Motion Characterizations of Lateral Micromachined Sensor Based on Stroboscopic Measurements

In this paper, we illustrate the capabilities of the Planar Motion Analyzer (PMA) with a study of the dynamic behavior of a micromachined structure. Dynamic characterizations and measurement settings are also demonstrated. The optical measurement system uses the light-emitting diode (LED) based vibration measurement technique for imaging, and then measuring the lateral resonant frequency and sensor displacements, as well. The PMA analyzes in-plane vibrations of a MEMS device under a clear microscope. Its working principle is based on the stroboscopic principle. Based on this principle, characterization results in both time and frequency domains can be accurately generated and analyzed. Our device example for the measurement is a tunneling-based micro-resonator, which was fabricated using the Backside Released SOI process. The tunneling behavior of the sensor can be observed by controlling the motion of the tunneling tip towards the opposing electrode with a typical gap of 10 Aring. This very small gap can be easily achieved by the Bode measurement of PMA for shifting the LED-strobe flashes at a small increment of phase angle over the whole motion of the sensor. In other words, smaller motions of the tip will be easily achieved, when the number of shots per period are larger. For our tunneling measurement, the phase angle shift is 0.5deg with 720 shots per period. The lateral moving proof mass is suspended by the folded springs, and its tip protrudes to an opposing electrode by means of electrostatic forces. The tunneling current has been observed to be exponentially increasing, when the tunneling gap is decreasing. However, the further large current is actually a contacting current, when the mechanical contact happens between the tunneling tip and the opposing electrode. The resonant frequency of the device is ~5 kHz obtained from the Bode measurement