A new design for bi-material microbeams is presented in this paper which enables the tuning of their thermal actuation
response to deliver out-of-plane rotation . The design is applied to a group of 300 μm long and 20 μm wide gold-over-polysilicon
microbeams with a 60 μm long top gold strip positioned in different locations along the beam length.
Numerical simulation predicts that if the gold strip is situated 20 μm from one end of the microbeam, a maximum out-of-
plane rotation angle of 0.9 degree can be achieved with a temperature increase of 150 °C. Thermal loading
experiments carried out on fabricated similar microbeams show similar responses to those predicted by finite element
simulations.
In this paper, a new MEMS capacitive temperature sensor is presented which is based on a circular silicon plate with a gold annulus deposited on top forming a novel bimaterial structure. The bimaterial structure is anchored to a substrate on its edge and forms the top electrode of a capacitor. A stationary silicon electrode beneath the bimaterial structure forms the second electrode. The PolyMUMPs® foundry process has been used to fabricate the device. Experiments show that for an effective area of about 0.1 mm2 this MEMS capacitive temperature sensor achieves a sensitivity of 0.75±0.25 fF/°C over the temperature range of 25 to 225 °C, which shows an improvement of more than 25% over equivalent microcantilever devices with the same effective area. Numerical modeling is used to show that the new design exhibits high flexibility in tailoring its thermomechanical response over the desired temperature range. The simplicity of its design and flexibility of the materials from which it can be constructed also makes this new MEMS sensor a good onchip temperature measurement device for MEMS characterization.
An investigation into the effects of dry plasma etching release process parameters, local wafer position and induced inplane
stress on the yield of MEMS devices is presented. Several identical wafer quarters, each subjected to different
releasing process conditions, are studied. Yield is evaluated by observational measurements of the stiction of MEMS
nanocantilevers fabricated alongside with bent beam strain sensors. Results show that lower yield is found for larger
processing times as well as higher releasing temperatures. On the other hand, yield improves when thicker
nanocantilevers are released using the same processing parameters. The distribution of process-induced in-plane stress of
PECVD silicon nitride films is shown to change widely from compressive to tensile based on the local wafer position,
whereas no clear correlation between stiction and stress distribution is found. Viability of determining MEMS yield at
the wafer-level based on process-induced residual stress is discussed. Other possible root causes of yield in MEMS due
to dry plasma release etching are also briefly touched.
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