Thin film silicon and germanium for uncooled microbolometer applications

Abstract

Hydrogenated silicon (Si:H) and germanium (Ge:H) are assessed for use as the resistive sensing layer in uncooled infrared microbolometer applications. N-type doped Si:H and undoped Ge:H thin films have been deposited using plasma enhanced chemical vapor deposition (PECVD) and monitored during growth using in situ, real time spectroscopic ellipsometry (RTSE) to track changes in the growth evolution and structure occurring within a single film as a function of thickness. Amorphous germanium (a-Ge) films prepared by sputtering and amorphous n-type doped silicon carbon alloy films (a-Si_1-xCx:H) films prepared by PECVD have also been studied by ex situ spectroscopic ellipsometry. Variations in the electrical properties of interest including film resistivity, temperature coefficient of resistance, and 1/f noise character in the form of the normalized Hooge parameter have been tracked as a function of the structure of the material as determined by deposition conditions and characterized by spectroscopic ellipsometry. Such notable variations observed include the effects of transitioning from amorphous to microcrystalline material in n-type Si:H; the addition of carbon to increase disorder in n-type a-Si:H; effects of process parameters for sputtered a-Ge; and a comparison of n-type a-Si:H, ntype a-Si_1-xCx:H, and undoped a-Ge:H properties for films all prepared by PECVD.