Amorphous SixGeyO1−x−y thin films for uncooled infrared microbolometers

Abstract

This paper presents a detailed characterization of Silicon Germanium Oxide (SixGeyO1−x−y) thin films for uncooled infrared microbolometers. The films were prepared by RF magnetron sputtering using simultaneous deposition from silicon and germanium targets in an argon and oxygen environment. The electrical properties of the films were studied as a function of oxygen (up to 10%) and silicon (up to 30%). The results demonstrated that a high temperature coefficient of resistance (TCR) and a low corresponding resistivity can be achieved using various compositions, for example, Si0.054Ge0.877O0.069 films have achieved a TCR and a resistivity of −3.5 %/K and 629 Ω-cm, respectively. X-ray diffraction (XRD) demonstrated that the films are amorphous, and the broadening of XRD spectra (full width at half maximum, FWHM) is related to the decrease and increase of TCR and resistivity, for example, oxygen and fixed Si concentrations of 6.16% and 4% result in narrow spectra which corresponds to a higher TCR value of −3.6 %/K. The Fourier transform infrared spectroscopy (FTIR) study shows that the absorption peaks corresponding to Ge-O and Si-O are located around 800 cm−1 and 960 cm−1, respectively. The peak intensity of Si-O increases as the Si content increases while Ge-O bond disappears as the Si content increases above 6%. These results are used to explain the TCR and resistivity behavior as the Si concentration increased in the film. In addition, the chemical bonding between Ge-Ge and Ge-Si, measured using the Raman spectroscopy study demonstrates that at a fixed oxygen concentration of 4%, The peak shift of Ge-Ge and Ge-Si are relatively small which corresponds to a small change in TCR and resistivity at this Si concentration range, while at oxygen concentration of 8%, the Ge-Si bond have more effects on increasing TCR values, and the larger peak shift corresponds to a higher TCR values.