Ultra-High Fatigue Life Elastocaloric Micro­cool­ing for Photonic Systems

This project devel­ops a novel elastocaloric micro­cool­ing technol­ogy for photonic systems. Elastocaloric cooling uses stress-induced temper­a­ture changes in shape memory alloys to gener­ate cooling without conven­tional refrig­er­ants. While highly promis­ing for minia­tur­ized devices, current thin-film systems suffer from limited fatigue life. The project inves­ti­gates the fatigue behav­ior of shape memory alloy films and devel­ops a new device archi­tec­ture based on a thermal switch mecha­nism that avoids repeated mechan­i­cal contact. The goal is to achieve an opera­tional lifetime exceed­ing one million cycles and demon­strate the cooling system within integrated photonic platforms.

Efficient thermal manage­ment is becom­ing increas­ingly impor­tant as electronic and photonic systems continue to shrink in size while growing in perfor­mance. Photonic compo­nents such as optical modula­tors, multi­plex­ers, and integrated circuits are partic­u­larly sensi­tive to temper­a­ture fluctu­a­tions. Even small local temper­a­ture changes can lead to signal degra­da­tion, wavelength drift, and reduced efficiency. At the same time, conven­tional cooling technolo­gies based on vapor-compres­sion systems consume signif­i­cant energy and rely on refrig­er­ants with high global warming potential.

Elastocaloric cooling offers a promis­ing alter­na­tive. This solid-state cooling technol­ogy uses stress-induced temper­a­ture changes in super­elas­tic shape memory alloys (SMAs) to gener­ate cooling without environ­men­tally harmful refrig­er­ants. Recent advances have demon­strated large temper­a­ture changes and high cooling efficiency. Thin-film SMA materi­als are especially promis­ing for microscale appli­ca­tions because their large surface-to-volume ratio enables rapid heat trans­fer and compact device integration.

However, current elastocaloric thin-film devices face a major challenge: their limited fatigue life. Many exist­ing systems fail after only a few thousand operat­ing cycles, which is insuf­fi­cient for practi­cal use in photonic systems that require long-term stabil­ity. The goal of this project is there­fore to develop an elastocaloric micro­cool­ing device capable of operat­ing reliably for more than one million cycles.

To achieve this goal, the project combines exper­tise from materi­als science, device engineer­ing, and photon­ics. First, the fatigue behav­ior of differ­ent SMA thin films will be analyzed using advanced micro­me­chan­i­cal testing methods and high-resolu­tion microscopy techniques. These exper­i­ments aim to identify mater­ial compo­si­tions and microstruc­tures that maximize fatigue resis­tance while maintain­ing strong elastocaloric performance.

Second, a novel device archi­tec­ture will be devel­oped that replaces conven­tional mechan­i­cal heat trans­fer mecha­nisms with an innov­a­tive thermal switch. Based on electrowet­ting technol­ogy, this thermal switch allows controlled heat trans­fer without repeated mechan­i­cal contact between the cooling element and the heat sink. This approach reduces mechan­i­cal stress and signif­i­cantly increases device reliability.

Finally, the optimized cooling device will be integrated into a repre­sen­ta­tive photonic platform and tested under realis­tic operat­ing condi­tions. The project aims to demon­strate that elastocaloric micro­cool­ing can effec­tively stabi­lize temper­a­ture in photonic circuits, improv­ing signal quality and energy efficiency.

The collab­o­ra­tion between Prof. Peter Gumbsch (KIT and Fraun­hofer IWM), Prof. Juerg Leuthold (ETH Zurich), and Dr. Jingyuan Xu (KIT) combines comple­men­tary exper­tise in fatigue mechan­ics, photonic systems, and elastocaloric microde­vices. Together, the partners aim to estab­lish a new class of durable and energy-efficient cooling technolo­gies for next-gener­a­tion micro­elec­tron­ics and photonic systems.