Resonant micromirror with symmetrical AIN thin film actuators: Invited paper

Micro-Opto-Electro-Mechanical resonant micromirror featuring a 4 mm aperture for laser-based measurement is presented. The MOEMS-mirror is fabricated on an SOI-wafer with piezoelectric actuators based on aluminium nitride thin films and packaged in a vacuum for a high-efficiency operation. The design of the device features four symmetrical co-radial beam structures, where each beam structure incorporates discrete piezoelectric elements for actuation and sensing. The integrated sensing element provides an accurate and real-time feedback signal for the control system, as it is directly mechanically coupled to the source of movement. Symmetrical design allows the mirror to be excited in the desired mode by modifying the frequency and phase on each of the driving actuators. For the laser measurement applications driving the mirror opposite actuators in opposite polarity and perpendicular axis with different frequencies, creates up to a 40-degree field of view Lissajous scanning pattern. The amplitude of the resonance is strongly affected by the Duffing-type nonlinearity and the derivative of the amplitude vs. frequency curve is small, allowing relatively large changes of frequencies without affecting the amplitude. Phe presented digital control method allows adjustment of frequencies via a phase accumulator to control Lissajous pattern parameters: ratio, phase and amplitude. Due to the high efficiency of aluminium nitride actuators and high Q value, a direct low-voltage CMOS interface can be implemented between the digital control system and piezoelectric actuators. The high amplitude feedback signals allow straightforward conversion to the digital domain and enable monitoring of operation mode and phase.