Lead titanate (PbTiO3) thin‐film pyroelectric infrared detectors have been fabricated on polycrystalline silicon micromechanical membranes. Pyroelectric PbTiO3thin films of thickness ranging from 0.2 to 0.6 &mgr;m were prepared by sol‐gel spin casting techniques and deposited on 1.0‐&mgr;m‐thick polycrystalline silicon membranes suspended 1.0 &mgr;m above the surface of a silicon wafer. This composite structure offers high sensitivity and low thermal mass. The measured pyroelectric coefficient for 0.36‐&mgr;m‐thick PbTiO3films is 90 nC/cm2 K. The measured blackbody voltage responsivity for a pyroelectric element with an active area of 7×10−4cm2at 297 K and a chopping frequency of 50 Hz is 4.2×104V/W. The measured normalized detectivityD* at 297 K and 50 Hz is 1.0×109cm Hz1/2/W.