News: Microelectronics
28 May 2025
Imec’s 300mm RF silicon interposer platform for chiplet-based heterogeneous integration demos record low insertion loss at frequencies up to 325GHz
At the IEEE’s 75th Electronic Components and Technology Conference (ECTC 2025) in Dallas, TX, USA (27–30 May), nanoelectronics research center imec of Leuven, Belgium is highlighting the performance and flexibility of its 300mm RF silicon interposer platform, which enables seamless integration of RF-to-sub-THz CMOS and III/V chiplets on a single carrier, achieving a record-low insertion loss of just 0.73dB/mm at frequencies up to 325GHz. This is said to pave the way for compact, low-loss and scalable next-generation RF and mixed-signal systems.
For advanced applications — from wireless data centers and high-resolution automotive radar to pluggable optical transceivers and ultra-high-speed wireless USB solutions for short-range device-to-device communications — industry momentum is rapidly shifting to mmWave (30–100GHz) and sub-THz (100–300GHz) frequency bands.
However, unlocking the potential of these higher frequencies requires components that combine the high output power and drive capabilities of III/V materials with the scalability and cost-efficiency of CMOS technology — all integrated on a single carrier. This is where chiplet-based heterogeneous systems, built on RF silicon interposer technology, make the difference, enabling seamless integration of digital and RF components, says imec.
A 300mm RF silicon interposer with record-low insertion loss of 0.73dB/mm at 325GHz
At last year’s IEDM, imec reported a breakthrough in the hetero-integration of InP chiplets on a 300mm RF silicon interposer — at frequencies up to 140GHz. Now, at ECTC 2025, imec’s new milestone uses the same silicon interposer platform to demonstrate a record low insertion loss of just 0.73dB/mm at frequencies up to 325GHz.
“What sets our approach apart is the ability to mix and match digital, RF-to-sub-THz CMOS technology nodes with a wide variety of III/V chiplets — not limited to InP [indium phosphide], but also including SiGe [silicon germanium], GaAs [gallium arsenide], and others,” says Xiao Sun, principal member of technical staff at imec.
Picture: imec’s 325GHz RF silicon interposer platform for advanced chiplet-based heterogeneous systems.
The platform’s digital interconnects benefit from copper (Cu) damascene back-end-of-line (BEOL) processing, while mmWave signal paths employ transmission lines on a low-loss RF polymer layer. Additionally, high-quality passive components — such as inductors — are integrated directly onto the RF silicon interposer, reducing the active chip area, lowering costs, and ensuring compact, low-loss RF interconnects for improved performance.
Imec’s technology combines RF/microwave links (with 5µm line-width and 5µm spacing), with high-density digital interconnects (with 1µm/1µm line/spacing), and a fine flip-chip pitch of 40µm – with efforts underway to scale down to 20µm. Together, these features enable high integration density and a compact footprint.
The path forward: opening the platform to partners for prototyping
As a next step, Xiao Sun and her team are preparing to augment the platform with additional features, including through-silicon vias, back-side redistribution layers, and MIMCAPs for supply decoupling. In parallel, imec is preparing to open its RF interposer R&D platform to partners for early assessment, system validation, and prototyping – amongst others by making it accessible via NanoIC, imec’s sub-2nm pilot line as part of the EU Chips Act.
At ECTC 2025, his research was discussed on 27 May during the special session ‘Advancements in mmWave and Sub-THz Packaging for Communication & Radar Applications’, followed by a detailed presentation of the results on 28 May during ECTC’s ‘Session 5: Advanced Design for Heterogeneous Integration’.
