Mid-infrared radiation source for spectroscopic applications based on multiwalled carbon nanotubes on top of silicon

In this work, we report a Multi-Walled Carbon Nanotubes (MWCNTs) MIR source for operation with MEMS spectrometers. We designed a miniaturized source that consists of a micro-machined joule heater on a highly doped silicon substrate, where the heater surrounds an active area. The micro heater filament is made of a platinum thin film on top of silicon with a thin titanium layer, which is used as an adhesive layer between the Silicon dioxide (SiO₂) and the platinum. After dicing the silicon chips, a multi-layered thin film of solution-based MWCNTs is plotted within the active area using a micro-plotting machine with a layer dimensions of 4x4 mm² and a layer thickness of about 1μm. Finally, the device is thermally annealed to improve the morphology of the MWCNTs thin film surface. The micro-machined platinum structure is joule heated by means of applying a voltage difference to the designated pads on the chip allowing a uniform surface heating of the active area containing the MWCNTs thin film. In order to measure the emitted radiation, a MEMS MIR FTIR spectrometer is used to measure the emitted power spectral density from the source with and without the plotting of the MWCNTs thin film, in the MIR range from 2.5μm up to 4.8μm while applying different voltages. The recorded results show that the plotting of the MWCNTs over the silicon substrate improved the recorded PSD of the spectrometer for the all applied voltages. The thermal distribution of the active area is also captured by means of infrared camera at different voltages showing maximum temperatures of 251 °C and 296 °C, while applying 25 and 30 Volts, respectively.