Fabrication And Characterization Of Cooled Silicon Bolometers For Mm Wave Detection

CEA has a long history of customizing optoelectronic components for space and astronomy applications. Based on this expertise, we are undertaking the development of cooled silicon bolometers for millimetre-wave (mm-wave) polarization detection in the next generation of space astronomy missions. Silicon bolometer technology has been demonstrated successfully in space conditions through the Herschel mission. There are many benefits of this technology such as the use of a simple and low-power read-out circuit that can be integrated below the detector array in an above-IC (Integrated Circuit) integration scheme. The advanced integration in a large array and the fabrication process based on microelectronics techniques are key challenges for these developments.This work presents the early results on the design, the fabrication and the first characterization of an innovative pixel for mm-wave polarization detection. The aim is to have an adapted absorption around lambda=1.5 mm. These bolometers are composed of an absorbing layer and a thermometer, which are thermally insulated from the substrate. To increase the sensitivity, these detectors are working at very low temperature typically between 50 and 100 mK. The suspended thermometer is made of silicon implanted with Phosphorus and Boron species, and we optimized the design to have a high sensitivity with a 3D Variable Range Hopping conduction (Efros law) and a low 1/f noise at low temperature. The heat capacity of the bolometer is optimized by using a meander shape of the thermometer together with superconducting Ti/TiN thin films for the electromagnetic wave absorption. This sensor is implemented on a standard SOI substrate.Measurements of test structures at room temperature, and first results at very low temperature have been performed to evaluate the electrical performances of the fabricated detectors. The mechanical behaviour of released structures, including pixels with a pitch of 1200 mu m and 500 mu m, is presented and discussed.