The preparation and characterization of in-plane polarized lead zirconate titanate (PZT) piezoelectric diaphragms for sensors and actuators applications are demonstrated in this letter. The single phase PZT films can be obtained on SiO2-passivated silicon substrates via sol-gel technique, in which PbTiO3 (PT) films are used as seed layers. Al reflective layer is deposited and patterned into concentric interdigitated top electrode by lithographic process, subsequently. The diaphragms are released using orientation-dependent wet etching (ODE) method. The size of the diaphragms is 5 mm in diameter and the outer interdigitated (IDT) electrode diameter (4.25 mm) is fixed at 85% of the diaphragm diameter. The three-dimensional (3D) profiles results indicate that the measured maximum central deflection at 15 V is approximately 9 \mu m. Sensing measurements show that the capacitance continually decreases with an increase of applied force, while the case of induced charge exhibits a reverse tendency.