Distributed intelligence using gallium nitride based active devices

Abstract

This research seeks to develop a novel branch of materials systems called Distributed Intelligent Materials Systems (DIMS) which incorporate actuation, sensing, electronics and intelligence as inherent parts of the material structure. A microcantilever optical switch is fabricated as a concept demonstrator with Gallium nitride (GaN) as host material. GaN has several material characteristics which enable it to outperform other semiconductor materials for electronic applications. It also displays exceptional chemical inertness, has a relatively high piezoelectric coefficient, good mechanical strength and toughness and is transparent to wavelengths in the visible spectrum. In this paper we develop and fabricate a GaN-based, piezoelectrically actuated microcantilever optical switch/waveguide. While the GaN-material offers the benefits mentioned above, the piezoelectric actuation and the cantilever design provide benefits of lighter weight, compactness, speed of actuation, reduced structural complexity enabling easier fabrication and low wear and tear due to minimal moving parts. The proposed design has a conventional unimorph configuration with GaN actuated in d 31 mode. In this configuration, a laminar metal electrode and a doped n-type GaN layer are used to apply an electric field in the top layer to actuate the unimorph. The unimorph is fabricated as a micro-cantilever by using surface micromachining methods on epitaxial GaN grown on a GaN substrate. The cantilever is then etched partially using conventional semiconductor processing techniques and using a recent microfabrication technique known as photoelectrochemical (PEC) etch. PEC etching enables the fabrication of MOEMS structures that are rather difficult to create using conventional methods. Novel modifications and improvements to the current state-of-the art in PEC for GaN are presented and discussed.