100-GHz front-end modules using III-V and III-N devices on Si
In wireless communication, with 5G as the next generation, there is a push towards higher operating frequencies, moving from the congested sub-6GHz bands towards mm-wave bands (and beyond). The introduction of these mm-wave bands has a significant impact on the overall 5G network infrastructure and the mobile devices. For mobile services and Fixed Wireless Access (FWA), this translates into increasingly complex front-end modules that send the signal to and from the antenna. To be able to operate at mm-wave frequencies, the RF front-end modules will have to combine high speed (enabling datarates of 10 Gbps and beyond) with high output power. In addition, their implementation in mobile handsets puts high demands on their form factor and power efficiency.
Beyond 5G, these requirements can no longer be achieved with today’s most advanced RF front-end modules that typically rely on a variety of different technologies amongst others GaAs-based HBTs for the power amplifiers – grown on small and expensive GaAs substrates.
“To enable the next-generation RF front-end modules beyond 5G, imec explores CMOS-compatible III-V-on-Si technology”, explains Nadine Collaert, program director at imec. “Imec is looking into co-integration of front-end components (such as power amplifiers and switches) with other CMOS-based circuits (such as control circuitry or transceiver technology), to reduce cost and form factor, and enabling new hybrid circuit topologies to address performance and efficiency.
Imec is exploring two different routes: one is Indium Phosphide (InP) on Si, targeting mm-wave and frequencies above 100 GHz (future 6G applications) and the other is GaN-based devices on Si, targeting (in a first phase) the lower mm-wave bands and addressing applications in need of high power densities. For both routes, the researchers have now obtained first functional devices with promising performance characteristics while identifying ways to further enhance their operating frequencies
The researchers demonstrated functional GaAs/InGaP HBT devices grown on 300mm Si, obtaining a defect-free device stack with below 3 x 106 cm-2 threading dislocation density using imec’s unique III-V nano-ridge engineering (NRE) process. The devices were shown to perform considerably better than reference devices, with GaAs fabricated on Si substrates with strain relaxed buffer (SRB) layers. Next, the researchers aim to explore higher-mobility InP-based devices (HBT and HEMT).
On a second research path, imec has fabricated CMOS-compatible GaN/AlGaN-based devices on 200-mm Si and compared three different device architectures – HEMTs, MOSFETs and MISHEMTs, concluding that MISHEMT devices outperform the other device types in terms of device scalability and noise performance for high-frequency operation. For 300-nm gate lengths, the researchers measured peak cut-off frequencies of fT/fmax around 50/40 GHz, which is in line with reported GaN-on-SiC devices. They are confident that further gate length scaling could further improve their device performance and increase the operating frequency within the mm-wave bands.
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