W. G. Wu

Fabrication and characterization of torsion-mirror actuators for optical networking applications

Abstract Novel torsion-mirror actuators with monolithically integrated new fiber holding structures, which can feature self-fixing and self-aligning of optical fibers, are fabricated in regular silicon wafers as well as in SOI wafers by using the mixed micromachining based on the surface and bulk silicon microelectronics. The electromechanical performances of the actuators and the optical properties of their micro-mirrors are investigated experimentally and theoretically. The electrostatic yielding voltages for driving the micro-mirrors of the actuators to tilt from 0° to 90° spontaneously are in the range of 270–290xa0V and the minimum holding voltages for keeping the tilting angle of the mirrors to be in 90° are found 55xa0V or so when the thickness of the torsion-beams suspending the mirrors is about 1xa0μm. Theoretical analysis manifests that the yielding voltage is most sensitive to the beam thickness among the series of design parameters about the torsion-mirror actuator structures. The micro-mirrors of the actuators can cyclically vibrate 10 8 times at least between 0° and 90°, and their shortest actuating time can reach an estimated less than 2xa0ms. The surface roughness and its distribution of the micro-mirrors of the actuators are small and smooth, respectively, which is acceptable for wavelength division multiplexing applications basically.

Filtration membrane with ultra-high porosity and pore size controllability fabricated by parylene c molding technique for targeted cell separation from bronchoalveolar lavage fluid (BALF)

This paper presented an effective fabrication strategy to prepare micropore arrayed membrane with ultra-high porosity and pore size controllability based on a Parylene C molding technique. The prepared filtration membrane had small supporting structure between adjacent micropores with width of 4 μm and thereby an ultra-high porosity up to 90.9%. The membrane was 10 μm thick and had a considerable mechanical strength. The aspect ratio even went to 7.5 in small micropore devices (pore size of 1.39 ± 0.067 μm). Bronchoalveolar lavage fluid (BALF) with sparked rare cancer cells was sequentially filtrated through membranes with different pore sizes in an integrated device. The preliminary results indicated that the present multiplex filtration device can get a high targeted cell separation yield of 96.5% and purity of 100% with throughput as high as 2 mL/min.

Resistive switching model for Electrolyte-Oxide-Semiconductor (EOS) structure

We find that the Electrolyte-Oxide-Semiconductor (EOS) structure, which is utilized a lot in micro/nanofluidic devices, is not perfectly insulated as previously believed. There is a significant leakage current through the insulator, and the I-V relationship shows one-way conductivity like a diode. We build a model considering the implantation of ions under forward bias and formation of conductive filaments in the oxide layer. Samples with oxide layers of different thicknesses and various fabrication processes were tested to verify our hypotheses. This structure provides a simple means to fabricate half-fluidic diodes, and can be utilized for ion detection and current control in microfluidic devices.

Design and Performance of MEMS Multifunction Optical Device Using a Combined In-Plane and Out-of-Plane Motion of Dual-Slope Mirror

A reflection-type MEMS multifunction-integrated optical device using the combined in-plane and out-of-plane motion of a dual-slope mirror is proposed. The motion of the mirrors results in the corresponding optical axis offsets in the transmitting and receiving optical signals, which can enable the device with variable optical power splitting, optical switching and variable optical attenuating functions. The optical models for splitting and attenuating are presented, respectively. The electro-mechanical characteristics of the device are also investigated. Measurements of the fabricated devices show that the switching times is less than 9 ms. The excess loss of the device is less than 3 dB and the controllable attenuation range is up to 39 dB, respectively. Moreover, polarization-dependent loss is less than 0.7 dB in the whole attenuation and splitting range.

Stacked SiO2/Si Nanonail Array Fabricated by Spacer Technology for Biomedical Applications

This paper reports well-controlled nanonail array with Si bodies and stacked SiO2 heads for biomedical nano-extractions and protein localizations. The nanonails with well controlled dimensions are fabricated by multi-crossed spacer technology which we have developed. The nail bodies with the minimum diameter of 24 nm and nailheads with 11 nm tip-radius are successfully achieved. 100 nm spacing and 1.2 mum nail height are also obtained. Nano water droplets are observed to condense at the hydrophilic nailheads in environment-scanning electron microscope. Fluorescent test shows that fluorescein solution is only dipped at the nailheads, while the hydrophobic Si is immune. The stacked nanonails are also used for protein capture after chemical decorations.

A 3D filter for plasma separation from whole blood

This work presented a simple and efficient 3D filter for plasma separation from whole blood. The filter was prepared by an origami of Parylene membrane with different sized micropore arrays and folding grooves. 1.64±0.08 μm micropores were designed for plasma filtration and 39.06±0.39 μm micropores functioned as a by-pass pathway for clogging-free operation. The results showed that the present device could achieve a high yield of 42% for plasma separation from whole blood. Further biological characterization of the separated plasma from the filter was conducted by testing total proteins and blood glucose concentrations, which indicated the present 3D filter separation could achieve a high quality of plasma as the conventional methods.

Ultrasensitive mass detection using dual-microcantilevers coupled by cruciform overhang

This paper reports the use of dual-microcantilevers coupled by cruciform overhang to enhance the mass sensitivity for minor mass detection. Driven by a piezoactuator in air, each cantilever of the structure can resonate in two different modes (in-phase and out-of-phase modes), and the resonant amplitude-ratios are compared before and after a mass adding. Using this sensing strategy, the cross-shaped overhang of the coupled system, by weakening the coupling effect between the two cantilevers, provides two orders of magnitude enhancement in mass sensitivity without scaling down the cantilevers.

Patterned ultrathin metal membranes with hexagonally packed sub-50nm nanopore arrays based on hydrophilicity-templated self-assembly monolayer

We report a simple method to fabricate a patterned ultrathin metal membrane with hexagonally arrayed sub-50 nm nanopores based on hydrophilicity-templated self-assembly monolayer (SAM) of polystyrene (PS) nanoparticles. Photolithography assisted hydrophilicity-template defines the membrane pattern, in which the arrayed nanopores are transferred from the hexagonally packed polystyrene nanoparticles by nanosphere lithography. The membrane thickness, depending on the physical vapor deposition process, is as thin as tens of nanometers. By changing the diameter of the original particles, the period of the array can be conveniently controlled. Above all, the nanopore size depends to a great extent on the diameter of shrunk nanoparticles and can be reduced further by uniform coating of parylene. The metal membrane with patterned nanopore array shows great promise in the application of biosensors, nanofiltration and nanofluidic devices.

Nanosolenoid inductor for high frequency application

This paper reports the fabrication, measurement and discussion about the nanosolenoid inductors for high frequency applications as much as 40 GHz, taking advantage of a much smaller size compared with traditional microinductors. Three small size nanosolenoid inductors are fabricated, such as a nanosolenoid inductor with a diameter of 4.8 μm, pitch of 10 μm, length of 22 μm. The nanohelix inductors are fabricated using focused ion beam stress introducing technology based on nanobeams, which are obtained by etching the aluminum deposited on SOI substrate. With different focused ion beam fabrication conditions, such as implementing does, etching number, we get different sets of nanosolenoid inductors with different pitches, diameters and solenoid turns. The inductor and quality factor of the nanohelix inductor vary with frequency. The inductanc decrease from 9 pH to an inductance smaller than 1 pH, when the frequency changes from 100 MHz to 40 GHz. And the quality factor of the nanosolenoid inductor first arises from 0.1 at 100 MHz to 0.3 at about 2 GHz, then the quality factor slightly decreases, at last it will arise to about 1.4 at 40 GHz.

Switching characteristic model and biochemical application analysis for electrolyte-oxide-semiconductor structure diodes

We present a model and applications analysis of the switching characteristic of electrolyte-oxide-semiconductor (EOS) structure diodes. The EOS structure consists of a heavily-doped silicon layer, an SiO2 layer, and an electrolyte-solution layer, and exhibits diode characteristics when a sweeping voltage is applied. A conduction model of the switching characteristic of EOS diodes is suggested, and implements aspects of ion diffusion theory. The application potential of the EOS structure is also analyzed in accordance with the suggested model. EOS structures provide a simple means to fabricate half-fluidic diodes without photolithography and other sophisticated structure-fabrication processes; hence, they can be utilized for many biochemical applications, such as ion detection and current control in microfluidic devices.