Focused ion beam (FIB) fabrication has become an invaluable tool to pattern nanoscale features on a vast range of materials otherwise not available due to the limitations on selectivity of chemical based reactions for etching. In addition, direct milling to create features allows precision patterning on a variety of surface topology. In this talk, we present work on using the FIB to pattern and integrate nanophotonic elements, e.g. photonic crystals, and microelectromechanical systems for novel device applications. In addition, we explore how the FIB can also be used for applications in integration of microsystems with plasmonic structures to achieve precision control of light-matter interactions at the nanoscale.

Nano-optomechanical systems (NOMS), in which guided light is utilized to actuate and transduce the motion of nanomechanical resonators, have received intense attention in recent years [1, 2]. This actuation and transduction scheme offers unprecedented displacement sensitivity and ultrahigh bandwidth, which is also able to be fully integrated with state-of-the-art opto-electronic and semiconductor technology. It can be envisioned that NOMS will see a large variety of applications in mass sensing, gradiometry, and high precision frequency counting.

Strong optical forces and large evanescent field gradient, both critical factors in defining the actuation efficiency and the motion transduction sensitivity in a nano-optomechanical system, only exist in a distance smaller than the wavelength of light from the nanophotonic waveguide. This requires the nanomechanical resonator in NOMS to be brought in close proximity to adjacent nanophotonic structures (normally in the range of 100 – 300 nm). A well known device failure mechanism in this case is stiction of released structures due to attractive forces with adjacent surfaces. A critical point drying process is so far conventionally utilized in NOMS fabrication to remedy this issue [1, 2].

In this work we report on our attempt in utilizing alternative device releasing protocols in fabricating NOMS structures. The test structure selected is a several tens of micrometers long doubly clamped beam embedded in a race-track nanophotonic resonator. The entire device was fabricated on a silicon-on-insulator substrate with deep-UV lithography. The race-track resonator possesses an optical quality factor of a few tens of thousands and a finesse of ~ 20. The large finesse of the optical resonator allows sensitive motion transduction in which thermomechanical noise of a ~ 10 μm long device was able to be detected. Device releasing methods tested include sublimation drying with dichlorobenzene and cyclohexane, and hard masked hydrofluoric acid vapour etching. Finally, we also discuss the influence of different device releasing methods on the photonic properties of the system and the undercut profile.

[1] M. Li et al., Nature Photon. 3, 464 (2009).

[2] J. Roels et al., Nature Nanotech. 4, 510 (2009).