Surface-micromachined pyroelectric infrared imaging array withvertically integrated signal processing circuitry

Surface-micromachining techniques have been used in the fabrication of a 64×64 element PbTiO₃ pyroelectric infrared imager. Polysilicon microbridges of 1.2 μm-thickness have been formed 0.8 μm above the surface of a silicon wafer. Each of the 4096 polysilicon microbridges measures 50×50 μm² and forms a low thermal mass support for a 30×30 μm² PbTiO₃ pyroelectric capacitor with a thickness of 0.36 μm. The air-bridge formed reduces the thermal conduction path between the detector element and substrate. An NMOS preamplifier cell is located directly beneath each microbridge element. The measured blackbody voltage responsivity at 30 Hz is 1.2×10⁴ V/W. The corresponding measured normalized detectivity (unamplified) D* is 2×10⁸ cm-Hz^1/2W at 30 Hz. The test chip fabricated measures 1×1 cm² and contains more than ten thousand transistors and 4096 micromechanical structures with integrated ferroelectric microsensors. The technique of stacking of microsensors and integrated circuits represents a new approach for achieving high-density and high-performance integrated pyroelectric microsensors through minimization of circuit to sensor interconnection with extremely small thermal crosstalk