The silicon photonics group at McMaster University

The Integration of Photonic and Electronic Functionality in Silicon

Silicon has remained the dominant material for microelectronics fabrication ever since the invention of the integrated circuit by Jack Kilby at Texas Instruments in 1958. During the following five decades the number of devices per cm-2 on an integrated circuit has doubled approximately every eighteen months following the famous prediction made by Gordon Moore in 1965.

The success of silicon-based fabrication technology has been the foundation for the microelectronics industry which is now worth in excess of $1000bn p.a., with an associated infrastructure capable of high volume, high yield manufacture of devices with a minimum feature size <100nm. It has been recognized for sometime that this same infrastructure could be used for the fabrication of photonic devices with cost benefits associated with silicon microelectronics manufacturing protocols. Further, silicon photonic devices could be integrated with electronic functionality in a seamless, single process flow. For this to be achievable, it is a requirement that all such device structures be fabricated using processing compatible with that used in the production of standard silicon microelectronic devices such as the CMOS transistor.

Electron micrograph of the cross-section of a lateral power coupler formed     in a silicon waveguide.

The original driving force behind the development of silicon photonics was the well-documented telecom boom of the late 1990’s. During that time a range of 1550nm compatible, planar waveguide devices were designed, simulated and fabricated, including waveguides, modulators, (de)multiplexes, integrated detectors etc. The leading commercial manufacturer of these optical components was the then UK-based Bookham Technology which fabricated a range of products using a silicon-on-insulator substrate. Although it has since refocused its efforts towards the development of more traditional photonic devices, the principle of device fabrication on a commercial scale was demonstrated. Currently a number of North American commercial institutions have an interest in device development including Luxtera Inc., Kotura, and most notably Intel Corp. In particular, work from the Intel group has received significant coverage in the popular science media. In 2004 they reported a silicon waveguide optical modulator capable of switching speeds in excess of 1GHz, while a recent publication described a continuous wave Raman silicon laser.

Fabrication Facilities Available to the McMaster Research Group

Silicon photonic devices should be designed to be fabricated using standard processing technology and

Making silicon waveguides at the McMaster University CEDT

facilities. Our group has access to a full processing suite via the facilities in-house at the Centre for Emerging Device Technologies; those housed at the Nano-fabrication and Ion Implantation Laboratories at the University of Western Ontario; and the microfabrication facility at Carleton University. The majority of devices are formed using silicon-on-insulator (SOI), or more precisely a silicon-on-oxide, substrate. The Si/SiO2 structure provides a natural waveguide for sub-bandgap light with a wavelength >1.1µm. Lateral confinement is achieved through the etching of a rib structure in the silicon overlayer. The size and position of the waveguides can be precisely defined via photolithography and etching. A recent project in collaboration with Carleton University has investigated the fabrication of waveguides using the Local Oxidation of Silicon (LOCOS) process. This approach shows great promise for the development of waveguides with very smooth sidewalls (necessary for devices with sub-micron dimensions).

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