Metal-based folded-thermopile for 2.5D micro-thermoelectric generators

We report on the simulation and fabrication of 2.5D micro-thermoelectric generators (µTEGs) with a thermopile topology periodically folded and distributed on a multi-membrane template, capable of harvesting lost heat directly into useful electrical energy. The originality of the folded thermopile is multiple: i/ it uses low-cost and eco-friendly alloy-based thermoelectrics (TEs) in the form of a series of Ni90Cr10/Cu55Ni45 thermocouples (TCs), ii/ in each TC both TE layers are stacked on top of each other allowing a better integration, iii/ the TCs are electrically associated in series and in parallel, reducing drastically the electrical resistance, iv/ the choice of membrane number permits to tune the module thermal resistance. All this results in an improvement of the conversion efficiency of the µTEG compared to our former all-Silicon planar modules. A finite element simulation allows defining the temperature distribution profiles in the module as a function of its dimensions. Several 2- and 3-membranes based µTEGs were fabricated using CMOS-compatible Silicon technology and characterized. In the best µTEG, the harvesting of 1 Watt of heat results in an output power density of 108.3 µW/cm2. This corresponds to an efficiency factor of 6.82 10−3 µW.cm-².K-² which is better than state-of-the-art metal-based modules.