Study On The Microbolometer In A Standard CMOS Technology

The uncooled infrared detectors have gained wide attention, as they have lots of advantages like no need of refrigeration, low cost, low power consumption, low weight, small size, fast start-up and easy to use. Among them microbolometer is the uncooled infrared detector which has the widest application. It's development originated from military applications. However, with the progress of infrared technology and growing market requirements, applying uncooled infrared microbolometer in a standard CMOS process to commercial and civil applications is becoming a research hotspot. This thesis proposed low-cost uncooled microbolometers based on a standard 0.5 ?m CMOS process systematically, including the structure design, fabricating processes and performance parameter measurements.Considering low cost and mass production, based on a standard CMOS process, two single-sacrifice-layer microbolometers based on one-layer micro-bridge structure are designed and fabricated. The microbridge structures of microbolometers are fabricated by etching the surface sacrificial layer without any additional lithography or deposition steps. The metal plug (tungsten) between the Metall layer and the Metal2 layer and the Metal3 layer (aluminum) in the standard CMOS process are employed as thermistors. The Poly2 layer and the Metal2 layer are employed as surface sacrificial layers, respectively. The sacrificial layer of polysilicon is removed by a TMAH solution which can not corrode aluminum. The sacrificial layer of aluminum is removed by a phosphoric acid solution. Measurements show that the responsivity and detectivity of the single-sacrifice-layer tungsten microbolometer is 139.95V/W and 8.19×107cmHz1/2/W and the responsivity and detectivity of the single-sacrifice-layer aluminum microbolometer is 643.6V/W and 3.44×108cmHz1/2/W.To improve the performance parameters, a double-sacrifice-layer aluminum microbolometer based on one-layer micro-bridge structure is designed and fabricated. The microbridge structure of the microbolometer is fabricated by etching the surface sacrificial layer without any additional lithography or deposition steps. The Metal3 layer in the standard CMOS process is employed as a thermistor. The Metal2 layer and the metal plug (tungsten) between the Metall layer and the Metal2 layer are employed as the sacrificial layers. They are removed by a phosphoric acid solution and a H2O2 solution, respectively. Compared with the single-sacrifice-layer microbolometer, the double-sacrifice-layer microbolometer can reduce the near-field thermal radiation and enhance absorption for the 3?5 ?m infrared. Measurements show that the responsivity is 1751V/W and the detectivity is 8.37×108cmHz1/2/W.To balance the thermal insulation and the fill fator of the one-layer micro-bridge structure when the pixel size decreseses, a multi-sacrifice-layer aluminum microbolometer based on two-layer micro-bridge structure is designed and fabricated. The two-layer microbridge structure with hidden legs of the microbolometer is fabricated by etching the surface sacrificial layer without any additional lithography step. The Metal3 layer in the standard CMOS process is employed as a thermistor. The Poly2 layer, the metal plug (tungsten) between the Poly2 layer and the Metall layer, the Metall layer, the metal plug (tungsten) between the Metall layer and the Metal2 layer, the Metal2 layer are employed as the sacrificial layers. They are removed by a TMAH solution, a H2O2 solution and a phosphoric acid solution, respectively. Compared with the one-layer micro-bridge structure, the two-layer micro-bridge structure can achieve a best fill factor and is suitable for fabricated smaller microblometer. Measurements show that the responsivity is 863.96V/W and the detectivity is 6.39×108cmHz1/2/W.To realize the monolithic integration, studies on aluminum microbolometer array and its integrated readout circuits are also implemented. The single-sacrifice-layer aluminum microbolometer with an optimal design of supporting legs is used as the pixel. The readout circuits of the microbolometer array can be designed beneath the microbridge structure to decrease the chip area cost. Measurements show that the responsivity is 1206V/W and the detectivity is 5.98×10 cmHz1/2. The array resistances are uniformly distributed with a high yield. Readout circuits work fine which proves the feasibility of the array. This research lays the foundation for fabricating low-cost, large-scale and high-integration microbolometer array.