Design optimization of silicon nitride-based micro-ring resonator systems in a CMOS mass production environment

Abstract

Micro-ring resonators (MRR) are basic photonic components, which serve as crucial building blocks for a variety of devices, e.g. integrated sensors, external cavity lasers, and high speed photonic data transmitters. Silicon nitride photonic platforms are particularly appealing in this field o f a pplication, s ince t his w aveguide material enables on-chip photonic circuitry with (ultra-) low losses in the NIR as well as across the whole visible spectral range. In this contribution we investigate key performance properties of MRRs in the wavelength range around 850 nm, such as free spectral range (FSR), quality factor (Q factor) and extinction ratio. We systematically investigate a large parameter space given by the MRR radii, coupling gaps between ring and bus waveguide, as well as waveguide width. Furthermore, we compare key properties such as the Q factor between low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) Si 3 N 4 platforms and find enhanced values for LPCVD ring resonators reaching nearly a Q factor of 10 6 .The fabrication is carried out with standard CMOS foundry equipment, utilizing photolithography and reactive ion etching on 250 nm thick silicon nitride films. A s c ladding m aterial, h igh d ensity P ECVD s ilicon o xide i s d eposited p rior t o the waveguide onto bare silicon and a sputtered oxide serves as upper cladding. With this process toolbox full CMOS backend compatibility is achieved when considering only PECVD Si 3 N 4 waveguide material. In terms of manufacturability, special focus is put on the die-to-die as well as on wafer-to-wafer variability of the performance parameters, which is crucial when considering mass production of MRR devices. Finally, the experimental findings are compared to finite difference time domain (FDTD) simulations of the MRR circuits revealing excellent agreement when considering the manufacturing variability.

Comparative analysis of fabrication techniques for sensing windows on silicon nitride waveguide platforms

“…In the domain of photonic sensor development, silicon nitride has emerged as a material of choice due to its wide transparency window and compatibility with complementary metal-oxide-semiconductor (CMOS) technology. 1,2 This research focuses on evaluating two pivotal fabrication techniques for constructing sensing windows on silicon nitride substrates: the conventional etching method that combines reactive ion etching (RIE) with wet chemical etching, and a lift-off approach that involves the deposition and subsequent removal of a top cladding layer to define the sensing waveguides. The conventional etching method is known for its precision and ability to produce highly defined features, crucial for the fabrication of complex photonic structures.…”

“…Figure6: Schematic measurement setup for wafer-level testing of propagation loss and bend excess loss structures 2,7. …”

“…Figure7: Wafermap with dies which are considered in measurement evaluation. Test structures are measured on the red and green dies and AFM measurements are carried out only on test structures on the green dies 2,7. …”

CART-based optimization of core and cladding layers in silicon nitride photonic integrated circuits towards propagation and bend loss minimization

“…From high-speed telecommunications and advanced computing to intricate sensing applications, integrated photonics has laid the foundation for many innovations. 1,2 At the core of this technological evolution are Photonic Integrated Circuits (PICs), which have come to redefine the dynamics of high-speed detection in biosensing and beyond (Smith et al, 2017). Despite such milestones, these systems are subject to a persistent challenge: robust optical loss minimization in devices for mass fabrication, primarily originating from surface-roughness-induced scattering and absorption losses.…”