0

Full Content is available to subscribers

Subscribe/Learn More  >

Suppression of Stress Relaxation in MEMS Multilayer Film Microstructures by Use of ALD Nanocoatings

[+] Author Affiliations
Yanhang Zhang, Martin L. Dunn, Jeffrey W. Elam, Steven M. George

University of Colorado at Boulder, Boulder, CO

Paper No. IMECE2002-39298, pp. 179-187; 9 pages
doi:10.1115/IMECE2002-39298
From:
  • ASME 2002 International Mechanical Engineering Congress and Exposition
  • Microelectromechanical Systems
  • New Orleans, Louisiana, USA, November 17–22, 2002
  • Conference Sponsors: Microelectromechanical Systems
  • ISBN: 0-7918-3642-8 | eISBN: 0-7918-1691-5, 0-7918-1692-3, 0-7918-1693-1
  • Copyright © 2002 by ASME

abstract

We study the suppression of stress relaxation in MEMS multilayer film microstructures by the use of alumina nanocoatings realized by atomic layer deposition (ALD). Gold (0.5 μm thick) / polysilicon (1.5 or 3.5 μm thick) beam and plate microstructures were fabricated by the MUMPs surface micromachining process. The microstructures were then coated on both sides with a 40 nm thick amorphous Al2 O3 layer by ALD. The beam and plate microstructures were initially thermal cycled between room temperature and 190°C tostabilize the gold microstructure. After the initial thermal cycles, the microstructures were cooled from 190°C to 120°C and held at 120°C for about 2000 hours (three months). We measured, using an interferometric microscope with a custom-built temperature chamber, full-field deformed shapes (and from these determined the average curvatures in x- and y- directions) of the microstructures during the initial thermal cycles, during the cooling process from 190 °C to 120 °C, and during the isothermal hold. Measurements were made on both coated and uncoated microstructures to assess the influence of the coating. We find that while the 40 nm thick coating has a small effect on the thermoelastic response of the microstructure, it significantly reduces the extent of stress relaxation during the isothermal hold. We modeled the curvature evolution with time assuming the stress relaxation mechanism is power-law creep in the gold, ε̇ = Aσn , and that the polysilicon and alumina deform elastically. The simple model describes the observed behavior reasonably well for the uncoated microstructures (when the power-law parameters are fit using the measured curvature), however, for the coated microstructures, the model predicts a decrease in the stress relaxation, but nowhere near the magnitude observed. This suggests that not only is the stress state in the gold film altered by the nanoscale coating, but also the fundamental deformation mechanisms are altered.

Copyright © 2002 by ASME

Figures

Tables

Interactive Graphics

Video

Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature

Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal

NOTE:
Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In