In the last 30 days

• Open/close Simultaneous actuation and displacement sensing for electrostatic drives

  Jingyan Dong and Placid M Ferreira 2008 J. Micromech. Microeng. 18 035011 Tag this article

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  This paper presents a method for driving a MEMS electrostatic actuator, while simultaneously sensing the resulting displacement/capacitance without the use of an additional physical sensing structure. The approach superposes the sensing and actuation signals into a single input into the system and obtains its mechanical (displacement) response from the modulation (amplitude or phase) it produces on the sensing input. The approach is analyzed and experimentally shown to produce an amplitude modulation of 0.1857 mV µm ⁻¹ of displacement on electrostatic drive that produces a displacement of 14 µm at 100 V and a 0.55 pF capacitance change from a nominal capacitance of 0.35 Pico farads. The approach enables a very cost-effective and convenient approach to detect the displacement of MEMS devices for a variety of applications in the laboratory environment, and provide a potential feedback signal for closed-loop control of electrostatically driven MEMS devices.

• Open/close Study on dielectric charging in low-stress silicon nitride with the MIS structure for reliable MEMS applications

  Haisheng San et al 2011 J. Micromech. Microeng. 21 125019 Tag this article

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  Charge-induced failure has been recognized as a primary reliability issue in capacitive micro-actuators. In this paper, we present a simple method to assess the effect of dielectric charging on reliability of a capacitive micro-actuator. By capacitance–voltage measurements for a metal–insulator–semiconductor (MIS) structure, the characteristics of dielectric charging can be investigated, and the obtained results can be used to study the charging behavior of a capacitive micro-actuator. An analytical model based on this method has been established. The silicon-rich nitride film was deposited by low-pressure chemical vapor deposition on silicon substrate. The current–voltage and capacitance–voltage measurements exhibit an asymmetric electrical characteristic under different polarity of stress voltage. The charging parameters of the silicon-rich nitride were extracted by the stretched exponential curve fitting method. This charging behavior suggests that silicon-rich nitride can be negatively or positively charged, and the injection and transport of holes are more favored than the injection and transport of electrons. The charge injection from movable electrode plays a dominant role in the dielectric charging of a capacitive micro-actuator. It is expected that the charge accumulation in dielectrics can be eliminated by employing the bipolar square-wave voltage to actuate a capacitive micro-actuator.

• Open/close Investigation of residual stress and its effects on the vibrational characteristics of piezoelectric-based multilayered microdiaphragms

  M Olfatnia et al 2010 J. Micromech. Microeng. 20 015007 Tag this article

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  In this study, residual stress influences on the vibrational behavior of piezoelectric circular microdiaphragm-based biosensors are investigated theoretically and experimentally. The piezoelectric microdiaphragm was first fabricated by combining sol–gel PZT thin film and MEMS technology. The stress measurements by the wafer curvature method and the micro-Raman technique demonstrate that high tensile stresses are generated in the upper films (Pt/PZT/Pt), while the silicon oxide layer experiences a compressive stress. After backside etching of the microdiaphragm, the suspended membrane method was used to measure the average stress and equivalent Young's modulus of the diaphragm, which were 96 MPa and 106.4 GPa, respectively. The dynamic behavior of the fabricated sensor under this stress was then investigated. A comprehensive mechanics model based on vibration modes is presented and the natural frequencies of the diaphragm are obtained. A nondimensional tension parameter is defined, and effects of this parameter on the resonant frequency of the diaphragm are presented. It was concluded that both flexural rigidity and tension contribute to the resonant frequency of the diaphragm sensor. Finally, the resonant frequencies of the fabricated sensor were measured by impedance analysis and laser vibrometry techniques. These frequencies were compared with their theoretical counterparts and a good agreement was observed.

• Open/close A review of MEMS oscillators for frequency reference and timing applications

  J T M van Beek and R Puers 2012 J. Micromech. Microeng. 22 013001 Tag this article

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  MEMS-based oscillators are an emerging class of highly miniaturized, batch manufacturable timing devices that can rival the electrical performance of well-established quartz-based oscillators. In this review, a description is given of the key properties of a MEMS resonator that determine the overall performance of a MEMS oscillator. Piezoelectric, capacitive and active resonator transduction methods are compared and their impact on oscillator noise and power dissipation is explained. An overview is given of the performance of MEMS resonators and MEMS-based oscillators that have been demonstrated to date. Mechanisms that affect the frequency stability of the resonator, such as temperature-induced frequency drift, are explained and an overview is given of methods that have been demonstrated to improve the frequency stability. The aforementioned performance indicators of MEMS-based oscillators are benchmarked against established quartz and CMOS technologies.

• Open/close A single-pixel wireless contact lens display

  A R Lingley et al 2011 J. Micromech. Microeng. 21 125014 Tag this article

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  We present the design, construction and in vivo rabbit testing of a wirelessly powered contact lens display. The display consists of an antenna, a 500 × 500 µm ² silicon power harvesting and radio integrated circuit, metal interconnects, insulation layers and a 750 × 750 µm ² transparent sapphire chip containing a custom-designed micro-light emitting diode with peak emission at 475 nm, all integrated onto a contact lens. The display can be powered wirelessly from ~1 m in free space and ~2 cm in vivo on a rabbit. The display was tested on live, anesthetized rabbits with no observed adverse effect. In order to extend display capabilities, design and fabrication of micro-Fresnel lenses on a contact lens are presented to move toward a multipixel display that can be worn in the form of a contact lens. Contact lenses with integrated micro-Fresnel lenses were also tested on live rabbits and showed no adverse effect.

• Open/close Portable oral cancer detection using a miniature confocal imaging probe with a large field of view

  Youmin Wang et al 2012 J. Micromech. Microeng. 22 065001 Tag this article

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  We demonstrate a MEMS micromirror enabled handheld confocal imaging probe for portable oral cancer detection, where a comparatively large field of view (FOV) was generated through the programmable Lissajous scanning pattern of the MEMS micromirror. Miniaturized handheld MEMS confocal imaging probe was developed, and further compared with the desktop confocal prototype under clinical setting. For the handheld confocal imaging system, optical design simulations using CODE V ^R® shows the lateral and axial resolution to be 0.98 µm and 4.2 µm, where experimental values were determined to be 3 µm and 5.8 µm, respectively, with a FOV of 280 µm×300 µm. Fast Lissajous imaging speed up to 2 fps was realized with improved Labview and Java based real-time imaging software. Properties such as 3D imaging through autofocusing and mosaic imaging for extended lateral view (6 mm × 8 mm) were examined for carcinoma real-time pathology. Neoplastic lesion tissues of giant cell fibroma and peripheral ossifying fibroma, the fibroma inside the paraffin box and ex vivo gross tissues were imaged by the bench-top and handheld imaging modalities, and further compared with commercial microscope imaging results. The MEMS scanner-based handheld confocal imaging probe shows great promise as a potential clinical tool for oral cancer diagnosis and treatment.

• Open/close An electric detection of immunoglobulin G in the enzyme-linked immunosorbent assay using an indium oxide nanoparticle ion-sensitive field-effect transistor

  Dongjin Lee and Tianhong Cui 2012 J. Micromech. Microeng. 22 015009 Tag this article

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  Semiconducting nanoparticle ion-sensitive field-effect transistors (ISFETs) are used to detect immunoglobulin G (IgG) in the conventional enzyme-linked immunosorbent assay (ELISA). Indium oxide and silica nanoparticles were layer-by-layer self-assembled with the oppositely charged polyelectrolyte as the electrochemical transducer and antibody immobilization site, respectively. The assay was conducted on a novel platform of indium oxide nanoparticle ISFETs, where the electric signals are generated in response to the concentration of target IgG using the labeled detecting antibody. The sandwiched ELISA structure catalyzed the conversion of the acidic substrate into neutral substance with the aid of horseradish peroxidase. The pH change in the substrate solution was detected by nanoparticle ISFETs. Normal rabbit IgG was used as a model antigen whose detection limit of 0.04 ng ml ⁻¹ was found. The facile electric detection in the conventional assay through the semiconducting nanoparticle ISFET has potential applications as a point-of-care detection or a sensing element in a lab-on-a-chip system.

• Open/close Microfabrication and characterization of an array of dielectric elastomer actuators generating uniaxial strain to stretch individual cells

  S Akbari and H R Shea 2012 J. Micromech. Microeng. 22 045020 Tag this article

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  Cells regulate their behavior in response to mechanical strains. Cell cultures to study mechanotransuction are typically cm ² in area, far too large to monitor single cell response. We have developed an array of dielectric elastomer microactuators as a tool to study mechanotransduction of individual cells. The array consists of 72 100 µm × 200 µm electroactive polymer actuators which expand uniaxially when a voltage is applied. Single cells will be attached on each actuator to study their response to periodic mechanical strains. The device is fabricated by patterning compliant microelectrodes on both sides of a 30 µm thick polydimethylsiloxane membrane, which is bonded to a Pyrex chip with 200 µm wide trenches. Low-energy metal ion implantation is used to make stretchable electrodes and we demonstrate here the successful miniaturization of such ion-implanted electrodes. The top electrode covers the full membrane area, while the bottom electrodes are 100 µm wide parallel lines, perpendicular to the trenches. Applying a voltage between the top and bottom electrodes leads to uniaxial expansion of the membrane at the intersection of the bottom electrodes and the trenches. To characterize the in-plane strain, an array of 4 µm diameter aluminum dots is deposited on each actuator. The position of each dot is tracked, allowing displacement and strain profiles to be measured as a function of voltage. The uniaxial strain reaches 4.7% at 2.9 kV with a 0.2 s response time, sufficient to stimulate most cells with relevant biological strains and frequencies.

• Open/close Microfluidics-a review

  P Gravesen et al 1993 J. Micromech. Microeng. 3 168 Tag this article

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  An overview is given of research activities in the field of fluid components or systems built with microfabrication technologies. This review focuses on the fluidic behaviour of the various devices, such as valves, pumps and flow sensors as well as the possibilities and pitfalls related to the modelling of these devices using simple flow theory. Finally, a number of microfluidic systems are described and comments on future trends are given.

• Open/close Three-dimensional magnetic terahertz metamaterials using a multilayer electroplating technique

  Kebin Fan et al 2012 J. Micromech. Microeng. 22 045011 Tag this article

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  In the last decade, the development of metamaterials has led to exotic phenomena not shown in nature, including negative refractive index, invisibility cloaking and perfect absorption. To achieve these effects requires creating magnetically resonant subwavelength structures, since naturally occurring magnetism typically occurs at relatively low frequencies. In the far-infrared, or terahertz (THz), region of the electromagnetic spectrum, it is difficult to obtain a strong magnetic response from planar metamaterials at normal incidence. In this paper, multilayer electroplating is used to fabricate three-dimensional (3D) split-ring resonators that stand up out of plane. This enables the maximum coupling to the magnetic response at normal incidence. Characterization using THz time-domain spectroscopy indicates a strong magnetic resonance, and parameter extraction reveals a negative permeability from 1 to 1.3 THz with the minimal value of −2. The successful design, fabrication and characterization of 3D metamaterials provide opportunities to achieve different electromagnetic properties and novel devices in the THz range.