Graphene has been well studied to be an excellent thermoelectric (TE) material of choice for thermal detection. It is widely considered a key enabler for next-in-class infrared (IR) detectors given its superb carrier mobility, sensitivities and broadband absorption in far-IR range surpassing that of current thermopiles. Normally, TE studies are conducted using graphene exfoliated from graphite crystal. It is then transferred onto Si/SiO2 substrate and fabricated into Hall bar configuration with microheater at one end. A gate voltage (Vg) is passed through the substrate and the response is examined in vacuum condition. By tuning the Vg, one can possibly obtain different thermoelectric power (TEP) values. The challenge is to maintain optimum Vg for the TE device to function which requires higher power consumption. This translate to the need for additional power supply. In this report, we proposed CVDG as TE material. Typically, CVDG are synthesized on Cu film and eventually transferred onto Si/SiO2 substrate. The benefit of CVDG is that it is large area, relatively inexpensive and does not require a Vg with associated circuitry. For the first time, CVDG system was extended to nonvacuum condition to simulate open detector system where detector is exposed to sensing environment. Average TEP was measured to be 168μV/K at 298K. Moreover, CVDG is tested to be stable in air over several months with little or no decrease in performance. A comprehensive characterization between exfoliated and CVDG will be presented. In addition, measurement results for vacuum and non-vacuum detector mode will be compared as well.
This paper discusses the two-step fabrication of a novel in-plane Si-air linear variable optical filter (LVOF). LVOF has alternating quarter-wave stack layers of high refractive and low refractive index materials sandwiching a tapered cavity. Different passbands can be observed at various positions along the length of the filter. Challenges of LVOF fabrication include depositing consistent thickness of quarter-wave stacks and precise control of the taper angle to be in the range of milli-degrees. In many instances, due to the limitations of thin film deposition systems, surface roughness and deposition thickness vary across entire wafer surface. Such deviations could result in different LVOFs possessing varying response to input signal.
Electron-beam lithography (EBL) was utilized for accurate patterning of Si pillars and taper angle which are difficult to achieve using traditional fabrication methods. In the absence of hardmask, SU-8 was used for pattern transfer with Si:SU-8 etch selectivity as high as 60:1. By optimizing SF6 and C4F8 gas flow and time parameters, aspect ratio of 10:1 and almost- 90° pillars were deep etched into Si with scallop depth <30 nm. High Bragg contrast mirrors were obtained with [HLH]-wedge-[HLH] configuration.
This LVOF operates in free space with continuous tuning from 3.1-3.8 μm. FWHM of 95 nm is observed at 3.3 μm. Simulation and other characterization results are discussed. Finally, the proposed LVOF can be wafer-level packaged with normal incidence detector array, suitable light source and other essential optical elements.
Recently, dielectric elastomer actuators (DEAs) have been adopted to tune liquid membrane lens, just like ciliary
muscles do to the lens in human eye. However, it faces some challenges, such as high stress, membrane puncture, high
driving voltage requirement, and limited focus distance (not more than 707cm), that limit its practical use. The design
problem gets more complex as the liquid lens shares the same elastomeric membrane as the DEA. To address these
challenges, we separate DEA from the lens membrane. Instead, a liquid-immersed DEA, which is safe from terminal
failure, is used as a diaphragm pump to inflate or deflate the liquid lens by hydraulic pressure. This opens up the
possibility that the DEA can be thinned down and stacked up to reduce the driving voltage, independent of the lens
membrane thickness. Preliminary study showed that our 8-mm-diameter tunable lens can focus objects in the range of
15cm to 50cm with a small driving voltage of 1.8kV. Further miniaturization of DEA could achieve a driving voltage
less than 1kV.
Though capable of generating a large strain, dielectric elastomer actuators (DEAs) generate only a moderate actuation
stress not more than 200kPa, which seriously limits its use as artificial muscles for robotic arm. Enhancement of
dielectric strength (greater than 500MV/m) by dielectric oil immersion could possibly enable it a larger force generation.
Previously, the immersion was done in an oil bath, which limits portability together with DEAs. In this study, we
developed portable capsules to enclose oil over the DEA substrate (VHB 4905). The capsules is made of a thinner soft
acrylic membrane and they seals dielectric liquid oil (Dow Corning Fluid 200 50cSt). The DEA substrate is a graphiteclad
VHB membrane, which is pre-stretched with pure-shear boundary condition for axial actuation. When activated
under isotonic condition, the oil-capsule DEA can sustain a very high dielectric field up to 903 MV/m and does not fail;
whereas, the dry DEA breaks down at a lower electric field at 570 MV/m. Furthermore, the oil-capsule DEA can
produces higher isometric stress change up to 1.05MPa, which is 70% more than the maximum produced by the dry
DEA. This study confirmed that oil capping helps DEA achieve very high dielectric strength and generate more stress
change for work.
This study found that compliant electrodes using charcoal powder enable self clearing property to dielectric elastomer
actuator. Charcoal powder is applied as compliant electrodes by smearing on a 100% bi-axially pre-stretched dielectric
elastomer membrane (VHB 9473), with nominal pre-stretched thickness of 62.3 μm. This DEA using charcoal-powder
electrodes can sustain up 10 kV without terminal breakdown, while those using graphite or silver grease break down at
slightly above 2 kV. It is noted that this DEA using charcoal-powder has maximum areal strain at about 45 % at 4 kV,
beyond which the strain does not increase further for reduced electrical conductivity. The dielectric elastomer actuator
using the charcoal-powder electrodes generate less actuation strain than that using the graphite. However, the former can
produce a large actuation stress as it can driven to a higher driving voltage without pre-mature breakdown.
Metallic thin films have not often been used as electrodes in dielectric elastomer actuators (DEAs) as the reported
actuated strains have been small. This is especially so when compared to commonly used conductive greases and
powders. Here, the use of thin silver films formed by electroless deposition (ELD silver) as electrodes in DEAs is
studied. As electroless deposition involves only the use of chemicals, expensive equipment is not needed. That, coupled
with the fact that the thin silver electrodes require only a small amount of silver per unit area, means that such electrodes
are simple and inexpensive to fabricate. In addition, unlike conductive powders and greases, these silver films adhere
well to most substrates that are or have been made hydrophilic. This is especially useful in maintaining structural
integrity of the actuator, such as when DEA units need to be stacked up one on top of each other. Most importantly, thin
silver film electrodes have the ability to self heal. Self-healing not only averts actuator failure brought about by localised
breakdowns, it also enables actuation to resume, even allowing higher driving voltages to be reached. In this paper, we
demonstrate that DEAs with corrugated ELD silver electrodes can allow actuated area strains of up to 125% at a
relatively low driving voltage of 1.9 kV. This is due to the low stiffening effect that the corrugated ELD silver electrodes
have on the dielectric layer, which was found to be close to that of graphite.
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