Monolithic-Wafer-Based Cascade-Actuation XYZ-Microstage With Large Displacement and Low Crosstalk by Integrating an In-Plane Comb-Drive XY-Microstage With Out-of-Plane Al/SiO₂ Bimorph Actuators

This study innovatively proposes and demonstrates a monolithic-wafer-based cascade-actuation XYZ-microstage featuring large displacement strokes and low-crosstalk movements, achieved by integrating an in-plane comb-drive XY-microstage with out-of-plane Al/SiO₂ bimorph thermoelectric actuators for the first time. A three-level serial kinematic scheme within a monolithic wafer, i.e., a three-level frame-in-frame structural configuration, is employed to mitigate motion crosstalk across the X-, Y-, and Z-axes. In the in-plane comb-drive XY-microstage, which comprises four actuation units, both decoupling-motion structural design and capacitance-coupling crosstalk constraints are implemented to ensure low-crosstalk movements along the ±X- and ±Y-axes. Four sets of out-of-plane Al/SiO₂ bimorph actuators independently actuate the comb-drive XY-microstage along the Z-axis. Additionally, mechanical Si-springs are introduced to facilitate electrical interconnections between the XY-microstage and external pads. This design also overcomes the limitation of out-of-plane stroke space in a monolithic wafer, thereby maximizing the actuation potential to achieve significant out-of-plane displacement. A critical step in the microfabrication process involves the successful creation of high-aspect-ratio silicon combs and Al/SiO₂ bimorphs by engineering “step” structures in the handle layer of an SOI wafer, enabling subsequent structure release. Finally, the fabricated monolithic-wafer-based XYZ-microstage can provide large displacements of 92.3 µm, 78.3 µm, and 2.0 µm in the X-, Y-, and Z-directions, respectively. Furthermore, the three-dimensional cascade-actuation configuration within a monolithic wafer is adaptable to various actuation-mode combinations, facilitating multi-degree-of-freedom actuations.