Pseudo-analog electrostatic piston micromirror

We report on the design, simulation, fabrication and testing of pseudo-analog micromirrors. Electrostatically actuated piston micromirrors were fabricated using the SUMMiT V process with a goal of achieving nearly analog displacement using digital voltage control. A mirror is controlled by multiple electrodes with varying areas that correspond to a binary system. As an example, a mirror is actuated using four electrodes with unit areas of 1, 2, 4 and 8. The same voltage level is applied to one or more of the electrodes to control the vertical displacement. This arrangement will allow up to 16 different displacements, with more levels possible with a larger number of electrodes. The system is amenable to digital control and can be scaled to large arrays. Parametric numerical models built in ANSYS simulations were used to predict performance and further refine the design parameter values derived from the theoretical models. An interferometric microscope has been used to measure the vertical displacement of the mirrors as voltage is applied. Experimental results show that mirror displacement is proportional to the total electrode area used to actuate the mirror. Reasonable repeatability in displacement has been seen for a mirror actuated by the same total electrode area and voltage.