Glassy carbon

The three powders used in this work were “Aeroperl (AP) 300/30” a specially granulated form of pyrogenic silicon dioxide (Evonik, Essen, Germany) with $D_{50}=33 \mathsf{\mu }\mathrm{m}$ , silicon nitride (Sigma Aldrich, Schnelldorf, Germany) with $D_{50}<10 \mathsf{\mu }\mathrm{m}$ , and glassy carbon (Sigma Aldrich, Germany) with $D_{50}=2-12 \mathsf{\mu }\mathrm{m}$ .
To obtain test structures in accordance with Figure 2c, the frontside of the substrate is coated with photoresist and laminated with UV tape to protect it during subsequent processing. Next, the wafers are transferred from the cleanroom into the dedicated PowderMEMS lab. In this lab, loose, dry powder is filled into the backside cavities and then agglomerated into solid 3D-microstructures by atomic layer deposition (ALD) of 75 nm Al₂O₃ at 75 °C [16 (link)]. Figure 5 shows a cross-section through a sensor after PowderMEMS processing (Figure 2c), UV tape detachment, and photoresist stripping in O₂ plasma.