The German design presents the concept of an array of fully digitally interfaced and programmable stimulation pad cells for a retinal implant in 0.35-micron HVCMOS, which has a maximum voltage swing of 15 V, includes full-custom ESD protection and an innovative active charge balancer.
"Currently, a complete retinal stimulator chip is being fabricated, which includes all global functions and 116 stimulation pad cells," said the IIP Technologies researchers. Clinical trials have started.
As for hearing-impaired cochlear prostheses, they have evolved significantly during the past 20 years. More than 90,000 such devices have been implanted to date, restoring functional hearing to many profoundly deaf and severely hearing-impaired patients. A cochlear implant bypasses the failed hair cells of the inner ear to electrically stimulate the auditory nerve using 16 to 22 wire electrodes. Although such implants have been remarkably effective, speech perception among patients varies widely, and there are difficulties in understanding tonal languages and appreciating music.
Researchers at the University of Michigan see a potential solution to these problems in the development of electrode arrays that increase the numbers of stimulating sites so that the arrays can more easily adapt to differing patterns of nerve survival and use multi-polar current shaping to increase pitch perception.
Increasing the number of wire electrodes is precluded by the size of the cochlea, which tapers from a diameter of about 1 mm to about 200 m over its length. Integrated array position sensors to help optimize array placement and minimize insertion damage are also needed.
Researcher Pamela Bhatti reported on a thin-film cochlear electrode array that achieves high site density and incorporates on-board circuitry for stimulus generation and position sensing. "The array is designed for use in guinea pig studies but offers the same features and site densities needed for a 128-site, 16-channel human array," said Bhatti.
The 8-mm-long substrate tapers from a width of 500 to 200 microns and supports thirty-two 180-micron-diameter iridium-oxide stimulating sites on 250-micron centers. A 14-micron-thick, boron-diffused silicon area forms the base of the array, which remains outside the cochlea to support circuitry for current generation, site selection and position sensing. An eight-lead polymeric cable connects the array to an hermetically sealed electronics package containing a microcontroller along with a wireless interface for power and bidirectional data transfer.