A dual-mode film bulk acoustic resonator (DM-FBAR) temperature sensor modulated by different phosphorous-doped silica insertion layers was reported in this paper. The relative drift of the second and third resonance peaks of FBAR could improve the temperature sensitivity through the dual-mode beat frequency calculation method. The temperature sensitivity can be regulated by different the PH 3 doping flow in the SiO 2 insertion layer. Among the fabricated devices, FBAR with a SiO 2 insertion layer doped 4 sccm PH 3 has the highest temperature sensitivity of 64.8 kHz • C −1 . It is discovered that the greater the Young's modulus of the insert film changes with temperature, the higher the temperature sensitivity of DM-FBAR device. Therefore, an important technical means to improve the performance of DM-FBAR devices is using the material whose Young's modulus is more sensitive to temperature in the future.
The temperature sensitivity is one of the critical parameters for the thin film bulk acoustic resonator (FBAR) based temperature sensors. In this work, FBARs with Au/Fe0.8Ga0.2/Ti/AlN/Mo structure are developed. The size effect of the Ti insertion layer on the temperature sensitivity of the devices is systematically investigated. The devices were fabricated by MEMS process and characterized by a network analyzer under variable temperatures. It is found that the temperature sensitivity of the devices is strongly related to the thickness of the Ti insertion layer. A super-high temperature sensitivity up to 546 kHz °C−1 was obtained with 20 nm Ti inserted thin film; that feature can even reach 825 kHz °C−1 for some devices, showing great potential for ultra-sensitive temperature monitoring. Mason model is used to analyze the extraordinary characteristics of the device and finite element method (FEM) is used to analyze the strain distribution in the device. The supreme performance of the temperature sensor can be explained by the size effect of the temperature coefficient of Young’s modulus (TCE) of Ti film, which means that the TCE was enhanced when the thickness of the Ti film is around 20 nm. This work provides a new approach for the design of high sensitivity temperature sensor based on FBAR.
A bulk acoustic wave (BAW) driven magnetoelectric (ME) antenna has narrow operating bandwidth due to its high Q factor, and an effective mechanism for bandwidth enhancement is yet to be explored. This article presents a bandwidth-enhanced magnetoelectric (BWE-ME) antenna made of a Mo/AlN/FeGa sandwich stack, which is composed of three different resonant regions. These resonant regions in the discrete device can be equated as a parallel connection of dual high-overtone bulk acoustic resonators (HBARs) and single film bulk acoustic resonators (FBARs) with tiny frequency shift among the three resonators resulting in bandwidth broadening of the BWE-ME antenna. The resonant mode and return loss curves (S11) are simulated in a two-dimensional finite element method and fitted with the Mason equivalent circuit model. The frequency domain analysis shows that the magnetic flux density bandwidth generated by the multi-resonant mode interaction is 18 MHz, which matches the bandwidth of the measured reference gain S21 curve of the BWE-ME antenna, and the far-field radiated power characterization also shows the corresponding effective bandwidth distributed. The fabricated microelectromechanical systems antenna achieves a fractional bandwidth of 2.7% while maintaining the advantage of small size (0.49 mm2). Discrete composite BAW resonators that effectively combine the multi-resonant regions of HBARs and FBARs have the potential to realize compact and broadband BAW-ME antennas in the future.
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