Research Of FBAR Temperature Sensor

Recent years, with the significant development of the MEMS(Micro-Electro-Mechanical Systems) fabrication, film bulk acoustic resonator(FBAR) has obtained an extensive business application. On one hand, FBAR plays an important role in mobile communication area. Because of these excellent properties of small size, high frequency, low insert-loss, high power capacity of the FBAR RF devices, the oscillators, filters, duplexers made of FBAR have been used extensively in mobile communication area. On the other hand, FBAR sensors are developing rapidly. Researchers are becoming more interested in FBAR sensors with very high sensitivity and reliability. Now, some research papers about FBAR sensors have been reported, such as micro-mass sensor, temperature sensor, pressure sensor, humidity sensor and ultraviolet sensor. It is believed that FBAR sensors will make a wide application in the not long future.Firstly, this paper makes a simple summarization about the fundamental knowledge of FBAR, such as structure, operation principle, equivalent circuit model and fabricating process. On this basis, a kind of new fabrication method of FBAR is invented. Compared with the existing FBAR fabrication method, this new method with simple process steps is easy to be implemented. Secondly, this paper researches and analyzes the relationship between the resonance frequency of FBAR and temperature. Measure the characteristics cure of the resonance frequency versus temperature in the range of 20℃-200℃and calculate the TCF(Temperature Coefficient of Frequency). The measurement results demonstrate a good linearity(nolinar error is 6.4% and 4.2% separately)between the resonance frequency and temperature and the hysteresis and repeatability are excellent. As a result, the feasibility of FBAR temperature sensor is proved. Then, a kind of FBAR is made by sealing air in the back-etched FBAR and its TCF is measured between 20℃and 100℃. The result shows that the sealed air does not affect the linearity between the resonance frequency and temperature, besides, it elevates the TCF of back-etch FBAR.Finite elements method is used frequently to analyze engineering projects. At last, FBAR finiate elements analysis is performed. The influence of electrode paramters and piezoelectric parameters on resonance frequence is analysized.