Thermal Management Using MEMS Bimorph Cantilever Beams

R A Coutu,R S Lafleur,L A Starman,J P K Walton

doi:10.1007/s11340-016-0170-1

Abstract

This paper examines a passive cooling technique using microelectromechanical systems (MEMS) for localized thermal management of electronic devices. The prototype was designed using analytic equations, simulated using finite element methods (FEM), and fabricated using the commercial PolyMUMPs™ process. The system consisted of an electronic device simulator (EDS) and MEMS bimorph cantilever beams (MBCB) array with beams lengths of 200, 250, and 300 μm that were tested to characterize deflection and thermal behavior. The specific beam lengths were chosen to actuate in response to heating associated with the EDS (i.e. the longest beams actuated first corresponding to the hottest portion of the EDS). The results show that the beams deflected as designed when thermally actuated and effectively transferred heat away via thermal conduction. The temperature when the beams reached “net-zero” deflection (i.e. uncurled and flat) was related to the initial deflection distance while the contact deflection temperature and rate of actuation was related to beam length. Initial beam deflections, after release, and contact temperatures, when fully actuated, were approximately 5.05, 9.45, 14.05 μm, and 231, 222, 216 °C, respectively with the longer beams making contact first. This innovative passive thermal management system enables selective device cooling without requiring active control or forced convection to maintain steady-state operating temperatures for sensitive microelectronic devices.

Highlights

Maintaining an ideal operating temperature for microelectronic devices is commonly achieved with heat sinks that regulate temperature through a combination of thermal conduction and forced convection
We investigate the response of a microelectromechanical systems (MEMS) bimorph cantilever beam (MBCB) array as a novel passive thermal management system
Low voltage and cooler complementary metal oxide semiconductor (CMOS) circuits will best cooled with shorter beams (e.g. 200 μm-long) while higher voltage and hotter power amplifier transistors will be best cooled with longer beams (e.g. 300 μm-long)

Summary

Introduction

Maintaining an ideal operating temperature for microelectronic devices is commonly achieved with heat sinks that regulate temperature through a combination of thermal conduction and forced convection. This approach often requires additional components, such as a cooling fan, that increases system size, weight and power requirements. Most thermal management approaches involve using thermal interface materials (TIMs), to increase thermal conductivity, by bridging the gap between the device and the heat sink. A unique approach to thermal management involved a 2D array of curled-up microelectromechanical systems (MEMS) cantilevers as the TIM between a high temperature component and a heat sink. The system was actively controlled and required an external load to bring the high temperature component and MEMS modified heat sink into contact [4]

Methods

Results

Conclusion