Establishment of High Channel-Count Packaging in Active Implantable Medical Devices for Neuroprosthesis.

Neuroprostheses have contributed extensively to humankind's capacity to treat disease and injury. Hearing loss is routinely overcome; pain is controlled; and myriad neurological, sensory, motor, and psychological disorders are managed through interventions involving neuromodulation. Fabrication of active implantable medical devices (AIMDs) often relies on highly skilled operators, leading to high costs, reliability challenges, and limitations to further device miniaturization and manufacturing output. Extending AIMD benefits to other disorders may also require a substantial increase in the number of stimulation or recording channels, exceeding the boundaries of existing fabrication techniques and human dexterity. In one-to-one correspondence, electrical signals must transition between the biological environment and a controlled atmosphere suitable for protecting active electronics-e.g., electrodes interfaced to excitable tissue must ultimately connect to a circuit node, each sensitive to corrosion or shorting when exposed to moisture and ions. Protection is typically achieved by hermetic encapsulation, with each signal crossing the hermetic barrier via a conductive pathway (feedthrough). As the quantity of signals increases, so does the complexity of the encapsulation. Herein, we describe a robust hermetic encapsulation approach with feedthrough densities of around 250 contacts/cm2 and establishment of interconnections to each feedthrough in an all-at-once fashion. The resulting interfaces offer impedances < 5 mΩ between a connection pad of the electronics to the electrode and bond strengths ~10 MPa. An illustrative example is presented as a visual neuroprosthesis for retinal dystrophies with 99 channels of electrical stimulation and associated power and communication interfaces-a device that we call the Phoenix99.