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Fabrication and performance of passive wireless pressure sensors based on LTCC technology
Keywords: Wireless, Pressure Sensor, LTCC
Wireless pressure sensors integrated with an inductor-capacitor (LC) resonant circuit have attracted more and more attentions because of their wide applications. The LC pressure sensor is composed of a planar spiral inductor and a cavity capacitor whose capacitance can vary according to the pressure, so that the pressure change can be detected remotely by measuring the impedance of an external coupled antenna as a function of frequency. Low temperature co-fired ceramic (LTCC) technology is a very promising approach for such applications, due to its feasibility for the fabrication of three-dimensional ceramic structures with embedded circuits and cavities. In particular, the good thermal, mechanical and electrical properties of the LTCC material as well as its compatibility with thick film hybrid technology makes it exceptionally suited for sensors and RF applications. Although a series of LTCC technology based LC pressure sensors have been reported. Most of them focus on improve the sensor performance through the optimizations of the sensor structure. According to the working mechanism of the cavity capacitive LTCC pressure sensor, the sensitivity of the LTCC pressure sensor is inversely proportional to the Young’s modulus value of LTCC materials. Thus, the properties of LTCC materials are the key factor for influencing the sensitivity of the wireless LTCC pressure sensor. Most of the reported LTCC sensors were fabricated using the DuPont 951 LTCC material. However, the DuPont 951 material has a high Young’s modulus of 120 GPa, which limits the sensor response. In this work, a kind of LTCC material produced by our lab was introduced. The sintered LTCC material has a low Young’s modulus value of ~ 65 GPa and is more suitable for obtaining high sensitivity sensors. We proposed a three-step lamination process to obtain a flat cavity structure without sacrificial materials. The effects of different thickness of the LTCC membranes on the sensitivity and the detecting range of the pressure sensor were investigated. The results showed that, with the increase of pressure sensitive membrane thickness, the sensitivity of the LTCC pressure sensor decreased but the detecting range increased. The optimized sensors showed a measurement sensitivity of 0.72947MHz/kPa and a detecting range of 0-2600 kPa, which are much higher than previous reports.
Zhifu Liu, Professor
Shanghai Institute of Ceramics, Chinese Academy of Sciences
Shanghai, Shanghai

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