Film bulk acoustic resonators (FBARs) have been evaluated for use as biosensors because of their high sensitivity and small size. This study fabricated a novel human IgE biosensor using shear-mode FBAR devices withc-axis 23°-tilted AlN thin films. Off-axis radio frequency (RF) magnetron sputtering method was used for deposition ofc-axis 23°-tilted AlN thin films. The deposition parameters were adopted as working pressure of 5 mTorr, substrate temperature of 300°C, sputtering power of 250 W, and 50 mm distance between off-axis and on-axis. The characteristics of the AlN thin films were investigated by X-ray diffraction and scanning electron microscopy. The frequency response was measured with an HP8720 network analyzer with a CASCADE probe station. The X-ray diffraction revealed (002) preferred wurtzite structure, and the cross-sectional image showed columnar structure with 23°-tilted AlN thin films. In the biosensor, an Au/Cr layer in the FBAR backside cavity was used as the detection layer and the Au surface was modified using self-assembly monolayers (SAMs) method. Then, the antigen and antibody were coated on biosensor through their high specificity property. Finally, the shear-mode FBAR device withk_t²of 3.18% was obtained, and the average sensitivity for human IgE detection of about 1.425 × 10⁵ cm²/g was achieved.

This study focused on the fabrication and the theoretical analysis of solidly mounted resonators (SMR) concerning dual-mode frequency responses and their frequency shift of bulk acoustic wave (BAW) resonance. For this device fabrication, RF/DC magnetron sputtering and photolithography were employed to constitute the required multilayer structure. For the theoretical analysis, the dual- mode frequency shift was characterized by the Sauerbrey's formula, and a modified formula was carried out following the trend for the large frequency shift. In the fabrication of the SMR device, Mo/SiO₂ was chosen to construct the Bragg reflector as the high/low acoustic impedance materials, respectively, and aluminum nitride (AlN) was used as a piezoelectric layer. To investigate the characteristics of BAW on the dual-mode frequency shift, the c-axis tilted angle of AlN was altered as well as the various mass loading on the SMR. Based on the experimental results, the dual-resonance frequencies showed a nonlinear decreasing trend with a linear increase of the mass loading. Therefore, a modified formula was carried out. Furthermore, the ratio of the longitudinal-resonant frequency to the shear-resonant frequency remained at a range around 1.76 despite the various c-axis tilted angles of AlN and gradual mass loading on the SMR. The electromechanical coupling coefficient, k_eff ², of the shear resonance rose with the increase of the c-axis tilted angle of AlN.

Dual‐mode thin film bulk acoustic resonator (TFBAR) devices are fabricated with c‐axis tilted AlN films. To fabricate dual‐mode TFBAR devices, the off‐axis RF magnetron sputtering method for the growth of tilted piezoelectric AlN thin films is adopted. In this report, the AlN thin films are deposited with tilting angles of 15° and 23°. The frequency response of the TFBAR device with 23° tilted AlN thin film is measured to reveal its ability to provide dual‐mode resonance. The sensitivities of the longitudinal and shear modes to mass loading are calculated to be 2295 Hz cm²/ng and 1363 Hz cm²/ng with the mechanical quality factors of 480 and 287, respectively. The sensitivities of the longitudinal and shear modes are calculated to be 0 and 15 Hz cm²/μg for liquid loading.

This study elucidates the combination of an oscillator circuit with a high-frequency amplifier, a matching network, and a layered surface acoustic wave device for detecting ultraviolet (UV) light. The oscillator circuit shows an excellent performance with the resonance frequency of 109.34MHz and phase noise of −107.137dB at 100kHz. The frequency shift that is caused by the interaction between the acoustic wave and carriers upon excitation by UV light in the ZnO thin film is discussed. The frequency variation of the oscillator steadily increases with the intensity of the UV light. An extreme frequency shift of 63.75kHz was observed as the UV light intensity reached 1250μW∕cm2.