Multi Degrees-of-Freedom Hybrid Piezoelectric-Electrostatic MEMS Actuators Integrated With Displacement Sensors

This work presents novel multi degrees-of-freedom (DOF) actuators based on piezoelectric and electrostatic actuation to generate both in-plane and out-of-plane motions, intended to position a suspended optical waveguide for chip-to-chip alignment in photonic integrated circuits. In this context, the mechanical structures of the actuators with a suspended platform to carry the waveguide, are designed to house aluminum nitride (AlN) as the piezoelectric material for generating out-of-plane motion and a comb-drive, whose fixed and moveable fingers are positioned on the same layer for in-plane motion. Two distinct designs, i.e., a 2-DOF design with motions along the Z-and Y-axes and a 3-DOF design with motions along the Z-, Y-, and X-axes were fabricated and tested. Both designs include capacitive-based displacement sensors to track the motions in Z-and Y-axes. Experimental results at ±60 V indicate that 3 devices of each design give an average displacement of 3.16 ± $0.34~\mu \text{m}$ and 0.63 ± $0.04~\mu \text{m}$ in the Z-axis for the 2-DOF and 3-DOF designs, respectively. For the Y-axis at 120 V, the average results for the two designs respectively were found to be 3.06 ± $0.17~\mu \text{m}$ and 7.38 ± $0.29~\mu \text{m}$ , with the ability to extended the later to $10.69~\mu \text{m}$ at 140 V. In the X-axis, the 3-DOF design can produce total of 300 nm of displacement at ±100 V. The capacitance measurements were found to correlate well with the tracked displacement. Furthermore, simultaneous activation of more than one actuator could mitigate misalignment and align the platform with a fixed surface. [2023-0148]