Micromachined Auditory Prostheses: Design, Fabrication and System Integration

In this report, we describe two Micro Electromechanical Systems (MEMS)

based implantable microelectrode arrays for use in auditory prostheses.

A novel curvature-controlled 3D micro-electrode array for cochlear

implants has been fabricated with the conducting polymer polypyrrole,

which deforms upon the application of an external electric field. This

electric field is used to control the curvature of the electrode,

facilitating its surgical insertion while minimizing mechanical trauma

to the scala tympani of the cochlea. In addition, the curved electrode

hugs the modiolus, reducing the distance between the electrodes and the

target neurons. The result is improved stimulation effectiveness in

terms of tonotopic specificity and stimulation threshold. We have both

simulated and demonstrated operation of the displacement of the

electrode array. An alternative to cochlear implants is direct

interface with the auditory nerve by way of penetrating electrode

arrays. A more accurate tonotopic representation may be functionally

restored if an electrode array with very small contact area is placed

directly within the auditory nerve instead of in the scala tympani. We

have explored a novel intraneural auditory prosthesis, consisting of a

form-fitting implantable microelectrode array integrated with wireless

on-chip circuitry for both digital signal processing (DSP) and power

delivery. A three-dimensional, high-aspect ratio, and high-density

electrode array has been developed using bulk machining technology.

On-going work includes creating the form-fitting contour at the

electrode base, which will help the accurate and secure placement of

the implantable electrodes on the target auditory nerves. A vendor

fabricated complementary metal oxide semiconductor (CMOS) chip will be

flip-chip bump bonded to a silicon wafer before the electrode array is

fabricated. The CMOS chip will have both wireless communication and

DSP functions for neural recording and stimulation. This on-chip

circuitry will eliminate the need for interconnection between the

electronic chip and the MEMS electrode. This wireless and integrated

design can be applied to other neural prostheses, including retinal

and vestibular implants. It can also serve as a general-purpose

miniaturized device for chronically stimulating and recording the

nervous system in electrophysiological and behavioral

experiments involving conscious animals.

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