Direct micromachining techniques

In view with microelectrode arrays F. Blair Simmons in 1965 performed the first multichannel auditory prosthesis stimulation study with five stainless steel electrodes insulated with Formvar inserted into the auditory nerve (and not into the ST) and emerging out from cochlea [27]. In recent years the interest in alternative stiff electrodes, to be inserted directly into the auditory nerve, has revived. In research conducted at University of Michigan, a batch-fabricated cochlear electrode array with stacked layers of parylene and metal was fabricated by silicon micromachining techniques. The 32-site array contained IrO (Iridium Oxide) stimulation sites with a centre-to-centre site spacing of 250 pm [28]. In the following sections the stiff and flexible electrode designs from the Delft University of the Technology (TU Delft), The Netherlands are described with its micro-fabrication sequence done at The Delft Institute of Microsystems and Nanoelectronics (DIMES), TU Delft, The Netherlands. 

The microfabrication of electrode arrays built with silicon micromachining techniques illustrates an positive approach towards future Cl electrode array development in respect to the traditional manufacturing method used now days. Also lithography and MEMS technology facilitates the addition of enhanced functionality to the microelectrode arrays. There is, however, still a long way to go until these devices can be used in real Cochlear Implants. The fabrication possibilities and characterization of different CMOS compatible metals (Ti, TiN and Al) provides a strong base to go ahead with further research in this direction. In our electrical tests done we conclude that TiN is able to withstand a high current density 2.8, while aluminium failed... 

Polymers fabrication processes are based on two major techniques replication micromachining and direct micromachining (Duffy et al., 1998 Becker, 2002). 

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