Long-Sun Huang

Fabrication of polymer microlens arrays using capillary forming with a soft mold of micro-holes array and UV-curable polymer

This paper reports a simple and effective method to fabricate microlens arrays with the ultraviolet-curable resins, and a soft mold of micro-holes array. During capillary forming operation, the surface of the soft mold of micro-holes array is being pressed against the ultraviolet-curable resin layer coated on the plastic substrate. An array of convex lense can be formed in the circular holes of the soft mold due to the capillary filling and surface tension. The microlens arrays have smooth surface and uniform focusing function. The shape and height of micolens can be controlled with a proper combination of pressing pressure, pressing duration and UV curing dose. This technique shows great potential for fabricating polymer microlens arrays with high productivity and low cost.

Effect of subwavelength annular aperture diameter on the nondiffracting region of generated Bessel beams.

A subwavelength annular aperture (SAA) made on metallic film and deposited on a glass substrate was fabricated by electron-beam lithography (EBL) and which was followed by a metal lift-off process to generate a long propagation range Bessel beam. We propose tuning the focal length and depth of focus (DOF) by changing the diameter of the SAA. We used finite-difference time domain (FDTD) simulations to verify our experimental data. We found that the position of the Bessel Beam focus spot (i.e. focal length) will be farther away from the SAA plane as the diameter of the SAA increases. In addition, the depth of focus (DOF) which is the length of the Bessel beam non-diffracting area, also increases as the diameter of the SAA expands.

A novel method for rapid fabrication of microlens arrays using micro-transfer molding with soft mold

This paper reports a novel technique for fabricating polymeric microlens arrays based on micro-transfer molding with soft mold. The soft mold with a micro-holes array is made by casting a pre-polymer of PDMS against a silicon master. The silicon master of the micro-cylinders array is prepared using photolithography and deep reactive ion etching. During the micro-transfer molding operation, the surface of the soft mold of the micro-holes array is filled with liquid UV curable photopolymer, and the soft mold is then pressed against the flat substrate with a slight pressure for a period of time. After the soft mold is removed from the substrate, surface tension causes the liquid photopolymer cylinders to assume a spherical shape. Finally, the liquid photopolymer is cured by UV irradiation at room temperature. A substrate with a microlens array pattern can be successfully fabricated. In this study, a micro-transfer molding facility with UV exposure capacity has been designed, constructed and tested. The 100 × 100 arrays of a polymeric microlens have been successfully produced. Under the condition of 50 kPa stamping pressure, 6 s duration and 500 mJ cm−2 UV curing dose, the microlenses were successfully formed on the plastic substrate. Their optical properties were verified with a beam profiler. In addition, microlenses of different curvatures and focal lengths can be obtained by using substrates with different surface wettabilities. This study shows that micro-transfer molding can be used for the fabrication of polymeric microlens arrays with high productivity and low cost.

Laser ablation of silicon using a Bessel-like beam generated by a subwavelength annular aperture structure

Using a femtosecond laser incident to an oxide-metal-oxide film engraved with a subwavelength annular aperture (SAA) structure, we generated a Bessel-like beam to ablate silicon. Experimental results show that the silicon can be ablated with a 0.05 J/cm(2) input ablation threshold at 120 fs pulse duration. We obtained a surface hole possessing a diameter less than 1 μm. Optical performance, including depth-of-focus and focal spot of the SAA structure, were simulated using finite-different time-domain calculations. We found that a far-field laser beam propagating through a SAA structure possesses a submicrometer focal spot and high focus intensity. Our method can be easily adopted for surface machining in microfabrication applications.

A novel reusable nanomechanics-based protein biosensor with electrical manipulation

A novel reusable biosensor of label-free biomolecular recognition based on the nanomechanics transduction in a micro-fabricated cantilever has been developed. The nanomechanics-based immunoassay biosensor was proven to be repeatedly used with desorption of the pre-bound antigen-antibody by an in-situ alternative electrical field. This new approach of electric manipulation in separating the antigen out of the antibody in a buffer fluid environment was confirmed in nanomechanics-based immunoassay biosensor in which a conventional desorption is long used with high concentrated acid solution in a range of pH 2/spl sim/3. The potential benefit of the electrical means over a conventional pre-bound antigen-antibody desorption of strong acid solution is to maintain long-standing protein activity in multiple uses such that the micro biosensor is reliable and reproducible in every detection. The complete sensing history from a monolayer of biolinker, to antibody and antigen is also first demonstrated in nanomechanics-based immunoassay.

A new integration of device-scale micropackaging with bi-directional tunable capacitors

This paper demonstrates a novel and device-scale vacuum-sealed variable capacitor that allows a movale capacitive plate to be actuated in bi-direction for large capacitance tuning. Meanwhile, the micro cap is served as the packaging structure as well as top electrode which can protect the variable capacitor structure from undesired physical attack. By taking advantages of device-scale micro cap, the subsequent packaging procedures are able to utilize conventional I.C. packaging, minimizing changes due to an addition of integrated MEMS devices. Furthermore, the vacuum sealing can also be achieved to reduce phase noise and to alleviate the thermal, humid, and air damping effect. This approach is compatible with CMOS process and able to integrate micromachined variable capacitor and electric circuit into a single chip.

A novel micro-scale recombining technique using lateral joining for a large-area molding with small features

A novel micro-scale recombining technique using a lateral joining of silicon crystal planes is first presented. The new concept of the technique is realized by fabricating a large silicon molding plate beyond a wafer size with small features. The replication of the joint plate using the hot embossing technique has been characterized in surface profiles, pictures, and optical performance. Both experiment and simulation results reached good agreement in diffractive optical intensity. Furthermore, the scalability of the technique was extensively demonstrated with three silicon wafers. As a result, the novel technique provides a potentially low-cost approach to fill the technology gap between the conventional precision machining and photolithography-based micromachining for a beyond-wafer-size silicon plate with small features.

DESIGN, FABRICATION, AND TEST OF A SILICATE MICROSENSOR

This work describes a portable microsensor for analyzing the silicate concentration in water. Conventionally adopted silicate analysis methods involve bulky instrumentation that are limited in portability and immediateness. The proposed silicate microsensor consists of a microliquid core waveguide, passive spiral micromixer, and bubble traps that possess excellent signal enhancement properties. The microsensor size is 52 × 26 mm, while each measurement requires only 115 μl of a sample and reagents, thereby reducing the sample requirement for a considerable amount of time and work to collect expensive reagents. The spiral micromixer has a mixing capability superior to that of a premix mixture. Bubble traps have been developed to trap air bubbles formed in the microchannel in order to prevent gas bubbles from interfering with the measurements. As a linear function of silicate concentration, the absorbance response ranges from 0 to 250 nM. Additionally, the linearity is excellent with a linear R value of 0.9...

A Study of the Long Propagation Range Bessel Beam Generated by a Subwavelength Annular Aperture Structure

The subwavelength annular apertures (SAA) made on metallic layers by electron beam lithography with metal lift-off processes have been demonstrated. We have experimentally enhanced the Bessel beam distance through the SAA structure with large diameters.