A high-density thin-film electrode array for a cochlear prosthesis.

The first high-density passive intracochlear electrode array is reported. Through direct electrical stimulation of auditory nerve elements, the array bypasses failed hair cells to elicit a response in the auditory nerve. The thin-film silicon device at least doubles the site density offered by commercial arrays to better exploit the cochlea's acoustic frequency-to-place mapping. The design, fabrication and characterization of the array are described with respect to safe and effective charge delivery with iridium-oxide stimulating sites, and development of a highly flexible substrate. The array has been validated in-vivo with animal models (cat and guinea pig) and it appropriately activated the respective subject's central auditory nervous system with intracochlear electrical stimulation. Measurement of action potentials in the central nucleus of the inferior colliculus demonstrated the expected frequency-specific neural activation. A 32-site 4-channel high-density active electrode array is also reported. The array delivers 500muA biphasic current levels with 8-bit resolution and less than 1% charge mismatch. Grounding sites between pulses may be used to reduce offsets. Stimulation on up to four parallel channels is possible with a voltage compliance of +/-2V. The minimum pulse width is 4psec, and the per-channel power dissipation is 2.5mW from +/-2.5V. The active array is integrated with position-sensing functions and also performs site-impedance measurements. A recording amplifier/buffer provides 6dB of gain with a bandwidth of 1.7MHz and a voltage swing of +/-2.1V to sense electrode potentials. The chip has a footprint of 2.4mm x 2.9mm. The circuitry, interface, and electrode array described here is scalable to a 128-site 16-channel human array. The feasibility of such a device is addressed in terms of substrate compliance, stimulating site traces, circuitry requirements and system integration.PhDApplied SciencesBiomedical engineeringElectrical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126098/2/3237908.pd