Characterization of amorphous GexSi1−xOy for micromachined uncooled bolometer applications

Abstract

Thin films of GexSi1−xOy were prepared by reactive magnetron sputtering using simultaneous sputtering of silicon and germanium targets in an environment of oxygen and argon. Silicon and oxygen content were varied from 0 to 30 at. % separately and the effect of the addition of each element on electrical and optical properties of amorphous germanium was studied. The electrical and optical behavior of the compound with varying elemental composition is explained based on the oxidation behavior of the Si and Ge. Increasing the silicon content was found to inhibit the formation of germanium–oxygen bonds. Values of temperature coefficient of resistance as high as −5% K−1 were obtained at moderate resistivity values around 3.8×104 Ω cm. These characteristics could be used to enhance the performance of micromachined uncooled bolometers. The composition control enabled by cosputtering components allows resistivity and activation energy to be tailored to suit different design specifications.

Noise behavior of amorphous GexSi1−xOy for microbolometer applications

“…The semiconductor material has high TCR of À5% K À1 [13] and has a refractive index suitable for forming a highly absorbing k/4 structure, and can be suspended by metal supports designed to minimize thermal conductivity [14]. These factors should combine to create high device detectivity.…”

“…Recent research [12] reported a promising possibility of using a-Ge x Si 1Àx O y compound for microbolometer fabrication. Previous studies [13] indicated that controlling both silicon and oxygen contents leads to high TCR values having moderate resistivity values suitable for such applications. Compound preparation was found to be highly CMOS processing compatible without any fabrication problems.…”

Noise Reduction of Amorphous SixGeyO1–x–yThin Films for Uncooled Microbolometers by Si3N4Passivation and Annealing in Vacuum

“…In addition, to the dangling bonds, the presence of deep traps and recombination centers in Si-Ge bond, and the metal-semiconductor contact between NiCr and Si x Ge y O 1-x-y film might have contributed to the increase in 1/f -noise level [60], [61]. The metal semiconductor interface might have contributed to the noise level due to the cleanliness of the contacts and the possible formation of Schottky junction [26]. After 4 hours annealing in vacuum at low pressure, we have observed significant reduction in noise in wafer W04, and small reduction in the wafer W01.…”

“…Another potential source of 1/f noise is the bond formation of Si x Ge y O 1-x-y sensing layer in terms of Si-O and Ge-O bond formation [26], [27]. The bonds might have resulted in large number of defects in the film and thus contributed to the presence of 1/f -noise.…”

“…Ahmed and Tait [26] determined that for a fixed oxygen concentration, the TCR, and resistivity increases as Si concentration increases up to 5-10 atomic % and then starts to decrease. They also found out that they are proportional to the oxygen concentration in Si x Ge 1-x O y films.…”