Worcester Polytechnic Institute Electronic Theses and Dissertations Collection

Title page for ETD etd-012207-112353

Document Typethesis
Author NameRodgers, Matthew T.
TitlePhase modulating interferometry with stroboscopic illumination for characterization of MEMS
DepartmentMechanical Engineering
  • Prof. Cosme Furlong, Advisor
  • Prof. Rysard Pryputniewicz, Committee Member
  • Prof. Gretar Tryggvason, Committee Member
  • Mr. Mark Koslowske, Committee Member
  • Prof. Mark Richman, Graduate Committee Rep
  • Keywords
  • MEMS characterization
  • stroboscopic illumination
  • interferometry
  • phase modulation
  • Date of Presentation/Defense2006-12-15
    Availability unrestricted


    This Thesis proposes phase modulating interferometry as an alternative to phase stepping and phase-shifting interferometry for use in the shape and displacement characterization of microelectromechanical systems (MEMS) [Creath, 1988; de Groot, 1995a; Furlong and Pryputniewicz, 2003]. A phase modulating interferometer is developed theoretically with the use of a stroboscopic illumination source and implemented on a Linnik configured interferometer using a software control package developed in the LabVIEW™ programming environment. Optimization of the amplitude and phase of the sinusoidal modulation source is accomplished through the investigation and minimization of errors created by additive noise effects on the recovered optical phase. A spatial resolution of 2.762 µm over a 2.97x2.37 mm field of view has been demonstrated with 4x magnification objectives within the developed interferometer. The measurement resolution lays within the design tolerance of a 500Å ±2.5% thick NIST traceable gold film and within 0.2 nm of data acquired under low modulation frequency phase stepping interferometry on the same physical system. The environmental stability of the phase modulating interferometer is contrasted to the phase stepping interferometer, exhibiting a mean wrapped phase drift of 40.1 mrad versus 91 mrad under similar modulation frequencies. Shape and displacement characterization of failed µHexFlex devices from MIT’s Precision Compliant Systems Laboratory is presented under phase modulating and phase stepping interferometry. Shape characterization indicates a central stage displacement of up to 7.6 µm. With a linear displacement rate of 0.75 Å/mV under time variant load conditions as compared to a nominal rate of 1.0 Å/mV in an undamaged structure [Chen and Culpepper, 2006].

  • control_system.zip
  • MRodgers_Thesis.pdf

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