CMOS compatible monolithic multi-layer Si_3N_4-on-SOI platform for low-loss high performance silicon photonics dense integration

Abstract

We demonstrated a low-loss CMOS-compatible multi-layer platform using monolithic back-end-of-line (BEOL) integration. 0.8dB/cm propagation loss is measured for the PECVD Si₃N₄ waveguide at 1580nm wavelength. The loss is further reduced to 0.24dB/cm at 1270nm wavelength, justifying the platform's feasibility for O-band operation. An inter-layer transition coupler is designed, achieving less than 0.2dB/transition loss across 70nm bandwidth. This is the lowest inter-layer transition loss ever reported. A thermally tuned micro-ring filter is also integrated on the platform, with performance comparable to similar device on SOI platform.

Expanding the Silicon Photonics Portfolio With Silicon Nitride Photonic Integrated Circuits

“…Moreover the manufacturing flexibility of SiN has been used to either stack multiple layers of SiN [74], [75] or combine SiN and SOI on a single platform [36], [76], [77]. This approach pavesthe way for low loss and high integration density PICs.…”

Silicon Photonics: silicon nitride versus silicon-on-insulator

“…A major driving factor to deviate from SOI is the desire to operate in spectral bands where silicon or silicon oxide are absorbing, but there are many more reasons why SOI is not necessarily the best option for device functionality and performance. An important candidate in this respect is the silicon nitride waveguide system, in which the silicon core of the SOI-system is replaced by a silicon nitride core, while remaining CMOScompatible [2][3][4].…”

“…Also, one can deposit the waveguide layer in two steps and add luminescent quantum dots to the waveguide core in between both steps [12]. This flexibility also means that one can combine SiN waveguides with SOI waveguides on a single platform, thereby combining the unique features of both platforms in a single chip [3,18].…”

Small Sensitivity to Temperature Variations of Si-Photonic Mach–Zehnder Interferometer Using Si and SiN Waveguides

“…Although the imbalance between two arms is large, the imbalance of the MMI branch improves the extinction ratio. The insertion loss and extinction ratio would be further improved because a well-controlled fabrication environment would reduce the SiN-waveguide loss (Huang et al, 2014). We must mention that the device was designed for only TE mode light.…”

“…The taper-tip width and the taper length of the fiber-chip interface were 200 nm and 300 µm, respectively. Since the Si and SiN waveguides were formed in different layers, the interlayer coupler (ILC) between them was designed using adiabatically tapers (Huang et al, 2014). We introduced the ILCs into both arms to cancel out their phase delays.…”