Large-aperture Fabry-Perot filters based on silicon/silicon carbonitride distributed Bragg reflectors for the near-infrared
This contribution presents silicon carbonitride as a new low refractive index material for integration together with silicon in suspended distributed Bragg reflector membranes. We show how its benign mechanical stress properties can be used to fabricate inherently flat mirror membranes of up to 5 mm diameter. Due to the large refractive index contrast to silicon such mirror membranes exhibit high reflectance over a wide spectral range. Using these mirrors, we demonstrate a proof of concept for a large aperture Fabry-Perot filter with narrow bandwidth that could help miniaturize hyperspectral imaging sensors.
MOEMS FPI sensors for NIR-MIR microspectrometer applications
This paper presents near- and mid- infrared (NIR-MIR) wavelength range optical MEMS Fabry-Perot interferometers (FPIs) developed for automotive and multi-gas sensing applications. MEMS FPI platform for NIR-range consist of LPCVD (low-pressure chemical vapour) deposited polySi-SiN λ/4-thin film Bragg reflectors, with the air gap formed by sacrificial SiO2 etching in HF vapour. Characterization results for the NIR MFPI devices for λ = 1.5 – 2.0 μm show resolution of 15 nm at the optimization wavelength of 1750 nm. We also present a MIR-range MEMS FPI for λ = 2.5 – 3.5 μm, which utilizes silicon and air in within the Bragg reflector structure to provide a high contrast for improved resolution. Characterization results show a FWHM (Full Width Half Maximum) of 20 nm in comparison to the 50 nm resolution provided by earlier MEMS FPIs realized for hydrocarbon sensing with conventional CVD-thin film materials. The improved resolution and the extended operation region shows potential to enable simultaneous sensing of CO2 and multiple hydrocarbons.
Properties of a-Si1−x Cx:H thin films deposited from the organosilane Triethylsilane
Abstract We deposited carbon-rich a -Si 1 −x C x :H thin films from the liquid organosilane source Triethylsilane (C 2 H 5 ) 3 -Si–H (TrES) in a PECVD process at 13.56 MHz. These films generally show a photoluminescence in the visible spectral range when excited with ultraviolet light. By increasing the substrate temperature from room temperature up to 300°C we can red shift the PL peak energy and also the optical Tauc gap. Furthermore, an increase in the film density and correspondingly in the refractive index is observed. FTIR measurements show that these films have a polymer–like character for all temperatures under investigation. The hydrogen concentration is calculated from the stretching modes of CH n and SiH n groups, respectively, and is shown to decrease with substrate temperature. We also show that the amount of hydrogen bonded to carbon decreases with respect to that bonded to silicon with substrate temperature.