RF front ends for 6G Integrate MEMS structures directly into CMOS layers

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With the compact approach of MEMS-within-CMOS, microelectromechanical systems can be integrated directly into CMOS processes. This not only increases the Q-factor, but the capacitors developed in this way also exhibit high linearity.

Nanusens has developed a solution using MEMS-within-CMOS technology that allows microelectromechanical systems (MEMS) to be integrated directly into standard CMOS processes. This allows MEMS structures to be integrated directly into the CMOS layers of a chip. The result is a highly integrated solution. The company has now presented a development based on this technology to optimize RF frontends for 6G.

Nanusens' CEO, Josep Montanyà, emphasized that this builds on their work with the upper 5G bands, with their unique technology now also aimed at providing cost-effective solutions for 6G. 6G technology requires handling a wider spectrum of higher frequencies compared to 5G. "This means that we need additional antennas in devices that need to be smaller to fit into the compact spaces of modern smartphones," says Montanyà.

Smaller antennas typically suffer from lower efficiency. For optimal performance, each antenna must be tunable to adapt to different bands and avoid mismatches with power amplifiers. Currently, this is achieved through tunable capacitors.

Integrated approach is compact

Nanusens uses its patented technique to integrate multiple digitally tunable capacitors of a few nanometers in size along with the control circuit in CMOS layers on a single chip. This integrated approach is more compact and powerful than competitive solutions, mainly due to its linearity, which leads to minimal distortion. In addition, these nano capacitors are more energy efficient and extend talk time by up to 30 percent.

Key performance features include a high Q factor. This quality factor is a measure of the quality of a resonant system, particularly in terms of the efficiency and damping of resonant circuits. Nanusens' Digital Tunable RF Capacitors (DTCs) have a Q factor of over 100 at 1 GHz, which remains high at higher frequencies, unlike competitive products whose Q factor significantly drops. This high Q factor is crucial for minimizing power losses and increasing range, leading to an improved user experience through fewer call drops and reception problems.

The nanoscale capacitors show high linearity, which exceeds the requirement of 90 dBc for IMD3 at 5G. In addition, the minimum capacitance can be reduced to 30 fF (femto Farad) for a single capacitor in the off state, with a current capacitance ratio of 2.2, which is to be improved to four in future iterations.

Better compared to competing products

The technique developed by Nanusens addresses the problems of competitive techniques. These include semiconductor switches, which suffer from low Q factors due to resistance in the on state and deteriorate at higher frequencies. The RF MEMS are unreliable due to dielectric charging and breakdown. Nanusens' design avoids this as no dielectric materials are used.

The special design of RF front ends for 6G

6G networks operate at much higher frequency ranges than 5G networks. These higher frequencies offer advantages such as higher data rates and lower latency times, but also pose significant technical challenges. One of the biggest challenges is that higher frequencies are more attenuated and have a shorter range, which requires more precise and efficient signal processing.

To cover the multitude of frequencies and bands that 6G has to support, more antennas are required in the devices. However, these additional antennas need to be accommodated in ever smaller devices, which can affect the efficiency and performance of each individual antenna. Each antenna must be optimally tuned to adapt to different frequency bands and to avoid mismatches with power amplifiers. This is currently achieved through tunable capacitors. In 6G networks, however, these capacitors need to provide even higher performance and efficiency to meet the requirements.

Another important point is the minimization of power losses. The Q-factor (quality factor) is a measure of a capacitor's efficiency. A high Q-factor means lower losses. With conventional semiconductor switches, the Q-factor decreases at higher frequencies, leading to higher losses. (heh)

This article was first published on our sister brand 'ELEKTRONIK PRAXIS' (German Edition), Vogel Communications Group