We present the design, fabrication and testing of a high-resolution 169-sensing cell capacitive flexible tactile imager (FTI) for normal and shear stress measurement as an auxiliary sensor for robotic grippers and gait analysis. The FTI consists of a flexible high-density array of normal stress and two-dimensional shear stress sensors fabricated using microelectromechanical systems (MEMS) and flexible printed circuit board (FPCB) techniques. The drive/sense lines of the FTI are realized using FPCB whereas the floating electrodes (Au) are patterned on a compressible PDMS layer spin coated on the FPCB layer. The use of unconnected floating electrodes significantly improves the reliability of traditional quad-electrode contact sensing devices by eliminating the need for patterning electrical wiring on PDMS. When placed at the heel of a boot, this FTI senses the position and motion of the line of contact with the ground. Normal stress readouts are obtained from the net capacitance of the cell and the shear-sense direction is determined by the amount of asymmetric overlap of the floating combs with respect to the bottom electrodes. The FTI is characterized using a high-speed switched-capacitor circuit with a 12-bit resolution at full frame rates of 100 Hz (∼0.8 Mb s−1) capable of resolving a displacement as low as 60 µm. The FTI and the readout circuitry contribute to a noise/interference level of 5 mV and the sensitivity of normal and shear stress for the FTI is 0.38 MPa−1 and 79.5 GPa−1 respectively.
The lateral thermal conductivity of heavily doped low-pressure chemical vapor deposited polycrystalline silicon films is measured using polycrystalline silicon microbridges elevated three micrometers above a silicon substrate. The bridges, lightly doped in their central regions and heavily doped elsewhere, are fabricated using a sacrificial silicon-dioxide layer and phosphorus out-diffusion from doped oxide. Voltage-current characteristics measured on the bridges both under high vacuum and in silicone oil are used to calculate lateral thermal conductivity in the polycrystalline silicon. The experimental values for the thermal conductivity of heavily doped polycrystalline silicon range from 0.29 to 0.34 W cm−1 K−1 and average 0.32 W cm−1 K−1. These values agree closely with results obtained by a second method that employs uniformly doped polycrystalline silicon bridges. In the second method, high-vacuum, voltage-current characteristics are measured and the indicated thermal conductivities for two samples are 0.29 and 0.30 W cm−1 K−1, respectively.
A silicon filament vacuum sealed incandescent light source has been fabricated using IC technology. The incandescent source consists of a heavily doped p(+) polysilicon filament coated with silicon nitride and enclosed in a vacuum sealed ( approximately 80-mT) cavity in the silicon chip surface. The filament is electrically heated to reach incandescence at a temperature near 1400 K. The power required to achieve this temperature for a filament 510 x 5 x 1 microm(3) is 5 mW yielding a total optical power of 250 microW with a peak distribution wavelength near 2.5 microm. The radiation emitted by this source approximately follows Lambert's cosine law. The energy conversion efficiency is 5%.
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