Three-dimensional folded MEMS manufacturing for an efficient use of area

Abstract:
Enablingthe third dimension for MEMS is the decisive lever to increase membrane area out of fix chip surface. This work presents the first three-dimensional folded MEMS membrane manufactured by surface micromachining. The manufacturing process is characterized by stepwise microscopy analysis of test structures and fully released membranes. Quantification of the etching selectivity of SiO2 stop layer versus Si between the sidewallsshows an aspect ratio (height to width)depending etching. For aspect ratios higher than 0.3, SiO2 loses up to 5.5 nm of thickness per etched micrometre of Si. Finally, these results enable the optimization of folded transducer membranes. They can increase the active area out of a fixed chip area by a factor of up to 20 compared to a planemembrane.