Piezoelectric diaphragms were fabricated using bulk micromachining. The diaphragms had a unimorph structure, where Pb(Zr0.52Ti0.48)O3 (PZT) and thermally grown silicon oxide (SiO2) films were used as the active and passive layers, respectively. To actuate the diaphragms, two modes were designed: d31 and d33-mode. For d31-mode diaphragms, a Si wafer with Pt/Ti/SiO2 (0.5 νm) was coated with ∼1.2 νm PZT. A Cr/Au top electrode was then evaporated. Each layer including the bottom electrode was patterned into a circular shape. To fabricate d33-mode diaphragms, a Si wafer with thermal SiO2 (0.5 νm) was coated with ∼0.3 νm ZrO2 and ∼1.6 νm of PZT. On top of these layers, a Cr/Au top electrode was deposited and patterned into a ring- shaped interdigitated transducer. Finally, both d31 and d33-mode diaphragms were released using deep reactive ion etching. Diameters of the fabricated diaphragms were in the range of 600 νm and 1000 νm. For d31-mode diaphragms, the dielectric constant and loss of the released piezoelectric layer at 1 kHz were > 800 and < 2%, respectively. The remanent polarization was ∼20 νC/cm2and the coercive field was ∼61 kV/cm. Ferroelectric measurements showed well- developed hysteresis loops for the d33-mode diaphragms. Both d31 and d33-mode diaphragms behave as membranes rather than plates. Their measured resonance frequencies were consistent with calculations from an analytic model for circular membranes and ANSYS finite element analysis.