Nonlinear spring effect of tense thin-film torsion bar combined with electrostatic driving

Subrata Kumar Kundu, Shouhei Ogawa, Shinya Kumagai, Masayuki Fujishima, Kazuhiro Hane, Minoru Sasaki

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


Tense thin-film polycrystalline (poly-) Si torsion bars are advantageous in behaving as compliant springs against the twisting motion of electrostatically low-voltage-driven micromirrors. In this study, the nonlinear spring effect of the tense thin-film poly-Si torsion bar of a micromirror was characterised. The nonlinear spring effect of this torsion bar was explained theoretically, considering the bending and stretching effects in addition to the shear stress effect. The tensile stress induced in the thin-film poly-Si torsion bar is 300-400 MPa, and the bar maintains its compliance during the rotation of the mirror and increases its stiffness to suppress the pull-in instability. The torsion bar exhibits a large hard-spring effect with the bending of the film, observed as an increase of the ringing frequency. The spring constant was experimentally observed to increase by 6.25 times. The theoretical results agree well with the experimental results regarding the magnitude of the nonlinear spring constant.

Original languageEnglish
Pages (from-to)83-89
Number of pages7
JournalSensors and Actuators, A: Physical
Publication statusPublished - 2013


  • Electrostatic actuation
  • Hard-spring effect
  • Nonlinear spring effect
  • Thin-film torsion bar

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Instrumentation
  • Condensed Matter Physics
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Electrical and Electronic Engineering


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