Towards CMUT for Neurostimulation

Abstract

Ultrasound (US) neurostimulation, the non-pharmacological, reversible excitation or inhibition of the nervous system using ultrasonic waves, is emerging as a high interest topic in neurostimulation research. In the current project, an attempt was made to demonstrate US neuromodulation in a Lumbricus Terrestris model of evoked compound action potentials (eCAP). Hardware and software for the electrophysiological observation of local field potentials were designed and assembled. The resulting system was used to perform mechanical, electrical and both direct and indirect ultrasonic neurostimulation experiments. It was shown electrical stimulation could be performed reliably in-vivo and ex-vivo. Mechanical stimulation only functioned in-vivo. Additionally, power transfer experiments showed that deeply embedded CMUT devices can be used to harvest acoustic power and use this signal to stimulate an explanted Lumbricus Terrestris medial nerve cord. Direct ultrasound neurostimulation was however not observed, likely due to a combination of misalignment and incorrect acoustic pressure profiles.
As an additional project, a microfabrication step was designed and performed for the etching of high aspect-ratio silicon bulk structures for the backside venting of low frequency CMUT devices. A two-step process deep reactive ion etch (DRIE) was attempted where smaller features were first introduced into the silicon (phase A) and then advanced using a larger etch frame (phase B). It was shown that phase A etching could be performed adequately, resulting in high quality deep silicon etch profiles with minimal tapering and an excellent etch rate. However, phase B etching resulted in the consumption of side-walls and removal of previously etched features. It is likely some slight adjustments to the passivation stage of the DRIE process would result in successful completion of this fabrication step.
Acknowledgements