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Thin films on substrate may crack due to tensile residual stress taking a mud crack like pattern. The pattern can be controlled by prescribing stress raisers that initiate, and arresters that terminate, cracks at desired locations. Here, we describe the mechanism by which stresses are amplified in plasma-deposited films. Stress raisers in the form of narrow slits or features with sharp corners are reactive ion etched in silicon. Plasma deposition of thin films on these stress raisers causes a nonconformal coverage leading to the formation of narrow voids within the slits. On annealing, the voids amplify the stress and initiate cracks through the thickness of the film.

We present a novel silicon carbide MEMS stage for in situ uniaxial test of micro/nanoscale samples at high temperature. The stage, which has a cofabricated temperature sensor, is used as a heat source by Joule heating during in situ tests. We theoretically study the temperature profile of the SiC stage and sample during Joule heating. The results show that sample temperature varies within 3% across the sample length up to 700 oC and is insensitive to sample resistance. We further explore a design parameter space for the SiC stage to minimize the electrical current through the sample and hence prevent potential damages on the sample. For the experimental study, we first present microfabrication and calibration procedures for the SiC MEMS stage and a cofabricated temperature sensor. Then, we experimentally consider the temperature profile of the stage and independently fabricated single crystal silicon (SCS) microsamples by precalibrated temperature sensors. We observe substantial temperature difference between the stage and sample due to the irregular surface contact at the gripping mechanism. Finally, to verify the feasibility of the in situ thermo-mechanical testing method, we obtain stress–strain responses of the SCS microsamples at temperatures from room to 400 oC which matches with the known elastic modulus of SCS in the literature.

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