Fabrication and modelling of microactuator systems derived from surface-machined zinc oxide-on-silicon nitride heterogeneous bimorphs

Microsensors and microactuators, fabricated by micromachining techniques, can be further integrated with microelectronics to form mobile microrobots. In this thesis, ZnO-on-Si{dollar}sb3{dollar}N{dollar}sb4{dollar} piezoelectric heterogeneous bimorphs have been studied as microactuators to provide microrobots with walking functions. The bimorphs are fabricated on silicon wafers using a surface-machining method with a separate bottommost layer of ZnO as the sacrificial etch layer. The etched-free bimorph is a composite cantilever comprised of five layers of materials which are, in the order of deposition, Si{dollar}sb3{dollar}N{dollar}sb4{dollar}, Au/Cr, ZnO, Au/Cr and photoresist. One end of the bimorph is clamped at the silicon substrate, the other is free.; Both single and dual-bimorphs (formed by two parallel single bimorphs coupled by a Si{dollar}sb3{dollar}N{dollar}sb4{dollar} bridge at their free ends) have been fabricated and characterized.; The constituent equations of a single and a dual-bimorph have been derived to describe their quasistatic responses under various combinations of electrical and mechanical inputs. Energy efficiencies of the single bimorph, deployed as micro-machines with various loading conditions, have been derived.; Flexural bending was obtained from both single and dual-bimorphs by applying a voltage across the ZnO layer. Measurement of the deflection as a function of dc voltages showed two different regimes of voltage dependence. For low voltage magnitude ({dollar}<{dollar}1V), small and linear deflection was obtained, consistent with theoretical prediction. At higher voltage magnitude ({dollar}>{dollar}1V), large deflection was obtained.; I-V characterization of the polycrystalline ZnO layer indicated an electrical system equivalent to two back-to-back Schottky diodes. Large electrical hysteresis was observed in the low frequency I-V curves at high voltage levels, while mechanical hysteresis was observed at low voltage levels. The large bimorph deflection could be attributed to Joule heating.; The fundamental resonance frequency of the bimorph has been measured and is in close agreement with the value as predicted by the Euler-Bernoulli equation. Resonance was also obtained at one half of the true resonance frequency.; Dual bimorphs were tested to demonstrate both symmetric and asymmetric bending modes. Flexural bending was obtained during symmetric driving, while twisting motion was obtained during asymmetric driving.