Electronic-photonic millimeter-wave systems-on-chip and passive devices in silicon CMOS photonics
Embargo Date
2026-09-17
OA Version
Citation
Abstract
Initially confined to academic laboratories, silicon photonics has emerged as a budding optical integrated circuit technology at the dawn of the 21st century. In recent years, its rapid commercialization has made several key semiconductor giants like GlobalFoundries, TSMC, Intel and IBM introducing silicon photonics processes. Concurrently, numerous enterprises and start-ups have rolled out products leveraging this technology, propelling its market value to a substantial portion of the semiconductor industry. Integrated silicon photonics has emerged as a ``More-than-Moore'' extension to advanced CMOS that is poised to generate high impact on numerous application domains. To realize and maximize its impact, future electronic-photonic systems-on-chip will require co-design of photonic devices and circuits, electronic designs, and CMOS foundry platforms, along with the system and application, as well possible hybrid integration of new materials.
Large scale mm-wave antenna arrays have emerged as a key technology across several application domains that leverage high-bandwidth beamforming, from 5G/6G+ communications to radar sensing. The performance scaling of these new systems depends heavily on the power-efficiency scaling of signal aggregation and processing across the arrays. Tight element pitch constraints are limiting both the per-element power dissipation and the available signal routing to the data processing subsystems. Limited per-element power dissipation leaves little room for local compute at the antenna element, or for ADCs and digital electrical links to carry the digitized data to downstream processing blocks (e.g. beam estimation and beamforming signal processors). Furthermore, the high energy, area and cost of pluggable optics modules prevents array disaggregation. These constraints significantly limit the array organization and architecture, as well as types of algorithms that can be applied to the array data. Furthermore, the signal integrity of electrical links is limiting the size scaling of antenna arrays, and is introducing unwanted electromagnetic radiation that interferes with radio signals of interest.
Utilizing higher frequency bands (50-100\,GHz and beyond) enables thousands of antenna elements per array panel for future communication and sensing systems, but is significantly limited by the above issues and brings unique challenges in size, weight, power and cost (SWAP-C). With increased carrier frequency, both the channel bandwidth and number of antennas increase leading to a quadratic increase in the baseband sample count and beamforming compute throughput. This causes both the beamforming processors and the links from ADCs/DACs to processors to begin dominating the SWAP-C of the array panel. These scaling issues are further exacerbated in future micro-cells, as well as in air and space borne platforms where the overall SWAP-C is severely constrained.
New solutions are needed to enable the scaling required for future communication and sensing systems. Integrated silicon photonics based mm-wave links are a promising solution to overcome such scaling constraints. In this desertation, we present the realization of various mmwave sensing elements composed of a low-noise amplifier (LNA) with photonic coupled-cavity modulators based on single and triple-rings in monolithic CMOS processes such as 45RFSOI and 45SPCLO. We demonstrate a scalable electronic-photonic solution to develop mm-wave analog photonic high-speed links connecting mm-wave antenna arrays and the remote hub with low-power and high-bandwidth density.
Another major problem with electronic-photonic integrated circuits in monolithic SOI platforms is the fluctuation of the polarization state of the input light to the chip from an optical fiber. A polarization
diversity scheme comprising a polarization splitter-rotator (PSR) is desirable to implement the working of photonic devices functioning at single optical polarization. We demonstrate a compact, low cross-talk
and ultra-broadband PSR based on the concepts of magic-T and rapid-adiabatic mode splitter(RAMS) in a monolithic SOI CMOS platform.
Finally, energy-efficient WDM communication links require miniaturised integrated sources producing optical frequency combs with a fixed, finite number of closely spaced (low-repetition rate, e.g. 1 to 200 GHz) comb lines. We investigate some designs related to linear configuration of coupled cavity resonators based on tri -
diagonal Kac matrix enabling such cavities to support finite equi-spaced comb of resonances. Such resonator may allow designing compact and efficient cavities which decouple cavity size from comb spacings.
This dissertation demonstrate novel electronic-photonic mm-wave sensing elements operating at 57 GHz based on a LNA monolithically integrated with photonic coupled-cavity modulators based on single and triple-rings in a 45RFSOI CMOS process. We later show the first demonstration of a dual-cavity photonic molecule modulator in the Global Foundries' 45CLO platform enabling electronic-photonic integration. We also demonstrate two types of polarization-diversity enabling devices in the monolithic SOI CMOS platform: magic-T and RA-PSR. Finally, the concept of coupled cavity resonators with finite number of supermode resonances is presented to enable efficient finite comb generation for WDM applications.