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A micro biosensor, which can be applied to a lab-on-a-chip (LOC), is developed in order to detect biomaterials such as protein or DNA. The biomaterials are detected by the mass micro-balancing technique, which measures the change of the resonant frequency of the sensor structure. The sensor structure consists of a micro cantilever actuated by piezoelectric PZT film. The PZT film is designed to act as both a sensor and an actuator. The geometry of the micro-cantilever is determined so as to maximize the sensitivity of the sensor, and environmental effects such as added mass effect in liquid are also considered in the design procedure. The microcantilever is 100 μm in length, 30 μm in width and 5 μm in thickness, and the PZT film thickness is 2.5 μm. The first resonant frequency of the PZT-micro cantilever is 1.2∼1.3 MHz. Lastly, the fabricated micro biosensor using the self-exciting PZT-micro cantilever is tested by detecting the insulin-anti insulin binding protein and poly T-sequence DNA.