Periodic Reporting for period 1 - MandMEMS (Magnonics meets micro-electro-mechanical systems: a new paradigm for communication technology and radio-frequency signal processing)
Reporting period: 2022-11-01 to 2024-04-30
In today’s fast-paced world, the significance of efficient radio-frequency (RF) signal processing cannot be overstated. It’s the beating heart of modern communication and radar technology, ensuring fast data transmission and pinpoint target detection. The global objective of M&MEMS is to create a novel spintronics-based platform with energy-efficient and tunable devices for microwave and RF technologies. With this platform, we aim to reduce energy consumption, achieve unprecedented agility, tunability and frequency ranges above 10 GHz, and reduce the size and ecological footprint of current RF and microwave technologies.
To achieve this ambitious goal, M&MEMS combines several technologies that have been researched separately in the past. The centerpiece of M&MEMS' RF processing is magnonics, i.e. the use of spin waves (SWs) for data processing. The frequencies of the spin waves can be continuously tuned in a magnonic device using magnetic fields and thus cover a spectrum from a few 100 MHz up to 20 GHz and higher, depending on the material and magnetic field. The spin wave frequencies therefore have a perfect overlap with applications in the field of communication for 5G and 6G, satellite communication and GPS, radar and other RF-based detection methods. What makes them interesting for miniaturized applications is that the wavelength of spin waves is 4 to 5 orders of magnitude shorter than electromagnetic waves of the same frequency. This leads to µm-long wavelength of SWs in the GHz range, which enables a strong miniaturization of the RF components, as required for mobile systems. Possible applications include RF filters, phase shifters (PS), time-delay units (TDU), isolators and also non-linear systems such as signal limiters and auto-tune filters. In these systems, RF-to-SW transducers are used to excite coherent spin waves, which propagate inside a magnetic material and can be manipulated during their propagation by appropriate magnetic field landscapes.
Magnonic components have already been used to construct such RF systems in the past, but the tunability of the frequencies was usually achieved by a magnetic field generated by charge currents in coils (electromagnets). However, the charge currents in the electromagnets cause large Joule losses, which negate the original high energy efficiency of the magnonic device. To reach the objective of increased energy efficiency, M&MEMS aims to develop demonstrators that use tunable magnetic fields without the use of charge currents. Two approaches are employed to reach the objective of tunable and energy-efficient RF devices:
In the first approach, micro-structured permanent magnets are used, whose stray magnetic field represents the bias field for the magnonic device. These micromagnets are placed at µm distances from the magnonic components. The stray field acting on the magnonic component is changed by using MEMS (micro-electromechanical systems) to change the position of the permanent magnets relative to the magnonic element.
The second approach utilises the fact that spin waves can also be influenced by many types of so-called "effective magnetic fields", which originate from other energy terms that contribute to the total magnetic energy. An important contribution here is the magnetoelastic energy, which describes the interaction of elastic deformations of the solid with magnetism. The magnetoelastic energy can be used to generate magnetoelastic fields that depend on the mechanical strains. It is important for the energy efficiency of this approach that mechanical stresses can be generated efficiently via the piezo-electric effect with the help of electric fields/voltages. This makes a constant charge current and the associated Joule losses obsolete. In the M&MEMS project, we use for instance acoustic waves (surface acoustic waves, SAW) to create dynamic strains in the magnetic material which translate into dynamic magneto-elastic fields.
Based upon these approaches, the final goal of M&MEMS is the fabrication of two demonstration devices which are exemplary for this novel hybrid platform. The first demonstrator is a tunable RF filter with high agility and the second is a multi-port phase shifter/time delay unit for directional RF antennas. These demonstrators are stand-alone devices with an advanced technological readiness level 5 (TRL 5) and they will serve as the cornerstones of a new technology platform for the application in 5G and beyond communication.
To achieve this ambitious goal, M&MEMS combines several technologies that have been researched separately in the past. The centerpiece of M&MEMS' RF processing is magnonics, i.e. the use of spin waves (SWs) for data processing. The frequencies of the spin waves can be continuously tuned in a magnonic device using magnetic fields and thus cover a spectrum from a few 100 MHz up to 20 GHz and higher, depending on the material and magnetic field. The spin wave frequencies therefore have a perfect overlap with applications in the field of communication for 5G and 6G, satellite communication and GPS, radar and other RF-based detection methods. What makes them interesting for miniaturized applications is that the wavelength of spin waves is 4 to 5 orders of magnitude shorter than electromagnetic waves of the same frequency. This leads to µm-long wavelength of SWs in the GHz range, which enables a strong miniaturization of the RF components, as required for mobile systems. Possible applications include RF filters, phase shifters (PS), time-delay units (TDU), isolators and also non-linear systems such as signal limiters and auto-tune filters. In these systems, RF-to-SW transducers are used to excite coherent spin waves, which propagate inside a magnetic material and can be manipulated during their propagation by appropriate magnetic field landscapes.
Magnonic components have already been used to construct such RF systems in the past, but the tunability of the frequencies was usually achieved by a magnetic field generated by charge currents in coils (electromagnets). However, the charge currents in the electromagnets cause large Joule losses, which negate the original high energy efficiency of the magnonic device. To reach the objective of increased energy efficiency, M&MEMS aims to develop demonstrators that use tunable magnetic fields without the use of charge currents. Two approaches are employed to reach the objective of tunable and energy-efficient RF devices:
In the first approach, micro-structured permanent magnets are used, whose stray magnetic field represents the bias field for the magnonic device. These micromagnets are placed at µm distances from the magnonic components. The stray field acting on the magnonic component is changed by using MEMS (micro-electromechanical systems) to change the position of the permanent magnets relative to the magnonic element.
The second approach utilises the fact that spin waves can also be influenced by many types of so-called "effective magnetic fields", which originate from other energy terms that contribute to the total magnetic energy. An important contribution here is the magnetoelastic energy, which describes the interaction of elastic deformations of the solid with magnetism. The magnetoelastic energy can be used to generate magnetoelastic fields that depend on the mechanical strains. It is important for the energy efficiency of this approach that mechanical stresses can be generated efficiently via the piezo-electric effect with the help of electric fields/voltages. This makes a constant charge current and the associated Joule losses obsolete. In the M&MEMS project, we use for instance acoustic waves (surface acoustic waves, SAW) to create dynamic strains in the magnetic material which translate into dynamic magneto-elastic fields.
Based upon these approaches, the final goal of M&MEMS is the fabrication of two demonstration devices which are exemplary for this novel hybrid platform. The first demonstrator is a tunable RF filter with high agility and the second is a multi-port phase shifter/time delay unit for directional RF antennas. These demonstrators are stand-alone devices with an advanced technological readiness level 5 (TRL 5) and they will serve as the cornerstones of a new technology platform for the application in 5G and beyond communication.
Within the first 18 months of the project, the first generation of building blocks of the different technologies to be combined in the final hybrid devices have been successfully designed, produced and tested. These include miniaturized spin-wave transmission lines (active area below 0.005 mm2) with low insertion losses (below -10 dB) and magnetic field tunable transmission frequencies between 2 and 20 GHz, micro-structured permanent hard magnets based on SmCo with large coercivity and large saturation magnetization as a micro-scaled magnetic field source, MEMS for lateral magnet movement with integrated magnetic flux concentrators based on soft magnets, surface acoustic wave (SAW) emitters based on interdigital transducers (IDTs) for frequencies up to the range of 5 GHz and printed circuit boards (PCBs) with different RF channels to accommodate the magnonic-MEMS hybrids. First prototype and test devices combining these individual building blocks have been realized and, in addition, the design and fabrication of a first hybrid demonstrator device acting as a phase shifter/time delay unit at a base frequency of 6GHz has started.
Within the first 18 months of the project, a hybrid device approach referred to as the monolithic approach has been explored. In this approach, the MEMS, the micro-magnets for the tunable bias field and the magnonic waveguide are fabricated on the same silicon chip. Thus, this approach delivers a highly integrated system with very good scalability on an industry-ready platform. However, the difficulty of this integration lies within the combination of thick (1 µm) permanent magnets, thin metallic magnonic elements and the interplay with the MEMS fabrication flow which relies on aggressive hydrofluoric acid. Exceeding state of the art technology, the integration of permanent magnets and magnonic elements on the same chip has been achieved in the first reporting period of the project, delivering a prototype device which operates in a self-bias regime without the need of external magnetic fields.