This work reports on the measured performance of an Aluminum Scandium Nitride (AlScN) Two-Dimensional Resonant Rods resonator (2DRR), fabricated by using a Sc-doping concentration of 24% , characterized by a low off-resonance impedance ( $\sim $ 25 $\Omega $ ) and exhibiting a record electromechanical coupling coefficient ( ${k}_{t}^{\textit {2}}$ ) of 23.9% for AlScN resonators. In order to achieve such performance, we identified and relied on optimized deposition and etching processes for highly-doped AlScN films, aiming at achieving high crystalline quality, low density of abnormally oriented grains in the 2DRR’s active region and sharp lateral sidewalls. Also, the 2DRR’s unit-cell has been acoustically engineered to maximize the piezo-generated mechanical energy within each rod and to ensure a low transduction of spurious modes around resonance. Due to its unprecedented ${k}_{t}^{\textit {2}}$ , the reported 2DRR opens exciting scenarios towards the development of next generation monolithic integrated radio-frequency (RF) filtering components. In fact, we show that $5^{th}$ -order 2DRR-based ladder filters with fractional bandwidths (BW) of $\sim $ 11% , insertion-loss (I.L) values of $\sim $ 2.5 dB and with $>$ 30 dB out-of-band rejections can now be envisioned, paving an unprecedented path towards the development of ultra-wide band (UWB) filters for next-generation Super-High-Frequency (SHF) radio front-ends. [2022-0024]

This work describes the implementation of acoustic metamaterials (AMs) made of a forest of rods at the sides of a suspended Aluminum Scandium Nitride (AlScN) contour-mode-resonator (CMR) to increase its power handling without causing degradations of its electromechanical performance. The increase in usable anchoring perimeter with respect to conventional CMR-designs, enabled by the adoption of two AMs-based lateral anchors, permits to achieve an improved heat conduction from the resonator’s active region to the substrate. Furthermore, thanks to such AMs-based lateral anchors’ unique acoustic dispersion features, the attained increase of anchored perimeter does not cause any degradations of the CMR’s electromechanical performance, even leading to a ~ 15% improvement in the measured quality factor. Finally, we experimentally show that using our AMs-based lateral anchors leads to a more linear CMR’s electrical response, which is enabled by a ~ 32% reduction of its Duffing nonlinear coefficient with respect to the corresponding value attained by a conventional CMR-design that uses fully-etched lateral sides.

We present the first microacoustic metamaterial filters (MMFs). The bandpass of the reported MMFs is not generated by coupling, electrically or mechanically, various acoustic resonances; instead, it originates from the passbands and stopbands of a chain of three acoustic metamaterial (AM) structures. These structures form an AM transmission line (AMTL) and two AM reflectors (AMRs), respectively. Two single metal strips serve as input and output transducers with a wideband frequency response. Since MMFs do not rely on resonators, they do not require high-resolution trimming or mass-loading steps to accurately tune the resonance frequency difference between various microacoustic resonant devices. These steps often involve finely controlling the thickness of a device layer, with resolutions that can be as low as a few Angstroms when building GHz filters. The acoustic bandwidth of MMFs is mostly determined by geometrical and mechanical parameters of their AM structures. MMFs necessitate external circuit components for impedance matching, in contrast to the existing microacoustic filters that often employ circuit components only to eliminate ripples within their passband. We have designed and constructed the first MMFs from a 400-nm-thick scandium-doped aluminum nitride (AlScN) film using a 30% scandium-doping concentration. These devices operate in the radio frequency (RF) range. We validated these devices’ performance through finite-element modeling (FEM) simulations and through measurements of a set of fabricated devices. When matched with ideal circuit components, the built MMFs exhibit filter responses with a center frequency in the ultrahigh-frequency range, a fractional bandwidth (FBW) of ~2.54%, a loss of ~4.9 dB, an in-band group delay between $70~\pm ~25$ ns, and a temperature coefficient of frequency (TCF) of ~22.2 ppm/° C.

We report on the performance of the first Two-Dimensional-Resonant-Rods (2DRR) acoustic delay line (ADL) for operation in the Radio-Frequency (RF) range. Contrary to any other ADLs reported to date, which are based on the piezoelectric excitation of Surface Acoustic Waves (SAW) or Lamb Waves (LW), the ADL reported here relies on the lithographically defined artificial dispersive characteristics of acoustic metamaterials formed by forests of locally resonant rods as well as on the superior piezoelectric coefficients of highly-doped Aluminum Scandium Nitride (Al 0.64 Sc 0.36 N) films. The 2DRR-based ADL discussed in this work operates at 133 MHz and shows a record-high 5 dB fractional bandwidth of 7.5% as well as an insertion-loss of 1.8 dB.

We present a new design for AlScN contour-mode-resonators (CMRs) operating in the radiofrequency (RF) range. This design relies on acoustic metamaterials (AM) based lateral anchors to greatly enhance the power handling compared to conventional CMR-designs. Such anchors generate acoustic stopbands that prevent the leakage of piezo-generated acoustic energy from the resonating body into the substrate. The AM anchors reported in this work consist of the same AlScN film as in the CMRs’ active region, combined with a periodic array of rods. Their use allows a reduction of CMRs’ thermal resistance with respect to conventional designs, and enables a significant temperature compensation. As a result, the CMRs with AM anchors reported in this work show a $\sim$ 60% reduction in their Duffing coefficient with respect to conventional designs with fully-etched lateral sides, hence an improved linearity. Furthermore, when used to set the output frequency of high-power feedback loop oscillators, the CMRs with the AM anchors reported here enable a lower phase-noise compared to what achievable when employing the conventional counterparts. 2024-0053

In this study we present a novel dual-resonator temperature sensor which can be embedded in other MEMS sensors for improved thermal compensation and on-the-run calibration. For accurate temperature measurements, the proposed method mitigates time base errors in frequency counting, eliminates the need for a highly accurate reference clock and can cancel out the effects of aging of the time base without using a calibration process. The sensor structure is composed of a strain amplifying beam and two Double Ended Tuning Fork (DETF) resonators with different temperature sensitivities. The DETFs are kept at resonance simultaneously with a dual PLL circuit. Experiments reveal that at the expense of decreasing sensitivity, one can suppress the measurement errors which can be as high as 0.164 °C for the long resonator and 0.240 °C for the short resonator when a time base of 50 ppm accuracy is used. Moreover, while the frequency stability characteristics of the single sensing elements deteriorate drastically as the accuracy of the time base decreases, the frequency stability of the proposed frequency ratio remains unaffected and it is superior compared to both of the resonators.