RF Components

RF (Radio Frequency) components are essential for the transmission and reception of wireless signals, used in telecommunications, radios and mobile devices. They include elements such as amplifiers, oscillators and filters, which modify or transmit signals at radio frequencies.

In the framework of the FAMES Pilot Line, 4 technologies are developed:

• RF Switches based on PCM (Phase-change chalcogenide materials) with a Figure of Merit (FOM = RON*COFF) of less than 10 fs, integrated into the Back End Of Line;
• RF acoustic filters (Bulk Acoustic Wave – BAW) for wide bandwidth filters in the 7-15 GHz range, based on single crystal piezoelectric thin films (LiNbO3 & AlScN);
• RF Magnetic-based miniaturized Circulators based on Ferrite materials, for two different frequency bands: 5G FR3 and 6G communications, and 5G FR2 and radio location;
• 3D Capacitors to power Systems-on-Chip (SoC) with high aspect ratios for capacitor applications, increasing the capacitance density up to 3.5µF/mm.

• RF PCM switches will enable direct links with active circuits, such as LNAs, without adding parasitic elements (inductance, capacitance, resistance). RF PCM switches can also be used for sub-THz frequency reconfigurable phased array antennas;
• RF acoustic filters will provide the flexibility and high rejection ratios required for operation in the 6G bands;
• 3D high density capacitor integration and interposer solutions are enablers for advanced 6G systems;
• RF magnetic-based miniaturized circulators can control power transfer in defined directions for Tx-Rx-antenna duplexers, isolators for linear/nonlinear devices isolation (e.g. amplifiers, mixers), and reflection amplifiers.

The interest of each type of RF component is summarized below:

PCM RF Switches

The sub-terahertz frequency band is particularly attractive to meet the future needs of 6G communications networks, mainly due to its high bandwidth, increased speed and high data exchange capacities. In addition to communications, applications in the THz bands include spectroscopy, astronomy, space observation, remote sensing, pharmaceutical and industrial control, imaging, holography and radar.

RF switches are essential components of these systems. They are used, for example, in multiband receivers and transceivers, for filter switching, impedance matching, switching matrices for complex routing of transmitted and received signals, and for reconfiguration of multi-mode and multiband antenna beams. RF switch technology based on PCM enables a factor 10 improvement relative to today’s best solid-state switches (Figure of Merit FOM = RON*COFF of less than 10 fs). PCM RF switches integrated into a BEOL enable direct connections with active circuits, such as LNAs, without adding parasitic elements (inductances, capacitances, resistances) resulting from hybrid assembly by wire bonding or bump bonding, thus improving circuit performance. Both electrical and optical actuation are being developed in the context of the FAMES project.

RF Switches based on Phase Change Materials

Exhibit the following features:

• High performance beyond 100 GHz with Zero-static power consumption;
• Control through optical actuation – no interference from heater and biasing lines;
• Hybrid Bonding to integrate on the same wafer the electromagnetic surface, the non-volatile switches, the SiN optical waveguides and the photonic platform with a laser source used to bias the switches;
• Breakthrough heterogeneous III-V-on-SiN-on-Si-HR integration technology;
• Disruptive co-packaging & functionalized wafer architectures.

Applications:

PCM switches enable sub-THz frequency reconfigurable phased-array antennas for:

• • Electronic beamforming,
  • Space-time modulation,
  • Detection and frequency conversion

Filters

To cover all the required frequency bands, wireless mobile communication devices need more than 50 analogue filters that must be miniaturized to fit in the compact device form factor, especially for hand-held devices. This is currently achieved with electro-mechanical Surface-Acoustic-Wave (SAW) and Bulk-Acoustic-Wave (BAW) filters.

Filters architectures

For key 6G frequency bands between 7 and 15 GHz, needed for network capacity enhancement, the processing accuracy and materials quality of acoustic filter technologies need to be improved and matched with the IC technology.

In FAMES, we develop a radio front-end module integrating acoustic filters in the 7 – 15 GHz range and a front-end IC with integrated passive devices.

Block Diagram of RFIC. RX and TX are the receive and transmit filters

RF Acoustic Filters

FAMES goals:

• Up-scaling acoustic filters (Bulk Acoustic Wave – BAW) for wide bandwidth filters in the 7-15 GHz range;
• Single crystal piezoelectric thin films (LiNbO3 & AlScN)
• Technological module development: High-quality multilayer electrodes with low ohmic and acoustic losses; passivation; acoustic isolation; trimming
• Acoustic & RF design availability via process design kit (PDK) add-on

Applications:

• Key 6G frequency bands between 7 GHz and 15 GHz / FR3 – these are needed for network capacity enhancement and require the processing accuracy and material quality of acoustic filter technologies targeted in FAMES and matched with the IC technology.

3D Caps to power Systems-on-chip

The ambition of 6G systems is to integrate advanced features, merging not only communications capability, but also computing, security and sensing modalities. The integration of power management has become a significant trend in System-on-Chip (SoC) or System-in-Package (SiP) design, due to the increasing system complexity and power efficiency demand. Because systems now integrate many power-domains (to reduce excessive power supply margins) and clock frequencies are escalating, the power delivery architecture is a tricky point.

Adding all these constraints, 3D passive integration for power supply and interposer solutions are key enablers for advanced 6G systems, as they are appearing (but still need to improve) for HPC applications.

The capacitors developed in FAMES target high aspect ratio 3D structures to increase the capacitance density up to 3.5µF/mm².

AAO (Anodic Aluminium Oxyde) top and cross section view

The fabrication of a DC-DC converter with high density capacity embedded in an interposer will be used as a demonstrator of this technology.

RF magnetic-based miniaturized Circulators

Circulators are passive, non-reciprocal 3-, 4- or multi-port devices designed to work at RF microwave and mmWave frequencies in applications demanding power transfer control in defined directions such as Tx-Rx-antenna duplexers, isolators for linear/nonlinear devices isolation (e.g. amplifiers, mixers), or for reflection amplifiers.

Antenna duplexers are typically used to share a common physical antenna between transmit (TX) and receive (RX) signal paths, and can be made using multiple access approaches.
Key performance parameters of antenna duplexers include the losses in the path from TX input to antenna output and from antenna port to RX output, as well as the impedance matching of all ports. The most important ones are the isolation between TX and RX ports (>15 – 20 dB), insertion loss (<1 – 3 dB), return loss (<10-15 dB), power handling, size, and mass. Broadband operation covering the required frequency bands is also key. The targeted frequency bands in FAMES are:

• the 7 to 15 GHz band, which is used for 5G FR3 and 6G communications;
• the 28 to 39 GHz K-band, which is used for 5G FR2, radio location or drone tracking.

The investigation on circulators in the scope of FAMES is dedicated to the miniaturization and cost-effectiveness of their integration with RF front-end components and FD-SOI technologies. The focus is on self-biased circulators based on Ferrite materials using hexa-ferrites and YIG187 (Y3Fe5O12) for improved performance.