A Single-Chip Optical Phased Array in a Wafer-Scale Silicon Photonics / CMOS 3D-Integration Platform Taehwan Kim , Student Member , IEEE, Pavan Bhargava, Student Member , IEEE, Christopher V . Poulton , Jelena Notaros , Student Member , IEEE, Ami Yaacobi, Erman Timurdogan, Christopher Baiocco, Nicholas Fahrenkopf, Seth Kruger, Tat Ngai, Yukta Timalsina, Michael R. Watts, Member , IEEE, and Vladimir Stojanovi´c , Senior Member , IEEE

Abstract

With the growing demand for automotive LiDAR and the maturation of silicon photonics platforms, optical phased arrays (OPAs) have emerged as a key technology for solid- state optical beam-steering. In order to meet realistic automotive specifications with OPAs, >500 antenna elements should work reliably under tight power and cost budgets. Existing multi-chip solutions necessitate expensive packaging and assembly to achieve high interconnect density. Even with 2-D monolithic integration, high-voltage drivers to deliver sufficient power to resistive phase shifters typically result in significant overhead in die area and limited power efficiency. In this article, we introduce a single- chip OPA realized through wafer-scale 3-D integration of silicon photonics and CMOS. Flexible and ultra-dense connections with through-oxide vias (TOVs) in our platform resolve the I/O density issue. Moreover, low-voltage L-shaped phase shifters and compact, efficient switch-mode drivers, connected vertically using TOVs, remove wiring/placement overhead and achieve a large active array aperture within a compact die. Our OPA prototype achieves wide-range 2-D steering over 18.5 ◦×16◦ by leveraging wavelength tuning and phase control, and array scaling up to 125 elements with a large aperture size of 0 .5m m × 0.5m m and 0.15 ◦×0.25◦ beamwidth while consuming 20 mW/element average power. Since our system supports per-element indepen- dent phase control, increased sensitivity to process variations in L-sha