Hermetic thin film encapsulation of mechanical transducers for smart label applications

For realizing an active smart RFID label monitoring mechanical shock and inclination during transport processes, a capacitive inertial sensor has been developed. Hermetic sealing of the microstructures has been done by a wafer level thin film encapsulation technology based on CF-polymer as sacrificial layer material and a stress-optimized dielectric layer stack as capping material. Long term stability of the thin film encapsulation hermeticity in dependence of the material stack was tested by measuring the pressure inside the package using the pressure dependency of viscous damping between the electrode plates. For the used material stacks containing SiO_x(H_y) or SiO_x(H_y)/SiN_x(H_y) and sputtered aluminum a sufficient hermeticity with leak rates of 2E-10 Pamiddotl/s and 6E-12 Pamiddotl/s, respectively, could be achieved.