We report the performance of silicon-on-insulator medium-length extended microcavity (3 to 4.5 μm long) one-dimensional photonic crystal waveguide. Quality-factor (Q-factor) values ranging from 2000 to 37,000 were observed. The waveguides/wire were fabricated using an inductively coupled plasma reactive ion etching with SF6 and C4F8 gasses. Optical transmission of the design is heavily influenced by the surface roughness of the waveguide wall. We achieved a good free spectral range control for resonance frequency separations in between 39 and 65 nm. Supported and suspended microcavity structures for the case of a medium-length extended microcavity were compared. We observed an inferior performance in terms of the optical transmission and Q-factor in the latter. We have selected 4-μm microcavity length for comparison. The suspended structure was obtained by utilizing the wet etching technique on the same device. A high Q-factor value of ∼26,000 was observed in one of the resonances excited for cladding-layer supported extended microcavity. However, the Q-factor was reduced to ∼17,000 after removing the silica cladding beneath the silicon waveguide core.
This paper presents the fabrication, characterization, and simulation of microelectrode arrays system with tapered profile having an aluminum surface for dielectrophoresis (DEP)-based manipulation of particles. The proposed structure demonstrates more effective electric field gradient compared with its counterpart with untapered profile. Therefore, according to the asymmetric distribution of the electric field in the active region of microelectrode, it produces more effective particle manipulation. The tapered aluminum microelectrode array (TAMA) fabrication process uses a state-of-the-art technique in the formation of the resist’s taper profile. The performance of TAMA with various sidewall profile angles (5 deg to 90 deg) was analyzed through finite-element method numerical simulations to offer a better understanding of the origin of the sidewall profile effect. The ability of capturing and manipulating of the device was examined through modification of the Clausius–Mossotti factor and cross-over frequency (fx0). The fabricated system has been particularly implemented for filtration of particles with a desired diameter from a mixture of particles with three different diameters in an aqueous medium. The microelectrode system with tapered side wall profile offers a more efficient platform for particle manipulation and sensing applications compared with the conventional microelectrode systems.
In this project, SiC based MEMS capacitive microphone was developed for detecting leaked gas in extremely harsh environment such as coal mines and petroleum processing plants via ultrasonic detection. The MEMS capacitive microphone consists of two parallel plates; top plate (movable diaphragm) and bottom (fixed) plate, which separated by an air gap. While, the vent holes were fabricated on the back plate to release trapped air and reduce damping. In order to withstand high temperature and pressure, a 1.0 μm thick SiC diaphragm was utilized as the top membrane. The developed SiC could withstand a temperature up to 1400°C. Moreover, the 3 μm air gap is invented between the top membrane and the bottom plate via wafer bonding. COMSOL Multiphysics simulation software was used for design optimization. Various diaphragms with sizes of 600 μm2, 700 μm2, 800 μm2, 900 μm2 and 1000 μm2 are loaded with external pressure. From this analysis, it was observed that SiC microphone with diaphragm width of 1000 μm2 produced optimal surface vibrations, with first-mode resonant frequency of approximately 36 kHz. The maximum deflection value at resonant frequency is less than the air gap thickness of 8 mu;m, thus eliminating the possibility of shortage between plates during operation. As summary, the designed SiC capacitive microphone has high potential and it is suitable to be applied in ultrasonic gas leaking detection in harsh environment.
First pristine graphene was successfully produced by mechanical exfoliation and electrically characterized in 2004 by Andre Geim and Konstantin Novoselov at University of Manchester. Since its discovery in 2004, graphene also known as ‘super’ material that has enticed many researchers and engineers to explore its potential in ultrasensitive detection of analytes in biosensing applications. Among myriad reported sensors, biosensors based on field effect transistors (FETs) have attracted much attention. Thus, implementing graphene as conducting channel material hastens the opportunities for production of ultrasensitive biosensors for future device applications. Herein, we have reported electrical characteristics of graphene based field effect transistor (GFET) for ADH detection. GFET was modelled and simulated using Lumerical DEVICE charge transport solver (DEVICE CT). Electrical characteristics comprising of transfer and output characteristics curves are reported in this study. The device shows ambipolar curve and achieved a minimum conductivity of 0.23912 e5A at Dirac point. However, the curve shifts to the left and introduces significant changes in the minimum conductivity as drain voltage is increased. Output characteristics of GFET exhibits linear Id - Vd dependence characteristics for gate voltage ranging from 0 to 1.5 V. In addition, behavior of electrical transport through GFET was analyzed for various simulation temperatures. It clearly proves that the electrical transport in GFET is dependent on the simulation temperature as it may vary the maximum resistance in channel of the device. Therefore, this unique electrical characteristics of GFET makes it as a promising candidate for ultrasensitive detection of small biomolecules such as ADH in biosensing applications.
Dielectrophoresis (DEP) is a phenomenon in which force exerted on a dielectric particle when it is subjected to a nonuniform electric field. There are many applications of dielectrophoresis and one of them is the separation of particles. In this paper, castellated and straight electrodes are being introduced for negative dep filter of an artificial kidney. In order to avoid the filters from clogging, negative dep will take part to repel the particles. Thus, a simulation by using COMSOL Multiphysics had been done to compare the electrical performances of electrodes. The intensities of electric field were stimulated on the planar electrodes from top to bottom and left to right. Electrodes are made of aluminum and both have thickness of 50μm. Distance between the castellated electrodes are 100μm while the straight electrodes are 300μm. Three graph of electric field vs. length had been compared. The first comparison shows that both designs have similar flow of electric field. The second graphs show that castellated electrodes have higher electric field, 27.14kV/m and third comparison shows a cluster increase for castellated electrodes and uniform increase for straight electrodes. Final result shows that castellated electrodes are intended to use for artificial kidney.
In the field of science, there is a significant interest in graphene due to its extraordinary properties such as high electrical
conductivity, good electrochemical stability and excellent mechanical behavior. This paper presents the direct graphene
growth on interdigital electrodes by plasma enhanced chemical vapor deposition (PECVD) using Ni catalyst and
methane (CH4) as the carbon source. The 100 nm of Ni was deposited on the top of SiO2 substrate functional as catalyst
and electrode of MEMS supercapacitor. The growth of graphene was investigated at temperature 1000°C at 10 minutes
and at fix power of 40 Watt. The morphology and structure of as- grown graphene were characterized by Raman
spectroscopy, Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscopy (AFM). From
Raman spectra, it is observed that the intensity ratio of the 2D band to G band produced a good quality bilayer graphene.
The absorption characteristics of complex medium structures having metasurfaces comprised of columnar nanorods of gold were investigated. In this stream, a periodically arranged assembly of vertical gold nanorods of circular and elliptical cross sections, backed by chromium nanorods of the same cross-sectional size and shape, was considered to be the metasurface, and the comparative features of the absorption characteristics were emphasized. The results exhibit very high absorption corresponding to certain wavelengths in the visible span, and the absorber having elliptical gold nanorods yields a better performance than the one with circular nanorods in terms of the magnitude/smoothness of the absorption peaks.
Metamaterials have been of great interest owing to multifarious technological applications. Among various applications of scientific need, the perfect absorber kind of property of metamaterials remains prudent. Within the context, this investigation describes the filtering/absorber applications of metasurfaces comprised of columnar nanorods of gold having circular and elliptical cross-sections. The spectral features of such absorbers are investigated in terms of absorptivity in the visible to infrared (IR) regimes. The results indicate of almost perfect absorption corresponding to certain wavelengths in the IR span. Also, multiple absorption peaks would determine the filtering characteristics of the structures under consideration. It has been found that the absorber having circular nanorods exhibits better performance than the one with elliptical nanorods in terms of the magnitude/smoothness of absorption peaks in the entire electromagnetic spectral region of interest; the case of elliptical nanorods makes the absorption spectra to yield too much of flickers in the IR range of wavelength.
A novel single-chip microelectromechanical systems (MEMS) capacitive microphone with a slotted diaphragm for sound sensing is developed to minimize the microphone size and improve the sensitivity by decreasing the mechanical stiffness of the diaphragm. According to the results, a clamped microphone with a 2.43×2.43-mm2 diaphragm and a slotted one with a 1.5-×1.5-mm2 diaphragm have the same mechanical sensitivity, but the size of slotted microphone is at least 1.62 times smaller than clamped structure. The results also yield a sensitivity of 5.33×10−6 pF/Pa for the clamped and 3.87×10−5 pF/Pa for the slotted microphone with a 0.5×0.5-mm2 diaphragm. The sensitivity of the slotted diaphragm is increased 7.27 times. The calculated pull-in voltage of the clamped microphone is 214 V, the measured pull-in voltage of the slotted one is 120 V. The pull-in voltage of the slotted microphone is about 50% decreased.
This paper studies spin-on glass (SOG) etching in T-shaped microchannels by hydrofluoric acid (HF). Since oxide etching by HF in microchannels is both reaction and diffusion limited, an etching model based on non-first order chemical reaction/steady-state diffusion sacrificial layer etching mechanism is presented to compensate for the etching effect at channel junction. Microchannels are formed on silicon substrate by deep reactive ion etching (DRIE). Samples with channel depth varying from 1μm to 6 μm are prepared by varying exposure time to reactant gas in DRIE chamber. Channel widths prior to the junction are varied from 2 μm to 10 μm while channel width beyond the junction is fixed at 5 μm. The channels are then filled with SOG by multiple spin, bake and cure processes. After etchback planarization using 5% HF solution, the samples are coated with 1.5 μm thick positive photoresist. An etch window is opened at channel fronts to expose underlying SOG. The samples are then time-etched in 5% HF solution and etch front propagation is observed under optical microscope through the transparent photoresist layer. It is observed that SOG etch rate in the microchannels is independent of channel width or channel depth. SOG etch rate at channel's T-junction is 0.67 times lower than etch rate in the straight channels preceding it due to HF concentration variation and etch product transfer rate variation effects. The proposed model fits experimental data well. Offset crosses vent pattern is determined as a good candidate for removing sacrificial oxide under an enclosed cap structure.
In this paper, silicon corrugated diaphragms with non-compensated and compensated mask layout have been fabricated on a single silicon (100) wafer by using potassium hydroxide (KOH) etching technique. Although, recently corrugated diaphragms have been used for a diaphragm structure due to its excellent properties, no theoretical and analytical studies on the fabrication process of these diaphragms have been performed. Therefore, the characterization of the KOH etching process with emphasized on convex corner behavior has been studied through both experiments and simulations in order to realize the perfect corrugated diaphragm. Details of the etching of corrugated diaphragms have been studied by using process simulation software of a three-dimensional anisotropic etching profile prior to fabrication process. The influence of the KOH etching temperature and concentration on the convex corner undercutting of corrugated diaphragm are observed. The convex corner behavior has been analyzed based on the geometrical parameters and the new emergent high index silicon planes. It was found that the convex corner undercutting phenomena is significantly reduced at low etching temperature and high KOH concentration respectively. It can be concluded that the prominent facets contributing to the undercutting of the convex corners of the corrugated diaphragm for the given etching condition
coincide with the {411} plane. The introduction of the additional mask layout for the protection of convex corners at all convex-mask geometry of the corrugated diaphragm during the KOH etching process has been proved by simulation to produce almost perfect square corners. These simulation results have been confirmed by experiments.
This paper presents a method to form thick spin-on glass (SOG) sacrificial layer for accelerometer encapsulation fabrication. SOG is chosen as the sacrificial material because it is easy to apply, has good thickness uniformity, and can be easily etched back before densification. Siloxane type SOG is applied on blank wafers and accelerometer patterns by multiple spin, bake, and cure processes. A series of gradual hot plate baking up to 250°C are experimented for each spun layer. After multiple spin and bake, the SOG layers are etched back in hydrofluoric acid (HF) solution of various concentrations to form rectangular encapsulation bases. 25 samples are prepared for SOG thickness uniformity characterization. Center thickness and four perimeter thickness measurements are taken for each sample using thin-film mapper. These five measurements are averaged to get sample thickness. Two surface profiler measurements are taken for each sample perpendicularly to each other using Tencor surface profiler. The minimum reading is subtracted from the maximum reading to get sample variation. Upon SEM inspection, mildly sloped etched walls from HF etching are observed. No surface cracking was visible. Shallow trench patterns are apparent on SOG deposited on accelerometer pattern. The average sample thickness is 5 μm with 3.7% thickness variation across samples. The average variation within each sample is 0.14 μm with an average of 2.6% thickness variation within sample. These thickness variations are acceptable for encapsulation structure deposition.
A novel H-Space electrode is introduced as an alternative design to the interdigitated electrode of a p-i-n photodetector. H-Space electrode is considered to be capable of increasing both the quantum efficiencies and the responsitivity of the photodectors by means of a bridge structure. In order to analyze the effect of the design, the design was systematically simplified into a single cell by utilizing Matlab. Methods to identify the minuscule effects of a very short light pulse in the lateral PIN photodetector structure were carried out in microscopic proportion and this technique displays the incident light's erratic nature upon entering the photodetector. The Matlab software was used to collect drift current data based on individual drift changes of electrons arriving at the electrodes at a relation time period. An ideal range of 10μm was chosen as the size of the intrinsic region and a set of randomly generated incident photon with Gaussian characteristics were bombarded into the single cell structure. By limiting a low number of incoming photons per unit time with coherent waterfronts, at random locations between p and n electrodes, a set of very precise electron characteristic were obtained for a beam with a Gaussian spread of 5 micron . Data for generated current were analyzed based on individual drift changes of electrons with bulk mobilities arriving at the electrodes in a very short time period. We relate the data obtained from the H space electrode with those obtained from an interdigitated electrode.
This paper presents the design, simulation and performance evaluation of an area-changed capacitive accelerometer for low-g applications. The movable mass of the accelerometer was designed with many fingers connected in parallel and suspended over stationary electrodes composed of differential comb fingers by means of suspension beams anchored onto the substrate. An area-changed differential capacitance method was used to sense the deflection of the proof mass. A folded suspension design with low spring constant and low cross-axis sensitivity was chosen. The simulation was performed using Coventorware2001.3 software. A 3-mask bulk micromachining wafer bonding fabrication process was utilized to produce this accelerometer. Silicon-on-glass was used to achieve high sensitivity and low mechanical noise while maintaining a simple structure. The general concept, main design considerations, fabrication procedure and performance of the resulted accelerometer was elaborated and presented. A linear relationship between the differential capacitance and acceleration was obtained. The accelerometer sensitivity was calculated to be 0.47pF/g with an acceleration range of ±5g.
Using the solid-liquid-solid method, silicon nanowires were grown by annealing the gold-coated silicon substrates under the nitrogen flow. In this method, gold diffused into the silicon substrate upon heating and AuSi alloy formed at their interface. This alloy was melted when temperature increases above their eutectic point and percentage of Si presence in the mixture increased as heating continues. Rapid cooling occurred at the surface of these alloy melted when nitrogen gas was flowed into the chamber. This had caused the phase separation of the silicon from the surface of the alloy droplets and eventually self-arranged to form nanowires. Controlled growth of the nanowires was achieved by manipulating the annealing parameters. Relatively straight nanowires were produced by annealed the sample at 1000°C with nitrogen flow set to 1.5 liters per minute. The as-growth nanowires had diameters varied between 30 and 70nm. Heating duration was used to control the amount and lengths of the nanowires. Heating for 15 minutes produced less amount and shorter nanowires, while a 4-hour heating produced nanowires more than hundreds of microns long and with much larger amount.
This paper presents an area-changed capacitive accelerometer using a 3-mask fabrication process. The accelerometer is designed as finger structures connected in parallel that have a differential capacitor arrangement. The movable electrodes are mounted on a proof mass of silicon and a pair of stationary electrodes of polysilicon is formed under the mass with a 3 μm air gap. The fabrication process utilizes silicon/glass anodic bonding and deep reactive ion etching (DRIE) for high aspect ratio etching. The simulated mass displacement change rate is 0.076 μm/g and the overall sensitivity is -0.04/μm. This type of accelerometer will be characterized for low-g as well as for medium-g applications.
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