Development of a novel micromirror based on surface micromaching technology

A novel 3 × 3 micromirror array is designed and successfully fabricated with multi-layer silicon surface micromaching technology. It is composed of bottom electrode, support part and mirror plate, in which a T type beam structure is used to support the mirror plate. It can provide mirror with the vertical movement and the rotation about two horizontal axes, thus enabling phase modulation and amplitude modulation for the incident light. The test results show that the maximum deflection length along the vertical direction of the mirror plate is 2 μm, while the rotation angle about X- and Y-axis are ±2.3° and ±1.45°, respectively.     

Mechanical design and characterization of a resonant magnetic field microsensor with linear response and high resolution

A resonant magnetic field microsensor based on Microelectromechanical Systems (MEMS) technology including a piezoresistive detection system has been designed, fabricated, and characterized. The mechanical design for the microsensor includes a symmetrical resonant structure integrated into a seesaw rectangular loop (700 μm × 450 μm) of 5 μm thick silicon beams. An analytical model for estimating the first resonant frequency and deflections of the resonant structure by means of Rayleigh and Macaulay's methods is developed. The microsensor exploits the Lorentz force and presents a linear response in the weak magnetic field range (40–2000 μT). It has a resonant frequency of 22.99 kHz, a sensitivity of 1.94 V T^?1, a quality factor of 96.6 at atmospheric pressure, and a resolution close to 43 nT for a frequency difference of 1 Hz. In addition, the microsensor has a compact structure, requires simple signal processing, has low power consumption (16 mW), as well as an uncomplicated fabrication process. This microsensor could be useful in applications such as the automotive sector, the telecommunications industry, in consumer electronic products, and in some medical applications.     

Photonic crystal slabs with hexagonal air holes fabricated by selective area metal organic vapor phase epitaxy

It is shown that the photonic crystal slab (PCS) with hexagonal air holes has band gaps in the guided mode spectrum, which can be compared to that of the PCS with circular air holes, thus it is also a good candidate to be used for the PC devices. The PC with hexagonal air holes and a = 0.5 μm and r = 0.15 μm was fabricated successfully by selective area metal organic vapor phase epitaxy (SA-MOVPE). The vertical and smooth sidewalls are formed and the uniformity is very good. The same process was also used to fabricate a hexagonal air hole array with the width of 0.1 μm successfully. The air-bridge PCS with hexagonal air holes and a = 0.3 μm and r = 0.09 μm was also fabricated successfully by SA-MOVPE. Further optimization of the growth conditions for the sacrificial layer and the selective etching of the GaAs cap layer is also needed. Our experimental results indicate that SA-MOVPE is a promising method for fabricating PC devices and photonic nanostructures.     

Electroactive polymer based microfluidic pump

A planar, valveless, microfluidic pump using electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymer as the actuator material is presented. P(VDF-TrFE) thick films having a large electrostrictive strain ∼5–7% and high elastic energy density of 1 J/cm³ have been used in a unimorph diaphragm actuator configuration. The microfluidic pump was realized by integrating a nozzle/diffuser type fluidic mechanical-diode structure with the polymer microactuator. The P(VDF-TrFE) unimorph diaphragm actuator, 80 μm thick and 2.2 mm × 2.2 mm in lateral dimensions, showed an actuation deflection of 80 μm for an applied electric field of 90 MV/m. The microfluidic pump could pump methanol at a flow rate of 25 μl/min at 63 Hz with a backpressure of 350 Pa. The flow rate of this pump could be easily controlled by external electrical field. Two different sizes of nozzle/diffuser elements were studied and the pumping efficiency of these structures is 11 and 16%, respectively.     

Electrical properties of nickel oxide thin films for flow sensor application

In this work, Ni oxide thin films, with thermal sensitivity superior to Pt and Ni thin films, were formed through annealing of Ni films deposited by a r.f. magnetron sputtering. The annealing was carried out in the temperature range of 300–500 °C under atmospheric conditions. Resistivity of the resulting Ni oxide films were in the range of 10.5 μΩ cm/°C to 2.84 × 10⁴ μΩ cm/°C, depending on the extent of Ni oxidation. The temperature coefficient of resistance (TCR) of the Ni oxide films also depended on the extent of Ni oxidation; the average TCR of Ni oxide resistors, measured between 0 and 150 °C, were 5630 ppm/°C for the 300 °C and 2188 ppm/°C for 500 °C films. Because of their high resistivity and very linear TCR, Ni oxide thin films are superior to pure Ni and Pt thin films for flow and temperature sensor applications.     

Micromachined quartz resonator based infrared detector array

We report the fabrication and performance of a micromachined Y-cut quartz resonator based thermal infrared detector array. 1 mm diameter and 18 μm thick (90 MHz) inverted mesa configuration quartz resonator arrays with excellent resonance characteristics have been fabricated by RIE etching of quartz. Temperature sensitivity of 7.2 kHz/K was experimentally measured. Infrared calibration tests on the resonator array even without the use of infrared absorbers gave a responsivity of 14.3 MHz/W and an NEP of 326 nW. In this first report on the performance of the Y-cut quartz resonator infrared thermal detector array, the response time measurements were found to be limited by the slow measurement time of the impedance scans and the undesired heating of the quartz substrate. Most importantly, this initial work demonstrates the possibility of realizing infrared detector arrays for room temperature thermal imaging applications that can rival current state of the art in the field.     

Fabrication and characterization of a thermal switch

The development of a thermal switch based on arrays of liquid–metal micro-droplets is presented. Prototype thermal switches are assembled from a silicon substrate on which is deposited an array of 1600 30-μm liquid–metal micro-droplets. The liquid–metal micro-droplet array makes and breaks contact with a second bare silicon substrate. A gap between the two silicon substrates is filled with either air at 760 Torr, air at of 0.5 Torr or xenon at 760 Torr. Heat transfer and thermal resistance across the thermal switches are measured for “on” (make contact) and “off” (break contact) conditions using guard-heated calorimetry. The figure of merit for a thermal switch, the ratio of “off” state thermal resistance over “on” state thermal resistance, R_off/R_on, is 129 ± 43 for a xenon-filled thermal switch that opens 100 μm and 60 ± 17 for an 0.5 Torr air-filled thermal switch that opens 25 μm. These thermal resistance ratios are shown to be markedly higher than values of R_off/R_on for a thermal switch based on contact between polished silicon surfaces. Transient temperature measurements for the liquid–metal micro-droplet switches indicate thermal switching times of less than 100 ms. Switch lifetimes are found to exceed one-million cycles.     

Spin-valve planar Hall sensor for single bead detection

The planar Hall effect (PHE) sensor with a junction size of 3 μm × 3 μm for a single micro-bead detection has been fabricated successfully using a typical spin-valve thin film Ta(5)/NiFe(16)/Cu(1.2)/NiFe(2)/IrMn(15)/Ta(5) nm. The PHE sensor exhibits a sensitivity of about 7.2 μV Oe^?1 in the magnetic field range of ±7 Oe approximately. We have performed an experiment to illustrated the possibility of single micro-bead detection by using a PHE sensor. A single micro-bead of 2.8 μm diameter size is secluded from 0.1% dilute solution of the Dynabeads^® M-280 dropped on the sensor surface and is located on the sensor junction by using a micro magnetic needle. The comparison of the PHE voltage profiles in the field range from 0 to 20 Oe in the absence and presence of a single micro-bead identifies a single Dynabeads^® M-280, the maximal signal change as large as ΔV ～ 1.1 μV can be obtained at the field ～6.6 Oe. The results are well described in terms of the reversal of a basic single domain structure.     

Thick film sensors based on laccases from different sources immobilized in polyaniline matrix

Thick film electrode based biosensors containing Trametes versicolor (TvL) and Aspergillus niger (AnL) laccases and Agaricus bisporus tissues (AbT) were developed for the determination of phenolic compounds and the measurement was based on oxygen consumption in relation to analyte oxidation. The electrodeposited organic polymer; polyaniline was used as a matrix for the immobilization in the preparation of thick film sensors. The systems were calibrated for different phenolic substances. A linearity was obtained in concentration range between 0.4 and 6.0 μM phenol, 0.2 and 1.0 μM catechol, 2.0 and 20.0 μM l-DOPA for TvL based biosensor; for AnL based enzyme electrode 0.4 and 4.0 μM phenol, 0.4 and 15 μM catechol, 0.4 and 6.0 μM l-DOPA; for AbT electrode 1.0 and 10 μM phenol, 0.4 and 1.6 μM catechol, 1.0 and 10 μM l-DOPA, respectively, in the response time of 300 s. Furthermore, as well as sample application and accuracy, optimum pH, temperature and thermal stabilities of the proposed systems were also detected.     

Glancing up or down: Mood management and selective social comparisons on social networking sites

Social networking sites (SNS) provide opportunities for mood management through selective exposure. This study tested the prediction that negative mood fosters self-enhancing social comparisons to SNS profiles. Participants were induced into positive or negative moods and then browsed manipulated profiles on an experimental SNS. Profiles varied in a 2 × 2 within-subjects design along two dimensions, ratings of career success and attractiveness, allowing for upward comparisons (high ratings) and downward comparisons (low ratings). Selective exposure was measured in seconds spent viewing profiles. Negative mood led to less exposure to upward comparisons and more to downward comparisons than positive mood. The comparison dimension did not influence selective exposure. Thus, in a negative mood, SNS users prefer self-enhancing social comparisons to manage their mood.     

Design and performance of a microcantilever-based hydrogen sensor

This paper describes the design of, and the effects of basic environmental parameters on, a microelectromechanical (MEMS) hydrogen sensor. The sensor contains an array of 10 micromachined cantilever beams. Each cantilever is 500 μm wide×267 μm long×2 μm thick and has a capacitance readout capable of measuring cantilever deflection to within 1 nm. A 20-nm-thick coating of 90% palladium–10% nickel bends some of the cantilevers in the presence of hydrogen. The palladium–nickel coatings are deposited in ultra-high-vacuum (UHV) to ensure freedom from a “relaxation” artifact apparently caused by oxidation of the coatings. The sensor consumes 84 mW of power in continuous operation, and can detect hydrogen concentrations between 0.1 and 100% with a roughly linear response between 10 and 90% hydrogen. The response magnitude decreases with increasing temperature, humidity, and oxygen concentration, and the response time decreases with increasing temperature and hydrogen concentration. The 0–90% response time of an unheated cantilever to 1% hydrogen in air is about 90 s at 25 °C and 0% humidity.     

Experimental investigation and thermodynamic calculation of the phase equilibria in the Fe–Ni–V system

The phase equilibria in the Fe–Ni–V ternary system were investigated by means of electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Three isothermal sections of the Fe–Ni–V ternary system at 1000 °C, 1100 °C and 1200 °C were established. On the basis of the obtained experimental data, the phase equilibria in the Fe–Ni–V system were thermodynamically assessed using (CALculation of PHAse Diagrams) CALPHAD method, and a consistent set of thermodynamic parameters leading to reasonable agreement between the calculated results and experimental data was obtained.     

Characteristics of a Pd–oxide–In0.49Ga0.51P high electron mobility transistor (HEMT)-based hydrogen sensor

An interesting hydrogen sensor based on a high electron mobility transistor (HEMT) device with a Pd–oxide–In_0.49Ga_0.51P gate structure is fabricated and demonstrated. The hydrogen sensing characteristics including hydrogen detection sensitivity and transient responses of the studied device under different hydrogen concentrations and temperature are measured and studied. The hydrogen detection sensitivity is related to a change in the contact potential at the Pd/insulator interface. The kinetic and thermodynamic properties of hydrogen adsorption are also studied. Experimentally, good hydrogen detection sensitivities, large magnitude of current variations (3.96 mA in 9970 ppm H₂/air gas at room temperature) and shorter absorption response time (22 s in 9970 ppm H₂/air gas at room temperature) are obtained for a 1.4 μm × 100 μm gate dimension device. Therefore, the studied device provides a promise for high-performance solid-state hydrogen sensor, integrated circuit (IC) and micro electro-mechanical system (MEMS) applications.     

Design,simulation and validation of a novel uncooled infrared focal plane array

This paper describes a novel single-layer bi-material cantilever microstructure without silicon (Si) substrate for focal plane array (FPA) application in uncooled optomechanical infrared imaging system (UOIIS). The UOIIS, responding to the radiate infrared (IR) source with spectral range from 8 to 14 μm, may receive an IR image through visible optical readout method. The temperature distribution of the IR source could be obtained by measuring the thermal–mechanical rotation angle distribution of every pixel in the cantilever array, which is consisted of two materials with mismatching thermal expansion coefficients. In order to obtain a high detection to the IR object, gold (Au) film is coated alternately on silicon nitride (SiN_x) film in the flection beams of the cantilevers. And a thermal–mechanical model for such cantilever microstructure is proposed. The thermal and thermal–mechanical coupling field characteristics of the cantilever array structure are optimized through numerical analysis method and simulated by using the finite element simulation method. The thermal–mechanical rotation angle simulated and thermal–mechanical sensitivity tested in the experiment are 2.459 × 10⁻³ and 3.322 × 10⁻⁴ rad/K, respectively, generally in good agreement with what the thermal–mechanical model and numerical analysis forecast, which offers an effective reference for FPA structure parameters design in UOIIS.     

Design,fabrication, and testing of MEMS solid propellant thruster array chip on glass wafer

This paper presents the internal ballistic design, fabrication procedure, and performance evaluation of a micro-electro mechanical systems (MEMS) solid propellant thruster array chip. The internal ballistic design was carried out to predict the performance of the thruster. Two different ignition models were used. The numerical results gave a maximum thrust of 3840 mN, and a total impulse of 0.42 mNs at the local ignition model. A photosensitive glass wafer only was used as the bare material for the thruster. The stability of the micro-igniter was improved by using a glass membrane with a thickness of tens of microns. The average thickness of the membrane was 35 μm. The proposed micro-igniter had a level of power consumption appropriate to ignite the solid propellant. The thermal, electrical, and mechanical characteristics of the fabricated micro-igniter were measured. The solid propellant was loaded into the propellant chamber without resort to a special technique due to the high structural stability of the glass membrane. An MEMS solid propellant thruster (MSPT) array was fabricated through anisotropic etching of photosensitive glass. An ignition control system was developed to control the ignition sequence. Ignition and combustion tests of the fully assembly MEMS thruster were performed successfully. The minimum ignition delay was 27.5 ms with an ignition energy of 19.3 mJ. The average of the measured maximum thrust and total impulse were 3619 mN and 0.381 mNs, respectively.     

Miniature orthogonal optical scanning mirror excited by torsional piezoelectric fiber actuator

A novel optical scanner excited by a torsional piezoelectric fiber actuator is presented. The device consists of a piezoelectric fiber actuator generating torsional and longitudinal vibrations simultaneously and a specially designed metal frame transforming the two vibrations to orthogonal deflections of the mirror. Theoretical and experimental studies were performed on the structure. The changing trends of the vibration modes and resonant frequencies were obtained from finite element simulations. Samples with 1 mm × 1 mm mirrors were fabricated from PZT hollow fibers with a diameter of 1 mm and a stainless steel sheet with a thickness of 50 μm. A horizontal scanning angle of 17.9° and a vertical scanning angle of 2.6° were achieved at 6780 and 10,330 Hz under an applied voltage of 400 V_p–p.     

A micro shear stress sensor based on laterally aligned carbon nanotubes

This paper reports the development of a micro thermal shear stress sensor that utilizes multiwalled carbon nanotubes as the sensing element. The sensor was fabricated by laterally aligning randomly distributed nanotubes into a 360 μm long and 90 μm wide conductive trace between two triangular shaped micro electrodes through the use of a high frequency AC electric field. During operation, the aligned nanotubes are electrically heated to an elevated temperature and surface shear stress is measured indirectly by the amount of convective heat transfer from the heated nanotubes to the surrounding fluid flow.The nanotube alignment process was primarily controlled by three different phenomena: dielectrophoresis, joule heating, and Brownian motion. Numerical simulations, together with experimental verifications, indicated that a successful alignment could only be realized if: (1) the dielectrophoretic force was positive, (2) the electro-thermal force was also positive, and (3) the dielectrophoretic force was high enough to overcome Brownian motion. The aligned nanotube trace has a room-temperature resistance of 580 Ω, which corresponds to a conductivity of 2.7 × 10⁴ S/m. The absolute temperature coefficient of resistivity ranges from 0.01 to 0.04% °C⁻¹. This is about one order of magnitude smaller than the highly doped polysilicon sensing material used in the MEMS micro shear stress sensor. The shear stress sensitivity of the nanotube trace operated at a 3% overheat ratio is found to follow the theoretical sensor power ∝ (shear stress)^1/3 relationship, provided the shear stress level is higher than 0.34 mPa. This result confirms the feasibility of using aligned multi-walled carbon nanotubes as a thermal shear stress sensing material.     

Aluminum diffusion in aluminide coatings deposited by the CVD method on pure nickel

The aluminum diffusion in aluminide coatings deposited on nickel by the CVD method was investigated. The microstructure, chemical and phase compositions of coatings were examined by SEM, EDS and XRD techniques. The triple zone structure was revealed. The β-NiAl phase was on the surface of the coatings, whereas γ-(Ni) and γ′-Ni₃Al formed deeper parts of the coatings. Diffusion coefficients were calculated from the concentration profiles in coatings deposited for various times (15 min, 1 h, 4 h and 8 h) at 1000 °C and 1050 °C. The procedure was based on the classic finite difference method (FDM). Diffusion coefficients in three phases were calculated simultaneously and the influence of diffusivity in one phase on the diffusivity in the neighboring phase was taken into account. The results of the calculation agree with the literature data obtained for each of the analyzed phases separately.     

Identifying plant species using mid-wave infrared (2.5–6 μm) and thermal infrared (8–14 μm) emissivity spectra

Plant species discrimination using remote sensing is generally limited by the similarity of their reflectance spectra in the visible, NIR and SWIR domains. Laboratory measured emissivity spectra in the mid infrared (MIR; 2.5 μm–6 μm) and the thermal infrared (TIR; 8 μm–14 μm) domain of different plant species, however, reveal significant differences. It is anticipated that with the advances in airborne and space borne hyperspectral thermal sensors, differentiation between plant species may improve. The laboratory emissivity spectra of thirteen common broad leaved species, comprising 3024 spectral bands in the MIR and TIR, were analyzed. For each wavelength the differences between the species were tested for significance using the one way analysis of variance (ANOVA) with the post-hoc Tukey HSD test. The emissivity spectra of the analyzed species were found to be statistically different at various wavebands. Subsequently, six spectral bands were selected (based on the histogram of separable pairs of species for each waveband) to quantify the separability between each species pair based on the Jefferies Matusita (JM) distance. Out of 78 combinations, 76 pairs had a significantly different JM distance. This means that careful selection of hyperspectral bands in the MIR and TIR (2.5 μm–14 μm) results in reliable species discrimination.     

Electrostatically actuated dip pen nanolithography probe arrays

Dip pen nanolithography (DPN) is a method of creating nanoscale chemical patterns on surfaces using an atomic force microscope (AFM) probe. Until now, efforts to increase the process throughput have focused on passive multi-probe arrays and active arrays based on thermal bimetallic actuation. This paper describes the first use of electrostatic actuation to create an active DPN probe array. Electrostatic actuation offers the benefit of actuation without the probe heating required for thermal bimetallic actuation. Actuator cross talk between neighboring probes is also reduced, permitting more densely spaced probe arrays. The array presented here consists of 10 cantilever probes, where each is 120 μm long and 20 μm wide. Each cantilever probe is actuated by the electrostatic force between the probe and a built-in counter electrode with a 20–25 μm gap. The tip-to-tip probe spacing, also called the array pitch, is 30 μm. Patterns of 1-octadecanethiol were created on gold surfaces to demonstrate single-probe actuation, simultaneous multi-probe actuation, and overlap of patterns from adjacent probes. The minimum line width was 25 nm with an average line width of 30–40 nm.