a new structure of the uncooled amorphous silicon (α-Si) infrared detector has been fabricated and characterized. The structure with thermal isolation and infrared absorption based on polyimide (PI) and bottom metal reflective layer is put forward. The fabrication process of the IR detectors is described. The temperature coefficient of resistance (TCR) of α-Si resistance has been investigated. The measurements show that the TCR is up to -2.8%. The detectivity of 1.7×108 cmHz1/2W-1 is achieved with chopping frequency of 30Hz at a bias voltage of 5V. Measurement results indicate that the polyimide layer exhibits excellent thermal isolating characteristics and the unique sandwich IR absorption structure is beneficial to the enhancement of detectivity. Compared with other techniques, the IR detectors using PI as thermal isolation layer are not only with simpler process, lower cost and higher yield, but also suitable for the application of large-scale uncooled infrared focal plane arrays (IRFPA).