This paper demonstrates the application of ultrashort-pulsed lasers as a unique tool for controllable modification of the surface wettability of polymers from high hydrophilicity to superhydrophobicity. This is achieved by exploiting the effect of laser pulse duration and photon energy on the surface chemistry and morphology and subsequent wetting properties of polymeric surfaces treated with UV laser pulses. In three different pulse duration regimes, ranging from femtosecond to nanosecond and two different photon wavelengths, we have systematically altered the wettability of polyethersulfone surfaces from highly hydrophilic to superhydrophobic. Our results indicate that, despite the remarkable changes in the surface morphology attained, the surface wettability variations are dominantly caused by laser-induced chemical modifications, which are highly dependent on the pulse energy and duration. The ability of tuning the wetting properties and thus the surface energy of laser-treat...

A comprehensive and completely parameterized model is proposed to determine the related electrical and mechanical dynamic system response of a voltage-driven capacitive coupled micromechanical switch. As an advantage over existing parameterized models, the model presented in this paper returns within few seconds all relevant system quantities necessary to design the desired switching cycle. Moreover, a sophisticated and detailed guideline is given on how to engineer a MEMS switch. An analytical approach is used throughout the modelling, providing representative coefficients in a set of two coupled time-dependent differential equations. This paper uses an equivalent mass moving along the axis of acceleration and a momentum absorption coefficient. The model describes all the energies transferred: the energy dissipated in the series resistor that models the signal attenuation of the bias line, the energy dissipated in the squeezed film, the stored energy in the series capacitor that...

This paper presents a novel method to effectively protect the structural material polycrystalline silicon (polysilicon) from electrochemical corrosion, which often occurs when the MEMS device is released in HF-based solutions, especially when the device contains a noble metal. This corrosion seriously degrades the electrical and mechanical performance as well as the reliability of MEMS devices. In this method, a photoresist (PR) is employed to cover the noble metal, which is electrically coupled with the underlying polysilicon layer. This PR cover can effectually prevent an HF-based solution from diffusing through and arriving at the surface of the noble metal, thus cutting off the electrical current of the electrochemical corrosion reaction. The polysilicon is well protected for longer than 80 min in 49% concentrated HF solutions by a 3 µm-thick AZ 6130 PR film. This fabrication process is simple, reliable and suitable for mass production of high-end micromechanical disk resonat...

An 8–12 GHz microwave frequency detector is presented, which is based on MEMS power sensors, by sensing the phase delay of two separated signals in two different tracks. The phase delay, proportional to frequency of the input microwave signal, leads to variation of the output power. Two different kinds of MEMS power sensors, a thermoelectric microwave power sensor and a MEMS capacitive power sensor, are adopted to measure the variation. The former is used for measuring the lower power while the latter for the higher one. The presented detector has been designed, optimized and fabricated successfully using the GaAs MMIC process. For the microwave signals of 10, 15 and 20 dBm, the measured result shows that the output thermovoltage decreases with the frequency based on the thermoelectric microwave power sensor and sensitivities of the detector better than 0.033, 0.110 and 0.343 µV MHz ⁻¹ are measured, respectively. Furthermore, the sensitivity of detector is directly prop...

We demonstrate parametric amplification of a multidegree of freedom resonant mass sensing array via an applied base motion containing the appropriate frequency content and phases. Applying parametric forcing in this manner is simple and aligns naturally with the vibrational properties of the sensing structure. Using this technique, we observe an increase in the quality factors of the coupled array resonances, which provides an effective means of improving device sensitivity.

Polydimethylsiloxane (PDMS) is a popularly used nontoxic and biocompatible material in microfluidic systems, which is relatively cheap and does not break easily like glass. The simple fabrication, optical transparency and elastomeric property make PDMS a handy material to work with. In order to develop different applications of PDMS in microfluidics and bioengineering, it is necessary to modify the PDMS surface nature to improve wetting characteristics, and to have a better control in nonspecific binding of proteins and cells, as well as to increase adhesion. At the moment, the hydrophilic surface modification performance of PDMS is known to recover its hydrophobicity shortly after oxidation modification, which is not stable in the long term (Owen and Smith 1994 J. Adhes. Sci. Technol. 8 1063–75). This paper presents a long-term stable hydrophilic surface modification processing of PDMS. The poly(dimethylsiloxane-ethylene oxide polymeric) (PDMS-b-PEO) is used in thi...

This paper presents a new fabrication method to manufacture alkali reference cells having dimensions larger than standard micromachined cells and smaller than glass-blown ones, for use in compact atomic devices such as vapour-cell atomic clocks or magnetometers. The technology is based on anodic bonding of silicon and relatively thick glass wafers and fills a gap in cell sizes and technologies available up to now: on one side, microfabrication technologies with typical dimensions ≤ 2 mm and on the other side, classical glass-blowing technologies for typical dimensions of about 6–10 mm or larger. The fabrication process is described for cells containing atomic Rb and spectroscopic measurements (optical absorption spectrum and double resonance) are reported. The analysis of the bonding strength of our cells was performed and shows that the first anodic bonding steps exhibit higher bonding strengths than the later ones. The spectroscopic results show a good quality of the cells. Fro...

The electro-osmotic flow limit of detection and separation efficiency of glass channels machined using abrasive jet micromachining (AJM) were measured and compared with those for channels machined using conventional wet etching with hydrofluoric acid. It was found that the electro-osmotic mobility in AJM channels was similar to that in wet-etched channels, ∼4 × 10 ⁻⁴ cm ² V ⁻¹ s ⁻¹ for 20 µm channels, despite a two-decade difference in surface roughness. Similarly, limits of detection measured on the two types of chips were roughly comparable to each other and on the order of 1 nM (injected sample concentration). The separation efficiency calculated from TAMRA dye injections in AJM channels, however, was found to be significantly lower, ∼0.2–0.25 times, than that in wet-etched channels. The effect of surface roughness on the separation efficiency and electro-osmotic mobility in micro-channels is discussed in the context of the literature. F...

This paper presents a fringe capacitance formula of microstructures. The formula is derived by curve fitting on ANSYS simulation results. Compared with the ANSYS and experimental results, the deviation is within ±2%. The application to determine the pull-in voltage of an electrostatic micro-beam is demonstrated, which agrees very well with the experimental data. The formula presented is very accurate, yields explicit physical meanings and is applicable to common dimension ranges for MEMS devices.

A recent application domain of MEMS technology is in the development of microthrusters for micro-/nanosatellites. Among the various types of MEMS microthruster developed so far, the vaporizing liquid microthruster (VLM) has been widely explored for its capability to produce continuously variable thrust in the micro-Newton (µN) to mili-Newton (mN) range. This paper reports the design and experimental validation of silicon MEMS VLM consisting of a microcavity, inlet channel and converging–diverging (C-D) in-plane exit nozzle integrated in two micromachined bonded chips and sandwiched between two p-diffused microheaters, located at the top and bottom surface of the device. Structural configuration was designed using simple analytical equations to achieve maximum thrust force by controlling the inlet propellant flow and heater power of VLM in an efficient way. In addition, a 3D model using a computational fluid dynamics technique was constructed to simulate the aft section of VLM for...