Bulk-Si Platform: Born for DRAM, Upgraded With On-Chip Lasers, and Transplanted to LiDAR

Abstract

The CMOS industry has been expecting silicon photonics to provide photonic and electro-photonic integrated circuits based on the CMOS processes and infrastructures for scalability of incumbent technology evolutions and creation of novel technologies. However, the compatibility with the legacy CMOS has been compromised with the development convenience of early silicon photonics in that the specialty silicon-on-insulator substrates have been widely used as integration platforms. Since this specialty substrate may hinder the photonics integration with legacy volume products later, a legacy-friendly integration platform with a generic bulk-silicon substrate has been developed for better compatibility. This paper overviews the bulk-silicon photonics platform born for DRAM integration, upgraded with III/V-on-bulk-Si lasers, and transplanted to LiDAR applications requiring the virtuous cycle of cost and volume. The photonics integration with DRAM was to resolve the speed-capacity tradeoff in the DRAM interconnects, and technical feasibility as well as lessons learned from the integration attempt are reviewed. The bulk-silicon device performance approaches that of silicon-oninsulator devices with the thermal advantage of ~40-% lower thermal impedance and the optical disadvantage of ~0.4-dB/mm higher waveguide loss. In the LiDAR applications, detection performance up to ~20 m at 20 fps by a single-chip scanner integrating tunable laser, semiconductor optical amplifiers, and optical phased array are presented with future outlooks.

Thermal Characterisation of Hybrid, Flip-Chip InP-Si DFB Lasers

“…The laser-length and thermal-resistance product of this work was 2.6 (K-m)/W. In Figure 10 , this value is compared with other reported values in the literature [ 7 , 11 , 19 , 20 , 21 ]. The normalised thermal resistance lay in the range of 1.5–4.7 (K-m)/W, placing the laser studied in this work inside the expected range.…”

“…R. Loi (2018) [ 11 ] reports µprinted lasers and M.N. Sysak (2007) [ 7 ] and D. Shin (2016) [ 19 ] report on heterogeneous laser integration. The thermal resistance was normalised as the laser length × thermal resistance product.…”

Phase shift optimization of III/V-on-bulk-Si DFB LD for single-mode stability

“…As the III/V portion of the optical mode distribution increases, the optical gain increases but the internal optical loss also increases. The local SOI structure on the BS substrate was implemented through a proprietary solid-phase epitaxy(SPE) process, and its details have been published in the literature [9,10,[25][26][27][28][29]. In the horizontal structure in Fig.…”

“…Therefore, recent light source development tends to pursue single-chip integration along with various photonic devices on top of a Si substrate instead of a conventional III/V one. In the incumbent CMOS industry, the integration tendency has been further strengthened so that the generic bulk-Si(BS) substrate is preferred instead of the specialty Si-on-insulator(SOI) substrate for light source development to facilitate future integration with volume CMOS products such as DRAM [25][26][27][28][29]. This paper presents design and verifying experimental results that avoid single-mode instability from the long PS in the III/V-on-BS DFB LD.…”

“…We present the change in single-mode stability over super-λ-scale and sub-λ-scale tuning of the PS length with a good agreement between design and measurement, and improved yield with the optimized design. This paper discusses on design and measurement only, because the fabrication processes on the BS substrate have been previously published [25][26][27][28][29]. This paper also focuses on the single-mode performance only, since the general performances including output power, wall plug efficiency(WPE), modulation speed, and thermal resistance have been also previously reported [9,10].…”