(Invited) SiOxNy Back-End Integration Technologies for Heterogeneously Integrated Si Platform

Abstract

Network traffic is continuously increasing, and the global IP traffic reaches 2 zettabytes in 2019 [1]. Photonic integrated circuits on Si-based substrates are highly demanded for coping with increasing telecommunication network traffic and energy consumption in low-cost ways. Particularly, Si and Ge provide modulators and photodetectors in telecom wavelength with a full monolithic way on SOI substrates. In addition, InP provides lightsources based on low-temperature direct-bonding technique. To connect these dynamic and active devices, we propose back-end photonic wiring by using SiOxNy-based waveguides. In this paper, I review recent progress of our work. First, I briefly review our early work; Si-Ge-SiOx integration technology and application to the WDM receiver. To increase integration density, recently, we also have developed a silicon-nitride (SiN) waveguide[1]. SiN has moderately high refractive index and provides moderately small passive devices with tolerance for nonlinear effects. We confirmed 1-dB/cm propagation loss for 1.3-, 1.5-, and 1.6-um wavelength range and applied to a compact and low-loss 16-ch. arrayed-waveguide grating (AWG) filter with 200GHz spacing. In addition, for lightsource integration, a InP-wire waveguide was successfully integrated with the SiOx waveguide via a spot-size converter (SSC) on SiO2/Si substrates[2]. The fabricated InP waveguide provides 5.2-dB/cm propagation loss and connected to the SiOx waveguide with a 0.7-dB loss and less than -50-dB reflectance. The InP waveguide can be used as output waveguide for the membrane laser, which utilizes strong optical confinement within the active area to obtain high modulation efficiency and low power consumption[3, 4]. With introducing distributed-reflector (DR) laser structure, the membrane laser exhibits low threshold current of 0.6 mA, output power of 0.7 mW, and 25.8-Gbit/s NRZ direct modulation with 132-fJ/bit energy consumption. In addition, the output InP wire waveguide is successfully integrated with the SiOxwaveguide, which exhibits fiber coupling loss of 2.7 dB and low reflectance at the chip facet to obtain sufficient optical output power and stable single-mode operation. [1] K. Okazaki et al., Proc. GFP 2014, Vancouver, paper WP43. [2] H. Nishi et al., IEEE Photonics Journal, vol. 7, pp. 4900308, 2015. [3] S. Matuso et al., J. Lightwave Technol., vol. 33, pp. 1217, 2015. [4] H. Nishi et al., Proc. ECOC 2015, Valencia, paper We.2.5.3.