Out-of-plane Although Bosch process can fabricate 90° (truly vertical) walls, but often the walls are slightly tapered, which may cause the shuttle to have an out-of-plane component of displacement during actuation. The insulator (oxide) is 2 um thick. If the out-of-plane component is large enough, the shuttle may hit the bottom handling wafer or packaging structures on the top. Using a Veeco interferometer, the displacement of the shuttle was determined. As shown in Figure 5, the out-of-plane and in-plane components of displacement are approximately 0.5 and 200 um, respectively, at 7 V excitation. (a) 0 V, dout-of-plane = 0 um (b) 5 V, dout-of-plane = 0.4 um (c) 7 V, dout-of-plane = 0.5 um Figure 5 In-plane and out-of-plane components of the shuttle displacement of at various levels of excitation. TEMPERATURE Calibration An Indigo thermal imaging system was used to characterize the temperature profiles of the actuator. The intensity or ADC (Analog to Digital Converter) count of each pixel does not provide the temperature reading directly. It represents the total thermal or photon energy (flux) detected during the integration time. The count number has to be converted to temperature through a calibration curve. The calibration was done by placing a die on a hot plate, as shown on Figure 6(a). A thermal couple was attached on the top surface of the die. The infrared camera was focused on the surface of the die at an area near the thermal couple, Figure 6(b). Another thermal couple was attached to the hot plate to control its temperature. When both thermal couple readings were stabilized, the temperature of the die surface and the corresponding averaged ADC count were recorded. The procedure was repeated at several discrete temperatures to obtain a calibration curve. Since the integration time could be adjusted to improve the sensitivity of measurement for a given temperature range, a number of calibration curves related to different integration times were acquired. Three calibration curves with integration times of 0.02, 0.05 and 0.5 ms are displayed in Figure 6(c). 200 250 300 350 400 450 500 550 600 0 2000 4000 6000 8000 10000 12000 Count Temperature, K data, dt = 0.02ms data, dt = 0.05ms data, dt = 0.5ms fit, 0.02ms fit, 0.05ms fit, 0.5ms (a) (b) (c) Figure 6 Calibration of a thermal imaging system 205
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