Search

We use a drop-port geometry to characterize frequency combs generated from silicon nitride on-chip microresonators in the normal group velocity regime. In sharp contrast with the traditional transmission geometry, we observe smooth output spectra with comparable powers in the pump and adjacent comb lines. The power transfer into the comb may be explained to a large extent by the coupling parameters characterizing the linear operation of the resonances studied. Furthermore, comparison of thru- and drop-port spectra shows that much of the ASE noise is filtered out by transmission to the drop-port. Autocorrelation measurements are performed on the drop-port output, without the need to filter out or suppress the strong pump line as is necessary in thru- port experiments. Passively mode-locked pulses with low background are observed in a normal dispersion microcavity. (c) 2013 Optical Society of America

The reliability performance of InxGa1-xAs n-MOSFETs with Al2O3 gate dielectric under positive-bias temperature instability stress is investigated. The following new phenomena are demonstrated: 1) There are high densities of fast interface traps N-it and slow oxide border traps N-SOX near the interface between InGaAs and Al2O3. The border traps are more fragile under stress, and therefore, the stress mainly induces border traps. 2) The stress-induced border traps consist of permanent acceptor traps and recoverable donor traps. Acceptor trap energy density Delta D-SOX(Acceptor) (E) is mainly distributed above the conduction band edge E-c of InGaAs with a tail extending to the midgap, whereas donor trap energy density Delta D-SOX(Donor) (E) has a large distribution inside the InGaAs energy gap with a tail extending to the conduction band. 3) Flicker noise variation after stress and its correlation to the acceptor and donor trap generation and recovery are demonstrated. 4) The recoverable donor traps induce the subthreshold slope and off-current degradation in the stress phase and recover in the recovery phase and also induce continuous degradation of on-current in the recovery phase. The permanent acceptor traps induce the transconductance and on-current degradation. The long-term device lifetime is mainly determined by the generation rate of the acceptor traps. 5) Comprehensive comparison between the Si and InGaAs MOSFETs' degradation behaviors under bias temperature instability stress is presented. The physical recovery of donor oxide traps in dielectric in InGaAs/Al2O3 has never been observed in a Si MOS structure, deserving special attention and further investigation.

We demonstrate high resonant absorption of visible light with a plasmonic nanocavity chain structure fabricated through resistless nanoimprinting in metal (RNIM). The RNIM approach provides a simple, reproducible, and accurate means to fabricate metallic nanopatterns with high fidelity. The nanocavities are shown to be efficiently excited using normally incident light, and the resonant wavelength can be controlled by either the width or the depth of the cavity. Numerical simulations confirm the experimental observations, and illustrate the behavior of the nanocavity chain waveguide and insensitivity to incident angle. The resonant absorption is due to the excitation of a localized metal-insulator-metal cavity mode. The interacting surface waves allow cavity lengths on the order of ten nanometers for light having a free space wavelength of about four hundred nanometers. Coupling of the cavities with an intervening surface plasmon wave results in a collective excitation and a chain waveguide mode that should prove valuable for more sensitive detection based on surface enhanced Raman scattering. (C) 2013 Optical Society of America

We demonstrate a process to fabricate silicon photonic devices directly on a plastic film which is both flexible and transparent. This process allows the integration of complex structures on plastic films without the need of transferring from another substrate. Waveguides, grating couplers, and microring resonators are fabricated and optically characterized. An optical strain sensor is shown as an application using 5 mu m-radius microring resonators on the flexible substrate. When strain is applied, resonance wavelength shifts of the microring resonators are observed. Contributions of different effects are analyzed and evaluated. Finally, we measure the influence of residual strain and confirm the material undergoes elastic deformation within the applied strain range. (C) 2012 Optical Society of America

A passive optical diode effect would be useful for on-chip optical information processing but has been difficult to achieve. Using a method based on optical nonlinearity, we demonstrate a forward-backward transmission ratio of up to 28 decibels within telecommunication wavelengths. Our device, which uses two silicon rings 5 micrometers in radius, is passive yet maintains optical nonreciprocity for a broad range of input power levels, and it performs equally well even if the backward input power is higher than the forward input. The silicon optical diode is ultracompact and is compatible with current complementary metal-oxide semiconductor processing.

We demonstrate an eight-channel reconfigurable optical filter on a silicon chip. It consists of cascaded microring resonators and integrated compact heaters. With an embedded Mach-Zehnder (MZ) arm coupling to a microring resonator, the important parameters of a filter such as center frequency, extinction ratio and bandwidth can be controlled simultaneously for purposes of filtering, routing and spectral shaping. Thus our device could potentially be useful in dense wavelength division multiplexing (DWDM) and radio frequency arbitrary waveform generation (RFAWG). Multichannel filter response was successfully tuned to match the International Telecommunication Unit (ITU) grid with 50, 100 and 200GHz in channel spacing. Programmable channel selectivity was demonstrated by heating the MZ arm, and continuous adjustment of through-port extinction ratio from 0dB to 27dB was achieved. Meanwhile, the 3dB bandwidth in the drop port changed from 0.12nm to 0.16nm. The device had an ultra-compact footprint (1200 mu mx100 mu m) excluding the metal leads and contact pads, making it suitable for large scale integration.

Triple junctions (TJs) are the lines where three grains or grain boundaries meet and become increasingly important in nanocrystalline materials where they have a high areal number density and occupy a significant fraction of the total volume of the material. Surface pits are associated with TJs, just as surface grooves are associated with grain boundaries, and these pits may have particularly deleterious effects on the behaviors of thin films. We evaluate the surface topography associated with TJs in nanocrystalline ZrO2 thin films using thickness mapping images produced by energy-filtered transmission electron microscopy (EFTEM), and compare our results with theoretical predictions. While many of the pits conform to the standard theoretical treatment, some of them exhibit considerably increased depth, possibly indicating that the junctions have line energy. No pits were observed with less than the theoretically predicted depth. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Fully transparent thin-film transistors (FFTs) based on well-aligned single-walled carbon nanotube (SWCNT) arrays with indium tin oxide (ITO) electrodes are achieved. The fully transparent SWCNT-TFTs could be attractive candidates for future flexible or transparent electronics.

Integrated-circuit patterns, such as those of transistor gates, usually consist of multivertex paths whose line segments are along two orthogonal directions. Such patterns are sometimes called "Manhattan structures" and are typically designed to achieve the highest packing density with a given linewidth. Owing to their arbitrary shapes, these patterns are predominantly generated via electron-beam lithography, a serial process which is inherently slow compared to parallel processes. Moreover, throughput is further reduced with the necessity of proximity correction in electron-beam lithography. On the other hand, interference lithography is a low-cost, parallel process that can achieve small linewidths and pitches, yet the achievable patterns are limited to gratings or other periodic structures. Here the authors propose to synthesize arbitrary Manhattan structures from regular structures such as gratings via cutting and stitching. They demonstrate the cutting and stitching of large-area, highly smooth gratings formed by interference lithography and orientation-dependent etch of silicon. Our method could significantly reduce the writing time in electron-beam lithography for pattern generation and requires no proximity correction.

Bacteriophage phi29 virus nanoparticles and its associated DNA packaging nanomotor can provide for novel possibilities towards the development of hybrid bio-nano structures. Towards the goal of interfacing the phi29 viruses and nanomotors with artificial micro and nanostructures, we fabricated nanoporous Anodic Aluminum Oxide (AAO) membranes with pore size of 70 nm and shrunk the pores to sub 40 nm diameter using atomic layer deposition (ALD) of Aluminum Oxide. We were able to capture and align particles in the anodized nanopores using two methods. Firstly, a functionalization and polishing process to chemically attach the particles in the inner surface of the pores was developed. Secondly, centrifugation of the particles was utilized to align them in the pores of the nanoporous membranes. In addition, when a mixture of empty capsids and packaged particles was centrifuged at specific speeds, it was found that the empty capsids deform and pass through 40 nm diameter pores whereas the particles packaged with DNA were mainly retained at the top surface of the nanoporous membranes. Fluorescence microscopy was used to verify the selective filtration of empty capsids through the nanoporous membranes.

The development of mechanically flexible and/or optically transparent electronics could enable next-generation electronics technologies, which would be easy-to-read, light-weight, unbreakable, transparent, and flexible. Potential applications could include transparent monitors, heads-up displays, and conformable products. Recent reports have demonstrated transparent thin film transistors (TFTs) using channels consisting of semiconductor nanowires (ZnO, SnO2, or In2O3) and random networks of single-walled carbon nanotubes (SWNTs).[1,2] Transparent TFTs are attractive for the drive circuitry in transparent and/or flexible active matrix display devices. These devices could overcome the limitations of conventional polycrystalline silicon and amorphous silicon thin film transistors, such as low mobility, nontransparency, or high temperature processing.[3–5]

A systematic capacitance-voltage (C-V) study has been performed on GaAs metal-oxide-semiconductor (MOS) structures with atomic-layer-deposited Al2O3 as gate dielectrics and indium tin oxide (ITO) as the metal gate. The transparent conducting ITO gate allows homogeneous photoillumination on the whole MOS capacitance area, such that one can easily observe the low-frequency (LF) C-V and quasistatic C-V of GaAs at room temperature. The semiconductor capacitance effect on GaAs MOS devices has also been identified and insightfully discussed based on the obtained LF C-V curves. The semiconductor capacitance effect becomes more important for devices with high-mobility channel materials and aggressively scaled high-k gate dielectrics.

Graphene is a hexagonally bonded sheet of carbon atoms that exhibits superior transport properties with a velocity of 10(8) cm/s and a room-temperature mobility of >15 000 cm(2)/V s. How to grow gate dielectrics on graphene with low defect states is a challenge for graphene-based nanoelectronics. Here, we present the growth behavior of Al2O3 and HfO2 films on highly ordered pyrolytic graphite (HOPG) by atomic layer deposition (ALD). To our surprise, large numbers of Al2O3 and HfO2 nanoribbons, with dimensions of 5-200 nm in width and >50 mu m in length, are observed on HOPG surfaces at growth temperature between 200 and 250 degrees C. This is due to the large numbers of step edges of graphene on HOPG surfaces, which serve as nucleation sites for the ALD process. These Al2O3 and HfO2 nanoribbons can be used as hard masks to generate graphene nanoribbons or as top-gate dielectrics for graphene devices. This methodology could be extended to synthesize insulating, semiconducting, and metallic nanostructures and their combinations.

Top-gated, few-layer graphene field-effect transistors (FETs) fabricated on thermally decomposed semi-insulating 4H-SiC substrates are demonstrated. Physical vapor deposited SiO2 is used as the gate dielectric. A two-dimensional hexagonal arrangement of carbon atoms with the correct lattice vectors, observed by high-resolution scanning tunneling microscopy, confirms the formation of multiple graphene layers on top of the SiC substrates. The observation of n-type and p-type transition further verifies Dirac Fermions' unique transport properties in graphene layers. The measured electron and hole mobilities on these fabricated graphene FETs are as high as 5400 and 4400 cm(2)/V s, respectively, which are much larger than the corresponding values from conventional SiC or silicon.

High performance single-walled carbon nanotube field effect transistors (SWCNT-FETs) fabricated with thin atomic layer deposited (ALD) Al2O3 as gate dielectrics and passivation layer are demonstrated. A 1.5 mu m gate-length SWCNT-FETs with 15 nm thick Al2O3 insulator shows a gate leakage current below 10(-11) A at -2.5 V

The development of optically transparent and mechanically flexible electronic circuitry is an essential step in the effort to develop next-generation display technologies, including 'see-through' and conformable products. Nanowire transistors (NWTs) are of particular interest for future display devices because of their high carrier mobilities compared with bulk or thin-film transistors made from the same materials, the prospect of processing at low temperatures compatible with plastic substrates, as well as their optical transparency and inherent mechanical flexibility. Here we report fully transparent In2O3 and ZnO NWTs fabricated on both glass and flexible plastic substrates, exhibiting high-performance n-type transistor characteristics with similar to 82% optical transparency. These NWTs should be attractive as pixel-switching and driving transistors in active-matrix organic light-emitting diode (AMOLED) displays. The transparency of the entire pixel area should significantly enhance aperture ratio efficiency in active-matrix arrays and thus substantially decrease power consumption.