Semiconducting YBaCuO microbolometers for uncooled broad-band IR sensing

This paper describes the modeling, design, fabrication and testing of advanced uncooled thermal detectors, based on semiconducting YBaCuO. The aim is to provide NASA with advanced broad-band infrared (IR) detectors to replace the current CERES (Clouds and the Earth's Radiant Energy System) hardware that utilizes three channels, each housing a 1.5 mm x 1.5 mm. thermister bolometer with 1X4 array of detectors in each of the three channels, thus yielding a total of 12 channels. A double mirror structure is used to obtain uniform spectral response from 0.3-100 mum wavelength. Double absorbers are utilized to further flatten the spectral response and to enhance the absorption of infrared radiation. The devices were fabricated using a polyimide sacrificial layer to achieve thermal isolation of the detector. A low thermal conductivity to the substrate enables the detector to integrate the energy from the incident radiation. An air gap was created by ashing the polyimide sacrificial layer from underneath the thermometer. A passivation layer was used to protect YBaCuO during ashing process and maintain a relatively high temperature coefficient of resistance of around 2.8%. These devices have successfully demonstrated voltage responsivities over 10(3) V/W, detectivities above 10(8) cm. Hz(1/2)/W, NEP per root Hertz bandwidth less than 4x10(-10) W/Hz(1/2) and thermal time constant less than 15 ins. Several specific designs were fabricated and tested. Relatively uniform response in the wavelength range of 0.6 to 15 mum was measured.