Pietro Simeoni

This paper presents a high-performance infrared sensor based on a Scandium Aluminum Nitride (ScAlN) laterally vibrating resonator integrated with plasmonic absorbers for spectrally selective IR absorption. The proposed technology enables fast, compact, and high-resolution IR detection, making it ideal for the implementation of mobile gas-spectroscopy systems for environmental monitoring over large areas for extended periods. The sensor was designed to exhibit high IR absorptance at $4.5~\mu $ m, matching the absorption peak of N₂O. The resonant sensor experimentally shows an outstanding mechanical quality factor ( $Q_{m}$ ) of 2000, a 2.7% electromechanical coupling ( $k_{t}^{2}$ ), a high responsivity of 0.9 Hz/nW, a fast response of 6 ms and a low NEP of 320 pW/ $\mathrm {Hz}^{1/2}$ . While we focus on $4.5~\mu $ m in this system, the absorption wavelength is lithographically tunable, enabling the fabrication of multi-gas sensors on the same chip without using additional masks. A key innovation in this work compared to prior resonant IR detectors is the use of a novel material stack: Aluminum Nitride (AlN) as the dielectric in the Metal–Insulator–Metal plasmonic absorbers, combined with 30%-doped Scandium Aluminum Nitride (ScAlN) for the acoustic resonant cavity. This combination enhances sensor performance by taking advantage of the higher thermal resistance of ScAlN, as well as the higher temperature coefficient of frequency (TCF) of AlN compared to silicon dioxide (SiO₂). SiO₂ is traditionally used for IR absorption due to its optical properties; however, it is also characterized by a positive TCF, thereby degrading the thermal response of the resonator. In this work, the influence of geometrical parameters is experimentally investigated in hundreds of devices. The effect of tethering configurations and anchors’ width-to-length ratios on the sensor’s quality factor, thermal isolation, time response, and TCF is reported. Following optimization, the best-performing sensors are vacuum-packaged to enhance thermal isolation and improve response to IR. The device’s IR response is tested both in open-loop configuration with a vector network analyzer and in closed-loop within an oscillator circuit optimized for reduced phase noise. [2025-0145]

This paper reports an 11.7-GHz compact 50- $\Omega $ ladder filter based on single-layer Scandium Aluminum Nitride (ScAlN) film bulk acoustic resonators (FBARs) with platinum (Pt) electrodes, and uses it as a quantitative case study of the limits encountered when directly scaling to higher frequencies. The measured filter achieves a 3-dB fractional bandwidth (FBW) of 4.0% and an out-of-band rejection greater than 23.1 dB, with a minimum insertion loss (IL) of 6.8 dB. We analyze the origin of this performance through a quantitative framework: (i) a loss decomposition study, (ii) frequency-shift sensitivity that explains the discrepancy between simulated and measured center frequency, (iii) FBW sensitivity to series–shunt separation and port impedance, and (iv) stress-limited aperture that constrains device size. The results establish a realistic, fabric able baseline for directly scaled single-layer ScAlN FBAR filters and outline materials, electrode, and stress-management directions toward lower-loss mmWave acoustic filters.[2025-0162]

This paper reports the first groups of low-loss acoustic solidly mounted resonators (SMR) and acoustic delay lines (ADL) at 14-20 GHz. Bulk acoustic waves (BAW) are confined in thin-film scandium aluminum nitride (ScAlN) on top of dielectric acoustic Bragg reflectors, consisting of alternating silicon dioxide with tantalum pentoxide (Ta₂O₅/SiO₂) or niobium pentoxide (Nb₂O₅/SiO₂) on Si carrier wafers. Stack material parameters are extracted via high-resolution X-ray diffraction (HRXRD) and X-ray reflectivity (XRR). The simulation and experiment show confinement for longitudinal BAW from 14-20 GHz. ADLs show high propagation Q above 478 and 171 for Ta₂O₅/SiO₂ and Nb₂O₅/SiO₂, respectively. SMRs in both stacks perform similarly, showing coupling coefficient (k²) of 2.0%, series Q (Q_s) of 156, and parallel Q (Qp) values of 140 for Ta₂O₅/SiO₂, while k² of 2.4%, Q_s of 140, and Qp of 109 for Nb₂O₅/SiO₂, both at 18.6 GHz. Upon development, ScAlN solidly mounted platforms will enable signal processing elements with better power handling.

This letter reports on Solidly-Mounted Bidimensional Mode Resonators (S2MRs) exploiting a highly-optimized Sezawa mode in 30% Scandium-doped Aluminum Nitride (ScAlN) on Silicon Carbide (SiC) and operating near 16 GHz. Experimental results demonstrate mechanical quality factors ( ${Q}_{m}$ ) as high as 380, Bode quality factors ( ${Q}_{\textit {Bode}}$ ) approaching 500, electromechanical coupling coefficients ( ${k}_{t}^{{2}}$ ) of 4.5%, an overall Figure of Merit ( $\textit {FOM} = {Q}_{m} \cdot {k}_{t}^{{2}}$ ) exceeding 17, and power handling greater than 20 dBm for devices closely matched to $50~\Omega $ . To the best of the authors’ knowledge, S2MRs exhibit the highest Key Performance Indicators (KPIs) among solidly mounted resonators in the Ku-band, paving the way for the integration of nanoacoustic devices on fast substrates with high-power electronics, tailored for military and harsh-environment applications.

This work reports an acoustic solidly mounted resonator (SMR) at 18.64 GHz, among the highest operating frequencies reported. The device is built in scandium aluminum nitride (ScAlN) on top of silicon dioxide (SiO $_{2})$ and tantalum pentoxide (Ta $_{2}$ O $_{5})$ Bragg reflectors on silicon (Si) wafer. The stack is analyzed with X-ray reflectivity (XRR) and high-resolution X-ray diffraction (HRXRD). The resonator shows a coupling coefficient ( $k^{2})$ of 2.0%, high series quality factor ( $Q_{s})$ of 156, shunt quality factor ( $Q_p)$ of 142, and maximum Bode quality factor ( $Q_{max})$ of 210. The third-order harmonics at 59.64 GHz is also observed with $k^{2}$ around 0.6% and $Q$ around 40. Upon further development, the reported acoustic resonator platform can enable various front-end signal-processing functions, e.g., filters and oscillators, at future frequency range 3 (FR3) bands.2024-0120

This article presents the first prototype of a novel threshold sensing system operating in the radiofrequency (RF) range, capable of passively detecting and recording instances of temperature violations with high sensitivity and without the need of DC-biased memory devices. The system comprises a microfabricated hafnium zirconium oxide (HZO) ferroelectric varactor, a microfabricated lithium niobate (LiNbO3) shear-horizontal (SH0) Lamb wave microacoustic resonator used as a temperature sensor, and an inductor. All components have been soldered onto a printed circuit board for testing and characterization. Through this threshold sensing system, we also provide the first demonstration of ferroelectric switching in a HZO varactor triggered exclusively by an RF signal without requiring any DC voltages. The findings reported in this paper offer a promising pathway for future RF passive tags leveraging micro-and nanosystems to implement a programmable threshold sensing functionality with high sensitivity and with embedded memory capabilities. 2023-0215

This work reports a millimeter wave (mmWave) thin-film bulk acoustic resonator (FBAR) in sputtered scandium aluminum nitride (ScAlN). This paper identifies challenges of frequency scaling sputtered ScAlN into mmWave and proposes a stack and new fabrication procedure with a sputtered Sc $_{\mathbf{0.3}}$ Al $_{\mathbf{0.7}}$ N on Al on Si carrier wafer. The resonator achieves electromechanical coupling ( k $^{\mathbf{2}}$ ) of 7.0% and quality factor ( Q) of 62 for the first-order symmetric (S1) mode at 21.4 GHz, along with k $^{\mathbf{2}}$ of 4.0% and Q of 19 for the third-order symmetric (S3) mode at 55.4 GHz, showing higher figures of merit (FoM, k $^{\mathbf{2}}$ $\cdot$ Q) than reported AlN/ScAlN-based mmWave acoustic resonators. The ScAlN quality is identified by transmission electron microscopy (TEM) and X-ray diffraction (XRD), identifying the bottlenecks in the existing piezoelectric-metal stack. Further improvement of ScAlN/AlN-based mmWave acoustic resonators calls for better crystalline quality from improved thin-film deposition methods. 2023-0151

This study describes a sputtered scandium aluminum nitride (ScAlN) thin-film bulk acoustic resonator (FBAR) at 55.4 GHz. The resonator leverages the third-order symmetric (S3) mode in 37 nm Al on 85 nm Sc 0.3 Al 0.7 N on a 37 nm Al film stack, enabled by a new fabrication procedure. The 55.4 GHz S3 tone achieves electromechanical coupling (k ² ) of 3.8% and a 3-dB quality factor (Q) of 30, surpassing the reported state-of-the-art figure of merits (FoM, k ² ∙Q). Besides, the first-order symmetric (S1) mode at 21.0 GHz achieves k ² of 6.4% and Q of 62. Upon further optimization of the sputtering procedure, ScAlN/AlN-based mmWave acoustic resonators will continue to be improved.