Powder MEMS Technology Platform

At Fraunhofer ISIT a novel technology has been developed which allows the integration of nearly any material onto planar substrates. It is based on the agglomeration of micron-sized powder (particles) by atomic layer deposition (ALD). Like for the fabrication of ceramics, firstly a mold, in this particular case a silicon substrate with dry etched micromold pattern, is filled with loose powder. However instead of sintering the particles together with high pressure at 800°C to 1400°C, the silicon substrate is subjected to an ALD process at much lower temperatures. Thanks to the outstanding coating capability of ALD the loose particles in the micromolds are fixated to porous 3D structures over the whole mold depth (up to 700 µm) by a layer with a thickness of only 75 nm. These porous 3D structures are shrinkage-free and stable mechanically as well as thermally. Lateral dimensions between 50 µm and several mm can be realized with high precision. The nearly perfect envelopment of each particle by the ALD layer ensures an excellent protection against environmental influences. Substrates with embedded porous 3D structures can be post-processed in a cleanroom using standard processes of IC and MEMS fabrication at up to 400 °C. That opens up a unique range of applications. One of the evaluated ones is the fabrication of integrated permanent micromagnets from NdFeB powder. Strong magnetic fields on small scale are of interest for many MEMS sensors and actuators. The focus at ISIT is currently on magnetically driven vibrational energy harvesters and microscanners. Other promising applications of the novel technology are miniaturized organic-free phosphor converters for solid state lighting (SSL) or the thermal isolation of calorimetric MEMS, like mass flow and gas sensors, from the substrate by evacuated porous 3D structures, which is comparable to conventional super vacuum insulation.