IR uncooled bolometers based on amorphous GexSi1-xOy on silicon micromachined structures

In this work, we present the fabrication of bulk micromachined microbolometers made of amorphous germanium-silicon-oxygen compounds (Ge_xSi_1-xO_y) grown by reactive sputtering of a Ge_0.85Si_0.15 target. We describe the complete procedure for fabricating thermally isolated microbolometers consisting of Ge_xSi_1-xO_y sensing films deposited on sputtered silicon dioxide membranes suspended over a silicon substrate. The electrical properties of the sensitive material are set by controlling the deposition parameters of the sputtering technique. Under optimum deposition conditions, Ge_xSi_1-xO_y layers with moderate electrical resistivity and thermal coefficient at room temperature as high as -4.2% · K^-1 can be obtained. Isolated structures measured at atmospheric pressure in air have a thermal conductance of 3 × 10^-6 W · K^-1 and a thermal capacitance of 6·10^-9 W · s · K^-1, yielding a response time of 1.8 ms. Bolometers with an IR responsivity of 380 V · W^-1 and a NEDT of 3.85 K at 100 nA bias current are obtained. The use of sputtered films allows designing a fully low-temperature fabrication process, wholly compatible with silicon integrated circuit technologies.