Micromachined piezoelectric diaphragms actuated by ring shaped interdigitated transducer electrodes

Piezoelectric diaphragms actuated by interdigitated transducer (IDT) electrodes were fabricated by bulk micromachining. To fabricate the diaphragms, a Si wafer with ∼0.5 μm of thermal SiO₂ was coated with ∼0.3 μm ZrO₂ and ∼1.6 μm thick Pb(Zr _0.52Ti_0.48)O₃ (PZT) layers. A Cr/Au top electrode was then deposited and patterned into ring-shaped IDT electrodes. The diaphragms were released using deep reactive ion etching. The fabricated diaphragms had three different IDT diameters of 500, 600 or 700 μm and their diameters were ∼40% larger than the IDT diameters. The PZT films on these diaphragms exhibited good ferroelectric properties. Their remanent polarizations were ∼20 μC/cm² and the coercive fields were about 50 kV/cm. Resonance measurements for these diaphragms indicated that the diaphragms behaved as membranes. Without an electric field, the diaphragms were almost flat to within ∼0.3 μm. At an electric field of 120 kV/cm, the diaphragm was depressed by ∼4.3 μm in the case of a 700 μm diaphragm with 10 μm electrode spacing. The deflection profiles were modeled via finite element analysis; deflections larger than the structure thickness can be achieved. This makes these devices useful for micropumps and other actuator applications.