Simple millimeter-scale robot using Pb(Zr, Ti) piezoelectric thin film actuator on titanium substrate

We have developed a piezoelectric-driven millimeter-scale robot with a simple structure. This millimeter-scale robot, which consists of a titanium (Ti) body and front/back legs integrated with a Pb(Zr, Ti)O₃ (PZT) piezoelectric thin film actuator, is driven by using mechanical resonance. To simply fabricate the millimeter-scale robot, the PZT thin film was directly deposited on an H-shaped Ti substrate by radio frequency magnetron sputtering and the shape of the robot was completed by plastic deformation of the monolithic Ti substrate. We obtained the transverse piezoelectric coefficient d ₃₁ of the deposited PZT thin film was −21.3 pm/V, which was sufficient for driving the fabricated millimeter-scale robot with a low driving voltage ≤10 V. We also evaluated the resonant characteristics of the fabricated robot and confirmed that the front/back legs of robot were oscillated in primary and secondary resonance modes at around 4.5 and 11 kHz, respectively. We demonstrated that the millimeter-scale robot with asymmetric structure in the front-back direction was controlled by changing driving voltage conditions and a bending angle formed by the front/back legs. The moving speed of the millimeter-scale robot was 13.6 cm/s by applying negative unipolar voltage of 10 V_pp at 10.6 kHz when the bending angle was set to 109°. We experimentally confirmed that the millimeter-scale robot can be driven forward and backward by optimizing the shape of the robot and mechanical resonant modes.