A Low Temperature Photonic Crystal Technology for Integration with Modern CMOS Technologies
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A Low Temperature Photonic Crystal Technology for Integration with Modern CMOS Technologies Khadijeh Bayat1, Mahdi Farrokh Baroughi2, Sujeet K. Chaudhuri1, and Safieddin Safavi-Naeini1 1 Electrical and Computer Engineering, University of Waterloo, 200, Univ. Ave. W., Waterloo, Ontario, N2L3G1, Canada 2 Electrical Engineering and Computer Science, South Dakota State University, 201 Harding Hall, Box 2220, South Dakota State University, Brookings, SD, 57007 ABSTRACT In this paper, low temperature amorphous silicon oxynitride (a-SixOyNz:H) thin film technology is proposed for implementation of CMOS compatible photonic crystal (PC) based optical integrated circuits (OICs). The a-SixOyNz films of different refractive indices were developed by plasma enhanced chemical vapor deposition (PECVD) technique using silane, nitrous oxide, and ammonia as gas phase precursors at 300˚C. The films with refractive indices between 1.43 ñ 1.75 were obtained by changing gas flow ratios. Such thin films can be used as cladding and core layers in photonic crystal structure. The bandgap and guiding properties of the a-SixOyNz based PCs were simulated. It is shown that the aSixOyNz:H based PC technology offers larger feature sizes than that of a conventional silicon based photonic crystals. INTRODUCTION Photonic crystals (PC) offer new methods for controlling light and open a window towards exploring novel photonic devices. Compact photonic circuits, compatible with CMOS technology, can be realized using PCs [1-2]. A PC consists of a periodic medium with periodic dielectric constant. The interference of light wave with the spatial wave of the lattice of a PC results in a photonic energy bandgap or a forbidden energy gap. No wave with photon energy (hv) inside the photonic bandgap (PBG) can propagate through the PC. This is quite similar to the concept of energy bandgap in semiconductors. A typical PC slab, as shown in Fig. 1, consists of a high refractive index slab with two-dimensional periodic holes and low refractive index cladding (normally air). The spatial period, called the lattice constant, is shown by ëaí in the figure. The radius of the holes is shown by ërí in the figure. One of the interesting applications of PC structures is optical interconnects. Waveguides in PC structures are good candidates for the integrated optical interconnects [3]. An optical waveguide can be realized by introducing a defect line in a perfect PC. This defect line would induce defect modes inside the PBG [4]. Thus, guiding takes place over the frequency range of the defect mode.
Figure 1 Schematic of a triangular PC slab. r and a represent the radius of the air holes and the lattice constant, respectively.
Currently, silicon-based PCs rely on silicon on insulator (SOI) PCs. SOI-PCs can be integrated easily on SOI CMOS ICs with minor modification of the fabrication process. However, the SOI-PC technology suffers from two major drawbacks: (i) This technology offers no control on the thickness and refractive indices of the film and the claddi
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