IR uncooled bolometers based on amorphous Ge/sub x/Si/sub 1-x/O/sub y/ on silicon micromachined structures

Abstract

In this work, we present the fabrication of bulk micromachined microbolometers made of amorphous germanium-silicon-oxygen compounds (Ge/sub x/Si/sub 1-x/O/sub y/) grown by reactive sputtering of a Ge/sub 0.85/Si/sub 0.15/ target. We describe the complete procedure for fabricating thermally isolated microbolometers consisting of Ge/sub x/Si/sub 1-x/O/sub 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/sub x/Si/sub 1-x/O/sub y/ layers with moderate electrical resistivity and thermal coefficient at room temperature as high as -4.2% /spl middot/ K/sup -1/ can be obtained. Isolated structures measured at atmospheric pressure in air have a thermal conductance of 3 /spl times/ 10/sup -6/ W /spl middot/ K/sup -1/ and a thermal capacitance of 6/spl middot/10/sup -9/ W /spl middot/ s /spl middot/ K/sup -1/, yielding a response time of 1.8 ms. Bolometers with an IR responsivity of 380 V /spl middot/ W/sup -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.