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

TL;DR

This paper investigates how the layout of double rotated serpentine springs affects cross-axis coupling in vertical-comb-driven torsional micromirrors, aiming to reduce alignment error impacts through theoretical and simulation analysis.

Contribution

It is the first study to analyze the effect of layout (centrosymmetric vs axisymmetric) of DRSSs on cross-axis coupled spring constants in micromirrors.

Findings

Centrosymmetrically-arranged DRSSs are more resistant to pull-in.

Theoretical and FEA analysis reveal layout impacts on spring constants.

Key parameters influencing cross-axis coupling are identified.

Abstract

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.