Table of contents

The design, fabrication and characterization of a novel out-of-plane vertical comb-drive actuator based lamellar grating interferometer (LGI) is reported. The interferometer utilizes resonant mode vertical comb actuators, where comb fingers are simultaneously used for actuation and as a movable diffraction grating, making the device very compact. The Fourier transform of the zeroth order intensity pattern as a function of the optical path difference gives the spectrum of light. The main advantages offered by the proposed device are a long travel range (i.e. good spectral resolution), a large clear aperture (i.e. high light efficiency), and a very simple, robust and compact spectrometer structure. Peak-to-peak 106 µm out-of-plane deflection is observed in ambient pressure and at 28 V, corresponding to a theoretical spectral resolution of about 0.4 nm in the visible band and 3.6 nm at 1.5 µm. A simple CMOS compatible process based on bulk micromachining of a silicon-on-insulator wafer is used for the device fabrication.

A novel design for thermo-pneumatically actuated, membrane-based micro-mirror devices, using an elastomer membrane fabricated in a spin-coating process on a dry-etched silicon substrate, is presented. The silicon mirror devices are etched from the substrate and fixed to the highly elastic 50 µm thick membrane and actuated by thermo-pneumatic pressure. This pressure is generated by a micro-hotplate bonded to the backside of the silicon substrate. Such devices provide strokes from 0 to 80 µm and tilting angles in the range from 0° to 13°, relative to the substrate surface. Thermo-pneumatic actuation achieves large angle and stroke deflection, making this approach suitable for a large array of applications. Tilting mirrors, piston mirrors as well as mirror arrays have been realized using this technology.

This paper describes the design, simulation and fabrication of a micro conveyer system (MCS) with straight displacement of micro containers based on ratchet mechanisms and electrostatic comb-drive actuators. This MCS consists of linear comb actuators, micro containers and ratchet racks. The micro containers can be moved with different velocities by comb-drive actuators through ratchet teeth. In this study, a SOI wafer with a device layer of 30 µm and a buried SiO₂ layer of 4 µm is used. Each module of the MCS has dimensions of 6 × 6 mm², is fabricated by using only one mask, ICP-RIE and vapor HF etching techniques, and can be assembled to create more complex conveyance systems for different applications, such as in bio-chemical analysis or a micro total analysis system (µ-TAS) to transport and classify small samples. In our experiments, the movement of the micro container has been tested with a driving frequency ranging from 5 Hz to 40 Hz. The velocity of the container was proportional to the frequency and matched very well with theoretical calculation.

This paper presents a novel SiO₂ microcantilever sensor for high-sensitive gaseous chemical detection. A thin single-crystalline silicon piezoresistor is integrated in the SiO₂ cantilever for low-noise and high-resoluble signal readout. The paper relates the MEMS formation, modeling and detecting experiments of the sensor. The micro-fabrication of the cantilever sensor is processed at a single side (front side) of the silicon wafer, combined with functionalization of a self-assembled monolayer (SAM) on the sensing cantilever for specific molecular capturing. The model of the piezoresistive SiO₂ cantilever sensor is given by using both analysis and simulation, resulting in good agreement with the measuremental data. With the cantilever modified by the specific SAM, the detecting performance of the sensor is experimentally obtained. Attributed to the high sensitivity and the low electric noise of the piezoresistive SiO₂ cantilever, ammonia gas of 0.1 ppm level concentration and dimethyl methylphosphonate vapor of 10 ppb concentration have been well detected. The integrated cantilevers are promising for inexpensive, highly resoluble and portable chemical/biological detection.

This paper presents two types of fuel cells: a miniature microbial fuel cell (µMFC) and a miniature photosynthetic electrochemical cell (µPEC). A bulk micromachining process is used to fabricate the fuel cells, and the prototype has an active proton exchange membrane area of 1 cm². Two different micro-organisms are used as biocatalysts in the anode: (1) Saccharomyces cerevisiae (baker's yeast) is used to catalyze glucose and (2) Phylum Cyanophyta (blue-green algae) is used to produce electrons by a photosynthetic reaction under light. In the dark, the µPEC continues to generate power using the glucose produced under light. In the cathode, potassium ferricyanide is used to accept electrons and electric power is produced by the overall redox reactions. The bio-electrical responses of µMFCs and µPECs are characterized with the open-circuit potential measured at an average value of 300–500 mV. Under a 10 ohm load, the power density is measured as 2.3 nW cm⁻² and 0.04 nW cm⁻² for µMFCs and µPECs, respectively.

This paper explores micromolding fabrication of alumina ceramic microstructures on flat and curved surfaces, the transfer of carbon nanotube (CNT) micropatterns into the ceramic and oxidation inhibition of these CNTs through ceramic encapsulation. Microstructured master mold templates were fabricated from etched silicon, thermally embossed sacrificial polymer and flexible polydimethylsiloxane (PDMS). The polymer templates were themselves made from silicon masters. Thus, once the master is produced, no further access to a microfabrication facility is required. Using the flexible PDMS molds, ceramic structures with mm scale curvature having microstructures on either the inside or the outside of the curved macrostructure were fabricated. It was possible to embed CNTs into the ceramic microstructures. To do this, micropatterned CNTs on silicon were transferred to ceramic via vacuum molding. Multilayered micropatterned CNT–ceramic devices were fabricated, and CNT electrical traces were encapsulated with ceramic to inhibit oxidation. During oxidation trials, encapsulated CNT traces showed an increase in resistance that was 62% less than those that were not encapsulated. The processes described here could allow fabrication of inexpensive 3D ceramic microstructures suitable for high temperature and harsh chemical environments.

We present a cantilever-based biosensor chip made for the detection of biochemical molecules. The device is fabricated entirely in the photosensitive polymer SU-8 except for integrated piezoresistors made of Au. The integrated piezoresistors are used to monitor the surface stress changes due to binding of biomolecules on the surface of the cantilever. Here we present the characterization of the chip with respect to temperature changes in the surrounding environment. Furthermore, self-heating of the piezoresistors due to the applied voltage over the resistors is investigated including the temperature increase of the cantilever surfaces. The obtained results indicate that although low voltages of about 0.5–1 V are required to avoid self-heating of the cantilevers, surface stress changes below 1 mN m⁻¹ can still be detected. The results are compared to previously presented results for Si-based cantilevers.

This paper presents research on modeling and simulation of the lag effect, which is one of the most important effects in a deep reactive ion etching (DRIE) process. From theoretical analysis and experimental investigation of the lag effect, it has been found that the shielding effect and flow change of reactive ions are two dominant factors. Based on our previous work on DRIE modeling, a modified model considering these two lag effect factors has been established, and a 2D DRIE simulator is developed according to this model. The simulation results were in good agreement with experiments.

Corrections were made to this article on 8 November 2006. Reproduction of figure 1 with permission from the author, Dr Chung, was acknowledged and referencing of the figure was corrected. In addition textual references to two of Dr Chung's articles (reference [10] and new reference [13]) were corrected. The corrected electronic version is identical to the print version.

The need for a flexible, low-cost and high-throughput process for the fabrication of a nano/micro glass-based micro fluidic device is becoming increasingly acute as the bio-MEMS industry is expanding very fast. In this study, repetitive-pass milling with a focused ion beam (FIB) was used for maskless and resistless fabrication of glassy carbon (GC) molds, which will then be the primary elements in the mass production of nano/micro glass devices by mold replication processes. The aim of the study is to establish basic process conditions and to investigate possible problems that occur during both FIB milling of GC and thermal imprint of glasses. First, the milled depth–beam dwell time curve for GC was investigated experimentally, and the relationship between the areal ion dose and the milled depth was formulated for application to the design of mold parts using FIB milling. Then, GC molds were produced and used for imprinting glasses to make micro fluidic parts. Surface contamination due to the FIB milling could be eliminated by a vacuum heat treatment at 1400 °C for 10 min. Finally, a dimensional mismatch arising from a thermal expansion coefficient mismatch between the GC mold and the glass materials was discussed.

304 stainless steel samples were patterned with either a photoresist (PR) mask or a silicon nitride (Si₃Ni₄) mask and then subjected to either wet immersion etching or spray etching techniques with ferric chloride (FeCl₃). The silicon nitride mask provides much better adhesion to the stainless steel substrate resulting in less undercut compared to the PR mask. When a silicon nitride mask was subjected to spray etching, better adhesion and less undercut enabled features as small as 1.8 µm with an etch depth of 5.6 µm. This is an order of magnitude smaller than current spray etching techniques (20–50 µm) used in the steel industry. This procedure will allow spray etching features for batch fabrication for a variety of metals including steels, aluminum, nickel-based alloys and copper-based alloys with microscale resolution.

Superhydrophobic nano-wire entanglement structures (NWES) were fabricated by the dipping method, based on an anodization process in oxalic acid. The pore diameter and the depth were influenced by the applied voltage and the anodizing time. To obtain the NWES, polytetrafluoroethylene (PTFT, Teflon®: DuPont™) replication based on the dipping method was used, with a PTFT solution (0.3 wt%). During replication, the polymer sticking phenomenon due to van der Waals interactions creates microscale bunch structures on the nanoscale wire-entanglement structures. This process provides a hierarchical structure with nanostructures on microstructures and enables commercialization. The diameter of the replicated wires was about 40 nm, and their lengths were 22–75 µm according to the anodizing time. The fabricated surface has superhydrophobicity; the apparent contact angle of the PTFT micro and nanostructures is about 160°–170° and the sliding angle is less than 1°.

In this paper, micromachined elevated coplanar waveguides (ECPWs) based on CMOS-grade silicon with a thin film interface are presented. The respective signal lines for the ECPWs are 10 µm elevated into the air with supporting conductors so as to obtain low attenuation characteristics. For the designed ECPWs, it has been shown that a low loss transmission line is obtainable compared to the conventional CPW and a very low effective dielectric constant close to 2 could be realized by confining most of the electromagnetic fields in the lossless air layer. The overlapped configuration with an elevated signal line placed partially above the planar ground planes on the thin film interface yielded the best attenuation performance, i.e., about 0.29 dB mm⁻¹ at 20 GHz. In addition, a Chebyshev low-pass filter (LPF) with 0.5 dB ripple is designed on the basis of the high-Z₀ and low-Z₀ ECPWs, and fabricated using the surface micromaching technique. The measured data show good agreement with the predicted values. It is expected that the suggested ECPWs can be applied to high-performance microwave/millimeterwave circuits by employing low-cost silicon surface micromachining technology.

High-density interconnection via drilling using a diode-pumped solid-state laser is one of the industrially accepted techniques for 3D packaging and backside contacting applications. The advancement in microelectronic systems requires this technique to be improved constantly. In this paper, we introduce the technique of applying a radially polarized UV laser beam for interconnect via drilling. Microvias drilled with a p-polarized beam were compared to those drilled with a radially polarized beam. Results revealed that a radially polarized laser beam significantly improves the performance of laser drilling in all aspects, including feature size, efficiency, the cross-section profile and cleanness of the finishing.

A draping technique was tested for the deposition of positive-tone AZ5214-E photo-resist layers on non-planar (1 0 0)-oriented III–V substrates, which had a variety of three-dimensional (3D) topographies micromachined in them that consisted, e.g., of mesa ridges confined to side facets with variable tilt, inverted pyramidal holes and stubs confined to perpendicular side facets. All objects were sharp-edged. In each draping experiment, an AZ5214-E sheet was (1) formed floating on the water surface, (2) lowered onto a non-planar substrate and (3) draped over it during drying to form either self-sustained, or conformal, or planarizing layers over the non-planar substrates. The draping process is based on the depression of the glass transition temperature T_g of AZ5214-E material induced by penetrant water molecules that interact with AZ5214-E. During the process, the molecules are initially trapped under an AZ5214-E sheet and then transported out through the sheet via permeation. The water–AZ5214-E interaction modifies the stiffness κ of the sheet. The magnitude of the effect depends on temperature T and on partial water vapour pressure difference p(T, P, κ): the net effect is that T_g = f(C(T, P), p(T, P, κ)) is lowered as the concentration C of water increases with T and p, where P is the permeability of the sheet. The interaction depressed the T_g of the sheets as low as or lower than 53 °C for 6 µm thick sheets. At room temperature T < T_g, the sheet is glassy and too stiff to yield to adhesion and capillary forces. Consequently, it cannot conform to a 3D topography, and it can form a self-sustained, bridging layer over it. By contrast, at T ≈ or > T_g, the sheet becomes rubbery and mouldable by adhesion and capillary forces. As a result, it can either contour or planarize the topography depending on its geometry and thickness of the sheet.

We have designed and characterized a MEMS-based Fabry–Perot device (MFPD) to measure vibration at high temperatures. The MFPD consists of a micromachined cavity formed between a substrate and a top thin film structure in the form of a cantilever beam. When affixed to a vibrating surface, the amplitude and frequency of vibration are determined by illuminating the MFPD top mirror with a monochromatic light source and analyzing the back-reflected light to determine the deflection of the beam with respect to the substrate. Given the device geometry, a mechanical transfer function is calculated to permit the substrate motion to be determined from the relative motion of the beam with respect to the substrate. Because the thin film cantilever beam and the substrate are approximately parallel, this two-mirror cavity arrangement does not require alignment or sophisticated stabilization techniques. The uncooled high-temperature operational capability of the MFPD provides a viable low-cost alternative to sensors that require environmentally controlled packages to operate at high temperature. The small size of the MFPD (85–175 µm) and the choice of materials in which it can be manufactured (silicon nitride and silicon carbide) make it ideal for high-temperature applications. Relative displacements in the sub-nanometer range have been measured and close agreement was found between the measured sensor frequency response and the theoretical predictions based on analytical models.

For near-field optical systems, an aperture in nano-size and a solid immersion lens (SIL) are two popular methods to overcome the diffraction limit and reduce the optical spot size. In previous research, combining a nano-aperture and SIL has been proposed to provide high throughput and ultra-high resolution. However, alignment between the nano-aperture and SIL is very critical in the fabrication process, and no effective alignment technique has been investigated yet. In this research, a novel self-alignment technique is proposed for the combination of the nano-aperture and SIL, where the nano-aperture is fabricated with the focused ion beam (FIB) system and the SIL is formed by the thermal reflowing process. The self-alignment technique is based on the backside exposure and the surface tension self-modulation technique during the thermal reflowing process. The maximum deviation of the fabricated SIL is less than 3% in comparison with the designed values. A SIL of 15 µm diameter has been measured with 65.2% transmission efficiency. The polymer SIL combined with the circular aperture of 329 nm diameter has 1.68 times enhancement on throughput compared with the circular aperture of 329 nm alone. This result shows that the SIL can effectively enhance the throughput of the nano-aperture, and the feasibility of the proposed self-alignment method is also verified.

We have developed a scanning laser manufacturing technique to produce microfluidic structures directly on photocopy transparency films. The reasons for the selection of transparency include (i) its insignificant water diffusion and vapor loss characteristics, (ii) its reduced viscoelastic behavior and (iii) its very low cost. The stiffness of the transparency membrane can be carefully tailored by adjusting laser ablation power. To show the feasibility of the approach, we have fabricated membrane valves on the transparency, and demonstrated a peristaltic micro-pumping system. Our investigation offers the potential for developing new types of very low-cost disposable devices including flexible microfluidic systems.

Magnetostatic microelectromechanical systems (MEMS) are based on the electromagnetic interactions between magnetic microstructures and active (coils) or passive (permanent magnets) magnetic field sources. They offer distinct advantages at the micrometer scale in strength, polarity and distance of actuation, when compared to other methods of actuation in MEMS. For proper understanding and detailed exploration of magnetostatic MEMS, it is important to have a reliable and efficient physical level simulation tool. In this paper, we propose an efficient technique, namely the hybrid full-Lagrangian technique for the static and dynamic analysis of magnetostatic MEMS. In this technique, the magnetostatic analysis needed to compute the magnetostatic force acting on the microstructure is performed using a hybrid BIE/Poisson approach. The Poisson equation is solved for the interior magnetostatic domains and the boundary integral equation (BIE) formulation of the potential equation is solved for the exterior magnetostatic domain and the different domains are coupled through interface conditions. A Lagrangian description of all the physical domains (magnetostatic, mechanical and fluidic) is used to eliminate geometry updates and rediscretization. The Lagrangian formulation along with the hybrid approach makes the proposed technique much more efficient than conventional tools for the analysis of magnetostatic MEMS. The new technique is used to simulate several magnetostatic MEMS switches and relays and validated by comparing numerical simulation results with experimental data. Dynamic analysis of a magnetostatic MEMS switch is performed using the new technique.

In this paper, we present the design, fabrication and characterization of the CMOS micromachined cantilevers for mass sensing in the femtogram range. The cantilevers consisting of multiple metal and dielectric layers are fabricated after completion of a conventional CMOS process by dry etching steps. The cantilevers are electrostatically actuated to resonance by in-plane electrodes. The mechanical resonant frequency is detected capacitively with on-chip circuitry, where the modulation technique is applied to eliminate capacitive feedthrough from the driving port and to lessen the effect of flicker noise. The highest resonant frequency of the cantilevers is measured at 396.46 kHz with a quality factor of 2600 at 10 mTorr. The resonant frequency shift after deposition of a 0.1 µm SiO₂ layer is 140 Hz, averaging 353 fg Hz⁻¹.

This paper presents a novel method using UV epoxy resin for the bonding of glass blanks and patterned plates at room temperature. There is no need to use a high-temperature thermal fusion process and therefore avoid damaging temperature-sensitive metals in a microchip. The proposed technique has the further advantage that the sealed glass blanks and patterned plates can be separated by the application of adequate heat. In this way, the microchip can be opened, the fouling microchannels may be easily cleaned-up and the plates then re-bonded to recycle the microchip. The proposed sealing method is used to bond a microfluidic device, and the bonding strength is then investigated in a series of chemical resistance tests conducted in various chemicals. Leakage of solution was evaluated in a microfluidic chip using pressure testing to 1.792 × 10² kPa (26 psi), and the microchannel had no observable leak. Electrical leakage between channels was tested by comparing the resistances of two bonding methods, and the result shows no significant electrical leakage. The performance of the device obtained from the proposed bonding method is compared with that of the thermal fusion bonding technique for an identical microfluidic device. It is found that identical results are obtained under the same operating conditions. The proposed method provides a simple, quick and inexpensive method for sealing glass microfluidic chips.

This paper describes a novel type of force transmission system for haptic display devices. The system consists of an array of end-effecter elements, a force/displacement transmitter and a single actuator producing a large force/displacement. It has tulip-shaped electrostatic clutch devices to distribute the force/displacement from the actuator among the individual end effecters. The specifications of three components were determined to stimulate touched human fingers. The components were fabricated by using micro-electromechanical systems and conventional machining technologies, and finally they were assembled by hand. The performance of the assembled transmission system was experimentally examined and it was confirmed that each projection in the arrayed end effecters could be moved individually. The actuator in a system whose total size was only 3.0 cm × 3.0 cm × 4.0 cm produced a 600 mN force and displaced individual array elements by 18 µm.

A novel PDMS-based microfluidic system incorporating an overlapping crisscross entrance with patterned groove microchannels in sequence serves as a high-performance micromixer. Such a design is characterized as involving two chaotic mixing mechanisms: the split entrance streams through the first overlapping crisscross junction are stretched and folded about the parabolic point within the patterned channel, and the reoriented streams are merged and restretched about the hyperbolic point at the next junction. The multiplicative mixing quality is thus revealed to increase 21% as installed with the staggered bas-relief structures on the walls and 29% through the second intersection of the overlapping crisscross micromixer. This microfluidic device has a fairly constant mixing index for the Reynolds number through a wide range between 0.01 and 10; it is potentially capable of being extended to achieve a key element of a lab-on-a-chip. Use of both numerical analysis and a confocal microscope elucidates the detailed mixing pattern; the results of these approaches agree convincingly.

A simple numerical approach based on the volume of fluid (VOF) method reveals that a 'W'-shaped, transient meniscus is ubiquitous during the formation of a uniformly curved meniscus within a microchannel, which has been believed to be dominant for the transients. The time that is needed to maintain the transient meniscus is correlated with viscosity, surface tension and geometry of the cavity. A generalized correlation is presented to predict the persistent time of the transient meniscus in a wettable microchannel (contact angle, θ < 90°) for Newtonian fluid.

This paper describes a technique to eject liquid droplets in almost any direction with a nozzleless self-focusing acoustic transducer (SFAT) built on a ZnO thin film as well as on a thick PZT substrate. Sectoring of the SFAT annular rings of half-wave-band sources to create a piezoelectrically inactive area causes the droplet ejections to be directed non-perpendicular (i.e., oblique) to the liquid surface. The direction of the droplet ejections depends on the size of the piezoelectrically inactive area within the area of the half-wave-band sources. Droplets are ejected from the center part of the annular rings toward the open inactive area. Various openings up to 90° of pie shape have been made and tested to show that the ejection direction becomes less vertical as the piezoelectrically inactive area in the transducer increases. Additionally, a multi-directional ejector built on ZnO film has been demonstrated to eject micron-sized liquid droplets (several microns in diameter) in any of eight predetermined directions on demand. Larger size liquid droplets (about a hundred microns in diameter) have also been directionally ejected from a sectored SFAT built on a PZT substrate.

This paper presents a novel process using micro-electro-discharge- machining (micro-EDM) combined with ultrasonic vibration by a helical micro-tool electrode to drill and finish micro-holes. During the machining processes, a micro-tool is directly fabricated by wire electro-discharge grinding (WEDG) using micro-EDM combined with various methods for machining the micro-hole and by ultrasonic vibration to finish the hole wall. In this work, circular micro-holes are machined in a high nickel alloy by cylindrical and helical electrodes. Using a helical micro-tool electrode for micro-EDM combined with ultrasonic vibration (HE-MEDM-UV) can substantially reduce the EDM gap, taper and machining time for deep micro-hole drilling. In addition, using a helical micro-tool with micro ultrasonic vibration finishing (HE-MUVF), good surface quality and less taper of the hole wall can be obtained by applying a suitable electrode step variation, rotational speed and ultrasonic amplitude with a machining time of approximately 25 min. According to scanning electron microscopy (SEM) micrographs and atomic force microscopy (AFM) measurement, HE-MUVF can indeed improve the surface roughness from 1.345 µm Rmax before finishing to 0.58 µm Rmax after HE-MUVF. This result demonstrates that using HE-MEDM-UV combined with MUVF can yield micro-holes of precise shape and smooth surface.

A method is introduced to study the effects of flexural deformation on the electrical performance of thin-film lithium-ion batteries. Flexural deformation of thin films is of interest to engineers for applications that can be effective in conformal spaces in conjunction with multi-functional composite laminates in structural members under mechanical deflections such as thin airfoils used in unmanned aerial vehicles (UAVs). A test fixture was designed and built using rapid prototyping techniques. A baseline reference charge/discharge cycle was initially obtained with the device in its un-flexed state, in order to later contrast the performance of the thin-film battery when subjected to deflections. Progressively larger deflections were introduced to the device starting with its un-deformed state. The cord flexure was applied in increments of 1.3% flex ratio, up to a maximum of 7.9%. At each successive increment, a complete charge/discharge cycle was performed. Up to a flex ratio of 1.3%, no effects of mechanical flexure on battery performance were observed, and the device performed reliably and predictably. Failure occurred at deflections above 1.3% flex ratio.

This work reports the fabrication and testing of flexible carbon nanotube microdevices made using hot embossing material transfer. Both micro-plasma and photodetector devices were made using as-grown unpurified multi-wall carbon nanotubes printed on PMMA substrates. Optical detectors were fabricated by attaching metal wires and monitoring the resistance as a function of light exposure. The electrical resistance of the nanotubes showed a strong sensitivity to light exposure which was also enhanced by heating the devices. While such processes in MWCNTs are not fully understood, the addition of thermal energy is believed to generate additional free charge carriers in the nanotubes. The plasma-generating microdevices consisted of a thin layer of thermoplastic polymer having the CNT electrode on one side and a metal electrode on the reverse side. The devices were electrically tested under atmospheric conditions with 0.01–1 kV ac and at 2.5 kHz, with the plasma igniting near 0.7 kV. The fabrication of these flexible organic devices demonstrates the ability to pattern useful carbon nanotube microdevices in low-cost thermoplastic polymers.

Thin film silicon MEMS electrostatic microresonators are fabricated on glass substrates by hot-wire chemical vapor deposition with the silicon structural layer spanning the amorphous-to-nanocrystalline transition. The amorphous-to-nanocrystalline transition is induced by increasing the hydrogen dilution of the reaction gases during the thin film silicon deposition. All processing steps are carried out at temperatures ⩽110 °C. Hot-wire deposition allows significantly faster deposition rates of thin-silicon films than standard RF plasma-enhanced chemical vapor deposition. In addition, the lower stress present in hot-wire films due to the absence of ion bombardment during growth allows the fabrication of thin film nanocrystalline silicon microresonators. The microresonators are electrostatically actuated and the resulting deflection is measured optically. The crystallinity of the structural layer does not have an observable effect in the rigidity of the resonators. The quality factor of the resonators shows a maximum at 85% H₂ dilution, corresponding to a material with a structure intermediate between amorphous and nanocrystalline. A sharp decrease in quality factors is observed for higher dilutions which correspond to nanocrystalline silicon films.

Control of residual stress and strain gradient of polycrystalline SiC films deposited via low-pressure chemical vapor deposition on 100 mm Si wafers is achieved by varying dichlorosilane (DCS) and 1,3-disilabutane (DSB) fractions in the inlet gas mixture. For films deposited at 800 °C and 45 sccm DSB, stress decreases from 1.2 GPa tensile with no added DCS to 240 MPa tensile with 40 sccm DCS added to the inlet gas stream. The lowest magnitude strain gradient achieved is 3.1 × 10⁻⁵ µm⁻¹ with 20 sccm DCS added. Electron probe microanalysis indicates that the films change from being slightly carbon-rich in the absence of DCS to successively more silicon-rich with the addition of DCS.

This work presents a new low-cost liquid dispenser for the dispensing of microliters to milliliter volumes. The dispensing mechanism is based on a thermal actuator where highly expandable microspheres expand into a liquid reservoir consequently displacing any stored liquid. All device components are made out of low-cost materials and the fabrication process has the potential for high volume batch manufacturing. The device utilizes the property of the expandable microspheres to form a heat insulating layer between the heat source and the delivered liquid. Moreover, it does not require any feed back or complicated flow metering. The device was successfully tested showing a mean dispensed volume of 101 µl with a standard deviation of 3.2% and with a maximum temperature of 59 °C in the liquid during actuation. It was shown that the dispenser is strong enough to deliver against counter pressures as high as 75 kPa. The device can also function as a low flow rate dispenser as demonstrated in a microfluidic dye laser application. The flow rate can be controlled between 1 µl h⁻¹ and 2400 µl h⁻¹ by adjusting the actuation power.

We propose a hysteresis and drift compensation scheme using proportional-integral feedback control for a nanopositioning Pb(ZrTi)O₃ (PZT) microstage. A multi-degree of freedom PZT microstage with integrated differential capacitive displacement sensors has been fabricated and tested, demonstrating the feasibility of compensating for hysteresis and creep. The feedback signal to the PZT actuators is fed from differential capacitive sensors of the displacement of the microstage. Experimental results show that the sensitivity of the displacement sensor is approximately 0.53 V µm⁻¹. A maximum resolution of 16 nm is achieved when hysteresis is compensated for, and the minimum detectable variation of capacitance ΔC is 1.25 × 10⁻³ pF. The hysteresis of the system varies with the proportional gain K_p, integral time constant T_i and reference input frequency. By using feedback control with a proportional and integration (PI) controller, the hysteresis decreases from 30% in open-loop operation to approximately 1% in closed-loop operation at a gain of 20, when the frequency of the sine reference input is 1 Hz and T_i is 20 ms. Efficient compensation of hysteresis is validated by the closed-loop control, especially when the frequency of the reference input is low. Elimination of creep/drift is also verified by the closed-loop control.

A process for batch fabrication of low-cost needle-shaped micro-coils for magnetic resonance (MR) spectroscopy is demonstrated. The conductors are embedded inside a cross-section designed to avoid the signal cancellation effects that can occur with completely immersed detectors. Simple models are developed for the sensitivity of an immersed coil and for the electrical performance of coils on silicon substrates. Conductors are fabricated on oxidized Si by electroplating metals inside a deep photoresist mould, and then capped with a thick layer of plastic. Through-wafer deep reactive ion etching is used to define needle shapes. At 63.8 MHz frequency, Q-factors obtained on Si are comparable to those on glass, and resonators based on single-turn coils have Q-factors of ≈14. Total immersion ¹H MR imaging and spectroscopy are demonstrated in a 1.5 T magnetic field using tomato fruits. Q-factors are raised at higher frequencies (to >30 at 255 MHz) using thick polymer isolation, and hybrid integration of additional circuitry is demonstrated.

We present high-resolution determination of AFM cantilever thickness and oxide layer thickness at the top and bottom surfaces of the cantilever. Optical reflection and transmission measurements are used for precise heterostructure layer thickness determination and detailed evaluation of surface oxidation of Si-AFM cantilever probes. Precise knowledge of cantilever heterostructure layer thickness is very important to guarantee cantilever probe functionality due to its direct correlation to the spring constant and resonant frequency. Thickness determination is achieved by using line shape fitting of the results of theoretical model calculations to experimental data. For Si cantilevers we demonstrated accuracy below 1 nm for a total thickness of 20 µm. In addition, we methodically present that even without line shape fitting an estimate of the oxide layer thickness can be obtained directly from an envelope slope of the measured undulations. This non-contact and non-destructive method can be used for thickness determination of individual layers or for verification, as well as for technological process control.

One-dimensional modeling of steady frictional radial flow of a perfect gas through a high-pressure piezoelectrically actuated microvalve under low leak-rate conditions is studied. Focusing on the micro-scale gap between the boss and seat plates, a model was developed for axisymmetric flow between two thermally insulated, parallel disks flowing radially toward an outlet hole at the center of the bottom disk. The fourth-order Runge–Kutta algorithm was utilized to integrate a system of nonlinear ordinary differential equations that govern the variations of flow properties. The most notable observation is that of a drastic increase in density and static pressure in contrast to a rather small increase in the Mach number (or velocity). The total pressure drop was also shown to be significant across the seat rings. A 2D Stokes flow model was also derived for incompressible, axisymmetric, radial flow between two concentric parallel disks in order to verify the trends of the flow property variations from the compressible radial flow model. The Stokes flow model trends for both static and total pressure concurred with the predictions of the radial compressible flow model. In addition, a comparison of Stokes flow values for both the static pressure rise and the total pressure drop to that of the numerical results demonstrates the necessity of accounting for compressibility effects.

A novel on-chip magnetic bead separator using micromachined magnetic tips for biocell sorting in microfluidic systems is presented. Magnetic interconnection technology is applied by using through-holes filled with NiFe permalloy material, which allows the fully integrated electromagnetic inductors to be placed underneath the device chip. Only the magnetic tips on the front side of the chip are exposed to integrated microchannels, which give wide flexibility in constructing microfluidic systems with the magnetic bead separator. Magnetic beads were separated effectively from a continuous flow using the developed on-chip magnetic bead separator.

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