Electrostatic Micro Mirror Array with Batch-Fabricated Torsion Beam of Silicon Nanowire

A new design of arrayed micro mirror device for a high performance spatial light modulator of high resonant frequency, large deflection angle with high mechanical reliability has been proposed. The mirror has $100-\mu \mathrm{m}$ square plate of $5\ \mu \mathrm{m}$ thick, which is suspended by thin silicon nanowire of about $1\ \mu \mathrm{m}$ thick and wide. The device was fabricated using Bosch process and isotropic plasma etching. We successfully demonstrated array operation of $4\times 4$ devices at relatively low actuation voltage (∼20 Vpp) and large mechanical deflection amplitude (∼9°). However, the deviation of vibration amplitude was large among unit resonators. By fitting the frequency response to the Duffing equation we found that self-enhancing actuation force caused by nonlinearity of the vertical combs was a main reason.