We report the machining of doubly-clamped SiCN nanomechanical resonators as narrow as 16 nm and lengths of up to 10 μm with a yield approaching 100%. The resonators were actuated using a piezoelectric disk, and their resonant response was detected using optical interferometry. Resonators with widths ranging from 16 to 375 nm and lengths from 10 to 50 μm were analyzed at room temperature at pressures ranging from 10 to 50 mTorr. Resonant frequencies in the 4–15 MHz range and quality factors in the 1000–7000 range were measured. We observed a significant decrease in resonant frequency with decreasing resonator width. The results of finite element analysis (FEA) show that this width dependence is mainly due to the resonators vibrating in the horizontal rather than vertical direction. At widths below 50 nm the comparison of experimental and FEA data suggest a gradual tensile stress reduction in the resonators as their width is reduced. Material softening is the most likely cause of this stress reduction. Additionally, the resonant behavior of 16, 55, and 375 nm wide devices was studied as a function of ambient pressure in the 10−5–10 Torr range. Resonance quality becomes dominated by gas damping effects at pressures above a threshold determined by the intrinsic Q-factor of the resonator. The intrinsic Q-factor tended to decrease with decreasing resonator width but was independent of length or resonant frequency. This suggests that surface-related mechanisms dominate the dissipation of energy in these devices.

We describe integrated air-core waveguides with Bragg reflector claddings, fabricated by controlled delamination and buckling of sputtered Si/SiO2 multilayers. Thin film deposition parameters were tailored to produce a desired amount of compressive stress, and a patterned, embedded fluorocarbon layer was used to define regions of reduced adhesion. Self-assembled air channels formed either spontaneously or upon heating-induced decomposition of the patterned film. Preliminary optical experiments confirmed that light is confined to the air channels by a photonic band-gap guidance mechanism, with loss ~5 dB/cm in the 1550 nm wavelength region. The waveguides employ standard silicon processes and have potential applications in MEMS and lab-on-chip systems.

We fabricated and tested periodic metal (Ag)-dielectric (SiO2 or TiO2) multilayers with transparency bands in the visible range. For samples with Ag-TiO2 interfaces, the optical properties exhibited relatively poor predictability, likely due to oxidation of the Ag layers. Ag/SiO2-based multilayers were found to be more predictable and stable, but the relatively low refractive index of SiO2 limits their inherent transparency and pass-band bandwidth. We show that termination of the multilayer with a single high-index layer reduces the admittance mismatch with the ambient media, and thus improves the properties of the transparency band.

We describe planar air-core waveguides with Bragg reflector claddings, fabricated by controlled delamination and buckling of sputtered Si/SiO 2 multilayers. We also report preliminary light guiding experiments in the 1550 nm wavelength range.Index Terms-Hollow Waveguide, Self Assembly. BACKGROUND AND MOTIVATIONAir-core integrated waveguides are attracting interest for lab-on-chip [1] and optical interconnect [2] applications. Conventional approaches for fabrication of these waveguides include sacrificial etching, wafer bonding, and chemical vapour deposition in a pre-defined trench [3]. We recently reported an alternative approach [4] based on the controlled formation of straight-sided delamination buckles [5] within a multilayer thin film stack.Those waveguides were fabricated using a combination of a chalcogenide glass and a commercial polymer. Here, we describe preliminary work on an analogous process using silicon-based materials and MEMS-compatible fabrication steps.Silicon-based processing should expand the scope for practical application of these self-assembled waveguides. FABRICATION PROCESS AND STRUCTURESPRODUCED In our process, controlled thin film buckling is exploited for the self-assembly of a three dimensional air core waveguide using otherwise planar (two-dimensional) processing steps. The process starts with a piranha cleaned silicon wafer, and follows the sequence of steps shown in Fig. 1. Si/SiO 2 Bragg reflectors were deposited using a pulsed magnetron sputtering system and a silicon target. The SiO 2 layers were deposited by reactive sputtering in an oxygen-rich environment. Sputtering allows a large degree of control over the extrinsic stress of the thin films, including the deposition of strongly compressive layers [6]. First, a four period Si-SiO 2 Bragg reflector was deposited at a substrate temperature of 150°C without breaking vacuum. This eventually acts as the bottom cladding of the hollow waveguides. After photoresist patterning, a fluorocarbon low adhesion layer (LAL) was deposited using the passivation process in a DRIE chamber [7]. The LAL was patterned by liftoff, thereby defining regions for subsequent delamination of the upper Bragg mirror. Next, the same sputtering system was used to deposit another four period Bragg reflector, which eventually acts as the upper cladding of the hollow waveguides. Deposition parameters were studied to ensure a desired level of compressive stress in the upper Bragg mirror. Deposition at low background pressure (~ 3.5 mTorr) and relatively high power (~200 W) produced a multilayer with a net compressive stress of ~260 MPa. Fig. 1. Process steps for creating planar waveguides: a) A fourperiod Bragg reflector is sputter deposited b) A LAL layer is applied using CVD and patterned using lithography c) A fourperiod top mirror is sputter deposited under compressive stress d) the sample is heated to reduce the adhesion, allowing the buckles to form along the patterned areas.258 978-1-4244-5369-6/10/$26.00 ©2010 IEEE