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2
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- Preventing undesirable changes in mechanical, micro-structural and
optical properties for functional thin films remains a challenge. Stress
control of as-deposited thin films is one of the critical requirements
for achieving optical, electronic, magnetic, and mechanical performances
in the state-of-art MOEMS devices. Stress of thin films can be harmful
or useful, depending on the applications. Undesired in most of cases,
residual stress in thin films may cause structural deformation,
cracking, buckling or even delamination. Yet stress may be beneficial to
optimize performance in some of optical devices, such as the top mirror
with a dome shape formed by precisely controlled residual stress in the
tunable vertical cavity surface emission laser (TVCSEL) devices.
- Controlling and stabilizing the film stress in a high-performance
MOEMS device can present challenges during the fabrication process and
in its application environments. In general, the residual stress (s) of a thin film can
include thermal stress (sT), intrinsic stress (sI), and
epitaxial stress (sE), which can be expressed as s=sT+sI+sE. Thermal stress arises from the
temperature changes due to differential thermal expansion between
different materials. This kind of stress is almost inevitable in reality
when different materials are used. The intrinsic stress is more related
to the film growth techniques and can be tuned to certain content in
process. The effect of epitaxial stress caused by the lattice mismatch
of different materials is more obvious when the film is sufficient thin
so that it has a perfect coherent interface with its substrate.
- In this paper, the stress evolution of an optical stack (SiO2-TiO2)
used in a MOEMS device had been investigated in the atmospheric
environment.
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Notes
