechanical systems (MEMS), solid-state cooling, thermoelectric (TE) devices. Manuscript received March 22, 2011; revised June 8, 2011; accepted July 7, 2011. Date of publication August 30, 2011; date of current version September 30, 2011. This work was supported by the Micro Cryogenic Coolers Program of the Defense Advanced Research Projects Agency under Grant W31P4Q-06-1-001. Portions of this work were performed at the Lurie Nanofabrication Facility, a member of the National Nanotechnology Infrastruc- ture Network, which is supported in part by the National Science Foundation. The work of M. Kaviany was also supported by the World Class University program through the National Research Foundation of Korea, Ministry of Education, under Grant R31-30005. Subject Editor C.-J. Kim. A. J. Gross was with the Electrical Engineering and Computer Science Department, University of Michigan, Ann Arbor, MI 48109 USA. He is now with Sandia National Laboratories, Albuquerque, NM 87185 USA (e-mail: ajgross@umich.edu). G. S. Hwang was with the Mechanical Engineering Department, University of Michigan, Ann Arbor, MI 48109 USA. He is now with the Environmen- tal Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA (e-mail: gshwang@lbl.gov). B. Huang was with the Mechanical Engineering Department, University of Michigan, Ann Arbor, MI 48109 USA. He is now with the Department of Me- chanical Engineering, The Hong Kong University of Science and Technology, Kowloon, Hong Kong (e-mail: mebhuang@ust.hk). H. Yang and C. Uher are with the Physics Department, University of Michigan, Ann Arbor, MI 48109 USA (e-mail: hxyang@umich.edu; cuher@umich.edu). N. Ghafouri, R. L. Peterson, and K. Najafi are with the Electrical Engineer- ing and Computer Science Department, University of Michigan, Ann Arbor, MI 48109-2122 USA (e-mail: nghafour@umich.edu; blpeters@umich.edu; najafi@umich.edu). H. Kim was with the Electrical Engineering and Computer Science Depart- ment, University of Michigan, Ann Arbor, MI 48109 USA. He is now with the Electrical and Computer Engineering Department, The University of Utah, Salt Lake City, UT 84112 USA (e-mail: hanseup@ece.utah.edu). M. Kaviany is with the Mechanical Engineering Department, University of Michigan, Ann Arbor, MI 48109 USA, and also with the Division of Advanced Nuclear Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea (e-mail: kaviany@umich.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JMEMS.2011.2163302 I. I NTRODUCTION T HE NEED for microscale coolers is driven by micro- electromechanical systems (MEMS) and electronic de- vices, such as resonators, gyroscopes, infrared sensors, and low-noise amplifiers, which exhibit enhanced performance when operated at temperatures below ambient. Resonant MEMS, in particular, have very low power dissipation, and many of the applications that integrate them seek to exploit these low-power features as well as their small size [1]. As a result, any cooling device designed for integration with these low-power MEMS devices should itself be both low power and compact. One approach to microscale cooling has been the develop- ment of miniaturized Joule–Thompson (J–T) coolers [2]–[6]. Some of these devices have effectively produced temperature differentials of 192 K with heat loads up to 16 mW, using a heat exchanger with a size of 2 mm × 35 mm × 1 mm [2]. However, the heat exchanger alone does not define a complete J–T cooling system. J–T coolers also require a source of com- pressed gas, which can be supplied by an external pressurized source [3] or by an attached compressor [7]. The lack of small simple implementation makes J–T coolers impractical for many microcooling applications. Thermoelectric (TE) cooling, although less efficient than J–T cooling, relies on solid-state operating principles that can be scaled to the microdomain. As a result, TE cooling can be effectively utilized in applications that require small, simple, and robust coolers. Additionally, TE materials can be deposited and patterned at the wafer level with standard microfabrica- tion techniques, making batch-mode production a possibility. Microscale TE coolers have been previously demonstrated by several groups [8]–[18] representing a wide range of choices in cooler design, TE materials, and fabrication techniques. A summary of devices from industry and academia is provided in Table I. The best performing coolers in this group are able to generate temperature differentials between 40 K and 100 K; however, they require power inputs of several hundred milliwatts or more. Such high power consumption makes these coolers incompatible with MEMS integration in many applica- tions. On the other hand, the low-power coolers to date have not demonstrated enough total temperature differential to be useful in achieving meaningful performance gains from the target electronics and MEMS devices. This paper presents a TE microcooling solution that can generate reasonably large temperature differences with very small power. The special features of micro TE coolers, including size ef- fects and interfacial transport phenomena, are addressed in [19]. 1057-7157/$26.00 © 2011 IEEE