Effects of thin film layers have been investigated on the actuating performance of micro heaters. Bubble behaviors on micro heaters were observed experimentally. Nine (9) kinds of tantalum nitride (TaN) micro heaters were prepared to have different thin film layers with same planar size of 22 μm by 22 μm. Step-stress test (SST) showed that maximum endurable voltage levels in the non-passivated heaters are less than 50% of those in the passivated heaters. Bubble test was carried out using de-ionized (DI) water as working fluid in an open pool. The results showed that the non-passivated heaters can produce comparable bubbles with only 20 to 50% of the input energy required for the passivated heaters. However, the non-passivated heaters could be operated only in a narrow range of driving voltage. Applicability of non-passivated heaters as promising micro actuators needs further investigation from the viewpoints of robustness and reliability.