Responsivity of infrared antenna-coupled microbolometers for air-side and substrate-side illumination

The response of an antenna-coupled microbolometer fabricated on a Si wafer coated on both sides with thin films of SiO2 was measured for two types of illumination: through the substrate and from the air side. The measurement was performed in the spectral range from 9.22 to 10.84 mu m. Both cases are modeled by using the transmission, reflection, and absorption properties of the three-layer wafer. The spectral characteristics of the SiO2 thin film play a major role in the response of the detector. The responses of the sensor to the parallel and perpendicular polarizations are modeled by using two main contributions: the heating by absorption in the SiO2 layer and the coupling of incident flux on the bolometer. Fitting this model to the experimental data allows us to conclude that the antenna response is the result of the incident flux coming from the substrate side. When the device is illuminated from the air side, the antenna signal results from the flux reflected at the film/substrate interface. The efficiencies of the contributions to the antenna signal coming from the substrate or from the air side have been obtained from the data fitted with the model. The substrate-side contribution is 50 times larger than the air-side contribution, confirming the theory of lithographic antenna on a dielectric substrate. (C) 2000 Elsevier Science B.V. All rights reserved.