Wireless Inertial Sensors Made on Flexible Substrates and Based on Thermal Convection and Near-Field-Communication Principles

摘要

In this study, several kinds of wireless inertial sensors, such as accelerometers, angular accelerometers and inclinometers based on the thermal convection principle, were integrated with near-field-communication (NFC) antennas and made on a flexible substrate so that the devices can become wireless sensors. The reason to apply a flexible substrate instead of the traditional silicon was to reduce the power leaked through the flexible substrate, because the thermal conductivity of silicon is 0.06-0.0017 W/(cm•K), which is 25 times larger than that of the flexible substrate, 1.48 W/(cm•K). Another key goal was to fabricate the nonfloating-type devices without making a cavity on the substrate, so that the new devices would be easier to fabricate and more reliable than the previous floating-type; in which the components of heaters and thermal sensors lay over the cavity on the silicon substrate. Also inert Xe gas was used to fill the chamber instead of the previously used CO_2 or air, so that the oxidization problem of the thermal sensors caused by the heater can be eliminated. On the other hand, one can fabricate the components of heaters and thermal sensors on the flexible substrate directly or stack them on a layer of aluminum nitride and then use some packages with hemispherical or hemicylindrical chambers instead of rectangular ones. The sensitivities were analyzed and compared with those of the previous sensors to prove the feasibility of these novel ideas.