The pyroelectric effect and the operating modes of infrared detectors using ferroelectric thin films are described. The key technology of low temperature integration of pyroelectric thin film onto Si-reacl-out integrated circuits and the requirements for pyroelectric thin film are summarized. Through the development of low temperature growth of ferroelectric thin films (e.g. ion beam assisted deposition, buffer layer insertion) and composite element design, a pyroelectric thin film infrared detector with good performance has been developed.