Enhancement of rotordynamic performance of high-speed micro-rotors for power MEMS applications by precision deep reactive ion etching

High-precision fabrication is indispensable for high-speed silicon micro-rotors for power MEMS applications so as to minimize the rotor imbalance that deteriorates the rotor performance. Etch variation of deep reactive ion etch (DRIE) process results in differences in rotor blade heights and thus rotor imbalance. A Fourier transform of the etch non-uniformity along the rotor circumference revealed the global etch variation across the wafer and local variations in etch rates depending on the concentration or proximity of the patterned geometry. Rotor imbalance arising from the global etch variation of DRIE process was estimated, which compared favorably to results obtained from spinning experiments. The global etch non-uniformity which culminates in rotor imbalance could be alleviated to 0.25% across a rotor of 4.2 mm diameter by optimizing the plasma chamber pressure. The developed DRIE recipe successfully reduced the rotor imbalance and thus enhanced the rotordynamic performance. The manufacturing processes presented herein are readily applicable to the construction of other microstructures containing intricate geometries and large etched areas.