Dirk Meyners

Kiel University
Talk Title: 
MEMS Energy Harvester with solidified powder magnet
Talk Abstract: 
"Miniaturized power supplies are an important building block for the realization of next generation mobile sensor applications. The work presented here focuses on a bulk micromachined energy harvester based on a 3 mm x 1 mm x 50 µm sized piezoelectric cantilever. Two micrometer thick AlN, AlScN or PZT layers are applied as the piezoelectric component. Whereas the AlN and AlScN layers are sputter deposited using a reactive pulsed-DC method, the PZT layer is grown by means of chemical solution deposition. To drive the harvester magnetically, a miniaturized permanent magnet is attached to the cantilever. This magnet is produced by filling a Si cavity with NdFeB powder (particle size of the order of a few microns) using the doctor blade method. Subsequently, atomic layer deposition of Al2O3 agglomerates the particles resulting in a high energy density magnet [1]. Four-point bending measurements reveal piezoelectric coefficients of e31,f = 1.4 C/m², 3.0 C/m² and 12.6 C/m² for the three different materials AlN, AlScN and PZT [2,3]. However, the maximum figure of merit FOM = e31,f^2/ε0ε33 = 60 GJ/m³ is measured for AlScN. Consequently, energy harvesters comprising AlScN exhibit the best performance yielding a power output of 13 µW for an alternating magnetic field with a 1 G amplitude and a frequency of 3.3 kHz matching the mechanical resonance. This corresponds to a high area-normalized power output of 4.3 µW/mm². As a first demonstration, the harvesters and a magnet wheel are tested in a drilling tool. The purpose of the harvester is to enable an integrated sensor system, which measures the position of the cutting edge in next generation tools. [1] Reimer, T., Lofink, F., Lisec, T., Thede, C., Chemnitz, S., & Wagner, B., Temperature-stable NdFeB micromagnets with high-energy density compatible with CMOS back end of line technology. MRS Advances, 1(3), 209-213, 2016. [2] Yarar, E., Hrkac, V., Zamponi, C., Piorra, A., Kienle, L. and Quandt, E., 2016. Low temperature aluminum nitride thin films for sensory applications. AIP Advances, 6(7), p.075115. [3] Fichtner, S., Reimer, T., Chemnitz, S., Lofink, F. and Wagner, B., 2015. Stress controlled pulsed direct current co-sputtered Al1−xScxN as piezoelectric phase for micromechanical sensor applications. APL Materials, 3(11), p.116102."