Resumen de Optically active Si-rich Si3N4 Mu-cavities for sensoristic applications
Federico Ferrarese Lupi
In this thesis we have presented a thorough study on the optical and sensoristic properties of SRSN Mu-disks, in an isolated configuration and when coupled to a passive Si3N4 waveguide placed underneath. The whole structure of the device have been previously simulated in order to study the behavior of the supported WGM when subject to a geometrical variation (i.e.: radius, thickness, shape of the edge of the isolated Mu-disk): the obtained results granted the realization of Mu-resonators with Q factor exceeding 104. The coupled structure have been then simulated with the main goal of maximizing the WGM intensity transmitted at the end of the WG. This task has been fulfilled through a careful optimization of the geometrical parameters (i.e.: X-Gap and Z-Gap). The subsequent step, involving the fabrication process of the sample - realized in the Centro Nacional de Microelectronica (CNM) of Bellaterra - has been carried out using standard CMOS compatible process. The deposition and the implantation of the Si3N4 has been performed by means of LPCVD technique, while for the SiO2 deposition the PECVD. Finally the optical elements has been defined by means of a two level photolithographic mask. On the produced samples we have performed a superficial analysis (SEM, AFM) with the aim of evaluate the presence of geometrical imperfections and estimation of the superficial roughness. Furthermore the EFTEM analysis revealed the absence of Si-nc inside the active layer. Using the Cut-back technique, low losses under 1 dB/cm have been found in both VIS and IR spectral range in the passive WG of different width. On the other hand, applying the SES technique on an Si-rich WG structure we have been able to extract the losses value of active material in a wide and continuous range of wavelength, defined inside the PL spectrum. As a result of a careful optimization of the active SRSN in terms of PL intensities and optical losses, we have been able to produce bright and high Q isolated Mu-disks, achieving maximum values about 1.4x104 in a wide spectral range in the VIS and emitting up to few nW on a single resonance. The reported Q values are the best ever reported in circular Si-based light emitting Mu-cavities and are just limited by the spectral resolution of our experimental setup. The coupled structures demonstrated Q values up to 1.48x103, which are susceptible to be greatly improved through optimization of the fabrication process. Through a prof of concept , we have demonstrated that these structures are very sensible to the surrounding material and are able to detect refractive index changes with sensitivities of 51.79 nm/RIU and minimum measured refractive index change of 1.15x10-3 RIU.
