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This paper proposes a novel method for the modulation and fabrication of an aspherical microlens from a photocurable polymer for use in optical pickup heads. This novel modulation method can be employed not only to dynamically control the focal length and morphology of the microlens but also to fabricate aspherical lenses after UV curing of the photosensitive polymer. Forces in two dimensions provided by electrowetting and gradient electrostatic forces are applied to shape the polymer liquid from a hemispherical shape into a parabolic or a nearconical shape. Aspherical microlenses are designed based on constant optical-path-length theory and self-aligned by surfacetension forces. For morphology modulation, 2-D voltages are applied at the lower electrodes and between the upper and lower substrates, respectively, on a SU-8 spherical liquid-polymer droplet. The voltage applied at the lower electrodes provides an electrowetting effect on the polymer droplets, thereby reducing the contact angle of the spherical droplet, resulting in a desirable droplet height/baseline ratio for a desirable focal length. The voltage applied between the upper and lower substrates pulls up the droplet mostly at its center portion to form an aspherical shape that is close to a parabolic shape or even a conical shape. As a result, the Strehl ratio of the lens can be varied from 0.0076, as with a spherical shape, to 0.8362, as with a near-parabolic shape, and the focal-spot size can be reduced from 2.302 to 0.778 pm. The proposed method has been successfully implemented and has proven suitable for optical applications in which millimeter-diameter-size lenses with numerical apertures higher than 0.66 and focus-spot resolutions better than 0.8 [micro]m are preferred. [2007-0098] Index Terms--Aspherical lens, electrostatic force, electrowetting, gradient electrostatic forces (GEFs), spherical aberration, tunable lens.

This paper develops a novel microcontact printing system for printing tens of protein solutions into an array with batch filling and parallel printing. This printing system consists of microfilling and microstamp chips. The microfilling chip can simultaneously transfer numerous protein solutions into the microstamp chip in seconds by capillary force without cross contamination while preserving the functionality of proteins. Different proteins can be dispensed into the corresponding channels and driven into the tips of the microstamps. The microstamp can then be brought to contact with the substrate to produce biofluid spot arrays. Teflon patterns are applied on both microfilling and microstamp chips to prevent cross contamination during filling. Thirty-six proteins can be printed in parallel with a spot size variation of less than 5%. This device has a potential to be expanded to a passive and high-throughput system for simultaneously printing hundreds of biofluid spots to form dense arrays for diagnosing disease or screening for drugs. [2007-0083] Index Terms--Microcontact printing, protein microarray.

There have been many microdeposition processes that are based on the evaporation of nanoliter-sized droplets, such as inkjet printing, deoxyribonucleic acid/protein microarrays, or lithography direct writing. However, it is important but still difficult to control the uniformity of the solute deposition from a nanoliter sessile droplet on a plane substrate. This paper proposes a method for uniform solute deposition from evaporable droplet by confining the droplet with rib structures (wells) of specific surface properties. The hydrodynamic process was experimentally investigated and analyzed in detail. Surface wett-ability on the well surface is verified to be critical for controlling a droplet as a flat film inside a well during evaporation to minimize horizontal solute transfer for uniform solute deposition. Pure water and water/tracing particle mixture (2.57% solid latex, dyed blue) were employed for the test. The results demonstrated that a 97% uniformity is obtained for the solute deposited from a 37-nL droplet in a well with hydrophobic surface (contact angle of 100[degrees]), whereas a 31% uniformity is obtained for a more hydrophilic surface (contact angle of 25[degrees]). The higher hydrophobicity (contact angle above 90[degrees]) on the well surface yields a flatter profile of film during droplet evaporation inside a well and, thus, promotes a more uniform deposition of the solute. [2006-0194] Index Terms--Evaporation, microdroplet, microwell, solute deposition.

In this paper, we introduce an innovative microinjector design, featuring a bubble valve, which entails superior droplet ejection characteristics and monolithic fabrication, which allows handling of a wide range of liquids. This new microinjector uses asymmetric bubbles to reduce crosstalk, increase frequency response and eliminate satellite droplets. During a firing, i.e., droplet ejection, the 'virtual valve' closes, by growing a thermal bubble in the microchannel, to isolate the microchamber from the liquid supply and neighboring chambers. Between firings, however, the virtual valve opens, by collapsing the bubble, to reduce flow restriction for fast refilling of the microchamber. The use of bubble valves brings about fast and reliable device operation without imposing the significant complication fabrication of physical microvalves would call for. In addition, through a special heater configuration and chamber designs, bubbles surrounding the nozzle cutoff the tail of the droplets being ejected and completely eliminate satellite droplets. A simple one-dimensional model of the operation of the microinjector is used to estimate the bubble formation and liquid refilling. Simulation results show that the reported bubble valve can improve the frequency response at least three times compared with the passive chamber neck design commonly used for commercial devices. [701] Index Terms--Bubble valve, inkjet printing, microinjector, satellite droplet, thermal bubble jet, top shooter.

This paper describes the fabrication, implementation and characterization of a thermal driven microinjector, featuring a bubble check valve and monolithic fabrication. Microfabrication of this microinjector is based on bulk/surface-combined micromachining of the silicon wafer, free of the bonding process that is commonly used in the fabrication of commercial printing head, so that even solvents and fuels can be ejected. Droplet ejection sequences of two microinjectors have been studied along with a commercial inkjet printhead for comparison. The droplet ejection of our microinjector with 10 [micro]m diameter nozzle has been characterized at a frequency over 35 kHz, at least 3 times higher than those of commercial counterparts. The droplet volume from this device is smaller than 1 pl, 10 times smaller than those of commercial ink jets employed in the consumer market at the time of testing [1]. Visualization results have verified that our design, although far from being optimized, operates in the frequency several times higher than those of commercial products and reduces the cross talk among neighboring chambers. In addition, the reported device eliminates satellite droplets, one of the most troublesome problems among top-shooting inkjets. The devices have been experimentally characterized and their key operation parameters are summarized. [702] Index Terms--Inkjet printing, micro injector, monolithic printhead, satellite droplet, thermal bubble jet.

This paper proposes a novel method for the modulation and fabrication of an aspherical microlens from a photocurable polymer for use in optical pickup heads. This novel modulation method can be employed not only to dynamically control the focal length and morphology of the microlens but also to fabricate aspherical lenses after UV curing of the photosensitive polymer. Forces in two dimensions provided by electrowetting and gradient electrostatic forces are applied to shape the polymer liquid from a hemispherical shape into a parabolic or a near- conical shape. Asphericat microlenses are designed based on constant optical-path-length theory and self-aligned by surface- tension forces. For morphology modulation, 2-D voltages are applied at the lower electrodes and between the upper and lower substrates, respectively, on a SU-8 spherical liquid-polymer droplet. The voltage applied at the lower electrodes provides an electrowetting effect on the polymer droplets, thereby reducing the contact angle of the spherical droplet, resulting in a desirable droplet height/baseline ratio for a desirable focal length. The voltage applied between the upper and lower substrates pulls up the droplet mostly at its center portion to form an aspherical shape that is close to a parabolic shape or even a conical shape. As a result, the Strehi ratio of the lens can be varied from 0.0076, as with a spherical shape, to 0.8362, as with a near-parabolic shape, and the focal-spot size can be reduced from 2.302 to 0.778 pm. The pro- posed method has been successfully implemented and has proven suitable for optical applications in which millimeter-diameter-size lenses with numerical apertures higher than 0.66 and focus-spot resolutions better than 0.8 pm are preferred. [2007-0098] [ABSTRACT FROM AUTHOR]

This paper develops a novel microcontact printing system for printing tens of protein solutions into an array with batch filling and parallel printing. This printing system consists of microfilling and microstamp chips. The microfilling chip can simultaneously transfer numerous protein solutions into the microstamp chip in seconds by capillary force without cross contamination while preserving the functionality of proteins. Different proteins can be dispensed into the corresponding channels and driven into the tips of the microstamps. The microstamp can then be brought to contact with the substrate to produce biofluid spot arrays. Teflon patterns are applied on both microfilling and microstamp chips to prevent cross contamination during filling. Thirty-six proteins can be printed in parallel with a spot size variation of less than 5%. This device has a potential to be expanded to a passive and high-throughput system for simultaneously printing hundreds of biofluid spots to form dense arrays for diagnosing disease or screening for drugs. [2007-0083] [ABSTRACT FROM AUTHOR]

There have been many microdeposition processes that are based on the evaporation of nanoliter-sized droplets, such as inkjet printing, deoxyribonucleic acid/protein microarrays, or lithography direct writing. However, it is important but still difficult to control the uniformity of the solute deposition from a nanoliter sessile droplet on a plane substrate. This paper proposes a method for uniform solute deposition from evaporable droplet by confining the droplet with rib structures (wells) of specific surface properties. The hydrodynamic process was experimentally investigated and analyzed in detail. Surface wettability on the well surface is verified to be critical for controlling a droplet as a flat film inside a well during evaporation to minimize horizontal solute transfer for uniform solute deposition. Pure water and water/tracing particle mixture (2.57% solid latex, dyed blue) were employed for the test. The results demonstrated that a 97% uniformity is obtained for the solute deposited from a 37-nL droplet in a well with hydrophobic surface (contact angle of 100°), whereas a 31% uniformity is obtained for a more hydrophilic surface (contact angle of 25°). The higher hydrophobicity (contact angle above 90°) on the well surface yields a flatter profile of film during droplet evaporation inside a well and, thus, promotes a more uniform deposition of the solute. [ABSTRACT FROM AUTHOR]

This paper proposes a novel passive micromixer design for mixing enhancement by forming a large three-dimensional (3-D) flow vortex in a counterflow microfluidic system. The counterflow fluids are self-driven by surface tension to perform mixing in an open chamber. The chamber design consists of two rectangular bars to house the chamber and to form two opening inlets from opposite directions. The best design is selected from various versions of mixing chambers. The mixing effectiveness is tremendously increased by folds of contacting surface between two fluids induced and enhanced due to the stretching of two fluid contacting interfaces by the formation of a 3-D large size vortex structure inside the mixing chamber itself with unaccountable numbers of fluid layers. Both numerical simulations and experiments are performed and compared to identify the design parameters for maximum utilization in this microfluidic system, such as the length of rectangular bar, microchannel wall height, and mixing chamber size. Compared to traditional micromixers operated by two-dimensional (2-D) vortex, this passive mixer can greatly enhance mixing efficiency and reduce mixing time by tenfold from around 10 s to less than 10 ms by 3-D effective chaotic flow structures in a more compact size. This mixing chamber is also suitable for an H-shape digital fluidic system for parallel mixing process in different mixing ratio simultaneously as a lab-on-a-chip system. [ABSTRACT FROM AUTHOR]

Introduces an innovative microinjector design for eliminating satellite droplets. Application of droplet injectors on thermal bubbles; Problems in controlling the thickness of liquid films; Description of thermal bubbles.

Describes the fabrication, implementation and characterization of a thermal driven microinjector. Features of a bubble check valve and monolithic fabrication; Details on the fabrication processes of commercial inkjet printheads; Lists of issues corresponding to the fabrication process.