Silicon-rich Nitride as a versatile and highly non-linear CMOS compatible material platform.
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Silicon-rich Nitride as a versatile and highly non-linear CMOS compatible material platform.


Silicon based photonic devices and systems are bringing a wealth of new capabilities and will continue towards large scale adaption in a variety of applications such as chip-chip communication. Such optical interconnects rely upon modulators as one of the key backbones in the interconnect link. Despite the growing importance of such interconnects however, CMOS compatible platforms still predominately utilize carrier dispersion-based modulators. Such modulators rely upon the plasma dispersion effect in which changes in electron and hole concentrations drives a change in the refractive index of the junction region of typically a PN or PIN junction device. This approach while a clearly successful one, has a number of drawbacks such as its undesirable impact on not only the real but also imaginary part of the refractive index, but also typically results in high propagation losses, with higher modulation speeds requiring higher dopant concentrations and thus resulting in further loss increases. The optimal candidate for modulation then has is likely electro-optic modulators as utilizing the Pockels effect, based on the second order nonlinear susceptibility can enable pure real part changes in the refractive index. The most commercially successful electro-optic modulator being the commonly available, typically bulk, lithium niobate modulators. While materials such as lithium niobate, barium titanate, and others, can result in large changes in refractive index, and thus make efficient modulators, these materials are not compatible with the CMOS process flow. As such applications which strictly utilize CMOS process flows in tapeouts still mostly utilize carrier dispersion-based modulators. In this thesis we will discuss Silicon rich nitride as a material platform. Why it is interesting, how it could bring new and powerful capabilities to a CMOS process flow, and why it deserves further exploration and adoption. We will discuss how Silicon-rich Nitride can be utilized in a variety of nonlinear applications, from modulation to optically bistable operation. Our research has focused on exploring nonlinearities in a material platform readily compatible with CMOS process flows. Specifically, our research has centered around Plasma Enhanced Chemical Vapor Deposition (PECVD) based silicon rich nitride films. It has been shown in literature that such films can exhibit a wide range of refractive index values ranging from stochiometric films as low as approximately 1.87 up to as high as 3.1 and that such changes in refractive index are reflective of its change in silicon concentration and nonlinear parameters. Such work in literature has shown that increases in silicon concentration result in increased second and third order nonlinear susceptibilities χ^(2) and χ^(3) respectively. In this thesis we have focused on exploring these nonlinearities in high refractive index CMOS compatible PECVD films. Our work has restricted itself to utilizing such fabrication flow, including low temperature deposition and annealing processes, in order to understand how such films, if adopted into CMOS process flows, could provide new and unique capabilities.

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