Characterization of thin film MEMS using photo-acoustic microscopy

Carmen M. Hernandez, Todd W. Murray, Sridhar Krishnaswamy

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Photo-acoustic microscopy (laser ultrasonics) is a potentially powerful tool for nondestructive, in situ, MEMS device characterization. This paper discusses the use of narrowband photo-acoustics to characterize the properties of free-standing nanometer-sized thin films. Photo-acoustic generation is achieved by use of a micro-chip laser which deposits pulsed laser energy (10μJ in 300 picoseconds) in the form of a spatially periodic source on the structure. The resulting narrowband ultrasonic modes are monitored using a Michelson interferometer. By varying the geometry of the spatially-periodic source, a wide range of wavenumbers is probed. Experiments were conducted on two-layer Al/Si3N4 membranes (aluminum thickness: 300-500nm; silicon nitride thickness: 240-400nm. For such thin films, only the two lowest order modes are generated and these in mm can be related to sheet and flexural modes in plates. The mechanical properties and residual stress in the thin films are evaluated from the dispersion curves for these two lowest order modes.

Original languageEnglish (US)
Pages (from-to)61-69
Number of pages9
JournalProceedings of SPIE - The International Society for Optical Engineering
Volume4400
DOIs
StatePublished - Jan 1 2001

Keywords

  • Laser ultrasonics
  • MEMS
  • Photoacoustics
  • Thin films

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

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