Tunable refractive beam steering using aluminum nitride thermal actuators

Step-structured thermo-mechanical actuators based on aluminum nitride (AlN) thin films and their application in refractive beam steering are investigated. The actuators will tilt a suspended plate and deform a liquid surface to realize a micro-prism. Arrays of tunable micro-prisms will increase the resolution of compound eye systems. A numerical actuator description is presented and the beam geometry is investigated, considering achievable tilt angles and actuator linearity. For an accurate design, the coefficient of thermal expansion (CTE) of AlN is determined, while measuring the bow of a coated silicon substrate at different temperatures. For a temperature difference of 300 K, the results show a maximum tilt angle of 7.1 °, which is independent of actuator length. Furthermore, the fabrication process is introduced and the nano-crystalline structure of AlN at facets, which are caused by pre-structured substrates, is investigated.