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Sensors, Focus on Tactile, Force and Stress Sensors 2011 Part 14

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Tham khảo tài liệu 'sensors, focus on tactile, force and stress sensors 2011 part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Compliant Tactile Sensors for High-Aspect-Ratio Form Metrology 381 microscopy AFM tips. Furthermore in contrast to AFM probes we located the tip at the bottom side of the cantilever. So robust tips of heights ranging from 10 to 200 pm could be realized while leaving the upper chip surface for a planar integration of the strain gauge. The cantilever deflection was measured using a balanced Wheatstone bridge located close to the cantilever clamping. Cantilever dimensions and bridge layout are displayed in Fig. 3. The large contact pads were provided for die testing and calibration. During the back-end processing of the probe head this area was used for the deposition of glue for the fixing of the sensor to the steel finger. Electrical connection was realized via wire bonds from the small pads on the sensor chip to a flexible circuit board glued onto the steel finger. sensor Fig. 3. Schematic of probe head based on a tactile cantilever sensor with enlarged representations of the probing tip and the Wheatstone bridge as well as the circuit diagram of the bridge and a temperature sensing device. Slender cantilevers of low stiffness as required for probing inside narrow and deep micro holes generate only small strain values upon tip deflection. Therefore a high gauge factor and an optimum location of the gauge on the cantilever were necessary to meet the sensitivity requirements. Simultaneously temperature drift susceptibility to ambient light power consumption and noise had to be kept as low as possible. As a trade-off we designed a full Wheatstone bridge of four p-type resistors of a sheet carrier concentration of 3 X 1014 cm-2 to obtain a bridge resistance of 2.5 kQ for which we could expect a gauge factor of K 80 a temperature drift of 1 - 2 X 10-3 K noise of 1 pV in a bandwidth of 20 kHz and a power consumption of 0.4 mW at U0 1 V. 2.2 Vertical loading Using the cantilever sensor in Fig. 3 as a tactile sensor three directions of force application to the cantilever .