Simple Fabrication of Metal-Based Piezoelectric MEMS by Direct Deposition of $\hbox {Pb}(\hbox {Zr}, \hbox {Ti})\hbox {O}_{3}$ Thin Films on Titanium Substrates

Piezoelectric Pb(Zr, Ti)O₃ (PZT) thin films were directly deposited on cantilever-shaped titanium substrates and evaluated for their piezoelectric properties and actuator performance. Because of the small difference in the thermal expansion coefficient between the PZT and the substrate, and the mitigation of the residual stress, large piezoelectric properties could be obtained for PZT/Ti unimorph actuators. X-ray diffraction measurements clearly revealed that the PZT thin films have a polycrystalline perovskite structure with a random orientation. Observations using a scanning electron microscope (SEM) demonstrated that PZT films, which were 3.8 mum thick, were densely deposited on Pt-coated Ti substrate without pores or cracks. The polarization-electric field (P- E) hysteresis of the PZT film clearly indicates ferroelectricity. The piezoelectric properties of the PZT films were evaluated from the tip displacement of PZT/Ti unimorph cantilevers. Simplified transverse piezoelectric coefficients (e₃₁ ^* = d₃₁/s₁₁ ^E, where d₃₁ and s₁₁ ^E are piezoelectric coefficient and elastic compliance, respectively) were measured, which ranged from -3.6 to 4.3 C/m² - about three times larger than those of the PZT thin films deposited on stainless-steel substrates. Measurement of resonant frequencies of the cantilevers shows a clear dependence on the cantilever length, which obeys the theoretical equation. This indicates that these cantilevers can be reliably applied as sensors and actuators in a resonance mode.