Reduction of out-of-plane warpage in surface micromachined beams using corrugation

Corrugation is proposed as a means of reducing the out-of-plane warpage in surface micromachined beams that result from an asymmetric vertical stress profile. Corrugation increases beam bending stiffness without increasing film thickness, making the beam more immune to intrinsic vertical stress gradients without requiring longer film deposition times, increased beam mass, or careful stress optimization. The technique was tested using a dual-thickness metal surface micromachining process with a photoresist sacrificial layer. Several corrugation patterns and geometries were tested, and the best performing pattern was implemented on a MEMS actuator array. The off-state to on-state capacitance delta of the array improved from 0.24 to 0.7pF and the beam curvature decreased from 180 to 50 nm compared with an uncorrugated array. Other device performance parameters, such as 30 V pull-in voltage and 5 billion cycle switching lifetime, were unaffected.