  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.
