A 0.1mm{sup}2, Digitally Programmable Nerve Stimulation Pad Cell with High-Voltage Capability for a Retinal Implant

摘要

Functional electrical stimulation of the retina has received increasing attention over the last several years [1][2]. It restores basic vision through electrical nerve stimulation within the eyeball of blind people with retina degeneration. The system, known as an epiretinal prosthesis, is shown in Fig. 2.4.1. Electrical stimulation generates a nerve reaction upon the transfer of charge into the tissue via electrodes. For a retinal stimulator the integration of several hundreds of such stimulation sites is required in order to restore basic vision functions [1][3], Reliable operation of a nerve stimulator demands high ESD robustness at the electrodes. In addition, electrolysis caused by excess dc-current flow must be safely prevented, since it yields electrode and tissue destruction. The electrode impedance Re (Fig. 2.4.1) depends on the electrode size. For the retinal implant it is typically >10kΩ. This requires high voltage (HV) swing capabilities at the stimulation electrodes for feasible stimulation currents of up to 1mA [3]. Concurrently, the implanted system must be low power and the possible chip size is limited.