A 28-nm CMOS Breakthrough for 6G: Compact 90–180 GHz Power Amplifier Achieves Octave Bandwidth And High Output Power

As 6G communications accelerate toward the terahertz regime (above 100 GHz), the 90–180 GHz spectrum has emerged as a key frequency range for enabling ultra-high-speed data transmission beyond 100 Gbps and high-precision terahertz sensing. However, power amplifiers operating in this band have long faced critical challenges, including the difficulty of achieving both wide bandwidth and high output power, severe high-frequency losses in silicon-based processes, and limited scalability in chip size.

Recently, a research team led by Academician Wei Hong and Professor Dawei Tang at Southeast University reported a major breakthrough in the IEEE Journal of Solid-State Circuits (JSSC). Using a 28-nm bulk CMOS process, the team demonstrated a compact power amplifier that simultaneously achieves octave-bandwidth operation from 90 to 180 GHz and a high output power of 15–18 dBm, providing a viable silicon-based solution for future 6G high-frequency hardware.

According to the researchers, conventional wideband high-frequency power amplifiers often sacrifice output power, while alternative technologies such as GaN or SiGe, though capable of higher performance, suffer from high cost and poor compatibility with mainstream CMOS manufacturing. In addition, bulky matching networks and power combiners at these frequencies severely limit system-level integration. To overcome these obstacles, the team introduced a set of original innovations spanning the amplifier core, signal conversion, and power combining architecture.

At the amplifier level, a compact neutralized amplifier based on an improved MOS capacitor structure was proposed. This design preserves effective neutralization while reducing the unit area to one quarter of that of conventional approaches, and it remains fully compatible with standard CMOS processes. For signal conversion, the team developed a three-conductor self-shielding load-open (SSLO) balun, which significantly suppresses electromagnetic coupling and achieves insertion loss below 1.8 dB across the entire 90–180 GHz band, with an area reduction of approximately 60% compared with traditional shielded baluns. For power combining, a slow-wave fourth-order LC ladder combiner was introduced, maintaining combining efficiency above 85% over an octave bandwidth while providing inherent filtering and reduced loss.

Measurement results confirm the competitive performance of the proposed power amplifier. The chip covers the full 90–180 GHz band, delivers a saturated output power of 15–18 dBm, achieves a peak small-signal gain of 21 dB, and occupies a core area of only 0.23 mm². Multiple key metrics outperform previously reported 28-nm CMOS power amplifiers at similar frequencies.

Experts note that this work not only pushes the performance limits of silicon-based CMOS technology beyond 150 GHz but also offers a low-cost, highly integrated radio-frequency solution for 6G ultra-high-speed communications, terahertz imaging and sensing, and low-Earth-orbit satellite links. As the technology advances toward practical deployment, it is expected to accelerate the miniaturization and large-scale adoption of terahertz communication and sensing systems.