Low-Temperature Crack-Free Si3N4 Nonlinear Photonic Circuits for CMOS-Compatible Optoelectronic Cointegration

In this communication, authors report for the first time on the fabrication and testing of Si3N4 non-linear photonic circuits for CMOS-compatible monolithic co-integration with silicon-based optoelectronics. In particular, a novel process has been developed to fabricate low-loss crack-free Si3N4 750-nm-thick films for Kerr-based nonlinear functions featuring full thermal budget compatibility with existing Silicon photonics and front-end Si optoelectronics. Briefly, differently from previous and state-of-the-art works, our nonlinear nitride-based platform has been realized without resorting to commonly-used high-temperature annealing (similar to 1200 degrees C) of the film and its silica uppercladding used to break N-H bonds otherwise causing absorption in the C-band and destroying its nonlinear functionality. Furthermore, no complex and fabrication-intolerant Damascene process - as recently reported earlier this year - aimed at controlling cracks generated in thick tensile-strained Si3N4 films has been used as well. Instead, a tailored Si3N4 multiple-step film deposition in 200-mm LPCVD-based reactor and subsequent low-temperature (400 degrees C) PECVD oxide encapsulation have been used to fabricate the nonlinear microresonant circuits aiming at generating optical frequency combs via optical parametric oscillators (OPOs), thus allowing the monolithic cointegration of such nonlinear functions on existing CMOS-compatible optoelectronics, for both active and passive components such as, for instance, silicon modulators and wavelength (de-) multiplexers. Experimental evidence based on wafer-level statistics show nitride-based 112-mu m-radius ring resonators using such low-temperature crack-free nitride film exhibiting quality factors exceeding Q > 3 x 10(5), thus paving the way to low-threshold power-efficient Kerr-based comb sources and dissipative temporal solitons in the C-band featuring full thermal processing compatibility with Si photonic integrated circuits (Si-PICs).