Study on layout of double rotated serpentine springs for vertical-comb-driven torsional micromirror

The combination of double rotated serpentine springs (RSS) and vertical comb-drive is a suitbale solution for the development of torsional micromirror with high fill factor, low fabrication difficulty and good performance. However, the alignment error between upper and lower comb set caused by fabrication can induce force with unexpected direction. And the cross-axis coupled spring constants in double rotated serpentine springs (DRSSs) makes micromirror more susceptible to this alignment error. Herein, in order to minimize the unexpected deflection caused by alignment error of vertical-comb-driven micromirror, this paper, for the first time, studies the effect of layout (centrosymmetrically-arranged and axisymmetrically-arranged) of DRSSs on cross-axis coupled spring constants. Both of theoretical analysis and finite element analysis (FEA) simulation are conducted to reveal this phenomenon. With an example, centrosymmetrically-arranged DRSSs are proved to be more resistant to pull-in of two comb sets. Finally, the relationship between key structure parameters and cross-axis coupled spring constants of centrosymmetrically -arranged DRSSs are presented.