Negative expansion materials are relatively rare but promise to be particularly useful in designing thermally sensitive mechanical devices. Although negative thermal expansion (NTE) in bulk materials such as ZrW2O8 has been extensively studied, this paper reports the first deposition of a NTE material thin film. ZrWxOy films were deposited by electron beam evaporation and reactive cosputtering. The films were processed and patterned for various microstructures. The coefficients of thermal expansion of the deposited thin films were determined by measuring the change in curvature with temperature. It was found that evaporated films but not sputtered films, which were denser than the evaporated films, exhibited NTE. It was also found that NTE behavior occurred across a variety of stoichiometries. Since crystalline ZrW2O8 and thin film ZrWxOy both have low densities and show negative expansion, it is speculated that similar physical mechanisms, as discussed in the text, are at work. Further, since the deposition conditions of a thin film can often be changed to control density, it is speculated that a wider variety of thin films than bulk crystals might be made to have NTE.
Bibliographical noteFunding Information:
Manuscript received October 14, 2003; revised January 28, 2004. This work was supported by the Air Force Office of Scientific Researchby Grant F49620-02-1-0384. Subject Editor H. Zappe. The authors are with the Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455 USA (e-mail: email@example.com). Digital Object Identifier 10.1109/JMEMS.2004.832191