In this article, a new generation of magnet-free circulators with high performance is proposed. Circulators are crucial devices in modern communication systems due to their ability to enable full-duplexing and double the spectral efficiency directly in the physical layer of the radio-frequency (RF) front end. Traditionally, the Lorentz reciprocity is broken by applying the magnetic bias to ferrite materials; therefore, conventional circulators are bulky and expensive. In this article, this problem is addressed by replacing the magnetic bias with periodic spatiotemporal modulation. Compared to previous works, the proposed circulator is constructed using surface acoustic wave (SAW) filters instead of transmission lines (TLs), which reduces the modulation frequency by at least a factor of 20 and ensures ultralow power consumption and high linearity. The miniaturized high quality (Q) factor SAW filters also lead to a low-loss nonreciprocal band with strong isolation (IX) and broad bandwidth (BW) on a chip scale, therefore addressing such limitations in previous magnet-free demonstrations. Furthermore, compared to the conventional differential circuit configuration, a novel quad configuration is developed, which doubles the intermodulation-free BW.

Sc-doped aluminum nitride is emerging as a new piezoelectric material which can substitute undoped aluminum nitride (AlN) in radio-frequency MEMS applications, thanks to its demonstrated enhancement of the piezoelectric coefficients. Furthermore, the recent demonstration of the ferroelectric-switching capability of the material gives AlScN the possibility to integrate memory functionalities in RF components. However, its high-coercive field and high-leakage currents are limiting its applicability. Residual stress, growth on different substrates, and testing-temperature have already been demonstrated as possible knobs to flatten the energy barrier needed for switching, but no investigation has been reported yet on the whole impact on the dielectric and ferroelectric dynamic behavior of a single process parameter. In this context, we analyze the complete spectrum of variations induced by the applied substrate-RF, from deposition characteristics to dielectric and ferroelectric properties, proving its effect on all of the material attributes. In particular, we demonstrate the possibility of engineering the AlScN lattice cell to properly modify leakage, breakdown, and coercive fields, as well as polarization charge, without altering the crystallinity level, making substrate-RF an effective and efficient fabrication knob to ease the limitations the material is facing.

The increasing use of mobile broadband requires new acoustic filtering technologies that can operate efficiently at frequencies above 6 GHz. Previous research has shown that AlN Super High Frequency (SHF) Cross-Sectional Lamé Mode resonators (CLMRs) can address this challenge, but their performance is limited by the piezoelectric strength of AlN. In this work, we explore the use of substitutional doping of Al in AlN with Sc to enhance the $k{}_t{}^2$ values of SHF CLMRs. Our results showed that the measured $k{}_t{}^2$·$Q{}_m$ product of Al${}_{72}$Sc${}_{28}$N CLMRs was four times greater than that of AlN CLMRs operating at the same frequency. Additionally, the measured fractional bandwidth (FWB) of Al${}_{72}$Sc${}_{28}$N 2nd order ladder filters was 4.13%, a fourfold improvement over AlN filters with the same design. We also discuss other aspects of the technology, such as power handling, losses, and spurious mode suppression, and identify potential areas for future research.

The present work reports on the novel usage of Scandium-doped Aluminum Nitride (AlScN) PMUT arrays for enhanced power transfer in implantable applications. As compared to identical arrays based on Aluminum Nitride (AlN), a 25dB increase in transmission was observed, and output power was increased by a factor of 50 as compared to previous work based on AlN arrays. After conjugate matching of the source impedance of the array, the output power showed a further 14x increase. Characterization of the transferred power versus incident acoustic intensity on the array enabled transmission of power levels of several milliwatts for intensities below the Food and Drug Administration's (FDA) limit. Finally, the array was interfaced to a commercially available boost converter to obtain rectified voltages of 1.8V and 1V in water and tissue phantom media, respectively, thus proving its practical applicability for powering and charging of intra-body electronics.