Electrostatically-actuated grating light modulator fabricated using SU-8 photoresist

This paper presents a novel SU-8 polymer-based grating light modulator fabricated using conventional process technology which requires no expensive equipments and materials. A set of fifty 2.5μm-thick SU-8 micro beams of 20μmwidth x 100μm-length is patterned by photolithography on the aluminum sacrificial layer to form a grating. The micro beams are arranged in parallel with an inter-beam gap of 20μm. The wide inter-beam gap tolerates low patterning precision. Narrow air gaps of 0.5μm beneath the micro beams are formed by combination of wet-etching of the aluminum sacrificial layer and freeze drying method, where cyclohexane is chose as sublimation liquid because of the high freezing point and the ease of sublimation. When a voltage is applied across the upper and lower electrodes to attract the micro beams to the substrate, neighboring micro beams are actuated to deflect in phase and the optical path length between the upper electrode/mirror on the micro beam and the lower mirror on the substrate decreases by quarter wavelength, the 0th and 1st order diffracted light intensities vary from maximum and minimum, respectively, or vice versa. The voltage to obtain maximum modulation for HeNe laser beam of 632.8nm wavelength is 70V. The rise and fall response times of the light modulation are 3.08 microsecond and 4.63 microsecond, respectively.