Transmittance curve
IntroductionMultimodal stimulation of the nervous systemThe human nervous system is among the most complex biological structures on this planet. The brain alone is composed of tens of billions of neurons \cite{Pakkenberg_1988} and is solely responsible for coordinating the behavioral responses to the sensory inputs of the body. As a result, it became apparent early on in the field of neuroscience, that the ability to selectively interrogate a population of neurons would be the key element in understanding and controlling the nervous system \cite{Crick_1979}. Over the years, researchers have devised numerous methods to interact with neural tissues such as electrical and chemical stimuli and, more recently, through mechanical and optical means. Each of these methods has its limitation, particularly when it comes to selectivity. In that regard, neuroscientist typically discriminate between three types of selectivity (figure): Spacial selectivity, which refers to the ability to stimulate a specific volume of tissue. Structural selectivity which describes the capability to stimulate specific structure within a neuron, such as neuronal somata or fibers of passage. Cell-type selectivity relates to the ability to discriminate between neuronal types, a particularly interesting proposition as it would allow to activate only a specific function within a complex network of neurons.At the LSBI we aim to fabricate so-called multimodal devices, that is, neural implants capable of stimulating the nervous system through multiple methods, in a simultaneous and collocal fashion. We thus hope to improve the selectivity of the combined stimulation and, consequently, to improve our ability to study and control nervous tissues. In particular, we are interested in designing an implant that would incorporate electrical and optical capabilities at the exact same location. In our current prototype, such a feature is realized by placing microLEDs behind transparent electrodes. The selection of the material used for the electrodes is critical as we thrive to maximize both the amount of electrical charges and light injected in the tissue. At the current stage of research, we use a ceramic called Indium Tin Oxide. This material was recently introduced in the cleanroom facility of Campus Biotech (Geneva) and as such, its deposition method has yet to be tuned for optimal performances of the final film. With this project, we aimed at addressing this shortcoming by optimizing the deposition parameters of the machine used to form Indium Tin Oxide.Indium Tin Oxide