Weibiao Wang

Structural and magnetic properties of (Al, Fe)-codoped SiC

In this study, as a first attempt, we choose Al and transition metals (TMs), Fe, as codoping atoms to synthesize (Al, TM)-codoped SiC. X-ray diffraction and Raman analysis showed that a series of single-phase codoped 4H-SiC samples were obtained and no trace of any other impurity phases, such as Fe3Si and polytypes of other types of SiC, was found. Measurement of magnetic properties showed that codoping by Al and Fe elements changed the original glassy ferromagnetism (FM) features in Al-doped SiC and induced a robust room temperature FM order that gradually dominated (Al, Fe)-codoped 4H-SiC with increase in Fe content. The contribution of Al elements to the magnetic properties of (Al, Fe)-codoped 4H-SiC can be neglected and the magnetic origin should be ascribed to be induced by Fe doping. The only major role of Al is to stabilize the codoped crystal structure as 4H- single phase. As the first investigation on (Al, TM)-codoped SiC, this study opens a new pathway to obtain TM-doped SiC-based diluted magnetic semiconductors with a high Tc via the codoping strategy.

Design and fabrication of a micro-optic switch

In this paper, a polyimide cantilever micro-optic switch of electromagnetic actuation is studied. The model of the electromagnetic actuation is proposed and simulated using finite element method. The best efficiency of electromagnetic force for switching operations is obtained and the parameters of the coil and magnet are determined. During the practical fabrication, the thick resist patterning and electroplating technology is employed to fabricate the electromagnetic actuation. Both the theoretical and experimental results indicate that the balanceable distance of the polyimide cantilever for implementing optical switches is about 1.28 mm with 0.4 A current pulse input, The final experimental results of optical performance for the fabricated micro-optic 1 x 4 switch include the switching time of about 20 ms and the insertion loss of about 0.73 dB.

Theoretical and experimental analysis of AlGaInP micro-LED array with square-circle anode

An array of 320 × 240 micro-light-emitting diodes (micro-LEDs) based on an AlGaInP epitaxial wafer and with a unit size of 100 µm×100 µm was designed and fabricated. The optimum width of the isolation groove between adjacent light-emitting units was determined based on a compromise between full isolation of each LED and maximization of the light emitting area, and was found to be 20 µm. The grooves were filled with a mixed Si granule-polyurethane composite medium, because this type of insulating material can reflect part of the emitted light from the sidewall to the window layer in each light-emitting unit, and could thus improve lighting output efficiency. The 10-µm-wide square-circle anode was designed to increase the light emitting area while simultaneously being simple to fabricate. The device current used was in the 0.42–1.06 mA range to guarantee internal quantum efficiency of more than 85%, with a corresponding voltage range of 2–2.3 V. The layered temperature distribution in a single unit was simulated under a drive voltage of 2.2 V, and the maximum device temperature was 341 K. The micro-opto-electro-mechanical systems (MOEMS) technology-based fabrication process, experimental images of the device and device test results are presented here.

Design of spatio-temporally modulated static infrared imaging Fourier transform spectrometer

A novel static medium wave infrared (MWIR) imaging Fourier transform spectrometer (IFTS) is conceptually proposed and experimentally demonstrated. In this system, the moving mirror in traditional temporally modulated IFTS is replaced by multi-step micro-mirrors to realize the static design. Compared with the traditional spatially modulated IFTS, they have no slit system and are superior with larger luminous flux and higher energy efficiency. The use of the multi-step micro-mirrors can also make the system compact and light.

Thermal Analysis and Design of AlGaInP-based Light Emitting Diode Arrays

LED arrays with pixel numbers of 3×3, 4×4, and 5×5 have been studied in this paper in order to enhance the optical output power and decrease heat dissipation of an AlGaInP-based light emitting diode display device (pixel size of 280×280 μm) fabricated by micro-opto-electro-mechanical systems. Simulation results showed that the thermal resistances of the 3×3, 4×4, 5×5 arrays were 52°C/W, 69.7°C/W, and 84.3°C/W. The junction temperature was calculated by the peak wavelength shift method, which showed that the maximum value appears at the center pixel due to thermal crosstalk from neighboring pixels. The central temperature would be minimized with 40 μm pixel pitch and 150 μm substrate thickness as calculated by thermal modeling using finite element analysis. The modeling can be used to optimize parameters of highly integrated AlGaInP-based LED arrays fabricated by micro-opto-electro-mechanical systems technology.

Heat dissipation analysis of bendable AlGaInP micro-LED arrays

A strategy for fabricating bendable AlGaInP light emitting diode (LED) arrays is presented in this paper. Sample LED arrays with 8 × 8 pixels were fabricated and subjected to bending. Bending only weakly affected the light output power and the current–voltage characteristics of the arrays. LED arrays suffer from a thermal problem owing to the energy loss during the electrical-to-optical energy conversion. We have designed a three-dimensional heat conduction model for analyzing the effect of the polymer substrate, the configuration of pixels, and the micro-structure on heat dissipation in bendable LED arrays. Thermal conductivity of the polymer substrate critically affected the heat dissipation, suggesting that the substrate thickness should be in the 500–1000 μm range. A larger pixel distance yielded more distributed heat sources and more uniform temperature distribution. Micro-structured polymer substrates yielded lower temperature, especially for the fins array micro-structure. Based on enhancing the po...

Simulation and experiment of the static FTIR based on micro multi-step mirrors

In recent years, Fourier transform spectrometer (FTS) with small size and low mass is required in many applications with growing need for real-time and small platform spectral detection. In this paper, a micro Fourier transform infrared spectrometer (μFTIR) based on spatial modulation mode was designed. This spectrometer has the advantages of high stability and simplified configuration. It also promises optical path differences (OPD) with high precision, as MOEMS technology is used in manufacturing the key components. The simulation and the experiments with regard to this FTIR configuration have been done. Firstly, the diffraction effect of the micro multi-step mirrors (MMSMs) is studied. We discuss the influence to the reversed spectrum by different mirror widths and different diffraction distances. Secondly, we simulate and analyze the influence of the source solid angle to the spectral resolution. Thirdly, we set up the theoretical model of the collimation error which is mainly from the defocus of the optical system and analyze the result caused by the collimation error. Fourthly, a new discrete Fourier transform arithmetic using least-squares cosines progression (LSCP) is proposed which can reconstruct the spectrum with nonuniform sampled signals. Finally, the MMSMs are fabricated used the MOEMS technology and the structural parameters are tested.

Spectrum Reconstruction of a Spatially Modulated Fourier Transform Spectrometer Based on Stepped Mirrors

Based on the basic configuration and interference principle of a static step-mirror-based Fourier transform spectrometer, an image segmentation method is proposed to obtain a one-dimensional interferogram. The direct current component of the interferogram is fit using the least squares (LS) method and is subsequently removed. An empirical-mode decomposition-method-based high-pass filter is constructed to denoise the spectrum and enhance the spectral resolution simultaneously. Several experiments were performed and the spectrum is reconstructed based on these methods. The spectrum resolution is 81 cm–1 at 2254 cm–1.

Design of micro, flexible light-emitting diode arrays and fabrication of flexible electrodes

In this study, we design micro, flexible light-emitting diode (LED) array devices. Using theoretical calculations and finite element simulations, we analyze the deformation of the conventional single electrode bar. Through structure optimization, we obtain a three-dimensional (3D), chain-shaped electrode structure, which has a greater bending degree. The optimized electrodes not only have a bigger bend but can also be made to spin. When the supporting body is made of polydimethylsiloxane (PDMS), the maximum bending degree of the micro, flexible LED arrays (4 × 1 arrays) was approximately 230 µm; this was obtained using the finite element method. The device (4 × 1 arrays) can stretch to 15%. This paper describes the fabrication of micro, flexible LED arrays using microelectromechancial (MEMS) technology combined with electroplating technology. Specifically, the isolated grooves are made by dry etching which can isolate and protect the light-emitting units. A combination of MEMS technology and wet etching is used to fabricate the large size spacing.

The synthesis of graphene on carbon nanotube surface

Layered graphene were synthesized on carbon nanotubes surface by MWCVD method with the pretreatment of carbon nanotube. The field emission property of graphene-carbon nanotube complex material emitter. This kind of emitter may have potential applications in field emission display device for improving emission uniform.