Pyroelectric infrared detectors based on La-modified PbTiO₃ (PLT) thin films have been fabricated by RF magnetron sputtering and micromachining technology. The detectors form Pbi_(1-x)La_xTi_(1-x/4)O₃ (x=0.05) thin film ferroelectric capacitors epitaxially grown by RF magnetron sputtering on Pt/MgO (100) substrate. The sputtered PLT thin film exhibits highly c-axis oriented crystal structure that no poling treatment for sensing applications is required. This is an essential factor to increase the yield for realization of an infrared image sensor. Micromachining technology is used to lower the thermal mass of the detector by giving maximum sensor efficiency. Polyimide is coated on top of the sensing elements to support the fragile structure and the backside of the Mg0 substrate is selectively etched to reduce the heat loss. The sensing element exhibited a very high detectivity D* of 8.5x10^8 cm·√ Hz/W at room temperature and it is about 100 times higher than the case of micromachining technology is not used. A sensing system that detects the position as well as the existence of a human body is realized using the array sensor.