Characterization of a hermetic silicon box fitted in a cardiac lead in order to measure the endocardial acceleration signal

Progressive cardiac diseases due to population aging lead to stimulate research and innovation. Moreover, recent development in the miniaturization of microsystem offers a tremendous opportunity for medical implantable application. This paper introduces a new technology that integrates a Micro Electro-Mechanical Systems (MEMS) accelerometer and an Application-Specific Integrated Circuit (ASIC) inside a hermetic silicon box that could be embedded in a cardiac lead in order to monitor the endocardial acceleration signal. The electronic components are attached on a wafer silicon interposer and encapsulated in a wafer silicon lid which is bonded using eutectic AuSi. The originality of the approach consists in using an interposer and a lid, both made of conductive doped silicon, to connect the device. The process is performed at the wafer level. The silicon box is finally connected to the electrical generator outside the heart thanks to two conductor wires. A prototype is described in this paper. The gas content and hermeticity of the package were analyzed using different techniques such as Residual Gas Analysis (RGA) and Helium or Krypton 85 testing. An estimate of the leak rate, which is assessed based on the formation of water droplet condensation in our package after 20 years, was evaluated.