This work describes extensive characterization and lifetime evaluation of a miniature hermetic glass-silicon packaging technology for implantable microsystem encapsulation. The package measures 2.3mm x 2.3mm x 10mm and is made to replace the titanium hermetic seals for chronic (> 40 years) applications. The packaging technology offers integrated high density feedthroughs (200/mm) to be utilized for lead transfer outside the package. Accelerated life tests have been developed and conducted to estimate lifetime at body temperature (37°C). Applying an Arrhenius model to the accelerated results in saline, an activation energy of 1.26 eV is calculated and a lifetime of 177 years is estimated at body temperature in saline. Tests in de-ionized water at 85°C that lasted close to 4 years demonstrate that, ignoring corrosion at the elevated temperatures, the glass-silicon package stays hermetic for > 164 years. Accelerated testing at high temperatures indicate that the corrosion problem, which does not occur at body temperature, needs to be addressed; hence, various measures including galvanic bias and heavy boron doping have been applied to the polysilicon layer which demonstrated satisfactory prevention of dissolution. The package can withstand tensile forces of up to 13 MPa. Alternate packaging technologies like (a) Au-Si eutectic and (b) evaporated glass assisted anodic sealing have been demonstrated as feasible means to be integrated into the microstimulator fabrication technology. The biocompatibility of the glass-silicon packages has been evaluated in various tissue samples and in different animal hosts which include guinea pigs (dura and abdomen), cats (bladder wall), and canines and rats (dorsum), up to a year. Histological evaluation of the tissue adjacent to implanted packages have shown no sign of infection, inflammation or tissue abnormality. The packages remained intact and hermetic during the course of the implants. A high-sensitivity ultra-thin film polyimide-based capacitive humidity sensor has also been developed to monitor internal humidity levels in anodically-bonded hermetic micropackages. This sensor is 1 mm on a side and utilizes CU1512 polyimide film with a thickness in the range of 300--1200A. The measured sensitivity for a sensor with a 1200A-thick film is 0.86pF/%RH and for a 300A-thick film is 3.4pF/%RH.Ph.D.Applied SciencesBiomedical engineeringElectrical engineeringPackagingUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132334/2/9963768.pd
