Technology | Centre for Programmable Photonic Integrated Circuits and Systems

CMOS compatible silicon photonics technology is our overall driving force. In general, there are two types of optical waveguide cores which are used for silicon photonic integrated circuits: (i) Si photonic wire waveguides either in SOI or in bulk silicon substrates, (ii) SiN waveguides on the surface of oxide grown bulk silicon substrate. Very recently, lithium niobate (LiNbO3) photonic wire waveguides are also becoming popular as bonded LiNbO3 thin film on the oxide grown silicon substrate (LNOI) is now commercially available, though relatively expensive. We have already developed state-of-the-art SOI based silicon photonics technology over the years and very recently started working on developing SiN waveguide process technology. We are also open to access commercial silicon photonics foundries through multi-project wafer (MPW) runs.

SOI Technology
SiN Technology

Silicon On Insulator (SOI) technology, which was initially developed to improve the parasitics of the transistors in the electronic chip, has also shown great promise for silicon photonic wire waveguides. The high index contrast of Si-SiO2 has allowed for strong confinement of light and tight waveguide bends (~5 µm) and, therefore, the design of low loss photonic devices with a small footprint. An already mature SOI-based CMOS technology has enabled the fast evolution of silicon photonics devices in the last two decades. Based on these two pieces of evidence, the SOI platform can potentially enable large-scale integration of photonic devices for areas like microwave photonics, quantum information processing, lab-on-chip sensing, artificial intelligence, neuromorphic computing.

We started working at IIT Madras in 2007 as an Integrated Optoelectronic laboratory to develop a world-class silicon photonics research facility. Our first waveguide demonstration has been on the 5 µm thick SOI platform. Over the years, we have scaled our technology to sub-micron and nanoscale dimensions in conjunction with industry standards. We have developed an in-house fabrication facility for silicon-based photonic devices at the Centre for NEMS and Nanophotonics (CNNP), IIT Madras. We have demonstrated various novel and state-of-the-art passive and active photonic devices. With our expertise in device level demonstrations, we at CPPICS aim to scale our technology for large-scale integration of photonic devices and circuits for Microwave and Quantum photonics applications.

Silicon nitride waveguide technology offers low loss waveguides because of its low index contrast with silicon dioxide. There are majorly two methods to fabricate silicon nitride based photonics devices. One is the subtractive method in which the silicon nitride film is deposited on silicon dioxide in LPCVD furnace. And then the waveguide is patterned and etched followed by the LTO deposition as cladding oxide. The second method is damascene process in which silicon nitride is deposited in etched SiO2 and planarized to form engraved waveguide followed by cladding oxide deposition.

We have optimized the deposition of stoichiometric silicon nitride film for lower device layer thickness and are currently optimizing oxide deposition for lower cladding (BOX layer) in LPCVD furnace. We aim to demonstrate low loss silicon nitride based photonic devices for different applications in Microwave and Quantum photonics.