One-step air bridge fabrication technique using 3D e-beam lithography

A new technique is demonstrated for the realisation of air bridges using one lithographic step. Gray scale lithography is used for the formation of 3D profiles on polymethyl methacrylate (PMMA) where a variable dose exposure is applied to create a trapezoid profile for the air bridge. In previous 3D electron beam lithography (EBL) methods the span area was exposed to a low dose or a low acceleration voltage [1,2,3]. Thus, the required discontinuity with the surrounding area for the lift-off process was created. In this technique, no exposure of the span area is needed. Another exposure of a gradient dose is applied to the sides of the highest part of the air bridge. The created profile, after developing the resist, is depicted in Figure 1. The surfaces with red and blue colour represent the metal to form the air bridge and the metal to lift-off, respectively. Using this configuration, the deposited metal at the sides of the top part of the air bridge is connected to the surrounding metal to lift-off and disconnect from the air bridge. The electron dose used in this area has to be smaller than the minimum dose that penetrates the total resist layer, so that the deposited metal does not reach the substrate. This method takes maximum advantage of the resist thickness for the fabrication of high structures, as no part of the resist is sacrifice

Hot Start Giant Planets Form With Radiative Interiors

In the hot-start core accretion formation model for gas giants, the interior of a planet is usually assumed to be fully convective. By calculating the detailed internal evolution of a planet assuming hot start outer boundary conditions, we show that such a planet will in fact form with a radially increasing internal entropy profile, so that its interior will be radiative instead of convective. For a hot outer boundary, there is a minimum value for the entropy of the internal adiabat $S_{min}$ below which the accreting envelope does not match smoothly onto the interior, but instead deposits high entropy material onto the growing interior. One implication of this would be to at least temporarily halt the mixing of heavy elements within the planet, which are deposited by planetesimals accreted during formation. The compositional gradient this would impose could subsequently disrupt convection during post-accretion cooling, which would alter the observed cooling curve of the planet. However even with a homogeneous composition, for which convection develops as the planet cools, the difference in cooling timescale will change the inferred mass of directly-imaged gas giants.Comment: 6 pages, 5 figure

CMOS Terahertz Metamaterial Based 64 × 64 Bolometric Detector Arrays

We present two terahertz detectors composed of microbolometer sensors (vanadium oxide and silicon pn diode) and metamaterial absorbers monolithically integrated into a complementary metal oxide semiconductor (CMOS) process. The metamaterial absorbers were created using the metal-dielectric-metal layers of a commercial CMOS technology resulting in low-cost terahertz detectors. The scalability of this technology was used to form a 64 × 64 pixel terahertz focal plane array

Evaluation of a VNA-based material characterization kit at frequencies from 0.75 THz to 1.1 THz

This paper describes an initial assessment of a commercially available THz material characterization kit (MCK). The assessment is based on the measurement of several material samples. The MCK comprises two conical waveguide horn transitions and two sections of low-loss corrugated waveguide. A gap between the two corrugated waveguides allows the material samples to be inserted into the system during measurement. The MCK is attached to a THz Vector Network Analyzer (VNA), which measures S-parameters, in the frequency domain, of a material under test (MUT). A computer-based algorithm employing an iterative calculation derives values for material parameters (e.g. permittivity) from the measured S-parameters of the MUT. A MCK has been evaluated over the frequency range 0.75 THz to 1.1 THz, to assess the plausibility of results that can be obtained using such a technique. Two VNAs utilizing frequency extender heads were used for the investigation, with measurements being made with reference to a range of different calibration techniques and different calibration standards. Whilst some of the results obtained look reasonable, a significant proportion of the results were either difficult to interpret or showed inexplicable (i.e. non-physical) behavior. This indicates that much work is still needed before this technique can be used routinely for the measurement of material parameters at these very high frequencies

Evaluation of the 20,000 days campaign

The aim of Counties Manuaku District Health Board (CMDHB) 20,000 Days Campaign was to give back to the community 20,000 healthy and well days to avoid predicted growth in hospital bed days. After tracking the difference between projected demand and actual use, at the end of the Campaign on 1st July 2013, CMDHB reported that 23,060 bed days were given back to the people of Counties Manukau. This evaluation report explains how using the Institute of Healthcare Improvement Breakthrough Series the Campaign was run with the expectation that small immediate changes to practical problems (in this case the work of 13 Collaborative teams), will accumulate into large effects (a reduction of 20,000 bed days against predicted bed days use by July 2013). The evaluation found the Campaign did save bed days, though attributing causality was always going to be difficult, and overall the Campaign was very successful in keeping the energy and motivation of participants

Recent Progress in Plasmonic Colour Filters for Image Sensor and Multispectral Applications

Using nanostructured thin metal films as colour filters offers several important advantages, in particular high tunability across the entire visible spectrum and some of the infrared region, and also compatibility with conventional CMOS processes. Since 2003, the field of plasmonic colour filters has evolved rapidly and several different designs and materials, or combination of materials, have been proposed and studied. In this paper we present a simulation study for a single- step lithographically patterned multilayer structure able to provide competitive transmission efficiencies above 40% and contemporary FWHM of the order of 30 nm across the visible spectrum. The total thickness of the proposed filters is less than 200 nm and is constant for every wavelength, unlike e.g. resonant cavity-based filters such as Fabry-Perot that require a variable stack of several layers according to the working frequency, and their passband characteristics are entirely controlled by changing the lithographic pattern. It will also be shown that a key to obtaining narrow-band optical response lies in the dielectric environment of a nanostructure and that it is not necessary to have a symmetric structure to ensure good coupling between the SPPs at the top and bottom interfaces. Moreover, an analytical method to evaluate the periodicity, given a specific structure and a desirable working wavelength, will be proposed and its accuracy demonstrated. This method conveniently eliminate the need to optimize the design of a filter numerically, i.e. by running several time-consuming simulations with different periodicities. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Multi-spectral materials: hybridisation of optical plasmonic filters and a terahertz metamaterial absorber

Multi-spectral materials, using hybridised plasmonic and metamaterial structures, can simultaneously exhibit unique resonant phenomena over several decades of wavelengths. A multi-spectral material that combines a plasmonic colour filter array and a terahertz metamaterial absorber into a single material is a promising prospect for a coaxial multi-spectral imager operating in the visible, near IR, and terahertz wavebands

CMOS compatible metamaterial absorbers for hyperspectral medium wave infrared imaging and sensing applications

We experimentally demonstrate a CMOS compatible medium wave infrared metal-insulator-metal (MIM) metamaterial absorber structure where for a single dielectric spacer thickness at least 93% absorption is attained for 10 separate bands centred at 3.08, 3.30, 3.53, 3.78, 4.14, 4.40, 4.72, 4.94, 5.33, 5.60 μm. Previous hyperspectral MIM metamaterial absorber designs required that the thickness of the dielectric spacer layer be adjusted in order to attain selective unity absorption across the band of interest thereby increasing complexity and cost. We show that the absorption characteristics of the hyperspectral metamaterial structures are polarization insensitive and invariant for oblique incident angles up to 25° making them suitable for practical implementation in an imaging system. Finally, we also reveal that under TM illumination and at certain oblique incident angles there is an extremely narrowband Fano resonance (Q < 50) between the MIM absorber mode and the surface plasmon polariton mode that could have applications in hazardous/toxic gas identification and biosensing

Plasmonic gold nanodiscs using piezoelectric substrate birefringence for liquid sensing

This article presents the simulation, fabrication, and experimental characterization of a surface plasmonic resonance (SPR) sensor integrated with an acoustic sensing compatible substrate. The SPR sensor is designed to work in the visible region with gold nanodisc arrays fabricated on LiNbO3, which is both piezoelectric and birefringent. A linear relationship between resonance wavelength and varying liquid refractive indices were observed in experiments, and a sensitivity of 165 nm/refractive index unit was obtained. Polarization effects of the birefringent property of the Y-cut LiNbO3 substrate have been investigated, which can also be applied to X-cut LiNbO3. Our study demonstrates the feasibility of an SPR sensor device utilizing a birefringent substrate, which has acoustic wave compatibility and can pave the way toward much more robust and flexible biosensing device

Series coupled resonant tunneling diode oscillators for terahertz applications

A series of resonant tunneling diode oscillators with frequencies up to W-band and output power around one milliwatt are presented. To our knowledge, the 75.2 GHz RTD oscillator with -0.2 dBm output power is the highest power reported. The technique demonstrated here shows the great potential to scale up the design to terahertz frequencies. Jue Wang, Khalid Alharbi, Afesomeh Ofiare, Ata Khalid, Liquan Wang, David Cumming and Edward Wasig