  Heterogeneous and monolithic integration of the versatile low loss silicon
nitride platform with low temperature materials such as silicon electronics and
photonics, III-V compound semiconductors, lithium niobate, organics, and
glasses, has been inhibited by the need for high temperature annealing as well
as the need for different process flows for thin and thick waveguides. New
techniques are needed to maintain the state-of-the-art losses, nonlinear
properties, and CMOS compatible processes while enabling this next generation
of 3D silicon nitride integration. We report a significant advance in silicon
nitride integrated photonics, demonstrating the lowest losses to date for an
anneal-free process at a maximum temperature of 250 C, with the same deuterated
silane based fabrication flow, for nitride and oxide, for an order of magnitude
range in nitride thickness without requiring stress mitigation or polishing. We
report record low losses for anneal-free nitride core and oxide cladding,
enabling 1.77 dB/m loss and 14.9 million Q for 80 nm nitride core waveguides,
more than half an order magnitude lower loss than previously reported 270 C
processes, and 8.66 dB/m loss and 4.03 million Q for 800 nm thick nitride. We
demonstrate laser stabilization with over 4 orders of magnitude frequency noise
reduction using a thin nitride reference cavity. And using a thick nitride
micro-resonator, we demonstrate parametric gain and Optical Parametric
Oscillation (OPO) with the lowest reported OPO threshold per unit resonator
length for low temperature fabricated nitride, and supercontinuum generation
over two octaves. These results represent a significant step towards a uniform
ultra-low loss silicon nitride homogeneous and heterogeneous platform for both
thin and thick waveguides capable of linear and nonlinear photonic circuits and
integration with low temperature materials and processes.
