Advanced small pixel high fill factor uncooled focal plane array

Abstract

A microbolometer detector element (10) for a focal plane array is provided including an optically absorptive material structure (12) characterized by an electrical resistivity that varies as a function of its temperature coupled in spaced relation to a thermal isolation structure (20). The thermal isolation structure (20) is coupled in spaced relation to a sensor (34) connected to the optically absorptive material structure (12) for sensing the absorptive structure's (12) electrical resistivity. The thermal isolation structure (20) facilitates very high fill factors even when the pixel size is shrunk below the baseline fifty micron size. The thickness of the optically absorptive material structure (12) and the thermal isolation structure (20) can be independently controlled since the thermal isolation structure (20) is disposed in spaced relation under the absorptive material structure (12). The thermal isolation structure (20) can be made several times longer than prior art designs to increase the thermal isolation of the optically absorptive material structure (12) and to increase pixel responsivity. The thermal isolation structure (20) may include a planar member (26) for reflecting incident optical radiation not absorbed by the absorptive material (12) back to the absorptive material (12). In a preferred embodiment of the present invention, the absorptive structure (12) is a polycrystalline semiconductive layer supported above the thermal isolation structure (20) by downwardly projecting leg members (18). The thermal isolation structure (20) also includes downwardly projecting leg members (28) for supporting it in spaced relation above a silicon substrate surface (30) overlying an integrated readout circuit (34).