The Effect of Laser Beam Intensity and Microscope Illumination Intensity, on the Response of Electrostatic Resonators

In this work we measure the response of an electrostatic MEMS resonator that is made from single-crystalline silicon. Our setup allows for simultaneous measurement of the resonator motion, using both capacitive sensing and optical sensing with a laser vibrometer. We demonstrate that both vibrometer laser illumination and microscope illumination, can affect the resonance frequency of the resonator. Furthermore, we demonstrate that this thermal effect may be non-monotonic. We demonstrate that for low levels of illumination power, the resonance frequency first increases, but then resonance frequency decreases when the illumination power is further increased. This peculiar response is attributed to the competing effects of prestress, and of thermal stress that is induced by illumination. We demonstrate that the measurement of device resistance is a good indicator of thermal heating.