Nanofabrication of Nanoelectromechanical Spectrometers.

Optical spectroscopy is a useful tool for characterisation in many different fields, but is currently largely limited to bulky benchtop equipment. Miniaturization to chipscale spectrometers could help bring spectroscopy to in-situ measurements and also allow it to be integrated in smart devices and wearable technology. Many different spectrometer designs have been investigated for chip-scale spectrometers but Fourier-transform spectrometers are of particular interest for low-cost spectrometers as they can function with a single light source and photo detector. These spectrometers are based on interferometers in which light is split into two paths with a tunable optical path difference before being recombined. A common approach for creating a tunable optical path length in research is to use heaters combined with the thermo-optic effect, but this method is power-hungry and suffers from thermal crosstalk. Nanoelectromechanical systems (NEMS) is a promising alternative to thermooptics that offers moderate operating frequencies, small device footprints and extremely low power consumption. Rather than tuning the material, photonic NEMS use electrostatic actuators known as comb drives to elastically and reversibly deform optical components. This adds some complexity to the fabrication of the spectrometer since the optical components now need to be suspended so they are free to deform, and the electrostatic actuators should be doped to operate at their full potential. Furthermore, as suspended nanostructures are fragile, a NEMS spectrometer requires packaging which should encapsulate and protect the nanostructures and allow electrical and optical signals to pass in and out of the packaged device. This thesis aims to provide the various necessities outside of optical components for making a NEMS spectrometer. Diffusion doping processes for both n- and p-type local doping, compatible with our process for creating suspended nanostructures, were developed. Thin comb drives were modeled and characterised, and the ubiquitous surface forces that can cause nanomechanical structures to collapse were investigated. Finally, fabrication processes for chip-scale packaging of multiple spectrometers, necessary for them to function in real-world applications, were developed. All of these results were developed in the context of creating a chip-scale spectrometer, but apply to photonic NEMS in general.