Influence of Etching Trench on Keff2 of Film Bulk Acoustic Resonator

As radio-frequency (RF) communication becomes more ubiquitous globally, film bulk acoustic resonators (FBAR) have attracted great attention for their superior performance. One of the key parameters of an FBAR, the effective electromechanical coupling coefficient (Keff2), has a great influence on the bandwidth of RF filters. In this work, we propose a feasible method to tune the Keff2 of the FBAR by etching the piezoelectric material to form a trench around the active area of the FBAR. The influence of the position of the etching trench on the Keff2 of the FBAR was investigated by 3D finite element modeling and experimental fabricating. Meanwhile, a theoretical electrical model was presented to test and verify the simulated and measured results. The Keff2 of the FBAR tended to be reduced when the distance between the edge of the top electrode and the edge of the trench was increased, but the Q value of the FBAR was not degraded. This work provides a new possibility for tuning the Keff2 of resonators to meet the requirements of different filter bandwidths.

Biaxial FBAR Magnetic Sensor Based on Fe80Ga20 Anisotropic ΔE Effect

With the increasing application of personal navigation system in consumer electronics, the demand for multi-axis magnetic sensors based on MEMS is growing. We report a biaxial MEMS DC magnetic sensor consisting of an Mo/AlN/Fe80Ga20 film bulk acoustic resonator (FBAR), with anisotropy ΔE effect-based sensing principle. Different from the previously reported one-dimensional magnetic sensor based on the ΔE effect, the anisotropic ΔE effect was used to realize in-plane and out-of-plane two-dimensional magnetic field responses on a discrete sensor, and the sensor had two readout methods: resonant frequency f and return loss S11. The magnetic sensor realized the resonant frequency f shifted by 1.03 MHz and 0.2 MHz in the 567 Oe in-plane magnetic field and 720 Oe out-of-plane magnetic field, respectively, and the S11 changes by -30.2 dB and -0.92 dB. As the applied magnetic field increases, the -3 dB bandwidth quality factor Q3dB of the S11 curve gradually increases, and its maximum values in the in-plane and out-of-plane magnetic fields are 77143 and 1828, respectively, which reduces the detection limit of the magnetic sensor. The resonant magnetic sensor has stable high linear temperature and frequency drift characteristics, and its temperature frequency coefficient is -48.7 ppm/℃.

Mechanically driven SMR-based NEMS magnetoelectric antennas

Mechanically driven magnetoelectric (ME) antennas have been demonstrated to be one of the most effective methods to miniaturise antennas compared to state-of-the-art compact antennas. However, the nanoelectromechanical systems (NEMS) ME antennas are fragile due to their suspended thin-film heterostructure, and have very low power handling capabilities. Here we show that solidly mounted resonator (SMR)-based NEMS ME antennas on a Bragg acoustic resonator, which have a circular resonating disk of 200 μm diameters and operate at 1.75 GHz, show a high antenna gain of -18.8 dBi and 1dB compression point (P1dB) of 30.4 dBm. Compared to same-size thin-film bulk acoustic resonator (FBAR) ME antennas with a free-standing membrane, the SMR-based antennas are much more structurally stable with 23.3 dB higher power handling capability and easier fabrication steps. These SMR-based ME antennas are fabricated with processes compatible with complementary metal-oxide-semiconductor (CMOS), exhibiting dramatic size miniaturisation, high power handling, high mechanical robustness, simple fabrication processes, and much higher antenna radiation gain compared to same-size state-of-the-art antennas.

Numerical Investigation of Phononic Crystal Based Film Bulk Acoustic Wave Resonators

Film bulk acoustic resonator (FBAR)-based filters have attracted great attention because they can be used to build high-performance RF filters with low cost and small device size. Generally, FBARs employ the air cavity and Bragg mirror to confine the acoustic energy within the piezoelectric layer, so as to achieve high quality factors and low insertion loss. Here, two-dimensional (2D) phononic crystals (PhCs) are proposed to be the acoustic energy reflection layer for an FBAR (PhC-FBAR). Four kinds of PhC structures are investigated, and their bandgap diagrams and acoustic wave reflection coefficients are analyzed using the finite element method (FEM). Then, the PhCs are used as the acoustic wave reflectors at the bottom of the piezoelectric stack, with high reflectivity for elastic waves in the specific frequency range. The results show that the specific PhC possesses a wide bandgap, which enables the PhC-FBAR to work at a broad frequency range. Furthermore, the impedance spectra of PhC-FBARs are very smooth with few spurious modes, and the quality factors are close to those of traditional FBARs with air cavities, showing the application potential of the PhC-FBAR filters with wide bandwidth and high power capability.