RESEARCH PAPERS: Micro/Nanoscale Heat Transfer

Raman Thermometry of Polysilicon Microelectro-mechanical Systems in the Presence of an Evolving Stress

[+] Author and Article Information
Mark R. Abel

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405

Samuel Graham1

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405sgraham@me.gatech.edu

Justin R. Serrano, Sean P. Kearney, Leslie M. Phinney

Engineering Sciences Center, Sandia National Laboratories, Albuquerque, NM 87185-0834


Corresponding author.

J. Heat Transfer 129(3), 329-334 (May 31, 2006) (6 pages) doi:10.1115/1.2409996 History: Received January 17, 2006; Revised May 31, 2006

In this work, the use of Raman Stokes peak location and linewidth broadening methods were evaluated for thermometry applications of polysilicon microheaters subjected to evolving thermal stresses. Calibrations were performed using the temperature dependence of each spectral characteristic separately, and the uncertainty of each method quantified. It was determined that the Stokes linewidth was independent of stress variation allowing for temperature determination, irrespective of stress state. However, the linewidth method is subject to greater uncertainty than the Stokes shift determination. The uncertainties for each method are observed to decrease with decreasing temperature and increasing integration times. The techniques were applied to mechanically constrained electrically active polysilicon microheaters. Results revealed temperatures in excess of 500°C could be achieved in these devices. Using the peak location method resulted in an underprediction of temperature due to the development of a relative compressive thermal stress with increasing power dissipation.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Layout showing the sample used for temperature measurements in this study. The sample consists of a polysilicon microheater beam on a thick PECVD silicon dioxide on bulk silicon. Constraint in the movement of the microheater from the oxide layer is used to induce stress variations in the device.

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Figure 2

Calibration of Stokes peak location for phosphorous doped polysilicon

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Figure 3

Effect of stress on the linewidth of doped polysilicon (top). The scatter of the linewidth with stress is far less than the measurement uncertainty. The effect of stress on the Stokes peak location results in a linear shift with applied stress (bottom).

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Figure 4

Linewidth calibration of phosphorous doped polysilicon which displays a quadratic behavior over the temperature range shown.

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Figure 5

Estimated measurement uncertainty as a function of temperature from all sources. The uncertainty is based on a vector summation of the individual contribution to uncertainty and then taking 20 samples to reduce the single measurement uncertainty according to Eq. 3.

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Figure 6

Temperature at the center of a microheater as a function of power dissipated. When comparing the Stokes and linewidth techniques, a thermally induced compressive stress was realized.

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Figure 7

Temperature distribution of a fixed–fixed microheater using half-symmetry. A comparison of the Stokes and linewidth calibration is seen, revealing good agreement near the bond pad (distance=0◻m) and a significant difference at the beam center (distance=100◻m). The measured temperature difference (33°C) is greater than the ±15°C uncertainty between the two measurements at 400°C. This difference suggests the presence of a compressive stress in the device.




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