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We report a thin-film piezoelectric microelectromechanical systems (MEMS) transducer suitable for in vivo implantation as audio prosthesis and a method for fabricating it. The transducer consists of a layered stack of thin films comprising a MEMS membrane made of an isolating oxide interface; two platinum (Pt) layers acting as electrodes, electrical paths, and contacting pads; a thin-film sputtered aluminum nitride (AlN) layer acting as acoustic active material of the transducer; a passivation layer for device protection; and a 3-D micromachined acoustic cavity fabricated on the bulk of a silicon-on-insulator supporting substrate. The transducer has a reduced size and a low cost associated with CMOS-like mass production. Finite-element modeling and experimental tests conducted at the audio and ultrasonic bands show that the device has the performance required in audio prosthesis applications. The technology offers possibilities for biocompatibility or biocompatible packaging and is integrable to microelectronic circuit technologies.[ 2012-0004]Index Terms-Aluminum nitride (AlN) devices and transducers, implantable audio prostheses, microelectromechanical systems (MEMS) transducer, piezoelectric transducers.

A micro-machined transducer and sensor for a new implantable audioprosthesis to substitute the human tympanic-ossicular system has been developed. The device is intended to restore hearing by implanting it in patients with a damaged or surgically removed ossicular chain. Different configurations of devices have been analysed. The proposed piezo-actuator has a diameter of 1.0 mm with a total thickness of 3.5 mm, which reaches deformations of up 16.8 nm with a typical excitation of 3 V.Introduction: Between the tympanic membrane and the cochlea is a three-bone mechanical linkage called the ossicular chain, which mechanically couples the tympanic membrane to the fluid-filled cochlea. One of these bones is the stapes, which contacts with the oval window in the cochlea. The stapes is moved practically like a piston over the cochlear fluid stimulating the nerves and driving the sound information to the brain. Many diseases affect the sound transmission process by damaging the tympanic-ossicular chain. Moreover, during their surgical treatment it could be necessary to completely or partially resect it. Many researches have tried to reconstruct the sound transmission mechanism by means of ear hearing aids; the more common types have been electromagnetic and piezoelectric systems [1,2].In this Letter a piezoelectric actuator is described, which could be directly connected to the oval or round window using a titanium screw similar to that used by dentists. This piezo-actuator will substitute the ossicular chain as it translates the electrical energy into vibrational energy. Normally, piezoelectric actuators in the audio field require high-voltage operation to reach high deflection rates, but the requirements in our actuator are not so high. For example, sound pressure levels of normal conversation occur at 60 dB SPL, while the discomfort threshold for most humans is between 105 and 120 dB SPL, but the stapes displacement for 80 dB is around 10 -20 nm [3].

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