This paper presents a ScAlN/AlN-based MEMS piezoelectric accelerometer using the trapezoidal with corners (TWC) shaped cantilevers. The composite Sc _0.2 Al _0.8 N/AlN piezoelectric film is deposited on a silicon-on-insulator (SOI) substrate to improve the sensitivity of the piezoelectric accelerometer. The theoretical and FEM model is established to analyze the relationship between the cantilever stiffness and the piezoelectric parameters on the sensitivity and resonance frequency. The fabricated accelerometer includes a trapezoidal part, a rectangular part, and a silicon proof mass. The experimental results show that the sensitivity, minimum detectable signal (MDS), resolution, and resonant frequency of the proposed TWC shaped accelerometer are 7.95 mV/g, 1 mg, 1 mg, and 1290 Hz, respectively. The manufactured accelerometer exhibits good linearity up to 2 g (non-linearity<0.087%). Moreover, the TWC and Sc components increase the electric output by about 36% compared with the traditional trapezoidal accelerometer. At room temperature ( ${T}=300$ K), the thermal noise of the fabricated accelerometer is lower than 94.7 nV/ $\surd $ Hz. Meanwhile, the charge amplifier circuit noise is about $1.97~\mu \text{V}/\surd $ Hz. The proposed TWC accelerometer is sensitive and suitable to sense vibration acceleration in low-frequency scenarios.

Microelectromechanical (MEMS) piezoelectric accelerometers are diversely used in consumer electronics and handheld devices due to their low power consumption as well as simple reading circuit and good dynamic performance. In this paper, a tri-axial piezoelectric accelerometer with folded beams is presented. The four beam suspensions are located at two sides of the mass aligned with edges of the mass, and the thickness of the beams is the same as the thickness of the mass block. In order to realize the multi-axis detection, a total of 16 sensing elements are distributed at the end of the folded beams. The structural deformations, stress distribution, and output characteristics due to the acceleration in x-, y-, and z-axis directions are theoretically analyzed and simulated. The proposed accelerometer is fabricated by MEMS processes to form Mo/AlN/ScAlN/Mo piezoelectric stacks as the sensing layer. Experiments show that the charge sensitivity along the x-, y-, and z-axes could reach up to ~1.07 pC/g, ~0.66 pC/g, and ~3.35 pC/g. The new structure can provide inspiration for the design of tri-axial piezoelectric accelerometers with great sensitivity and linearity.

This paper presents three-dimensional (3D) models of high-frequency piezoelectric micromachined ultrasonic transducers (PMUTs) based on the finite element method (FEM). These models are verified with fabricated aluminum nitride (AlN)-based PMUT arrays. The 3D numerical model consists of a sandwiched piezoelectric structure, a silicon passive layer, and a silicon substrate with a cavity. Two types of parameters are simulated with periodic boundary conditions: (1) the resonant frequencies and mode shapes of PMUT, and (2) the electrical impedance and acoustic field of PMUT loaded with air and water. The resonant frequencies and mode shapes of an electrically connected PMUT array are obtained with a laser Doppler vibrometer (LDV). The first resonant frequency difference between 3D FEM simulation and the measurement for a 16-MHz PMUT is reasonably within 6%, which is just one-third of that between the analytical method and the measurement. The electrical impedance of the PMUT array measured in air and water is consistent with the simulation results. The 3D model is suitable for predicting electrical and acoustic performance and, thus, optimizing the structure of high-frequency PMUTs. It also has good potential to analyze the transmission and reception performances of a PMUT array for future compact ultrasonic systems.

This article presents a high quality factor ( ${Q}$ ) load sensor based on Sc _0.2 Al _0.8 N/aluminum nitride (AlN)-on-silicon surface acoustic wave (SAW) resonator. Finite element method (FEM) analysis is performed to predict the resonance frequency and the wave propagation mode. A high- ${Q}$ of 7200 at the parallel resonance frequency ( ${f}_{p}$ ) of 447.50 MHz is measured for Sc _0.2 Al _0.8 N/AlN configured SAW resonator on a silicon substrate. Experimental values for variation of series resonance frequency ( ${\Delta } {f}_{s}$ ) and variation of ${f}_{p}$ ( ${\Delta } {f}_{p}$ ) are found to be −75.3 and −186.8 kHz with variation of applied force $({\Delta } \textit {F)} = 4.155$ N, operating in the analyzed range. The linear approximation of measured frequency variations under force is ${\Delta } {f}_{s}/{F} = -12.7$ kHz/N and ${\Delta } {f}_{p}/{F} = -46.2$ kHz/N. Moreover, the force sensitivities for this sensor are −28.4 and −103.2 ppm/N for ${f}_{s}$ and ${f}_{p}$ , respectively. This high- ${Q}$ scandium-doped AlN (ScAlN)/AlN-based SAW resonator exhibits high sensitivity, demonstrating that the structure can be used as load sensors in industrial applications such as manufacturing, medical, grocery, and automotive industries.

The demand for filters with a large fractional bandwidth, up to 5%, still puts a great challenge to the typical aluminum nitride (AlN) thin films-based bulk acoustic wave (BAW) filters in an acoustic-only approach. This paper presents the design, fabrication, and characterization of film bulk acoustic wave resonator (FBAR) and filters using aluminum scandium nitride (Al $_{0.8}$ Sc $_{0.2}$ N) thin films. The fundamental thickness-mode resonance of the FBAR is measured at 4.235 GHz with an excellent effective electromechanical coupling factor ( $K_{eff}^{2})$ of 14%. The filters employ a modified structure with additional $\vphantom{^{\int}}$ molybdenum (Mo) layers formed on the connection strips between each adjacent resonator. The proposed filtering topologies including ladder topology, lattice topology, and ladder-lattice topology are constructed. Results show that the modified connection strips can decrease the magnitude impedance at series resonant frequency and improve the insertion loss (IL) of the filters. The fabricated ladder filter demonstrates a high center frequency of 4.25GHz, low IL of 1.804 dB, wide bandwidth of 189 MHz, and out-of-band rejection of 30 dB, holding a great potential for the 5G wideband applications. 2022-0201

Laterally excited bulk acoustic resonators (XBARs) using interdigital electrodes are currently limited in potential 5G applications due to the accompanied spurious modes and small capacitance. This Letter presents an XBAR with scattering vias in electrodes, named SV-BAR. The non-parallel boundaries thoroughly disrupt the coherent formation of standing waves in the lateral direction, thereby suppressing the higher-order spurious modes. The duty factor of SV-BAR is optimized as 0.5 using COMSOL Multiphysics finite element analysis for the 50 Ω impedance matching. The SV-BAR is fabricated using a 390 nm Z-cut LiNbO3 on an insulator substrate and exhibits an impressive ratio of Zp/Zs near 64.5 dB, a Kt2 of 21.80% at 4.762 GHz, as well as a large value f · Bode_Qmax · Kt2 (3.43 × 1011). The measured temperature coefficient of frequency is −69.8 ppm/°C, which can be compensated using SiO2 thin films. The SV-BAR provides an effective solution for high-performance radio frequency filters for 5G communication.