A simple method is reported to manufacture a planar compound eye using a microlens array. The compound eye, inspired by insects, consists of a microlens array and a waveguide coupled with it. A microlens array with lenses of 50 µm in diameter is fabricated by melting AZ1500 photoresist and then transferring it onto SU-8. With the self-focus method applied, a waveguide array is formed, and each is exactly coupled to a lens. The formation of the waveguide is simulated using finite difference time domain (FDTD) arithmetic, resembling the ommatidia produced in our experiment. The ommatidia is also testified to astrict beam, just as the natural compound eyes do.
Micro- and nanopolycrystalline VO2 thin films with hysteretic first-order metal-insulator transition were fabricated by the reactive ion-beam sputtering method. The phase transition temperatures of the micro- and nanopolycrystalline films are at 68 and 45 °C, respectively. Using the random-resistor-network model, the characteristics of hysteretic resistance versus temperature are simulated for these films. The modeling results are checked against the experimental measurements. There is satisfactory agreement between the calculated resistance-temperature trajectories and the measured major hysteresis loops for both micro- and nanopolycrystalline films over the whole temperature range from the low-temperature semiconductor behavior to the high-temperature metallic state, which gives strong support to the present approach.
A new nanopolycrystal of vanadium dioxide has been prepared. The average grain size is 8-10nm and the phase transition temperature drops down to 35°C. The temperature coefficiency of resistance (TCR) is 6-7%/°C in semiconductor zone. A linear senor has been fabricated based on the nanostructure of vanadium dioxide thin films and the test indicates that the characteristics has been improved greatly compared with sensors based on using conventional vanadium dioxide thin films.
Rotational prisms or reflectors are used for conventional optical scanners. Their disadvantages are large size, low scanning speed and high power consumption. In the paper a microoptical scanner based on the integration of piezoelectrical driver and microlens arrays is described. The microlens arrays consist of a convex microlens array and a cocave microlens array with 256×256 elements respectively. Each element dimension is 50×50 μm2. The scanner is driven by a piezoelectrical(PZT) crystal. A PA90 amplifier is controlled by an input signal produced by a single chip computer. The amplifier supplies a high voltage pulse signal to driving the PZT. The scanning frequency can reach 200Hz to 300Hz and the scanner's size is a few cubic centimeters.
Thin films of vanadium dioxide (VO2) were selected for microbolometers. The thin films were fabricated with a novel method mainly including ion-sputtering and annealing. It is found that the electrical properties of these thin films can be controlled by adjusting the time of ion-sputtering and annealing. A standard microbolometer pixel structure of micro-bridge has been applied. Two-dimensional arrays of microbolometers have been fabricated on silicon integrated circuit wafers using a surface micromachining technique. A new type of on-chip readout integrated circuit (ROIC) for 32×32 pixel bolometric detector arrays has been designed and fabricated using a 1.5μm double metal poly complementary metal oxide semiconductor (CMOS) processing. The readout circuit consists of three stages, which provides low noise, a highly stable detector bias, high photon current injection efficiency, high gain, and high speed.
Several prototypes of 32×32 pixel bolometric detector arrays have been designed and fabricated. These arrays consist of detectors with lateral dimensions of 50μm 50μm, and each bolometric detector is on a 100μm pitch. The results of measurement show that the fabricated uncooled infrared focal plane arrays (UIRFPAs) have excellent performance. The frame rate is 50Hz, the pixel operability is above 96%, the responsivity (R) @ f/1 value is up to 15000V/W, the noise equivalent temperature difference (NETD) @ f/1 and 30Hz is about 50mK, and the average power dissipation is only 24.7mW. The results indicate that the technology of fabricating these 32×32 UIRFPAs has potential to be utilized for fabricating low cost and large-scale UIRFPAs.
Polymer microfluidic chips have stimulated great instrests in the field of biochemical and medical analysis due to their low prices, easy fabrication and biocompatibility. Recently multilayer microfluidic chips have been fabricated by adhesive bonding to form 3-D multilayer laminate. However adhesive bonding may introduce pollution as well as complexity in coating. A bonding system with compact diode laser is introduced and a novel method based on transparent bonding line for multilayer microfluidic chips is developed. This bonding method is based on transmission laser microwelding technique. In this method, a special colorless dye as laser absorber, thus transparent polymer sheets can be stacked and bonded layer by layer. Initial results and bonding performance have demonstrate the feasibility of this method.
Fabrication of Polymer microlens array based on UV-molding techniques is presented. UV-molding enables for the integration of polymer microlens array on top of arbitrary substrates like glass, silicon other polymeric films. In this technique, photoresist or glass mold is first fabricated by conventional photolithnic method and subsequently served as transparent replication tool. UV curable polymer resin is then coated on patterned or unpatterned substrates and a contact mask aligner is used to align substrates and replication mold tool and then make the mold immersed into the resin. Replication of polymer on substrates is achieved by UV photopolymerisation of the resin. Resin thickness and gap distance between mold and substrate are carefully controlled in order to obtain acceptable thickness of cured polymer base. The UV molding technique was used to molding of a polymer film carring microlens array on the surface of an experimental CCD imaging sensor chip in this paper to enhance its fill factor and sensitivity.
Anisotropic reactive ion etching of silicon has been widely used in fabrication of diffractive optical elements, waveguides and structures of Micro-Electro-Mechanical Systems (MEMS) in recent years. It is important to achieve minimal roughness on both horizontal surfaces and sidewalls in reactive ion etching (RIE) of silicon. Now reactive ion etching of silicon in an RF parallel plate system, using SF6/O2/CHF3 plasmas, has been experimentally studied. Black silicon method (BSM) is a powerful tool that can be used to find the best conditions under which the anisotropic etching of silicon is optimized. In the process of etching silicon, SF6 serves as the major reactive etching species on silicon, while O2 is added to build the passivation layer on the sidewalls and surfaces to get anisotropic profiles and CHF3 to suppress the formation of passivation on horizontal surfaces in order to achieve smooth etch surfaces. BSM provides a convenient way to know the function of the gases adding into the RIE and to find how to adjust the proportion of the gas combination. Experimental parameters including the etching rate, selectivity, anisotropy, and self-bias voltage under different parameters have been examined through SEM and AFM. As a result, anisotropic etching conditions and the parameters corresponding to the minimal roughness on the surfaces were obtained.
A simple reflow technique and reactive-ion etching are employed to fabricate and integrate a refractive square-apertured arch Si microlens array (MLA) on the back of an IR focal plane array device (IRFPA), resulting in the formation of a monolithic MLA/IRFPA device. The fabricated on-chip Si MLA behaves as optical concentrators and is used to collect most of the incident light from each pixel area on a smaller photosensitive area of the IRFPA, causing the IR response characteristics of the monolithic device to be improved greatly when compared with an ordinary IRFPA device without the MLA. The advantages of employing the reflow technique and the reactive-ion etching lie not only in the excellent surface smoothness and dimensional uniformity of the fabricated MLA, but also as a cost-effective and mass production technology.
Nanostructural vanadium dioxide thin films are investigated as intelligent window coatings. The films are fabricated using reactive sputtering and post annealing. A reversible semiconductor to metal phase transition for as-deposited VO2 nanostructure films with grain size of ~8nm takes place at a temperature of 35°C, which lowers about 33°C in comparison with a phase transition temperature of 68°C in conventional VO2 films with a grain size of 1-2 μm. The results indicate that the nanostructural VO2 films are more suitable to the application for smart thermochromic glazing of windows than that of conventional VO2 films.
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